Special stretchable conductive silver paste for dip-coating and preparation method thereof

Abstract

The invention provides special stretchable conductive silver paste for dip-coating and a preparation method of the special stretchable conductive silver paste. The special stretchable conductive silver paste comprises the following components in parts by weight: 50-70% of metal silver powder; 5-18% of polymer resin; 15-40% of a solvent; 3-8% of an auxiliary agent; the metal silver powder is formed by compounding flake silver powder, nano silver powder and sphere-like silver powder in proportion, the particle size of the flake silver powder is 3-5 micrometers, the particle size of the sphere-like silver powder is 0.5-0.8 micrometer, the flake silver powder accounts for 55%-80% of the total mass of the silver powder, the sphere-like silver powder accounts for 10%-25% of the total mass of the silver powder, and the nano silver powder accounts for 5%-20% of the total mass of the silver powder; by optimizing the proportion of the raw materials such as the silver powder, the high polymer material and the auxiliaries, the conductive silver paste is suitable for the dip-coating process, the problems that in the prior art, conductive silver paste is poor in tensile property, conductivity and tensile property are difficult to balance, and the dip-coating process is poor in adaptability can be effectively solved, and the requirement for manufacturing of flexible electronic devices is met.

Description

Technical Field

[0001] The present invention relates to the field of solar energy industry application technology, and in particular to a stretchable conductive silver paste specifically for dip coating of stretchable solar cells and flexible electronic devices and a preparation method thereof. Background Art

[0002] Dip-coating silver paste: A material used to form a conductive coating on surfaces through a dip-coating process. It typically consists of silver powder, an organic vehicle, and other additives. During the dip-coating process, the object to be coated is immersed in a container of silver paste, allowing the silver paste to evenly adsorb onto the surface. Then, through drying and curing processes, the organic vehicle evaporates or undergoes a cross-linking reaction, leaving behind the silver powder to form a continuous conductive layer, imparting excellent electrical conductivity to the surface.

[0003] Stretchable conductive silver paste: A functional material with unique properties, it's primarily used to achieve stretchable conductive connections in flexible electronics and other fields. Its excellent conductivity ensures smooth current flow, meeting the circuit connectivity requirements of electronic devices. Furthermore, it exhibits exceptional stretchability, maintaining stable conductivity within a certain tensile strain range—for example, withstanding 50% or even higher strain—without experiencing a significant drop in conductivity or breakage of the conductive path due to stretching. Furthermore, its excellent flexibility, adhesion, and stability allow it to firmly adhere to various flexible substrates, adapting to diverse environments and conditions.

[0004] Conductive silver paste, as an important conductive functional material, is widely used in electronic circuits, flexible electronic devices and other fields. As electronic products develop towards miniaturization, portability, and flexibility, higher requirements are placed on conductive silver paste, requiring excellent conductivity and good stretchability for flexible electronic devices.

[0005] Currently, electronic products are moving towards flexibility and wearability, resulting in the emergence of flexible screens, stretchable solar cells, and wearable electronic devices. This has led to an increasing demand for stretchable conductive materials. Stretchable conductive silver pastes are widely used in electronic devices, medical, photovoltaic, and automotive fields, as well as in the manufacture of flexible displays, flexible circuit boards, and bendable components. Stretchable silver pastes can meet the conductivity and flexibility requirements under varying conditions. In medical devices, they are used to create skin sensors and bioelectrodes, helping to monitor human health. In the photovoltaic field, in thin-film solar cells, stretchable silver pastes are used to create electrodes and conductive circuits to ensure the cell's photoelectric conversion efficiency. In the automotive field, various sensors on vehicles require reliable conductive connections to ensure stability and accuracy during driving. However, existing conductive silver pastes suffer from poor stretchability and difficulty balancing conductivity and stretchability. For example, when stretched to a high degree, existing conductive silver pastes experience a sharp increase in resistance and a decrease in conductivity. Furthermore, during curing, the silver pastes shrink, generating internal stress that can break the polymer layer, leading to film cracking and shedding, significantly reducing conductivity.

