A detachable optical adhesive film and its preparation method

Abstract

This invention discloses a detachable optical film and its preparation method, comprising a three-layer structure (edge ​​layer / intermediate layer / edge layer). An intermediate layer of acrylic resin is prepared by combining acrylic resin, a crosslinking agent, and a photoinitiator. An edge layer of acrylic resin is prepared by combining acrylic resin, a chain transfer agent, a crosslinking agent, a photoinitiator, and a polymerization inhibitor. The intermediate layer acrylic resin and the two edge layer acrylic resins are pumped into the middle mold cavity and the upper and lower edge layer mold cavities of a three-layer co-extrusion coating head, respectively, and sprayed onto a release film according to the required thickness through the lip of the coating head. Then, a release film is applied, and finally, the film is cured in a UV-cured oven and wound up to obtain the three-layer optical film. The intermediate and edge layers have good compatibility; the intermediate layer has high hardness, while the edge layers have low hardness and are easy to cut. The difference in initiator concentration gradient causes different polymerization rates between the layers. The soft layer, by adding a polymerization inhibitor, forms a relatively clear and defined boundary, which is beneficial for the integrity of the cut.

Description

Technical Field

[0001] This invention relates to optical adhesive film (OCA) for full lamination, which is a three-layer OCA adhesive prepared using multilayer co-extrusion technology. Background Technology

[0002] Optically Clear Adhesive (OCA) for full lamination is mainly used for bonding display modules such as LCDs and OLEDs to touch panels or cover plates. It is required to be colorless and transparent, with a light transmittance of over 95%, good bonding strength, and the ability to cure at room temperature or medium temperature. It also has the characteristics of low curing shrinkage, making it the best adhesive for touch screens at present.

[0003] As a crucial display material, OCA (Optical Cord Adhesive) requires high optical properties, adhesion, filler properties (also known as step followability), bonding reliability, and weather resistance. During the full lamination process, poor bonding or defects such as bubbles or other flaws often occur, resulting in defective or scrapped products. Because display modules are highly valuable, defective or scrapped products must be disassembled and re-laminated, thus requiring the OCA to be easily removable. Disassembly typically involves two methods: cold disassembly and hot disassembly. The former involves placing the defective product in an ultra-low temperature environment (usually below -100°C) to cause the OCA to lose its adhesiveness, thus separating the module and the OCA. Then, heating is used to separate the OCA from the glass cover. However, this method has the drawback of high energy consumption, and the ultra-low temperature environment also has a certain impact on module performance. The latter method involves placing defective products on a 70-90℃ disassembly platform, cutting the OCA in half with a metal wire, and then cleaning away any remaining OCA from the membrane assembly or cover plate. This method is simple and convenient, and is currently the mainstream disassembly method, but it requires the OCA to have very high disassemblyability. Highly efficient disassemblyability includes several elements: first, it must be very easy to cut; second, the cut OCA should remain intact on one side of the module (if the OCA remains on the cover plate side, the metal wire may damage the module during the cutting process); and third, the cut adhesive layer needs to have a certain mechanical strength to allow for efficient cleaning from the module or cover plate. When hot-cutting conventional OCA (single adhesive layer), sometimes the adhesive layer is cut as a whole, and sometimes it is completely cut apart. This results in difficulty in cutting, residue on both the cover plate and the module, loss of mechanical properties after cutting, and complete lack of hot disassembly capability, requiring only cold disassembly. Furthermore, single adhesive layer OCA usually cannot simultaneously possess strong filling mechanical properties, making it difficult to clean in the second step of cold disassembly.

[0004] To accommodate the hot-disassembly process, three-layer OCA structures are currently used: a soft layer, a hard layer, and a soft layer. Besides providing excellent filling properties, the soft layer is actively sacrificed during wire cutting to protect the hard layer from damage. The hard layer provides mechanical properties. Therefore, three-layer OCA is very easy to cut, cuts completely, and retains good mechanical properties after cutting. Currently, the common practice for producing three-layer OCA is to coat each layer separately or to bond several layers together after production. This cumbersome process results in low production efficiency, high waste, high cost, and also affects the yield rate of OCA.

