Preparation method of solvent recovery type nano conductive filler dispersed conductive coating

Abstract

The invention discloses a preparation method of a solvent recovery type nano conductive filler dispersed conductive coating, belongs to the technical field of electronic functional materials, and aims to solve the problems that VOCs (volatile organic compounds) are formed and the environment is polluted in the processes of mixing, grinding, coating and drying, and a conductive path is discontinuous due to the fact that nano silver powder is large in specific surface area and high in surface energy. Comprising the following steps: selecting a recoverable organic solvent system, inhibiting agglomeration of a nano conductive filler in combination with a composite dispersion mechanism, designing a closed reduced pressure distillation recovery system to realize efficient recovery and reuse of a solvent, optimizing a modified glass powder formula to reduce the sintering temperature, and finally preparing the conductive coating with high conductivity and high stability. According to the method, impurities such as trace filler particles and auxiliaries in the solvent are removed through rectification and purification, the key properties such as viscosity and solubility of the recovered solvent are consistent with those of a new solvent, the core indexes such as conductivity and adhesive force of the conductive paste and the coating prepared after repeated use are not obviously attenuated, and the stability of the production process and the consistency of product quality are ensured.

Description

Technical Field

[0001] This invention belongs to the field of electronic functional materials technology, specifically relating to a method for preparing a solvent-recoverable nano-conductive filler-dispersed conductive coating. Background Technology

[0002] In recent years, with the rapid development of the optoelectronic industry, a number of new-generation optoelectronic products, represented by display touch screens, organic light-emitting diodes, smart wearable devices, and solar cells, are gradually influencing and improving people's lives. Nano-conductive fillers (such as carbon nanotubes, graphene, and nano-silver powder) exhibit significantly improved conductivity compared to traditional fillers due to their unique quantum and surface effects. Nano-fillers can also enhance the mechanical properties, corrosion resistance, and electromagnetic shielding effectiveness of coatings, and are widely used in electronic packaging, antistatic coatings, and new energy batteries.

[0003] The existing technology, patent publication number CN112820440B, describes a highly conductive silver paste and its preparation method. This patent involves preparing silver pastes separately using different silver powders, then mixing them in a specific ratio to form a highly conductive silver paste. This avoids uneven grinding and mixing caused by different particle sizes of silver powders passing through a three-roll mill simultaneously. It also facilitates the proportioning of the highly conductive silver paste with different silver content, making the mixing process more convenient and faster, and beneficial for experimental research. However, in practical use, it still has the following shortcomings: From a practical standpoint, this method uses organic solvents such as terpineol and butylcarbidol, which are prone to volatilization during mixing, grinding, coating, and drying, forming VOCs and polluting the environment. Furthermore, there is no solvent recovery mechanism, meaning the volatilized organic solvents cannot be reused, resulting in resource waste and increased production costs. The invention relies solely on a single dispersant system to improve dispersibility, but nano-silver powder has a large specific surface area and high surface energy, and secondary agglomeration may still occur during long-term storage, coating, or the initial stage of sintering, leading to discontinuous conductive pathways and affecting the conductivity and stability of the coating.

[0004] Therefore, a solvent-recovery nano-conductive filler dispersion conductive coating preparation method is needed to solve the problems in the existing technology, such as the easy volatilization of VOCs during mixing, grinding, coating and drying, which pollutes the environment, and the large specific surface area and high surface energy of nano silver powder, which leads to discontinuous conductive pathways. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a solvent-recoverable nano-conductive filler-dispersed conductive coating to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a solvent-recoverable nano-conductive filler-dispersed conductive coating, comprising the following steps:

[0007] Step S1: Prepare a recyclable organic carrier. Add the recyclable organic solvent system, thickener, and additives to the reaction vessel in proportion. Stir at 70-85℃ for 30-60 minutes until completely dissolved. Cool to room temperature to obtain the recyclable organic carrier.

[0008] Step S2: Prepare the composite dispersion by adding the composite dispersant to a portion of the recyclable organic carrier, ultrasonically dispersing for 10-20 min, adding the nano-conductive filler, and high-speed shearing dispersion for 20-40 min to obtain the composite dispersion.

[0009] Step S3: Prepare a premixed slurry by adding micron-sized spherical silver powder, micron-sized flake silver powder, and modified glass powder to the remaining recyclable organic carrier, stirring and mixing, and then grinding the mixture through a three-roll mill to a fineness of <8μm to obtain the premixed slurry.

[0010] Step S4: Prepare conductive paste by mixing the composite dispersion with the premixed paste, stirring and ultrasonically dispersing to obtain a uniform conductive paste.

