A protective film for diffusion sheet and a method for manufacturing the same

Abstract

This invention discloses a protective film for diffusion sheets and its preparation method, belonging to the field of protective film technology. The protective film uses vinylphenyl-modified polysiloxane as the main adhesive, combined with a low-hydrogen silicone oil and vinyl MQ silicone resin composite crosslinking agent, a two-component compound anchoring agent, PMMA optically compatible microspheres, polyether-modified polysiloxane antistatic agent, and a mixed solvent, and is prepared by step-by-step temperature curing. This invention inhibits small molecule migration at its source through phenyl modification of the main adhesive, constructs a stable adhesive layer structure through a double crosslinking network, achieves non-destructive protection of the diffusion sheet microstructure through microspheres, and significantly enhances the anchoring force of the substrate through the compound system. The resulting protective film has a peel strength of 6~13 g / in at room temperature, peel strength fluctuation ≤5% after aging at 85℃ / 85%RH for 30 days, leaves no residue or film mark after peeling, has a diffusion particle damage rate of 0%, and a surface resistivity stable at 10 Ω·cm. 9 ~10 11 Ωcm can be applied to the entire process of protection for diffuser sheets in high-end display backlight modules.

Description

Technical Field

[0001] This invention belongs to the field of protective film technology, specifically relating to a protective film for diffusion sheets and its preparation method. Background Technology

[0002] The diffuser is a core optical component of the backlight module. Its core function is to transform point / line light sources into uniform and soft surface light sources. The surface of the diffuser is usually coated with an optical coating containing micron-sized diffusion particles. Once this microstructure is contaminated, damaged, or electrostatically broken down, it will directly lead to problems such as uneven light output, bright spots, dark spots, haze, and reduced light transmittance, causing display device failure. Therefore, the diffuser must be protected with a special protective film throughout the entire process of production, die-cutting, storage, transportation, and lamination. The performance of the protective film is subject to stringent comprehensive requirements: ① Stable peel force with light peel characteristics, neither warping nor tearing the diffuser coating; ② Excellent anti-migration properties, with no migration of small molecules in the adhesive layer after long-term storage, and no adhesive residue after peeling; ③ Good microstructure protection; ④ Meets antistatic performance standards; ⑤ Good optical compatibility.

[0003] Currently, the mainstream protective film for diffusion sheets is the silicone system. Compared with acrylic adhesives, it has better high and low temperature resistance and peel strength stability. However, existing silicone protective films still have insurmountable technical defects. Chinese patent CN115960547A discloses a protective film for diffusion sheets, using a common vinyl siloxane polymer as the main adhesive, a single hydrogen-containing silicone oil as the crosslinking agent, and a silane coupling agent KH171 as the anchoring agent. Although it achieves basic peeling effect, it has the following drawbacks: 1. The main adhesive is a common linear vinyl siloxane, which lacks migration-resistant and weather-resistant modifying groups. Under high temperature and high humidity conditions, small molecule cyclosiloxanes and unreacted monomers are prone to migration, causing optical performance degradation. 2. The single hydrogen-containing silicone oil crosslinking system forms a crosslinking network only through hydrosilylation. The crosslinking density is uneven, the cohesion of the adhesive layer is insufficient, and the degree of crosslinking continues to change after long-term storage, easily resulting in residual adhesive and adhesive layer transfer; moreover, there is no secondary crosslinking structure, which cannot form a dense network to bind the migration of small molecules.

[0004] In summary, there is an urgent need to develop a protective film specifically for diffusion sheets with excellent overall performance. Summary of the Invention

[0005] One of the objectives of this invention is to provide a protective film specifically for diffuser sheets, in order to solve the problems of existing diffuser sheet protective films being prone to leaving film imprints and adhesive residue, and having unstable peel strength.

[0006] The second objective of this invention is to provide a method for preparing a protective film for diffusion sheets, which is simple and controllable and suitable for large-scale industrial production.

[0007] The objective of this invention can be achieved through the following technical solutions: In a first aspect, a protective film for diffusion sheets comprises, by weight, the following components: 100 parts of vinylphenyl modified polysiloxane, 1.5 to 4.0 parts of composite crosslinking agent, 0.6 to 2.0 parts of compound anchoring agent, 0.2 to 0.5 parts of platinum catalyst, 1.0 to 3.0 parts of optically adaptable microspheres, 0.3 to 1.0 parts of polymeric antistatic agent, and an appropriate amount of mixed solvent; The vinylphenyl-modified polysiloxane has a linear molecular structure, with the main chain composed of dimethylsiloxane segments and methylphenylsiloxane segments. Both ends of the molecule are capped with vinyl groups. The phenyl molar content is 5%–10%, the vinyl content is 0.4–0.7 mmol / g, and the viscosity at 25°C is 2000–2600 mPa. s, with a number-average molecular weight of 70,000~100,000 g / mol; The composite crosslinking agent is composed of low-hydrogen silicone oil and vinyl MQ silicone resin in a mass ratio of 1:1.5~3.

