Polyvinyl chloride packaging adhesive containing polycaprolactone glycol and preparation method thereof

Abstract

The invention relates to a polyvinyl chloride packaging adhesive containing polycaprolactone glycol and a preparation method of the polyvinyl chloride packaging adhesive, in particular to a packaging adhesive based on a polyvinyl chloride and polycaprolactone glycol blending system, belongs to the field of material science and engineering, and particularly relates to application of high polymer materials in the packaging field. The packaging adhesive is based on PVC and PCL in a weight ratio of (8-10): 1, benzoyl peroxide, trimethylolpropane triacrylate and hexadecyl trimethoxy silane are added for crosslinking, and the packaging adhesive shows high crosslinking degree, low friction coefficient, excellent light transmittance and ultraviolet resistance. The packaging adhesive is applied to photovoltaic module packaging to enhance the light transmittance and weather resistance, flexible electronic device packaging to meet the flexible requirement, lithium battery packaging and building glass sealing are achieved, a composite material prepared through blending modification effectively breaks through the performance bottleneck of an existing material, and wide application prospects are shown in multiple fields.

Description

Technical Field

[0001] The present invention relates to a polyvinyl chloride encapsulant containing polycaprolactone diol and a preparation method thereof, and particularly to an encapsulant based on a polyvinyl chloride and polycaprolactone diol blend system, belonging to the field of materials science and engineering, and specifically relating to the application of polymer materials in the field of encapsulation. Background Art

[0002] In the current field of material applications, the performance requirements of encapsulation materials in different industries are becoming increasingly diverse and stringent. In the encapsulation of photovoltaic modules, traditional encapsulation materials are lacking in light transmittance, ultraviolet aging resistance, and insulation performance, which directly affects the long-term stability and power generation efficiency of photovoltaic modules. The encapsulation of flexible electronic devices requires materials to have excellent flexibility, low friction characteristics, and bending resistance to meet the needs of their unique application scenarios. The encapsulation of lithium battery separators or electrode sheets places strict requirements on the insulation performance, electrolyte corrosion resistance, and mechanical strength of the materials. The sealing of building glass materials has excellent requirements for the light transmittance, impact resistance, and weather resistance of the materials. However, existing encapsulation materials are difficult to meet these multi-faceted performance requirements simultaneously, restricting the further development of related industries. Therefore, it is of great practical significance to develop an encapsulant with excellent performance that can meet the requirements of various application scenarios. Summary of the Invention

[0003] The present invention aims to provide an encapsulant with excellent comprehensive performance. Through specific raw material formulations and preparation processes, it has high crosslinking degree, low friction coefficient (stable at low temperature), high light transmittance, excellent ultraviolet resistance, and good mechanical properties, insulation properties, etc., to meet the application requirements in different fields such as the encapsulation of photovoltaic modules, flexible electronic devices, lithium battery separators or electrode sheets, and the sealing of building glass materials.

[0004] Technical Solution:

[0005] Composition of the encapsulant: The encapsulant of the present invention is prepared by blending and crosslinking polyvinyl chloride and polycaprolactone diol. Among them, the number average molecular weight of the polyvinyl chloride > 50,000 and the molecular weight distribution index ≤ 1.5; the number average molecular weight of the polycaprolactone diol is 20,000 ± 500, and the hydroxyl functionality ≥ 98%. The weight ratio of polyvinyl chloride to polycaprolactone diol is controlled between 8 and 10:1. In addition, based on the total mass of polyvinyl chloride and polycaprolactone diol, 0.5% of benzoyl peroxide, 8% to 12% of trimethylolpropane triacrylate, and 1% to 18% of cetyltrimethoxysilane are additionally added.

[0006] Preparation method of encapsulant: First, polyvinyl chloride and polycaprolactone diol are mixed and dissolved in tetrahydrofuran according to a specific weight ratio, heated and stirred until completely dissolved to prepare a blend solution. To ensure the reaction effect, tetrahydrofuran needs to be dried before use. Then, benzoyl peroxide, trimethylolpropane triacrylate and cetyltrimethoxysilane in a specified ratio are added to the blend solution and stirring is continued. Then, the solution is placed in an oil bath at 65 °C for polycondensation reaction. After the reaction is completed, ethanol with a volume multiple times that of the reaction solution is poured into the reaction solution to precipitate the copolymer, and the copolymer is obtained by filtration or centrifugation. Finally, the copolymer is washed with deionized water or ethanol and dried to obtain the final encapsulant.

[0007] In the preparation method provided in some embodiments, the mass ratio of the polyvinyl chloride to the polycaprolactone diol is 8:1, the dosage of the trimethylolpropane triacrylate is 12% of the total amount of the matrix material, and the dosage of the cetyltrimethoxysilane is 18% of the total amount of the matrix material.

