A modified epoxy resin adhesive and a method for preparing the same

Abstract

The application belongs to the technical field of adhesives, and particularly relates to a modified epoxy resin adhesive and a preparation method thereof. The preparation method comprises the following steps: (1) activating graphene by using a silane coupling agent containing active groups to obtain modified graphene; (2) reacting POSS containing polyamino groups with the modified graphene to obtain POSS modified graphene; (3) uniformly mixing epoxy resin, a curing agent and a curing accelerator to obtain a resin matrix; and (4) adding the POSS modified graphene and micron flaky silver powder, uniformly stirring, and curing to obtain the modified epoxy resin adhesive. By adding the POSS modified graphene, the technical problems of difficult dispersion of the micron flaky silver powder and difficulty in building a conductive path are solved, the uniform dispersion of the graphene and the micron flaky silver powder is promoted, the volume resistivity of the conductive adhesive is reduced, and the conductive capacity and the mechanical properties are enhanced.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, specifically relating to a modified epoxy resin adhesive and its preparation method. Background Technology

[0002] Adhesives, also known as "bonding agents" or "adhesives," are substances that firmly bond two or more parts or materials together through interfacial adhesion and cohesion (chemical and physical forces). Conductive adhesives are particularly widely used. Conductive adhesives are applied and then cured or dried to achieve bonding, while simultaneously allowing electrical signals to be conducted between the two bonded interfaces. Conductive adhesives mainly consist of two parts: a resin matrix and conductive fillers. Correspondingly, the two most important performance indicators for evaluating the quality of conductive adhesives are: bond strength (tensile shear strength), primarily provided by the resin matrix; and conductivity (volume resistivity), primarily provided by the conductive fillers. Therefore, both parts are indispensable for high-performance conductive adhesive products.

[0003] Epoxy resin is a commonly used structural adhesive with wide applications in industry and other fields. It is highly versatile and has good performance in structural bonding of various metals, plastics and composite materials. It is also a good choice as a conductive adhesive matrix.

[0004] Conductive fillers used in conductive adhesive products include metals such as gold, silver, copper, and nickel, as well as non-metals such as carbon. Gold, with its excellent and stable conductivity, is widely used in advanced industries such as aerospace and military. However, its high cost hinders its widespread adoption. Copper, with its superior conductivity and low price, is a good choice, but its chemical stability makes it prone to oxidation in air. The resulting oxides lose their conductivity, affecting the adhesive's performance. Nickel is often alloyed with metals like gold and silver to create conductive fillers, but its high electrical resistance and susceptibility to oxidation make it less than ideal. Non-metallic carbon, compared to metal fillers, exhibits better compatibility and dispersibility with the epoxy resin matrix, but its conductivity is relatively poor. Metallic silver is an excellent choice for conductive adhesives and fillers due to its superior conductivity, relatively stable chemical properties, resistance to oxidation, and the fact that even when oxidized, the resulting silver oxide retains its conductivity. Furthermore, it is less expensive than gold or nickel. For example, CN114806476A discloses an epoxy resin conductive adhesive containing a composite conductive filler and its preparation method. The composite conductive filler is prepared by adding hydroxylated nano-titanium diboride powder, carboxylated nano-titanium diboride powder, silver nanoparticles, and an ionic liquid to deionized water to prepare a composite hydrogel. This hydrogel is then ultrasonically stirred, crushed, and freeze-dried to obtain titanium diboride aerogel microparticles loaded with nano-silver and ionic liquid. Finally, a PEDOT:PSS aqueous dispersion is spray-deposited onto the surface of the aerogel microparticles. The prepared composite conductive filler exhibits good conductivity and reduces silver migration tendency. Epoxy resin conductive adhesives containing this composite conductive filler show stable resistivity during use. However, the above preparation process is complex, costly, and offers limited performance improvement, restricting its further application. Summary of the Invention

[0005] This invention proposes a modified epoxy resin adhesive and its preparation method. By adding POSS-modified graphene, the technical problems of difficult dispersion of micron-sized flake silver powder and difficulty in constructing conductive pathways are solved. This promotes the uniform dispersion of graphene and micron-sized flake silver powder, reduces the volume resistivity of the conductive adhesive, and enhances conductivity and mechanical properties.

[0006] To achieve the above objectives, the specific technical solution involved in this invention is as follows:

[0007] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0008] (1) Graphene is activated by a silane coupling agent containing active groups to obtain modified graphene; the mass ratio of the silane coupling agent containing active groups to graphene is (0.1-0.3):1; the active groups can undergo nucleophilic substitution reactions with amino groups;

[0009] (2) POSS containing polyamines was reacted with modified graphene to obtain POSS modified graphene; the molar ratio of POSS containing polyamines to silane coupling agent containing active groups was (0.1-0.3):1;

[0010] (3) Mix the epoxy resin, curing agent, and curing accelerator evenly to obtain the resin matrix;

[0011] (4) Add POSS modified graphene and micron-sized flake silver powder to the resin matrix, stir evenly, and cure to obtain modified epoxy resin adhesive.

[0012] While traditional epoxy resin-micron-sized flake silver powder conductive adhesive is a mainstream material in electronic packaging, the micron-sized flake silver powder is an inert metal and lacks chemical bonding with the organic epoxy resin matrix. Furthermore, compared to spherical silver powder, the flake silver powder has weaker contact interaction, making it more likely to affect the processing flowability of the epoxy resin. Simultaneously, the surface of the silver powder is usually smooth, and its coefficient of thermal expansion differs significantly from that of the resin. Under thermal or mechanical stress, the interface is prone to debonding, becoming the starting point for crack initiation and propagation. This is the main reason for low shear strength, especially the significant strength decay after high temperature or thermal cycling. To achieve high conductivity, the flake silver powder filling amount is usually high. High filler content severely compresses the continuous phase space of the resin matrix, preventing the resin from forming a complete and strong continuous network, further deteriorating the overall mechanical properties of the material and making the adhesive brittle. At the same time, the conductive path depends on point or surface contact between the flake silver powders. This contact is physical and unstable. The volume shrinkage during epoxy resin curing may pull apart the previously contacting flake silver powders, increasing contact resistance.

