A support film for a folding screen containing a double-layer sus and a method for manufacturing the same

Abstract

The application relates to the technical field of folding screen supporting films, and specifically discloses a folding screen supporting film containing double-layer SUS and a preparation method thereof. The folding screen supporting film containing double-layer SUS comprises a first foldable adhesive layer, an upper-layer SUS layer, a second foldable adhesive layer, a lower-layer SUS layer and a protective film layer which are sequentially stacked; the first foldable adhesive layer and the second foldable adhesive layer are from the same foldable adhesive tape, and the foldable adhesive tape is solidified from raw materials in the following mass fractions: long-alkyl-chain acrylate monomer 60-100 parts, polyether acrylate monomer 30-60 parts, vinyl MQ silicone resin 10-20 parts, functional monomer 14-26 parts, initiator 0.9-2 parts, crosslinking agent 0.9-2 parts, antioxidant 1.5-4 parts, anti-aging agent 1.5-4 parts, light stabilizer 1-2 parts and organic solvent. The supporting film prepared by the application has excellent interlayer peeling strength, bending resistance and anti-aging performance.

Description

Technical Field

[0001] This application relates to the technical field of support films for foldable screens, and more specifically, to a support film containing double-layer SUS for foldable screens and a method for preparing the same. Background Technology

[0002] Currently, most foldable displays use a SUS folding bracket structure for their support film, typically composed of three components: a buffer layer, a metal support layer, and a protective film layer. The buffer layer in traditional folding bracket structures is made of a single layer of black PI film coated with foldable adhesive on both sides. Due to the low modulus of PI material, its rigid support for the foldable screen is limited, serving primarily as a buffer. When this buffer layer is bonded to the screen's support film (usually made of PET or PI), a composite structure of multiple layers of film and adhesive is formed, resulting in a relatively soft screen. With prolonged and repeated folding, screen creases become increasingly pronounced, significantly affecting display quality and user experience.

[0003] To address these issues, the industry has attempted to develop a folding bracket with a double-layer SUS structure to improve support for the screen. For example, patent application CN120840177A discloses a lower support film for a flexible folding display screen, characterized in that the support film comprises, from top to bottom, a protective film layer, a stainless steel substrate layer, an adhesive layer and a release film layer; wherein, the adhesive layer is prepared by coating a modified silicone liquid onto the release film and drying and curing; the preparation method of the modified silicone liquid includes the following steps: (1) under anaerobic conditions, polycaprolactone polyol, 4,4-dicyclohexylmethane diisocyanate and dibutyltin dilaurate are mixed evenly, reacted once, and hydroxyethyl acrylate is added for a second reaction to obtain a PU-V system; (2) 4-methyl-5-vinylthiazole, azobisisobutyronitrile and acetone are mixed evenly, added to the PU-V system and reacted further to obtain a PU-MVT system; (3) vinyl-terminated polymethylvinylsiloxane is added to the PU-MVT system and mixed evenly, a crosslinking agent, a photoinitiator and an antioxidant are added, and acetone is removed by rotary evaporation to obtain a modified silicone liquid.

[0004] In this technical solution, the introduced vinyl-terminated polymethyl vinyl siloxane has poor compatibility with the PU-V system, posing a serious risk of small molecule and siloxane chain segment migration and precipitation, which can easily contaminate the optical film layer of foldable screens and OLED light-emitting materials, posing a fatal reliability hazard to terminal applications; moreover, the polyurethane chain segments are prone to hydrolysis and aging under high temperature and high humidity environments, which will lead to the decay of the cohesive strength of the adhesive layer and the interfacial adhesion performance. Summary of the Invention

[0005] In order to overcome the defects of small molecule migration pollution and easy degradation of adhesive performance of polyurethane segments after hygrothermal aging in the existing organosilicon modified adhesive system, this application provides a support film containing double-layer SUS for foldable screens and its preparation method.

[0006] In a first aspect, this application provides a support film containing double-layer SUS for foldable screens, employing the following technical solution:

[0007] A support film for foldable screens containing double-layer SUS comprises a first foldable adhesive layer, an upper SUS layer, a second foldable adhesive layer, a lower SUS layer, and a protective film layer, which are sequentially stacked. The first and second foldable adhesive layers are derived from the same foldable adhesive tape, which is cured from raw materials in the following proportions by weight:

[0008] The system comprises 60-100 parts of long-alkyl chain acrylate monomers, 30-60 parts of polyether acrylate monomers, 10-20 parts of vinyl MQ silicone resin, 14-26 parts of functional monomers, 0.9-2 parts of initiator, 0.9-2 parts of crosslinking agent, 1.5-4 parts of antioxidant, 1.5-4 parts of anti-aging agent, 1-2 parts of light stabilizer, and an organic solvent; the amount of the organic solvent is based on the solid content of the system reaching 35%-45%; the functional monomers are at least one selected from phosphate acrylate monomers, ethyl acetoacetate methacrylate, and nitrogen-containing monomers.

