Adhesive composition, optical protective film and preparation method thereof

Abstract

The invention relates to an adhesive composition, an optical protective film and a preparation method of the optical protective film, and belongs to the technical field of optical films. The composition comprises 100 parts of acrylate copolymer resin, 5-20 parts of tackifying resin, 3-10 parts of core-shell structure dynamic response microspheres A, 2-8 parts of hollow stress dissipation microspheres B, 0.5-2.5 parts of an end-capping cross-linking agent and 0.2-1.5 parts of an epoxy silane coupling agent. The optical protective film comprises a PET base material layer and a 18-20 [mu] m gradient structure adhesive layer prepared from the composition. The preparation method comprises the following steps: step-by-step mixing, delayed crosslinking, settlement gradient structure distribution and a three-section procedure curing process. Through cooperation of the bifunctional microspheres and the gradient structure design, perfect surface attachment of the high-haze polaroid is achieved under the thick adhesive layer, the stripping force is excellent in time stability, the system is free of PFAS, the contradiction between the filling property and cohesive stability of a traditional adhesive is solved, and the OLED display screen polaroid protection requirement is met.

Description

Technical Field

[0001] This application relates to the field of optical film technology, specifically to an adhesive composition, an optical protective film, and a method for preparing the same. Background Technology

[0002] In OLED display manufacturing, the polarizers on their surfaces are typically covered with a temporary protective film to prevent damage. To improve visual comfort, high-end polarizers generally undergo anti-glare treatment, creating a specific micro-rough surface, such as the AG LR40% specification, which has high haze and a rough surface. This presents a significant challenge to the adhesive layer of the protective film: the adhesive layer needs to be thick enough to fill the rough microstructure, but it must also avoid the risk of residual adhesive due to a sharp increase in peel force over time caused by adhesive creep. Simultaneously, global environmental regulations strictly prohibit the use of PFAS substances, imposing stringent requirements on the environmental friendliness of the adhesive layer.

[0003] Current technologies often involve adjusting the amount of tackifying resin or crosslinking agent in basic acrylic adhesives, or simply adding ordinary fillers. However, these methods struggle to ensure long-term stable peel strength while simultaneously increasing adhesive layer thickness to fully adhere to high-haze surfaces. The fundamental reason is that traditional homogeneous adhesive layer structures cannot synergistically resolve the contradiction between interfacial filling and cohesive reinforcement. Therefore, a novel approach to adhesive layer material design and structural construction is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a novel adhesive composition, an optical protective film, and a method for preparing the same.

[0005] To solve the above-mentioned technical problems, this application can be implemented through the following technical solutions:

[0006] This application provides an adhesive composition comprising, by weight, the following components: 100 parts of acrylate copolymer resin; 5-20 parts of tackifying resin; Dynamic response microspheres A3-10 parts; Stress dissipation microspheres B2-8 parts; 0.5–2.5 parts of end-capping crosslinking agent; 0.2–1.5 parts of epoxy-based silane coupling agent; Among them, the dynamic response microsphere A is a temperature-sensitive core-shell polymer microsphere with a core-shell structure. The core is selected from at least one of polystyrene, polybutadiene, or acrylate elastomers, and the shell is a polymer containing temperature-sensitive polymer segments. The stress dissipation microsphere B is a microsphere with a hollow structure. The adhesive composition is configured to spontaneously layer and form a gradient structure.

[0007] As a further improvement of this application, the crosslinking agent is a capped isocyanate.

[0008] As a further improvement to this application, the tackifying resin is selected from at least one of hydrogenated terpene resin, hydrogenated rosin resin, and C5 / C9 petroleum resin.

[0009] As a further improvement of this application, the tackifying resin is 10-14 parts by weight, the dynamic response microsphere A is 4-8 parts by weight, and the stress dissipation microsphere B is 3-7 parts by weight.

[0010] To achieve the above objectives, this application also provides an optical protective film, comprising a PET substrate layer and an adhesive layer disposed on any one side surface of the PET substrate layer, wherein the adhesive layer is prepared from the adhesive composition according to any one of claims 1-4.

[0011] As a further improvement of this application, the thickness of the adhesive layer is 18–20 μm.

[0012] As a further improvement of this application, the adhesive layer has a gradient structure: the side of the adhesive layer closest to the PET substrate layer is a cohesive reinforcement layer, which includes 1% to 30% of the total weight of the dynamic response microspheres A; the side of the adhesive layer furthest from the PET substrate layer is an interface adaptation layer, which includes 70% to 99% of the total weight of the dynamic response microspheres A.

[0013] To achieve the above objectives, this application also provides a method for preparing the aforementioned optical protective film, comprising the following steps: S1. Preparation of premix A: Mix 50% by weight of acrylate copolymer resin, tackifying resin, dynamic response microspheres A and silane coupling agent at low speed under moisture-free conditions to obtain premix A. S2. Preparation of dispersion B: Stress dissipation microspheres B and 50% of the total weight of silane coupling agent are dispersed in a solvent by high-speed shearing to obtain dispersion B. S3. Mixing and Crosslinking: Mix premix A and dispersion B, and add crosslinking agent online before coating to perform instantaneous mixing and crosslinking to obtain coating liquid; S4. Gradient structure coating: The coating liquid enters the single-layer coating die head, and the viscosity difference is used to make the coating liquid settle in layers. After a preset set time of settling, a gradient distribution composite wet film is formed. S5. Curing: After the substrate layer and the composite wet film thereon pass through the first zone at a temperature of 70-85℃, the second zone at a temperature of 100-115℃, and the third zone at a temperature of 125-140℃, the composite wet film is cured to form a dry film, thus obtaining an optical protective film.

[0014] As a further improvement of this application, in step S4, the composite wet film includes a lower wet film and an upper wet film, and the ratio of the film thickness of the lower wet film to the upper wet film is in the range of 6:4 to 7:3.

[0015] As a further improvement of this application, in step S5, the temperature of the first zone is 80°C, the temperature of the second zone is 110°C, and the temperature of the third zone is 130°C.

[0016] As a further improvement to this application, the solvent is selected from at least one of butanone, ethyl acetate, butyl acetate, and toluene.

