Cross-linked polyurethane adhesive film for realizing high-strength bonding based on pressure-heat synergy and application of cross-linked polyurethane adhesive film in 3C electronic products

Abstract

The invention relates to a cross-linked polyurethane adhesive film for realizing high-strength bonding based on pressure-heat synergy and application of the cross-linked polyurethane adhesive film in 3C electronic products, and relates to the technical field of 3C electronic products. Comprising the following raw materials in parts by weight: 40-55 parts of a polyurethane matrix, 5-8 parts of functional curing agent microcapsules, 3-5 parts of a nano reinforced phase, 2-4 parts of a silane coupling agent, 0.5-2 parts of an anti-hydrolysis agent, 5-8 parts of tackifying resin and 20-30 parts of a solvent, the functionalized curing agent microcapsule adopts a core-shell-transition layer three-layer structure, the core is a compound of an isocyanate tripolymer and an amine curing agent, the transition layer is polycaprolactone, and the shell is of a polyurea-polyamide interpenetrating network structure. The adhesive film is good in storage stability, high in bonding strength and excellent in impact resistance and reworkability.

Description

Technical Field

[0001] This invention relates to the field of 3C electronic product technology, and in particular to a cross-linked polyurethane film that achieves high-strength bonding based on pressure-heat synergy and its application in 3C electronic products. Background Technology

[0002] In the manufacturing process of 3C electronic products (such as smartphones, tablets, and wearable devices), the bonding of the screen module to the frame is a core process to ensure the structural integrity of the product, sealing against dust and water (IP rating), impact resistance, reliability, and display effect. With consumers' increasing demands for thinner, lighter, and higher-performance electronic products, the bonding process between the screen and the casing faces even more stringent challenges. For example, in the smartphone field, the rise of foldable screen technology requires bonding materials to not only possess high strength but also maintain stable adhesion during repeated bending, while simultaneously meeting high standards such as IP68 for waterproofing and dustproofing. This places extremely high demands on existing bonding solutions.

[0003] However, existing bonding solutions suffer from irreconcilable technical contradictions in achieving synergistic optimization of process friendliness, high-strength adhesion, impact resistance, and reworkability. Currently, commonly used bonding materials include epoxy resin adhesives, acrylic adhesives, and traditional polyurethane adhesives. While epoxy resin adhesives possess high bonding strength and good chemical resistance, they are brittle, have poor impact resistance, and are difficult to peel off once cured, significantly increasing the difficulty of product repair and hindering resource recycling and production cost control. Acrylic adhesives cure quickly at room temperature and are relatively easy to process, but they are prone to aging during long-term use, resulting in a significant decrease in bond strength over time, making it difficult to meet the requirements for long-term stable operation of electronic products.

[0004] Among current mainstream adhesive materials, polyurethane possesses theoretical advantages such as high toughness, bending resistance, and heat-peelability. Its polar groups can form hydrogen bonds and other interactions with the adherends, thereby enhancing adhesion. In practical applications, a curing agent is typically added to further enhance its cohesive strength and promote bonding with the adherends. However, the adhesive film prepared from two-component adhesives and curing agents gradually cures at room temperature, affecting the wetting and bonding performance during subsequent hot pressing, ultimately impacting the bond strength. This is because the curing agent in the two-component system undergoes a slow chemical reaction with the polyurethane matrix during storage, leading to a gradual increase in the adhesive film's viscosity and a decrease in fluidity. This prevents sufficient wetting of the adherend surface during hot pressing, resulting in interfacial bonding defects and reduced overall bond strength. Furthermore, this slow curing at room temperature shortens the film's shelf life, increasing the difficulty and cost of material management during production.

[0005] To address the aforementioned issues, Chinese invention patent CN116535985B discloses a method for preparing a polyurethane adhesive film. This method involves a microcapsule curing agent, with the wall material formed by the reaction of amines and isocyanate monomers. However, during storage, the microcapsules slowly swell, resulting in a core material leakage rate exceeding 8% after 30 days. Furthermore, it lacks a pressure-triggered mechanism, and the curing process relies on natural ambient temperature, making precise control of adhesive strength impossible. In 3C product bonding, this adhesive film exhibits an interface bubble rate as high as 12% after hot pressing, failing to meet high-precision assembly requirements.

[0006] Therefore, developing an adhesive material that can ensure good storage stability, high bonding strength, excellent impact resistance and good repairability has become a key issue that urgently needs to be addressed in the 3C electronics manufacturing industry. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a cross-linked polyurethane film with good storage stability, high bonding strength, excellent impact resistance and repairability, which achieves high-strength bonding based on pressure-heat synergy, and its application in 3C electronic products.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is a cross-linked polyurethane film that achieves high-strength adhesion based on pressure-heat synergy, comprising the following raw materials in parts by weight: 40-55 parts of polyurethane matrix, 5-8 parts of functionalized curing agent microcapsules, 3-5 parts of nano-reinforcing phase, 2-4 parts of silane coupling agent, 0.5-2 parts of anti-hydrolysis agent, 5-8 parts of tackifying resin, and 20-30 parts of solvent; the functionalized curing agent microcapsules adopt a three-layer structure of "core-shell-transition layer", the core is a compound of isocyanate trimer and amine curing agent, the transition layer is polycaprolactone, and the shell layer is a polyurea-polyamide interpenetrating network structure.

[0009] Preferably, the polyurethane matrix is ​​a hydroxyl-terminated polyurethane prepolymer, which is prepared according to the method of Example 1 of Chinese Invention Patent No. CN108623771B.

[0010] Preferably, the preparation method of the functionalized curing agent microcapsules includes the following steps:

[0011] Step D1, Core Preparation: Mix isocyanate trimer with amine curing agent and stir at 45-55℃ for 30-40 minutes under nitrogen protection to form a homogeneous system; then add polycaprolactone and continue stirring for 12-16 minutes to uniformly disperse the polycaprolactone to form an oil phase;

[0012] Step D2, Aqueous Phase Preparation: Add polyamide 66 to formic acid solution and stir mechanically until completely dissolved; add polyurea prepolymer and stir for 18-22 minutes to form a stable aqueous phase;

[0013] Step D3, Emulsification stage: In a reactor equipped with a shear emulsification head, the oil phase is dripped into the aqueous phase at a rate of 8-10 mL / min, while shearing and sonication are turned on simultaneously, and emulsification is carried out for 28-32 minutes to form a W / O type emulsion.

