A heat and humidity resistant epoxy adhesive film and an insulated busbar and a preparation method thereof

Abstract

The present invention relates to the technical field of insulating adhesive films, and specifically discloses a moisture and heat resistant epoxy adhesive film, an insulating busbar and a preparation method thereof. The moisture and heat resistant epoxy adhesive film includes a high adhesion bottom layer and a high insulation surface layer laminated together. The high adhesion bottom layer and the high insulation surface layer are both prepared from the following components: an epoxy resin matrix, a branched structure modifier, an initiator, a nano-enhanced filler and a curing agent; the epoxy resin matrix includes bisphenol A epoxy resin and fluorine-containing epoxy resin. The moisture and heat resistant epoxy adhesive film of the present invention exhibits good stability in a high humidity and high temperature environment, can maintain excellent insulation performance for a long time, thereby ensuring the overall electrical performance and reliability of electrical equipment, and extending the service life of electrical equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of insulating adhesive films, and particularly to a moisture and heat resistant epoxy adhesive film, an insulating busbar, and a preparation method thereof. Background Art

[0002] With the continuous improvement of the power density and working environment of modern electrical equipment, traditional insulating materials are prone to performance degradation under harsh conditions such as high temperature, high humidity, and high voltage, resulting in shortened service life of electrical equipment and increased safety hazards. In particular, epoxy resin-based materials are widely used in the insulating layers of electrical equipment, but their performance deteriorates significantly in high humidity and high temperature environments, mainly manifested as a decrease in the glass transition temperature (Tg), a decrease in insulation performance, and an aggravation of the tracking phenomenon. In addition, in the application of hot-pressed adhesive films in high-voltage electrical equipment, problems such as unstable fluidity, glue overflow, and uneven glue film thickness are often encountered, resulting in increased manufacturing difficulty and difficult to guarantee the quality of the final product.

[0003] Commercially available insulating busbars usually use PET hot-pressed adhesive films as the main insulating material, and its typical structure is a double-layer system composed of a PET film and an epoxy resin adhesive layer. Although this structure exhibits excellent electrical insulation performance and processability, its inherent defects gradually appear during long-term operation, especially in harsh environments such as high temperature and high humidity. Insufficient material stability: The inherent hygroscopic property of the PET film easily leads to a decrease in insulation resistance, and the dielectric performance deteriorates significantly in a high humidity environment, directly affecting the long-term electrical reliability of the busbar. Interface compatibility problem: The difference in the expansion coefficients of heterogeneous materials (PET and epoxy resin) easily causes interface stress concentration under thermal cycling conditions, which may lead to structural failures such as delamination and peeling. Environmental tolerance limitation: Under continuous high temperature working conditions, the glass transition temperature of the PET material (Tg≈78°C) limits its easy creep deformation, further exacerbating the risk of interface debonding. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a moisture and heat resistant epoxy adhesive film, an insulating busbar, and a preparation method thereof. The moisture and heat resistant epoxy adhesive film exhibits good stability in high humidity and high temperature environments, can maintain excellent insulation performance for a long time, thereby ensuring the overall electrical performance and reliability of electrical equipment, and extending the service life of electrical equipment.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] The present invention first provides a moisture and heat resistant epoxy adhesive film, which includes a high-bonding bottom layer and a high-insulation surface layer combined together. The high-bonding bottom layer and the high-insulation surface layer are both prepared from the following components: an epoxy resin matrix, a branched structure modifier, an initiator, a nano-enhanced filler, and a curing agent; the epoxy resin matrix includes bisphenol A epoxy resin and fluorine-containing epoxy resin.

[0007] As a further improvement of the above solution of the present invention, by mass parts, the components in the high-bonding bottom layer are: 100 parts of epoxy resin matrix, 5-15 parts of branched-chain structure modifier, 0.5-2 parts of initiator, 3-5 parts of nano-enhanced filler, and 25-35 parts of curing agent;

[0008] And / or, by mass parts, the components in the high-insulation surface layer are: 100 parts of epoxy resin matrix, 5-15 parts of branched-chain structure modifier, 0.5-2 parts of initiator, 8-12 parts of nano-enhanced filler, and 25-35 parts of curing agent.

[0009] The high-bonding bottom layer of the present invention has a relatively high bonding strength, and the high-insulation surface layer ensures the excellent insulation performance of the adhesive film. The double-layer structure can ensure that the adhesive film has good adhesiveness and insulation performance under different working conditions.

[0010] As a further improvement of the above solution of the present invention, the preparation method of the nano-enhanced filler is: dispersing silica and isopropyl titanate in absolute ethanol, adding deionized water at a predetermined temperature, and stirring and reacting; after the reaction, centrifuging, washing, and calcining to obtain SiO2-TiO2 hybrid filler; mixing the SiO2-TiO2 hybrid filler with a silane coupling agent, reacting by water bath heating, and drying to obtain the nano-enhanced filler. Using a silane coupling agent to modify the surface of the SiO2-TiO2 hybrid filler can improve the compatibility between the filler and the resin matrix, and further enhance the comprehensive performance of the adhesive film.

