A pressure-sensitive adhesive protective film for PMMA optical films without surface treatment and its preparation method

Abstract

This application relates to a pressure-sensitive adhesive protective film for PMMA optical films without surface treatment and its preparation method. The protective film is composed of a substrate layer, a release layer, and an anchoring layer stacked sequentially. The release layer and the anchoring layer use differentiated acrylate formulations. The release layer does not contain phosphate-modified acrylate, while the anchoring layer adds this component to improve interfacial adhesion. Furthermore, the glass transition temperature, crosslinking density, and storage modulus of the release layer are all lower than those of the anchoring layer. This application employs a stepwise UV pre-curing, main curing, and thermal annealing process to prepare the product. This application utilizes a dual-layer gradient structure to construct a stress dissipation system, which can stably control the peel force at 20–50 g / 25 mm. High-temperature and high-humidity aging results in no adhesive residue or peeling, and high-temperature holding power exceeds 48 hours. Tearing the film will not cause silver streaks or edge chipping damage to the PMMA optical film. The product is PFAS-free and suitable for the protection of various PMMA optical products.

Description

Technical Field

[0001] This application relates to the field of optical film technology, specifically to a pressure-sensitive adhesive protective film for PMMA optical films without surface treatment and its preparation method. Background Technology

[0002] PMMA (polymethyl methacrylate) is widely used in products such as displays, automotive panels, and optical lenses due to its high light transmittance and excellent optical properties. However, PMMA optical films without surface treatments such as plasma, corona, or primer have extremely low surface energy (typically <36 mN / m), making it difficult for traditional pressure-sensitive adhesives to effectively wet and spread them. This makes the protective film prone to accidental detachment during transportation. Furthermore, residual internal stress exists in PMMA optical films during the molding and cooling process. If the adhesive strength is too high or the cohesion is insufficient, peeling the film can easily cause cracking of the substrate (such as edge chipping or silver streaks).

[0003] Furthermore, while existing commercially available low-tack pressure-sensitive adhesives exhibit acceptable initial adhesion to untreated PMMA optical films, after aging under high temperature and humidity (e.g., 60°C / 90%RH), the mismatch in thermal expansion coefficients between the adhesive layer and the PMMA optical film easily leads to cohesive failure of the adhesive layer, leaving difficult-to-remove residues on the PMMA optical film surface, severely impacting product yield. To meet increasingly stringent environmental regulations (such as the EU's draft PFAS restriction), developing a low-tack, residue-free pressure-sensitive adhesive that is free of per- and polyfluoroalkyl substances (PFAS) and can be directly applied to untreated PMMA optical films has become a pressing technical challenge in this field. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of the prior art and provide a pressure-sensitive adhesive protective film for PMMA optical films without surface treatment and a preparation method thereof.

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

[0006] This application provides a pressure-sensitive adhesive protective film for PMMA optical films without surface treatment, comprising a substrate layer, a release layer, and an anchoring layer stacked sequentially; wherein: The release layer is formed by UV curing of a release layer adhesive containing the following components: isooctyl acrylate, butyl acrylate, polyurethane acrylate, epoxy acrylate, 2-phenoxyethyl acrylate, and a photoinitiator. The anchoring layer is formed by UV curing of an anchoring layer adhesive containing the following components: isooctyl acrylate, butyl acrylate, polyurethane acrylate, epoxy acrylate, phosphate-modified acrylate, and photoinitiator. The glass transition temperature, crosslinking density, and energy storage modulus of the release layer are all lower than those of the anchoring layer.

[0007] As a further improvement of this application, the thickness of the peeling layer is 10-14 μm, and the thickness of the anchoring layer is 6-10 μm.

[0008] As a further improvement to this application, the release layer, by weight, is formed by ultraviolet light curing of a release layer adhesive comprising the following components: 50-70 parts of isooctyl acrylate; 10-20 parts of butyl acrylate; 5-15 parts of polyurethane acrylate; 0.1 to 5 parts of epoxy acrylate; 10-30 parts of 2-phenoxyethyl acrylate; And 0.5 to 3 parts of photoinitiator.

[0009] As a further improvement to this application, the anchoring layer, by weight, is formed by ultraviolet light curing of an anchoring layer adhesive comprising the following components: 30-50 parts of isooctyl acrylate; 15-25 parts of butyl acrylate; 10-20 parts of polyurethane acrylate; 3-8 parts of epoxy acrylate; 1-5 parts of phosphate-modified acrylate; And 1 to 3 parts of photoinitiator.

[0010] As a further improvement of this application, the glass transition temperature of the release layer is -40℃ to -25℃, and the glass transition temperature of the anchoring layer is -20℃ to -10℃.

[0011] As a further improvement of this application, at 25°C, a tensile speed of 300 mm / min, and a peel angle of 180°, the surface peel force between the pressure-sensitive adhesive protective film and the untreated PMMA optical film is 20-50 g / 25 mm.

[0012] To achieve the above objectives, this application also provides a method for preparing the pressure-sensitive adhesive protective film for surface-treated PMMA optical films described above, comprising the following steps: S1. Prepare the release layer adhesive and the anchoring layer adhesive; S2. Apply the release layer adhesive to the substrate layer and perform UV pre-curing to obtain a pre-cured release layer. S3. Apply the anchoring layer adhesive to the pre-cured release layer to form a double adhesive layer; S4. Perform primary curing on the double-layer adhesive layer; S5. After the product has been cured, it is subjected to heat annealing, then rewound and slit to obtain a pressure-sensitive adhesive protective film.