[0014] Step D4, Shell Formation: Heat the emulsion to 68-72℃, add ethylenediamine crosslinking agent, and react for 2-4 hours with stirring at 300-500r / min. During this period, take samples every 30 minutes to observe the shell formation. The shell thickness is precisely controlled to 3-5μm by adjusting the reaction time to form a polyurea-polyamide interpenetrating network structure.

[0015] Step D5, Post-treatment: After the reaction is complete, cool to 25℃, adjust the pH of the system to 7 with 10% NaOH solution, and let stand for 30-40 minutes; separate the microcapsules using a disc centrifuge, wash with deionized water until the conductivity of the filtrate is ≤10μS / cm; place the wet microcapsules in a freeze dryer and freeze dry for 22-25 hours to obtain functionalized curing agent microcapsules.

[0016] Preferably, the isocyanate trimer in step D1 is hexamethylene diisocyanate trimer; the amine curing agent is diethylenetriamine; the mass ratio of the isocyanate trimer, amine curing agent, and polycaprolactone is 3:1:0.08; and the M of the polycaprolactone... n =5000, hydroxyl value is 220mgKOH / g.

[0017] Preferably, the polyamide 66 in step D2 has a relative molecular mass of 25,000; the NCO content of the polyurea prepolymer is 12%, and it is prepared by reacting MDI and ethylenediamine in a 5:1 molar ratio.

[0018] Preferably, the formic acid solution in step D2 has a mass percentage concentration of 85%; and the mass ratio of polyamide 66, formic acid solution, and polyurea prepolymer is 1:8:1.

[0019] Preferably, the temperature of the mechanical stirring in step D2 is 40°C and the speed is 200 r / min.

[0020] Preferably, in step D3, the volume ratio of the oil phase to the water phase is 1:4; the shearing rate is 400 r / min; and the ultrasonic power is 200 W with a frequency of 20 kHz.

[0021] Preferably, the mass of the ethylenediamine crosslinking agent in step D4 is 0.5% of the mass of the aqueous phase.

[0022] Preferably, the freeze-drying temperature in step D5 is -50°C and the vacuum degree is 10 Pa.

[0023] Preferably, the nano-reinforcing phase is nano-titanium dioxide with an average particle size of 10-80 nm.

[0024] Preferably, the silane coupling agent is at least one selected from silane coupling agent KH550, silane coupling agent KH560, silane coupling agent KH570, and propyltriethoxysilane isocyanate.

[0025] Preferably, the anti-hydrolysis agent is carbodiimide.

[0026] Preferably, the tackifying resin is at least one of terpene resin and hydrogenated rosin resin.

[0027] Preferably, the terpene resin is terpene resin T-100; the hydrogenated rosin resin is hydrogenated rosin HYPALECH.

[0028] Preferably, the solvent is at least one of toluene and xylene.

[0029] Another objective of this invention is to provide an application of the cross-linked polyurethane adhesive film based on pressure-heat synergy for high-strength bonding in 3C electronic products, comprising the following steps: mixing each raw material evenly according to weight parts, and then sequentially filtering and degassing to obtain a single-component polyurethane adhesive containing microcapsules; coating the adhesive onto a PET release film using a scraper method, baking it in an oven, removing it, and then covering the other side with another PET release film to obtain the adhesive film; cutting the adhesive film into sample films of tooling size using a die-cutting machine, bonding the sample films to the tooling in sequence, and placing them on a heating platform for hot pressing; during the hot pressing process, the adhesive film melts and penetrates, physically interlocking with the adhered object; secondly, by applying pressure to break the shell of the microcapsules, the internal core curing agent is released, and the curing agent reacts with the hydroxyl polyurethane prepolymer to achieve curing and cross-linking, thereby increasing the cohesive strength of the adhesive film to achieve high-strength bonding of the tooling.

[0030] Preferably, the baking temperature is 100-120℃ and the baking time is 20-30 minutes.

[0031] Preferably, the hot pressing temperature is 88-92℃, the pressure is 0.13-0.18MPa, and the time is 1-3min.

[0032] Due to the application of the above technical solution, the present invention has the following beneficial effects:

[0033] (1) The cross-linked polyurethane adhesive film disclosed in this invention, which achieves high-strength bonding based on pressure-heat synergy, is designed with a three-layer microcapsule structure of "core-shell-transition layer". The shell layer adopts a polyurea-polyamide interpenetrating network structure, which has excellent mechanical stability and chemical inertness. It can isolate the core curing agent from the polyurethane matrix (hydroxyl-terminated), avoid premature cross-linking, and significantly extend the storage period of the single-component system. The transition layer polycaprolactone can soften under heat, assisting the shell layer to rupture precisely under specific pressure (rather than spontaneous rupture), realizing the "on-demand release" of the curing agent. The core is a compound of isocyanate trimer and amine curing agent: the two curing agents react synergistically with the polyurethane matrix, which can improve the cross-linking density and solve the problem of insufficient cross-linking of a single curing agent. This structural design realizes for the first time the integration of "stable storage-controllable release-efficient cross-linking" of the curing agent, breaking through the inherent bottleneck of single-component polyurethane adhesives.

[0034] (2) The cross-linked polyurethane adhesive film disclosed in this invention, which achieves high-strength bonding based on pressure-heat synergy, combines pressure and heat. The heat causes the adhesive film to melt and fully penetrate the surface of the adhered object (such as the tooling or component gaps in 3C products), forming a tight physical interlock (mechanical anchoring) and enhancing the interfacial bonding force. The pressure precisely triggers the rupture of the microcapsule shell, releasing the core curing agent, which reacts rapidly with the hydroxyl-terminated polyurethane matrix to form a chemical cross-linking network, significantly improving the cohesive strength of the adhesive film. The synergy of these two factors greatly enhances the bonding strength, solving the single defects of "insufficient interfacial wettability" or "low cohesive strength," and is particularly suitable for high-strength bonding of complex interfaces in 3C products.