[0005] Multilayer co-extrusion is a common method for producing functional plastic films, characterized by high production efficiency and simple process. However, applying multilayer co-extrusion technology to the production of three-layer OCA adhesives results in significant interlayer diffusion, leading to the following series of problems: First, after the inter-diffusion of the prepolymer adhesives in the intermediate hard layer and the upper and lower soft layers, incompatibility between polymers occurs, resulting in whitening and severely affecting optical transparency. Second, small-molecule functional additives in the intermediate hard layer diffuse into the upper and lower soft layers, altering the properties between the soft layers. Third, diffusion causes some polymer chains in the intermediate and upper and lower soft layers to penetrate from the hard layer into the soft layer during the curing process, resulting in an unclear interface between the hard and soft layers and affecting the integrity of the cut. Summary of the Invention

[0006] To solve the above problems, the present invention uses the following method to produce multilayer adhesive films:

[0007] This multilayer adhesive film production equipment uses a three-layer co-extrusion slotted coating head. Three types of adhesives—the middle hard layer and the top and bottom soft layers—enter the coating head (which has three independent cavities that converge into one layer at the lip) and are coated onto a polyester release film (thickness 50-200μm, peel weight 20-50g, also known as heavy film). Then, another layer of polyester release film (thickness 50-100μm, peel weight 1-10g, also known as light film) is applied, forming a polyester release film / three-layer adhesive film / polyester release film structure.

[0008] The three-layer film employs a soft / hard / soft layer structure. First, the prepolymer for the middle hard layer and the top and bottom soft layers uses the same acrylic resin, ensuring complete compatibility and preventing any whitening or optical defects. Second, a suitable crosslinking agent is added to the middle hard layer to increase hardness, while the soft layers contain no or only a small amount of crosslinking agent to ensure filling capacity and cutability. Third, utilizing the initiator concentration gradient, a relatively high concentration of initiator is added to the hard layer, and a relatively low concentration to the soft layers, allowing the middle hard layer to react more rapidly. Finally, an additional polymerization inhibitor is added to the soft layers to further delay their reaction, allowing the top and bottom soft layers to react only after the middle hard layer has fully or partially reacted, forming a clear and defined boundary that facilitates complete cutting.

[0009] The thickness of the intermediate hard layer ranges from 20 to 200 μm, and the thickness of the upper and lower soft layers ranges from 20 to 100 μm; the thickness of each layer includes, but is not limited to, 30, 50, 70, 100, 130, 150, and 180 μm.

[0010] Preferably, the total thickness of the three-layer structure is ≥150μm, while the thickness difference between the edge layer and the middle layer is ≤50μm, and the thickness of the middle layer is ≥ the thickness of any edge layer; more preferably, the thickness of the edge layer / middle layer / edge layer structure is 35~55μm / 40~80μm / 35~55μm.

[0011] The prepolymer of the intermediate hard layer and the upper and lower soft layers is a solvent-free, bulk UV-curable acrylic resin with a weight-average molecular weight ranging from 30,000 to 1,000,000 and a viscosity ranging from 500 to 30,000 cps. The weight-average molecular weight includes, but is not limited to, 50,000, 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000, and 900,000. The viscosity includes, but is not limited to, 1,000, 2,000, 3,000, 4,000, 5,000, 8,000, 10,000, 15,000, 20,000, and 25,000 cps.

[0012] The acrylic resin is composed of a polymer with an acrylate structure and corresponding monomers, wherein the monomers are monomers that polymerize to form the polymer with the acrylate structure. The monomers that polymerize to form the polymer with the acrylate structure are acrylate monomers. The "acrylate monomers" include alkyl acrylates, hydroxy acrylates, carboxyl acrylates, aryl acrylates, and some special acrylic monomers.

[0013] The alkyl acrylate is selected from the following monomers: 2-ethylhexyl (meth)acrylate, pentyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, hexyl (meth)acrylate, n-nonyl (meth)acrylate, isoamyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, isooctadecyl (meth)acrylate, 2-methylbutyl (meth)acrylate, bicyclodecane acrylate, cyclohexyl acrylate, and 3,3,5-trimethylcycloethyl acrylate. In preparing the acrylic resin described above, the alkyl acrylate used can be one or several of these monomers. (Meth)acrylate-2-ethylhexyl ester refers to 2-ethylhexyl methacrylate or 2-ethylhexyl acrylate; (Meth)acrylate-pentyl ester refers to pentyl methacrylate or pentyl acrylate; (Meth)acrylate-n-octyl ester refers to octyl methacrylate or octyl acrylate; other alkyl acrylate monomers are interpreted in the same way.

[0014] The hydroxy acrylate is selected from hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, etc. When preparing the acrylic resin, the hydroxy acrylate used can be one or more of these. Hydroxyethyl methacrylate refers to hydroxyethyl methacrylate or hydroxyethyl acrylate; hydroxypropyl methacrylate refers to hydroxypropyl methacrylate or hydroxypropyl acrylate; hydroxybutyl methacrylate refers to hydroxybutyl methacrylate or hydroxybutyl acrylate; other similar expressions are interpreted in the same way.