[0011] As a further improvement of the above solution of the present invention, the mass ratio of the silica, isopropyl titanate, and absolute ethanol is 1:(2-4.5):(5-15);

[0012] And / or, the predetermined temperature of the deionized water is 50-70 °C, and the addition rate of the deionized water is 1-2 mL / min; the stirring reaction time is 2-3 h, and a 0.05-0.2 M hydrochloric acid solution is added dropwise during the reaction to adjust the pH of the reaction solution to 4-5;

[0013] And / or, the calcination is carried out at 400-600 °C for 1-3 h;

[0014] And / or, the mass ratio of the SiO2-TiO2 hybrid filler to the silane coupling agent is 1:1, and the water bath heating reaction is carried out by stirring in an 80 °C water bath for 1.5-2.5 h.

[0015] As a further improvement of the above solution of the present invention, the branched-chain structure modifier is at least one of glycidyl methacrylate, acrylic acid, styrene, epoxy acrylate, or 2-amino acrylic acid;

[0016] And / or, the initiator is benzoyl peroxide, tert-butyl peroxybenzoate, azobisisobutyronitrile, a compound prepared from benzoyl peroxide and tert-butyl peroxybenzoate in a mass ratio of 1:(0.2-0.5), or a compound prepared from benzoyl peroxide and triethanolamine in a mass ratio of 2:(1-1.5);

[0017] And / or, the curing agent is a compound prepared from 4,4'-diaminodiphenyl sulfone and 1,3-bis(aminomethyl)cyclohexane in a mass ratio of (1-2):1, a compound prepared from 4,4'-diaminodiphenyl sulfone and polyamide in a mass ratio of (1-3):1, or a compound prepared from 4,4'-diaminodiphenyl sulfone and 4,4'-diaminodiphenylmethane in a mass ratio of (1-2):1.

[0018] As a further improvement of the above solution of the present invention, the thickness of the high-bonding bottom layer is 45-55 μm, and the thickness of the high-insulation surface layer is 90-110 μm.

[0019] As a further improvement of the above solution of the present invention, by mass, the epoxy resin matrix includes: 60-80 parts of bisphenol A epoxy resin and 20-40 parts of fluorinated epoxy resin. The fluorinated epoxy resin preferably uses a fluorinated epoxy resin containing trifluoromethyl groups. Due to its strong electron-withdrawing effect, the trifluoromethyl (-CF3) group can effectively enhance the chemical corrosion resistance of the epoxy resin, especially its stability in acid-base, solvent, and high-temperature environments; at the same time, the introduction of trifluoromethyl can improve the hydrophobicity and moisture resistance of the resin, reduce the penetration of moisture and polar solvents, and improve the insulation performance and weather resistance of the material.

[0020] The present invention also provides a method for preparing the moisture and heat resistant epoxy film as described above, which includes the following steps:

[0021] S1. Prepare the high-bonding bottom layer material: Under nitrogen protection, mix the epoxy resin matrix at 80-90 °C, add the branched-chain structure modifier and the initiator, and react for 3-5 h to obtain a modified epoxy resin matrix. Add the nano-enhancing filler and the curing agent to the modified epoxy resin matrix and mix to obtain the high-bonding bottom layer material;

[0022] S2. Prepare the high-insulation surface layer material: Under nitrogen protection, mix the epoxy resin matrix at 80-90 °C, add the branched-chain structure modifier and the initiator, and react for 3-5 h to obtain a modified epoxy resin matrix. Add the nano-enhancing filler and the curing agent to the modified epoxy resin matrix and mix to obtain the high-bonding bottom layer material;

[0023] S3. Cast the high-bonding bottom layer material and the high-insulation surface layer material into a film through a slot coater, cure them gradiently, and anneal to obtain the moisture and heat resistant epoxy film.

[0024] As a further improvement of the above solution of the present invention, in step S3, the gradient curing includes the following steps:

[0025] Pre-curing stage: Pre-cure at 80 - 90 °C and 0.3 - 0.5 MPa for 20 - 40 min;

[0026] Leveling stage: Level at 110 - 130 °C and 0.1 - 0.2 MPa for 5 - 15 min;

[0027] Final curing stage: Final cure at 170 - 190 °C and 1.5 - 2.5 MPa for 1.5 - 2.5 h, with vacuum degassing.

[0028] As a further improvement of the above solution of the present invention, in step S3, the annealing is carried out at 145 - 155 °C for 30 min.

[0029] The present invention also provides an insulated busbar, which includes a metal conductor substrate and the moisture-resistant epoxy adhesive film as described above, and the high-adhesion bottom layer of the moisture-resistant epoxy adhesive film is laminated on the metal conductor substrate.

[0030] As a further improvement of the above solution of the present invention, the metal conductor substrate is a copper substrate or an aluminum alloy substrate, and the surface roughness Ra of the metal conductor substrate is 1.2 - 1.8 μm, and Rz is 8 - 12 μm. The surface of the metal conductor is micro-etched to form a multi-level rough structure with a higher roughness, which can enhance the bonding strength between the adhesive film and the metal conductor substrate and ensure the firm bonding of the adhesive film and the metal conductor.

[0031] The present invention also provides a method for preparing the insulated busbar as described above, which includes the following steps: micro-etch and clean the metal conductor substrate; laminate the high-adhesion bottom layer of the moisture-resistant epoxy adhesive film with the metal conductor substrate, and press the moisture-resistant epoxy adhesive film onto the metal conductor substrate through a hot pressing process to obtain the insulated busbar.

