Nanoparticle-modified high-efficiency light diffusing film and method of forming the same

Abstract

The present application relates to the technical field of optical functional film material, disclose a kind of nano-particle modified high-efficiency light diffusion film and its forming method, the method is first prepared UV curing resin matrix, and inorganic nano-particle, tannic acid and polyvinylpyrrolidone are dispersed in alcohol solvent to obtain polar complex slurry;Subsequently, by high shear dispersion, slurry is added to matrix to build alcohol-in-oil transient microemulsion;After coating, through two-stage hot air drying, induce tannic acid and polyvinylpyrrolidone compound in situ collapse coating on particle surface, finally, it is cured and shaped by ultraviolet radiation.The present application uses the mechanism of transient microemulsion construction and in-situ induced collapse, effectively solves the agglomeration problem of inorganic particles in organic resin, forms organic coating layer with refractive index gradient on the surface of particles, and realizes the excellent balance of high total light transmittance and high haze of light diffusion film.

Description

Technical Field

[0001] This invention relates to the field of optical functional thin film materials technology, specifically to high-efficiency light diffusion films modified with nanoparticles and their forming methods. Background Technology

[0002] Light diffusion films are core optical components in LCD backlight modules, LED lighting fixtures, and various flat panel display devices. Their main function is to convert point or line light sources into uniformly bright surface light sources, while simultaneously shielding the backlight's LED structure (i.e., achieving high haze) and minimizing light energy loss during propagation (i.e., achieving high total light transmittance). As display technology advances towards ultra-thinness and high definition, the market has placed more stringent demands on the optical performance of light diffusion films, requiring both high transmittance and high haze to be achieved simultaneously with an extremely thin film thickness.

[0003] However, existing light diffusion film preparation technologies typically employ the direct physical blending of micron- or nano-sized inorganic particles (such as silica, titanium dioxide, etc.) or organic polymer microspheres into a transparent resin matrix as light scattering agents. This approach faces a dilemma: to achieve sufficient shielding effect (high haze), it is often necessary to increase the amount of scattering particles or increase the refractive index difference between the particles and the matrix. However, this leads to backscattering of light, thereby reducing the total light transmittance and causing a loss of brightness in the display image. Conversely, if the amount of particles is reduced to maintain high transmittance, the haze is insufficient, making it difficult to effectively eliminate hot spots or LED shadows. Therefore, traditional physical blending techniques struggle to simultaneously achieve high transmittance and high haze in a single film layer.

[0004] Furthermore, while inorganic nanoparticles theoretically offer more refined light scattering effects, their practical application is limited by the dispersion challenges in organic resins. Commonly used UV-curable resin systems are typically hydrophobic (non-polar), while inorganic nanoparticles are rich in hydroxyl groups, exhibiting strong polarity and high surface energy. This difference in polarity makes it easy for inorganic nanoparticles to aggregate in the resin matrix, making it difficult to form a uniform monodisperse state. Although existing technologies often use silane coupling agents to modify the particle surface, this process is cumbersome, and the modified layer is prone to detachment or failure during long-term storage of the coating solution or during coating shearing, leading to secondary aggregation or sedimentation of the particles. Particle aggregation not only disrupts optical uniformity and produces appearance defects such as crystal points, but also further exacerbates light loss, posing a challenge to the industrial preparation of high-performance nanocomposite light diffusion films. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high-efficiency light diffusion film modified with nanoparticles and its molding method. This solves the problems of existing light diffusion films being unable to achieve both high total light transmittance and high haze, as well as the problem that inorganic nanoparticles are prone to agglomeration in hydrophobic organic resin matrices, resulting in poor coating dispersion stability and low optical uniformity.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a high-efficiency light diffusion film modified with nanoparticles, employing the following technical solution: The high-efficiency light diffusion film modified with nanoparticles is formed by coating, drying, and curing a light diffusion coating liquid containing the following raw materials in parts by weight: UV-curable resin matrix raw materials: 45-55 parts UV-curable oligomer; 40-50 parts reactive diluent monomer; 3-6 parts photoinitiator; 0.1-0.6 parts leveling agent; Polar dispersed phase raw materials: 5-50 parts inorganic nanoparticles; 0.2-5 parts tannic acid; 0.5-10 parts polyvinylpyrrolidone; 40-60 parts alcohol solvent.

[0007] By employing the above-mentioned technical solution, a thermodynamically unstable transient microemulsion system was constructed by utilizing the solubility difference between the polar dispersed phase raw material and the non-polar UV-curable resin matrix raw material. In this system, tannic acid and polyvinylpyrrolidone pre-form a hydrogen-bonded complex in an alcohol solvent and coat the inorganic nanoparticles. After the coating liquid is dried and cured, the components in the dispersed phase form microscopic scattering units with specific morphologies within the resin matrix. The polyphenolic hydroxyl structure of tannic acid and the amide groups of polyvinylpyrrolidone interact through multiple hydrogen bonds to form a flexible organic coating layer on the surface of the nanoparticles. This coating layer not only improves the compatibility of inorganic particles in the organic resin matrix and prevents aggregation, but also introduces a transition layer with a refractive index gradient between the particles and the matrix. This structure can effectively control the scattering path of light within the film, ensuring high light transmittance while improving the haze value of the light diffusion film, thus solving the technical challenge of traditional light diffusion films that struggle to achieve both high transmittance and high haze.

