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

Abstract

The invention discloses low-silver-content composite conductive silver paste based on a three-dimensional conductive network and a preparation method, and relates to the technical field of composite conductive silver paste preparation, and the low-silver-content composite conductive silver paste comprises a low-silver-content conductive phase, an interface bonding layer, a support body and an organic carrier; and the conductive phase with low silver content comprises the following components: 25 wt%-30 wt% of silver-plated hollow glass beads and 12 wt%-18 wt% of a three-dimensional conductive network. According to the invention, through accurate proportioning of the conductive phase with low silver content, the use amount of silver is greatly reduced. The silver-plated hollow glass bead takes light glass as a core and an ultrathin silver layer as a conductive shell, so that the silver consumption is reduced by more than 60wt%; the three-dimensional conductive network adopts a synergistic structure of silver nanowire fragments and graphene composite fragments, and the high conductivity of graphene is utilized to replace part of silver materials, so that the dependency degree of silver is further reduced. The silver content of the silver paste is greatly reduced, the cost of raw materials is greatly reduced, and the economical efficiency of the silver paste in large-scale application scenes such as photovoltaic and electronic packaging is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite conductive silver paste preparation, in particular to a low-silver-content composite conductive silver paste based on a three-dimensional conductive network and a preparation method thereof. Background Art

[0002] Conductive silver paste, a paste-like functional material that integrates multiple technologies, including metallurgy, chemical engineering, and electronics, plays a crucial role in the modern electronics industry. It is widely used in membrane switch circuits, printed circuit boards, solar photovoltaics, 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 vast majority of the total paste cost. To reduce this cost, the development of composite conductive silver pastes with low silver content has become a research hotspot.

[0003] Currently, strategies for reducing silver content primarily include using non-precious metal nanomaterials as conductive fillers in combination with silver powder. For example, mixing silver nanowires with traditional silver powder allows a small amount of silver nanowires to connect the original silver particles in series and form a conductive network, thereby reducing the silver powder content to a certain extent. Alternatively, silver-coated glass powder can be used to partially replace pure silver powder, reducing the silver content while maintaining conductivity. Regarding resin systems, some technologies utilize a blend of various halogen-free resins, such as phenolic resin, epoxy resin, and silicone resin, to improve the adhesion, conductivity, and cured film flexibility of conductive silver pastes while meeting environmental requirements.

[0004] When the silver content drops below a certain level, the resistance of existing low-silver composite conductive silver pastes easily exceeds the specified resistance. When the silver powder content in conventional conductive silver pastes is high, denser conductive pathways form between the silver powder particles, allowing for smoother electron transfer. However, at low silver content, the number of contact points between silver powder particles decreases, forcing electrons to bypass more insulating areas. This increases resistance, hinders current flow, and fails to meet the demands of electronic devices requiring high low-resistance performance.

[0005] However, the addition of alternative materials or the reduction of silver content can affect the stability of the conductive path. During use, conductivity can fluctuate, especially when environmental conditions change (such as temperature and humidity) or when subjected to external forces. For example, the bond between some alternative materials and silver powder is weak, and during vibration or bending, the interface may separate, resulting in a decrease in conductivity.

[0006] Reducing the silver content changes the rheological properties of the paste, potentially leading to problems such as line breakage and film cracking during printing. When the silver powder content is reduced, it becomes difficult to maintain rheological parameters such as viscosity and thixotropy within the ideal printing range. For high-precision printing processes (such as microprinting with touch electrode line widths down to 3μm), existing low-silver content silver pastes can easily clog the screen, affecting print quality and production efficiency.

[0007] Under low-temperature curing conditions, such as the 140°C required for photovoltaic silver grids, the adhesion of traditional resin systems approaches zero at this temperature, making it impossible to effectively bond the silver powder to the substrate, resulting in insufficient electrode adhesion. Increasing the curing temperature can damage some heat-sensitive substrates, limiting its application range. Summary of the Invention

[0008] In order to solve the above technical problems, the present invention provides a low-silver content composite conductive silver paste based on a three-dimensional conductive network and a preparation method thereof. The following technical solutions are adopted:

[0009] A 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;

[0010] The low silver content conductive phase comprises the following components: 25wt%-30wt% of silver-plated hollow glass microspheres and 12wt%-18wt% of a 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 vehicle comprises the following components: 20 wt%-25 wt% of a lipid matrix, 12 wt%-16 wt% of a terpineol solvent, and 2 wt%-5 wt% of a conductive polymer.

