UTG folding screen protection sticker and preparation method thereof

Abstract

This application relates to the field of foldable screen protector technology, specifically disclosing a UTG foldable screen protector and its preparation method. A UTG foldable screen protector comprises, from top to bottom: a CPI film layer, a first polymer film layer, an ultrathin glass layer, a second polymer film layer, and an OCA adhesive layer. The CPI film layer raw materials include: CPI resin, fluorocarbon surfactant, polysiloxane-polyimide block copolymer microspheres, modified nano-silica, silane coupling agent, antioxidant, and stabilizer. The OCA adhesive layer raw materials include: epoxy acrylate, polyurethane acrylate, methacrylate, trimethylolpropane triglycidyl ether, phenyltriethoxysilane, phenyl methacrylate, initiator, toughening agent, and phenoxyethyl acrylate. The foldable screen protector of this application exhibits excellent long-term optical stability and impact resistance.

Description

Technical Field

[0001] This application relates to the field of foldable screen protector technology, and more specifically, to a UTG foldable screen protector and its preparation method. Background Technology

[0002] Currently, ultra-thin glass (UTG) is commonly used as a flexible protective film for foldable screens in the foldable display device field. The thinner UTG offers excellent bending performance, meeting the stringent requirements of flexible screens for extremely small radii of curvature. However, the mechanical properties of UTG are negatively correlated with its thickness: as the thickness decreases, its impact resistance significantly declines, resulting in a critical damage height of less than 10mm in pen drop tests (simulating drops or impacts from daily use), posing a very high risk of crack propagation. This reliability defect severely restricts the large-scale application of UTG in scenarios such as mobile terminals.

[0003] To improve the impact resistance of UTG, existing technologies often employ multi-layer composite structures for reinforcement. For example, patent application CN114571832A discloses a multi-layer material of UTG and PET hardened film. This multi-layer material includes UTG, with a first PET film bonded to the front of the UTG via an OCA optical adhesive layer, and a second PET film bonded to the back of the UTG via an OCA optical adhesive layer. A hardened layer is provided on the side of the first PET film away from the UTG. This multi-layer UTG material effectively enhances the impact resistance of the UTG, while also serving as a hardened layer for the upper PET layer, thus overcoming the shortcomings of PET film being too soft and easily scratched.

[0004] However, the aforementioned screen protectors based on PET and UTG composites suffer from insurmountable optical performance degradation during long-term use of foldable screens. On one hand, the PET film of the screen protector is prone to molecular chain fatigue, orientation disorder, and plastic deformation under the cyclic stress of repeated bending. At the same time, under the influence of light and humid environments during daily use, the PET substrate will undergo slow oxidative degradation, resulting in a large number of microcracks, silver streaks, and loose structural areas inside the film. These micron-level structural defects will have a strong scattering and absorption effect on light, directly leading to a continuous increase in screen protector haze and a significant decrease in light transmittance, ultimately causing blurry display and reduced brightness of the foldable screen, seriously affecting the visual experience. On the other hand, the OCA adhesive between the UTG layer and the PET film layer is prone to adhesion failure, micro-voids, interface separation, and even micro-bubbles due to the cyclic stress and thermal expansion and contraction effect caused by repeated bending. Due to the significant difference in refractive index between air and OCA adhesive, PET film, and UTG substrate, the heterogeneous gaps formed at the interface become strong optical scattering centers, further exacerbating the problems of increased haze and deteriorated light transmittance of the screen protector. Coupled with the optical degradation caused by the aging of the PET film itself, the light transmittance of the screen protector drops significantly after long-term use, failing to meet the long-term stable optical performance requirements of foldable screens. Summary of the Invention

[0005] To enhance the long-term stability of the light transmittance of UTG foldable screen protectors, this application provides a UTG foldable screen protector and its preparation method.

[0006] The UTG foldable screen protector provided in this application adopts the following technical solution: A UTG foldable screen protector comprises, from top to bottom: a CPI film layer, a first polymer film layer, an ultra-thin glass layer, a second polymer film layer, and an OCA adhesive layer; The CPI membrane layer comprises the following raw materials in parts by weight: 90-95 parts CPI resin, 4-8 parts fluorocarbon surfactant, 2-4 parts polysiloxane-polyimide block copolymer microspheres, 1.5-2.5 parts modified nano silica, 0.4-0.8 parts silane coupling agent, 0.3-0.5 parts antioxidant, and 0.3-0.5 parts stabilizer; The OCA adhesive layer comprises the following raw materials in parts by weight: 30-50 parts epoxy acrylate, 20-40 parts polyurethane acrylate, 10-20 parts methacrylate, 5-15 parts trimethylolpropane triglycidyl ether, 2-8 parts phenyltriethoxysilane, 1-5 parts phenyl methacrylate, 1-3 parts initiator, 5-10 parts toughening agent, and 3-8 parts phenoxyethyl acrylate. Both the first polymer film layer and the second polymer film layer are epoxy resin film layers.

[0007] By adopting the above technical solution, firstly, the composite structure effectively compensates for the insufficient impact resistance of UTG itself. Existing technologies using only UTG or PET-UTG composite structures struggle to balance impact resistance and bending performance. This application, however, uses two epoxy resin film layers (first and second polymer film layers) symmetrically covering the UTG layer. The epoxy resin film layer possesses excellent flexibility and adhesion, serving as a stress buffer transition layer. It effectively absorbs cyclic stress and external impact energy during folding, reducing stress concentration on the UTG layer and lowering the risk of crack initiation and propagation. Simultaneously, it avoids the drawbacks of existing PET films being prone to softening and scratching, thus balancing the impact resistance and surface hardness of the protective film.

