Preparation process of flaky silver-coated copper powder and conductive paste

Abstract

This invention discloses a process for preparing flake-shaped silver-coated copper powder, comprising the following steps: S1, preparing a dispersant; S2, preparing flake-shaped copper powder; S3, preparing flake-shaped silver-coated copper powder. This invention, through precise control of the reaction and the preparation of an effective dispersant system, precisely controls the morphology, particle size, and silver plating amount of the flake-shaped copper powder, and also provides a silver-coated copper powder electronic conductive paste that can be sintered in air.

Description

Technical Field

[0001] This invention relates to the field of copper powder and conductive paste preparation, and specifically to a preparation process for flake-shaped silver-coated copper powder and conductive paste. Background Technology

[0002] Silver-coated copper powder is a composite metal powder material that uses advanced surface treatment technology to deposit silver plating layers of different thicknesses on the surface of copper micro- and nano-particles, thereby improving the oxidation resistance and conductivity of copper powder.

[0003] Silver-coated copper powder can be prepared by selecting copper powders with different morphologies, silver content, and surface modifications according to application requirements. The material offers high design flexibility and can be widely used in conductive and electromagnetic shielding fields such as microelectronics, solar cells, and communication equipment.

[0004] Mechanical ball milling, melt atomization, and electroless plating are the main publicly reported methods for preparing silver-coated copper powder. Electroless plating is currently the simplest, lowest-cost, and most widely used method, and is recognized as the most suitable means for metal coating of powder surfaces, i.e., for preparing silver-coated copper powder. For example, Chinese patent CN102773475B uses a displacement reaction to coat a layer of silver on the surface of copper powder, and then uses a reducing agent to reduce silver nitrate to make the silver layer more dense. Another example is Chinese patent CN100467169C, which describes a preparation process for Cu-Ag core-shell composite metal powder. This process includes a front-end process of pre-plating, two reduction treatments, and two atmosphere furnace densification treatments; the back-end process, such as Chinese patent 100429727C, discloses a copper-silver alloy conductive paste and its preparation method. Due to the low melting point of the metal phase, it can be sintered in a vacuum. Currently, there are few methods that combine the front-end and back-end processes, effectively control costs, and achieve the target requirements.

[0005] Conductive paste, also known as conductive adhesive, is a mixture of precious metal powder, base metal powder, glass powder, and synthetic resin. The emergence of silver-coated copper powder satisfies the current requirements for conductive pastes where the metal powder must possess excellent conductivity, be economical, and durable. Simultaneously, the performance of the conductive paste truly reflects the quality of the silver-coated copper powder. Therefore, silver-coated copper powder and conductive paste are inextricably linked in application and validation. By adjusting the synthesis method of silver-coated copper powder in real time based on the performance of the conductive paste, a high degree of unification between production and application can be achieved, thereby reducing costs and increasing efficiency. Summary of the Invention

[0006] One technical problem solved by this invention is the end-to-end preparation process from front-end raw material preparation to back-end application. It provides a highly efficient end-to-end technical process for preparing flake-shaped silver-coated copper powder paste, including reduction preparation of flake-shaped copper powder, chemical silver plating preparation of flake-shaped silver-coated copper powder, and preparation of silver-coated copper powder conductive paste. The aim is to precisely control the morphology, particle size, and silver plating amount of the flake-shaped copper powder by precisely controlling the reaction and preparing an effective dispersant system. At the same time, it provides a silver-coated copper powder electronic conductive paste that can be sintered in air.

