A screen support film for a foldable display and a method of manufacturing the same

Abstract

This application relates to the field of support film technology, specifically disclosing a screen support film for foldable displays and its preparation method. The screen support film for foldable displays comprises, from top to bottom, a first UV-type acrylic polymer film layer, a UTG glass layer, a second UV-type acrylic polymer film layer, and an acrylic-based foldable OCA layer. Through the synergistic cooperation of the rigidity and flexibility of each layer, a dynamic balance is achieved, significantly improving the structural stability, impact resistance, and long-term folding reliability of the foldable display.

Description

Technical Field

[0001] This application relates to the field of support film technology, and more specifically, to a screen support film for foldable displays and a method for preparing the same. Background Technology

[0002] With the rapid development of flexible OLED display technology, foldable displays, with their advantages of being foldable and highly portable, are widely used in electronic products such as smartphones, tablets, and wearable devices. As a core component of foldable displays, the performance of the support film directly affects the folding reliability, structural stability, optical transmittance, and lifespan of the display. Therefore, developing screen support films that are suitable for folding scenarios and have excellent overall performance has become a key focus of industry research.

[0003] Currently, existing technologies, such as patent application CN118853031A, disclose acrylic pressure-sensitive adhesive, a support film, and a preparation method for flexible OLED support films. This support film comprises a protective film layer, a PET substrate layer, an acrylic pressure-sensitive adhesive layer, and a release layer stacked sequentially. This solution uses PET plastic film as the core substrate, combined with the acrylic pressure-sensitive adhesive layer to achieve bonding with the display module, offering advantages such as low cost, simple processing, and convenient room-temperature bonding. However, as foldable displays develop towards high-frequency folding, ultra-thinness, and high definition, the aforementioned existing technologies... The existing technical solutions have gradually revealed several insurmountable defects: First, the PET substrate itself lacks rigidity, making it prone to deformation and wrinkling during high-frequency folding. Long-term use can lead to the failure of the support film, thus affecting the display's performance and lifespan. Second, the acrylic pressure-sensitive adhesive layer has limited bending resistance, easily leading to delamination and cracking after high-frequency folding, failing to meet the long-term usage requirements of foldable displays. Third, while the light transmittance of the PET substrate meets basic requirements, its optical performance still has room for improvement in high-end foldable displays, making it difficult to match the requirements of high-definition display modules. Furthermore, the PET substrate support film has poor scratch and impact resistance, making it susceptible to damage during display assembly and use due to external forces, which can then damage the internal display panel. Therefore, addressing the technical shortcomings of existing flexible OLED display support films, such as insufficient rigidity, poor bending resistance, and the need for improved optical performance, developing a screen support film for foldable displays that balances rigidity and flexibility, withstands high-frequency folding, has excellent optical transmittance, and possesses a stable structure has become a pressing technical problem for those skilled in the art. Summary of the Invention

[0004] In order to develop a screen support film for foldable displays that can balance rigidity and flexibility, withstand high-frequency folding, have excellent optical transmittance and structural stability, this application provides a screen support film for foldable displays and its preparation method.

[0005] In a first aspect, this application provides a screen support film for a foldable display screen, employing the following technical solution. A screen support film for a foldable display screen comprises, from top to bottom, a first UV-type acrylic polymer film layer, a UTG glass layer, a second UV-type acrylic polymer film layer, and an acrylic-based foldable OCA layer.

[0006] This application employs a four-layer rigid-elastic composite laminate structure: a first UV-type acrylic polymer film layer, a UTG glass layer, a second UV-type acrylic polymer film layer, and an acrylic-based foldable OCA layer. This structure uses the upper and lower UV-type acrylic polymer film layers as rigidity reinforcement and stress buffer layers, effectively holding and supporting the middle UTG glass layer. The high rigidity of the UTG glass provides reliable support, while the high flexibility of the upper and lower UV film layers and the good adhesion of the OCA layer achieve a dynamic balance between rigidity and flexibility. This support film structure significantly improves the structural stability, impact resistance, and long-term folding reliability of the foldable display screen.

[0007] Preferably, both the first UV-type acrylic polymer film layer and the second UV-type acrylic polymer film layer comprise the following raw materials in parts by weight: 35-45 parts of aliphatic polyurethane acrylate, 18-25 parts of isobornyl methacrylate, 15-22 parts of isooctyl acrylate, 8-12 parts of modified polyurethane acrylate prepolymer, 0.8-1.5 parts of non-yellowing photoinitiator, 1.2-2 parts of stabilizer, 2.5-4 parts of silane-modified nano-silica, 4-6 parts of reactive diluent, and 0.5-1 parts of antioxidant; The modified polyurethane acrylate prepolymer is prepared by first performing a branching and chain extension reaction between glycerol and isocyanate-terminated polyurethane prepolymer, followed by a capping reaction with hydroxyethyl acrylate to obtain a branched polyurethane acrylate prepolymer with acrylate-terminated groups, which is then modified by maleic anhydride grafting.

[0008] By employing the above technical solution, the ternary composite resin system of aliphatic polyurethane acrylate, isobornyl methacrylate, and isooctyl acrylate balances the hardness, flexibility, and film-forming properties of the film. In particular, the introduction of the modified polyurethane acrylate prepolymer, with its unique branched structure and maleic anhydride-grafted polar groups, allows it to form an interpenetrating network with the aliphatic polyurethane acrylate and also to form strong chemical or physical bonds with the hydroxyl groups, nano-silica, and OCA layer on the UTG glass surface. This not only significantly improves the interfacial adhesion and cohesion between the film and each substrate layer, effectively suppressing the risk of delamination and peeling under long-term folding, but also enhances the film's resistance to chemical corrosion and yellowing.

[0009] Preferably, the preparation method of the modified polyurethane acrylate prepolymer includes the following steps: (1) Prepolymerization reaction: Under nitrogen protection, isophorone diisocyanate and polycarbonate diol are stirred evenly at a weight ratio of 1:(1.8-2.5), and then 0.03%-0.08% of dibutyltin dilaurate catalyst (total mass of isophorone diisocyanate and polycarbonate diol) is added. The reaction is carried out at 70-85℃ for 2-3.5h to obtain isocyanate-terminated polyurethane prepolymer; (2) Branching chain extension reaction: While maintaining the reaction temperature at 75-85℃, glycerol is added dropwise to the polyurethane prepolymer with terminal isocyanate groups under stirring. After the addition is complete, the reaction is continued at the temperature for 1-2 hours. The amount of glycerol used is 4%-6% of the mass of polycarbonate diol. (3) Acrylate end-capping reaction: The reaction temperature is lowered to 70-80℃, hydroxyethyl acrylate is added, and after stirring evenly, the reaction is kept at the temperature for 1.5-3h to obtain branched polyurethane acrylate prepolymer with acrylate end groups; the amount of hydroxyethyl acrylate is 45%-55% of the mass of isophorone diisocyanate; (4) Modification reaction: Reduce the reaction temperature to 55-70℃, add maleic anhydride, stir evenly, and keep the reaction at the temperature for 1.5-2.5h; cool the reaction system to 20-30℃ to obtain modified polyurethane acrylate prepolymer; the amount of maleic anhydride is 3.5%-5.5% of the total mass of isophorone diisocyanate and polycarbonate diol.