[0015] The acrylate carboxyl group (ester) is selected from acrylic acid, methacrylic acid, cyanoacrylic acid, ethylacrylic acid, n-propylacrylic acid, isobutylacrylic acid, itaconic acid (i.e., methylene succinic acid, H 2C=C(COOH)-CH 2-COOH), β-carboxyethyl acrylate, maleic acid, etc. When preparing the acrylic resin, the acrylate carboxyl group (ester) used can be one or several of these.

[0016] Aromatic acrylates refer to phenyl (meth)acrylate and 2-phenoxyethyl (meth)acrylate. When preparing high-purity acrylic adhesives, the aryl acrylate used can be one or several of these. Phenyl (meth)acrylate refers to phenyl methacrylate or phenyl acrylate, and 2-phenoxyethyl (meth)acrylate refers to 2-phenoxyethyl methacrylate or 2-phenoxyethyl acrylate.

[0017] The specific acrylic monomers are selected from ethyl 2-vinyloxyethoxy(meth)acrylate, hydroxyethylcaprolactone (meth)acrylate, tetrahydrofuran (meth)acrylate, N-vinylpyrrolidone, N-vinylcaprolactam, N-isobutoxymethylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, acetylacetone, acrylamide, acryloylmorpholine, acrylonitrile, styrene, methylstyrene, glycidyl (meth)acrylate, cyclotrimethylolpropane methyl acetal acrylate, etc. When preparing the acrylic resin, the specific acrylic monomers used can be one or several of these monomers. Ethyl 2-vinyloxyethoxy(meth)acrylate refers to ethyl 2-vinyloxyethoxymethacrylate or ethyl 2-vinyloxyethoxyacrylate; hydroxyethylcaprolactone (meth)acrylate refers to hydroxyethylcaprolactone methacrylate or hydroxyethylcaprolactone acrylate; tetrahydrofuran (meth)acrylate refers to tetrahydrofuran methacrylate or tetrahydrofuran acrylate; glycidyl (meth)acrylate refers to glycidyl (meth)acrylate or glycidyl methacrylate.

[0018] The amount of crosslinking agent added to the intermediate hard layer is between 0.05% and 2% (relative to 100 parts by weight of an acrylate-structured polymer solution); the amount of crosslinking agent added to the upper and lower soft layers is between 0% and 0.15% (relative to 100 parts by weight of an acrylate-structured polymer solution). According to some embodiments of the present invention, the amount of crosslinking agent added to the intermediate hard layer may be selected from 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.70%, 0.80%, 0.90%, 1.00%, 1.10%, 1.20%, 1.30%, 1.40%, 1.50%, 1.60%, 1.70%, 1.80%, or 1.90%, but is not limited to these examples. According to some embodiments of the present invention, the amount of crosslinking agent added to the upper and lower soft layers may be selected as 0.01%, 0.03%, 0.05%, 0.07%, 0.09%, 0.10%, 0.12% or 0.14%, but is not limited to these listed percentages.

[0019] The crosslinking agent may be selected from single crosslinking agents known in the industry, such as hexanediol diacrylate (HDDA), ethylene glycol dimethacrylate (EGDMA), polyethylene glycol n dimethacrylate (PEGnDMA), ethoxylated (2) bisphenol A dimethacrylate (E2BADMA), trimethylolpropane trimethacrylate (TMPTMA), diallyl phthalate (DAP), pentaerythritol acrylate (PETA), or trimethylolpropane triacrylate (TMPTA), as well as mixtures thereof.

[0020] High glass transition temperature monomers can also be added to the intermediate hard layer to further improve the hardness and heat resistance of the intermediate layer. The amount added is between 0-15 wt%.

[0021] The high glass transition temperature monomers are selected from ethyl 2-vinyloxyethoxy(meth)acrylate, hydroxyethylcaprolactone (meth)acrylate, tetrahydrofuran (meth)acrylate, N-vinylpyrrolidone, N-vinylcaprolactam, N-isobutoxymethylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, acrylamide, acrylamide, acrylamide, acrylonitrile, styrene, methylstyrene, glycidyl (meth)acrylate, cyclotrimethylolpropane methyl acetal acrylate, etc.

[0022] Chain transfer agents, such as dodecyl mercaptan and thioglycerol, can be added to the upper and lower soft layers to reduce the molecular weight of the colloid, which helps to further improve the easy cutting performance. The amount added is between 0-0.5%.

[0023] The concentration of the photoinitiator in the intermediate hard layer (e.g., 651) is between 0.05% and 0.5%; the amount of initiator added to the upper and lower soft layers is between 0% and 0.25%; the types of initiators can be the same or different; the difference between the photoinitiator concentration of the intermediate hard layer and the photoinitiator concentration of any soft layer is at least 0.05%, preferably not less than 0.2%.

