A flaky silver powder with low tap density, its preparation method and application

Abstract

The invention discloses a flaky silver powder with low bulk density and a preparation method and application thereof, and relates to the technical field of metal powder metallurgy. The preparation method of the flaky silver powder with low bulk density comprises the following steps: S1, preparing nano silver crystal seeds; S2, preparing spherical silver powder slurry; S3, adding the spherical silver powder slurry obtained in step S2 and stainless steel grinding balls into a ball mill for ball milling; S4, after the ball milling is completed, separating the flaky silver powder from the grinding balls, washing to less than 20 μS / cm, drying, and sieving to obtain an average particle size D50: 2-4 μm, a diameter-to-thickness ratio of 20-100:1, and a bulk density of 0.3-0.6 g / cm <supgt;3< / supgt;的片状银粉。本发明中,通过预先制备纳米银晶种,将银颗粒的成核与生长过程分离,使得在后续氧化还原反应中生成的银单质不必再生成晶核,而以纳米银晶种为核生长,生长时间同步使得球形银颗粒粒径更加集中,最终达到收窄片状银粉片径分布的效果。

Description

Technical Field

[0001] The present invention relates to the technical field of metal powder metallurgy, and particularly to a flaky silver powder with low tap density, a preparation method thereof, and an application thereof. Background Art

[0002] At present, flaky silver powder is one of the important materials for low-temperature curing conductive pastes. By mixing with organic adhesive resins and solvents, various conductive coatings and electronic pastes suitable for different scenarios are made, and are widely used in electronic components such as membrane switches, filters, flexible circuit boards, semiconductor chip bonding, etc. Limited by the low-temperature curing process, the silver powder cannot be melted. Compared with the point-to-point contact of spherical silver powder, the flaky silver powder is in line contact or surface contact, and the formed conductive network has a lower resistance and better conductivity. In addition, the flaky silver powder has a wide deflection range and anti-fracture stretching characteristics, and the produced electronic components have high reliability. At the same time, for flaky silver powder with a lower tap density, when using the same volume of silver powder, the required silver consumption is lower, which can greatly reduce the amount of silver powder used, reduce the coating thickness, and is beneficial to the miniaturization of electronic components; at the same time, the denser the paste after low-temperature curing, the better the electrical properties.

[0003] Industrially, mechanical ball milling is mainly used to prepare flaky silver powder. The flaky silver powder prepared by the chemical method is only dozens of nanometers thick. When the silver powder is made into an electronic paste, during the heating and curing process in use, the silver flakes shrink, causing holes and reducing the electrical properties, making it of no practical value; while the mechanical ball milling method for preparing flaky silver powder has a high yield and is easy to achieve batch amplification; however, the mechanical ball milling method has many control factors, and the product quality is difficult to guarantee. At the same time, the flaky silver powder prepared by the conventional ball milling method is difficult to be thinned, has a wide particle size distribution, and a high tap density, making it difficult to meet the requirement of reducing silver consumption in electronic pastes, and at the same time resulting in poor printing flatness of the electronic paste and uneven printed circuits, and a decline in electrical properties.

[0004] The invention patent application with the publication number CN117961080A discloses a preparation method of flaky silver powder, and the method includes the following steps: mixing solution A and solution B and then reacting to prepare the flaky silver powder; wherein, solution A includes Ag+, silver nanosheet seeds, and ions with oxidation effect, and solution B includes ions with reduction effect, and the ions with oxidation effect include Ce 4+ or Fe 3+ at least one of them. In the preparation process of the flaky silver powder of the present invention, no polymer dispersant or polymer surfactant needs to be added, and the flaky silver powder is prepared by a one-step reduction method. Under the combined action of the ions with oxidation effect and silver nanosheet seeds in solution A, the flakiness degree, surface smoothness and flatness of the prepared flaky silver powder are improved, and thus the conductivity of the prepared flaky silver powder is improved.

[0005] However, the flaky silver powder prepared by the preparation method described in this patent has a relatively thin sheet type, only dozens of nanometers thick. When configured into a slurry in actual applications, it often shrinks severely, affecting the electrical properties and having no practical application value. At the same time, during the preparation process, Ce 4+ or Fe 3+ and other impurity metal ions are introduced, affecting the purity and performance of the nano silver flakes. In addition, during the preparation process of this patent, the nano silver flakes are prone to aggregation, affecting their dispersibility and stability. Summary of the Invention

[0006] The present invention aims to provide a flaky silver powder with low tap density and its preparation method and application, so as to prepare flaky silver powder with high flakiness degree, narrow particle size distribution, high tap density, and low burn-off rate at 538°C, to meet the usage requirements of conductive slurries for electronic components. By introducing nano silver seeds, spherical silver powders with different particle sizes are prepared and controlled. The introduction of surfactants promotes the monodispersion of spherical silver powders and plays a role in assisting grinding, preventing sticking of flakes, and narrowing the flake diameter distribution. It overcomes the disadvantages of poor stability, wide flake diameter distribution, and low flakiness degree of the traditional ball milling method, and at the same time significantly shortens the production process.

[0007] In order to achieve the above invention purpose, the technical solution of the present invention is as follows:

[0008] A kind of flaky silver powder prepared by the above preparation method, the flaky silver powder with low tap density is prepared by reducing silver ammonia solution I to a nano silver seed solution, and then mixing the nano silver seed solution with silver ammonia solution II, and forming a spherical silver powder slurry through a reduction reaction; finally, the spherical silver powder slurry is ball milled, washed, dried, and screened. The performance indexes of the flaky silver powder meet: the average particle size D50 is 2μm - 4μm, the aspect ratio is 20:1 - 100:1, and the tap density is 0.3g / cm 3 ~0.6g / cm 3 ; the burn-off rate at 538°C ≤ 0.9%.

[0009] A preparation method of a flaky silver powder with low tap density, comprising the following steps:

[0010] S1. Preparation of nano silver seeds: Drop silver ammonia solution I into the dispersant solution, stir for 5min - 10min after dropping, obtain mixed solution I, and then drop reducing agent solution I into mixed solution I, stir for 30min - 40min after dropping, and obtain nano silver seed solution;

[0011] S2. Add the nano silver seed solution in step S1 to the surfactant solution, stir and disperse at a constant temperature for 5 min to 10 min to obtain a mixed solution II. Drop the silver ammonia solution II and the reducing agent solution II into the mixed solution II simultaneously. After the dropping is completed, continue the reaction for 5 min to 10 min. After the reaction is completed, perform solvent replacement to obtain a spherical silver powder slurry.