[0006] Dip coating offers several advantages over printing. First, it is suitable for a variety of complex and curved substrates (such as fibers, films, and three-dimensional structures), whereas printing is typically limited to flat or simply curved surfaces. Second, dip coating achieves uniform coating coverage, avoiding edge effects or pattern unevenness that can occur with printing. Furthermore, dip coating is suitable for large-scale continuous production, particularly for long or large-area substrates (such as roll-to-roll production), whereas printing typically requires layer-by-layer or area-by-area operation, resulting in lower efficiency. Furthermore, dip coating equipment is simple, material utilization is high, and it is suitable for low-cost manufacturing. These advantages have led to its widespread adoption.

[0007] Dip-coating stretchable conductive silver paste can achieve continuous production in the roll-to-roll manufacturing process, thereby improving production efficiency. Printed silver paste is limited by the printing process and template, and has relatively poor adaptability to complex shapes. Dip-coating silver paste can adapt to substrates of various shapes and sizes, and can better coat complex shapes to form a uniform conductive layer. In addition, the dip-coating silver paste can flow and spread naturally on the surface of the substrate to form a conductive film with uniform thickness and good continuity, which can effectively avoid problems such as discontinuous lines and uneven thickness that may occur in the printing process, thereby ensuring the stability of conductivity. However, most of the existing conductive silver pastes are suitable for printing processes, and have poor adaptability in dip-coating processes, and cannot meet the needs of flexible electronic device manufacturing. Summary of the Invention

[0008] In view of the above drawbacks, the present invention proposes a stretchable conductive silver paste specifically for dip coating, comprising the following components in parts by weight: Metallic silver powder 50-70%; Polymer resin 5-18%; Solvent 15-40%; Additives 3-8%; The metallic silver powder is a mixture of flaky silver powder, nano silver powder and spherical silver powder in proportion, wherein the particle size of the flaky silver powder is 3-5 μm, the particle size of the spherical silver powder is 0.5-0.8 μm, the flaky silver powder accounts for 55%-80% of the total mass of the silver powder, the spherical silver powder accounts for 10-25% of the total mass of the silver powder, and the nano silver powder accounts for 5%-20% of the total mass of the silver powder.

[0009] The present invention also provides a method for preparing a special dip-coating stretchable conductive silver paste, comprising the following steps: Preparation of the main resin solution: Mix the polymer resin and the solvent in a weight ratio of 5-18%:15-40% of the total weight of the formula, heat in a water bath at 70-100°C, disperse in a high-speed disperser for 3-5 hours, and filter to obtain the main resin solution; Prepare carrier solution: add 3-8% of the total weight of the additive to the main resin solution, stir to ensure uniform mixing, and prepare carrier solution; Mixing: Flake silver powder, nano silver powder and spherical silver powder are mixed in proportion to obtain a mixed silver powder, and the carrier solution is added at 50-70% of the total weight of the formula, stirred, and mixed to obtain a coarse slurry; the particle size of the flake silver powder is 3-5 μm, the particle size of the spherical silver powder is 0.5-0.8 μm, and the particle size of the nano silver powder is 50-100 nm. The flake silver powder accounts for 55%-80% of the total mass of the mixed silver powder, the spherical silver powder accounts for 10-25% of the total mass of the mixed silver powder, and the nano silver powder accounts for 5%-20% of the total mass of the mixed silver powder; Grinding: Circulate grinding until the slurry fineness is less than 10μm; Filtration: Filter the ground silver slurry to remove impurities and large particles in the slurry; Degassing: vacuum degas the filtered silver paste to remove bubbles in the paste.

[0010] By optimizing the ratio of raw materials such as silver powder, polymer materials, and additives, and adopting a special preparation process, the resulting conductive silver paste has good stretchability and conductivity, and is suitable for dip-coating process. It can effectively solve the problems of poor stretchability of conductive silver paste in the existing technology, difficulty in balancing conductivity and stretchability, and poor adaptability of dip-coating process, and meet the needs of flexible electronic device manufacturing.

[0011] In terms of silver paste components, the present invention uses a compound of thermoplastic polyurethane elastomer resin 2100P and a special tin-modified PU curing agent to accelerate the curing reaction, increase the cross-linking density and improve the film performance. The silver paste has good stretchability and conductivity. 3-5μm flake silver powder is compounded with 50-100nm nano silver powder and spherical silver powder with an average particle size of 0.5-0.8μm to ensure the density of the slurry after coating. The cured silver layer has a certain ductility and can withstand bending or stretching. On the one hand, it can reduce the curing temperature and avoid high temperature damage to the flexible substrate. On the other hand, it can achieve high conductivity and good flexibility.