[0024] The photoinitiator may be selected from benzophenone (BP), 4-methylbenzophenone (MBZ), 4-phenylbenzophenone (PBZ), benzoin diethyl ether (BDK), benzoin butyl ether, 2-hydroxy-methylphenylpropane-1-one (1173), 1-hydroxycyclohexylphenyl ketone (184), 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone (907), 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO), 2,4,6- Ethyl trimethylbenzoylphenylphosphonate (TPO-L), isopropylthioxanthone (ITX), ethyl 4-(N,N-dimethylamino)benzoate (EDAB), methyl o-benzoylbenzoate (1156), diphenyliodonium hexafluorophosphate (810), isooctyl para-N,N-dimethylaminobenzoate, methyl o-benzoylbenzoate (OMBB), α,α-dimethoxy-α-phenylacetophenone (651), and other single photoinitiators and mixtures thereof known in the industry.

[0025] Preferably, one or more of 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO), ethyl 2,4,6-trimethylbenzoyl phenylphosphonate (TPO-L), diethyl benzoyl ether (BDK), 2-hydroxy-methylphenylpropane-1-one (1173), and 1-hydroxycyclohexylphenyl ketone (184) are used.

[0026] The amount of polymerization inhibitor added to the upper and lower soft layers should be between 0.01% and 1%. Too little inhibitor will not delay curing, while too much will lead to incomplete curing. The amount of polymerization inhibitor can be selected from 0.05%, 0.10%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, or 0.95%, but is not limited to these listed percentages.

[0027] The polymerization inhibitors include common polymerization inhibitors such as hydroquinone, p-hydroxyanisole, 2,6-di-tert-butyl-p-cresol, 2,5-di-tert-butyl-p-hydroxyquinone, 2-tert-butyl-p-hydroxyquinone, p-benzoquinone, methylhydroquinone, phenathiazide (c), and β-phenylnaphthylamine (d).

[0028] The curing method is UV curing.

[0029] In addition to the aforementioned essential additives, antioxidants, rust inhibitors, and other additives can be added to the intermediate hard layer and the top and bottom soft layers, depending on the actual usage requirements.

[0030] The optical film with detachable properties obtained by the present invention has a three-layer structure, namely a soft layer / hard layer / soft layer. It is made of the above-mentioned acrylic resin, crosslinking agent, photoinitiator and polymerization inhibitor as the main raw materials. High glass transition temperature monomer, chain transfer agent, antioxidant, rust inhibitor and other commonly used additives in the art may also be added to the raw materials.

[0031] The raw material formulation of one type of hard layer (i.e., intermediate layer) of the removable optical adhesive film of the present invention mainly includes (calculated by mass percentage):

[0032] Acrylic resin 97.5-99.90%;

[0033] Crosslinking agent 0.05-2%;

[0034] Photoinitiator 0.05-0.5%.

[0035] The raw material formulation of one type of soft layer (i.e., edge layer) of the detachable optical adhesive film of the present invention mainly includes (calculated by mass percentage):

[0036]

[0037] Preferably, the acrylic resin is prepared by mixing 2-ethylhexyl acrylate, hydroxyethyl acrylate, isobornyl acrylate, and acrylic acid in a mass ratio of 6-8:0.8-1.2:0.8-1.2:1 to obtain a solution, adding a photoinitiator (containing 0.01%-0.25% in the solution) and a chain transfer agent (containing 0.01%-0.5% in the solution), and irradiating until the solution viscosity reaches 3000 cps before stopping the reaction.

[0038] Unless otherwise stated, the "%" used in this invention refers to a percentage by mass.

[0039] Compared with the prior art, the present invention has at least the following beneficial effects:

[0040] The preparation method of the present invention can prepare a three-layer optical film in one step. Compared with three-step coating processes, only a single coating process is required to complete the production. The preparation process is relatively simple, the cost is low, and the production efficiency is higher.

[0041] The preparation method of the present invention can prepare a three-layer optical film in one step, which solves the problems of large raw material loss and delamination that may occur during the use of the product when the three layers are coated in steps or bonded together.

[0042] The preparation method of the present invention can prepare a three-layer optical film in one step, overcoming the serious interlayer diffusion phenomenon in the conventional multilayer co-extrusion process, which cannot effectively obtain a three-layer product.

[0043] The preparation method of the present invention can easily adjust the performance of each layer of the three-layer optical film, and can adapt to more application scenarios.