[0008] Preferably, the raw materials are in the following weight proportions: in the UV-curable resin matrix raw material, 50-55 parts of UV-curable oligomer, 40-50 parts of reactive diluent monomer, 4.5-4.8 parts of photoinitiator, and 0.2-0.5 parts of leveling agent; in the polar dispersed phase raw material, 5-48 parts of inorganic nanoparticles, 0.25-4.8 parts of tannic acid, 0.75-9.6 parts of polyvinylpyrrolidone, and 44-58 parts of alcohol solvent.

[0009] By adopting the above technical solution, the ratio of matrix resin to dispersed phase was further optimized, ensuring the rheological stability of the microemulsion system during the coating process. At the same time, it avoided the sudden increase in viscosity due to excessive solid content or the drying defects due to excessive solvent, so that the optical performance of the final film reached the best balance.

[0010] Preferably, the UV-curable oligomer is selected from one or a combination of hexafunctional aliphatic polyurethane acrylate, bisphenol A epoxy acrylate; the reactive diluent monomer is selected from one or a combination of 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, and trimethylolpropane triacrylate; the inorganic nanoparticles are selected from fumed silica or nano-zirconia, with a native particle size of 20-40 nm; and the alcohol solvent is selected from anhydrous ethanol or isopropanol.

[0011] By adopting the above technical solutions, the specific combination of oligomers and monomers provides excellent curing speed and coating hardness; the selection of nanoparticles with a native particle size of 20-40nm, combined with a specific solvent system, is conducive to the formation of submicron-scale aggregates in the microemulsion to control the structure. This scale can generate efficient Mie scattering of visible light, further enhancing the diffusion effect.

[0012] Preferably, the K value of the polyvinylpyrrolidone is 30-90; the mass ratio of tannic acid to polyvinylpyrrolidone is 1:2 to 1:3.

[0013] By employing the above technical solution, the molecular weight and steric hindrance effect of the complex can be precisely controlled by limiting the K value and mass ratio. Suitable molecular chain lengths and ratios ensure that, during solvent evaporation, the complex can tightly encapsulate the surface of the nanoparticles at an appropriate shrinkage rate, forming a core-shell structure of uniform thickness.

[0014] Preferably, the dry film thickness of the light diffusion film is 6-30 μm, the total light transmittance is 89.1%-92.4%, and the haze is 84.6%-97.8%. By adopting the above technical solution, the obtained light diffusion film has excellent overall optical performance and is suitable for high-performance backlight modules or lighting devices.

[0015] Secondly, the present invention provides a method for forming a high-efficiency light diffusion film modified with nanoparticles, using the following technical solution: A method for forming a high-efficiency light diffusion film modified with nanoparticles includes the following steps: (1) Preparation of B-phase resin matrix: UV-curable oligomer, reactive diluent monomer and leveling agent are mixed evenly, and photoinitiator is added to dissolve to obtain B-phase resin matrix; (2) Preparation of polar complex slurry: Inorganic nanoparticles, tannic acid and polyvinylpyrrolidone are dispersed in an alcohol solvent to prepare a polar complex slurry; (3) Construction of transient microemulsion coating liquid: Under stirring, the polar complex slurry obtained in step (2) is added to the B phase resin matrix obtained in step (1) and dispersed by high shear to form an oil-in-alcohol type microemulsion; (4) Coating and in-situ induced collapse: The microemulsion obtained in step (3) is coated on the surface of the substrate and dried by two-stage hot air to induce the tannic acid and polyvinylpyrrolidone complex to collapse and coat in-situ on the surface of inorganic nanoparticles to obtain a dry coating. (5) Curing and shaping: The dried coating is cured by ultraviolet radiation.

[0016] By employing the above technical solution, this invention innovatively introduces a film-forming mechanism combining transient microemulsions with in-situ induced collapse. Through precise control of physicochemical processes, the controlled assembly of nanoparticles in a resin matrix is ​​achieved. Its core innovative principle and stepwise action mechanism are as follows: Polar complex pre-dispersion (step 2): In an alcohol solvent environment, tannic acid (polyphenol donor) and polyvinylpyrrolidone (acceptor) undergo hydrogen bonding to form a supramolecular complex precursor. This precursor is adsorbed onto the surface of inorganic nanoparticles, and the steric hindrance provided by the solvation layer prevents the hard agglomeration of nanoparticles in the slurry stage.

[0017] Transient microemulsion construction (step 3): Polar complex slurry is dispersed in a nonpolar B-phase resin matrix through high shear stress. Due to the immiscibility of the resin phase (oil phase) and the alcohol solvent phase (dispersed phase), an oil-in-alcohol (O / A) type microemulsion droplet is formed. At this point, nanoparticles are confined within micron- or submicron-sized alcohol droplets, and the droplet interface is stabilized by a tannic acid / polyvinylpyrrolidone complex, forming a three-phase structure in which the resin matrix encapsulates the alcohol solvent, and nanoparticles are dispersed within the alcohol solvent.

[0018] In-situ induced collapse mechanism (step 4): This is a crucial step in forming the special light-diffusing structure. During hot air drying, the alcohol solvent undergoes a phase transition and volatilizes. As the alcohol solvent is rapidly removed, the volume of the dispersed phase droplets shrinks dramatically; The reduced solubility of tannic acid and polyvinylpyrrolidone in the system leads to phase separation of the supramolecular complex; Driven by the surface energy gradient, the precipitated complex rapidly collapses and deposits on the surface of the inorganic nanoparticles, locking and encapsulating the nanoparticles that were originally loosely dispersed in the droplets, forming dense organic-inorganic hybrid microspheres. This in-situ collapse avoids disordered migration and large-scale secondary aggregation of particles during the drying process, ultimately leaving uniformly distributed, controllable core-shell scattering centers in the solidified film.