[0032] As a further improvement of the above solution of the present invention, the temperature of the hot pressing process is 200 °C, the pressure is 2 MPa, and the holding time is 5 - 15 min.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention prepares a high - adhesion bottom layer and a high - insulation surface layer using an epoxy resin substrate. The epoxy resin matrix is compounded from bisphenol A epoxy resin and fluorinated epoxy resin. The fluorinated epoxy resin shows significant advantages in terms of heat and humidity resistance, which can improve the hydrophobicity and moisture resistance of the substrate, reduce the penetration of moisture and polar solvents, thereby improving the insulation performance and weather resistance of the material. Further, through a branched - chain structure modifier, the epoxy resin free radicals are grafted to form a branched - chain structure, which can further improve the heat and humidity resistance of the adhesive film. The glass transition temperature (Tg) of the adhesive film of the present invention is greater than 160 °C. After 1000 - hour hygrothermal aging at 85 °C / 85% relative humidity (RH), it can still maintain a peel strength of more than 90%, and the volume resistivity ≥ 8×10 15 Ω·cm. It shows good stability in a high - humidity and high - temperature environment, can maintain excellent insulation performance for a long time, thereby ensuring the overall electrical performance and reliability of electrical equipment, and extending the service life of electrical equipment.

[0035] In the epoxy resin substrate of the present invention, nano - reinforcing fillers are also introduced. The modification of the branched - chain structure of the epoxy resin can improve the dispersion effect of the nano - reinforcing fillers in the epoxy resin matrix, construct a stable transition at the filler - resin interface, enhance the interfacial interaction force, and the introduced nano - reinforcing fillers can fill in the microporous structure of the resin matrix through the rigid particle effect to form a three - dimensional reinforcement network, making the cross - section of the adhesive film show a dense nano - composite morphology, thereby improving the mechanical properties and environmental aging resistance of the adhesive film. Further, the nano - reinforcing filler of the present invention is a SiO2 - TiO2 hybrid filler surface - modified by a silane coupling agent. Its active groups can form chemical bonding with epoxy resin groups, and the TiO2 component can form a coordination bond with the hydroxyl groups of the epoxy resin, which can further enhance the interfacial bonding force between the filler and the resin matrix, improve the compatibility between the filler and the resin matrix, and further enhance the comprehensive performance of the adhesive film.

[0036] Both the high - adhesion bottom layer and the high - insulation surface layer of the adhesive film of the present invention are made of epoxy resin substrate. As an excellent insulating material, epoxy resin has high mechanical strength, good heat resistance and chemical stability. Using epoxy resin substrate for both the bottom layer and the surface layer can improve the overall performance of the entire adhesive film and ensure its stability in harsh environments such as high temperature and high humidity. Moreover, the excellent adhesion of epoxy resin makes the combination between the bottom layer and the surface layer closer, avoiding delamination or peeling caused by differences in thermal expansion coefficients between different materials. Using the same material for the bottom layer and the surface layer can not only improve the balance of the overall performance, but also enhance the durability and reliability of the adhesive film. The high - adhesion bottom layer can effectively enhance the adhesion between the adhesive film and the substrate, while the high - insulation surface layer provides excellent electrical insulation performance. This double - layer structure not only improves the comprehensive performance of the adhesive film, but also realizes the advantages of both high adhesion strength and excellent insulation performance in the same material.

[0037] When the adhesive film of the present invention is prepared, a gradient curing process is adopted. Through the precise control of the multi-stage synergistic action of temperature - pressure - time, a gradient cross-linked structure of the epoxy adhesive film from the surface layer to the interior is achieved: a preliminary network framework is formed in the pre-curing stage to ensure uniform infiltration of the resin into the reinforcing material; the leveling stage eliminates interface defects and regulates the molecular chain orientation; the final curing stage combines vacuum degassing to form a dense three-dimensional cross-linked network, finally enabling the adhesive film to have good bonding strength, heat and humidity resistance stability, and insulation.

[0038] When the adhesive film of the present invention is used for insulating busbars, it has an excellent electrical insulation strength of 30 kV / mm, which is a 272% increase compared to the PET adhesive film (11 kV / mm). Description of the Drawings

[0039] Figure 1 SEM image of the nano-enhanced filler obtained in Example 1;

[0040] Figure 2 SEM image of the heat and humidity resistant epoxy adhesive film obtained in Example 1;

[0041] Figure 3 SEM image of the adhesive film obtained in Comparative Example 1;

[0042] Figure 4 SEM image of the adhesive film obtained in Comparative Example 2;

[0043] Figure 5 Glass transition temperature diagram of the adhesive films obtained in Examples 1 - 2 and Comparative Examples 1 - 2;

[0044] Figure 6 Tensile strength test result diagram of the adhesive films obtained in Examples 1 - 2 and Comparative Examples 1 - 2;

[0045] Figure 7 Peeling strength retention rate of the adhesive films obtained in Examples 1 - 2 and Comparative Examples 1 - 2 after hygrothermal aging;

[0046] Figure 8 Volume resistivity of the adhesive films obtained in Examples 1 - 2 and Comparative Examples 1 - 2 after hygrothermal aging. Detailed Embodiments

[0047] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the specification of this invention are for the purpose of describing specific embodiments only and are not intended to limit the invention.

