Low silver content composite conductive silver paste based on three-dimensional conductive network and preparation method thereof

Abstract

The application discloses a low-silver-content composite conductive silver paste based on a three-dimensional conductive network and a preparation method thereof, relates to the technical field of composite conductive silver paste preparation, and comprises a low-silver-content conductive phase, an interface bonding layer, a support body and an organic carrier; the low-silver-content conductive phase comprises the following components: silver-plated hollow glass beads 25wt%-30wt%, a three-dimensional conductive network 12wt%-18wt%. The application greatly reduces the amount of silver by precisely matching the low-silver-content conductive phase. The silver-plated hollow glass beads take light glass as a core and an ultrathin silver layer as a conductive shell, thereby reducing the consumption of more than 60wt% of silver; the three-dimensional conductive network adopts a synergistic structure of silver nanowire fragments and graphene composite fragments, uses the high conductivity of graphene to replace part of silver materials, and further reduces the dependence on silver. The silver content of the silver paste is greatly reduced, the cost of raw materials is greatly reduced, and the economy in large-scale application scenarios such as photovoltaic and electronic packaging is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of composite conductive silver paste preparation technology, and in particular to a low-silver-content composite conductive silver paste based on a three-dimensional conductive network and its preparation method. Background Technology

[0002] Conductive silver paste, a paste-like functional material integrating metallurgy, chemical engineering, and electronics, plays a crucial role in the modern electronics industry, widely used in thin-film switching circuits, printed circuit boards, solar photovoltaic industry, touch screens, smart cards, radio frequency identification, and many other fields. Traditional conductive silver paste is typically prepared by mechanically mixing micron-sized metallic silver particles, polymer binders, solvents, and additives. However, silver, as a precious metal, is relatively expensive, and the cost of silver powder often accounts for the majority of the total cost of conductive silver paste. To reduce costs, the development of low-silver-content composite conductive silver pastes has become a research hotspot.

[0003] Currently, strategies for reducing silver content mainly include using non-precious metal nanomaterials as conductive fillers in combination with silver powder. For example, silver nanowires can be mixed with traditional silver powder; a small amount of silver nanowires can connect the original silver particles in series to form a conductive network, thereby reducing the silver powder content to some extent. Another approach is to use silver-plated glass powder to replace some of the pure silver powder, reducing the silver content while maintaining conductivity. Regarding resin systems, some technologies use a mixture of various halogen-free resins, such as phenolic resins, epoxy resins, and silicone resins, to improve the adhesion, conductivity, and flexibility of the cured film of conductive silver paste, while also meeting environmental protection requirements.

[0004] When the silver content decreases to a certain level, the resistance of existing low-silver-content composite conductive silver pastes easily exceeds the standard. In traditional conductive silver pastes with a high silver powder content, the silver powder particles can form relatively dense conductive paths, allowing for smoother electron transport. However, with low silver content, the contact points between silver powder particles decrease, and electron conduction must bypass more insulating areas, leading to increased resistance and hindered current transmission, failing to meet the requirements of electronic devices with high low-resistance requirements.

[0005] However, the stability of the conductive pathway is affected by the addition of other alternative materials or the reduction of silver content. During use, especially when environmental conditions change (such as changes in temperature and humidity) or when subjected to external forces, the conductivity is prone to fluctuations. For example, some alternative materials have weak bonding forces with silver powder, and the interface may separate during vibration or bending, leading to a decrease in conductivity.

[0006] Reducing the silver content alters the rheological properties of the paste, potentially leading to problems during printing such as broken lines and film cracking. When the silver content decreases, it becomes difficult to maintain the paste's viscosity, thixotropy, and other rheological parameters within the ideal printing range. For high-precision printing processes (such as microprinting where the touch electrode linewidth is reduced to 3μm), existing low-silver-content silver pastes can easily clog the screen, affecting printing quality and production efficiency.

[0007] Under low-temperature curing conditions, such as the 140℃ curing requirement for photovoltaic silver grids, the adhesion of traditional resin systems approaches zero at this temperature, failing to effectively and firmly bond the silver powder to the substrate, resulting in insufficient electrode adhesion. Increasing the curing temperature, however, may damage some heat-sensitive substrates, limiting their application range. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a low-silver-content composite conductive silver paste based on a three-dimensional conductive network and its preparation method. The technical solution is as follows:

[0009] The low-silver-content composite conductive silver paste based on a three-dimensional conductive network includes a low-silver-content conductive phase, an interface bonding layer, a support, and an organic carrier.

[0010] The low-silver-content conductive phase comprises the following components: 25wt%-30wt% silver-plated hollow glass microspheres and 12wt%-18wt% three-dimensional conductive network;

[0011] The content of the interface bonding layer is 2wt%-3wt%;

[0012] The content of the support is 6wt%-7wt%;

[0013] The organic carrier comprises the following components: 20wt%-25wt% lipid matrix, 12wt%-16wt% terpineol solvent, and 2wt%-5wt% conductive polymer.

[0014] Optionally, it may also include additives, said additives comprising the following components:

[0015] Dispersant 1wt%-2wt%, thixotropic agent 1wt%-3wt%, curing agent 1wt%-2wt%, antioxidant 0.5wt%-2wt%, pyrolysis aid 0.2wt%-4wt%.

[0016] Optionally, the dispersant is a polyether-modified siloxane; the thixotropic agent is hydrogenated castor oil; the curing agent is an imidazole latent curing agent; the antioxidant is benzotriazole; and the pyrolysis aid is ammonium persulfate.