[0011] Step S5, Coating and Solvent Pre-recovery: The conductive paste is coated onto the substrate surface to obtain a wet film. The wet film is placed in a closed recovery device and distilled under reduced pressure at 40-60℃ and 0.03-0.06MPa to recover the organic solvent.

[0012] Step S6: Drying and low-temperature sintering. After drying the pre-recovered wet film, sinter it at 350-450℃ for 30-60 minutes and then let it cool naturally to room temperature.

[0013] Step S7: Post-processing, the sintered coating is polished and cleaned to obtain a conductive coating;

[0014] The raw materials, by mass parts, are: 60-80 parts conductive filler, 1-5 parts composite dispersant, 10-25 parts recyclable organic solvent system, 3-10 parts modified glass powder, 0.5-3 parts additives, and 1-4 parts thickener;

[0015] The conductive filler comprises 40-60 parts of micron-sized spherical silver powder, 5-20 parts of nano-conductive filler, and 5-20 parts of micron-sized flake silver powder.

[0016] The composite dispersant is composed of a main dispersant and an auxiliary dispersant in a mass ratio of 2-4:1;

[0017] The recyclable organic solvent system is composed of a low-volatile organic solvent and a co-solvent in a mass ratio of 3-5:1;

[0018] The modified glass powder is a B2O3-SiO2-ZnO-Li2O series glass powder.

[0019] It should be noted in the scheme that the average particle size of the micron-sized spherical silver powder is 1.0-3.0μm and the tap density is >4.0g / cm³; the nano-conductive filler is selected from one or two of nano-silver powder and nano-copper powder, with an average particle size of 50-200nm; and the average flake size of the micron-sized flake silver powder is 1.0-2.0μm and the flake thickness is <100nm.

[0020] It is further worth noting that the main dispersant is selected from one or more of citric acid, sodium citrate, and polyvinylpyrrolidone; the auxiliary dispersant is selected from one or two of silane coupling agent KH550, silane coupling agent KH560, and polyethylene glycol.

[0021] Furthermore, it should be noted that the low-volatile organic solvent is selected from one or both of propylene glycol methyl ether acetate and ethylene glycol butyl ether; the co-solvent is selected from one of ethanol and isopropanol; the recovered organic solvent is purified by distillation and reused in step S1, with a solvent recovery rate ≥90% and a reuse rate ≥85%.

[0022] In a preferred embodiment, the mass ratio of the components of the modified glass powder is 45-65% B2O3, 10-20% SiO2, 15-30% ZnO, and 1-5% Li2O.

[0023] In a preferred embodiment, in step S2, the ultrasonic dispersion power is 300-500W and the high-speed shear dispersion speed is 8000-12000r / min; in step S4, the stirring speed is 5000-8000r / min and the ultrasonic dispersion time is 15-25min.

[0024] In a preferred embodiment, the thickener is selected from one or two of ethyl cellulose and nitrocellulose; the auxiliary agent is selected from one or more of lecithin, castor oil, and polyoxyethylene castor oil.

[0025] In a preferred embodiment, in step S5, the coating method is selected from screen printing, spraying or scraping; in step S6, the drying temperature is 80-120℃ and the drying time is 15-30min.

[0026] In a preferred embodiment, the substrate is selected from a ceramic substrate, a metal substrate, or a flexible polymer substrate.

[0027] Compared with the prior art, the method for preparing a solvent-recovery type nano-conductive filler-dispersed conductive coating provided by the present invention has at least the following beneficial effects:

[0028] (1) This invention avoids the formation of VOCs from the volatilization of organic solvents and pollutes the atmosphere through a fully closed solvent recovery process, which solves the problem of solvent pollution in traditional processes. Compared with the existing production mode without solvent recovery, this invention reduces VOC emissions, meets the policy requirements for green production in the current electronic materials industry, and enhances the environmental competitiveness of the products. Furthermore, by distilling and purifying to remove trace filler particles, additives and other impurities from the solvent, the key properties of the recovered solvent, such as viscosity and solubility, are consistent with those of the new solvent. The conductive paste and coating prepared after reuse do not show significant attenuation in their core indicators such as conductivity and adhesion, ensuring the stability of the production process and the consistency of product quality.

