Method and system for manufacturing high-dispersion high-crystallization spherical silver powder

Abstract

According to the manufacturing method and system for the high-dispersion high-crystallization spherical silver powder, a small amount of polybasic acid complexing silver salt is added into a silver nitrate aqueous solution to form seed crystals, a dispersing agent is added into a reducing agent aqueous solution, and the PH value in the reaction process is adjusted through an alkaline aqueous solution. The feeding and mixing process of the system comprises three modes, finally, high-dispersion and high-crystallization spherical silver powder with different particle sizes can be generated, the first mode is that a reducing agent solution is pressed into a reaction kettle through compressed nitrogen to be mixed and react with a silver nitrate solution, and the second mode is that the silver nitrate solution is pressed into the reaction kettle through compressed nitrogen to be mixed and react with the reducing agent solution. And thirdly, simultaneously pressing the reducing agent solution and the silver nitrate solution into a reaction kettle by using compressed nitrogen to mix and react. According to the method, the reaction process is effectively controlled, good crystallization and dispersion of silver powder particles can be formed, and the method is verified in industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of conductive precious metal powder preparation, and in particular relates to a method and system for manufacturing highly dispersed and highly crystalline spherical silver powder. Background Art

[0002] Silver powder, a key electronic material, is widely used in solar photovoltaic panel electrodes, integrated circuits, light sources, new energy vehicles, and other electronic appliances, as well as conductive inks, due to its high electrical and thermal conductivity. The dispersion and crystallization of silver powder affect its performance and use. Good dispersion maintains the stability of the silver paste over time and prints a defect-free, densely deposited silver metal structure, improving electrical conductivity. Good crystallization enhances the conductivity of the silver particles themselves.

[0003] Currently, the main method for producing silver powder is liquid-phase reduction. This involves adding a silver nitrate solution to a large reactor (1-5 cubic meters), controlling the temperature and pH, and then adding a dispersant and a reducing agent for liquid-phase reduction to produce silver powder. The silver powder undergoes solid-liquid separation, drying, dispersion, and screening to obtain the finished product. However, this traditional method, due to the large amount of raw materials loaded into the reactor at once, produces a large amount of silver powder. The reduced silver powder has a small particle size and high surface energy, so the large amount used in each reaction easily aggregates in the reactor, resulting in poor dispersibility. Furthermore, the large amount used in a single reduction makes it difficult to uniformly mix the silver nitrate solution and the reducing agent solution within a short period of time. This results in multiple nucleation and growth of the silver powder, making it difficult to control crystallization and forming irregular morphologies, which in turn affects the performance and application of the silver powder. Therefore, developing a method and system for producing highly dispersed, highly crystalline, spherical silver powder is of great practical significance. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the existing technology and solve the problems of dispersibility and crystallinity of silver powder. It provides a semi-continuous silver powder preparation method and system with high efficiency, low cost and good environmental performance, with small reaction volume per time, so as to produce a series of highly dispersed and highly crystalline spherical silver powders with an average particle size between 0.3μm and 5μm. The silver powders have excellent performance parameters such as dispersibility and conductivity, which can meet the market demand for this type of silver powder.

[0005] A manufacturing system for highly dispersed and highly crystalline spherical silver powder, comprising a silver nitrate dissolving tank 1, a reducing agent dissolving tank 2, an alkaline solution tank 3, a silver nitrate rapid feeding tank 4, a reducing agent rapid feeding tank 5, a reactor 6, a compressed nitrogen source 1 7, and a compressed nitrogen source 2 8; The silver nitrate dissolving tank 1 is equipped with an electronic scale W1 and a temperature measuring thermal resistor T1. The silver nitrate dissolving tank 1 is connected to the water outlet of the deionized water source and the feed port of the silver nitrate rapid feeding tank 4 through a pneumatic valve V1 and a pneumatic valve V2, respectively. The silver nitrate rapid feeding tank 4 is connected to a compressed nitrogen source 7 and a pressure measuring transmitter P1 through a pneumatic valve V10. A pneumatic valve V11 is installed on the silver nitrate rapid feeding tank 4 for exhaust. The silver nitrate rapid feeding tank 4 is connected to the reactor 6 through a pneumatic valve V12. The reducing agent dissolving tank 2 is equipped with an electronic scale W3 and a temperature measuring thermal resistor T3. The reducing agent dissolving tank 2 is connected to the water outlet of the deionized water source and the feed port of the raw agent rapid feeding tank 5 through a pneumatic valve V5 and a pneumatic valve V6, respectively. The reducing agent rapid feeding tank 5 is connected to the compressed nitrogen source 8 and the pressure measuring transmitter P2 through a pneumatic valve V7. The reducing agent rapid feeding tank 5 is provided with a pneumatic valve V8 for exhaust. The reducing agent rapid feeding tank 5 is connected to the reactor 6 through a pneumatic valve V9. The alkaline solution tank 3 is equipped with an electronic scale W2 and a temperature measuring resistor T2. The alkaline solution tank 3 is connected to the water outlet of the deionized water source through a pneumatic valve V3. The alkaline solution tank 3 is connected to the reactor 6 through an electric regulating valve V4. The reactor 6 is a hexagonal reactor with a conical bottom and a volume of 0.15-0.3 cubic meters. The reactor 6 is equipped with a temperature measuring resistor T4 and a pH meter. The reactor 6 is also equipped with a pneumatic valve V14 for discharging. The silver nitrate dissolution tank 1, reducing agent dissolution tank 2, alkaline solution tank 3, silver nitrate quick feeding tank 4, reducing agent quick feeding tank 5 and reactor 6 are made of 316L stainless steel. The silver nitrate quick feeding tank 4 and reducing agent quick feeding tank 5 are sealed tanks with a tank volume of 0.05-0.1 cubic meters.

