Spherical silver powder with high sphericity degree and high activity and manufacturing method thereof

Abstract

The invention discloses high-sphericity-degree and high-activity spherical silver powder and a manufacturing method thereof.The manufacturing method comprises the following steps that a silver source is prepared, specifically, silver nitrate crystals are dissolved in deionized water, and an aqueous solution with the silver content being 0.2-2 mol / L is obtained; a reducing solution is prepared, specifically, a 37% formaldehyde solution, L-ascorbic acid, glucose or hydrazine hydrate and other reducing agents are dissolved in deionized water, and the weight ratio of the configured reducing agents to the silver nitrate crystals is 0.75-2.5; preparing a first dispersion liquid, selecting a combination of polyvinylpyrrolidone, Arabic gum and the like as a first dispersing agent, and controlling the weight ratio of the preparation weight to the silver nitrate crystal to be 0.1-0.6; preparing a second dispersion liquid, namely selecting the second dispersion liquid of sodium potassium salt such as anhydrous citric acid and the like; reduction reaction: adding the first dispersion liquid into a reaction kettle, stirring for 1-2 minutes, then adding 50% of reduction liquid, stirring for 1-3 minutes, then pumping the remaining reduction liquid and oxidation liquid into the reaction kettle, and then adding a second dispersing agent into the reaction kettle; and after the reaction is finished, a fatty acid ethanol solution is added into the reaction kettle, and the silver powder with the high sphericity degree is obtained after cleaning and centrifugal dewatering.

Description

Technical Field

[0001] The invention belongs to the field of conductive material preparation, and in particular relates to a spherical silver powder with high sphericity and high activity and a manufacturing method thereof. Background Art

[0002] Silver, a precious metal since ancient times, is widely used due to its stable physical and chemical properties and excellent electrical and thermal conductivity. Silver powder, a precious metal conductive powder, is widely used in various conductive pastes for solar photovoltaic cells. The microscopic morphology and activity of silver powder are often directly related to the printability and electrical conductivity of the conductive paste, thus affecting the ultimate conversion efficiency of solar cells.

[0003] The current level of powder preparation in China is uneven. The high activity of most silver powders is achieved by reducing the particle size to increase parameters such as specific surface area and tap compaction. The hidden danger brought about by this is that the porosity of the conductive paste is too high during the high-temperature rapid firing process, resulting in a decrease in the silver wire current and a decrease in efficiency.

[0004] Therefore, there is an urgent need for a silver powder with high sphericity and high activity that does not reduce the particle size and has high activity while also being able to pass the sieve. Summary of the Invention

