Electron beam curing hot melting optical adhesive film and preparation method thereof

Abstract

The invention discloses an electron beam curing hot melting optical adhesive film and a preparation method thereof. The invention aims to provide an optical adhesive film which has the characteristics of good adhesive strength, damp and heat resistance, optical performance, water resistance and the like. The method comprises the following steps: premixing the ethylene-vinyl acetate elastomer and the functional small molecules in a stirrer, and fully drying to form a premix 1; melting the premix 1, plasticizing, filtering, and coating on a release film to form a mixed melt 2 of 0.1-0.8 mm; the mixed melt 2 is subjected to electron beam irradiation on line, and a solid adhesive film 3 is obtained; coating a layer of release film on the surface of the solid adhesive film 3, and then rolling to obtain the hot-melt optical adhesive film. According to the method, on-line polymerization modification of the ethylene-vinyl acetate elastomer and the micromolecular functional additive component is realized by utilizing the characteristics of strong penetration and curing capability and oxygen-free polymerization inhibition of electron beams, and the method has more diversified feasibility and is used for display packaging in the field of touch display.

Description

Technical Field

[0001] This invention relates to an optical adhesive for touch screens, specifically a hot-melt optical adhesive film that is cured by electron beam. The invention also relates to a method for preparing the hot-melt optical adhesive film, belonging to the field of touch screen bonding and encapsulation. Background Technology

[0002] Touchscreens, as the most common and frequently used human-computer interaction interface, are seeing increasingly wider applications and greater market demand due to the rapid development of emerging fields such as 5G, IoT, big data, and artificial intelligence. Hot melt optical adhesives, a new category of optical adhesives developed in recent years, are beginning to replace traditional pressure-sensitive optical tapes and liquid optical adhesives, and are widely used in the optical bonding of touchscreens, thanks to their high strength, easy adhesion, and reworkability.

[0003] The widespread application of hot-melt optical adhesives in touchscreen encapsulation has also brought about some new problems. For example, hot-melt optical adhesives achieve compatibility and coating between the base resin and small-molecule functional additives in a molten state. After bonding and cooling, the small-molecule additives gradually migrate to the surface, forming a lubricating effect at the bonding interface. This can lead to bubble lines and fogging on the touchscreen appearance under certain observation conditions. Another example is that hot-melt optical adhesives achieve bonding by filling step differences through the flow of molten adhesive. During bonding, the molten flow can compress the cover plate and functional sheets, causing uneven stress and resulting in insufficient adhesive and bubbles at the corners and edges. This situation is more pronounced in the bonding of large-size touchscreens. To solve this problem, the thickness of the adhesive film and the amount of adhesive are generally increased, but this increases material costs. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the first objective of this invention is to provide a hot-melt optical adhesive film for touchscreens. This hot-melt optical adhesive film is cured by electron beam curing and exhibits superior composition stability and bonding performance compared to existing hot-melt optical adhesive films. Simultaneously, this hot-melt optical adhesive film possesses excellent melt dimensional stability, improving the bonding efficiency and yield of large-size touchscreens while reducing material costs.

[0005] The second objective of this invention is to provide a method for preparing the above-mentioned electron beam cured hot melt optical adhesive film.

[0006] Therefore, the first technical solution provided by this invention is as follows:

[0007] A method for preparing an electron beam-cured hot melt optical adhesive film includes the following steps in sequence:

[0008] 1) Weigh 70-90 parts by weight of ethylene-vinyl acetate elastomer and 10-30 parts by weight of small molecule functional additive components; then put them into a high-speed mixer for premixing until they are evenly mixed and thoroughly dried to form premix 1;

[0009] 2) The premix 1 prepared in step 1) is put into the hopper of the casting machine, melted and plasticized to obtain a melt. After the melt is filtered, it is coated on the release film and the thickness is adjusted to form a mixed melt 2 of 0.1 to 0.8 mm.

[0010] 3) The mixed melt 2 prepared in step 2) is irradiated online with an electron beam to obtain a solid film 3;

[0011] 4) Apply a release film to the surface of the solid adhesive film 3 prepared in step 3), and then roll it up to obtain the electron beam cured hot melt optical adhesive film.

[0012] Furthermore, in the above-mentioned method for preparing electron beam cured hot melt optical adhesive film, the plasticizing is performed using a twin-screw extruder.