[0008] In the preparation method provided in some embodiments, the mass ratio of the polyvinyl chloride to the polycaprolactone diol is 9:1, the dosage of the trimethylolpropane triacrylate is 8% of the total amount of the matrix material, and the dosage of the cetyltrimethoxysilane is 11% of the total amount of the matrix material.

[0009] In the preparation method provided in some embodiments, the mass ratio of the polyvinyl chloride to the polycaprolactone diol is 10:1, the dosage of the trimethylolpropane triacrylate is 10% of the total amount of the matrix material, and the dosage of the cetyltrimethoxysilane is 15% of the total amount of the matrix material.

[0010] In the preparation method provided in some embodiments, the blend solution contains 5% of the matrix material.

[0011] In the preparation method provided in some embodiments, after washing the copolymer, it is dried at 50 °C for 48 hours to obtain the encapsulant.

[0012] Application of the encapsulant:

[0013] The encapsulant prepared by the method of the present invention can be applied to the field of photovoltaic encapsulation, such as being used as a lamination encapsulation material for crystalline silicon solar cells and thin-film solar cells; or for edge sealing of building-integrated photovoltaic modules.

[0014] The encapsulant prepared by the method of the present invention can be applied to the field of flexible electronics, such as being used as an encapsulation medium for flexible OLED displays; or for the circuit protection layer of intelligent wearable devices; or as an interface bonding material for electronic skin sensors.

[0015] The encapsulating adhesive prepared by the method of the present invention can be applied in the field of energy storage devices, for example, as a surface modification coating for lithium-ion battery separators; or for the insulation encapsulation of the edges of power battery electrodes.

[0016] The encapsulating adhesive prepared by the method of the present invention can be applied in the construction field, for example, as a structural sealant for insulating glass units, or for the weather-resistant seal of curtain wall joints.

[0017] Beneficial effects:

[0018] 1. Performance advantages: Through the synergistic cross-linking effect of trimethylolpropane triacrylate and cetyltrimethoxysilane, the encapsulating adhesive of the present invention achieves a high degree of cross-linking. The high degree of cross-linking not only enhances the cohesive energy of the material and improves the mechanical properties, specifically manifested as both the tensile strength and elongation at break exceeding those of traditional encapsulating materials, but also ensures the stability of the friction coefficient of the encapsulating adhesive in a low-temperature environment. Its initial surface friction coefficient is low, and the change in the friction coefficient at low temperature is very small, thus showing excellent performance in the opening and stacking operations. In addition, the high degree of cross-linking also significantly improves the light transmittance and effectively reduces the light scattering phenomenon. Especially at a wavelength of 550 nm, its light transmittance far exceeds that of existing similar products. In addition, the cross-linking network can inhibit the aging effect of ultraviolet rays on the polymer, prevent internal chain breakage, and has a low yellowing index and a high tensile strength retention rate in the artificial accelerated ultraviolet aging test, possessing excellent ultraviolet resistance.

[0019] 2. Application advantages: In the encapsulation of photovoltaic modules, the encapsulating adhesive of the present invention, with its high light transmittance, ultraviolet aging resistance, strong adhesion, and good insulation, can effectively improve the power generation efficiency and service life of photovoltaic modules. Compared with traditional materials, the encapsulating adhesive of the present invention performs better in terms of light transmittance and ultraviolet aging resistance, and the volume insulation resistance meets the insulation performance requirements of photovoltaic modules. In the field of flexible electronic device encapsulation, its good flexibility, low friction coefficient, bend resistance, and interfacial adhesion enable it to perfectly adapt to the encapsulation requirements of flexible displays, wearable devices, etc., ensuring the normal operation and reliability of the devices. For the encapsulation of lithium-ion battery separators or electrodes, the insulation, electrolyte corrosion resistance, and mechanical strength of the encapsulating adhesive can effectively protect the internal structure and improve the safety and stability of the battery. In the sealing application of building glass materials, its excellent light transmittance, impact resistance, and weather resistance jointly ensure the long-term stability and durability of building glass, thereby significantly improving the overall quality of the building.

[0020] In summary, the encapsulating adhesive of the present invention and its preparation method have significant innovation and practicality, show great application potential in multiple fields, can effectively solve the problems of insufficient performance of existing encapsulating materials, and promote the technological progress and development of related industries. Description of the drawings

[0021] Figure 1 Infrared spectra of the encapsulating adhesives provided for Examples 1 to 3 and Comparative Examples 1 to 3 respectively.

[0022] Figure 2 Crosslinking degrees of the encapsulating adhesives provided for Examples 1 to 3 and Comparative Examples 1 to 3 respectively.

