Preparation method of optical diffusion film

Abstract

The invention relates to the field of optical thin films, in particular to a preparation method of an optical diffusion film. A preparation method of an optical diffusion film comprises the following steps: uniformly mixing a curing agent and polydimethylsiloxane, curing, and then carrying out oxygen plasma treatment and room temperature aging treatment to obtain a polydimethylsiloxane flat plate; dissolving PET particles and PMMA particles in a solvent to obtain a polymer solution; and placing a polydimethylsiloxane flat plate above the polymer solution, and standing to obtain the optical diffusion film. According to the application, PMMA is used as a high glass transition temperature component to be blended with PET, so that the overall glass transition temperature of a blending system is improved, and the practicability of the optical diffusion film in a high-temperature environment is improved; strong scattering is provided through the refractive index difference between air holes and a polymer phase, and a refractive index gradient is formed by using the refractive index difference between PET and PMMA, so that a secondary scattering interface is formed, and light absorption is reduced and high transmittance is maintained while high haze is ensured.

Description

Technical Field

[0001] The present application relates to the field of optical films, and in particular to a method for preparing an optical diffusion film. Background Art

[0002] Optical diffuser film is an industrial film used in the backlight source of LCD modules. Its primary function in backlight structures is to modify the diffusion angle. It increases the area of ​​light radiation while simultaneously reducing the light intensity per unit area, thereby reducing luminance. After being diffused by the diffuser material, the luminous light source becomes a secondary light source with a larger area, better uniformity, and more stable color.

[0003] In related technology, Chinese patent publication number CN112433278A discloses a method for preparing a light-diffusing film, comprising the following steps: A. Preparing a polydimethylsiloxane flat plate: Mixing a curing agent and polydimethylsiloxane uniformly, pouring the mixture into a casting mold, and peeling it off after thermal curing; then treating the cured polydimethylsiloxane sheet with oxygen plasma and aging it at room temperature for 8 hours to prepare the polydimethylsiloxane flat plate; B. Dissolving PET particles in a solvent, placing the polymer solution in a cleaned glass container, and then placing the polydimethylsiloxane flat plate on top of the container. The container is then left at 20-50°C for a period of time. The polydimethylsiloxane flat plate absorbs the solvent from the polymer solution, causing phase separation of the polymer solution, thereby forming a porous structure within the PET film and a concave-convex surface on the PET film. This invention introduces a porous structure within the light-diffusing film and creates a concave-convex textured surface on the light-diffusing film using a simple and low-cost method.

[0004] Regarding the above-mentioned related technologies, the glass transition temperature of PET is relatively low. When in a high-temperature environment, the PET film will soften and deform, causing its internal pore structure to become blocked. At the same time, the concave and convex structure on the surface of the PET film will also tend to be smooth due to high-temperature softening, destroying the microstructure originally formed by the phase separation process, and directly weakening the light scattering ability of the light diffusion film. In actual application scenarios, it is difficult to meet the long-term stable optical performance requirements, and further optimization and improvement are urgently needed. Summary of the Invention

[0005] In order to improve the problem that the PET film will soften and deform when in a high temperature environment, causing its internal pore structure to become blocked, and the concave and convex structure on the surface of the PET film will also tend to be smooth due to high temperature softening, the present application provides a method for preparing an optical diffusion film.

[0006] A method for preparing an optical diffusion film comprises the following steps: S1. The curing agent and polydimethylsiloxane were mixed and cured, and then subjected to oxygen plasma treatment and room temperature aging to obtain a polydimethylsiloxane flat plate; S2. Dissolve the PET particles and PMMA particles in a solvent to obtain a polymer solution; place the polydimethylsiloxane plate on top of the polymer solution and let it stand to obtain an optical diffusion film.

[0007] By adopting the above technical solution, when PET and PMMA are blended, PMMA, as a high glass transition temperature component, can have its rigid molecular chains (containing side methyl groups) embedded in the molecular network of PET, restricting the movement of PET chain segments through physical entanglement and van der Waals forces, thereby increasing the overall glass transition temperature of the blended system. As a result, the prepared optical diffusion film is not easily softened at high temperatures, and can effectively maintain the porous structure inside the diffusion film and the concave and convex parts on the surface, thereby improving the practicality of the diffusion film at higher temperatures.