[0007] The technical solution adopted in this invention is: a preparation process of flake-shaped silver-coated copper powder, comprising the following steps: S1, preparation of dispersant: N-vinylpyrrolidone, benzoyl peroxide and butyl acrylate in a mass ratio of 2250:1:1500 are placed in a three-necked flask, sealed with a rubber stopper and connected to a syringe tube. The air in the flask is removed by a vacuum pump, and then purged with nitrogen three times. After repeating the operation three times, distilled water is injected into the flask with a syringe, stirring is started and an oil bath is used, and the reaction is carried out for 24 hours, with nitrogen purging maintained throughout the reaction. After the reaction is completed, the transparent liquid in the flask is transferred to a rotary evaporator, and after natural cooling, most of the water is removed on a rotary evaporator. Then the remaining viscous liquid is gradually separated. The product was added dropwise to diethyl ether, and then filtered to remove the ether. The remaining solid product was dried in a vacuum drying oven at 40–60°C for 36–60 h, followed by further drying to remove water for 10–20 h. The product was then ground into powder, and the resulting powder was the modified dispersant named BA-PVP. The powder was mixed with a certain amount of copper salt to prepare an aqueous solution of BA-PVP. S2, Preparation of flake copper powder: A certain amount of aqueous solution of copper salt with a concentration of 0.1–0.4 mol / L, aqueous solution of sodium hypophosphite with a concentration of 0.07–0.28 mol / L, and aqueous solution of BA-PVP were prepared. First, the aqueous solution of copper salt was placed in the first reactor vessel, and the first reactor vessel was... Place the solution in a constant temperature water bath at a temperature below 40°C, and rapidly add BA-PVP aqueous solution while stirring. After the reaction is complete, adjust the pH of the copper salt aqueous solution and sodium hypophosphite aqueous solution to 0.25–0.75. Then raise the temperature to 70–90°C, slowly add sodium hypophosphite aqueous solution dropwise to the copper salt aqueous solution while stirring rapidly. After the reaction is complete, let it stand, pour off the supernatant, and then centrifuge and wash to obtain flake copper powder; S3, prepare a certain amount of 5% dilute sulfuric acid, 20% ammonia solution, 0.18–0.19 mol / L silver nitrate aqueous solution, and 0.13–0.15 mol / L glucose aqueous solution; add the ammonia solution dropwise to the silver nitrate solution while stirring until... The solution is clarified to obtain a silver ammonia solution. The flake copper powder obtained in step S2 above is soaked in dilute sulfuric acid for a certain period of time, washed with deionized water until neutral, and filtered. The filtered copper powder is added to an appropriate amount of deionized water to prepare a suspension, and 3% ammonia solution by mass of the suspension is added and stirred thoroughly. The suspension is placed in a second reactor vessel and placed in a constant temperature water bath at 20-30°C. Under stirring, the BA-PVP aqueous solution prepared in step S2 is added, and the silver ammonia solution and glucose aqueous solution prepared in this step are added slowly at the same time. After the reaction is completed, the mixture is allowed to stand, filtered, washed, and dried in a vacuum drying oven at 50°C. The resulting product is flake silver-coated copper powder.

[0008] A process for preparing a conductive paste includes the following steps: Step 1: Preparing flake-shaped silver-coated copper powder according to any one of claims 1 to 5; Step 2: Preparing flake-shaped silver powder: preparing a silver nitrate aqueous solution with a concentration of 0.5–0.8 mol / L and an ascorbic acid aqueous solution with a concentration of 0.8–1.2 mol / L; slowly adding the prepared 20% ammonia solution to the silver nitrate solution while stirring until the solution becomes clear to prepare a silver ammonia solution; placing an appropriate amount of ascorbic acid aqueous solution and a BA-PVP aqueous solution with a copper salt mass of 5% in a third reaction vessel, and placing the third reaction vessel in a constant temperature water bath at a temperature of 20–30°C; slowly adding the prepared silver ammonia solution while stirring; after the reaction is complete, allowing it to stand, filtering, washing, and drying in a vacuum drying oven at 50°C; the resulting product is flake-shaped silver powder; Step 3: Preparation of the organic carrier: Weigh out the components of the organic carrier according to the following mass percentages: 40% terpineol, 25% butyl carbitol, 10% butyl carbitol acetate, 5% thixotropic agent, 5% thickener, 10% surfactant, and 5% plasticizer in a beaker and mix. Heat in a water bath at a constant temperature of 60℃ for 2 hours until the mixture is dissolved and homogeneous, then keep warm for another hour. After that, cool at room temperature and cover with plastic wrap to prevent solvent evaporation. The prepared organic carrier is colorless, transparent, and viscous. Fourth step: Preparation of conductive paste: Weigh out glass powder, silver powder, and silver-coated copper powder according to the following mass percentages: 5:70:5:20. Mix them together and grind them finely until homogeneous. Then add the organic carrier according to the proportion and stir and grind in a mortar until homogeneous to complete the preparation of the conductive paste.