[0008] Secondly, the design of the raw material composition of the CPI film layer fundamentally solves the optical attenuation problem caused by aging and bending fatigue of existing PET films. Compared with existing PET films that are prone to aging and have poor bending resistance, CPI resin itself has excellent high temperature resistance, aging resistance, and flexibility. Combined with fluorocarbon surfactants, polysiloxane-polyimide block copolymer microspheres, modified nano-silica, and other components, it can significantly improve the bending fatigue resistance and structural stability of the CPI film layer, reduce molecular chain fatigue, orientation disorder, and microcrack generation during repeated bending, and inhibit structural loosening caused by photo-oxidative aging, avoid light scattering and absorption, and maintain the long-term low haze and high light transmittance of the protective film. Among them, fluorocarbon surfactants can significantly reduce the surface tension of the CPI film coating solution, making the coating process more uniform and smooth, thereby avoiding microstructural inhomogeneities caused by coating defects. Simultaneously, the fluorocarbon segments in the surfactant molecules have extremely low surface energy, spontaneously migrating to the film surface during film formation, creating a nanoscale self-lubricating interface between the CPI film and the adjacent first polymer film. The presence of this interface significantly reduces the shear stress transmission between layers during bending, resulting in a significant reduction in the cyclic strain experienced by the underlying OCA adhesive layer, thus delaying adhesion failure and microvoid formation caused by fatigue in the OCA adhesive layer. The polysiloxane-polyimide block copolymer microspheres play a crucial role with their unique core-shell structure: the low glass transition temperature polysiloxane soft segments in the microspheres exhibit a rubbery state at room temperature. After being uniformly dispersed in the CPI matrix, they can undergo large, recoverable deformation under bending stress, acting like countless nanoscale micro-springs absorbing and dissipating strain energy, effectively preventing stress concentration from being transmitted to the CPI matrix and avoiding the generation of brittle cracks. Modified nano-silica achieves permanent anchoring of anti-aging components through surface covalent grafting of hindered amine light stabilizers. It can capture free radicals generated during photothermal oxidation in a long-term and efficient manner, interrupt the chain degradation reaction of CPI matrix, and thus ensure that the film layer maintains the integrity of molecular structure under long-term light and humid heat environment.

[0009] Finally, the raw material formulation design of the OCA adhesive layer effectively solves the problems of adhesion failure and optical deterioration caused by interfacial voids in existing OCA adhesive layers. This OCA adhesive layer uses a compound system of epoxy acrylate and polyurethane acrylate, combined with components such as trimethylolpropane triglycidyl ether and phenoxyethyl acrylate. This not only improves the adhesive layer's bonding strength and flexibility, adapting to the deformation caused by the long-term opening and closing of foldable screens and avoiding defects such as interface separation, micro-voids, and bubbles, but also optimizes the optical performance of the adhesive layer through component synergy. It reduces light scattering caused by differences in interfacial refractive index, forming a good optical match with the CPI film layer, epoxy resin film layer, and UTG layer, further consolidating the long-term light transmission stability of the screen protector. Ultimately, it achieves a synergistic improvement in impact resistance and optical stability, meeting the needs of long-term use of foldable screens.

[0010] Optionally, the polysiloxane-polyimide block copolymer microspheres are prepared using the following method: A1. Mix bis(3-aminopropyl)polydimethylsiloxane with hexafluorodianhydride, add anhydrous DMF, and stir the mixture at room temperature for 20-24 h under nitrogen protection to obtain a polyamic acid diblock copolymer. A2. The polyamic acid diblock copolymer was dissolved in tetrahydrofuran to obtain a polymer solution. The polymer solution was added dropwise to deionized water to form an emulsion. Then, the emulsion was subjected to rotary evaporation, centrifugation and filtration to collect the solid. After freeze-drying, polysiloxane-polyimide block copolymer microspheres were obtained.

[0011] By employing the above-mentioned technical solution, this preparation method constructs structurally stable block copolymer microspheres through a two-step reaction, which can effectively improve the overall performance of CPI film layers. The preparation process uses anhydrous DMF as a solvent, and under nitrogen protection, achieves a complete reaction between bis(3-aminopropyl)polydimethylsiloxane and hexafluorodianhydride, ensuring the formation of a uniform polyamic acid-type diblock copolymer. Subsequent steps such as solution precipitation, rotary evaporation, centrifugal filtration, and freeze-drying yield microspheres with uniform particle size and good dispersibility. These microspheres combine the flexibility of polysiloxane with the high-temperature resistance and anti-aging properties of polyimide. When added to a CPI film layer, they can be uniformly dispersed, effectively dispersing bending stress and reducing the generation of microcracks. Simultaneously, they improve the flexibility and structural uniformity of the CPI film layer, avoiding optical defects caused by localized stress concentration, further enhancing the bending fatigue resistance and optical stability of the CPI film layer, and helping to solve the problem of decreased light transmittance caused by bending aging of existing PET films.

[0012] Optionally, in step A1, the molecular weight of the bis(3-aminopropyl)polydimethylsiloxane is 1000-2000; the molar ratio of the bis(3-aminopropyl)polydimethylsiloxane to hexafluorodianhydride is 1:(1.10-1.15); and the amount of anhydrous DMF added is 5-7 times the total mass of the bis(3-aminopropyl)polydimethylsiloxane and hexafluorodianhydride.

[0013] By adopting the above technical solution, and by clarifying the molecular weight range of bis(3-aminopropyl)polydimethylsiloxane, its molar ratio with hexafluorodianhydride, and the amount of anhydrous DMF added, the structural stability and performance consistency of the block copolymer microspheres are ensured.

[0014] Optionally, in step A2, the mass ratio of the polyamic acid diblock copolymer, tetrahydrofuran, and deionized water is 1:(8-10):(30-40), and the polymer solution drop rate is 1-3 mL / min.

[0015] Optionally, the preparation method of the modified nano-silica includes the following steps: (1) Disperse nano-silica in anhydrous ethanol, add γ-aminopropyltriethoxysilane, reflux at 60-80℃ for 4-8 hours, and obtain aminated nano-silica after centrifugation and washing. (2) The aminated nano silica was dispersed in anhydrous DMF and ultrasonically dispersed for 20-30 min. Then, 4-epoxypropyloxy-2,2,6,6-tetramethylpiperidine was added and stirred evenly. The temperature was raised to 80-100℃ and the reaction was kept constant for 6-12 h. After the reaction was completed, the modified nano silica was obtained by centrifugation, washing and vacuum drying.