[0008] By designing vinylphenyl-modified polysiloxane, small molecule migration is suppressed. Combined with a composite crosslinking agent to construct a double crosslinking network, a compound anchoring agent to enhance substrate adhesion, optically adaptable microspheres to achieve microstructure suspension protection, and a polymeric antistatic agent to achieve migration-free antistatic properties, thus solving the core pain points of existing diffusion sheet protective films. The aforementioned ratio range ensures that the main adhesive possesses excellent anti-migration properties, heat resistance, and crosslinking reactivity, providing stable mechanical properties and peel characteristics for the adhesive layer. The ratio range of the composite crosslinking agent ensures that the adhesive layer forms a uniform and dense crosslinking network, balancing cohesion and flexibility, and preventing the adhesive layer from becoming brittle or sticky. The ratio range of the compound anchoring agent ensures that the adhesive layer forms a high-strength bond with the PET substrate, without delamination or transfer. The ratio range of the optically adaptable microspheres and the polymeric antistatic agent achieves functionality without affecting the optical and adhesive properties of the adhesive layer.

[0009] Furthermore, the vinylphenyl-modified polysiloxane is prepared by the following steps: A1. Monomer dehydration: Octamethylcyclotetrasiloxane and methylphenylcyclotrisiloxane were added to the reactor and dehydrated at 110℃ and a vacuum of -0.095 to -0.1 MPa for 1.5 to 2 hours, controlling the monomer moisture content to ≤0.02%; the end-capping agent tetramethyldivinyldisiloxane and the potassium hydroxide alcohol solution catalyst were dried by molecular sieve and set aside for later use. A2. Polymerization reaction: Add tetramethyldivinyldisiloxane to the dehydrated monomer, purge the air in the reactor with nitrogen three times, start stirring, control the speed at 300~400 rpm, raise the temperature to 80~85℃, add potassium hydroxide alcohol solution, stir and mix evenly, raise the temperature to 100~110℃, and keep the reaction at this temperature for 3~4 hours. A3. Neutralization Termination: Cool the reaction system to 40~50℃, add the measured amount of glacial acetic acid, stir and neutralize for 15~20min, adjust the pH of the system to 6.5~7.0, and terminate the polymerization reaction; A4. Refining to remove low-boiling-point substances: The neutralized system is heated to 140~150℃ and distilled under reduced pressure for 2~3 hours under vacuum conditions of -0.098~-0.1MPa to remove unreacted cyclosiloxane monomers and low-boiling-point substances; A5. Filtration: Vinylphenyl modified polysiloxane is obtained by filtration through a plate and frame filter press.

[0010] First, the moisture content of the system is strictly controlled through monomer dehydration to avoid side reactions caused by moisture and ensure the controllability of the polymerization reaction. Then, methylphenylsiloxane segments are introduced into the polydimethylsiloxane backbone through anionic ring-opening polymerization, with both ends capped by vinyl groups. The introduction of phenyl groups can significantly increase the cohesive energy density of the molecular chain and reduce the surface energy, inhibiting the migration of small molecule cyclic siloxanes at the source, while greatly improving the heat resistance and UV aging resistance of the adhesive layer. By precisely controlling the phenyl content, the refractive index of the diffuser optical coating can be accurately matched to avoid interfacial reflection. The uniform distribution of vinyl active sites at both ends provides a regular reaction basis for the crosslinking system, ensuring that the crosslinking network is uniform and dense, and the peel force is stable.

[0011] Furthermore, in step A1, the mass concentration of the potassium hydroxide alcohol solution is 20%, and the solvent is anhydrous ethanol; in step A2, the mass ratio of octamethylcyclotetrasiloxane, methylphenylcyclotrisiloxane, tetramethyldivinyldisiloxane, and potassium hydroxide alcohol solution is 100:(5~12):(2~5):(0.1~0.3). This ratio range allows for precise control of the phenyl content, vinyl content, molecular weight, and viscosity of the main adhesive, ensuring that the performance of the main adhesive meets the design requirements.

[0012] Furthermore, in step A2, the stirring speed is 300-400 rpm, and the reaction time is 3-4 hours; in step A4, the vacuum distillation temperature is 140-150℃, the vacuum degree is ≥-0.098 MPa, and the time is 2-3 hours; in step A5, filtration is performed using a 200-mesh plate and frame filter. The stirring speed and reaction time ensure a uniform and complete polymerization reaction with a narrow molecular weight distribution; vacuum distillation thoroughly removes unreacted monomers and low-boiling substances, reducing the amount of migratable small molecules at the source; filtration removes mechanical impurities from the system, ensuring the cleanliness of the main adhesive and meeting the requirements for optical-grade applications.

