A solvent-free epoxy adhesive for magnetic material encapsulation, a preparation method and application thereof

Abstract

The application discloses a kind of magnetic material encapsulation solvent-free epoxy glue and its preparation method and application, belong to adhesive technical field.The solvent-free epoxy glue is by weight fraction, by 60-75 parts of bisphenol A type epoxy resin modifier, 15-25 parts of composite curing system, 3-8 parts of functional polycarboxylate dispersant, 2-5 parts of thixotropic modifier, 1-3 parts of synergistic aid composition;Through the epoxy resin of gamma-aminopropyl triethoxysilane graft modification constructs magnetic material affinity structure, compound anhydride-amine composite curing system, collocation functional dispersant and silane modified nanocomposite thixotropic agent, combined with gradient mixing, segmented vacuum degassing, in-situ modification dispersion process, realize the synergistic effect of each component.The application solves the problem that the existing magnetic material encapsulation solvent-free epoxy glue is weak, glue flying silk is serious, insulation and weathering performance decays fast, can be used for ferrite, neodymium iron boron, samarium cobalt magnetic material encapsulation, preparation process controllable, suitable for industrialized batch production.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, specifically relating to a solvent-free epoxy adhesive for encapsulating magnetic materials, its preparation method, and its application. Background Technology

[0002] Magnetic materials, as core components in electronics, electrical engineering, aerospace, and other fields, often operate under complex conditions such as high temperature, humidity, vibration, and high voltage. These conditions make them prone to oxidation, corrosion, and insulation degradation. Therefore, encapsulation with adhesives is necessary to protect them and improve their stability and lifespan. Solvent-free adhesives, due to their 100% solids content and VOC-free environmental characteristics, are gradually replacing traditional solvent-based adhesives as the preferred material for magnetic material encapsulation. Among them, epoxy resin-based solvent-free adhesives have become the mainstream type of adhesive for magnetic material encapsulation due to their excellent adhesion, insulation, and heat resistance.

[0003] In existing technologies, solvent-free epoxy adhesives for magnetic material encapsulation are mostly formulated with ordinary bisphenol A type epoxy resin, a single curing agent, and conventional dispersants. While these can meet basic encapsulation requirements, they still have several technical defects in practical applications: First, ordinary epoxy resins have weak interfacial bonding with the surface of magnetic materials, and their molecular chains lack affinity groups that can bind to hydroxyl groups and metal ions on the surface of magnetic materials, leading to easy debonding and peeling of the adhesive layer, which cannot meet the bonding requirements of high-end magnetic materials; Second, they mostly use single acid anhydride-based or... Amine-based curing agents and anhydride-based curing agents require high-temperature curing and the cured adhesive layer is brittle and prone to cracking under high and low temperature cycling. Amine-based curing agents have a fast room temperature curing speed but poor heat resistance. Thirdly, they have poor thixotropic modification effects, which can easily lead to serious adhesive fly-off problems during the coating process, polluting the production environment and causing uneven adhesive layer thickness. Fourthly, existing solvent-free epoxy adhesives have poor wide-temperature stability, easily becoming brittle at -40℃ and softening at 150℃, which cannot meet the wide-temperature working requirements of high-end fields such as aerospace.

[0004] Patent application CN117417619A discloses a medium-temperature curing single-component elastic epoxy resin composition. Although it has low stress and certain heat resistance, it does not perform interface modification for the surface characteristics of magnetic materials, resulting in insufficient bonding force with magnetic materials. Furthermore, the dispersion system has poor compatibility and is not suitable for the uniform encapsulation of magnetic particles. Patent application CN121362550A discloses a polyurethane-modified epoxy resin adhesive. Although it improves toughness and strength, its thixotropic properties are poorly designed, making it prone to sagging and fraying during the coating process. Moreover, its wide temperature range stability is limited, failing to meet the requirements of extreme working environments from -40℃ to 150℃.

[0005] Therefore, developing a solvent-free epoxy adhesive for encapsulating magnetic materials that achieves synergistic effects among its components through material structure modification, and possesses high interfacial bonding strength, wide temperature range stability, high insulation performance, no flywire, and low internal stress, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] One of the objectives of this invention is to provide a solvent-free epoxy adhesive for encapsulating magnetic materials, thereby solving the problems of weak interfacial bonding, severe coating fraying, and rapid degradation of insulation and weather resistance in existing solvent-free epoxy adhesives for encapsulating magnetic materials.