[0044] The optically transparent adhesive film of the present invention has good disassembly, filling and bonding properties, and can be used as a display adhesive material. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0046] Preparation of acrylic resin A

[0047] 70 kg of 2-ethylhexyl acrylate, 10 kg of hydroxyethyl acrylate, 10 kg of isobornyl acrylate, 10 kg of acrylic acid, 0.2 kg of diethyl benzoate (photoinitiator BDK), and 0.1 kg of dodecyl mercaptan (chain transfer agent) were mixed and placed in a 200 L stainless steel reactor. Nitrogen gas was bubbled through the reactor to remove oxygen for 20 min. A low-pressure mercury lamp was turned on in the reactor to irradiate the solution. The reaction was stopped when the solution viscosity reached 3000 cps, yielding acrylic resin A. Acrylic resin A can be used in the following examples and comparative examples.

[0048] Example 1

[0049] Acrylic resin A (50 kg parts), hexanediol diacrylate (crosslinking agent HDDA 0.25 kg parts) and benzoin diethyl ether (photoinitiator BDK, 0.1 kg parts) were mixed evenly to obtain the intermediate layer acrylic resin.

[0050] Acrylic resin A (50 kg parts), benzoin diethyl ether (photoinitiator BDK, 0.1 kg parts), p-hydroxyanisole (polymerization inhibitor MEHQ, 0.25 kg parts), and dodecyl mercaptan (chain transfer agent, 0.1 kg parts) were mixed evenly to obtain a two-sided acrylic resin.

[0051] The intermediate layer acrylic resin and the two side layer acrylic resins are pumped into the middle mold cavity and the upper and lower side layer mold cavities of the three-layer co-extrusion coating head, respectively, and then sprayed onto the heavy release film through the lip of the coating head. A light release film is then applied, and finally, the mixture is cured in a UV oven and wound up to obtain a three-layer optical film. The thickness of each layer can be adjusted by the pumping flow rate, and the final thickness of each layer of the three-layer optical film is set to 50μm / 50μm / 50μm.

[0052] The optical properties, filling properties, bonding properties, and disassembly properties of the optical adhesive film were evaluated, and the results are shown in Table 1.

[0053] Example 2

[0054] The same intermediate layer acrylic resin as in Example 1 was used;

[0055] The same two-sided acrylic resin as in Example 1 was used;

[0056] The intermediate layer acrylic resin and the two side layer acrylic resins are pumped into the middle mold cavity and the upper and lower side layer mold cavities of the three-layer co-extrusion coating head, respectively, and then sprayed onto the heavy release film through the lip of the coating head. A light release film is then applied, and finally, the mixture is cured in a UV oven and wound up to obtain a three-layer optical film. The thickness of each layer can be adjusted by controlling the pumping flow rate, and the final thickness of each layer of the three-layer optical film is set to 35μm / 80μm / 35μm.

[0057] The optical properties, filling properties, bonding properties, and disassembly properties of the optical adhesive film were evaluated, and the results are shown in Table 1.

[0058] Example 3

[0059] The same intermediate layer acrylic resin as in Example 1 was used;

[0060] The same two-sided acrylic resin as in Example 1 was used;

[0061] The intermediate layer acrylic resin and the two side layer acrylic resins are pumped separately into the middle mold cavity and the upper and lower side layer mold cavities of the three-layer co-extrusion coating head, and then sprayed onto the heavy release film through the lip of the coating head. A light release film is then applied, and finally, the mixture is cured in a UV oven and wound up to obtain a three-layer optical film. The thickness of each layer can be adjusted by the pumping flow rate, and the final thickness of each layer of the three-layer optical film is set to 10μm / 130μm / 10μm.

[0062] The optical properties, filling properties, bonding properties, and disassembly properties of the optical adhesive film were evaluated, and the results are shown in Table 1.

[0063] Example 4

[0064] The same intermediate layer acrylic resin as in Example 1 was used;

[0065] The same two-sided acrylic resin as in Example 1 was used;

[0066] The intermediate layer acrylic resin and the two side layer acrylic resins are pumped separately into the middle mold cavity and the upper and lower side layer mold cavities of the three-layer co-extrusion coating head, and then sprayed onto the heavy release film through the lip of the coating head. A light release film is then applied, and finally, the mixture is cured in a UV oven and wound up to obtain a three-layer optical film. The thickness of each layer can be adjusted by the pumping flow rate, and the final thickness of each layer of the three-layer optical film is set to 55μm / 40μm / 55μm.

[0067] The optical properties, filling properties, bonding properties, and disassembly properties of the optical adhesive film were evaluated, and the results are shown in Table 1.

[0068] Example 5

[0069] The same intermediate layer acrylic resin as in Example 1 was used;

[0070] The same two-sided acrylic resin as in Example 1 was used;

[0071] The intermediate layer acrylic resin and the two side layer acrylic resins are pumped separately into the middle mold cavity and the upper and lower side layer mold cavities of the three-layer co-extrusion coating head, and then sprayed onto the heavy release film through the lip of the coating head. A light release film is then applied, and finally, the mixture is cured in a UV oven and wound up to obtain a three-layer optical film. The thickness of each layer can be adjusted by the pumping flow rate, and the final thickness of each layer of the three-layer optical film is set to 65μm / 20μm / 65μm.