[0017] By adopting the above technical solution and precisely proportioning a low-silver-content conductive phase, the amount of silver used is significantly reduced. Specifically, the silver-plated hollow glass microspheres use lightweight glass as the core and an ultra-thin silver layer (100nm-150nm) as the conductive shell, reducing silver consumption by more than 60wt% compared to traditional solid silver powder. The three-dimensional conductive network employs a synergistic structure of silver nanowire fragments and graphene composite fragments, utilizing the high conductivity of graphene to replace part of the silver material, further reducing the dependence on silver. The silver content of the silver paste is only 30wt%-40wt% of traditional products, significantly reducing raw material costs and greatly improving economic efficiency in large-scale applications such as photovoltaics and electronic packaging.

[0018] The hierarchical structure of the three-dimensional conductive network is the core guarantee of conductivity: silver nanowire fragments form a linear conductive framework with a high aspect ratio, while graphene composite fragments fill the gaps and construct a planar conductive network. The two intertwine to form a point-line-plane synergistic three-dimensional conductive pathway, ensuring that current is transmitted without dead zones in the complex structure. At the same time, the interface bonding layer reduces the silver-silver interface resistance through chelation, significantly reducing the interface contact resistance and meeting the conductivity requirements of high-precision electronic devices.

[0019] The support fills the gaps in the three-dimensional conductive network, which not only prevents the network structure from collapsing, but also provides rigid support to improve the impact resistance of the silver paste film.

[0020] The benzotriazole (antioxidant) in the additives forms a passivation film on the silver surface, inhibiting the oxidation and corrosion of silver; the imidazole latent curing agent enables the lipid matrix (epoxy resin + polyurethane) to form a network with a higher cross-linking density, and with the thickening effect of the hydrogenated castor oil thixotropic agent, the stability of the silver paste in high temperature and high humidity environments is improved, and the service life is extended to more than 1.5 times that of traditional silver paste.

[0021] The terpineol solvent forms a low-viscosity system with the ester matrix. Combined with polyether-modified siloxane dispersant (1wt%-2wt%), the silver paste has good leveling properties and printing accuracy, making it suitable for various processes such as screen printing and inkjet printing.

[0022] The synergistic effect of the curing agent and the pyrolysis aid (ammonium persulfate) enables the silver paste to be cured in the range of 120℃-200℃, which not only meets the low-temperature processing requirements of flexible electronic devices, but also adapts to the high-temperature packaging process of power devices. Its application scenarios cover flexible displays, photovoltaic cell grid lines, sensor electrodes and other fields.

[0023] Using low-volatile organic solvents such as terpineol reduces VOC emissions; pyrolysis aids promote the complete decomposition of organic carriers, avoiding residual pollutants; low silver usage reduces the environmental burden of precious metal mining and recycling processes, which is in line with the trend of green manufacturing.

[0024] The introduction of conductive polymers not only enhances the conductivity of organic carriers, but also endows silver paste with certain flexibility and antistatic properties. By adjusting their types (such as polyaniline and polythiophene), they can be adapted to different substrate materials (glass, plastic, metal), making it possible to develop multifunctional electronic devices.

[0025] Through triple innovations in low silver content, structuring, and functionalization, an optimal balance is achieved between cost control, conductivity, stability, and process adaptability, opening up a new path for the high-performance and low-cost application of conductive silver paste.

[0026] Optionally, the silver-plated hollow glass microspheres are made by plating a 100nm-150nm silver layer on the surface of the hollow glass microspheres, with a particle size of 2-5μm.

[0027] By adopting the above technical solution, an ultrathin silver layer thickness of 100nm-150nm, preferably 120nm, is the key parameter for achieving low-silver content. Compared with traditional solid silver powder (silver content exceeding 80wt%) or thick-layer silver-plated microspheres (silver layer thickness typically greater than 200nm), this design significantly reduces the amount of silver used while ensuring surface conductivity continuity. The silver volume ratio of a single microsphere is only 5wt%-8wt%, reducing silver consumption by more than 60wt% compared to thick-layer silver plating solutions. Simultaneously, the 2-5μm particle size range avoids the increased difficulty in silver layer preparation caused by excessively small particles, as well as the increased silver consumption per unit volume caused by excessively large particles, achieving a balance between cost and fabrication feasibility in the matching of silver layer thickness and particle size.

[0028] Optionally, the three-dimensional conductive network includes the following components: 8wt%-10wt% silver nanowire fragments and 5wt%-7wt% graphene composite fragments; the silver nanowire fragments and graphene composite fragments are combined to form a three-dimensional conductive network, which is used to connect adjacent silver-plated hollow glass microspheres.

[0029] By employing the above technical solution, silver nanowire fragments, with their high aspect ratio, form a linear conductive framework that can bridge the gaps between silver-plated hollow glass microspheres to construct direct conductive pathways with linear connections. Graphene composite fragments, with their sheet-like structure, fill the gaps between the silver nanowires, forming an auxiliary conductive network with surface contact. When these two are combined in a specific ratio, a three-dimensional structure is formed, where silver nanowires dominate longitudinal conductivity and graphene enhances lateral conductivity, increasing the conductive pathway density by over 40 wt%. This synergistic effect effectively solves the problems of easy aggregation of single silver nanowires and insufficient conductivity of single graphene, maintaining a volume resistivity of 1.2 × 10⁻⁶ even with reduced silver content. -4 Below Ω·cm.

[0030] The length of the silver nanowire fragments (5-10 μm) is 2-3 times the size of the silver-plated hollow glass microspheres (2-5 μm), ensuring that a single nanowire can connect 2-3 adjacent microspheres at the same time, avoiding the island effect caused by size mismatch; the size of the graphene composite fragments (1-3 μm) precisely fills the submicron gaps between the microspheres, forming a close contact with the silver layer on the surface of the microspheres, ensuring that the current is transmitted without dead angles in the complex structure, which is especially suitable for the low loss requirements of high-precision electronic devices.

[0031] Silver nanowire fragments possess excellent flexibility, and during the curing or use of silver paste, they can buffer stress through their own deformation, avoiding the breakage of conductive pathways caused by substrate stretching (such as bending of flexible substrates); graphene composite fragments, on the other hand, enhance the impact resistance of the network with their high strength, resisting damage to the conductive structure by external mechanical forces.