[0007] The second objective of this invention is to provide a method for preparing a solvent-free epoxy adhesive for encapsulating magnetic materials, which is used to prepare the above-mentioned solvent-free epoxy adhesive for encapsulating magnetic materials.

[0008] The third objective of this invention is to provide the application of the solvent-free epoxy adhesive for encapsulating the above-mentioned magnetic materials.

[0009] The objective of this invention can be achieved through the following technical solutions: In the first aspect, a solvent-free epoxy adhesive for encapsulating magnetic materials comprises, by weight, the following components: 60-75 parts of bisphenol A type epoxy resin modifier, 15-25 parts of composite curing system, 3-8 parts of functionalized polycarboxylate dispersant, 2-5 parts of thixotropic modifier, and 1-3 parts of synergistic additive. The bisphenol A type epoxy resin modifier is prepared by grafting γ-aminopropyltriethoxysilane onto bisphenol A type epoxy resin E-51, with a grafting rate of 8-12% and a number average molecular weight of 4000-6000. The composite curing system is composed of methyl hexahydrophthalic anhydride and aliphatic amine modified curing agent T31 in a mass ratio of (7-8):(2-3). The acid value of methyl hexahydrophthalic anhydride is 600-620 mg KOH / g, and the amine value of aliphatic amine modified curing agent T31 is 450-500 mg KOH / g.

[0010] Bisphenol A type epoxy resin (E-51) is grafted with γ-aminopropyltriethoxysilane to introduce magnetic affinity groups into the molecular chain, strengthening the interfacial bonding through chemical covalent bonds. Simultaneously, the molecular weight and grafting rate are controlled to balance flowability and adhesive strength. Methylhexahydrophthalic anhydride and aliphatic amine-modified curing agent T31 are compounded in a specific ratio, integrating the high-temperature heat resistance of anhydrides with the room-temperature rapid curing advantages of amines, overcoming the performance limitations of single curing agents. Functionalized dispersants, thixotropic modifiers, and synergistic additives complement each other. The dispersant ensures uniform distribution of magnetic particles, the thixotropic agent inhibits coating fly-off, and the synergistic additives optimize interfacial, anti-aging, and defoaming properties. Through precise component ratios, comprehensive goals such as high adhesion, wide temperature range, no fly-off, and low internal stress are achieved.

[0011] Furthermore, the preparation method of the bisphenol A type epoxy resin modifier is as follows: heating bisphenol A type epoxy resin E-51 to 80°C, adding 5-8% by weight of γ-aminopropyltriethoxysilane and 0.3% by weight of boron trifluoride diethyl ether, reacting under nitrogen protection for 3-4 hours, cooling, and then removing low-boiling substances by vacuum distillation to obtain the grafted modified epoxy resin.

[0012] The siloxane group in γ-aminopropyltriethoxysilane can be hydrolyzed to generate hydroxyl groups, which can form covalent bonds with the hydroxyl groups on the surface of the magnetic material. The amino group can undergo a grafting reaction with the epoxy group of the epoxy resin. Under nitrogen protection, oxidation side reactions can be avoided during the reaction. Vacuum distillation removes low-boiling substances to ensure the purity of the modified body. Finally, chemical bonding enhances the interfacial bonding force between the epoxy resin and the magnetic material.

[0013] Furthermore, the functionalized polycarboxylate dispersant is prepared by grafting sodium polycarboxylate with maleic anhydride and introducing phosphate groups, with a degree of polymerization of 20-30, a carboxylate grafting rate of 30-40%, and a phosphate group grafting rate of 5-8%.

[0014] The carboxylate groups introduced by maleic anhydride grafting can enhance electrostatic repulsion, and the phosphate groups can form coordination complexes with metal ions on the surface of the magnetic material. The two work together to give the dispersant a triple dispersion mechanism of electrostatic repulsion, steric hindrance and coordination complexation, which effectively inhibits the agglomeration of magnetic material particles and improves the uniformity of the encapsulation layer.

[0015] Furthermore, the preparation method of the functionalized polycarboxylate dispersant is as follows: dissolve sodium polycarboxylate in deionized water, heat to 70°C, add 10-15% maleic anhydride and 0.5% ammonium persulfate by mass of sodium polycarboxylate, and react for 2 hours; add 5-8% dihydrogen phosphate by mass of sodium polycarboxylate, continue the reaction for 1 hour, and spray dry to obtain the functionalized dispersant.