[0013] As a further improvement of this application, in step S2, the energy of the UV pre-curing is 70–90 mJ / cm². 2 .

[0014] As a further improvement of this application, in step S4, the energy of the primary curing is 280–320 mJ / cm². 2 Furthermore, the double bond conversion rate is greater than 95%.

[0015] As a further improvement of this application, in step S5, the temperature of the heat annealing treatment is 65-75°C and the time is 1.5-2.5 hours.

[0016] The specific benefits of this application are as follows: This application is for the development of a dual-layer gradient structure pressure-sensitive adhesive protective film for PMMA optical films without surface treatment. It adopts a dual-layer composite architecture of a release layer and an anchoring layer, and relies on the gradient difference in glass transition temperature, crosslinking density and energy storage modulus between the two to construct a stress dissipation system.

[0017] The anchoring layer utilizes phosphate-modified acrylate to form a quasi-chemical bond with the low surface energy PMMA optical film surface, effectively improving interfacial adhesion and preventing the protective film from detaching during transportation and use. Simultaneously, the high cross-linking density ensures the cohesiveness of the adhesive layer, effectively preventing residual adhesive after film removal and high-temperature, high-humidity aging. The release layer, with its low Tg and low cross-linking characteristics, forms a flexible buffer layer. Combined with 2-phenoxyethyl acrylate, it achieves good wetting without generating strong adhesion, allowing peel stress to dissipate within the release layer and preventing stress transmission to the PMMA optical film. This also prevents problems such as edge chipping, silver streaks, and cracking in the PMMA optical film substrate.

[0018] The combination of anchoring and release layers with stepwise UV curing and thermal annealing processes allows for precise control of the cross-linking degree of the adhesive layer, releasing residual internal stress and shrinkage stress between the adhesive layer and the substrate, and further improving the product's weather resistance and dimensional stability.

[0019] The pressure-sensitive adhesive protective film prepared by the technical solution of this application can stably achieve a controllable peel force of 20-50g / 25mm, taking into account both adhesion firmness and cleanness of film removal. It is suitable for the protection needs of various PMMA optical films such as displays, automotive panels, and optical lenses, and has a wide range of applications and excellent comprehensive performance. Detailed Implementation

[0020] Based on the technical problems to be solved in the background art, this application provides a pressure-sensitive adhesive protective film for PMMA optical films without surface treatment, comprising a substrate layer, a release layer, and an anchoring layer stacked sequentially; wherein: the release layer is formed by UV curing of a release layer adhesive containing the following components: isooctyl acrylate, butyl acrylate, polyurethane acrylate, epoxy acrylate, 2-phenoxyethyl acrylate (POEA), and a photoinitiator; the anchoring layer is formed by UV curing of an anchoring layer adhesive containing the following components: isooctyl acrylate, butyl acrylate, polyurethane acrylate, epoxy acrylate, phosphate-modified acrylate, and a photoinitiator; the glass transition temperature (Tg), crosslinking density, and storage modulus of the release layer are all lower than those of the anchoring layer. Preferably, the thickness of the release layer is 10–14 μm, and the thickness of the anchoring layer is 6–10 μm.

[0021] Based on the above technical solution, the pressure-sensitive adhesive protective film provided in this application is not simply two layers of adhesive stacked together, but rather a stress dissipation system is constructed. When this pressure-sensitive adhesive protective film is applied to an untreated PMMA optical film, the high-Tg, highly cross-linked, and high-modulus anchoring layer is close to the PMMA. The phosphate-modified acrylate within this layer forms a strong interfacial bond with the low-surface-energy PMMA through Lewis acid-base interactions, ensuring that this layer will not detach from the PMMA during film removal. The low-Tg, low-cross-linked, and low-modulus release layer is far from the PMMA optical film. The POEA contained within this layer provides moderate wettability through π-π stacking interactions, but does not form strong chemical bonds. When the film is removed, due to the modulus gradient, the peel stress is preferentially dissipated within this soft release layer through shear / yield mechanisms, preventing stress concentration at the interface between the pressure-sensitive adhesive protective film and the PMMA optical film, or even within the PMMA optical film itself.

[0022] In an optional embodiment, the release layer, by weight, is formed by UV curing of a release layer adhesive comprising the following components: 50-70 parts isooctyl acrylate; 10-20 parts butyl acrylate; 5-15 parts polyurethane acrylate; 0.1-5 parts epoxy acrylate; 10-30 parts 2-phenoxyethyl acrylate; and 0.5-3 parts photoinitiator. Preferably, the glass transition temperature of the release layer is -40°C to -25°C, which is obtained by dynamic thermomechanical analysis (DMA) at a heating rate of 10°C / min and a testing frequency of 1Hz.