[0029] (2) The present invention adopts a synergistic dispersion scheme of "main dispersant + auxiliary dispersant + ultrasonic-high-speed shear composite process". The main dispersant reduces the surface energy of the nano-conductive filler through electrostatic adsorption, and the auxiliary dispersant forms a steric barrier. The dual effect inhibits the agglomeration tendency of nano silver powder and nano copper powder from the source, effectively avoiding the problem of discontinuous conductive pathway caused by agglomeration, and providing microstructure guarantee for the high conductivity of the coating. In addition, the phased process avoids the problem of uneven dispersion caused by grinding after mixing fillers of different particle sizes.

[0030] (3) The present invention constructs a dense synergistic conductive network by rationally combining micron-sized spherical silver powder, nano-conductive filler and micron-sized sheet silver powder: micron-sized spherical silver powder serves as the core conductive framework to ensure macroscopic conductive pathways; nano-filler fills the gaps between micron particles, reduces the spacing between conductive particles and lowers the resistance to electron transport; micron-sized sheet silver powder increases the particle contact area by overlapping, further optimizing the conductive pathways.

[0031] (4) This invention introduces Li2O into glass powder to develop B2O3-SiO2-ZnO-Li2O modified glass powder. Low-temperature sintering not only significantly reduces energy consumption, but also avoids thermal damage to flexible polymer substrates caused by high temperatures. This allows the coating to be adapted to various substrates such as ceramics, metals, and flexible polymers, breaking through the limitation of existing technologies that are only adapted to AlN ceramic substrates, and expanding the application scenarios in emerging fields such as flexible displays and flexible solar cells. Attached Figure Description

[0032] Figure 1 This is a flowchart of the method for preparing a solvent-recovery type nano-conductive filler dispersion conductive coating according to the present invention. Detailed Implementation

[0033] The present invention will be further described below with reference to embodiments.

[0034] See Figure 1 As shown, the present invention provides a method for preparing a solvent-recoverable nano-conductive filler-dispersed conductive coating, comprising the following steps:

[0035] S1. Preparation of recyclable organic carriers

[0036] Add the recyclable organic solvent system, thickener, and additives to the reactor in proportion, stir at 70-85℃ for 30-60 minutes until completely dissolved, and cool to room temperature to obtain a uniform recyclable organic carrier.

[0037] In one embodiment, the specific operation process includes the following steps: according to the mass ratio, 10-25 parts of recyclable organic solvent system (low volatile organic solvent and cosolvent are mixed in a ratio of 3-5:1), 1-4 parts of thickener, and 0.5-3 parts of additive are sequentially added to a reaction vessel equipped with a temperature control device and a stirring device.

[0038] Start the stirring device and set the stirring speed to 300-500 r / min. At the same time, turn on the heating system to raise the temperature inside the reactor to 70-85℃ and maintain this temperature while stirring for 30-60 minutes.

[0039] Observe the system status in real time during stirring until the thickener is completely dissolved, the additives are evenly dispersed, and the system is a transparent or semi-transparent uniform liquid with no visible particles or stratification.

[0040] Turn off the heating system, stop stirring, and allow it to cool naturally to room temperature (25±5℃) to obtain a recyclable organic carrier. Seal and store for later use.

[0041] Specifically, a temperature range of 70-85℃ ensures that thickeners (such as ethyl cellulose and nitrocellulose) dissolve rapidly in the organic solvent system while avoiding excessively high temperatures that could lead to the evaporation and loss of co-solvents (such as ethanol and isopropanol), and also prevents the thermal decomposition of additives (such as lecithin). The stirring time is 30-60 minutes, optimized according to the dissolution rate of the thickener to ensure complete dissolution and prevent undissolved thickener particles from affecting the uniformity of the subsequent slurry. Cooling at room temperature prevents local agglomeration or sudden changes in system viscosity when the high-temperature carrier directly contacts the subsequent low-temperature raw materials.

[0042] By selecting a recyclable system with low volatility and co-solvents to replace difficult-to-recover solvents such as terpineol in existing technologies, a prerequisite for subsequent closed-loop solvent recovery is provided, solving the problems of solvent waste and VOC pollution in traditional processes. The thickener forms a network structure through dissolution, which is suitable for subsequent coating processes (screen printing, spraying, etc.) and avoids slurry flow or uneven coating. Additives (such as castor oil and lecithin) are uniformly dispersed in the carrier. When mixed with conductive fillers and glass powder, they can reduce the solid-liquid interfacial tension and improve the wetting effect of the fillers, laying the foundation for uniform dispersion. Through temperature-controlled stirring and room temperature cooling processes, the components of the carrier are ensured to be uniformly integrated, and there is no stratification or precipitation during long-term storage, ensuring the consistency of subsequent slurry preparation.