[0006] A method for producing highly dispersed and highly crystalline spherical silver powder comprises the following steps: S1. Add silver nitrate and deionized water to a silver nitrate dissolving tank 1 to form a silver nitrate aqueous solution, add a small amount of polyacid complex silver salt to form seed crystals, and control the solution temperature and weight; Add reducing agent and deionized water into reducing agent dissolving tank 2 to form reducing agent aqueous solution, add a small amount of dispersant, and control the solution temperature and weight; In the alkaline solution tank 3, deionized water is first added and then an alkaline reagent is added to form an alkaline aqueous solution. The temperature and weight of the solution are controlled to adjust the pH value during the reaction; S2, quantitatively put the silver nitrate solution and reducing agent solution prepared in S1 into the silver nitrate rapid feeding tank 4 and the original agent rapid feeding tank 5 respectively; S3, using compressed nitrogen source 1 7 and compressed nitrogen source 2 8, pressurize the silver nitrate solution and the reducing agent solution into the reaction kettle 6 for mixing and reaction, and add the alkaline aqueous solution prepared in S1 into the reaction kettle 6 to adjust the pH value; S4, the mixed solution after mixing and adjusting the pH in S3 is reacted in the reactor 6 and after a short aging, the valve V14 is opened to release the mixture of silver powder and the reaction liquid; S5, repeat S2-S4 until the solutions in the silver nitrate dissolving tank 1 and the reducing agent dissolving tank 2 are consumed; S6. Clean the silver powder released in S5 with deionized water in a vacuum filtration device; S7, dissolving the surface modifier in pure water or alcohol and adding it to the silver powder cleaned in S6 under high-speed stirring to modify the surface of the silver powder, and then placing it in a vacuum drying oven for drying; S8, put the silver powder dried in S7 into a powdering machine to grind and disperse; S9, the silver powder dispersed in S8 is classified by air flow classification equipment to obtain highly dispersed and highly crystalline spherical silver powder with an average particle size between 0.3um and 5um.

[0007] Furthermore, in S1, the amount of deionized water added is 1000-2500 kg, the molar concentration of the silver nitrate aqueous solution is 0.4 mol-0.85 mol / L, and the temperature is 40°C-80°C; the polyacid is one or a combination of malonic acid, glutaric acid, and malic acid, and the amount added is 0.03%-0.08% of the weight of silver nitrate. The deionized water used to dissolve the polyacid is 5-8 kg, and the addition speed is 60-110 seconds.

[0008] Furthermore, in S1, the reducing agent is ascorbic acid, the added deionized water is 1000-2500 kg, the molar concentration of the reducing agent aqueous solution is controlled between 0.26-0.57 mol / L, and the temperature is controlled at 40-80°C; the dispersant is one or two or a combination of three of lauric acid, myristic acid, palmitic acid, and fatty alcohol polyoxyethylene ether, and the added amount is 0.3%-1.0% of the weight of silver nitrate, and the deionized water ethanol used to dissolve the dispersant is 0.5-5 kg.

[0009] Furthermore, in said S1, the alkaline reagent is a hydroxide or carbonate of an alkali metal, the concentration of the alkaline aqueous solution is 1.5-2.5 mol / L, and the temperature is controlled at 40-80°C.