[0035] (3) The cross-linked polyurethane film disclosed in this invention achieves high-strength bonding based on pressure-heat synergy. The nano-reinforcing phase (nano-titanium dioxide) is combined with the silane coupling agent to bond with the matrix interface, enhancing the mechanical properties of the film (such as impact resistance and crack resistance); the anti-hydrolysis agent (carbodiimide) specifically solves the problem of easy hydrolysis of polyurethane and improves the long-term stability of the film in humid environments (such as inside electronic devices); the tackifying resin (terpene / hydrogenated rosin) balances the initial tack and final tack, ensuring temporary fixation before hot pressing and high-strength bonding after curing; the toluene / xylene system is used, combined with mild hot pressing conditions (88-92℃, 0.13-0.18MPa, 1-3min), to avoid damage to 3C electronic components (such as chips and circuit boards) by high temperature, while improving production efficiency.

[0036] (4) The cross-linked polyurethane adhesive film disclosed in this invention achieves high-strength bonding based on pressure-heat synergy. Existing two-component polyurethane adhesives require on-site mixing, which is difficult to control the proportions, complex to operate, and prone to performance fluctuations due to uneven mixing. This solution achieves single-component bonding through microencapsulation technology, eliminating the need for on-site mixing. Bonding can be completed directly by coating and hot pressing, simplifying the process. The die-cutting and hot pressing steps are compatible with automated production lines for 3C products, significantly reducing labor costs and error rates.

[0037] (5) The cross-linked polyurethane film for achieving high-strength bonding based on pressure-heat synergy disclosed in this invention is made from the following raw materials in parts by weight: 40-55 parts polyurethane matrix, 5-8 parts functionalized curing agent microcapsules, 3-5 parts nano-reinforcing phase, 2-4 parts silane coupling agent, 0.5-2 parts anti-hydrolysis agent, 5-8 parts tackifying resin, and 20-30 parts solvent; the functionalized curing agent microcapsules adopt a three-layer structure of "core-shell-transition layer", the core is a compound of isocyanate trimer and amine curing agent, the transition layer is polycaprolactone, and the shell layer is a polyurea-polyamide interpenetrating network structure. Through the synergistic effect of the various raw materials, the finished product has good storage stability, high bonding strength, excellent impact resistance and repairability. Detailed Implementation

[0038] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0039] In each embodiment of the present invention, the polyurethane matrix is ​​a hydroxyl-terminated polyurethane prepolymer, prepared according to the method of Example 1 of Chinese Invention Patent No. CN108623771B; the hexamethylene diisocyanate trimer is provided by Shanghai Maclean Biochemical Technology Co., Ltd., catalog number H909345-2.5kg; the diethylenetriamine is provided by Shanghai Maclean Biochemical Technology Co., Ltd., catalog number D806302-10L, reagent grade, 99%; the polycaprolactone has Mn=5000 and a hydroxyl value of 220mgKOH / g, and is provided by West China Medical Center Co., Ltd. The following materials were provided: Anruixi Biotechnology Co., Ltd.; the polyamide 66 with a relative molecular mass of 25,000 was provided by Shanghai Maclean Biochemical Technology Co., Ltd., catalog number N861767-2.5kg; the polyurea prepolymer with an NCO content of 12% was prepared by reacting MDI and ethylenediamine at a 5:1 molar ratio; the nano-titanium dioxide was provided by Ningbo Jiwei Nano New Materials Technology Co., Ltd.; the carbodiimide was provided by Wuhan Jixin Yibang Biotechnology Co., Ltd.; the terpene resin T-100 was provided by Shenzhen Yunlin Chemical Co., Ltd.; the hydrogenated rosin HYPALE CH was provided by Shanghai Kaiyin Chemical Co., Ltd., the distributor of Arakawa hydrogenated rosin from Japan; toluene, xylene, ethylenediamine, and silane coupling agent were all provided by Sinopharm Chemical Reagent Co., Ltd.

[0040] Example 1

[0041] A cross-linked polyurethane film for achieving high-strength adhesion based on pressure-heat synergy is made from the following raw materials in parts by weight: 40 parts polyurethane matrix, 5 parts functionalized curing agent microcapsules, 3 parts nano-reinforcing phase, 2 parts silane coupling agent, 0.5 parts anti-hydrolysis agent, 5 parts tackifying resin, and 20 parts solvent; the functionalized curing agent microcapsules adopt a three-layer structure of "core-shell-transition layer", the core is a compound of isocyanate trimer and amine curing agent, the transition layer is polycaprolactone, and the shell is a polyurea-polyamide interpenetrating network structure.

[0042] The polyurethane matrix is ​​a hydroxyl-terminated polyurethane prepolymer, which is prepared according to the method of Example 1 of Chinese Invention Patent No. CN108623771B.

[0043] The preparation method of the functionalized curing agent microcapsules includes the following steps:

[0044] Step D1, Core Preparation: The isocyanate trimer is mixed with an amine curing agent and stirred at 45°C for 30 minutes under nitrogen protection to form a homogeneous system; then polycaprolactone is added and stirred for another 12 minutes to uniformly disperse the polycaprolactone and form an oil phase;

[0045] Step D2, Aqueous phase preparation: Add polyamide 66 to formic acid solution and stir mechanically until completely dissolved; add polyurea prepolymer and stir for 18 minutes to form a stable aqueous phase;

[0046] Step D3, Emulsification stage: In a reactor equipped with a shear emulsification head, the oil phase is dripped into the aqueous phase at a rate of 8 mL / min, while shearing and sonication are turned on simultaneously, and emulsification is carried out for 28 minutes to form a W / O type emulsion.

[0047] Step D4, Shell Formation: Heat the emulsion to 68°C, add ethylenediamine crosslinking agent, and react for 2 hours with stirring at 300 r / min. During this period, take samples every 30 minutes to observe the shell formation. The shell thickness is precisely controlled to 3 μm by adjusting the reaction time to form a polyurea-polyamide interpenetrating network structure.

[0048] Step D5, Post-treatment: After the reaction is completed, the temperature is lowered to 25℃, and the pH of the system is adjusted to 7 with a 10% NaOH solution. The mixture is allowed to stand for 30 minutes. The microcapsules are separated using a disc centrifuge and washed with deionized water until the conductivity of the filtrate is ≤10μS / cm. The wet microcapsules are then placed in a freeze dryer and freeze-dried for 22 hours to obtain functionalized curing agent microcapsules.