[0043] S2. Preparation of composite dispersion

[0044] The composite dispersant is added to a portion of the recyclable organic carrier (accounting for 30-50% of the total mass of the organic carrier) and ultrasonically dispersed at a power of 300-500W for 10-20 minutes to ensure uniform dispersion of the dispersant. Then, the nano-conductive filler is added and high-speed sheared dispersed at a speed of 8000-12000r / min for 20-40 minutes. Through the combined effect of ultrasonic dispersion and high-speed shearing, the initial agglomerates of the nano-filler are broken, allowing the dispersant molecules to be fully adsorbed on the surface of the nano-filler, forming a stable composite dispersion, thus inhibiting the agglomeration of the nano-filler from the source.

[0045] In one embodiment, the specific operation process includes the following steps: take 30-50% of the total amount of recyclable organic carrier prepared in step S1, add 1-5 parts of composite dispersant (the main dispersant and the auxiliary dispersant are mixed at a ratio of 2-4:1), and transfer it into an ultrasonic dispersion device.

[0046] Set the ultrasonic power to 300-500W and ultrasonically disperse for 10-20 minutes to allow the dispersant molecules to diffuse evenly in the carrier and form a uniform dispersion system.

[0047] Add 5-20 parts of nano-conductive filler (nano silver powder, nano copper powder or a mixture thereof, with an average particle size of 50-200 nm) according to the formula, and transfer the mixture into a high-speed shear disperser.

[0048] Set the shearing speed to 8000-12000 r / min and continue shearing and dispersing for 20-40 min. Take samples every 5 min during this period and observe until there are no visible agglomerated particles in the system and the system is in a homogeneous suspension state to obtain a composite dispersion.

[0049] Specifically, when the ultrasonic power is set to 300-500W, too low a power will not be able to break the intermolecular forces of the dispersant, while too high a power will easily lead to local overheating and evaporation of the solvent. An ultrasonic time of 10-20 minutes can ensure uniform dispersion of the dispersant and avoid excessively high local concentrations. The shearing speed is set to 8000-12000 r / min. The shearing force generated by this speed can effectively break the initial agglomerates of the nanofillers. A shearing time of 20-40 minutes ensures complete dissociation of the agglomerates. The carrier dosage is 30-50%. Sufficient carrier volume provides space for the dispersion of nanofillers and avoids secondary agglomeration caused by excessively high filler concentration.

[0050] The primary dispersant (such as citric acid and polyvinylpyrrolidone) adheres to the surface of the nanofiller through electrostatic adsorption, reducing surface energy; the auxiliary dispersant (such as silane coupling agent KH550) forms a steric barrier. The two work synergistically to fundamentally solve the problems of easy agglomeration of silver nanopowder and discontinuous conductive pathways in existing technologies. The combination of ultrasonic and high-speed shear composite processes allows for microscopic uniform mixing of the dispersant and the carrier through ultrasonication, and mechanical dissociation of nanofiller agglomerates through high-speed shearing. This dual action ensures that the composite dispersion does not exhibit significant agglomeration during long-term storage. After uniform dispersion, the nanofiller can precisely fill the gaps between micron-sized silver powder particles during subsequent mixing, laying the microstructural foundation for the formation of a dense conductive network and improving the conductivity of the coating.

[0051] S3. Preparation of premixed slurry

[0052] Micron-sized spherical silver powder, micron-sized flake silver powder, and modified glass powder are added to the remaining recyclable organic carrier and stirred at room temperature for 15-30 minutes to initially wet the solid particles. Then, the mixture is ground to a fineness of <8μm using a three-roll mill to obtain a uniform premixed slurry, ensuring that the micron-sized filler and glass powder are evenly dispersed and avoiding large particles from affecting the smoothness of the coating.

[0053] In one embodiment, the specific operation process includes the following steps: take the remaining recyclable organic carrier from step S1, add 40-60 parts of micron-sized spherical silver powder, 5-20 parts of micron-sized flake silver powder, and 3-10 parts of modified glass powder, and transfer it into a stirring and mixing device;

[0054] Set the stirring speed to 500-800 r / min and stir at room temperature (25±5℃) for 15-30 min to fully wet the solid particles (silver powder, glass powder) with the organic carrier and initially form a suspension system.

[0055] The pre-mixed system is fed into a three-roll mill, the gap between the rolls is adjusted to 5-10 μm, and the mill is repeatedly ground 3-5 times. During this process, samples are taken to test the fineness until the fineness of the system is <8 μm and there are no large particles visible to the naked eye, thus obtaining the premixed slurry.