[0014] Optionally, additives are also included, and the additives include 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 polyether-modified silicone; 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 solutions and accurately matching the conductive phase with low silver content, the amount of silver used can be greatly reduced. Among them, the silver-plated hollow glass microspheres use lightweight glass as the core and an ultra-thin silver layer (100nm-150nm) as the conductive shell, which reduces silver consumption by more than 60wt% compared to traditional solid silver powder; the three-dimensional conductive network adopts a synergistic structure of silver nanowire fragments and graphene composite fragments, and uses 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 that of traditional products, which greatly reduces the cost of raw materials and significantly improves the economic efficiency in large-scale application scenarios such as photovoltaics and electronic packaging.

[0018] The hierarchical structure of the three-dimensional conductive network is the core guarantee of its conductive performance: silver nanowire fragments, with their high aspect ratio, form a linear conductive skeleton, while graphene composite fragments fill the gaps and construct a planar conductive network. The two interweave to form a coordinated three-dimensional conductive path of points, lines, and surfaces, ensuring seamless current transmission within the complex structure. Simultaneously, the interfacial 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 enhance the impact resistance of the silver paste film layer.

[0020] The benzotriazole (antioxidant) in the additive forms a passivation film on the silver surface, inhibiting the oxidative 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 combined with the thickening effect of the hydrogenated castor oil thixotropic agent, it improves the stability of the silver paste in high temperature and high humidity environments, extending its service life to more than 1.5 times that of traditional silver paste.

[0021] The terpineol solvent and the lipid matrix form a low-viscosity system, which, combined with the polyether-modified silicone dispersant (1wt%-2wt%), gives the silver paste good leveling 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. The application scenarios cover flexible display screens, photovoltaic cell grid lines, sensor electrodes and other fields.

[0023] Low-volatile organic solvents such as terpineol are used to reduce VOC emissions; pyrolysis additives promote the complete decomposition of organic carriers to avoid residual pollutants; low silver usage reduces the environmental load of precious metal mining and recycling processes, in line with the trend of green manufacturing.

[0024] The introduction of conductive polymers not only enhances the conductivity of organic carriers, but also gives silver pastes 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), providing possibilities for the development of multifunctional electronic devices.

[0025] Through the triple innovation of low silver content, structuring and functionalization, an optimal balance is achieved between cost control, conductive performance, 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, and have a particle size of 2-5μm.

[0027] By adopting the above technical solution, the ultra-thin 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 exceeds 80wt%) or thick-layer silver-plated microbeads (silver layer thickness is usually greater than 200nm), this design significantly reduces the amount of silver while ensuring surface conductivity continuity. The silver volume of a single microbead accounts for only 5wt%-8wt%, which reduces silver consumption by more than 60wt% compared to thicker silver-plated solutions. At the same time, the particle size range of 2-5μm avoids the increased difficulty in preparing the silver layer caused by too small particles and the increased silver consumption per unit volume caused by too large particles, achieving a balance between cost and manufacturability in the matching of silver layer thickness and particle size.

[0028] Optionally, the three-dimensional conductive network includes the following components: 8wt%-10wt% of silver nanowire fragments and 5wt%-7wt% of graphene composite fragments; the silver nanowire fragments and the 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 adopting the above technical solution, silver nanowire fragments form a linear conductive skeleton with a high aspect ratio, which can span the gaps between silver-plated hollow glass microspheres to build a direct conductive path for line connection; graphene composite fragments fill the gaps between silver nanowires with a flaky structure, forming an auxiliary conductive network with surface contact. After the two are compounded in proportion, a three-dimensional structure is formed in which silver nanowires dominate the longitudinal conductivity and graphene strengthens the lateral conductivity, which increases the density of the conductive path by more than 40wt%. This synergistic effect effectively solves the problems of easy agglomeration of single silver nanowires and insufficient conductivity of single graphene. When the amount of silver is reduced, the volume resistivity can still be controlled at 1.2×10 -4 Ω·cm or less.

