Uv semi-structural adhesive and preparation method thereof, uv semi-structural adhesive film and preparation method thereof

Abstract

The application relates to a UV semi-structural adhesive and a preparation method thereof, and a UV semi-structural adhesive film and a preparation method thereof. Raw materials for preparing the UV semi-structural adhesive include 30-35 parts of polyacrylate modified epoxy resin, 95-105 parts of polyacrylate pressure-sensitive adhesive, 0.8-1.5 parts of cationic photoinitiator and 0.45-0.55 parts of curing agent; raw materials for preparing the polyacrylate modified epoxy resin include 25-35 parts of soft monomer, 15-25 parts of hard monomer, 1.5-2.5 parts of functional monomer, 0.1-0.2 parts of free radical thermal initiator, 40-60 parts of solvent and 400-550 parts of bisphenol A epoxy resin; and raw materials for preparing the polyacrylate pressure-sensitive adhesive include 25-30 parts of soft monomer, 15-25 parts of hard monomer, 1-1.5 parts of first functional monomer, 0.25-0.5 parts of second functional monomer, 40-60 parts of solvent and 0.1-0.2 parts of free radical thermal initiator.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and in particular to a UV semi-structural adhesive and its preparation method, and a UV semi-structural adhesive film and its preparation method. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the safety of power batteries, as core components, has become a critical challenge. Battery packaging typically uses aluminum-plastic film or composite film structures, with the PET layer being widely used due to its excellent mechanical strength and insulation. However, PET film has low surface energy and lacks polar groups in its molecular chains, making it difficult to form effective chemical bonds with adhesives, resulting in significant bonding challenges.

[0003] To improve the adhesion performance of PET films, existing technologies often employ corona treatment to impart polar functional groups to the PET film surface. Regarding adhesive selection, while acrylic pressure-sensitive adhesives can achieve effective adhesion to PET films, their bonding strength is insufficient to meet the requirements for semi-structural adhesives. Traditional semi-structural adhesives such as hot melt adhesives and thermosetting adhesives require heat curing, which conflicts with the non-heatable operating conditions in power battery assembly and packaging processes, thus limiting their application.

[0004] UV cationic polymerized semi-structural adhesives have become a preferred option for power battery packaging processes due to their advantages such as no need for heating and fast curing speed. Traditional UV cationic polymerized semi-structural adhesives mainly consist of cationically polymerizable epoxy resins (such as alicyclic epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, etc.), polyacrylates (containing no carboxyl, amino, or other groups that can open the epoxy ring), and cationic photoinitiators. However, in the bonding scenario of PET film for power battery packaging, there are specific requirements for adhesive shear strength, namely, the shear strength needs to be controlled between 1-2 MPa: less than 1 MPa results in insufficient adhesive force, failing to guarantee structural stability; greater than 2 MPa leads to excessive brittleness of the adhesive layer, resulting in decreased adhesion to the PET film and easy debonding.

[0005] Bisphenol A epoxy resin possesses excellent adhesive properties, and its rigid molecular structure makes it widely used in semi-structural and structural adhesives. However, it also suffers from significant brittleness. While there are attempts to modify bisphenol A epoxy resin to improve its toughness, achieving a precise match between toughness, adhesion, and specific shear strength (1MPa~2MPa) remains an unsolved technical challenge in the field of UV semi-structural adhesives. Relying solely on polyacrylate for toughening and adhesion is insufficient to achieve stable adhesion to PET films while maintaining a shear strength of 1MPa~2MPa. Therefore, there is an urgent need to develop a UV cationic semi-structural adhesive with good toughness, strong adhesion, and suitable shear strength to meet the requirements of outer packaging for new energy vehicle power batteries. Summary of the Invention

[0006] Therefore, it is necessary to provide a UV semi-structural adhesive with good toughness, strong adhesion, and suitable shear strength, as well as its preparation method and a UV semi-structural adhesive film and its preparation method.