[0008] There is a significant difference in the refractive index of PET and PMMA. In step S2, when a polydimethylsiloxane plate is placed above the polymer solution, the solvent is absorbed by the polydimethylsiloxane plate, and the area close to the polydimethylsiloxane plate preferentially forms a microphase region rich in PMMA or PET; while the solvent in the internal area is absorbed more slowly, and the component distribution is more even, thereby forming a refractive index gradient from the surface to the matrix inside the film; at the same time, the polydimethylsiloxane plate absorbs the solvent to promote the phase separation of the polymer solution, thereby forming a porous structure inside the optical diffusion film and forming concave and convex parts on the surface.

[0009] The refractive index difference between the air pores and the polymer phase provides strong scattering ability, while the refractive index difference between PMMA and PET forms a secondary scattering interface through gradient distribution, which can reduce light absorption and maintain high transmittance while ensuring high haze.

[0010] Preferably, in step S2, the mass ratio of the PET particles to the PMMA particles is 7:(2-4).

[0011] By adopting the above technical solution, when the PMMA particle content is too low, the effect of improving the glass transition temperature of the PET and PMMA blend system is weak; when the PMMA particle content is too high, due to the slightly poor compatibility of the PET and PMMA blend system, it may cause excessive phase separation between PET and PMMA, thereby reducing the light transmittance; for this reason, after extensive research and experimental verification, the applicant finally determined that the mass ratio of PET particles and PMMA particles in this application is preferably the above.

[0012] Preferably, in step S2, EVA is dissolved in a solvent together with the PET particles and PMMA particles.

[0013] By adopting the above technical solution, the molecular chain of EVA is composed of non-polar ethylene segments and polar vinyl acetate segments. The addition of EVA can increase the interfacial contact area between PET and PMMA through "molecular chain entanglement". The polar ester group of EVA can form van der Waals force and weak hydrogen bond interaction with the polar groups of PET particles and PMMA particles, while the non-polar ethylene segment is compatible with the methylene segment of PET and the side methyl group of PMMA through dispersion force, thereby forming an "anchoring" effect at the interface between the two phases, reducing interfacial tension and reducing the possibility of excessive phase separation between PET and PMMA.

[0014] Because EVA has both polar and non-polar segments, it is between PET (strong polarity) and PMMA (weak polarity), forming a "PMMA-EVA-PET" gradient distribution from the surface to the matrix. The refractive index of EVA is between PET and PMMA. In the process of forming an optical diffusion film, EVA can further transition the refractive index between PET and PMMA, reduce the interface refractive index difference, reduce the reflection loss when light passes through, and further improve the light transmittance.

[0015] Preferably, the mass ratio of the PET particles to EVA is 7:(0.5-1).

[0016] By adopting the above technical solution, when the EVA content is too low, the effect of EVA on improving the compatibility of PET and PMMA is weak; when the EVA content is too high, it may cause local aggregation of EVA and destroy the original gradient refractive index distribution; for this reason, the applicant finally determined after a lot of research and experimental verification that the mass ratio of PET particles and EVA in this application is preferably the above.

[0017] Preferably, the VA content of the EVA is 20-30 wt%.

[0018] By adopting the above technical solution, when the VA content of EVA is too low, the non-polar chain segments of EVA dominate, and it may be difficult to effectively reduce the interfacial tension between the two phases; when the VA content of EVA is too high, there are too many polar groups in the EVA molecular chain, and the polarity of EVA is close to that of PET, which may weaken the compatibilization effect on PMMA; for this reason, the applicant finally determined after a lot of research and experimental verification that the VA content of the EVA in this application is preferably as above.

[0019] Preferably, in step S2, nano-titanium dioxide is added to the polymer solution, and the mixture is stirred sufficiently to uniformly disperse the nano-titanium dioxide in the polymer solution to obtain a mixed solution, and then the polydimethylsiloxane plate is placed on the mixed solution.

[0020] By adopting the above technical solution, nano-titanium dioxide particles can serve as phase separation nucleation points, guiding the PET / PMMA polymer solution to phase separate more evenly during the process of the solvent being absorbed by the polydimethylsiloxane flat plate, optimizing the uniformity of the internal pore structure of the membrane and the regularity of the surface concave and convex parts, thereby ensuring the high haze and high light transmittance of the optical diffusion film.