[0013] To address the aforementioned problems of traditional micron-sized sheet-like silver powder conductive adhesives, this invention employs multi-level chemical modification. By introducing a two-dimensional carbon material with the same sheet-like structure as silver powder, a "rigid-flexible, organic-inorganic synergistic" nano-reinforced / conductive composite filler (POSS-graphene) is constructed. This filler is then introduced into the traditional epoxy-micron-sized sheet-like silver powder system to improve the adhesive's conductivity and mechanical properties.

[0014] Among them, the original graphene sheets, with their extremely high specific surface area and modulus, can effectively hinder the propagation of microcracks in the resin matrix as a two-dimensional nanofiller. It is worth noting that the reason graphene was chosen instead of graphene oxide in this invention is that although graphene oxide has better dispersibility in epoxy resin, its poor conductivity makes it unsuitable as a conductive filler in epoxy conductive adhesives, and it cannot play a role in constructing a conductive network. In contrast, polyamino POSS is a nanoscale rigid cage-like siloxane structure. When it is grafted onto the graphene surface through chemical bonds of a silane coupling agent, it is equivalent to welding numerous three-dimensional rigid nanobumps onto a two-dimensional plane. The remaining amino groups on the surface of POSS-modified graphene can participate in the epoxy curing reaction, anchoring the graphene sheets in the epoxy three-dimensional network through multi-point chemical bonding, greatly enhancing the filler-matrix interfacial bonding force and reducing interfacial slippage. Meanwhile, the surface of micron-sized flake silver powder usually has a certain degree of roughness; while graphene also has a two-dimensional flake structure, and the nano-protrusion structure of POSS on the graphene surface can better interlock with the surface of flake silver powder, thereby improving the bonding strength of the flake silver powder-resin interface, which is difficult to achieve with traditional coupling agents.

[0015] Traditional epoxy-silver sheet conductive adhesives rely on physical contact between the silver sheet particles to form conductive pathways. This invention introduces POSS-graphene as a conductive bridge and network framework: graphene itself is an excellent conductor. When the silver sheet particles fail to form perfect contact due to resin shrinkage or uneven arrangement, the conductive graphene sheets dispersed in the gaps can connect adjacent silver sheet particles, providing additional electron tunneling or conduction paths and reducing contact resistance. POSS has auxiliary dispersion and positioning functions, improving the dispersion of graphene and allowing it to be distributed in the gaps between the silver sheet particles in a more efficient bridging manner, rather than agglomerating into isolated islands. This helps to form a more complete silver sheet-graphene hybrid conductive network. More importantly, through the chemical anchoring effect of POSS, the bond between graphene and epoxy resin is stronger, and it is less prone to detachment from the matrix during curing shrinkage and thermal cycling, thereby maintaining the long-term stability of the conductive pathway and indirectly improving reliable conductivity. Meanwhile, the addition of rigid POSS-graphene can change the rheological properties of the resin system, affect the sedimentation and arrangement of the flake silver powder before curing, promote the accumulation of denser flake silver powder, and facilitate the formation of a stable conductive network.

[0016] In one embodiment, step (1) specifically involves ultrasonically dispersing a silane coupling agent containing active groups and graphene in a mixed solvent of ethanol and deionized water. After heating and reacting, the resulting product is filtered, washed, and dried to obtain modified graphene. Specifically, the volume ratio of ethanol to deionized water is (0.5-2):1, and can be 0.5:1, 1:1, 1.5:1, or 2:1.

[0017] In one embodiment, the heating reaction temperature is 50-65°C, and the heating reaction time is 1-2.5 h. Specifically, the heating reaction temperature is 55-60°C. A suitable reaction can significantly accelerate the hydrolysis and condensation reaction rates of the silane coupling agent, placing them within the ideal kinetic range, which is beneficial for silane molecules to have sufficient kinetic energy to effectively collide and react with the graphene surface.

[0018] In one embodiment, the active group in step (1) is one or more of the following: carboxyl group, sulfonic acid group, phosphate group, acyl chloride, acid anhydride, isocyanate, sulfonyl chloride, and epoxy group. Specifically, a silane coupling agent with a highly active carboxylic acid group or epoxy group can be selected. Specifically, 3-glycidyl etheroxypropyltrimethoxysilane or 3-glycidyl etheroxypropyltriethoxysilane can be selected.

[0019] The alkyl segments of silane coupling agents containing active groups form the connecting chains between POSS and graphene. These chains possess a degree of flexibility, allowing for better absorption and dissipation of impact energy, thus enhancing the material's toughness. Silane coupling agents with active groups not only connect the inert graphene and POSS groups but, more importantly, promote the uniform dispersion of amino-containing POSS on the graphene surface, preventing POSS accumulation and ensuring the effective isolation and dispersion functions of graphene. This reaction step requires a sufficiently high silane grafting rate to provide ample POSS anchoring sites, but not excessive amounts that would completely encapsulate the graphene in the insulating layer. In other words, a small amount of silane coupling agent forms a monolayer on the graphene surface, chemically bonding with the resin and POSS through its active end groups (such as amino and epoxy groups), improving the interface without affecting direct electron transport between fillers. When the dosage is too high, the excess silane molecules cannot be arranged in an orderly manner at the interface. This will form an excessively thick, disordered multi-molecular layer or even a physical stacking layer on the filler surface. This will not only significantly increase the contact resistance between conductive particles (sheet silver powder, graphene), but also form a weak interfacial bonding layer, which is not conducive to improving conductivity and mechanical properties.

[0020] In one embodiment, the specific process in step (2) is as follows: POSS containing multiple amino groups and modified graphene are dispersed in an organic solvent, heated and stirred to react, and then filtered, washed and dried to obtain POSS modified graphene.

