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

Abstract

The invention discloses a preparation process of flaky silver-coated copper powder, which comprises the following steps: S1, preparing a dispersing agent; s2, flaky copper powder is prepared; and S3, preparing the flaky silver-coated copper powder. According to the silver-coated copper powder electronic conductive paste and the preparation method thereof, the morphology, the particle size and the silver plating amount of the flaky copper powder are accurately controlled by accurately controlling the reaction and preparing an effective dispersing agent system, and meanwhile, the silver-coated copper powder electronic conductive paste capable of being sintered in the air is provided.

Description

Technical Field

[0001] The invention relates to the field of preparation of copper powder and conductive slurry, and in particular to a preparation process of flaky silver-coated copper powder and conductive slurry. Background Art

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

[0003] Silver-coated copper powder can be prepared by selecting different morphology, silver content and surface modification of copper powder according to application requirements. The material is highly designable 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 chemical plating are the main methods for preparing silver-coated copper powder that have been publicly reported. Chemical plating is the method with the simplest process, the lowest preparation cost and the most applications. It is recognized as the most suitable means for metal coating on the surface of powder, that is, the preparation of silver-coated copper powder. For example, Chinese patent CN102773475B uses a replacement 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, a preparation process for Cu-Ag core-shell composite metal powder, which 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. At present, there are few methods that combine the front-end and back-end processes, effectively control costs and meet target requirements.

[0005] Conductive paste Conductive paste, also known as conductive glue, is a mixture of precious metal powder and base metal powder, glass powder and synthetic resin. The emergence of silver-coated copper powder meets the current requirements for metal powder in conductive paste to have excellent conductive properties, be economical and durable. At the same time, the performance of conductive paste can truly reflect the advantages and disadvantages of silver-coated copper powder. For this reason, silver-coated copper powder and conductive paste are inseparable in application and proof. The synthesis method of silver-coated copper powder is adjusted in real time through the performance of conductive paste, which promotes a high degree of unity between production and application, so as to achieve cost reduction and efficiency improvement. Summary of the invention

[0006] A technical problem solved by the present invention is a full-process preparation process from front-end raw material preparation to back-end application, and provides an efficient full-process technical process for preparing flaky silver-coated copper powder slurry, including reducing to prepare flaky copper powder, chemically plating silver to prepare flaky silver-coated copper powder, and preparing silver-coated copper powder conductive slurry. The purpose is to accurately control the morphology, particle size and silver plating amount of the flaky copper powder through precise control of the reaction and preparation of an effective dispersant system, and at the same time provide a silver-coated copper powder electronic conductive slurry that can be sintered in air.

[0007] The technical scheme adopted by the present invention is: a preparation process of flaky silver-coated copper powder, comprising the following steps: S1, preparing a dispersant: putting raw materials of N-vinyl pyrrolidone, benzoyl peroxide and butyl acrylate in a mass ratio of 2250:1:1500 into a three-necked flask, sealing it with a rubber stopper and connecting a cillin tube, evacuating the air in the flask with a vacuum pump, and then purging it with nitrogen three times; after repeating the operation three times, injecting distilled water into the flask with a syringe, starting stirring and oil bathing, reacting for 24 hours, and always keeping nitrogen purging during the reaction process; after the reaction is completed, transferring the transparent liquid in the flask to a rotary evaporator, removing most of the water on a rotary evaporator after natural cooling, and then gradually evaporating the remaining viscous liquid. The solid product is then added dropwise to ether, and then filtered to remove the ether. The remaining solid product is dried in a vacuum drying oven at a drying temperature of 40-60°C for 36-60 hours, and then dried to remove water for 10-20 hours, and ground into powder. The obtained powder is the modified dispersant named BA-PVP; the obtained powder is mixed with a certain amount of copper salt to prepare a BA-PVP aqueous solution; S2, preparation of flaky copper powder: a certain amount of a copper salt aqueous solution with a concentration of 0.1-0.4 mol / L, a sodium hypophosphite aqueous solution with a concentration of 0.07-0.28 mol / L, and a BA-PVP aqueous solution are prepared: first, the copper salt aqueous solution is placed in a first reaction vessel, and the first reaction vessel is Place in a constant temperature water bath, at a temperature below 40°C, quickly add BA-PVP aqueous solution while stirring, after the end, adjust the pH of 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 to the copper salt aqueous solution, and quickly stir, the reaction is completed, stand and pour the supernatant, and then centrifuge and wash to obtain flaky 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; add the ammonia solution dropwise to the silver nitrate solution and stir until The solution is clarified to obtain a silver ammonia solution; the flaky copper powder obtained in the above 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 of the mass of the suspension is added and fully stirred, placed in a second reaction vessel, and the second reaction vessel is placed in a constant temperature water bath, the temperature is set to 20-30°C, and the BA-PVP aqueous solution prepared in step S2 is added under stirring, and the silver ammonia solution and glucose aqueous solution prepared in this step are slowly added at the same time. After the reaction is completed, it is allowed to stand, filtered and washed, and placed in a 50°C vacuum drying oven for drying. The obtained product is a flaky silver-coated copper powder.