[0019] Preferably, the preparation method of the polar complex slurry in step (2) is as follows: first, tannic acid is completely dissolved in an alcohol solvent; then, inorganic nanoparticles are added and ultrasonically dispersed or ground and dispersed; finally, polyvinylpyrrolidone powder is added under stirring and stirred until completely dissolved to obtain a uniform slurry; wherein, the solid content of the slurry is controlled at 12%-52%.

[0020] By employing the above technical solution, the specific order of addition ensures that tannic acid preferentially forms a homogeneous phase in the solvent, subsequently effectively adsorbing onto the particle surface. The finally added polymer PVP further stabilizes the system through complexation with tannic acid. Controlling the solids content between 12% and 52% ensures sufficient dispersion efficiency while providing an appropriate amount of solvent carrier to maintain the subsequent formation of microemulsions.

[0021] Preferably, the high shear dispersion speed in step (3) is 3000-6000 rpm, the dispersion time is 10-20 minutes, and the material temperature is controlled between 25℃ and 35℃ during the dispersion process.

[0022] By adopting the above technical solution, high shear input energy breaks the dispersed phase droplets into the target size range, and temperature control prevents premature solvent evaporation or component thermal degradation, ensuring the uniformity of microemulsion particle size distribution, thereby guaranteeing the optical uniformity of the final coating.

[0023] Preferably, the specific process of the two-stage hot air drying in step (4) is as follows: the first stage phase separation induction zone: the temperature is 60-75℃ and the residence time is 60-120 seconds; the second stage deep drying zone: the temperature is 80-90℃ and the residence time is 60-120 seconds.

[0024] By adopting the above technical solution, the two-stage drying process achieves precise control of the solvent evaporation rate. The first stage, a medium-temperature treatment, serves as a phase separation induction zone, gently driving the evaporation of ethanol or isopropanol, inducing the orderly collapse and assembly of the tannic acid / polyvinylpyrrolidone complex on the particle surface, thus avoiding surface cracking or structural defects caused by excessively rapid evaporation. The second stage, a high-temperature treatment, serves as a deep drying zone, ensuring complete removal of residual solvent and promoting the leveling of the resin matrix, eliminating defects such as orange peel on the surface.

[0025] Preferably, the ultraviolet radiation energy used in step (5) is 300-800 mJ / cm2, and the light source used is a high-pressure mercury lamp or a UV-LED light source.

[0026] By adopting the above technical solution, the appropriate radiation energy ensures the complete conversion of acrylate double bonds, endowing the light diffusion film with excellent mechanical strength and weather resistance, while rapidly curing and locking in the microscopic scattering structure formed after drying.

[0027] This invention provides a high-efficiency light diffusion film modified with nanoparticles and its molding method. It has the following beneficial effects: 1. This invention constructs a transient microemulsion system and combines it with a two-stage drying process. By utilizing solvent evaporation to induce in-situ collapse and coating of tannic acid and polyvinylpyrrolidone on the surface of inorganic nanoparticles, this special film-forming mechanism forms core-shell organic-inorganic hybrid microspheres with uniform particle size and excellent dispersibility in the resin matrix. This microsphere structure not only effectively inhibits the aggregation of nanoparticles, but also introduces a flexible organic interface layer with a refractive index gradient between the particles and the matrix, thereby enhancing the Mie scattering efficiency of light inside the film.

[0028] 2. This invention utilizes the strong hydrogen bonding complexation between tannic acid and polyvinylpyrrolidone to pre-encapsulate inorganic nanoparticles in an alcohol solvent. Subsequently, the polar slurry is dispersed in the form of microemulsion droplets in a non-polar UV resin through high-shear dispersion. This oil-in-alcohol microemulsion structure effectively isolates the high surface energy inorganic particles from the hydrophobic organic resin. By leveraging the steric hindrance effect of the amphiphilic polymer, secondary aggregation and sedimentation of nanoparticles during coating solution storage and coating process are prevented, thereby improving the storage stability of the coating solution and the optical uniformity of the final product.

[0029] 3. The molding method of the present invention uses conventional coating and UV curing equipment, without the need for complicated subsequent chemical treatment or high-temperature sintering steps. By adjusting the solid content of the polar complex slurry and the drying process parameters, the size of the microemulsion droplets and the morphology of the scattering units in the final coating can be flexibly controlled. It is not only applicable to a variety of substrates, but the structure formed by the in-situ induced collapse mechanism is universally applicable to inorganic particles of different sizes and types, and is easy to realize large-scale continuous industrial production. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, examples, comparative examples, and test examples in this specification. 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.

[0031] Preparation Examples 1-3: Preparation Example 1: Raw material composition: Inorganic nanoparticles: fumed silica (native particle size 20 nm), 100.0 parts; Tannic acid: 5.0 parts; Polyvinylpyrrolidone (K30): 15.0 parts; Carrier solvent: anhydrous ethanol, 880.0 parts; (At this point, the mass ratio of tannic acid to polyvinylpyrrolidone is 1:3, and the solid content is approximately 12%).

[0032] Preparation steps: Add 880.0 parts of anhydrous ethanol to a clean, covered, stirred container, and start the mechanical stirrer at 400 rpm.

[0033] Slowly add 5.0 parts of tannic acid and stir at room temperature for 10 minutes until the tannic acid is completely dissolved, resulting in a clear light brown solution.

