Low-modulus and high-adhesive-force adhesive film for folding display screen

Abstract

The invention discloses an adhesive film with low modulus and high adhesive force for a folding display screen. The adhesive film simultaneously meets the following conditions: 1) the storage modulus at 25 DEG C is lower than 30Kpa, and the storage modulus at-20 DEG C is lower than 140Kpa; according to the present invention, the adhesive film has the following characteristics that (1) the adhesive film has the 180-degree peeling force on the glass at 25 DEG C of more than 10 N / inch and the PET peeling force on the glass at 25 DEG C of more than 6 N / inch, (2) the strain recovery rate at 25 DEG C under 20 Kpa of more than 90% and the deformation quantity of more than 300%, and (4) the modulus at 120 DEG C under 1 Hz of 3000-5000 Pa and the phase angle of 6-10, and has characteristics of good peeling force, good creep recovery rate and good bending performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical adhesive for folding display screen, and particularly relates to a low-modulus high-adhesion adhesive film for folding display screen. BACKGROUND

[0002] Optical clear adhesive (OCA) is a new type of material used in liquid crystal-based display devices, which has the functions of light transmission, light homogenization, display enhancement, and protection. However, the traditional OCA structure has significant limitations in performance. OCA often cannot meet multiple performance requirements such as low modulus at low temperature, high creep recovery, and good adhesion. At low temperatures, OCA is prone to bending failure due to its high modulus. For folding OCA, in order to reduce the modulus and glass transition temperature, the hard monomer and functional monomer have a small proportion, which results in low peel strength and poor high-temperature resistance, especially in high-temperature and high-humidity environments.

[0003] CN119931543A reports that by using UV polymerization cross-linking, the adhesive has high adhesion while achieving low modulus, and also has high deformation, greatly reducing the risk of deformation and warping. However, the high deformation will affect the cohesive strength, and the gel fraction is low. Although it has good folding effect, there are problems of poor reliability in high-temperature and high-humidity folding.

[0004] CN118389101A reports that the OCA adhesive of the present application adds a monomer S-06E which has good compatibility with the system. The monomer contains a double epoxy functional group, has high reactivity and cohesive force, reacts with the acrylic ester monomer in the adhesive to form a branched polymer, greatly improves the cohesive strength, and can improve the creep performance of the glue, and also can increase the adhesion strength with inorganic substrates. However, S-06 needs a strong acid produced by cationic initiator to deactivate the reaction, and there will be some strong acid in the whole OCA, which will cause corrosion to the display module.

[0005] CN119736024A reports that the multi-layer folding OCA successfully solves the performance contradiction that single-layer OCA cannot balance, so that the folding device can still maintain good flexibility at low temperature, effectively reducing the problem of increased modulus and increased brittleness caused by low temperature, thereby reducing the risk of fold generation. However, the three-layer structure is formed by compounding, especially in the folding process, the interaction force between the layers is weakened, and the glue bodies are prone to displacement from each other, resulting in poor performance.

[0006] How to solve the above technical problems is the direction that the person skilled in the art is committed to researching. SUMMARY

[0007] The present application aims to overcome the deficiencies of the prior art and provide a low modulus high adhesive force adhesive film for a folding display screen.

[0008] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows: a low modulus high adhesive force adhesive film for a folding display screen, which simultaneously satisfies the following conditions: 1) The storage modulus at 25°C is less than 30 KPa, and the storage modulus at -20°C is less than 140 KPa; 2) The 180° peeling force on glass at 25°C is greater than 10 N / inch, and the peeling force on PET is greater than 6 N / inch; 3) The strain recovery rate at 25°C and 20 KPa is greater than 90%, and the deformation amount is greater than 300%; 4) The 120°C 1Hz modulus is between 3000 Pa and 5000 Pa, and the phase angle is between 6 and 10.

[0009] As a specific embodiment, the raw materials of the adhesive film include, by weight fraction: 1) 90-100 parts of an acrylic derivative polymer, the glass transition temperature of the acrylic derivative being between -50°C and -30°C; 2) 0.01-1 part of a photoinitiator; 3) 0.01-1 part of a crosslinking agent.