[0072] The optical properties, filling properties, bonding properties, and disassembly properties of the optical adhesive film were evaluated, and the results are shown in Table 1.

[0073] Example 6

[0074] The same intermediate layer acrylic resin as in Example 1 was used;

[0075] Acrylic resin A (50 kg parts), benzoin diethyl ether (photoinitiator BDK, 0.1 kg parts), p-hydroxyanisole (polymerization inhibitor MEHQ, 0.25 kg parts), dodecyl mercaptan (chain transfer agent, 0.1 kg parts), and hexanediol diacrylate (crosslinking agent HDDA, 0.05 kg parts) were mixed evenly to obtain a two-sided acrylic resin.

[0076] The intermediate layer acrylic resin and the two side layer acrylic resins are pumped into the middle mold cavity and the upper and lower side layer mold cavities of the three-layer co-extrusion coating head, respectively, and then sprayed onto the heavy release film through the lip of the coating head. A light release film is then applied, and finally, the mixture is cured in a UV oven and wound up to obtain a three-layer optical film. The thickness of each layer can be adjusted by the pumping flow rate, and the final thickness of each layer of the three-layer optical film is set to 50μm / 50μm / 50μm.

[0077] The optical properties, filling properties, bonding properties, and disassembly properties of the optical adhesive film were evaluated, and the results are shown in Table 1.

[0078] Example 7

[0079] Acrylic resin A (45 kg parts), hexanediol diacrylate (crosslinking agent HDDA 0.25 kg parts), acrylamide morpholine (ACMO 5 kg parts) and benzoin diethyl ether (photoinitiator BDK, 0.1 kg parts) were mixed evenly to obtain the intermediate layer acrylic resin.

[0080] The same two-sided acrylic resin as in Example 1 was used;

[0081] The intermediate layer acrylic resin and the two side layer acrylic resins are pumped into the middle mold cavity and the upper and lower side layer mold cavities of the three-layer co-extrusion coating head, respectively, and then sprayed onto the heavy release film through the lip of the coating head. A light release film is then applied, and finally, the mixture is cured in a UV oven and wound up to obtain a three-layer optical film. The thickness of each layer can be adjusted by the pumping flow rate, and the final thickness of each layer of the three-layer optical film is set to 50μm / 50μm / 50μm.

[0082] The optical properties, filling properties, bonding properties, and disassembly properties of the optical adhesive film were evaluated, and the results are shown in Table 1.

[0083] Example 8

[0084] The same intermediate layer acrylic resin as in Example 1 was used;

[0085] Acrylic resin A (45 kg parts), acrylamide morpholine (ACMO 5 kg parts), benzoin diethyl ether (photoinitiator BDK, 0.1 kg parts), p-hydroxyanisole (polymerization inhibitor MEHQ 0.25 kg parts), and dodecyl mercaptan (chain transfer agent, 0.1 kg parts) were mixed evenly to obtain a two-sided acrylic resin.

[0086] The intermediate layer acrylic resin and the two side layer acrylic resins are pumped into the middle mold cavity and the upper and lower side layer mold cavities of the three-layer co-extrusion coating head, respectively, and then sprayed onto the heavy release film through the lip of the coating head. A light release film is then applied, and finally, the mixture is cured in a UV oven and wound up to obtain a three-layer optical film. The thickness of each layer can be adjusted by the pumping flow rate, and the final thickness of each layer of the three-layer optical film is set to 50μm / 50μm / 50μm.

[0087] The optical properties, filling properties, bonding properties, and disassembly properties of the optical adhesive film were evaluated, and the results are shown in Table 1.

[0088] Comparative Example 1

[0089] The same intermediate layer acrylic resin as in Example 1 was used;

[0090] The intermediate layer of acrylic resin is pumped into the middle mold cavity and the upper and lower side layer mold cavities of the three-layer co-extrusion coating head, and then sprayed onto the heavy release film through the lip of the coating head. A light release film is then applied, and finally, the film is cured in a UV oven and wound up to obtain a three-layer optical film. The thickness of each layer can be adjusted by the pumping flow rate, and the final thickness of each layer of the three-layer optical film is set to 50μm / 50μm / 50μm.

[0091] The optical properties, filling properties, bonding properties, and disassembly properties of the optical adhesive film were evaluated, and the results are shown in Table 1.