[0008] A preparation process of a conductive paste, comprising the following steps: a first step, preparing flaky silver-coated copper powder according to the preparation process described in any one of requirements 1 to 5; a second step, preparing flaky 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 water to the silver nitrate solution until the solution is clarified with auxiliary stirring 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, setting the temperature to 20-30°C, slowly adding the prepared silver ammonia solution under stirring, standing and filtering and washing after the reaction is completed, and drying in a 50°C vacuum drying oven, the resulting product is flaky silver powder; a third step, Preparation of organic carrier: weigh the components of the organic carrier according to the mass percentage of 40% pineol, 25% butyl carbitol, 10% butyl carbitol acetate, 5% thixotropic agent, 5% thickener, 10% surfactant, and 5% plasticizer in a beaker and mix them, heat them in a water bath, control the temperature at a constant temperature of 60°C, stir for 2 hours, until the mixture is dissolved and mixed evenly, and then keep warm for 1 hour; then cool it at room temperature, cover it with plastic wrap to prevent the solvent from volatilizing, and the prepared organic carrier is colorless, transparent and viscous; Step 4, preparation of conductive slurry: according to the mass percentage of flaky silver powder, silver-coated copper powder, glass powder, and organic carrier of 5:70:5:20, weigh the glass powder and mix it with silver powder and silver-coated copper powder, then grind it finely until it is uniform, then add the organic carrier according to the proportion, stir and grind it in a mortar to mix it evenly, and complete the preparation of conductive slurry.

[0009] As a further improvement of the present invention, in step S1, the oil bath temperature is 70-80°C. The temperature of the oil bath reaction is controlled at 70-80°C, and the purpose is to keep the chemical reaction at a moderate rate within this temperature range, neither too fast nor too slow. Too fast may lead to out-of-control reaction or unstable products, while too slow may affect the experimental efficiency and product generation. At the same time, most of the compounds involved in the reaction can remain stable at this temperature, and are not prone to thermal decomposition or unnecessary by-products.

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

[0011] As a further improvement of the present invention, in step S2, the copper salt mass of the BA-PVP aqueous solution is 5%. If the amount of the dispersant is too small, the dispersion effect cannot be optimal and the growth of the grains cannot be effectively hindered. If the amount of the dispersant is too much, it will remain in the reaction solution. The excess dispersant will compress the double electric layer of the reaction ions, reduce the absolute value of the Zeta potential, and thus reduce the stabilizing effect of electrostatic repulsion. This will affect the stability of the reaction, and the viscosity of the reaction solution will also rise, which will cause the growth and agglomeration of the particles.

[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 contents of the components of the glass powder are: PbO4 6.0%, 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 present invention has the following beneficial effects: 1. In the copolymer dispersant BA-PVP prepared by the present invention, an appropriate amount of vinyl pyrrolidone groups can act as a steric hindrance to resist the attraction between particles, thereby improving the dispersibility of the copper powder. The unsaturated olefin bonds and hydrogen bonds are tightly adsorbed on the surface of the particles, and the macromolecular film formed thereby inhibits the three-dimensional growth of the particles, thereby significantly enhancing the growth orientation of the particles on the two-dimensional surface, thereby forming a flaky product; 2. Accurate control of the reaction and preparation of an effective dispersant system to accurately control the morphology, particle size and silver plating amount of the flaky copper powder; 3. The contact between the particles of the granular silver-coated copper powder and silver powder is point contact, and the number of contact between the conductive particles is small, which affects the conductivity. The high degree of flaking of the silver-coated copper powder and silver powder makes them have a large specific surface area. The silver-coated copper powder and silver powder are layered and flattened on the coated surface in the conductive paint film in the shape of fallen leaves, thereby increasing the number of contacts between the particles of the conductive filler. Although the highly flaky copper powder increases the difficulty of the reaction and the amount of silver consumed during the silver plating process, its conductivity is much better than that of the general spherical silver powder and silver-coated copper powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a SEM image of the flaky copper powder prepared in the present invention;