[0049] Example 1

[0050] This example provides a moisture and heat resistant epoxy film, which includes a high adhesion bottom layer and a high insulation top layer laminated together. Among them:

[0051] The high adhesion bottom layer is prepared from the following components in parts by mass: 70 parts of bisphenol A epoxy resin (Momentive Hexion Epon828, EEW = 190), 30 parts of fluorinated epoxy resin (Hexion, grade ERL-4221), 10 parts of glycidyl methacrylate GMA, 2 parts of initiator (obtained by compounding azobisisobutyronitrile AIBN and benzoyl peroxide BPO in a mass ratio of 1:0.3), 5 parts of nano-enhanced filler, 18 parts of 4,4'-diaminodiphenyl sulfone DDS, and 9 parts of 1,3-bis(aminomethyl)cyclohexane.

[0052] The high insulation top layer is prepared from the following components in parts by mass: 70 parts of bisphenol A epoxy resin (EEW = 190), 30 parts of fluorinated epoxy resin (Hexion, grade ERL-4221), 10 parts of glycidyl methacrylate GMA, 2 parts of initiator (obtained by compounding azobisisobutyronitrile AIBN and benzoyl peroxide BPO in a mass ratio of 1:0.3), 12 parts of nano-enhanced filler, 18 parts of 4,4'-diaminodiphenyl sulfone DDS, and 9 parts of 1,3-bis(aminomethyl)cyclohexane.

[0053] In this embodiment, the preparation method of the nano-enhanced filler is as follows: (1) First, 20 g of SiO2 particles (Hangzhou Wanjing New Materials Co., Ltd., grade: WJ-SiO2-20E) and 80 g of isopropyl titanate are added to 150 g of absolute ethanol, and ultrasonically stirred for 30 minutes to ensure uniform dispersion. Then, deionized water preheated to 60 °C is slowly added, and the addition rate is controlled at 1.5 mL per minute, and the reaction is maintained for 2-3 hours, during which stirring is continued to ensure uniform reaction; the temperature is maintained at 65 °C during the reaction to promote the hydrolysis and condensation of the titanium source, and the pH of the reaction solution is adjusted to 4-5 by dropping 0.1 M dilute hydrochloric acid solution to improve the deposition efficiency of TiO2 and prevent aggregation. After the reaction is completed, the precipitate is separated by centrifugation, washed three times alternately with absolute ethanol and deionized water to remove the unreacted isopropyl titanate, and then calcined at 500 °C for 2 hours to enhance the binding force between TiO2 and SiO2, and finally the SiO2-TiO2 hybrid filler with TiO2-coated SiO2 is obtained. (2) The prepared SiO2-TiO2 hybrid filler and silane coupling agent (KH-550, Jiangsu Baoli Chemical Co., Ltd.) are mixed in a mass ratio of 1:1, and stirred and reacted in a water bath at 80 °C for 2 hours, and finally dried in an oven at 60 °C to remove the unreacted silane coupling agent and other solvent residues, thereby successfully modifying the surface of the filler and obtaining the nano-enhanced filler.

[0054] Figure 1 is the SEM photograph of the nano-enhanced filler prepared in this embodiment. From Figure 1 it can be seen that the particle size distribution of the nano-enhanced filler spheres prepared in this embodiment is uniform, the monodispersity is good, all the particles are spherical and complete without obvious agglomeration phenomenon, the surface is smooth and defect-free, the TiO2 coating layer completely covers the core material SiO2, and no bare or cracked areas are observed, and the uniform coating of TiO2 is successfully achieved.

[0055] The preparation method of the moisture and heat resistant epoxy adhesive film in this embodiment includes the following steps:

[0056] S1. Prepare the high-bonding bottom layer material: Under nitrogen protection and water bath heating at 80 °C, bisphenol A epoxy resin (EEW = 190) and fluorinated epoxy resin are mixed, glycidyl methacrylate and initiator are added, and the reaction is carried out for 3 h, during which the reaction temperature is controlled within 85 °C until the reaction ends to obtain a modified epoxy resin matrix. Nano-enhanced filler, 4,4'-diaminodiphenyl sulfone DDS, and 1,3-bis(aminomethyl)cyclohexane are added to the modified epoxy resin matrix in proportion and put into a planetary mixer for vacuum dispersion treatment, keeping the vacuum degree ≤ 0.09 MPa and the dispersion time 2 hours to ensure uniform dispersion of the nano-enhanced filler, and then the high-bonding bottom layer material is obtained;

[0057] S2. Preparation of high-insulation surface layer material: Under nitrogen protection and water bath heating at 80°C, bisphenol A epoxy resin (EEW = 190) and fluorinated epoxy resin are mixed, glycidyl methacrylate and initiator are added, and the reaction is carried out for 3 h. During the reaction, the reaction temperature is controlled within 85°C until the reaction ends to obtain a modified epoxy resin matrix. Nano-enhanced filler, 4,4'-diaminodiphenyl sulfone DDS, and 1,3-bis(aminomethyl)cyclohexane are added to the modified epoxy resin matrix in proportion and put into a planetary mixer for vacuum dispersion treatment. The vacuum degree is maintained ≤0.09 MPa, and the dispersion time is 2 h to ensure uniform dispersion of the nano-enhanced filler, thus obtaining the high-bonding bottom layer material;

[0058] S3. The high-bonding bottom layer material prepared in step S1 and the high-insulation surface layer material prepared in step S2 are cast into films using a precisely controlled slot coater. The coating gap accuracy is controlled within ±1 μm, and the thickness of the coated adhesive film is 150 ± 2 μm. After gradient curing, it is taken out and annealed at 150°C for 30 minutes to reduce the residual stress in the adhesive film and improve the mechanical properties, thus obtaining the moisture and heat resistant epoxy adhesive film.