[0013] Furthermore, the compound anchoring agent is prepared by compounding vinyltrimethoxysilane (A171) and γ-glycidoxypropyltrimethoxysilane (KH560) in a mass ratio of 1:1.2~2.0; the low-hydrogen silicone oil has a hydrogen content of 0.8%~1.2%, the vinyl MQ silicone resin has a vinyl content of 1.0~1.6 mmol / g, and the M / Q ratio is 0.6~0.9.

[0014] The two components form a synergistic anchoring system: the vinyl group of A171 can participate in the hydrosilylation reaction, directly grafting anchoring agent molecules into the crosslinking network of the adhesive layer, preventing anchoring agent migration; the alkoxy group of KH560 can form covalent bonds with the hydroxyl groups on the corona-exposed surface of the PET substrate, and the epoxy group can improve the adhesion to the substrate, while forming a synergistic combination with the crosslinking system. After the two are combined, the anchoring force between the adhesive layer and the PET substrate is improved, solving the problem of debonding and transfer after repeated peeling. The low-hydrogen silicone oil provides active sites for the hydrosilylation reaction, forming a chemical crosslinking network; the M segment of the vinyl MQ silicone resin has excellent compatibility with the main adhesive, and the Q segment provides rigid support and physical entanglement. The two are combined to form an interpenetrating network structure, improving the cohesive force of the adhesive layer and reducing the migration rate of small molecules.

[0015] Furthermore, the platinum catalyst is a Castells platinum catalyst with a platinum content of 3000~5000ppm; the optically compatible microspheres are polymethyl methacrylate (PMMA) microspheres with an average particle size of 2~5μm and a refractive index of 1.49~1.51; and the polymeric antistatic agent is a polyether-modified polysiloxane, which is compatible and stable with the silicone system, does not migrate, and does not leave residues.

[0016] The Castel platinum catalyst exhibits high catalytic activity, rapid curing speed, and no side reactions. It enables rapid curing at low temperatures, avoiding damage to the PET substrate caused by high temperatures. PMMA microspheres are uniformly dispersed in the adhesive layer, forming a uniform micron-scale micro-protrusion structure on the adhesive layer surface. When the diffuser sheet is laminated, the micro-protrusions contact the planar area of ​​the diffuser sheet, while the diffusion particles on the diffuser sheet surface are located in the gaps between the micro-protrusions, protecting the microstructure of the diffuser sheet. Simultaneously, there is no interfacial reflection after lamination, which does not affect the transmittance and haze of the diffuser sheet. Polyether-modified polysiloxane is a high-molecular-weight antistatic agent with excellent compatibility with the main adhesive polysiloxane system, solving the problems of easy migration and contamination of small-molecule antistatic agents. Extremely low addition amounts can stabilize the surface resistance of the adhesive layer, effectively releasing static electricity during processing and preventing electrostatic breakdown of the optical coating of the diffuser sheet.

[0017] Furthermore, the mixed solvent is composed of ethyl acetate and No. 200 solvent oil in a volume ratio of 1:1~2, and the solid content of the adhesive is adjusted to 20%~30%. Ethyl acetate is a fast-drying solvent, while No. 200 solvent oil is a slow-drying solvent. The combination of the two can precisely adjust the evaporation rate of the adhesive, avoiding problems such as pinholes, shrinkage cavities, and poor leveling during the curing process, and improving the smoothness and appearance quality of the adhesive layer.

[0018] Furthermore, it also includes a PET substrate and a release film; the PET substrate has a thickness of 25~50μm; the release film is a single-sided fluorinated release PET film with a thickness of 25~38μm. The PET substrate provides a supporting carrier for the adhesive layer, and corona treatment can improve surface activity and enhance the anchoring force with the adhesive layer; the fluorinated release film has good compatibility with the silicone adhesive layer, stable release, and no problems such as poor release or silicone shedding.

[0019] Secondly, a method for preparing a protective film specifically for diffusion sheets includes the following steps: S1. Preparation of adhesive solution: Under light-protected conditions and at 25~30℃, vinylphenyl modified polysiloxane, composite crosslinking agent, composite anchoring agent, optically compatible microspheres, and polymeric antistatic agent are added to the mixed solvent according to the formula. Stir at 300~500r / min for 30~45min until the mixture is uniform. Then, add platinum catalyst and continue stirring for 15~20min. Finally, allow the mixture to stand under a vacuum of -0.08~-0.1MPa for 20~30min to degas, and the functional silicone adhesive solution is obtained. S2. Coating and curing: The functional silicone adhesive is coated onto the corona-treated surface of the PET substrate using a slit coating method at a coating speed of 30~50m / min. Then, it is placed in an oven for step-by-step heating and curing. After curing, a functional silicone adhesive layer with a thickness of 5~12μm is obtained. S3. Lamination and winding: Align the surface of the cured adhesive layer in step S2 with the release surface of the release film and laminate it. Control the lamination pressure to be 0.2~0.4MPa and the lamination speed to be 30~50m / min. After lamination, wind it up and cure it at 25~30℃ for 24~48h to obtain the special protective film for diffusion sheet.