[0056] Specifically, the stirring speed is set at 500-800 r / min. Low-speed stirring can prevent the silver powder particles from being mechanically broken, while ensuring that the carrier fully wets the solid particles. A stirring time of 15-30 min ensures uniform wetting. The gap between the three rollers is 5-10 μm. Based on the particle size optimization of micron-sized silver powder (1.0-3.0 μm) and glass powder (particle size <2 μm), grinding 3-5 times can ensure uniform particle dispersion. A fineness of <8 μm can prevent protrusions or defects from appearing on the coating surface. Stirring at room temperature can prevent the organic carrier from volatilizing due to temperature rise, which would affect the solid-liquid ratio of the slurry.

[0057] The "preliminary wetting + three-roll milling" process solves the problem of uneven mixing of micron-sized silver powder and glass powder in existing technologies, ensuring that micron-sized spherical silver powder (conductive skeleton), flake silver powder (increases contact area), and modified glass powder (bonding and densification) are evenly distributed, thus guaranteeing macroscopic conductivity and mechanical properties. The shearing and extrusion action of the three-roll mill makes the surface of solid particles smoother, further improving the compatibility with organic carriers, making the rheological properties of the slurry more stable, and reducing the likelihood of problems such as screen clogging (screen printing) and sagging (spraying) during subsequent coating.

[0058] S4: Preparation of conductive paste

[0059] The composite dispersion and the premixed slurry are stirred at 5000-8000 r / min for 20-30 min to achieve macroscopic mixing; then ultrasonically dispersed at 300-500 W power for 15-25 min to achieve microscopic uniform dispersion, resulting in a conductive slurry with no agglomeration and appropriate viscosity.

[0060] In one embodiment, the specific operation process includes the following: the composite dispersion prepared in step S2 is slowly added to the premixed slurry in step S3 while stirring, and the addition rate is controlled at 5-10 mL / min (calculated based on the total system volume).

[0061] Transfer to a high-speed mixing device, set the mixing speed to 5000-8000 r / min, and mix for 20-30 minutes to achieve uniform mixing at the macroscopic level;

[0062] The mixture is then transferred to an ultrasonic dispersion device, the ultrasonic power is set to 300-500W, and ultrasonic dispersion is performed for 15-25 minutes to achieve uniform dispersion at the microscopic level.

[0063] After dispersion, the viscosity of the slurry was measured using a rotational viscometer (8000-20000 mPa·s at 25℃), and the particle size of the agglomerates was measured using a laser particle size analyzer (≤5μm). Once qualified, the conductive slurry was obtained and sealed for later use.

[0064] Specifically, the stirring speed is set at 5000-8000 r / min. High-speed stirring can quickly achieve macroscopic fusion of the composite dispersion and the premixed slurry, avoiding local enrichment or absence of nanofillers. The ultrasonic power is set at 300-500W and the time is set at 15-25min, which can further eliminate microscopic agglomeration that may exist after macroscopic mixing, ensuring that the nanofillers and micron-sized particles are uniformly interwoven. The viscosity is controlled at 8000-20000 mPa·s, which can be adapted to the subsequent coating process, while ensuring that the slurry does not flow easily after coating and the wet film thickness is uniform.

[0065] By employing a composite dispersion process combining macroscopic stirring and microscopic ultrasound, nano-conductive fillers uniformly fill the gaps between micron-sized silver powder particles. The micron-sized flake-like silver powder particles overlap to form a conductive framework, while the nano-fillers fill the voids, creating an integrated "framework-filler" conductive network that significantly improves the conductivity of the coating. This process avoids the uneven particle distribution problem caused by the "mixing before grinding" method in existing technologies, ensuring that all components in the conductive slurry are uniformly distributed at both the macroscopic and microscopic levels, with no localized concentration differences. The stable viscosity and dispersion state make the slurry more adaptable to coating applications, compatible with various processes such as screen printing, spraying, and scraping, meeting the fabrication needs of different electronic devices.

[0066] S5, Coating and Solvent Pre-recovery

[0067] Conductive paste is coated onto the substrate surface using screen printing, spraying, or scraping methods, with the wet film thickness controlled at 5-30 μm. The wet film is then placed in a closed recovery device and subjected to vacuum distillation at 40-60℃ and a negative pressure of 0.03-0.06 MPa. The volatile organic solvents are condensed, collected, and then sent to a distillation purification device to remove trace impurities. The purified solvents are stored in a recovery tank and can be reused in step S1. This step achieves closed-loop recovery of organic solvents, reducing VOC emissions and resource waste.

