Preparation and application of temperature-sensitive water-based pressure-sensitive adhesive

Abstract

This invention discloses the preparation and application of a temperature-sensitive waterborne pressure-sensitive adhesive. The preparation method of the temperature-sensitive waterborne pressure-sensitive adhesive is as follows: a water-soluble RAFT chain transfer agent and a reactive emulsifier are dissolved in water, and then an acrylate mixed monomer is added and stirred to obtain a first emulsion; under an inert atmosphere, the first emulsion is heated, and a water-soluble initiator is added dropwise, resulting in a second emulsion after reaction; the second emulsion is then mixed and dispersed with a temperature-sensitive monomer, a water-dispersible photoacid generator, a waterborne blocked isocyanate, and a water-soluble photoinitiator to obtain the temperature-sensitive waterborne pressure-sensitive adhesive. This temperature-sensitive waterborne pressure-sensitive adhesive is applied in the process protection of flexible OLED screens. This invention achieves active and reversible control of the peel force of the temporary protective film from "firmly adhered" to "easily peelable," perfectly balancing the high adhesion requirements and low stress requirements during screen process protection, fundamentally reducing the risk of damage to flexible screens, and has good application prospects.

Description

Technical Field

[0001] This invention relates to a pressure-sensitive adhesive, and more particularly to the preparation of a smart water-based pressure-sensitive adhesive with heat-triggered reversible peel force characteristics and its application in the process protection of flexible OLED screens. Background Technology

[0002] Flexible OLED screens represent a significant development direction in current display technology, with substrates typically made of flexible materials such as polyimide (PI). During the manufacturing, cutting, handling, and assembly of flexible OLED screen modules, the screen surface is highly susceptible to scratches, dust contamination, and chemical corrosion, necessitating the use of high-performance temporary protective films. Currently, most commercially available temporary protective films are made using traditional acrylic pressure-sensitive adhesives. While these adhesives offer acceptable initial tack, they fall short in meeting the specific requirements of flexible OLED manufacturing processes, primarily in the following three aspects: 1. Uncontrollable peel force, easily causing screen damage: The peel force of traditional pressure-sensitive adhesives is often fixed. If the peel force is too high, the huge adhesive force may exceed the bearing limit of the flexible substrate when peeling off the protective film, causing the thin film layer of the screen itself to be pulled up (interlayer peeling), or residual stress to cause slight deformation of the screen, causing irreversible damage to the precision circuitry. If the peel force is too low, it cannot provide sufficient protection during the manufacturing process, causing the protective film to warp and fall off prematurely.

[0003] 2. Insufficient temperature resistance, unable to adapt to high-temperature processes: Key processes such as curing and encapsulation of OLED modules are often carried out at high temperatures (e.g., 60-80℃). Ordinary pressure-sensitive adhesives are prone to softening and reduced cohesive strength at high temperatures, which may not only cause adhesive overflow and contaminate the screen, but also cause uncontrollable changes in their peel force, and even leave residues that are difficult to clean after use.

[0004] 3. Mismatched optical performance affects online inspection: The optical performance of the protective film itself is crucial. If the light transmittance of the pressure-sensitive adhesive is insufficient or the haze is too high, it will interfere with the accuracy of automated optical inspection (AOI) based on machine vision during the manufacturing process, which may lead to missed defects and affect product yield.

[0005] To address the aforementioned issues, existing technologies have developed ultra-low peel strength adhesives or high-temperature resistant silicone systems. However, ultra-low peel strength adhesives often have low initial tack, making them prone to peeling during screen manufacturing and resulting in low reliability in screen protection. While silicone pressure-sensitive adhesives offer good temperature resistance, they suffer from issues such as easily adsorbing small silicone oil molecules that contaminate the screen and poor compatibility with acrylic substrates. Chinese patent CN121319799A discloses a flexible screen optically transparent adhesive film and its preparation method, which uses traditional emulsion polymerization to prepare the pressure-sensitive adhesive layer. Although this technology provides some protection, its peel strength changes by less than 20% between room temperature and 60°C (from 1.8 N / 25mm to 1.5 N / 25mm), failing to meet the requirement of "easy peeling" after manufacturing. Furthermore, visible adhesive residue is observed after testing at 80°C. This further confirms that developing a pressure-sensitive adhesive that can intelligently respond to temperature, achieve significant reversible changes in peel strength, and leave no residue after high temperatures is a pressing technical challenge in this field. Therefore, developing a pressure-sensitive adhesive that can dynamically respond to process requirements, intelligently adjust adhesion, and simultaneously possess high light transmittance, high temperature resistance, and no residue has become an urgent and clear technical challenge in the field of flexible OLED manufacturing.