[0034] 100.0 parts of fumed silica were added to the above solution in three portions. After the addition was complete, the solution was transferred to an ultrasonic disperser and ultrasonically dispersed for 30 minutes at a frequency of 40kHz and a power of 300W, while keeping the slurry temperature below 40℃.

[0035] Transfer the dispersion back to the mixer, increase the speed to 600 rpm, and slowly add 15.0 parts of polyvinylpyrrolidone K30 powder to prevent clumping.

[0036] Continue stirring for 45 minutes until polyvinylpyrrolidone is completely dissolved, to obtain a uniform, low-viscosity polar complex slurry A1 without visible particles.

[0037] Preparation Example 2: Raw material composition: Inorganic nanoparticles: fumed silica (native particle size 40 nm), 250.0 parts; Tannic acid: 20.0 parts; Polyvinylpyrrolidone (K90): 60.0 parts; Carrier solvent: anhydrous ethanol, 670.0 parts; (At this point, the mass ratio of tannic acid to polyvinylpyrrolidone is 1:3. Polyvinylpyrrolidone K90 has a larger molecular weight and stronger steric hindrance, with a solid content of approximately 33%).

[0038] Preparation steps: Add 670.0 parts of anhydrous ethanol to the mixing container, start the mechanical stirrer, and set the speed to 500 rpm.

[0039] Add 20.0 parts of tannic acid and stir at room temperature for 15 minutes until completely dissolved.

[0040] Add 250.0 parts of fumed silica, pre-disperse at 1500 rpm for 10 minutes using a high-speed dispersion disk, and then perform ultrasonic dispersion (power 500W) for 30 minutes.

[0041] Adjust the rotation speed to 800 rpm and slowly add 60.0 parts of polyvinylpyrrolidone K90 powder. Since K90 has a significant thickening effect, viscosity changes need to be closely monitored.

[0042] Continue stirring for 60 minutes until the system forms a thixotropic, semi-transparent polar complex slurry A2.

[0043] Preparation Example 3: Raw material composition: Inorganic nanoparticles: Zirconia nanoparticles (native particle size 20nm), 400.0 parts; Tannic acid: 40.0 parts; Polyvinylpyrrolidone (K90): 80.0 parts; Carrier solvent: isopropanol, 480.0 parts; (Zirconium oxide was used to verify different particles; the mass ratio of tannic acid to polyvinylpyrrolidone was 1:2; the solvent was changed to isopropanol; the solids content was about 52%, verifying the high filling limit).

[0044] Preparation steps: Add 480.0 parts of isopropanol to the mixing container, start the mechanical stirrer, and set the speed to 600 rpm.

[0045] Add 40.0 parts of tannic acid and stir for 20 minutes until dissolved.

[0046] 400.0 parts of nano-zirconia were added. Due to the high solid content, the mixture was ground and dispersed using a basket mill for 30 minutes to control the fineness to <5μm.

[0047] Slowly add 80.0 parts of polyvinylpyrrolidone K90 powder while stirring (1000 rpm).

[0048] Continue stirring for 90 minutes. If necessary, use a water bath to heat to 40°C to assist in dissolution, and finally obtain a high-viscosity paste-like polar complex slurry A3.

[0049] Examples 1-3: Example 1: This embodiment provides a high-efficiency light diffusion film modified with nanoparticles and its forming method, specifically including the following steps: (1) Preparation of phase B resin matrix: In a light-proof stainless steel stirred tank, 55.0 parts of hexafunctional aliphatic polyurethane acrylate, 40.0 parts of 1,6-hexanediol diacrylate, and 0.2 parts of polyether-modified polydimethylsiloxane (as a leveling agent) were added sequentially. The system was heated to 50°C and stirred at 400 rpm for 20 minutes until homogeneous. Then, 4.8 parts of photoinitiator 1-hydroxycyclohexylphenyl ketone were added, and stirring was continued for 15 minutes until completely dissolved. The mixture was then cooled to 25°C to obtain a clear and transparent B-phase resin matrix.

[0050] (2) Construction of transient microemulsion coating solution: Weigh 100.0 parts of the B-phase resin matrix obtained in step (1) above and place it in a dispersion container. Measure 50.0 parts of the polar complex slurry A1 (containing nano-silica, tannic acid, polyvinylpyrrolidone K30 and anhydrous ethanol) obtained in Preparation Example 1. Slowly add the low-viscosity polar complex A1 dropwise to the B-phase resin matrix under low-speed stirring. At this time, the system appears turbid. Then start the high-shear emulsifier and set the speed to 3000 rpm for shear dispersion treatment for 10 minutes. During this process, the material temperature is controlled at 25℃±2℃ using a cooling water jacket. After dispersion, the resulting milky white microemulsion is degassed under vacuum at -0.08 MPa for 5 minutes to obtain the light diffusion coating liquid.

[0051] (3) Coating and in-situ induced collapse: An optical-grade PET film with a light transmittance of 92% and a thickness of 50 μm was selected as the substrate. The light-diffusing coating liquid obtained in step (2) was coated onto the surface of the PET substrate using a slot extrusion coating method, controlling the wet film thickness to be 15 μm. The coated wet film was then placed in a hot air drying oven for two-stage drying. Phase 1 (Phase Separation Induction Zone): The temperature is set at 60℃, and the residence time is 60 seconds. In this stage, the ethanol solvent evaporates, inducing the tannic acid and polyvinylpyrrolidone complex to undergo in-situ shrinkage and coating on the surface of the nanoparticles.

[0052] Second stage (deep drying zone): Set the temperature to 80°C and the residence time to 60 seconds to completely remove residual solvent and promote resin leveling.