[0023] Figure 3 Coefficient of friction and rate of change of coefficient of friction of the encapsulating adhesives provided for Examples 1 to 3 and Comparative Examples 1 to 3 respectively.

[0024] Figure 4 Light transmittance of the encapsulating adhesives provided for Examples 1 to 3 and Comparative Examples 1 to 3 respectively.

[0025] Figure 5 Tensile strength of the encapsulating adhesives provided for Examples 1 to 3 and Comparative Examples 1 to 3 respectively.

[0026] Figure 6 Elongation at break of the encapsulating adhesives provided for Examples 1 to 3 and Comparative Examples 1 to 3 respectively.

[0027] Figure 7 Peel strength of the encapsulating adhesives provided for Examples 1 to 3 and Comparative Examples 1 to 3 respectively.

[0028] Figure 8 Yellowing index of the encapsulating adhesives provided for Examples 1 to 3 and Comparative Examples 1 to 3 respectively.

[0029] Figure 9 Tensile strength retention rate of the encapsulating adhesives provided for Examples 1 to 3 and Comparative Examples 1 to 3 respectively.

[0030] Figure 10 Volume resistivity of the encapsulating adhesives provided for Examples 1 to 3 and Comparative Examples 1 to 3 respectively. Detailed implementation manners

[0031] In order to more clearly elaborate the purpose, technical solutions and their advantages of the present invention, the following will be described in detail with specific examples. Please note that these examples are only used to explain the present invention and do not limit its application scope. Reagents not specifically mentioned in the present invention are all conventional reagents and can be purchased through commercial channels; similarly, methods not described in detail also belong to conventional test methods and can refer to existing technical materials.

[0032] I. Preparation of encapsulating adhesive

[0033] (1) Raw material preparation

[0034] Polyvinyl chloride (PVC), CAS: 9002-86-2, purity: 99%, number average molecular weight > 50,000 and molecular weight distribution index ≤ 1.5, Jiangsu Pulosi.

[0035] Polycaprolactone diol (PCL-diol): CAS: 36890-68-3, number average molecular weight 20,000±500, hydroxyl functionality ≥98%, Beijing Bailingwei Technology Co., Ltd.

[0036] Trimethylolpropane triacrylate (TMPTA): CAS: 15625-89-5, reagent grade 99%, Qingdao Reinars Polymer Materials Co., Ltd.

[0037] Hexadecyltrimethoxysilane: CAS: 16415-12-6, purity: 98%, Huangshan Kebery Chemical Co., Ltd.

[0038] Benzoyl peroxide, CAS: 94-36-0, purity: 99.0%, Shanghai McLean.

[0039] Solvent (optional): If necessary, tetrahydrofuran (THF), dimethylformamide (DMF) and the like can be used as solvents and must be dried before use.

[0040] (2) Preparation process

[0041] Example 1: PCL and PVC are mixed and dissolved in tetrahydrofuran at a weight ratio of 8:1, heated and stirred for 6 hours until completely dissolved, and then a blended solution with a mass fraction of 5% is prepared. Add 0.5% benzoyl peroxide of the total mass of PCL and PVC, 12% trimethylolpropane triacrylate of the total mass of PCL and PVC, and 18% hexadecyltrimethoxysilane of the total mass of PCL and PVC, continue stirring, oil bath 65°C, and react for 6 hours. Pour 10 times the volume of ethanol into the reaction solution to precipitate the copolymer, and filter or centrifuge to obtain the copolymer. After further washing with deionized water or ethanol, pour into a culture dish and dry at 50°C for 48 hours to obtain the final encapsulation film.

[0042] Example 2: PCL and PVC are mixed and dissolved in tetrahydrofuran at a weight ratio of 9:1, heated and stirred for 6 hours to completely dissolve, and a blended solution with a mass fraction of 5% is prepared. Add 0.5% benzoyl peroxide of the total mass of PCL and PVC, 8% trimethylolpropane triacrylate of the total mass of PCL and PVC, and 11% hexadecyltrimethoxysilane of the total mass of PCL and PVC, continue stirring, oil bath 65°C, and react for 6 hours. Pour 10 times the volume of ethanol into the reaction solution to precipitate the copolymer, and filter or centrifuge to obtain the copolymer. After further washing with deionized water or ethanol, pour it into a culture dish and dry it at 50°C for 48 hours to obtain the final encapsulation glue.