[0012] S3. Add the spherical silver powder slurry obtained in step S2 and stainless steel grinding balls to a ball mill for ball milling. The mass ratio of the spherical silver powder to the stainless steel grinding balls is 1:20 to 1:30; the diameter of the stainless steel grinding balls is 1 mm to 3 mm. Start the external circulation system of the ball mill, the ball milling speed is 400 rpm to 800 rpm, and the ball milling time is 4 h to 8 h.

[0013] S4. After the ball milling is completed, separate the flaky silver powder from the grinding balls, wash with deionized water until below 20 μS / cm, dry at a temperature of 70 °C to 80 °C for 12 h to 24 h, and then sieve through a sieve to obtain flaky silver powder with an average particle size D50 of 2 μm to 4 μm, an aspect ratio of 20:1 to 100:1, and a loose bulk density of 0.3 g / cm 3 ~0.6 g / cm 3 of the flaky silver powder.

[0014] The dispersant solution is an aqueous solution of one or a mixture of two of methyl cellulose or carboxymethyl cellulose.

[0015] Both the silver ammonia solution I and the silver ammonia solution II are transparent Ag(NH3)2OH solutions prepared by adding ammonia water to an aqueous silver nitrate solution.

[0016] Both the reducing agent solution I and the reducing agent solution II are aqueous glucose solutions.

[0017] The surfactant solution is an aqueous solution of any one or a mixture of oleic acid, stearic acid, palmitic acid, palmitic acid, lauric acid.

[0018] In step S1, the mass concentration of silver ammonia in the silver ammonia solution I is 28 g / L to 56 g / L; the mass concentration of the dispersant solution is 10 g / L to 20 g / L; the mass concentration of the reducing agent solution I is 15 g / L to 36 g / L.

[0019] In step S1, the molar ratio of silver ammonia to the reducing agent in the silver ammonia solution I and the reducing agent solution I is 1:0.5 to 1:0.6.

[0020] In step S1, preheat the dispersant solution, the reducing agent solution I and the silver ammonia solution I to 45 °C to 55 °C respectively, and drop the silver ammonia solution I and the reducing agent solution I at a temperature of 45 °C to 55 °C respectively. After the dropping is completed, stir and react at a temperature of 45 °C to 55 °C.

[0021] In the step S1, the dropping rate of the silver ammonia solution I is 30 mL / min to 50 mL / min; the dropping rate of the reducing agent is 60 mL / min to 90 mL / min.

[0022] In the step S2, the molar ratio of silver ammonia to the reducing agent in the silver ammonia solution II and the reducing agent solution II is 1:0.5 to 1:0.6.

[0023] In the step S2, the silver ammonia solution II, the reducing agent solution II, the nano silver seed solution and the surfactant solution are respectively preheated to 25°C to 35°C, the constant temperature stirring temperature is 25°C to 35°C, and the silver ammonia solution II and the reducing agent solution II are dropped under the temperature condition of 25°C to 35°C. After the dropping is completed, the reaction continues under the temperature condition of 25°C to 35°C.

[0024] In the step S2, the dropping rates of the silver ammonia solution II and the reducing agent solution II are both 185 mL / min to 280 mL / min.

[0025] In the step S2, the mass of the surfactant in the surfactant solution is 1.5% to 3% of the mass of silver nitrate added in the silver ammonia solution II.

[0026] In the step S2, the mass of the nano silver seed solution is 20% to 60% of the mass of silver nitrate in the silver ammonia solution II.

[0027] In the step S2, the solvent replacement is to use absolute ethanol to replace the aqueous solution, and the amount of absolute ethanol used is 1.18 times to 1.90 times the mass of silver nitrate added in the silver ammonia solution II.

[0028] In the step S2, the mass concentration of silver ammonia in the silver ammonia solution II is 318 g / L; the mass concentration of the reducing agent solution II is 180 g / L; the mass concentration of the surfactant solution is 24 g / L to 47 g / L.

[0029] In the step S3, the cooling medium of the external circulation system of the ball mill is cold water, and the circulation speed is 0.5 L / min to 1 L / min.

[0030] An application of the flaky silver powder with low tap density. The flaky silver powder with low tap density prepared by the preparation method of the above flaky silver powder with low tap density is used for producing electronic silver paste.

[0031] The beneficial effects of the present invention:

[0032] 1. In the present invention, by preparing nano silver seeds in advance, the nucleation and growth processes of silver particles are separated, so that the silver element generated in the subsequent redox reaction does not need to generate nuclei again, but grows with the nano silver seeds as the nucleus. The growth time is synchronized so that the particle size of the spherical silver particles is more concentrated, and finally the effect of narrowing the particle size distribution of the flaky silver powder is achieved. Spherical silver powders of different particle sizes and narrow particle size distribution can be prepared by adjusting the dosage of the nano silver seed solution; the spherical silver powder prepared by the present invention is almost in a monodisperse state, with a narrow particle size distribution, and a simple control method.

[0033] 2. In the present invention, a sufficient amount of surfactant is added during the preparation stage of spherical silver powder, which can not only ensure a good dispersion effect during the growth stage of the spherical silver powder, but also serve as a grinding aid in the subsequent grinding stage of flaky silver powder, thereby improving the lubrication effect of the grinding balls and the silver powder, improving the efficiency of spherical silver powder flake formation and breaking up large flaky silver powder; at the same time, it plays a steric role, avoiding adhesion between flakes to form large-sized flaky silver powder, thereby achieving the effect of narrowing the flake diameter.

[0034] 3. The present invention introduces nano silver seeds to make the particle size distribution of spherical silver particles narrower, so that the particle size is more concentrated when grinding flaky silver powder; the number of fine particles is reduced in the two stages of preparing spherical silver powder and flaky silver powder, so that the specific surface area is reduced, thereby reducing the number of adsorbed surfactants; and the free surfactants between the silver particles are removed in the washing step, so that the 538°C burnout rate is low.

[0035] 4. The preparation method of the present invention can realize the continuous production and preparation of spherical silver powder and flaky silver powder. After replacing the solvent with anhydrous ethanol, it can be directly used for grinding flaky silver powder. Compared with the traditional preparation method, the drying process of spherical silver powder is reduced, and the production efficiency is greatly improved; at the same time, the agglomeration and compaction of spherical silver powder during the drying process are avoided, which causes the flaky silver powder to be unable to disperse during the grinding process and cause the size to be too large.

