A preparation method of fine-line printing small particle size flaky silver powder

Abstract

The present application relates to a kind of preparation methods for fine line printing small particle size flaky silver powder, which comprises the following steps: (1) preparing silver powder for ball milling: silver nitrate solution is added to ammonia water to obtain silver ammonia oxidation solution, which is added to a reducing agent solution containing dispersant A within 5-10 seconds for reaction; after solid-liquid separation, washing, coating and ultrasonic dispersion, silver powder is obtained; (2) ball milling: adding grinding balls into a vertical ball mill, adding ball milling aids to hide grinding balls, then adding silver powder and dispersant B into the ball mill; first start the external circulation system of the ball mill, then start the ball mill, control the temperature of ball milling process not to exceed 20℃, after stirring, the ball and material are uniformly mixed, then separate the ball and liquid to obtain silver powder slurry; (3) post-treatment: filter, dry, crush and sieve the silver powder slurry to obtain silver powder with an average particle size of 3-4 μm and a tap density of 4.0-5.0 g / cm 3 Small flaky silver powder. The present application has simple process, controllable parameters, stable production, easy industrialization and no pollution, with low cost.

Description

Technical Field

[0001] This invention relates to the field of metal powder material preparation, and more particularly to a method for preparing small-particle-size flake silver powder for fine-line printing. Background Technology

[0002] Conductive silver paste is a fundamental and crucial functional material in the electronics industry. It is a viscous paste composed of silver powder, conductive binder, solvent, and additives, forming a mechanical mixture. Electronic pastes with silver powder as the conductive phase are characterized by high quality, high efficiency, advanced technology, and wide applicability, holding an irreplaceable position in the electronic paste industry.

[0003] Flake silver powder, a special type of silver powder, is used in the production of electronic pastes by mixing spherical and flake silver powders in a specific ratio. This greatly improves the performance of the electronic paste, thus directly or indirectly affecting the performance of the final electronic products. The morphology of flake silver powder is not perfectly spherical; its thickness varies in different areas. Generally, flake silver powder with a larger aspect ratio tends to have a lower bulk density and a greater number of silver powder particles per unit volume. It is commonly used in conductive silver pastes for membrane switches, exhibiting excellent conductivity even with low silver content. Conversely, flake silver powder with a smaller aspect ratio often exhibits a higher tap density and is generally used in conductive pastes for high-precision, fine-line printing.

[0004] Currently, the main method for producing flake silver powder is ball milling. Mechanical ball milling methods include vertical stirred ball milling, horizontal ball milling, and planetary ball milling. The particle size of flake silver powder prepared by mechanical ball milling is generally in the micron or submicron range.

[0005] The ball milling method for preparing flake silver powder involves using chemically prepared silver powder as a precursor, adding a grinding aid, and then grinding spherical or near-spherical silver powder into flake silver powder using a ball milling method.

[0006] The key to preparing flake silver powder by mechanical ball milling lies in how to control the uniformity of the ball milling process and how to prevent the flake silver powder from agglomerating due to the exothermic process. This ensures the stability of the production process, which is conducive to the preparation of flake silver powder of different specifications and with stable physicochemical properties, and its excellent performance in subsequent slurry applications. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing small-particle-size flake silver powder for fine-line printing that is simple in process, controllable in parameters, stable in production, and easy to realize industrial production.

[0008] To address the above problems, the present invention provides a method for preparing small-particle-size flake silver powder for fine-line printing, comprising the following steps: (1) Preparation of silver powder for ball milling: A silver nitrate solution with a mass concentration of 600-650 g / L is added to ammonia water to obtain a silver ammonia oxidation solution. This silver ammonia oxidation solution is then added to a reducing agent solution containing dispersant A within 5-10 seconds, and the reaction is stopped after 30-60 seconds. After solid-liquid separation and washing, a silver powder slurry A is obtained. The silver powder slurry A is then coated with a surface coating agent and ultrasonically dispersed in an ethanol medium to obtain silver powder. (2) Ball mill: Add grinding balls to a vertical ball mill, add a ball milling aid to submerge the grinding balls, and then add the silver powder and dispersant B into the ball mill; first start the external circulation system of the ball mill, the cooling medium in the external circulation system begins to circulate, then start the ball mill, control the temperature of the ball milling process to not exceed 20°C, after stirring the ball and material are mixed evenly, and then the ball and liquid are separated to obtain silver powder slurry B; (3) Post-processing: The silver powder slurry B was filtered, dried, crushed, and sieved to obtain an average particle size of 3-4 μm and a tap density of 4.0-5.0 g / cm³. 3 Small-diameter flake-shaped silver powder.