[0017] Figure 2 This is an energy spectrum test diagram of the flaky copper powder prepared by the present invention;

[0018] Figure 3 This is a SEM image of the flaky silver-coated copper powder prepared by the present invention;

[0019] Figure 4 This is an energy spectrum test diagram of the flaky silver-coated copper powder prepared by the present invention; DETAILED DESCRIPTION

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

[0021] Example 1

[0022] A process for preparing flaky silver-coated copper powder and conductive slurry comprises the following steps:

[0023] S1. Preparation of dispersant: Add 12g of N-vinyl pyrrolidone, 0.4mg of initiator benzoyl peroxide and 0.8g of butyl acrylate to a three-necked flask, then put the thermometer into the three-necked flask, seal it with a rubber stopper and connect the cillin tube, use a vacuum pump to remove the air in the flask, and then purge it with nitrogen three times. After repeating the operation three times, inject distilled water into the flask with a syringe, start stirring and set the oil bath temperature to 70℃ for 24h, and keep nitrogen purging during the reaction. After the reaction is completed, transfer the transparent liquid in the flask to a rotary evaporator, cool it naturally, remove most of the water on a rotary evaporator, and then add the remaining viscous liquid dropwise to ether, then filter and remove ether, and the remaining solid product is dried at 40℃ for 36h in a vacuum drying oven, and then dried at 100℃ for 10h to remove water, and ground into powder. The resulting powder is the modified dispersant named BA-PVP.

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

[0025] S3. First, a copper salt aqueous solution is placed in a first reaction vessel, and the first reaction vessel is placed in a constant temperature water bath, and a BA-PVP aqueous solution is quickly added under room temperature (below 40° C.) and stirring conditions, and after completion, the pH of the copper salt aqueous solution and the sodium hypophosphite aqueous solution are adjusted to 0.25, and then the temperature is raised to 70° C., and the sodium hypophosphite aqueous solution is slowly added dropwise to the copper salt aqueous solution, and rapidly stirred. After the reaction is completed, the supernatant is poured out after standing, and then centrifuged and washed to obtain flaky copper powder;

[0026] S4, the flaky 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, and 3% ammonia solution of the mass of the suspension is added and fully stirred, and placed in a second reaction vessel, and the second reaction vessel is placed in a constant temperature water bath, the temperature is set to 20 ° C, and the BA-PVP aqueous solution is added under stirring, and the prepared silver ammonia solution 1 and glucose aqueous solution are slowly added at the same time. After the reaction is completed, it is allowed to stand, filtered and washed, and placed in a 50 ° C vacuum drying oven to dry, and the resulting product is silver-coated copper powder;

[0027] S5, placing an appropriate amount of ascorbic acid aqueous solution and BA-PVP aqueous solution in a third reaction vessel, and placing the third reaction vessel in a constant temperature water bath, setting the temperature to 20°C, slowly adding the prepared silver ammonia solution 2 under stirring, standing for filtration and washing after the reaction is completed, and placing in a 50°C vacuum drying oven for drying, the resulting product is flaky silver powder;

[0028] S6. Weigh the components of the organic carrier according to their mass percentage, including 40% pineol, 25% butyl carbitol, 10% butyl carbitol acetate, 5% hydrogenated castor oil, 5% ethyl cellulose, 10% ethanol, and 5% tributyl citrate, and mix them in a beaker. Heat them in a water bath with the temperature controlled at 60°C, stir for 2 hours, until the mixture is dissolved and mixed evenly, and then keep warm for 1 hour. After that, cool them at room temperature, cover them with plastic wrap to prevent the solvent from volatilizing, and the prepared organic carrier is obtained.