[0036] 5. The flaky silver powder prepared by the present invention has a burning loss rate of ≤0.9% at 538°C and a bulk density of 0.3g / cm 3 ~0.6g / cm 3 , far lower than the national standard GB / T1773-2008 "Flake Silver Powder" 538℃ burning rate ≤ 2%, bulk density 1.2g / cm 3 ~2.5g / cm 3Performance indicators; the low burn-off rate of flaky silver powder at 538°C enables it to be formulated into a low-temperature curable silver paste, leaving less insulating material after printing and curing, and providing better electrical performance; the low apparent density of flaky silver powder indicates that its flake shape is thinner. When formulated into a low-temperature curable silver paste for printing and curing, more surface lap joints are formed to create a path. At the same time, the sintering activity of the flaky silver powder is higher, enabling it to partially sinter and melt even under low-temperature curing processes, forming better lap joints and providing good electrical performance, meeting the usage requirements for burn-off rate and low apparent density of flaky silver powder in the process conditions of low-temperature curable silver paste for membrane switches.

[0037] 6. In the present invention, by externally connecting circulating condensed water, overheating phenomena caused by the energy generated by the high-speed collision of grinding balls and spherical silver powder are avoided, and the adhesion and cold welding of flaky silver powder caused by too high temperature, resulting in the thickening of the flake shape and the increase of apparent density, are also avoided.

[0038] 7. The flaky silver powder prepared by the method of the present invention has a narrow particle size distribution, a thin flake shape, a low apparent density, and a low ignition loss rate, meeting the usage requirements of electronic pastes such as membrane switches / flexible circuit boards / varistors. Description of the Drawings

[0039] Figure 1 This is a scanning electron microscope image of the monodisperse spherical silver powder in the nano silver seed solution prepared in Example 1 of the present invention.

[0040] Figure 2 This is a scanning electron microscope image of the flaky silver powder with a thin flake shape and a low apparent density prepared by the present invention.

[0041] Figure 3 This is a scanning electron microscope image of the flaky silver powder with a relatively low degree of flaking in the comparative example of the present invention.

[0042] Figure 4 This is a scanning electron microscope image of the flaky silver powder with a relatively low diameter-to-thickness ratio in the comparative example of the present invention. Detailed Embodiments

[0043] The present invention will be further described in detail below in conjunction with the embodiments, but the embodiments of the present invention are not limited thereto.

[0044] Example 1

[0045] This example provides a flaky silver powder with a thin flake shape and a low apparent density, and its preparation method includes the following steps:

[0046] S1. Add 10 g of methylcellulose to 1000 g of deionized water, stir to disperse and dissolve it, and keep it at a constant temperature of 50 °C to obtain a dispersant solution A with a concentration of 10 g / L; add 8.7 g of silver nitrate to 170 g of deionized water, stir to dissolve it, add ammonia water until it becomes colorless and transparent, and keep it at a constant temperature of 50 °C to obtain a silver ammonia solution IA with a concentration of 48 g / L; add 5.08 g of anhydrous glucose to 180 g of deionized water, stir to disperse it, and keep it at a constant temperature of 50 °C to obtain a reducing agent solution IA with a concentration of 28 g / L; then add the silver ammonia solution IA to the dispersant solution A at a flow rate of 40 mL / min, stir for 5 min to obtain a mixed solution IA, and then add the reducing agent solution IA to the mixed solution IA at a speed of 75 mL / min, and continue to stir for 30 min to obtain a nano silver seed solution A;

[0047] Sampling and drying with a pipette in the nano silver seed solution A to obtain monodisperse spherical silver powder, and performing a scanning electron microscope on the monodisperse spherical silver powder to obtain a scanning electron micrograph as Figure 1 shown;

[0048] S2. Add 189 g of silver nitrate to 556 g of deionized water, stir to dissolve it, add ammonia water until it becomes colorless and transparent, and keep it at a constant temperature of 30 °C to obtain a silver ammonia solution IIA with a concentration of 318 g / L; add 110.26 g of anhydrous glucose to 612 g of deionized water, stir to dissolve it, and keep it at a constant temperature of 30 °C to obtain a reducing agent solution IIA with a concentration of 180 g / L; add 3.6 g of stearic acid to 120 g of deionized water, stir to dissolve it, and keep it at a constant temperature of 30 °C to obtain a surfactant solution A with a concentration of 30 g / L;

[0049] Take 75.6 g of the nano silver seed solution A obtained in step S1, add it to the surfactant solution A to obtain a mixed solution IIA, stir and disperse for 5 min, and then transfer the silver ammonia solution IIA and the reducing agent solution IIA to the mixed solution IIA simultaneously at a speed of 280 mL / min. After the addition is completed, continue to react for 10 min; after the reaction is completed, replace the aqueous solution with anhydrous ethanol, and the amount of anhydrous ethanol used is 1.48 times the mass of silver nitrate in the silver ammonia solution IIA to obtain a spherical silver powder slurry;

[0050] S3. Add the spherical silver powder slurry obtained in step S2 and φ2 mm stainless steel grinding balls to a ball mill for ball milling. The mass ratio of the spherical silver powder to the stainless steel grinding balls is 1:25. Start the outer circulation system of the ball mill, the ball milling speed is 600 rpm, and the ball milling time is 6 h;

[0051] The cooling medium of the outer circulation system of the ball mill is cold water, and the circulation speed is 1 L / min;

[0052] After the ball milling is completed, separate the flaky silver powder from the grinding balls, wash it with deionized water until it is below 20 μS / cm, dry it at 80 °C for 18 h, and then perform ultrasonic screening using a 500-mesh sieve to obtain flaky silver powder.

[0053] The flaky silver powder obtained in this example was subjected to scanning electron microscopy to obtain a scanning electron micrograph as shown in Figure 2 below.

[0054] In this example, the flaky silver powder obtained in this example was mixed with a halogen-free resin carrier to prepare an electronic paste containing 47% silver. After printing on a 75μm PET substrate, it was sintered and cured at 150°C / 30 min. A film thickness gauge and a digital multimeter were used to measure the thickness of the electronic paste and calculate the sheet resistance, and its resistance value was 10.8 mΩ / □ / mil, meeting the electrical performance requirements of the low-temperature curing paste for thin-film switches.