[0068] In one embodiment, the following operation process is specifically included: selecting a target substrate (ceramic, metal, flexible polymer, etc.) and pre-treating the substrate surface (grinding ceramic substrates to remove impurities, degreasing and removing rust from metal substrates, and cleaning and dusting flexible substrates).

[0069] Using a suitable coating method (screen printing: 200-400 mesh, squeegee pressure 0.1-0.3MPa; spraying: nozzle diameter 0.2-0.5mm, spraying distance 10-20cm; squeegee: squeegee gap 5-30μm), the conductive paste is coated onto the substrate surface, and the wet film thickness is controlled at 5-30μm;

[0070] Immediately transfer the substrate coated with the wet film into the coating chamber of the closed recovery device, close the chamber door, and ensure that the device is sealed.

[0071] Start the closed recovery system, set the distillation temperature to 40-60℃ and the negative pressure to 0.03-0.06MPa, and start vacuum distillation;

[0072] During distillation, solvent vapor enters the condenser through a pipeline (condensation temperature 5-10℃), condenses into a liquid state, and then flows into the rectification and purification unit (rectification column temperature gradient 30-60℃) to remove trace amounts of filler particles, additives, and other impurities (purity ≥98%).

[0073] The purified organic solvent is collected in a recovery tank and distilled for 15-30 minutes until there is no obvious solvent luster on the wet film surface. The solvent recovery rate is tested (≥90%) to complete the solvent pre-recovery.

[0074] Specifically, the coating parameters are optimized according to the substrate type and wet film thickness requirements. For example, low-pressure screen printing is used for flexible substrates to avoid substrate damage; the wet film thickness of 5-30μm is adapted to the conductive layer thickness requirements of different electronic devices; the distillation temperature is set at 40-60℃ and the negative pressure is set at 0.03-0.06MPa, which can efficiently volatilize recyclable organic solvent systems (such as propylene glycol methyl ether acetate and ethanol) while avoiding excessive temperature from causing wet film flow or premature agglomeration of nanofillers; the negative pressure environment accelerates solvent volatilization and improves recovery efficiency; the condensation temperature is set at 5-10℃ to ensure complete condensation of solvent vapor and reduce solvent loss; the distillation temperature gradient is set at 30-60℃ to achieve effective separation of solvent and impurities and ensure the purity of the recovered solvent.

[0075] By using a closed-loop, vacuum distillation-condensation-rectification integrated system, the core problems of organic solvent evaporation and waste, and environmental pollution in existing technologies are solved. The pre-recovery process is gentle (low temperature, low pressure), avoiding rapid solvent evaporation that could lead to wet film shrinkage and cracking, ensuring uniform and defect-free wet film thickness. Most of the organic solvent is recovered in advance, reducing the risk of solvent residue in the subsequent drying and sintering processes, and preventing residual solvent from affecting the coating's density and conductivity. Multiple coating methods are available, combined with substrate pretreatment, to ensure the initial adhesion of the slurry to different substrates, laying the foundation for high adhesion after subsequent sintering.

[0076] S6. Drying and Low-Temperature Sintering

[0077] The pre-recovered wet film is dried at 80-120℃ for 15-30 minutes to remove residual trace solvents; then the substrate and coating are placed together in a sintering furnace and sintered at 350-450℃ for 30-60 minutes. The modified glass powder melts and fills the gaps between particles to form a dense conductive network; low-temperature sintering not only reduces energy consumption, but also avoids damage to flexible substrates, etc., caused by high temperature.

[0078] In one embodiment, the specific operation process includes the following steps: opening the sealed recycling device, taking out the pre-recycled substrate and wet film, and transferring them to a drying oven;

[0079] Set the drying temperature to 80-120℃ and the drying time to 15-30 minutes. Start the drying oven to remove any residual solvent (residual amount <0.5%) from the wet film.

[0080] After drying, the substrate and the dry film are placed together in a sintering furnace and protected with nitrogen or argon gas (oxygen content <1%) to prevent silver powder oxidation.

[0081] Set the sintering temperature to 350-450℃, the heating rate to 5-10℃ / min, and hold at the target temperature for 30-60min for low-temperature sintering.

[0082] After sintering, the heating system is turned off, and the inert gas atmosphere is maintained. The mixture is allowed to cool naturally to room temperature (25±5℃) to obtain a preliminary sintered conductive coating.

