A flexible folding display screen lower support film and a method of manufacturing the same

Abstract

The application belongs to the technical field of film materials, and particularly relates to a flexible folding display screen supporting film and a preparation method thereof. The supporting film comprises, from top to bottom, a protective film layer, a stainless steel substrate layer, a glue layer and a release film layer. The glue layer is prepared by coating a modified organic silicone glue solution on the release film, drying and curing. The application uses ultra-thin stainless steel as the substrate layer, which can resist external impact and scratching, has low and stable thermal expansion coefficient, can reduce the influence of environmental temperature and humidity on the size of the supporting film, and ensures the structural consistency of the screen module during long-term use. Through multi-component composite modification of polyurethane-thiazole-silicone, the peeling strength of the glue layer and the stainless steel and the bending frequency of the supporting film are improved, and the service life of the supporting film is prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of film materials, and particularly relates to a lower supporting film for a flexible folding display screen and a preparation method thereof. BACKGROUND

[0002] OLED display technology has become the core display scheme of folding mobile phones, wearable devices, flexible vehicle screens and other products due to its advantages of self-luminous, high contrast, thin and light, etc. Among them, the supporting film as the key structure layer of the OLED display screen bears the functions of supporting the flexible OLED substrate, buffering the bending stress and blocking the external environmental interference, and its performance determines the durability and display stability of the flexible device.

[0003] At present, polyethylene terephthalate (PET) or polyimide (PI) is often used as the supporting film substrate, and a pressure-sensitive adhesive is coated on the surface of the substrate to form a complete structure by compounding a release film and a protective film. However, in the process of upgrading the folding screen to "high-frequency folding, long-life use, and complex environment adaptation", the mechanical performance decay problem caused by folding fatigue is increasingly serious.

[0004] The Chinese patent application file with the application publication number CN118853031A discloses an acrylic pressure-sensitive adhesive applied to a flexible OLED supporting film, a supporting film and a preparation method thereof. The supporting film includes a protective film layer, a PET substrate layer, an acrylic pressure-sensitive adhesive layer and a release layer which are stacked in sequence. At the same time, 5-methyl-3-vinyl-2-oxazolone monomer and hydroxyl-containing acrylic ester monomer are introduced into the formula of the acrylic pressure-sensitive adhesive, which improves the product adhesion and enables the product to be well attached to the surface of the polyimide film for supporting and reinforcing. However, local heat is generated during the working process of the OLED display screen, and the thermal expansion coefficients of the supporting film and the metal hinge are significantly different. This mismatch causes significant thermal stress at the interface between the supporting film and the hinge during temperature cycling, which easily causes the adhesion between the acrylic pressure-sensitive adhesive layer and the substrate to decay under repeated action, and finally leads to failure phenomena such as delamination and bubbles. SUMMARY

[0005] The supporting film in the prior art has the problem of easy delamination between the pressure-sensitive adhesive layer and the substrate layer during long-term use. In order to solve this problem, the present application provides a lower supporting film for a flexible folding display screen and a preparation method thereof.

[0006] In order to achieve the purpose of the present application, the following technical solutions are adopted:

[0007] In a first aspect, the present application provides a lower supporting film for a flexible folding display screen, which includes a protective film layer, a stainless steel substrate layer, an adhesive layer and a release film layer from top to bottom.

[0008] The adhesive layer is prepared by coating and drying a modified silicone adhesive solution on a release film;

[0009] The preparation method of the modified silicone adhesive solution comprises the following steps:

[0010] (1) Under anaerobic conditions, polycaprolactone polyol, 4,4-dicyclohexyl methane diisocyanate and dibutyl tin dilaurate are mixed uniformly, and then hydroxyethyl acrylate is added for a second reaction to obtain a PU-V system;

[0011] (2) 4-methyl-5-vinylthiazole, azobisisobutyronitrile and acetone are mixed uniformly, and then added to the PU-V system for continuous reaction to obtain a PU-MVT system;

[0012] (3) Vinyl-terminated polymethylvinylsiloxane is added to the PU-MVT system and mixed uniformly, and then a crosslinking agent, a photoinitiator and an antioxidant are added, and acetone is removed by rotary evaporation to obtain a modified silicone adhesive solution.