[0017] The specific benefits of this application are as follows: This application designs a composite adhesive layer system containing specific two-component functional microspheres, and constructs an asymmetric functional gradient structure in space through stepwise mixing and sedimentation gradient structure distribution process. Thus, with an adhesive layer thickness of 18-20 μm, it simultaneously achieves perfect adhesion to high haze surfaces and excellent long-term stability of peel force, and the entire system does not contain PFAS (per- and polyfluoroalkyl substances). Detailed Implementation

[0018] Based on the technical problems to be solved in the background art, this application provides an adhesive composition, which, by weight, comprises the following components: 100 parts of acrylate copolymer resin; 5-20 parts of tackifying resin; Dynamic response microspheres A3-10 parts; Stress dissipation microspheres B2-8 parts; 0.5–2.5 parts of end-capping crosslinking agent; 0.2–1.5 parts of epoxy-based silane coupling agent; Among them, the dynamic response microsphere A is a temperature-sensitive core-shell polymer microsphere with a core-shell structure. The core is selected from at least one of polystyrene, polybutadiene, or acrylate elastomers, and the shell is a polymer containing temperature-sensitive polymer segments. The stress dissipation microsphere B is a microsphere with a hollow structure. The adhesive composition is configured to spontaneously layer and form a gradient structure.

[0019] Based on the above technical solutions, acrylate copolymer resin serves as the main film-forming substance in the adhesive composition, providing basic adhesion and film-forming properties; the tackifying resin improves the initial adhesion to rough surfaces without significantly reducing the cohesive force of the adhesive layer; the dynamic response microsphere A has a core-shell structure, with its core being a cross-linked acrylate elastomer and its shell containing temperature-sensitive polymeric segments, enabling it to dynamically respond to temperature changes, effectively filling the microstructure on the polarizer surface without causing an abnormal increase in the modulus of the adhesive layer; the stress dissipation microsphere B has a hollow elastic wall structure, which is formed by gas expansion and, when subjected to peeling... When stress is released, the interfacial stress concentration is dispersed through elastic deformation, preventing interfacial damage and residual adhesive. The crosslinking agent is used to form a chemical crosslinking network to enhance the cohesion of the adhesive layer and inhibit creep. The silane coupling agent is used to improve the interfacial bonding force and component compatibility between the adhesive layer and the substrate and polarizer surface. The solvent is used for the uniform dispersion of each component and the coating process. The above components work synergistically in a specific ratio to fundamentally solve the contradiction between interfacial filling, cohesive strength and stress dispersion ability that is difficult to balance in traditional homogeneous adhesives while satisfying excellent optical transparency. Moreover, the entire composition system does not contain perfluorinated or polyfluoroalkyl substances.

[0020] In an optional embodiment, the acrylate copolymer resin is a hydroxy acrylate copolymer with a weight-average molecular weight (Mw) of 200,000–600,000 g / mol, a glass transition temperature (Tg) of -10°C to +10°C, and a hydroxyl value of 20–50 mg KOH / g. It can be selected from at least one of DIC CT-6060 (Japan) and Dow B-48N (USA). The hydrogenated terpene resin has a softening point of 100–130°C and a molecular weight of 500–2000, and can be selected from the commercially available Eastman H-100. The end-capped isocyanate crosslinking agent has the following characteristics: end-capping agent type: butanone oxime; NCO content: e.g., 6.5%–9.1%; uncapping temperature: e.g., 90–110°C. The epoxy silane coupling agent can be γ-glycidoxypropyltrimethoxysilane (KH-560). In an optional implementation, the dynamic response microspheres A are prepared using a seed emulsion polymerization method or a soap-free emulsion polymerization method. The core of the microsphere is polystyrene (PS) or polybutadiene (PB) with a glass transition temperature (Tg) < 0℃, and the shell is a poly(N-isopropylacrylamide) (PNIPAM) copolymer. The overall particle size of the microspheres is controlled at 80-200 nm, the shell thickness is 20-50 nm, and the low critical solution temperature (LCST) of the poly(N-isopropylacrylamide) copolymer is 30-35℃. The specific preparation steps are as follows: First, a polystyrene (PS) or polybutadiene (PB) seed emulsion is synthesized. Then, N-isopropylacrylamide monomer and a crosslinking agent are added to the seed emulsion system. Through a polymerization reaction, the N-isopropylacrylamide monomer polymerizes on the surface of the polystyrene (PS) or polybutadiene (PB) seed to form a poly(N-isopropylacrylamide) (PNIPAM) copolymer shell, ultimately obtaining the core-shell structured dynamic response microspheres A.

[0021] In an optional implementation, stress-dissipating microspheres B are prepared by suspension polymerization. The outer shell of the microspheres is composed of a vinylidene chloride (VDC)-acrylonitrile (AN) copolymer, wherein the content of vinylidene chloride is greater than 50%, and isobutane or isopentane is encapsulated inside as a gas. The median particle size (D50) of the microspheres is controlled between 5-20 μm, and the shell wall thickness is 0.1-0.5 μm. The specific preparation steps are as follows: First, an oil phase system containing a foaming agent is prepared, and then the oil phase system is dispersed in an aqueous phase to form a stable suspension system. By initiating a polymerization reaction, vinylidene chloride and acrylonitrile copolymerize in the suspension system to form a vinylidene chloride (VDC)-acrylonitrile (AN) copolymer shell wall. At the same time, isobutane or isopentane is encapsulated inside the shell wall, and finally, a hollow microsphere, namely stress-dissipating microspheres B, is obtained.

[0022] In an optional implementation, the end-capping crosslinking agent is an end-capped isocyanate. The crosslinking agent is specifically limited to end-capped isocyanates to adapt to the delayed crosslinking process design while ensuring the stable construction of the crosslinked network in the adhesive layer. The molecular structure of end-capped isocyanates contains isocyanate groups protected by the end-capping agent. Under normal temperature or low-speed mixing conditions, the end-capping agent will not detach, and the isocyanate groups will not undergo crosslinking reactions. Therefore, it can be added online before coating, avoiding pre-crosslinking of the adhesive and a sharp increase in viscosity caused by premature addition of the crosslinking agent, thus ensuring the working life and coating performance of the adhesive. During the medium-high temperature stage (100–140°C) of the subsequent curing process, the end-capping agent will be decapsulated by heat, releasing active isocyanate groups, which will undergo crosslinking reactions with active hydrogen in components such as acrylate copolymer resins, gradually building a stable chemical crosslinked network. The crosslinking reaction can be carried out in stages (preliminary crosslinking → complete crosslinking), matching the programmed curing process, gradually increasing the cohesive force of the adhesive layer, and avoiding excessive internal stress and decreased adhesion caused by rapid crosslinking. Compared to ordinary crosslinking agents, the crosslinking reaction of end-capped isocyanates has temperature controllability, which perfectly matches the overall process system of stepwise mixing, gradient coating and programmed curing of this invention. It is a key component design to ensure the stability of the adhesive layer over time.