[0009] As a further improvement of the present invention, in step S1, the oil bath temperature is 70–80°C. The purpose of controlling the temperature at 70–80°C during the oil bath reaction is that within this temperature range, the chemical reaction can maintain a moderate rate, neither too fast nor too slow. Too fast a rate may lead to runaway reaction or unstable products, while too slow a rate may affect experimental efficiency and product yield. Simultaneously, most of the compounds involved in the reaction remain stable at this temperature, making them less prone to thermal decomposition or the generation of unnecessary byproducts.

[0010] As a further improvement of the present invention, in step S1, the temperature of the dried water is controlled at 100-120°C. Within this temperature range, the moisture in the substance can be effectively evaporated without compromising its thermal stability.

[0011] As a further improvement of the present invention, in step S2, the copper salt content of the BA-PVP aqueous solution is 5% by mass. Using a BA-PVP aqueous solution with 5% copper salt content can lead to several issues. If the amount of dispersant is too small, the dispersion effect will not be optimal, and it will not effectively hinder grain growth. If the amount of dispersant is too large, it will remain in the reaction solution, and excessive dispersant will compress the double layer of the reactant ions, reducing the absolute value of the Zeta potential and thus reducing the stabilizing effect of electrostatic repulsion. This will affect the stability of the reaction, and the viscosity of the reaction solution will also increase, causing particle growth and agglomeration.

[0012] As a further improvement of the present invention, the salt is at least one of copper sulfate, copper nitrate or copper chloride.

[0013] As a further improvement of the present invention, in the third step, the thickener is ethyl cellulose, the surfactant is ethanol, the plasticizer is tributyl citrate, and the thixotropic agent is hydrogenated castor oil.

[0014] As a further improvement of the present invention, in the fourth step, the mass fraction content of each component of the glass powder is as follows: PbO 46.0%, TeO2 20.0%, SiO2 7.0%, B2O3 9.0%, Li2O 0.4%, Na2O 0.2%, P2O5 4.3%, ZnO 8.6%, TiO2 2%, and V2O5 2.5%.

[0015] The beneficial effects of this invention are as follows: 1. The copolymer dispersant BA-PVP prepared by this invention contains an appropriate amount of vinylpyrrolidone groups, which can act as a steric hindrance to resist the attraction between particles, thereby improving the dispersibility of copper powder. Furthermore, the unsaturated olefin bonds and hydrogen bonds are tightly adsorbed on the surface of the particles, and the resulting macromolecular film inhibits the three-dimensional growth of the particles, thus significantly enhancing the growth orientation of the particles in the two-dimensional plane, thereby forming a sheet-like product; 2. Precise control of the reaction and preparation of an effective dispersant system, thereby precisely controlling the morphology, particle size and silver plating amount of the sheet-like copper powder; 3. The contact mode between granular silver-coated copper powder and silver powder is point contact, and the number of conductive particle contacts is small, thus affecting conductivity. However, the high sheet-like structure of the silver-coated copper powder and silver powder results in a large specific surface area. The silver-coated copper powder and silver powder are layered and spread flat on the coated surface in a leaf-like manner in the conductive paint film, thereby increasing the number of contacts between conductive filler particles. Although the highly sheet-like copper powder increases the reaction difficulty and silver consumption during the silver plating process, its conductivity is much better than that of ordinary spherical silver powder and silver-coated copper powder. Attached Figure Description

[0016] Figure 1 This is a SEM image of the flake-shaped copper powder obtained by the present invention.

[0017] Figure 2 This is the energy dispersive spectroscopy (EDS) spectrum of the flake copper powder prepared according to the present invention.

[0018] Figure 3 This is a SEM image of the flake-shaped silver-coated copper powder obtained by the present invention.