[0010] Furthermore, the pH value of the reaction process in S3 is controlled between 5 and 7. According to the set pH value, the pH value of the reaction solution in the reactor is used as the feedback value, and a PID control method can be introduced to adjust the amount of alkaline solution added to achieve automatic control and ensure the stability of the pH value of the reaction solution in the reactor. The entire manufacturing step and method of the present application is automatically controlled and recorded by a programmable controller to achieve product stability, reliability and consistency.

[0011] Furthermore, there are three ways to perform the mixing process in S3, which will eventually produce silver powders with different particle sizes: 1. Pressurize the reducing agent solution into the reactor 6 with compressed nitrogen to mix with the silver nitrate solution for reaction: (1) Open valve V2 and add a certain amount of silver nitrate solution into the silver nitrate quick feeding tank 4. Close valves V2 and V11, open valves V12 and V10, and use compressed nitrogen 7 to pressurize the silver nitrate solution into the reactor 6. After the addition is complete, close valves V12 and V10 and open valve V11 to exhaust.

[0012] (2) Open valve V6 and add the reducing agent solution into the reducing agent solution rapid feeding tank 5 in a quantitative manner. Close valves V6 and V8, open valves V7 and V9, and use compressed nitrogen 8 to pressurize the reducing agent solution into the reactor 6. While opening valve V7, open the regulating valve V4 and control the amount of alkaline solution added to ensure the stability of the pH value during the reaction. After adding the materials, close valves V7, V9, and V4, and open valve V8 to exhaust.

[0013] 2. Pressurize the silver nitrate solution into the reactor 6 with compressed nitrogen and mix it with the reducing agent solution to react: (1) Open valve V6 and add the reducing agent solution into the raw material solution rapid feeding tank 5 in a quantitative manner. Close valves V6 and V8, open valves V7 and V9, and use compressed nitrogen 8 to pressurize the reducing agent solution into the reactor 6. After adding the materials, close valves V7 and V9 and open valve V8 to exhaust.

[0014] (2) Open valve V2 and add a certain amount of silver nitrate solution into the silver nitrate quick feeding tank 4. Close valves V2 and V11, open valves V12 and V10, and use compressed nitrogen 7 to pressurize the silver nitrate solution into the reactor 6. While opening valve V10, open regulating valve V4 and control the amount of alkaline solution added to ensure the stability of the pH value during the reaction. After adding the materials, close valves V12 and V10 and open valve V11 to exhaust.

[0015] 3. The reducing agent solution and the silver nitrate solution are simultaneously pressed into the reactor 6 with compressed nitrogen for mixed reaction: (1) Open valve V6, add the reducing agent solution into the rapid feeding tank 5 in a quantitative manner, close valves V6 and V8, open valve V2, add the silver nitrate solution into the rapid feeding tank 4 in a quantitative manner, and close valves V2 and V11; (2) Open valves V7, V9, V10, V12 and regulating valve V4 simultaneously, and use compressed nitrogen 7 and 8 to pressurize the silver nitrate solution and reducing agent solution into the reactor 6 for reaction. At the same time, control the pH value in the reactor 6 through regulating valve V4. After the addition of materials, close valves V7, V9, V10, V12 and regulating valve V4, and open valves V8 and V11 to exhaust.

[0016] Furthermore, in S2-S3, the amount of silver nitrate solution added to the silver nitrate solution quick feeding tank 4 is 11-42 kg each time, and the amount of reducing agent solution added to the reducing agent solution quick feeding tank 5 is 10-40 kg each time; the pressure of the compressed nitrogen is 0.1-0.6 MPa, and the purity is above 99%. The time for pressing the silver nitrate solution and the reducing agent solution from the quick feeding tank into the reactor with compressed nitrogen is 3-30 seconds.

[0017] The present invention has the following advantages: 1. The system of the present invention adopts a "small amount, multiple times" and semi-continuous method. Under the premise of ensuring production efficiency, since the amount of each addition is much smaller than that of the traditional method (less than 1 / 5), it is easy to mix the silver nitrate solution and the reducing agent solution evenly, and the amount of silver powder generated by the reaction is small, the aggregation of silver powder particles is greatly reduced, and the dispersion of silver powder particles is guaranteed; 2. The feeding method of this application uses compressed nitrogen as the power source. On the one hand, the feeding speed and time can be stably controlled by the pressure, ensuring the thermodynamic and kinetic conditions of the silver powder particles during crystal growth, so that the silver powder has better crystallinity and more consistent morphology. On the other hand, due to the stable nature of nitrogen, it can be ensured that the feeding solution does not react with the nitrogen, thereby ensuring that no new impurities are introduced. 3. Compared with the traditional method, the production method of the system of the present application can achieve the precise introduction of silver nitrate solution and reducing agent solution into the reactor, and can prepare highly crystalline, highly dispersed, and spherical silver powder with a relatively regular morphology.

