Highly dispersed metal powder preparation method and highly dispersed metal powder preparation device

Abstract

The present invention provides a method for preparing highly dispersed metal powder and a device for preparing highly dispersed metal powder. The method comprises the steps of (1) adding a base liquid into a synthesis reactor, and performing internal and external circulation of the synthesis reactor through an external circulation dispersion device connected to the synthesis reactor to achieve a stable circulation; (2) after the stable circulation meets a predetermined requirement, continuously adding an oxidizing liquid and a reducing liquid into the synthesis reactor to mix with the base liquid to form a reaction liquid, and continuously passing the reaction liquid through the external circulation dispersion device for forced dispersion, and then feeding it into the synthesis reactor; (3) performing sampling analysis and testing during the synthesis reaction, and when the particle size of the metal powder generated by the synthesis reaction meets the requirement, stopping the addition of the oxidizing liquid and the reducing liquid to stop the synthesis reaction; and (4) discharging the reaction liquid from the synthesis reactor, performing solid-liquid separation, cleaning, post-treatment, and drying to obtain highly dispersed metal powder.

Description

Technical Field

[0001] The invention relates to the technical field of synthetic metal powder, and in particular to a method and a device for preparing highly dispersed metal powder. Background Art

[0002] The dispersibility, particle size distribution and particle uniformity of metal powder synthesized by chemical reduction method have a decisive influence on the performance of metal powder. The production equipment and synthesis process of metal powder affect the morphology, dispersibility, particle size distribution, width and other parameters of metal powder, and ultimately affect its application performance. The high-performance metal powder used in the photovoltaic industry must have the characteristics of excellent dispersion, concentrated particle size distribution and high sphericity.

[0003] At present, the method for synthesizing and preparing metal powder by existing methods is to add an oxidizing liquid, a reducing liquid, a dispersing liquid and other additives to a synthesis reactor under certain control conditions to carry out a redox reaction. During the reaction process, the uniformity of the reaction system is generally ensured by an agitator and / or other enhanced disperser on the synthesis reactor, but these stirring methods cannot fully guarantee the uniformity of the reaction liquid, and the powder particle clusters that appear in the reaction system cannot be depolymerized in time. This results in poor dispersibility of the produced metal particles, low sphericity, excessive irregular powder, and a wide particle size distribution. The slurry prepared directly using this powder is prone to problems such as poor printability, uneven lines, and poor electrical properties during the printing process, and various powder post-treatments are required to achieve better application performance. Summary of the invention

[0004] In order to solve the above-mentioned existing technical problems or part of them, the purpose of the present invention is to provide a method for preparing highly dispersed metal powder and a device for preparing highly dispersed metal powder, which controls the synthesis of highly dispersed metal powder with narrow particle size dispersion and high uniformity through a forced external circulation dispersion device with high dispersion function.

[0005] According to one aspect of the present invention, a method for preparing a highly dispersed metal powder is provided, the method comprising the following steps:

[0006] Step (1) adding the bottom liquid into the synthesis reactor, and performing internal and external circulation of the synthesis reactor through an external circulation dispersion device connected to the synthesis reactor to achieve stable circulation;

[0007] Step (2) after the stable circulation meets the predetermined requirements, the oxidizing liquid and the reducing liquid are continuously added into the synthesis reaction kettle to mix with the bottom liquid to form a reaction liquid, and a synthesis reaction is performed. During the synthesis reaction, the reaction liquid is continuously forced to be dispersed by the external circulation dispersion device and then fed into the synthesis reaction kettle;

[0008] Step (3) sampling, analyzing and testing are performed during the synthesis reaction. When the particle size of the metal powder generated by the synthesis reaction meets the requirements, the addition of the oxidizing liquid and the reducing liquid is stopped to stop the synthesis reaction;

[0009] Step (4) After the reaction liquid is discharged from the synthesis reactor, it is subjected to solid-liquid separation, cleaning, post-treatment and drying to obtain highly dispersed metal powder.

[0010] According to another aspect of the present invention, there is provided a device for preparing highly dispersed metal powder using the above-mentioned method for preparing highly dispersed metal powder, comprising:

[0011] Synthesis reactor;

[0012] An external circulation dispersing device, which is connected to the pipeline of the synthesis reactor, and the bottom liquid or the reaction liquid is forcibly dispersed in the external circulation dispersing device;

[0013] The circulation device is respectively connected to the synthesis reaction kettle and the external circulation dispersion device pipeline, so that the bottom liquid or the reaction liquid is continuously circulated in the high-dispersion metal powder preparation device.