[0013] Furthermore, in the above-mentioned method for preparing electron beam cured hot melt optical adhesive film, the small molecule functional component is composed of acrylate monomer, photoinitiator, silane coupling agent, and antioxidant.

[0014] Furthermore, in the above-mentioned method for preparing electron beam cured hot melt optical adhesive film, the mass ratio of the acrylate monomer, photoinitiator, silane coupling agent, and antioxidant is 5-20:2-6:2-4:1-2.

[0015] Furthermore, in the above-mentioned method for preparing electron beam cured hot melt optical adhesive film, the melting temperature in step 2) is 110°C.

[0016] Furthermore, in the above-mentioned method for preparing electron beam-cured hot melt optical adhesive film, the electron beam accelerator voltage is 100KV~500KV, the irradiation energy is 10~60kgy, and the linear velocity is 15-30m / min.

[0017] Furthermore, in the above-mentioned method for preparing electron beam cured hot melt optical adhesive film, the coating is performed by T-die extrusion coating.

[0018] Furthermore, in the above-mentioned method for preparing electron beam cured hot melt optical adhesive film, the release film is a PET release film.

[0019] Furthermore, in the above-mentioned method for preparing electron beam cured hot melt optical adhesive film, the ethylene-vinyl acetate elastomer is a resin with a VA content of 26% to 42%.

[0020] Preferably, the ethylene-vinyl acetate elastomer (EVA) is a resin with a VA content of 28% and 33%. More preferably, the EVA resin has a VA content of 28% and a melt index (MI) of 25 g / 10 min, or a VA content of 33% and a melt index (MI) of 15 g / 10 min.

[0021] Furthermore, in the above-mentioned method for preparing electron beam cured hot melt optical adhesive film, the acrylic monomer is one or a mixture of two or more of the following: trimethylolpropane triacrylate, pentaerythritol tetraacrylate, triallyl isocyanurate, pentaerythritol triacrylate, bis(trimethylolpropane) acrylate, and 1,6-hexanediol diacrylate.

[0022] Preferably, the acrylic monomer is triallyl isocyanurate or 1,6-hexanediol diacrylate.

[0023] The photoinitiator is one or a mixture of two or more of 1-hydroxy ketone, benzophenone, acrylated benzophenone, dimethyl benzoyl ether, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide;

[0024] Preferably, the photoinitiator is one or a mixture of two of 1-hydroxy ketone, benzoin dimethyl ether, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0025] The silane coupling agent is one or a mixture of two of γ-glycidoxypropyltriethoxysilane, vinyltrimethoxysilane, γ-(methacryloyloxy)propyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, and vinyltriethoxysilane.

[0026] Preferably, the silane coupling agent is one or a mixture of two of vinyltrimethoxysilane and vinyltriethoxysilane.

[0027] The antioxidant is one or a mixture of two or more of 2,2'-methylene-bis-(4-methyl-6-tert-butylphenol), β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester, and tris(nonylphenyl) phosphite.

[0028] The second technical solution provided by the present invention is an electron beam cured hot melt optical adhesive film, which is prepared by the preparation method described in the first technical solution.

[0029] The degree of crosslinking of the electron beam cured hot melt optical adhesive film is 10-60%.

[0030] Compared with the prior art, the technical solution provided by the present invention has the following technical advantages:

[0031] 1. The technical solution provided in this application utilizes the strong penetration and curing ability of electron beam (EB) and the oxygen-free polymerization inhibition characteristics to realize the online polymerization of ethylene-vinyl acetate elastomer and small molecule functional additive components. The modified performance design has more diverse feasibility, making it a new preparation technology for optical adhesives.

[0032] 2. The technical solution provided in this application utilizes an electron beam (EB) to pre-react the active small molecule functional components and polymer resin of the hot melt optical adhesive composition, so that the small molecule functional components form a stable chemical bond structure on the polymer chain, which can significantly improve the stability of the composition and slow down or avoid probabilistic appearance defects such as bubble lines and fogging caused by the migration of small molecule functional components.

[0033] 3. The hot melt optical adhesive for touch screens of the present invention has a certain degree of pre-crosslinking, exhibits excellent dimensional stability during the hot pressing process of touch screens, avoids stress compression on electronic components such as cover plates and functional sheets, and can effectively prevent problems such as missing adhesive and air bubbles at the four corners and edges without increasing the thickness of the adhesive film, which is conducive to cost reduction. Detailed Implementation

[0034] The present invention will be described in detail below with reference to specific embodiments, but this does not constitute any limitation on the present application. Any limited modifications made by any person within the scope of the claims of this application are still within the protection scope of the claims of this application.