[0021] In one embodiment, the organic solvent in step (2) is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, sulfolane, and tetrahydrofuran.

[0022] In one embodiment, the heating reaction temperature in step (2) is 50-60°C and the reaction time is 5-10h.

[0023] In one embodiment, the POSS containing multiple amino groups in step (2) is a POSS containing 2-8 amino groups. Specifically, it can be one or more of diaminopropyl POSS, diaminophenyl POSS, tetraaminopropyl POSS, tetraaminophenyl POSS, hexaaminopropyl POSS, hexaaminophenyl POSS, octaaminophenyl POSS, and octaaminopropyl POSS.

[0024] In epoxy resin systems, graphene readily aggregates due to π-π stacking, forming stress concentration points. POSS grafting introduces steric hindrance and surface chemical differences, effectively hindering the recombination of graphene sheets and resulting in more uniform dispersion within the resin. A small number of POSS molecules are grafted onto the graphene sheets as discrete nanodots, leaving large exposed or conductive areas on the graphene surface for direct electron transport or tunneling. Excessive POSS molecules form a high-density, nearly continuous insulating layer on the graphene surface, hindering efficient electron transport between the sheet-like silver powders and potentially introducing high-resistance nodes into the conductive pathways. Furthermore, excessive POSS may not only graft onto the graphene surface but also self-aggregate within the system, forming POSS aggregates tens or even hundreds of nanometers in size. These aggregates have poor interfacial bonding with the epoxy matrix, becoming internal stress concentration points and defect origins, easily inducing microcracks.

[0025] In one embodiment, the epoxy resin in step (3) is one or more of the following: bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol AD ​​type epoxy resin, phenolic epoxy resin, and alicyclic epoxy resin.

[0026] In one embodiment, the curing agent in step (3) is one or more of amine, carboxylic acid, and anhydride curing agents. Specifically, one or more of m-phenylenediamine, m-phenylenediamine, polyazelite anhydride, methylhexahydrophthalic anhydride, tetrahydrophthalic anhydride, and methylnadic anhydride may be selected.

[0027] In one embodiment, the curing accelerator in step (3) is one or more of benzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol and its modified forms, 2-ethyl-4-methylimidazole, cyanoethyl-2-ethyl-4-methylimidazole, modified benzyldimethylamine, methylimidazole, diaminodiphenyl sulfone, 2-undecylimidazole, and 2-heptadecanylimidazole. In particular, cyanoethyl-2-ethyl-4-methylimidazole latent curing accelerator may be selected.

[0028] In one embodiment, the mass ratio of epoxy resin, curing agent, and curing accelerator in step (3) is 1:(0.5-1):(0.01-0.03). Further, the mass ratio of epoxy resin, curing agent, and curing accelerator is 1:(0.6-0.9):(0.015-0.025). Insufficient curing agent results in low matrix strength and poor toughness. Unreacted epoxy groups lead to insufficient cohesive strength, making the material prone to cohesive failure under stress. Simultaneously, due to the soft matrix, the "holding power" for the flake silver powder decreases, making the interface prone to failure. Excessive curing agent leads to a denser but potentially more brittle network, and the plasticizing effect reduces strength. Furthermore, excess curing agent may migrate to the interface, forming a weak boundary layer, which is detrimental to improving mechanical properties.

[0029] In one embodiment, in step (4), based on the total weight of the resin matrix, POSS-modified graphene, and micron-sized flake silver powder, the content of POSS-modified graphene is 0.5-1.5 wt.%, the content of micron-sized flake silver powder is 65-75 wt.%, and the remainder is the resin matrix. The size of the micron-sized flake silver powder is not particularly limited in this invention; any powder commonly used in the art can be selected. For example, flake silver powder with a particle size of 1-10 µm can be chosen. Specifically, this invention uses flake silver powder with an average particle size of 5 µm. Further, the micron-sized flake silver powder can be washed as needed to remove surface organic matter and improve conductivity. Further, by stirring, the POSS-modified graphene and micron-sized flake silver powder can be fully dispersed in the resin matrix. To promote the formation of conductive pathways, a stepwise feeding process can be adopted. Specifically, a solvent can be added to promote the dispersion of each component and the stirring process. Specifically, micron-sized flake silver powder can be added first and stirred evenly before adding POSS-modified graphene and stirring again to obtain a mixed resin. In resins with relatively low viscosity, adding micron-sized flake silver powder beforehand ensures sufficient wetting and relatively uniform distribution of the silver powder, laying the foundation for constructing a conductive framework. The subsequently added POSS-modified graphene, due to space competition, tends to distribute more readily on the surface of the already formed silver powder or in the gaps between silver powder clusters, better fulfilling its role as a conductive bridge and interface enhancer. This directly improves the flake silver powder-resin interface and bridges adjacent flake silver powders, protecting the flake silver powder from excessive agglomeration and improving the mechanical and conductive properties of the conductive adhesive. Specifically, the POSS-modified graphene content is 0.8-1.3 wt.%, and the micron-sized flake silver powder content is 68-70 wt.%. An appropriate amount of micron-sized flake silver powder satisfies the need for constructing conductive pathways while avoiding excessive agglomeration of silver powder. An appropriate amount of POSS-modified graphene can be effectively dispersed in the gaps between sheet-like silver powders, acting as a highly efficient conductive bridge to connect parts not directly contacted by the sheet-like silver powders, significantly reducing contact resistance and causing a rapid decrease in resistivity. However, excessive use of POSS-modified graphene can easily lead to agglomeration and physically block silver powder-to-silver powder contact, introducing high-resistance nodes in the conductive path, which is detrimental to improving product performance.

[0030] In one embodiment, the curing temperature in step (4) is 145-155°C and the curing time is 2-3 hours.