[0016] By employing the above-mentioned technical solution, surface modification of nano-silica effectively solves the problems of poor compatibility and easy agglomeration between ordinary nano-silica and CPI resin, while also endowing it with anti-aging properties. The first step, amination modification, introduces amino active groups onto the surface of nano-silica, providing reaction sites for subsequent hindered amine grafting. The second step, through the grafting reaction of 4-epoxypropyloxy-2,2,6,6-tetramethylpiperidine, stably binds the hindered amine to the surface of nano-silica, preventing its migration and loss. The modified nano-silica not only exhibits good compatibility with CPI resin, fluorocarbon surfactants, and other components, and can be uniformly dispersed in the CPI film, improving the mechanical strength and bending resistance of the film, but also, through the anti-aging effect of the hindered amine, inhibits the loosening of the film structure caused by photo-oxidative aging, reduces light scattering, and further enhances the long-term optical stability of the protective film.

[0017] Optionally, in step (1), the mass ratio of nano-silica, anhydrous ethanol and γ-aminopropyltriethoxysilane is 10:(100-120):(1.5-2.5).

[0018] Optionally, in step (2), the mass ratio of aminated nano silica, anhydrous DMF and 4-epoxypropyloxy-2,2,6,6-tetramethylpiperidine is (8-10):(80-100):(1-2.5).

[0019] Optionally, the fluorocarbon surfactant in the CPI membrane layer is one of FS-50 and FC-4430.

[0020] By adopting the above technical solution and selecting FS-50 or FC-4430 fluorocarbon surfactants, the overall performance of the CPI film layer can be optimized in a targeted manner. These fluorocarbon surfactants possess excellent surface activity, high-temperature resistance, and anti-fouling properties. Adding them to the CPI film layer reduces surface tension, improves coating uniformity, and avoids optical defects such as bubbles and pinholes during coating. Simultaneously, their good compatibility allows them to synergistically interact with CPI resin, polysiloxane-polyimide block copolymer microspheres, and other components, further enhancing the CPI film layer's resistance to bending fatigue and aging, reducing light scattering, and imparting excellent anti-fouling properties to the film layer, preventing stains from affecting light transmission and indirectly ensuring the long-term optical stability of the protective film.

[0021] Optionally, the toughening agent in the OCA adhesive layer is carboxyl-terminated liquid nitrile rubber.

[0022] By adopting the above technical solution, carboxyl-terminated liquid nitrile rubber can effectively improve the flexibility and flexural fatigue resistance of the OCA adhesive layer. Carboxyl-terminated liquid nitrile rubber possesses good flexibility and adhesion, and exhibits excellent compatibility with components such as epoxy acrylate and polyurethane acrylate in the OCA adhesive layer. Through the synergistic effect of molecular chains, it enhances the toughness and deformation resistance of the adhesive layer, preventing embrittlement, cracking, or adhesive failure caused by cyclic stress during long-term opening and closing of foldable screens. It also reduces the generation of interfacial voids and bubbles, thereby preventing interfacial light scattering, ensuring the adhesive stability and optical performance of the OCA adhesive layer, and helping to solve the problem of decreased light transmittance caused by interfacial failure in existing OCA adhesive layers.

[0023] This application also provides a method for preparing a UTG foldable screen protector, which adopts the following technical solution: A method for preparing a UTG foldable screen protector includes the following steps: S1. CPI resin, fluorocarbon surfactant, polysiloxane-polyimide block copolymer microspheres, modified nano-silica, silane coupling agent, antioxidant, and stabilizer are mixed and dissolved in anhydrous DMF to obtain a CPI film coating solution; the CPI film coating solution is cast onto a glass plate, dried and cured, and then peeled off from the glass plate to obtain a CPI film layer; S2. Stack the CPI film layer, the first polymer film layer, the ultrathin glass layer and the second polymer film layer in sequence, and hot press them at 140-170℃ and 0.1-0.4MPa for 20-30 minutes to obtain a multilayer composite intermediate. S3. Mix epoxy acrylate, polyurethane acrylate, methacrylate, trimethylolpropane triglycidyl ether, phenyltriethoxysilane, phenyl methacrylate, initiator, toughening agent and phenoxyethyl acrylate, stir for 1-2 hours to obtain OCA adhesive coating solution; uniformly coat the OCA adhesive coating solution on the surface of the second polymer film layer of the multilayer intermediate obtained in S2, and then perform UV curing. After curing, attach a PET release film to the surface of the OCA adhesive layer to obtain UTG foldable screen protector.

[0024] The above-described preparation method is reasonable and specifically addresses the problems of loose bonding between layers, easy appearance of interfacial voids, or performance defects caused by insufficient curing of the film layer in existing preparation processes. Specifically, the drying and curing process of the CPI film layer ensures sufficient solvent evaporation, forming a film layer with uniform structure and stable performance; the UV curing process of the OCA adhesive layer ensures sufficient curing of the adhesive layer, improving adhesion strength and optical performance; the hot-pressing treatment at specific temperature, pressure, and time ensures tight bonding between layers, reduces interfacial voids, strengthens interlayer adhesion, and prevents interlayer separation during folding. Ultimately, this ensures that the protective film possesses excellent impact resistance, bending resistance, and long-term light transmittance stability, making large-scale production feasible.

[0025] In summary, this application has the following beneficial effects: 1. This application uses a CPI film layer to replace the PET film in the existing technology, which is prone to aging and has poor bending resistance. This effectively solves the problem of long-term light transmittance degradation caused by aging and bending fatigue of the PET film in existing screen protectors. As the surface structure of the screen protector, the CPI film layer, combined with two epoxy resin film layers symmetrically covering the UTG layer, not only compensates for the insufficient impact resistance of UTG itself, but also improves the overall bending fatigue resistance of the screen protector by leveraging the excellent high temperature resistance, anti-aging, and flexibility of CPI resin. The CPI film layer can effectively reduce molecular chain fatigue, orientation disorder, and microcrack generation during repeated bending, inhibit the loosening of the film structure caused by photo-oxidative aging, avoid light scattering and absorption, maintain the screen protector's long-term low haze and high light transmittance, and at the same time take into account the surface hardness and stain resistance of the screen protector. This completely solves the core pain point of poor optical stability of the existing PET-UTG composite structure and meets the visual requirements of long-term use of foldable screens.