[0009] In this technical solution, a double-layer SUS gradient support structure provides stable rigid support for the screen, effectively dispersing stress during bending and suppressing deformation and creases after long-term bending. The foldable tape uses long-chain alkyl acrylate monomers and polyether acrylate monomers as the main monomers, giving the adhesive layer excellent interfacial wettability and bending stress relaxation ability. Through copolymerization, functional groups of functional monomers are grafted in situ onto the polymer backbone. Among them, phosphate ester groups can form stable covalent bonds with metal oxides and hydroxyl groups on the SUS stainless steel surface, and acetoacetic acid groups can form strong chelation with metal ions on the stainless steel surface. The two work synergistically to enhance the interfacial anchoring effect between the adhesive layer and the SUS substrate. Significantly improves the interlayer peel strength of the support film, nitrogen-containing monomers can simultaneously enhance the cohesive strength of the polymer, optimizing the storage stability and long-term reliability of the system; the vinyl MQ silicone resin introduced into the system can participate in free radical copolymerization in situ through polymerizable double bonds, maintaining good compatibility with the acrylate matrix, further optimizing the high and low temperature resistance and bending fatigue resistance of the adhesive layer. With a suitable crosslinking system, a uniform and controllable crosslinking network is constructed while ensuring the flexibility of the adhesive layer. Combined with an anti-aging protection system composed of antioxidants, anti-aging agents and light stabilizers, the performance stability of the adhesive layer is ensured under long-term use and harsh environments, which can fully meet the high-frequency repeated bending requirements of flexible folding screens.

[0010] Preferably, the phosphate ester acrylic monomer is at least one of phosphate methacrylate, 2-hydroxyethyl phosphate methacrylate, and polyethylene glycol phosphate methacrylate.

[0011] More preferably, the phosphate ester acrylic monomer is polyethylene glycol methacrylate phosphate.

[0012] In this technical solution, the phosphate ester acrylic monomer can be grafted in situ onto the acrylate polymer backbone. The phosphate ester groups it contains can form stable coordination bonds with the SUS stainless steel surface, achieving strong interfacial anchoring between the adhesive layer and the metal substrate, and significantly improving the interlayer peel strength of the support film. A further preferred polyethylene glycol methacrylate phosphate has flexible polyether long chains, exhibiting excellent compatibility with the system matrix. While strengthening interfacial adhesion, it does not compromise the flexibility and stress relaxation ability of the adhesive layer.

[0013] Preferably, the nitrogen-containing monomer is either N-vinylpyrrolidone or acrylomorpholine.

[0014] In this technical solution, N-vinylpyrrolidone and acrylamide morpholine are preferred as nitrogen-containing monomers. Both of them contain stable amide groups in their molecular structure and do not have the active hydrogen structure of acrylamide primary amides. On the one hand, the strong polarity of the amide groups can improve the cohesive energy density of the copolymer, providing sufficient cohesive strength for the adhesive layer and ensuring tack and creep resistance. On the other hand, it can avoid the brittleness problem of the adhesive layer caused by acrylamide strong hydrogen bond monomers, maintain the low modulus and high stress relaxation characteristics of the adhesive layer, and adapt to the high-frequency bending requirements of foldable screens.

[0015] Preferably, the polyether acrylate monomer is at least one of methoxy polyethylene glycol methacrylate and polypropylene methacrylate.

[0016] Preferably, the polyether acrylate monomer further includes a polyether-type multifunctional acrylate monomer.

[0017] Preferably, the polyether-type multifunctional acrylate monomer is at least one of polypropylene glycol diacrylate and polyethylene glycol diacrylate.

[0018] In this technical solution, the introduction of polyether-type multifunctional acrylate monomers can optimize the uniformity of the crosslinking network and improve the cohesive strength and creep resistance of the adhesive layer without significantly sacrificing the flexibility of the adhesive layer. At the same time, its flexible polyether backbone can ensure the stress relaxation ability of the adhesive layer and further improve the bending resistance.

[0019] Preferably, the long alkyl chain acrylate monomer has not less than 12 carbon atoms.

[0020] Preferably, the long alkyl chain acrylate monomer is at least one of lauryl acrylate, octadecyl acrylate, and hexadecyl acrylate.

[0021] Preferably, the crosslinking agent is at least one of a multifunctional isocyanate crosslinking agent and a metal chelate crosslinking agent.

[0022] Preferably, the multifunctional isocyanate crosslinking agent is either HDI trimer or IPDI trimer.

[0023] Preferably, the metal chelating crosslinking agent is zirconium acetylacetonate.

[0024] Preferably, the antioxidant is a hindered phenolic antioxidant, including but not limited to antioxidant 1010 and antioxidant 1076.

[0025] Preferably, the anti-aging agent is a benzotriazole class, including but not limited to UV-327 and UV-328.