[0031] On the other hand, the present invention also provides a modified epoxy resin adhesive prepared by the above method. By adding sheet-like POSS modified graphene, the technical problems of difficult dispersion of micron-sized sheet-like silver powder and difficulty in constructing conductive pathways are solved, promoting the uniform dispersion of graphene and micron-sized sheet-like silver powder, reducing the volume resistivity of the conductive adhesive, and enhancing conductivity and mechanical properties, thus showing broad application prospects.

[0032] Beneficial effects:

[0033] (1) The two-step chemical method of “silane coupling agent → POSS” was used to achieve precise customization and functional enhancement of the surface properties of graphene. The interfacial bonding strength of chemical bonding is much higher than that of physical adsorption or simple coupling agent treatment, which solves the problem of difficult dispersion of micron-sized silver powder in epoxy resin and greatly improves the ability of micron-sized silver powder to construct conductive pathways.

[0034] (2) This invention introduces POSS-graphene as a conductive bridge and network framework into the traditional epoxy-micron-scale silver powder conductive adhesive. Both micron-scale silver powder and graphene exhibit two-dimensional sheet structures, and POSS has auxiliary dispersion and positioning functions, which improves the dispersion of graphene and sheet-scale silver powder, allowing graphene to be distributed in the gaps between sheet-scale silver powder in a more efficient bridging manner, rather than agglomerating into isolated islands. This helps to form a more complete silver powder-graphene hybrid conductive network. More importantly, through the chemical anchoring effect of POSS, the bonding between graphene and epoxy resin is stronger, and it is not easy to debond from the matrix during curing shrinkage and thermal cycling, thereby maintaining the long-term stability of the conductive pathway and indirectly improving reliable conductivity. At the same time, the addition of rigid POSS-graphene can change the rheological properties of the resin system, affecting the sedimentation and arrangement of silver powder before curing, promoting a denser silver powder accumulation, which is beneficial to the formation of a stable conductive network. Detailed Implementation

[0035] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention are described in detail below with reference to examples. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Unless otherwise specified, the types of raw materials and processes used in the following embodiments are the same.

[0036] Performance testing: The tensile shear properties (refer to GB7124-86) and resistivity (refer to ASTM D257-91) of the modified epoxy resin adhesives prepared in the following examples and comparative examples were tested respectively.

[0037] Example 1

[0038] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0039] (1) The silane coupling agent 3-glycidyl etheroxypropyltrimethoxysilane containing active groups and graphene were ultrasonically dispersed in a mixed solvent of ethanol and deionized water (volume ratio of 1:1). After heating and reacting at 50°C for 2.5 h, the modified graphene was obtained by filtration, washing and drying. The mass ratio of the silane coupling agent containing active groups to graphene was 0.1:1.

[0040] (2) POSS containing polyamino group (octaaminophenyl POSS) and modified graphene were dispersed in tetrahydrofuran, heated and stirred at 50°C for 10 h, and then filtered, washed and dried to obtain POSS modified graphene; the molar ratio of POSS containing polyamino group to silane coupling agent containing active group was 0.1:1.

[0041] (3) Mix E51 epoxy resin, curing agent methyl hexahydrophthalic anhydride and curing accelerator cyanoethyl-2-ethyl-4-methylimidazolium evenly to obtain a resin matrix; the mass ratio of epoxy resin, curing agent and curing accelerator is 1:0.75:0.014.

[0042] (4) After adding micron-sized flake silver powder to the resin matrix and stirring evenly, POSS-modified graphene is added and stirred evenly. The mixture is then cured at 145℃ for 3 hours to obtain the modified epoxy resin adhesive. Based on the total weight of the resin matrix, POSS-modified graphene, and micron-sized flake silver powder, the POSS-modified graphene content is 0.5 wt.%, the micron-sized flake silver powder content is 67 wt.%, and the remainder is the resin matrix. The tensile shear strength is 12.5 MPa, and the volume resistivity is 6.3 × 10⁻⁶. -4 Ω·cm.

[0043] Example 2

[0044] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0045] (1) The silane coupling agent 3-glycidyl etheroxypropyltriethoxysilane containing active groups and graphene were ultrasonically dispersed in a mixed solvent of ethanol and deionized water (volume ratio of 1:1). After heating and reacting at 65°C for 1 h, the modified graphene was obtained by filtration, washing and drying. The mass ratio of the silane coupling agent containing active groups to graphene was 0.3:1.

[0046] (2) POSS containing polyamino group (octaaminophenyl POSS) and modified graphene were dispersed in tetrahydrofuran, heated and stirred at 60°C for 5 h, and then filtered, washed and dried to obtain POSS modified graphene; the molar ratio of POSS containing polyamino group to silane coupling agent containing active group was 0.3:1.

[0047] (3) Mix E51 epoxy resin, curing agent methyl hexahydrophthalic anhydride and curing accelerator cyanoethyl-2-ethyl-4-methylimidazolium evenly to obtain a resin matrix; the mass ratio of epoxy resin, curing agent and curing accelerator is 1:0.9:0.023.

[0048] (4) After adding micron-sized flake silver powder to the resin matrix and stirring evenly, POSS-modified graphene is added and stirred evenly. The mixture is then cured at 155℃ for 2 hours to obtain the modified epoxy resin adhesive. Based on the total weight of the resin matrix, POSS-modified graphene, and micron-sized flake silver powder, the POSS-modified graphene content is 1.1 wt.%, the micron-sized flake silver powder content is 70 wt.%, and the remainder is the resin matrix. The tensile shear strength is 11.2 MPa, and the volume resistivity is 4.9 × 10⁻⁶. -4 Ω·cm.

[0049] Example 3

[0050] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0051] (1) The silane coupling agent 3-glycidyl etheroxypropyltrimethoxysilane containing active groups and graphene were ultrasonically dispersed in a mixed solvent of ethanol and deionized water (volume ratio of 1:1). After heating and reacting at 60°C for 2 hours, the modified graphene was obtained by filtration, washing and drying. The mass ratio of the silane coupling agent containing active groups to graphene was 0.2:1.