[0006] While existing technologies have attempted to introduce temperature-sensitive monomers or functional fillers, the poor compatibility between oily components and aqueous emulsions leads to uneven dispersion and unstable performance. For example, oil-soluble photoinitiators tend to aggregate in the aqueous phase, affecting curing efficiency; traditional RAFT polymerization is carried out in organic solvents, making it difficult to use directly in aqueous systems. Summary of the Invention

[0007] Objective of this invention: The objective of this invention is to provide a method for preparing a temperature-sensitive waterborne pressure-sensitive adhesive, solving the problem of how to prepare a smart waterborne pressure-sensitive adhesive with heat-triggered reversible peel force characteristics. Another objective of this invention is to propose the application of temperature-sensitive waterborne pressure-sensitive adhesives in the process protection of flexible OLED screens, solving the problem of how to protect flexible OLED screens during the manufacturing process.

[0008] Technical solution: The preparation method of the temperature-sensitive water-based pressure-sensitive adhesive of the present invention includes the following steps: (1) Dissolve the water-soluble RAFT chain transfer agent and the reactive emulsifier in water, and then add the acrylate mixed monomers and stir to obtain the first emulsion; (2) Under an inert atmosphere, the first emulsion is heated and a water-soluble initiator is added dropwise to it. After the reaction, the second emulsion is obtained. (3) The second emulsion is mixed and dispersed with a temperature-sensitive monomer, a water-dispersible photoacid generator, a water-based blocked isocyanate and a water-soluble photoinitiator to obtain a temperature-sensitive water-based pressure-sensitive adhesive.

[0009] Preferably, in step (1), the water-soluble RAFT chain transfer agent is 4-cyano-4-[(dodecylthiothiocarbonyl)thio]pentanoate, and the reactive emulsifier is allyloxyhydroxypropyl sulfonate.

[0010] Preferably, in step (1), the acrylate mixed monomers include isooctyl acrylate, butyl acrylate, methyl methacrylate, acrylic acid, and hydroxyethyl acrylate.

[0011] Furthermore, the mass ratio of isooctyl acrylate, butyl acrylate, methyl methacrylate, acrylic acid, and hydroxyethyl acrylate is 50-70:20-30:6-10:2-6:1-5.

[0012] Preferably, the mass ratio of the water-soluble RAFT chain transfer agent, reactive emulsifier, water, and acrylate mixed monomers is 0.1-0.5:1-3:80-120:90-110.

[0013] Preferably, in step (2), the water-soluble initiator is potassium persulfate, and the reaction conditions are 60-80℃ for 6-10h.

[0014] Preferably, in step (3), the thermosensitive monomer is N-isopropylacrylamide, and the water-soluble photoinitiator is a polyethylene glycol-modified derivative of 2-hydroxy-2-methyl-1-phenyl-1-propanone, such as Irgacure 2959.

[0015] Preferably, in step (3), the mass ratio of the second emulsion, the thermosensitive monomer, the water-dispersible photoacid generator, the water-based blocked isocyanate and the water-soluble photoinitiator is 90-110:3-7:0.5-1.5:3-7:1-2.

[0016] This invention uses a structurally regular acrylate emulsion synthesized by the RAFT method as the matrix to ensure the uniformity and stability of the adhesive layer's intrinsic mechanical properties. A thermosensitive monomer, N-isopropylacrylamide (NIPAM), is introduced as a smart responsive unit. Its molecular chains undergo a reversible conformational transition from extension to contraction when the temperature exceeds its LCST (approximately 32°C), macroscopically manifesting as a significant reduction in adhesion. A photoacid generator and a latent curing agent are used in conjunction to construct a photothermal dual-curing system.

[0017] The second aspect of this invention discloses the application of the above-mentioned temperature-sensitive water-based pressure-sensitive adhesive in the process protection of flexible OLED screen manufacturing.