[0092] Comparative Example 2

[0093] Acrylic resin A (50 kg portions), benzoin diethyl ether (photoinitiator BDK, 0.1 kg portions), p-methoxyphenol (inhibitor MEHQ 0.25 kg portions), and dodecyl mercaptan (chain transfer agent, 0.1 kg portions) were mixed evenly to obtain a two-layer acrylic resin;

[0094] The two-layer acrylic resin was respectively pumped into the middle die cavity and the upper and lower two-layer die cavities of a three-layer co-extrusion die head, and was jointly sprayed on a heavy release film through the die lips of the die head, then covered with a light release film, and finally entered a UV light oven for curing and winding to obtain an optical adhesive film with a three-layer structure. The thickness between each layer can be adjusted by the pumping flow rate of each layer, and the thickness of each layer of the final three-layer structure optical adhesive film was set to 50 μm / 50 μm / 50 μm.

[0095] The optical properties, filling properties, bonding properties, and disassembly properties of the optical adhesive film were evaluated, and the results are shown in Table 1.

[0096] Comparative Example 3

[0097] The same middle-layer acrylic resin as in Example 1 was used;

[0098] Acrylic resin A (50 kg portions), benzoin diethyl ether (photoinitiator BDK, 0.1 kg portions), and dodecyl mercaptan (chain transfer agent, 0.1 kg portions) were mixed evenly to obtain a two-layer acrylic resin;

[0099] The middle-layer acrylic resin and the two-layer acrylic resin were respectively pumped into the middle die cavity and the upper and lower two-layer die cavities of a three-layer co-extrusion die head, and were jointly sprayed on a heavy release film through the die lips of the die head, then covered with a light release film, and finally entered a UV light oven for curing and winding to obtain an optical adhesive film with a three-layer structure. The thickness between each layer can be adjusted by the pumping flow rate of each layer, and the thickness of each layer of the final three-layer structure optical adhesive film was set to 50 μm / 50 μm / 50 μm.

[0100] The optical properties, filling properties, bonding properties, and disassembly properties of the optical adhesive film were evaluated, and the results are shown in Table 1.

[0101] In order to verify the relevant properties of the optical adhesive film, the following testing methods were adopted:

[0102] 1. Optical property test

[0103] After tearing off the light-side release film, it was bonded to optical glass. After tearing off the release film on the other side, it was put into the instrument for testing. The test was carried out 3 times in parallel and the average value was taken. The light transmittance ≥ 91% was qualified, otherwise it was unqualified. The test instrument was Hangzhou Caipu TH-09 haze meter.

[0104] 2. Filling performance test

[0105] Peel off the light release film and attach it to a clean cover glass with an ink step height of 20μm. Remove excess sample along the edge of the cover glass. Peel off the heavy release film and attach it to another identical piece of glass without an ink step. Place the prepared sample in a high-pressure degassing machine at 50℃ and 4kg for 10 minutes. After degassing, check if there are any residual air bubbles. If not, let it stand at 60℃ and 90% humidity for 24 hours and observe if any new air bubbles appear. Prepare 10 samples. If no air bubbles are generated in all 10 samples, the filling performance is qualified.

[0106] 3. Adhesion performance

[0107] Peel off the light release film and attach it to a clean cover glass with an ink step height of 20μm. Remove excess sample along the edge of the cover glass. Peel off the heavy release film and attach it to another identical piece of glass without an ink step. Place the prepared sample in a high-pressure degassing machine at 30℃ and 4kg for 10 minutes. After degassing, check for any residual air bubbles. Prepare 10 samples. If none of the 10 samples have residual air bubbles, the filling performance is considered satisfactory.

[0108] 4. Disassembly performance

[0109] Peel off the light release film and attach it to a clean cover glass with an ink step height of 20μm. Remove excess sample along the edge of the cover glass. Peel off the heavy release film and attach it to another identical glass without an ink step. Place the prepared sample in a high-pressure degassing machine at 50℃ with 4kg of degassing for 10 minutes and let it stand for 24 hours. Then place the sample on a heating platform at 80℃ and cut the adhesive layer with a 50μm thick molybdenum wire (cut twice). After cutting, separate the two pieces of glass and peel off the adhesive layer remaining on the glass. If the molybdenum wire breaks during the cutting process, the cut adhesive layer becomes powdery or granular, the two pieces of glass cannot be separated naturally after cutting, or the adhesive layer remaining on the glass cannot be peeled off as a whole, the disassembly performance is poor. Conversely, the disassembly performance is good.