[0021] Nano-titanium dioxide particles are combined with the polymer matrix through physical entanglement and interfacial forces, which can act as a "rigid skeleton" to enhance the mechanical strength of the film, reduce the blockage of the pore structure and smooth the surface texture caused by the softening of PET, and further enhance the heat resistance of the optical diffusion film.

[0022] Preferably, the mass ratio of the PET particles to nano-titanium dioxide is 7:(0.1-0.5).

[0023] By adopting the above technical solution, when the content of nano-titanium dioxide is too little, it is difficult for nano-titanium dioxide to guide the PET / PMMA polymer solution to phase separate more evenly and to act as a "rigid skeleton" to enhance the mechanical strength of the membrane; when the content of nano-titanium dioxide is too much, the nano-titanium dioxide may agglomerate, resulting in a sudden increase in the viscosity of the solution and uneven dispersion, which in turn reduces the optical properties; for this reason, the applicant has finally determined, after extensive research and experimental verification, that the mass ratio of the PET particles and nano-titanium dioxide in this application is preferably the above.

[0024] Preferably, the solvent is one of chloroform and tetrahydrofuran.

[0025] By adopting the above technical solution, both PET and PMMA have good solubility in chloroform and tetrahydrofuran. As solvents act as media for the movement of molecular chains, chloroform and tetrahydrofuran can effectively reduce the viscosity difference between PET and PMMA, making it easier for rigid PMMA segments to embed into the PET network; at the same time, chloroform and tetrahydrofuran can also dissolve EVA, allowing EVA to fully play its role in promoting the compatibility of PET and PMMA.

[0026] Preferably, in step S2, the temperature of the polymer solution is 40-55°C.

[0027] By adopting the above technical solution, when the temperature of the polymer solution is too low, the solubility of each component in the solvent decreases, which is not conducive to the uniform mixing of the components in the solvent. In addition, the solvent evaporates slowly at low temperatures, and the efficiency of the polydimethylsiloxane plate in absorbing the solvent will be reduced; when the temperature of the polymer solution is too high, the solvent evaporates too quickly, and the polydimethylsiloxane plate absorbs a large amount of solvent in a short period of time, which will cause the local concentration of the polymer solution to rise sharply, thereby causing the phase separation process to be violent and difficult to control. For this reason, after extensive research and experimental verification, the applicant finally determined that the temperature of the polymer solution of this application is preferably above.

[0028] Preferably, the mass concentration of the polymer solution is 15-25 wt%.

[0029] By adopting the above technical solution, when the mass concentration of the polymer solution is too low, the effective components such as PET and PMMA in the solution are too few, the formed film layer is too thin, the internal pore structure and the surface uneven parts are easy to collapse, and it is difficult to maintain a stable microstructure; when the mass concentration of the polymer solution is too high, the solution viscosity is high, and the solvent's dissolution efficiency of high-concentration polymers decreases, which may lead to a violent phase separation process and uneven pore structure distribution; for this reason, the applicant finally determined after a lot of research and experimental verification that the mass concentration of the polymer solution of this application is preferably above.

[0030] In summary, this application has the following beneficial effects: 1. This application utilizes PMMA as a high-glass-transition-temperature component blended with PET to increase the overall glass-transition temperature of the blended system, effectively maintaining the internal pore structure and surface irregularities, and improving the practicality of the optical diffuser film in high-temperature environments. The refractive index difference between PET and PMMA is utilized to form a refractive index gradient, and a polydimethylsiloxane plate is used to induce phase separation of the polymer solution, forming a pore structure and irregularities. The refractive index difference between the air pores and the polymer phase provides strong scattering, and the refractive index gradient between PMMA and PET forms a secondary scattering interface, which reduces light absorption while maintaining high transmittance while ensuring high haze. 2. This application utilizes EVA to increase the interfacial contact area between PET and PMMA through "molecular chain entanglement." Its polar ester groups form van der Waals forces and weak hydrogen bonds with the polar groups of PET and PMMA. The non-polar segments are compatible with PET and PMMA through dispersion forces, forming an "anchoring" effect at the interface, reducing interfacial tension and the possibility of excessive phase separation. EVA has both polar and non-polar segments, which is between PET (strong polarity) and PMMA (weak polarity). Its refractive index is also between the two. During the film formation process, it can bridge the refractive index difference, reduce interfacial reflection loss, and increase light transmittance. 3. This application uses nano-titanium dioxide particles as phase separation nucleation points to guide the uniform phase separation of the mixed liquid, optimize the pore structure and surface morphology within the membrane, and ensure the high haze and high transmittance of the optical diffusion film; at the same time, nano-titanium dioxide is combined with the polymer matrix to form a "rigid skeleton", which enhances the mechanical strength and heat resistance of the diffusion film and prevents structural deformation. DETAILED DESCRIPTION