[0035] Example 1

[0036] The electron beam-cured hot melt optical adhesive film provided in this embodiment is prepared through the following steps:

[0037] 1) Weigh 90 kg of ethylene-vinyl acetate elastomer (VA content 28%, MI 25 g / 10 min), 5 kg of triallyl isocyanurate, 2 kg of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2 kg of vinyltrimethoxysilane, and 1 kg of 2,2'-methylene-bis-(4-methyl-6-tert-butylphenol) and add them to a high-speed mixer for premixing until homogeneous. Dry thoroughly to form premix 1-1. The total mass of the small molecule functional components is 10 kg.

[0038] 2) The premix 1-1 prepared in step 1) is put into the hopper of the casting machine, melted at 110°C, plasticized and filtered, and the filtered melt is extruded through a T-die and coated onto an optical grade PET release film. The thickness is adjusted to form a 0.2 mm mixed melt 1-2.

[0039] 3) The mixed melt 1-2 prepared in step 2) is irradiated online with electron beam (EB) to obtain solid film 1-3.

[0040] The electron beam irradiation conditions are: electron beam accelerator voltage of 300KV, irradiation energy of 30kgy, and linear velocity of 20m / min.

[0041] 4) Apply an optical-grade PET release film to the surface of the solid adhesive film 1-3 prepared in 3), and then roll it up to obtain the electron beam cured hot melt optical adhesive film 1.

[0042] Example 2

[0043] The electron beam-cured hot melt optical adhesive film provided in this embodiment is prepared through the following steps:

[0044] 1) Weigh 80 kg of ethylene-vinyl acetate elastomer (VA content 28%, MI 25 g / 10 min), 10 kg of triallyl isocyanurate, 5 kg of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 3 kg of vinyltrimethoxysilane, and 2 kg of 2,2'-methylene-bis-(4-methyl-6-tert-butylphenol) and add them to a high-speed mixer for premixing until homogeneous. Dry thoroughly to form premix 2-1. The total mass of the small molecule functional components is 20 kg.

[0045] 2) The premix 2-1 prepared in step 1) is put into the hopper of the casting machine, melted at 110°C, plasticized and filtered, and the filtered melt is extruded through a T-die and coated onto an optical grade PET release film. The thickness is adjusted to form a 0.2 mm mixed melt 2-2.

[0046] 3) The mixed melt 2-2 prepared in step 2) is subjected to electron beam irradiation (EB) in-line to obtain a solid film 2-3. The electron beam irradiation conditions are: electron beam accelerator voltage of 300 kV, irradiation energy of 30 kgy, and linear velocity of 20 m / min.

[0047] 4) Apply an optical-grade PET release film to the surface of the solid adhesive film 2-3 prepared in 3), and then roll it up to obtain the electron beam cured hot melt optical adhesive film 2.

[0048] Example 3

[0049] The electron beam-cured hot melt optical adhesive film provided in this embodiment is prepared through the following steps:

[0050] 1) Weigh 70 kg of ethylene-vinyl acetate elastomer (VA content 28%, MI 25 g / 10 min), 20 kg of triallyl isocyanurate, 6 kg of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2.5 kg of vinyltrimethoxysilane, and 1.5 kg of 2,2'-methylene-bis-(4-methyl-6-tert-butylphenol) and add them to a high-speed mixer for premixing until homogeneous. Dry thoroughly to form premix 3-1. The total mass of the small molecule functional components is 30 kg.

[0051] 2) The premix 3-1 prepared in step 1) is put into the hopper of the casting machine, melted at 110°C, plasticized, and filtered. The filtered melt is extruded through a T-die and coated onto an optical grade PET release film. The thickness is adjusted to form a 0.2 mm mixed melt 3-2.

[0052] 3) The mixed melt 3-2 prepared in step 2) is irradiated online with electron beam (EB) to obtain a solid film 3-3.

[0053] The electron beam irradiation conditions are: electron beam accelerator voltage of 300KV, irradiation energy of 30kgy, and linear velocity of 20m / min.

[0054] 4) Apply an optical-grade PET release film to the surface of the solid adhesive film 3-3 prepared in preparation 3), and then roll it up to obtain the electron beam cured hot melt optical adhesive film 3.