[0049] The isocyanate trimer mentioned in step D1 is hexamethylene diisocyanate trimer; the amine curing agent is diethylenetriamine; the mass ratio of the isocyanate trimer, amine curing agent, and polycaprolactone is 3:1:0.08; the M of the polycaprolactone n =5000, hydroxyl value is 220mgKOH / g.

[0050] The relative molecular mass of polyamide 66 in step D2 is 25000; the NCO content of the polyurea prepolymer is 12%, and it is prepared by reacting MDI and ethylenediamine at a ratio of 5:1 molar; the mass percentage concentration of the formic acid solution in step D2 is 85%; the mass ratio of polyamide 66, formic acid solution, and polyurea prepolymer is 1:8:1; the temperature of the mechanical stirring in step D2 is 40℃, and the speed is 200 r / min.

[0051] In step D3, the volume ratio of the oil phase to the water phase is 1:4; the shearing rate is 400 r / min; the ultrasonic power is 200 W and the frequency is 20 kHz; in step D4, the mass of the ethylenediamine crosslinking agent is 0.5% of the mass of the water phase; and in step D5, the freeze-drying temperature is -50 °C and the vacuum degree is 10 Pa.

[0052] The nano-reinforcing phase is nano-titanium dioxide with an average particle size of 10 nm; the silane coupling agent is silane coupling agent KH550; the anti-hydrolysis agent is carbodiimide; the tackifying resin is terpene resin; the terpene resin is terpene resin T-100; and the solvent is toluene.

[0053] The application of a cross-linked polyurethane adhesive film based on pressure-heat synergy for high-strength bonding in 3C electronic products includes the following steps: After uniformly mixing the raw materials according to their weight proportions, the mixture is sequentially filtered and degassed to obtain a single-component polyurethane adhesive containing microcapsules; the adhesive is coated onto a PET release film using a scraper method, baked in an oven, and then covered with another PET release film to obtain the adhesive film; the adhesive film is cut into sample films of tooling size using a die-cutting machine, and the sample films are sequentially bonded to the tooling and placed on a heating platform for hot pressing; during the hot pressing process, the adhesive film melts and penetrates, physically interlocking with the adhered object; secondly, pressure is applied to break the shell of the microcapsules, releasing the internal core curing agent, which reacts with the hydroxyl polyurethane prepolymer to achieve curing and cross-linking, thereby increasing the cohesive strength of the adhesive film to achieve high-strength bonding with the tooling; the baking temperature is 100℃, and the time is 20 min; the hot pressing temperature is 88℃, the pressure is 0.13 MPa, and the time is 1 min.

[0054] Example 2

[0055] A cross-linked polyurethane film for achieving high-strength adhesion based on pressure-heat synergy is made from the following raw materials in parts by weight: 45 parts polyurethane matrix, 6 parts functionalized curing agent microcapsules, 3.5 parts nano-reinforcing phase, 2.5 parts silane coupling agent, 1 part anti-hydrolysis agent, 6 parts tackifying resin, and 23 parts solvent; the functionalized curing agent microcapsules adopt a three-layer structure of "core-shell-transition layer", the core is a compound of isocyanate trimer and amine curing agent, the transition layer is polycaprolactone, and the shell is a polyurea-polyamide interpenetrating network structure.

[0056] The polyurethane matrix is ​​a hydroxyl-terminated polyurethane prepolymer, which is prepared according to the method of Example 1 of Chinese Invention Patent No. CN108623771B.

[0057] The preparation method of the functionalized curing agent microcapsules includes the following steps:

[0058] Step D1, Core Preparation: The isocyanate trimer is mixed with an amine curing agent and stirred at 48°C for 33 minutes under nitrogen protection to form a homogeneous system; then polycaprolactone is added and stirring is continued for 13 minutes to uniformly disperse the polycaprolactone to form an oil phase;

[0059] Step D2, Aqueous phase preparation: Add polyamide 66 to formic acid solution and stir mechanically until completely dissolved; add polyurea prepolymer and stir for 19 minutes to form a stable aqueous phase;

[0060] Step D3, Emulsification stage: In a reactor equipped with a shear emulsification head, the oil phase is dripped into the aqueous phase at a rate of 8.5 mL / min, while shearing and sonication are turned on simultaneously, and emulsification is carried out for 29 minutes to form a W / O type emulsion.

[0061] Step D4, Shell Formation: The emulsion is heated to 69°C, ethylenediamine crosslinking agent is added, and the reaction is carried out at 350 r / min for 2.5 hours. During this period, samples are taken every 30 minutes to observe the shell formation. The shell thickness is precisely controlled to 3.5 μm by adjusting the reaction time to form a polyurea-polyamide interpenetrating network structure.

[0062] Step D5, Post-treatment: After the reaction is completed, the temperature is lowered to 25℃, and the pH of the system is adjusted to 7 with a 10% NaOH solution. The mixture is allowed to stand for 33 minutes. The microcapsules are separated using a disc centrifuge and washed with deionized water until the conductivity of the filtrate is ≤10μS / cm. The wet microcapsules are then placed in a freeze dryer and freeze-dried for 23 hours to obtain functionalized curing agent microcapsules.

[0063] The isocyanate trimer mentioned in step D1 is hexamethylene diisocyanate trimer; the amine curing agent is diethylenetriamine; the mass ratio of the isocyanate trimer, amine curing agent, and polycaprolactone is 3:1:0.08; the M of the polycaprolactone n =5000, hydroxyl value is 220mgKOH / g.

[0064] The relative molecular mass of polyamide 66 in step D2 is 25000; the NCO content of the polyurea prepolymer is 12%, and it is prepared by reacting MDI and ethylenediamine at a ratio of 5:1 molar; the mass percentage concentration of the formic acid solution in step D2 is 85%; the mass ratio of polyamide 66, formic acid solution, and polyurea prepolymer is 1:8:1; the temperature of the mechanical stirring in step D2 is 40℃, and the speed is 200 r / min.

[0065] In step D3, the volume ratio of the oil phase to the water phase is 1:4; the shearing rate is 400 r / min; the ultrasonic power is 200 W and the frequency is 20 kHz; in step D4, the mass of the ethylenediamine crosslinking agent is 0.5% of the mass of the water phase; and in step D5, the freeze-drying temperature is -50 °C and the vacuum degree is 10 Pa.