[0014] The method and device for preparing highly dispersed metal powder according to the embodiments of the present invention have at least one of the following advantages or part of one of the advantages:

[0015] 1. The present invention adopts a method in which the reaction liquid is continuously fed into an external circulation dispersion device outside the synthesis reactor for efficient dispersion during the synthesis reaction, so that the metal powder that may agglomerate in the synthesis reactor is dispersed in time, thereby solving the defect of not being able to disperse in time and effectively caused by only using the agitator of the synthesis reactor; the present invention can ensure that the particles in the entire synthesis reactor are always in a monodisperse state for uniform growth, thereby solving the problem of uniform dispersion of the metal powder.

[0016] 2. While the oxidizing liquid, reducing liquid and dispersing liquid are added to the synthesis reactor for synthesis, the reaction liquid is sent to an external circulation disperser with high dispersing function of an ultrasonic device and / or a shearing disperser for cyclic shearing dispersion to complete the synthesis of highly dispersed and highly uniform metal powder. This method has good repeatability and strong operability. The metal powder prepared by this method has the advantages of high dispersion, narrow particle size distribution and high uniformity, which solves the shortcomings of existing metal powders such as poor dispersibility, wide particle size distribution and poor uniformity. It is suitable for conductive slurries, conductive adhesives and other fields that have high requirements for the dispersibility, particle size distribution and uniformity of metal powders.

[0017] 3. By utilizing the characteristics of the external circulation disperser, which is small in size and does not have a dead angle during stirring, the agglomerated powder inevitably formed during the synthesis process of the large-sized synthesis reactor for production due to the existence of a dead angle in stirring is continuously and completely dispersed. In the present invention, the particles forcibly dispersed by the small external circulation disperser are continuously returned to the large-sized synthesis reactor to continue to participate in the reaction until the particle size of the silver particles meets the requirements. During the reaction process, various reaction liquid parameters can be conveniently adjusted on the large-sized synthesis reactor.

[0018] 4. The silver particles formed after the mixed reaction of the oxidizing solution and the reducing solution will continue to participate in the next cycle of synthesis reaction as seeds. The newly generated silver particles will grow and adjust the microcrystalline morphology on the original silver particles, and this cycle will be repeated until the particle size of the silver powder meets the requirements. When using this method, in addition to controlling the particle size of the silver powder by adjusting the parameters of the oxidizing solution and the reducing solution during the synthesis of silver powder, the particle size and morphology of the silver powder can also be controlled by controlling the amount of silver source during the reaction cycle.

[0019] 5. In the present invention, a small disperser is used in conjunction with a large synthesis reactor to achieve large-scale production while reducing the amplification effect of production. The small disperser is used mainly to fully ensure the dispersion and particle size uniformity of the silver powder by utilizing its small size and the absence of a stirring dead angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of the preferred embodiments in conjunction with the accompanying drawings, in which:

[0021] Figure 1 A flowchart of a method for preparing highly dispersed metal powder according to an embodiment of the present invention;

[0022] Figure 2 It is a schematic structural diagram of a device for preparing highly dispersed metal powder according to another embodiment of the present invention;

[0023] Figure 3-Figure 7 is a scanning electron microscope image of the silver powder prepared according to the method shown in Examples 1-5 of the present invention;

[0024] Figure 8-Figure 9 is a scanning electron microscope image of the silver powder prepared according to the method shown in Comparative Example 1-2 of the present invention. DETAILED DESCRIPTION

[0025] The features of the present invention are further described below through specific embodiments. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall concept of the present invention and should not be construed as a limitation of the present invention.

[0026] See also Figure 1 , shows a flow chart of a method for preparing highly dispersed metal powder according to an embodiment of the present invention. As shown in the figure, the preparation method mainly includes the following four steps.

[0027] Specifically, the method for preparing highly dispersed metal powder comprises the following steps:

[0028] Step (1) adding the bottom liquid into the synthesis reactor, and performing internal and external circulation of the synthesis reactor through an external circulation dispersion device connected to the synthesis reactor to achieve stable circulation;

[0029] Step (2) after the stable circulation meets the predetermined requirements, the oxidizing liquid and the reducing liquid are continuously added into the synthesis reaction kettle to mix with the bottom liquid to form a reaction liquid, and a synthesis reaction is performed. During the synthesis reaction, the reaction liquid is continuously forced to be dispersed by the external circulation dispersion device and then fed into the synthesis reaction kettle;

[0030] Step (3) sampling, analyzing and testing are performed during the synthesis reaction. When the particle size of the metal powder generated by the synthesis reaction meets the requirements, the addition of the oxidizing liquid and the reducing liquid is stopped to stop the synthesis reaction;

[0031] Step (4) After the reaction liquid is discharged from the synthesis reactor, it is subjected to solid-liquid separation, cleaning, post-treatment and drying to obtain highly dispersed metal powder.