[0052] (2) POSS containing polyamino group (octaaminophenyl POSS) and modified graphene were dispersed in tetrahydrofuran, heated and stirred at 55°C for 7 h, and then filtered, washed and dried to obtain POSS modified graphene; the molar ratio of POSS containing polyamino group to silane coupling agent containing active group was 0.2:1.

[0053] (3) Mix E51 epoxy resin, curing agent methyl hexahydrophthalic anhydride and curing accelerator cyanoethyl-2-ethyl-4-methylimidazolium evenly to obtain a resin matrix; the mass ratio of epoxy resin, curing agent and curing accelerator is 1:0.8:0.018.

[0054] (4) After adding POSS-modified graphene to the resin matrix and stirring evenly, add micron-sized flake silver powder and stir evenly. Cure at 150℃ for 2.5 hours to obtain the modified epoxy resin adhesive. Based on the total weight of the resin matrix, POSS-modified graphene, and micron-sized flake silver powder, the POSS-modified graphene content is 1.2 wt.%, the micron-sized flake silver powder content is 69 wt.%, and the remainder is the resin matrix. The tensile shear strength is 10.8 MPa, and the volume resistivity is 5.8 × 10⁻⁶. -4 Ω·cm.

[0055] Example 4

[0056] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0057] (1) The silane coupling agent 3-glycidyl etheroxypropyltriethoxysilane containing active groups and graphene were ultrasonically dispersed in a mixed solvent of ethanol and deionized water (volume ratio of 1:1). After heating and reacting at 52°C for 1.3 h, the modified graphene was obtained by filtration, washing and drying. The mass ratio of the silane coupling agent containing active groups to graphene was 0.12:1.

[0058] (2) POSS containing polyamino group (octaaminophenyl POSS) and modified graphene were dispersed in tetrahydrofuran, heated and stirred at 50°C for 9 h, and then filtered, washed and dried to obtain POSS modified graphene; the molar ratio of POSS containing polyamino group to silane coupling agent containing active group was 0.12:1.

[0059] (3) Mix E51 epoxy resin, curing agent methyl hexahydrophthalic anhydride and curing accelerator cyanoethyl-2-ethyl-4-methylimidazolium evenly to obtain a resin matrix; the mass ratio of epoxy resin, curing agent and curing accelerator is 1:0.75:0.023.

[0060] (4) After adding micron-sized flake silver powder to the resin matrix and stirring evenly, POSS-modified graphene is added and stirred evenly. The mixture is then cured at 145℃ for 2 hours to obtain the modified epoxy resin adhesive. Based on the total weight of the resin matrix, POSS-modified graphene, and micron-sized flake silver powder, the content of POSS-modified graphene is 0.7 wt.%, the content of micron-sized flake silver powder is 69.5 wt.%, and the remainder is the resin matrix. The tensile shear strength is 11.0 MPa, and the volume resistivity is 4.7 × 10⁻⁶. -4 Ω·cm.

[0061] Example 5

[0062] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0063] (1) The silane coupling agent 3-glycidyl etheroxypropyltrimethoxysilane containing active groups and graphene were ultrasonically dispersed in a mixed solvent of ethanol and deionized water (volume ratio of 1:1). After heating and reacting at 60°C for 2 hours, the modified graphene was obtained by filtration, washing and drying. The mass ratio of the silane coupling agent containing active groups to graphene was 0.2:1.

[0064] (2) POSS containing polyamino group (octaaminophenyl POSS) and modified graphene were dispersed in tetrahydrofuran, heated and stirred at 55°C for 7 h, and then filtered, washed and dried to obtain POSS modified graphene; the molar ratio of POSS containing polyamino group to silane coupling agent containing active group was 0.2:1.

[0065] (3) Mix E51 epoxy resin, curing agent methyl hexahydrophthalic anhydride and curing accelerator cyanoethyl-2-ethyl-4-methylimidazolium evenly to obtain a resin matrix; the mass ratio of epoxy resin, curing agent and curing accelerator is 1:0.8:0.018.

[0066] (4) After adding micron-sized flake silver powder to the resin matrix and stirring evenly, POSS-modified graphene is added and stirred evenly. The mixture is then cured at 150℃ for 2.5 hours to obtain the modified epoxy resin adhesive. Based on the total weight of the resin matrix, POSS-modified graphene, and micron-sized flake silver powder, the POSS-modified graphene content is 1.5 wt.%, the micron-sized flake silver powder content is 69 wt.%, and the remainder is the resin matrix. The tensile shear strength is 12.0 MPa, and the volume resistivity is 5.5 × 10⁻⁶. -4 Ω·cm.

[0067] Example 6

[0068] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0069] (1) The silane coupling agent 3-glycidyl etheroxypropyltriethoxysilane containing active groups and graphene were ultrasonically dispersed in a mixed solvent of ethanol and deionized water (volume ratio of 1:1). After heating and reacting at 54°C for 2.2 h, the modified graphene was obtained by filtration, washing and drying. The mass ratio of the silane coupling agent containing active groups to graphene was 0.17:1.

[0070] (2) POSS containing polyamino group (octaaminophenyl POSS) and modified graphene were dispersed in tetrahydrofuran, heated and stirred at 52°C for 8 hours, and then filtered, washed and dried to obtain POSS modified graphene; the molar ratio of POSS containing polyamino group to silane coupling agent containing active group was 0.15:1.

[0071] (3) Mix E51 epoxy resin, curing agent methyl hexahydrophthalic anhydride and curing accelerator cyanoethyl-2-ethyl-4-methylimidazolium evenly to obtain a resin matrix; the mass ratio of epoxy resin, curing agent and curing accelerator is 1:0.8:0.018.

[0072] (4) After adding micron-sized flake silver powder to the resin matrix and stirring evenly, POSS-modified graphene is added and stirred evenly. The mixture is then cured at 148℃ for 2.3 hours to obtain the modified epoxy resin adhesive. Based on the total weight of the resin matrix, POSS-modified graphene, and micron-sized flake silver powder, the POSS-modified graphene content is 1 wt.%, the micron-sized flake silver powder content is 67.5 wt.%, and the remainder is the resin matrix. The tensile shear strength is 13.3 MPa, and the volume resistivity is 6.0 × 10⁻⁶. -4 Ω·cm.