[0007] A UV semi-structural adhesive, wherein the raw materials for preparing the UV semi-structural adhesive, by weight parts, include the following components:

[0008] 30 to 35 parts of polyacrylate-modified epoxy resin;

[0009] 95-105 parts of polyacrylate pressure-sensitive adhesive;

[0010] 0.8 to 1.5 parts of cationic photoinitiator; and

[0011] Hardener: 0.45 parts to 0.55 parts;

[0012] The raw materials for preparing the polyacrylate-modified epoxy resin, by weight, include the following components:

[0013] Soft monomers, 25-35 parts;

[0014] 15 to 25 parts of hard monomer;

[0015] 1.5 to 2.5 parts of functional monomers;

[0016] 0.1 to 0.2 parts of free radical thermal initiator;

[0017] Solvent 40-60 parts; and

[0018] 400-550 parts of bisphenol A epoxy resin;

[0019] The raw materials for preparing the polyacrylate pressure-sensitive adhesive, by weight, include the following components:

[0020] 25-30 parts of soft monomer;

[0021] 15 to 25 parts of hard monomer;

[0022] 1 to 1.5 parts of the first functional monomer;

[0023] The second functional monomer is 0.25 to 0.5 parts;

[0024] Solvent 40-60 parts; and

[0025] 0.1 to 0.2 parts of free radical thermal initiator;

[0026] Wherein, the first functional monomer is an acrylate monomer that can be UV cationically polymerized;

[0027] The second functional monomer is an acrylate monomer with hydroxyl groups, and the second functional monomer does not contain any groups that allow the epoxy group to open the ring.

[0028] The UV semi-structural adhesive of this invention first synthesizes a polyacrylate-modified epoxy resin (EPA). This resin chemically grafts flexible polyacrylate segments onto a rigid bisphenol A epoxy resin via isocyanate groups, achieving a molecular-level synergy between toughness and strength. This EPA is then compounded with a specific polyacrylate pressure-sensitive adhesive, thereby precisely controlling the shear strength, toughness, and adhesion of the final adhesive at a macroscopic level. This satisfies the adhesive strength requirements of a semi-structural adhesive while avoiding brittleness caused by excessive strength, ensuring stable adhesion to PET films and significantly improving the toughness and adhesion of the adhesive.

[0029] In one embodiment, the soft monomer is selected from one or both of butyl acrylate and isooctyl acrylate; the hard monomer is selected from one or more of methyl acrylate, vinyl acetate and methyl methacrylate.

[0030] In one embodiment, the functional monomer used to prepare the polyacrylate-modified epoxy resin is ethyl isocyanate acrylate; the first functional monomer used to prepare the polyacrylate pressure-sensitive adhesive is glycidyl methacrylate, and the second functional monomer is 2-hydroxyethyl acrylate.

[0031] In one embodiment, the bisphenol A epoxy resin is selected from one or both of E51 epoxy resin and E44 epoxy resin; the solvent is selected from one or both of ethyl acetate and toluene, and the water content of the solvent is controlled to be below 500 ppm.

[0032] In one embodiment, the free radical thermal initiator is azobisisobutyronitrile; the cationic photoinitiator is selected from one or two of iodonium salt photoacid generators and thionium salt photoacid generators; and the curing agent is polytetrabutyl titanate.

[0033] A method for preparing any of the above-mentioned UV semi-structural adhesives includes the following steps:

[0034] The soft monomer, hard monomer, functional monomer, solvent and free radical thermal initiator are mixed evenly and reacted completely at 75℃~80℃ under a protective atmosphere. The solid content is detected. When the solid content is ≥48%, polyacrylate is obtained.

[0035] Bisphenol A epoxy resin was preheated at 55℃~65℃ and then added dropwise to the polyacrylate. During the dropwise addition, the temperature of the reaction system was maintained at 80℃~85℃. The dropwise addition was completed within 4 hours, and the material was discharged at room temperature to obtain polyacrylate modified epoxy resin.

[0036] Soft monomers, hard monomers, a first functional monomer, a second functional monomer, a solvent, and a free radical thermal initiator are reacted thoroughly at 75°C to 80°C under a protective atmosphere. The solid content is then measured. When the solid content is ≥48%, a polyacrylate pressure-sensitive adhesive is obtained.