[0023] Based on the components of the release layer described above: isooctyl acrylate, as the main soft monomer, has a long alkyl flexible structure in its molecular side chains. Under UV light, the carbon-carbon double bonds undergo free radical polymerization to form flexible polymer segments. This component accounts for 50-70 parts and forms the main matrix of the release layer. It can significantly reduce the overall glass transition temperature of the release layer, giving it excellent flexibility and initial tack. At the same time, it weakens the cohesive strength of the adhesive layer, matching the overall design requirements of low glass transition temperature, low crosslinking density, and low storage modulus of the release layer. This avoids the adhesive layer being too hard, which would result in residual adhesive or warping during subsequent removal. Edge issues; Butyl acrylate is also a soft monomer with good molecular chain flexibility. After participating in free radical copolymerization, it can further adjust the overall softness and wetting ability of the adhesive layer. An addition of 10-20 parts can improve the uniformity of the release layer adhesive on the substrate surface, optimize the film-forming properties of the adhesive layer, and simultaneously, synergistically with isooctyl acrylate, regulate the basic mechanical properties of the release layer, preventing insufficient cohesion and low mechanical strength caused by an excessively high proportion of a single soft monomer; Polyurethane acrylate is a functional prepolymer containing a urethane structure, with carbon-carbon double bonds in its molecule that can participate in UV curing, and... Polyurethane's high toughness and flexural strength are introduced into the adhesive layer after polymerization. An addition of 5-15 parts can moderately improve the overall mechanical strength and weather resistance of the release layer without increasing the crosslinking density and storage modulus due to excessive rigid groups. This maintains the design low modulus of the release layer, ensuring a smooth and noiseless peeling process. Epoxy acrylate, possessing both epoxy groups and acrylic double bonds, participates in the crosslinking reaction at a low addition of 0.1-5 parts, slightly enhancing the cohesiveness and heat resistance of the adhesive layer. This small addition only plays a supporting modification role and does not significantly increase the glass transition temperature or crosslinking process of the release layer. If the addition amount is too high, it will cause the adhesive layer to harden, violating the performance requirements of the release layer; 2-phenoxyethyl acrylate contains phenoxy rigid groups and polymerizable double bonds. A ratio of 10-30 parts can adjust the surface interface properties of the adhesive layer after copolymerization, optimize the interfacial bonding force between the release layer and the anchoring layer, and prevent interlayer separation during use. At the same time, this monomer can fine-tune the surface tension of the release layer, and further reduce the glass transition temperature of the release layer in conjunction with the overall formulation, differentiating its thermal properties from those of the anchoring layer, and ensuring the performance gradient difference between the two adhesive layers; the photoinitiator addition amount is 0.5-3 parts, the core component of the UV curing system, decomposes under UV light to generate free radicals, triggering a chain reaction of free radical polymerization and cross-linking reactions in all the monomers and prepolymers containing double bonds. This transforms the adhesive from a liquid to a solid adhesive layer. Appropriate addition ensures the release layer fully completes initial curing under the preset UV pre-curing energy, controlling the cross-linking density at a low level. This guarantees the complete formation of the release layer while strictly adhering to the technical characteristic that the cross-linking density of the release layer is lower than that of the anchoring layer. Ultimately, during the application of the pressure-sensitive adhesive protective film, the release layer can stably adhere to the substrate layer and easily separate when the substrate layer is peeled off, without tearing or residue remaining on the anchoring layer surface. Together with the anchoring layer, it achieves a suitable peel force of 20-50g / 25mm for the protective film against untreated PMMA optical films, balancing adhesion stability and clean peeling.

[0024] In an optional embodiment, the anchoring layer, by weight, is formed by UV curing an anchoring layer adhesive comprising the following components: 30-50 parts isooctyl acrylate; 15-25 parts butyl acrylate; 10-20 parts polyurethane acrylate; 3-8 parts epoxy acrylate; 1-5 parts phosphate-modified acrylate; and 1-3 parts photoinitiator. Preferably, the glass transition temperature of the anchoring layer is -20°C to -10°C, which is obtained by dynamic thermomechanical analyzer (DMA) testing at a heating rate of 10°C / min and a testing frequency of 1Hz.

[0025] Based on the above components, isooctyl acrylate and butyl acrylate serve as the basic soft monomers in the system. Under ultraviolet light excitation, they participate in free radical copolymerization reactions, which is basically the same as the release layer. The long alkyl flexible segments give the adhesive layer basic film-forming properties and wetting ability. However, the anchoring layer reduces the proportion of isooctyl acrylate to 30-50 parts and increases the proportion of butyl acrylate to 15-25 parts. Compared with the release layer, this significantly reduces the proportion of highly flexible monomers, improves the overall rigidity and Tg of the adhesive layer from the source of the formulation, and avoids slippage and cohesive failure caused by the adhesive layer being too soft. At the same time, the appropriate amount of soft monomers also ensures that the adhesive has good coating performance and ensures uniform film formation of the thin anchoring layer (6-10 μm). Polyurethane acrylate, as a multifunctional crosslinked prepolymer, contains polymerizable acrylic double bonds in its molecules. After participating in the UV crosslinking reaction, it constructs a dense crosslinked network. Its addition amount in the anchoring layer is increased to 10-20 parts, which is much higher than the 5-15 parts in the release layer. The higher addition amount significantly improves the crosslinking density and cohesive strength of the adhesive layer, forming a high-strength hard shell structure. Combined with the system design, the anchoring layer has a storage modulus that is much higher than that of the release layer. Even under conditions such as film peeling and high temperature and humidity aging, it can maintain the integrity of the adhesive layer itself and effectively prevent the adhesive layer from breaking and remaining on the surface of the PMMA optical film. At the same time, the toughness brought by this component can also buffer the residual stress of the PMMA optical film itself and reduce the risk of substrate cracking. Epoxy acrylates possess both epoxy groups and polymerizable double bonds. The amount added to the anchoring layer is 3-8 parts, which is significantly higher than the amount of 0.1-5 parts used in the release layer. After participating in the cross-linking reaction, this component can further strengthen the cross-linking network of the adhesive layer, improve the heat resistance, creep resistance, and adhesion to adjacent adhesive layers of the anchoring layer, effectively improve the tack performance of the protective film at a high temperature of 70℃, prevent the protective film from slipping and falling off during long-term use, make up for the lack of high temperature resistance of the pure acrylate system, and will not excessively increase the hardness of the adhesive layer and affect the interface bonding effect. Phosphate-modified acrylate is the core functional component that distinguishes the anchoring layer from the release layer. This monomer contains polymerizable acrylic double bonds and polar phosphate groups. The double bonds can participate in UV free radical copolymerization and are fully bonded into the polymer network of the anchoring layer. The exposed phosphate groups can form quasi-chemical bonds and strong physical adsorption with the non-polar, low surface energy PMMA optical film surface through Lewis acid-base interactions, significantly improving the interfacial adhesion between the anchoring layer and the PMMA optical film. This solves the industry pain points of low surface energy, difficulty in wetting adhesives, and easy peeling of protective films in untreated PMMA optical films. The addition amount of this component is controlled at 1 to 5 parts, which is precise and controllable. This ensures sufficient anchoring effect and meets the high-temperature adhesion requirements of more than 48 hours, while avoiding excessive interfacial adhesion due to too many polar groups. This avoids problems such as sudden increase in peeling force, silver streaks, and edge chipping of the PMMA optical film when peeling off the film. The release layer does not add this component to prevent excessive interfacial adhesion and damage to the gradient structure.The photoinitiator is added in the range of 1 to 3 parts. Its mechanism of action is the same as that of the release layer. Under ultraviolet light irradiation, it decomposes to generate free radicals, which initiate the polymerization and crosslinking reaction of all monomers and prepolymers containing double bonds. The anchoring layer uses a higher range of initiator dosage, combined with a higher content of multifunctional crosslinking agent, which can fully stimulate the crosslinking reaction under the established curing process, ensure that the double bond conversion rate meets the standard, and stably achieve the design indicators of high crosslinking density and high Tg (-20℃ to -10℃) of the anchoring layer.