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

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

[0032] Optionally, the interface bonding layer is a polydopamine-silver ion chelate shell for reducing the silver-silver interface resistance.

[0033] By adopting the above technical solution, the polydopamine molecular chain is rich in catechol and amino groups, which can form a stable five-membered ring chelate with silver ions through chelation, forming 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 30wt%. At the same time, silver ions bridge adjacent silver phases through chelate bonds, forming an "electron tunneling effect" shortcut, which greatly reduces the interface resistance and significantly improves the conductive efficiency. For low-silver content systems, this reduction in interface resistance can effectively compensate for the loss of conductive performance caused by the reduction in silver dosage, ensuring that the overall resistivity remains at a high level.

[0034] Optionally, the support is a polyacrylonitrile microsphere with a diameter 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 adopting the above technical solution, a three-dimensional conductive network is formed by interweaving silver nanowire fragments (length 5-10μm) and graphene composite fragments (particle size 1-3μm), and micron- to submicron-scale voids (size 0.1-1μm) are inevitable. Polyacrylonitrile microspheres with a diameter of less than 0.5μm can accurately match the size of these voids, and reduce the void ratio of the network structure through mechanical filling before the silver paste solidifies, so that the void volume ratio is reduced to less than 5wt%. The conductive carbon spheres generated after pyrolysis at 200°C retain the size and morphology of the original microspheres, which not only maintains the filling effect, but also participates in current transmission through the conductivity of the carbon spheres, forming a synergistic conductive mode in which the silver network is dominant and the carbon spheres are supplemented. This design greatly improves the continuity of the conductive path, avoids the current jump phenomenon caused by voids, and can further reduce the volume resistivity, especially in low silver content systems.

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

[0037] By adopting this technical solution, the epoxy groups in the epoxy resin molecules react chemically with the hydroxyl groups on the surface of the silver-plated hollow glass microspheres and the amino groups in the interfacial layer of polydopamine in the three-dimensional conductive network, forming chemical bonds. The urethane groups in the polyurethane, in turn, 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 balances the polarity and reactivity of the two resins: too high a proportion of epoxy resin will reduce its compatibility with non-polar components (such as graphene) due to its strong polarity, while too high a proportion of polyurethane will reduce the interfacial bonding strength due to its insufficient reactivity.

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

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

[0040] Step 2, preparing silver nanowires;

[0041] Step 3, preparing graphene composite fragments;

[0042] Step 4, adding the silver nanowire fragments and the graphene composite fragments into an ethanol solvent, ultrasonically treating and magnetically stirring the mixture to form an interwoven three-dimensional conductive network precursor, and vacuum drying the mixture for later use;

[0043] Step 5: adding the three-dimensional conductive network precursor to a polydopamine hydrochloride solution and stirring at room temperature, adding a silver nitrate solution and continuing to stir to form a polydopamine-silver ion chelate shell through chelation, centrifuging and vacuum drying to obtain a three-dimensional conductive network with an interfacial bonding layer;

[0044] Step 6: adding acrylonitrile monomer, sodium lauryl sulfate, and potassium persulfate to deionized water by emulsion polymerization to obtain a polyacrylonitrile microsphere emulsion; centrifuging, washing, and freeze-drying the emulsion to select microspheres with a diameter of less than 0.5 μm as a support;

[0045] Step 7, weighing epoxy resin and polyurethane according to the mass ratio, heating and stirring until completely blended to obtain a lipid matrix;

[0046] Step 8, adding the conductive polymer to the terpineol solvent in proportion, and ultrasonically dispersing the mixture until a uniform dispersion is formed;

[0047] Step 9, mixing the lipid matrix and the terpineol-conductive polymer dispersion to obtain an organic carrier;

[0048] Step 10, adding additives;