[0013] By adopting the above technical solution, the stainless steel substrate layer provides rigid support to prevent the internal elements of the display screen from being damaged under pressure when folding, and its ductility can adapt to the deformation when folding; the adhesive layer can relieve the interface stress concentration when folding through the composite modification of polyurethane-thiazole-silicone; the functional complementary structure of the protective film layer-stainless steel substrate layer-adhesive layer-release film layer from top to bottom can balance the support strength and folding flexibility.

[0014] By adopting the above technical solution, the modified silicone adhesive solution realizes component synergy through three-step reaction, the polyurethane segment formed from the polyol and the isocyanate provides excellent flexibility and substrate wettability, which can ensure that the adhesive layer does not become brittle after repeated folding; 4-methyl-5-vinylthiazole (MVT) introduces a thiazole ring to improve the adhesion to the stainless steel substrate layer, and its vinyl group participates in crosslinking to improve the cohesive force of the adhesive layer; the vinyl-terminated polymethylvinylsiloxane introduces a siloxane segment to endow the adhesive layer with high and low temperature resistance and weather resistance, solving the problem of softening of traditional polyurethane adhesive layers at high temperatures; finally, the adhesive layer is rapidly crosslinked through curing to form a three-dimensional network structure; the silicone component is fixed in the network through covalent crosslinking, avoiding silicon migration and pollution of the display screen optical elements.

[0015] Preferably, in step (1), the mass ratio of polycaprolactone polyol to 4,4-dicyclohexyl methane diisocyanate is 1:(0.096-0.1); the amount of dibutyl tin dilaurate is 0.8%-1.1% of the total mass of polycaprolactone polyol and 4,4-dicyclohexyl methane diisocyanate; and the amount of hydroxyethyl acrylate is 5%-8% of the total mass of polycaprolactone polyol and 4,4-dicyclohexyl methane diisocyanate.

[0016] By adopting the above technical scheme, under the ratio, the molecular chain formed by the soft segment and the hard segment of the polyurethane is balanced, which gives the PU-V system excellent flexibility and moderate cohesion; too much dibutyltin dilaurate as a catalyst will cause the reaction to be too fast, and too little dibutyltin dilaurate will easily cause incomplete first reaction; the ethylene group introduced by hydroxyethyl acrylate can make it copolymerize with 4-methyl-5-vinylthiazole in step (2) fully under the amount.

[0017] Preferably, in step (1), the temperature of the first reaction is 75-85℃, and the time of the first reaction is 2-3h; the temperature of the second reaction is 55-65℃, and the time of the second reaction is 1-2h.

[0018] By adopting the above technical scheme, if the temperature of the first reaction is too high, 4,4-dicyclohexylmethane diisocyanate will easily self-polymerize; if the temperature is too low, the reaction will be incomplete, and the residual -NCO may have a side reaction with the thiazole ring of the subsequent 4-methyl-5-vinylthiazole; if the temperature of the second reaction is too low, the reaction rate of -OH and -NCO is slow, and if the temperature is too high, the ethylene group is easy to have free radical self-polymerization, which causes local crosslinking of the system.

[0019] Preferably, in step (2), the amount of 4-methyl-5-vinylthiazole is 5%-10% of the mass of PU-V; and the amount of azobisisobutyronitrile is 1.6%-2% of the mass of 4-methyl-5-vinylthiazole.

[0020] By adopting the above technical scheme, the thiazole ring in 4-methyl-5-vinylthiazole can form coordination with metal ions on the surface of stainless steel, and the amount of 5%-10% can make the density of the thiazole ring moderate, thereby improving the peeling strength; too high amount will easily form a rigid layer at the interface, thereby reducing the interface toughness when folding; too low amount will result in less thiazole ring and vinyl content, which cannot effectively improve the adhesion and is also difficult to be compatible with the subsequent siloxane segment; and azobisisobutyronitrile can uniformly initiate and gradually copolymerize under the amount, so that the reaction proceeds smoothly.