[0026] Preferably, the light stabilizer is a hindered amine light stabilizer, including but not limited to light stabilizer 944 and light stabilizer 622.

[0027] Preferably, the initiator is an azo initiator or a peroxide initiator, selected from, but not limited to, any one of azobisisobutyronitrile and benzoyl peroxide.

[0028] Preferably, a release film layer is also provided on the side of the first foldable adhesive layer away from the upper SUS layer.

[0029] Preferably, the thickness of the first foldable adhesive layer is 20~50μm.

[0030] Preferably, the thickness of the second foldable adhesive layer is 20~50μm.

[0031] Preferably, the thickness of the release film layer is 50~100μm.

[0032] Preferably, the upper SUS layer is made of ultra-thin high-strength stainless steel with a thickness of 10~30μm, a tensile strength ≥1500MPa, and a Young's modulus ≥190GPa.

[0033] Preferably, the lower SUS layer is made of high-strength stainless steel with a thickness of 100~150μm, a tensile strength ≥1500MPa, and a Young's modulus ≥200GPa.

[0034] More preferably, before use, the lower SUS layer is formed into a hollow mesh pattern in the bending area by etching.

[0035] More preferably, the hollowed-out mesh pattern is selected from any one of rhomboid mesh, hexagonal honeycomb mesh, circular mesh, and elliptical mesh.

[0036] More preferably, the hollowed-out mesh pattern is a hexagonal honeycomb mesh.

[0037] In this technical solution, the hollowed-out mesh structure design in the bending area not only retains the high rigidity support capacity of the non-bending area, but also reduces the deformation resistance of the bending area, disperses bending stress, reduces metal fatigue and plastic deformation, and improves bending life. At the same time, it can form a mechanical interlocking structure with the foldable adhesive layer, further improving the interlayer bonding force and avoiding delamination and slippage problems after repeated bending, thus meeting the long-term high-frequency bending requirements of foldable screens.

[0038] Preferably, the protective film layer is a non-silicone PET protective film with a thickness of 100~150μm.

[0039] Preferably, the raw materials of the foldable tape further include 3 to 5 parts by weight of polypropylene glycol glycidyl ether acrylate.

[0040] Preferably, the raw materials of the foldable tape further include 1 to 2 parts by weight of short fluorocarbon chain monomers.

[0041] Preferably, the short fluorocarbon chain monomer is hexafluorobutyl acrylate.

[0042] Secondly, this application provides a support film containing double-layer SUS for foldable screens and a method for preparing the same, comprising the following steps:

[0043] S1: Mix long alkyl chain acrylate monomers, polyether acrylate monomers, vinyl MQ silicone resin, functional monomers and organic solvents evenly, add initiator under an inert atmosphere of 60~80℃, react for 5~8h, cool to obtain acrylate copolymer solution;

[0044] S2: Add crosslinking agent, antioxidant, anti-aging agent and light stabilizer to the acrylate copolymer solution, mix evenly, degas, and obtain a homogeneous adhesive solution;

[0045] S3: Apply a uniform adhesive liquid onto the PET release film layer, cure by gradient heating in the range of 60~120℃, cool, and roll up to obtain a foldable tape.

[0046] S4: Apply the foldable tape to the top and bottom surfaces of the upper SUS layer to form a semi-finished product.

[0047] S5: The semi-finished product, the lower SUS layer, and the protective film layer are sequentially laminated to form a support film.

[0048] In this technical solution, all functional components with polymerizable double bonds are uniformly grafted onto the acrylate backbone through in-situ free radical polymerization, laying the foundation for the core performance of the pressure-sensitive tape. A gradient temperature curing process is adopted to remove organic solvents in a stepwise manner, avoiding defects such as pinholes, orange peel, and shrinkage craters in the adhesive layer caused by rapid solvent evaporation, thus ensuring the density and performance uniformity of the tape layer. Through pre-fabricated tape and layered alignment bonding, the interlayer peel strength, bending resistance, and long-term stability of the final support film are guaranteed.

[0049] Preferably, in step S1, after the polyether acrylate monomer, a step of adding polypropylene glycol glycidyl ether acrylate is further included.

[0050] Preferably, in step S1, after the polyether acrylate monomer, a step of adding a short fluorocarbon chain monomer is further included.

[0051] In summary, this application has the following beneficial effects:

[0052] This application utilizes in-situ free radical polymerization of long-chain alkyl acrylate monomers, polyether acrylate monomers, vinyl MQ silicone resin, and functional monomers to prefabricate foldable tape, thus constructing a double-layer SUS gradient support structure. The strong interfacial interaction between the phosphate ester and acetoacetic acid groups in the functional monomers and the SUS substrate, along with the enhancement of polymer cohesive strength by the nitrogen-containing monomers, significantly strengthens the interlayer peel strength of the support film. Simultaneously, the introduction of vinyl MQ silicone resin and the optimization of the gradient curing process ensure the stress relaxation capability and long-term reliability of the adhesive layer under dynamic bending, adapting to the small-radius, high-frequency bending requirements of flexible foldable screens. Detailed Implementation

[0053] The present application will be further described in detail below with reference to the embodiments.