[0026] Overall, the anchoring layer, through differentiated design of component types and ratios, forms characteristics of high modulus, high cohesion, and strong interfacial bonding. Together with the low modulus, low cross-linking, and high buffering release layer, it constructs a complete double-layer gradient adhesive structure. This ensures that stress concentration and adhesive layer damage during the film peeling process mainly occur within the release layer. The anchoring layer remains firmly attached to the PMMA optical film surface and can be completely peeled off. Ultimately, the product achieves comprehensive performance including controllable peel force of 20-50g / 25mm, no adhesive residue after high temperature and humidity aging, no damage to the PMMA optical film, and no slippage or detachment during long-term use. At the same time, no harmful PFAS substances are used throughout the process, meeting environmental regulations.

[0027] In an optional embodiment, at 25°C, a tensile speed of 300 mm / min, and a peel angle of 180°, the surface peel force between the pressure-sensitive adhesive protective film and the untreated PMMA optical film is 20–50 g / 25 mm.

[0028] This application also provides a method for preparing the pressure-sensitive adhesive protective film for the above-mentioned surface-treated PMMA optical film, comprising the following steps: S1. Prepare the release layer adhesive and the anchoring layer adhesive; S2. Apply the release layer adhesive to the substrate layer and perform UV pre-curing to obtain a pre-cured release layer. S3. Apply the anchoring layer adhesive to the pre-cured release layer to form a double adhesive layer; S4. Perform primary curing on the double-layer adhesive layer; S5. After the product has been cured, it is subjected to heat annealing, then rewound and slit to obtain a pressure-sensitive adhesive protective film.

[0029] Preferably, in step S2, the UV pre-curing energy is 70–90 mJ / cm². 2 In step S4, the energy for primary curing is 280–320 mJ / cm². 2 Furthermore, the double bond conversion rate is greater than 95%. In step S5, the temperature of the thermal annealing treatment is 65–75°C, and the time is 1.5–2.5 hours.

[0030] In the above preparation method, a stepwise UV curing combined with thermal annealing process is used, which is synergistically matched with the adhesive formulation system to ensure the stable realization of the gradient performance of the double-layer adhesive layer. S1: The release layer and anchoring layer adhesive solutions are prepared separately according to the specified ratio, ensuring uniform dispersion of each functional monomer, prepolymer, and photoinitiator, laying the foundation for subsequent polymerization reactions. S2: After the release layer adhesive solution is applied to the substrate layer, it is heated to 70–90 mJ / cm². 2 Low-energy UV pre-curing involves the decomposition of the photoinitiator to generate free radicals, triggering only a portion of the double bonds to undergo mild polymerization, forming a semi-cured state. This process both fixes the morphology of the release layer, preventing flow-through and layer mixing during subsequent anchoring layer application, and strictly controls the crosslinking density of the release layer to a low level, aligning with its low Tg and low storage modulus formulation design. In step S3, the anchoring layer adhesive is applied to the surface of the pre-cured release layer, achieving a tight bond between the two layers through the semi-cured interface, preventing interlayer separation. Step S4 applies 280–320 mJ / cm². 2 High-energy UV primary curing enables double bond conversion rates of over 95% in the bilayer adhesive layer. The photoinitiator fully initiates deep free radical crosslinking of the two types of adhesive layer monomers and prepolymers. The anchoring layer, due to the high proportion of multifunctional prepolymers and phosphate-modified monomers, fully reacts to form a dense network with high crosslinking density and high Tg, strengthening the interfacial bonding and cohesion with the PMMA optical film. The release layer maintains the low crosslinking state set in the formulation, creating a gradient difference in modulus and Tg between the two. The S5 setting, with a heat annealing treatment at 65–75℃ for 1.5–2.5 hours, releases internal stress caused by UV curing and the difference in thermal expansion coefficients between the adhesive layer and the substrate, alleviating the stress sensitivity of the PMMA optical film. Simultaneously, it further improves the microstructure of the adhesive layer, enhancing stability under high temperature and humidity conditions and effectively preventing aging residue and film slippage. The entire process and formula complement each other, ultimately enabling the protective film to achieve a controllable peel force of 20-50g / 25mm, resulting in a firm adhesion, clean tearing, and no damage to the surface-treated PMMA optical film.