[0031] The raw materials in this application include the following parts: Polydimethylsiloxane: a commercially available product with CAS number 9016-00-6; Curing agent: aniline methyl triethoxysilane, γ-aminopropyl triethoxysilane and ethyl orthosilicate, etc. This application uses the commercially available product of aniline methyl triethoxysilane with CAS number 3473-76-5; PET: polyethylene terephthalate, a commercially available product with CAS number 25038-59-9; PMMA: polymethyl methacrylate, a commercially available product with CAS number 9011-14-7; EVA: ethylene-vinyl acetate copolymer, using models V5274 (VA content: 17 wt%), V422 (VA content: 20 wt%), EV360 (VA content: 25 wt%), V422 (VA content: 28 wt%), and V523 (VA content: 33 wt%) produced by Mitsui Chemicals of Japan for illustration; Nano titanium dioxide: a commercially available product with CAS number 13463-67-7 is used; Chloroform: a commercial product with CAS number 67-66-3 was used; Tetrahydrofuran: a commercially available product with CAS number 109-99-9 was used; The present application is further described in detail below with reference to the following examples and comparative examples.

[0032] Example 1 A method for preparing an optical diffusion film comprises the following steps: S1 1000g of aniline methyl triethoxysilane and 10000g of polydimethylsiloxane were mixed and cured for 4h, followed by 10min of oxygen plasma treatment and then aged at room temperature for 8h to obtain a polydimethylsiloxane plate; S2. Dissolve 700 g of PET particles and 300 g of PMMA particles in 4000 g of chloroform to obtain a polymer solution with a mass concentration of 20 wt% (control the solution temperature at 45°C); place the polydimethylsiloxane plate prepared in step S1 on top of the polymer solution and let it stand for 12 hours to obtain an optical diffusion film.

[0033] Examples 2-5 In Example 2-5, based on the preparation method of Example 1, the total mass of the PET particles and the PMMA particles was maintained at 1000 g, and the mass ratio of the PET particles to the PMMA particles was adjusted. The specific adjustments are shown in Table 1.

[0034] Comparative Example 1 Comparative Example 1 Based on the preparation method of Example 1, in step S2, 700 g of PET particles and 300 g of PMMA particles were replaced with 1000 g of PET particles, and other conditions remained unchanged.

[0035] Table 1 Mass ratio of PET particles and PMMA particles and performance test table of Examples 1-5 and Comparative Example 1 Performance Test The optical diffusion films of Examples 1-5 and Comparative Example 1 were subjected to the following performance tests. The test results are shown in Table 1: (1) Optical performance The haze and total light transmittance of the optical diffusion film were measured using a NDH 2000N haze meter produced by Nippon Denshoku Co., Ltd. using the transmitted light method.

[0036] (2) Heat resistance The optical diffuser film was placed in a 70°C environment for 72 hours, then taken out and the haze and total light transmittance of the optical diffuser film after high temperature treatment were measured using a NDH 2000N haze meter from Japan Denshoku. The haze retention rate and total light transmittance retention rate were calculated as follows: Haze retention rate = haze after high temperature treatment / original haze × 100%; Total light transmittance retention rate = total light transmittance after high temperature treatment / original total light transmittance × 100%.

[0037] Referring to Table 1, by comparing Examples 1-5 with Comparative Example 1, it can be seen that the haze, total light transmittance, and heat resistance of Examples 1-5 are better than those of Comparative Example 1. This is because in Examples 1-5, PET and PMMA are mixed to prepare an optical diffusion film. Due to the difference in refractive index and solubility in chloroform between PET and PMMA, a refractive index gradient can be formed in the diffusion film. At the same time, the polydimethylsiloxane flat plate absorbs the solvent to promote the phase separation of the polymer solution, and a porous structure can be formed inside the optical diffusion film and a concave-convex portion can be formed on the surface. The refractive index difference between the air pores and the polymer phase can provide strong scattering ability, and the refractive index gradient distribution of the optical diffusion film can form a secondary scattering interface, thereby improving the haze of the diffusion film; the refractive index gradient distribution can also optimize light conduction and reduce absorption, thereby improving the total light transmittance.