[0083] Specifically, the drying temperature is set at 80-120℃ and the time is set at 15-30 minutes. Low-temperature, long-time drying can thoroughly remove residual solvents and avoid high-temperature, rapid drying that can cause the coating surface to crust over and the internal solvent to be unable to drain, resulting in pores. The sintering temperature is set at 350-450℃, which, based on the low melting point of the modified glass powder (B2O3-SiO2-ZnO-Li2O system), allows the glass powder to melt while avoiding thermal damage to the flexible substrate (such as PET). Inert gas protection is used to prevent the silver powder from oxidizing during sintering to form silver oxide, which would reduce conductivity. The heating rate is set at 5-10℃ / min, which slowly increases the temperature to avoid internal stress caused by the difference in thermal expansion coefficients between the coating and the substrate, which could lead to coating cracking and peeling.

[0084] Modified glass powder melts at 350-450℃, filling the gaps between conductive particles and densifying the coating. This solves the problems of high energy consumption and limited substrate compatibility in existing technologies, reducing energy consumption while maintaining compatibility with low-temperature resistant substrates such as flexible polymers. During sintering, the nano-conductive filler, due to its low melting point caused by surface effects, can act as a sintering aid to promote the bonding between micron-sized silver powder particles, further optimizing the "micron-nano" conductive network and improving conductivity and stability. The molten glass powder undergoes physical adsorption and chemical bonding with the substrate surface, while simultaneously forming a strong adhesive structure with the conductive particles, resulting in a coating adhesion of ≥5B (cross-cut adhesion test), solving the problems of easy coating peeling and cracking in existing technologies.

[0085] S7, Post-processing

[0086] The sintered coating was lightly polished to remove surface burrs, and then the surface residue was cleaned with anhydrous ethanol to obtain a smooth and dense solvent-recoverable nano-conductive filler-dispersed conductive coating.

[0087] In one embodiment, the specific operation process includes the following steps: Take out the cooled substrate and conductive coating, and use 1000-2000 grit fine sandpaper to gently polish the coating surface at a speed of 50-100 r / min to remove surface burrs, glass phase precipitates and other impurities that may be generated during the sintering process.

[0088] Wipe the coating surface with a lint-free cloth soaked in anhydrous ethanol to remove dust and residual impurities generated during sanding;

[0089] The coating was tested for performance: a four-probe tester was used to test the sheet resistance, a cross-cut adhesion tester was used to test the adhesion (≥5B required), and a microscope was used to observe the surface smoothness of the coating (roughness Ra<0.5μm).

[0090] After passing the inspection, the final solvent-recovery type nano-conductive filler dispersed conductive coating is obtained; unqualified products can be reworked according to the defects.

[0091] Specifically, the sandpaper grit should be 1000-2000 grit. Fine sandpaper can remove surface impurities while avoiding scratching the main structure of the coating. The sanding speed should be set at 50-100 r / min. Low-speed sanding prevents excessive wear on the coating and ensures that the coating thickness meets the requirements. Wiping with anhydrous ethanol can effectively remove dust and impurities because anhydrous ethanol is volatile and leaves no residue, without affecting the coating performance.

[0092] Organic solvents are recovered through closed-loop vacuum distillation, significantly reducing VOC emissions and solvent consumption, and lowering overall production costs. The recovered solvents are purified by distillation and maintain stable performance, without affecting product quality. A composite dispersion mechanism of "composite dispersant + ultrasonic dispersion + high-speed shearing" is adopted. The main dispersant adsorbs onto the surface of the nanofiller to reduce surface energy, while the auxiliary dispersant forms steric hindrance, effectively inhibiting the agglomeration of the nanofiller. No significant agglomeration occurs after long-term storage. The nano-conductive filler fills the gaps between micron-sized silver powders, while the micron-sized flake-like silver powders increase the contact area. Modified glass powder enhances the coating's density. Li2O is added to the modified glass powder, and the glass powder has good thermal expansion coefficient matching with various substrates such as ceramics, metals, and flexible polymers, resulting in no peeling or cracking. Drying and low-temperature sintering processes thoroughly remove solvent residues, resulting in a high-density coating with excellent aging resistance.

