A sand mill for grinding flaky silver powder and a method for preparing the same

Abstract

This invention discloses a method for preparing flake silver powder using a sand mill, belonging to the field of conductive silver paste technology. The method includes: mechanically dispersing metallic silver powder with pure water to obtain a dispersion slurry; mixing an emulsifier and ethanol to obtain an emulsifier solution; mixing the emulsifier solution and the dispersion slurry, then dispersing again, followed by cyclic feeding and discharging under the operation of a pneumatic diaphragm pump, and then grinding; adding an alkyl hydroxyl ammonium salt wetting and dispersing agent to the sand mill feed tank, and grinding it together with the ground emulsifier solution and dispersion slurry under the operation of a pneumatic diaphragm pump to obtain a flake silver powder slurry; washing and filtering the flake silver powder slurry with pure water to obtain a flake silver powder filter cake; and sequentially centrifuging, vacuum baking, and sieving the flake silver powder using ethanol to obtain the sand mill-ground flake silver powder. The flake silver powder of this invention exhibits good dispersibility, uniform flake formation, and a loss on ignition ≤1%, making it suitable for preparing conductive silver paste.

Description

Technical Field

[0001] This invention belongs to the field of conductive silver paste technology, and particularly relates to a method for preparing flake silver powder by grinding with a sand mill. Background Technology

[0002] Due to its relatively large specific surface area and surface or line contact between particles, flake-shaped silver powder exhibits good electrical conductivity. It also possesses a wide range of flexibility and resistance to bending and tensile stresses, significantly improving the reliability of electronic components. Therefore, flake-shaped silver powder has wide applications in many fields, including microelectronics, flexible display technology, and the photovoltaic industry.

[0003] Methods for preparing flake silver powder include mechanical ball milling, template method, chemical reduction method, and photoinduced method. Mechanical ball milling is the main method for preparing flake silver powder in industrial production. This method usually uses AgNO3 or Ag2O as the silver source. Under the protection of additives or dispersants, a reducing agent is used to reduce the silver to spherical silver particles of different sizes using a chemical precipitation method. Then, by controlling parameters such as the ball-to-particle ratio, ball milling aid, solid-liquid ratio, and ball milling time, the spherical silver particles are ball-milled to obtain flake silver powder. The ball milling process actually involves the movement of grinding balls within a container. When the balls fall from the highest point of the container, they exert a "hitting" or "smashing" effect on the spherical silver powder below, deforming the spherical silver powder into flake silver powder.

[0004] Sand mills, a type of wet ultrafine grinding equipment, evolved from ball mills. Their working principle involves grinding media and materials being agitated together by a high-speed rotating dispersion disc within a fixed cylinder. This causes intense shearing, scouring, and collision between the solid particles in the material and the grinding media, achieving the purpose of pulverization, grinding, and dispersion. For example, a method for preparing flake silver powder disclosed in national patent CN102974833A uses an organic solvent with a mass concentration of 90-99.9% as the grinding media. Due to the high cost of organic reagents and the large quantity used during grinding, the cost is high. Furthermore, the high volatility of the solvent during the grinding cycle causes changes in the material-to-liquid ratio, making it difficult to control. It is also unfriendly to the operating environment, requiring strict temperature control to prevent excessive evaporation of the organic solvent. While spray drying can directly dry into powder, reducing the need for sieving, it is not the first choice for flake silver powder manufacturers due to high heat consumption, expensive powder recovery equipment, and large footprint. Summary of the Invention

[0005] One of the objectives of this invention is to provide a method for preparing flake silver powder by grinding with a sand mill. The flake silver powder prepared by this method has good dispersibility, uniform flake formation, and a loss on ignition of ≤1%, making it suitable for preparing conductive silver paste.

[0006] The second objective of this invention is to provide a method for grinding flake silver powder using a sand mill.