[0059] The gradient curing in step S3 of this embodiment includes: (1) Pre-curing stage: The adhesive film is placed at 80°C for 30 minutes and cured under a pressure of 0.4 MPa, while maintaining the viscosity of the adhesive film between 800 - 2000 Pa·s; (2) Levelling stage: The temperature of the adhesive film is raised to 120°C for 10 minutes to ensure the flat surface of the adhesive film and maintain the viscosity decrease rate ≤10% / min; (3) Final curing stage: The adhesive film is heated to 180°C for 2 h and cured under a pressure of 2 MPa, and vacuum degassing treatment is applied (vacuum degree ≤0.095 MPa, maintained for 15 minutes).

[0060] The total thickness of the moisture and heat resistant epoxy adhesive film prepared in this embodiment is 161 μm, the thickness of the high-bonding bottom layer is 55 μm, and the thickness of the high-insulation surface layer is 106 μm.

[0061] Comparative Example 1

[0062] This comparative example adopts the same implementation method as Example 1. The difference from Example 1 is that in the high-bonding bottom layer and high-insulation surface layer of this comparative example, 100 parts of bisphenol A epoxy resin (EEW = 180 - 200), 0 part of fluorinated epoxy resin, 0 part of initiator, and 0 part of branched-chain structure modifier are used.

[0063] Comparative Example 2

[0064] This comparative example adopts the same implementation method as Example 1. The difference from Example 1 is that in the high-bonding bottom layer and high-insulation surface layer of this comparative example, the nano-enhanced fillers are both 0 part.

[0065] Figure 2 SEM photograph of the moisture and heat resistant epoxy film prepared in Example 1. It can be seen from Figure 2 that the moisture and heat resistant epoxy film prepared in Example 1 has highly uniform and dense microstructural characteristics. It can be clearly observed from Figure 2 that: the nano-enhanced filler particles are evenly dispersed in the epoxy resin matrix without visible agglomeration; the interface transition between the filler and the resin is continuous, and no defects such as pores and cracks are found; the overall morphology is smooth and dense, showing good compatibility. This excellent structural property of the moisture and heat resistant epoxy film in this example is because after the surface of the nano-enhanced filler is modified by a silane coupling agent, its active groups form chemical bonds with the epoxy resin groups, and at the same time, the gradient curing process promotes the orderly cross-linking of the resin network, jointly constructing a stable three-dimensional network structure. This structural feature provides excellent moisture and heat resistance and mechanical strength for the film material.

[0066] Figure 3 SEM photograph of the film prepared in Comparative Example 1. It can be seen from Figure 3 that there are pores at the interface of the film prepared in Comparative Example 1, the filler distribution is uneven, and there is local aggregation. Comparing Example 1 with Comparative Example 1 shows that the introduction of the branched structure significantly optimizes the dispersion state of the nano-enhanced filler in the epoxy resin matrix. On the one hand, the polar functional groups at the end of the branched structure form chemical bonds with the epoxy resin molecular chains, constructing a stable transition at the filler-resin interface; on the other hand, the three-dimensional configuration of the branched chains in the transition layer effectively blocks the van der Waals force between the filler particles; under the dual action mechanism of the steric hindrance effect and the surface active groups of the branched structure, not only the dispersion stability of the nano-enhanced filler is improved, but also a denser microstructure is formed in the film material by enhancing the interfacial interaction force, which is directly reflected in the more flat and uniform cross-sectional morphology of the film in Example 1.

[0067] Figure 4 SEM photograph of the film prepared in Comparative Example 2. It can be seen from Figure 4 that there are large-area pores at the interface of the film prepared in Comparative Example 2, and the structure is loose and not dense. Comparing Example 1 with Comparative Example 2 shows that the introduction of SiO2-TiO2 nano-enhanced filler can significantly improve the structural integrity of the film material: the nano-enhanced filler effectively fills the microporous structure in the resin matrix through the rigid particle effect; the TiO2 component forms a coordination bond with the hydroxyl group of the epoxy resin, enhancing the interfacial bonding force between the filler and the matrix; this synergistic effect makes the cross-section of the film present a dense nano-composite morphology. This structural optimization makes the densification degree of Example 1 significantly higher than that of Comparative Example 2, providing a structural basis for its excellent mechanical properties and environmental aging resistance.

[0068] Example 2

[0069] This embodiment adopts the same implementation method as Embodiment 1. The difference from Embodiment 1 is as follows:

[0070] In this embodiment, the high-bonding bottom layer is prepared from the following components in parts by mass: 60 parts of bisphenol A epoxy resin (Tianjin Binhai Huatai, E-51, EEW = 180), 40 parts of fluorinated epoxy resin (Jinhuan FEPOX-428), 10 parts of epoxy acrylate (Shenzhen Fuhua Chemical Co., Ltd., FHY-700), 1 part of initiator tert-butyl perbenzoate, 3 parts of nano-enhanced filler, 10 parts of 4,4'-diaminodiphenylmethane, and 17 parts of diphenylsulfone diamine;

[0071] The high-insulation surface layer is prepared from the following components in parts by mass: 60 parts of bisphenol A epoxy resin (Tianjin Binhai Huatai, E-51, EEW = 180), 40 parts of fluorinated epoxy resin (Jinhuan FEPOX-428), 10 parts of epoxy acrylate (Shenzhen Fuhua Chemical Co., Ltd., FHY-700), 1 part of initiator tert-butyl perbenzoate, 12 parts of nano-enhanced filler, 10 parts of 4,4'-diaminodiphenylmethane, and 17 parts of diphenylsulfone diamine.