[0053] (4) Curing and shaping: The dried coating was then placed in a UV curing machine and irradiated using a high-pressure mercury lamp. The total irradiation energy was set to 300 mJ / cm². 2 After curing, the film is wound up to obtain a nanoparticle-modified light diffusion film with a dry film thickness of approximately 6-8 μm.

[0054] Example 2: This embodiment provides a high-efficiency light diffusion film modified with nanoparticles and its forming method, specifically including the following steps: (1) Preparation of phase B resin matrix: In a light-proof stainless steel stirred tank, 50.0 parts of hexafunctional aliphatic polyurethane acrylate, 45.0 parts of tripropylene glycol diacrylate, and 0.3 parts of polyether-modified polydimethylsiloxane (leveling agent) were added sequentially. The system was heated to 55°C and stirred at 500 rpm for 25 minutes until homogeneous. Then, 4.7 parts of photoinitiator 184 were added, and stirring was continued for 20 minutes until completely dissolved. The mixture was then cooled to 25°C to obtain a clear and transparent B-phase resin matrix.

[0055] (2) Construction of transient microemulsion coating solution: Weigh 100.0 parts of the B-phase resin matrix obtained in step (1) above and place it in a dispersion container. Measure 80.0 parts of the polar complex slurry A2 obtained in Preparation Example 2 (containing nano-silica, tannic acid, polyvinylpyrrolidone K90 and anhydrous ethanol, representing medium solid content and molecular weight). Add the translucent polar complex slurry A2 dropwise to the B-phase resin matrix while stirring. Then start the high-shear emulsifier and set the speed to 4500 rpm for shear dispersion treatment for 15 minutes. During this process, the material temperature is controlled at 30℃±2℃ using a cooling water jacket, and the higher shear force is used to construct oil-in-alcohol microemulsion droplets with finer particle size. After dispersion, the resulting emulsion is degassed under vacuum at -0.09 MPa for 8 minutes to obtain a thixotropic light diffusion coating liquid.

[0056] (3) Coating and in-situ induced collapse: An optical-grade PET film with a light transmittance of 92% and a thickness of 75 μm was selected as the substrate. The light-diffusing coating liquid obtained in step (2) was applied to the surface of the PET substrate using a microgravure coating method, controlling the wet film thickness to be 30 μm. The coated wet film was then placed in a hot air drying oven for two-stage drying. Phase 1 (Phase Separation Induction Zone): The temperature is set at 70℃, and the residence time is 90 seconds. The moderate temperature promotes the orderly evaporation of ethanol, allowing the tannic acid and polyvinylpyrrolidone K90 complex to form a dense coating layer on the particle surface.

[0057] Second stage (deep drying zone): Set the temperature to 85℃ and the dwell time to 90 seconds to ensure no solvent residue and a smooth coating surface.

[0058] (4) Curing and shaping: The dried coating was then placed in a UV curing machine and irradiated using a UV-LED surface light source (395nm). The total irradiation energy was set to 500mJ / cm². 2 After curing, the film is rolled up to obtain a nanoparticle-modified light diffusion film with a dry film thickness of approximately 12-15 μm.

[0059] Example 3: This embodiment provides a high-efficiency light diffusion film modified with nanoparticles and its forming method, specifically including the following steps: (1) Preparation of phase B resin matrix: In a light-proof stainless steel stirred tank, 45.0 parts of bisphenol A epoxy acrylate, 50.0 parts of trimethylolpropane triacrylate, and 0.5 parts of polyether-modified polydimethylsiloxane were added sequentially. The system was heated to 60°C and stirred at 600 rpm for 30 minutes until homogeneous. Then, 4.5 parts of photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide were added, and stirring was continued for 20 minutes until completely dissolved. The mixture was then cooled to 30°C to obtain a B-phase resin matrix with high viscosity.

[0060] (2) Construction of transient microemulsion coating solution: Weigh 100.0 parts of the B-phase resin matrix obtained in step (1) above and place it in a dispersion container. Measure 120.0 parts of the polar complex slurry A3 obtained in Preparation Example 3 (containing nano-zirconia, tannic acid, polyvinylpyrrolidone K90 and isopropanol, representing high filling volume and different types of particles). Under stirring, rapidly add the polar complex slurry A3 to the B-phase resin matrix. Due to the extremely high solid content and high viscosity of the slurry, start the high-shear emulsifier and set the speed to 6000 rpm for strong shear dispersion treatment for 20 minutes. During this process, strictly control the material temperature to not exceed 35°C using a cooling water jacket to prevent premature vaporization of isopropanol. After dispersion, degas the obtained high-viscosity white emulsion under vacuum at -0.09 MPa for 10 minutes to obtain a high-thixotropic light-diffusing coating liquid.

[0061] (3) Coating and in-situ induced collapse: An optical-grade polycarbonate film with a light transmittance of 90% and a thickness of 125 μm was selected as the substrate. The coating solution obtained in step (2) was applied to the surface of the polycarbonate substrate using a comma-shaped doctor blade coating method, controlling the wet film thickness to be 50 μm. The coated wet film was then placed in a hot air drying oven for two-stage drying. Phase 1 (Phase Separation Induction Zone): The temperature is set at 75°C, and the residence time is 120 seconds. The high temperature, combined with the volatility of isopropanol, drives the high concentration of tannic acid and polyvinylpyrrolidone complex to rapidly collapse and lock in position on the surface of the zirconia particles.

[0062] Second stage (deep drying zone): Set the temperature to 90℃ and the dwell time to 120 seconds to thoroughly remove high-boiling-point residual components and complete the densification of the coating.