[0010] Preferably, in step (1), the polycarbonate diol is a mixture of polycarbonate diol with a molecular weight of 800 and polycarbonate diol with a molecular weight of 1000 in a mass ratio of 1:(0.8-1.2).

[0011] By employing the above technical solution, polycarbonate diol with a molecular weight of 800 provides high modulus and rigidity, endowing the prepolymer and the final film with excellent bending recovery ability and preventing permanent creases after folding; while polycarbonate diol with a molecular weight of 1000 provides excellent flexibility and toughness, buffering the huge stress generated during folding. When the two are compounded in a specific ratio, the synergistic effect of long and short chains achieves an optimal balance between the soft and hard segments of the prepolymer, resulting in a more stable microstructure. This compounding system significantly improves the overall mechanical properties of the prepolymer and the UV film, ensuring that the supporting film maintains structural integrity and excellent performance even under high-frequency, large-angle folding conditions.

[0012] Preferably, in step (1) the prepolymerization reaction: under nitrogen protection, isophorone diisocyanate and polycarbonate diol are stirred evenly at a weight ratio of 1:(1.8-2.5), then a catalyst is added, and the reaction is carried out at 70-85℃ for 2-2.5h to obtain isocyanate-terminated polyurethane prepolymer; the catalyst is a mixture of dibutyltin dilaurate and stannous octoate in a mass ratio of (1.5-2.5):1, and the amount of catalyst used is 0.03%-0.08% of the total mass of isophorone diisocyanate and polycarbonate diol.

[0013] By employing the above-mentioned technical solution, dibutyltin dilaurate exhibits mild reaction and strong controllability, effectively regulating the prepolymerization reaction rate of IPDI and PCDL and avoiding local overheating or gelation. Meanwhile, stannous octoate possesses higher catalytic activity, significantly accelerating subsequent branching and chain extension reactions and shortening the overall reaction cycle. The combined use of these two technologies combines precise controllability with high efficiency, providing a reliable process guarantee for the preparation of high-quality isocyanate-terminated polyurethane prepolymers.

[0014] Preferably, in step (4) the modification reaction: the reaction temperature is lowered to 55-70℃, maleic anhydride and itaconic acid are added, stirred evenly, and kept at the temperature for 1.5-2.5h; the reaction system is cooled to 20-30℃ to obtain the modified polyurethane acrylate prepolymer; the amount of maleic anhydride is 3.5%-5.5% of the total mass of isophorone diisocyanate and polycarbonate diol; the amount of itaconic acid is 0.4%-0.6% of the total mass of isophorone diisocyanate and polycarbonate diol.

[0015] By employing the above-mentioned technical solution, maleic anhydride and itaconic acid are used together to graft-modify branched polyurethane acrylate prepolymers. Compared to the solution using only maleic anhydride, this compound modification system brings synergistic benefits: maleic anhydride, as the main modifier, can efficiently open the ring and graft onto the prepolymer side chains, introducing a large number of carboxyl groups, which significantly improves the interfacial adhesion and polarity matching between the prepolymer and UTG glass, nano-silica, and OCA layers. Itaconic acid, as an auxiliary modifier, contains methylene groups in its molecular structure, resulting in greater steric hindrance. This effectively slows down the molecular chain packing density during the modification reaction, avoiding system embrittlement or phase separation caused by excessive grafting density of maleic anhydride alone. Simultaneously, the introduction of itaconic acid can suppress side reactions at high temperatures and reduce the generation of oxidative degradation products, thereby further improving the thermal stability and color stability of the modified prepolymer and the final UV film. This compound modification strategy improves interfacial performance while optimizing the mechanical and weather resistance properties of the material.

[0016] Preferably, in step (4) the modification reaction: the reaction temperature is lowered to 55-70℃, maleic anhydride is added, and after stirring evenly, phosphite anti-yellowing agent is added, and stirring is continued for 5-10 min. The reaction is kept warm for 1.5-2.5 h; the reaction system is cooled to 20-30℃ to obtain modified polyurethane acrylate prepolymer; the amount of maleic anhydride is 3.5%-5.5% of the total mass of isophorone diisocyanate and polycarbonate diol; the amount of phosphite anti-yellowing agent is 0.15%-0.25% of the total mass of isophorone diisocyanate and polycarbonate diol.

[0017] By adopting the above technical solution, the addition of phosphite-based anti-yellowing agents during the modification reaction not only does not interfere with the grafting modification reaction of maleic anhydride, but also provides crucial anti-yellowing protection for the prepolymer. During the modification reaction and subsequent UV curing, the system is prone to generating free radicals and initiating oxidative yellowing. The mechanism of action of phosphite-based anti-yellowing agents is to efficiently capture these peroxide free radicals, interrupt the oxidation chain reaction, and thus inhibit yellowing of the prepolymer and film layer from the source.

[0018] Preferably, the stabilizer is a mixture of light stabilizer 400 and hindered amine light stabilizer 944 in a mass ratio of 1:(0.5-1.5); and the antioxidant is a mixture of antioxidant 1010 and antioxidant 1076 in a mass ratio of 1:(0.8-1.2).

[0019] By employing the above technical solution, light stabilizer 400 is responsible for absorbing ultraviolet light in the 280-400nm range, preventing light energy from directly damaging the polymer backbone; hindered amine light stabilizer 944 is responsible for capturing various free radicals generated during photo-oxidation and thermal oxidation. This dual protection ensures the structural stability of the film layer under long-term ultraviolet irradiation and high-temperature environments. The combination of antioxidants 1010 and 1076 effectively inhibits thermo-oxidative degradation by synergistically capturing free radicals during thermo-oxidative processing and long-term storage, preventing embrittlement and color deepening of the film layer at high temperatures. This composite protection system complements the aforementioned phosphite-based anti-yellowing agents, jointly constructing a comprehensive protection network from ultraviolet to thermo-oxidative processes, from short-term processing to long-term use, ensuring that the supporting film maintains excellent optical and mechanical properties under various harsh environments.

[0020] Preferably, the raw materials for the first UV-type acrylic polymer film layer and the second UV-type acrylic polymer film layer further include 0.2-0.3 parts by weight of polyether-modified polysiloxane dispersant.

[0021] By adopting the above technical solution, the polyether-modified polysiloxane dispersant has a unique amphiphilic structure. Its polyether segments are well compatible with the acrylate resin matrix, while the siloxane segments can adsorb and coat the surface of nano-silica particles. Through steric hindrance and electrostatic repulsion, it effectively prevents the agglomeration of filler particles, so that they can be uniformly distributed in a monodisperse state in the resin.

[0022] Preferably, the thickness of both the first UV-type acrylic polymer film layer and the second UV-type acrylic polymer film layer is 15-60 μm; the thickness of the UTG glass layer is 30-100 μm; and the thickness of the acrylic folded OCA layer is 15-60 μm.