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

[0030] Example 2

[0031] A process for preparing flaky silver-coated copper powder and conductive slurry comprises the following steps:

[0032] S1. Preparation of dispersant: Add 15g of N-vinyl pyrrolidone, 0.6mg of initiator benzoyl peroxide and 1g of butyl acrylate to a three-necked flask, then put the thermometer into the three-necked flask, seal it with a rubber stopper and connect the cillin tube, use a vacuum pump to remove the air in the flask, and then purge it with nitrogen three times. After repeating the operation three times, inject distilled water into the flask with a syringe, start stirring and set the oil bath temperature to 75℃ for 24h, and keep nitrogen purging during the reaction. After the reaction is completed, transfer the transparent liquid in the flask to a rotary evaporator, cool it naturally, remove most of the water on a rotary evaporator, and then add the remaining viscous liquid dropwise to ether, then filter and remove ether, and the remaining solid product is dried at 60℃ in a vacuum drying oven for 60h, and then dried at 120℃ for 20h, and ground into powder. The resulting powder is the modified dispersant named BA-PVP.

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

[0034] S3. First, a copper salt aqueous solution is placed in a first reaction vessel, and the first reaction vessel is placed in a constant temperature water bath, and a BA-PVP aqueous solution is quickly added under room temperature (below 40° C.) and stirring conditions. After the reaction, the pH of the copper salt aqueous solution and the sodium hypophosphite aqueous solution is adjusted to 0.5, and then the temperature is raised to 80° C., and the sodium hypophosphite aqueous solution is slowly added dropwise to the copper salt aqueous solution, and the reaction is quickly stirred. After the reaction is completed, the supernatant is poured out after standing, and then the flaky copper powder is obtained by centrifugal washing;

[0035] S4, the flaky 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, and 3% ammonia solution of the mass of the suspension is added and fully stirred, and placed in a second reaction vessel, and the second reaction vessel is placed in a constant temperature water bath, the temperature is set to 25 ° C, and the BA-PVP aqueous solution is added under stirring, and the prepared silver ammonia solution 1 and glucose aqueous solution are slowly added at the same time. After the reaction is completed, it is allowed to stand, filtered and washed, and placed in a 50 ° C vacuum drying oven to dry, and the resulting product is silver-coated copper powder;

[0036] S5, placing an appropriate amount of ascorbic acid aqueous solution and BA-PVP aqueous solution in a third reaction vessel, and placing the third reaction vessel in a constant temperature water bath, setting the temperature to 25°C, slowly adding the prepared silver ammonia solution 2 under stirring, and after the reaction is completed, standing, filtering, washing, and placing in a 50°C vacuum drying oven to dry, the resulting product is flaky silver powder;

[0037] S6. Weigh the components of the organic carrier according to their mass percentage, including 40% pineol, 25% butyl carbitol, 10% butyl carbitol acetate, 5% hydrogenated castor oil, 5% ethyl cellulose, 10% ethanol, and 5% tributyl citrate, and mix them in a beaker. Heat them in a water bath with the temperature controlled at 60°C, stir for 2 hours, until the mixture is dissolved and mixed evenly, and then keep warm for 1 hour. After that, cool them at room temperature, cover them with plastic wrap to prevent the solvent from volatilizing, and the prepared organic carrier is obtained.

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

[0039] Example 3

[0040] A process for preparing flaky silver-coated copper powder and conductive slurry comprises the following steps:

[0041] S1. Preparation of dispersant: 18g of N-vinyl pyrrolidone, 0.8mg of initiator benzoyl peroxide and 1.2g of butyl acrylate were added to a three-necked flask, then a thermometer was placed in the three-necked flask, sealed with a rubber stopper and connected to a cillin tube, the air in the flask was evacuated with a vacuum pump, and then purged with nitrogen three times. After repeating the operation three times, distilled water was injected into the flask with a syringe, stirring was turned on and the oil bath temperature was set to 80°C for 24h, and nitrogen was always purged during the reaction. After the reaction was completed, the transparent liquid in the flask was transferred to a rotary evaporator, and after natural cooling, most of the water was removed on a rotary evaporator, and then the remaining viscous liquid was added dropwise to ether, and then the ether was removed by suction filtration. The remaining solid product was dried at 50°C in a vacuum drying oven for 48h, and then dried at 110°C for 15h to remove water, and ground into powder. The resulting powder was the modified dispersant named BA-PVP.