[0012] Among them, flaky silver powder is easier to form a stacked structure, and can maintain a conductive path through sheet sliding during stretching, thereby enhancing the ductility and fracture resistance of the paste, and taking into account both conductivity and flexibility; spherical silver powder can fill the gaps between flaky silver powder layers, increase the overall packing density of silver powder, and enhance the fluidity and coating properties of the silver paste; nano silver powder can fill the micron-level gaps between flaky silver powder and spherical silver powder, forming a denser conductive network, reducing the breakpoints of the conductive path, and significantly reducing the volume resistivity of the silver paste. At the same time, nano silver powder has a small particle size and a large specific surface area, and can form a stronger bond with the substrate and other silver powder particles, reducing the breakage of the silver powder network during stretching and maintaining conductive stability. The combination of flaky silver powder, spherical silver powder, and nano silver powder achieves a synergistic improvement in conductivity, stretchability, and coating uniformity through the combined structure of "skeleton (flaky) + filler (spherical) + micro-bridge (nano)", which is beneficial to improving the overall performance of silver paste, especially improving and optimizing the resistivity change performance after the deformation of the silver paste layer after infiltration and the recovery of deformation. Figure 1 .

[0013] Fumed silica is used as an anti-settling agent to reduce the sedimentation rate and ensure the uniformity of the silver paste. A composite coupling system of silane and titanate coupling agents is adopted to achieve chemical bonding and steric stabilization at the same time, thereby improving the dispersion of silver powder and the interface strength.

[0014] In terms of preparation technology, to ensure uniform dispersion and fineness of silver paste, the traditional silver paste preparation method uses a three-roll mill for grinding and dispersion. This method is more suitable for pastes with higher viscosities. However, three-roll milling of silver pastes with lower viscosities can be inconvenient due to the low viscosity and can result in significant leakage and loss. This patented invention utilizes a sand mill for grinding and dispersion, addressing the problem of severe leakage and inconvenience caused by low viscosity (give a numerical value for viscosity) when using a roller mill to grind silver paste. Furthermore, by controlling sand mill parameters, excellent dispersion and grinding results are achieved, with a slurry fineness of less than 10μm. Fineness affects the fluidity of the silver paste. Coarse particles can lead to poor fluidity and difficulty controlling coating thickness during coating. A more uniform silver paste makes it easier to form a smooth, continuous coating during the dip coating process, reducing localized thickness variations caused by particle agglomeration and avoiding coating defects such as pinholes. Furthermore, the fineness of the silver paste directly affects the contact area between silver particles. An appropriate fineness results in denser packing of silver particles, smoother conductive paths, and improved conductivity.

[0015] Dip-coating conductive silver paste is a silver paste applied through a dip-coating process. Its main feature lies in its process adaptability. The substrate is immersed in the silver paste, which is then lifted up by the wetting action of the substrate surface and then solidified to form a coating. Therefore, dip-coating silver paste needs to meet the requirements of low viscosity, high fluidity, and good wettability to ensure that the substrate can be evenly coated with the paste. The key indicators of dip-coating silver paste are fluidity and wettability, while the key indicators of printing silver paste are thixotropy and printability. The two types of silver paste have different requirements in terms of viscosity, thixotropy, solid content, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the powder system in the ingredients of the present invention. DETAILED DESCRIPTION

[0017] The present invention provides a special-purpose stretchable conductive silver paste for dip coating, comprising the following components by weight: 50-70% metallic silver powder; 5-18% polymer resin; 15-40% solvent; 3-8% additive; The metallic silver powder is a mixture of flaky silver powder, nano silver powder and spherical silver powder in proportion, wherein the particle size of the flaky silver powder is 3-5 μm, the particle size of the spherical silver powder is 0.5-0.8 μm, the flaky silver powder accounts for 55%-80% of the total mass of the silver powder, the spherical silver powder accounts for 10-25% of the total mass of the silver powder, and the nano silver powder accounts for 5%-20% of the total mass of the silver powder.