[0019] Figure 4 This is an energy dispersive spectroscopy (EDS) spectrum of the flake-shaped silver-coated copper powder prepared according to the present invention. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Example 1

[0022] A process for preparing flake-shaped silver-coated copper powder and conductive paste includes the following steps:

[0023] S1. Preparation of the dispersant: Add 12g of N-vinylpyrrolidone, 0.4mg of benzoyl peroxide (initiator), and 0.8g of butyl acrylate to a three-necked flask. Place a thermometer inside the flask, seal it with a rubber stopper, and connect a syringe. Evacuate the flask of air using a vacuum pump, then purge with nitrogen three times. Repeat this process three times. Inject distilled water into the flask using a syringe, start stirring, and set the oil bath temperature to 70℃ for 24 hours, maintaining nitrogen purging throughout the reaction. After the reaction, transfer the clear liquid from the flask to a rotary evaporator. After natural cooling, remove most of the water using a rotary evaporator. Add the remaining viscous liquid dropwise to diethyl ether, then filter to remove the ether. Dry the remaining solid product in a vacuum drying oven at 40℃ for 36 hours, then at 100℃ for 10 hours to remove water. Grind the product into powder; the resulting powder is the modified dispersant, named BA-PVP.

[0024] S2. Prepare a certain amount of the following solutions: a 0.1 mol / L copper salt aqueous solution, a 0.07 mol / L sodium hypophosphite aqueous solution, a 5% dilute sulfuric acid solution, a 20% ammonia solution, a 0.18 mol / L silver nitrate aqueous solution, a 0.13 mol / L glucose aqueous solution, a 0.5 mol / L silver nitrate aqueous solution, a 0.8 mol / L ascorbic acid aqueous solution, and a 5% (by weight) BA-PVP aqueous solution of copper salt. Add the ammonia solution dropwise to the 0.18 mol / L and 0.5 mol / L silver nitrate solutions and stir until the solution is clear to obtain silver ammonia solutions, named silver ammonia solution 1 and silver ammonia solution 2.

[0025] S3. First, place the copper salt aqueous solution in the first reactor vessel and place the first reactor vessel in a constant temperature water bath. Under the conditions of room temperature (below 40℃) and stirring, quickly add the BA-PVP aqueous solution. After the reaction is completed, adjust the pH of the copper salt aqueous solution and the sodium hypophosphite aqueous solution to 0.25. Then raise the temperature to 70℃, slowly add the sodium hypophosphite aqueous solution to the copper salt aqueous solution and stir quickly. After the reaction is completed, let it stand and pour off the supernatant. Then, centrifuge and wash to obtain flake copper powder.

[0026] S4. The flake copper powder obtained in the above steps is soaked in dilute sulfuric acid for a certain period of time, washed with deionized water until neutral, and filtered. The filtered copper powder is added to an appropriate amount of deionized water to prepare a suspension. Then, 3% ammonia solution (by weight of the suspension) is added and stirred thoroughly. The suspension is placed in a second reactor vessel and placed in a constant temperature water bath at 20°C. BA-PVP aqueous solution is added under stirring, and the prepared silver ammonia solution 1 and glucose aqueous solution are added slowly at the same time. After the reaction is completed, the mixture is allowed to stand, filtered, washed, and dried in a vacuum drying oven at 50°C. The resulting product is silver-coated copper powder.

[0027] S5. Place an appropriate amount of ascorbic acid aqueous solution and BA-PVP aqueous solution in the third reactor vessel, and place the third reactor vessel in a constant temperature water bath. Set the temperature to 20℃ and slowly add the prepared silver ammonia solution 2 under stirring. After the reaction is completed, let it stand, filter and wash, and place it in a vacuum drying oven at 50℃ to dry. The resulting product is flake silver powder.

[0028] S6. Weigh out the components of the organic carrier according to the following mass percentages: 40% terpineol, 25% butyl carbitol, 10% butyl carbitol acetate, 5% hydrogenated castor oil, 5% ethyl cellulose, 10% ethanol, and 5% tributyl citrate. Mix them in a beaker, heat in a water bath at a constant temperature of 60°C, and stir for 2 hours until the mixture is dissolved and homogeneous. Then keep it at this temperature for another hour. After that, let it cool at room temperature and cover it with plastic wrap to prevent solvent evaporation. The prepared organic carrier is now ready.