[0005] A spherical silver powder with high sphericity and high activity and a method for manufacturing the same, comprising the following steps: (1) Preparation of a silver source. In the present invention, the silver source is silver nitrate crystals that are easily soluble in deionized water. Dissolve the silver nitrate crystals in deionized water, stir, and dissolve to obtain a uniform, clear aqueous solution. The silver content is controlled to be 0.2-2 mol / L by adding different ratios of silver nitrate crystals and deionized water, preferably 0.4-1.5 mol / L. After dissolution is completed, the temperature is kept constant at 15°C-60°C. This step obtains an oxidizing solution. (2) Preparation of reducing solution: dissolve the reducing agent in deionized water, stir and dissolve to obtain a uniform and clear aqueous solution, wherein the weight ratio of the reducing agent to the silver nitrate crystals is 0.75-2.5:1, preferably 0.95-1.5:1. After the reducing agent solid is added to the deionized water solution, the ratio is adjusted, and after the dissolution is completed, the temperature is kept constant at 15°C-60°C; the reducing agent is selected from one or a combination of two or more of 37% formaldehyde solution, L-ascorbic acid, glucose or hydrazine hydrate; (3) Preparation of the first dispersion. Select one or a combination of two or more of polyvinyl pyrrolidone (PVP-K30), gum arabic, polysorbate 80 or gelatin as the first dispersant, and the weight ratio of the first dispersant to the silver nitrate crystals is 0.1-0.6:1. Add the above dispersant into deionized water, stir, dissolve to obtain a uniform and clear aqueous solution, and then keep the temperature constant at 15°C-60°C; (4) Preparation of the second dispersion. Select one or a combination of two or more of anhydrous citric acid, anhydrous sodium citrate, and potassium citrate as the second dispersion, and the weight ratio of the second dispersant to the silver nitrate crystals is 0.1-0.4:1. Add the above dispersant into deionized water, stir, and dissolve to obtain a uniform and clear aqueous solution, and then keep the temperature constant at 5°C-10°C; (5) Reduction reaction, control the volume ratio of the reducing liquid solution to the oxidizing liquid solution to be 0.8-1.1:1. First, add the prepared first dispersion liquid into the reactor with a pump, stir for 1-2 minutes, then add 50% of the reducing liquid, continue stirring for 1-3 minutes, and then pump the remaining reducing liquid and oxidizing liquid into the reactor at a fixed flow rate through a metering pump. The flow rate of the reducing liquid and the oxidizing liquid are both: 10-20L / min; when the reducing liquid is added, stop the reducing and oxidizing metering pumps, add the second dispersant, continue stirring for 10-30 seconds, and then open the oxidizing liquid metering pump until the addition is complete and the reaction is completed; (6) Surface coating. After the reduction reaction is completed, immediately (within 3 seconds) add fatty acid ethanol solution to the reactor in an amount of 0.2%-1.5% of the theoretically calculated silver powder yield. After adding the coating agent, continue stirring for 5-10 minutes and then stand for stratification. After washing, centrifuge and dehydrate to obtain silver powder with high sphericity. The fatty acid is one or a combination of two of lauric acid, myristic acid, palmitic acid, and stearic acid; (7) Flow chart of the patented process of this invention, see the accompanying drawings Figure 5 .

[0006] Preferably, in the above step (2), the reducing agent is preferably L-ascorbic acid, and the weight ratio of the reducing agent to the silver nitrate crystals is preferably 0.95-1.5:1; the temperature is controlled at 15°C-60°C.

[0007] Preferably, in the above step (3), one or more of polyvinyl pyrrolidone (PVP-K30), gum arabic, polysorbate 80 or gelatin is selected as the first dispersant, preferably polyvinyl pyrrolidone (PVP-K30), and the weight ratio of the first dispersant to the silver nitrate crystals is 0.2:1-0.3:1; the temperature is controlled at 15°C-60°C.

[0008] Preferably, in the above step (4), one or a combination of two or more of anhydrous citric acid, anhydrous sodium citrate, and potassium citrate is selected as the second dispersion liquid, and the weight ratio of the second dispersant to the silver nitrate crystals is 0.1:1-0.2:1; the temperature is controlled at 5°C-10°C.

[0009] Preferably, in the above step (5), the fatty acid used is one or a combination of two of lauric acid, myristic acid, palmitic acid, and stearic acid; preferably, the fatty acid is a combination of palmitic acid and stearic acid, with a weight ratio of 0.8:1.2. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a SEM image of the silver particles prepared in Example 1 of the present invention.

[0011] Figure 2 is a SEM image of the silver particles prepared in Example 2 of the present invention.

[0012] Figure 3 is a SEM image of the silver particles prepared in Example 3 of the present invention.

[0013] Figure 4 1 is a SEM image of the silver particles prepared in Comparative Example 1 of the present invention. Figure 5 This is the process flow chart of the patented process of the present invention. The flow chart is from top to bottom. The Chinese characters in the boxes represent the names of the steps. The specific configuration method can be found in the invention content section. The arrow indicates the direction of flow of the process flow. DETAILED DESCRIPTION

[0014] The technical solution of the present application will be further described in detail below in conjunction with the embodiments. The raw materials specifically specified in this application are all commonly available raw materials on the market. Latin characters not specifically specified, such as "L" represents the volume unit "liter", "Kg" represents the weight unit "kilogram", "℃" represents the temperature unit Celsius, and "min" represents the time unit minute, are all commonly accepted unit expressions.