[0110] Table 1. Performance of the optical films in Examples 1-8 and Comparative Examples 1-3

[0111] Serial Number project Optical performance Filling performance Adhesion performance Disassembly performance 1 Example 1 √ √ √ √ 2 Example 2 √ √ √ √ 3 Example 3 √ △ √ × 4 Example 4 √ √ √ √ 5 Example 5 √ √ √ × 6 Example 6 √ √ √ √ 7 Example 7 √ √ √ √ 8 Example 8 √ △ √ √ 9 Comparative Example 1 √ × △ × 10 Comparative Example 2 √ √ √ × 11 Comparative Example 3 √ √ √ △

[0112] Note: Excellent performance "√", average performance "△", poor performance "×"

[0113] As can be seen from Table 1, in Example 3, the thickness of the two side layers is too small to achieve effective filling, and therefore it cannot act as a sacrificial layer during cutting, thus lacking disassembly performance. In Example 5, the thickness of the middle layer is too small, resulting in poor disassembly performance. In Comparative Example 1, both the middle and side layer resins contain crosslinking agents, resulting in a high crosslinking density and cohesive force, but generally poor filling and bonding performance. Furthermore, the resin formulations of the middle and side layers are identical, with no obvious interlayer interface behavior, thus losing disassembly performance. In Comparative Example 2, neither the middle nor side layer resins contain crosslinking agents, resulting in low mechanical properties of the cured film. Although it has good filling and bonding performance, it still lacks interlayer interface behavior during cutting, leading to overall destruction and lack of disassembly performance. In Comparative Example 3, the two side layers do not contain polymerization inhibitors, resulting in simultaneous curing of the middle and side layers during curing, reducing interlayer interface behavior and making interlayer destruction easy to occur during cutting, resulting in poor disassembly performance.

[0114] Although the invention has been described herein with reference to illustrative embodiments, it should be understood that many other modifications and implementations can be devised by those skilled in the art, which will fall within the scope and spirit of the principles disclosed herein. More specifically, various variations and modifications can be made to the components and / or layout of the subject matter combination within the scope of this disclosure. Besides variations and modifications to the components and / or layout, other uses will be apparent to those skilled in the art.

Claims

1. A method for preparing a detachable optical adhesive film, characterized in that, Includes the following steps: (1) Prepare an intermediate layer acrylic resin by mass percentage of 97.5-99.90% acrylic resin, 0.05-2% crosslinking agent, and 0.05-0.5% photoinitiator; (2) Prepare a side layer acrylic resin by mass percentage of 98.2-99.96% acrylic resin, 0.01-0.5% chain transfer agent, 0.01-0.15% crosslinking agent, 0.01-0.25% photoinitiator and 0.01-1% polymerization inhibitor; (3) The intermediate layer acrylic resin and the two side layer acrylic resin are pumped into the middle mold cavity and the upper and lower side layer mold cavities of the three-layer co-extrusion coating head, respectively, and sprayed onto the release film according to the required thickness through the lip of the coating head. Then the release film is covered, and finally cured in a UV light oven and rolled up to obtain an optical adhesive film with a three-layer structure of side layer / intermediate layer / side layer. The acrylic resin used in steps (1) and (2) is composed of an acrylate polymer and / or corresponding monomers, including alkyl acrylate, hydroxy acrylate, carboxyl acrylate, aryl acrylate, and acryloylmorpholine; the acrylate polymer is obtained by mixing 2-ethylhexyl acrylate, hydroxyethyl acrylate, isobornyl acrylate, and acrylic acid in a mass ratio of 6-8:0.8-1.2:0.8-1.2:1 to obtain a solution, adding a photoinitiator and a chain transfer agent, and irradiating until the solution viscosity reaches 3000 cps before stopping the reaction. The photoinitiator added to the solution is 0.01%-0.25%, and the chain transfer agent added to the solution is 0.01%-0.5%. The crosslinking agent is hexanediol diacrylate, the photoinitiator is benzoin diethyl ether, the chain transfer agent is dodecyl mercaptan, and the polymerization inhibitor is p-hydroxyanisole.

2. The method for preparing a detachable optical adhesive film according to claim 1, characterized in that, The three-layer co-extrusion coating head has three independent cavities that converge into one layer at the lip.

3. The method for preparing a detachable optical adhesive film according to claim 1, characterized in that, The difference between the photoinitiator content of the intermediate layer and the photoinitiator content of any edge layer is greater than or equal to 0.2%.

4. The method for preparing a detachable optical adhesive film according to claim 1, characterized in that, The thickness of the edge layer is 20-100 μm, and the thickness of the middle layer is 20-200 μm.

5. The method for preparing a detachable optical adhesive film according to claim 4, characterized in that, The total thickness of the three-layer structure is ≥150μm, while the thickness difference between the edge layer and the middle layer is ≤50μm, and the thickness of the middle layer is ≥ the thickness of any edge layer.

6. The method for preparing a detachable optical adhesive film according to claim 5, characterized in that, The thickness of the edge layer / intermediate layer / edge layer structure is 35~55μm / 40~80μm / 35~55μm.

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