[0029] S7. Preparation of conductive paste: Weigh out the glass powder, silver powder and silver-coated copper powder according to the mass percentage of silver powder, silver-coated copper powder, glass powder and organic carrier in the ratio of 5:70:5:20, mix them together, then grind them finely until uniform, then add the organic carrier according to the ratio, stir and grind them in a mortar until they are mixed evenly, and complete the preparation of conductive paste.

[0030] Example 2

[0031] A process for preparing flake-shaped silver-coated copper powder and conductive paste includes the following steps:

[0032] S1. Preparation of the dispersant: Add 15g of N-vinylpyrrolidone, 0.6mg of benzoyl peroxide (initiator), and 1g of butyl acrylate to a three-necked flask. Place a thermometer inside the flask, seal it with a rubber stopper, and connect a syringe. Evacuate the flask of air using a vacuum pump, then purge with nitrogen three times. Repeat this process three times. Inject distilled water into the flask using a syringe, start stirring, and set the oil bath temperature to 75℃ for 24 hours, maintaining nitrogen purging throughout the reaction. After the reaction, transfer the clear liquid from the flask to a rotary evaporator. After natural cooling, remove most of the water using a rotary evaporator. Add the remaining viscous liquid dropwise to diethyl ether, then filter to remove the ether. Dry the remaining solid product in a vacuum drying oven at 60℃ for 60 hours, then at 120℃ for 20 hours to remove water. Grind the product into powder; the resulting powder is the modified dispersant, named BA-PVP.

[0033] S2. Prepare a certain amount of the following solutions: a 0.25 mol / L copper salt aqueous solution, a 0.14 mol / L sodium hypophosphite aqueous solution, a 5% dilute sulfuric acid solution, a 20% ammonia solution, a 0.185 mol / L silver nitrate aqueous solution, a 0.14 mol / L glucose aqueous solution, a 0.6 mol / L silver nitrate aqueous solution, a 1.0 mol / L ascorbic acid aqueous solution, and a 5% (by weight) BA-PVP aqueous solution of copper salt. Add the ammonia solution dropwise to the 0.185 mol / L and 0.6 mol / L silver nitrate solutions and stir until the solution is clear to obtain silver ammonia solutions, named silver ammonia solution 1 and silver ammonia solution 2.

[0034] S3. First, place the copper salt aqueous solution in the first reactor vessel and place the first reactor vessel in a constant temperature water bath. Under the conditions of room temperature (below 40℃) and stirring, quickly add the BA-PVP aqueous solution. After the reaction is completed, adjust the pH of the copper salt aqueous solution and the sodium hypophosphite aqueous solution to 0.5. Then raise the temperature to 80℃, slowly add the sodium hypophosphite aqueous solution to the copper salt aqueous solution and stir quickly. After the reaction is completed, let it stand and pour off the supernatant. Then, centrifuge and wash to obtain flake copper powder.

[0035] S4. The flake copper powder obtained in the above steps is soaked in dilute sulfuric acid for a certain period of time, washed with deionized water until neutral, and filtered. The filtered copper powder is added to an appropriate amount of deionized water to prepare a suspension. Then, 3% ammonia solution (by weight of the suspension) is added and stirred thoroughly. The suspension is placed in a second reactor vessel and placed in a constant temperature water bath at 25°C. BA-PVP aqueous solution is added under stirring, and the prepared silver ammonia solution 1 and glucose aqueous solution are added slowly at the same time. After the reaction is complete, the mixture is allowed to stand, filtered, washed, and dried in a vacuum drying oven at 50°C. The resulting product is silver-coated copper powder.

[0036] S5. Place an appropriate amount of ascorbic acid aqueous solution and BA-PVP aqueous solution in the third reactor vessel, and place the third reactor vessel in a constant temperature water bath. Set the temperature to 25℃ and slowly add the prepared silver ammonia solution 2 under stirring. After the reaction is complete, let it stand, filter and wash, and place it in a vacuum drying oven at 50℃ to dry. The resulting product is flake silver powder.