[0049] Step 11: Add silver-plated hollow glass microspheres and a three-dimensional conductive network with an interface bonding layer into a planetary mixer, and then add supporting polyacrylonitrile microspheres and an 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, a three-roll mill is used to grind three times to remove agglomerated particles, and the roller spacing of the three grindings 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 includes at least one of the following beneficial technical effects:

[0053] The present invention provides a low-silver composite conductive silver paste based on a three-dimensional conductive network and a preparation method. Through the precise proportioning of the low-silver conductive phase, silver usage is significantly reduced. Silver-plated hollow glass microspheres utilize a lightweight glass core and an ultra-thin silver layer as a conductive shell, reducing silver consumption by over 60% by weight. The three-dimensional conductive network utilizes a synergistic structure of silver nanowire fragments and graphene composite fragments, leveraging graphene's high conductivity to partially replace silver, further reducing dependence on silver. The silver content of the silver paste is only 30%-40% of that of traditional products, significantly reducing raw material costs and significantly improving economic efficiency in large-scale applications such as photovoltaics and electronic packaging.

[0054] Silver nanowire fragments, with their high aspect ratio, form a linear conductive skeleton, while graphene composite fragments fill the gaps and construct a planar conductive network. The two interweave to form a three-dimensional conductive path that coordinates points, lines, and surfaces, ensuring seamless current transmission within the complex structure. Simultaneously, the interfacial bonding layer reduces the silver-silver interface resistance through chelation, significantly reducing the interface contact resistance and meeting the electrical 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 enhance the impact resistance of the silver paste film layer.

[0056] Through the triple innovation of low silver content, structuring and functionalization, an optimal balance is achieved between cost control, conductive performance, stability and process adaptability, opening up a new path for the high-performance and low-cost application of conductive silver paste. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 Schematic diagram of a sample of a low-silver content composite conductive silver paste based on a three-dimensional conductive network of the present invention;

[0058] Figure 2 It is a schematic diagram of the effect of applying the low-silver content composite conductive silver paste based on the three-dimensional conductive network of the present invention on a circuit board. DETAILED DESCRIPTION

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

[0060] The embodiments of the present invention disclose a low-silver content composite conductive silver paste based on a three-dimensional conductive network and a preparation method thereof.

[0061] Reference Figure 1 and Figure 2 , Example 1, a 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 includes the following components: 25wt%-30wt% of silver-plated hollow glass microspheres and 12wt%-18wt% of a 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: 20 wt%-25 wt% of a lipid matrix, 12 wt%-16 wt% of a terpineol solvent, and 2 wt%-5 wt% of a conductive polymer.

[0066] Example 2 further comprises an additive, wherein the additive 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 is polyether-modified silicone; 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.

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

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

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

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

[0073] The use of silver is greatly reduced through the precise proportion of the low-silver content conductive phase. Among them, the silver-plated hollow glass microspheres use lightweight glass as the core and an ultra-thin silver layer (100nm-150nm) as the conductive shell, which reduces silver consumption by more than 60wt% compared to traditional solid silver powder; the three-dimensional conductive network adopts a synergistic structure of silver nanowire fragments and graphene composite fragments, using 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, which greatly reduces the cost of raw materials and significantly improves the economic efficiency in large-scale application scenarios such as photovoltaics and electronic packaging.

[0074] The hierarchical structure of the three-dimensional conductive network is the core guarantee of its conductive performance: silver nanowire fragments, with their high aspect ratio, form a linear conductive skeleton, while graphene composite fragments fill the gaps and construct a planar conductive network. The two interweave to form a coordinated three-dimensional conductive path of points, lines, and surfaces, ensuring seamless current transmission within the complex structure. Simultaneously, the interfacial 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 enhance the impact resistance of the silver paste film layer.

[0076] The benzotriazole (antioxidant) in the additive forms a passivation film on the silver surface, inhibiting the oxidative 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 combined with the thickening effect of the hydrogenated castor oil thixotropic agent, it improves the stability of the silver paste in high temperature and high humidity environments, extending its service life to more than 1.5 times that of traditional silver paste.