[0037] Under yellow light, the polyacrylate-modified epoxy resin, the polyacrylate pressure-sensitive adhesive, and the cationic photoinitiator are mixed evenly, then a curing agent is added, and after mixing evenly, a degassing treatment is performed to obtain a UV semi-structural adhesive.

[0038] A method for preparing a UV semi-structural adhesive film includes the following steps:

[0039] The UV semi-structural adhesive described above is coated onto a heavy release film. After drying, a light release film is covered on the other side of the UV semi-structural adhesive. After curing, a UV semi-structural adhesive film is obtained.

[0040] The UV semi-structural adhesive film preparation method provided by this invention successfully produces an adhesive film product with stable performance and suitable for industrial production by coating a special adhesive liquid onto a release film and then subjecting it to a precisely controlled drying and curing process. This method not only effectively avoids air bubbles in the adhesive layer and ensures uniform thickness, but also enables the adhesive film to have excellent processing stability and initial tack before curing through the curing process. It is particularly easy to die-cut and precision bonding. The resulting "sandwich" structure adhesive film has good storage properties and is convenient to use, making it perfectly suited for UV curing bonding processes that do not require heating and require precise alignment, such as those used in new energy vehicle power batteries.

[0041] In one embodiment, the thickness of the dried UV semi-structural adhesive is 50 μm to 100 μm.

[0042] In one embodiment, the curing temperature is 40°C to 50°C, and the curing time is 48h to 72h.

[0043] A UV semi-structural adhesive film is prepared using any of the above-mentioned UV semi-structural adhesive film preparation methods.

[0044] The UV semi-structural adhesive film prepared by this invention has excellent initial tack and processability, making it easy to die-cut and position. Its unique structural design ensures stable performance of the product during storage and transportation. When in use, the adhesive film can be quickly cured into a high-strength adhesive layer by UV irradiation, ultimately achieving a stable shear strength of 1MPa to 2MPa for difficult-to-bond materials such as PET, perfectly meeting the heatless bonding requirements of precision components such as new energy vehicle battery assembly. Attached Figure Description

[0045] Figure 1 This is a flowchart of a method for preparing a UV semi-structural adhesive according to an embodiment of the present invention. Detailed Implementation

[0046] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0048] According to one embodiment of the UV semi-structural adhesive, the raw materials for preparing the UV semi-structural adhesive include the following components in parts by weight:

[0049] 30 to 35 parts of polyacrylate-modified epoxy resin;

[0050] 95-105 parts of polyacrylate pressure-sensitive adhesive;

[0051] 0.8 to 1.5 parts of cationic photoinitiator; and

[0052] Hardener: 0.45 parts to 0.55 parts;

[0053] The raw materials for preparing polyacrylate-modified epoxy resin, by weight, include the following components:

[0054] Soft monomers, 25-35 parts;

[0055] 15 to 25 parts of hard monomer;

[0056] 1.5 to 2.5 parts of functional monomers;

[0057] 0.1 to 0.2 parts of free radical thermal initiator;

[0058] Solvent 40-60 parts; and

[0059] 400-550 parts of bisphenol A epoxy resin;

[0060] The raw materials for preparing polyacrylate pressure-sensitive adhesive, by weight, include the following components:

[0061] 25-30 parts of soft monomer;

[0062] 15 to 25 parts of hard monomer;

[0063] 1 to 1.5 parts of the first functional monomer;

[0064] The second functional monomer is 0.25 to 0.5 parts;

[0065] Solvent 40-60 parts; and

[0066] 0.1 to 0.2 parts of free radical thermal initiator;

[0067] The first functional monomer is an acrylate monomer that can be cationically polymerized under UV light; the second functional monomer is an acrylate monomer with hydroxyl groups, and the second functional monomer does not contain any groups that allow the epoxy groups to open the ring.