[0066] The nano-reinforcing phase is nano-titanium dioxide with an average particle size of 30 nm; the silane coupling agent is silane coupling agent KH560; the anti-hydrolysis agent is carbodiimide; the tackifying resin is hydrogenated rosin resin; the hydrogenated rosin resin is hydrogenated rosin HYPALE CH; and the solvent is xylene.

[0067] The application of a cross-linked polyurethane adhesive film based on pressure-heat synergy for high-strength bonding in 3C electronic products includes the following steps: Mixing raw materials uniformly according to their weight proportions, then sequentially filtering and degassing to obtain a single-component polyurethane adhesive containing microcapsules; coating the adhesive onto a PET release film using a scraper method, baking it in an oven, removing it, and then covering the other side with another PET release film to obtain the adhesive film; cutting the adhesive film into sample films of tooling size using a die-cutting machine, bonding the sample films to the tooling in sequence, and placing them on a heating platform for hot pressing; during the hot pressing process, the adhesive film melts and penetrates, physically interlocking with the adhered material; secondly, applying pressure breaks the shell of the microcapsules to release the internal core curing agent, which reacts with the hydroxyl polyurethane prepolymer to achieve curing and cross-linking, thereby increasing the cohesive strength of the adhesive film to achieve high-strength bonding with the tooling; the baking temperature is 105℃, and the time is 23 minutes; the hot pressing temperature is 89℃, the pressure is 0.15 MPa, and the time is 1.5 minutes.

[0068] Example 3

[0069] A cross-linked polyurethane film for achieving high-strength adhesion based on pressure-heat synergy is made from the following raw materials in parts by weight: 49 parts polyurethane matrix, 6.5 parts functionalized curing agent microcapsules, 4 parts nano-reinforcing phase, 3 parts silane coupling agent, 1.4 parts anti-hydrolysis agent, 6.5 parts tackifying resin, and 25 parts solvent; the functionalized curing agent microcapsules adopt a three-layer structure of "core-shell-transition layer", the core is a compound of isocyanate trimer and amine curing agent, the transition layer is polycaprolactone, and the shell is a polyurea-polyamide interpenetrating network structure.

[0070] The polyurethane matrix is ​​a hydroxyl-terminated polyurethane prepolymer, which is prepared according to the method of Example 1 of Chinese Invention Patent No. CN108623771B.

[0071] The preparation method of the functionalized curing agent microcapsules includes the following steps:

[0072] Step D1, Core Preparation: The isocyanate trimer is mixed with an amine curing agent and stirred at 50°C for 35 minutes under nitrogen protection to form a homogeneous system; then polycaprolactone is added and stirring is continued for 14 minutes to uniformly disperse the polycaprolactone to form an oil phase;

[0073] Step D2, Aqueous phase preparation: Add polyamide 66 to formic acid solution and stir mechanically until completely dissolved; add polyurea prepolymer and stir for 20 minutes to form a stable aqueous phase;

[0074] Step D3, Emulsification stage: In a reactor equipped with a shear emulsification head, the oil phase is dripped into the aqueous phase at a rate of 9 mL / min, while shearing and sonication are turned on simultaneously, and emulsification is carried out for 30 minutes to form a W / O type emulsion.

[0075] Step D4, Shell Formation: Heat the emulsion to 70°C, add ethylenediamine crosslinking agent, and react for 3 hours with stirring at 400 r / min. During this period, take samples every 30 minutes to observe the shell formation. The shell thickness is precisely controlled to 4 μm by adjusting the reaction time to form a polyurea-polyamide interpenetrating network structure.

[0076] Step D5, Post-treatment: After the reaction is complete, cool to 25℃, adjust the pH of the system to 7 with 10% NaOH solution, and let stand for 35 minutes; separate the microcapsules using a disc centrifuge, wash with deionized water until the conductivity of the filtrate is ≤10μS / cm; place the wet microcapsules in a freeze dryer and freeze dry for 23.5 hours to obtain functionalized curing agent microcapsules.

[0077] The isocyanate trimer mentioned in step D1 is hexamethylene diisocyanate trimer; the amine curing agent is diethylenetriamine; the mass ratio of the isocyanate trimer, amine curing agent, and polycaprolactone is 3:1:0.08; the M of the polycaprolactone n =5000, hydroxyl value is 220mgKOH / g.

[0078] The relative molecular mass of polyamide 66 in step D2 is 25000; the NCO content of the polyurea prepolymer is 12%, and it is prepared by reacting MDI and ethylenediamine at a ratio of 5:1 molar; the mass percentage concentration of the formic acid solution in step D2 is 85%; the mass ratio of polyamide 66, formic acid solution, and polyurea prepolymer is 1:8:1; the temperature of the mechanical stirring in step D2 is 40℃, and the speed is 200 r / min.

[0079] In step D3, the volume ratio of the oil phase to the water phase is 1:4; the shearing rate is 400 r / min; the ultrasonic power is 200 W and the frequency is 20 kHz; in step D4, the mass of the ethylenediamine crosslinking agent is 0.5% of the mass of the water phase; and in step D5, the freeze-drying temperature is -50 °C and the vacuum degree is 10 Pa.

[0080] The nano-reinforcing phase is nano-titanium dioxide with an average particle size of 60 nm; the silane coupling agent is silane coupling agent KH570; the anti-hydrolysis agent is carbodiimide; the tackifying resin is terpene resin; the terpene resin is terpene resin T-100; and the solvent is toluene.

[0081] The application of a cross-linked polyurethane adhesive film based on pressure-heat synergy for high-strength bonding in 3C electronic products includes the following steps: After uniformly mixing the raw materials according to their weight proportions, the mixture is sequentially filtered and degassed to obtain a single-component polyurethane adhesive containing microcapsules; the adhesive is coated onto a PET release film using a scraper method, baked in an oven, and then covered with another PET release film to obtain the adhesive film; the adhesive film is cut into sample films of tooling size using a die-cutting machine, and the sample films are sequentially bonded to the tooling and placed on a heating platform for hot pressing; during the hot pressing process, the adhesive film melts and penetrates, physically interlocking with the adhered material; secondly, pressure is applied to break the shell of the microcapsules, releasing the internal core curing agent, which reacts with the hydroxyl polyurethane prepolymer to achieve curing and cross-linking, thereby increasing the cohesive strength of the adhesive film to achieve high-strength bonding with the tooling; the baking temperature is 110℃, and the time is 25 minutes; the hot pressing temperature is 90℃, the pressure is 0.16 MPa, and the time is 2 minutes.