[0010] As a specific embodiment, the acrylic derivative polymer, by 100% of the mass percentage, is composed of 90%-99% C4-C18 (methyl) acrylate monomer and 1%-10% acid functional olefinic unsaturated monomer.

[0011] Preferably, the C4-C18 (methyl) acrylate monomer is selected from one or more of 2-ethylhexyl acrylate, isooctyl acrylate, butyl acrylate, and lauryl acrylate, and the acid functional olefinic unsaturated monomer is a mixture of β-acryloyloxypropionic acid, acrylic acid, and methyl methacrylate.

[0012] Specifically, the mass ratio of β-acryloyloxypropionic acid, acrylic acid, and methyl methacrylate is 3:1:2.

[0013] Preferably, the acrylic derivative polymer contains 30%-40% lauryl acrylate in its raw materials.

[0014] As a specific embodiment, the photoinitiator is selected from a combination of one or more of organic peroxides, azo compounds, and persulfates.

[0015] As a specific embodiment, the cross-linking agent is a multi-functional compound selected from a combination of one or more of a polyisocyanate, a polyepoxide, a polyamine, a polyacid, a polyol, and a metal chelate.

[0016] As a specific embodiment, the cross-linking agent is 1,3-bis(N,N-diglycidyl- aminomethyl)cyclohexane.

[0017] Thanks to the use of the above technical solution, the low-modulus high-adhesion adhesive film for folding display screens of the present application has the following advantages over the prior art: the adhesive film has good peeling force and creep recovery rate, and good bending performance, thanks to the combination of the acrylic derivative polymer and the photoinitiator and the cross-linking agent. DETAILED DESCRIPTION

[0018] The technical solution of the present application will be further described below in conjunction with specific examples.

[0019] Provided below is a low-modulus high-adhesion adhesive film for folding display screens, which meets the following conditions simultaneously: 1) The storage modulus at 25°C is lower than 30 KPa, and the storage modulus at -20°C is lower than 140 KPa; 2) The 180° peeling force on glass at 25°C is greater than 10 N / inch, and the peeling force on PET is greater than 6 N / inch; 3) The strain recovery rate at 25°C under 20 KPa is greater than 90%, and the deformation amount is greater than 300%; 4) The 120°C 1Hz modulus is between 3000 Pa and 5000 Pa, and the phase angle is between 6 and 10.

[0020] Specifically, the raw materials of the adhesive film include, by weight fraction: 1) 90-100 parts of an acrylic derivative polymer, the glass transition temperature of the acrylic derivative being between -50°C and -30°C, the acrylic derivative polymer being composed of 90%-99% C4-C18 (methyl) acrylate monomer and 1%-10% acid-functional olefinically unsaturated monomer, based on 100% by mass; 2) 0.01-1 part of a photoinitiator, the photoinitiator being selected from a combination of one or more of an organic peroxide, an azo compound, and a persulfate; 3) 0.01-1 part of a cross-linking agent, the cross-linking agent being a multi-functional compound selected from a combination of one or more of a polyisocyanate, a polyepoxide, a polyamine, a polyacid, a polyol, and a metal chelate. Example 1

[0021] The example provides an adhesive film, which is prepared as follows: Accurately take 58 g of 2-ethylhexyl acrylate, 36 g of lauryl acrylate, 3 g of β-acryloyloxy propionic acid, 1 g of acrylic acid, 2 g of methyl methacrylate, 100 parts of butanone, and place them in a four-necked flask equipped with a stirrer, a condenser, and a nitrogen tube. After stirring at 60-62°C for 30 minutes, 0.3‰ parts of ABVN are added, and the temperature is kept for 2 hours of stirring reaction. Then, the temperature is raised to 65°C for 3 hours of reaction. 0.3‰ parts of ABVN are added, and the temperature is raised to 70-72°C for 5 hours of continuous reaction. After cooling, a glue with a solid content of 35% is obtained. After adding 0.2% TETRAD-C (1,3-bis(N,N-diglycidyl-aminomethyl) cyclohexane), OCA glue is obtained.