[0023] In an optional implementation, the epoxy-based silane coupling agent possesses a bifunctional molecular structure, enabling efficient coupling between the adhesive layer and the inorganic / organic interface while simultaneously improving the compatibility of the components. One end of the epoxy-based silane coupling agent molecule contains a hydrolyzable siloxane group, which hydrolyzes to generate silanol groups. These silanol groups can undergo condensation reactions with active groups such as hydroxyl groups on the PET substrate and polarizer surface, forming chemical bonds and significantly enhancing the interfacial adhesion between the adhesive layer and the substrate / polarizer, preventing delamination, bubbles, and other problems after bonding. The epoxy group at the other end of the molecule has high reactivity and can react with organic components such as acrylate copolymer resins and the temperature-sensitive polymeric segments of the A-shell of dynamically responsive microspheres, combining the inorganic and organic phases into a unified whole, thereby improving the overall cohesiveness and structural stability of the adhesive layer. Meanwhile, the addition of epoxy silane coupling agent can improve the dispersion of dynamic response microspheres A and stress dissipation microspheres B in acrylate copolymer resin matrix, avoid the uneven performance of adhesive layer caused by microsphere agglomeration, ensure the optical transparency and functional consistency of adhesive layer, and adapt to the optical performance requirements of OLED display.

[0024] In an optional embodiment, the tackifying resin is selected from at least one of hydrogenated terpene resin, hydrogenated rosin resin, and C5 / C9 petroleum resin.

[0025] In an optional embodiment, the tackifying resin comprises 10-14 parts by weight, the dynamic response microspheres A comprises 4-8 parts by weight, and the stress dissipation microspheres B comprises 3-7 parts by weight. The preferred ratio of the tackifying resin, dynamic response microspheres A, and stress dissipation microspheres B is defined based on the optimal synergistic effect of each component's function and is the best ratio range verified through multiple embodiments. The preferred range of tackifying resin is 10-14 parts, which, compared to a wider range of 5-20 parts, ensures sufficient tackification, resulting in moderate initial tack of the adhesive layer on rough surfaces with high haze, without causing a decrease in the cohesion of the adhesive layer or an increase in creep due to excessive tackifying resin. The preferred range of dynamic response microspheres A is 4-8 parts, which ensures that it forms sufficient physical cross-linking points in the adhesive layer, allowing the thermo-responsive filling and reinforcing functions to be fully utilized, while avoiding excessive microspheres that would cause the adhesive layer to become too hard and the adhesion to be too sensitive to pressure. The preferred range of stress dissipation microspheres B is 3-7 parts, which can achieve efficient dispersion of peel stress, while avoiding excessive hollow microspheres that would cause the overall modulus of the adhesive layer to be too low or the creep resistance to decrease. Under this preferred formulation, the initial tack of the tackifying resin, the filling and physical cross-linking effect of the dynamic response microspheres, and the stress dispersion effect of the stress dissipation microspheres can achieve the best balance, so that the adhesive layer has excellent adhesion, stable peel force, and good creep resistance. As can be seen from the data of the examples, the peel force change rate of the adhesive layer within this formulation range after aging at 60°C for 168 hours can be controlled within +15%. There are no bubbles in the bonding and no adhesive residue after peeling. It is the optimal formulation design for high haze anti-glare polarizing film such as AG LR40%.

[0026] To achieve the above objectives, this application also provides an optical protective film, comprising a PET substrate layer and an adhesive layer disposed on any one surface of the PET substrate layer, wherein the adhesive layer is prepared from the adhesive composition described above. PET is used as the substrate layer because PET film possesses excellent optical transparency, mechanical strength, temperature resistance, and weather resistance, and will not affect the optical detection of the OLED display. Simultaneously, it can effectively prevent physical damage such as scratches and collisions to the polarizer during production and transportation. The adhesive layer, disposed on any one surface of the PET substrate layer, can be flexibly bonded according to production process requirements. The adhesive layer, prepared from the aforementioned adhesive composition, inherits the core properties of the composition, including good filling properties, high cohesion, stable peel force, and PFAS-free properties. It can tightly adhere to the rough surface of the polarizer treated with high haze anti-glare, without bubbles or edge lifting. Furthermore, in subsequent peeling processes, the peel force is moderate and there is no adhesive residue, avoiding secondary damage to the polarizer surface. The combination of the PET substrate layer and the adhesive layer achieves the dual functions of physical protection and interface compatibility, solving the technical problems of poor adhesion of traditional optical protective films on high-haze polarizers, sharp increase in peel force after aging, and easy residue of adhesive. Moreover, the overall film layer has excellent optical performance and is suitable for the production requirements of high-end OLED display devices.

[0027] In an optional implementation, the adhesive layer has a thickness of 18–20 μm. This thickness is designed to match the microscopic roughness of the high-haze anti-glare polarizer while also ensuring the cohesive stability of the adhesive layer. The surface of high-haze anti-glare polarizers such as AG LR40% has micrometer-level micro-grooves and protrusions. The adhesive layer needs to be thick enough to completely fill these microstructures and achieve a bubble-free, tight bond. If the adhesive layer thickness is insufficient (e.g., 12 μm), it cannot fill the micro-grooves, resulting in bubbles and rainbow-like patterns after bonding, thus failing both the protective function and the bonding effect. A thickness of 18–20 μm is the optimal range verified by the process. This ensures that the adhesive layer can fully wet and fill the rough microstructure of the polarizer to achieve perfect adhesion, while avoiding the increased risk of colloid creep and the sharp increase in peel force over time due to excessive adhesive layer thickness. At the same time, combined with the gradient structure design and synergistic effect of the bifunctional microspheres of this invention, the 18–20 μm thick adhesive layer can effectively suppress colloid creep and ensure long-term stability of peel force by means of both chemical cross-linking network and physical cross-linking points, while ensuring filling performance. This solves the technical problem of the inability to achieve both filling performance and stability in thick adhesive layers in traditional technologies.