[0007] To achieve one of the above objectives, the present invention employs the following technical solution:

[0008] A method for preparing flake silver powder by grinding with a sand mill, the method comprising the following steps:

[0009] Step S1: Mix metallic silver powder with a particle size of 0.5-1.5μm and a silver content of >99.99% with pure water in a ratio of 1:4 to 2:3, and then mechanically disperse for 10-20 minutes to obtain a dispersion slurry;

[0010] Step S2: Mix the emulsifier and ethanol at a mass ratio of 0.1-1:5-20 to obtain an emulsifier solution;

[0011] Step S3: Mix the emulsifier solution and dispersion slurry, then disperse for 10-30 minutes and pour into the feed tank of the sand mill. With the pneumatic diaphragm pump turned on, the emulsifier solution and dispersion slurry are fed and discharged in a cycle for 10-25 minutes under the action of air pressure impact. Then turn on the main switch of the sand mill and grind for 10-30 minutes.

[0012] Step S4: After pouring the alkyl hydroxyl ammonium salt wetting and dispersing agent containing acidic group copolymer into the feed tank of the sand mill, it is fed and discharged together with the ground emulsifier solution and dispersion slurry under the action of air pressure impact for 10-25 minutes. Then turn on the main switch of the sand mill and grind for 0.5-2 hours to obtain flake silver powder slurry.

[0013] The mass ratio of the alkyl hydroxyl ammonium salt wetting and dispersing agent, the emulsifier solution, and the dispersion slurry is 0.2–1.3:0.5–10:100;

[0014] Step S5: Wash and filter the flake silver powder slurry with pure water to obtain flake silver powder filter cake;

[0015] Step S6: Using ethanol, the flake silver powder filter cake is centrifuged and stirred for 2-7 minutes, then vacuum baked at 65-75°C for 10-14 hours, and then ultrasonically vibrated and sieved to obtain flake silver powder ground by a sand mill.

[0016] Furthermore, in step S2, the emulsifier includes one or more of Tween, Span, OP-10, fatty acids, and fatty alcohols.

[0017] Furthermore, the fatty acid is one or a mixture of several of hexadecanoic acid, oleic acid and stearic acid;

[0018] The fatty alcohol is one or a mixture of several of hexadecyl alcohol, tetradecyl alcohol, and n-octanol.

[0019] Furthermore, in step S3, a ball-to-material ratio of 0.8 to 1.3:1 is used for grinding;

[0020] The grinding beads used in the grinding process are zirconia beads with a diameter of 0.5 to 1.5 mm, and the materials include emulsifier solution and dispersion slurry.

[0021] Furthermore, in step S4, the alkyl hydroxyl ammonium salt wetting and dispersing agent is BYK180.

[0022] Furthermore, in step S4, a ball-to-material ratio of 0.8 to 1.3:1 is used for grinding;

[0023] The grinding beads used in the grinding process are zirconia beads with a diameter of 0.5 to 1.5 mm, and the materials include alkyl hydroxyl ammonium salt wetting and dispersing agent, emulsifier solution and dispersion slurry.

[0024] Furthermore, in step S5, the mass ratio of pure water to flake silver powder paste is 290-310:100, and the conductivity of the pure water in this invention is <0.5μs / cm.

[0025] The washing and filtration process is repeated 4 to 6 times.

[0026] Furthermore, in step S6, the mass ratio of ethanol to flake silver powder filter cake is 0.7 to 1.3:1;

[0027] The ultrasonic vibrating screen used for ultrasonic screening has a mesh size of 300 to 400 mesh.

[0028] To achieve the second objective mentioned above, the present invention employs the following technical solution:

[0029] A method for grinding flake silver powder using a sand mill, wherein the flake silver powder is prepared using the preparation method described above.

[0030] Furthermore, the D50 particle size of the flake silver powder ground by the sand mill is 2–5 μm, and the loose packing density is 0.8–1.8 g / cm³. 3 Loss on ignition ≤1%.