[0055] Example 4

[0056] The electron beam-cured hot melt optical adhesive film provided in this embodiment is prepared through the following steps:

[0057] 1) Weigh 80 kg of ethylene-vinyl acetate elastomer (VA content 33%, MI 15 g / 10 min), 10 kg of 1,6-hexanediol diacrylate, 2 kg of 1-hydroxy ketone, 2 kg of benzoin dimethyl ether, 4 kg of vinyltriethoxysilane, and 2 kg of tris(nonylphenyl) phosphite and add them to a high-speed mixer for premixing until homogeneous. Dry thoroughly to form premix 4-1. The total mass of the small molecule functional components is 20 kg.

[0058] 2) The premixed material 4-1 prepared in step 1) is put into the hopper of the casting machine, melted at 110°C, plasticized, and filtered. The filtered melt is extruded through a T-die and coated onto an optical grade PET release film. The thickness is adjusted to form a 0.2 mm mixed melt 4-2.

[0059] 3) The mixed melt 4-2 prepared in step 2) is irradiated online with electron beam (EB) to obtain a solid film 4-3.

[0060] The electron beam irradiation conditions are: electron beam accelerator voltage of 300KV, irradiation energy of 30kgy, and linear velocity of 20m / min.

[0061] 4) Apply an optical-grade PET release film to the surface of the solid adhesive film 4-3 prepared in 3), and then roll it up to obtain the electron beam cured hot melt optical adhesive film 4.

[0062] Example 5

[0063] The electron beam-cured hot melt optical adhesive film provided in this embodiment is prepared through the following steps:

[0064] 1) Weigh 80 kg of ethylene-vinyl acetate elastomer (VA content 33%, MI 15 g / 10 min), 10 kg of 1,6-hexanediol diacrylate, 4 kg of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2 kg of vinyltrimethoxysilane, 2 kg of vinyltriethoxysilane, 1 kg of 2,2'-methylene-bis-(4-methyl-6-tert-butylphenol), and 1 kg of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester and add them to a high-speed mixer for premixing until uniform. Dry thoroughly to form premix 5-1. The total mass of the small molecule functional components is 20 kg.

[0065] 2) The premix 5-1 prepared in step 1) is put into the hopper of the casting machine, melted at 110°C, plasticized, and filtered. The filtered melt is extruded through a T-die and coated onto an optical grade PET release film. The thickness is adjusted to form a 0.2 mm mixed melt 5-2.

[0066] 3) The mixed melt 5-2 prepared in step 2) is irradiated online with electron beam (EB) to obtain a solid film 5-3.

[0067] The electron beam irradiation conditions are: electron beam accelerator voltage of 300KV, irradiation energy of 30kgy, and linear velocity of 20m / min.

[0068] 4) Apply an optical-grade PET release film to the surface of the solid adhesive film 5-3 prepared in 3), and then roll it up to obtain the electron beam cured hot melt optical adhesive film 5.

[0069] Example 6

[0070] The only difference from Example 2 is that the acrylic monomer used is trimethylolpropane triacrylate, and the electron beam cured hot melt optical film 6 is obtained through the same preparation steps.

[0071] Example 7

[0072] The only difference from Example 2 is that the photoinitiator used is benzophenone, and the electron beam-cured hot melt optical film 7 is obtained through the same preparation steps.

[0073] Example 8

[0074] The only difference from Example 2 is that the silane coupling agent used is γ-glycidyl etheroxypropyltrimethoxysilane, and the electron beam cured hot melt optical film 8 is obtained through the same preparation steps.

[0075] Example 9

[0076] The formulation components and casting melt plasticizing process are exactly the same as those in Example 2. The difference lies in the electron beam irradiation parameters. The electron beam irradiation conditions are: voltage 100KV, irradiation energy 10kgy, and linear velocity 20m / min.

[0077] Example 10

[0078] The formulation components and casting melt plasticizing process are exactly the same as those in Example 2. The difference lies in the electron beam irradiation parameters. The electron beam irradiation conditions are: voltage 400KV, irradiation energy 50kgy, and linear velocity 20m / min.

[0079] Example 11

[0080] The formulation components and casting melt plasticizing process are exactly the same as those in Example 2. The difference lies in the electron beam irradiation parameters. The electron beam irradiation conditions are: voltage 500KV, irradiation energy 60kgy, and linear velocity 20m / min.