[0028] In an optional implementation, the adhesive layer has a gradient structure: the side of the adhesive layer closest to the PET substrate layer is a cohesive reinforcement layer, which comprises 1% to 30% of the total weight of the dynamic response microspheres A; the side of the adhesive layer furthest from the PET substrate layer is an interface adaptation layer, which comprises 70% to 99% of the total weight of the dynamic response microspheres A. This gradient structure works based on a functional partitioning design, allowing the adhesive layer to perform dedicated functions of interface adaptation and cohesive reinforcement in the thickness direction, maximizing the role of each component. The interface adaptation layer directly contacts the rough surface of the polarizer, enriching all the stress dissipation microspheres B and most of the dynamic response microspheres A. The dynamic response microspheres A soften during heating and bonding, fully filling the microstructure of the polarizer to achieve bubble-free bonding. After cooling, they harden to form physical cross-linking points, improving the structural stability at the interface. The stress dissipation microspheres B disperse stress concentration at the interface during peeling, preventing interface damage and residual adhesive, achieving optimal interface adaptation and stress dispersion. The cohesive reinforcement layer is bonded to the PET substrate layer and is rich in acrylate copolymer resin and a small amount of dynamic-responsive microspheres A. With the main resin as the core and a chemical cross-linking network, it constructs the core cohesive framework of the adhesive layer, enhancing the overall cohesive strength and creep resistance of the adhesive layer, inhibiting the overall creep behavior of the colloid, and ensuring long-term stability of peel force. Simultaneously, the small amount of dynamic-responsive microspheres A can improve the interlayer bonding force between the cohesive reinforcement layer and the interface adaptation layer, preventing delamination. This asymmetric gradient structure abandons the traditional homogeneous adhesive layer design, achieving perfect interfacial adhesion and excellent cohesive stability through functional partitioning.

[0029] To achieve the above objectives, this application also provides a method for preparing the aforementioned optical protective film, comprising the following steps: S1. Preparation of premix A: Mix 50% by weight of acrylate copolymer resin, tackifying resin, dynamic response microspheres A and silane coupling agent at low speed under moisture-free conditions to obtain premix A. S2. Preparation of dispersion B: Stress dissipation microspheres B and 50% of the total weight of silane coupling agent are dispersed in a solvent by high-speed shearing to obtain dispersion B. S3. Mixing and Crosslinking: Mix premix A and dispersion B, and add crosslinking agent online before coating to perform instantaneous mixing and crosslinking to obtain coating liquid; S4. Gradient structure coating: The coating liquid enters the single-layer coating die head, and the viscosity difference is used to make the coating liquid settle in layers. After a preset set time of settling, a gradient distribution composite wet film is formed. S5. Curing: After the substrate layer and the composite wet film thereon pass through the first zone at a temperature of 70-85℃, the second zone at a temperature of 100-115℃, and the third zone at a temperature of 125-140℃, the composite wet film is cured to form a dry film, thus obtaining an optical protective film.

[0030] The above technical solution, through a stepwise mixing, delayed crosslinking, utilization of viscosity difference sedimentation gradient structure, and programmed curing integrated process design, transforms the above adhesive composition into an adhesive layer with a gradient structure, ensuring the full utilization of the functions of each component and the precise construction of the gradient structure, ultimately achieving the excellent performance of the optical protective film. In step S1, when preparing premix A, the acrylate copolymer resin, tackifying resin, dynamic response microspheres A, and 50% by weight of silane coupling agent are mixed at low speed under moisture-free conditions. Low-speed mixing avoids damage to the core-shell structure of the dynamic response microspheres A, and moisture isolation prevents premature hydrolysis of the silane coupling agent and side reactions of the crosslinking agent, ensuring the component uniformity and structural integrity of premix A. In step S2, when preparing dispersion B, stress dissipation microspheres B and the remaining 50% by weight of silane coupling agent are dispersed by high-speed shearing in a solvent. High-speed shearing ensures the hollow structure of the stress dissipation microspheres B... The microspheres are uniformly dispersed in the solvent without agglomeration. Simultaneously, the silane coupling agent modifies the surface of the microspheres, improving their compatibility with the host resin. Step S3, mixing and crosslinking, employs a delayed crosslinking design of "adding the crosslinking agent online before coating and mixing instantaneously." This avoids pre-crosslinking and viscosity increase in the adhesive caused by premature addition of the crosslinking agent, ensuring the coating performance and service life of the adhesive. Instant mixing ensures uniform dispersion of the crosslinking agent in the adhesive. Step S4, gradient structure coating, utilizes the viscosity difference between premix A and dispersion B (the viscosity of premix A is much higher than that of dispersion B). After premix A and dispersion B are combined... Due to the inherent physical properties that prevent uniform mixing, the mixture of premix A and dispersion B will exhibit stratification during coating and leveling on the substrate: the high-density component sinks, and the dynamic response microspheres A, with their higher density, tend to sink downwards (towards the substrate) along with the high-viscosity premix A; the low-density component rises, and the stress-dissipating microspheres B, with their extremely low density, naturally migrate upwards (towards the air) along with the low-viscosity dispersion. By pre-setting the settling time, a precise gradient structure is constructed, preventing random distribution of microspheres in the thickness direction and ensuring the effectiveness of functional zoning. The three-stage curing process in step S5 not only... The matching of component performance changes also "freezes" the gradient distribution of the premixed material A at the bottom and dispersion B at the top. Specifically: the first zone (70–85℃) achieves gradual solvent evaporation and softening of the shell of the dynamically responsive microspheres A, ensuring the flow and filling of the adhesive layer; the second zone (100–115℃) achieves the desealing of the end-capping crosslinking agent and preliminary crosslinking, constructing a basic crosslinking network; the third zone (125–140℃) achieves complete crosslinking and a firm bond between the shell of the dynamically responsive microspheres A and the colloidal network, forming a dual network of chemical and physical crosslinking, ensuring the cohesion and stability of the adhesive layer. The entire preparation process is interconnected, with process parameters highly adapted to component performance, which is the key guarantee for achieving the gradient structure adhesive layer and its excellent performance.

[0031] In an optional implementation, in step S4, the composite wet film comprises a lower wet film and an upper wet film, wherein the thickness ratio of the lower wet film to the upper wet film ranges from 6:4 to 7:3. This thickness ratio design matches the functional requirements of the gradient structure, taking into account both the filling performance of the interface adaptation layer and the stability performance of the cohesive reinforcement layer. The lower wet film is the interface adaptation layer in contact with the polarizer. A thickness ratio of 6:4 to 7:3 ensures that the interface adaptation layer occupies the majority of the adhesive layer's thickness, guaranteeing sufficient distribution of dynamic response microspheres A and stress dissipation microspheres B at the interface. This effectively fills the microscopic roughness of the polarizer's structure while achieving efficient stress dispersion. If the interface adaptation layer is too thin, the interface adaptation function of the bifunctional microspheres cannot be fully utilized. The upper wet film is the cohesive reinforcement layer bonded to the PET substrate, occupying 30% to 40% of the adhesive layer's thickness. This ensures sufficient main resin to construct the core cohesive framework, improving the overall creep resistance of the adhesive layer. If the cohesive reinforcement layer is too thin, the overall cohesive force of the adhesive layer will be insufficient, easily leading to creep and increased peel force. As can be seen from the data in the following examples, a thickness ratio of 6:4 is the baseline optimal value, achieving the best balance between adhesive adhesion and stability. A thickness ratio of 7:3 can further improve the filling performance on extremely rough surfaces, meeting the needs of polarizers with special specifications. This thickness ratio range ensures both the filling and stress dispersion functions of the interface adaptation layer and the cohesive stabilization function of the cohesive reinforcement layer, making it a key process parameter for the precise construction of gradient structures.