[0063] (4) Curing and shaping: The dried coating was then placed in a UV curing machine and irradiated using a high-power, high-pressure mercury lamp. The total irradiation energy was set to 800 mJ / cm². 2After curing, the film is wound up to obtain a high-haze nanoparticle modified light diffusion film with a dry film thickness of about 25-30μm.

[0064] Comparative Examples 1-4: Comparative Example 1: This comparative example aims to demonstrate that the supramolecular physical coating effect of the present invention is superior to that of traditional chemical bonding modification. The difference compared to Example 2 is: Microemulsions are constructed without using tannic acid and polyvinylpyrrolidone, or a carrier solvent (ethanol).

[0065] The nanoparticles were replaced with an equal amount of hydrophobic nano-silica that had been surface-modified with methacryloyloxypropyltrimethoxysilane.

[0066] The preparation process was changed to: the modified nano-silica was directly added to the B-phase resin matrix and dispersed at 3000 rpm for 20 minutes using the same dispersion equipment to directly obtain the coating liquid. The other raw material types, coating and curing steps were the same as in Example 2.

[0067] Comparative Example 2: This comparative example aims to demonstrate that stable dispersion cannot be achieved solely through the steric hindrance of polyvinylpyrrolidone in the absence of key linker sites anchored by tannic acid. The difference compared to Example 2 is: In the preparation of phase A polar complex slurry, no tannic acid was added; only polyvinylpyrrolidone K90 was dissolved in anhydrous ethanol and nano-silica was dispersed.

[0068] The amounts of other raw materials, the preparation steps of the A-phase polar complex slurry, the construction of the microemulsion and the subsequent coating and curing steps are exactly the same as in Example 2.

[0069] Comparative Example 3: This comparative example aims to demonstrate that, in the absence of the flexible long-chain steric hindrance provided by polyvinylpyrrolidone, the surface adsorption of tannic acid alone cannot prevent hard agglomeration of particles under high packing conditions. The difference compared to Example 2 is: In the preparation of phase A polar complex slurry, no polyvinylpyrrolidone was added; only tannic acid was dissolved in anhydrous ethanol and nano-silica was dispersed.

[0070] The amounts of other raw materials, the preparation steps of the A-phase polar complex slurry, the construction of the microemulsion and the subsequent coating and curing steps are exactly the same as in Example 2.

[0071] Comparative Example 4: This comparative example is the most crucial comparison, designed to demonstrate that even with the same formulation, direct mixing without the protective isolation of the oil-in-alcohol microemulsion structure can lead to resin interference with supramolecular assembly and reduced effectiveness. The difference compared to Example 2 is: No pre-preparation of A-phase polar complex slurry was performed, nor was a microemulsion structure constructed.

[0072] The preparation process was changed to a one-pot direct mixing method: tannic acid, polyvinylpyrrolidone K90, nano silica, anhydrous ethanol, and all components of the B-phase resin matrix were directly added to the same mixing tank.

[0073] The coating liquid was prepared by mixing and dispersing under the same high shear conditions (4500 rpm, 15 min) as in Example 2. All other coating, drying (solvent evaporation), and curing parameters were the same as in Example 2.

[0074] Test Example 1-2: Test Example 1: Rheological Properties and Storage Stability Test of Coating Liquid Test objective: The differences in rheological behavior (especially thixotropy) and long-term storage stability of light-diffusing coatings prepared in different embodiments and comparative examples were evaluated to verify the influence of transient microemulsion structure and hydrogen bond network on the process performance of dispersion system.

[0075] Test method: Thixotropic index test: Steady-state flow tests were conducted on the freshly prepared and degassed coating solutions using a rotational rheometer. The test temperature was kept constant at 25℃.

[0076] Test procedure: A controlled shear rate mode was used, with the shear rate starting from 0.1 s. −1 linearly increased to 100s −1 Record the viscosity change curve.

[0077] TI value calculation: Select the viscosity value at low shear rate (Take 0.5s) −1 Viscosity at high shear rates and viscosity at high shear rates (Take 50s) −1 The ratio of viscosity at a given point to viscosity at a given point is used as the thixotropic index.

[0078] Calculation formula: ; Centrifugation accelerated sedimentation stability test: To simulate the dispersion stability under long-term storage conditions, a dispersion stability analyzer was used for accelerated testing.

[0079] Test procedure: Take 1.5 mL of sample and put it into the test tube. Set the centrifugation speed to 2000 rpm, the temperature to 25℃, and the test duration to 2 hours (equivalent to several months of conventional gravity sedimentation).

[0080] Evaluation index: Record the rate of change of transmittance integral at the end of the test. The smaller the value, the more stable the system is, with no obvious stratification or sedimentation.

[0081] Static natural sedimentation observation: Take 50 mL of sample and place it in a transparent stoppered graduated cylinder, and let it stand at room temperature (25℃) for 168 hours (7 days).

[0082] Evaluation index: Measure the height of the bottom sediment layer and the height of the upper clear liquid, and calculate the sedimentation rate (sediment layer height / total height × 100%).