[0018] Specifically, the method for protecting flexible OLED screens using the aforementioned temperature-sensitive water-based pressure-sensitive adhesive includes the following steps: The temperature-sensitive water-based pressure-sensitive adhesive is coated onto the base film, dried at 75-85℃ for 1-5 minutes, and then subjected to a pressure of 300-800 mJ / cm. 2 The temperature-sensitive water-based pressure-sensitive adhesive is irradiated with ultraviolet light to complete the primary curing, and then placed at 50-80℃ for 10-20 minutes to complete the secondary curing, forming a temporary protective film on the surface of the flexible OLED screen.

[0019] In some embodiments, the thickness of the temperature-sensitive water-based pressure-sensitive adhesive coating on the base film is 10-35 μm, and the base film is made of PET or polyimide.

[0020] The mechanism of action of this invention is as follows: UV curing first forms a preliminary cross-linked network, giving the pressure-sensitive adhesive basic initial tack and cohesive strength. The subsequent heat treatment has a dual effect: first, it activates the phase change of the temperature-sensitive monomer, directly reducing interfacial adhesion; second, it promotes the release of acidic substances from the photoacid generator, triggering the latent curing agent to undergo deep cross-linking (secondary curing), greatly improving the cohesive strength and temperature resistance of the adhesive layer, ensuring clean peeling even after high-temperature use.

[0021] This invention employs a stepwise method to prepare a temperature-sensitive waterborne pressure-sensitive adhesive. First, an emulsion with a narrow molecular weight distribution is obtained through RAFT polymerization. Then, it is mixed with other functional components to form a slurry. When preparing a temporary protective film with this slurry, curing and performance setting are completed through UV irradiation and programmed heat treatment.

[0022] The temperature sensitivity of this invention is achieved without relying on a traditional aqueous solution environment, but rather through multiple synergistic mechanisms that take effect in a solid film, including: 1. Microenvironment hydration: Hydrophilic monomers (such as hydroxyethyl acrylate and acrylic acid) in acrylate emulsions can adsorb trace amounts of moisture in the environment, forming a local hydration microenvironment within the cross-linked network, providing the driving conditions for conformational changes of N-isopropylacrylamide (NIPAM) segments. 2. Network internal stress regulation: When the temperature exceeds the LCST (32℃) of NIPAM, its chain segments undergo hydrophobic collapse, generating internal stress in the three-dimensional network, which directly reduces the modulus of the adhesive layer and the interfacial adhesion work, macroscopically manifested as a decrease in peel force (e.g., reduced to 0.1-0.3N / 25mm at 60℃). 3. Curing Synergistic Effect: The dual curing of light and heat forms a stable network, ensuring reversible and repeatable temperature-sensitive response.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention realizes the active and reversible control of the peeling force of the temporary protective film from "adhesive" to "easy to peel off", which perfectly balances the high adhesion requirement in the screen manufacturing process and the low stress requirement during peeling, fundamentally reducing the risk of damaging the flexible screen.

[0024] (2) The temporary protective film prepared by this invention has extremely high light transmittance (≥92%) and extremely low haze (≤1.2%), ensuring the accuracy of online detection. This invention uses an environmentally friendly and non-toxic water-based system, avoiding the potential damage to the screen caused by oil-based solvents.

[0025] (3) Excellent high temperature stability: The stable three-dimensional network formed by photothermal dual curing enables the pressure-sensitive adhesive to withstand the high temperature environment in the OLED process, preventing high temperature softening, overflow or performance degradation.

[0026] (4) Environmental protection and process compatibility: The entire process does not require organic solvents, which is in line with the trend of green manufacturing. The preparation process is compatible with existing coating production lines and is easy to scale up. Detailed Implementation

[0027] The technical solution of the present invention will be further described below.

[0028] Example 1: A method for preparing a temperature-sensitive water-based pressure-sensitive adhesive is as follows: (1) By weight, 60 parts of isooctyl acrylate, 25 parts of butyl acrylate, 8 parts of methyl methacrylate, 4 parts of acrylic acid and 3 parts of hydroxyethyl acrylate are mixed to obtain a mixed monomer of acrylates. (2) Dissolve 0.3 parts of sodium 4-cyano-4-[(dodecylthiothiocarbonyl)thio]valerate (CDTPA) and 2 parts of sodium allyl hydroxypropyl sulfonate (HAPS) in 100 parts of deionized water, then add 100 parts of acrylate mixed monomers, and pre-emulsify by high-speed stirring and shearing at 8000 rpm for 30 min to obtain the first emulsion.