[0032] In an optional implementation, in step S5, the temperature of the first zone is 80°C, the temperature of the second zone is 110°C, and the temperature of the third zone is 130°C. This specific temperature design precisely matches the physicochemical changes of each component, achieving gradual optimization of the adhesive layer performance, and represents the optimal curing temperature combination verified by the process. The first zone, at 80℃, is a medium-low temperature zone. This temperature allows for the gradual evaporation of the solvent, preventing the formation of a skin on the adhesive surface and internal bubbles caused by rapid solvent evaporation. Simultaneously, this temperature softens the temperature-sensitive polymer chains in the shell of the dynamic response microspheres A, ensuring sufficient fluidity to fully wet and fill the microscopic rough structure of the polarizer. The second zone, at 110℃, is a medium temperature zone. This temperature allows for precise desealing of the end-capping agent in the isocyanate crosslinking agent, releasing active isocyanate groups that undergo preliminary crosslinking reactions with the components, constructing a basic chemical crosslinking network. At this point, the cohesion of the adhesive layer begins to gradually increase without losing fluidity due to excessively rapid crosslinking. The third zone, at 130℃, is a medium-high temperature zone. This temperature allows the crosslinking reaction to proceed completely, constructing a dense and stable chemical crosslinking network. Simultaneously, it hardens the softened shell of the dynamic response microspheres A, forming a strong chemical bond with the colloidal network, creating a dual network structure of chemical and physical crosslinking. This maximizes the cohesion and creep resistance of the adhesive layer. The combination of these three specific temperatures ensures that the solvent evaporation, microsphere softening and filling, cross-linking reaction, and microsphere hardening and point formation processes proceed sequentially and orderly without mutual interference, ultimately guaranteeing the core performance of the adhesive layer: perfect adhesion, stable peel force, and no adhesive residue.

[0033] In an optional embodiment, the solvent is selected from at least one of methyl ethyl ketone (MEK), ethyl acetate, butyl acetate, and toluene. The construction solids content of the mixed adhesive is controlled at 30%-40%.

[0034] The present application will now be described in detail with reference to various embodiments. However, these embodiments do not limit the present application, and any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the scope of protection of the present application.

[0035] Example 1 This embodiment provides an adhesive composition comprising, by weight, the following components: 100 parts acrylate copolymer resin, 5 parts hydrogenated terpene resin, 3 parts dynamic responsive microspheres A, 2 parts stress dissipation microspheres B, 0.5 parts end-capped isocyanate crosslinking agent, 0.2 parts epoxy silane coupling agent, and 50 parts solvent; wherein, the dynamic responsive microspheres A have a core-shell structure, the core being at least one selected from polystyrene, polybutadiene, or acrylate elastomers, and the shell being a polymer containing temperature-sensitive polymeric segments; the stress dissipation microspheres B are microspheres with a hollow structure, encapsulating gas inside; the adhesive composition is configured to spontaneously layer and form a gradient structure.

[0036] This embodiment also provides an optical protective film, which is prepared by the following steps: S1. Preparation of premix A: 100 parts of acrylate copolymer resin, 5 parts of hydrogenated terpene resin, 3 parts of dynamic response microspheres A and 0.1 parts of epoxy silane coupling agent are mixed at low speed under moisture-free conditions to obtain premix A. S2. Preparation of dispersion B: 2 parts of stress dissipation microspheres B and 0.1 parts of epoxy silane coupling agent are dispersed in 50 parts of solvent by high-speed shearing to obtain dispersion B; S3. Mixing and Crosslinking: Mix premix A and dispersion B, and add 0.5 parts of end-capped isocyanate crosslinking agent online before coating to perform instantaneous mixing and crosslinking to obtain coating liquid; S4. Gradient structure coating: The coating liquid is introduced into a single-layer coating die head, and the viscosity difference is used to cause the coating liquid to settle in layers. After a preset set time of settling, a gradient distribution composite wet film is formed; wherein, the composite wet film includes a lower wet film and an upper wet film, and the ratio of the film thickness of the lower wet film to the upper wet film is in the range of 6:4. S5. Curing: After the substrate layer and the composite wet film thereon pass through the first zone at 70℃, the second zone at 100℃, and the third zone at 125℃ in sequence, the composite wet film is cured to form a dry film, thus obtaining an optical protective film. The thickness of the adhesive layer in the optical protective film is 18μm.

[0037] Example 2 This embodiment provides an adhesive composition comprising, by weight, the following components: 100 parts acrylate copolymer resin, 20 parts hydrogenated terpene resin, 10 parts dynamic responsive microspheres A, 8 parts stress dissipation microspheres B, 2.5 parts end-capped isocyanate crosslinking agent, 1.5 parts epoxy silane coupling agent, and 80 parts solvent; wherein, the dynamic responsive microspheres A have a core-shell structure, the core being at least one selected from polystyrene, polybutadiene, or acrylate elastomers, and the shell being a polymer containing temperature-sensitive polymeric segments; the stress dissipation microspheres B are hollow microspheres encapsulated with gas; the adhesive composition is configured to spontaneously layer and form a gradient structure.

[0038] This embodiment also provides an optical protective film, which is prepared by the following steps: S1. Preparation of premix A: 100 parts of acrylate copolymer resin, 20 parts of hydrogenated terpene resin, 10 parts of dynamic response microspheres A and 0.8 parts of epoxy silane coupling agent are mixed at low speed under moisture-free conditions to obtain premix A. S2. Preparation of dispersion B: 8 parts of stress dissipation microspheres B and 0.7 parts of epoxy silane coupling agent are dispersed in 80 parts of solvent by high-speed shearing to obtain dispersion B; S3. Mixing and Crosslinking: Mix premix A and dispersion B, and add 2.5 parts of end-capped isocyanate crosslinking agent online before coating to perform instantaneous mixing and crosslinking to obtain coating liquid; S4. Gradient structure coating: The coating liquid is introduced into a single-layer coating die head, and the viscosity difference is used to cause the coating liquid to settle in layers. After a preset set time of settling, a gradient distribution composite wet film is formed; wherein, the composite wet film includes a lower wet film and an upper wet film, and the ratio of the film thickness of the lower wet film to the upper wet film is in the range of 6:4. S5. Curing: After the substrate layer and the composite wet film thereon pass through the first zone at 85℃, the second zone at 115℃, and the third zone at 140℃ in sequence, the composite wet film is cured to form a dry film, thus obtaining an optical protective film. The thickness of the adhesive layer in the optical protective film is 20μm.