[0031] The present application will be described in detail below with reference to various embodiments. However, these embodiments do not limit the present application, and structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are all included within the protection scope of the present application.

[0032] Example 1 This embodiment provides a pressure-sensitive adhesive protective film for PMMA optical films without surface treatment. The substrate layer is a conventional PET film. The adhesive solutions are prepared according to the following weight parts: the release layer is prepared by mixing and stirring 70 parts isooctyl acrylate, 20 parts butyl acrylate, 15 parts polyurethane acrylate, 5 parts epoxy acrylate, 30 parts 2-phenoxyethyl acrylate, and 3 parts photoinitiator; the anchoring layer is prepared by mixing and stirring 50 parts isooctyl acrylate, 25 parts butyl acrylate, 20 parts polyurethane acrylate, 8 parts epoxy acrylate, 5 parts phosphate-modified acrylate, and 3 parts photoinitiator. The thickness of the release layer is controlled at 14 μm, and the thickness of the anchoring layer is controlled at 10 μm. During preparation, the two adhesive solutions are prepared first, and then the release layer adhesive solution is applied to the surface of the substrate layer using a 90 mJ / cm² pressure. 2 UV pre-curing is applied to obtain a pre-cured release layer. An anchoring layer adhesive is then applied to this release layer to form a double adhesive layer. Finally, an energy source of 320 mJ / cm² is used. 2 Energy is used to perform primary curing of the double-layer adhesive to ensure that the double bond conversion rate is greater than 95%. Finally, the cured product is placed in a 75°C environment for 2.5 hours of heat annealing. After cooling, it is rewound and slit to finally obtain the pressure-sensitive adhesive protective film.

[0033] Example 2 This embodiment provides a pressure-sensitive adhesive protective film for PMMA optical films without surface treatment. The substrate layer is a conventional PET film. The adhesive solutions are prepared according to the following weight parts: the release layer is prepared by mixing and stirring 50 parts isooctyl acrylate, 10 parts butyl acrylate, 5 parts polyurethane acrylate, 0.1 parts epoxy acrylate, 10 parts 2-phenoxyethyl acrylate, and 0.5 parts photoinitiator; the anchoring layer is prepared by mixing and stirring 30 parts isooctyl acrylate, 15 parts butyl acrylate, 10 parts polyurethane acrylate, 3 parts epoxy acrylate, 1 part phosphate-modified acrylate, and 1 part photoinitiator. The thickness of the release layer is controlled to be 10 μm, and the thickness of the anchoring layer is controlled to be 6 μm. During preparation, the two adhesive solutions are prepared first, and then the release layer adhesive solution is applied to the surface of the substrate layer using a 70 mJ / cm² pressure. 2 UV pre-curing is applied to obtain a pre-cured release layer. An anchoring layer adhesive is then applied to this release layer to form a double adhesive layer. Finally, an energy source of 280 mJ / cm² is used for UV pre-curing. 2 Energy is used to perform primary curing of the double adhesive layer to ensure that the double bond conversion rate is greater than 95%. Finally, the cured product is placed in a 65°C environment for 1.5 hours of heat annealing. After cooling, it is rewound and slit to finally obtain the pressure-sensitive adhesive protective film.

[0034] Example 3 This embodiment provides a pressure-sensitive adhesive protective film for PMMA optical films without surface treatment. The substrate layer is a conventional PET film. The adhesive solutions are prepared according to the following weight parts: the release layer is prepared by mixing and stirring 60 parts of isooctyl acrylate, 15 parts of butyl acrylate, 10 parts of polyurethane acrylate, 2 parts of epoxy acrylate, 20 parts of 2-phenoxyethyl acrylate, and 1.8 parts of photoinitiator; the anchoring layer is prepared by mixing and stirring 40 parts of isooctyl acrylate, 20 parts of butyl acrylate, 15 parts of polyurethane acrylate, 5 parts of epoxy acrylate, 3 parts of phosphate-modified acrylate, and 2 parts of photoinitiator. The thickness of the release layer is controlled to be 12 μm, and the thickness of the anchoring layer is controlled to be 8 μm. During preparation, the two adhesive solutions are prepared first, and then the release layer adhesive solution is applied to the surface of the substrate layer using 80 mJ / cm². 2 UV pre-curing is applied to obtain a pre-cured release layer. An anchoring layer adhesive is then applied to this release layer to form a double adhesive layer. Finally, an energy source of 300 mJ / cm² is used for UV pre-curing. 2 Energy is used to perform primary curing of the double-layer adhesive to ensure that the double bond conversion rate is greater than 95%. Finally, the cured product is placed in a 70°C environment for 2 hours of heat annealing. After cooling, it is rewound and slit to finally obtain the pressure-sensitive adhesive protective film.

[0035] Comparative Example 1 The difference between this comparative example and Example 3 is that the anchoring layer does not contain phosphate-modified acrylate.

[0036] Comparative Example 2 The difference between this comparative example and Example 3 is that, by weight, 3 parts of phosphate-modified acrylate were also added to the release layer.

[0037] Comparative Example 3 The difference between this comparative example and Example 3 is that, by weight, the release layer contains 35 parts of 2-phenoxyethyl acrylate.