[0068] In the raw materials for preparing the UV semi-structural adhesive described above, polyacrylate-modified epoxy resin is the core component of this invention. This resin combines the high cohesive strength of epoxy resin with the excellent toughness of polyacrylate segments. The epoxy groups in its molecular structure can participate in UV cationic curing, forming a robust cross-linked network that provides the necessary structural strength, enabling the adhesive to achieve the bonding level of a semi-structural adhesive. Simultaneously, the polyacrylate segments introduced through chemical grafting effectively improve the brittleness of pure epoxy resin, significantly enhancing the flexibility and impact resistance of the adhesive. This ensures that when bonding flexible films such as PET, it is not prone to detachment due to brittleness even under high strength. This component is key to balancing adhesive strength and toughness.

[0069] Polyacrylate pressure-sensitive adhesives (PPAs) impart excellent initial tack, durability, and wetting and adhesion to substrates, especially PET films. They form a continuous phase, ensuring good application tack before UV curing. The specific functional monomers (first and second functional monomers) introduced enable them to synergistically interact with EPA components and the curing system, jointly contributing to the construction of the final cured network. This provides pressure-sensitive properties without affecting, and may even enhance, the overall cohesive strength and curing effect.

[0070] One method for preparing polyacrylate-modified epoxy resins is to introduce highly reactive isocyanate groups (-NCO) during the synthesis of polyacrylate. These groups can react with the hydroxyl groups (-OH) on the subsequently added bisphenol A epoxy resin molecular chain, thereby grafting polyacrylate segments onto the epoxy resin via chemical bonds, achieving toughening modification at the molecular level rather than simple physical blending.

[0071] The first functional monomer can introduce epoxy groups that can react with protic acids generated by cationic photoinitiators, enabling the pressure-sensitive adhesive to deeply participate in the UV-cured crosslinking network, thereby significantly improving the cohesive strength and heat resistance of the adhesive after curing. The second functional monomer can introduce hydroxyl groups (-OH), which can react with residual NCO groups in the polyacrylate-modified epoxy resin (EPA) component or with the curing agent, further enhancing the interfacial compatibility and chemical bonding between EPA and pressure-sensitive adhesive A, optimizing the cured network structure, and simultaneously improving adhesion to the substrate.

[0072] The UV semi-structural adhesive of this embodiment first synthesizes a polyacrylate-modified epoxy resin (EPA). This resin chemically grafts flexible polyacrylate segments onto a rigid bisphenol A epoxy resin via isocyanate groups, achieving a molecular-level synergy between toughness and strength. This EPA is then compounded with a specific polyacrylate pressure-sensitive adhesive, thereby precisely controlling the shear strength, toughness, and adhesion of the final adhesive at a macroscopic level. This satisfies the adhesive strength requirements of the semi-structural adhesive while avoiding brittleness caused by excessive strength, ensuring stable adhesion to the PET film and significantly improving the toughness and adhesion of the adhesive.

[0073] Based on the aforementioned embodiments, the soft monomer is selected from one or both of butyl acrylate and isooctyl acrylate; the hard monomer is selected from one or more of methyl acrylate, vinyl acetate, and methyl methacrylate. The main function of the soft monomer is to provide flexibility to the polyacrylate segments and lower the glass transition temperature (Tg), which is the main source of the toughness of EPA. The main function of the hard monomer is to copolymerize with the soft monomer to adjust the rigidity, cohesive strength, and glass transition temperature (Tg) of the polyacrylate, so that the polymer segments have appropriate mechanical properties.

[0074] Based on the aforementioned embodiments, the functional monomer for preparing the polyacrylate-modified epoxy resin is ethyl isocyanate acrylate; the first functional monomer for preparing the polyacrylate pressure-sensitive adhesive is glycidyl methacrylate, and the second functional monomer is 2-hydroxyethyl acrylate.

[0075] Based on the aforementioned embodiments, the bisphenol A epoxy resin is selected from one or both of E51 and E44 epoxy resins; the solvent is selected from one or both of ethyl acetate and toluene, and the water content of the solvent is controlled below 500 ppm. E51 and E44 epoxy resins serve as the backbone of the EPA, providing strong rigidity, thermal stability, and excellent adhesive properties. Their molecular weight (epoxy value) and dosage determine the functionality of the final EPA component, directly affecting the density and strength of the crosslinked network after UV curing. The solvent acts as a medium for the polymerization reaction, ensuring uniform and controllable reaction and adjusting the viscosity of the reaction system. Strict control of the water content (below 500 ppm) is to prevent water from reacting with the isocyanate groups, consuming functional monomers, and affecting the final grafting modification effect.