[0031] In summary, the technical solution of the present invention has the following technical effects:

[0032] This invention uses water as the grinding medium, reducing the use of organic reagents, effectively lowering costs, and avoiding changes in the material-to-liquid ratio caused by the large-scale volatilization of organic reagents during grinding. This facilitates precise control of the material-to-liquid ratio, ensuring process stability, and providing a more user-friendly and safer operating environment. Emulsifiers ensure good dispersibility of silver powder particles during grinding and circulation, improving the dispersibility of flake-shaped silver powder. The steric stabilization effect of the alkyl hydroxyl ammonium salt additive containing acidic group copolymers deflocculates the silver powder, improving the fluidity of the slurry and ensuring a more uniform degree of flake formation, effectively preventing the stacking of flakes caused by silver particle adhesion. Washing and filtration using a combination of vacuum filtration and water washing removes excessive emulsifier residue from the surface of the silver powder. This invention uses a vacuum oven for drying, solving the problems of spray drying and offering advantages such as good dehumidification, oxidation prevention, and fast drying speed. The resulting silver powder exhibits good dispersibility, uniform flake formation, a D50 particle size of 2–5 μm, and a loose packing density of 0.8–1.8 g / cm³. 3 With a loss on ignition of ≤1%, conductive silver paste can be prepared. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1:

[0035] Step S1: Mix 99.992% pure silver powder with a particle size of 1 μm with pure water with a conductivity of 0.4 μs / cm at a ratio of 1:3, and then mechanically disperse for 20 min to obtain a dispersion slurry.

[0036] Step S2: Mix Tween and hexadecanoic acid mixed emulsifier with ethanol at a mass ratio of 0.5:10 to obtain an emulsifier solution.

[0037] Step S3: After mixing the emulsifier solution and dispersion slurry, disperse for 20 minutes and then pour into the feed tank of the sand mill. With the pneumatic diaphragm pump turned on, the emulsifier solution and dispersion slurry circulate in the chamber for 20 minutes under the action of air pressure impact, ensuring thorough mixing and improving dispersibility. Then turn on the main switch of the sand mill and grind for 20 minutes using a 1:1 ball-to-material ratio. The grinding balls used during the grinding process are 1mm diameter zirconia beads.

[0038] Step S4: After pouring the BYK180 dispersant into the feed tank of the sand mill, it is fed and discharged together with the ground emulsifier solution and dispersion slurry under the action of air pressure impact. This process is repeated for 20 minutes to fully mix the materials and improve their dispersibility. Then, the main switch of the sand mill is turned on, and the mill is ground for 1 hour with a ball-to-material ratio of 1:1 to obtain flake silver powder slurry.

[0039] The mass ratio of BYK180, emulsifier solution, and dispersion slurry is 1:5:100. The grinding balls used in the grinding process are 1mm diameter zirconia beads.

[0040] Step S5: Wash the flaky silver powder slurry with pure water to obtain a flaky silver powder filter cake. Repeat the washing and filtration process 5 times. The mass ratio of pure water to flaky silver powder slurry is 300:100.

[0041] Step S6: Using ethanol, the flake silver powder filter cake is centrifuged and stirred for 5 minutes, then vacuum baked at 70°C for 12 hours, and then sieved using a 350-mesh ultrasonic vibrating sieve to obtain flake silver powder ground by a sand mill. The mass ratio of ethanol to flake silver powder filter cake is 1:1.

[0042] The D50 particle size of the flake silver powder ground by the sand mill in this embodiment is 2.318 μm, and the loose packing density is 1.65 g / cm³. 3 The loss on ignition was 0.75%.

[0043] Example 2:

[0044] Step S1: Mix 1.5μm, 99.993% pure silver powder with a particle size of 1.5μm and pure water with a conductivity of 0.3μs / cm at a ratio of 1:4, and then mechanically disperse for 20 minutes to obtain a dispersion slurry.

[0045] Step S2: Mix the emulsifier consisting of Span, oleic acid and tetradecyl alcohol with ethanol at a mass ratio of 0.1:20 to obtain an emulsifier solution.