[0038] On the other hand, the glass transition temperature of PMMA added in Examples 1-5 is higher than that of PET, and its rigid molecular chains can be embedded in the molecular network of PET, restricting the movement of PET chain segments, thereby increasing the overall glass transition temperature of the blending system, making the optical diffusion films of Examples 1-5 less likely to soften during high-temperature treatment, and can effectively maintain the porous structure inside the diffusion film and the concave and convex parts on the surface, maintaining its haze and total light transmittance.

[0039] A comprehensive comparison of Examples 1-5 shows that Example 1 has better performance. This is because when the PMMA particle content is too low, the effect of improving the glass transition temperature of the PET and PMMA blend system is weak; when the PMMA particle content is too high, the compatibility of the PET and PMMA blend system is slightly poor, which may lead to excessive phase separation between PET and PMMA, thereby reducing the transmittance. Therefore, Example 1 is preferred.

[0040] Examples 6-10 Example 6 Based on the preparation method of Example 4, in step S2, 75g of EVA model EV360 (VA content is 25wt%), 700g of PET particles and 300g of PMMA particles are dissolved in 4000g of chloroform, and the other conditions remain unchanged.

[0041] In Examples 7-10, based on the preparation method of Example 6, the amount of EVA added was adjusted. The specific adjustments are shown in Table 2.

[0042] The optical diffusion films of Examples 6-10 were subjected to the above performance tests, and the test results are shown in Table 2. Table 2 Mass ratio of PET particles and EVA and performance test table of Examples 1, 4 and 6-10 Referring to Table 2, by comparing Example 4 with Example 6-10, it can be seen that the haze, total light transmittance and heat resistance of Example 6-10 are all better than those of Example 4. This is because EVA is added to Example 6-10, which can increase the interfacial contact area between PET and PMMA through "molecular chain entanglement" and form an "anchoring" effect at the interface between the two phases, thereby reducing excessive phase separation between PET and PMMA and improving the compatibility between PET and PMMA, which is beneficial for PMMA as a high glass transition temperature component to improve the heat resistance of the blending system; EVA can also further transition the refractive index between PET and PMMA, reduce the interfacial refractive index difference, reduce the reflection loss when light passes through, and improve the total light transmittance.

[0043] By comparing Examples 6-10, it can be seen that when the amount of EVA added is too low or too high, the performance of the optical diffusion film will be reduced. This is because when the EVA content is too low, the effect of EVA on improving the compatibility of PET and PMMA is weak; when the EVA content is too high, it may cause local aggregation of EVA and destroy the original gradient refractive index distribution.

[0044] The optical diffusion films of Examples 6 and 8-9 improve the negative effects of insufficient compatibility of PET and PMMA on optical properties and heat resistance in Example 4, making the optical diffusion films of Examples 6 and 8-9 superior to those of Example 1.

[0045] Examples 11-14 Example 11 Based on the preparation method of Example 6, in step S2, 75g of EVA with model EV360 (VA content of 25wt%) is replaced with 75g of EVA with model V5274 (VA content of 17wt%), and the other conditions remain unchanged.

[0046] Example 12 Based on the preparation method of Example 6, in step S2, 75g of EVA with model EV360 (VA content of 25wt%) is replaced with 75g of EVA with model V422 (VA content of 20wt%), and the other conditions remain unchanged.

[0047] Example 13 is based on the preparation method of Example 6. In step S2, 75g of EVA with model EV360 (VA content of 25wt%) is replaced with 75g of EVA with model V422 (VA content of 28wt%), and the other conditions remain unchanged.

[0048] Example 14 Based on the preparation method of Example 6, in step S2, 75g of EVA with model EV360 (VA content of 25wt%) is replaced with 75g of EVA with model V523 (VA content of 33wt%), and other conditions remain unchanged.

[0049] The optical diffusion films of Examples 11-14 were subjected to the above performance tests, and the test results are shown in Table 3.

[0050] Table 3 Performance test table of Example 6 and Examples 11-14 Referring to Table 3, it can be seen from the comparison between Example 16 and Examples 11-14 that when the VA content of EVA is too low or too high, the heat resistance of the optical diffusion film will be reduced. This is because when the VA content of EVA is too low, the non-polar chain segment of EVA is dominant, and it may be difficult to effectively reduce the interfacial tension between the two phases, and the effect of improving the compatibility between PET and PMMA is small; when the VA content of EVA is too high, there are too many polar groups in the EVA molecular chain, and the polarity of EVA is close to that of PET, which may weaken the compatibilization effect on PMMA.