[0009] In step (1), the mass ratio of silver nitrate to ammonia is 1:1.2~1.3.

[0010] The reducing agent solution containing dispersant A in step (1) refers to a mixed solution with a concentration of 25~32g / L formed by mixing dispersant A and reducing agent; the dispersant A refers to at least one of fatty acids, fatty acid salts, polymers, and surfactants, and its addition amount is 0.1~0.5% of the mass of silver powder; the reducing agent is one or more of formaldehyde, hydrazine hydrate, ascorbic acid, and phenolic compounds.

[0011] The dispersant A is one or more of polyvinylpyrrolidone, Tween, gelatin, succinic acid, and polyethylene glycol 4000.

[0012] In step (1), the surface coating agent refers to a substance of fatty acids or fatty acid salts, and the amount added is 0.1 to 0.5% of the mass of the silver powder.

[0013] The surface coating agent is one or more of oleic acid, erucic acid, isostearic acid, and octanoic acid.

[0014] In step (2), the grinding balls refer to zirconia balls with a gradation of 1~5:1 and a particle size of 0.5~2mm; the mass ratio of the grinding balls to the silver powder is 10~15:1.

[0015] In step (2), the ball milling aid is 98% anhydrous ethanol, and the amount added is 2-3L per kilogram of silver powder.

[0016] In step (2), dispersant B refers to one of saturated fatty acids, unsaturated fatty acids, and surfactants, and its addition amount is 0.1% to 1.0% of the total mass of silver powder.

[0017] The dispersant B is one or two of hexadecanoic acid, hexadecyl alcohol, stearic acid, erucic acid, or oleic acid.

[0018] The external circulation speed of the ball mill is 500~1000 mL / min.

[0019] The ball milling speed is 200~400 rpm, and the time is 4~7 hours.

[0020] In step (3), the drying temperature is 50~60℃ and the drying time is 5~10h.

[0021] Compared with the prior art, the present invention has the following advantages: 1. This invention uses a liquid-phase chemical reduction method to prepare ball-milled raw powder. Silver ammonia oxidation liquid is added to the reducing agent solution within 30-60 seconds. The reducing agent and silver react instantly to produce a large number of flocculent soft aggregates composed of single-crystal small-particle silver powder, which facilitates solid-liquid separation and washing.

[0022] 2. This invention uses 98% anhydrous ethanol as a ball milling aid and a dispersant as the ball milling medium. It selects grinding balls with a specific particle size distribution to create the ball milling conditions, strictly controlling the ratio of grinding balls to silver powder raw material. Under the action of the ball milling medium, key factors affecting the ball milling process were analyzed and controlled. Furthermore, by adding an external circulation system with cooling medium, an average particle size of 3~4μm and a tap density of 4.0~5.0 g / cm³ were obtained. 3 Small-diameter flake-shaped silver powder with a smooth, flat surface and no impurities.

[0023] 3. This invention uses anhydrous ethanol with a mass percentage concentration of over 98%, which provides better dispersibility and ensures the purity of the silver powder by preventing the introduction of any impurities.

[0024] 4. This invention uses a 1-S type vertical stirred ball mill, which has a unique stirring structure. Under the action of high-speed stirring, the grinding media applies shear force and pressure to the material, so that the energy transmitted by the stirrer is evenly distributed in the material, resulting in high fine grinding efficiency, less over-grinding, uniform material mixing, and no dead corners. At the same time, the addition of external circulation ensures that there are no dead corners left in the silver powder during the ball milling process, and that the silver powder and the grinding media are in full contact and fully ground, thereby improving the ball milling efficiency.