[0083] Test results: Table 1. Summary of Rheological Properties and Stability Test Data of Coating Liquids for Each Group Results Analysis and Conclusions: Based on the data in Table 1, the following analysis is performed: The samples from Examples 1 to 3 all exhibited shear-thinning behavior, with TI values ​​ranging from 4.18 to 4.70, classifying them as strongly thixotropic fluids. This indicates the formation of a supramolecular hydrogen-bonded network within the system, centered on a tannic acid-polyvinylpyrrolidone complex. Under static or low-shear conditions, this supramolecular hydrogen-bonded network restricts the Brownian motion and gravitational sedimentation of nanoparticles, endowing the system with extremely high low-shear viscosity (3850-7890 mPa·s) and anti-settling properties (centrifugal instability index as low as 0.028-0.042). Under high-shear conditions, the supramolecular hydrogen-bonded network reversibly dissociates, and the viscosity rapidly decreases to a suitable coating range (920-1680 mPa·s), which is beneficial for coating leveling and thickness control.

[0084] In contrast, Comparative Example 1, modified with a silane coupling agent, exhibited near-Newtonian fluid characteristics with a TI value of only 1.29. Lacking the support of a supramolecular hydrogen bond network structure, it resulted in an instability index as high as 0.582 in centrifugation tests and a natural sedimentation rate of 12.4%, indicating that the inorganic particles underwent hard sedimentation.

[0085] The TI values ​​of Comparative Example 2 (polyvinylpyrrolidone only) and Comparative Example 3 (tannic acid only) were 2.14 and 1.76, respectively, which were lower than those of the Examples, indicating that a single component cannot construct an effective spatial network structure. Although polyvinylpyrrolidone has a certain thickening effect, it lacks the anchoring effect of tannic acid, resulting in poor particle stability.

[0086] Comparative Example 4 employed a direct mixing process. Although the formulation components were the same as in Example 2, the TI value was only 2.25, and the centrifugal stability was inferior to that of Example 2. This confirms that without the microemulsion construction step, the polar monomers in the resin matrix interfere with the hydrogen bond assembly between tannic acid and polyvinylpyrrolidone, resulting in the inability to form an effective microstructure and long-range ordered network, thus failing to achieve the expected rheological modification effect.

[0087] In summary, the supramolecular network structure constructed by the transient microphase separation process in this technical solution effectively solves the contradiction between sedimentation and leveling in high-filling-content nanoparticle dispersions, and its process adaptability is superior to conventional modification techniques.

[0088] Test Example 2: Optical and Physical-Mechanical Properties Testing of Light Diffusion Films Test objective: To comprehensively characterize the performance of the nanoparticle-modified light diffusion film after curing, focusing on its transmittance, haze, appearance defects (crystal points) and coating adhesion, and to verify the effect of in-situ induced collapse process on improving the uniformity of optical performance and the interfacial bonding strength.

[0089] Test method: Total light transmittance and haze testing: The tests were conducted using a haze meter in accordance with ASTM D1003, "Standard Test Method for Haze and Light Transmittance of Transparent Plastics".

[0090] Sampling: Cut 50mm×50mm samples from three different positions on the left, center and right of each group of light diffusion film samples.

[0091] Test: Record the total light transmittance and haze value at each location, and take the arithmetic mean of three measurements as the final result.

[0092] Appearance Defect (Crystal Point) Rating: In a dark room environment, use a high-intensity side light source (LED panel light) to illuminate the film surface at a low angle and visually observe whether there are bright spots (crystal points) caused by particle aggregation in a 100mm×100mm area.

[0093] Rating criteria: Grade A: Uniform surface, no bright spots visible to the naked eye.

[0094] Grade B: 1-5 tiny bright spots (diameter <0.2mm) are present.

[0095] Grade C: There are more than 5 bright spots, or there are obvious large particle agglomerations (diameter > 0.2 mm).

[0096] Grade D: Dense clusters of bright spots resembling stars, with severe aggregation.

[0097] Coating adhesion test: conducted according to Method B (cross-cut test) of ASTM D3359-09 "Standard Test Methods for Adhesion Measurement by Tape Method".

[0098] Procedure: Use a cross-cutting tool to cut 10×10 1mm×1mm grids into the coated surface, cutting through to the substrate. Securely adhere 3M 610 tape to the grid areas and peel it off quickly.

[0099] Rating: 5B: The cut edges are completely smooth, with no mesh falling off.

[0100] 4B: Minor peeling occurs at the intersection of the incisions, with a peeling area of ​​<5%.

[0101] 3B: Small pieces of skin have peeled off at the edges and intersections of the incision, with a peeling area of ​​5%-15%.

[0102] 0B-2B: Peeling area >15%, poor adhesion.

[0103] Test results: Table 2. Summary of test data on the optical and physical properties of light diffusion films Results Analysis and Conclusions: Based on the data in Table 2, the following analysis is performed: The light-diffusing films prepared in Examples 1 to 3 achieved high haze (84.6%-97.8%) while maintaining high transmittance (89.1%-92.4%). The standard deviation of transmittance at each measurement point was extremely small (0.12-0.21), and all films received an appearance rating of A, indicating that the inorganic nanoparticles were highly uniformly dispersed in the resin matrix without agglomeration. Adhesion test results were all 5B, showing a strong bond between the coating and the substrate. This is attributed to the dense coating layer formed by the in-situ collapse of the tannic acid and polyvinylpyrrolidone composite during drying. This flexible interface layer not only eliminated stress concentration between the inorganic rigid particles and the organic resin matrix but also enhanced interfacial adhesion through the abundant phenolic hydroxyl groups of tannic acid.

[0104] Although Comparative Example 1 achieved a haze of 88.5%, its transmittance dropped to 85.3%, and its transmittance standard deviation was relatively large (1.45), resulting in an appearance rating of C (obvious agglomerated bright spots were visible). This indicates that conventional silane coupling agent modification failed to effectively prevent secondary agglomeration of nanoparticles under high filling conditions, and the large agglomerates caused severe light scattering loss and a decrease in transmittance.