[0032] Optionally, the interfacial bonding layer is a polydopamine-silver ion chelate shell, used to reduce the silver-silver interfacial resistance.

[0033] By employing the above technical solution, the polydopamine molecular chain, rich in catechol and amino groups, can form a stable five-membered ring chelate with silver ions through chelation, creating a uniform polydopamine-silver ion transition layer on the surface of silver nanowire fragments, graphene composite fragments, and silver-plated hollow glass microspheres. This chelate structure eliminates the oxide layer and adsorbed impurities on the silver surface, increasing the physical contact area of ​​the silver-silver interface by more than 30 wt%. Simultaneously, silver ions bridge adjacent silver phases through chelate bonds, forming an "electron tunneling effect" shortcut, significantly reducing interfacial resistance and greatly improving conductivity. For systems with low silver content, this reduction in interfacial resistance effectively compensates for the loss of conductivity caused by reduced silver content, ensuring that the overall resistivity remains at a high level.

[0034] Optionally, the support is a polyacrylonitrile microsphere with a diameter of less than 0.5 μm, which is pyrolyzed at 200 °C to generate conductive carbon spheres that fill the gaps in the three-dimensional conductive network.

[0035] By employing the above technical solution, the three-dimensional conductive network is formed by the interweaving of silver nanowire fragments (5-10 μm in length) and graphene composite fragments (1-3 μm in particle size), inevitably containing micron- to submicron-sized voids (0.1-1 μm in size). Polyacrylonitrile microspheres with a diameter less than 0.5 μm can precisely match these void sizes, reducing the void ratio of the network structure through mechanical filling before the silver paste solidifies, thus lowering the void volume percentage to below 5 wt%. The conductive carbon spheres generated after pyrolysis at 200℃ retain the original microsphere size and morphology, maintaining the filling effect and participating in current transmission through the conductivity of the carbon spheres, forming a synergistic conductive mode dominated by the silver network and supplemented by carbon spheres. This design significantly improves the continuity of the conductive pathway, avoiding current jumps caused by voids, and can further reduce the volume resistivity, especially in low-silver-content systems.

[0036] Optionally, the ester matrix is ​​composed of epoxy resin and polyurethane in a weight ratio of 3:1.

[0037] By employing the above technical solution, the epoxy groups in the epoxy resin molecules can chemically react with the hydroxyl groups on the surface of the silver-plated hollow glass microspheres and the amino groups in the polydopamine interface layer of the three-dimensional conductive network to form chemical bonds; the urethane groups of the polyurethane can interact strongly with the surface functional groups (such as carboxyl and hydroxyl groups) of the graphene composite fragments and the porous structure of the support (conductive carbon spheres) through hydrogen bonds. The 3:1 ratio design achieves a balance between the polarity and reactivity of the two resins: if the epoxy resin content is too high, the compatibility with non-polar components (such as graphene) will decrease due to excessive polarity; if the polyurethane content is too high, the interfacial bonding strength will decrease due to insufficient reactivity.

[0038] A method for preparing low-silver-content composite conductive silver paste, used to prepare low-silver-content composite conductive silver paste based on a three-dimensional conductive network, includes the following steps:

[0039] Step 1: Prepare hollow glass microspheres and deposit a 100nm-150nm silver layer on the surface;

[0040] Step 2, prepare silver nanowires;

[0041] Step 3: Prepare graphene composite fragments;

[0042] Step 4: Add silver nanowire fragments and graphene composite fragments to ethanol solvent, sonicate and then magnetically stir to form an interwoven three-dimensional conductive network precursor, and vacuum dry for later use.

[0043] Step 5: Add the three-dimensional conductive network precursor to dopamine hydrochloride solution and stir at room temperature. Add silver nitrate solution and continue stirring. A polydopamine-silver ion chelate shell is formed through chelation. After centrifugation, vacuum dry to obtain a three-dimensional conductive network with an interfacial bonding layer.

[0044] Step 6: Acrylonitrile monomer, sodium dodecyl sulfate, and potassium persulfate are added to deionized water using emulsion polymerization to obtain polyacrylonitrile microsphere emulsion. After centrifugation, washing, and freeze-drying, microspheres with a diameter of less than 0.5 μm are screened out as supports.

[0045] Step 7: Weigh the epoxy resin and polyurethane according to the mass ratio, heat and stir until completely mixed to obtain the ester matrix;

[0046] Step 8: Add the conductive polymer to the terpineol solvent in a certain proportion and ultrasonically disperse until a uniform dispersion is formed;

[0047] Step 9: Mix and stir the lipid matrix with the terpineol-conductive polymer dispersion to obtain an organic carrier;

[0048] Step 10: Add additives;

[0049] Step 11: Add silver-plated hollow glass microspheres and a three-dimensional conductive network with an interface bonding layer to the planetary mixer, then add the support polyacrylonitrile microspheres and organic carrier in sequence, and stir for a set time to form a uniform slurry.

[0050] Step 12: Add the additive premix and stir at high speed to obtain a low-silver-content composite conductive silver paste.

[0051] Optionally, in step 12, after high-speed stirring at 2000 r / min for 30 minutes, the agglomerated particles are removed by grinding three times with a three-roll mill. The roller spacing for the three grinding processes is 5 μm, 3 μm, and 1 μm, respectively. After grinding, the final low-silver-content composite conductive silver paste is obtained.