[0020] First, during the adhesive preparation stage, light-protected conditions prevent deactivation of the platinum catalyst, stepwise addition ensures uniform dispersion of each component, and vacuum degassing removes air bubbles from the adhesive, guaranteeing a pinhole-free and defect-free coating. The key lies in the stepped temperature curing process. Four-stage gradient heating allows the solvent to gradually evaporate, avoiding problems such as pinholes, craters, and poor leveling caused by rapid evaporation. Simultaneously, it allows the hydrosilylation reaction to proceed gradually and fully, resulting in a more regular crosslinking network and preventing localized over-crosslinking leading to embrittlement and decreased cohesion, or insufficient crosslinking leading to stickiness and migration. Finally, by laminating the release film and curing, the crosslinking reaction is fully completed, the adhesive layer performance is stabilized, and the finished protective film is obtained.

[0021] Furthermore, in step S2, the stepped temperature-curing and drying process is as follows: First temperature zone: 60-70℃, dwell time 15-20s; Second temperature zone: 80-90℃, dwell time 20-25s; Third temperature zone: 110-120℃, dwell time 25-30s; Fourth temperature zone: 130-140℃, dwell time 30-40s; Total curing and drying time is 90-115s, and the cured adhesive layer has a curing degree ≥98%. The first temperature zone is a low-temperature pre-baking zone, allowing the solvent to evaporate slowly and the adhesive to level; the second and third temperature zones are reaction zones, where the hydrosilylation reaction proceeds gradually, and the cross-linking network is gradually formed; the fourth temperature zone is a high-temperature curing zone, ensuring the complete cross-linking reaction and thoroughly removing residual solvent.

[0022] Furthermore, in step S1, the stirring speed is 300~500 r / min, and the degassing is performed under vacuum with a vacuum degree of -0.08~-0.1 MPa; in step S3, direct sunlight is avoided during the curing process. The stirring speed ensures uniform dispersion of each component while avoiding the generation of bubbles from high-speed stirring; vacuum degassing can completely remove bubbles from the adhesive solution, ensuring the appearance quality of the adhesive layer; the curing conditions ensure complete cross-linking reaction of the adhesive layer, stable performance, and avoid yellowing and aging of the adhesive layer caused by direct sunlight.

[0023] The beneficial effects of this invention are: (1) In terms of composition, the present invention uses 100 parts of vinylphenyl modified polysiloxane as the core adhesive, which inhibits the migration of small molecules through phenyl modification and precisely controls the refractive index; 1.5~4.0 parts of composite crosslinking agent constructs an interpenetrating network structure of chemical and physical crosslinking, which greatly improves the cohesion of the adhesive layer and stabilizes the peel force; 0.6~2.0 parts of compound anchoring agent realizes the high-strength bonding between the adhesive layer and the PET substrate and avoids debonding and transfer; 1.0~3.0 parts of optically adaptable microspheres realize the suspended non-destructive protection of the diffuser sheet microstructure; 0.3~1.0 parts of polymeric antistatic agent realizes non-migrating electron-level antistatic. The components work synergistically to solve the problems of easy film imprint residue and unstable peel force of existing diffuser sheet protective films.

[0024] (2) This invention solves the problems of easy migration and refractive index mismatch of existing ordinary vinyl polysiloxanes by designing vinylphenyl modified polysiloxanes. The introduction of phenyl increases the cohesive energy density within the molecular chain, inhibiting the migration of small molecule cyclic siloxanes from the source. There is no residue or film mark under high temperature and high humidity conditions. At the same time, the refractive index of the adhesive layer is precisely controlled by the phenyl content, matching the optical coating of the diffuser sheet, with no interface reflection and no impact on optical performance. The vinyl active sites at both ends provide a uniform reaction basis for the crosslinking system, ensuring that the crosslinking network is dense and uniform.

[0025] (3) This invention introduces a composite crosslinking agent and a compound anchoring agent. The interpenetrating polymer network structure formed by the composite crosslinking agent enhances the cohesive force of the adhesive layer and reduces the migration rate of small molecules. The compound anchoring agent, through the different reaction mechanisms of the two silane coupling agents, forms an integrated chemical bond with the PET substrate and the crosslinking network of the adhesive layer, respectively, thereby enhancing the anchoring force and solving the problems of debonding and transfer after repeated peeling. In addition, the optically compatible microspheres used form a micro-protrusion structure on the surface of the adhesive layer, achieving zero-damage protection of the micron-level microstructure of the diffuser sheet. At the same time, the refractive index is precisely matched, without affecting the core optical parameters of the diffuser sheet. The polymeric antistatic agent is non-migrating and non-polluting, effectively avoiding the problem of electrostatic breakdown during processing and improving the product yield. Detailed Implementation