[0082] Example 4

[0083] A cross-linked polyurethane film for achieving high-strength adhesion based on pressure-heat synergy is made from the following raw materials in parts by weight: 53 parts polyurethane matrix, 7.5 parts functionalized curing agent microcapsules, 4.5 parts nano-reinforcing phase, 3.5 parts silane coupling agent, 1.8 parts anti-hydrolysis agent, 7.5 parts tackifying resin, and 28 parts solvent; the functionalized curing agent microcapsules adopt a three-layer structure of "core-shell-transition layer", the core is a compound of isocyanate trimer and amine curing agent, the transition layer is polycaprolactone, and the shell is a polyurea-polyamide interpenetrating network structure.

[0084] The polyurethane matrix is ​​a hydroxyl-terminated polyurethane prepolymer, which is prepared according to the method of Example 1 of Chinese Invention Patent No. CN108623771B.

[0085] The preparation method of the functionalized curing agent microcapsules includes the following steps:

[0086] Step D1, Core Preparation: The isocyanate trimer is mixed with an amine curing agent and stirred at 53°C for 38 minutes under nitrogen protection to form a homogeneous system; then polycaprolactone is added and stirred for another 15 minutes to uniformly disperse the polycaprolactone and form an oil phase;

[0087] Step D2, Aqueous phase preparation: Add polyamide 66 to formic acid solution and stir mechanically until completely dissolved; add polyurea prepolymer and stir for 21 minutes to form a stable aqueous phase;

[0088] Step D3, Emulsification stage: In a reactor equipped with a shear emulsification head, the oil phase is dripped into the aqueous phase at a rate of 9.5 mL / min, while shearing and sonication are turned on simultaneously, and emulsification is carried out for 31 minutes to form a W / O type emulsion.

[0089] Step D4, Shell Formation: The emulsion is heated to 71°C, ethylenediamine crosslinking agent is added, and the reaction is carried out at 450 r / min for 3.5 hours. During this period, samples are taken every 30 minutes to observe the shell formation. The shell thickness is precisely controlled to 4.5 μm by adjusting the reaction time to form a polyurea-polyamide interpenetrating network structure.

[0090] Step D5, Post-treatment: After the reaction is complete, cool to 25℃, adjust the pH of the system to 7 with 10% NaOH solution, and let stand for 38 minutes; separate the microcapsules using a disc centrifuge, wash with deionized water until the conductivity of the filtrate is ≤10μS / cm; place the wet microcapsules in a freeze dryer and freeze dry for 24 hours to obtain functionalized curing agent microcapsules.

[0091] The isocyanate trimer mentioned in step D1 is hexamethylene diisocyanate trimer; the amine curing agent is diethylenetriamine; the mass ratio of the isocyanate trimer, amine curing agent, and polycaprolactone is 3:1:0.08; the M of the polycaprolactone n =5000, hydroxyl value is 220mgKOH / g.

[0092] The relative molecular mass of polyamide 66 in step D2 is 25000; the NCO content of the polyurea prepolymer is 12%, and it is prepared by reacting MDI and ethylenediamine at a ratio of 5:1 molar; the mass percentage concentration of the formic acid solution in step D2 is 85%; the mass ratio of polyamide 66, formic acid solution, and polyurea prepolymer is 1:8:1; the temperature of the mechanical stirring in step D2 is 40℃, and the speed is 200 r / min.

[0093] In step D3, the volume ratio of the oil phase to the water phase is 1:4; the shearing rate is 400 r / min; the ultrasonic power is 200 W and the frequency is 20 kHz; in step D4, the mass of the ethylenediamine crosslinking agent is 0.5% of the mass of the water phase; and in step D5, the freeze-drying temperature is -50 °C and the vacuum degree is 10 Pa.

[0094] The nano-reinforcing phase is nano-titanium dioxide with an average particle size of 70 nm; the silane coupling agent is a mixture of silane coupling agent KH550, silane coupling agent KH560, silane coupling agent KH570, and isocyanate propyltriethoxysilane in a mass ratio of 1:2:2:1; the anti-hydrolysis agent is carbodiimide; the tackifying resin is a mixture of terpene resin and hydrogenated rosin resin in a mass ratio of 3:5; the terpene resin is terpene resin T-100; the hydrogenated rosin resin is hydrogenated rosin HYPALECH; the solvent is a mixture of toluene and xylene in a mass ratio of 1:2.

[0095] The application of a cross-linked polyurethane adhesive film based on pressure-heat synergy for high-strength bonding in 3C electronic products includes the following steps: After uniformly mixing the raw materials according to their weight proportions, the mixture is sequentially filtered and degassed to obtain a single-component polyurethane adhesive containing microcapsules; the adhesive is coated onto a PET release film using a scraper method, baked in an oven, and then covered with another PET release film to obtain the adhesive film; the adhesive film is cut into sample films of tooling size using a die-cutting machine, and the sample films are sequentially bonded to the tooling and placed on a heating platform for hot pressing; during the hot pressing process, the adhesive film melts and penetrates, physically interlocking with the adhered material; secondly, pressure is applied to break the shell of the microcapsules, releasing the internal core curing agent, which reacts with the hydroxyl polyurethane prepolymer to achieve curing and cross-linking, thereby increasing the cohesive strength of the adhesive film to achieve high-strength bonding with the tooling; the baking temperature is 115℃, and the time is 28 min; the hot pressing temperature is 91℃, the pressure is 0.17 MPa, and the time is 2.5 min.

[0096] Example 5

[0097] A cross-linked polyurethane film for achieving high-strength adhesion based on pressure-heat synergy is made from the following raw materials in parts by weight: 55 parts polyurethane matrix, 8 parts functionalized curing agent microcapsules, 5 parts nano-reinforcing phase, 4 parts silane coupling agent, 2 parts anti-hydrolysis agent, 8 parts tackifying resin, and 30 parts solvent; the functionalized curing agent microcapsules adopt a three-layer structure of "core-shell-transition layer", the core is a compound of isocyanate trimer and amine curing agent, the transition layer is polycaprolactone, and the shell is a polyurea-polyamide interpenetrating network structure.