[0025] 5. By adding an external circulation system with cooling medium, the present invention controls the temperature of the ball milling process to not exceed 20°C, maintains the heat dissipation during the ball milling process, prevents the silver powder from agglomerating due to excessive heat during ball milling and prevents cold welding during the ball milling process, and improves the dispersibility of the silver powder.

[0026] 6. The production process of this invention is simple, the parameters are controllable, the production is stable, it is easy to realize industrial production, and it is pollution-free and low in cost.

[0027] 7. The silver powder prepared by the method of the present invention has a smooth and flat surface, no impurities, small aspect ratio and good dispersibility, and is suitable for conductive pastes for high-precision and fine-line printing. Attached Figure Description

[0028] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0029] Figure 1 This is a SEM image of the flake-shaped silver powder prepared in Example 1 of the present invention.

[0030] Figure 2 This is a SEM image of the flake-shaped silver powder prepared in Comparative Example 1 of this invention. Detailed Implementation

[0031] A method for preparing small-particle-size flake silver powder for fine-line printing includes the following steps: (1) Preparation of silver powder for ball milling: A silver nitrate solution with a mass concentration of 600-650 g / L is added to ammonia water to obtain a silver ammonia oxidation solution. This silver ammonia oxidation solution is added to a reducing agent solution containing dispersant A within 5-10 seconds, and the reaction is stopped after 30-60 seconds. After solid-liquid separation and washing, silver powder slurry A is obtained. Silver powder slurry A is coated with a surface coating agent and ultrasonically dispersed in an ethanol medium to obtain silver powder.

[0032] The mass ratio (g / g) of silver nitrate to ammonia is 1:1.2~1.3.

[0033] The reducing agent solution containing dispersant A refers to a mixture of dispersant A and a reducing agent with a concentration of 25-32 g / L. Dispersant A is at least one of fatty acids, fatty acid salts, polymers, and surfactants, preferably one or more of polyvinylpyrrolidone, Tween, gelatin, succinic acid, and polyethylene glycol 4000, and its addition amount is 0.1-0.5% of the mass of the silver powder. The reducing agent is one or more of formaldehyde, hydrazine hydrate, ascorbic acid, and phenolic compounds.

[0034] The surface coating agent refers to a substance of fatty acids or fatty acid salts, preferably one or more of oleic acid, erucic acid, isostearic acid, and octanoic acid, and its addition amount is 0.1 to 0.5% of the mass of the silver powder.

[0035] (2) Ball mill: Add grinding balls to a 1-S type vertical stirred ball mill, add a ball milling aid to submerge the grinding balls, and then add silver powder and dispersant B into the ball mill; first start the external circulation system of the ball mill, and the cooling medium (cooling medium is cooling water) in the external circulation system starts circulating at a speed of 500~1000 mL / min; then start the ball mill, and control the temperature during the ball milling process to prevent cold welding and not exceed 20℃, and the ball milling speed is 200~400 rpm. After stirring for 4~7 hours, the ball and material are mixed evenly, and then the ball and liquid are separated to obtain silver powder slurry B.

[0036] Among them: grinding balls refer to zirconia balls with a gradation of 1~5:1 and a particle size of 0.5~2mm; the mass ratio (g / g) of grinding balls and silver powder is 10~15:1.

[0037] The ball milling aid is 98% anhydrous ethanol, and it is added at a rate of 2-3L per kilogram of silver powder.

[0038] Dispersant B refers to one of saturated fatty acids, unsaturated fatty acids, and surfactants, preferably one or two of hexadecanoic acid, hexadecyl alcohol, stearic acid, erucic acid, or oleic acid, and its addition amount is 0.1% to 1.0% of the total mass of silver powder.

[0039] (3) Post-processing: Silver powder slurry B is filtered, dried at 50-60℃ for 5-10 hours, crushed, and sieved to obtain an average particle size of 3-4 μm and a tap density of 4.0-5.0 g / cm³. 3 Small-diameter flake-shaped silver powder.

[0040] Example 1: A method for preparing small-particle-size flake silver powder for fine-line printing, comprising the following steps: (1) Preparation of silver powder for ball milling: Dissolve 20 kg of silver nitrate in 32 L of pure water, add 16.35 kg of ammonia solution to obtain an oxidizing solution, and keep the temperature constant at 35 °C.