[0043] Example 3: PCL and PVC were mixed and dissolved in tetrahydrofuran at a weight ratio of 10:1, heated and stirred for 6 hours until completely dissolved, and then a blend solution with a mass fraction of 5% was prepared. 0.5% of benzoyl peroxide based on the total mass of PCL and PVC, 10% of trimethylolpropane triacrylate based on the total mass of PCL and PVC, and 15% of cetyltrimethoxysilane based on the total mass of PCL and PVC were added, and stirring was continued. The oil bath was at 65 °C, and after reacting for 6 h, 10 times the volume of ethanol was poured into the reaction solution and poured into a petri dish to precipitate the copolymer, and the copolymer was obtained by filtration or centrifugation. After further washing with deionized water or ethanol and pouring into a petri dish, it was dried at 50 °C for 48 h to obtain the final encapsulating adhesive.

[0044] Comparative Example 1: PCL and PVC were mixed and dissolved in tetrahydrofuran at a weight ratio of 7:3 to prepare a blend solution with a mass fraction of 5%. The blend solution was poured into a petri dish and left to stand in a fume hood at room temperature and normal pressure for 48 h until the solvent had completely evaporated to obtain a copolymer of PCL and PVC.

[0045] Comparative Example 2: PCL and PVC were mixed and dissolved in tetrahydrofuran at a weight ratio of 8:1 to prepare a blend solution with a mass fraction of 5%. The blend solution was poured into a petri dish and left to stand in a fume hood at room temperature and normal pressure for 48 h until the solvent had completely evaporated to obtain a copolymer of PCL and PVC.

[0046] Comparative Example 3: PCL and PVC were mixed and dissolved in tetrahydrofuran at a weight ratio of 7:3 to prepare a blend solution with a mass fraction of 5%. 0.5% of benzoyl peroxide, 12% of trimethylolpropane triacrylate, and 18% of cetyltrimethoxysilane based on the total mass of PCL and PVC were added thereto, stirring was continued, and the reaction was carried out in an oil bath at 65 °C for 6 hours. 10 times the volume of ethanol was poured into the reaction solution to precipitate the copolymer, and the copolymer was obtained by filtration or centrifugation. Then the copolymer was washed with deionized water or ethanol, poured into a petri dish, and dried at 50 °C for 48 hours to obtain the final encapsulating adhesive film.

[0047] II. Testing and Characterization

[0048] 1. Fourier Transform Infrared Spectroscopy Analysis

[0049] The encapsulating adhesive films prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were characterized in detail by a Nicolet Avatar 370 Fourier transform infrared spectrometer (FT-IR), and the test wavelength was 500 - 4000 cm -1 .

[0050] As Figure 1As shown, in Examples 1 - 3, complete cross - linking (no peak at 1630 cm⁻¹) and effective coupling (strong Si - O - C peak at 1100 - 1120 cm⁻¹) are the core evidence for performance optimization. The intensity balance of the PCL ester carbonyl (1720 cm⁻¹) and the C - Cl peak of PVC (615 / 690 cm⁻¹) reflects good compatibility between the two phases. In Comparative Examples 1 - 3, unreacted double bonds (Comparative Example 2), absence of Si - O - C (Comparative Example 1), and uneven interfacial bonding (Comparative Example 3) directly lead to performance deterioration. The enrichment of the PVC phase (enhanced C - Cl peak in Comparative Examples 1 / 3) and dilution of PCL (weak peak at 1720 cm⁻¹ in Comparative Example 1) confirm insufficient mechanical and weather resistance.

[0051] 2. Cross - linking degree determination

[0052] The xylene extraction method was adopted. Weigh (0.5 ± 0.01) g of the rubber film, cut it into small particles, place them in a small pocket made of 120 - mesh copper mesh to make a sample package. Immerse the sample package in xylene in a flask, heat it to 140 °C and reflux for 5 h. Take out the sample package, dry it and weigh it. The formula for calculating the cross - linking degree is 100%×(M3 - M1) / (M2 - M1), where M1 represents the mass of the empty copper - mesh bag, M2 is the mass of the bag with the sample, and M3 is the mass of the sample package after extraction and drying.

[0053] As Figure 2 shown, the cross - linking degrees of the encapsulation rubber films provided in Examples 1 - 3 are significantly higher than those in Comparative Examples 1 - 3. Both Comparative Example 1 and Comparative Example 2 are pure physical mixtures with no obvious chemical cross - linking. In Examples 1 - 3, through the synergistic cross - linking of trimethylolpropane triacrylate and cetyltrimethoxysilane, it participates in the grafting of PCL and PVC, improving the cross - linking degree, while in Comparative Example 3, a high content of PVC hinders the formation of the cross - linking network.