[0023] Secondly, this application provides a method for preparing a screen support film for a foldable display screen, employing the following technical solution: A method for preparing a screen support film for a foldable display screen includes the following steps: According to the formula, aliphatic polyurethane acrylate, isobornyl methacrylate, isooctyl acrylate, and reactive diluent are mixed evenly; while stirring, modified polyurethane acrylate prepolymer is added, and after stirring, stabilizer, antioxidant, and optional polyether-modified polysiloxane dispersant are added sequentially, and stirred; finally, silane-modified nano-silica is added to obtain a mixture; a non-yellowing photoinitiator is added to the mixture, stirred, and vacuum degassed to obtain an adhesive; the adhesive is coated onto a PET release film at 150-300 mJ / cm². 2 Under light curing for 10-20 seconds, a PET release film is laminated on the other side of the film layer, and the film is wound up to obtain a UV-type acrylic polymer film roll; the UV-type acrylic polymer film roll is cut to obtain a first UV-type acrylic polymer film layer and a second UV-type acrylic polymer film layer. The layers are stacked sequentially from top to bottom: a first UV-type acrylic polymer film layer, a UTG glass layer, a second UV-type acrylic polymer film layer, and an acrylic-based folded OCA layer, at a concentration of 800-1200 mJ / cm². 2 Under light curing for 30-60 seconds, a screen support film for foldable displays is obtained.

[0024] Through the above technical solution, this application adopts a process design that first uses UV pre-curing to form a semi-cured film layer, and then performs a second UV curing after bonding it with UTG glass and OCA layer. On the one hand, the self-adhesion of the semi-cured film layer can be used to achieve stress-free bonding between layers, avoiding film layer damage and interface bubble problems caused by hot pressing and other processes, and ensuring that the composite structure is flat and dense. On the other hand, the second curing can further improve the crosslinking density and modulus of the UV-type acrylic polymer film layer, enhance the film layer's support and protection effect on UTG glass, and improve the overall structure's bending stability, aging resistance and interlayer bonding strength. Ultimately, the resulting screen support film for foldable displays has excellent support, bending reliability and usage stability.

[0025] In summary, this application has the following beneficial effects: 1. This application adopts a four-layer composite stacked structure of first UV-type acrylic polymer film layer - UTG glass layer - second UV-type acrylic polymer film layer - acrylic folding OCA layer. Through the synergistic cooperation of rigidity and flexibility of each layer, dynamic balance is achieved, which significantly improves the structural stability, impact resistance and long-term folding reliability of the folding display screen.

[0026] 2. The UV-type acrylic polymer film of this application adopts a ternary compound resin system of aliphatic polyurethane acrylate, isobornyl methacrylate and isooctyl acrylate, combined with a modified polyurethane acrylate prepolymer with branched structure and grafted polar groups, which can balance the hardness, flexibility and film-forming properties of the film, while enhancing the interfacial adhesion with UTG glass, nano silica and OCA layer, suppressing the risk of delamination and improving the chemical resistance and anti-yellowing ability of the film.

[0027] 3. In this application, maleic anhydride and itaconic acid are combined to graft and modify branched polyurethane acrylate prepolymer. Maleic anhydride can introduce a large number of carboxyl groups to improve interfacial adhesion, while itaconic acid can prevent system embrittlement and inhibit side reactions. The two work synergistically to improve interfacial performance while optimizing the mechanical and weather resistance properties of the material. Detailed Implementation

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

[0029] Unless otherwise specified, the raw materials used in the preparation examples, embodiments, and comparative examples of this application are all commercially available.

[0030] Preparation Example 1 This preparation example discloses a method for preparing a modified polyurethane acrylate prepolymer, specifically including the following steps: (1) Prepolymerization reaction: 22.2g of isophorone diisocyanate and 50g of polycarbonate diol (25g of polycarbonate diol with a molecular weight of 800 and 25g of polycarbonate diol with a molecular weight of 1000) were added to a four-necked reactor equipped with a stirrer, thermometer and nitrogen inlet tube. The reactor was protected with nitrogen and the stirring was started. The stirring speed was controlled at 250r / min. The reactor was stirred at room temperature for 12min. The temperature was raised to 80℃ and 0.040g of dibutyltin dilaurate catalyst was added. The reactor was kept at this temperature and the reaction was carried out. Samples were taken every 30min during the reaction. The NCO content was determined by di-n-butylamine titration. When the NCO content reached 3.8%±0.1%, the heat preservation was stopped. If the NCO content did not reach 3.8%, the heat preservation was continued. Samples were taken every 10min for retesting until the NCO content reached 3.8%±0.1%, and the NCO-terminated polyurethane prepolymer was obtained. (2) Branching and chain extension reaction: Keep the temperature of the reactor at 80°C, and add 2.5g of glycerol at a rate of 1 drop / s while stirring at 250r / min. After the addition is complete, continue to keep the reaction at the temperature for 1.5h, and keep the stirring speed constant during the process. (3) Acrylate end-capping reaction: The temperature of the reactor was lowered to 75°C, the stirring speed was kept at 250 r / min, 11.1 g of hydroxyethyl acrylate was added, stirred for 6 min, and kept at the temperature for reaction. During the reaction, samples were taken every 30 min, and the NCO content was detected by di-n-butylamine titration until the NCO content was <0.1%, and branched polyurethane acrylate prepolymer with acrylate end groups was obtained. (4) Modification reaction: Reduce the temperature of the reactor to 62°C, keep the stirring speed at 250 r / min, add 3.97 g of maleic anhydride, stir for 6 min, keep the temperature for 2 h, and keep the stirring speed constant during the reaction; after the reaction is completed, stop stirring and cool naturally to 25°C to obtain modified polyurethane acrylate prepolymer.

[0031] Preparation Example 2 This preparation example is basically the same as Preparation Example 1, except that in step (1) the prepolymerization reaction is as follows: 22.2g of isophorone diisocyanate and 50g of polycarbonate diol (25g of polycarbonate diol with a molecular weight of 800 and 25g of polycarbonate diol with a molecular weight of 1000) are added to a four-necked reactor equipped with a stirrer, thermometer and nitrogen inlet tube. Nitrogen gas is used for protection. Stirring is started and the speed is controlled at 250r / min. Stirring is carried out at room temperature for 12min and then the temperature is increased. At 80℃, add 0.040g of catalyst (0.024g of dibutyltin dilaurate and 0.016g of stannous octoate), and maintain the temperature for reaction. During the reaction, take samples every 30 minutes and use the di-n-butylamine titration method to detect the NCO content. When the NCO content reaches 3.8%±0.1%, stop the temperature maintenance. If it does not reach the target, continue the temperature maintenance and take samples every 10 minutes for retesting until the NCO content reaches 3.8%±0.1%, thus obtaining the NCO-terminated polyurethane prepolymer.

[0032] Preparation Example 3 This preparation example is basically the same as preparation example 1, except that in step (4) modification reaction: the temperature of the reactor is reduced to 62°C, the stirring speed is kept at 250 r / min, 3.97 g maleic anhydride and 0.36 g itaconic acid are added, stirred for 6 min, and kept warm for 2 h, during which the stirring speed is kept constant; after the reaction is completed, stirring is stopped, and the mixture is naturally cooled to 25°C to obtain the modified polyurethane acrylate prepolymer.