[0077] The terpineol solvent and the lipid matrix form a low-viscosity system, which, combined with the polyether-modified silicone dispersant (1wt%-2wt%), gives the silver paste good leveling 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. The application scenarios cover flexible display screens, photovoltaic cell grid lines, sensor electrodes and other fields.

[0079] Low-volatile organic solvents such as terpineol are used to reduce VOC emissions; pyrolysis additives promote the complete decomposition of organic carriers to avoid residual pollutants; low silver usage reduces the environmental load of precious metal mining and recycling processes, in line with the trend of green manufacturing.

[0080] The introduction of conductive polymers not only enhances the conductivity of organic carriers, but also gives silver pastes 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), providing possibilities for the development of multifunctional electronic devices.

[0081] Through the triple innovation of low silver content, structuring and functionalization, an optimal balance is achieved between cost control, conductive performance, 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] The ultra-thin 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 exceeds 80wt%) or thick-layer silver-plated microbeads (silver layer thickness is usually greater than 200nm), this design significantly reduces the amount of silver while ensuring surface conductivity continuity. The silver volume of a single microbead accounts for only 5wt%-8wt%, which reduces silver consumption by more than 60wt% compared to thicker silver-plated solutions. At the same time, the particle size range of 2-5μm avoids the increased difficulty in preparing the silver layer caused by too small particles and the increased silver consumption per unit volume caused by too large particles, achieving a balance between cost and manufacturability in the matching of silver layer thickness and particle size.

[0084] In Example 5, a three-dimensional conductive network includes the following components: 8wt%-10wt% of silver nanowire fragments and 5wt%-7wt% of graphene composite fragments; the silver nanowire fragments and the 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 skeleton that can span the gaps between silver-plated hollow glass microspheres to construct a direct conductive path for line connection; graphene composite fragments fill the gaps between silver nanowires with a flake structure, forming an auxiliary conductive network for surface contact. After the two are compounded in proportion, a three-dimensional structure is formed in which silver nanowires dominate the longitudinal conductivity and graphene strengthens the lateral conductivity, increasing the density of the conductive path by more than 40wt%. This synergistic effect effectively solves the problems of easy agglomeration of single silver nanowires and insufficient conductivity of single graphene. Even with a reduced amount of silver, the volume resistivity can still be controlled at 1.2×10 -4 Ω·cm or less.

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

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

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

[0089] Polydopamine molecular chains are rich in catechol and amino groups, which can form stable five-membered ring chelates with silver ions through chelation, forming a uniform polydopamine-silver ion transition layer on the surfaces 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 30wt%. At the same time, silver ions bridge adjacent silver phases through chelate bonds, forming an "electron tunneling effect" shortcut, significantly reducing interfacial resistance and significantly improving conductivity. For low-silver content systems, this reduction in interfacial resistance can effectively compensate for the loss of conductivity caused by the reduced silver dosage, ensuring that the overall resistivity remains high.

[0090] In Example 7, the support is polyacrylonitrile microspheres with a diameter less than 0.5 μm, which are 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 (length 5-10μm) and graphene composite fragments (particle size 1-3μm), and micron- to submicron-scale voids (size 0.1-1μm) are inevitable. Polyacrylonitrile microspheres with a diameter of less than 0.5μm can accurately match the size of these voids, and reduce the void ratio of the network structure through mechanical filling before the silver paste solidifies, so that the void volume ratio is reduced to less than 5wt%. The conductive carbon spheres generated after pyrolysis at 200°C retain the size and morphology of the original microspheres, which not only maintains the filling effect, but also participates 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 greatly improves the continuity of the conductive path, avoids the current jump phenomenon caused by voids, and can further reduce the volume resistivity, especially in low silver content systems.

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

[0093] The epoxy groups in the epoxy resin molecules react chemically with the hydroxyl groups on the surface of the silver-coated hollow glass microspheres and the amino groups in the interfacial layer of polydopamine in the three-dimensional conductive network, forming chemical bonds. The urethane groups in the polyurethane, in turn, 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 ensures a balance between the polarity and reactivity of the two resins: too high a proportion of epoxy resin will reduce its compatibility with non-polar components (such as graphene) due to its excessive polarity, while too high a proportion of polyurethane will reduce its interfacial bonding strength due to its insufficient reactivity.