[0021] Preferably, in step (2), the mass ratio of the end-vinyl poly-methyl-vinyl siloxane to the polycaprolactone polyol is (0.14-0.18)∶1, the amount of the crosslinking agent is 1%-3% of the mass of the end-vinyl poly-methyl-vinyl siloxane, and the amount of the photoinitiator is 0.5%-1% of the mass of the end-vinyl poly-methyl-vinyl siloxane.

[0022] By adopting the above technical scheme, the proportion of siloxane is moderate, the vinyl group of siloxane crosslinks with the vinyl group of the PU-MVT system, the siloxane chain segment is anchored in the polyurethane network through covalent bond, and the adhesion of the adhesive layer to the stainless steel substrate is long-term stable; the crosslinking network formed by the crosslinking agent in the amount is moderate, which can ensure that the siloxane chain segment fully participates in crosslinking; and the light initiator can be efficiently initiated in the amount, and curing is complete.

[0023] Preferably, the thickness of the adhesive layer is 15-30 um.

[0024] By adopting the above technical scheme, when the thickness of the adhesive layer is insufficient, the buffer space of the crosslinking network is limited, the stress concentration coefficient of the adhesive layer to be borne during folding is increased, local cracking or poor adhesion of the substrate is prone to occur, and the entire support film may fail after being folded for several times; if the thickness of the adhesive layer is too thick, a depression is generated at the folded part after long-term folding, and the overall thickness of the support film is increased; when the thickness of the adhesive layer is 15-30 um, the adhesive layer can adapt to the folding stress, and the overall flexibility of the support film is not affected.

[0025] Preferably, the stainless steel substrate layer is an ultra-thin high-strength stainless steel with a thickness of 10 um-30 um.

[0026] By adopting the above technical scheme, the ultra-thin high-strength stainless steel with a thickness of 10 um-30 um can provide sufficient rigidity to prevent the OLED device inside the display screen from being damaged under pressure during pressing or folding, and also has excellent flexibility and can not be plastically deformed or broken when the screen is folded; the ultra-thin high-strength stainless steel can be made into a roll material, which is compatible with the coating process of the adhesive layer, and can meet the continuous mass production requirements of flexible display screens.

[0027] Preferably, the protective film layer is a PET release film with a thickness of 50 um-75 um.

[0028] By adopting the above technical scheme, the PET release film with a thickness of 50-75 um can cover the actual needs of the support film, and has a low cost.

[0029] Preferably, the thickness of the protective film layer is 50 um-75 um of an acrylate PET protective film or a polyurethane PET protective film.

[0030] By adopting the above technical scheme, the thickness of 50 um-75 um can ensure that the protective film has sufficient supportability and can cover the surface of the support film without wrinkles, and also has moderate flexibility and can be rolled with the support film, which is suitable for roll-to-roll storage and transportation.

[0031] In a second aspect, the present application provides a preparation method of the above-mentioned lower support film for a flexible and foldable display screen, comprising the following steps:

[0032] The modified organic silicone glue liquid is coated on the release film, dried, a glue layer is formed, the other side of the glue layer is attached to the stainless steel, pressed into shape, cured, and finally a protective film layer is attached to the top of the stainless steel to obtain the flexible folding display screen lower supporting film.

[0033] By adopting the technical scheme, the modified organic silicone glue liquid is coated on the release film and dried, the flat surface of the release film is used to uniformly coat the glue layer, the glue layer and the stainless steel layer are infiltrated by pressing, and finally the protective film layer is attached to the surface of the stainless steel, so that the surface of the stainless steel is prevented from being scratched or contaminated in the early process; the preparation method is simple and can be mass-produced.

[0034] In summary, the beneficial effects of the present application are:

[0035] (1) The ultra-thin stainless steel is used to replace the PET / PI base material as the base material layer, which can resist external impact and scratching, has low and stable thermal expansion coefficient, can reduce the influence of environmental temperature and humidity on the size of the supporting film, and ensure the structural consistency of the screen module during long-term use.

[0036] (2) The multi-component composite modification of polyurethane-thiazole-silicone is used to improve the peeling strength of the glue layer and the stainless steel and the folding times of the supporting film.