[0055] Example 2

[0056] This example provides a flaky silver powder with a low tap density, and its preparation method includes the following steps:

[0057] S1. Add 20 g of carboxymethyl cellulose to 1000 g of deionized water, stir to disperse and dissolve it, and keep it at a constant temperature of 50°C to obtain a dispersant solution B with a concentration of 20 g / L; add 5.1 g of silver nitrate to 170 g of deionized water, stir to disperse it, add ammonia water until it is colorless and transparent, and keep it at a constant temperature of 50°C to obtain a silver ammonia solution IB with a concentration of 28 g / L; add 2.70 g of anhydrous glucose to 180 g of deionized water, stir to disperse it, and keep it at a constant temperature of 50°C to obtain a reducing agent solution IB with a concentration of 15 g / L; then add the silver ammonia solution IB to the dispersant solution B at a flow rate of 30 mL / min, stir for 10 min to obtain a mixed solution IB, and then add the reducing agent solution IB to the mixed solution IB at a speed of 60 mL / min, and continue to stir for 30 min to obtain a nano-silver seed solution B;

[0058] S2. Add 189 g of silver nitrate to 556 g of deionized water, stir to dissolve it, add ammonia water until it is colorless and transparent, and keep it at a constant temperature of 30°C to obtain a silver ammonia solution IIB with a concentration of 318 g / L; add 100.24 g of anhydrous glucose to 556 g of deionized water, stir to dissolve it, and keep it at a constant temperature of 30°C to obtain a reducing agent solution IIB with a concentration of 180 g / L; add 2.83 g of oleic acid to 120 g of deionized water, stir to dissolve it, and keep it at a constant temperature of 30°C to obtain a surfactant solution B with a concentration of 24 g / L;

[0059] Take 75.6 g of the nano-silver seed solution B obtained in step S1, add it to the surfactant solution B to obtain a mixed solution IIB. After stirring and dispersing for 10 min, transfer the silver ammonia solution IIB and the reducing agent solution IIB to the mixed solution IIB simultaneously at a speed of 185 mL / min. After the dropping is completed, continue to react for 10 min; after the reaction is completed, replace the aqueous solution with anhydrous ethanol, and the amount of anhydrous ethanol used is 1.48 times the mass of silver nitrate in the silver ammonia solution IIB to obtain a spherical silver powder slurry;

[0060] S3. Add the spherical silver powder slurry obtained in step S2 and φ2mm stainless steel grinding balls into a ball mill for ball milling. The mass ratio of the spherical silver powder to the stainless steel grinding balls is 1:25. Start the external circulation system of the ball mill, with a ball milling speed of 600 rpm and a ball milling time of 6 h;

[0061] The cooling medium of the external circulation system of the ball mill is cold water, and the circulation speed is 1 L / min;

[0062] S4. After the ball milling is completed, separate the flaky silver powder from the grinding balls, wash it with deionized water until it is below 20 μS / cm, then dry it at 80 °C for 12 h, and then ultrasonically screen it using a 500-mesh sieve to obtain flaky silver powder.

[0063] In this embodiment, the flaky silver powder obtained in this embodiment is mixed with a halogen-free resin carrier to prepare an electronic paste containing 47% silver. After printing on a 75-μm PET substrate, it is sintered and cured at 150 °C for 30 min. Use a film thickness gauge and a digital multimeter to measure the thickness of the electronic paste and calculate the sheet resistance, and its resistance value is 11.6 mΩ / □ / mil, meeting the electrical performance requirements of the low-temperature curing paste for membrane switches.

[0064] Example 3

[0065] This embodiment provides a flaky silver powder with a low tap density, and its preparation method includes the following steps:

[0066] S1. Add 15 g of methyl cellulose into 1000 g of deionized water, stir, disperse, dissolve and keep the temperature constant at 45 °C to obtain a dispersant solution C with a concentration of 15 g / L; add 10.2 g of silver nitrate into 170 g of deionized water, stir and dissolve, add ammonia water until it is colorless and transparent, and keep the temperature constant at 45 °C to obtain a silver ammonia solution IC with a concentration of 56 g / L; add 6.49 g of anhydrous glucose into 180 g of deionized water, stir and disperse and keep the temperature constant at 50 °C to obtain a reducing agent solution IC with a concentration of 36 g / L; then add the silver ammonia solution IC into the dispersant solution C at a flow rate of 50 mL / min, stir for 10 min to obtain a mixed solution IC, and then add the reducing agent solution IC into the mixed solution IC at a speed of 90 mL / min, and continue to stir for 30 min to obtain a nano silver seed solution C;

[0067] S2. Add 189 g of silver nitrate into 556 g of deionized water, stir and dissolve, add ammonia water until it is colorless and transparent, and keep the temperature constant at 25 °C to obtain a silver ammonia solution ⅡC with a concentration of 318 g / L; add 120.28 g of anhydrous glucose into 667 g of deionized water, stir and dissolve and keep the temperature constant at 25 °C to obtain a reducing agent solution ⅡC with a concentration of 180 g / L; add 5.67 g of palmitic acid into 120 g of deionized water, stir and dissolve and keep the temperature constant at 30 °C to obtain a surfactant solution C with a concentration of 47 g / L;

[0068] Take 75.6 g of the nano silver seed solution C obtained in step S1, add it to the surfactant solution C to obtain the mixed solution II C. After stirring and dispersing for 5 min, transfer the silver ammonia solution II C and the reducing agent solution II C to the mixed solution II C simultaneously at a speed of 225 mL / min. After the dropping is completed, continue the reaction for 10 min; after the reaction is completed, replace the aqueous solution with anhydrous ethanol, and the amount of anhydrous ethanol used is 1.48 times the mass of silver nitrate in the silver ammonia solution II C to obtain a spherical silver powder slurry;

[0069] S3. Add the spherical silver powder slurry obtained in step S2 and φ2 mm stainless steel grinding balls to a ball mill for ball milling. The mass ratio of the spherical silver powder to the stainless steel grinding balls is 1:25. Start the external circulation system of the ball mill, the ball milling speed is 600 rpm, and the ball milling time is 6 h;

[0070] The cooling medium of the external circulation system of the ball mill is cold water, and the circulation speed is 0.8 L / min;

[0071] S4. After the ball milling is completed, separate the flaky silver powder from the grinding balls, wash it with deionized water until it is below 20 μS / cm, then dry it at 70 °C for 24 h, and then ultrasonically screen it through a 500-mesh sieve to obtain flaky silver powder.

[0072] In this embodiment, the flaky silver powder obtained in this embodiment is mixed with a halogen-free resin carrier to prepare an electronic paste containing 47% silver. After printing on a 75-μm PET substrate, it is sintered and cured at 150 °C for 30 min. Use a film thickness gauge and a digital multimeter to measure the thickness of the electronic paste and calculate the sheet resistance, and its resistance value is 11.5 mΩ / □ / mil, meeting the electrical performance requirements of the low-temperature curing paste for membrane switches.