[0029] (3) Transfer all of the first emulsion to the reactor and purge with nitrogen for 30 min to remove oxygen. Heat the first emulsion to 70°C and add 0.2 parts of a 5 wt% potassium persulfate (KPS) aqueous solution. React for 8 hours to obtain a second emulsion with a solid content of about 50%. According to GPC testing, the polymer PDI is 1.21, indicating that the molecular weight distribution is very narrow. (4) By weight, 100 parts of the second emulsion, 5 parts of N-isopropylacrylamide (NIPAM), BASF's Luviquat™ series water-dispersible photoacid generator nano-slurry (converted to 1 part by solid content), Bayer's Bayhydur® BL 5335 water-based blocked isocyanate dispersion (converted to 5 parts by solid content), and 1.5 parts of Irgacure2959 are mixed and then stirred at low speed (300 rpm, 30 min) with ultrasonic assistance (400 W power, 5 s working time, 5 s interval, 10 min total time) to ensure that the mixture is fully dispersed and uniform, thus obtaining a temperature-sensitive water-based pressure-sensitive adhesive slurry.

[0030] Example 2: A method for preparing a temperature-sensitive water-based pressure-sensitive adhesive is as follows: (1) By weight, 50 parts of isooctyl acrylate, 20 parts of butyl acrylate, 6 parts of methyl methacrylate, 2 parts of acrylic acid and 1 part of hydroxyethyl acrylate are mixed to obtain a mixed monomer of acrylates. (2) Dissolve 0.1 parts of sodium 4-cyano-4-[(dodecylthiothiocarbonyl)thio]valerate (CDTPA) and 1 part of sodium allyl hydroxypropyl sulfonate (HAPS) in 80 parts of deionized water, then add 90 parts of acrylate mixed monomers, and pre-emulsify by high-speed stirring and shearing at 9000 rpm for 30 min to obtain the first emulsion.

[0031] (3) Transfer all of the first emulsion to the reactor and purge with nitrogen for 30 min to remove oxygen. Heat the first emulsion to 60°C and add 0.1 part of a 4 wt% potassium persulfate (KPS) aqueous solution. React for 10 hours to obtain a second emulsion with a solid content of about 50%. (4) By weight, 90 parts of the second emulsion, 3 parts of N-isopropylacrylamide (NIPAM), water-dispersible photoacid generator nano-slurry (0.5 parts based on solid content), water-based blocked isocyanate dispersion (3 parts based on solid content), and 1 part of Irgacure 2959 are mixed and then stirred at low speed (300 rpm, 30 min) with ultrasonic assistance (400 W power, 5 s working time, 5 s interval, 10 min total time) to ensure that the mixture is fully dispersed and uniform, thus obtaining a temperature-sensitive water-based pressure-sensitive adhesive slurry.

[0032] Example 3: A method for preparing a temperature-sensitive water-based pressure-sensitive adhesive is as follows: (1) By weight, 65 parts of isooctyl acrylate, 28 parts of butyl acrylate, 9 parts of methyl methacrylate, 4 parts of acrylic acid, and 2 parts of hydroxyethyl acrylate are mixed to obtain a mixed monomer of acrylates. (2) Dissolve 0.4 parts CDTPA and 3 parts HAPS in 110 parts deionized water by weight, then add 105 parts acrylate mixed monomers, and pre-emulsify by high-speed stirring and shearing at 7000 rpm for 30 minutes to obtain the first emulsion.

[0033] (3) Transfer the entire first emulsion to the reactor and purge with nitrogen for 30 min to remove oxygen. Heat the first emulsion to 80°C and add 0.3 parts of KPS aqueous solution dropwise. React for 9 hours to obtain a second emulsion with a solid content of about 50%. (4) By weight, 110 parts of the second emulsion, 6 parts of NIPAM, BASF's Luviquat™ series water-dispersible photoacid generator nano-slurry (equivalent to 3 parts by solid content), Bayer's Bayhydur® BL 5335 water-based blocked isocyanate dispersion (equivalent to 6 parts by solid content), and 1.3 parts of Irgacure 2959 are mixed and then stirred at low speed (300 rpm, 30 min) with ultrasonic assistance (400 W power, 5 s working time, 5 s interval, 10 min total time) to ensure that the mixture is fully dispersed and uniform, thus obtaining a temperature-sensitive water-based pressure-sensitive adhesive slurry.