[0073] Example 7

[0074] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0075] (1) The silane coupling agent 3-glycidyl etheroxypropyltrimethoxysilane containing active groups and graphene were ultrasonically dispersed in a mixed solvent of ethanol and deionized water (volume ratio of 1:1). After heating and reacting at 60°C for 2 hours, the modified graphene was obtained by filtration, washing and drying. The mass ratio of the silane coupling agent containing active groups to graphene was 0.2:1.

[0076] (2) POSS containing polyamino group (octaaminophenyl POSS) and modified graphene were dispersed in tetrahydrofuran, heated and stirred at 55°C for 7 h, and then filtered, washed and dried to obtain POSS modified graphene; the molar ratio of POSS containing polyamino group to silane coupling agent containing active group was 0.2:1.

[0077] (3) Mix E51 epoxy resin, curing agent methyl hexahydrophthalic anhydride and curing accelerator cyanoethyl-2-ethyl-4-methylimidazolium evenly to obtain a resin matrix; the mass ratio of epoxy resin, curing agent and curing accelerator is 1:0.8:0.018.

[0078] (4) After adding micron-sized flake silver powder to the resin matrix and stirring evenly, POSS-modified graphene is added and stirred evenly. The mixture is then cured at 150℃ for 2.5 hours to obtain the modified epoxy resin adhesive. Based on the total weight of the resin matrix, POSS-modified graphene, and micron-sized flake silver powder, the POSS-modified graphene content is 1.2 wt.%, the micron-sized flake silver powder content is 71 wt.%, and the remainder is the resin matrix. The tensile shear strength is 10.5 MPa, and the volume resistivity is 3.5 × 10⁻⁶. -4 Ω·cm.

[0079] Example 8

[0080] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0081] (1) The silane coupling agent 3-glycidyl etheroxypropyltrimethoxysilane containing active groups and graphene were ultrasonically dispersed in a mixed solvent of ethanol and deionized water (volume ratio of 1:1). After heating and reacting at 58°C for 1.6 h, the modified graphene was obtained by filtration, washing and drying. The mass ratio of the silane coupling agent containing active groups to graphene was 0.25:1.

[0082] (2) POSS containing multiple amino groups (octaaminophenyl POSS) and modified graphene were dispersed in tetrahydrofuran, heated and stirred at 58°C for 6 hours, and then filtered, washed and dried to obtain POSS modified graphene; the molar ratio of POSS containing multiple amino groups to silane coupling agent containing active groups was 0.25:1.

[0083] (3) Mix E51 epoxy resin, curing agent methyl hexahydrophthalic anhydride, and curing accelerator cyanoethyl-2-ethyl-4-methylimidazolium evenly to obtain a resin matrix; the mass ratio of epoxy resin, curing agent, and curing accelerator is 1:0.88:0.021.

[0084] (4) After adding micron-sized flake silver powder to the resin matrix and stirring evenly, POSS-modified graphene is added and stirred evenly. The mixture is then cured at 152℃ for 2.8 hours to obtain the modified epoxy resin adhesive. Based on the total weight of the resin matrix, POSS-modified graphene, and micron-sized flake silver powder, the content of POSS-modified graphene is 1.3 wt.%, the content of micron-sized flake silver powder is 68.5 wt.%, and the remainder is the resin matrix. The tensile shear strength is 11.6 MPa, and the volume resistivity is 5.2 × 10⁻⁶. -4 Ω·cm.

[0085] Example 9

[0086] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0087] (1) The silane coupling agent 3-glycidyl etheroxypropyltriethoxysilane containing active groups and graphene were ultrasonically dispersed in a mixed solvent of ethanol and deionized water (volume ratio of 1:1). After heating and reacting at 57°C for 1.9 h, the modified graphene was obtained by filtration, washing and drying. The mass ratio of the silane coupling agent containing active groups to graphene was 0.22:1.

[0088] (2) POSS containing polyamino group (octaaminophenyl POSS) and modified graphene were dispersed in tetrahydrofuran, heated and stirred at 57°C for 7.5 h, and then filtered, washed and dried to obtain POSS modified graphene; the molar ratio of POSS containing polyamino group to silane coupling agent containing active group was 0.16:1.

[0089] (3) Mix E51 epoxy resin, curing agent methyl hexahydrophthalic anhydride, and curing accelerator cyanoethyl-2-ethyl-4-methylimidazolium evenly to obtain a resin matrix; the mass ratio of epoxy resin, curing agent, and curing accelerator is 1:0.78:0.02.

[0090] (4) After adding micron-sized flake silver powder to the resin matrix and stirring evenly, POSS-modified graphene is added and stirred evenly. The mixture is then cured at 148℃ for 2.6 hours to obtain the modified epoxy resin adhesive. Based on the total weight of the resin matrix, POSS-modified graphene, and micron-sized flake silver powder, the POSS-modified graphene content is 0.9 wt.%, the micron-sized flake silver powder content is 68 wt.%, and the remainder is the resin matrix. The tensile shear strength is 12.8 MPa, and the volume resistivity is 5.6 × 10⁻⁶. -4 Ω·cm.

[0091] Example 10

[0092] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0093] (1) The silane coupling agent 3-glycidyl etheroxypropyltrimethoxysilane containing active groups and graphene were ultrasonically dispersed in a mixed solvent of ethanol and deionized water (volume ratio of 1:1). After heating and reacting at 60°C for 2 hours, the modified graphene was obtained by filtration, washing and drying. The mass ratio of the silane coupling agent containing active groups to graphene was 0.2:1.