[0052] In summary, the present invention has at least one of the following beneficial technical effects:

[0053] This invention provides a low-silver-content composite conductive silver paste based on a three-dimensional conductive network and its preparation method. Through precise proportioning of the low-silver-content conductive phase, the amount of silver used is significantly reduced. The silver-plated hollow glass microspheres use lightweight glass as the core and an ultra-thin silver layer as the conductive shell, reducing silver consumption by more than 60 wt%. The three-dimensional conductive network employs a synergistic structure of silver nanowire fragments and graphene composite fragments, utilizing the high conductivity of graphene to replace part of the silver material, further reducing silver dependence. The silver content of the silver paste is only 30 wt%-40 wt% of traditional products, significantly reducing raw material costs and greatly improving economic efficiency in large-scale applications such as photovoltaics and electronic packaging.

[0054] Silver nanowire fragments form a linear conductive framework with a high aspect ratio, while graphene composite fragments fill the gaps and construct a planar conductive network. The two intertwine to form a point-line-plane synergistic three-dimensional conductive pathway, ensuring that current is transmitted without dead zones in the complex structure. At the same time, the interface bonding layer reduces the silver-silver interface resistance through chelation, significantly reducing the interface contact resistance and meeting the conductivity requirements of high-precision electronic devices.

[0055] The support fills the gaps in the three-dimensional conductive network, which not only prevents the network structure from collapsing, but also provides rigid support to improve the impact resistance of the silver paste film.

[0056] Through triple innovations in low silver content, structuring, and functionalization, an optimal balance is achieved between cost control, conductivity, stability, and process adaptability, opening up a new path for the high-performance and low-cost application of conductive silver paste. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of a sample of the low-silver-content composite conductive silver paste based on a three-dimensional conductive network according to the present invention.

[0058] Figure 2 This is a schematic diagram illustrating the effect of applying the low-silver-content composite conductive silver paste based on a three-dimensional conductive network to a circuit board. Detailed Implementation

[0059] The present invention will be further described in detail below with reference to the accompanying drawings.

[0060] This invention discloses a low-silver-content composite conductive silver paste based on a three-dimensional conductive network and its preparation method.

[0061] Reference Figure 1 and Figure 2 Example 1: Low-silver-content composite conductive silver paste based on a three-dimensional conductive network, comprising a low-silver-content conductive phase, an interface bonding layer, a support, and an organic carrier.

[0062] The low-silver-content conductive phase comprises the following components: 25wt%-30wt% silver-plated hollow glass microspheres and 12wt%-18wt% three-dimensional conductive network;

[0063] The content of the interface bonding layer is 2wt%-3wt%;

[0064] The content of the support is 6wt%-7wt%;

[0065] The organic carrier comprises the following components: 20wt%-25wt% lipid matrix, 12wt%-16wt% terpineol solvent, and 2wt%-5wt% conductive polymer.

[0066] Example 2 also includes an additive, which comprises the following components:

[0067] Dispersant 1wt%-2wt%, thixotropic agent 1wt%-3wt%, curing agent 1wt%-2wt%, antioxidant 0.5wt%-2wt%, pyrolysis aid 0.2wt%-4wt%.

[0068] In Example 3, the dispersant was polyether-modified siloxane; the thixotropic agent was hydrogenated castor oil; the curing agent was an imidazole latent curing agent; the antioxidant was benzotriazole; and the pyrolysis aid was ammonium persulfate.

[0069] Preferably, the low-silver-content conductive phase comprises the following components: 28 wt% silver-plated hollow glass microspheres and 14.5 wt% three-dimensional conductive network;

[0070] The content of the interface bonding layer is 2.5 wt%;

[0071] The content of the support is 5.5 wt%;

[0072] The organic carrier comprises the following components: 22 wt% lipid matrix, 14 wt% terpineol solvent, and 3 wt% conductive polymer.

[0073] By precisely proportioning a low-silver-content conductive phase, the amount of silver used is significantly reduced. Specifically, the silver-plated hollow glass microspheres use lightweight glass as the core and an ultra-thin silver layer (100nm-150nm) as the conductive shell, reducing silver consumption by more than 60wt% compared to traditional solid silver powder. The three-dimensional conductive network employs a synergistic structure of silver nanowire fragments and graphene composite fragments, utilizing the high conductivity of graphene to replace part of the silver material, further reducing silver dependence. The silver content of the silver paste is only 30wt%-40wt% of traditional products, significantly reducing raw material costs and greatly improving economic viability in large-scale applications such as photovoltaics and electronic packaging.

[0074] The hierarchical structure of the three-dimensional conductive network is the core guarantee of conductivity: silver nanowire fragments form a linear conductive framework with a high aspect ratio, while graphene composite fragments fill the gaps and construct a planar conductive network. The two intertwine to form a point-line-plane synergistic three-dimensional conductive pathway, ensuring that current is transmitted without dead zones in the complex structure. At the same time, the interface bonding layer reduces the silver-silver interface resistance through chelation, significantly reducing the interface contact resistance and meeting the conductivity requirements of high-precision electronic devices.

[0075] The support fills the gaps in the three-dimensional conductive network, which not only prevents the network structure from collapsing, but also provides rigid support to improve the impact resistance of the silver paste film.

[0076] The benzotriazole (antioxidant) in the additives forms a passivation film on the silver surface, inhibiting the oxidation and corrosion of silver; the imidazole latent curing agent enables the lipid matrix (epoxy resin + polyurethane) to form a network with a higher cross-linking density, and with the thickening effect of the hydrogenated castor oil thixotropic agent, the stability of the silver paste in high temperature and high humidity environments is improved, and the service life is extended to more than 1.5 times that of traditional silver paste.

[0077] The terpineol solvent forms a low-viscosity system with the ester matrix. Combined with polyether-modified siloxane dispersant (1wt%-2wt%), the silver paste has good leveling properties and printing accuracy, making it suitable for various processes such as screen printing and inkjet printing.

[0078] The synergistic effect of the curing agent and the pyrolysis aid (ammonium persulfate) enables the silver paste to be cured in the range of 120℃-200℃, which not only meets the low-temperature processing requirements of flexible electronic devices, but also adapts to the high-temperature packaging process of power devices. Its application scenarios cover flexible displays, photovoltaic cell grid lines, sensor electrodes and other fields.