[0026] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0027] Example 1 This embodiment provides a protective film specifically for diffusion sheets, which is prepared through the following steps: (1) Preparation of vinylphenyl modified polysiloxane A1. Monomer dehydration: 100 parts of octamethylcyclotetrasiloxane and 8 parts of methylphenylcyclotrisiloxane were added to a reaction vessel and dehydrated at 110℃ and a vacuum of -0.098MPa for 1.5h, controlling the monomer moisture content to ≤0.02%; 3.2 parts of tetramethyldivinyldisiloxane and 0.2 parts of 20% potassium hydroxide ethanol solution were dried using 4A molecular sieves for later use. A2. Polymerization reaction: Tetramethyldivinyldisiloxane was added to the dehydrated monomer, nitrogen gas was introduced to replace the air in the reactor 3 times, stirring was started at 350 rpm, the temperature was raised to 82°C, potassium hydroxide ethanol solution was added, and after stirring and mixing evenly, the temperature was raised to 105°C and the reaction was maintained for 3.5 h. A3. Neutralization Termination: Cool the reaction system to 45°C, add 0.22 parts of glacial acetic acid, stir and neutralize for 18 minutes, adjust the pH of the system to 6.8, and terminate the polymerization reaction; A4. Low-boiling point removal purification: The neutralized system is heated to 145℃ and distilled under reduced pressure at a vacuum of -0.099MPa for 2.5 hours to remove unreacted cyclosiloxane monomers and low-boiling points; A5. Filtration: The mixture is filtered through a 200-mesh plate and frame filter to obtain the target vinylphenyl-modified polysiloxane. Testing showed a phenyl molar content of 7%, a vinyl content of 0.5 mmol / g, and a viscosity of 2300 mPa at 25℃. s, number average molecular weight 85000 g / mol.

[0028] (2) Preparation of protective film for diffusion sheet S1. Preparation of the adhesive solution: Under light-protected conditions and at 25°C, 100 parts of the vinylphenyl modified polysiloxane prepared above, 2.5 parts of the composite crosslinking agent (low-hydrogen silicone oil: vinyl MQ silicone resin = 1:2), 1.2 parts of the compound anchoring agent (A171:KH560 = 1:1.5), 1.5 parts of PMMA optical adapter microspheres, and 0.5 parts of polyether modified polysiloxane antistatic agent were added to a mixed solvent (ethyl acetate: No. 200 solvent oil = 1:1.5). The mixture was stirred at 400 r / min for 35 min until homogeneous. Then, 0.3 parts of Castel platinum catalyst were added, and the mixture was stirred for another 15 min. Finally, the mixture was allowed to stand under a vacuum of -0.09 MPa for 25 min to remove bubbles, resulting in a functional silicone adhesive solution with a solid content of 25%. S2. Coating and Curing: The functional silicone adhesive obtained in step S1 is coated onto the corona-treated surface of the PET substrate using a slot coating method at a speed of 40 m / min. Then, it is placed in an oven for stepped temperature curing and drying: first temperature zone 65℃, dwell time 18 s; second temperature zone 85℃, dwell time 22 s; third temperature zone 115℃, dwell time 28 s; fourth temperature zone 135℃, dwell time 35 s; total curing time 103 s. After curing, a functional silicone adhesive layer with a thickness of 10 μm is obtained, with a curing degree of 98.5%. S3. Lamination and winding: Align the surface of the cured adhesive layer in step S2 with the release surface of the release film and laminate it. Control the lamination pressure to be 0.3MPa and the lamination speed to be 40m / min. After lamination, wind it up and cure it at 25℃ for 36h. Avoid direct sunlight to obtain the special protective film for diffusion sheets.

[0029] Example 2 This embodiment provides a protective film specifically for diffusion sheets, which is prepared through the following steps: (1) Preparation of vinylphenyl modified polysiloxane The difference from Example 1 is that the amount of methylphenylcyclotrisiloxane added is 5 parts, while the remaining raw material ratios and process parameters are completely consistent with Example 1. The final vinylphenyl modified polysiloxane has a phenyl molar content of 5%, a vinyl content of 0.4 mmol / g, and a viscosity of 2000 mPa at 25°C. s, number average molecular weight 70000 g / mol.

[0030] (2) Preparation of protective film for diffusion sheet Compared with Example 1, the difference is that the amount of composite crosslinking agent added is 2.0 parts, the amount of compound anchoring agent added is 0.8 parts, and the remaining raw materials and preparation process are the same as in Example 1.

[0031] Example 3 This embodiment provides a protective film specifically for diffusion sheets, which is prepared through the following steps: (1) Preparation of vinylphenyl modified polysiloxane The difference from Example 1 is that the amount of methylphenylcyclotrisiloxane added is 12 parts, while the remaining raw material ratios and process parameters are completely consistent with Example 1. The final vinylphenyl modified polysiloxane has a phenyl molar content of 10%, a vinyl content of 0.7 mmol / g, and a viscosity of 2600 mPa at 25°C. s, number average molecular weight 100000 g / mol.