[0038] Comparative Example 4 The difference between this comparative example and Example 3 is that, by weight, the release layer contains 5 parts of 2-phenoxyethyl acrylate.

[0039] Comparative Example 5 The difference between this comparative example and Example 3 is that both the release layer and the anchoring layer use the same formulation as the anchoring layer in Example 3. That is, both the release layer and the anchoring layer are composed of 40 parts of isooctyl acrylate, 20 parts of butyl acrylate, 15 parts of polyurethane acrylate, 5 parts of epoxy acrylate, 3 parts of phosphate-modified acrylate, and 2 parts of photoinitiator. The thicknesses of the two layers are 12 μm for the release layer and 8 μm for the anchoring layer, and the preparation process is completely consistent with that of Example 3.

[0040] Comparative Example 6 The difference between this comparative example and Example 3 is that the thickness of the release layer is controlled at 8 μm and the thickness of the anchoring layer is controlled at 12 μm, that is, the thicknesses of the two layers are interchanged, and the formulations of the release layer and the anchoring layer are the same as those in Example 3.

[0041] Comparative Example 7 The difference between this comparative example and Example 3 is that, by weight, the number of phosphate-modified acrylates in the anchoring layer is increased to 7 parts, while the remaining components are the same as in Example 3.

[0042] Comparative Example 8 The difference between this comparative example and Example 3 is that, by weight, the amount of phosphate-modified acrylate in the anchoring layer is reduced to 0.5 parts (below the lower limit of 1 part), while the remaining components are the same as in Example 3.

[0043] Comparative Example 9 The difference between this comparative example and Example 3 is that no heat annealing is performed after the main curing in step S5 (i.e., the annealing step of 70℃ / 2h is omitted), while the other process parameters are the same as those in Example 3.

[0044] The manufacturers or models of the components used in the above examples or comparative examples are as follows: isooctyl acrylate (2-EHA) was purchased from Dow Chemical, butyl acrylate (BA) and 2-phenoxyethyl acrylate (POEA) were both provided by BASF, the polyurethane acrylate was selected from Covestro products, and the polyurethane acrylate was preferably a hexafunctional polyurethane acrylate, the epoxy acrylate was purchased from Amgen Corporation, the phosphate ester modified acrylate was from Jōhoku Chemicals of Japan, and the photoinitiator was 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP) model Omnirad 1173, which was provided by IGM Resins.

[0045] The pressure-sensitive adhesive protective films obtained in the above embodiments and comparative examples were subjected to performance tests. The performance data included initial peel force, residual adhesive and peeling after high temperature and high humidity aging, holding power, and surface condition of the PMMA optical film after peeling. The following are the test standards or test methods for the above performance data.

[0046] 1. Initial peel force The test was conducted according to the national standard GB / T 2792-1998 (Test Method for 180° Peel Strength of Pressure-Sensitive Adhesive Tape). The specific steps are as follows: A pre-cut pressure-sensitive adhesive protective film sample (25mm wide) was attached to a standard untreated PMMA optical film test plate. A 2kg standard rubber roller was used to roll the film back and forth once at a speed of approximately 300mm / min to ensure full adhesion between the adhesive layer and the substrate. The plate was then left to stand for 20–30 minutes under standard testing conditions (25℃±2℃, relative humidity 50%±5%). Next, the test plate was fixed to the lower clamp of an electronic tensile testing machine. The free end of the protective film was folded upwards at a 180° angle and clamped in the upper clamp. Peeling was performed at a constant tensile speed of 300mm / min. The average force value during the peeling process was recorded, expressed in g / 25mm. The final result was the arithmetic mean of at least three valid samples, with a target window of 20–50 g / 25mm.

[0047] 2. Residual adhesive and peeling after high temperature and humidity aging. The PMMA optical film test panel with the pressure-sensitive adhesive protective film attached was placed in a constant temperature and humidity test chamber and aged continuously for 72 hours at 85℃±2℃ and 85%±3% RH (relative humidity). After aging, the test panel was carefully removed and placed in a standard environment (25℃±2℃, 50%±5% RH) to cool for 2 hours. Then, the pressure-sensitive adhesive protective film was manually peeled off from the PMMA optical film at a speed of approximately 300 mm / min. Immediately after peeling, the surface of the PMMA optical film was visually inspected under a black background and a standard light source (D65) for any adhesive residue, white adhesive spots, adhesive marks, or hazy traces. At the same time, it was recorded whether the protective film curled up, floated, or fell off during the aging process. The result was judged as "no adhesive residue, no peeling" or "with adhesive residue / with peeling" to verify its interfacial stability and cohesion under high temperature and high humidity conditions.

[0048] 3. Holding power (shear adhesion) The test was conducted in accordance with the national standard GB / T 4851-1998 (Test Method for Holding Strength of Pressure-Sensitive Adhesive Tapes) and the high-temperature requirements of high-end applications (such as automotive panels). A pressure-sensitive adhesive protective film sample with a width of 25mm and a length of 100mm was adhered to an untreated PMMA optical film test board with an adhesion area of ​​25mm × 25mm. After rolling with a 2kg standard roller, it was left to stand in a standard environment (25℃±2℃) for 20 minutes. Subsequently, the test board was vertically suspended in a constant temperature oven, maintaining the test temperature at 70℃±2℃. A standard 1kg weight was suspended at the free end of the protective film, and the time from the start of suspension to the protective film detaching from the PMMA optical film or slipping more than a given distance (e.g., 3mm) was recorded. At least three parallel samples were tested for each sample, and the arithmetic mean was taken. The unit of measurement was hours (h), and the holding strength was required to be greater than 48 hours.