[0073] Example 4

[0074] This embodiment provides a flaky silver powder with a low apparent density, and its preparation method includes the following steps:

[0075] S1. Add 20 g of methyl cellulose to 1000 g of deionized water, stir, disperse and dissolve it, and keep it at a constant temperature of 55 °C to obtain a dispersant solution D with a concentration of 20 g / L; add 10.2 g of silver nitrate to 170 g of deionized water, stir and dissolve it, add ammonia water until it is colorless and transparent, and keep it at a constant temperature of 55 °C to obtain a silver ammonia solution ID with a concentration of 56 g / L; add 5.95 g of anhydrous glucose to 180 g of deionized water, stir and dissolve it, and keep it at a constant temperature of 55 °C to obtain a reducing agent solution ID with a concentration of 33 g / L; then add the silver ammonia solution ID to the dispersant solution D at a flow rate of 50 mL / min, stir for 10 min to obtain a mixed solution ID, and then add the reducing agent solution ID to the mixed solution ID at a speed of 90 mL / min, and continue to stir for 40 min to obtain a nano silver seed solution D;

[0076] S2. Add 189 g of silver nitrate into 556 g of deionized water, stir to dissolve, add ammonia water until it becomes colorless and transparent, keep the temperature at 35 °C to obtain silver ammonia solution II D with a concentration of 318 g / L; add 110.26 g of anhydrous glucose into 612 g of deionized water, stir to dissolve and keep the temperature at 35 °C to obtain reducing agent solution II D with a concentration of 180 g / L; add 5.67 g of stearic acid into 120 g of deionized water, stir to dissolve and keep the temperature at 30 °C to obtain surfactant solution D with a concentration of 47 g / L.

[0077] Take 75.6 g of the nano silver seed solution D obtained in step S1, add it into the surfactant solution D to obtain mixed solution II D. After stirring and dispersing for 10 min, transfer the silver ammonia solution II D and the reducing agent solution II D to the mixed solution II D simultaneously at a speed of 280 mL / min. After the dropping is completed, continue the reaction for 10 min; after the reaction is completed, replace the aqueous solution with absolute ethanol, and the amount of absolute ethanol used is 1.48 times the mass of silver nitrate in the silver ammonia solution II D to obtain spherical silver powder slurry.

[0078] S3. Add the spherical silver powder slurry obtained in step S2 and φ2 mm stainless steel grinding balls into a ball mill for ball milling. The mass ratio of spherical silver powder to stainless steel grinding balls is 1:25. Start the outer circulation system of the ball mill, the ball milling speed is 600 rpm, and the ball milling time is 6 h.

[0079] The cooling medium of the outer circulation system of the ball mill is cold water, and the circulation speed is 0.5 L / min.

[0080] S4. After ball milling is completed, separate the flaky silver powder from the grinding balls, wash it with deionized water until it is below 20 μS / cm, then dry it at 75 °C for 18 h, and then ultrasonically screen it through a 500-mesh sieve to obtain flaky silver powder.

[0081] In this embodiment, the flaky silver powder obtained in this embodiment is mixed with a halogen-free resin carrier to prepare an electronic paste containing 47% silver. After printing on a 75-μm PET substrate and then sintering and curing at 150 °C for 30 min, use a film thickness gauge and a digital multimeter to measure the thickness of the electronic paste and calculate the sheet resistance. Its resistance value is 13.3 mΩ / □ / mil, meeting the electrical performance requirements of low-temperature curing paste for membrane switches.

[0082] Example 5

[0083] Compared with Example 1, the difference in this embodiment is that in this embodiment, the dispersant solution E in step S1 is an aqueous solution of carboxymethyl cellulose; the surfactant solution E in step S2 is an aqueous solution of a mixture of stearic acid and lauric acid with a mass ratio of 2:1; the other steps are the same as those in Example 1.

[0084] Example 6

[0085] Compared with Example 1, this example is different in that in this example, the dispersant solution F in step S1 is an aqueous solution of carboxymethyl cellulose; the surfactant solution F in step S2 is an aqueous solution of a mixture of oleic acid and palmitic acid with a mass ratio of 2:1; the remaining steps are the same as those in Example 1.

[0086] Example 7

[0087] Compared with Example 1, this example is different in that in this example, the dispersant solution G in step S1 is an aqueous solution of a 1:1 mass ratio of methyl cellulose and carboxymethyl cellulose; the surfactant solution G in step S2 is an aqueous solution of stearic acid; the remaining steps are the same as those in Example 1.

[0088] Example 8

[0089] Compared with Example 1, this example is different in that in this example, the dispersant solution H in step S1 is an aqueous solution of a 1:1 mass ratio of methyl cellulose and carboxymethyl cellulose; the surfactant solution H in step S2 is an aqueous solution of a mixture of palmitic acid and lauric acid with a mass ratio of 2:1; the remaining steps are the same as those in Example 1.

[0090] Example 9

[0091] Compared with Example 1, this example is different in that in this example, the mass of the nano silver seed solution A in step S2 is 37.8 g; the remaining steps are the same as those in Example 1.

[0092] Example 10

[0093] Compared with Example 1, this example is different in that in this example, the mass of the nano silver seed solution A in step S2 is 113.4 g; the remaining steps are the same as those in Example 1.

[0094] Example 11

[0095] Compared with Example 1, this example is different in that in this example, the absolute ethanol for replacing the aqueous solution in step S2 is 1.18 times the mass of silver nitrate in the silver ammonia solution IIA; the remaining steps are the same as those in Example 1.

[0096] Example 12

[0097] Compared with Example 1, this example is different in that in this example, the absolute ethanol for replacing the aqueous solution in step S2 is 1.90 times the mass of silver nitrate in the silver ammonia solution IIA; the remaining steps are the same as those in Example 1.

[0098] Example 13

[0099] This embodiment is different from Embodiment 1 in that in this embodiment, the mass ratio of the spherical silver powder to the stainless steel grinding balls in step S3 is 1:20; the size of the stainless steel grinding balls is φ1 mm; the remaining steps are the same as those in Embodiment 1.

[0100] Embodiment 14

[0101] This embodiment is different from Embodiment 1 in that in this embodiment, the mass ratio of the spherical silver powder to the stainless steel grinding balls in step S3 is 1:30; the size of the stainless steel grinding balls is φ3 mm; the remaining steps are the same as those in Embodiment 1.

[0102] Embodiment 15

[0103] This embodiment is different from Embodiment 1 in that in this embodiment, the ball milling rotation speed in step S3 is set to 400 rpm; the remaining steps are the same as those in Embodiment 1.