[0046] Step S3: After mixing the emulsifier solution and dispersion slurry, disperse for 30 minutes and then pour into the feed tank of the sand mill. With the pneumatic diaphragm pump turned on, the emulsifier solution and dispersion slurry circulate in the chamber for 10 minutes under the action of air pressure impact, ensuring thorough mixing and improving dispersibility. Then turn on the main switch of the sand mill and grind for 30 minutes using a ball-to-material ratio of 0.8:1. The grinding balls used during the grinding process are 1.5mm diameter zirconia beads.

[0047] Step S4: After pouring the BYK180 dispersant into the feed tank of the sand mill, it is fed together with the ground emulsifier solution and dispersion slurry. With the pneumatic diaphragm pump turned on, the BYK180 and the ground emulsifier solution and dispersion slurry are circulated in the chamber for 25 minutes under the action of air pressure impact, so that the above materials are fully mixed and the dispersibility is improved. Then turn on the main switch of the sand mill and grind for 2 hours with a ball-to-material ratio of 0.8:1 to obtain flake silver powder slurry.

[0048] The mass ratio of BYK180, emulsifier solution, and dispersion slurry is 0.2:10:100. The grinding balls used in the grinding process are 1.5 mm diameter zirconia beads.

[0049] Step S5: Wash the flaky silver powder slurry with pure water to obtain a flaky silver powder filter cake. Repeat the washing and filtration process 6 times. The mass ratio of pure water to flaky silver powder slurry is 290:100.

[0050] Step S6: Using ethanol, the flake silver powder filter cake is centrifuged and stirred for 2 minutes, then vacuum baked at 65°C for 14 hours, and then sieved using a 300-mesh ultrasonic vibrating sieve to obtain flake silver powder ground by a sand mill. The mass ratio of ethanol to flake silver powder filter cake is 0.7:1.

[0051] The D50 particle size of the flake silver powder ground by the sand mill in this embodiment is 2.822 μm, and the loose packing density is 1.13 g / cm³. 3 The loss on ignition was 0.83%.

[0052] Example 3:

[0053] Step S1: Mix 99.995% pure silver powder with a particle size of 0.5 μm with pure water with a conductivity of 0.1 μs / cm in a ratio of 2:3, and then mechanically disperse for 10 min to obtain a dispersion slurry.

[0054] Step S2: Mix oleic acid emulsifier and ethanol at a mass ratio of 1:5 to obtain an emulsifier solution.

[0055] Step S3: After mixing the emulsifier solution and dispersion slurry, disperse for 10 minutes and then pour into the feed tank of the sand mill. With the pneumatic diaphragm pump turned on, the emulsifier solution and dispersion slurry circulate in the chamber for 25 minutes under the action of air pressure impact, ensuring thorough mixing and improving dispersibility. Then turn on the main switch of the sand mill and grind for 10 minutes using a ball-to-material ratio of 1.3:1. The grinding balls used during the grinding process are 0.5mm diameter zirconia beads.

[0056] Step S4: After pouring the BYK180 dispersant into the feed tank of the sand mill, it is fed together with the ground emulsifier solution and dispersion slurry. With the pneumatic diaphragm pump turned on, the BYK180 and the ground emulsifier solution and dispersion slurry are circulated in the chamber for 10 minutes under the action of air pressure impact, so that the above materials are fully mixed and the dispersibility is improved. Then turn on the main switch of the sand mill and grind for 0.5 hours with a ball-to-material ratio of 1.3:1 to obtain flake silver powder slurry.

[0057] The mass ratio of BYK180, emulsifier solution, and dispersion slurry is 1.3:0.5:100. The grinding balls used in the grinding process are 0.5 mm diameter zirconia beads.

[0058] Step S5: Wash the flaky silver powder slurry with pure water to obtain a flaky silver powder filter cake. Repeat the washing and filtration process 44 times. The mass ratio of pure water to flaky silver powder slurry is 310:100.

[0059] Step S6: Using ethanol, the flake silver powder filter cake is centrifuged and stirred for 7 minutes, then vacuum baked at 75°C for 10 hours, and then sieved using a 400-mesh ultrasonic vibrating sieve to obtain flake silver powder ground by a sand mill. The mass ratio of ethanol to flake silver powder filter cake is 1.3:1.