[0094] (2) POSS containing polyamino group (octaaminophenyl POSS) and modified graphene were dispersed in tetrahydrofuran, heated and stirred at 55°C for 7 h, and then filtered, washed and dried to obtain POSS modified graphene; the molar ratio of POSS containing polyamino group to silane coupling agent containing active group was 0.2:1.

[0095] (3) Mix E51 epoxy resin, curing agent methyl hexahydrophthalic anhydride and curing accelerator cyanoethyl-2-ethyl-4-methylimidazolium evenly to obtain a resin matrix; the mass ratio of epoxy resin, curing agent and curing accelerator is 1:0.8:0.018.

[0096] (4) After adding micron-sized flake silver powder to the resin matrix and stirring evenly, POSS-modified graphene is added and stirred evenly. The mixture is then cured at 150℃ for 2.5 hours to obtain the modified epoxy resin adhesive. Based on the total weight of the resin matrix, POSS-modified graphene, and micron-sized flake silver powder, the POSS-modified graphene content is 1.2 wt.%, the micron-sized flake silver powder content is 69 wt.%, and the remainder is the resin matrix. The tensile shear strength is 13.2 MPa, and the volume resistivity is 3.6 × 10⁻⁶. -4 Ω·cm.

[0097] Comparative Example 1

[0098] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0099] (1) The silane coupling agent 3-glycidyl etheroxypropyltrimethoxysilane containing active groups and graphene were ultrasonically dispersed in a mixed solvent of ethanol and deionized water (volume ratio of 1:1). After heating and reacting at 60°C for 2 hours, the modified graphene was obtained by filtration, washing and drying. The mass ratio of the silane coupling agent containing active groups to graphene was 0.6:1.

[0100] (2) POSS containing polyamino group (octaaminophenyl POSS) and modified graphene were dispersed in tetrahydrofuran, heated and stirred at 55°C for 7 h, and then filtered, washed and dried to obtain POSS modified graphene; the molar ratio of POSS containing polyamino group to silane coupling agent containing active group was 0.2:1.

[0101] (3) Mix E51 epoxy resin, curing agent methyl hexahydrophthalic anhydride and curing accelerator cyanoethyl-2-ethyl-4-methylimidazolium evenly to obtain a resin matrix; the mass ratio of epoxy resin, curing agent and curing accelerator is 1:0.8:0.018.

[0102] (4) After adding micron-sized flake silver powder to the resin matrix and stirring evenly, POSS-modified graphene is added and stirred evenly. The mixture is then cured at 150℃ for 2.5 hours to obtain the modified epoxy resin adhesive. Based on the total weight of the resin matrix, POSS-modified graphene, and micron-sized flake silver powder, the POSS-modified graphene content is 1.2 wt.%, the micron-sized flake silver powder content is 69 wt.%, and the remainder is the resin matrix. The tensile shear strength is 10.2 MPa, and the volume resistivity is 7.7 × 10⁻⁶. -4 Ω·cm.

[0103] Comparative Example 2

[0104] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0105] (1) The silane coupling agent 3-glycidyl etheroxypropyltrimethoxysilane containing active groups and graphene were ultrasonically dispersed in a mixed solvent of ethanol and deionized water (volume ratio of 1:1). After heating and reacting at 60°C for 2 hours, the modified graphene was obtained by filtration, washing and drying. The mass ratio of the silane coupling agent containing active groups to graphene was 0.2:1.

[0106] (2) E51 epoxy resin, curing agent methyl hexahydrophthalic anhydride, and curing accelerator cyanoethyl-2-ethyl-4-methylimidazolium are mixed evenly to obtain a resin matrix; the mass ratio of epoxy resin, curing agent, and curing accelerator is 1:0.8:0.018.

[0107] (3) After adding micron-sized flake silver powder to the resin matrix and stirring evenly, add modified graphene and stir evenly. Cure at 150℃ for 2.5 hours to obtain the modified epoxy resin adhesive. Based on the total weight of the resin matrix, modified graphene, and micron-sized flake silver powder, the modified graphene content is 1.2 wt.%, the micron-sized flake silver powder content is 69 wt.%, and the remainder is the resin matrix. The tensile shear strength is 9.3 MPa, and the volume resistivity is 8.1 × 10⁻⁶. -4 Ω·cm.

[0108] Comparative Example 3

[0109] A method for preparing a modified epoxy resin adhesive includes the following steps:

[0110] (1) The silane coupling agent 3-glycidyl etheroxypropyltrimethoxysilane containing active groups and graphene were ultrasonically dispersed in a mixed solvent of ethanol and deionized water (volume ratio of 1:1). After heating and reacting at 60°C for 2 hours, the modified graphene was obtained by filtration, washing and drying. The mass ratio of the silane coupling agent containing active groups to graphene was 0.2:1.

[0111] (2) POSS containing polyamino group (octaaminophenyl POSS) and modified graphene were dispersed in tetrahydrofuran, heated and stirred at 55°C for 7 h, and then filtered, washed and dried to obtain POSS modified graphene; the molar ratio of POSS containing polyamino group to silane coupling agent containing active group was 0.6:1.

[0112] (3) Mix E51 epoxy resin, curing agent methyl hexahydrophthalic anhydride and curing accelerator cyanoethyl-2-ethyl-4-methylimidazolium evenly to obtain a resin matrix; the mass ratio of epoxy resin, curing agent and curing accelerator is 1:0.8:0.018.

[0113] (4) After adding micron-sized flake silver powder to the resin matrix and stirring evenly, POSS-modified graphene is added and stirred evenly. The mixture is then cured at 150℃ for 2.5 hours to obtain the modified epoxy resin adhesive. Based on the total weight of the resin matrix, POSS-modified graphene, and micron-sized flake silver powder, the POSS-modified graphene content is 1.2 wt.%, the micron-sized flake silver powder content is 69 wt.%, and the remainder is the resin matrix. The tensile shear strength is 9.8 MPa, and the volume resistivity is 7.3 × 10⁻⁶. -4 Ω·cm.