[0033] Preparation Example 4 This preparation example is basically the same as Preparation Example 1, except that in step (4) modification reaction: the temperature of the reactor is reduced to 62°C, the stirring speed is kept at 250 r / min, 3.97 g of maleic anhydride is added, and the mixture is stirred for 6 min. Then 0.14 g of triphenyl phosphite (phosphite anti-yellowing agent) is added, and the mixture is stirred for 8 min. The mixture is kept warm for 2 h, and the stirring speed is kept constant during the reaction. After the reaction is completed, the stirring is stopped, and the mixture is naturally cooled to 25°C to obtain the modified polyurethane acrylate prepolymer.

[0034] Preparation Example 5 This preparation example discloses a method for preparing a modified polyurethane acrylate prepolymer, specifically including the following steps: (1) Prepolymerization reaction: 22.2g of isophorone diisocyanate and 40.0g of polycarbonate diol (22.2g of polycarbonate diol with a molecular weight of 800 and 17.8g of polycarbonate diol with a molecular weight of 1000, with a mass ratio of 1:0.8) were added to a four-necked reactor equipped with a stirrer, thermometer and nitrogen inlet pipe. Nitrogen gas was used for protection. Stirring was started and the speed was controlled at 200r / min. Stirring was carried out at room temperature for 10min. The temperature was then raised to 70°C. At ℃, add 0.019g of catalyst (0.012g of dibutyltin dilaurate and 0.007g of stannous octoate), and maintain the temperature for reaction. During the reaction, take samples every 30 minutes and use the di-n-butylamine titration method to detect the NCO content. When the NCO content reaches 3.8%±0.1%, stop the temperature maintenance. If it does not reach the target, continue the temperature maintenance and take samples every 10 minutes for retesting until the NCO content reaches 3.8%±0.1%, and obtain the NCO-terminated polyurethane prepolymer. (2) Branching chain extension reaction: Keep the temperature of the reactor at 75°C, and add 1.6 g of glycerol dropwise at a rate of 1 drop / s while stirring at 200 r / min. After the addition is complete, continue to keep the temperature for 1 h while maintaining the stirring speed. (3) Acrylate end-capping reaction: The temperature of the reactor was lowered to 70°C, the stirring speed was kept at 200 r / min, 9.99 g of hydroxyethyl acrylate was added, stirred for 5 min, and kept at the temperature for reaction. During the reaction, samples were taken every 30 min, and the NCO content was detected by di-n-butylamine titration until the NCO content was <0.1%, and branched polyurethane acrylate prepolymer with acrylate end groups was obtained. (4) Modification reaction: Reduce the temperature of the reactor to 55°C, keep the stirring speed at 200 r / min, add 2.18 g maleic anhydride and 0.25 g itaconic acid, stir for 5 min, then add 0.09 g triphenyl phosphite, continue stirring for 5 min, keep the reaction at the temperature for 1.5 h, and keep the stirring speed constant during the reaction; after the reaction is completed, stop stirring and cool naturally to 20°C to obtain the modified polyurethane acrylate prepolymer.

[0035] Preparation Example 6 This preparation example discloses a method for preparing a modified polyurethane acrylate prepolymer, specifically including the following steps: (1) Prepolymerization reaction: 22.2g of isophorone diisocyanate and 55.5g of polycarbonate diol (25.2g of polycarbonate diol with a molecular weight of 800 and 30.3g of polycarbonate diol with a molecular weight of 1000, with a mass ratio of 1:1.2) were added to a four-necked reactor equipped with a stirrer, thermometer and nitrogen inlet pipe. Nitrogen gas was used for protection. Stirring was started and the speed was controlled at 300r / min. Stirring was carried out at room temperature for 15min and then the temperature was raised to 85℃. Add 0.062g of catalyst (0.044g of dibutyltin dilaurate and 0.018g of stannous octoate), and keep the reaction at the specified temperature. Take samples every 30 minutes during the reaction and use di-n-butylamine titration to detect the NCO content. When the NCO content reaches 3.8%±0.1%, stop the reaction. If it does not reach the specified value, continue the reaction and take samples every 10 minutes for retesting until the NCO content reaches 3.8%±0.1%, thus obtaining the NCO-terminated polyurethane prepolymer. (2) Branching and chain extension reaction: Keep the temperature of the reactor at 85°C, and add 3.33 g of glycerol at a rate of 1 drop / s while stirring at 300 r / min. After the addition is complete, continue to keep the reactor at the temperature for 2 h while keeping the stirring speed constant. (3) Acrylate end-capping reaction: The temperature of the reactor was lowered to 80°C, the stirring speed was kept at 300 r / min, 12.21 g of hydroxyethyl acrylate was added, stirred for 8 min, and kept at the temperature for reaction. During the reaction, samples were taken every 30 min, and the NCO content was detected by di-n-butylamine titration until the NCO content was <0.1%, and branched polyurethane acrylate prepolymer with acrylate end groups was obtained. (4) Modification reaction: Reduce the temperature of the reactor to 70°C, keep the stirring speed at 300 r / min, add 4.27 g maleic anhydride and 0.47 g itaconic acid, stir for 8 min, then add 0.19 g triphenyl phosphite, continue stirring for 10 min, keep the reaction at the temperature for 2.5 h, and keep the stirring speed constant during the reaction; after the reaction is completed, stop stirring and cool naturally to 30°C to obtain the modified polyurethane acrylate prepolymer.

[0036] Example 1 This embodiment provides a method for preparing the screen support film for the above-mentioned foldable display screen, including the following steps: 6.5 g of γ-methacryloxypropyltrimethoxysilane was added to 1 L of mixed solvent (800 mL of anhydrous ethanol and 200 mL of deionized water), and glacial acetic acid was added dropwise to adjust the pH to 5. The mixture was stirred at room temperature for 30 min to obtain a hydrolysate. 100 g of nano-silica with a particle size of 20-50 nm was added to the above hydrolysate, and the temperature was raised to 60 °C. The mixture was stirred at 350 r / min for 2 h. After the reaction was completed, the system was centrifuged at 5000 r / min for 15 min, the precipitate was collected, washed three times with anhydrous ethanol, and then dried in an 80 °C oven for 4 h. After cooling to room temperature, the precipitate was pulverized and passed through a 200-mesh standard sieve to obtain silane-modified nano-silica.

[0037] In a mixing vessel equipped with a stirrer and a thermometer, 40g of aliphatic polyurethane acrylate (L-6206), 22g of isobornyl methacrylate, 18g of isooctyl acrylate, and 5g of reactive diluent (trimethylolpropane triacrylate) were added sequentially. The stirring was started, and the speed was controlled at 250r / min. The mixture was stirred at room temperature for 18min to obtain a mixture. While stirring, 10g of modified polyurethane acrylate prepolymer (obtained from Preparation Example 1) was added to the above mixture, and stirring was continued for 25min. Subsequently, 1.6g of stabilizer (0.8g of light stabilizer 400 and 0.8g of hindered amine light stabilizer 944) and 0.8g of antioxidant (0.4g of antioxidant 1010 and 0.4g of antioxidant 1076) were added sequentially. Stir for 12 min; finally, add 3.2 g of silane-modified nano-silica, increase the stirring speed to 550 r / min, and stir for 35 min; reduce the stirring speed to 250 r / min, add 1.2 g of photoinitiator TPO-L (non-yellowing photoinitiator), and continue stirring for 12 min to obtain a mixture; transfer the mixture to a vacuum degassing machine, and degas for 18 min under a vacuum of -0.085 MPa and at room temperature to obtain an adhesive; apply the adhesive evenly to the PET release film using a slot coating method, controlling the coating thickness to 40 μm; place the coated adhesive in a UV curing machine and cure it using an LED UV lamp at a curing wavelength of 365 nm and a curing energy of 300 mJ / cm². 2The curing time is 15s to obtain a semi-cured film layer. A PET release film is laminated on the other surface of the film layer, and the film is wound up to obtain a UV-type acrylic polymer film roll. The UV-type acrylic polymer film roll is then cut into a first UV-type acrylic polymer film layer and a second UV-type acrylic polymer film layer.