[0037] (3) The ultra-thin high-strength stainless steel base material provides sufficient rigidity, the glue layer relieves the interface stress concentration during folding, the PET protective film layer has high scratch resistance and self-repairing property, the release film layer prevents the glue layer from being contaminated during storage and processing, the multi-layer cooperation controls the total thickness of the supporting film within a relatively thin range, adapts to the design requirements of the light and thin flexible folding screen, the multi-layer structure functions complement each other, and the supporting rigidity and the flexible folding requirements are balanced. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 FIG. 1 is a structural schematic diagram of the flexible folding display screen lower supporting film of the present application;

[0039] Figure 2 FIG. 3 is an infrared spectrum diagram of the glue layer in the flexible folding display screen lower supporting film of the present application;

[0040] MARKED DESCRIPTION:

[0041] 1, protective film layer; 2, stainless steel base material layer; 3, glue layer; 4, release film layer. DETAILED DESCRIPTION

[0042] The technical scheme of the present application will be explained in detail below with reference to several representative embodiments of the present application.

[0043] The experimental methods used in the following examples and comparative examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples and comparative examples are commercially available unless otherwise specified.

[0044] Preparation Example 1

[0045] The preparation method of the modified silicone glue solution of the present preparation example is as follows:

[0046] (1) Under nitrogen protection, 100 g polycaprolactone polyol with a molecular weight of 3000, 9.8 g 4,4-dicyclohexyl methane diisocyanate, and 0.88 g dibutyl tin dilaurate were mixed and stirred for 30 min, and then once heated to 78°C for 3 h; cooled to 65°C, and then 6.6 g hydroxyethyl acrylate was added for secondary reaction for 1 h to obtain a PU-MVT system;

[0047] (2) 9.38 g 4-methyl-5-vinylthiazole, 0.16 g azobisisobutyronitrile, and 150 g acetone were uniformly mixed and added to the PU-V system for further reaction at 70°C for 4 h to obtain a PU-MVT system;

[0048] (3) 14 g vinyl-terminated poly(methyl vinyl) siloxane with a molecular weight of 5000 was added to the PU-MVT system for high-speed stirring at 1500 rpm for 30 min, and then 0.28 g triallyl isocyanurate (TAIC), 0.12 g 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide (TPO), and 0.16 g antioxidant 1010 were added for further stirring for 30 min, and then acetone was removed by rotary evaporation to obtain a modified silicone glue solution.

[0049] Preparation Example 2

[0050] The preparation method of the modified silicone glue solution of the present preparation example is as follows:

[0051] (1) Under nitrogen protection, 100 g polycaprolactone polyol with a molecular weight of 3000, 9.8 g 4,4-dicyclohexyl methane diisocyanate, and 0.88 g dibutyl tin dilaurate were mixed and stirred for 30 min, and then once heated to 78°C for 3 h; cooled to 65°C, and then 6.6 g hydroxyethyl acrylate was added for secondary reaction for 1 h to obtain a PU-MVT system;

[0052] (2) 9.38 g 4-methyl-5-vinylthiazole, 0.16 g azobisisobutyronitrile, and 150 g acetone were uniformly mixed and added to the PU-V system for further reaction at 70°C for 4 h to obtain a PU-MVT system;

[0053] (3) 18 g of vinyl-terminated polymethylvinylsiloxane with a molecular weight of 5000 was added to the PU-MVT system and stirred at 1500 rpm for 30 min, 0.18 g of TAIC, 0.1 g of TPO and 0.16 g of antioxidant 1010 were added and stirred for another 30 min, and then acetone was removed by rotary evaporation to obtain the modified silicone adhesive solution.