[0093] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A method for preparing a solvent-recovered, nanoelectrically conductive filler-dispersed, electrically conductive coating, characterized by: The method comprises the following steps: Step S1, preparing a recyclable organic carrier, adding a recyclable organic solvent system, a thickening agent, and an additive into a reaction kettle in proportion, stirring at 70-85°C for 30-60 min until completely dissolved, and cooling to room temperature to obtain the recyclable organic carrier; Step S2, preparing a composite dispersion liquid, adding a composite dispersant into part of the recyclable organic carrier, ultrasonic dispersing for 10-20 min, then adding nano conductive fillers, and high-speed shearing dispersing for 20-40 min to obtain the composite dispersion liquid; Step S3, preparing a premixed slurry, adding micron-level spherical silver powder, micron-level flaky silver powder, and modified glass powder into the remaining recyclable organic carrier, stirring and mixing, and then grinding to a fineness of <8μm by a three-roll mill to obtain the premixed slurry; Step S4, preparing a conductive slurry, mixing the composite dispersion liquid with the premixed slurry, stirring and ultrasonic dispersing to obtain a uniform conductive slurry; Step S5, coating and solvent pre-recovery, coating the conductive slurry on the surface of a substrate to obtain a wet film, and placing the wet film in a closed recovery device for distillation under reduced pressure at 40-60°C and a negative pressure of 0.03-0.06MPa to recover the organic solvent; Step S6, drying and low-temperature sintering, drying the wet film after pre-recovery, sintering at 350-450°C for 30-60 min, and naturally cooling to room temperature; Step S7, post-treatment, polishing and cleaning the sintered coating to obtain a conductive coating; The raw materials comprise, by mass fraction, 60-80 parts of conductive fillers, 1-5 parts of a composite dispersant, 10-25 parts of a recyclable organic solvent system, 3-10 parts of modified glass powder, 0.5-3 parts of an additive, and 1-4 parts of a thickening agent; The conductive fillers comprise 40-60 parts of micron-level spherical silver powder, 5-20 parts of nano conductive fillers, and 5-20 parts of micron-level flaky silver powder; The composite dispersant is composed of a main dispersant and an auxiliary dispersant in a mass ratio of 2-4:1; The recyclable organic solvent system is composed of a low-volatility organic solvent and a cosolvent in a mass ratio of 3-5:1; The modified glass powder is a B2O3-SiO2-ZnO-Li2O system glass powder.

2. The method according to claim 1, wherein the solvent recovery type nanoelectrically conductive filler dispersed electrically conductive coating preparation method is characterized by: The micron-level spherical silver powder has an average particle size of 1.0-3.0μm and a tap density of >4.0g / cm³; the nano conductive fillers are selected from one or both of nano silver powder and nano copper powder, and have an average particle size of 50-200nm; and the micron-level flaky silver powder has an average flake diameter of 1.0-2.0μm and a flake thickness of <100nm.

3. The method according to claim 1, wherein the solvent recovery type nanoscale conductive filler dispersed conductive coating preparation method is characterized by: The main dispersant is selected from one or more of citric acid, sodium citrate, and polyvinylpyrrolidone; and the auxiliary dispersant is selected from one or both of silane coupling agent KH550 and silane coupling agent KH560.

4. The method according to claim 1, wherein the solvent recovery type nanoscale conductive filler dispersed conductive coating preparation method is characterized by: The low-volatility organic solvent is selected from one or both of propylene glycol methyl ether acetate and ethylene glycol butyl ether; the cosolvent is selected from one of ethanol and isopropyl alcohol; the recovered organic solvent is repeatedly used in step S1 after rectification and purification, and has a solvent recovery rate of ≥90% and a repeated utilization rate of ≥85%.

5. The method according to claim 1, wherein the solvent recovery type nanoscale conductive filler dispersed conductive coating preparation method is characterized by: The modified glass powder has the following mass ratio: B2O345-65%, SiO210-20%, ZnO15-30%, and Li2O1-5%.

6. The method according to claim 1, wherein the solvent recovery type nanoscale conductive filler dispersed conductive coating preparation method is characterized by: In the step S2, the ultrasonic dispersion power is 300-500 W, and the high-speed shearing dispersion rotating speed is 8000-12000 r / min; in the step S4, the stirring rotating speed is 5000-8000 r / min, and the ultrasonic dispersion time is 15-25 min.

7. The method according to claim 1, wherein the solvent recovery type nanoscale conductive filler dispersed conductive coating preparation method is characterized by: The thickening agent is selected from one or both of ethyl cellulose and nitrocellulose; and the auxiliary agent is selected from one or more of lecithin, castor oil and polyoxyethylene castor oil.

8. The method according to claim 1, wherein the solvent recovery type nanoscale conductive filler dispersed conductive coating preparation method is characterized by: In the step S5, the coating mode is selected from silk screen printing, spraying or scraping; and in the step S6, the drying temperature is 80-120 ℃, and the drying time is 15-30 min.

9. The method according to claim 1, wherein the solvent recovery type nanoscale conductive filler dispersed conductive coating preparation method is characterized by: The substrate is selected from one of a ceramic substrate, a metal substrate and a flexible polymer substrate.

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