[0034] Example 4: A method for preparing a temperature-sensitive water-based pressure-sensitive adhesive is as follows: (1) By weight, 70 parts of isooctyl acrylate, 30 parts of butyl acrylate, 10 parts of methyl methacrylate, 6 parts of acrylic acid and 5 parts of hydroxyethyl acrylate are mixed to obtain a mixed monomer of acrylates. (2) Dissolve 0.5 parts CDTPA and 3 parts HAPS in 120 parts deionized water by weight, then add 110 parts acrylate mixed monomers, and pre-emulsify by high-speed stirring and shearing at 8000 rpm for 30 minutes to obtain the first emulsion.

[0035] (3) Transfer all of the first emulsion to the reactor and purge with nitrogen for 30 min to remove oxygen. Heat the first emulsion to 80°C and add 0.3 parts of KPS aqueous solution dropwise. React for 6 hours to obtain a second emulsion with a solid content of about 50%. (4) By weight, 110 parts of the second emulsion, 7 parts of NIPAM, water-dispersible photoacid generator nano-slurry (equivalent to 1.5 parts based on solid content), water-based blocked isocyanate dispersion (equivalent to 7 parts based on solid content), and 2 parts of Irgacure2959 are mixed and then stirred at low speed (300 rpm, 30 min) with ultrasonic assistance (400 W power, 5 s working time, 5 s interval, 10 min total time) to ensure that the mixture is fully dispersed and uniform, thus obtaining a temperature-sensitive water-based pressure-sensitive adhesive slurry.

[0036] Example 5: Preparation of a temporary protective film on a base film, the method is as follows: The temperature-sensitive water-based pressure-sensitive adhesive paste prepared in Example 1 was coated onto a 25μm thick PET base film. The film was first dried at 80°C for 3 minutes, and then subjected to a pressure of 800 mJ / cm². 2 The temperature-sensitive water-based pressure-sensitive adhesive is irradiated with ultraviolet light to complete the primary curing, and then placed at 60℃ for 15 minutes to complete the secondary curing, forming a temporary protective film on the surface of the flexible OLED screen.

[0037] Example 6: A temporary protective film was prepared on the base film, as follows: The temperature-sensitive water-based pressure-sensitive adhesive paste prepared in Example 2 was coated onto a 25 μm thick PET base film with a thickness of 10 μm. It was first dried at 75°C for 5 minutes, and then subjected to a 300 mJ / cm² coating. 2 The temperature-sensitive water-based pressure-sensitive adhesive is irradiated with ultraviolet light to complete the primary curing, and then placed at 50℃ for 20 minutes to complete the secondary curing, forming a temporary protective film on the surface of the flexible OLED screen.

[0038] Example 7: Preparation of a temporary protective film on a base film, the method is as follows: The temperature-sensitive water-based pressure-sensitive adhesive paste prepared in Example 4 was coated onto a 25μm thick PET base film with a thickness of 35μm. It was first dried at 85℃ for 1 min, and then subjected to 500 mJ / cm² pressure. 2 The temperature-sensitive water-based pressure-sensitive adhesive is irradiated with ultraviolet light to complete the primary curing, and then placed at 70℃ for 20 minutes to complete the secondary curing, forming a temporary protective film on the surface of the flexible OLED screen.

[0039] Comparative Example 1: Everything else is the same as in Example 1, except that: Sodium 4-cyano-4-[(dodecylthiothiocarbonyl)thio]valerate is not added in step (2).

[0040] Comparative Example 2: Everything else is the same as in Example 1, except that: Without performing step (3), under a nitrogen atmosphere, 0.3 parts by weight of sodium 4-cyano-4-[(dodecylthiothiocarbonyl)thio]valerate and 2 parts by weight of sodium allyloxyhydroxypropylsulfonate were dissolved in 100 parts of deionized water, and then 100 parts of acrylate mixed monomers and 0.2 parts of KPS aqueous solution were added. The mixture was stirred and sheared at high speed at 8000 rpm for 30 minutes at room temperature to obtain the second emulsion.