[0076] Based on the aforementioned embodiments, the free radical thermal initiator is azobisisobutyronitrile; the cationic photoinitiator is selected from one or two of iodonium salt photoacid generators and thiodonium salt photoacid generators, and further, for example, it can be diphenyliodonium hexafluorophosphate; the curing agent is polytetrate.

[0077] The UV semi-structural adhesive of this invention first synthesizes a polyacrylate-modified epoxy resin (EPA). This resin chemically grafts flexible polyacrylate segments onto a rigid bisphenol A epoxy resin via isocyanate groups, achieving a molecular-level synergy between toughness and strength. This EPA is then compounded with a specific polyacrylate pressure-sensitive adhesive, thereby precisely controlling the shear strength, toughness, and adhesion of the final adhesive at a macroscopic level. This satisfies the adhesive strength requirements of a semi-structural adhesive while avoiding brittleness caused by excessive strength, ensuring stable adhesion to PET films and significantly improving the toughness and adhesion of the adhesive.

[0078] Please see Figure 1 The preparation method of any of the above-mentioned UV semi-structural adhesives according to one embodiment of the present invention includes the following steps:

[0079] S10. Mix the soft monomer, hard monomer, functional monomer, solvent and free radical thermal initiator evenly, and react them completely at 75℃~80℃ under a protective atmosphere. Detect the solid content. When the solid content is ≥48%, polyacrylate is obtained.

[0080] In step S10, the soft monomer is selected from one or both of butyl acrylate and isooctyl acrylate; the hard monomer is selected from one or more of methyl acrylate, vinyl acetate and methyl methacrylate. Further, the functional monomer does not contain carboxyl groups, hydroxyl groups, or other groups that can react with NCO groups, and is preferably isocyanate-based ethyl acrylate.

[0081] The polyacrylate obtained after step S10 contains NCO groups.

[0082] S20. After preheating the bisphenol A epoxy resin at 55℃~65℃, add it dropwise to the polyacrylate. During the dropwise addition, maintain the reaction system temperature at 80℃~85℃. The dropwise addition is completed within 4 hours. Cool down to room temperature and discharge to obtain the polyacrylate-modified epoxy resin.

[0083] The bisphenol A epoxy resin is heated and maintained at a temperature of 55°C to 65°C. This heating reduces the viscosity of the epoxy resin, making it easier to add dropwise. Furthermore, the dropwise addition time is preferably 2 to 4 hours, which ensures a complete reaction with minimal energy consumption.

[0084] The reaction mechanism between bisphenol A epoxy resin and polyacrylate with NCO groups is as follows:

[0085]

[0086] ;

[0087] Where R represents the polyacrylate structure.

[0088] S30. The soft monomer, hard monomer, first functional monomer, second functional monomer, solvent and free radical thermal initiator are reacted fully at 75℃~80℃ under a protective atmosphere. The solid content is detected. When the solid content is ≥48%, polyacrylate pressure-sensitive adhesive is obtained.

[0089] In step S30, the soft monomer is selected from one or both of butyl acrylate and isooctyl acrylate; the hard monomer is selected from one or more of methyl acrylate, vinyl acetate and methyl methacrylate.

[0090] Furthermore, the first functional monomer is a UV-catalytically polymerizable acrylate monomer, and the second functional monomer is a hydroxyl-containing acrylate monomer, and the second functional monomer does not contain any groups that allow the epoxy group to open the ring, such as carboxyl or amino groups that allow the epoxy group to open the ring during synthesis or drying. Further, the first functional monomer is glycidyl methacrylate, and the second functional monomer is 2-hydroxyethyl acrylate.

[0091] The protective atmosphere is nitrogen.

[0092] S40. Under yellow light, the polyacrylate-modified epoxy resin obtained in step S20, the polyacrylate pressure-sensitive adhesive obtained in step S30, and the cationic photoinitiator are mixed evenly. Then, a curing agent is added, and after mixing evenly, degassing treatment is performed to obtain a UV semi-structural adhesive.