[0039] Example 3 This embodiment provides an adhesive composition comprising, by weight, the following components: 100 parts acrylate copolymer resin, 12 parts hydrogenated terpene resin, 6 parts dynamic response microspheres A, 5 parts stress dissipation microspheres B, 1.2 parts end-capped isocyanate crosslinking agent, 0.8 parts epoxy silane coupling agent, and 65 parts solvent; wherein, the dynamic response microspheres A have a core-shell structure, the core being at least one selected from polystyrene, polybutadiene, or acrylate elastomers, and the shell being a polymer containing temperature-sensitive polymeric segments; the stress dissipation microspheres B are hollow microspheres encapsulated with gas; the adhesive composition is configured to spontaneously layer and form a gradient structure.

[0040] This embodiment also provides an optical protective film, which is prepared by the following steps: S1. Preparation of premix A: 100 parts of acrylate copolymer resin, 12 parts of hydrogenated terpene resin, 6 parts of dynamic response microspheres A and 0.4 parts of epoxy silane coupling agent are mixed at low speed under moisture-free conditions to obtain premix A. S2. Preparation of dispersion B: 5 parts of stress dissipation microspheres B and 0.4 parts of epoxy silane coupling agent are dispersed in 65 parts of solvent by high-speed shearing to obtain dispersion B; S3. Mixing and Crosslinking: Mix premix A and dispersion B, and add 1.2 parts of end-capped isocyanate crosslinking agent online before coating to perform instantaneous mixing and crosslinking to obtain coating liquid; S4. Gradient structure coating: The coating liquid is introduced into a single-layer coating die head, and the viscosity difference is used to cause the coating liquid to settle in layers. After a preset set time of settling, a gradient distribution composite wet film is formed; wherein, the composite wet film includes a lower wet film and an upper wet film, and the ratio of the film thickness of the lower wet film to the upper wet film is in the range of 6:4. S5. Curing: After the substrate layer and the composite wet film thereon pass through the first zone at 80℃, the second zone at 110℃, and the third zone at 130℃ in sequence, the composite wet film is cured to form a dry film, thus obtaining an optical protective film. The thickness of the adhesive layer in the optical protective film is 20μm.

[0041] Example 4 The difference between this embodiment and Embodiment 3 is that the components of the adhesive composition are adjusted by weight as follows: dynamic response microspheres A are increased to 8 parts, stress dissipation microspheres B are reduced to 3 parts, hydrogenated terpene resin is 10 parts, end-capped isocyanate crosslinking agent is 1.0 part, and epoxy silane coupling agent is 0.8 parts.

[0042] Example 5 The difference between this embodiment and Example 3 is that the components of the adhesive composition are adjusted by weight as follows: dynamic response microspheres A are reduced to 4 parts, stress dissipation microspheres B are increased to 7 parts, hydrogenated terpene resin is 14 parts, end-capped isocyanate crosslinking agent is 1.5 parts, and epoxy silane coupling agent is 0.8 parts.

[0043] Example 6 The difference between this embodiment and Embodiment 3 is that the components of the adhesive composition, by weight, are adjusted as follows: the end-capped isocyanate crosslinking agent is increased to 1.8 parts.

[0044] Example 7 The difference between this embodiment and Embodiment 3 is that the ratio of the thickness of the lower wet film to the upper wet film is in the range of 7:3.

[0045] Comparative Example 1 The difference between this comparative example and Example 3 is that dynamic response microspheres A and stress dissipation microspheres B are not used. Instead, 20 parts of ordinary acrylate solid microspheres (200 nm) and 20 parts of hydrogenated terpene resin, 2.0 parts of end-capped isocyanate crosslinking agent, 0.8 parts of epoxy silane coupling agent, and 65 parts of solvent are added.

[0046] This comparative example also provides an optical protective film, which is prepared by the following steps: 100 parts of acrylate copolymer resin, 20 parts of hydrogenated terpene resin, 20 parts of ordinary acrylate solid microspheres, 0.8 parts of epoxy silane coupling agent, and 2.0 parts of end-capped isocyanate crosslinking agent are thoroughly mixed under moisture-free conditions to obtain a coating liquid. The coating liquid is then fed into a single coating die and extruded onto a substrate layer to form a wet film. The substrate layer and the wet film thereon are then passed sequentially through a first zone at 100°C and a second zone at 130°C. The wet film is then cured to form a dry film, thus obtaining an optical protective film.

[0047] Comparative Example 2 The difference between this comparative example and Example 3 is that stress-dissipating microspheres B are not used.

[0048] This comparative example also provides an optical protective film, which is prepared by the following steps: S1. Preparation of premix A: 100 parts of acrylate copolymer resin, 12 parts of hydrogenated terpene resin, 6 parts of dynamic response microspheres A and 0.4 parts of epoxy silane coupling agent are mixed at low speed under moisture-free conditions to obtain premix A. S2. Preparation of dispersion B: 0.4 parts of epoxy silane coupling agent are dispersed in 65 parts of solvent by high-speed shearing to obtain dispersion B; S3. Mixing and Crosslinking: Mix premix A and dispersion B, and add 1.2 parts of end-capped isocyanate crosslinking agent online before coating to perform instantaneous mixing and crosslinking to obtain coating liquid; S4. Gradient structure coating: The coating liquid is introduced into a single-layer coating die head, and the viscosity difference is used to cause the coating liquid to settle in layers. After a preset set time of settling, a gradient distribution composite wet film is formed; wherein, the composite wet film includes a lower wet film and an upper wet film, and the ratio of the film thickness of the lower wet film to the upper wet film is in the range of 6:4. S5. Curing: After the substrate layer and the composite wet film thereon pass through the first zone at 80°C, the second zone at 110°C, and the third zone at 130°C in sequence, the composite wet film is cured to form a dry film, thus obtaining an optical protective film.

[0049] Comparative Example 3 The difference between this comparative example and Example 3 is that dynamic response microspheres A are not used.