[0054] Preparation Example 3

[0055] The preparation method of the modified silicone adhesive solution in the present preparation example is as follows:

[0056] (1) 100 g of polycaprolactone polyol with a molecular weight of 3000, 9.6 g of 4,4-dicyclohexylmethane diisocyanate and 1.2 g of dibutyltin dilaurate were mixed and stirred for 30 min, and then the temperature was raised to 75°C at one time and reacted for 3 h; the temperature was lowered to 55°C, 8.7 g of hydroxyethyl acrylate was added and reacted for another 2 h to obtain the PU-MVT system;

[0057] (2) 6 g of 4-methyl-5-vinylthiazole and 0.12 g of azobisisobutyronitrile were uniformly mixed with 150 g of acetone, and then added to the PU-V system and reacted at 65°C for another 3 h to obtain the PU-MVT system;

[0058] (3) 16 g of vinyl-terminated polymethylvinylsiloxane with a molecular weight of 5000 was added to the PU-MVT system and stirred at 1500 rpm for 30 min, 0.48 g of TAIC, 0.16 g of TPO and 0.16 g of antioxidant 1010 were added and stirred for another 30 min, and then acetone was removed by rotary evaporation to obtain the modified silicone adhesive solution.

[0059] Example 1

[0060] The lower supporting film for flexible folding display screen in the present example comprises, from top to bottom, a protective film layer of acrylate PET protective film with a thickness of 75 μm, a stainless steel substrate layer of ultra-thin high-strength stainless steel with a thickness of 15 μm, an adhesive layer of modified silicone adhesive with a thickness of 20 μm, and a release film layer of PET release film with a thickness of 75 μm.

[0061] The preparation method of the lower supporting film for flexible folding display screen in the present example is as follows:

[0062] The modified silicone adhesive solution prepared in Preparation Example 1 was coated on the PET release film after vacuum degassing, and baked at 80°C for 1 min to form an adhesive layer. The other side of the adhesive layer was attached to the stainless steel, and then pressed and formed, and then cured by ultraviolet light irradiation and baked in an oven at 80°C. Finally, a protective film layer was attached to the top of the stainless steel to obtain the lower supporting film for flexible folding display screen.

[0063] Figure 1 Structure diagram of the lower supporting film for flexible folding display screen; Figure 1 In the figure, 1 represents the protective film layer, 2 represents the stainless steel substrate layer, 3 represents the adhesive layer, and 4 represents the release film layer.

[0064] Figure 2 Infrared spectrum of the adhesive layer; Figure 2 At 3392 cm -1 At 1526 cm -1 At 2967 cm -1 At 1746 cm -1 At 1500-1600 cm -1 At 1231 cm -1 At 1065 cm -1 At 831 cm -1 At 831 cm

[0065] Example 2

[0066] The lower supporting film for flexible folding display screen of the present example comprises, from top to bottom, a protective film layer of acrylate PET protective film with a thickness of 60 μm, a stainless steel substrate layer of ultra-thin high-strength stainless steel with a thickness of 30 μm, an adhesive layer of modified organic silicone adhesive with a thickness of 15 μm, and a release film layer of PET release film with a thickness of 55 μm.

[0067] The preparation method of the lower supporting film for flexible folding display screen of the present example comprises the following specific steps:

[0068] The modified organic silicone adhesive solution prepared in Preparation Example 2 is vacuum degassed and then coated on the PET release film, baked at 80°C for 1 min to form an adhesive layer, the other side of the adhesive layer is attached to the stainless steel, and then pressed and formed, irradiated with ultraviolet light for curing, baked in an oven at 80°C, and finally a protective film layer is attached to the top of the stainless steel to obtain the lower supporting film for flexible folding display screen.

[0069] Example 3

[0070] The lower supporting film for flexible folding display screen of the present example comprises, from top to bottom, a protective film layer of polyurethane PET protective film with a thickness of 50 μm, a stainless steel substrate layer of ultra-thin high-strength stainless steel with a thickness of 10 μm, an adhesive layer of modified organic silicone adhesive with a thickness of 30 μm, and a release film layer of PET release film with a thickness of 65 μm.

[0071] The preparation method of the lower supporting film for flexible folding display screen of the present example comprises the following specific steps:

[0072] The modified silicone glue solution prepared in Preparation Example 3 was coated on a PET release film after vacuum degassing, baked at 80°C for 1 min to form a glue layer, the other side of the glue layer was attached to stainless steel, pressed into shape, cured by ultraviolet lamp irradiation, baked in an oven at 80°C, and finally a protective film layer was attached on the top of the stainless steel to obtain a flexible folding display screen lower supporting film.

[0073] Comparative Example 1

[0074] The difference from Example 1 is that the PI film is used instead of the ultra-thin high-strength stainless steel in this comparative example.