[0041] Comparative Example 3: Everything else is the same as in Example 1, except that: Replace the acrylate mixed monomers with isooctyl acrylate.

[0042] Comparative Example 4: Everything else is the same as in Example 1, except that: Replace the acrylate mixed monomers with butyl acrylate.

[0043] Comparative Example 5: Everything else is the same as in Example 1, except that: Methyl methacrylate, acrylic acid, and hydroxyethyl acrylate are not added to the acrylate mixed monomers.

[0044] Comparative Example 6: Everything else is the same as in Example 1, except that: Hydroxyethyl acrylate is not added to the acrylate mixed monomers.

[0045] Comparative Example 7: Everything else is the same as in Example 1, except that: By weight, 2 parts of sodium dodecyl sulfate (SDS) were dissolved in 100 parts of deionized water, and then 100 parts of the same acrylate mixed monomers as in Example 1 were added. Under nitrogen purging and at 70°C, 0.3 parts of potassium persulfate (KPS) aqueous solution were added dropwise, and the reaction was carried out for 8 hours to obtain a conventional free radical polymerization emulsion. The remaining steps were the same as in Example 1, except that this emulsion replaced the second emulsion.

[0046] To verify the comprehensive performance of the temperature-sensitive waterborne pressure-sensitive adhesive described in this invention, the slurries obtained in Examples 1-4 and Comparative Examples 1-7 were processed under the same conditions as in Example 5 (coated onto a 25μm PET base film, dried at 80℃ for 3 min, 800 mJ / cm). 2 Protective film samples were prepared by UV curing and heat treatment at 60℃ for 15 min, and the following tests were performed: Optical properties: Transmittance and haze were measured in the wavelength range of 380-780 nm using a haze meter according to ASTM D1003 standard. Temperature-sensitive peel performance: The 180° peel force of the protective film under conditions of 25℃ & 30%RH and 60℃ & 30%RH was measured using a universal testing machine according to GB / T 2792 standard. High-temperature residue assessment: The samples treated at 60℃ & 30%RH were peeled off, visually inspected, and the substrate surface was wiped unidirectionally 3 times with a lint-free cloth soaked in isopropyl alcohol. The following rating standards were applied: Grade 0 (No residue): The substrate surface is clean after peeling, and there are no marks or changes in haze after wiping. Grade 1 (Slight residue): Slight marks are visible after peeling, but disappear completely after wiping. Grade 2 (Significant residue): Significant colloidal residue remains after peeling, and cannot be completely removed after wiping.

[0047] The test results are as follows: Table 1. Test results of film performance under different temperature and humidity conditions

[0048] As can be seen from the comprehensive analysis of the test results in Table 1, the temporary protective films prepared in Examples 1-4 of this invention exhibit excellent comprehensive performance. Their core advantages lie in the synergistic achievement of high light transmittance, strong temperature sensitivity, and high-temperature residue-free operation. Firstly, regarding temperature-sensitive peel performance, the sample films exhibit suitable initial peel force (1.65-1.74 N / 25mm) at 25°C, while the peel force drops sharply to below 0.3 N / 25mm at 60°C, with a peel force change rate exceeding 85%. This significant and reversible temperature-sensitive response is the basis of its "intelligent peel" function. Simultaneously, this characteristic shows low dependence on humidity (comparing data from 25°C / 30%RH and 25°C / 80%RH, the peel force fluctuation is minimal), perfectly adapting to the drying process environment of flexible OLED screens.

[0049] Secondly, regarding optical performance and interface stability, the transmittance of the sample examples was ≥91.5%, and the haze was ≤1.4%, meeting the stringent requirements for optical transparency in high-precision screen manufacturing processes. More importantly, after treatment at 60°C, all sample examples showed a residual adhesive rating of "Level 0 (no residue)," demonstrating that the photo-thermal dual curing system can construct a stable cross-linked network, fundamentally solving the risk of residual adhesive contamination after high-temperature processing.

[0050] In contrast, Comparative Examples 1-7 failed to simultaneously achieve the aforementioned combination of properties. The protective films prepared by Comparative Examples 1 and 7 (lacking RAFT reagent and using conventional free radical polymerization, respectively) exhibited no temperature sensitivity whatsoever, with extremely low peel strength change rates (<6%), and Comparative Example 7 showed significant residue after high-temperature treatment. This confirms that water-soluble RAFT polymerization is a necessary prerequisite for constructing regular polymer chains and achieving controllable temperature-sensitive response. Comparative Example 2 (due to the lack of RAFT polymerization conditions) and Comparative Examples 3-6 (due to incorrect monomer selection) also lost their temperature-sensitive properties, indicating that successful RAFT polymerization is indispensable for the synergistic effect of a specific monomer combination.