[0054] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0055] The vinyl MQ silicone resin is from Wuhan Lanabai Pharmaceutical Chemical Co., Ltd., with an M / Q value of (0.5~0.8):1 and a vinyl content of approximately 2wt%.

[0056] The polyethylene glycol methacrylate phosphate comes from Hubei Xinjiecheng Chemical Technology Co., Ltd., and its content is not less than 99%.

[0057] Polypropylene glycol diacrylate is polypropylene glycol 400 diacrylate;

[0058] The polyethylene glycol diacrylate is polyethylene glycol 400 diacrylate;

[0059] The number average molecular weight of polypropylene methacrylate is 375.

[0060] The upper SUS layer is made of ultra-thin high-strength stainless steel with a thickness of 10~30μm, tensile strength ≥1500MPa, and Young's modulus ≥190GPa;

[0061] The lower SUS layer is made of high-strength stainless steel with a thickness of 100~150μm, tensile strength ≥1500MPa, and Young's modulus ≥200GPa; the hollowed-out mesh pattern is a hexagonal honeycomb grid.

[0062] All organic solvents were prepared by mixing ethyl acetate and toluene in a mass ratio of 7:3, with the amount used to control the solid content of the system to be 35%~45%.

[0063] Example 1

[0064] The method for preparing a support film containing double-layer SUS for a foldable screen in this embodiment includes the following steps:

[0065] S1: Add long alkyl chain acrylate monomers, polyether acrylate monomers, vinyl MQ silicone resin and functional monomers to a reactor, add organic solvent to adjust the solid content of the system to 40%, heat to 70°C under nitrogen atmosphere, add initiator and mix evenly, keep the reaction at the temperature for 6 hours, cool to room temperature to obtain acrylate copolymer solution.

[0066] S2: Add crosslinking agent, antioxidant, anti-aging agent and light stabilizer to the acrylate copolymer solution and stir to mix evenly. Add organic solvent to adjust the solid content of the system to about 40%. Vacuum degassing for 30 minutes to obtain a homogeneous adhesive solution.

[0067] S3: Coat a uniform adhesive solution onto a PET fluoropolymer release film with a thickness of 50 μm. The wet film thickness is about 90 μm. Heat to 70℃ and dry for 5 min, then heat to 90℃ and dry for 5 min, then continue to heat to 110℃ and dry for 5 min. Cool to room temperature and roll up to obtain a foldable tape with a thickness of about 35 μm.

[0068] S4: After aligning the roll of foldable tape with the top and bottom surfaces of the 20μm thick ultra-thin high-strength stainless steel, the semi-finished product is obtained by stamping with a hardware mold.

[0069] S5: After removing the release film from one side of the semi-finished product, use a fully automatic laminating machine to align and laminate the side of the 120μm thick high-strength stainless steel (before using the high-strength stainless steel, the bending area is pre-etched to form a hollow mesh pattern). Then, laminate a 100μm thick non-silicone PET protective film on the side away from the semi-finished product. After lamination, punch the shape as needed to obtain the support film.

[0070] The raw materials for making foldable tape are as follows:

[0071] The mixture comprises 800g of long-chain alkyl acrylate monomer, 400g of polyether acrylate monomer, 160g of vinyl MQ silicone resin, 220g of functional monomer, 10g of initiator, 10g of crosslinking agent, 24g of antioxidant, 24g of anti-aging agent, 14g of light stabilizer, and an organic solvent; the amount of the organic solvent is based on the solid content of the system reaching 40%.

[0072] Among them, the long alkyl chain acrylate monomer is lauryl acrylate; the polyether acrylate monomer is methoxy polyethylene glycol 600 methacrylate; the functional monomer is polyethylene glycol methacrylate phosphate; the initiator is azobisisobutyronitrile; the crosslinking agent is Wanhua HDI trimer; the antioxidants are antioxidant 1010 and antioxidant 1076 in a mass ratio of 2:1; the anti-aging agents are UV-327 and UV-328 in a mass ratio of 1:1; and the light stabilizers are light stabilizer 944 and light stabilizer 622 in a mass ratio of 3:1.

[0073] Example 2

[0074] The method for preparing a support film containing double-layer SUS for a foldable screen in this embodiment includes the following steps:

[0075] S1: Add long alkyl chain acrylate monomers, polyether acrylate monomers, vinyl MQ silicone resin and functional monomers to a reactor, add organic solvent to adjust the solid content of the system to 45%, heat to 80°C under nitrogen atmosphere, add initiator and mix evenly, keep the reaction at the temperature for 5 hours, cool to room temperature to obtain acrylate copolymer solution.