[0026] 2. In this application, the CPI film layer preferably utilizes the synergistic effect of three core raw materials: fluorocarbon surfactant, polysiloxane-polyimide block copolymer microspheres, and modified nano-silica. This further enhances the comprehensive performance of the CPI film layer and helps solve the optical and mechanical defects of existing protective films. The polysiloxane-polyimide block copolymer microspheres possess both flexibility and anti-aging properties, and can be uniformly dispersed in the CPI film layer, effectively dispersing bending stress, reducing microcrack formation, and improving the uniformity of the film layer structure. The modified nano-silica, through surface modification treatment, solves the problems of poor compatibility and easy aggregation between ordinary nanoparticles and CPI resin, while also imparting anti-aging properties to the film layer, inhibiting structural loosening caused by photo-oxidative aging, and reducing light scattering. The fluorocarbon surfactant optimizes the coating uniformity of the CPI film layer, avoids optical defects, and improves stain resistance. The synergistic effect of these three materials further enhances the bending fatigue resistance and optical stability of the CPI film layer, providing strong support for the long-term light transmission stability of the protective film.

[0027] 3. The OCA adhesive layer and raw material formulation design of this application specifically addresses the optical deterioration problem caused by adhesion failure and interfacial voids in existing OCA adhesive layers, further consolidating the long-term light transmission stability of the screen protector. The OCA adhesive layer adopts a compound system of epoxy acrylate and polyurethane acrylate, combined with raw materials such as trimethylolpropane triglycidyl ether, phenoxyethyl acrylate, and carboxyl-terminated liquid nitrile rubber. This not only significantly improves the adhesion strength and flexibility of the adhesive layer, adapting to the deformation caused by the long-term opening and closing of foldable screens and avoiding defects such as interface separation, micro-voids, and bubbles, but also optimizes the optical performance of the adhesive layer through component synergy, reducing light scattering caused by interfacial refractive index differences, forming a good optical match with the CPI film layer, epoxy resin film layer, and UTG layer. At the same time, it improves the bending fatigue resistance of the adhesive layer, preventing the adhesive layer from becoming brittle and cracking, ensuring that each layer of the screen protector is tightly bonded, and achieving a synergistic improvement in impact resistance and optical stability. Detailed Implementation

[0028] The present application will be further described in detail below with reference to the embodiments.

[0029] Preparation example of polysiloxane-polyimide block copolymer microspheres Preparation Example 1 Polysiloxane-polyimide block copolymer microspheres were prepared using the following method: A1. Bis(3-aminopropyl)polydimethylsiloxane and hexafluorodianhydride were mixed at a molar ratio of 1:1.1. Anhydrous DMF was added, and the amount of anhydrous DMF added was 5 times the total mass of bis(3-aminopropyl)polydimethylsiloxane and hexafluorodianhydride. The mixture was stirred at 200 r / min for 20 h at room temperature (25 °C) under nitrogen protection to obtain a polyamic acid diblock copolymer. A2. The polyamic acid diblock copolymer was dissolved in tetrahydrofuran to obtain a polymer solution. The polymer solution was added dropwise to deionized water at a dropping rate of 1 mL / min while stirring at 150 r / min to form a homogeneous emulsion. The mass ratio of polyamic acid diblock copolymer, tetrahydrofuran and deionized water was 1:8:30. The emulsion was placed in a rotary evaporator and evaporated at 40℃ for 30 min. Then, it was centrifuged and filtered at 3500 r / min for 15 min, and the solid was collected. The solid was placed in a freeze dryer and freeze-dried at -40℃ for 12 h to obtain polysiloxane-polyimide block copolymer microspheres.

[0030] Preparation Example 2 Polysiloxane-polyimide block copolymer microspheres were prepared using the following method: A1. Bis(3-aminopropyl)polydimethylsiloxane and hexafluorodianhydride were mixed at a molar ratio of 1:1.12. Anhydrous DMF was added, and the amount of anhydrous DMF added was 6 times the total mass of bis(3-aminopropyl)polydimethylsiloxane and hexafluorodianhydride. The mixture was stirred at 250 r / min for 22 h at room temperature (25 °C) under nitrogen protection to obtain a polyamic acid diblock copolymer. A2. The polyamic acid diblock copolymer was dissolved in tetrahydrofuran to obtain a polymer solution. The polymer solution was added dropwise to deionized water at a dropping rate of 2 mL / min while stirring at 180 r / min to form a homogeneous emulsion. The mass ratio of polyamic acid diblock copolymer, tetrahydrofuran and deionized water was 1:9:35. The emulsion was placed in a rotary evaporator and evaporated at 45℃ for 35 min. Then, it was centrifuged and filtered at 4000 r / min for 18 min, and the solid was collected. The solid was placed in a freeze dryer and freeze-dried at -40℃ for 12 h to obtain polysiloxane-polyimide block copolymer microspheres.

[0031] Preparation Example 3 Polysiloxane-polyimide block copolymer microspheres were prepared using the following method: A1. Bis(3-aminopropyl)polydimethylsiloxane and hexafluorodianhydride were mixed at a molar ratio of 1:1.15. Anhydrous DMF was added, and the amount of anhydrous DMF added was 7 times the total mass of bis(3-aminopropyl)polydimethylsiloxane and hexafluorodianhydride. The mixture was stirred at 300 r / min for 24 h at room temperature (25 °C) under nitrogen protection to obtain a polyamic acid diblock copolymer. A2. The polyamic acid diblock copolymer was dissolved in tetrahydrofuran to obtain a polymer solution. The polymer solution was added dropwise to deionized water at a dropping rate of 3 mL / min while stirring at 200 r / min to form a homogeneous emulsion. The mass ratio of polyamic acid diblock copolymer, tetrahydrofuran and deionized water was 1:10:40. The emulsion was placed in a rotary evaporator and evaporated at 50℃ for 25 min. Then, it was centrifuged and filtered at 4000 r / min for 20 min, and the solid was collected. The solid was placed in a freeze dryer and freeze-dried at -40℃ for 12 h to obtain polysiloxane-polyimide block copolymer microspheres.