[0041] 6.06 kg of ascorbic acid was dissolved in 200 L of pure water, and 32 g of polyvinylpyrrolidone was added to obtain a reducing agent solution, which was kept at a constant temperature of 35 °C.

[0042] The silver ammonia oxidation solution was added to the reducing agent solution within 5 seconds, and the reaction was stopped after stirring for 60 seconds. After solid-liquid separation and washing, silver powder slurry A was obtained. 25g of isomeric stearic acid was added to silver powder slurry A, mixed evenly, and then ultrasonically dispersed in ethanol medium to obtain silver powder.

[0043] (2) Ball mill: Add 13 kg of zirconia balls with a grinding ball ratio of Φ1mm:Φ0.8mm of 1:3 to a 1-S type vertical stirred ball mill. Submerge the grinding balls in 2.5 L of 98% anhydrous ethanol. Then add 1000 g of silver powder, 5 g of stearic acid, and 3 g of hexadecanoic acid to the ball mill. First, start the external circulation system of the ball mill, and start circulating the cooling water in the external circulation system at a speed of 800 mL / min. Then start the ball mill at a speed of 200 rpm. After stirring for 4 hours, the ball and material are mixed evenly. Then, separate the ball and liquid by filtration and rinsing with anhydrous ethanol to obtain silver powder slurry B.

[0044] (3) Post-processing: Silver powder slurry B was filtered, dried at 60℃ for 16 hours, crushed, and sieved to obtain an average particle size of 3.25 μm and a tap density of 4.5 g / cm³. 3 High-vibration-density, small-diameter, flake-shaped silver powder, such as Figure 1 As shown.

[0045] Example 2: A method for preparing small-particle-size flake silver powder for fine-line printing, comprising the following steps: (1) The preparation of ball-milled silver powder is the same as in Example 1.

[0046] (2) Ball mill: Add 13 kg of zirconia balls with a grinding ball ratio of 1:4 (Φ1mm:Φ0.8mm) to a 1-S type vertical stirred ball mill. Submerge the grinding balls in 2.5 L of anhydrous ethanol. Then add 5000 g of silver powder, 40 g of stearic acid, and 10 g of hexadecanoic acid to the ball mill. First, start the external circulation system of the ball mill, and begin circulating the cooling water in the external circulation system at a speed of 600 mL / min. Then, start the ball mill at a speed of 250 rpm and stir for 5 hours. After the ball and material are evenly mixed, separate the ball and liquid by filtration and rinsing with anhydrous ethanol to obtain silver powder slurry B.

[0047] (3) Post-processing: Silver powder slurry B was filtered, dried at 60℃ for 16 hours, crushed, and sieved to obtain an average particle size of 4.0 μm and a tap density of 4.0 g / cm³. 3 High-vibration-density, small-diameter flake-shaped silver powder.

[0048] Example 3: A method for preparing small-particle-size flake silver powder for fine-line printing, comprising the following steps: (1) The preparation of ball-milled silver powder is the same as in Example 1.

[0049] (2) Ball mill: Add 70 kg of zirconia balls with a grinding ball ratio of Φ1mm:Φ0.8mm of 1:3 to a 1-S type vertical stirred ball mill. Submerge the grinding balls in 15 L of anhydrous ethanol. Then add 5000 g of silver powder, 40 g of stearic acid, and 10 g of hexadecanoic acid to the ball mill. First, start the external circulation system of the ball mill, and start circulating the cooling water in the external circulation system at a speed of 600 mL / min. Then start the ball mill at a speed of 250 rpm and stir for 5 hours. After the ball and material are evenly mixed, separate the ball and liquid by filtration and rinsing with anhydrous ethanol to obtain silver powder slurry B.

[0050] (3) Post-processing: Silver powder slurry B was filtered, dried at 60℃ for 16 hours, crushed, and sieved to obtain an average particle size of 3.65 μm and a tap density of 4.2 g / cm³. 3 High-vibration-density small-diameter flake silver powder Comparative Example 1: A method for preparing small-particle-size flake silver powder for fine-line printing, comprising the following steps: (1) The preparation of ball-milled silver powder is the same as in Example 1.