[0072] The total thickness of the moisture and heat resistant epoxy film prepared in this embodiment is 160 μm, the thickness of the high-insulation surface layer is 110 μm, and the thickness of the high-bonding bottom layer is 50 μm.

[0073] Test Example 1

[0074] The films prepared in Embodiments 1-2 and Comparative Examples 1-2 were subjected to the following performance tests:

[0075] (1) Glass transition temperature (Tg): The film was tested using a differential scanning calorimeter (DSC) at a heating rate of 10 °C / min; the glass transition temperature diagram of the film as shown was obtained. As can be seen from Figure 5 it, the glass transition temperatures Tg of the moisture and heat resistant epoxy films prepared in Embodiments 1 and 2 were 162 °C and 189 °C, respectively, indicating good thermal stability; the glass transition temperatures Tg of the films in Comparative Examples 1-2 were 113 °C and 125 °C, respectively. This shows that the moisture and heat resistant epoxy film prepared in the embodiments of the present application can still maintain rigidity under high temperature and high humidity conditions, is not easily softened or deformed, and maintains its good use performance. Figure 5

[0076] (2) Tensile strength of the film: The film sample to be tested was cut into a specific size (width 10 mm, length 100 mm) and clamped between two fixtures of a tensile testing machine (Sans Electronic Universal Tensile Testing Machine, CMT5305), and tensile testing was carried out in accordance with GB / T2792-2014, applying a tensile force at a constant tensile rate of 5 mm / min until the sample broke. The results are as shown in Figure 6 ​As shown. The results indicate that the tensile strength of the moisture and heat resistant epoxy adhesive film prepared in Examples 1-2 is significantly higher than that of the adhesive film prepared in Comparative Examples 1-2. This shows that by introducing a branched structure modifier, the crosslinking density of the polymer network of the adhesive film is significantly improved, the intermolecular force between molecular chains is enhanced, thereby effectively improving the compactness of the microstructure of the material; at the same time, the uniform dispersion of the nano-enhanced filler in the resin matrix forms a three-dimensional reinforcement network, and its unique size effect and interface effect further enhance the stress transfer efficiency; the combined action of these two synergistic mechanisms makes the tensile strength of the adhesive film significantly higher than that before modification, and finally realizes a significant improvement in the mechanical properties of the adhesive film.

[0077] (3) Glue overflow width: The adhesive film was subjected to a hot pressing test at a test temperature of 200 °C, a pressure of 2 MPa, and a time of 15 min. During the hot pressing test, the moisture and heat resistant epoxy adhesive films prepared in Example 1 and Example 2 showed excellent low glue overflow performance, and their glue overflow widths were only 0.4 mm and 0.35 mm respectively. In contrast, the glue overflow phenomenon of the adhesive films in Comparative Example 1 and Comparative Example 2 was more obvious, and the glue overflow widths reached 1 mm and 0.8 mm respectively, which were significantly higher than those of the Example samples. This difference is mainly attributed to the optimized design of the composite gradient curing system, which enables the adhesive film to achieve more precise melting-curing behavior during heating, thereby effectively suppressing the excessive flow of the resin. In addition, this system endows the adhesive film with higher heat resistance stability, enabling it to maintain good dimensional stability under the high temperature conditions of the hot pressing process, further reducing the risk of glue overflow. Therefore, the composite gradient curing technology not only improves the moisture and heat resistance of the adhesive film, but also significantly optimizes its processing applicability in the encapsulation process.

[0078] (4)90° peel strength of the adhesive film to copper: The epoxy adhesive film was laminated onto the surface of a copper plate through a hot pressing process (temperature: 200 °C, pressure: 2 MPa, for 15 minutes) to obtain a sample. Then, referring to the GB / T 2792-2014 standard, a standard tensile testing machine (Sans Electronic Universal Tensile Testing Machine, CMT5305) was used to conduct the peel strength test. The sample was cut into specific dimensions: width 25 mm and length 300 mm. The sample was clamped in the fixture of the peel tester, ensuring that the peeling surface was perpendicular. A tensile force was applied to peel the adhesive film from the copper plate. During the test, a tensile force was applied at a constant tensile rate of 300 mm / min until complete peeling. During the test, the epoxy adhesive films prepared in Examples 1-2 exhibited excellent interfacial bonding strength, with initial peel strengths reaching 16 MPa and 25 MPa respectively, significantly higher than those of Comparative Example 1 (12 MPa) and Comparative Example 2 (10 MPa). This improvement in performance is mainly attributed to the optimized design of the gradient curing system, which forms a gradient crosslinked network during the curing process, not only enhancing the cohesive strength of the adhesive film but also significantly improving the interfacial bonding force between the adhesive film and the copper substrate through the synergistic effect of chemical bonding and physical anchoring.