[0054] 3. Differential scanning calorimetry analysis and analysis of spherulite size

[0055] The DSC8500 differential scanning calorimeter (DSC) of PE Company in the United States was used to measure the melting and crystallization curves of the POE rubber film. Accurately weigh 8 mg of the sample in an aluminum crucible, place it in an N₂ environment, set the gas flow rate to 20 mL / min, the heating rate to 10 °C / min, and the test temperature range to 0 to 120 °C. And the spherulite sizes of the colloids obtained in Examples 1 - 3 and Comparative Examples 1 - 3 were analyzed by a polarized light microscope. According to the DSC melting curve data, the crystallization parameters were calculated, as shown in Table 1.

[0056] Table 1

[0057]

[0058]

[0059] As shown in Table 1, the encapsulation adhesives provided in Examples 1 to 3, especially the "Lingxi" pure POE film, significantly increased the cross-linking reaction rate through unique technical means, so that its crystallinity was significantly higher than that of Comparative Example 1 and Comparative Example 3. And there are PCL phase and PVC phase in the encapsulation adhesives obtained in Comparative Example 1 and Comparative Example 3, and the PVC phase is embedded in the PCL phase, which may lead to a decrease in its modulus and strength, and the material shows hard and brittle characteristics.

[0060] 4. Coefficient of friction test

[0061] The surface coefficient of friction (μ0) of the encapsulation adhesive films prepared in Examples 1 to 3 and Comparative Examples 1 to 2 was tested using a friction and wear tester (load of 1 N, sliding speed of 10 mm / s). Subsequently, the encapsulation adhesive film was sealed in a self-sealing bag and refrigerated in a refrigerator at -20 °C for 24 hours, taken out and restored to room temperature, and its surface coefficient of friction (μL) was measured again. The calculation formula for the change rate (R) of the surface coefficient of friction of the film is: R = 100% × (μ0 - μL) / μ0.

[0062] As Figure 3 shown, the initial surface coefficient of friction of Examples 1 to 3 was lower than that of Comparative Examples 1 to 3, and the change rate of its low-temperature coefficient of friction was also lower than that of Comparative Examples 1 to 3. The surface coefficient of friction of Example 1 was as low as 0.15 - 0.20 (close to polytetrafluoroethylene), which was 60% - 70% lower than that of unmodified Comparative Example 1 (0.45 - 0.55), reducing the frictional loss during the battery encapsulation and assembly process. The long-chain alkyl of CTMS inhibits water molecule adsorption, and the change rate of the coefficient of friction after damp heat aging (85 °C / 85% RH) < 5%, while the coefficient of friction of Comparative Example 1 fluctuates > 25% due to moisture absorption.

[0063] TMPTA cross-linking densifies the surface and reduces the adhesion of PCL segments under pressure (the increase rate of the coefficient of friction of Example 1 after 1000 friction tests < 3%, and the increase rate of Comparative Example 2 > 15%). The cross-linking network and the PCL flexible phase cooperate, and the surface of Example 1 is still smooth after 1000 folds at 180° (SEM shows that microcracks appear in Comparative Example 3 due to the rigidity of PVC, and the coefficient of friction increases by 20%). CTMS reduces the melt viscosity, and the surface roughness (Ra) of Example 1 after hot pressing into a film < 50 nm (Ra of Comparative Example 1 > 200 nm), directly reducing the coefficient of friction. The low coefficient of friction (0.15 - 0.20) reduces the interfacial wear between the encapsulation adhesive and the lithium metal / separator, and improves the battery cycle life (the capacity retention rate of the battery assembled with Example 1 > 95% after 500 cycles).

[0064] The encapsulation adhesives provided in Examples 1 to 3 exhibit optimal performance in terms of coefficient of friction, stability, and durability, and are suitable for the encapsulation of high-precision flexible batteries (such as roll-to-roll production processes). In Comparative Example 3, the high PVC ratio results in surface rigidity defects, and the coefficient of friction (0.30 - 0.35) is still significantly higher than that in Example 1, and the performance attenuation under mechanical stress is obvious. This shows that the present invention breaks through the bottleneck that it is difficult to balance low friction and high durability of traditional encapsulation materials through the synergistic design of silane lubrication-crosslinked network, and provides a reliable encapsulation solution for high-energy density batteries.

[0065] 5. Transmittance Test

[0066] The transmittance of the adhesive film was tested using a UV-visible spectrophotometer (Shimadzu UV-2450, Japan) according to the national standard GB / T 2410-2008. The wavelength range was 200 - 900 nm, and the transmittance value was the average value of the transmittance at a wavelength of 550 nm. The specimen size was 30 mm × 30 mm.

[0067] As Figure 4 shown, the transmittance of the encapsulation adhesive films provided in Examples 1 to 3 is higher than that in Comparative Examples 1 to 3, meeting the industry standard that the transmittance of automotive films is greater than or equal to 70%. Due to the high degree of crosslinking in Examples 1 to 3, their transmittance can be improved. Comparative Examples 1 to 3 contain a two-phase structure, resulting in enhanced spherulite scattering and thus reduced light transmittance performance.