[0051] In summary, the data in Table 1 fully demonstrates that only through the water-soluble RAFT emulsion polymerization process described in this invention, the specific combination of acrylate monomers and temperature-sensitive monomers (NIPAM), and the photo-thermal dual curing system, can a pressure-sensitive adhesive with high light transmittance, significant temperature sensitivity (easy to peel off at high temperatures), and high-temperature stability without residue be synergistically obtained, thereby resolving the key technical contradictions in the protection of flexible OLED manufacturing processes.

Claims

1. A method for preparing a temperature-sensitive water-based pressure-sensitive adhesive, characterized in that, Includes the following steps: (1) Dissolve the water-soluble RAFT chain transfer agent and the reactive emulsifier in water, and then add the acrylate mixed monomers and stir to obtain the first emulsion; (2) Under an inert atmosphere, the first emulsion is heated and a water-soluble initiator is added dropwise to it. After the reaction, the second emulsion is obtained. (3) The second emulsion is mixed and dispersed with a temperature-sensitive monomer, a water-dispersible photoacid generator, a water-based blocked isocyanate and a water-soluble photoinitiator to obtain a temperature-sensitive water-based pressure-sensitive adhesive.

2. The preparation method of the temperature-sensitive water-based pressure-sensitive adhesive according to claim 1, characterized in that, In step (1), the water-soluble RAFT chain transfer agent is 4-cyano-4-[(dodecylthiothiocarbonyl)thio]pentanoate, and the reactive emulsifier is allyloxyhydroxypropyl sulfonate.

3. The preparation method of the temperature-sensitive water-based pressure-sensitive adhesive according to claim 1, characterized in that, In step (1), the acrylate mixed monomers include isooctyl acrylate, butyl acrylate, methyl methacrylate, acrylic acid, and hydroxyethyl acrylate.

4. The preparation method of the temperature-sensitive water-based pressure-sensitive adhesive according to claim 3, characterized in that, The mass ratio of isooctyl acrylate, butyl acrylate, methyl methacrylate, acrylic acid, and hydroxyethyl acrylate is 50-70:20-30:6-10:2-6:1-5.

5. The preparation method of the temperature-sensitive water-based pressure-sensitive adhesive according to claim 3, characterized in that, The mass ratio of the water-soluble RAFT chain transfer agent, reactive emulsifier, water, and acrylate mixed monomers is 0.1-0.5:1-3:80-120:90-110.

6. The preparation method of the temperature-sensitive water-based pressure-sensitive adhesive according to claim 1, characterized in that, In step (2), the water-soluble initiator is potassium persulfate, and the reaction conditions are 60-80℃ for 6-10h.

7. The preparation method of the temperature-sensitive water-based pressure-sensitive adhesive according to claim 1, characterized in that, In step (3), the thermosensitive monomer is N-isopropylacrylamide, and the water-soluble photoinitiator is a polyethylene glycol-modified derivative of 2-hydroxy-2-methyl-1-phenyl-1-propanone.

8. The method for preparing the temperature-sensitive water-based pressure-sensitive adhesive according to claim 1, characterized in that, In step (3), the mass ratio of the second emulsion, the thermosensitive monomer, the water-dispersible photoacid generator, the water-based blocked isocyanate and the water-soluble photoinitiator is 90-110:3-7:0.5-1.5:3-7:1-2.

9. The application of the temperature-sensitive water-based pressure-sensitive adhesive according to claim 1 in the process protection of flexible OLED screen manufacturing.

10. The application according to claim 9, characterized in that, Includes the following steps: The temperature-sensitive water-based pressure-sensitive adhesive is coated onto the base film, dried at 75-85℃ for 1-5 minutes, and then subjected to a pressure of 300-800 mJ / cm. 2 The temperature-sensitive water-based pressure-sensitive adhesive is irradiated with ultraviolet light to complete the primary curing, and then placed in a heat treatment at 50-70℃ for 10-20 minutes to complete the secondary curing.

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