[0016] The reaction temperature of 70℃ ensures the efficient progress of the maleic anhydride grafting and phosphate ester group introduction reaction. Ammonium persulfate, as an initiator, promotes the grafting polymerization of maleic anhydride and sodium polycarboxylate. Spray drying can quickly obtain a powdered dispersant, avoiding the influence of residual moisture on the subsequent adhesive properties.

[0017] Furthermore, the thixotropic modifier is a compound of fumed silica and nano-montmorillonite in a mass ratio of (1-2):1, and both are surface modified by silane coupling agent KH560.

[0018] Fumed silica can form a three-dimensional network structure to enhance thixotropy, while nano-montmorillonite has intercalation and dispersion characteristics. The combination of the two can synergistically enhance the thixotropic effect. Surface modification with silane coupling agent KH560 can improve the compatibility between the thixotropic agent and epoxy resin, avoid agglomeration, and ensure stable thixotropic properties.

[0019] Furthermore, the preparation method of the thixotropic modifier is as follows: fumed silica and nano-montmorillonite are mixed, 10% of the total mass of silane coupling agent KH560 and an equal mass of anhydrous ethanol are added, ultrasonically dispersed for 30 min, stirred and reacted at 60℃ for 2 h, filtered, dried, and ground through a 200-mesh sieve to obtain the silane-modified composite thixotropic agent.

[0020] Ultrasonic dispersion enables the silane coupling agent to be uniformly coated on the powder surface. Stirring at 60°C promotes the reaction between the silane coupling agent and the hydroxyl groups on the powder surface. Filtration, drying, grinding and sieving ensure that the thixotropic agent has a uniform particle size, meeting the requirements for dispersing the adhesive.

[0021] Furthermore, the synergistic agent is composed of γ-glycidyl etheroxypropyltrimethoxysilane, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and polyether-modified polysiloxane in a mass ratio of 1:1:0.5, and the polyether-modified polysiloxane has a particle size of 1-5 μm.

[0022] γ-glycidyl etheroxypropyltrimethoxysilane can further enhance interfacial bonding, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] can inhibit high-temperature oxidative aging of the adhesive layer, and polyether-modified polysiloxane can quickly eliminate microbubbles in the adhesive solution. When the three are compounded in a specific ratio, they can respectively optimize the interfacial, anti-aging and defoaming properties, and achieve synergistic effects.

[0023] Secondly, a method for preparing a solvent-free epoxy adhesive for encapsulating magnetic materials includes the following steps: S1. Raw material pretreatment: Place the bisphenol A type epoxy resin modifier and composite curing system in a vacuum drying oven at 60±5℃ and dry for 2-3 hours, with a moisture content ≤0.05%; place the functionalized polycarboxylate dispersant, thixotropic modifier, and synergistic additive in a high-speed mixer and premix at 800-1000rpm for 5-10 minutes to obtain the premixed additive. S2. Gradient mixing: Add the pretreated epoxy resin modifier to a double-jacketed high-speed mixing tank, heat to 70±5℃, stir at 1000-1500rpm, add to the composite curing system in 3 batches, with an interval of 10min between each batch, and continue stirring for 20min after each addition; cool to 50±5℃, add the premixed additives, stir at 1500-2000rpm for 15min, and then high-speed shear stirring at 2500-3000rpm for 30-40min; S3. Vacuum degassing: Transfer the mixed adhesive to a vacuum degassing machine, first pump to 0.05MPa and hold for 10 minutes, then pump to 0.09-0.1MPa, stir at 50rpm at 45±5℃ for 20 minutes to degas, and let stand for 20 minutes to degas. S4. In-situ modification and dispersion: Under nitrogen protection with a purity of ≥99.99% and a pressure of 0.01-0.02MPa, stir the adhesive solution at 800-1000rpm, add 0.5% of the total mass of the adhesive solution of azobisisobutyronitrile, and heat to 60±5℃ for 15min. S5. Finished Product Inspection and Packaging: After the adhesive solution is cooled to room temperature and its performance is found to be qualified, it is packaged in a sealed container under a nitrogen atmosphere and stored in a dry environment at 25±5℃.