[0022] Then, the OCA adhesive is coated on the PET substrate, the dry film thickness is controlled to be 25μm, and the temperature is raised to 120°C for 2min in the oven at room temperature 25°C. After drying, the glue film is attached to the PET release film, and the OCA glue film product is obtained after curing at 35°C for 48h. Example 2

[0023] Accurately take 58 g of 2-ethylhexyl acrylate, 36 g of lauryl acrylate, 3 g of β-acryloyloxy propionic acid, 1 g of acrylic acid, 2 g of methyl methacrylate, 100 parts of butanone, and place them in a four-necked flask equipped with a stirrer, a condenser, and a nitrogen tube. After stirring at 60-62°C for 30 minutes, 0.3‰ parts of ABVN are added, and the temperature is kept for 2 hours of stirring reaction. Then, the temperature is raised to 65°C for 3 hours of reaction. 0.3‰ parts of ABVN are added, and the temperature is raised to 70-72°C for 5 hours of continuous reaction. After cooling, a glue with a solid content of 35% is obtained. After adding 0.2% TETRAD-C (1,3-bis(N,N-diglycidyl-aminomethyl) cyclohexane), OCA glue is obtained.

[0024] Then, the OCA adhesive is coated on the PET substrate, the dry film thickness is controlled to be 25μm, and the temperature is raised to 120°C for 2min in the oven at room temperature 25°C. After drying, the glue film is attached to the PET release film, and the OCA glue film product is obtained after curing at 35°C for 48h. Example 3

[0025] Accurately take 78g of 2-ethylhexyl acrylate, 16g of lauryl acrylate, 3g of β-acryloyloxypropionic acid, 1g of acrylic acid, 2g of methyl methacrylate, 100 parts of butanone, and place them in a four-necked flask equipped with a stirrer, a condenser, and a nitrogen tube. After stirring at 60-62°C for 30 minutes, 0.3‰ parts of ABVN are added, and the reaction is maintained at the temperature for 2 hours. Then, the temperature is increased to 65°C for 3 hours. 0.3‰ parts of ABVN are added, and the temperature is increased to 70-72°C for 5 hours. After cooling, a glue with a solid content of 35% is obtained. After adding 0.2% TETRAD-C (1,3-bis(N,N-diglycidyl-aminomethyl)cyclohexane), OCA glue is obtained.

[0026] Then, the OCA adhesive is coated on the PET substrate, the dry film thickness is controlled to be 25μm, and the temperature is increased to 120°C for 2min in an oven at room temperature 25°C. After drying, the glue film is attached to a PET release film, and the product is obtained after curing at 35°C for 48h.

[0027] Comparative Example 1 Accurately take 78g of 2-ethylhexyl acrylate, 16g of lauryl acrylate, 3g of β-acryloyloxypropionic acid, 1g of acrylic acid, 2g of methyl methacrylate, 100 parts of butanone, and place them in a four-necked flask equipped with a stirrer, a condenser, and a nitrogen tube. After stirring at 60-62°C for 30 minutes, 0.3‰ parts of ABVN are added, and the reaction is maintained at the temperature for 2 hours. Then, the temperature is increased to 65°C for 3 hours. 0.3‰ parts of ABVN are added, and the temperature is increased to 70-72°C for 5 hours. After cooling, a glue with a solid content of 35% is obtained. After adding 0.2% TETRAD-C (1,3-bis(N,N-diglycidyl-aminomethyl)cyclohexane), OCA glue is obtained.

[0028] Then, the OCA adhesive is coated on the PET substrate, the dry film thickness is controlled to be 25μm, and the temperature is increased to 120°C for 2min in an oven at room temperature 25°C. After drying, the glue film is attached to a PET release film, and the product is obtained after curing at 35°C for 48h.