[0114] As can be seen from the above embodiments and comparative examples, this invention introduces POSS-graphene as a conductive bridge and network framework. The silane coupling agent containing active groups not only connects the inert graphene and POSS groups, but more importantly, it promotes the uniform dispersion of amino-containing POSS on the graphene surface, preventing POSS from accumulating on the graphene surface and affecting the isolation and dispersion effects of graphene. Graphene itself is an excellent conductor. When sheet-like silver powder fails to form perfect contact due to resin shrinkage or uneven arrangement, the conductive graphene sheets dispersed in the gaps can connect adjacent silver powder, providing additional electron tunneling or conduction paths and reducing contact resistance. Furthermore, POSS has an auxiliary dispersion and positioning effect, improving the dispersion of graphene and allowing it to be distributed in the gaps between sheet-like silver powder in a more efficient bridging manner, rather than agglomerating into isolated islands. This helps to form a more complete sheet-like silver powder-graphene hybrid conductive network. More importantly, through the chemical anchoring effect of the amino groups on POSS, the bonding between graphene and epoxy resin is stronger, and it is less likely to detach from the matrix during curing shrinkage and thermal cycling, thus maintaining the long-term stability of the conductive pathway and indirectly improving reliable conductivity. The addition of rigid POSS-graphene can change the rheological properties of the resin system, affecting the sedimentation and arrangement of the flake silver powder before curing, promoting denser silver powder deposition, and facilitating the formation of a stable conductive network.

[0115] In this invention, POSS-graphene is not used as the main conductive filler, but primarily serves to promote the dispersion of silver powder and construct conductive pathways. Therefore, the amount of non-conductive silane coupling agent and POSS significantly affects the performance of the epoxy resin. Specifically, compared to Example 10, the amount of silane coupling agent containing active groups in Comparative Example 1 was excessive, resulting in a certain degree of reduction in both conductivity and mechanical properties. This indicates that this reaction step requires a small amount of silane coupling agent to form a monolayer on the graphene surface, which chemically bonds with the resin and POSS through its active end groups, improving the interface without affecting the direct electron transport between fillers. When the amount is excessive, the excess silane molecules cannot all be arranged in an orderly manner at the interface, forming an excessively thick, disordered multilayer or even a physically stacked layer on the filler surface. This not only significantly increases the contact resistance between conductive particles (silver powder, graphene) but also forms a weak interfacial bonding layer, which is detrimental to improving conductivity and mechanical properties.

[0116] Compared to Example 10, Comparative Example 2 did not add POSS containing polyamines, making the graphene prone to stacking, which is detrimental to the construction of conductive pathways and enhanced networks. In Comparative Example 3, the amount of POSS containing polyamines was excessive. Excessive POSS molecules formed a high-density, nearly continuous insulating layer on the graphene surface, hindering efficient electron transfer between silver powders and potentially introducing high-resistance nodes into the conductive pathways. Furthermore, the excessive POSS not only grafted onto the graphene surface but also self-aggregated within the system, forming POSS aggregates tens or even hundreds of nanometers in size. These aggregates have poor interfacial bonding with the epoxy matrix, becoming internal stress concentration points and defect origins, easily inducing microcracks and leading to performance degradation.

[0117] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a modified epoxy resin adhesive, characterized in that, Includes the following steps: (1) Graphene is activated by a silane coupling agent containing active groups to obtain modified graphene; the mass ratio of the silane coupling agent containing active groups to graphene is (0.1-0.3):1; the active groups can undergo nucleophilic substitution reactions with amino groups; (2) POSS containing polyamines was reacted with modified graphene to obtain POSS modified graphene; the molar ratio of POSS containing polyamines to silane coupling agent containing active groups was (0.1-0.3):1; (3) Mix the epoxy resin, curing agent, and curing accelerator evenly to obtain the resin matrix; (4) Add POSS modified graphene and micron-sized flake silver powder to the resin matrix, stir evenly, and cure to obtain modified epoxy resin adhesive.

2. The method for preparing a modified epoxy resin adhesive as described in claim 1, characterized in that, The specific process of step (1) is as follows: the silane coupling agent containing active groups and graphene are ultrasonically dispersed in a mixed solvent of ethanol and deionized water, heated and reacted, and then filtered, washed and dried to obtain modified graphene.

3. The method for preparing a modified epoxy resin adhesive as described in claim 2, characterized in that, The heating reaction temperature is 50-65℃, and the heating reaction time is 1-2.5h.

4. The method for preparing a modified epoxy resin adhesive as described in claim 1, characterized in that, In step (1), the active group is one or more of acyl chloride, acid anhydride, sulfonyl chloride, and epoxy group.

5. The method for preparing a modified epoxy resin adhesive as described in claim 1, characterized in that, In step (2), the POSS containing multiple amino groups is a POSS containing 2-8 amino groups.

6. The method for preparing a modified epoxy resin adhesive as described in claim 1, characterized in that, In step (3), the epoxy resin is one or more of the following: bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol AD ​​type epoxy resin, phenolic type epoxy resin, and alicyclic epoxy resin.

7. The method for preparing a modified epoxy resin adhesive as described in claim 1, characterized in that, In step (3), the curing agent is one or more of the following: amine, carboxylic acid, and acid anhydride curing agents.

8. The method for preparing a modified epoxy resin adhesive as described in claim 1, characterized in that, In step (3), the curing accelerator is one or more of the following: benzyl dimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol and its modified forms, 2-ethyl-4-methylimidazole, cyanoethyl-2-ethyl-4-methylimidazole, modified benzyl dimethylamine, methylimidazole, diaminodiphenyl sulfone, 2-undecylimidazole, and 2-heptadecanylimidazole.

9. The method for preparing a modified epoxy resin adhesive as described in claim 1, characterized in that, In step (4), the curing temperature is 145-155℃ and the curing time is 2-3h.

10. A modified epoxy resin adhesive, characterized in that, It is prepared by the method of any one of claims 1-9 for a modified epoxy resin adhesive.