[0094] Example 9, a method for preparing a low-silver content composite conductive silver paste, for preparing 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 plate a 100nm-150nm silver layer on the surface;

[0096] Step 2, preparing silver nanowires;

[0097] Step 3, preparing graphene composite fragments;

[0098] Step 4, adding the silver nanowire fragments and the graphene composite fragments into an ethanol solvent, ultrasonically treating and magnetically stirring the mixture to form an interwoven three-dimensional conductive network precursor, and vacuum drying the mixture for later use;

[0099] Step 5: adding the three-dimensional conductive network precursor to a polydopamine hydrochloride solution and stirring at room temperature, adding a silver nitrate solution and continuing to stir to form a polydopamine-silver ion chelate shell through chelation, centrifuging and vacuum drying to obtain a three-dimensional conductive network with an interfacial bonding layer;

[0100] Step 6: adding acrylonitrile monomer, sodium lauryl sulfate, and potassium persulfate to deionized water by emulsion polymerization to obtain a polyacrylonitrile microsphere emulsion; centrifuging, washing, and freeze-drying the emulsion to select microspheres with a diameter of less than 0.5 μm as a support;

[0101] Step 7, weighing epoxy resin and polyurethane according to the mass ratio, heating and stirring until completely blended to obtain a lipid matrix;

[0102] Step 8, adding the conductive polymer to the terpineol solvent in proportion, and ultrasonically dispersing the mixture until a uniform dispersion is formed;

[0103] Step 9, mixing the lipid matrix and the terpineol-conductive polymer dispersion to obtain an organic carrier;

[0104] Step 10, adding additives;

[0105] Step 11: Add silver-plated hollow glass microspheres and a three-dimensional conductive network with an interface bonding layer into a planetary mixer, and then add supporting polyacrylonitrile microspheres and an 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 2 μm-5 μm, ultrasonically clean them with anhydrous ethanol and deionized water in sequence, and vacuum dry them. Immerse the dried hollow glass microspheres in a mixed plating solution containing silver nitrate, glucose, and ammonia water, stir and react to form a 120 nm thick silver layer. After the reaction is completed, centrifuge and separate them, wash them with deionized water until they are neutral, and vacuum dry them to obtain silver-plated hollow glass microspheres.

[0109] Step 2: preparing silver nanowires with a diameter of 50-100 nm and a length of 10-20 μm by a polyol method, washing with deionized water and then shearing to obtain silver nanowire fragments with a length of 8 μm;

[0110] Step 3: mixing graphene and carbon nanotubes in a mass ratio of 3:1, adding the mixture to an N-methylpyrrolidone solvent for ultrasonic dispersion, spray drying, crushing the mixture with a ball mill, and sieving to obtain graphene composite fragments with a particle size of 1 μm to 3 μm;

[0111] Step 4, adding the silver nanowire fragments and the graphene composite fragments into an ethanol solvent, ultrasonically treating and magnetically stirring the mixture to form an interwoven three-dimensional conductive network precursor, and vacuum drying the mixture for later use;

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

[0113] Step 6: using an emulsion polymerization method, adding acrylonitrile monomer, sodium lauryl sulfate, and potassium persulfate in a mass ratio of 100:3:1 to deionized water, stirring and reacting under nitrogen protection to obtain a polyacrylonitrile microsphere emulsion; after centrifugation, washing, and freeze-drying, screening microspheres with a diameter of less than 0.5 μm as a support;

[0114] Step 7, weighing epoxy resin and polyurethane in a mass ratio of 3:1, heating and stirring until completely blended to obtain a lipid matrix;

[0115] Step 8, adding the conductive polymer to the terpineol solvent in proportion, and ultrasonically dispersing the mixture until a uniform dispersion is formed;

[0116] Step 9, mixing the lipid matrix and the terpineol-conductive polymer dispersion to obtain an organic carrier;