[0068] CTMS enhances the compatibility of PCL / PVC. The microdomain size in Example 1 is <50 nm (in Comparative Example 1 >1 μm), and the light scattering loss is reduced by more than 80%. TMPTA crosslinking restricts the ordered arrangement of PCL segments. The crystallinity in Example 1 is <10% (the crystallinity of unmodified PCL in Comparative Example 2 is ~40%), and the transmittance is increased to the 90% level. CTMS improves the melt fluidity. The surface roughness (Ra) after hot pressing in Example 1 is <50 nm (Ra in Comparative Example 1 >200 nm), reducing surface scattering. When the transmittance in Example 1 >90%, the tensile strength is still about 30 MPa (the strength in Comparative Example 3 is 35 MPa but the transmittance is only 65%), meeting the dual requirements of high strength and transparency for flexible encapsulation.

[0069] 6. Mechanical Property Test

[0070] The tensile strength and elongation at break of the adhesive film were tested using an electronic material testing machine. According to the national standard GB / T528-1998, the adhesive film was cut into dumbbell-shaped specimens of 25 mm×6 mm and stretched at a rate of 500 mm / min, and the average value of 5 tests was taken. The specimens for testing the peel strength were prepared on a laminator, and the specimen structure was glass / POE adhesive film / TPT backplane. According to the national standard GB / T2792, using an electronic material testing machine (CMT-4502, Mest Industrial System Co., Ltd.), the 180° peel strength at the interface between the glass and the adhesive film was measured at a tensile rate of 300 mm / min, and the average value of 3 tests was taken.

[0071] As Figure 5 , 6 As shown in Fig. 7, the tensile strength of Example 1 reached 28-32 MPa, more than twice that of Comparative Example 2 (10-15 MPa). At the same time, the elongation at break remained at 350-400% (much higher than 50-80% of Comparative Example 1). This shows that the silane groups of CTMS form chemical bonds with PCL / PVC, reducing phase separation (microdomain size <100 nm) and avoiding the brittle fracture caused by the rigid phase of PVC in Comparative Example 1.

[0072] In addition, the peel strength of Example 1 reached 4.5-5.0 N / mm, more than three times that of Comparative Example 2 (1.0-1.5 N / mm). CTMS enhanced the adhesion between the adhesive layer and the electrode / separator. The flexible chain segments of PCL (89% in Example 1) adapted to the interface deformation, reducing stress concentration and avoiding the interface peel failure caused by high PVC in Comparative Example 3.

[0073] Examples 1-3 achieved flexible design from high strength and medium toughness (Example 1) to medium strength and high toughness (Example 2) by adjusting the PCL / PVC ratio (8:1-10:1) and the dosages of TMPTA / CTMS. The tensile strength retention rate of Example 1 remained >90% after 1000 bends, while the strength of Comparative Example 3 decreased >30% due to the propagation of microcracks.

[0074] The encapsulation adhesives provided in Examples 1-3 showed the best performance in the balance of tensile strength, peel strength and toughness, and were suitable for high-reliability flexible battery encapsulation. Although Comparative Examples 1 and 3 had high tensile strength, their elongation at break was extremely low (<120%) and their peel performance was poor, unable to meet the dynamic deformation requirements of flexible devices. The present invention breaks through the contradiction of traditional encapsulation materials of "high strength - low toughness" or "high flexibility - low adhesion" through the TMPTA-CTMS-PCL / PVC ternary synergistic system, providing a mechanical adaptation encapsulation solution for the next generation of flexible electronics.

[0075] 7. Ultraviolet accelerated aging test

[0076] Place the specimen in an aging test chamber, with the irradiation intensity between ultraviolet light wavelengths of 313 nm being 0.5 W / m 2 , irradiate for 72 h, and evaluate the yellowing index (ΔY1) and the tensile strength retention rate.

[0077] As Figure 8 and Figure 9 shown, the yellowing index of the encapsulating adhesives provided in Examples 1 to 3 is lower than that of the comparative examples, and their tensile strength retention rate is higher than that of the comparative examples.

[0078] The silyl group absorbs ultraviolet energy (200 - 400 nm), and the yellowing index ΔYI of Example 1 is only 1.5 - 2.5 (up to 8.0 - 12.0 for Comparative Example 1). The crosslinking of TMPTA restricts the movement of chain segments and reduces the oxidation active sites. After aging of Example 1, the growth of the carbonyl index (CI) is <5% (the growth of Comparative Example 2 is >30%). The compatibility of PCL / PVC is optimized (for example, the microdomains in Example 1 are <50 nm), reducing the ultraviolet penetration path. The tensile strength retention rate of Example 1 is 90 - 95% (only 40 - 50% for Comparative Example 1). CTMS forms Si - O - C bonds with PCL / PVC, inhibiting interfacial hydrolysis. After 1000 hours of UV aging, there is no delamination in Example 1 (the interfacial peel strength of Comparative Example 3 decreases by >40%).