[0018] 4. When the present application uses polyacid complexed silver salt to form seed crystals, different polyacid combinations, the concentration of the polyacid solution, the concentration of the silver nitrate solution, the temperature of the silver nitrate solution, the time of adding the polyacid solution, etc. are controlled to produce different seed crystals such as single crystals, single twin crystals, and multiple twin crystals, which facilitates the formation of good spherical crystals when the crystal particles grow subsequently, thereby achieving high crystallinity of the silver powder particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of the system of the manufacturing method of the present invention; Figure 2 This is a scanning electron microscope image of the silver powder prepared in Example 1; Figure 3 This is a scanning electron microscope image of the silver powder prepared in Example 2; Figure 4 This is a scanning electron microscope image of the silver powder prepared in Example 3; Figure 5 This is a scanning electron microscope image of the silver powder prepared in Example 4; Figure 6 This is a scanning electron microscope image of the silver powder prepared in Example 5; Figure 7 This is a scanning electron microscope image of the silver powder prepared in Comparative Example 1. DETAILED DESCRIPTION

[0020] The manufacturing method and system of the present invention are further described below with reference to examples: Example 1: S1: Add silver nitrate and 1500 kg of deionized water to the silver nitrate dissolving tank 1 to form a silver nitrate aqueous solution. The molar concentration of the silver nitrate aqueous solution is 0.6 mol / L, and the solution temperature is controlled at 60°C. Add 0.03% malic acid and 0.03% malonic acid to the weight of the silver nitrate and 6 kg of deionized water to form an aqueous solution. Use a metering pump to add the solution to the silver nitrate solution for 80 seconds to form seed crystals. Ascorbic acid and 1500 kg of deionized water were added to the reducing agent dissolving tank 2 to form a reducing agent aqueous solution. The molar concentration of the reducing agent aqueous solution was 0.4 mol / L, and the solution temperature was controlled at 60° C. 0.6% of the weight of silver nitrate in lauric acid was dissolved in 3 kg of ethanol, and 0.2% of the weight of silver nitrate in fatty alcohol polyoxyethylene ether was dissolved in 1 kg of pure water. After mixing, the mixture was adjusted to an emulsified dispersant and added to the reducing agent solution. First, add 100 kg of deionized water into the alkaline solution tank 3, and then add sodium hydroxide to form an alkaline aqueous solution with a molar concentration of 2 mol / L. The solution temperature is controlled at 60°C to adjust the pH value during the reaction. S2: Open valve V6, add 19 kg of reducing agent solution to the rapid feeding tank 5 using an electronic scale, close valves V6 and V8, open valve V2, add 20 kg of silver nitrate solution to the rapid feeding tank 4 using an electronic scale, and close valves V2 and V11; S3: Simultaneously open valves V7, V9, V10, V12 and regulating valve V4, and use 0.4 MPa compressed nitrogen 7 and 8 to simultaneously pressurize the silver nitrate solution and the reducing agent solution into the reactor 6 within 5 seconds for reaction. At the same time, the alkaline solution added through the regulating valve V4 controls the pH value in the reactor 6 to 6. After the addition is complete, close valves V7, V9, V10, V12 and regulating valve V4, and open valves V8 and V11 for exhaust. S4: After aging for 50 seconds in the reactor 6, valve V14 is opened to release the silver powder; S5: Repeat S2-S4 until the solutions in the silver nitrate dissolving tank 1 and the reducing agent dissolving tank 2 are consumed; S6: The silver powder released in S5 is cleaned with deionized water in a vacuum filtration device; S7: dissolving a surface modifier of 0.1% by weight of silver nitrate in alcohol and adding it to the silver powder cleaned in S6 under high-speed stirring to modify the surface of the silver powder, and then drying it in a vacuum drying oven; S8: After the drying in S7 is completed, the silver powder is put into a powdering machine to be powdered and dispersed; S9: The silver powder dispersed in S8 is classified by airflow classification equipment to obtain highly dispersed and highly crystalline spherical silver powder.

[0021] The main parameters of the silver powder prepared in Example 1 are as follows: tap density = 4.8 g / cm 3 , specific surface area SBET = 0.95m 2 / g, particle size D50 = 0.65 μm, the equivalent particle size calculated by specific surface area is DBET = 0.60 μm, the agglomeration coefficient AF = D50 / DBET = 1.08 (close to 1, indicating good dispersion), the volume resistivity of the printed circuit after drying (silver powder addition is 85%) = 2.2×10 -5 Ωcm, crystallization and morphology see Figure 2 shown.