[0060] The D50 particle size of the flake silver powder ground by the sand mill in this embodiment is 4.146 μm, and the loose packing density is 1.25 g / cm³. 3 The loss on ignition was 0.89%.

[0061] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing flake silver powder by grinding with a sand mill, characterized in that, The preparation method includes the following steps: Step S1: Mix metallic silver powder with a particle size of 0.5~1.5μm and a silver content of >99.99% with pure water in a ratio of 1:4~2:3, and then mechanically disperse for 10~20min to obtain a dispersion slurry; Step S2: Mix the emulsifier and ethanol at a mass ratio of 0.1~1:5~20 to obtain an emulsifier solution; In step S2, the emulsifier includes one or more of Tween, Span, OP-10, fatty acids, and fatty alcohols; Step S3: Mix the emulsifier solution and dispersion slurry, then disperse for 10-30 minutes and pour into the feed tank of the sand mill. With the pneumatic diaphragm pump turned on, the emulsifier solution and dispersion slurry are fed and discharged in a cycle for 10-25 minutes under the action of air pressure impact. Then turn on the main switch of the sand mill and grind for 10-30 minutes. Step S4: After pouring the alkyl hydroxyl ammonium salt wetting and dispersing agent containing acidic group copolymer into the feed tank of the sand mill, it is fed and discharged together with the ground emulsifier solution and dispersion slurry under the action of air pressure impact for 10~25 minutes. Then turn on the main switch of the sand mill and grind for 0.5~2 hours to obtain flake silver powder slurry. The mass ratio of the alkyl hydroxyl ammonium salt wetting and dispersing agent, the emulsifier solution, and the dispersion slurry is 0.2~1.3:0.5~10:100; In step S4, the alkyl hydroxyammonium salt wetting and dispersing agent is BYK180; Step S5: Wash and filter the flake silver powder slurry with pure water to obtain flake silver powder filter cake; Step S6: Using ethanol, the flake silver powder filter cake is centrifuged and stirred for 2-7 minutes, then vacuum baked at 65-75℃ for 10-14 hours, and then ultrasonically vibrated and sieved to obtain flake silver powder ground by a sand mill.

2. The preparation method according to claim 1, characterized in that, The fatty acid is one or a mixture of several of palmitic acid, oleic acid and stearic acid; The fatty alcohol is one or a mixture of several of hexadecyl alcohol, tetradecyl alcohol, and n-octanol.

3. The preparation method according to claim 2, characterized in that, In step S3, a ball-to-material ratio of 0.8 to 1.3:1 is used for grinding; The grinding beads used in the grinding process are zirconia beads with a diameter of 0.5~1.5mm, and the materials include emulsifier solution and dispersion slurry.

4. The preparation method according to claim 3, characterized in that, In step S4, a ball-to-material ratio of 0.8 to 1.3:1 is used for grinding; The grinding beads used in the grinding process are zirconia beads with a diameter of 0.5~1.5mm, and the materials include alkyl hydroxyl ammonium salt wetting and dispersing agent, emulsifier solution and dispersion slurry.

5. The preparation method according to claim 4, characterized in that, In step S5, the mass ratio of pure water to flake silver powder paste is 290~310:100; The washing and filtration process is repeated 4 to 6 times.

6. The preparation method according to claim 5, characterized in that, In step S6, the mass ratio of ethanol to flake silver powder filter cake is 0.7~1.3:1; The ultrasonic vibrating screen used for ultrasonic screening has a mesh size of 300-400 mesh.

7. A method for grinding flake silver powder using a sand mill, characterized in that, The flake silver powder ground by the sand mill is prepared by the preparation method described in any one of claims 1 to 6.

8. The method of grinding flake silver powder using a sand mill according to claim 7, characterized in that, The silver powder produced by the sand mill has a D50 particle size of 2~5μm and a loose packing density of 0.8~1.8g / cm³. 3 Loss on ignition ≤1%.