[0032] (2) Preparation of protective film for diffusion sheet Compared with Example 1, the difference is that the amount of composite crosslinking agent added is 3.5 parts, the amount of compound anchoring agent added is 1.8 parts, and the remaining raw materials and preparation process are the same as in Example 1.

[0033] Example 4 This embodiment provides a protective film specifically for diffusion sheets, which is prepared through the following steps: (1) Preparation of vinylphenyl modified polysiloxane The raw material ratio and process parameters are completely consistent with those in Example 1.

[0034] (2) Preparation of protective film for diffusion sheet Compared with Example 1, the difference is that the amount of optical adapter microspheres added is 1.0 part, the amount of polymer antistatic agent added is 0.3 parts, and the remaining raw materials and preparation process are the same as in Example 1.

[0035] Example 5 This embodiment provides a protective film specifically for diffusion sheets, which is prepared through the following steps: (1) Preparation of vinylphenyl modified polysiloxane The raw material ratio and process parameters are completely consistent with those in Example 1.

[0036] (2) Preparation of protective film for diffusion sheet Compared with Example 1, the difference is that the temperature of each temperature zone in the stepped heating curing process in step S2 is increased by 5°C, specifically: the first temperature zone is 70°C with a residence time of 18s; the second temperature zone is 90°C with a residence time of 22s; the third temperature zone is 120°C with a residence time of 28s; and the fourth temperature zone is 140°C with a residence time of 35s. The curing time in step S3 is 48h, and the other raw materials and preparation process are the same as in Example 1.

[0037] Example 6 This embodiment provides a protective film specifically for diffusion sheets, which is prepared through the following steps: (1) Preparation of vinylphenyl modified polysiloxane The raw material ratio and process parameters are completely consistent with those in Example 1.

[0038] (2) Preparation of protective film for diffusion sheet Compared with Example 1, the difference is that the mass ratio of A171 to KH560 in the compound anchoring agent is 1:2.0, while the other raw materials and preparation process remain the same as in Example 1.

[0039] Comparative Example 1 The difference between this comparative example and Example 1 is that the main adhesive used is 100 parts of ordinary vinyl polydimethylsiloxane, and the formula is 0.5 parts of hydrogen-containing silicone oil, 0.12 parts of KH171, and 0.24 parts of platinum catalyst. No composite crosslinking agent, compound anchoring agent, optically adaptable microspheres, or polymeric antistatic agent are added. The rest of the preparation process is the same as in Example 1.

[0040] Comparative Example 2 The difference between this comparative example and Example 1 is that the main adhesive used is ordinary vinyl polydimethylsiloxane without phenyl modification, while the other raw materials and preparation process remain the same as in Example 1.

[0041] Comparative Example 3 The difference between this comparative example and Example 1 is that only 2.5 parts of low-hydrogen silicone oil were used as the composite crosslinking agent, and vinyl MQ silicone resin was not added. The other raw materials and preparation process remained the same as in Example 1.

[0042] Comparative Example 4 The difference between this comparative example and Example 1 is that the compound anchoring agent uses only 1.2 parts of A171 and does not add KH560, while the other raw materials and preparation process remain the same as in Example 1.

[0043] Comparative Example 5 The difference between this comparative example and Example 1 is that no optical adapter microspheres are added, while the other raw materials and preparation process remain the same as in Example 1.

[0044] Performance testing All protective films for diffusion sheets prepared in the examples and comparative examples were subjected to the following core performance tests after curing at 25°C and 50% relative humidity for 72 hours: 1. Peel strength and stability test: According to GB / T2792-2014 "Test method for peel strength of adhesive tape", the protective film was adhered to a standard stainless steel plate, and the initial peel strength was tested using a universal tensile testing machine at a peel angle of 180° and a peel speed of 300 mm / min. After the sample was placed in a constant temperature and humidity chamber of 85℃ / 85%RH for 720h, the peel strength was tested again, and the peel strength change rate was calculated: Peel strength change rate = |peel strength after storage - initial peel strength| / initial peel strength × 100%.

[0045] 2. Residual Adhesive and Film Imprint Test: The protective film was adhered to the surface of a commercially available MiniLED backlight diffuser sheet and placed in an 85℃ / 85%RH constant temperature and humidity chamber for 720 hours. Then, it was peeled off at a speed of 300 mm / min. The surface of the diffuser sheet was observed for residual adhesive using a metallographic microscope. The haze change of the diffuser sheet before and after peeling was tested using a haze meter. At the same time, the presence of film imprint was visually observed under a 2000 lux standard lamp.