[0032] Preparation example of modified nano silica Preparation Example 4 Modified nano-silica was prepared using the following method: (1) Disperse nano-silica in anhydrous ethanol, add γ-aminopropyltriethoxysilane (mass ratio of nano-silica, anhydrous ethanol and γ-aminopropyltriethoxysilane is 10:100:1.5), ultrasonically disperse for 30 min, reflux at 60 °C for 8 hours, after the reaction is completed, cool to room temperature, centrifuge and filter at 4000 r / min for 20 min, collect solid precipitate; wash the precipitate repeatedly with anhydrous ethanol 3 times to remove unreacted γ-aminopropyltriethoxysilane, place the precipitate in a vacuum drying oven and dry at 60 °C for 8 h to obtain aminated nano-silica; (2) Aminated nano-silica was dispersed in anhydrous DMF and ultrasonically dispersed at 300W for 20 min. Then, 4-epoxypropyloxy-2,2,6,6-tetramethylpiperidine was added and stirred until homogeneous (the mass ratio of aminated nano-silica, anhydrous DMF, and 4-epoxypropyloxy-2,2,6,6-tetramethylpiperidine was 8:80:1). The temperature was raised to 80℃ and the reaction was kept constant for 12 h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 5000 r / min for 25 min to collect the solid precipitate. The precipitate was washed twice with DMF and once with anhydrous ethanol. The precipitate was placed in a vacuum drying oven and dried at 70℃ for 10 h to obtain modified nano-silica.

[0033] Preparation Example 5 Modified nano-silica was prepared using the following method: (1) Disperse nano-silica in anhydrous ethanol, add γ-aminopropyltriethoxysilane (mass ratio of nano-silica, anhydrous ethanol and γ-aminopropyltriethoxysilane is 10:110:2), ultrasonically disperse for 35 min, reflux at 70 °C for 6 hours, after the reaction is completed, cool to room temperature, centrifuge and filter at 4000 r / min for 20 min, collect solid precipitate; wash the precipitate repeatedly with anhydrous ethanol 3 times to remove unreacted γ-aminopropyltriethoxysilane, place the precipitate in a vacuum drying oven and dry at 60 °C for 8 h to obtain aminated nano-silica; (2) Aminated nano-silica was dispersed in anhydrous DMF and ultrasonically dispersed at 300W for 25 min. Then, 4-epoxypropyloxy-2,2,6,6-tetramethylpiperidine was added and stirred until homogeneous (the mass ratio of aminated nano-silica, anhydrous DMF, and 4-epoxypropyloxy-2,2,6,6-tetramethylpiperidine was 9:90:1.8). The temperature was raised to 90℃ and the reaction was kept constant for 9 h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 5000 r / min for 25 min to collect the solid precipitate. The precipitate was washed twice with DMF and once with anhydrous ethanol. The precipitate was placed in a vacuum drying oven and dried at 70℃ for 10 h to obtain modified nano-silica.

[0034] Preparation Example 6 Modified nano-silica was prepared using the following method: (1) Disperse nano-silica in anhydrous ethanol, add γ-aminopropyltriethoxysilane (mass ratio of nano-silica, anhydrous ethanol and γ-aminopropyltriethoxysilane is 10:120:2.5), ultrasonically disperse for 35 min, reflux at 80 °C for 4 hours, after the reaction is completed, cool to room temperature, centrifuge and filter at 5000 r / min for 30 min, collect the solid precipitate; wash the precipitate repeatedly with anhydrous ethanol 3 times to remove unreacted γ-aminopropyltriethoxysilane, place the precipitate in a vacuum drying oven and dry at 60 °C for 8 h to obtain aminated nano-silica; (2) Aminated nano-silica was dispersed in anhydrous DMF and ultrasonically dispersed at 300W for 30 min. Then, 4-epoxypropyloxy-2,2,6,6-tetramethylpiperidine was added and stirred evenly (the mass ratio of aminated nano-silica, anhydrous DMF and 4-epoxypropyloxy-2,2,6,6-tetramethylpiperidine was 10:100:2.5). The temperature was raised to 100℃ and the reaction was kept constant for 6 h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 5000 r / min for 25 min to collect the solid precipitate. The precipitate was washed twice with DMF and once with anhydrous ethanol. The precipitate was placed in a vacuum drying oven and dried at 70℃ for 10 h to obtain modified nano-silica.

[0035] Example Example 1 A UTG foldable screen protector comprises, from top to bottom: a CPI film layer, a first polymer film layer, an ultra-thin glass layer, a second polymer film layer, and an OCA adhesive layer. The CPI film layer has a thickness of 25 μm, the first polymer film layer has a thickness of 20 μm, the ultra-thin glass layer has a thickness of 30 μm, the second polymer film layer has a thickness of 10 μm, and the OCA adhesive layer has a thickness of 25 μm.

[0036] The raw material composition and dosage of the CPI film are shown in Table 1. The number average molecular weight of the CPI resin is 80,000, the fluorocarbon surfactant is FS-50, the polysiloxane-polyimide block copolymer microspheres are the polysiloxane-polyimide block copolymer microspheres prepared in Preparation Example 1, the modified nano silica is the modified nano silica prepared in Preparation Example 4, the silane coupling agent is KH-560, the antioxidant is antioxidant 1010, and the stabilizer is light stabilizer 770.

[0037] The raw material composition and dosage of the OCA adhesive layer are shown in Table 1. Among them, the epoxy acrylate is bisphenol A type epoxy acrylate, the polyurethane acrylate has a number average molecular weight of 10,000; the initiator is 1173 photoinitiator; and the toughening agent is carboxyl-terminated liquid nitrile rubber.

[0038] Both the first and second polymeric membrane layers are epoxy resin membrane layers, and the epoxy resin is bisphenol A type epoxy resin with a number average molecular weight of 7000.

[0039] The preparation method of the above-mentioned UTG foldable screen protector includes the following steps: S1. CPI resin, fluorocarbon surfactant, polysiloxane-polyimide block copolymer microspheres, modified nano-silica, silane coupling agent, antioxidant, and stabilizer are mixed and dissolved in anhydrous DMF (the amount of anhydrous DMF is 6 times the mass of CPI resin) to obtain a CPI film coating solution; the CPI film coating solution is cast onto a glass plate, dried and cured, and then peeled off from the glass plate to obtain a CPI film layer; S2. The CPI film layer, the first polymer film layer, the ultrathin glass layer and the second polymer film layer are stacked in sequence and hot-pressed at 140℃ and 0.4MPa for 30 minutes to obtain a multilayer composite intermediate. S3. Mix epoxy acrylate, polyurethane acrylate, methacrylate, trimethylolpropane triglycidyl ether, phenyltriethoxysilane, phenyl methacrylate, initiator, toughening agent and phenoxyethyl acrylate, stir for 1 hour to obtain OCA adhesive coating liquid; uniformly coat the OCA adhesive coating liquid onto the surface of the second polymer film layer of the multilayer intermediate obtained in S2, and then perform UV curing. After curing, attach a PET release film to the surface of the OCA adhesive layer to obtain UTG foldable screen protector.