[0105] The adhesion of Comparative Examples 2 and 3 was only 3B, and the appearance rating was B. This indicates that the single-component modification could not form a complete coating structure, the interfacial bonding was weak, and the particle dispersion was not uniform.

[0106] The test results of Comparative Example 4 showed that although the formulation was the same as in Example 2, the transmittance was only 86.8%, lower than the 90.8% of Example 2, and the adhesion decreased to 4B. This further confirms that without the phase separation induction mechanism of transient microemulsions, tannic acid and polyvinylpyrrolidone tend to be randomly distributed in the resin rather than enriched on the particle surface, failing to form an effective dense coating layer, resulting in reduced light scattering efficiency and weakened interface modification effect.

[0107] In summary, the light diffusion film prepared using this technical solution achieves ideal dispersion of nanoparticles and interface strengthening through process control, demonstrating advantages in eliminating optical crystal point defects, improving light transmittance and haze balance, and enhancing coating adhesion.

Claims

1. A high-efficiency light diffusion film modified with nanoparticles, characterized in that, A light-diffusing coating liquid is prepared by coating, drying, and curing from raw materials comprising the following parts by weight: UV-curable resin matrix raw materials: 45-55 parts UV-curable oligomer; 40-50 parts reactive diluent monomer; 3-6 parts photoinitiator; 0.1-0.6 parts leveling agent; Polar dispersed phase raw materials: Inorganic nanoparticles 5-50 parts; tannic acid 0.2-5 parts; polyvinylpyrrolidone 0.5-10 parts; alcohol solvent 40-60 parts.

2. The high-efficiency light diffusion film modified with nanoparticles according to claim 1, characterized in that, The weight parts of the raw materials are: UV-curable resin matrix raw materials: 50-55 parts UV-curable oligomer; 40-50 parts reactive diluent monomer; 4.5-4.8 parts photoinitiator; 0.2-0.5 parts leveling agent; Polar dispersed phase raw materials: Inorganic nanoparticles 5-48 parts; tannic acid 0.25-4.8 parts; polyvinylpyrrolidone 0.75-9.6 parts; alcohol solvent 44-58 parts.

3. The high-efficiency light diffusion film modified with nanoparticles according to claim 1, characterized in that, The specific types of raw materials are selected as follows: The UV-curable oligomer is selected from one or a combination of hexafunctional aliphatic polyurethane acrylate or bisphenol A epoxy acrylate. The reactive diluent monomer is selected from one or a combination of 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, or trimethylolpropane triacrylate. The inorganic nanoparticles are selected from fumed silica or nano-zirconia, and their original particle size is 20-40 nm. The alcohol solvent is selected from anhydrous ethanol or isopropanol.

4. The high-efficiency light diffusion film modified with nanoparticles according to claim 1, characterized in that, The K value of the polyvinylpyrrolidone is 30-90; the mass ratio of the tannic acid to the polyvinylpyrrolidone is 1:2 to 1:

3.

5. The high-efficiency light diffusion film modified with nanoparticles according to claim 1, characterized in that, The light diffusion film has a dry film thickness of 6-30 μm, a total light transmittance of 89.1%-92.4%, and a haze of 84.6%-97.8%.

6. A method for forming a high-efficiency light diffusion film modified with nanoparticles, characterized in that, The method for preparing the nanoparticle-modified high-efficiency light diffusion film as described in any one of claims 1-5 comprises the following steps: (1) Preparation of B-phase resin matrix: UV-curable oligomer, reactive diluent monomer and leveling agent are mixed evenly, and photoinitiator is added to dissolve to obtain B-phase resin matrix; (2) Preparation of polar complex slurry: Inorganic nanoparticles, tannic acid and polyvinylpyrrolidone are dispersed in an alcohol solvent to prepare a polar complex slurry; (3) Construction of transient microemulsion coating liquid: Under stirring, the polar complex slurry obtained in step (2) is added to the B phase resin matrix obtained in step (1) and dispersed by high shear to form an oil-in-alcohol type microemulsion; (4) Coating and in-situ induced collapse: The microemulsion obtained in step (3) is coated on the surface of the substrate and dried by two-stage hot air to induce the tannic acid and polyvinylpyrrolidone complex to collapse and coat in-situ on the surface of inorganic nanoparticles to obtain a dry coating. (5) Curing and shaping: The dried coating is cured by ultraviolet radiation.

7. The molding method according to claim 6, characterized in that, The specific method for preparing the polar complex slurry in step (2) is as follows: First, completely dissolve the tannic acid in an alcohol solvent; Then add inorganic nanoparticles and disperse them by ultrasonication or grinding. Finally, add polyvinylpyrrolidone powder while stirring, and continue stirring until completely dissolved to obtain a homogeneous slurry; The solids content of the slurry is controlled between 12% and 52%.

8. The molding method according to claim 6, characterized in that, In step (3), the high shear dispersion speed is 3000-6000 rpm, the dispersion time is 10-20 minutes, and the material temperature is controlled between 25℃ and 35℃ during the dispersion process.

9. The molding method according to claim 6, characterized in that, The specific process of the two-stage hot air drying described in step (4) is as follows: The first stage of phase separation induction zone: temperature 60-75℃, residence time 60-120 seconds; The second stage is the deep drying zone: the temperature is 80-90℃, and the residence time is 60-120 seconds.

10. The molding method according to claim 6, characterized in that, The ultraviolet radiation energy used in step (5) is 300-800 mJ / cm². 2 The light source used is a high-pressure mercury lamp or a UV-LED light source.

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