[0022] Example 2: S1: Add silver nitrate and 1000 kg of deionized water to the silver nitrate dissolving tank 1 to form a silver nitrate aqueous solution. The molar concentration of the silver nitrate aqueous solution is 0.4 mol / L, and the solution temperature is controlled at 40°C. Add 0.02% malic acid and 0.02% succinic acid to the weight of the silver nitrate and 5 kg of deionized water to form an aqueous solution. Use a metering pump to add the solution to the silver nitrate solution for 60 seconds to form seed crystals. Ascorbic acid and 1000 kg of deionized water were added to the reducing agent dissolving tank 2 to form a reducing agent aqueous solution. The molar concentration of the reducing agent aqueous solution was 0.26 mol / L, and the solution temperature was controlled at 40° C. Palmitic acid containing 0.2% of the weight of silver nitrate was dissolved in 3 kg of ethanol, and fatty alcohol polyoxyethylene ether containing 0.1% of the weight of silver nitrate was dissolved in 0.5 kg of pure water. After mixing, the mixture was adjusted to an emulsified dispersant and added to the reducing agent solution. In the alkaline solution tank 3, 80 kg of deionized water was first added, and then sodium hydroxide was added to form an alkaline aqueous solution with a molar concentration of 1.5 mol / L. The solution temperature was controlled at 40°C to adjust the pH value during the reaction. S2: Open valve V6, add 10 kg of reducing agent solution to the rapid feeding tank 5 using an electronic scale, close valves V6 and V8, open valve V2, add 11 kg of silver nitrate solution to the rapid feeding tank 4 using an electronic scale, and close valves V2 and V11; S3: Simultaneously open valves V7, V9, V10, V12 and regulating valve V4, and use 0.1 MPa compressed nitrogen 7 and 8 to simultaneously pressurize the silver nitrate solution and the reducing agent solution into the reactor 6 within 3 seconds for reaction. At the same time, the alkaline solution added through the regulating valve V4 controls the pH value in the reactor 6 to 5. After the addition is complete, close valves V7, V9, V10, V12 and regulating valve V4, and open valves V8 and V11 for exhaust. Steps S4-S9 are the same as those in embodiment 1.

[0023] The main parameters of the silver powder prepared in Example 2 are as follows: tap density = 4.51 g / cm 3 , specific surface area SBET = 1.66m 2 / g, particle size D50 = 0.31 μm, the equivalent particle size calculated by specific surface area is DBET = 0.34 μm, the agglomeration coefficient AF = D50 / DBET = 0.91 (close to 1, indicating good dispersion), the volume resistivity of the printed circuit after drying (silver powder addition is 85%) = 2.11×10 -5 Ωcm. For crystallization and morphology, see Figure 3 shown.

[0024] Example 3: S1: Add silver nitrate and 2500 kg of deionized water to the silver nitrate dissolving tank 1 to form a silver nitrate aqueous solution. The concentration of the silver nitrate aqueous solution is 0.85 mol, and the solution temperature is controlled at 80°C. Add 0.08% malic acid and 0.08% glutaric acid to 8 kg of deionized water to form an aqueous solution, and add the solution to the silver nitrate solution for 110 seconds using a metering pump to form seed crystals. Add ascorbic acid and 2500 kg of deionized water to the reducing agent dissolving tank 2 to form a reducing agent aqueous solution. The concentration of the reducing agent aqueous solution is 0.57 mol, and the solution temperature is controlled at 80°C. Dissolve 1.0% of the weight of silver nitrate in myristic acid with 3 kg of ethanol and 0.53% of the weight of silver nitrate in fatty alcohol polyoxyethylene ether with 5 kg of pure water. After mixing, adjust to an emulsified dispersant and add it to the reducing agent solution. In the alkaline solution tank 3, 120 kg of deionized water was first added, and then sodium hydroxide was added to form an alkaline aqueous solution with a molar concentration of 2.5 mol / L. The solution temperature was controlled at 80°C to adjust the pH value during the reaction. S2: Open valve V6, add 40 kg of reducing agent solution to the rapid feeding tank 5 using an electronic scale, close valves V6 and V8, open valve V2, add 42 kg of silver nitrate solution to the rapid feeding tank 4 using an electronic scale, and close valves V2 and V11; S3: Simultaneously open valves V7, V9, V10, V12 and regulating valve V4, and use 0.6 MPa compressed nitrogen 1 and 2 to simultaneously pressurize the silver nitrate solution and the reducing agent solution into the reactor 6 for reaction within 30 seconds. At the same time, the alkaline solution added through the regulating valve V4 controls the pH value in the reactor 6 to 7. After the addition is complete, close valves V7, V9, V10, V12 and regulating valve V4, and open valves V8 and V11 to exhaust. Steps S4-S9 are the same as those in embodiment 1.