[0040] Example 2 A UTG foldable screen protector comprises, from top to bottom: a CPI film layer, a first polymer film layer, an ultra-thin glass layer, a second polymer film layer, and an OCA adhesive layer. The CPI film layer has a thickness of 50 μm, the first polymer film layer has a thickness of 40 μm, the ultra-thin glass layer has a thickness of 40 μm, the second polymer film layer has a thickness of 25 μm, and the OCA adhesive layer has a thickness of 50 μm.

[0041] The raw material composition and dosage of the CPI film are shown in Table 1. The number average molecular weight of the CPI resin is 80,000, the fluorocarbon surfactant is FC-4430, the polysiloxane-polyimide block copolymer microspheres are the polysiloxane-polyimide block copolymer microspheres prepared in Preparation Example 2, the modified nano silica is the modified nano silica prepared in Preparation Example 5, the silane coupling agent is KH-560, the antioxidant is antioxidant 1010, and the stabilizer is light stabilizer 770.

[0042] The raw material composition and dosage of the OCA adhesive layer are shown in Table 1. Among them, the epoxy acrylate is bisphenol A type epoxy acrylate, the polyurethane acrylate has a number average molecular weight of 10,000; the initiator is 1173 photoinitiator; and the toughening agent is carboxyl-terminated liquid nitrile rubber.

[0043] Both the first and second polymeric membrane layers are epoxy resin membrane layers, and the epoxy resin is bisphenol A type epoxy resin with a number average molecular weight of 7000.

[0044] The preparation method of the above-mentioned UTG foldable screen protector includes the following steps: S1. CPI resin, fluorocarbon surfactant, polysiloxane-polyimide block copolymer microspheres, modified nano-silica, silane coupling agent, antioxidant, and stabilizer are mixed and dissolved in anhydrous DMF (the amount of anhydrous DMF is 6 times the mass of CPI resin) to obtain a CPI film coating solution; the CPI film coating solution is cast onto a glass plate, dried and cured, and then peeled off from the glass plate to obtain a CPI film layer; S2. The CPI film layer, the first polymer film layer, the ultrathin glass layer and the second polymer film layer are stacked in sequence and hot-pressed at 155℃ and 0.2MPa for 25 minutes to obtain a multilayer composite intermediate. S3. Mix epoxy acrylate, polyurethane acrylate, methacrylate, trimethylolpropane triglycidyl ether, phenyltriethoxysilane, phenyl methacrylate, initiator, toughening agent and phenoxyethyl acrylate, stir for 1.5 h to obtain OCA adhesive coating solution; uniformly coat the OCA adhesive coating solution on the surface of the second polymer film layer of the multilayer intermediate obtained in S2, and then perform UV curing. After curing, attach a PET release film to the surface of the OCA adhesive layer to obtain UTG foldable screen protector.

[0045] Example 3 A UTG foldable screen protector comprises, from top to bottom: a CPI film layer, a first polymer film layer, an ultra-thin glass layer, a second polymer film layer, and an OCA adhesive layer. The CPI film layer has a thickness of 50 μm, the first polymer film layer has a thickness of 60 μm, the ultra-thin glass layer has a thickness of 50 μm, the second polymer film layer has a thickness of 40 μm, and the OCA adhesive layer has a thickness of 50 μm.

[0046] The raw material composition and dosage of the CPI film are shown in Table 1. The number average molecular weight of the CPI resin is 80,000, the fluorocarbon surfactant is FC-4430, the polysiloxane-polyimide block copolymer microspheres are the polysiloxane-polyimide block copolymer microspheres prepared in Preparation Example 3, the modified nano silica is the modified nano silica prepared in Preparation Example 6, the silane coupling agent is KH-560, the antioxidant is antioxidant 1010, and the stabilizer is light stabilizer 770.

[0047] The raw material composition and dosage of the OCA adhesive layer are shown in Table 1. Among them, the epoxy acrylate is bisphenol A type epoxy acrylate, the polyurethane acrylate has a number average molecular weight of 10,000; the initiator is 1173 photoinitiator; and the toughening agent is carboxyl-terminated liquid nitrile rubber.

[0048] Both the first and second polymeric membrane layers are epoxy resin membrane layers, and the epoxy resin is bisphenol A type epoxy resin with a number average molecular weight of 7000.

[0049] The preparation method of the above-mentioned UTG foldable screen protector includes the following steps: S1. CPI resin, fluorocarbon surfactant, polysiloxane-polyimide block copolymer microspheres, modified nano-silica, silane coupling agent, antioxidant, and stabilizer are mixed and dissolved in anhydrous DMF (the amount of anhydrous DMF is 8 times the mass of CPI resin) to obtain a CPI film coating solution; the CPI film coating solution is cast onto a glass plate, dried and cured, and then peeled off from the glass plate to obtain a CPI film layer; S2. The CPI film layer, the first polymer film layer, the ultrathin glass layer and the second polymer film layer are stacked in sequence and hot-pressed at 170℃ and 0.1MPa for 20 minutes to obtain a multilayer composite intermediate. S3. Mix epoxy acrylate, polyurethane acrylate, methacrylate, trimethylolpropane triglycidyl ether, phenyltriethoxysilane, phenyl methacrylate, initiator, toughening agent and phenoxyethyl acrylate, stir for 2 hours to obtain OCA adhesive coating solution; uniformly coat the OCA adhesive coating solution on the surface of the second polymer film layer of the multilayer intermediate obtained in S2, and then perform UV curing. After curing, attach a PET release film to the surface of the OCA adhesive layer to obtain UTG foldable screen protector.

[0050] Table 1. Raw material components and proportions (g) of the protective films in Examples 1-3

[0051] Example 4 The UTG foldable screen protector differs from Example 3 in that the polysiloxane-polyimide block copolymer microspheres in the CPI film layer of this example are selected from the polysiloxane-polyimide block copolymer microspheres prepared in Preparation Example 2.

[0052] Example 5 A UTG foldable screen protector differs from Example 3 in that the modified nano-silica in the CPI film layer of this example is the modified nano-silica prepared in Preparation Example 5.