[0117] Step 10, weighing a dispersant, a thixotropic agent, a curing agent, an antioxidant, and a pyrolysis aid in proportion, first adding hydrogenated castor oil to a small amount of terpineol and stirring until completely dispersed, then adding other additives in sequence, and stirring at room temperature to obtain an additive premix;

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

[0119] Step 12: Add the additive premix solution and stir at a high speed of 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, a three-roll mill is used to grind three times to remove agglomerated particles. The roller spacing of the three grindings is 5 μm, 3 μm, and 1 μm, respectively. After grinding, the final low-silver content composite conductive silver paste is obtained.

[0121] The following specific embodiments are used to 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 with anhydrous ethanol and deionized water for 30 minutes, removing surface impurities and then vacuum dried (60°C, 2 hours). Using the 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 water (temperature 50°C) and stirred for 30 minutes to form a silver layer with a thickness of 100nm-150nm. After the reaction, the microspheres were centrifuged, washed with deionized water until neutral, and vacuum dried at 60°C for 4 hours to obtain silver-plated hollow glass microspheres.

[0124] Construction of three-dimensional conductive network:

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

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

[0127] Three-dimensional network composite: silver nanowire fragments 9wt% and graphene composite fragments 6wt% were added to ethanol solvent, ultrasonicated for 20 minutes, and then magnetically stirred for 1 hour to form an interwoven three-dimensional conductive network precursor, which was then vacuum dried for later use.

[0128] Preparation of interface bonding layer materials:

[0129] A 2g / L dopamine hydrochloride solution (pH adjusted to 8.5 with Tris-HCl buffer) was prepared, and the aforementioned three-dimensional conductive network precursor was added. The mixture was stirred at room temperature for 6 hours to form a polydopamine coating on the surface. Subsequently, a 0.1mol / L silver nitrate solution was added and stirred for another 2 hours to form a polydopamine-silver ion chelate shell through chelation. The mixture was centrifuged and vacuum-dried to obtain a three-dimensional conductive network with an interfacial bonding layer.

[0130] Support preparation:

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

[0132] Organic carrier preparation:

[0133] Epoxy resin and polyurethane were weighed in a mass ratio of 3:1, heated and stirred at 60°C for 30 minutes until completely fused to obtain a lipid matrix.

[0134] The conductive polymer (such as polyaniline) is added to the terpineol solvent in proportion and ultrasonically dispersed for 20 minutes to form a uniform dispersion.

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

[0136] Additive mixing:

[0137] The dispersant (polyether modified silicone), thixotropic agent (hydrogenated castor oil), curing agent (imidazole latent type), antioxidant (benzotriazole), and pyrolysis aid (ammonium persulfate) were weighed in proportion. First, hydrogenated castor oil was added to a small amount of terpineol and stirred at 50°C until completely dispersed. Then, other additives were added in sequence and stirred at room temperature for 30 minutes to obtain an additive premix.

[0138] Mixing in steps:

[0139] Silver-plated hollow glass microspheres and a three-dimensional conductive network with an interfacial bonding layer were added to a planetary mixer and stirred at a low speed (500 r / min) for 10 min for preliminary mixing.

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

[0141] The organic carrier was slowly added in 3 additions (10 min interval between each addition) and stirred at 1500 r / min for 1 h to form a uniform slurry.

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

[0143] The prepared silver paste needs to be vacuum degassed at 25°C for 30 minutes, and the viscosity (controlled within 5000-8000 mPa·s) and conductivity (target square resistance <10 mΩ / □) should be tested. After sealing, store in a refrigerator at 4°C.

[0144] Table 1 is a performance test table of low-silver content composite conductive silver paste based on the preparation method, covering key performance indicators, test methods and target ranges. The test frequency and accuracy can be adjusted according to the actual application scenario:

[0145] Table 1

[0146]

[0147]

[0148]

[0149]

[0150] Testing frequency: It is recommended to conduct full testing for each batch during the R&D stage, and key indicators (such as viscosity, square resistance, adhesion, and storage stability) can be randomly tested during the mass production stage.