[0051] Examples 15-19 Example 15 Based on the preparation method of Example 1, in step S2, 25 g of nano-titanium dioxide is added to the polymer solution, and the mixture is stirred thoroughly so that the nano-titanium dioxide is evenly dispersed in the polymer solution to obtain a mixed solution, and then the polydimethylsiloxane plate prepared in step S1 is placed on the mixed solution, and the other conditions remain unchanged.

[0052] In Examples 16-19, based on the preparation method of Example 15, the addition amount of nano-titanium dioxide was adjusted. The specific adjustments are shown in Table 4.

[0053] The optical diffusion films of Examples 15-19 were subjected to the above performance tests, and the test results are shown in Table 4.

[0054] Table 4 Addition amount and performance test table of nano titanium dioxide in Example 1 and Examples 15-19 Referring to Table 4, by comparing Example 1 and Examples 15-19, it can be seen that the optical properties and heat resistance of Examples 15-19 are better than those of Example 1. This is because the nano-titanium dioxide in Examples 15-19 can serve as a phase separation nucleation point. In the process of the solvent being absorbed by the polydimethylsiloxane flat plate, the PET / PMMA polymer solution is guided to phase separate more evenly, thereby optimizing the uniformity of the internal pore structure of the membrane and the regularity of the surface concave and convex parts, thereby ensuring the high haze and high light transmittance of the optical diffusion film.

[0055] On the other hand, during the high-temperature treatment process, nano-titanium dioxide acts as a "rigid skeleton" to enhance the mechanical strength of the film, provide rigid support during the softening process of PET, reduce the blockage of the pore structure and smooth the surface texture caused by the softening of PET, thereby improving the heat resistance of the optical diffusion film.

[0056] By comparing Examples 15-19, it can be seen that too little or too much content of nano-titanium dioxide will reduce the optical properties and heat resistance of the optical diffusion film. This is because when the content of nano-titanium dioxide is too little, it is difficult for nano-titanium dioxide to guide the polymer solution to phase separate more evenly and to act as a "rigid skeleton" to enhance the mechanical strength of the film; when the content of nano-titanium dioxide is too much, the nano-titanium dioxide may agglomerate, resulting in a sudden increase in the viscosity of the solution and uneven dispersion, which in turn reduces the optical properties.

[0057] Examples 20-24 Example 20 Based on the preparation method of Example 1, in step S2, 4000 g of chloroform was replaced with 4000 g of tetrahydrofuran, and the other conditions remained unchanged.

[0058] In Examples 21-24, based on the preparation method of Example 1, 700 g of PET particles and 300 g of PMMA were kept unchanged, and the mass concentration of the polymer solution was adjusted. The specific adjustments are shown in Table 5.

[0059] The optical diffusion films of Examples 20-24 were subjected to the above performance tests, and the test results are shown in Table 5.

[0060] Table 5 Mass concentration and performance test table of polymer solutions of Example 1 and Examples 20-24 Referring to Table 5, by comparing Example 1 and Example 20, it can be seen that chloroform and tetrahydrofuran can both be used as solvents for the polymer solution. This is because both PET and PMMA have good solubility in chloroform and tetrahydrofuran. Solvents act as media for molecular chain movement. Chloroform and tetrahydrofuran can effectively reduce the viscosity difference between PET and PMMA, making it easier for rigid PMMA segments to embed into the PET network. In comparison, the optical diffusion film prepared in Example 1 has better performance, so Example 1 is preferred.

[0061] By comparing Example 1 and Examples 21-24, it can be seen that both too low and too high mass concentrations of the polymer solution will lead to the optical properties of the optical diffusion film. This is because when the mass concentration of the polymer solution is too low, the effective components such as PET and PMMA in the unit volume of the polymer solution are too few, and the formed film layer is too thin, making it difficult to maintain a stable microstructure; when the mass concentration of the polymer solution is too high, the solution viscosity is high, and the solvent's dissolution efficiency of the high-concentration polymer decreases, which may lead to a violent phase separation process.