[0051] (2) Ball mill: Add 18 kg of zirconia balls with a grinding ball ratio of Φ2mm:Φ1mm of 1:3 to a ball mill. Submerge the grinding balls in 3L of anhydrous ethanol. Then add 1500g of silver powder, 75g of stearic acid, and 15g of erucic acid to the ball mill. First, mix the materials evenly at a low speed, then ball mill at 250rpm for 3 hours. Finally, separate the ball and liquid by filtration and rinsing with anhydrous ethanol to obtain silver powder slurry B.

[0052] (3) Post-processing: Silver powder slurry B was filtered, dried at 60℃ for 16 hours, crushed, and sieved to obtain an average particle size of 2.1 μm and a tap density of 4.5 g / cm³. 3 The flake-shaped silver powder was unevenly ball-milled, containing a large amount of near-spherical silver powder, such as... Figure 2 As shown.

Claims

1. A method for preparing small-particle-size flake silver powder for fine-line printing, comprising the following steps: (1) Preparation of silver powder for ball milling: A silver nitrate solution with a mass concentration of 600-650 g / L is added to ammonia water to obtain a silver ammonia oxidation solution. This silver ammonia oxidation solution is added to a reducing agent solution containing dispersant A within 5-10 seconds, and the reaction is stopped after 30-60 seconds. After solid-liquid separation and washing, a silver powder slurry A is obtained. The silver powder slurry A is coated with a surface coating agent and ultrasonically dispersed in an ethanol medium to obtain silver powder. The reducing agent solution containing dispersant A refers to a mixture of dispersant A and a reducing agent with a concentration of 25-32 g / L. The dispersant A is one or more of polyvinylpyrrolidone, Tween, gelatin, succinic acid, and polyethylene glycol 4000, and its addition amount is 0.1-0.5% of the mass of silver powder. The reducing agent is one or more of formaldehyde, hydrazine hydrate, ascorbic acid, and phenolic compounds. (2) Ball mill: Grinding balls are added to a vertical ball mill, and a grinding aid is added to submerge the grinding balls. Then, the silver powder and dispersant B are added to the ball mill. First, the external circulation system of the ball mill is started, and the cooling medium in the external circulation system begins to circulate. Then, the ball mill is started, and the temperature during the grinding process is controlled to not exceed 20°C. After stirring, the ball and material are mixed evenly, and then the ball and liquid are separated to obtain silver powder slurry B. The grinding balls refer to zirconia balls with a Φ1mm:Φ0.8mm ratio of 1:3 or 1:

4. The grinding aid is 98% anhydrous ethanol, added at a rate of 2-3 L per kilogram of silver powder. The dispersant B is one or two of hexadecanoic acid, hexadecyl alcohol, stearic acid, erucic acid, or oleic acid. (3) Post-processing: The silver powder slurry B was filtered, dried, crushed, and sieved to obtain an average particle size of 3-4 μm and a tap density of 4.0-5.0 g / cm³. 3 Small-diameter flake-shaped silver powder.

2. The method for preparing small-particle-size flake silver powder for fine-line printing as described in claim 1, characterized in that: In step (1), the mass ratio of silver nitrate to ammonia is 1:1.2~1.

3.

3. The method for preparing small-particle-size flake silver powder for fine-line printing as described in claim 1, characterized in that: In step (1), the surface coating agent refers to a substance of fatty acids or fatty acid salts, and the amount added is 0.1 to 0.5% of the mass of the silver powder.

4. The method for preparing small-particle-size flake silver powder for fine-line printing as described in claim 3, characterized in that: The surface coating agent is one or more of oleic acid, erucic acid, isostearic acid, and octanoic acid.

5. The method for preparing small-particle-size flake silver powder for fine-line printing as described in claim 1, characterized in that: In step (2), the mass ratio of grinding balls to silver powder is 10-15:

1.

6. The method for preparing small-particle-size flake silver powder for fine-line printing as described in claim 1, characterized in that: In step (2), the amount of dispersant B added is 0.1% to 1.0% of the total mass of silver powder.

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