[0104] Embodiment 16

[0105] This embodiment is different from Embodiment 1 in that in this embodiment, the ball milling rotation speed in step S3 is set to 800 rpm; the remaining steps are the same as those in Embodiment 1.

[0106] Embodiment 17

[0107] This embodiment is different from Embodiment 1 in that in this embodiment, the ball milling time in step S3 is 4 h; the remaining steps are the same as those in Embodiment 1.

[0108] Embodiment 18

[0109] This embodiment is different from Embodiment 1 in that in this embodiment, the ball milling time in step S3 is 8 h; the remaining steps are the same as those in Embodiment 1.

[0110] Comparative Example 1

[0111] This comparative example is different from Embodiment 1 in that in this comparative example, the mass of the nano silver seed solution A in step S2 is 18.9 g; the remaining steps are the same as those in Embodiment 1.

[0112] Comparative Example 2

[0113] This comparative example is different from Embodiment 1 in that in this comparative example, the mass of the nano silver seed solution A in step S2 is 151.2 g; the remaining steps are the same as those in Embodiment 1.

[0114] Comparative Example 3

[0115] This comparative example is different from Example 1 in that, in this comparative example, the absolute ethanol for replacing the aqueous solution in step S2 is 2.54 times the mass of silver nitrate in silver ammonia solution IIA; the remaining steps are the same as those in Example 1.

[0116] Comparative Example 4

[0117] This comparative example is different from Example 1 in that, in this comparative example, the absolute ethanol for replacing the aqueous solution in step S2 is 0.95 times the mass of silver nitrate in silver ammonia solution IIA; the remaining steps are the same as those in Example 1.

[0118] Comparative Example 5

[0119] This comparative example is different from Example 1 in that, in this comparative example, the surfactant in step S2 is 1.2 g of stearic acid; 1.2 g of stearic acid is added to 120 g of deionized water, stirred and dissolved, and kept at a constant temperature of 30 °C to obtain a 10 g / L surfactant solution I; the remaining steps are the same as those in Example 1.

[0120] Comparative Example 6

[0121] This comparative example is different from Example 1 in that, in this comparative example, the surfactant in step S2 is 8.4 g of stearic acid; 8.4 g of stearic acid is added to 120 g of deionized water, stirred and dissolved, and kept at a constant temperature of 30 °C to obtain a 70 g / L surfactant solution J; the remaining steps are the same as those in Example 1.

[0122] Comparative Example 7

[0123] This comparative example is different from Example 1 in that, in this comparative example, the mass ratio of the spherical silver powder to the stainless steel grinding balls in step S3 is 1:10; the remaining steps are the same as those in Example 1.

[0124] Comparative Example 8

[0125] This comparative example is different from Example 1 in that, in this comparative example, the mass ratio of the spherical silver powder to the stainless steel grinding balls in step S3 is 1:40; the remaining steps are the same as those in Example 1.

[0126] Comparative Example 9

[0127] This comparative example is different from Example 1 in that, in this comparative example, the ball milling time in step S3 is 3 h; the remaining steps are the same as those in Example 1.

[0128] The flaky silver powder obtained in this comparative example was subjected to scanning electron microscopy to obtain a scanning electron micrograph as Figure 3 shown.

[0129] Comparative Example 10

[0130] This comparative example is different from Example 1 in that in this comparative example, the ball milling time in step S3 is 8 h; the remaining steps are the same as those in Example 1.

[0131] Comparative Example 11

[0132] This comparative example is different from Example 1 in that in this comparative example, the ball milling speed in step S3 is 300 rpm; the remaining steps are the same as those in Example 1.

[0133] Comparative Example 12

[0134] This comparative example is different from Example 1 in that in this comparative example, the ball milling speed in step S3 is 1000 rpm; the remaining steps are the same as those in Example 1.

[0135] Comparative Example 13

[0136] This comparative example is different from Example 1 in that in this comparative example, the reducing agent solutions IK and IIK in steps S1 and S2 are both aqueous solutions of hydrazine hydrate; the remaining steps are the same as those in Example 1.

[0137] Comparative Example 14

[0138] This comparative example is different from Example 1 in that in this comparative example, the dispersant in step S1 is polyvinylpyrrolidone K90; the remaining steps are the same as those in Example 1.

[0139] Comparative Example 15

[0140] This comparative example is different from Example 1 in that in this comparative example, the surfactant in step S2 is oleylamine; the remaining steps are the same as those in Example 1.

[0141] The flaky silver powder obtained in this comparative example was subjected to scanning electron microscopy to obtain a scanning electron micrograph as Figure 4 shown.

[0142] Experimental Example

[0143] In this experimental example, the mass of spherical silver powder was obtained from Examples 1 to 18 and Comparative Examples 1 to 15 through the following steps:

[0144]

[0145] The laser particle size data, the burn-off rate data at 538 °C, and the tapped density data of the flaky silver powder obtained in Examples 1 to 18 and Comparative Examples 1 to 15 were listed in Table 1;

[0146] Among them, the burnout rate at 538 °C was determined with reference to the national standard GB / T 1773—2008: Take 3.0 g of the sample, place it in a crucible that has been weighed to a constant weight, put it into a tube resistance furnace, heat it up to 538 °C along with the furnace, keep it at 538 °C ± 5 °C for 30 min, cool it down along with the furnace, take it out and weigh it, and calculate the burnout rate (X2) according to formula (2), with the value expressed in %:

[0147]

[0148] In the formula:

[0149] m3———The weight of the sample before burning, in grams (g);

[0150] m4———The weight of the sample after burning, in grams (g);

[0151] The burnout rate characterizes the proportion of non-silver components in the silver powder, such as organic component coating agents, etc. These substances often play a role in reducing the electrical performance in the circuit, but will play a role in adjusting the compatibility, adaptability, viscosity, etc. of the slurry when formulated into a slurry. Therefore, it is necessary to ensure that the burnout rate is at a relatively low value.

[0152] Table 1 Data of the flaky silver powder obtained in Examples 1~18 and Comparative Examples 1~15

[0153]

[0154]

[0155] As can be seen from Table 1, compared with Comparative Examples 1~15, the flaky silver powder prepared in Examples 1~18 is more in line with the usage requirements of the flaky silver powder for the low-temperature curing silver paste of the membrane switch in terms of parameters such as particle size distribution, burnout rate at 538 °C, loose bulk density, tapped density, aspect ratio, etc.