[0049] 4. Surface condition of the PMMA optical film after peeling This test is typically performed after the 180° peel force test or the film removal operation following high-temperature and high-humidity aging. Under standard conditions (25℃±2℃), a comprehensive scan of the PMMA optical film surface after the protective film has been removed is conducted using an observation device equipped with a microscopic imaging system or a high-magnification lens (20x or higher is recommended). The focus is on observing the test area (i.e., the area originally covered by the adhesive layer) for microcracks (silver streaks), edge chipping (chipping), or any form of visible damage to the PMMA optical film caused by stress concentration. The surface condition is judged as "no damage" or "with silver streaks / chipping / cracks," and combined with the peel force data, a comprehensive assessment is made to determine whether the protective film successfully dissipated the peel force within the peel layer during the removal process, thereby protecting the integrity of the PMMA optical film.

[0050] The performance test results of the pressure-sensitive adhesive protective films obtained in the above embodiments and comparative examples are shown in Table 1.

[0051] Table 1

[0052] As shown in Table 1, the initial peel force of Examples 1-3 all fell within the range of 20-50 g / 25 mm, meeting the requirements for low adhesion and stable adhesion. In the high-temperature and high-humidity aging test, Examples 1-3 all showed no residue and no peeling, indicating that the phosphate-modified acrylate in the anchoring layer effectively improved the interfacial bonding force with the low surface energy PMMA optical film. The cross-linked structure of the double-layer adhesive layer ensured excellent cohesion, avoiding the problems of residual adhesive and film edge lifting and detachment after aging due to cohesive breakdown. Examples 1-3 also demonstrated good high-temperature adhesion. The stress resistance is greater than 48 hours, which meets the requirements of high-end applications such as automotive and optical panels. It also verifies the effect of polyurethane acrylate and epoxy acrylate in the formula on improving the heat resistance and creep resistance of the adhesive layer. The PMMA optical film was not damaged after the pressure-sensitive adhesive protective film in Examples 1-3 was applied and peeled off. This shows that the flexible buffering effect of the low glass transition temperature, low crosslinking density and low energy storage modulus of the release layer is fully utilized. The peeling stress is dissipated inside the release layer and is not transmitted to the PMMA optical film. The design of the double-layer gradient stress dissipation system has been implemented and is effective.

[0053] Comparing Comparative Example 1 with Example 3, it can be seen that Comparative Example 1 removed the core functional component phosphate-modified acrylate in the anchoring layer, thus losing its ability to form quasi-chemical bonds with the PMMA optical film surface. The initial peel force dropped to 15g / 25mm, which is lower than the lower limit of 20g / 25mm. The high-temperature holding power was less than 24 hours, and residual adhesive appeared after aging, and the film was easy to fall off. This shows that phosphate-modified acrylate is an indispensable component to ensure interfacial adhesion and cohesion.

[0054] Comparing Comparative Example 2 with Example 3, it can be seen that Comparative Example 2 added phosphate-modified acrylate to the release layer, which broke the performance gradient between the two adhesive layers. The overall adhesion force increased significantly to 120g / 25mm, resulting in a serious over-limit of the peel force. The excessive interfacial stress caused the PMMA optical film to chip and silver streaks. Therefore, phosphate-modified acrylate, a polar adhesive component, cannot be added to the release layer.

[0055] Comparing Comparative Example 3 with Example 3, it can be seen that Comparative Example 3 increased the content of 2-phenoxyethyl acrylate in the release layer to 35 parts, which exceeds the upper limit of 10-30 parts. The peel force increased to 58g / 25mm, which means that a higher peel force is required to peel the pressure-sensitive adhesive protective film off the PMMA optical film, causing silver streaks to appear on the substrate.

[0056] Comparing Comparative Example 4 with Example 3, it can be seen that Comparative Example 4 adjusted the content of 2-phenoxyethyl acrylate in the release layer to 5 parts, and the initial peel force was 17g / 25mm. The low content of this component resulted in poor wetting effect of the adhesive layer on the surface of the PMMA optical film, insufficient interfacial adhesion, easy detachment of the protective film, and a significant decrease in holding power. Although it would not cause stress damage to the substrate, the overall performance was poor.

[0057] Comparing Comparative Example 5 with Example 3, it can be seen that Comparative Example 5 unifies the release layer and anchoring layer into a highly cross-linked, high-modulus anchoring layer formulation, completely losing the double-layer gradient structure. The peel force reaches 85g / 25mm, and residual adhesive is generated after aging and the substrate is damaged. This proves that the differentiated formulation, differentiated thermal and mechanical properties of the two adhesive layers are the core of stress dissipation, prevention of residual adhesive, and protection of the substrate.

[0058] Comparing Comparative Example 6 with Example 3, it can be seen that in Comparative Example 6, the thicknesses of the two adhesive layers were interchanged. The thickness of the release layer was adjusted to 8 μm, deviating from the required thickness of 10–14 μm, and the thickness of the anchoring layer was adjusted to 12 μm, deviating from the required thickness of 6–10 μm. The overall peel force of the pressure-sensitive adhesive protective film was 55 g / 25 mm, and residual adhesive, peeling, and silver streaks appeared on the substrate. This indicates that the thickness range specified in this application is also an important condition for ensuring the stability of the double-layer structure and the reasonable distribution of stress.