[0046] 3. Antistatic performance test: The surface resistance of the protective film adhesive layer was tested using a high resistance meter in accordance with GB / T1410-2006 "Test methods for volume resistivity and surface resistivity of solid insulating materials".

[0047] 4. Substrate anchoring force test: A universal tensile testing machine is used to test the 180° peel force between the protective film adhesive layer and the PET substrate. The peeling speed is 300 mm / min. The higher the peel force, the better the anchoring force. At the same time, observe whether there is any adhesive layer residue on the surface of the PET substrate after peeling.

[0048] The results are shown in Table 1: Table 1

[0049] As shown in Table 1, in terms of peel strength stability, the initial peel strength of all examples remained stable at 6~10 g / in, meeting the requirements for light peeling of the diffuser sheet protective film. After 30 days of high temperature and humidity aging, the peel strength change rate was ≤4.1%, which was far superior to Comparative Example 1 and Comparative Example 2. Among them, Example 3 showed the best peel strength stability, thanks to the higher phenyl content and the amount of composite crosslinking agent. Phenyl modification inhibited chain migration at the molecular level, and the double crosslinking network further ensured the long-term stability of the cohesive force of the adhesive layer. The peel strength change rates of Comparative Example 3 and Comparative Example 4 both exceeded 18%, directly confirming that the double network structure of the composite crosslinking agent and the compound anchoring system are the key to maintaining long-term peel strength stability.

[0050] Regarding the resistance to migration and contamination, all examples showed no residue or film marks after aging, with a haze change of ≤0.1%. In contrast, Comparative Examples 1-4 all exhibited varying degrees of residue, film marks, and haze degradation. Comparative Example 2, using ordinary vinyl polysiloxane without phenyl modification, showed severe residue and film marks after aging, with a haze change as high as 2.3%, fully verifying the role of phenyl modification in inhibiting the migration of small molecule cyclosiloxanes and resolving film mark contamination. Comparative Examples 3 and 4, due to the lack of crosslinking and anchoring systems, had insufficient cohesion in the adhesive layer, also exhibiting significant small molecule migration and film mark problems.

[0051] Regarding antistatic properties, the surface resistivity of the adhesive layer in all embodiments remained stable at 10 Ω·cm. 9 ~10 11 Ω The surface resistivity of the sample reaches the electronic-grade antistatic standard, effectively releasing static electricity during die-cutting and peeling processes, and preventing the optical coating of the diffuser sheet from being damaged by static electricity; while the surface resistivity of Comparative Examples 1 and 2 exceeds 10. 14 Ω cm, lacks anti-static protection capabilities, and cannot meet the precision machining requirements of high-end display devices.

[0052] Regarding the anchoring force of the substrate, the anchoring force of all embodiments exceeded 106 g / in, which is much higher than 48 g / in of Comparative Example 1 and 58 g / in of Comparative Example 4, and no adhesive layer residue was found on the PET substrate after peeling. Comparative Example 4 used a single anchoring agent, and the anchoring force decreased significantly, confirming that the two-component compound anchoring system of the present invention can achieve a high-strength bond between the adhesive layer and the PET substrate through different reaction mechanisms, solving the problem of adhesive layer debonding and transfer during repeated peeling and sticking.

[0053] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A protective film for diffusion sheets, characterized in that, By weight, it comprises the following components: 100 parts vinylphenyl modified polysiloxane, 1.5 to 4.0 parts composite crosslinking agent, 0.6 to 2.0 parts compound anchoring agent, 0.2 to 0.5 parts platinum catalyst, 1.0 to 3.0 parts optically adaptable microspheres, 0.3 to 1.0 parts polymeric antistatic agent, and appropriate amount of mixed solvent; The vinylphenyl-modified polysiloxane has a linear molecular structure, with the main chain composed of dimethylsiloxane segments and methylphenylsiloxane segments. Both ends of the molecule are capped with vinyl groups. The phenyl molar content is 5%–10%, the vinyl content is 0.4–0.7 mmol / g, and the viscosity at 25°C is 2000–2600 mPa. s, with a number-average molecular weight of 70,000~100,000 g / mol; The composite crosslinking agent is composed of low-hydrogen silicone oil and vinyl MQ silicone resin in a mass ratio of 1:1.5~3.