[0081] Example 12

[0082] The formulation components and casting melt plasticizing process are exactly the same as those in Example 2. The difference lies in the electron beam irradiation parameters. The electron beam irradiation conditions are: voltage 300KV, irradiation energy 30kgy, and linear velocity 15m / min.

[0083] Example 13

[0084] The formulation components and casting melt plasticizing process are exactly the same as those in Example 2. The difference lies in the electron beam irradiation parameters. The electron beam irradiation conditions are: voltage 300KV, irradiation energy 30kgy, and linear velocity 30m / min.

[0085] Example 14

[0086] The formulation components and electron beam irradiation parameters are exactly the same as those in Example 2, except that the thickness of the melt coating on the optical grade PET release film in step 2) is 0.1 mm.

[0087] Example 15

[0088] The formulation components and electron beam irradiation parameters are exactly the same as those in Example 2, except that the thickness of the melt coating on the optical grade PET release film in step 2) is 0.3 mm.

[0089] Example 16

[0090] The formulation components and electron beam irradiation parameters are exactly the same as those in Example 2, except that the thickness of the melt coating on the optical grade PET release film in step 2) is 0.5 mm.

[0091] Example 17

[0092] The formulation components and electron beam irradiation parameters are exactly the same as those in Example 2, except that the thickness of the melt coating on the optical grade PET release film in step 2) is 0.6 mm.

[0093] Example 18

[0094] The formulation components and electron beam irradiation parameters are exactly the same as those in Example 2, except that the thickness of the melt coating on the optical grade PET release film in step 2) is 0.8 mm.

[0095] Comparative Example 1

[0096] The difference from Example 2 is that it was not irradiated with an electron beam and the thickness was 0.2 mm.

[0097] Comparative Example 2

[0098] The difference from Example 6 is that it was not irradiated with an electron beam and the thickness was 0.2 mm.

[0099] Comparative Example 3

[0100] The difference from Example 7 is that it was not irradiated with an electron beam and the thickness was 0.2 mm.

[0101] Comparative Example 4

[0102] The difference from Example 8 is that it was not irradiated with an electron beam and the thickness was 0.2 mm.

[0103] Comparative Examples 5-9

[0104] The difference from Example 2 is that it was not irradiated with an electron beam, and the thicknesses were 0.1 mm, 0.3 mm, 0.5 mm, 0.6 mm and 0.8 mm, respectively.

[0105] To better demonstrate the beneficial effects of the technical solutions provided in this application, the following performance tests are conducted on Examples 1-18 and Comparative Examples 1-9:

[0106] 1. Adhesion force

[0107] Sample preparation method: The glass cover plate / optical adhesive / PET structure is stacked and pre-pressed in an 80℃ vacuum press for 100 seconds. After defoaming, a bubble-free sample is obtained, and then irradiated with an energy of 2000mJ / cm². 2 The sample was cured using a UV mercury lamp, and then peeled off at a speed of 500 mm / min at a 180-degree angle to measure the adhesion strength.

[0108] 2. Accelerated Aging Test under Humid Heat

[0109] The adhesion strength of the sample was tested after being subjected to a temperature of 65℃, a humidity of 95%, and a time of 500 hours.

[0110] 3. Degree of pre-crosslinking

[0111] Sample preparation method: After cutting the unbonded sample, it was extracted in xylene and then baked to calculate the degree of crosslinking.

[0112] 4. Degree of crosslinking

[0113] The glass cover / optical adhesive / PET layers are stacked and pre-pressed in an 80℃ vacuum press for 100 seconds. After defoaming, a bubble-free sample is obtained, and then irradiated with an energy of 2000 mJ / cm². 2 The sample was cured using a UV mercury lamp. After cutting the sample, it was extracted in xylene and baked to calculate the degree of crosslinking.

[0114] 5. Bubble line verification

[0115] A 10.5-inch glass cover plate and a matching functional sheet are laminated together using optical adhesive. The laminating machine is set to a lamination temperature of 80℃ and a pressure of 3kg, with pre-compression completed in 100 seconds. After defoaming, the surface is irradiated with an energy of 2000mj / cm². 2 Cured by UV mercury lamp.

[0116] Probabilistic testing: 20 samples were tested in each group, and the touch screen samples were observed under a strong light source.

[0117] 6. Large-size touchscreen bonding

[0118] One 80-inch glass cover plate and one matching functional sheet are laminated with optical adhesive. The laminating machine is set to a lamination temperature of 85℃ and a pressure of 4.5kg. The pre-pressing is completed in 200 seconds. After defoaming, the bubbles in the four corners and edges are observed.