[0029] Comparative Example 2 Accurately take 2-ethylhexyl acrylate 58 g, lauryl acrylate 36 g, β-acryloyloxy propionic acid 3 g, acrylic acid 1 g, methyl methacrylate 2 g, butanone 100 parts, place in a four-necked flask equipped with a stirrer, condenser and nitrogen tube, introduce nitrogen, stir for 30 minutes at 60-62°C, then add 0.3 ‰ parts of ABVN, keep the temperature and stir for 2 hours; then increase the temperature to 65°C and react for 3h; add 0.3 ‰ parts of ABVN, increase the temperature to 70-72°C and continue to react for 5 hours; after cooling, a glue with solid content of 35% is obtained, add 0.2% EP-PEG-EP (epoxy polyethylene glycol epoxy) to obtain OCA glue.

[0030] Then coat the OCA adhesive on the PET substrate, control the dry film thickness to be 25μm, put it into the oven at room temperature 25℃ and increase to 120℃ and keep for 2min, after drying, adhere the PET release film on the glue film, and then mature at 35℃ for 48h to obtain the OCA glue film product.

[0031] Comparative Example 3 Accurately take 2-ethylhexyl acrylate 58 g, lauryl acrylate 36 g, β-acryloyloxy propionic acid 3 g, acrylic acid 1 g, methyl methacrylate 2 g, butanone 100 parts, place in a four-necked flask equipped with a stirrer, condenser and nitrogen tube, introduce nitrogen, stir for 30 minutes at 60-62°C, then add 0.3 ‰ parts of ABVN, keep the temperature and stir for 2 hours; then increase the temperature to 65°C and react for 3h; add 0.3 ‰ parts of ABVN, increase the temperature to 70-72°C and continue to react for 5 hours; after cooling, a glue with solid content of 35% is obtained, add 0.2% TETRAD-C (1,3-bis(N,N-diglycidyl-amino methyl) cyclohexane) to obtain OCA glue.

[0032] Then coat the OCA adhesive on the PET substrate, control the dry film thickness to be 25μm, put it into the oven at room temperature 25℃ and increase to 120℃ and keep for 2min, after drying, adhere the PET release film on the glue film, and then mature at 35℃ for 48h to obtain the OCA glue film product.

[0033] Comparative Example 4 Accurately take 2-ethylhexyl acrylate 58 g, lauryl acrylate 36 g, β-acryloyloxy propionic acid 3 g, acrylic acid 1 g, methyl methacrylate 2 g, butanone 100 parts, place in a four-necked flask equipped with a stirrer, condenser and nitrogen tube, introduce nitrogen, stir for 30 minutes at 60-62°C, then add 0.3 ‰ parts of ABVN, keep the temperature and stir for 2 hours; then increase the temperature to 65°C and react for 3h; add 0.3 ‰ parts of ABVN, increase the temperature to 70-72°C and continue to react for 5 hours; after cooling, a glue with solid content of 35% is obtained, add 0.2% TETRAD-C (1,3-bis(N,N-diglycidyl-amino methyl) cyclohexane) to obtain OCA glue.

[0034] Then, OCA adhesive is coated on the PET substrate, the dry film thickness is controlled to be 25μm, and the film is placed in an oven at room temperature of 25℃ to 120℃ and kept at that temperature for 2 minutes. After drying, PET release film is laminated onto the adhesive film, and the film is cured at 35℃ for 48 hours to obtain the OCA adhesive film product.

[0035] The following tests were conducted on the OCA films obtained in Examples 1-3 and Comparative Examples 1-4, and the test results are shown in Table 1: 1) Peel force test: According to the ASTM D3330 method, the sample was made into a 300 mm long and 25 mm wide sample and rolled back and forth three times on a glass using a 2 kg rubber roller. After being placed for 20 minutes at a temperature of 23°C and a humidity of 50%RH, it was tested with a tensile testing machine. Peeling was performed at a peel angle of 180° and a peel speed of 300 mm / min to test the 180° peel force.

[0036] 2) Modulus: The adhesive films were stacked to form test specimens with a thickness of 0.9 mm to 1.1 mm (e.g., 1.0 mm), and then stamped into cylinders with a diameter of 8 mm. These cylinders were used as samples. A TA rheometer HR-10 was used, and the test standard was ASTM D4440-15. Temperature scans were performed by increasing the temperature from -40 °C to 100 °C at a rate of 2 °C / min, with the samples oscillating at a frequency of 1 Hz and a shear strain of 0.1%. The shear storage modulus (G') at different temperatures was recorded. The maximum value of the loss factor tanδ was taken as the Tg of the material.