[0037] S6. Weigh out the components of the organic carrier according to the following mass percentages: 40% terpineol, 25% butyl carbitol, 10% butyl carbitol acetate, 5% hydrogenated castor oil, 5% ethyl cellulose, 10% ethanol, and 5% tributyl citrate. Mix them in a beaker, heat in a water bath at a constant temperature of 60°C, and stir for 2 hours until the mixture is dissolved and homogeneous. Then keep it at this temperature for another hour. After that, let it cool at room temperature and cover it with plastic wrap to prevent solvent evaporation. The prepared organic carrier is now ready.

[0038] S7. Preparation of conductive paste: Weigh out the glass powder, silver powder and silver-coated copper powder according to the mass percentage of silver powder, silver-coated copper powder, glass powder and organic carrier in the ratio of 5:70:5:20, mix them together, then grind them finely until uniform, then add the organic carrier according to the ratio, stir and grind them in a mortar until they are mixed evenly, and complete the preparation of conductive paste.

[0039] Example 3

[0040] A process for preparing flake-shaped silver-coated copper powder and conductive paste includes the following steps:

[0041] S1. Preparation of the dispersant: Add 18g of N-vinylpyrrolidone, 0.8mg of benzoyl peroxide (initiator), and 1.2g of butyl acrylate to a three-necked flask. Place a thermometer inside the flask, seal it with a rubber stopper, and connect a syringe. Evacuate the flask of air using a vacuum pump, then purge with nitrogen three times. Repeat this process three times. Inject distilled water into the flask using a syringe, start stirring, and set the oil bath temperature to 80℃ for 24 hours, maintaining nitrogen purging throughout the reaction. After the reaction, transfer the clear liquid from the flask to a rotary evaporator. After natural cooling, remove most of the water using a rotary evaporator. Add the remaining viscous liquid dropwise to diethyl ether, then filter to remove the ether. Dry the remaining solid product in a vacuum drying oven at 50℃ for 48 hours, then at 110℃ for 15 hours to remove water. Grind the product into powder; the resulting powder is the modified dispersant, named BA-PVP.

[0042] S2. Prepare a certain amount of the following solutions: a 0.4 mol / L copper salt aqueous solution, a 0.28 mol / L sodium hypophosphite aqueous solution, a 5% dilute sulfuric acid solution, a 20% ammonia solution, a 0.19 mol / L silver nitrate aqueous solution, a 0.15 mol / L glucose aqueous solution, a 0.8 mol / L silver nitrate aqueous solution, a 1.2 mol / L ascorbic acid aqueous solution, and a 5% (by weight) BA-PVP aqueous solution of copper salt. Add the ammonia solution dropwise to the 0.19 mol / L and 0.8 mol / L silver nitrate solutions and stir until the solution is clear to obtain silver ammonia solutions, named silver ammonia solution 1 and silver ammonia solution 2.

[0043] S3. First, place the copper salt aqueous solution in the first reactor vessel and place the first reactor vessel in a constant temperature water bath. Under the conditions of room temperature (below 40℃) and stirring, quickly add the BA-PVP aqueous solution. After the reaction is completed, adjust the pH of the copper salt aqueous solution and the sodium hypophosphite aqueous solution to 0.75. Then raise the temperature to 90℃, slowly add the sodium hypophosphite aqueous solution to the copper salt aqueous solution and stir quickly. After the reaction is completed, let it stand and pour off the supernatant. Then, centrifuge and wash to obtain flake copper powder.

[0044] S4. After soaking the flake copper powder obtained in the above steps in dilute sulfuric acid for a certain period of time, wash it with deionized water until neutral and filter it. Add the filtered copper powder to an appropriate amount of deionized water to prepare a suspension. Add 3% ammonia solution by mass of the suspension and stir thoroughly. Place the suspension in a second reactor vessel and place the second reactor vessel in a constant temperature water bath. Set the temperature to 30°C and add BA-PVP aqueous solution under stirring. At the same time, slowly add the prepared silver ammonia solution 1 and glucose aqueous solution. After the reaction is completed, let it stand, filter and wash, and dry it in a vacuum drying oven at 50°C. The product obtained is silver-coated copper powder.

[0045] S5. Place an appropriate amount of ascorbic acid aqueous solution and BA-PVP aqueous solution in the third reactor vessel, and place the third reactor vessel in a constant temperature water bath. Set the temperature to 30℃ and slowly add the prepared silver ammonia solution 2 under stirring. After the reaction is completed, let it stand, filter and wash, and place it in a vacuum drying oven at 50℃ to dry. The resulting product is flake silver powder.