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

[0043] S3. First, a copper salt aqueous solution is placed in a first reaction vessel, and the first reaction vessel is placed in a constant temperature water bath, and a BA-PVP aqueous solution is quickly added at room temperature (below 40° C.) and under stirring conditions. After the reaction, the pH of the copper salt aqueous solution and the sodium hypophosphite aqueous solution is adjusted to 0.75, and then the temperature is raised to 90° C., and the sodium hypophosphite aqueous solution is slowly added dropwise to the copper salt aqueous solution, and the reaction is quickly stirred. After the reaction is completed, the supernatant is poured out after standing, and then centrifuged and washed to obtain flaky copper powder;

[0044] S4, the flaky 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, and 3% ammonia solution of the mass of the suspension is added and fully stirred, and placed in a second reaction vessel, and the second reaction vessel is placed in a constant temperature water bath, the temperature is set to 30 ° C, and the BA-PVP aqueous solution is added under stirring, and the prepared silver ammonia solution 1 and glucose aqueous solution are slowly added at the same time. After the reaction is completed, it is allowed to stand, filtered and washed, and placed in a 50 ° C vacuum drying oven to dry, and the resulting product is silver-coated copper powder;

[0045] S5, placing an appropriate amount of ascorbic acid aqueous solution and BA-PVP aqueous solution in a third reaction vessel, and placing the third reaction vessel in a constant temperature water bath, setting the temperature to 30°C, slowly adding the prepared silver ammonia solution 2 under stirring, and after the reaction is completed, standing, filtering, washing, and placing in a 50°C vacuum drying oven to dry, the resulting product is flaky silver powder;

[0046] S6. Weigh the components of the organic carrier according to their mass percentage, including 40% pineol, 25% butyl carbitol, 10% butyl carbitol acetate, 5% hydrogenated castor oil, 5% ethyl cellulose, 10% ethanol, and 5% tributyl citrate, and mix them in a beaker. Heat them in a water bath with the temperature controlled at 60°C, stir for 2 hours, until the mixture is dissolved and mixed evenly, and then keep warm for 1 hour. After that, cool them at room temperature, cover them with plastic wrap to prevent the solvent from volatilizing, and the prepared organic carrier is obtained.

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

[0048] The following table shows the electrode square resistance test results of the conductive paste prepared in the above examples, as well as the particle size data and bulk density of the silver-coated copper powder and silver powder.

[0049]

[0050] It can be seen from the data in the table that the particle size and bulk density of the silver-coated copper powder and the flaky silver powder are basically at the same level, and the impurity content conforms to the national standard GB / T 26049-2010, which proves the stability of the production method; the electrode square resistance of the conductive paste obtained in all embodiments is basically at the same level, and its conductive performance is excellent, and it can be used as a high-quality conductive paste, which also proves the production stability and economic efficiency of the production method.

[0051] Those skilled in the art should be aware that the protection scheme of the present invention is not limited to the above-mentioned embodiments, and various arrangements, combinations and transformations can be performed on the basis of the above-mentioned embodiments. Without violating the spirit of the present invention, various transformations of the present invention fall within the protection scope of the present invention.