[0076] S2: Add crosslinking agent, antioxidant, anti-aging agent and light stabilizer to the acrylate copolymer solution and stir to mix evenly. Add organic solvent to adjust the solid content of the system to about 45%. Vacuum degassing for 30 minutes to obtain a homogeneous adhesive solution.

[0077] S3: Coat a uniform adhesive solution onto a 100μm thick PET fluoropolymer release film. The wet film thickness is approximately 110μm. Heat the film to 60℃ and dry for 5 minutes, then heat it to 100℃ and dry for 5 minutes. Continue heating the film to 120℃ and dry for 5 minutes. Cool the film to room temperature and roll it up to obtain a foldable tape with a thickness of approximately 50μm.

[0078] S4: After aligning the roll of foldable tape with the top and bottom surfaces of an ultra-thin, high-strength stainless steel sheet with a thickness of 10μm, the sheet is stamped with a metal mold to obtain a semi-finished product.

[0079] S5: After removing the release film from one side of the semi-finished product, use a fully automatic laminating machine to align and adhere it to the side of the 100μm thick high-strength stainless steel (before using the high-strength stainless steel, the bending area is pre-etched to form a hollow mesh pattern). Then, apply a 150μm thick non-silicone PET protective film to the side away from the semi-finished product. After lamination, punch the shape as needed to obtain the support film.

[0080] The raw materials for making foldable tape are as follows:

[0081] The mixture comprises 600g of long alkyl chain acrylate monomer, 300g of polyether acrylate monomer, 100g of vinyl MQ silicone resin, 140g of functional monomer, 9g of initiator, 9g of crosslinking agent, 15g of antioxidant, 15g of anti-aging agent, 10g of light stabilizer, and an organic solvent; the amount of the organic solvent is based on the system solid content reaching 45%.

[0082] The long alkyl chain acrylate monomers are lauryl acrylate and octadecyl acrylate in a mass ratio of 1:1; the polyether acrylate monomers are methoxy polyethylene glycol 600 methacrylate and polypropylene methacrylate in a mass ratio of 1:1; the functional monomer is phosphate methacrylate; the initiator is benzoyl peroxide; the crosslinking agent is Wanhua IPDI trimer; the antioxidants are antioxidant 1010 and antioxidant 1076 in a mass ratio of 2:1; the anti-aging agents are UV-327 and UV-328 in a mass ratio of 1:1; and the light stabilizers are light stabilizer 944 and light stabilizer 622 in a mass ratio of 3:1.

[0083] Example 3

[0084] The method for preparing a support film containing double-layer SUS for a foldable screen in this embodiment includes the following steps:

[0085] S1: Add long alkyl chain acrylate monomers, polyether acrylate monomers, vinyl MQ silicone resin and functional monomers to a reactor, add organic solvent to adjust the solid content of the system to 35%, heat to 60°C under nitrogen atmosphere, add initiator and mix evenly, keep the reaction at the temperature for 8 hours, cool to room temperature to obtain acrylate copolymer solution.

[0086] S2: Add crosslinking agent, antioxidant, anti-aging agent and light stabilizer to the acrylate copolymer solution and stir to mix evenly. Add organic solvent to adjust the solid content of the system to about 35%. Vacuum degassing for 30 minutes to obtain a homogeneous adhesive solution.

[0087] S3: Coat a uniform adhesive solution onto a 100μm thick PET fluoropolymer release film. The wet film thickness is about 60μm. Heat to 60℃ and dry for 5 minutes, then heat to 90℃ and dry for 5 minutes. Continue to heat to 120℃ and dry for 5 minutes. Cool to room temperature and roll up to obtain a foldable tape with a thickness of about 20μm.

[0088] S4: After aligning the roll of foldable tape with the top and bottom surfaces of the 30μm thick ultra-thin high-strength stainless steel, the semi-finished product is obtained by stamping with a hardware mold.

[0089] S5: After removing the release film from one side of the semi-finished product, use a fully automatic laminating machine to align and laminate the side of the 150μm thick high-strength stainless steel (before using the high-strength stainless steel, the bending area is pre-etched to form a hollow mesh pattern). Then, laminate a 100μm thick non-silicone PET protective film on the side away from the semi-finished product. After lamination, punch the shape as needed to obtain the support film.

[0090] The raw materials for making foldable tape are as follows:

[0091] The mixture comprises 1000g of long alkyl chain acrylate monomer, 600g of polyether acrylate monomer, 200g of vinyl MQ silicone resin, 260g of functional monomer, 20g of initiator, 20g of crosslinking agent, 40g of antioxidant, 40g of anti-aging agent, 20g of light stabilizer, and an organic solvent; the amount of the organic solvent is based on the solid content of the system reaching 35%.