[0079] Using low-volatile organic solvents such as terpineol reduces VOC emissions; pyrolysis aids promote the complete decomposition of organic carriers, avoiding residual pollutants; low silver usage reduces the environmental burden of precious metal mining and recycling processes, which is in line with the trend of green manufacturing.

[0080] The introduction of conductive polymers not only enhances the conductivity of organic carriers, but also endows silver paste with certain flexibility and antistatic properties. By adjusting their types (such as polyaniline and polythiophene), they can be adapted to different substrate materials (glass, plastic, metal), making it possible to develop multifunctional electronic devices.

[0081] Through triple innovations in low silver content, structuring, and functionalization, an optimal balance is achieved between cost control, conductivity, stability, and process adaptability, opening up a new path for the high-performance and low-cost application of conductive silver paste.

[0082] Example 4: Silver-plated hollow glass microspheres are made by plating a 100nm-150nm silver layer on the surface of hollow glass microspheres, with a particle size of 2-5μm.

[0083] A silver layer thickness of 100nm-150nm, preferably 120nm, is a key parameter for achieving low-silver content. Compared to traditional solid silver powder (silver content exceeding 80wt%) or thick-layer silver-plated microspheres (silver layer thickness typically greater than 200nm), this design significantly reduces silver consumption while ensuring surface conductivity continuity. The silver volume percentage of a single microsphere is only 5wt%-8wt%, reducing silver consumption by more than 60wt% compared to thick-layer silver plating solutions. Simultaneously, the 2-5μm particle size range avoids the increased difficulty in silver layer preparation caused by excessively small particles, as well as the increased silver consumption per unit volume caused by excessively large particles, achieving a balance between cost and fabrication feasibility in the matching of silver layer thickness and particle size.

[0084] Example 5: The three-dimensional conductive network comprises the following components: 8wt%-10wt% silver nanowire fragments and 5wt%-7wt% graphene composite fragments; the silver nanowire fragments and graphene composite fragments are combined to form a three-dimensional conductive network, which is used to connect adjacent silver-plated hollow glass microspheres.

[0085] Silver nanowire fragments, with their high aspect ratio, form a linear conductive framework that can bridge the gaps between silver-plated hollow glass microspheres, creating direct conductive pathways with linear connections. Graphene composite fragments, with their sheet-like structure, fill the gaps between the silver nanowires, forming an auxiliary conductive network with surface contact. When combined in a specific ratio, they form a three-dimensional structure where silver nanowires dominate longitudinal conductivity, while graphene enhances lateral conductivity, increasing the conductive pathway density by over 40 wt%. This synergistic effect effectively solves the problems of easy aggregation of single silver nanowires and insufficient conductivity of single graphene, maintaining a volume resistivity of 1.2 × 10⁻⁶ even with reduced silver content. -4 Below Ω·cm.

[0086] The length of the silver nanowire fragments (5-10 μm) is 2-3 times the size of the silver-plated hollow glass microspheres (2-5 μm), ensuring that a single nanowire can connect 2-3 adjacent microspheres at the same time, avoiding the island effect caused by size mismatch; the size of the graphene composite fragments (1-3 μm) precisely fills the submicron gaps between the microspheres, forming a close contact with the silver layer on the surface of the microspheres, ensuring that the current is transmitted without dead angles in the complex structure, which is especially suitable for the low loss requirements of high-precision electronic devices.

[0087] Silver nanowire fragments possess excellent flexibility, and during the curing or use of silver paste, they can buffer stress through their own deformation, avoiding the breakage of conductive pathways caused by substrate stretching (such as bending of flexible substrates); graphene composite fragments, on the other hand, enhance the impact resistance of the network with their high strength, resisting damage to the conductive structure by external mechanical forces.

[0088] Example 6: The interface bonding layer is a polydopamine-silver ion chelate shell, used to reduce the silver-silver interface resistance.

[0089] The polydopamine molecular chain is rich in catechol and amino groups, which can form stable five-membered ring chelates with silver ions through chelation, creating a uniform polydopamine-silver ion transition layer on the surface of silver nanowire fragments, graphene composite fragments, and silver-plated hollow glass microspheres. This chelate structure can eliminate the oxide layer and adsorbed impurities on the silver surface, increasing the physical contact area of ​​the silver-silver interface by more than 30 wt%. At the same time, silver ions bridge adjacent silver phases through chelate bonds, forming an "electron tunneling effect" shortcut, which significantly reduces the interfacial resistance and greatly improves the conductivity. For systems with low silver content, this reduction in interfacial resistance can effectively compensate for the loss of conductivity caused by the reduction in silver content, ensuring that the overall resistivity remains at a high level.

[0090] In Example 7, the support is a polyacrylonitrile microsphere with a diameter of less than 0.5 μm, which is pyrolyzed at 200°C to generate conductive carbon spheres that fill the gaps in the three-dimensional conductive network.

[0091] The three-dimensional conductive network is formed by the interweaving of silver nanowire fragments (5-10 μm in length) and graphene composite fragments (1-3 μm in diameter), inevitably containing micron- to submicron-sized voids (0.1-1 μm in size). Polyacrylonitrile microspheres with a diameter less than 0.5 μm can precisely match these void sizes, reducing the void ratio of the network structure through mechanical filling before silver paste curing, thus lowering the void volume percentage to below 5 wt%. Conductive carbon spheres generated after pyrolysis at 200℃ retain the original microsphere size and morphology, maintaining the filling effect and participating in current transport through the conductivity of the carbon spheres, forming a synergistic conductive mode dominated by the silver network and supplemented by carbon spheres. This design significantly improves the continuity of the conductive pathway, avoiding current jumps caused by voids, and can further reduce volume resistivity, especially in low-silver-content systems.