[0046] S6. Weigh out the components of the organic carrier according to the following mass percentages: 40% terpineol, 25% butyl carbitol, 10% butyl carbitol acetate, 5% hydrogenated castor oil, 5% ethyl cellulose, 10% ethanol, and 5% tributyl citrate. Mix them in a beaker, heat in a water bath at a constant temperature of 60°C, and stir for 2 hours until the mixture is dissolved and homogeneous. Then keep it at this temperature for another hour. After that, let it cool at room temperature and cover it with plastic wrap to prevent solvent evaporation. The prepared organic carrier is now ready.

[0047] S7. Preparation of conductive paste: Weigh out the glass powder, silver powder and silver-coated copper powder according to the mass percentage of silver powder, silver-coated copper powder, glass powder and organic carrier in the ratio of 5:70:5:20, mix them together, then grind them finely until uniform, then add the organic carrier according to the ratio, stir and grind them in a mortar until they are mixed evenly, and complete the preparation of conductive paste.

[0048] The table below shows the electrode sheet resistance test results of the conductive paste prepared in the above embodiments, as well as the particle size data and loose packing density of silver-coated copper powder and silver powder.

[0049]

[0050] The data in the table show that the particle size and loose density of the silver-coated copper powder and the flake silver powder are basically at the same level, and the impurity content meets the national standard GB / T 26049-2010, which proves the stability of the production method. The electrode sheet resistance of the conductive pastes obtained in all examples are basically at the same level, and their conductivity is excellent. They can be used as high-quality conductive pastes, which also proves the production stability and economic efficiency of the production method.

[0051] Those skilled in the art should understand that the protection scheme of the present invention is not limited to the above embodiments, and various arrangements, combinations and transformations can be made on the basis of the above embodiments. Without departing from the spirit of the present invention, all transformations made to the present invention fall within the protection scope of the present invention.

Claims

1. A preparation process for flake-shaped silver-coated copper powder, characterized in that: Includes the following steps: S1. Preparation of dispersant: N-vinylpyrrolidone, benzoyl peroxide, and butyl acrylate (mass ratio 2250:1:1500) were placed in a three-necked flask, sealed with a rubber stopper, and connected to a syringe. Air was removed from the flask using a vacuum pump, followed by purging with nitrogen three times. This process was repeated three times. Distilled water was then injected into the flask using a syringe, and stirring and an oil bath were started. The reaction was carried out for 24 hours, with nitrogen purging maintained throughout the process. After the reaction, the transparent liquid in the flask was transferred to a rotary evaporator. After natural cooling, most of the water was removed using a rotary evaporator. The remaining viscous liquid was then added dropwise to diethyl ether, followed by filtration to remove the ether. The remaining solid product was dried in a vacuum drying oven at 40–60°C for 36–60 hours, then dried again for 10–20 hours to remove water. The product was then ground into powder, which was the modified dispersant named BA-PVP. The obtained powder was mixed with a certain amount of copper salt to prepare an aqueous solution of BA-PVP. S2. Preparation of flake copper powder: Prepare a certain amount of copper salt aqueous solution with a concentration of 0.1-0.4 mol / L, sodium hypophosphite aqueous solution with a concentration of 0.07-0.28 mol / L, and BA-PVP aqueous solution: First, place the copper salt aqueous solution in the first reactor vessel and place the first reactor vessel in a constant temperature water bath. At a temperature below 40°C, add the BA-PVP aqueous solution rapidly while stirring. After the reaction is completed, adjust the pH of the copper salt aqueous solution and the sodium hypophosphite aqueous solution to 0.25-0.