[0038] The composite layer was prepared by sequentially bonding the above-mentioned 40μm first UV-type acrylic polymer film layer (PET release film removed), 50μm UTG glass layer, 40μm second UV-type acrylic polymer film layer (PET release film removed), and 25μm acrylic folded OCA layer (3M8211 series). The composite layer was then placed in a UV curing machine and cured using an LED UV lamp at a curing wavelength of 365nm and a curing energy of 1000mJ / cm². 2 The curing time is 45 seconds to obtain a composite film; the dimensions of the first UV-type acrylic polymer film layer, the second UV-type acrylic polymer film layer, and the acrylic folded OCA layer are all 5 mm larger than the UTG glass outline; the composite film is laser-cut to the dimensions of the UTG glass layer to obtain the screen support film for the foldable display screen.

[0039] Example 2 This embodiment is basically the same as Example 1, except that the modified polyurethane acrylate prepolymer is the one obtained in Preparation Example 2.

[0040] Example 3 This embodiment is basically the same as Example 1, except that the modified polyurethane acrylate prepolymer is the one obtained in Preparation Example 3.

[0041] Example 4 This embodiment is basically the same as Example 1, except that the modified polyurethane acrylate prepolymer is the one obtained in Preparation Example 4.

[0042] Example 5 This embodiment is basically the same as Example 1, except that 40g of aliphatic polyurethane acrylate (L-6206), 22g of isobornyl methacrylate, 18g of isooctyl acrylate, and 5g of reactive diluent (trimethylolpropane triacrylate) were added sequentially to a stirring vessel equipped with a stirrer and a thermometer. Stirring was started at 250 rpm for 18 minutes at room temperature to obtain a mixture. While stirring, 10g of modified polyurethane acrylate prepolymer (obtained in Preparation Example 1) was added to the mixture, and stirring continued for 25 minutes. Subsequently, 1.6g of stabilizer (0.8g of light stabilizer 400 and 0.8g of hindered amine light stabilizer 944) and 0.8g of antioxidant (0.4g of antioxidant 1010 and 0.4g of antioxidant 1076) were added sequentially, and stirring was continued for 12 minutes. Finally, 0.25g of... Polyether-modified polysiloxane dispersant (BYK-333 type) was stirred at 250 rpm for 10 min. Then, 3.2 g of silane-modified nano-silica was added, and the stirring speed was increased to 550 rpm for 35 min. The stirring speed was then reduced to 250 rpm, and 1.2 g of photoinitiator TPO-L (non-yellowing photoinitiator) was added. Stirring was continued for 12 min to obtain a mixture. The mixture was transferred to a vacuum degassing machine and degassed at a vacuum of -0.085 MPa and room temperature for 18 min to obtain an adhesive. The adhesive was then evenly coated onto a PET release film using a slot coating method, with a coating thickness controlled at 40 μm. The coated adhesive was then placed in a UV curing machine and cured using an LED UV lamp at a wavelength of 365 nm and a curing energy of 300 mJ / cm². 2 The curing time is 15s to obtain a semi-cured film layer. A PET release film is laminated on the other surface of the film layer, and the film is wound up to obtain a UV-type acrylic polymer film roll. The UV-type acrylic polymer film roll is then cut into a first UV-type acrylic polymer film layer and a second UV-type acrylic polymer film layer.

[0043] Example 6 This embodiment provides a method for preparing the screen support film for the above-mentioned foldable display screen, including the following steps: To a mixing vessel equipped with a stirrer and thermometer, add 35g of aliphatic polyurethane acrylate (L-6206), 18g of isobornyl methacrylate, 15g of isooctyl acrylate, and 4g of reactive diluent (trimethylolpropane triacrylate). Start stirring at 250 rpm for 18 minutes at room temperature to obtain a mixture. While stirring, add 8g of modified polyurethane acrylate prepolymer (obtained in Preparation Example 5) to the mixture and continue stirring for 25 minutes. Then, add 1.2g of stabilizer (0.8g of light stabilizer 400 and 0.4g of hindered amine light stabilizer 944), 0.8g of antioxidant (0.44g of antioxidant 1010 and 0.36g of antioxidant 1076), and stir for 12 minutes. Finally, add 0.2g of polyether-modified polysiloxane dispersant (BYK- (Type 333) Maintain a stirring speed of 250 r / min and continue stirring for 10 min; finally, add 2.5 g of silane-modified nano-silica (preparation method same as in Example 1), increase the stirring speed to 550 r / min, and stir for 35 min; reduce the stirring speed to 250 r / min, add 0.8 g of photoinitiator TPO-L (non-yellowing photoinitiator), and continue stirring for 12 min to obtain a mixture; transfer the mixture to a vacuum degassing machine, and degas for 18 min under a vacuum of -0.085 MPa and at room temperature to obtain an adhesive; apply the adhesive evenly to the PET release film using a slit coating method, controlling the coating thickness to 40 μm; place the coated adhesive in a UV curing machine and cure it using an LED UV lamp at a curing wavelength of 365 nm and a curing energy of 300 mJ / cm². 2 The curing time is 15s to obtain a semi-cured film layer. A PET release film is laminated on the other surface of the film layer, and the film is wound up to obtain a UV-type acrylic polymer film roll. The UV-type acrylic polymer film roll is then cut into a first UV-type acrylic polymer film layer and a second UV-type acrylic polymer film layer.

[0044] The composite layer was prepared by sequentially bonding the above-mentioned 40μm first UV-type acrylic polymer film layer (PET release film removed), 50μm UTG glass layer, 40μm second UV-type acrylic polymer film layer (PET release film removed), and 25μm acrylic folded OCA layer (3M8211 series). The composite layer was then placed in a UV curing machine and cured using an LED UV lamp at a curing wavelength of 365nm and a curing energy of 1000mJ / cm². 2 The curing time is 45 seconds to obtain a composite film; the dimensions of the first UV-type acrylic polymer film layer, the second UV-type acrylic polymer film layer, and the acrylic folded OCA layer are all 5 mm larger than the UTG glass outline; the composite film is laser-cut to the dimensions of the UTG glass layer to obtain the screen support film for the foldable display screen.