[0075] Comparative Example 2

[0076] The difference from Example 1 is that the PI film is used instead of the ultra-thin high-strength stainless steel in this comparative example, and the glue layer is prepared using a commercially available silicone glue.

[0077] Comparative Example 3

[0078] The difference from Example 1 is that the modification of 4-methyl-5-vinylthiazole is not performed in the modified silicone glue solution in this comparative example.

[0079] Comparative Example 4

[0080] The difference from Example 1 is that the glue layer is prepared using a commercially available silicone glue in this comparative example.

[0081] Related performance tests

[0082] The flexible folding display screen lower supporting films prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to related performance tests, and the test results are shown in Table 1.

[0083] Table 1 Test results

[0084]

[0085] The above has exemplarily described the present application, it should be explained that, without departing from the core of the present application, any simple modification, change or other equivalent replacement which can not cost creative labor of the person skilled in the art, falls into the protection scope of the present application.

Claims

1. A lower support film for a flexible folding display screen, characterized by, The support film comprises, from top to bottom, a protective film layer, a stainless steel substrate layer, a glue layer and a release film layer; The glue layer is prepared by coating a modified silicone glue solution on the release film, drying and curing; The preparation method of the modified silicone glue solution comprises the following steps: (1) Under anaerobic conditions, mix polycaprolactone polyol, 4,4-dicyclohexyl methane diisocyanate and dibutyl tin dilaurate uniformly, carry out one-time reaction, add hydroxyethyl acrylate for two-time reaction, and obtain a PU-V system; (2) Mix 4-methyl-5-vinylthiazole, azobisisobutyronitrile and acetone uniformly, add the PU-V system for continuous reaction, and obtain a PU-MVT system; (3) Add end-vinyl polymethylvinylsiloxane to the PU-MVT system, mix uniformly, add a crosslinking agent, a photoinitiator and an antioxidant, remove acetone by rotary evaporation, and obtain a modified silicone glue solution.

2. The under-support film for a flexible folding display according to claim 1, wherein In step (1), the mass ratio of polycaprolactone polyol to 4,4-dicyclohexyl methane diisocyanate is 1:(0.096-0.1); the amount of dibutyl tin dilaurate is 0.8%-1.1% of the total mass of polycaprolactone polyol and 4,4-dicyclohexyl methane diisocyanate; and the amount of hydroxyethyl acrylate is 5%-8% of the total mass of polycaprolactone polyol and 4,4-dicyclohexyl methane diisocyanate. 3.The under-support film for a flexible folding display according to claim 1, characterized in that, In step (1), the temperature of one-time reaction is 75-85℃, and the time of one-time reaction is 2-3h; the temperature of two-time reaction is 55-65℃, and the time of two-time reaction is 1-2h. 4.The under-support film for a flexible folding display according to claim 1, characterized in that, In step (2), the amount of 4-methyl-5-vinylthiazole is 5%-10% of the mass of PU-V; and the amount of azobisisobutyronitrile is 1.6%-2% of the mass of 4-methyl-5-vinylthiazole. 5.The under-supporting film for a flexible folding display screen according to claim 1, characterized in that, In step (2), the mass ratio of end-vinyl polymethylvinylsiloxane to polycaprolactone polyol is (0.14-0.18):1, the amount of crosslinking agent is 1%-3% of the mass of end-vinyl polymethylvinylsiloxane, and the amount of photoinitiator is 0.5%-1% of the mass of end-vinyl polymethylvinylsiloxane.

6. The lower support film for a flexible folding display screen according to claim 1, wherein the thickness of the glue layer is 15-30um. 7.The under-supporting film for a flexible folding display screen according to claim 1, characterized in that, The protective film layer is a PET release film with a thickness of 50-75um.

8. The method of producing a lower support film for a flexible folding display according to any one of claims 1 to 7, characterized in that, The preparation method comprises the following steps: Coat the modified silicone glue solution on the release film, dry, form a glue layer, adhere the other side of the glue layer to the stainless steel, press into shape, cure, finally coat the protective film layer on the top of the stainless steel, and obtain the lower support film for a flexible folding display screen.

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