[0092] The long alkyl chain acrylate monomers are lauryl acrylate and hexadecyl acrylate in a mass ratio of 1:1; the polyether acrylate monomer is methoxy polyethylene glycol 600 methacrylate; the functional monomers are polyethylene glycol methacrylate phosphate and 2-hydroxyethyl methacrylate phosphate in a mass ratio of 4:1; the initiator is azobisisobutyronitrile; the crosslinking agent is Wanhua IPDI trimer; the antioxidants are antioxidant 1010 and antioxidant 1076 in a mass ratio of 2:1; the anti-aging agents are UV-327 and UV-328 in a mass ratio of 1:1; and the light stabilizers are light stabilizer 944 and light stabilizer 622 in a mass ratio of 3:1.

[0093] Example 4

[0094] The method for preparing a support film containing double-layer SUS for a foldable screen in this embodiment includes the following steps:

[0095] S1: Add long alkyl chain acrylate monomers, polyether acrylate monomers, vinyl MQ silicone resin and functional monomers to a reactor, add organic solvent to adjust the solid content of the system to 40%, heat to 70°C under nitrogen atmosphere, add initiator and mix evenly, keep the reaction at the temperature for 7 hours, cool to room temperature to obtain acrylate copolymer solution.

[0096] S2: Add crosslinking agent, antioxidant, anti-aging agent and light stabilizer to the acrylate copolymer solution and stir to mix evenly. Add organic solvent to adjust the solid content of the system to about 40%. Vacuum degassing for 30 minutes to obtain a homogeneous adhesive solution.

[0097] S3: Coat a uniform adhesive solution onto a PET fluoropolymer release film with a thickness of 50 μm. The wet film thickness is about 76 μm. Heat to 60℃ and dry for 5 min, then heat to 90℃ and dry for 5 min, then continue to heat to 120℃ and dry for 5 min. Cool to room temperature and roll up to obtain a foldable tape with a thickness of about 35 μm.

[0098] S4: After aligning the roll of foldable tape with the top and bottom surfaces of the 20μm thick ultra-thin high-strength stainless steel, the semi-finished product is obtained by stamping with a hardware mold.

[0099] S5: After removing the release film from one side of the semi-finished product, use a fully automatic laminating machine to align and adhere it to the side of the 100μm thick high-strength stainless steel (before using the high-strength stainless steel, the bending area is pre-etched to form a hollow mesh pattern). Then, apply a 100μm thick non-silicone PET protective film to the side away from the semi-finished product. After lamination, punch the shape as needed to obtain the support film.

[0100] The raw materials for making foldable tape are as follows:

[0101] The mixture comprises 800g of long alkyl chain acrylate monomer, 470g of polyether acrylate monomer, 160g of vinyl MQ silicone resin, 220g of functional monomer, 15g of initiator, 12g of crosslinking agent, 30g of antioxidant, 30g of anti-aging agent, 15g of light stabilizer, and an organic solvent; the amount of the organic solvent is based on the solid content of the system reaching 40%.

[0102] The long alkyl chain acrylate monomer is lauryl acrylate; the polyether acrylate monomer is methoxy polyethylene glycol 600 methacrylate and polypropylene glycol 400 diacrylate in a mass ratio of 4:1; the functional monomer is polyethylene glycol methacrylate phosphate; the initiator is azobisisobutyronitrile; the crosslinking agent is Wanhua IPDI trimer; the antioxidant is antioxidant 1010 and antioxidant 1076 in a mass ratio of 2:1; the anti-aging agent is UV-327 and UV-328 in a mass ratio of 1:1; and the light stabilizer is light stabilizer 944 and light stabilizer 622 in a mass ratio of 3:1.

[0103] Example 5

[0104] The difference between this embodiment and embodiment 4 is that:

[0105] The amount of functional monomer used is 245g;

[0106] The polyether acrylate monomers are methoxy polyethylene glycol 600 methacrylate and polyethylene glycol 400 diacrylate in a mass ratio of 3:1; the functional monomers are 220g of polyethylene glycol methacrylate phosphate and 25g of acetoacetic acid methacrylate; the crosslinking agent is Wanhua IPDI trimer.

[0107] The rest is the same as in Example 4.

[0108] Example 6

[0109] The difference between this embodiment and embodiment 4 is that:

[0110] The amount of functional monomer used is 260g;

[0111] The polyether acrylate monomers are methoxy polyethylene glycol 600 methacrylate and polyethylene glycol 400 diacrylate in a mass ratio of 3:1; the functional monomers are 220g of polyethylene glycol methacrylate phosphate, 25g of acetoacetic acid methacrylate, and 15g of acrylamide morpholine; the crosslinking agent is Wanhua IPDI trimer.

[0112] The rest is the same as in Example 4.

[0113] Example 7

[0114] The difference between this embodiment and embodiment 4 is that:

[0115] The raw materials for making foldable tape are as follows:

[0116] The mixture comprises 800g of long-chain alkyl acrylate monomers, 470g of polyether acrylate monomers, 160g of vinyl MQ silicone resin, 30g of polypropylene glycol glycidyl ether acrylate, 260g of functional monomers, 15g of initiator, 15g of crosslinking agent, 30g of antioxidant, 30g of anti-aging agent, 15g of light stabilizer, and an organic solvent; the amount of the organic solvent is based on the system solid content reaching 40%.