[0025] The main parameters of the silver powder prepared in Example 3 are as follows: tap density = 5.1 g / cm 3 , specific surface area SBET = 1.23m 2 / g, particle size D50 = 0.42 μm, equivalent particle size calculated by specific surface area is DBET = 0.46 μm, agglomeration coefficient AF = D50 / DBET = 0.91 (close to 1, indicating good dispersion), the volume resistivity of the printed circuit after drying (silver powder addition is 85%) is 2.18×10 -5 Ωcm. For crystallization and morphology, see Figure 4 shown.

[0026] Example 4: S1-S2, S4-S9 of this embodiment are the same as those of embodiment 1, except that step S3 is: (1) Open valves V12 and V10, and use 0.4 MPa compressed nitrogen 7 to pressurize the silver nitrate solution into the reactor 6 in 5 seconds. After the addition is complete, close valves V12 and V10, and open valve V11 to exhaust.

[0027] (2) Open valves V7 and V9, and use 0.4 MPa compressed nitrogen 8 to press the reducing agent solution into the reactor 6 in 5 seconds. While opening valve V7, open the regulating valve V4 and control the amount of alkaline solution added to ensure that the pH value is 6 during the reaction. After adding the materials, close valves V7, V9, and V4, and open valve V8 to exhaust.

[0028] The main parameters of the silver powder prepared in Example 4 are as follows: tap density = 6.63 g / cm 3 , specific surface area SBET = 0.17m 2 / g, particle size D50 = 3.29 μm, the equivalent particle size calculated by specific surface area is DBET = 3.36 μm, the agglomeration coefficient AF = D50 / DBET = 0.979 (close to 1, indicating good dispersion), the volume resistivity of the printed circuit after drying (silver powder addition is 85%) = 2.8×10 -5 Ωcm, crystallization and morphology see Figure 5 shown.

[0029] Example 5: S1-S2, S4-S9 of this embodiment are the same as those of embodiment 1, except that step S3 is: (1) Open valves V7 and V9, and use 0.4 MPa compressed nitrogen 2 to press the reducing agent solution into the reactor 6 in 5 seconds. After the addition is completed, close valves V7 and V9, and open valve V8 to exhaust.

[0030] (2) Open valves V12 and V10, and use 0.4 MPa compressed nitrogen 1 to press the silver nitrate solution into the reactor 6 in 5 seconds. While opening valve V10, open the regulating valve V4 and control the amount of alkaline solution added to ensure that the pH value is 6 during the reaction. After adding the materials, close valves V12 and V10, and open valve V11 to vent.

[0031] The main parameters of the silver powder prepared in Example 5 are as follows: tap density = 4.4 g / cm 3 , specific surface area SBET = 1.81m 2 / g, particle size D50 = 0.305 μm, the equivalent particle size calculated by specific surface area is DBET = 0.316 μm, agglomeration coefficient AF = D50 / DBET = 0.965 (close to 1, indicating good dispersion), the volume resistivity of the printed circuit after drying (silver powder addition is 85%) = 2.0 × 10 -5 Ωcm, crystallization and morphology see Figure 6 shown.

[0032] Comparative Example 1: The production parameters of this comparative example are the same as those of Implementation 1, and steps S6-S9 of this comparative example are the same as those of Implementation 1, except that in steps S1-S5 of this comparative example, 1500 kg of deionized water is added to a conventional large reactor (3 cubic meters) to form a silver nitrate aqueous solution. The molar concentration of the silver nitrate aqueous solution is 0.6 mol / L, and the solution temperature is controlled at 60°C. 0.03% malic acid and 0.03% malonic acid, based on the weight of the silver nitrate, are added to 8 kg of deionized water to form an aqueous solution, which is then added to the silver nitrate solution using a metering pump for 110 seconds to form seed crystals. Add ascorbic acid and 1500 kg of deionized water to a reducing agent dissolving tank (3 cubic meters) to form a reducing agent aqueous solution. The molar concentration of the reducing agent aqueous solution is 0.4 mol / L, and the solution temperature is controlled at 60°C. Dissolve 0.6% of the weight of silver nitrate in lauric acid in 3 kg of ethanol and 0.2% of the weight of silver nitrate in fatty alcohol polyoxyethylene ether in 0.5 kg of water. Mix and prepare an emulsified dispersant, which is then added to the reducing agent solution. In an alkaline solution tank (0.3 cubic meters), 100 kg of deionized water was first added, followed by sodium hydroxide to form an alkaline aqueous solution with a molar concentration of 2 mol / L. The solution temperature was controlled at 60°C to adjust the pH value during the reaction. Use a mechanical lifting device to add the reducing agent solution in the reducing agent dissolution tank into the large reactor within 5 seconds, and at the same time adjust the pH value of the reaction process to 6. After aging in the reactor, release the silver powder.