[0050] This comparative example also provides an optical protective film, which is prepared by the following steps: S1. Preparation of premix A: 100 parts of acrylate copolymer resin, 12 parts of hydrogenated terpene resin, and 0.4 parts of epoxy silane coupling agent are mixed at low speed under moisture-free conditions to obtain premix A. S2. Preparation of dispersion B: 5 parts of stress dissipation microspheres B and 0.4 parts of epoxy silane coupling agent are dispersed in 65 parts of solvent by high-speed shearing to obtain dispersion B; S3. Mixing and Crosslinking: Mix premix A and dispersion B, and add 1.2 parts of end-capped isocyanate crosslinking agent online before coating to perform instantaneous mixing and crosslinking to obtain coating liquid; S4. Gradient structure coating: The coating liquid is introduced into a single-layer coating die head, and the viscosity difference is used to cause the coating liquid to settle in layers. After a preset set time of settling, a gradient distribution composite wet film is formed; wherein, the composite wet film includes a lower wet film and an upper wet film, and the ratio of the film thickness of the lower wet film to the upper wet film is in the range of 6:4. S5. Curing: After the substrate layer and the composite wet film thereon pass through the first zone at 80°C, the second zone at 110°C, and the third zone at 130°C in sequence, the composite wet film is cured to form a dry film, thus obtaining an optical protective film.

[0051] Comparative Example 4 The difference between this comparative example and Example 3 is that the end-capped isocyanate crosslinking agent is added to the mixture at the initial stage of preparing premix A, while the remaining steps are the same as in Example 3.

[0052] Comparative Example 5 The difference between this comparative example and Example 3 is that the thickness of the adhesive layer in the optical protective film is 12 μm.

[0053] The performance of the optical protective films of Examples 3-7 and Comparative Examples 1-5 was tested using the following standards or methods: Peel strength (gf / inch): The optical protective films of Examples 3-7 and Comparative Examples 1-5 were bonded to the surface of a polarizer to form test samples, and the cut size was 2.5cm. 15cm, then use 31B tape to fix the auxiliary tape to the sample, and gently roll it with a (2KG) manual roller; peel off the polarizer protective film at a speed of 300mm / min, and record the average force value during the stabilization phase (remove the peak value in the first 10mm and at the end).

[0054] Surface filling: Visual inspection and light pressing to check for air bubbles in the finished polarizer after the protective film is applied.

[0055] Residual adhesive assessment: After uniformly peeling off the protective film, observe whether there are any adhesive marks, adhesive spots, or stickiness on the surface of the polarizer.

[0056] The test results are shown in Table 1: Table 1

[0057] As shown in Table 1: After adjusting the composition of the adhesive composition in Example 4: the dynamic response microspheres A were increased to 8 parts, the stress dissipation microspheres B were reduced to 3 parts, and the hydrogenated terpene resin was 10 parts. The peel force was 4.3 gf / inch, and after aging, it was 4.7 gf / inch, with a peel force change rate of 9.3%. The adhesive bond was bubble-free, and there was no residue after removal. Compared to Example 3, the increase in dynamic response microspheres A and the decrease in stress dissipation microspheres B resulted in a lower peel force change rate and improved creep resistance, while maintaining excellent adhesion and residue-free characteristics. This indicates that peel force stability can be optimized by adjusting the ratio of dynamic response microspheres A and stress dissipation microspheres B.

[0058] After adjusting the composition of the adhesive composition in Example 5: the dynamic response microspheres A were reduced to 4 parts, the stress dissipation microspheres B were increased to 7 parts, and the hydrogenated terpene resin was 14 parts. The peel strength was 3.7 gf / inch, and after aging it was 4.0 gf / inch, with a peel strength change rate of 8.1%. There were no air bubbles during bonding, and no adhesive residue was left after removal. Compared with Example 3, the reduction of dynamic response microspheres A and the increase of stress dissipation microspheres B further reduced the peel strength change rate. The initial tack was slightly reduced but still met the usage requirements, indicating that adjusting the ratio of dynamic response microspheres A and stress dissipation microspheres B can better suit high-haze surfaces and improve stability.

[0059] After adjusting the composition of the adhesive composition in Example 6: the crosslinking agent was increased to 1.8 parts, the peel strength was 4.6 gf / inch, and after aging it was 4.9 gf / inch, with a peel strength change rate of 6.5%. There were no air bubbles during bonding, and no adhesive residue was left after removal. Compared to Example 3, the increased crosslinking agent resulted in a denser chemical crosslinking network, a significantly reduced peel strength change rate, and improved cohesion without affecting adhesion, indicating that an appropriate increase in the amount of crosslinking agent can enhance creep resistance.

[0060] In Example 7, the adhesive flow-to-thickness ratio was adjusted to 7:3, with a peel force of 3.9 gf / inch and 4.6 gf / inch after aging, representing a peel force change rate of 17.9%. The bonding was bubble-free, and no adhesive residue was left after removal. In contrast, Example 3, with its 6:4 adhesive flow-to-thickness ratio, showed improved filling performance due to a thicker interface adaptation layer. While the peel force change rate increased slightly, it remained within a reasonable range, adapting to extremely rough surfaces and demonstrating the flexibility of the thickness ratio design.

[0061] Comparative Example 1 used ordinary acrylate solid microspheres, with a peel force of 5.8 gf / inch and a peel force of 13.5 gf / inch after aging, representing a peel force change rate of 133%. It also showed the presence of bubbles and significant adhesive residue. Compared to Example 3, which did not use bifunctional microspheres and had a homogeneous structure, it could not balance filling and cohesion, resulting in a sharp increase in peel force and adhesion failure. This demonstrates the necessity of the bifunctional microspheres and gradient structure in this application.

[0062] Comparative Example 2, without stress-dissipating microspheres B, had a peel force of 5.5 gf / inch and a peel force of 6.5 gf / inch after aging, with a peel force change rate of 18%. The bonding was bubble-free and residue-free. During bonding, high pressure resulted in no bubbles, while low pressure resulted in bubbles, indicating pressure sensitivity. Comparative Example 3, lacking stress-dissipating microspheres B, resulted in insufficient stress dispersion, and the adhesion was affected by pressure, leading to an increased peel force change rate. This demonstrates the crucial role of stress-dissipating microspheres B in interface adaptation and stress dispersion.

[0063] Comparative Example 3, without dynamic response microspheres A, had a peel force of 3.5 gf / inch and a peel force of 4.9 gf / inch after aging, with a peel force change rate of 40%. The bonding was bubble-free and slightly sticky. Compared to Example 3, the absence of dynamic response microspheres A resulted in insufficient physical cross-linking points, decreased creep resistance, a dramatic increase in the peel force change rate, and interface stickiness, demonstrating the core role of dynamic response microspheres A in enhancing cohesion and structural stability.

[0064] In Comparative Example 4, the crosslinking agent was added in advance, resulting in a peel strength of 4.9 gf / inch and a peel strength of 6.1 gf / inch after aging, with a peel strength change rate of 25%. The bonding was bubble-free and residue-free. Compared to Example 3, the failure to add the crosslinking agent online led to pre-crosslinking, increased adhesive viscosity, uneven cohesive distribution after coating, and an increased peel strength change rate, demonstrating the necessity of the delayed crosslinking process.