[0079] The ternary synergy of CTMS (physical shielding) + TMPTA (chemical crosslinking) + PCL (flexible buffer) makes the performance degradation of the encapsulating adhesive films provided in Examples 1 to 3 slower than that of the comparative examples by more than 3 times after UV combined aging. In addition, by adjusting the CTMS / TMPTA ratio provided in Examples 1 to 3, it can adapt to the environmental requirements of different ultraviolet intensities.

[0080] In summary, Examples 1 to 3 perform optimally in terms of anti - yellowing and mechanical retention rate, and are suitable for high - ultraviolet - exposure scenarios (such as photovoltaic modules, outdoor electronics). Due to phase separation, lack of protective groups or interfacial defects in Comparative Examples 1 - 3, significant yellowing occurs after ultraviolet aging and the mechanical properties drop sharply, unable to meet the long - term outdoor use requirements. Through the molecular synergistic design of CTMS - TMPTA - PCL / PVC, the present invention realizes triple protection of ultraviolet shielding - free radical stabilization - interfacial strengthening, breaks through the weather resistance bottleneck of traditional encapsulating adhesives, and provides a long - term reliable encapsulation solution for new energy and flexible electronic devices.

[0081] 9. Volume resistivity test

[0082] According to the national standard GB / T1410 - 2006, use a high - resistance meter (ZC36, Suzhou Jingge Electronics Co., Ltd.) to test the volume resistivity. The specimen is a circular film with a diameter of 100 mm and a thickness of 1 mm, and the test temperature is 25°C. Take the average value of 3 measurements.

[0083] As Figure 10As shown, trimethylolpropane triacrylate was added as a crosslinking agent to the encapsulating adhesives provided in Examples 1 to 3. Under the conditions of oil bath reaction, the copolymer can form a crosslinked structure. The crosslinked structure can restrict the movement of molecular chains, improve the stability and compactness of the material, thereby contributing to the improvement of volume resistivity. In contrast, there is no crosslinking reaction in Comparative Examples 1 and 2, and the insulation performance of the materials is relatively poor.

[0084] In the examples, cetyltrimethoxysilane was added, which can improve the microstructure of the adhesive film, enhance the interfacial bonding performance with other materials, and may also reduce the polarity of the system, which has a positive effect on improving the volume resistivity. By adjusting the content of the additive, the performance of the encapsulating adhesive was optimized in the examples. However, the usage of the additive in the comparative examples was different from that in the examples, and the same optimization effect could not be achieved.

[0085] All the examples underwent processes such as heating and stirring for dissolution and oil bath reaction at a specific temperature, and the reaction was relatively sufficient, enabling the molecular weight and crosslinking degree of the copolymer to reach a relatively high level, which is beneficial to the formation of an encapsulating adhesive film with good performance. In contrast, Comparative Examples 1 and 2 only volatilized the solvent by standing at room temperature, and the material properties could not be fully improved.

[0086] In the encapsulating adhesives provided by Comparative Examples 1 and 2, it is easier to form a conductive channel by separating chlorine in the PVC phase, resulting in a decrease in resistivity. Moreover, the uncrosslinked PCL crystalline region is prone to leakage. The encapsulating adhesives provided in Examples 1 to 3 adopt the synergistic crosslinking technology of trimethylolpropane triacrylate and cetyltrimethoxysilane, effectively inhibiting the charge migration phenomenon, thereby significantly improving the insulation performance of the encapsulating adhesive. Although Comparative Example 3 also has a relatively high resistivity, its flexibility is poor, the material is hard and brittle, and it is not suitable for flexible encapsulation.

[0087] In summary, the encapsulating adhesives provided in Examples 1 to 3 achieve high crosslinking degree, low friction coefficient (stable at low temperature), high light transmittance, and excellent ultraviolet resistance through the synergistic crosslinking of trimethylolpropane triacrylate and cetyltrimethoxysilane. Among them, Example 3 provides the best comprehensive performance in terms of crosslinking degree, low friction coefficient (stable at low temperature), high light transmittance, and excellent ultraviolet resistance, which balances crystallization inhibition and interfacial stability. In addition, the encapsulating adhesive provided in Example 3 takes into account strength, flexibility, and resistivity, and has excellent peel strength.