[0151] Sample preparation: The film sample needs to be prepared by a 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] Abnormal tracing: If a certain indicator does not meet the standard, the preparation steps (such as three-dimensional network composite parameters and interface bonding layer reaction time) can be reversely traced in combination with microstructure detection (such as SEM observation of network fracture and EDS analysis of element segregation).

[0153] Through the above tests, the comprehensive performance of low-silver content silver paste can be comprehensively evaluated, especially highlighting the contribution of the three-dimensional conductive network to low-silver high conductivity, 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, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. Low silver content composite conductive silver paste based on three-dimensional conductive network, characterized by: It includes a low silver content conductive phase, an interface bonding layer, a support and an organic carrier; The low silver content conductive phase comprises the following components: 25wt%-30wt% of silver-plated hollow glass microspheres and 12wt%-18wt% of a three-dimensional conductive network; The content of the interface bonding layer is 2wt%-3wt%; The content of the support is 6wt%-7wt%; The organic vehicle comprises the following components: 20 wt%-25 wt% of a lipid matrix, 12 wt%-16 wt% of a terpineol solvent, and 2 wt%-5 wt% of a conductive polymer.

2. The low-silver content composite conductive silver paste based on a three-dimensional conductive network according to claim 1, characterized in that: Also included are additives comprising 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 silicone; 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 of hollow glass microspheres with a 100nm-150nm silver layer plated on the surface, and the particle size is 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 includes the following components: 8wt%-10wt% of silver nanowire fragments and 5wt%-7wt% of graphene composite fragments; the silver nanowire fragments and the 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 5, characterized in that: The interfacial bonding layer is a polydopamine-silver ion chelate shell, which is used to reduce the silver-silver interface resistance.

7. The low-silver content composite conductive silver paste based on a three-dimensional conductive network according to claim 6, characterized in that: The support is polyacrylonitrile microspheres with a diameter of less than 0.5 μm. The polyacrylonitrile microspheres are pyrolyzed at 180°C-200°C to generate conductive carbon balls, which fill the gaps in the three-dimensional conductive network.

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

1.

9. A method for preparing a low-silver content composite conductive silver paste according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1: prepare hollow glass microspheres and plate a 100nm-150nm silver layer on the surface; Step 2, preparing silver nanowires; Step 3, preparing graphene composite fragments; Step 4, adding the silver nanowire fragments and the graphene composite fragments into an ethanol solvent, ultrasonically treating and magnetically stirring the mixture to form an interwoven three-dimensional conductive network precursor, and vacuum drying the mixture for later use; Step 5: adding the three-dimensional conductive network precursor to a polydopamine hydrochloride solution and stirring at room temperature, adding a silver nitrate solution and continuing to stir to form a polydopamine-silver ion chelate shell through chelation, centrifuging and vacuum drying to obtain a three-dimensional conductive network with an interfacial bonding layer; Step 6: adding acrylonitrile monomer, sodium lauryl sulfate, and potassium persulfate to deionized water by emulsion polymerization to obtain a polyacrylonitrile microsphere emulsion; centrifuging, washing, and freeze-drying the emulsion to select microspheres with a diameter of less than 0.5 μm as a support; Step 7, weighing epoxy resin and polyurethane according to the mass ratio, heating and stirring until completely blended to obtain a lipid matrix; Step 8, adding the conductive polymer to the terpineol solvent in proportion, and ultrasonically dispersing the mixture until a uniform dispersion is formed; Step 9, mixing the lipid matrix and the terpineol-conductive polymer dispersion to obtain an organic carrier; Step 10, adding additives; Step 11, adding silver-plated hollow glass microspheres and a three-dimensional conductive network with an interface bonding layer into a planetary mixer, and then adding support polyacrylonitrile microspheres and an organic carrier in sequence, and stirring 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.

10. The method for preparing a low-silver content composite conductive silver paste according to claim 9, characterized in that: In step 12, after high-speed stirring at 2000 r / min, a three-roll mill is used to grind three times to remove agglomerated particles. The roller spacing of the three grindings 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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