[0045] Example 7 This embodiment provides a method for preparing the screen support film for the above-mentioned foldable display screen, including the following steps: In a mixing vessel equipped with a stirrer and thermometer, 45g of aliphatic polyurethane acrylate (L-6206), 25g of isobornyl methacrylate, 22g of isooctyl acrylate, and 6g of reactive diluent (trimethylolpropane triacrylate) were added sequentially. Stirring was started at 250 rpm for 18 minutes at room temperature to obtain a mixture. While stirring, 12g of modified polyurethane acrylate prepolymer (obtained in Preparation Example 6) was added to the mixture, and stirring continued for 25 minutes. Subsequently, 2g of stabilizer (0.8g of light stabilizer 400 and 1.2g of hindered amine light stabilizer 944) and 1g of antioxidant (0.45g of antioxidant 1010 and 0.55g of antioxidant 1076) were added sequentially, and stirring was continued for 12 minutes. Finally, 0.3g of polyether-modified polysiloxane dispersant (BYK-3) was added. (Type 33) Maintain a stirring speed of 250 r / min and continue stirring for 10 min; finally, add 4 g of silane-modified nano-silica (preparation method same as in Example 1), increase the stirring speed to 550 r / min, and stir for 35 min; reduce the stirring speed to 250 r / min, add 1.5 g of photoinitiator TPO-L (non-yellowing photoinitiator), and continue stirring for 12 min to obtain a mixture; transfer the mixture to a vacuum degassing machine, and degas for 18 min under a vacuum of -0.085 MPa and at room temperature to obtain an adhesive; apply the adhesive evenly to the PET release film using a slit coating method, controlling the coating thickness to 40 μm; place the coated adhesive in a UV curing machine and cure it using an LED UV lamp at a curing wavelength of 365 nm and a curing energy of 300 mJ / cm². 2 The curing time is 15s to obtain a semi-cured film layer. A PET release film is laminated on the other surface of the film layer, and the film is wound up to obtain a UV-type acrylic polymer film roll. The UV-type acrylic polymer film roll is then cut into a first UV-type acrylic polymer film layer and a second UV-type acrylic polymer film layer.

[0046] The composite layer was prepared by sequentially bonding the above-mentioned 40μm first UV-type acrylic polymer film layer (PET release film removed), 50μm UTG glass layer, 40μm second UV-type acrylic polymer film layer (PET release film removed), and 25μm acrylic folded OCA layer (3M8211 series). The composite layer was then placed in a UV curing machine and cured using an LED UV lamp at a curing wavelength of 365nm and a curing energy of 1000mJ / cm². 2The curing time is 45 seconds to obtain a composite film; the dimensions of the first UV-type acrylic polymer film layer, the second UV-type acrylic polymer film layer, and the acrylic folded OCA layer are all 5 mm larger than the UTG glass outline; the composite film is laser-cut to the dimensions of the UTG glass layer to obtain the screen support film for the foldable display screen.

[0047] Comparative Example 1 This comparative example is a support film prepared according to Example 1 in the patent application document with publication number CN118853031A entitled "Acrylic Pressure-Sensitive Adhesive, Support Film and Preparation Method for Flexible OLED Support Film".

[0048] Comparative Example 2 This comparative example provides a method for preparing the screen support film for the above-mentioned foldable display screen, comprising the following steps: Add 50g of aliphatic polyurethane acrylate (L-6206), 22g of isobornyl methacrylate, 18g of isooctyl acrylate, and 5g of reactive diluent (trimethylolpropane triacrylate) to a mixing vessel equipped with a stirrer and thermometer. Start stirring at 250 rpm for 18 minutes at room temperature to obtain a mixture. While stirring, add 1.6g of stabilizer (0.8g of light stabilizer 400 and 0.8g of hindered amine light stabilizer 944) and 0.8g of antioxidant (0.4g of antioxidant 1010 and 0.4g of antioxidant 1076) to the mixture and stir for 12 minutes. Finally, add 3.2g of silane-modified nano-silica and increase the stirring speed to 550 rpm. Stir at 250 rpm for 35 min; reduce the stirring speed to 250 rpm, add 1.2 g of photoinitiator TPO-L (non-yellowing photoinitiator), and continue stirring for 12 min to obtain a mixture; transfer the mixture to a vacuum degassing machine and degas for 18 min at a vacuum of -0.085 MPa and room temperature to obtain an adhesive; apply the adhesive evenly to the PET release film using a slit coating method, controlling the coating thickness to 40 μm; place the coated adhesive in a UV curing machine and cure it using an LED UV lamp at a curing wavelength of 365 nm and a curing energy of 300 mJ / cm². 2 The curing time is 15s to obtain a semi-cured film layer. A PET release film is laminated on the other surface of the film layer, and the film is wound up to obtain a UV-type acrylic polymer film roll. The UV-type acrylic polymer film roll is then cut into a first UV-type acrylic polymer film layer and a second UV-type acrylic polymer film layer.

[0049] The composite layer was prepared by sequentially bonding the above-mentioned 40μm first UV-type acrylic polymer film layer (PET release film removed), 50μm UTG glass layer, 40μm second UV-type acrylic polymer film layer (PET release film removed), and 25μm acrylic folded OCA layer (3M8211 series). The composite layer was then placed in a UV curing machine and cured using an LED UV lamp at a curing wavelength of 365nm and a curing energy of 1000mJ / cm². 2 The curing time is 45 seconds to obtain a composite film; the dimensions of the first UV-type acrylic polymer film layer, the second UV-type acrylic polymer film layer, and the acrylic folded OCA layer are all 5 mm larger than the UTG glass outline; the composite film is laser-cut to the dimensions of the UTG glass layer to obtain the screen support film for the foldable display screen.

[0050] Performance testing 1. Transmittance and haze test: The support films obtained in Examples 1-7 and Comparative Examples 1-2 were tested using a transmittance tester, and the test results are recorded in Table 1.

[0051] 2. Yellowing Index Test: The initial yellowing index of the support films obtained in Examples 1-7 and Comparative Examples 1-2 was tested using a colorimeter. Then, they were placed in a UV aging test chamber at 40°C, with a UV wavelength of 365 nm and an irradiation intensity of 1000 mJ / cm². 2 The sample was aged for 1000 hours under the specified conditions. The yellowing index was tested after aging, and the change in yellowing index (ΔYI) was calculated. The test results are recorded in Table 1.

[0052] 3. Bending resistance test: The support films obtained in Examples 1-7 and Comparative Examples 1-2 were attached to a 0.1mm flexible tempered glass film and then fixed to a folding screen test fixture. The bending resistance test was conducted using an LW-102W folding screen bending life tester at a temperature of 25℃, a bending radius R=2.0mm, and a bending angle of 180°. The test was applied to both the unfolded and folded states of the support film for the folding screen, and 200,000 and 250,000 bending tests were performed respectively. When the test reached 200,000 times, the experiment was stopped, and the support film was observed for phenomena such as bubbles, cracks, detachment, and folding. If these phenomena occurred, the number of tests was recorded as 200,000. If no such phenomena occurred, the test was continued. When the folding reached 250,000 times, the experiment was stopped, and the support film was observed for phenomena such as bubbles, cracks, detachment, and folding. If these phenomena occurred, the number of tests was recorded as 250,000. If no such phenomena occurred, the number of folding tests was recorded as >250,000. The test results are recorded in Table 2.