[0018] Furthermore, the polymer resin includes thermoplastic polyurethane elastomer resin, acrylic resin, and phenoxy resin, and the weight ratio of the three polymer resins is 5-10:3-5:1-2. The acrylic resin model is 2162, 1722, LP51 / 03N, and the phenoxy resin model is one of MW50000, PHEN-5035, and HYR-1912. The polyurethane elastomer resin gives the silver paste excellent flexibility and anti-deformation ability, the phenoxy resin helps the silver paste have good flexibility while maintaining a certain strength, and the acrylic resin can provide good adhesion and leveling properties. Furthermore, the auxiliary agent comprises a curing agent, an anti-settling agent, a coupling agent, and a conductivity promoter in a weight ratio of 1-4:0.5-2:0.5-2:1-2. The curing agent is a special tin-modified PU curing agent, the anti-settling agent is fumed silica, and the coupling agent is a composite coupling system of silane and titanate coupling agents, which can simultaneously achieve chemical bonding and steric stabilization, improving the dispersibility and interfacial strength of silver powder. The specific silane coupling agent is one of KH-550, KH-560, and KH-570, and the specific titanate coupling agent is one of TTS and NDZ-101. The composite ratio of the two coupling agents is 1:2-3:1. The conductivity promoter is one of graphene, carbon nanotubes, and conductive carbon black.

[0019] Furthermore, the solvent is a highly polar solvent, selected from one or more of N-N-dimethylformamide, N-N-dimethylacetamide, N-methylpyrrolidone, γ-butyrolactone, and dimethyl sulfoxide. This highly polar solvent has excellent solubility for various resins and additives, allowing for a more uniform dispersion of the silver paste components and a more even and dense distribution of silver particles, facilitating the formation of a continuous conductive network and thereby improving conductivity. Its slow evaporation allows for sufficient leveling of the silver paste, reducing defects caused by excessive solvent evaporation.

[0020] Furthermore, the conductive silver paste has a square resistance of no more than 40Ω / □, an elongation at break greater than 200%, a 50% tensile resistance change rate no more than 18%, an adhesion of 5B, and a viscosity no less than 7900mps.

[0021] Furthermore, the silver paste has a recovery resistance change rate of less than 10% after a 50% stretching change.

[0022] The present invention also provides a method for preparing a special dip-coating stretchable conductive silver paste, comprising the following steps: Preparation of the main resin solution: The polymer resin and the solvent are mixed in a weight ratio of 5-18%:15-40% of the total weight of the formula, dispersed in a water bath at 70-100°C, at a speed of 1300-1600 rpm using a high-speed disperser for 3-5 hours, and filtered through a 150-mesh polyester mesh to obtain the main resin solution; Prepare carrier solution: Add 3-8% of the total weight of the additive to the main resin solution, stir at 800-1000 rpm using a high-speed disperser for 30-60 minutes to ensure uniform mixing to prepare a carrier solution; Mixing: Flake silver powder, nano silver powder and spherical silver powder are mixed in proportion to obtain a mixed silver powder, 50-70% of the total weight of the formula of the carrier solution is added, and the mixture is stirred at a speed of 600-800 rpm for 10-30 minutes to obtain a coarse slurry; the particle size of the flake silver powder is 3-5 μm, the particle size of the spherical silver powder is 0.5-0.8 μm, and the particle size of the nano silver powder is 50-100 nm. The flake silver powder accounts for 55%-80% of the total mass of the mixed silver powder, the spherical silver powder accounts for 10-25% of the total mass of the mixed silver powder, and the nano silver powder accounts for 5%-20% of the total mass of the mixed silver powder; Grinding: Circulate grinding until the slurry fineness is less than 10μm; Filtration: Filter the ground silver slurry to remove impurities and large particles in the slurry; Degassing: vacuum degas the filtered silver paste to remove bubbles in the paste.

[0023] The grinding step further comprises: pouring the slurry into the feed bin of a sand mill, using zirconia beads with a diameter of 0.8-1.6 mm, with an amount of 30-60% of the grinding chamber volume, adjusting the speed to 400-800 rpm, and grinding 3-5 times in a cycle until the slurry fineness is less than 10 μm.

[0024] Furthermore, the filtration step is: closing the sand mill circulation system, opening the discharge port and discharging the material into a clean container, filtering the ground silver paste with a 400-mesh stainless steel mesh to remove impurities and large particles in the paste, thereby improving the quality and stability of the silver paste.

[0025] Furthermore, the degassing step is: subjecting the filtered silver paste to planetary double-axis stirring vacuum degassing with a vacuum degree of -0.08 to -0.098 MPa for 15-30 minutes to remove bubbles in the slurry, thereby improving the density and conductivity of the silver paste.