[0079] To further evaluate the long-term reliability of the adhesive film, the cut splines were placed in a harsh humid heat environment of 85 °C / 85% RH for 1000 hours of aging test, and the peel strength after humid heat aging was tested (the method is the same as above). The results are as Figure 7 、 Figure 8 shown. It can be seen that the epoxy adhesive films prepared in Examples 1-2 can still maintain a peel strength of more than 90% after aging, showing excellent humid heat stability, with a volume resistivity ≥ 8×10 15 Ω·cm; while the peel strength retention rates of the adhesive films prepared in Comparative Examples 1-2 are only 50% - 60%, indicating that their bonding performance significantly degrades in a humid heat environment.

[0080] Example 3

[0081] This example provides an insulating busbar, which includes a copper substrate and an adhesive film laminated on the copper substrate. The adhesive film is the humid heat resistant epoxy adhesive film prepared in Example 1. The preparation method of the insulating busbar in this example is as follows:

[0082] The copper substrate after micro-etching treatment was cleaned to remove surface oil stains and impurities, ensuring uniform surface roughness. The roughness Ra of the copper substrate after micro-etching treatment was 1.6 μm, and Rz was 11 μm. The high adhesion bottom layer of the humid heat resistant epoxy adhesive film prepared in Example 1 was adhered to the micro-etching treated copper substrate, and then the humid heat resistant epoxy adhesive film was laminated onto the surface of the micro-etching treated copper substrate through a hot pressing process: temperature 200 °C, pressure 2 MPa, for 15 minutes, to ensure the bonding strength and electrical insulation performance of the adhesive film.

[0083] Example 4

[0084] This example uses the same implementation method as Example 3. The difference from Example 3 is that in this example, the moisture and heat resistant epoxy adhesive film prepared in Example 2 is used instead of the moisture and heat resistant epoxy adhesive film prepared in Example 1.

[0085] Comparative Example 3

[0086] This comparative example uses the same implementation method as Example 3. The difference from Example 3 is that in this comparative example, a commercially available PET hot-pressing adhesive film with a thickness of 160 μm (SKC, Korea, Skyrol® SH72, structure: surface layer PET film + bottom layer epoxy resin adhesive) is used instead of the moisture and heat resistant epoxy adhesive film prepared in Example 1.

[0087] The 90-degree peel strength test was carried out on the insulating busbar of Comparative Example 3 (the method is the same as that in Test Example 1(4)). The test results show that the initial peel strength is 10 MPa, and the peel strength is only 3.9 MPa after 1000 hours of aging test, with a peel strength loss of 61%.

[0088] Test Example 2

[0089] The insulating busbars prepared in Examples 3-4 and Comparative Example 3 were subjected to an electrical insulation strength test: An insulation resistance tester (Shenzhen Shenggong Technology, SENGW-2500D) was used to test the voltage withstand capacity of the samples in an electrical insulation medium: The insulating busbar samples were clamped in the fixture of the insulation resistance tester, and a gradually increasing DC voltage was applied until the samples broke down or leaked electricity. During the test, the breakdown voltage was monitored and recorded. The electrical insulation strength of the insulating busbar in Example 3 was measured to be 30 kV / mm, the electrical insulation strength of the insulating busbar in Example 4 was 28 kV / mm, and the electrical insulation strength of the insulating busbar in Comparative Example 3 was 11 kV / mm.

[0090] In summary, the moisture and heat resistant epoxy film prepared in the embodiments of the present application is significantly superior to the commercially available PET hot pressing film in terms of comprehensive performance. In terms of mechanical properties, the initial peel strength of the film in the embodiments of the present application reaches 16 - 25 MPa, which is 60% - 150% higher than that of the PET film (10 MPa), and more than 90% of the peel strength can still be maintained after 1000 hours of double 85 aging (only 39% remains for the PET film); in terms of electrical properties, the film in the embodiments of the present application has an excellent electrical strength of 30 kV / mm, which is 272% higher than that of the PET film (11 kV / mm). This significant advantage stems from the dense cross - linked network constructed by the composite gradient curing system, which not only enhances the interfacial bonding force through chemical bonding, but also ensures long - term stability in a humid and hot environment due to its low moisture absorption characteristics and the dispersion of nano - enhanced fillers. However, the performance of the PET film is greatly attenuated due to problems such as the easy hydrolysis of epoxy resin and weak interfacial bonding. Therefore, the film in the embodiments of the present application is particularly suitable for harsh application scenarios such as high - voltage systems of new energy vehicles that require high reliability and long life.

[0091] The technical features of the above - described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above - described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0092] The above - described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims.

Claims

1. A moisture and heat resistant epoxy film, characterized in that, It includes a highly adhesive bottom layer and a highly insulating top layer compounded together. By mass, the components in the highly adhesive bottom layer are: 100 parts of epoxy resin matrix, 5 - 15 parts of branched - chain structure modifier, 0.5 - 2 parts of initiator, 3 - 5 parts of nano - reinforcing filler, and 25 - 35 parts of curing agent. By mass, the components in the highly insulating top layer are: 100 parts of epoxy resin matrix, 5 - 15 parts of branched - chain structure modifier, 0.5 - 2 parts of initiator, 8 - 12 parts of nano - reinforcing filler, and 25 - 35 parts of curing agent. The epoxy resin matrix includes: 60 - 80 parts of bisphenol A epoxy resin and 20 - 40 parts of fluorine - containing epoxy resin. The preparation method of the nano - reinforcing filler is as follows: Disperse silicon dioxide and isopropyl titanate in absolute ethanol, add deionized water at a predetermined temperature, and stir for reaction. After the reaction, centrifuge, wash, and calcine to obtain SiO2 - TiO2 hybrid filler. Mix the SiO2 - TiO2 hybrid filler with a silane coupling agent, react by water - bath heating, and dry to obtain the nano - reinforcing filler. The branched - chain structure modifier is glycidyl methacrylate or epoxy acrylate.