75. Then, raise the temperature to 70-90°C and slowly add the sodium hypophosphite aqueous solution dropwise to the copper salt aqueous solution while stirring rapidly. After the reaction is completed, let it stand and pour off the supernatant. Then, centrifuge and wash to obtain flake copper powder. S3. Prepare a certain amount of 5% dilute sulfuric acid, 20% ammonia water, 0.18-0.19 mol / L silver nitrate aqueous solution, and 0.13-0.15 mol / L glucose aqueous solution; Ammonia solution is added dropwise to silver nitrate solution and stirred until the solution becomes clear to obtain silver ammonia solution. The flake copper powder obtained in step S2 is soaked in dilute sulfuric acid for a certain period of time, washed with deionized water until neutral, and filtered. The filtered copper powder is added to an appropriate amount of deionized water to prepare a suspension, and 3% ammonia solution by mass of the suspension is added and stirred thoroughly. The suspension is placed in a second reactor vessel and placed in a constant temperature water bath at 20-30°C. Under stirring, the BA-PVP aqueous solution prepared in step S2 is added, and the silver ammonia solution and glucose aqueous solution prepared in this step are added slowly. After the reaction is completed, the mixture is allowed to stand, filtered, washed, and dried in a vacuum drying oven at 50°C. The resulting product is flake silver-coated copper powder.

2. The preparation process of flake-shaped silver-coated copper powder according to claim 1, characterized in that: In step S1, the oil bath temperature is 70-80℃.

3. The preparation process of flake-shaped silver-coated copper powder according to claim 1, characterized in that: In step S1, the temperature of the dried water is controlled at 100-120℃.

4. The preparation process of flake-shaped silver-coated copper powder according to claim 1, characterized in that: In step S2, the copper salt content of the BA-PVP aqueous solution is 5%.

5. A preparation process for flake-shaped silver-coated copper powder according to any one of claims 1 to 4, characterized in that: The copper salt is at least one of copper sulfate, copper nitrate, or copper chloride.

6. A process for preparing a conductive paste, characterized in that: Includes the following steps: Step 1: Prepare flake-shaped silver-coated copper powder according to any one of claims 1 to 5; Step 2: Preparation of flake silver powder: Prepare a silver nitrate aqueous solution with a concentration of 0.5-0.8 mol / L and an ascorbic acid aqueous solution with a concentration of 0.8-1.2 mol / L. Slowly add the prepared 20% ammonia solution to the silver nitrate solution while stirring until the solution is clear to prepare a silver ammonia solution. Place an appropriate amount of ascorbic acid aqueous solution and a 5% copper salt BA-PVP aqueous solution in a third reactor vessel. Place the third reactor vessel in a constant temperature water bath and set the temperature to 20-30℃. Slowly add the prepared silver ammonia solution while stirring. After the reaction is complete, allow it to stand, filter and wash, and dry it in a vacuum drying oven at 50℃. The obtained product is flake silver powder. Step 3: Preparation of the organic carrier: Weigh out the components of the organic carrier according to the following mass percentages: 40% terpineol, 25% butyl carbitol, 10% butyl carbitol acetate, 5% thixotropic agent, 5% thickener, 10% surfactant, and 5% plasticizer in a beaker and mix them. Heat the mixture in a water bath at a constant temperature of 60°C for 2 hours until the mixture is dissolved and homogeneous, then keep it at that temperature for another hour. After that, cool it to room temperature and cover it with plastic wrap to prevent solvent evaporation. The prepared organic carrier is colorless, transparent, and viscous. Step 4: Preparation of conductive paste: Weigh out glass powder, silver powder and silver-coated copper powder according to the mass percentage of flake silver powder, silver powder and organic carrier in the ratio of 5:70:5:20, mix them together, and then grind them finely until uniform. Then add the organic carrier according to the ratio, stir and grind them in a mortar until they are mixed evenly, and the preparation of conductive paste is completed.

7. The preparation process of the conductive paste according to claim 6, characterized in that: In the third step, the thickener is ethyl cellulose, the surfactant is ethanol, the plasticizer is tributyl citrate, and the thixotropic agent is hydrogenated castor oil.

8. The preparation process of the conductive paste according to claim 6 or 7, characterized in that: In the fourth step, the mass fraction of each component of the glass powder is as follows: PbO 46.0%, TeO2 20.0%, SiO2 7.0%, B2O3 9.0%, Li2O 0.4%, Na2O 0.2%, P2O5 4.3%, ZnO 8.6%, TiO2 2%, and V2O5 2.5%.

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