[0117] The long-chain alkyl acrylate monomer is lauryl acrylate; the polyether acrylate monomer is methoxy polyethylene glycol 600 methacrylate and polyethylene glycol 400 diacrylate in a mass ratio of 4:1; the functional monomers are 220g of polyethylene glycol methacrylate phosphate, 25g of ethyl acetoacetate methacrylate and 15g of N-vinylpyrrolidone; the initiator is azobisisobutyronitrile; the crosslinking agent is 12g of Wanhua IPDI trimer and 3g of zirconium acetylacetonate; the antioxidant is antioxidant 1010 and antioxidant 1076 in a mass ratio of 2:1; the anti-aging agent is UV-327 and UV-328 in a mass ratio of 1:1; and the light stabilizer is light stabilizer 944 and light stabilizer 622 in a mass ratio of 3:1.

[0118] The rest is the same as in Example 4.

[0119] Example 8

[0120] The difference between this embodiment and embodiment 7 is as follows:

[0121] The raw materials for making foldable tape are as follows:

[0122] The mixture comprises 800g of long-chain alkyl acrylate monomers, 470g of polyether acrylate monomers, 160g of vinyl MQ silicone resin, 30g of polypropylene glycol glycidyl ether acrylate, 10g of hexafluorobutyl acrylate, 260g of functional monomers, 15g of initiator, 15g of crosslinking agent, 30g of antioxidant, 30g of anti-aging agent, 15g of light stabilizer, and an organic solvent; the amount of the organic solvent is based on a system solid content of 40%.

[0123] The long-chain alkyl acrylate monomer is lauryl acrylate; the polyether acrylate monomer is methoxy polyethylene glycol 600 methacrylate and polyethylene glycol 400 diacrylate in a mass ratio of 4:1; the functional monomer is 220g of polyethylene glycol methacrylate phosphate, 25g of ethyl acetoacetate methacrylate and 15g of acryloylmorpholine; the initiator is azobisisobutyronitrile; the crosslinking agent is 12g of Wanhua IPDI trimer and 3g of zirconium acetylacetonate; the antioxidant is antioxidant 1010 and antioxidant 1076 in a mass ratio of 2:1; the anti-aging agent is UV-327 and UV-328 in a mass ratio of 1:1; and the light stabilizer is light stabilizer 944 and light stabilizer 622 in a mass ratio of 3:1.

[0124] The rest is the same as in Example 7.

[0125] Example 9

[0126] The difference between this embodiment and embodiment 8 is as follows:

[0127] The amount of polypropylene glycol glycidyl ether acrylate used is 50g;

[0128] 20g of hexafluorobutyl acrylate.

[0129] The rest is the same as in Example 8.

[0130] Comparative Example 1

[0131] The difference between this comparative example and Example 1 is as follows:

[0132] Vinyl MQ silicone resin was not added to the raw materials for the preparation of foldable tape;

[0133] Everything else is the same as in Example 1.

[0134] Comparative Example 2

[0135] The difference between this comparative example and Example 1 is as follows:

[0136] In the raw materials for preparing foldable tape, no functional monomer (polyethylene glycol methacrylate phosphate) was added, and an equal mass of lauryl acrylate was used to replace the functional monomer.

[0137] Everything else is the same as in Example 1.

[0138] Performance testing

[0139] The support films prepared in Examples 1-9 and Comparative Examples 1-2 were subjected to the following performance tests, as detailed in Table 1.

[0140] 1. In accordance with GB / T 2792-2014 standard, the support film was made into standard samples. After being placed in a standard environment (temperature 23℃±2℃, humidity 50%±5%) for 24 hours, the peel strength between the semi-finished product and high-strength stainless steel was tested at a tensile speed of 300 mm / min using a 180° peel mode. Five samples were tested in each group, and the average value was taken.

[0141] 2. Prepare standard samples of the support film and place them in a constant temperature and humidity chamber. After 500 hours of treatment at 85℃ and 85% relative humidity (RH), test the interlayer peel strength using the above method and calculate the peel strength retention rate after wet heat aging.

[0142] 3. Fix the support film sample in the testing machine fixture, set the folding angle to 180°, the folding radius R=0.3mm, and the folding frequency to 20 times / min. During the continuous bending process, observe the core area of ​​the crease in real time and record the number of first failure bends when the adhesive layer shows micro-cracks, interlayer delamination and debonding, or substrate cracking and breakage. The unit is 10,000 times.