[0015] Example 1 (1) Preparation of silver source: Add 25 kg of silver nitrate to a 250 L batching tank A, add 180 L of deionized water, dissolve and stir evenly, heat and keep warm to 40 ° C for use; (2) Preparation of reducing solution: Add 15.83 kg of L-ascorbic acid to a 250 L batching tank B, add 120 L of deionized water, dissolve and stir evenly, heat and keep warm to 40 ° C for use; (3) Preparation of the first dispersion: Add 0.8 kg of polyvinyl pyrrolidone (PVP-K30) to a 250 L batching tank C, add 200 L of deionized water, dissolve and stir evenly, heat to 40 ° C for use; (4) Preparation of the second dispersion: Add 5 kg of anhydrous sodium citrate to a 50 L batching tank D, add 32.5 L of deionized water, dissolve and stir evenly, cool down and keep constant temperature to 8 ° C for use; (5) Reduction reaction: first, add the prepared first dispersion liquid into the reactor with a pump, stir for 2 minutes, then add 50% of the reducing liquid, continue stirring for 3 minutes, and then pump the remaining reducing liquid and oxidizing liquid into the reactor at a fixed flow rate through a metering pump. The reducing liquid and the oxidizing liquid are the same, and the flow rate is: 10-20L / min; when the reducing liquid is added, stop the reducing and oxidizing metering pumps, add the second dispersant, continue stirring for 30 seconds, and then turn on the oxidizing liquid metering pump until the reaction is completed; (6) Surface coating: after the reduction reaction is completed, add a combination of palmitic acid and stearic acid into the reactor, wherein the amount of palmitic acid added is 0.127kg, and the amount of stearic acid added is 0.190kg. Continue stirring at high speed for 5 minutes, then let it stand and separate, wash and centrifuge to obtain silver powder with high sphericity.

[0016] Example 2 The difference from Example 1 is that after the metering pump of the reducing solution is added in step (5), the metering pump of the oxidizing solution is not turned off, and the reaction is continued until the reaction is completed before adding the second dispersant. The rest is the same as Example 1.

[0017] Example 3 The difference from Example 1 is that in step (4), anhydrous citric acid is used in place of anhydrous sodium citrate in the batching tank, and the rest is the same as Example 1.

[0018] Comparative Example 1 (1) Preparation of silver source: Add 25 kg of silver nitrate to a 250 L batching tank A, add 180 L of deionized water, dissolve and stir evenly, heat and keep warm to 40 ° C for use; (2) Preparation of reducing solution: Add 15.83 kg of L-ascorbic acid to a 250 L batching tank B, add 120 L of deionized water, dissolve and stir evenly, heat and keep warm to 40 ° C for use; (3) Preparation of dispersion: Add 0.8 kg of polyvinyl pyrrolidone (PVP-K30) to a 250 L batching tank C, add 200 L of deionized water, dissolve and stir evenly, heat to 40 ° C for use; (4) Reduction reaction: First, add the prepared dispersion into the reactor with a pump, stir for 2 minutes, then add 50% of the reducing solution, continue stirring for 3 minutes, and then pump the remaining reducing solution and oxidizing solution into the reactor at a fixed flow rate through a metering pump. The reducing solution is the same as the oxidizing solution, and the flow rate is 10-20 L / min; until the reaction is completed; (5) Surface coating: After the reduction reaction is completed, a combination of palmitic acid and stearic acid is added to the reactor, wherein the amount of palmitic acid added is 0.127 kg, and the amount of stearic acid added is 0.190 kg. Continue to stir at high speed for 5 minutes, then let it stand and separate, wash and centrifuge to obtain silver powder.

[0019] Comparative Example 2 The difference from Comparative Example 1 is that only 0.190 kg of stearic acid is added for surface coating in step (5), and the rest is the same as Comparative Example 1.