[0093] The preparation method of the UV semi-structural adhesive of this invention is simple. First, a polyacrylate-modified epoxy resin (EPA) is synthesized. This resin chemically grafts flexible polyacrylate segments onto a rigid bisphenol A epoxy resin through isocyanate groups, achieving molecular-level synergy between toughness and strength. Then, this EPA is compounded with a specific polyacrylate pressure-sensitive adhesive, thereby precisely controlling the shear strength, toughness, and adhesion of the final adhesive on a macroscopic scale. This satisfies the adhesive strength requirements of the semi-structural adhesive while avoiding brittleness caused by excessive strength, ensuring stable adhesion to PET films and significantly improving the toughness and adhesion of the adhesive.

[0094] A method for preparing a UV semi-structural adhesive film according to one embodiment includes the following steps:

[0095] Apply any of the above-mentioned UV semi-structural adhesives onto a heavy release film, dry them, cover the other side of the UV semi-structural adhesive with a light release film, and after curing, obtain a UV semi-structural adhesive film.

[0096] In one embodiment, the thickness of the dried UV semi-structural adhesive is 50 μm to 100 μm. Further, the thickness of the dried UV semi-structural adhesive can be, but is not limited to, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm.

[0097] In one embodiment, the curing temperature is 40°C to 50°C, and the curing time is 48h to 72h. Further, the curing temperature may be, but is not limited to, 40°C, 45°C, or 50°C, and the curing time may be, but is not limited to, 48h, 60h, or 72h.

[0098] The UV semi-structural adhesive film preparation method provided by this invention successfully produces an adhesive film product with stable performance and suitable for industrial production by coating a special adhesive liquid onto a release film and then subjecting it to a precisely controlled drying and curing process. This method not only effectively avoids air bubbles in the adhesive layer and ensures uniform thickness, but also enables the adhesive film to have excellent processing stability and initial tack before curing through the curing process. It is particularly easy to die-cut and precision bonding. The resulting "sandwich" structure adhesive film has good storage properties and is convenient to use, making it perfectly suited for UV curing bonding processes that do not require heating and require precise alignment, such as those used in new energy vehicle power batteries.

[0099] The UV semi-structural adhesive film of one embodiment is prepared using any of the above-described methods for preparing UV semi-structural adhesive films.

[0100] The UV semi-structural adhesive film prepared by this invention has excellent initial tack and processability, making it easy to die-cut and position. Its unique structural design ensures stable performance of the product during storage and transportation. When in use, the adhesive film can be quickly cured into a high-strength adhesive layer by UV irradiation, ultimately achieving a stable shear strength of 1MPa to 2MPa for difficult-to-bond materials such as PET, perfectly meeting the heatless bonding requirements of precision components such as new energy vehicle battery assembly.

[0101] Referring to the above embodiments, in order to make the technical solution of the present invention more specific, clear and easy to understand, examples of the technical solution of the present invention are given below. However, it should be noted that the content to be protected by the present invention is not limited to the following embodiments.

[0102] Examples 1-5 and Comparative Examples 1-5

[0103] Weigh the raw materials according to Table 1. Add the soft monomer, hard monomer, functional monomer, solvent, and free radical thermal initiator to a dry, impurity-free reactor equipped with a reflux device, a high-level tank, and a reflux reflux system. Purge the air with nitrogen and maintain the reaction temperature at 75℃~80℃ for 8 hours. Measure the solid content. If it is qualified (greater than or equal to 48%), add bisphenol A epoxy resin to the high-level tank. Heat the high-level tank and maintain it at 60℃, then begin dripping it into the polyacrylate. Complete the dripping within 4 hours, maintaining the temperature at 80℃~85℃ during this period. Cool to room temperature and discharge into an HDPE container, labeled EPA, and seal for later use.