[0024] Raw material pretreatment removes moisture, impurities, and premixed additives to avoid side reactions and uneven dispersion; gradient mixing employs segmented temperature control and variable-speed shearing, with low temperature promoting prepolymerization and high temperature and high speed achieving molecular-level dispersion; staged vacuum degassing combined with stirring efficiently removes microbubbles and prevents encapsulation layer cracking; in-situ modification and dispersion under nitrogen protection isolates moisture and promotes slight grafting of thixotropic agents and epoxy resin, improving dispersion stability; nitrogen atmosphere encapsulation and dry storage prevent moisture absorption and oxidation of the adhesive, ensuring stable performance throughout the shelf life.

[0025] Thirdly, the present invention provides the application of solvent-free epoxy adhesive for encapsulating magnetic materials. The solvent-free epoxy adhesive for encapsulating magnetic materials is suitable for encapsulating ferrite, neodymium iron boron, and samarium cobalt magnetic materials, and can be applied to the encapsulation and protection of electronic components such as motors, transformers, and inductors, as well as aerospace satellite components and aircraft sensors.

[0026] Furthermore, the application of the solvent-free epoxy adhesive for encapsulating the magnetic material is specifically carried out as follows: the magnetic material surface is pretreated by ultrasonic cleaning with acetone for 10 min, acid washing with 10% dilute hydrochloric acid for 5 min, rinsing with deionized water, and drying at 80℃ for 1 h, resulting in a surface roughness Ra of 0.8-1.2 μm; the adhesive is applied by spraying or vacuum impregnation, with the distance between the adhesive applicator and the magnetic material surface being 10-15 cm and the pressure being 0.3-0.5 MPa during spraying, and the vacuum degree being 0.08-0.09 MPa and the time being 15-20 min during vacuum impregnation; after coating, the material is cured in stages: the anhydride curing stage is kept at 80℃ for 1 h and at 120℃ for 1.5 h; the amine curing stage is placed at 25℃ for 6 h, kept at 40℃ for 2 h, and then naturally cooled to room temperature.

[0027] Magnetic material surface pretreatment removes oil and oxide layers through cleaning and adjusts roughness, increasing the contact area and bonding force between the adhesive layer and the magnetic material; spraying and vacuum impregnation are two adhesive application methods suitable for magnetic materials of different shapes, and precise control of adhesive parameters can ensure uniform adhesive layer thickness; segmented curing process can avoid internal stress caused by rapid curing, ensure full cross-linking of the adhesive layer, and balance curing efficiency and performance stability.

[0028] The beneficial effects of this invention are: (1) The solvent-free epoxy adhesive for magnetic material encapsulation of the present invention comprises, by weight, a bisphenol A type epoxy resin modifier, a composite curing system, a functionalized polycarboxylate dispersant, a thixotropic modifier, and a synergistic additive. The bisphenol A type epoxy resin (E-51) is modified by grafting with γ-aminopropyltriethoxysilane, which introduces magnetic material affinity groups into the molecular chain, forming a stable chemical bond with the surface of the magnetic material, improving the interfacial bonding force, and avoiding peeling. The composite curing system is formulated with methyl hexahydrophthalic anhydride and aliphatic amine modified curing agent T31 in a specific ratio, which has both high temperature resistance and room temperature rapid curing characteristics, enabling the adhesive layer to adapt to a wide temperature range working environment and solving the problem of limited application scenarios caused by the performance limitations of a single curing agent. The functionalized polycarboxylate dispersant inhibits the agglomeration of magnetic material particles through multiple mechanisms of action. Combined with the optimization effect of the synergistic additive, it improves the uniformity and insulation performance of the encapsulation layer and provides a reliable protective barrier.

[0029] (2) By introducing silane-modified nanocomposite thixotropic agent, the present invention endows the adhesive with excellent thixotropic properties, which can effectively suppress the generation of fly filaments during the coating process. Combined with optimized closed coating equipment, it can ensure uniform adhesive layer thickness and improve the production environment, meeting the needs of clean industrial production. The linear expansion coefficient of the adhesive layer is well matched with the magnetic material through the synergistic regulation of each component. Combined with the segmented curing process, the internal stress after curing is greatly reduced, avoiding cracking of the magnetic material due to stress concentration and extending the service life of the magnetic material. At the same time, the adhesive is designed with 100% solid content and has no volatile organic compound emissions, which is in line with green manufacturing and "dual carbon" industrial policies, achieving high performance while taking into account environmental benefits.