[0156] Figure 1 It is the scanning electron microscope image of the monodisperse spherical silver powder in the nano silver seed solution A prepared in Example 1. It can be seen that the spherical silver powder prepared by this method has a concentrated particle size distribution, high sphericity, and good dispersibility, which is beneficial to obtaining flaky silver powder with a narrow flake diameter distribution and good dispersibility when grinding into flaky silver powder subsequently.

[0157] Figure 2 It is the scanning electron microscope image of the flaky silver powder with low loose bulk density prepared in Example 1. When it is formulated into a low-temperature curing silver paste for printing and curing, more surface lap joints are formed to form a path. At the same time, the sintering activity of the flaky silver powder is higher, enabling it to partially sinter and melt even under the low-temperature curing process, forming better lap joints and providing good electrical performance, meeting the usage requirements of the flaky silver powder for the low-temperature curing silver paste of the membrane switch.

[0158] Figure 3 SEM image of the flaky silver powder with a low degree of flakiness prepared in Comparative Example 9. When configured for printing and curing of the low-temperature curing silver paste, due to the low degree of flakiness, the sintering activity is low, and the degree of melting after curing is low. Some particles are in point-to-point contact or point-to-line contact, resulting in poor electrical properties and not meeting the usage requirements for flaky silver powder put forward by the usage process conditions of the low-temperature curing silver paste for membrane switches.

[0159] Figure 4 SEM image of the flaky silver powder with a low aspect ratio prepared in Comparative Example 15. When configured for printing and curing of the low-temperature curing silver paste, due to the relatively high aspect ratio, the sintering activity at the edges of the flaky silver powder is weak, and the degree of melting during low-temperature curing is low. It is difficult to effectively melt and bond to conduct the circuit, resulting in poor electrical properties and not meeting the usage requirements for flaky silver powder put forward by the usage process conditions of the low-temperature curing silver paste for membrane switches.

[0160] Compared with Example 1, the content of nano silver crystal seeds in Comparative Example 1 is low, resulting in a relatively large size of the synthesized spherical silver powder, and then leading to an increase in the particle size of the obtained flaky silver powder and a decrease in the degree of flakiness, making the loose bulk density and tapped density on the high side, not meeting the usage requirements of the low-temperature curing silver paste for membrane switches.

[0161] Compared with Example 1, the content of nano silver crystal seeds in Comparative Example 2 is high, resulting in a relatively small size of the synthesized spherical silver powder, and then leading to a small particle size of the obtained flaky silver powder and more adsorbed surfactants, resulting in a relatively high burn-off rate at 538 °C, not meeting the usage requirements of the low-temperature curing silver paste for membrane switches.

[0162] Compared with Example 1, the amount of absolute ethanol used in Comparative Example 3 is low, resulting in a high solid content when grinding the flaky silver powder. The spherical silver particles are cold-welded to form large flakes during the extension process, resulting in a relatively large particle size and a wider particle size distribution of the flaky silver powder, not meeting the usage requirements of the low-temperature curing silver paste for membrane switches.

[0163] Compared with Example 1, the amount of absolute ethanol used in Comparative Example 3 is low, resulting in a high solid content when grinding the flaky silver powder. The spherical silver particles are prone to collide and cold-weld to form large flakes during the extension process, resulting in a relatively large particle size and a wider particle size distribution of the flaky silver powder, not meeting the usage requirements of the low-temperature curing silver paste for membrane switches.

[0164] Compared with Example 1, the amount of absolute ethanol used in Comparative Example 4 is high, resulting in a low solid content when grinding the flaky silver powder. The spherical silver particles are resisted by the absolute ethanol during the extension process, reducing the collision energy between the grinding balls and the silver particles, resulting in a relatively low degree of flakiness and aspect ratio of the flaky silver powder. At the same time, the loose bulk density and tapped density are on the high side, not meeting the usage requirements of the low-temperature curing silver paste for membrane switches.

[0165] Compared with Example 1, in Comparative Example 5, the amount of surfactant used is low, resulting in insufficient dispersion effect of spherical silver powder during preparation, making the size of spherical silver particles relatively large. At the same time, when grinding into flaky silver powder, the flaky silver powder lacks the dispersion effect of surfactant, resulting in a relatively large size of flaky silver powder, which does not meet the requirements for the use of low-temperature curing silver paste for membrane switches.

[0166] Compared with Example 1, in Comparative Example 6, the amount of surfactant used is high, resulting in good dispersion effect of spherical silver powder during preparation, making the size of spherical silver particles relatively small. At the same time, it plays a lubricating role when grinding into flaky silver powder, making the size of flaky silver powder small and the flake type thin, thus adsorbing more surfactant, resulting in a relatively high burn-off rate at 538°C, which does not meet the requirements for the use of low-temperature curing silver paste for membrane switches.

[0167] Compared with Example 1, in Comparative Examples 7, 9, and 11, due to the low ball-to-material ratio, short ball-milling time, and low ball-milling speed, the energy of spherical silver particles deformed by the grinding balls is too small, resulting in too low a degree of flakiness of spherical silver powder. The final product is a mixture of flake powder and spherical silver particles that are hardly flaked. The statistical aspect ratio has no practical significance, resulting in relatively high loose bulk density and tapped density of flaky silver powder, which does not meet the requirements for the use of low-temperature curing silver paste for membrane switches.

[0168] Compared with Example 1, in Comparative Examples 8, 10, and 12, due to the high ball-to-material ratio, long ball-milling time, and high ball-milling speed, the energy of spherical silver particles deformed by the grinding balls is too high, resulting in too high a degree of flakiness of spherical silver powder, resulting in a relatively high burn-off rate at 538°C of flaky silver powder, which does not meet the requirements for the use of low-temperature curing silver paste for membrane switches.

[0169] Compared with Example 1, in Comparative Example 13, due to the relatively strong reducing ability of the reducing agent hydrazine hydrate, the sizes of nano silver seeds and spherical silver particles are relatively small during the forming process. Furthermore, when grinding into flaky silver powder, the specific surface area increases, adsorbing more surfactant, resulting in a relatively high burn-off rate at 538°C of flaky silver powder, which does not meet the requirements for the use of low-temperature curing silver paste for membrane switches.

[0170] Compared with Example 1, in Comparative Example 14, due to the relatively weak dispersion effect of polyvinylpyrrolidone, the size of nano silver seed particles is relatively large. Furthermore, when taking the same mass of nano silver seed solution, the number of nano silver particles is relatively small, resulting in relatively large spherical silver particles, and further resulting in relatively large particle size and wider particle size distribution of flaky silver powder, which does not meet the requirements for the use of low-temperature curing silver paste for membrane switches.