[0026] Example 1 Step 1: Preparing a main resin solution: Mix a polymer resin and a solvent in a weight ratio of 5%:18% of the total weight of the formula, disperse at a high speed of 1300 rpm in a water bath at 70°C for 5 hours, and filter through a 150-mesh polyester mesh to obtain a main resin solution for later use; the polymer resin includes a thermoplastic polyurethane elastomer resin, an acrylic resin, and a phenoxy resin, and the weight ratio of the three polymer resins is 10:3:1; Step 2: Prepare the carrier solution: Add 3% of the total weight of the additive to the main resin solution and stir at 800 rpm for 30 minutes using a disperser to ensure uniform mixing. This will prepare the carrier solution for later use. The additive consists of a curing agent, an anti-settling agent, a coupling agent, and a conductivity promoter in a weight ratio of 1:0.5:1:2. Step 3: Flake silver powder, nano silver powder and spherical silver powder are mixed in proportion, and the above-mentioned carrier solution is added at 50% of the total weight of the formula, and stirred at a speed of 600 rpm for 15 minutes to obtain a coarse slurry.

[0027] The particle size of the flaky silver powder is 3.0 μm, the particle size of the spherical silver powder is 0.6 μm, and the particle size of the nano silver powder is 100 nm. The flaky silver powder accounts for 70% of the total mass of the mixed silver powder, the spherical silver powder accounts for 20% of the total mass of the mixed silver powder, and the nano silver powder accounts for 10% of the total mass of the mixed silver powder.

[0028] Step 4: Pour the slurry into the feed bin of a sand mill. Use 0.8mm diameter zirconium oxide beads, adding an amount that covers 60% of the grinding chamber volume. Adjust the speed to 800 rpm and grind three times until the slurry is less than 10μm in fineness.

[0029] Step 5: Turn off the sand mill circulation system, open the discharge port and discharge the material into a clean container. Filter the ground silver paste with a 400-mesh polyester mesh to remove impurities and large particles in the paste, thereby improving the quality and stability of the silver paste.

[0030] Step 6: The filtered silver paste is subjected to planetary double-axis stirring vacuum degassing with a vacuum degree of -0.08 to -0.098 MPa for 30 minutes to remove bubbles in the paste, thereby improving the density and conductivity of the silver paste.

[0031] Example 2 Step 1: Preparing a main resin solution: Mix a polymer resin and a solvent in a weight ratio of 18%:40%, disperse the mixture in a water bath at 100°C and 1600 rpm for 3 hours, filter through a 150-mesh polyester mesh to obtain a main resin solution for later use; the polymer resin includes a thermoplastic polyurethane elastomer resin, an acrylic resin, and a phenoxy resin, and the weight ratio of the three polymer resins is 5:5:2; Step 2: Prepare the carrier solution: Add 8% of the total weight of the additive to the main resin solution and stir at 1000 rpm for 60 minutes using a disperser to ensure uniform mixing. This will prepare the carrier solution for later use. The additive consists of a curing agent, an anti-settling agent, a coupling agent, and a conductivity promoter in a weight ratio of 4:2:2:1. Step 3: Flake silver powder, nano silver powder and spherical silver powder are mixed in proportion, and the above-mentioned carrier solution is added according to 70% of the total weight of the formula, and stirred at a speed of 800 rpm for 30 minutes to obtain a coarse slurry.

[0032] The particle size of the flaky silver powder is 5 μm, the particle size of the spherical silver powder is 0.5-0.8 μm, and the particle size of the nano silver powder is 50 nm. The flaky silver powder accounts for 55% of the total mass of the mixed silver powder, the spherical silver powder accounts for 25% of the total mass of the mixed silver powder, and the nano silver powder accounts for 20% of the total mass of the mixed silver powder.

[0033] Step 4: Pour the slurry into the feed chamber of a sand mill. Use 1.6mm diameter zirconium oxide beads, adding an amount that is 50% of the grinding chamber volume. Adjust the speed to 400 rpm and grind five times until the slurry is less than 10μm in fineness.

[0034] Step 5: Turn off the sand mill circulation system, open the discharge port and discharge the material into a clean container. Filter the ground silver paste with a 400-mesh stainless steel mesh to remove impurities and large particles in the paste, thereby improving the quality and stability of the silver paste.