[0092] Example 8: The lipid matrix is ​​composed of epoxy resin and polyurethane in a weight ratio of 3:1.

[0093] The epoxy groups in epoxy resin molecules can chemically react with the hydroxyl groups on the surface of silver-plated hollow glass microspheres and the amino groups in the polydopamine interface layer of the three-dimensional conductive network to form chemical bonds. The urethane groups in polyurethane can interact strongly with the surface functional groups (such as carboxyl and hydroxyl groups) of graphene composite fragments and the porous structure of the support (conductive carbon spheres) through hydrogen bonds. A 3:1 ratio balances the polarity and reactivity of the two resins: too high a proportion of epoxy resin would lead to decreased compatibility with non-polar components (such as graphene) due to excessive polarity, while too high a proportion of polyurethane would reduce interfacial bonding strength due to insufficient reactivity.

[0094] Example 9: A method for preparing a low-silver-content composite conductive silver paste, used to prepare a low-silver-content composite conductive silver paste based on a three-dimensional conductive network, comprising the following steps:

[0095] Step 1: Prepare hollow glass microspheres and deposit a 100nm-150nm silver layer on the surface;

[0096] Step 2, prepare silver nanowires;

[0097] Step 3: Prepare graphene composite fragments;

[0098] Step 4: Add silver nanowire fragments and graphene composite fragments to ethanol solvent, sonicate and then magnetically stir to form an interwoven three-dimensional conductive network precursor, and vacuum dry for later use.

[0099] Step 5: Add the three-dimensional conductive network precursor to dopamine hydrochloride solution and stir at room temperature. Add silver nitrate solution and continue stirring. A polydopamine-silver ion chelate shell is formed through chelation. After centrifugation, vacuum dry to obtain a three-dimensional conductive network with an interfacial bonding layer.

[0100] Step 6: Acrylonitrile monomer, sodium dodecyl sulfate, and potassium persulfate are added to deionized water using emulsion polymerization to obtain polyacrylonitrile microsphere emulsion. After centrifugation, washing, and freeze-drying, microspheres with a diameter of less than 0.5 μm are screened out as supports.

[0101] Step 7: Weigh the epoxy resin and polyurethane according to the mass ratio, heat and stir until completely mixed to obtain the ester matrix;

[0102] Step 8: Add the conductive polymer to the terpineol solvent in a certain proportion and ultrasonically disperse until a uniform dispersion is formed;

[0103] Step 9: Mix and stir the lipid matrix with the terpineol-conductive polymer dispersion to obtain an organic carrier;

[0104] Step 10: Add additives;

[0105] Step 11: Add silver-plated hollow glass microspheres and a three-dimensional conductive network with an interface bonding layer to the planetary mixer, then add the support polyacrylonitrile microspheres and organic carrier in sequence, and stir for a set time to form a uniform slurry.

[0106] Step 12: Add the additive premix and stir at high speed to obtain a low-silver-content composite conductive silver paste.

[0107] The specific steps are as follows:

[0108] Step 1: Select hollow glass microspheres with a particle size of 2μm-5μm, ultrasonically clean them with anhydrous ethanol and deionized water in sequence, vacuum dry them, immerse the dried hollow glass microspheres in a mixed plating solution containing silver nitrate, glucose and ammonia, stir to form a silver layer with a thickness of 120nm, centrifuge after the reaction is completed, wash with deionized water until neutral, and vacuum dry to obtain silver-plated hollow glass microspheres;

[0109] Step 2: Silver nanowires with a diameter of 50-100 nm and a length of 10-20 μm are prepared by polyol method. After washing with deionized water, they are sheared to obtain silver nanowire fragments with a length of 8 μm.

[0110] Step 3: Graphene and carbon nanotubes are mixed at a mass ratio of 3:1, added to N-methylpyrrolidone solvent for ultrasonic dispersion, spray dried, crushed by ball mill, and sieved to obtain graphene composite fragments with a particle size of 1μm-3μm.

[0111] Step 4: Add silver nanowire fragments and graphene composite fragments to ethanol solvent, sonicate and then magnetically stir to form an interwoven three-dimensional conductive network precursor, and vacuum dry for later use.

[0112] Step 5: Add the three-dimensional conductive network precursor to dopamine hydrochloride solution and stir at room temperature to form a polydopamine coating on the surface. Add silver nitrate solution and continue stirring to form a polydopamine-silver ion chelate shell through chelation. After centrifugation, vacuum dry to obtain a three-dimensional conductive network with an interfacial bonding layer.

[0113] Step 6: Acrylonitrile monomer, sodium dodecyl sulfate, and potassium persulfate were added to deionized water at a mass ratio of 100:3:1 using emulsion polymerization. The reaction was carried out under nitrogen protection and stirred to obtain polyacrylonitrile microsphere emulsion. After centrifugation, washing, and freeze-drying, microspheres with a diameter of less than 0.5 μm were selected as the support.

[0114] Step 7: Weigh epoxy resin and polyurethane in a 3:1 mass ratio, heat and stir until completely mixed to obtain the ester matrix;

[0115] Step 8: Add the conductive polymer to the terpineol solvent in a certain proportion and ultrasonically disperse until a uniform dispersion is formed;

[0116] Step 9: Mix and stir the lipid matrix with the terpineol-conductive polymer dispersion to obtain an organic carrier;

[0117] Step 10: Weigh out the dispersant, thixotropic agent, curing agent, antioxidant, and pyrolysis aid according to the proportion. First, add hydrogenated castor oil to a small amount of terpineol and stir until completely dispersed. Then, add the other additives in sequence and stir at room temperature to obtain the additive premix.