[0059] Comparing Comparative Examples 7 and 8 with Example 3, it can be seen that in Comparative Example 7, the phosphate-modified acrylate component in the anchoring layer was increased to 7 parts, exceeding the upper limit of 1-5 parts, resulting in excessive interfacial adhesion and a peel strength of 68g / 25mm, which easily caused silver streaks on the substrate edges. In Comparative Example 8, the phosphate-modified acrylate component in the anchoring layer was reduced to 0.5 parts, below the lower limit, resulting in insufficient interfacial adhesion, a peel strength of 18g / 25mm, insufficient holding power for 24 hours, and easy film detachment. This indicates that the content of phosphate-modified acrylate in the anchoring layer is also a very important factor affecting the performance of the pressure-sensitive adhesive protective film.

[0060] Comparing Comparative Example 9 with Example 3, it can be seen that Comparative Example 9 omitted the heat annealing process, and the residual internal stress generated by curing could not be released. Even if the peel force was controlled within the normal range, residual adhesive would appear after high-temperature aging. This indicates that the heat annealing process is a necessary step to eliminate internal stress and improve aging resistance.

[0061] In summary, this application provides a pressure-sensitive adhesive protective film composed of a three-layer structure: a substrate layer, a release layer, and an anchoring layer. The release layer and the anchoring layer use differentiated formulations. The release layer uses 2-phenoxyethyl acrylate to regulate the interfacial properties, while the anchoring layer adds phosphate-modified acrylate to enhance the adhesion to the surface of the untreated PMMA optical film. The two layers form a gradient difference in glass transition temperature, crosslinking density, and storage modulus. This is combined with a limited ratio, adhesive layer thickness, and a stepwise UV curing and thermal annealing preparation process.

[0062] The pressure-sensitive adhesive protective film prepared based on the above technical solution has the following excellent properties: controllable initial peel force of 20-50g / 25mm; no residue or peeling after high temperature and humidity aging; holding power of more than 48 hours at 70℃; and no silver streaks, edge chipping, cracks, or other damage to the PMMA optical film after peeling. Furthermore, by relying on the component differences, performance gradients, standard layer thickness, and complete preparation process between the release layer and anchoring layer, the pain points of traditional protective films such as easy peeling, easy residue, and easy damage to the PMMA optical film are solved.

[0063] 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. A pressure-sensitive adhesive protective film for PMMA optical films without surface treatment, characterized in that, It includes a substrate layer, a release layer, and an anchoring layer stacked sequentially; wherein: The release layer is formed by UV curing of a release layer adhesive containing the following components: isooctyl acrylate, butyl acrylate, polyurethane acrylate, epoxy acrylate, 2-phenoxyethyl acrylate, and a photoinitiator. The anchoring layer is formed by UV curing of an anchoring layer adhesive containing the following components: isooctyl acrylate, butyl acrylate, polyurethane acrylate, epoxy acrylate, phosphate-modified acrylate, and photoinitiator. The glass transition temperature, crosslinking density, and energy storage modulus of the release layer are all lower than those of the anchoring layer.

2. The pressure-sensitive adhesive protective film for PMMA optical films without surface treatment according to claim 1, characterized in that, The thickness of the peeling layer is 10–14 μm, and the thickness of the anchoring layer is 6–10 μm.

3. The pressure-sensitive adhesive protective film for PMMA optical films without surface treatment according to claim 1, characterized in that, By weight, the release layer is formed by UV curing of a release layer adhesive comprising the following components: 50-70 parts of isooctyl acrylate; 10-20 parts of butyl acrylate; 5-15 parts of polyurethane acrylate; 0.1 to 5 parts of epoxy acrylate; 10-30 parts of 2-phenoxyethyl acrylate; And 0.5 to 3 parts of photoinitiator.

4. The pressure-sensitive adhesive protective film for PMMA optical films without surface treatment according to claim 1, characterized in that, By weight, the anchoring layer is formed by UV curing of an anchoring layer adhesive comprising the following components: 30-50 parts of isooctyl acrylate; 15-25 parts of butyl acrylate; 10-20 parts of polyurethane acrylate; 3-8 parts of epoxy acrylate; 1-5 parts of phosphate-modified acrylate; And 1 to 3 parts of photoinitiator.

5. The pressure-sensitive adhesive protective film for PMMA optical films without surface treatment according to claim 1, characterized in that, The glass transition temperature of the release layer is -40℃ to -25℃, and the glass transition temperature of the anchoring layer is -20℃ to -10℃.

6. The pressure-sensitive adhesive protective film for PMMA optical films without surface treatment according to claim 1, characterized in that, At 25°C, a tensile speed of 300 mm / min, and a peel angle of 180°, the surface peel force between the pressure-sensitive adhesive protective film and the untreated PMMA optical film is 20–50 g / 25 mm.

7. A method for preparing a pressure-sensitive adhesive protective film for a surface-treated PMMA optical film according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Prepare the release layer adhesive and the anchoring layer adhesive; S2. Apply the release layer adhesive to the substrate layer and perform UV pre-curing to obtain a pre-cured release layer. S3. Apply the anchoring layer adhesive to the pre-cured release layer to form a double adhesive layer; S4. Perform primary curing on the double-layer adhesive layer; S5. After the product has been cured, it is subjected to heat annealing, then rewound and slit to obtain a pressure-sensitive adhesive protective film.

8. The preparation method according to claim 7, characterized in that, In step S2, the energy of the UV pre-curing is 70–90 mJ / cm². 2 .

9. The preparation method according to claim 7, characterized in that, In step S4, the energy for primary curing is 280–320 mJ / cm². 2 Furthermore, the double bond conversion rate is greater than 95%.

10. The preparation method according to claim 7, characterized in that, In step S5, the temperature of the heat annealing treatment is 65-75°C, and the time is 1.5-2.5 hours.

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