[0062] Examples 25-28 In Examples 25-28, based on the preparation method of Example 1, the temperature of the polymer solution was adjusted. The specific adjustments are shown in Table 6.

[0063] The optical diffusion films of Examples 25-28 were subjected to the above performance tests, and the test results are shown in Table 6.

[0064] Table 6 Temperature and performance test table of polymer solutions of Example 1 and Examples 25-28 Referring to Table 6, by comparing Example 1 with Examples 25-28, it can be seen that when the temperature of the polymer solution is too low or too high, the performance of the optical diffusion film will be reduced. This is because when the temperature of the polymer solution is too low, the solubility of each component in the solvent decreases, which is not conducive to the uniform mixing of the components in the solvent; when the temperature of the polymer solution is too high, the solvent volatilization rate is too fast, and the polydimethylsiloxane plate absorbs a large amount of solvent in a short period of time, which will cause the local concentration of the polymer solution to rise sharply, resulting in a violent and difficult to control phase separation process.

[0065] Example 29 A method for preparing an optical diffusion film comprises the following steps: S1 1000g of aniline methyl triethoxysilane and 10000g of polydimethylsiloxane were mixed and cured for 4h, followed by 10min of oxygen plasma treatment and then aged at room temperature for 8h to obtain a polydimethylsiloxane plate; S2. Dissolve 700 g of PET particles, 300 g of PMMA particles, and 75 g of EVA model EV360 (VA content is 25 wt%) in 4000 g of chloroform to obtain a polymer solution (control the solution temperature at 45°C); then add 25 g of nano-titanium dioxide to the polymer solution, stir thoroughly so that the nano-titanium dioxide is evenly dispersed in the polymer solution to obtain a mixed solution, place the polydimethylsiloxane plate prepared in step S1 on top of the mixed solution, and let it stand for 12 hours to obtain an optical diffusion film.

[0066] The optical diffusion film of Example 29 was subjected to the above performance test, and the test results are shown in Table 7.

[0067] Table 7 Performance test table of Examples 1, 6, 15 and 29 Referring to Table 7, by comparing Example 1, Example 6, Example 15 and Example 29, it can be seen that the heat resistance of Example 29 is better than that of Example 1, Example 6 and Example 15. This is because when EVA and nano-titanium dioxide are added at the same time, EVA can improve the polymer compatibility and provide a more uniform dispersion environment for nano-titanium dioxide, so that nano-titanium dioxide can give full play to its mechanical reinforcement effect and protect the gradient structure to exist stably at high temperatures.

[0068] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing an optical diffusion film, characterized in that: The following steps are involved: S1. The curing agent and polydimethylsiloxane were mixed and cured, and then subjected to oxygen plasma treatment and room temperature aging to obtain a polydimethylsiloxane plate; S2. Dissolve the PET particles and PMMA particles in a solvent to obtain a polymer solution; place the polydimethylsiloxane plate on top of the polymer solution and let it stand to obtain an optical diffusion film.

2. The method for preparing an optical diffusion film according to claim 1, wherein: In step S2, the mass ratio of the PET particles to the PMMA particles is 7:(2-4).

3. The method for preparing an optical diffusion film according to claim 1, wherein: In step S2, EVA, the PET particles and the PMMA particles are dissolved in a solvent.

4. The method for preparing an optical diffusion film according to claim 3, wherein: The mass ratio of the PET particles to EVA is 7:(0.5-1).

5. The method for preparing an optical diffusion film according to claim 4, wherein: The VA content of the EVA is 20-30 wt %.

6. The method for preparing an optical diffusion film according to claim 1, wherein: In step S2, nano-titanium dioxide is added to the polymer solution, and the mixture is stirred sufficiently to uniformly disperse the nano-titanium dioxide in the polymer solution to obtain a mixed solution, and then the polydimethylsiloxane plate is placed on the mixed solution.

7. The method for preparing an optical diffusion film according to claim 6, wherein: The mass ratio of the PET particles to the nano-titanium dioxide is 7:(0.1-0.5).

8. The method for preparing an optical diffusion film according to claim 1, wherein: The solvent is one of chloroform and tetrahydrofuran.

9. The method for preparing an optical diffusion film according to claim 1, wherein: In step S2, the temperature of the polymer solution is 40-55°C.

10. The method for preparing an optical diffusion film according to claim 1, wherein: The mass concentration of the polymer solution is 15-25 wt %.

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