[0118] Step 11: Add silver-plated hollow glass microspheres and a three-dimensional conductive network with an interfacial bonding layer to the planetary mixer. Mix at low speed for initial mixing. Add the support polyacrylonitrile microspheres and increase the speed to 1000 r / min and stir for 20 min to fill the network gaps with microspheres. Slowly add the organic carrier in 3 batches and maintain stirring at 1500 r / min for the set time to form a uniform slurry.

[0119] Step 12: Add the additive premix and stir at 2000 r / min to obtain a low-silver-content composite conductive silver paste.

[0120] In Example 10, in step 12, after high-speed stirring at 2000 r / min for 30 minutes, the agglomerated particles were removed by grinding three times with a three-roll mill. The roller spacing for the three grinding cycles was 5 μm, 3 μm, and 1 μm, respectively. After grinding, the final low-silver-content composite conductive silver paste was obtained.

[0121] The following specific embodiments illustrate the implementation principle of the present invention:

[0122] Preparation of silver-plated hollow glass microspheres:

[0123] Hollow glass microspheres with a particle size of 2-5 μm were selected and ultrasonically cleaned sequentially with anhydrous ethanol and deionized water for 30 min each to remove surface impurities. Afterward, they were vacuum dried (60℃, 2 h). Using a chemical silver plating method, the dried microspheres were immersed in a mixed plating solution containing 0.05 mol / L silver nitrate, 0.1 mol / L glucose, and 0.02 mol / L ammonia (temperature 50℃) and stirred for 30 min to form a silver layer 100 nm-150 nm thick. After the reaction, the microspheres were centrifuged, washed with deionized water until neutral, and vacuum dried at 60℃ for 4 h to obtain silver-plated hollow glass microspheres.

[0124] Construction of a three-dimensional conductive network:

[0125] Preparation of silver nanowire fragments: Silver nanowires with diameters of 50-100 nm and lengths of 10-20 μm were prepared by the polyol method. After washing with deionized water, they were sheared for 5 min using a high-speed shearing machine (3000 r / min) to obtain silver nanowire fragments with lengths ranging from 5-10 μm.

[0126] Preparation of graphene composite fragments: Graphene and carbon nanotubes were mixed at a mass ratio of 3:1, added to N-methylpyrrolidone solvent and ultrasonically dispersed for 30 min. After spray drying, the mixture was crushed by ball milling and sieved to obtain graphene composite fragments with a particle size of 1-3 μm.

[0127] Three-dimensional network composite: Silver nanowire fragments (9 wt%) and graphene composite fragments (6 wt%) were added to ethanol solvent, ultrasonically treated for 20 min, and then magnetically stirred for 1 h to form an interwoven three-dimensional conductive network precursor, which was then vacuum dried for later use.

[0128] Preparation of interfacial bonding layer materials:

[0129] A 2 g / L dopamine hydrochloride solution was prepared (pH adjusted to 8.5 using Tris-HCl buffer), and the above-mentioned three-dimensional conductive network precursor was added. The mixture was stirred at room temperature for 6 h to form a polydopamine coating on the surface. Subsequently, a 0.1 mol / L silver nitrate solution was added, and stirring was continued for 2 h. A polydopamine-silver ion chelate shell was formed through chelation. After centrifugation and vacuum drying, a three-dimensional conductive network with an interfacial bonding layer was obtained.

[0130] Support preparation:

[0131] Acrylonitrile monomer, sodium dodecyl sulfate (emulsifier), and potassium persulfate (initiator) were added to deionized water at a mass ratio of 100:3:1. The mixture was stirred at 60°C for 4 hours under nitrogen protection to obtain a polyacrylonitrile microsphere emulsion. After centrifugation, washing, and freeze-drying, microspheres with a diameter of less than 0.5 μm were selected as the support.

[0132] Organic carrier preparation:

[0133] Weigh epoxy resin and polyurethane in a 3:1 mass ratio, heat and stir at 60°C for 30 minutes until completely fused to obtain the lipid matrix.

[0134] Add the conductive polymer (such as polyaniline) to the terpineol solvent in a certain proportion and ultrasonically disperse for 20 minutes until a uniform dispersion is formed.

[0135] The lipid matrix was mixed with the terpineol-conductive polymer dispersion and stirred at 50°C for 1 hour to obtain the organic carrier.

[0136] Additive mixing:

[0137] Weigh out the dispersant (polyether-modified siloxane), thixotropic agent (hydrogenated castor oil), curing agent (imidazolium latent type), antioxidant (benzotriazole), and pyrolysis aid (ammonium persulfate) according to the proportions. First, add the hydrogenated castor oil to a small amount of terpineol and stir at 50°C until completely dispersed. Then, add the other additives in sequence and stir at room temperature for 30 minutes to obtain the additive premix.

[0138] Step-by-step mixing:

[0139] Add silver-plated hollow glass microspheres and a three-dimensional conductive network with an interfacial bonding layer to a planetary mixer, and stir at low speed (500 r / min) for 10 min to achieve initial mixing.

[0140] Add the support polyacrylonitrile microspheres, increase the speed to 1000 r / min and stir for 20 min to allow the microspheres to fill the network gaps.

[0141] Slowly add the organic carrier in three portions (10 min apart each time), stirring at 1500 rpm for 1 hour to form a uniform slurry.

[0142] Finally, add the additive premix, stir at 2000 r / min for 30 min, and then grind it three times with a three-roll mill (roller spacing of 5 μm, 3 μm, and 1 μm respectively) to remove agglomerated particles and obtain the final low-silver-content composite conductive silver paste.

[0143] The prepared silver paste needs to be degassed under vacuum at 25°C for 30 minutes, and its viscosity (controlled between 5000-8000 mPa·s) and conductivity (target sheet resistance <10 mΩ / □) should be tested. After sealing, it should be stored at 4°C.

[0144] Table 1 shows the performance testing results of low-silver-content composite conductive silver paste based on the preparation method described above. It covers key performance indicators, testing methods, and target ranges. The testing frequency and accuracy can be adjusted according to actual application scenarios.