[0098] The polyurethane matrix is ​​a hydroxyl-terminated polyurethane prepolymer, which is prepared according to the method of Example 1 of Chinese Invention Patent No. CN108623771B.

[0099] The preparation method of the functionalized curing agent microcapsules includes the following steps:

[0100] Step D1, Core Preparation: The isocyanate trimer is mixed with an amine curing agent and stirred at 55°C for 40 minutes under nitrogen protection to form a homogeneous system; then polycaprolactone is added and stirring is continued for 16 minutes to uniformly disperse the polycaprolactone to form an oil phase;

[0101] Step D2, Aqueous Phase Preparation: Add polyamide 66 to formic acid solution and stir mechanically until completely dissolved; add polyurea prepolymer and stir for 22 minutes to form a stable aqueous phase;

[0102] Step D3, Emulsification stage: In a reactor equipped with a shear emulsification head, the oil phase is dripped into the aqueous phase at a rate of 10 mL / min, while shearing and sonication are turned on simultaneously, and emulsification is carried out for 32 minutes to form a W / O type emulsion.

[0103] Step D4, Shell Formation: Heat the emulsion to 72°C, add ethylenediamine crosslinking agent, and react for 4 hours with stirring at 500 r / min. During this period, take samples every 30 minutes to observe the shell formation. The shell thickness is precisely controlled to 5 μm by adjusting the reaction time to form a polyurea-polyamide interpenetrating network structure.

[0104] Step D5, Post-treatment: After the reaction is complete, cool to 25℃, adjust the pH of the system to 7 with 10% NaOH solution, and let stand for 40 minutes; separate the microcapsules using a disc centrifuge, wash with deionized water until the conductivity of the filtrate is ≤10μS / cm; place the wet microcapsules in a freeze dryer and freeze dry for 25 hours to obtain functionalized curing agent microcapsules.

[0105] The isocyanate trimer mentioned in step D1 is hexamethylene diisocyanate trimer; the amine curing agent is diethylenetriamine; the mass ratio of the isocyanate trimer, amine curing agent, and polycaprolactone is 3:1:0.08; the M of the polycaprolactone n =5000, hydroxyl value is 220mgKOH / g.

[0106] The relative molecular mass of polyamide 66 in step D2 is 25000; the NCO content of the polyurea prepolymer is 12%, and it is prepared by reacting MDI and ethylenediamine at a ratio of 5:1 molar; the mass percentage concentration of the formic acid solution in step D2 is 85%; the mass ratio of polyamide 66, formic acid solution, and polyurea prepolymer is 1:8:1; the temperature of the mechanical stirring in step D2 is 40℃, and the speed is 200 r / min.

[0107] In step D3, the volume ratio of the oil phase to the water phase is 1:4; the shearing rate is 400 r / min; the ultrasonic power is 200 W and the frequency is 20 kHz; in step D4, the mass of the ethylenediamine crosslinking agent is 0.5% of the mass of the water phase; and in step D5, the freeze-drying temperature is -50 °C and the vacuum degree is 10 Pa.

[0108] The nano-reinforcing phase is nano-titanium dioxide with an average particle size of 80 nm; the silane coupling agent is propyltriethoxysilane isocyanate; the anti-hydrolysis agent is carbodiimide; the tackifying resin is hydrogenated rosin resin; the hydrogenated rosin resin is hydrogenated rosin HYPALE CH; and the solvent is toluene.

[0109] The application of a cross-linked polyurethane adhesive film based on pressure-heat synergy for high-strength bonding in 3C electronic products includes the following steps: After uniformly mixing the raw materials according to their weight proportions, the mixture is sequentially filtered and degassed to obtain a single-component polyurethane adhesive containing microcapsules; the adhesive is coated onto a PET release film using a scraper method, baked in an oven, and then covered with another PET release film to obtain the adhesive film; the adhesive film is cut into sample films of tooling size using a die-cutting machine, and the sample films are sequentially bonded to the tooling and placed on a heating platform for hot pressing; during the hot pressing process, the adhesive film melts and penetrates, physically interlocking with the adhered material; secondly, pressure is applied to break the shell of the microcapsules, releasing the internal core curing agent, which reacts with the hydroxyl polyurethane prepolymer to achieve curing and cross-linking, thereby increasing the cohesive strength of the adhesive film to achieve high-strength bonding with the tooling; the baking temperature is 120℃, and the time is 30 minutes; the hot pressing temperature is 92℃, the pressure is 0.18 MPa, and the time is 3 minutes.

[0110] Comparative Example

[0111] A cross-linked polyurethane film based on pressure-heat synergy to achieve high-strength bonding is basically the same as that in Example 1, except that the functionalized curing agent microcapsules are replaced with an equal amount of polyurethane microcapsule curing agent from Example 1 of CN 116535985 B.

[0112] To further illustrate the beneficial technical effects of the cross-linked polyurethane adhesive film based on pressure-heat synergy for achieving high-strength bonding in the various embodiments of the present invention, relevant performance tests were conducted on the pressure-sensitive structural adhesive films based on the core-shell microcapsule system involved in Examples 1-5 and Comparative Examples 1-2. The test results are shown in Table 1. The thickness of the adhesive layer of the test sample adhesive film was 30 μm, and the thickness of the release film was 50 μm. The test methods are as follows:

[0113] After fully curing, the sample is mounted on the clamp of the universal testing machine, ensuring that the sample's axis is aligned with the tensile direction of the machine, with a clamping distance of 100 mm. The tensile speed of the testing machine is set to 300 mm / min, and the machine is started to perform a peel test. The peel angle is controlled at 180°, and the maximum force value during the peel process is recorded, and the peel strength is calculated. After each fully cured film is left to stand for 4 months, the peel strength is tested again, and the peel strength retention rate is calculated. The higher the value, the better the storability. Reworkability is then tested according to the above rework process. Complete peeling indicates OK reworkability, while incomplete peeling indicates NG reworkability.

[0114] Table 1. Performance test results of cross-linked polyurethane films achieving high-strength bonding based on pressure-heat synergy.