[0053] Example 6 A UTG foldable screen protector differs from Example 3 in that, in this example, the CPI film layer thickness is 50μm, the first polymer film layer thickness is 40μm, the ultrathin glass layer thickness is 40μm, the second polymer film layer thickness is 30μm, and the OCA adhesive layer thickness is 50μm.

[0054] Example 7 A UTG foldable screen protector differs from Example 3 in that the number-average molecular weight of the CPI resin in the CPI film layer of this example is 150,000.

[0055] Example 8 The UTG foldable screen protector differs from Example 3 in that the toughening agent in the OCA adhesive layer of this example is liquid chlorinated rubber.

[0056] Comparative Example Comparative Example 1 According to Example 1 of the patent application document with publication number CN114571832A entitled "A Multilayer Material of UTG and PET Hardened Film", a multilayer material protective film for foldable screens was prepared.

[0057] Comparative Example 2 A UTG foldable screen protector differs from Example 3 in that the CPI film layer in this example does not contain polysiloxane-polyimide block copolymer microspheres, and the difference is made up with CPI resin.

[0058] Comparative Example 3 A UTG foldable screen protector differs from Example 3 in that, in the CPI film layer of this example, an equal amount of nano-silica is used instead of modified nano-silica.

[0059] Comparative Example 4 A UTG foldable screen protector differs from Example 3 in that the OCA adhesive layer in this comparative example does not contain toughening agents or phenoxyethyl acrylate, but instead uses epoxy acrylate.

[0060] Performance testing Test subjects: Foldable screen protectors prepared in Examples 1-8 and Comparative Examples 1-4.

[0061] 1. Impact resistance test The glass cover was placed horizontally on a fixed device. A test steel ball with a diameter of 20mm and a mass of 32.6g was dropped freely from different heights to impact the surface of the glass cover. The surface damage after impact was observed, such as whether cracks, breakage, or edge chipping occurred. The critical height at which the glass cover began to show damage under different impact heights was recorded to evaluate its impact resistance. The test results are shown in Table 2.

[0062] 2. Initial transmittance Using a UV-Vis spectrophotometer, the UTG laminated assembly was placed in the optical path, and the transmittance was measured within specific wavelength ranges of 500 nm, 600 nm, and 700 nm. The results were averaged. The test results are shown in Table 2.

[0063] 3. Light transmittance after bending Using a fully automated servo-controlled bending fatigue testing machine, the actual operating conditions of mainstream inward-folding screens were simulated. The bending radius was set to 1.5 mm, and the reciprocating bending frequency was 60 cycles / min. The specimens were precisely clamped and fixed without additional stress compression or slippage, and 100,000 uninterrupted reciprocating bending cycles were continuously completed. After the bending test, the specimens were allowed to stand for 30 minutes to return to a stable state at room temperature. The transmittance was then measured again using a UV-Vis spectrophotometer within specific wavelength ranges of 500 nm, 600 nm, and 700 nm, and the average value of the results was taken. The test results are shown in Table 2.

[0064] 4. Appearance after bending After completing the 100,000 bending fatigue tests, each piece was visually inspected under a backlit workbench, followed by magnified observation of the interlayer interfaces using a microscope. The presence of interface defects such as whitening, microbubbles, localized delamination, edge curling, and fine lines was observed. The test results are shown in Table 2.

[0065] Table 2 Detection Results

[0066] As shown in Table 2, regarding initial transmittance, all embodiments achieved an initial transmittance of over 93%, with Embodiment 2 reaching the highest at 94.5%. Embodiments 1-8 maintained an initial transmittance between 93.3% and 94.5%, indicating that the composite structure and raw material formulation designed in this application possess excellent intrinsic optical properties. This result is mainly attributed to the rational design of the CPI film layer. The CPI resin itself has excellent transmittance, and the combination with fluorocarbon surfactants can improve coating uniformity and avoid light scattering caused by coating defects. The modified nano-silica, after surface modification, has good compatibility with the CPI resin and will not cause optical defects due to agglomeration. Furthermore, the optical refractive index of the OCA adhesive layer matches that of each film layer, further reducing interfacial light loss. In contrast, the comparative examples show that Comparative Example 1 (traditional PET-UTG composite structure) had an initial light transmittance of only 91.5%, because the light transmittance of PET film itself is lower than that of CPI film, and it is prone to uneven coating. Comparative Examples 2-4 had an initial light transmittance of less than 93% due to the lack of core components such as polysiloxane-polyimide block copolymer microspheres and modified nano silica, or unreasonable OCA adhesive layer formulation.

[0067] The light transmittance after 100,000 bends is a key indicator for measuring the long-term optical stability of the protective film. The examples demonstrated significant advantages, with transmittance remaining above 92% after bending, and Example 3 still reaching 93.8%, exhibiting extremely high transmittance retention. This effectively solves the problem of long-term transmittance degradation in existing technologies. The core reason lies in the fact that the polysiloxane-polyimide block copolymer microspheres in the CPI film layer can disperse bending stress and reduce microcrack formation. The modified nano-silica can inhibit photo-oxidative aging and avoid light scattering caused by the loose film structure. Combined with the buffering effect of the epoxy resin film layer, this effectively mitigates the impact of repeated bending on optical performance. In Comparative Example 1, the light transmittance was only 78.2% after bending. This is because long-term bending of the PET film easily leads to molecular chain fatigue and oxidative degradation, resulting in a large number of microcracks and loose structural areas, which intensifies light scattering. Comparative Example 2 lacks polysiloxane-polyimide block copolymer microspheres, resulting in insufficient stress dispersion and easy generation of microcracks after bending. Comparative Example 3 uses unmodified nano-silica, which is prone to agglomeration and optical defects, and has no anti-aging effect. In Comparative Example 4, the OCA adhesive layer lacks toughening agent and phenoxyethyl acrylate, resulting in adhesion failure and interfacial voids. All of these factors lead to a significant decrease in light transmittance after bending.