[0030] (3) The present invention ensures uniform dispersion of each component through gradient mixing and stirring, segmented vacuum degassing, and in-situ modification and dispersion process design, effectively avoiding the generation of bubbles in the adhesive and the sedimentation of functional fillers, improving the batch stability of products, and the equipment used are all conventional equipment in the industry, which can achieve large-scale production without additional modification; the epoxy adhesive is specially used for encapsulation of various magnetic materials such as ferrite, neodymium iron boron, and samarium cobalt. Its excellent resistance to damp heat, salt spray and high and low temperature performance enables it to meet the diversified encapsulation needs from ordinary electronic components to high-end magnetic components in aerospace, and has significant economic value and industrial significance. Detailed Implementation

[0031] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0032] Example 1

[0033] A solvent-free epoxy adhesive for encapsulating magnetic materials comprises the following components by weight: 65 parts of bisphenol A type epoxy resin modifier, 20 parts of composite curing system (14 parts of methylhexahydrophthalic anhydride and 6 parts of aliphatic amine modified curing agent T31, mass ratio 7:3), 6 parts of functionalized polycarboxylate dispersant, 4 parts of thixotropic modifier (2.67 parts of fumed silica and 1.33 parts of nano-montmorillonite, mass ratio 2:1), and 2 parts of synergistic additive.

[0034] (1) Preparation of intermediates: Preparation of bisphenol A type epoxy resin modifier: Take 100 parts of bisphenol A type epoxy resin E-51, heat to 80℃ under nitrogen protection, add 6 parts of γ-aminopropyltriethoxysilane and 0.3 parts of boron trifluoride diethyl ether, stir at 600 rpm for 3.5 h; after the reaction is completed, remove low-boiling substances by vacuum distillation (0.09 MPa, 80℃) for 30 min to obtain a modifier with a grafting rate of 10% and a number average molecular weight of 5000.

[0035] Preparation of functionalized polycarboxylate dispersant: Dissolve 100 parts of sodium polycarboxylate in 200 parts of deionized water, heat to 70℃, add 12 parts of maleic anhydride and 0.5 parts of ammonium persulfate, react at 800 rpm for 2 hours; then add 6 parts of dihydrogen phosphate and continue the reaction for 1 hour, and spray dry (inlet air 180℃, outlet air 80℃) to obtain the functionalized dispersant.

[0036] Preparation of thixotropic modifier: Fumed silica and nano-montmorillonite were mixed in a 2:1 ratio, and 10% of the total mass of silane coupling agent KH560 and an equal mass of anhydrous ethanol were added. After ultrasonic dispersion for 30 min, the mixture was stirred at 60℃ for 2 h, dried, ground and passed through a 200-mesh sieve to obtain a composite thixotropic modifier.

[0037] Preparation of synergistic additives: γ-glycidyl etheroxypropyltrimethoxysilane, antioxidant 1010 and defoamer BYK-066N were mixed in a ratio of 1:1:0.5 and stirred at 900 rpm for 8 min to obtain synergistic additives.

[0038] (2) Preparation method: Raw material pretreatment: The epoxy resin modifier, methylhexahydrophthalic anhydride, and T31 were vacuum dried at 60℃ for 2.5h (moisture content ≤0.05%). The functionalized dispersant, thixotropic modifier, and synergistic agent were premixed at 900rpm for 8min to obtain the premixed additive.

[0039] Gradient mixing: Add the epoxy resin modifier to a high-speed mixing tank, heat to 70℃, add to the composite curing system in 3 portions at 1200 rpm (10 min interval), and stir for 20 min; cool to 50℃, add the premixed additive, stir at 1800 rpm for 15 min, and then shear at 2800 rpm for 35 min.

[0040] Vacuum degassing: Transfer the mixed adhesive to a vacuum degassing machine, first pump to 0.05 MPa and hold for 10 min, then pump to 0.095 MPa, stir at 50 rpm at 45℃ for 20 min to degas, and let stand for 20 min to degas.

[0041] In-situ modified dispersion: Under nitrogen protection (pressure 0.015MPa), the gel was stirred at 900rpm, 0.5% azobisisobutyronitrile was added, and the reaction was carried out at 60℃ for 15min.

[0042] Finished product packaging: After cooling to room temperature and passing the performance test, the product is sealed in a sealed container under a nitrogen atmosphere and stored at 25°C in a dry place.

[0043] (3) Application method: Pretreatment of magnetic materials: Neodymium iron boron magnets are ultrasonically cleaned with acetone for 10 min, acid-washed with 10% dilute hydrochloric acid for 5 min, rinsed with deionized water, and dried at 80℃ for 1 h, with a surface roughness Ra=1.0μm.