[0033] The main parameters of the silver powder prepared in Comparative Example 1 are as follows: tap density = 3.90 g / cm 3 , specific surface area SBET = 1.31m 2 / g, particle size D50 = 0.31 μm, equivalent particle size calculated by specific surface area is DBET = 0.44 μm, agglomeration coefficient AF = D50 / DBET = 0.70 (close to 1, indicating good dispersion), the volume resistivity of the printed circuit after drying (silver powder addition amount is 85%) is 2.53×10 -5 Ωcm. For crystallization and morphology, see Figure 7 shown.

[0034] Table 1 Product performance comparison table As shown in Table 1, the average particle size of the silver powder produced by Examples 1-5 is between 0.3um and 5um, which has better dispersibility and conductivity than that of Comparative Example 1. Figure 1-6 It can be seen that the silver powder produced by this technical solution has a more regular and consistent morphology.

Claims

1. A system for producing highly dispersed and highly crystalline spherical silver powder, characterized by: It includes a silver nitrate dissolving tank 1, a reducing agent dissolving tank 2, an alkaline solution tank 3, a silver nitrate rapid feeding tank 4, a reducing agent rapid feeding tank 5, a reaction kettle 6, a compressed nitrogen source 1 7 and a compressed nitrogen source 2 8; The silver nitrate dissolving tank 1 is equipped with an electronic scale W1 and a temperature measuring thermal resistor T1. The silver nitrate dissolving tank 1 is connected to the water outlet of the deionized water source and the feed port of the silver nitrate rapid feeding tank 4 through a pneumatic valve V1 and a pneumatic valve V2, respectively. The silver nitrate rapid feeding tank 4 is connected to a compressed nitrogen source 7 and a pressure measuring transmitter P1 through a pneumatic valve V10. A pneumatic valve V11 is installed on the silver nitrate rapid feeding tank 4 for exhaust. The silver nitrate rapid feeding tank 4 is connected to the reactor 6 through a pneumatic valve V12. The reducing agent dissolving tank 2 is equipped with an electronic scale W3 and a temperature measuring thermal resistor T3. The reducing agent dissolving tank 2 is connected to the water outlet of the deionized water source and the feed port of the reducing agent rapid feeding tank 5 through a pneumatic valve V5 and a pneumatic valve V6, respectively. The reducing agent rapid feeding tank 5 is connected to the compressed nitrogen source 8 and the pressure measuring transmitter P2 through a pneumatic valve V7. The reducing agent rapid feeding tank 5 is provided with a pneumatic valve V8 for exhaust. The reducing agent rapid feeding tank 5 is connected to the reactor 6 through a pneumatic valve V9. The alkaline solution tank 3 is equipped with an electronic scale W2 and a temperature measuring resistor T2. The alkaline solution tank 3 is connected to the water outlet of the deionized water source through a pneumatic valve V3. The alkaline solution tank 3 is connected to the reactor 6 through an electric regulating valve V4. The reactor 6 is a hexagonal reactor with a conical bottom and a volume of 0.15-0.3 cubic meters. The reactor 6 is equipped with a temperature measuring resistor T4 and a pH meter. The reactor 6 is also equipped with a pneumatic valve V14 for discharging. The silver nitrate dissolution tank 1, reducing agent dissolution tank 2, alkaline solution tank 3, silver nitrate quick feeding tank 4, reducing agent quick feeding tank 5 and reactor 6 are made of 316L stainless steel. The silver nitrate quick feeding tank 4 and reducing agent quick feeding tank 5 are sealed tanks with a tank volume of 0.05-0.1 cubic meters.