[0053] 4. Impact Resistance Test: Following GB / T2423.8-1995 standard, the support films obtained in Examples 1-7 and Comparative Examples 1-2 were tested using an MK-2M-DX directional drop tester. The support films adhered to the folding display screen were required to be flat, tight, and free of bubbles and wrinkles. The folding display screen was placed face down on a flat surface at a height of 1.0m and allowed to fall freely onto the concrete surface. After a total of 50 drops, the proportion of broken glass was observed, and the test results are recorded in Table 2.

[0054] 5. Peel strength test: The support films obtained in Examples 1-7 and Comparative Examples 1-2 were cut into standard specimens with a width of 25.4 mm and a length of 300 mm. They were rolled onto SUS304 steel plates with a 2 KG roller at a speed of 600 mm / min and left to stand for 20 min. The 180° peel adhesion was tested using a tensile testing machine. The specific test method was in accordance with the ASTM D3330 international standard. The test results are recorded in Table 2.

[0055] 6. High-temperature holding power test: Perform the test according to the national standard. The support films obtained in Examples 1-7 and Comparative Examples 1-2 are bonded to SUS304 steel plates and placed in an 85℃ high-temperature test chamber for 72 hours. Observe whether the support film falls off or whether the bonding surface detaches. If it does not fall off within 72 hours and the bonding surface does not appear to detach, it is judged as qualified. If it falls off or the bonding surface detaches, it is judged as unqualified. The test results are recorded in Table 2.

[0056] Table 1. Performance test data of screen support film for foldable displays in Examples 1-7 and Comparative Examples 1-2.

[0057] Table 2 Performance test data of screen support film for foldable displays in Examples 1-7 and Comparative Examples 1-2

[0058] Referring to Tables 1 and 2, and combining Example 1 and Comparative Example 1, it can be seen that Example 1 has better overall performance than Comparative Example 1, and is more suitable for the long-term use requirements of foldable displays. Comparative Example 1 uses a traditional pressure-sensitive adhesive and PET substrate system. Although the peel force value is relatively high, the overall rigidity is insufficient, and the bending resistance and impact resistance are weak. Long-term use is prone to deformation, yellowing, and delamination, resulting in poor stability. Example 1 of this application adopts a four-layer composite stacked structure of a first UV-type acrylic polymer film layer - a UTG glass layer - a second UV-type acrylic polymer film layer - an acrylic foldable OCA layer. Through the synergistic cooperation of the rigidity and flexibility of each layer, a dynamic balance is achieved. It performs better in terms of bending resistance, impact resistance, yellowing resistance, and structural stability, and can better meet the actual needs of high-frequency folding and long-term reliable use.

[0059] Referring to Tables 1 and 2, and combining Example 1 and Comparative Example 2, it can be seen that Example 1 added a modified polyurethane acrylate prepolymer. Its branched structure and grafted polar groups can form strong chemical bonds with each film layer, improving interfacial adhesion and cohesion. Simultaneously, it is combined with silane-modified nano-silica to enhance rigidity and impact resistance, and the composite protection system improves anti-yellowing ability. Comparative Example 2, however, did not add the modified polyurethane acrylate prepolymer, resulting in insufficient film layer cohesion and interfacial bonding, and lacking corresponding performance enhancement and protection design. In terms of performance, Example 1 exhibits superior optical performance, stronger anti-yellowing ability, is less prone to abnormalities during high-frequency folding, has more ideal impact protection, stable peel strength, and meets high-temperature retention standards. Comparative Example 2, due to formulation defects, suffers from insufficient adhesion performance and substandard high-temperature retention; all core performance aspects are inferior to Example 1, failing to meet the actual usage requirements of foldable displays.

[0060] Referring to Tables 1 and 2, and combining Examples 1 and 2, it can be seen that Example 1 uses dibutyltin dilaurate as a single catalyst for the prepolymerization reaction, while Example 2 uses a catalyst system composed of dibutyltin dilaurate and stannous octoate. When dibutyltin dilaurate and stannous octoate are used in combination, they exert a synergistic effect. Dibutyltin dilaurate ensures that the prepolymerization reaction is mild and controllable, avoiding local overheating or gelation, while stannous octoate significantly enhances catalytic activity, accelerating the prepolymerization and subsequent branching and chain extension reactions, making the reaction more complete and thorough, and resulting in a more stable structure and more uniform performance of the prepared prepolymer. Consequently, the supporting film of Example 2 shows a slight improvement in optical performance, bending resistance, and interfacial adhesion performance compared to Example 1, and its anti-yellowing and impact protection effects are also more stable, with overall comprehensive performance slightly better than that of Example 1.

[0061] Referring to Tables 1 and 2, and combining Examples 1 and 3, it can be seen that Example 1 uses maleic anhydride alone to modify the branched polyurethane acrylate prepolymer, while Example 3 uses a system of maleic anhydride and itaconic acid to modify the prepolymer. When maleic anhydride and itaconic acid are used in combination, they exert a synergistic effect. Maleic anhydride can efficiently open the ring and graft onto the side chains of the prepolymer, introducing a large number of carboxyl groups, which greatly improves the interfacial adhesion and polarity matching between the prepolymer and each film layer. Itaconic acid can effectively slow down the molecular chain stacking density during the modification reaction, avoiding system embrittlement or phase separation caused by excessively high grafting density of maleic anhydride alone. At the same time, it suppresses side reactions under high temperature reaction and reduces the generation of oxidative degradation products. As a result, the support film of Example 3 has slightly improved optical performance, bending resistance, and interfacial adhesion performance compared to Example 1, and its anti-yellowing and impact protection effects are also more stable. The overall comprehensive performance is slightly better than that of Example 1.

[0062] Referring to Tables 1 and 2, and combining Examples 1 and 4, it can be seen that Example 1 only used maleic anhydride to modify the branched polyurethane acrylate prepolymer, while Example 4, based on maleic anhydride modification, additionally added a phosphite anti-yellowing agent to participate in the prepolymer modification reaction. When the phosphite anti-yellowing agent and maleic anhydride are used together, they exert a synergistic effect. Maleic anhydride can efficiently open the ring and graft onto the side chains of the prepolymer, introducing a large number of carboxyl groups and improving the interfacial adhesion between the prepolymer and each film layer. The phosphite anti-yellowing agent can efficiently capture the peroxide free radicals generated during the modification reaction and subsequent UV curing process, interrupting the oxidation chain reaction and inhibiting the yellowing of the prepolymer and film layer from the source, while not interfering with the grafting modification reaction of maleic anhydride. As a result, the support film of Example 4 has a slight improvement in optical performance, bending resistance, and interfacial adhesion performance compared to Example 1, especially in anti-yellowing performance, and the impact protection effect is more stable. The overall comprehensive performance is slightly better than that of Example 1.

[0063] Referring to Tables 1 and 2, and in conjunction with Examples 1 and 5, it can be seen that Example 5 added a polyether-modified polysiloxane dispersant to the film material. When the polyether-modified polysiloxane dispersant is used in conjunction with the silane-modified nano-silica, the two exert a synergistic effect. The silane-modified nano-silica can improve the rigidity and impact resistance of the film, while the polyether-modified polysiloxane dispersant, due to its amphiphilic structure, has polyether segments that are well compatible with the acrylate resin body, and siloxane segments that adsorb and coat the surface of the nano-silica particles. Through steric hindrance and electrostatic repulsion, it effectively prevents the nanoparticles from agglomerating, allowing them to be uniformly dispersed in the resin. As a result, the support film of Example 5 has certain improvements in optical performance, bending resistance, and impact protection performance compared to Example 1, while maintaining stable interfacial adhesion performance and better overall comprehensive performance.