[0088] The encapsulating adhesive provided in Example 3, with its high light transmittance, ultraviolet aging resistance, strong adhesion, and excellent insulation, is very suitable for the encapsulation of photovoltaic modules. Its light transmittance and ultraviolet aging resistance are superior to traditional materials. Its low volume resistivity meets the insulation requirements of photovoltaic modules.

[0089] In addition, due to good flexibility, low friction coefficient, bend resistance, and interfacial adhesion, the encapsulation adhesives provided in Examples 2 and 3 can also be applied to the encapsulation of flexible electronic devices, such as flexible display screens and wearable devices.

[0090] The encapsulation process provided in Example 1 can be used for the encapsulation of lithium-ion battery diaphragms or electrode sheets based on its insulation, resistance to electrolyte corrosion, and mechanical strength, and can also be used for the interlayer material of building glass based on its light transmittance, impact resistance, and weather resistance.

[0091] The above content is only the preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or replacement solutions that can be easily conceived by those skilled in the art within the technical idea of the present invention should fall within the protection scope of the present invention.

Claims

1. A high-performance encapsulating adhesive, characterized in that, It comprises a matrix material composed of polyvinyl chloride and polycaprolactone diol in a mass ratio of 8-10:1, benzoyl peroxide accounting for 0.2-0.7% of the total amount of the matrix material, trimethylolpropane triacrylate accounting for 8-12% of the total amount of the matrix material, and cetyltrimethoxysilane accounting for 11-18% of the total amount of the matrix material; wherein, the matrix material forms a three-dimensional network structure through the copolymerization cross-linking reaction of benzoyl peroxide, trimethylolpropane triacrylate and cetyltrimethoxysilane.

2. The encapsulating adhesive according to claim 1, wherein: The number-average molecular weight of the polyvinyl chloride > 50,000 and the molecular weight distribution index ≤ 1.5; the number-average molecular weight of the polycaprolactone diol is 20,000 ± 500, and the hydroxyl functionality ≥ 98%.

3. A method for preparing the encapsulant according to any one of claims 1-2, characterized in that, It includes: a) Adding polyvinyl chloride and polycaprolactone diol in a mass ratio of 8-10:1 to a tetrahydrofuran solvent to prepare a blend solution; b) Adding benzoyl peroxide accounting for 0.2-0.7% of the total amount of the matrix material, trimethylolpropane triacrylate accounting for 8-12% of the total amount of the matrix material and cetyltrimethoxysilane accounting for 11-18% of the total amount of the matrix material to the blend solution, and continuing to stir; c) Transferring the system to a constant-temperature oil bath at 65 ± 0.5 °C for polycondensation reaction; d) After gradient sedimentation with multiple volumes of ethanol, centrifuging to obtain a copolymer; e) Washing the copolymer with deionized water and ethanol in sequence, and drying to obtain the encapsulation adhesive.

4. The method according to claim 3, wherein In step a), the mass ratio of the polyvinyl chloride to the polycaprolactone diol is 8:1, the dosage of trimethylolpropane triacrylate is 12% of the total amount of the matrix material, and the dosage of cetyltrimethoxysilane is 18% of the total amount of the matrix material.

5. The method according to claim 3, characterized in that In step a), the mass ratio of the polyvinyl chloride to the polycaprolactone diol is 9:1, the dosage of trimethylolpropane triacrylate is 8% of the total amount of the matrix material, and the dosage of cetyltrimethoxysilane is 11% of the total amount of the matrix material.

6. The method according to claim 3, characterized in that, In step a), the mass ratio of the polyvinyl chloride to the polycaprolactone diol is 10:1, the dosage of trimethylolpropane triacrylate is 10% of the total amount of the matrix material, and the dosage of cetyltrimethoxysilane is 15% of the total amount of the matrix material.

7. Application of the encapsulation adhesive prepared by the method according to any one of claims 3-5 in the field of photovoltaic encapsulation, characterized in that: As a lamination encapsulation material for crystalline silicon solar cells and thin-film solar cells; For edge sealing of photovoltaic building integrated components.

8. Application of the encapsulation adhesive prepared by the method according to any one of claims 3-5 in the field of flexible electronics, characterized in that: As an encapsulation medium for flexible OLED displays; For the circuit protection layer of intelligent wearable devices; As an interface bonding material for electronic skin sensors.

9. Application of the encapsulation adhesive prepared by the method according to any one of claims 3-5 in the field of energy storage devices, characterized in that: As a surface modification coating for lithium-ion battery separators; For insulating encapsulation of the edges of power battery electrode sheets.

10. Application of the encapsulation adhesive prepared by the method according to any one of claims 3-5 in the field of construction, characterized in that: Structural sealant for insulating glass units; Weather-resistant sealing for curtain wall joints.

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