2. The protective film for diffusion sheets according to claim 1, characterized in that, The vinylphenyl-modified polysiloxane is prepared by the following steps: A1. Octamethylcyclotetrasiloxane and methylphenylcyclotrisiloxane were added to a reaction vessel and dehydrated at 110℃ and a vacuum of -0.095 to -0.1 MPa for 1.5 to 2 hours, controlling the monomer moisture content to be ≤0.02%; the end-capping agent tetramethyldivinyldisiloxane and the potassium hydroxide alcohol solution catalyst were dried by molecular sieve and set aside for later use. A2. Add tetramethyldivinyldisiloxane to the dehydrated monomer, purge the air in the reactor with nitrogen three times, start stirring, control the speed at 300~400 rpm, raise the temperature to 80~85℃, add potassium hydroxide alcohol solution, stir and mix evenly, raise the temperature to 100~110℃, and keep the reaction at this temperature for 3~4 hours. A3. Cool the reaction system to 40~50℃, add the measured amount of glacial acetic acid, stir and neutralize for 15~20min, adjust the pH of the system to 6.5~7.0, and terminate the polymerization reaction; A4. Heat the neutralized system to 140~150℃ and distill under reduced pressure for 2~3 hours under vacuum of -0.098~-0.1MPa to remove unreacted cyclosiloxane monomers and low-boiling substances; A5. Filtration: Vinylphenyl modified polysiloxane is obtained by filtration through a plate and frame filter press.

3. The protective film for diffusion sheets according to claim 2, characterized in that, In step A1, the mass concentration of the potassium hydroxide alcohol solution is 20%, and the solvent is anhydrous ethanol; in step A2, the mass ratio of octamethylcyclotetrasiloxane, methylphenylcyclotrisiloxane, tetramethyldivinyldisiloxane, and potassium hydroxide alcohol solution is 100:(5~12):(2~5):(0.1~0.3). In step A2, the stirring speed is 300~400 rpm and the reaction time is 3~4 h; in step A4, the vacuum distillation temperature is 140~150℃, the vacuum degree is ≥-0.098MPa, and the time is 2~3 h; in step A5, the filtration is carried out using a 200 mesh plate and frame filter.

4. The protective film for diffusion sheets according to claim 2, characterized in that, The compound anchoring agent is prepared by compounding vinyltrimethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:1.2~2.0; the low-hydrogen silicone oil has a hydrogen content of 0.8%~1.2%; the vinyl MQ silicone resin has a vinyl content of 1.0~1.6 mmol / g; and the M / Q ratio is 0.6~0.

9.

5. The protective film for diffusion sheets according to claim 1, characterized in that, The platinum catalyst is a Castells platinum catalyst with a platinum content of 3000~5000ppm; the optically compatible microspheres are polymethyl methacrylate microspheres with an average particle size of 2~5μm and a refractive index of 1.49~1.51; the polymeric antistatic agent is a polyether-modified polysiloxane.

6. The protective film for diffusion sheets according to claim 1, characterized in that, The mixed solvent is composed of ethyl acetate and No. 200 solvent oil in a volume ratio of 1:1~2, and the solid content of the adhesive is adjusted to 20%~30%.

7. The protective film for diffusion sheets according to claim 1, characterized in that, The special protective film for the diffusion sheet also includes a PET substrate and a release film; the thickness of the PET substrate is 25~50μm; the release film is a single-sided fluorine release PET film with a thickness of 25~38μm.

8. A method for preparing a protective film specifically for diffusion sheets, characterized in that, The preparation of the protective film for the diffusion sheet according to any one of claims 1-7 includes the following steps: S1. Preparation of adhesive solution: Under light-protected conditions and at 25~30℃, vinylphenyl modified polysiloxane, composite crosslinking agent, composite anchoring agent, optically compatible microspheres, and polymeric antistatic agent are added to the mixed solvent according to the formula. Stir at 300~500r / min for 30~45min until the mixture is uniform. Then, add platinum catalyst and continue stirring for 15~20min. Finally, allow the mixture to stand under a vacuum of -0.08~-0.1MPa for 20~30min to degas, and the functional silicone adhesive solution is obtained. S2. Coating and curing: The functional silicone adhesive is coated onto the corona-treated surface of the PET substrate using a slit coating method at a coating speed of 30~50m / min. Then, it is placed in an oven for step-by-step heating and curing. After curing, a functional silicone adhesive layer with a thickness of 5~12μm is obtained. S3. Lamination and winding: Align the surface of the cured adhesive layer in step S2 with the release surface of the release film and laminate it. Control the lamination pressure to be 0.2~0.4MPa and the lamination speed to be 30~50m / min. After lamination, wind it up and cure it at 25~30℃ for 24~48h to obtain the special protective film for diffusion sheet.

9. The method for preparing a protective film for a diffusion sheet according to claim 8, characterized in that, In step S2, the stepped heating curing and drying process is as follows: the first temperature zone is 60~70℃, with a dwell time of 15~20s; the second temperature zone is 80~90℃, with a dwell time of 20~25s; the third temperature zone is 110~120℃, with a dwell time of 25~30s; the fourth temperature zone is 130~140℃, with a dwell time of 30~40s; the total curing and drying time is 90~115s, and the curing degree of the adhesive layer after curing is ≥98%.

10. The method for preparing a protective film for a diffusion sheet according to claim 8, characterized in that, In step S1, the stirring speed is 300~500 r / min, and the static degassing is vacuum degassing with a vacuum degree of -0.08~-0.1 MPa; in step S3, direct sunlight should be avoided during the maturation process.

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