[0035] Step 6: The filtered silver paste is subjected to planetary double-axis stirring vacuum degassing with a vacuum degree of -0.08 to -0.098 MPa for 15 minutes to remove bubbles in the paste, thereby improving the density and conductivity of the silver paste.

[0036] Example 3 Step 1: Preparing a main resin solution: Mix a polymer resin and a solvent in a weight ratio of 13%:32%, disperse the mixture in a water bath at 85°C at a speed of 1400 rpm for 4 hours, and filter the mixture through a 150-mesh polyester mesh to obtain a main resin solution for later use; the polymer resin includes a thermoplastic polyurethane elastomer resin, an acrylic resin, and a phenoxy resin, and the weight ratio of the three polymer resins is 8:4:1; Step 2: Prepare the carrier solution: Add 6% of the total weight of the additive to the main resin solution and stir at 900 rpm in a disperser for 45 minutes to ensure uniform mixing. The carrier solution is prepared for use. The additive is a mixture of curing agent, anti-settling agent, coupling agent, and conductivity promoter in a weight ratio of 3:1.2:1.2:1.5. Step 3: Flake silver powder, nano silver powder and spherical silver powder are mixed in proportion, and the above-mentioned carrier solution is added according to 60% of the total weight of the formula, and stirred at a speed of 700 rpm for 20 minutes to obtain a coarse slurry.

[0037] The particle size of the flaky silver powder is 3.8 μm, the particle size of the spherical silver powder is 0.7 μm, and the particle size of the nano silver powder is 70 nm. The flaky silver powder accounts for 68% of the total mass of the mixed silver powder, the spherical silver powder accounts for 20% of the total mass of the mixed silver powder, and the nano silver powder accounts for 12% of the total mass of the mixed silver powder.

[0038] Step 4: Pour the slurry into the feed chamber of a sand mill. Use 1.2mm diameter zirconium oxide beads, adding an amount that covers 50% of the grinding chamber volume. Adjust the speed to 600 rpm and grind four times until the slurry is less than 10μm in fineness.

[0039] Step 5: Turn off the sand mill circulation system, open the discharge port and discharge the material into a clean container. Filter the ground silver paste with a 400-mesh stainless steel mesh to remove impurities and large particles in the paste, thereby improving the quality and stability of the silver paste.

[0040] Step 6: The filtered silver paste is subjected to planetary double-axis stirring vacuum degassing with a vacuum degree of -0.08 to -0.098 MPa for 25 minutes to remove bubbles in the paste, thereby improving the density and conductivity of the silver paste.

[0041] The silver pastes prepared in the above three examples were infiltrated into layers under the same conditions, and samples were taken for performance testing. The results are as follows:

[0042] The table shows that in each embodiment of the present invention, the conductive silver paste has a square resistance of less than 40mΩ / □, an elongation at break of 450% without cracking, adhesion reaching 5B, and a viscosity of no less than 7900mPa.s. These performances are superior to existing technologies.

[0043] The "50% resistance change rate" refers to the resistance change rate of the silver paste layer at a 50% deformation, which were 15%, 12%, and 18%, respectively. These rates are significantly lower than the prior art's resistance change rate at a 20% deformation. Furthermore, the prior art does not document the resistance change rate at 50% deformation, so it is conceivable that its level could not possibly reach that of this embodiment.

[0044] At the same time, the resistance change rates within 30 minutes and 2 hours after 50% deformation recovery were detected, and the change rates were based on the original level without deformation. The resistance change rate of the silver paste layer at the deformation position was detected. Within 30 minutes, they were 8%, 8%, and 6%, respectively. It can be seen that after the deformation is recovered, the resistance change rate can be restored in a relatively short time, and the deviation from the original level is less than 8%. At 2.5 hours, they were 5%, 4%, and 5%, respectively. It can be seen that after the deformation is recovered, the resistance change rate can be restored in a relatively short time, and the deviation from the original level is less than 5%, and the deviation is small. It can be seen that the silver paste prepared by the present invention has a small resistivity change rate at the deformation site when the deformation reaches 50%, and the resistivity at the original deformation site can still be restored to a level with a deviation of less than 5% from the original level after recovery. This is a very excellent level in the application field of extensible conductive silver paste, and this technical level cannot be achieved in the existing technology.

[0045] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the scope of knowledge possessed by ordinary technicians in the relevant technical field without departing from the purpose of this patent.