[0044] Adhesive application: Spraying is used, with the adhesive applicator 12cm away from the magnetic material surface, spraying pressure 0.4MPa, and adhesive layer thickness 0.3mm; during the adhesive application process, the airtight safety door and directional ventilation system (wind speed 4m / s) are opened.

[0045] Segmented curing: Keep warm at 80℃ for 1 hour, keep warm at 120℃ for 1.5 hours, place at room temperature (25℃) for 6 hours, then keep warm at 40℃ for 2 hours, and allow to cool naturally to room temperature to complete the encapsulation.

[0046] Example 2

[0047] The difference from Example 1 is that the composite curing system consists of 20 parts (16 parts methylhexahydrophthalic anhydride and 4 parts T31, mass ratio 8:2), while the other components, preparation and application methods are the same.

[0048] Example 3

[0049] The difference from Example 1 is that: 4 parts of thixotropic modifier (2 parts of fumed silica and 2 parts of nano-montmorillonite, mass ratio 1:1), while the other components, preparation and application methods are the same.

[0050] Example 4

[0051] The difference from Example 1 is that: 60 parts of bisphenol A type epoxy resin modifier and 25 parts of composite curing system are used, while the other components, preparation and application methods are the same.

[0052] Example 5

[0053] The difference from Example 1 is that 75 parts of bisphenol A type epoxy resin modifier and 15 parts of composite curing system are used, while the remaining components, preparation and application methods are the same.

[0054] Example 6

[0055] The difference from Example 1 is that 3 parts of functionalized polycarboxylate dispersant are used, while the other components, preparation and application methods are the same.

[0056] Example 7

[0057] The difference from Example 1 is that 8 parts of functionalized polycarboxylate dispersant were used, while the other components, preparation and application methods were the same.

[0058] Comparative Example 1

[0059] The difference from Example 1 is that unmodified bisphenol A type epoxy resin E-51 is used instead of epoxy resin modifier, while the other components, preparation and application methods are the same.

[0060] Comparative Example 2

[0061] The difference from Example 1 is that 20 parts of a single methylhexahydrophthalic anhydride are used as the curing agent, while the other components, preparation and application methods are the same.

[0062] Comparative Example 3

[0063] The difference from Example 1 is that conventional sodium polycarboxylate dispersant is used instead of functionalized polycarboxylate dispersant, while the other components, preparation and application methods are the same.

[0064] Comparative Example 4

[0065] The difference from Example 1 is that 4 parts of single fumed silica are used as thixotropic modifier, while the other components, preparation and application methods are the same.

[0066] Performance testing

[0067] Performance tests were conducted on the embodiments and comparative examples: 1. Shear strength: GB / T7124-2008, the test substrate is neodymium iron boron magnet; 2. Volume resistivity: GB / T 31838.2-2019; 3. Thixotropic index: GB / T2794-2022, test speed 6rpm / 60rpm; 4. Internal stress: Measured using a stress testing instrument; 5. Double 85 aging performance: 85℃ / 85%RH, 1000h, test the shear strength retention rate after aging, GB / T3511-2018; 6. High and low temperature cycling performance: -40℃×2h→150℃×2h, 50 cycles, test the shear strength retention rate; 7. Flying thread phenomenon: In actual glue application tests, it is rated as no flying thread, slight flying thread, and severe flying thread; 8. VOC content: GB 33372-2020.

[0068] The results are shown in Table 1: Table 1

[0069] As shown in Table 1, the overall performance of the solvent-free epoxy adhesives for magnetic material encapsulation prepared in Examples 1-7 is significantly better than that in Comparative Examples 1-5. Example 1, as the optimal formulation, achieves a shear strength of 22.5 MPa and a volume resistivity of 2.5 × 10⁻⁶. 14 Ω The epoxy resin modifier has a thixotropic index of 4.2, an internal stress of only 0.07 MPa, and a shear strength retention rate exceeding 96% after double 85 aging and high and low temperature cycling. The adhesive coating exhibits no fly filaments, and the VOC content is 8.2 g / L. All performance characteristics meet design requirements. In Example 2, due to the increased proportion of methylhexahydrophthalic anhydride in the composite curing system, the heat resistance of the adhesive layer slightly improved, but the flexibility decreased slightly, and the shear strength was slightly lower than in Example 1. In Example 3, the thixotropic modifier was a 1:1 mixture, resulting in a slight decrease in the thixotropic index but still achieving a fly filament-free effect. In Examples 4-5, the ratio of the epoxy resin modifier to the composite curing system was adjusted. A higher epoxy resin ratio resulted in better interfacial bonding and insulation performance in Example 5, with a shear strength of 23.1 MPa and a volume resistivity of 3.2 × 10⁻⁶. 14 Ω cm; In Examples 6-7, the dosage of functionalized dispersant was adjusted. A dosage of 3 parts was sufficient to achieve good dispersion, while a dosage of 8 parts further improved the uniformity of the encapsulation layer and slightly optimized the aging performance of the double 85.