[0068] The data on impact resistance and post-bending morphology further confirm the advantages of the technical solution of this application. The critical impact height of all embodiments reached over 2230 mm, with Embodiment 3 reaching a maximum of 2520 mm, significantly higher than Comparative Example 1. This is because the two epoxy resin films symmetrically cover the UTG layer, effectively absorbing impact energy and dispersing stress, thus compensating for the insufficient impact resistance of UTG. In terms of appearance, all embodiments showed no interface whitening, delamination, or bubbles after bending, indicating that the OCA adhesive formulation and hot-pressing process of this application can ensure tight adhesion between layers, adapting to long-term bending deformation. In contrast, the comparative examples all exhibited varying degrees of interface defects, mainly due to PET film aging, OCA adhesive failure, or the absence of core functional components, resulting in loose interlayer adhesion.

[0069] The above test data fully verify the effectiveness of the technical solution of this application. By replacing PET film with CPI film, optimizing the raw material formulation of CPI film and OCA adhesive layer, and designing a symmetrically wrapped composite structure, the performance requirements of the protective film of more than 93% initial light transmittance and more than 2200mm impact resistance are not only achieved, but also the problem of light transmittance decay caused by long-term bending is effectively solved. At the same time, the interlayer bonding stability is guaranteed, which fully meets the needs of long-term use of foldable screen.

[0070] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A UTG folding screen protection sticker, characterized in that, From top to bottom, it includes: CPI film layer, first polymer film layer, ultrathin glass layer, second polymer film layer and OCA adhesive layer; The CPI membrane layer comprises the following raw materials in parts by weight: 90-95 parts CPI resin, 4-8 parts fluorocarbon surfactant, 2-4 parts polysiloxane-polyimide block copolymer microspheres, 1.5-2.5 parts modified nano silica, 0.4-0.8 parts silane coupling agent, 0.3-0.5 parts antioxidant, and 0.3-0.5 parts stabilizer; The OCA adhesive layer comprises the following raw materials in parts by weight: 30-50 parts epoxy acrylate, 20-40 parts polyurethane acrylate, 10-20 parts methacrylate, 5-15 parts trimethylolpropane triglycidyl ether, 2-8 parts phenyltriethoxysilane, 1-5 parts phenyl methacrylate, 1-3 parts initiator, 5-10 parts toughening agent, and 3-8 parts phenoxyethyl acrylate. Both the first polymer film layer and the second polymer film layer are epoxy resin film layers.

2. The UTG foldable screen protector according to claim 1, characterized in that, The polysiloxane-polyimide block copolymer microspheres were prepared using the following method: A1. Mix bis(3-aminopropyl)polydimethylsiloxane with hexafluorodianhydride, add anhydrous DMF, and stir the mixture at room temperature for 20-24 h under nitrogen protection to obtain a polyamic acid diblock copolymer. A2. The polyamic acid diblock copolymer was dissolved in tetrahydrofuran to obtain a polymer solution. The polymer solution was added dropwise to deionized water to form an emulsion. Then, the emulsion was subjected to rotary evaporation, centrifugation and filtration to collect the solid. After freeze-drying, polysiloxane-polyimide block copolymer microspheres were obtained.

3. The UTG foldable screen protector according to claim 2, characterized in that: In step A1, the molecular weight of the bis(3-aminopropyl)polydimethylsiloxane is 1000-2000; the molar ratio of the bis(3-aminopropyl)polydimethylsiloxane to hexafluorodianhydride is 1:(1.10-1.15); and the amount of anhydrous DMF added is 5-7 times the total mass of the bis(3-aminopropyl)polydimethylsiloxane and hexafluorodianhydride.

4. A UTG foldable screen protector according to claim 2, characterized in that: In step A2, the mass ratio of polyamic acid diblock copolymer, tetrahydrofuran, and deionized water is 1:(8-10):(30-40), and the polymer solution drop rate is 1-3 mL / min.

5. A UTG foldable screen protector according to claim 1, characterized in that: The method for preparing the modified nano-silica includes the following steps: (1) Disperse nano-silica in anhydrous ethanol, add γ-aminopropyltriethoxysilane, reflux at 60-80℃ for 4-8 hours, and obtain aminated nano-silica after centrifugation and washing. (2) The aminated nano silica was dispersed in anhydrous DMF and ultrasonically dispersed for 20-30 min. Then, 4-epoxypropyloxy-2,2,6,6-tetramethylpiperidine was added and stirred evenly. The temperature was raised to 80-100℃ and the reaction was kept constant for 6-12 h. After the reaction was completed, the modified nano silica was obtained by centrifugation, washing and vacuum drying.

6. A UTG foldable screen protector according to claim 5, characterized in that: In step (1), the mass ratio of nano-silica, anhydrous ethanol and γ-aminopropyltriethoxysilane is 10:(100-120):(1.5-2.5).

7. A UTG foldable screen protector according to claim 5, characterized in that: In step (2), the mass ratio of aminated nano silica, anhydrous DMF and 4-epoxypropyloxy-2,2,6,6-tetramethylpiperidine is (8-10):(80-100):(1-2.5).

8. A UTG foldable screen protector according to claim 1, characterized in that: The fluorocarbon surfactant in the CPI membrane is one of FS-50 and FC-4430.

9. A UTG foldable screen protector according to claim 1, characterized in that: The toughening agent in the OCA adhesive layer is a carboxyl-terminated liquid nitrile rubber.

10. A method for preparing a UTG foldable screen protector according to any one of claims 1-9, characterized in that, Includes the following steps: S1. CPI resin, fluorocarbon surfactant, polysiloxane-polyimide block copolymer microspheres, modified nano-silica, silane coupling agent, antioxidant, and stabilizer are mixed and dissolved in anhydrous DMF to obtain a CPI film coating solution; the CPI film coating solution is cast onto a glass plate, dried and cured, and then peeled off from the glass plate to obtain a CPI film layer; S2. Stack the CPI film layer, the first polymer film layer, the ultrathin glass layer and the second polymer film layer in sequence, and hot press them at 140-170℃ and 0.1-0.4MPa for 20-30 minutes to obtain a multilayer composite intermediate. S3. Mix epoxy acrylate, polyurethane acrylate, methacrylate, trimethylolpropane triglycidyl ether, phenyltriethoxysilane, phenyl methacrylate, initiator, toughening agent and phenoxyethyl acrylate, stir for 1-2 hours to obtain OCA adhesive coating solution; uniformly coat the OCA adhesive coating solution on the surface of the second polymer film layer of the multilayer intermediate obtained in S2, and then perform UV curing. After curing, attach a PET release film to the surface of the OCA adhesive layer to obtain UTG foldable screen protector.

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