[0119] The performance test results are shown in Tables 1 and 2.

[0120] Table 1. Performance test comparison between Examples 1-13 and Comparative Examples 1-4

[0121] sample Adhesion strength (N / cm) Adhesion strength under humid heat aging (N / cm) Degree of pre-crosslinking (%) Degree of crosslinking (%) Number of bubble threads per group Example 1 46 40 33 55 0 Example 2 48 43 32 66 0 Example 3 45 40 30 72 0 Example 4 43 36 38 65 0 Example 5 40 33 40 66 0 Example 6 30 24 30 35 0 Example 7 38 29 32 36 0 Example 8 15 Degumming 33 54 0 Example 9 55 35 11 63 1 Example 10 35 30 45 65 0 Example 11 30 27 52 66 0 Example 12 50 45 33 65 0 Example 13 48 44 33 68 0 Comparative Example 1 60 25 0 60 10 Comparative Example 2 55 22 0 55 8 Comparative Example 3 58 20 0 56 11 Comparative Example 4 50 20 0 55 15

[0122] As can be seen from the test comparison results in Table 1, compared with Comparative Example 1, Examples 1-5, under a suitable formulation system and employing electron beam irradiation pretreatment, exhibit a pre-crosslinking degree of approximately 30%. The small molecule functional components in the formulation system can undergo chemical bonding reactions with the resin polymer chains, making the multi-component formulation system more stable and inhibiting the physical migration of small molecule functional components. Compared with Comparative Example 1, the prepared hot-melt optical adhesive films 1-5 effectively avoid the formation of bubble lines. Although the initial adhesion strength is slightly reduced (but still remains above 40 N / cm), the adhesion strength remains excellent after damp heat aging. It can also be seen that the final crosslinking degree of the hot-melt optical adhesive film is not significantly related to the electron beam pretreatment, but rather to the photoinitiator and monomers in the formulation system.

[0123] The test results in Table 1 also show that, compared with Comparative Examples 2-4, the hot-melt optical adhesive films 6-8 prepared after electron beam irradiation pretreatment effectively avoid the formation of bubble lines. Compared with Example 2, Examples 6-8, due to the selection of different small-molecule functional components in their formulation systems, exhibit significant reductions in important properties such as initial adhesion, wet heat aging adhesion, and final crosslinking degree. Even compared with Comparative Examples 2-4, which were not pretreated with electron beam irradiation, Examples 6-8 show significant reductions in these important properties. This indicates that even with electron beam irradiation pretreatment, if a suitable formulation system is not selected, not only will the overall performance of the hot-melt optical adhesive film not be improved, but it will also decrease its overall performance. A possible reason is that mismatched small-molecule functional components undergo damage or side reactions under electron beam irradiation energy.

[0124] The test results in Table 1 also show that, compared to Example 2, Examples 9-11 used different electron beam irradiation energies. With increasing electron beam irradiation energy, the pre-crosslinking degree of the hot-melt optical adhesive film increased, while the initial adhesion decreased. The increase in electron beam irradiation energy did not affect the final crosslinking degree, further demonstrating that the final crosslinking degree of the hot-melt optical adhesive film after lamination is related to the small molecule functional components in its formulation system. Although the increase in electron beam irradiation energy led to a decrease in the initial adhesion of the optical adhesive film, the adhesion retention rate during wet heat aging was excellent, indicating that irradiation pretreatment can improve the stability of small molecule functional components in the formulation system. When the irradiation intensity reaches 30 kgy or higher, the formation of bubble lines can be completely prevented.

[0125] Compared with Example 2, the irradiation linear velocity in Examples 12-13 does not affect the overall performance of the hot melt optical adhesive film.

[0126] Table 2 Performance test comparison between Examples 14-18 and Comparative Examples 5-9

[0127] sample Adhesion strength (N / cm) Adhesion during damp heat aging (N / cm) Degree of pre-crosslinking (%) Degree of crosslinking (%) Large size fit (80 inches) corners and edge air bubbles Example 2 48 43 32 66 none Example 14 38 34 43 65 slight Example 15 48 40 30 62 none Example 16 52 44 22 66 none Example 17 55 40 15 68 none Example 18 56 36 10 63 none Comparative Example 1 60 25 0 60 Relatively dense Comparative Example 5 60 22 0 63 large-scale gathering Comparative Example 6 62 22 0 65 slight Comparative Example 7 65 20 0 62 none Comparative Example 8 63 25 0 60 none Comparative Example 9 62 23 0 62 none