[0070] Comparative Example 1 used unmodified epoxy resin. Due to the lack of magnetic affinity groups, the interfacial bonding strength decreased significantly, with a shear strength of only 12.3 MPa and an internal stress of 0.12 MPa. After high and low temperature cycling, the shear strength retention rate was only 76.5%, proving that silane grafting modification of epoxy resin is the main technical feature for improving interfacial bonding strength. Comparative Example 2 used a single methylhexahydrophthalic anhydride curing agent. Although it showed good thixotropic index and filamentation, the adhesive layer was brittle, with an internal stress as high as 0.15 MPa. After high and low temperature cycling, the shear strength retention rate was 85.2%, indicating that the compounding of the composite curing system is the key to achieving a balance between heat resistance and flexibility. Comparative Example 3 used a conventional polycarboxylate dispersant, which only had electrostatic repulsion. The magnetic particle dispersion stability was poor, and the volume resistivity dropped to 6.8 × 10⁻⁶. 13 Ω The performance retention rate after aging at 85°C was 90.2%, confirming the importance of the coordination and complexation effect of the functionalized dispersant in improving insulation and dispersion performance. Comparative Example 4 used a single fumed silica as a thixotropic modifier, with a thixotropic index of only 2.8, resulting in severe fiber shedding during the coating process. However, it maintained a performance retention rate of 90.1% after high and low temperature cycling, indicating that the synergistic effect of the nanocomposite thixotropic agent can significantly improve thixotropic and mechanical properties.

[0071] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A solvent-free epoxy adhesive for encapsulating magnetic materials, characterized in that, By weight, it includes the following components: 60-75 parts of bisphenol A type epoxy resin modifier, 15-25 parts of composite curing system, 3-8 parts of functionalized polycarboxylate dispersant, 2-5 parts of thixotropic modifier, and 1-3 parts of synergistic additive. The bisphenol A type epoxy resin modifier is prepared by grafting γ-aminopropyltriethoxysilane onto bisphenol A type epoxy resin E-51, with a grafting rate of 8-12% and a number average molecular weight of 4000-6000. The composite curing system is composed of methyl hexahydrophthalic anhydride and aliphatic amine modified curing agent T31 in a mass ratio of (7-8):(2-3). The acid value of methyl hexahydrophthalic anhydride is 600-620 mg KOH / g, and the amine value of aliphatic amine modified curing agent T31 is 450-500 mg KOH / g.

2. The solvent-free epoxy adhesive for encapsulating magnetic materials according to claim 1, characterized in that, The preparation method of the bisphenol A type epoxy resin modifier is as follows: bisphenol A type epoxy resin E-51 is heated to 80°C, 5-8% by weight of γ-aminopropyltriethoxysilane and 0.3% by weight of boron trifluoride diethyl ether are added, and the reaction is carried out under nitrogen protection for 3-4 hours. After cooling, the low-boiling substances are removed by vacuum distillation to obtain the grafted modified epoxy resin.

3. The solvent-free epoxy adhesive for encapsulating magnetic materials according to claim 1, characterized in that, The functionalized polycarboxylate dispersant is prepared by grafting sodium polycarboxylate with maleic anhydride and introducing phosphate groups, with a degree of polymerization of 20-30, a carboxylate grafting rate of 30-40%, and a phosphate group grafting rate of 5-8%.

4. The solvent-free epoxy adhesive for encapsulating magnetic materials according to claim 1, characterized in that, The preparation method of the functionalized polycarboxylate dispersant is as follows: dissolve sodium polycarboxylate in deionized water, heat to 70°C, add 10-15% maleic anhydride and 0.5% ammonium persulfate by mass of sodium polycarboxylate, and react for 2 hours; add 5-8% dihydrogen phosphate by mass of sodium polycarboxylate, continue to react for 1 hour, and spray dry to obtain the functionalized dispersant.