[0065] Comparative Example 5 had an adhesive layer thickness of 12 μm, a peel strength of 2.5 gf / inch, and an aged peel strength of 2.8 gf / inch, with a peel strength change rate of 12%. It contained air bubbles but had no adhesive residue. In contrast, the 20 μm thickness of Comparative Example 3 was insufficient to fill the high-haze surface microstructure of the AG surface. After bonding, localized air bubbles and rainbow patterns appeared, and the protective function failed. This indicates that an adhesive layer thickness of 18–20 μm is a necessary design for adapting to rough surfaces.

[0066] This application also prepares three types of polarizers with AG-treated surfaces and nominal haze values ​​of LR30%, LR40%, and LR50%, respectively. The optical protective film of Example 1 was attached to the above three types of polarizers using standard processes. The initial bonding state was evaluated, and the peel force at 180° (peel speed 300 mm / min), the peel force after being placed at 60°C for 500 h, and the peel force change rate were tested. The residual adhesive state after removing the optical protective film was also calculated.

[0067] Methods for testing the mechanical properties of adhesive layers: 1. The standards or methods for evaluating peel strength, surface filling properties, and residual adhesive are as described above and will not be repeated here.

[0068] 2. Tensile test: Use a universal testing machine to test the tensile strength and elongation at break.

[0069] 3. Dynamic thermomechanical analysis: Using a DMA instrument, the storage modulus directly reflects the rigidity (creep resistance) of the material.

[0070] The performance data of the aforementioned optical protective film are shown in Table 2.

[0071] Table 2

[0072] As shown in Table 2, the adhesive layer of this application exhibits perfect adhesion and stable peel force within a haze range of LR30%-LR50%, especially overcoming the adhesion problem on surfaces with higher haze (LR50%). Furthermore, it demonstrates excellent durability and stability under extreme high temperature and humidity, long-term thermal aging, and severe thermal shock, with controllable peel force growth. Meanwhile, mechanical test data such as DMA confirm that the technical solution of this application solves the creep problem of thick adhesive layers, demonstrating broad adaptability.

[0073] In summary, this application successfully prepared an optical protective film containing a gradient adhesive layer by using a specific combination of dynamic response microspheres A and stress dissipation microspheres B, combined with a stepwise premixing-delayed crosslinking mixing sequence and a sedimentation gradient structure distribution to construct a functionally gradient structure. The gradient adhesive layer, at a specific thickness of 18-20 μm, perfectly balances the filling adhesion to the surface of a high-haze polarizer with long-term peel stability. A systematic comparison of multiple examples and comparative examples fully demonstrates the synergistic effect and non-obviousness of the various technical features. For example, the absence of any key component (Comparative Examples 1-3), changes in the mixing sequence (Comparative Example 4), or disruption of the gradient structure all lead to a significant decrease in performance.

[0074] It should be noted that the above description is only for explaining the preferred embodiments of this application and is not intended to limit this application in any way. Therefore, any modifications or changes made to this application under the same inventive spirit should still be included within the scope of protection intended by this application.

Claims

1. An adhesive composition, characterized in that, Based on parts by weight, it comprises the following components: 100 parts of acrylate copolymer resin; 5-20 parts of tackifying resin; Dynamic response microspheres A3-10 parts; Stress dissipation microspheres B2-8 parts; 0.5–2.5 parts of end-capping crosslinking agent; 0.2–1.5 parts of epoxy-based silane coupling agent; The dynamic response microsphere A is a temperature-sensitive core-shell polymer microsphere with a core-shell structure. The core is selected from at least one of polystyrene, polybutadiene, or acrylate elastomers, and the shell is a polymer containing temperature-sensitive polymer segments. The stress dissipation microsphere B is a microsphere with a hollow structure.

2. The adhesive composition according to claim 1, characterized in that, The crosslinking agent is a capped isocyanate.

3. The adhesive composition according to claim 1, characterized in that, The tackifying resin is selected from at least one of hydrogenated terpene resin, hydrogenated rosin resin, and C5 / C9 petroleum resin.

4. The adhesive composition according to claim 1, characterized in that, The tackifying resin is in the form of 10-14 parts by weight, the dynamic response microsphere A is in the form of 4-8 parts by weight, and the stress dissipation microsphere B is in the form of 3-7 parts by weight.

5. An optical protective film, characterized in that, It includes a PET substrate layer and an adhesive layer disposed on any one surface of the PET substrate layer, wherein the adhesive layer is prepared from the adhesive composition according to any one of claims 1-4.

6. The optical protective film according to claim 5, characterized in that, The thickness of the adhesive layer is 18–20 μm.

7. The optical protective film according to claim 5, characterized in that, The adhesive layer has a gradient structure: the side of the adhesive layer closest to the PET substrate layer is a cohesive reinforcement layer, which comprises 1% to 30% of the total weight of dynamic responsive microspheres A; the side of the adhesive layer furthest from the PET substrate layer is an interface adaptation layer, which comprises 70% to 99% of the total weight of dynamic responsive microspheres A.

8. A method for preparing the optical protective film according to any one of claims 5-7, characterized in that, Includes the following steps: S1. Preparation of premix A: Mix 50% by weight of acrylate copolymer resin, tackifying resin, dynamic response microspheres A and silane coupling agent at low speed under moisture-free conditions to obtain premix A. S2. Preparation of dispersion B: Dispersion B is prepared by high-speed shearing of stress dissipation microspheres B and 50% of the total weight of silane coupling agent in a solvent. S3. Mixing and Crosslinking: Mix premix A and dispersion B, and add crosslinking agent online before coating to perform instantaneous mixing and crosslinking to obtain coating liquid; S4. Gradient structure coating: The coating liquid enters the single-layer coating die head, and the viscosity difference is used to make the coating liquid settle in layers. After a preset set time of settling, a gradient distribution composite wet film is formed. S5. Curing: After the substrate layer and the composite wet film thereon pass through the first zone at a temperature of 70-85℃, the second zone at a temperature of 100-115℃, and the third zone at a temperature of 125-140℃, the composite wet film is cured to form a dry film, thus obtaining an optical protective film.

9. The method according to claim 8, characterized in that, In step S4, the composite wet membrane includes a lower wet membrane and an upper wet membrane, and the ratio of the membrane thickness of the lower wet membrane to the upper wet membrane is in the range of 6:4 to 7:

3.

10. The method according to claim 8, characterized in that, In step S5, the temperature of the first zone is 80°C, the temperature of the second zone is 110°C, and the temperature of the third zone is 130°C.

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