[0128] As can be seen from the test comparison results in Table 2, Examples 14-18 and Example 2, using the same formulation system and the same preparation process, yielded hot melt optical adhesive films of different thicknesses. Under the same electron beam irradiation energy, the pre-crosslinking degree decreased with the increase of the hot melt adhesive film thickness, while the overall performance remained good. Due to its certain pre-crosslinking degree, the hot melt adhesive film can maintain good melt dimensional stability during the touch screen bonding process, avoiding stress compression on electronic components such as cover plates and functional sheets. Using a hot melt adhesive film with a thickness of 0.2 mm can also effectively prevent the problems of insufficient adhesive and bubbles at the four corners and edges of large-size touch screens (80 inches). In contrast, Comparative Examples 5-9 and Comparative Example 1, which did not use electron beam irradiation pretreatment, required hot melt adhesive films with a thickness of 0.5 mm or more to avoid insufficient adhesive and bubbles at the four corners and edges of large-size touch screens (80 inches).

[0129] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make many modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing an electron beam-cured hot melt optical adhesive film, characterized in that, The steps are as follows: 1) Weigh 70-90 parts by weight of ethylene-vinyl acetate elastomer and 10-30 parts by weight of small molecule functional additive components; then put them into a high-speed mixer for premixing until they are evenly mixed and fully dried to form premix 1; 2) The premix 1 prepared in step 1) is put into the hopper of the casting machine, melted and plasticized to obtain a melt. After the melt is filtered, it is coated on the release film and the thickness is adjusted to form a mixed melt 2 of 0.1 to 0.8 mm. 3) The mixed melt 2 prepared in step 2) is irradiated online with an electron beam to obtain a solid film 3; 4) Apply a release film to the surface of the solid adhesive film 3 prepared in step 3), and then roll it up to obtain the electron beam cured hot melt optical adhesive film.

2. The method for preparing an electron beam-cured hot melt optical adhesive film according to claim 1, characterized in that, The small molecule functional components consist of acrylate monomers, photoinitiators, silane coupling agents, and antioxidants.

3. The method for preparing an electron beam-cured hot melt optical adhesive film according to claim 2, characterized in that, The mass ratio of the acrylate monomer, photoinitiator, silane coupling agent, and antioxidant is 5-20:2-6:2-4:1-2.

4. The method for preparing an electron beam-cured hot melt optical adhesive film according to claim 1, characterized in that, The melting temperature in step 2) is 110°C.

5. The method for preparing an electron beam-cured hot melt optical adhesive film according to claim 1, characterized in that, The electron beam accelerator has a voltage of 100KV to 500KV, an irradiation energy of 10 to 60 kgy, and a linear velocity of 15 to 30 m / min.

6. The method for preparing an electron beam-cured hot melt optical adhesive film according to claim 1, characterized in that, The coating is applied by extrusion coating using a T-die.

7. The method for preparing an electron beam-cured hot melt optical adhesive film according to claim 1, characterized in that, The release film mentioned is a PET release film.

8. The method for preparing an electron beam-cured hot melt optical adhesive film according to claim 1, characterized in that, The ethylene-vinyl acetate elastomer is a resin with a VA content of 26% to 42%.

9. The method for preparing an electron beam-cured hot melt optical adhesive film according to claim 1, characterized in that, The acrylic monomers mentioned are one or a mixture of two or more of the following: trimethylolpropane triacrylate, pentaerythritol tetraacrylate, triallyl isocyanurate, pentaerythritol triacrylate, bis(trimethylolpropane) acrylate, and 1,6-hexanediol diacrylate. The photoinitiator is one or a mixture of two or more of 1-hydroxy ketone, benzophenone, acrylated benzophenone, dimethyl benzoyl ether, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; The silane coupling agent is one or a mixture of two of γ-glycidoxypropyltriethoxysilane, vinyltrimethoxysilane, γ-(methacryloyloxy)propyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, and vinyltriethoxysilane. The antioxidant is one or a mixture of two or more of 2,2'-methylene-bis-(4-methyl-6-tert-butylphenol), β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester, and tris(nonylphenyl) phosphite.

10. An electron beam-cured hot melt optical adhesive film, characterized in that, It is prepared by any one of the preparation methods described in claims 1-8.