[0104] Table 1. Formulation of Synthetic Polyacrylic Acid Modified Epoxy Resin EPA

[0105]

[0106] Weigh each raw material according to Table 2. Add soft monomer, hard monomer, functional monomer, solvent and free radical thermal initiator to a dry and impurity-free reaction chamber equipped with a reflux device. Replace the air with nitrogen and keep the reaction at 75℃~80℃ for 8 hours. Measure the solid content. If it is qualified (greater than or equal to 48%), the cationic polymerizable polyacrylate pressure-sensitive adhesive is obtained and marked as A. Seal and wait for use.

[0107] Table 2 Formulation of Synthetic Polyacrylate Pressure-Sensitive Adhesive

[0108]

[0109] According to Table 3, weigh out each raw material, add EPA, polyacrylate pressure-sensitive adhesive and cationic photoinitiator into the reactor under yellow light, mix at room temperature until the cationic initiator is completely dissolved (for formulations without crosslinking agent, directly degas and discharge the material to be tested in the dark), then add crosslinking agent, stir evenly and degas to obtain semi-structural adhesive.

[0110] Table 3 UV Semi-structural Adhesive Formulation

[0111]

[0112] Note: Blank spaces in Tables 1-3 indicate that the ingredient is not included in the formulation; the manufacturer of polytetrabutyl titanate is McLean Reagents.

[0113] Coating is applied to a silicone oil release film (referred to as heavy release film), and after drying, a dry adhesive thickness of 85 μm is obtained. Then, another silicone oil release film with low release force (referred to as light release film) is applied, and the film is cured at 50 degrees for 72 hours to obtain a semi-structural adhesive film, which is then tested in the dark.

[0114] Performance testing:

[0115] Pre-test treatment: To better measure the dynamic shear strength, a 188μm thick PET film was used. Furthermore, to better reflect the adhesion of this formulation, no surface treatment, such as corona treatment, was performed for this test. Seven parallel samples were tested for each shear strength group. The highest and lowest values ​​were removed, and the average value was taken. The test results are shown in Table 4.

[0116] Film-forming property test method: After peeling off the light release film, it is adhered to the substrate. When peeling off the heavy release film, it can be easily separated without obvious stringing or adhesion. It is recorded as good. Slight stringing or adhesion is recorded as slightly poor. Severe stringing or adhesion is recorded as poor.

[0117] Table 4 Performance test data of Examples 1-5 and Comparative Examples 1-5

[0118]

[0119] As can be seen from Table 4, Examples 1-5, Comparative Examples 2 and 5 have good film-forming properties and do not have obvious stringing or residue when peeling off the release film. This is because a certain amount of polytetrafluoroethylene (PTFE) was added, which improved the cohesive force. Comparative Examples 1 and 3 have poor film-forming properties because they do not contain PTFE and the overall cohesive force is too low. Comparative Example 4 has slightly poor film-forming properties because although PTFE was added, the amount added was not enough to form a good film.

[0120] Examples 1-5 and Comparative Example 4 exhibit superior shear strength. This is because the combined effect of bisphenol A epoxy resin modified with polyacrylate and appropriate amounts of polytetrate increases flexibility and adhesion to PET without altering cohesion. Comparative Example 2 shows slightly higher shear strength than Comparative Example 1 because it incorporates polytetrate. Comparative Example 3 uses bisphenol A epoxy resin modified with polyacrylate but does not contain polytetrate, resulting in lower shear strength compared to the examples. Comparative Example 5 contains excessive polytetrate (0.7 parts), leading to excessive cohesion and decreased flexibility, which weakens the wetting and adhesion of polyacrylate segments to the PET surface. Consequently, its shear strength (0.76 MPa) is significantly lower than that of Example 1 (1.36 MPa), which uses a moderate amount of curing agent.