2. A method for producing highly dispersed and highly crystalline spherical silver powder, characterized in that: The following steps are involved: S1. Add silver nitrate and deionized water to a silver nitrate dissolving tank 1 to form a silver nitrate aqueous solution, add a small amount of polyacid complex silver salt to form seed crystals, and control the solution temperature and weight; Add reducing agent and deionized water into reducing agent dissolving tank 2 to form reducing agent aqueous solution, add a small amount of dispersant, and control the solution temperature and weight; In the alkaline solution tank 3, deionized water is first added and then an alkaline reagent is added to form an alkaline aqueous solution. The temperature and weight of the solution are controlled to adjust the pH value during the reaction; S2, quantitatively put the silver nitrate solution and reducing agent solution prepared in S1 into the silver nitrate rapid feeding tank 4 and the reducing agent rapid feeding tank 5 respectively; S3, using compressed nitrogen source 1 7 and compressed nitrogen source 2 8, pressurize the silver nitrate solution and the reducing agent solution into the reaction kettle 6 for mixing and reaction, and add the alkaline aqueous solution prepared in S1 into the reaction kettle 6 to adjust the pH value; S4, the mixed solution after mixing and adjusting the pH in S3 is reacted in the reactor 6 and after a short aging, the valve V14 is opened to release the mixture of silver powder and the reaction liquid; S5, repeat S2-S4 until the solutions in the silver nitrate dissolving tank 1 and the reducing agent dissolving tank 2 are consumed; S6. Clean the silver powder released in S5 with deionized water in a vacuum filtration device; S7, dissolving the surface modifier in pure water or alcohol and adding it to the silver powder cleaned in S6 under high-speed stirring to modify the surface of the silver powder, and then placing it in a vacuum drying oven for drying; S8, put the silver powder dried in S7 into a powdering machine to grind and disperse; S9, the silver powder dispersed in S8 is classified by air flow classification equipment to obtain highly dispersed and highly crystalline spherical silver powder with an average particle size between 0.3um and 5um.

3. The method for producing highly dispersed and highly crystalline spherical silver powder according to claim 2, characterized in that: In S1, 1000-2500 kg of deionized water is added, the molar concentration of the silver nitrate aqueous solution is 0.4 mol-0.85 mol / L, and the temperature is 40°C-80°C; the polyacid is one or a combination of malonic acid, glutaric acid, and malic acid, and the added amount is 0.04%-0.16% of the weight of the silver nitrate. The deionized water used to dissolve the polyacid is 5-8 kg, and the addition speed is 60-110 seconds.

4. The method for producing highly dispersed and highly crystalline spherical silver powder according to claim 2, wherein: In S1, the reducing agent is ascorbic acid, the added deionized water is 1000kg-2500kg, the molar concentration of the reducing agent aqueous solution is controlled between 0.26-0.57mol / L, and the temperature is controlled at 40-80°C; the dispersant is one or two or a combination of three of lauric acid, myristic acid, palmitic acid, and fatty alcohol polyoxyethylene ether, and the added amount is 0.3%-1.53% of the weight of silver nitrate, and the deionized water or ethanol used to dissolve the dispersant is 0.5-5kg.

5. The method for producing highly dispersed and highly crystalline spherical silver powder according to claim 2, wherein: In the above-mentioned S1, the alkaline reagent is a hydroxide or carbonate of an alkali metal, the molar concentration of the alkaline aqueous solution is 1.5-2.5 mol / L, and the temperature is controlled at 40-80°C.

6. The method for producing highly dispersed and highly crystalline spherical silver powder according to claim 2, wherein: The pH value of the reaction process in S3 is controlled between 5-7.

7. The method for producing highly dispersed and highly crystalline spherical silver powder according to claim 2, characterized in that: The adding method in S3 is to press the reducing agent solution into the reaction kettle 6 with compressed nitrogen gas to mix with the silver nitrate solution for reaction.

8. The method for producing highly dispersed and highly crystalline spherical silver powder according to claim 2, characterized in that: The feeding method in S3 is to press the silver nitrate solution into the reaction kettle 6 with compressed nitrogen to mix with the reducing agent solution for reaction.

9. The method for producing highly dispersed and highly crystalline spherical silver powder according to claim 2, characterized in that: The adding method in S3 is to press the reducing agent solution and the silver nitrate solution into the reaction kettle 6 with compressed nitrogen gas at the same time for mixing and reaction.

10. The method for producing highly dispersed and highly crystalline spherical silver powder according to claim 2, wherein: In S2-S3, the amount of silver nitrate solution added to the silver nitrate solution quick feeding tank 4 is 11-42 kg each time, and the amount of reducing agent solution added to the reducing agent solution quick feeding tank 5 is 10-40 kg each time; the pressure of the compressed nitrogen is 0.1-0.6 MPa, and the purity is above 99%. The time for pressing the silver nitrate solution and the reducing agent solution from the quick feeding tank into the reactor with compressed nitrogen is 3-30 seconds.

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