2. The moisture and heat resistant epoxy adhesive film according to claim 1, wherein, The mass ratio of the silicon dioxide, isopropyl titanate, and absolute ethanol is 1:(2 - 4.5):(5 - 15). And / or, the predetermined temperature of the deionized water is 50 - 70 °C, and the addition rate of the deionized water is 1 - 2 mL / min. The stirring reaction time is 2 - 3 h, and a 0.05 - 0.2 M hydrochloric acid solution is added dropwise during the reaction to adjust the pH of the reaction solution to 4 - 5. And / or, the calcination is carried out at 400 - 600 °C for 1 - 3 h. And / or, the mass ratio of the SiO2 - TiO2 hybrid filler to the silane coupling agent is 1:1, and the water - bath heating reaction is carried out by stirring in an 80 °C water bath for 1.5 - 2.5 h.

3. The heat and humidity resistant epoxy adhesive film according to claim 1, characterized in that, The initiator is benzoyl peroxide, tert - butyl peroxybenzoate, azobisisobutyronitrile, a compound prepared by mixing benzoyl peroxide and tert - butyl peroxybenzoate in a mass ratio of 1:(0.2 - 0.5), or a compound prepared by mixing benzoyl peroxide and triethanolamine in a mass ratio of 2:(1 - 1.5). And / or, the curing agent is a compound prepared by mixing 4,4'-diaminodiphenyl sulfone and 1,3 - bis(aminomethyl)cyclohexane in a mass ratio of (1 - 2):1, a compound prepared by mixing 4,4'-diaminodiphenyl sulfone and polyamide in a mass ratio of (1 - 3):1, or a compound prepared by mixing 4,4'-diaminodiphenyl sulfone and 4,4'-diaminodiphenylmethane in a mass ratio of (1 - 2):

1.

4. The moisture and heat resistant epoxy film according to claim 1, wherein The thickness of the highly adhesive bottom layer is 45 - 55 μm, and the thickness of the highly insulating top layer is 90 - 110 μm.

5. A method for preparing a moisture and heat resistant epoxy adhesive film as described in any one of claims 1-4, characterized in that, It includes the following steps: S1. Prepare the highly adhesive bottom layer material: Under nitrogen protection, mix the epoxy resin matrix at 80 - 90 °C, add the branched - chain structure modifier and the initiator, react for 3 - 5 h to obtain a modified epoxy resin matrix, and add the nano - reinforcing filler and the curing agent to the modified epoxy resin matrix and mix to obtain the highly adhesive bottom layer material. S2. Preparation of high-insulation surface layer material: Under nitrogen protection, the epoxy resin matrix is mixed at 80 - 90 °C, and a branched-chain structure modifier and an initiator are added, and the reaction is carried out for 3 - 5 h to obtain a modified epoxy resin matrix. Nano-enhanced filler and curing agent are added to the modified epoxy resin matrix and mixed to obtain the high-bonding bottom layer material; S3. The high-bonding bottom layer material and the high-insulation surface layer material are cast into a film by a slot coater, gradient cured, and annealed to obtain a moisture and heat resistant epoxy film.

6. The method for preparing a moisture and heat resistant epoxy adhesive film according to claim 5, characterized in that, In step S3, the gradient curing includes the following steps: Pre-curing stage: Pre-cure at 80 - 90 °C and 0.3 - 0.5 MPa for 20 - 40 min; Leveling stage: Level at 110 - 130 °C and 0.1 - 0.2 MPa for 5 - 15 min; Final curing stage: Final cure at 170 - 190 °C and 1.5 - 2.5 MPa for 1.5 - 2.5 h, and degas under vacuum.

7. The method for preparing a moisture and heat resistant epoxy film according to claim 5, wherein In step S3, the annealing is carried out at 145 - 155 °C for 30 min.

8. An insulating busbar, characterized in that, It includes a metal conductor substrate and the moisture and heat resistant epoxy film as described in any one of claims 1 - 4, and the high-bonding bottom layer of the moisture and heat resistant epoxy film is laminated on the metal conductor substrate.

9. The insulating bus bar according to claim 8, wherein, The metal conductor substrate is a copper substrate or an aluminum alloy substrate, and the surface roughness Ra of the metal conductor substrate is 1.2 - 1.8 μm, and Rz is 8 - 12 μm.

10. A method for preparing an insulating busbar as claimed in claim 8 or 9, characterized in that, It includes the following steps: Micro-etch and clean the metal conductor substrate; laminate the high-bonding bottom layer of the moisture and heat resistant epoxy film with the metal conductor substrate, and press the moisture and heat resistant epoxy film onto the metal conductor substrate by a hot pressing process to obtain an insulated busbar.

11. The method for preparing an insulated busbar according to claim 10, wherein, The temperature of the hot pressing process is 200 °C, the pressure is 2 MPa, and the holding time is 5 - 15 min.

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