[0037] 3) Creep recovery: At a constant temperature of 25°C, apply a stress of 20 kPa for 600 seconds. Remove the external force and test the OCA. The recovery curve lasts for 600 seconds, where the maximum deformation is denoted as Creep, and the creep recovery rate is (maximum value - minimum value) / maximum value.

[0038] 4) Dynamic bending test: A 25 μm thick adhesive pressure-sensitive layer was bonded between two 50 μm polyimide (PI) sheets, and then cut into dimensions of 25 mm wide and 125 mm long. The samples were mounted in a dynamic folding device with two folding stages, controlled at 25°C and 55% RH. These stages rotated from 180° (planar state) to 0° (folded state) and underwent 200,000 cycles at a rate of 6 cycles / min. The observed sample passed if no fracture or delamination of the composite structure was observed after the cycles.

[0039] Table 1

[0040] As can be seen from Examples 1 to 3 in Table 1, the adhesive film obtained by using the technical solution of the present invention has good creep recovery rate and good peel force, and also has good dynamic bending performance.

[0041] Comparing Comparative Example 1 with Example 1, when the amount of LA added is low, the film exhibits poor bending performance at -20°C and 500,000 cycles, and also has low peel strength to PET. Comparing Comparative Examples 2 and 4 with Example 1, it is evident that when TETRAD-C is used as the crosslinking agent, the film performance is superior, while other crosslinking agents result in unstable bending performance. Comparing Comparative Example 3 with Example 1, it is clear that when the amount of acid-functionalized olefinic unsaturated monomer exceeds 10%, the film exhibits poor peel strength to glass and unsatisfactory bending performance at 85°C / 85% RH for 500,000 cycles.

[0042] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. An adhesive film for a low-modulus, high-adhesion folding display screen, characterized in that, The adhesive film simultaneously meets the following conditions: 1) The energy storage modulus is less than 30 kPa at 25℃ and less than 140 kPa at -20℃; 2) At 25°C, the 180° peel force on glass is greater than 10 N / inch, and the peel force on PET is greater than 6 N / inch; 3) The strain recovery rate at 25℃ and 20Kpa is greater than 90%, and the deformation is greater than 300%; 4) The modulus at 120℃ and 1Hz is between 3000Pa and 6000Pa, and the phase angle is between 6 and 10.

2. The adhesive film for a low-modulus, high-adhesion folding display screen according to claim 1, characterized in that, The raw materials for the adhesive film, by weight, include: 1) 90-100 parts of an acrylic derivative polymer, wherein the glass transition temperature of the acrylic derivative is between -50°C and -30°C; 2) 0.01-1 parts of photoinitiator; 3) 0.01-1 part crosslinking agent.

3. The adhesive film for a low-modulus, high-adhesion folding display screen according to claim 2, characterized in that, The acrylic derivative polymer, by mass percentage, consists of 90%-99% C4-C18 (meth)acrylate monomers and 1%-10% acid-functionalized olefinic unsaturated monomers.

4. The adhesive film for a low-modulus, high-adhesion folding display screen according to claim 3, characterized in that, The raw materials for the acrylic derivative polymer contain 30%-40% lauryl acrylate.

5. The adhesive film for a low-modulus, high-adhesion folding display screen according to claim 2, characterized in that, The photoinitiator is selected from one or more combinations of organic peroxides, azo compounds, and persulfates.

6. The adhesive film for a low-modulus, high-adhesion folding display screen according to claim 2, characterized in that, The crosslinking agent is a multifunctional compound selected from one or more combinations of polyisocyanates, polyepoxides, polyamines, polyacids, polyols, and metal chelates.

7. The adhesive film for a low-modulus, high-adhesion folding display screen according to claim 6, characterized in that, The crosslinking agent used is 1,3-bis(N,N-diglycidyl-aminomethyl)cyclohexane.

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