Claims

1. A special type of stretchable conductive silver paste for dip coating, characterized in that The composition comprises the following components in parts by weight: Metallic silver powder 50-70%; Polymer resin 5-18%; Solvent 15-40%; Additives 3-8%; The metallic silver powder is a mixture of flaky silver powder, nano silver powder and spherical silver powder in proportion, wherein the particle size of the flaky silver powder is 3-5 μm, the particle size of the spherical silver powder is 0.5-0.8 μm, the flaky silver powder accounts for 55%-80% of the total mass of the silver powder, the spherical silver powder accounts for 10-25% of the total mass of the silver powder, and the nano silver powder accounts for 5%-20% of the total mass of the silver powder.

2. The stretchable conductive silver paste for dip coating according to claim 1, wherein: The polymer resin comprises thermoplastic polyurethane elastomer resin, acrylic resin and phenoxy resin, and the weight ratio of the three polymer resins is 5-10:3-5:1-2.

3. The stretchable conductive silver paste for dip coating according to claim 1, wherein: The auxiliary agent is a mixture of a curing agent, an anti-settling agent, a coupling agent, and a conductivity promoter in a weight ratio of 1-4:0.5-2:0.5-2:1-2.

4. The stretchable conductive silver paste for dip coating according to claim 1, wherein: The solvent is a highly polar solvent, which is one or more of N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, γ-butyrolactone, and dimethyl sulfoxide.

5. The stretchable conductive silver paste for dip coating according to claim 1, wherein: The conductive silver paste has a square resistance of no more than 40Ω / □, an elongation at break greater than 200%, a 50% pull-up resistance change rate no more than 18%, an adhesion of 5B, and a viscosity no less than 7900mps.

6. The stretchable conductive silver paste for dip coating according to claim 4, wherein: The silver paste has a recovery resistance change rate of less than 10% after a 50% pull-up change.

7. A method for preparing a stretchable conductive silver paste for dip coating according to any one of claims 1 to 6, characterized in that The following steps are involved: Preparation of the main resin solution: Mix the polymer resin and the solvent in a weight ratio of 5-18%:15-40% of the total weight of the formula, heat in a water bath at 70-100°C, disperse in a high-speed disperser for 3-5 hours, and filter to obtain the main resin solution; Prepare carrier solution: add 3-8% of the total weight of the additive to the main resin solution, stir to ensure uniform mixing, and prepare carrier solution; Mixing: Flake silver powder, nano silver powder and spherical silver powder are mixed in proportion to obtain a mixed silver powder, and the carrier solution is added at 50-70% of the total weight of the formula, stirred, and mixed to obtain a coarse slurry; the particle size of the flake silver powder is 3-5 μm, the particle size of the spherical silver powder is 0.5-0.8 μm, and the particle size of the nano silver powder is 50-100 nm. The flake silver powder accounts for 55%-80% of the total mass of the mixed silver powder, the spherical silver powder accounts for 10-25% of the total mass of the mixed silver powder, and the nano silver powder accounts for 5%-20% of the total mass of the mixed silver powder; Grinding: Circulate grinding until the slurry fineness is less than 10μm; Filtration: Filter the ground silver slurry to remove impurities and large particles in the slurry; Degassing: vacuum degas the filtered silver paste to remove bubbles in the paste.

8. A method for preparing a stretchable conductive silver paste for dip coating as claimed in claim 7, characterized in that The grinding process is as follows: Pour the slurry into the feed bin of a sand mill, use zirconia beads with a diameter of 0.8-1.6 mm, and add an amount that is 30-60% of the grinding chamber volume. Adjust the speed to 400-800 rpm and cycle through the mill 3-5 times until the slurry fineness is less than 10 μm.

9. A method for preparing a stretchable conductive silver paste for dip coating as claimed in claim 7, characterized in that The filtration step is as follows: closing the sand mill circulation system, opening the discharge port and discharging the material into a clean container, filtering the ground silver paste with a 400-mesh stainless steel mesh to remove impurities and large particles in the paste, thereby improving the quality and stability of the silver paste.

10. A method for preparing a stretchable conductive silver paste for dip coating as claimed in claim 7, characterized in that The degassing step is: the filtered silver paste is subjected to planetary double-axis stirring vacuum degassing with a vacuum degree of -0.08 to -0.098 MPa for 15-30 minutes to remove bubbles in the paste, thereby improving the density and conductivity of the silver paste.

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