Claims

1. A process for preparing flaky silver-coated copper powder, Its characteristics are The steps include: S1. Preparation of dispersant: Put the raw materials of N-vinyl pyrrolidone, benzoyl peroxide and butyl acrylate in a mass ratio of 2250:1:1500 into a three-necked flask, seal it with a rubber stopper and connect a cillin tube, remove the air in the flask with a vacuum pump, and then purge it with nitrogen three times; after repeating the operation three times, inject distilled water into the flask with a syringe, start stirring and oil bath, react for 24 hours, and keep nitrogen purging during the reaction; after the reaction is completed, transfer the transparent liquid in the flask to a rotary evaporator, cool it naturally, remove most of the water on a rotary evaporator, and then add the remaining viscous liquid dropwise into ether, then filter and remove the ether, and dry the remaining solid product in a vacuum drying oven at a drying temperature of 40-60°C and a drying time of 36-60 hours, then dry out the water for 10-20 hours, grind it into powder, and the obtained powder is the modified dispersant named BA-PVP; mix the obtained powder with a certain amount of copper salt to prepare a BA-PVP aqueous solution; S2, preparing flaky copper powder: preparing a certain amount of a copper salt aqueous solution with a concentration of 0.1-0.4 mol / L, a sodium hypophosphite aqueous solution with a concentration of 0.07-0.28 mol / L, and a BA-PVP aqueous solution: first, placing the copper salt aqueous solution in a first reaction vessel, and placing the first reaction vessel in a constant temperature water bath, at a temperature below 40°C, quickly adding the BA-PVP aqueous solution while stirring, and after the completion, adjusting the pH of the copper salt aqueous solution and the sodium hypophosphite aqueous solution to 0.25-0.75, then heating to 70-90°C, slowly adding the sodium hypophosphite aqueous solution to the copper salt aqueous solution, and quickly stirring, the reaction is completed, and the supernatant is poured out after standing, and then centrifuged and washed to obtain flaky 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; The ammonia solution is added dropwise to the silver nitrate solution and stirred until the solution is clarified to obtain a silver ammonia solution; the flaky copper powder obtained in the above 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 of the mass of the suspension is added and fully stirred, placed in a second reaction vessel, and the second reaction vessel is placed in a constant temperature water bath, the temperature is set to 20-30°C, and the BA-PVP aqueous solution prepared in step S2 is added under stirring, and the silver ammonia solution and glucose aqueous solution prepared in this step are slowly added at the same time. After the reaction is completed, it is allowed to stand, filtered and washed, and placed in a 50°C vacuum drying oven for drying. The obtained product is a flaky silver-coated copper powder.

2. A process for preparing a flaky silver-coated copper powder according to claim 1, Its characteristics are In the step S1, the oil bath temperature is 70-80°C.

3. A process for preparing a flaky silver-coated copper powder according to claim 1, Its characteristics are In the step S1, the temperature of the dried water is controlled at 100-120°C.

4. A process for preparing a flaky silver-coated copper powder according to claim 1, Its characteristics are In the step S2, the copper salt mass of the BA-PVP aqueous solution is 5%.

5. A process for preparing a flaky silver-coated copper powder according to any one of claims 1 to 4, Its characteristics are The copper salt is at least one of copper sulfate, copper nitrate or copper chloride.

6. A process for preparing a conductive paste, Its characteristics are The steps include: The first step is to prepare flaky silver-coated copper powder according to the preparation process described in any one of requirements 1 to 5; Step 2: Prepare flaky 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 water into the silver nitrate solution and stir until the solution is clarified to prepare a silver ammonia solution, place 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 place the third reaction vessel in a constant temperature water bath pot, set the temperature to 20-30°C, slowly add the prepared silver ammonia solution under stirring, let the reaction stand, filter and wash after completion, and place in a 50°C vacuum drying oven to dry, the resulting product is flaky silver powder; Step 3, preparation of organic carrier: weigh the components of the organic carrier according to the mass percentage of 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 them in a water bath, control the temperature at a constant temperature of 60°C, stir for 2 hours, until the mixture is dissolved and mixed evenly, and then keep warm for 1 hour; then cool it at room temperature, cover it with plastic wrap to prevent the solvent from volatilizing, and the prepared organic carrier is colorless, transparent and viscous; Step 4. Preparation of conductive paste: according to the mass percentage of flaky silver powder, silver-coated copper powder, glass powder and organic carrier of 5:70:5:20, weigh the glass powder, silver powder and silver-coated copper powder and mix them, then grind them finely until they are uniform, then add the organic carrier according to the proportion, stir and grind in a mortar to mix them evenly, and complete the preparation of the conductive paste.

7. The process for preparing the conductive paste according to claim 6, Its characteristics are In the third step, ethyl cellulose is selected as the thickener, ethanol is selected as the surfactant, tributyl citrate is selected as the plasticizer, and hydrogenated castor oil is selected as the thixotropic agent.

8. A process for preparing the conductive paste according to claim 6 or 7, Its characteristics are In the fourth step, the mass fractions of the components of the glass powder are: PbO 46.0%, TeO 2 20.0%、SiO 2 7.0%, B 2 O 3 9.0%、Li 2 O 0.4%, Na 2 O0.2%, P 2 O 5 4.3%, ZnO 8.6%, TiO 2 2%, V 2 O 5 2.5%.

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