5. The solvent-free epoxy adhesive for encapsulating magnetic materials according to claim 1, characterized in that, The thixotropic modifier is a compound of fumed silica and nano-montmorillonite in a mass ratio of (1-2):1, and both are surface modified by silane coupling agent KH560.

6. The solvent-free epoxy adhesive for encapsulating magnetic materials according to claim 1, characterized in that, The preparation method of the thixotropic modifier is as follows: fumed silica and nano-montmorillonite are mixed, 10% of the total mass of silane coupling agent KH560 and an equal mass of anhydrous ethanol are added, ultrasonically dispersed for 30 min, stirred and reacted at 60℃ for 2 h, filtered, dried, and ground through a 200-mesh sieve to obtain the silane-modified composite thixotropic modifier.

7. The solvent-free epoxy adhesive for encapsulating magnetic materials according to claim 1, characterized in that, The synergistic agent is composed of γ-glycidyl etheroxypropyltrimethoxysilane, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and polyether-modified polysiloxane in a mass ratio of 1:1:0.5, with the polyether-modified polysiloxane having a particle size of 1-5 μm.

8. A method for preparing a solvent-free epoxy adhesive for encapsulating magnetic materials, characterized in that, The solvent-free epoxy adhesive for encapsulating magnetic materials according to any one of claims 1-7 comprises the following steps: S1. Raw material pretreatment: Place the bisphenol A type epoxy resin modifier and composite curing system in a vacuum drying oven at 60±5℃ and dry for 2-3 hours, with a moisture content ≤0.05%; place the functionalized polycarboxylate dispersant, thixotropic modifier, and synergistic additive in a high-speed mixer and premix at 800-1000rpm for 5-10 minutes to obtain the premixed additive. S2. Gradient mixing: Add the pretreated epoxy resin modifier to a double-jacketed high-speed mixing tank, heat to 70±5℃, stir at 1000-1500rpm, add to the composite curing system in 3 batches, with an interval of 10min between each batch, and continue stirring for 20min after each addition; cool to 50±5℃, add the premixed additives, stir at 1500-2000rpm for 15min, and then high-speed shear stirring at 2500-3000rpm for 30-40min; S3. Vacuum degassing: Transfer the mixed adhesive to a vacuum degassing machine, first pump to 0.05MPa and hold for 10 minutes, then pump to 0.09-0.1MPa, stir at 50rpm at 45±5℃ for 20 minutes to degas, and let stand for 20 minutes to degas. S4. In-situ modification and dispersion: Under nitrogen protection with a purity of ≥99.99% and a pressure of 0.01-0.02MPa, stir the adhesive solution at 800-1000rpm, add 0.5% of the total mass of the adhesive solution of azobisisobutyronitrile, and heat to 60±5℃ for 15min. S5. Finished Product Inspection and Packaging: After the adhesive solution is cooled to room temperature and its performance is found to be qualified, it is packaged in a sealed container under a nitrogen atmosphere and stored in a dry environment at 25±5℃.

9. The application of the solvent-free epoxy adhesive for encapsulating magnetic materials as described in any one of claims 1-7, characterized in that, Used for encapsulating magnetic materials and / or packaging electronic devices; The magnetic material includes ferrite, neodymium iron boron or samarium cobalt magnets, and the electronic device includes motor, transformer, inductor, aerospace satellite component or aircraft sensor.

10. The application of the solvent-free epoxy adhesive for magnetic material encapsulation according to claim 9, characterized in that, The application of the solvent-free epoxy adhesive for encapsulating the magnetic material is as follows: the magnetic material surface is pretreated by ultrasonic cleaning with acetone for 10 min, acid washing with 10% dilute hydrochloric acid for 5 min, rinsing with deionized water, and drying at 80℃ for 1 h, resulting in a surface roughness Ra of 0.8-1.2 μm; the adhesive is applied by spraying or vacuum impregnation. During spraying, the distance between the applicator and the magnetic material surface is 10-15 cm and the pressure is 0.3-0.5 MPa. During vacuum impregnation, the vacuum degree is 0.08-0.09 MPa and the time is 15-20 min; after coating, the material is cured in stages: the anhydride curing stage is kept at 80℃ for 1 h and at 120℃ for 1.5 h; the amine curing stage is placed at 25℃ for 6 h, kept at 40℃ for 2 h, and then naturally cooled to room temperature.

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