[0064] 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 screen support film for a foldable display screen, characterized in that, From top to bottom, it includes a first UV-type acrylic polymer film layer, a UTG glass layer, a second UV-type acrylic polymer film layer, and an acrylic folded OCA layer; Both the first UV-type acrylic polymer film and the second UV-type acrylic polymer film contain the following raw materials in parts by weight: 35-45 parts of aliphatic polyurethane acrylate, 18-25 parts of isobornyl methacrylate, 15-22 parts of isooctyl acrylate, 8-12 parts of modified polyurethane acrylate prepolymer, 0.8-1.5 parts of non-yellowing photoinitiator, 1.2-2 parts of stabilizer, 2.5-4 parts of silane-modified nano silica, 4-6 parts of reactive diluent, and 0.5-1 parts of antioxidant; The modified polyurethane acrylate prepolymer is prepared by first performing a branching and chain extension reaction between glycerol and isocyanate-terminated polyurethane prepolymer, followed by a capping reaction with hydroxyethyl acrylate to obtain a branched polyurethane acrylate prepolymer with acrylate-terminated groups, which is then modified by maleic anhydride grafting.

2. The screen support film for a foldable display screen according to claim 1, characterized in that, The preparation method of the modified polyurethane acrylate prepolymer includes the following steps: (1) Prepolymerization reaction: Under nitrogen protection, isophorone diisocyanate and polycarbonate diol are stirred evenly at a weight ratio of 1:(1.8-2.5), and then 0.03%-0.08% of dibutyltin dilaurate catalyst (total mass of isophorone diisocyanate and polycarbonate diol) is added. The reaction is carried out at 70-85℃ for 2-3.5h to obtain isocyanate-terminated polyurethane prepolymer; (2) Branching chain extension reaction: While maintaining the reaction temperature at 75-85℃, glycerol is added dropwise to the polyurethane prepolymer with terminal isocyanate groups under stirring. After the addition is complete, the reaction is continued at the temperature for 1-2 hours. The amount of glycerol used is 4%-6% of the mass of polycarbonate diol. (3) Acrylate end-capping reaction: The reaction temperature is lowered to 70-80℃, hydroxyethyl acrylate is added, and after stirring evenly, the reaction is kept at the temperature for 1.5-3h to obtain branched polyurethane acrylate prepolymer with acrylate end groups; the amount of hydroxyethyl acrylate is 45%-55% of the mass of isophorone diisocyanate; (4) Modification reaction: Reduce the reaction temperature to 55-70℃, add maleic anhydride, stir evenly, and keep the reaction at the temperature for 1.5-2.5h; cool the reaction system to 20-30℃ to obtain modified polyurethane acrylate prepolymer; the amount of maleic anhydride is 3.5%-5.5% of the total mass of isophorone diisocyanate and polycarbonate diol.

3. The screen support film for a foldable display screen according to claim 2, characterized in that, In step (1), the polycarbonate diol is a mixture of polycarbonate diol with a molecular weight of 800 and polycarbonate diol with a molecular weight of 1000 in a mass ratio of 1:(0.8-1.2).

4. The screen support film for a foldable display screen according to claim 2, characterized in that, Step (1) Prepolymerization reaction: Under nitrogen protection, isophorone diisocyanate and polycarbonate diol are stirred evenly at a weight ratio of 1:(1.8-2.5), and then a catalyst is added. The mixture is kept at 70-85℃ for 2-2.5h to obtain isocyanate-terminated polyurethane prepolymer. The catalyst is a mixture of dibutyltin dilaurate and stannous octoate in a mass ratio of (1.5-2.5):

1. The amount of catalyst used is 0.03%-0.08% of the total mass of isophorone diisocyanate and polycarbonate diol.

5. The screen support film for a foldable display screen according to claim 2, characterized in that, Step (4) Modification reaction: Reduce the reaction temperature to 55-70℃, add maleic anhydride and itaconic acid, stir evenly, and keep the reaction at the temperature for 1.5-2.5h; cool the reaction system to 20-30℃ to obtain modified polyurethane acrylate prepolymer; the amount of maleic anhydride is 3.5%-5.5% of the total mass of isophorone diisocyanate and polycarbonate diol; the amount of itaconic acid is 0.4%-0.6% of the total mass of isophorone diisocyanate and polycarbonate diol.

6. The screen support film for a foldable display screen according to claim 2, characterized in that, Step (4) Modification reaction: Reduce the reaction temperature to 55-70℃, add maleic anhydride, stir evenly, then add phosphite anti-yellowing agent, continue stirring for 5-10 min, and keep the reaction at the temperature for 1.5-2.5 h; cool the reaction system to 20-30℃ to obtain modified polyurethane acrylate prepolymer; the amount of maleic anhydride is 3.5%-5.5% of the total mass of isophorone diisocyanate and polycarbonate diol; the amount of phosphite anti-yellowing agent is 0.15%-0.25% of the total mass of isophorone diisocyanate and polycarbonate diol.

7. The screen support film for a foldable display screen according to claim 1, characterized in that, The stabilizer is a mixture of light stabilizer 400 and hindered amine light stabilizer 944 in a mass ratio of 1:(0.5-1.5); the antioxidant is a mixture of antioxidant 1010 and antioxidant 1076 in a mass ratio of 1:(0.8-1.2).

8. The screen support film for a foldable display screen according to claim 1, characterized in that, The raw materials for the first UV-type acrylic polymer film and the second UV-type acrylic polymer film also include 0.2-0.3 parts by weight of polyether-modified polysiloxane dispersant.

9. A method for preparing a screen support film for a foldable display screen as described in any one of claims 1-8, characterized in that, Includes the following steps: According to the formula, aliphatic polyurethane acrylate, isobornyl methacrylate, isooctyl acrylate, and reactive diluent are mixed evenly; while stirring, modified polyurethane acrylate prepolymer is added, and after stirring, stabilizer, antioxidant, and optional polyether-modified polysiloxane dispersant are added sequentially, and stirred; finally, silane-modified nano-silica is added to obtain a mixture; a non-yellowing photoinitiator is added to the mixture, stirred, and vacuum degassed to obtain an adhesive; the adhesive is coated onto a PET release film at 150-300 mJ / cm². 2 Under light curing for 10-20 seconds, a PET release film is laminated on the other side of the film layer, and the film is wound up to obtain a UV-type acrylic polymer film roll; the UV-type acrylic polymer film roll is cut to obtain a first UV-type acrylic polymer film layer and a second UV-type acrylic polymer film layer. The layers are stacked sequentially from top to bottom: a first UV-type acrylic polymer film layer, a UTG glass layer, a second UV-type acrylic polymer film layer, and an acrylic-based folded OCA layer, at a concentration of 800-1200 mJ / cm². 2 Under light curing for 30-60 seconds, a screen support film for foldable displays is obtained.

Images