[0020] The technical indicators of the silver powder product of the present invention are as follows:

[0021] The silver powder product of the present invention was prepared into silver paste at the customer end and then printed on a TOPCON battery. The efficiency and current data are shown in the following table:

Claims

1. A spherical silver powder with high sphericity and high activity and a method for producing the same, characterized in that: The following steps are involved: (1) Preparation of silver source: dissolving silver nitrate crystals in deionized water, stirring and dissolving to obtain a uniform and clear aqueous solution, and controlling the silver content to be 0.2-2 mol / L by adding different ratios of silver nitrate crystals and deionized water, preferably 0.4-1.5 mol / L, and maintaining the temperature at 15°C-60°C after dissolution is completed; (2) Preparation of reducing solution: dissolve the reducing agent in deionized water, stir and dissolve to obtain a uniform clear aqueous solution, the weight ratio of the reducing agent to the silver nitrate crystals is 0.75-2.5:1, and the temperature is kept constant at 15°C-60°C after the dissolution is completed; the reducing agent is selected from one or a combination of two or more of 37% formaldehyde solution, L-ascorbic acid, glucose or hydrazine hydrate; (3) Preparation of the first dispersion: using one or a combination of two or more of polyvinyl pyrrolidone (PVP-K30), gum arabic, polysorbate 80 or gelatin as the first dispersant, with the weight ratio of the first dispersant to the silver nitrate crystals being 0.1-0.6:

1. Add the above dispersant into deionized water, stir, dissolve to obtain a uniform and clear aqueous solution, and then maintain constant temperature; (4) Preparation of the second dispersion: one or a combination of two or more of anhydrous citric acid, anhydrous sodium citrate, and potassium citrate is selected as the second dispersion; the weight ratio of the second dispersant to the silver nitrate crystals is 0.1-0.4:1, preferably 0.1-0.2; the above dispersant is added to deionized water, stirred, and dissolved to obtain a uniform and clear aqueous solution, and then the temperature is maintained at 5°C-10°C; (5) Reduction reaction: first, add the prepared first dispersion liquid into the reactor with a pump, stir for 1-2 minutes, then add 50% of the reducing liquid, continue stirring for 1-3 minutes, and then pump the remaining reducing liquid and oxidizing liquid into the reactor at a fixed flow rate through a metering pump. The flow rate of the reducing liquid and the oxidizing liquid are both 10-20 L / min. When the reducing liquid is added, stop the reducing and oxidizing metering pumps, add the second dispersant, continue stirring for 10-30 seconds, and then open the oxidizing liquid metering pump until the reaction is completed. (6) Surface coating: After the reduction reaction is completed, add fatty acid ethanol solution to the reactor within 3 seconds. The amount added is 0.2%-1.5% of the silver powder output. After adding the coating agent, continue stirring for 5-10 minutes and then let it stand for stratification. After washing, centrifugal dehydration is performed to obtain silver powder with high sphericity. The fatty acid is one or a combination of two of lauric acid, myristic acid, palmitic acid, and stearic acid.

2. The spherical silver powder with high sphericity and high activity and the method for producing the same according to claim 1, characterized in that: In step (2), the reducing agent is preferably L-ascorbic acid, the weight ratio of the reducing agent to the silver nitrate crystals is 0.95-1.5:1, and the temperature is controlled at 15°C-60°C.

3. The spherical silver powder with high sphericity and high activity and the method for producing the same according to claim 1, characterized in that: In step (3), the first dispersant is preferably polyvinyl pyrrolidone (PVP-K30), the weight ratio of the first dispersant to the silver nitrate crystals is 0.2:1-0.3:1, and the temperature is controlled at 15°C-60°C.

4. The spherical silver powder with high sphericity and high activity and the method for producing the same according to claim 1, characterized in that: In the step (6), the fatty acid is preferably a combination of palmitic acid and stearic acid, with a combination ratio of 0.8:1.2.

Images