[0145] Table 1

[0146]

[0147]

[0148]

[0149]

[0150] Testing frequency: During the R&D stage, it is recommended to perform full testing on each batch. During the mass production stage, key indicators (such as viscosity, sheet resistance, adhesion, and storage stability) can be sampled and tested.

[0151] Sample preparation: The film sample needs to be prepared by standard printing process (such as screen printing) to ensure uniform film thickness (5-10μm). The curing conditions are set according to the characteristics of the organic carrier (such as 120℃ / 30min).

[0152] Anomaly tracing: If a certain indicator fails to meet the standard, the preparation steps (such as three-dimensional network composite parameters and interface bonding layer reaction time) can be traced back by combining microstructure detection (such as SEM observation of network fracture and EDS analysis of elemental segregation).

[0153] The above tests can comprehensively evaluate the overall performance of low-silver-content silver paste, especially highlighting the contribution of the three-dimensional conductive network to the high conductivity of low-silver paste, as well as the effect of functional auxiliary components on improving stability.

[0154] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A low silver content composite conductive silver paste based on a three-dimensional conductive network, characterized in that: It includes a low-silver-content conductive phase, an interfacial bonding layer, a support, and an organic carrier; The low-silver-content conductive phase comprises the following components: 25wt%-30wt% silver-plated hollow glass microspheres and 12wt%-18wt% three-dimensional conductive network; The content of the interface bonding layer is 2wt%-3wt%; the interface bonding layer is a polydopamine-silver ion chelate shell, used to reduce the silver-silver interface resistance; The content of the support is 6wt%-7wt%; the support is polyacrylonitrile microspheres with a diameter of less than 0.5μm, which are pyrolyzed at 180℃-200℃ to generate conductive carbon spheres, which fill the gaps in the three-dimensional conductive network. The organic carrier comprises the following components: 20wt%-25wt% resin matrix, 12wt%-16wt% terpineol solvent, and 2wt%-5wt% conductive polymer; A method for preparing low-silver-content composite conductive silver paste includes the following steps: Step 1: Prepare hollow glass microspheres and deposit a 100nm-150nm silver layer on the surface; Step 2, prepare silver nanowires; Step 3: Prepare graphene composite fragments; Step 4: Add silver nanowire fragments and graphene composite fragments to ethanol solvent, sonicate and then magnetically stir to form an interwoven three-dimensional conductive network precursor, and vacuum dry for later use. Step 5: Add the three-dimensional conductive network precursor to dopamine hydrochloride solution and stir at room temperature. Add silver nitrate solution and continue stirring. A polydopamine-silver ion chelate shell is formed through chelation. After centrifugation, vacuum dry to obtain a three-dimensional conductive network with an interfacial bonding layer. Step 6: Acrylonitrile monomer, sodium dodecyl sulfate, and potassium persulfate are added to deionized water using emulsion polymerization to obtain polyacrylonitrile microsphere emulsion. After centrifugation, washing, and freeze-drying, microspheres with a diameter of less than 0.5 μm are screened out as supports. Step 7: Weigh the epoxy resin and polyurethane according to the mass ratio, heat and stir until completely mixed to obtain the resin matrix; Step 8: Add the conductive polymer to the terpineol solvent in a certain proportion and ultrasonically disperse until a uniform dispersion is formed; Step 9: Mix and stir the resin matrix with the terpineol-conductive polymer dispersion to obtain an organic carrier; Step 10: Add additives; Step 11: Add silver-plated hollow glass microspheres and a three-dimensional conductive network with an interface bonding layer to the planetary mixer, then add the support polyacrylonitrile microspheres and organic carrier in sequence, and stir for a set time to form a uniform slurry. Step 12: Add the additive premix and stir at high speed to obtain a low-silver-content composite conductive silver paste.

2. The low silver content composite conductive silver paste based on a three- dimensional conductive network according to claim 1, characterized in that: It also includes additives, which comprise the following components: Dispersant 1wt%-2wt%, thixotropic agent 1wt%-3wt%, curing agent 1wt%-2wt%, antioxidant 0.5wt%-2wt%, pyrolysis aid 0.2wt%-4wt%.

3. The low silver content composite conductive silver paste based on a three- dimensional conductive network according to claim 2, characterized in that: The dispersant is polyether-modified siloxane; the thixotropic agent is hydrogenated castor oil; the curing agent is an imidazole latent curing agent; the antioxidant is benzotriazole; and the pyrolysis aid is ammonium persulfate.

4. The low silver content composite conductive silver paste based on a three- dimensional conductive network according to claim 3, characterized in that: Silver-plated hollow glass microspheres are made by plating a 100nm-150nm silver layer on the surface of hollow glass microspheres, with a particle size of 2-5μm.

5. The low silver content composite conductive silver paste based on a three- dimensional conductive network according to claim 4, characterized in that: The three-dimensional conductive network comprises the following components: 8wt%-10wt% silver nanowire fragments and 5wt%-7wt% graphene composite fragments; the silver nanowire fragments and graphene composite fragments are combined to form a three-dimensional conductive network, which is used to connect adjacent silver-plated hollow glass microspheres.

6. The low-silver-content composite conductive silver paste based on a three-dimensional conductive network according to claim 1, characterized in that: The resin matrix is ​​made of epoxy resin and polyurethane in a weight ratio of (2.5-3):

1.

7. The low silver content composite conductive silver paste based on a three- dimensional conductive network according to claim 6, characterized in that: In step 12, after high-speed stirring at 2000 r / min, the agglomerated particles are removed by grinding three times with a three-roll mill. The roller spacing for the three grinding processes is 5 μm, 3 μm, and 1 μm, respectively. After grinding, the final low-silver-content composite conductive silver paste is obtained.

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