[0121] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0122] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A UV semi-structural adhesive, characterized in that, The raw materials for preparing the UV semi-structural adhesive, by weight, include the following components: 30 to 35 parts of polyacrylate-modified epoxy resin; 95-105 parts of polyacrylate pressure-sensitive adhesive; 0.8 to 1.5 parts of cationic photoinitiator; and Hardener: 0.45 parts to 0.55 parts; The raw materials for preparing the polyacrylate-modified epoxy resin, by weight, include the following components: Soft monomers, 25-35 parts; 15 to 25 parts of hard monomer; 1.5 to 2.5 parts of functional monomers; 0.1 to 0.2 parts of free radical thermal initiator; Solvent 40-60 parts; and 400-550 parts of bisphenol A epoxy resin; The raw materials for preparing the polyacrylate pressure-sensitive adhesive, by weight, include the following components: 25-30 parts of soft monomer; 15 to 25 parts of hard monomer; 1 to 1.5 parts of the first functional monomer; The second functional monomer is 0.25 to 0.5 parts; Solvent 40-60 parts; and 0.1 to 0.2 parts of free radical thermal initiator; Wherein, the first functional monomer is an acrylate monomer that can be UV cationically polymerized; The second functional monomer is an acrylate monomer with hydroxyl groups, and the second functional monomer does not contain any groups that allow the epoxy group to open the ring. The functional monomer used to prepare the polyacrylate-modified epoxy resin is ethyl isocyanate acrylate. The curing agent is polytetrate.

2. The UV semi-structural adhesive according to claim 1, characterized in that, The soft monomer is selected from one or two of butyl acrylate and isooctyl acrylate; the hard monomer is selected from one or more of methyl acrylate, vinyl acetate and methyl methacrylate.

3. The UV semi-structural adhesive according to claim 1, characterized in that, The first functional monomer used to prepare the polyacrylate pressure-sensitive adhesive is glycidyl methacrylate, and the second functional monomer is 2-hydroxyethyl acrylate.

4. The UV semi-structural adhesive according to claim 1, characterized in that, The bisphenol A epoxy resin is selected from one or both of E51 epoxy resin and E44 epoxy resin; the solvent is selected from one or both of ethyl acetate and toluene, and the water content of the solvent is controlled below 500 ppm.

5. The UV semi-structural adhesive according to claim 1, characterized in that, The free radical thermal initiator is azobisisobutyronitrile; the cationic photoinitiator is selected from one or two of iodonium salt photoacid generators and thionium salt photoacid generators.

6. A method for preparing a UV semi-structural adhesive according to any one of claims 1 to 5, characterized in that, Includes the following steps: The soft monomer, hard monomer, functional monomer, solvent and free radical thermal initiator are mixed evenly and reacted completely at 75℃~80℃ under a protective atmosphere. The solid content is detected. When the solid content is ≥48%, polyacrylate is obtained. Bisphenol A epoxy resin was preheated at 55℃~65℃ and then added dropwise to the polyacrylate. During the dropwise addition, the temperature of the reaction system was maintained at 80℃~85℃. The dropwise addition was completed within 4 hours, and the material was discharged at room temperature to obtain polyacrylate modified epoxy resin. Soft monomers, hard monomers, a first functional monomer, a second functional monomer, a solvent, and a free radical thermal initiator are reacted thoroughly at 75°C to 80°C under a protective atmosphere. The solid content is then measured. When the solid content is ≥48%, a polyacrylate pressure-sensitive adhesive is obtained. Under yellow light, the polyacrylate-modified epoxy resin, the polyacrylate pressure-sensitive adhesive, and the cationic photoinitiator are mixed evenly, then a curing agent is added, and after mixing evenly, a degassing treatment is performed to obtain a UV semi-structural adhesive.

7. A method for preparing a UV semi-structural adhesive film, characterized in that, Includes the following steps: The UV semi-structural adhesive according to any one of claims 1 to 5 is coated onto a heavy release film, dried, and then covered with a light release film on the other side of the UV semi-structural adhesive. After curing, a UV semi-structural adhesive film is obtained.

8. The method for preparing the UV semi-structural adhesive film according to claim 7, characterized in that, The thickness of the dried UV semi-structural adhesive is 50μm~100μm.

9. The method for preparing the UV semi-structural adhesive film according to claim 7, characterized in that, The curing temperature is 40℃~50℃, and the curing time is 48h~72h.

10. A UV semi-structural adhesive film, characterized in that, The UV semi-structural adhesive film was prepared using the preparation method described in any one of claims 7 to 9.

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