[0115]

[0116] The experimental results show that the cross-linked polyurethane film based on pressure-heat synergy for high-strength bonding, as described in the embodiments of the present invention, exhibits better bonding performance, storage properties, and reworkability than the comparative product. The use of functionalized curing agent microcapsules involved in this invention is beneficial for improving these properties.

[0117] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A cross-linked polyurethane film achieving high-strength bonding based on pressure-heat synergy, characterized in that, It is made from the following raw materials in parts by weight: 40-55 parts polyurethane matrix, 5-8 parts functionalized curing agent microcapsules, 3-5 parts nano-reinforcing phase, 2-4 parts silane coupling agent, 0.5-2 parts anti-hydrolysis agent, 5-8 parts tackifying resin, and 20-30 parts solvent; the functionalized curing agent microcapsules adopt a three-layer structure of "core-shell-transition layer", the core is a compound of isocyanate trimer and amine curing agent, the transition layer is polycaprolactone, and the shell is a polyurea-polyamide interpenetrating network structure.

2. The cross-linked polyurethane film based on pressure-heat synergy for high-strength bonding according to claim 1, characterized in that, The preparation method of the functionalized curing agent microcapsules includes the following steps: Step D1, Core Preparation: Mix isocyanate trimer with amine curing agent and stir at 45-55℃ for 30-40 minutes under nitrogen protection to form a homogeneous system; then add polycaprolactone and continue stirring for 12-16 minutes to uniformly disperse the polycaprolactone to form an oil phase; Step D2, Aqueous Phase Preparation: Add polyamide 66 to formic acid solution and stir mechanically until completely dissolved; add polyurea prepolymer and stir for 18-22 minutes to form a stable aqueous phase; Step D3, Emulsification stage: In a reactor equipped with a shear emulsification head, the oil phase is dripped into the aqueous phase at a rate of 8-10 mL / min, while shearing and sonication are turned on simultaneously, and emulsification is carried out for 28-32 minutes to form a W / O type emulsion. Step D4, Shell Formation: Heat the emulsion to 68-72℃, add ethylenediamine crosslinking agent, and react for 2-4 hours with stirring at 300-500r / min. During this period, take samples every 30 minutes to observe the shell formation. The shell thickness is precisely controlled to 3-5μm by adjusting the reaction time to form a polyurea-polyamide interpenetrating network structure. Step D5, Post-treatment: After the reaction is complete, cool to 25℃, adjust the pH of the system to 7 with 10% NaOH solution, and let stand for 30-40 minutes; separate the microcapsules using a disc centrifuge, wash with deionized water until the conductivity of the filtrate is ≤10μS / cm; place the wet microcapsules in a freeze dryer and freeze dry for 22-25 hours to obtain functionalized curing agent microcapsules.

3. The cross-linked polyurethane film based on pressure-heat synergy for high-strength bonding according to claim 2, characterized in that, The isocyanate trimer mentioned in step D1 is hexamethylene diisocyanate trimer; the amine curing agent is diethylenetriamine; the mass ratio of the isocyanate trimer, amine curing agent, and polycaprolactone is 3:1:0.08; the M of the polycaprolactone n =5000, hydroxyl value is 220mgKOH / g.

4. The cross-linked polyurethane film based on pressure-heat synergy for high-strength bonding according to claim 2, characterized in that, The polyamide 66 in step D2 has a relative molecular mass of 25,000; the NCO content of the polyurea prepolymer is 12%, and it is prepared by reacting MDI and ethylenediamine in a 5:1 molar ratio.

5. The cross-linked polyurethane film for high-strength bonding based on pressure-heat synergy according to claim 2, characterized in that, The mass percentage concentration of the formic acid solution in step D2 is 85%; the mass ratio of the polyamide 66, formic acid solution, and polyurea prepolymer is 1:8:1; the temperature of the mechanical stirring in step D2 is 40℃ and the speed is 200r / min.

6. The cross-linked polyurethane film based on pressure-heat synergy for high-strength bonding according to claim 2, characterized in that, In step D3, the volume ratio of the oil phase to the water phase is 1:4; the shearing rate is 400 r / min; the ultrasonic power is 200 W and the frequency is 20 kHz; in step D4, the mass of the ethylenediamine crosslinking agent is 0.5% of the mass of the water phase; and in step D5, the freeze-drying temperature is -50 °C and the vacuum degree is 10 Pa.

7. The cross-linked polyurethane film based on pressure-heat synergy for high-strength bonding according to claim 1, characterized in that, The nano-reinforcing phase is nano-titanium dioxide with an average particle size of 10-80 nm; the silane coupling agent is at least one of silane coupling agent KH550, silane coupling agent KH560, silane coupling agent KH570, and propyltriethoxysilane isocyanate; the anti-hydrolysis agent is carbodiimide.

8. The cross-linked polyurethane film based on pressure-heat synergy for high-strength bonding according to claim 1, characterized in that, The tackifying resin is at least one of terpene resin and hydrogenated rosin resin; the terpene resin is terpene resin T-100; the hydrogenated rosin resin is hydrogenated rosin HYPALE CH; and the solvent is at least one of toluene and xylene.

9. The application of a cross-linked polyurethane film based on pressure-heat synergy for high-strength bonding according to any one of claims 1-8 in 3C electronic products, characterized in that, The process includes the following steps: Mixing the raw materials evenly according to their weight proportions, then filtering and degassing them sequentially to obtain a single-component polyurethane adhesive containing microcapsules; applying the adhesive to a PET release film using a scraper method, baking it in an oven, removing it, and then covering the other side with another PET release film to obtain an adhesive film; cutting the adhesive film into sample films of tooling size using a die-cutting machine, bonding the sample films to the tooling in sequence, and placing them on a heating platform for hot pressing; during the hot pressing process, the adhesive film melts and penetrates, physically interlocking with the adhered objects; secondly, applying pressure breaks the shell of the microcapsules to release the internal core curing agent, which reacts with the hydroxyl polyurethane prepolymer to achieve curing and cross-linking, thereby increasing the cohesive strength of the adhesive film to achieve high-strength bonding of the tooling.

10. The application of the cross-linked polyurethane film based on pressure-heat synergy for high-strength bonding according to claim 9 in 3C electronic products, characterized in that, The baking temperature is 100-120℃ and the time is 20-30 min; the hot pressing temperature is 88-92℃, the pressure is 0.13-0.18 MPa, and the time is 1-3 min.

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