[0143] Table 1. Performance test data of the support membranes prepared in Examples 1-9 and Comparative Examples 1-2

[0144]

[0145] As can be seen from the performance test data in Table 1, the support films prepared in Examples 1-3 are significantly superior to those in Comparative Examples 1-2 in terms of interlayer peel strength, damp heat aging stability, and bending resistance. They achieve a balance between high bonding strength, bending resistance, and long-term stability, fully meeting the requirements for flexible foldable screens. Example 4 introduced polypropylene glycol 400 diacrylate into the basic formulation, optimizing the crosslinking network and cohesive strength of the adhesive layer, resulting in a slight increase in peel strength, and simultaneous optimization of aging retention rate and bending resistance. Examples 5-6 further introduced ethyl acetoacetate methacrylate and acryloylmorpholine, achieving simultaneous improvement in interfacial bonding strength and cohesive strength, and further increasing the damp heat aging retention rate without negatively impacting the flexibility and bending resistance of the adhesive layer. Examples 7-9 introduced polypropylene glycol glycidyl ether acrylate and / or hexafluorobutyl acrylate, and compounded with a small amount of zirconium acetylacetonate, further optimizing interfacial wettability and crosslinking network stability. While ensuring high interfacial peel strength and excellent bending fatigue resistance, the damp heat aging stability was further improved.

[0146] Comparative Example 1, which did not contain vinyl MQ silicone resin, showed a decrease in the weather resistance and cohesive strength of the adhesive layer, resulting in a slight decrease in interlayer peel strength, resistance to damp heat aging, and flexural strength. Comparative Example 2, which did not contain functional monomers and lacked phosphate ester anchoring groups and polar groups, showed a decrease in interfacial bonding force, and a significant reduction in peel strength, aging resistance, and flexural life.

[0147] 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 support film containing double-layer SUS for foldable screens, characterized in that, The tape comprises a first foldable adhesive layer, an upper SUS layer, a second foldable adhesive layer, a lower SUS layer, and a protective film layer, which are stacked sequentially. The first and second foldable adhesive layers are derived from the same foldable tape. The foldable tape is cured from the following raw materials in parts by weight: 60-100 parts of long-chain alkyl acrylate monomer, 30-60 parts of polyether acrylate monomer, 10-20 parts of vinyl MQ silicone resin, 14-26 parts of functional monomer, 0.9-2 parts of initiator, 0.9-2 parts of crosslinking agent, 1.5-4 parts of antioxidant, 1.5-4 parts of anti-aging agent, 1-2 parts of light stabilizer, and an organic solvent. The amount of organic solvent is based on a system solid content of 35%-45%. The functional monomer is at least one of phosphate acrylate monomer, ethyl acetoacetate methacrylate, and nitrogen-containing monomer. The long alkyl chain acrylate monomer has not less than 12 carbon atoms.

2. The support film containing double-layer SUS for foldable screens according to claim 1, characterized in that, The phosphate ester acrylic monomer is at least one of phosphate methacrylate, 2-hydroxyethyl phosphate methacrylate, and polyethylene glycol phosphate methacrylate.

3. The support film containing double-layer SUS for foldable screens according to claim 1, characterized in that, The nitrogen-containing monomer is either N-vinylpyrrolidone or acryloylmorpholine.

4. The support film containing double-layer SUS for foldable screens according to claim 1, characterized in that, The polyether acrylate monomer is at least one of methoxy polyethylene glycol methacrylate and polypropylene methacrylate.

5. The support film containing double-layer SUS for foldable screens according to claim 4, characterized in that, The polyether acrylate monomer also includes polyether-type multifunctional acrylate monomers.

6. The support film containing double-layer SUS for foldable screens according to claim 1, characterized in that, Before use, the lower SUS layer is etched to form a hollow mesh pattern in the bending area.

7. The support film containing double-layer SUS for foldable screens according to claim 1, characterized in that, The raw materials for the foldable tape also include 3 to 5 parts by weight of polypropylene glycol glycidyl ether acrylate.

8. A method for preparing a support film containing double-layer SUS for a foldable screen as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1: Mix long alkyl chain acrylate monomers, polyether acrylate monomers, vinyl MQ silicone resin, functional monomers and organic solvents evenly, add initiator under an inert atmosphere of 60~80℃, react for 5~8h, cool to obtain acrylate copolymer solution; S2: Add crosslinking agent, antioxidant, anti-aging agent and light stabilizer to the acrylate copolymer solution, mix evenly, degas, and obtain a homogeneous adhesive solution; S3: Apply a uniform adhesive liquid onto the PET release film layer, cure by gradient heating in the range of 60~120℃, cool, and roll up to obtain a foldable tape. S4: Apply the foldable tape to the top and bottom surfaces of the upper SUS layer to form a semi-finished product. S5: The semi-finished product, the lower SUS layer, and the protective film layer are sequentially laminated to form a support film.

9. The method for preparing a support film containing double-layer SUS for foldable screens according to claim 8, characterized in that, In step S1, after the polyether acrylate monomer, a step of adding polypropylene glycol glycidyl ether acrylate is also included.

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