[0171] Comparative Example 15, compared with Example 1, since the adsorption effect of the amino group in oleylamine on silver is inferior to that of the carboxyl group in organic acid on silver, it leads to a reduction in the surface energy of silver particles or causes dislocation migration of the lattice in the near-surface layer, and the effect of reducing the strength and hardness of silver particles is inferior to that of organic acid grinding aids. As a result, the degree of flaking of spherical silver powder is relatively low under the same ball milling energy, and the loose bulk density and tapped density of flaky silver powder are relatively high, which does not meet the usage requirements of the low-temperature curing silver paste for membrane switches.

[0172] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that, without departing from the spirit and scope of the present invention, various changes or equivalent substitutions can be made to these features and embodiments. Additionally, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A method for preparing flaky silver powder with low tap density, characterized in that: It includes the following steps: S1. Preparation of nano silver seeds: Drop silver ammonia solution I into the dispersant solution, stir for 5 min to 10 min after dropping, obtain mixed solution I, then drop reducing agent solution I into mixed solution I, stir for 30 min to 40 min after dropping, and obtain nano silver seed solution; S2. Add the nano silver seed solution in step S1 into the surfactant solution, stir and disperse at a constant temperature for 5 min to 10 min to obtain mixed solution II. Drop silver ammonia solution II and reducing agent solution II into mixed solution II simultaneously, continue to react for 5 min to 10 min after dropping, and perform solvent replacement after the reaction to obtain spherical silver powder slurry; The surfactant solution is an aqueous solution of any one or a mixture of oleic acid, stearic acid, palmitic acid, palmitic acid, lauric acid, etc.; the mass of the surfactant in the surfactant solution is 1.5% to 3% of the mass of silver nitrate added in silver ammonia solution II; The solvent replacement is to use absolute ethanol to replace the aqueous solution; The mass of the nano silver seed solution is 20% to 60% of the mass of silver nitrate added in silver ammonia solution II; S3. Add the spherical silver powder slurry obtained in step S2 and stainless steel grinding balls into a ball mill for ball milling. The mass ratio of spherical silver powder to stainless steel grinding balls is 1:20 to 1:30; the diameter of the stainless steel grinding balls is 1 mm to 3 mm. Start the external circulation system of the ball mill, the ball milling speed is 400 rpm to 800 rpm, and the ball milling time is 4 h to 8 h; S4. After ball milling is completed, separate the flaky silver powder from the grinding balls, wash it with deionized water until it is below 20 μS / cm, dry it at a temperature of 70°C to 80°C for 12 h to 24 h, and then sieve it through a sieve to obtain flaky silver powder with an average particle size D50 of 2 μm to 4 μm, a diameter-to-thickness ratio of 20:1 to 100:1, and a loose bulk density of 0.3 g / cm 3 ~0.6 g / cm 3 ; flaky silver powder with a burn-off rate of ≤0.9% at 538°C.

2. The preparation method of the flaky silver powder with low tap density according to claim 1, characterized in that: The dispersant solution is an aqueous solution of one or a mixture of methyl cellulose or carboxymethyl cellulose.

3. The preparation method of the flaky silver powder with low tap density according to claim 1, characterized in that: Both silver ammonia solution I and silver ammonia solution II are transparent Ag(NH3)2OH solutions prepared by adding ammonia water to an aqueous silver nitrate solution; both reducing agent solution I and reducing agent solution II are aqueous glucose solutions.

4. The preparation method of the flaky silver powder with low tap density according to any one of claims 2-3, characterized in that: In step S1, the mass concentration of silver ammonia in silver ammonia solution I is 28 g / L to 56 g / L; the mass concentration of the dispersant solution is 10 g / L to 20 g / L; the mass concentration of reducing agent solution I is 15 g / L to 36 g / L.

5. The preparation method of the flaky silver powder with low tap density according to claim 4, characterized in that: In step S1, the molar ratio of silver ammonia to the reducing agent in silver ammonia solution I and reducing agent solution I is 1:0.5 to 1:0.

6.

6. The preparation method of the flaky silver powder with low tap density according to claim 5, characterized in that: In step S1, preheat the dispersant solution, reducing agent solution I and silver ammonia solution I to 45°C to 55°C respectively, drop silver ammonia solution I and reducing agent solution I at 45°C to 55°C respectively, and stir and react at 45°C to 55°C after dropping.

7. The preparation method of the flaky silver powder with low tap density according to claim 6, characterized in that: In step S1, the dropping speed of silver ammonia solution I is 30 mL / min to 50 mL / min; the dropping speed of the reducing agent is 60 mL / min to 90 mL / min.

8. The preparation method of the flaky silver powder with low tap density according to claim 2, characterized in that: In step S2, the molar ratio of silver ammonia to the reducing agent in silver ammonia solution II and reducing agent solution II is 1:0.5 to 1:0.

6.

9. The preparation method of the flaky silver powder with low tap density according to claim 8, wherein: In the step S2, the silver ammonia solution II, the reducing agent solution II, the nano silver seed solution and the surfactant solution are respectively preheated to 25°C to 35°C, the constant temperature stirring temperature is 25°C to 35°C, and the silver ammonia solution II and the reducing agent solution II are added dropwise under the temperature condition of 25°C to 35°C. After the addition is completed, the reaction continues under the temperature condition of 25°C to 35°C.

10. The preparation method of the flaky silver powder with low tap density according to claim 9, characterized in that: In the step S2, the dropping rates of the silver ammonia solution II and the reducing agent solution II are both 185 mL / min to 280 mL / min.

11. The preparation method of the flaky silver powder with low tap density according to claim 3, wherein: In the step S2, the amount of absolute ethanol used for solvent replacement is 1.18 times to 1.90 times the mass of silver nitrate added in the silver ammonia solution II.

12. The preparation method of the flaky silver powder with low tap density according to claim 3, characterized in that: In the step S2, the mass concentration of silver ammonia in the silver ammonia solution II is 318 g / L; the mass concentration of the reducing agent solution II is 180 g / L; the mass concentration of the surfactant solution is 24 g / L to 47 g / L.

13. The preparation method of the flaky silver powder with low tap density according to claim 1, wherein: In the step S3, the cooling medium of the outer circulation system of the ball mill is cold water, and the circulation speed is 0.5 L / min to 1 L / min.

14. Application of a flaky silver powder with low tap density, characterized in that: The flaky low tap density flaky silver powder prepared by the method for preparing flaky low tap density flaky silver powder according to any one of claims 1-13 is used for producing electronic silver paste.

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