[0032] The high dispersion in the present application can refer to any of the following two types: one is that when observed under a scanning electron microscope, there are basically no more than two single silver powder particles bonded together in the silver powder, and the particle size distribution of the silver powder is uniform; the other is measured by the particle size distribution width, which is measured by testing the particle size D10, D50, and D90 on a laser diffraction particle size analyzer, and then calculated according to the following formula: particle size distribution width = (D90-D10) / D50. When the value is below 1, it means that the silver powder is basically not agglomerated, and the particle size of the silver powder is uniform, and the dispersion of the silver powder is high, which is high dispersion. When it is between 1 and 1.2, it is relatively high dispersion, and when it is greater than 1.2, it means that the dispersion of the silver powder is poor, the particle size of the silver powder is uneven, the distribution is wide, or the silver powder is seriously agglomerated.

[0033] As discussed in the background technology section of the present invention, in order to at least partially solve the proposed technical problem, the embodiment of the present invention adopts a method of continuously sending the reaction liquid into the external circulation dispersion device outside the synthesis reactor for efficient dispersion during the synthesis reaction, so that the metal powder that may agglomerate in the synthesis reactor is dispersed in time, thereby solving the defects caused by using only the agitator of the synthesis reactor. The technical solution of the present invention can ensure that the particles in the entire synthesis reactor are always in a monodisperse state for uniform growth, thereby solving the problem of uniform dispersion of metal powder.

[0034] First, I will introduce the preparation of the base liquid (or dispersion liquid), oxidizing liquid, and reducing liquid, and will not introduce them in detail later.

[0035] 1. Preparation of oxidizing solution: Add a certain amount or a predetermined amount of metal salt to a certain amount of pure water, stir and dissolve, and keep the temperature at 15°C-45°C. The metal salt in the oxidizing solution includes any one of oxalates, carbonates, sulfates, citrates, nitrates, metal oxides, and metal ammonia complexes, or any combination thereof. The concentration of the metal salt is 30g / L-300g / L, preferably 120g / L-240g / L. In one example, when preparing the oxidizing solution with silver nitrate, ammonia water can also be added to prepare it into a silver ammonia complex solution for use.

[0036] 2. Preparation of reducing solution: Add a certain amount or a predetermined amount of reducing agent to a certain amount of pure water, stir and dissolve, and keep the temperature at 15°C-45°C. The reducing agent in the reducing solution includes any one of hydrazine hydrate, formaldehyde, formic acid, ammonium formate, ascorbic acid, hydrogen peroxide, triethanolamine, glycerol, glucose, hydroxylamine or any combination thereof. The concentration of the reducing agent is 20g / L-200g / L, preferably 50g / L-150g / L.

[0037] 3. Preparation of dispersion: Add a certain amount or a predetermined amount of dispersant to a certain amount of pure water, stir and dissolve, and keep the temperature at 15°C-45°C. The dispersant in the dispersion includes one of polyvinyl alcohol, guar gum, arabic resin, polyvinyl pyrrolidone, fatty acid, copper nitrate, magnesium nitrate or any combination thereof. The concentration of the dispersant is 0g / L-500g / L, preferably 10g / L-100g / L.

[0038] The "post-treatment" mentioned here refers to coating the surface of the silver powder with a layer of organic matter to modify the surface of the powder. The organic matter can be one or a mixture of fatty acid salts, fatty acid ammonium amides, organic acids, fatty amines, fatty enamines, surfactants, and organosilicon compounds.

[0039] See also Figure 2 , shows a schematic structural diagram of a highly dispersed metal powder preparation device according to an embodiment of the present invention.

[0040] The highly dispersed metal powder preparation device 100 includes a synthesis reactor 10, an external circulation dispersion device 20, and a circulation device 30. The external circulation dispersion device 20 is connected to the synthesis reactor 10 by a pipeline, and the bottom liquid or the reaction liquid is forcibly dispersed in the external circulation dispersion device 20. The circulation device 30 is respectively connected to the synthesis reactor 10 and the external circulation dispersion device 20 by pipelines, so that the bottom liquid or the reaction liquid is continuously circulated in the highly dispersed metal powder preparation device 100. In one example, the circulation device 30 can be a circulation pump, etc.

[0041] like Figure 2 As shown, the outlet of the synthesis reactor 10 is connected to the first pipeline 51, and the first pipeline 51 is branched into two flow paths. The first flow path 52 of the two flow paths passes through the first valve 53, the circulation device 30, the second valve 54, the external circulation dispersion device 20 in sequence and is connected to the inlet 55 of the synthesis reactor 10 via the second pipeline 59.

[0042] The second flow path 56 of the two flow paths is provided with a third valve 57 to discharge the reaction liquid after the synthesis reaction is stopped from the synthesis reactor 10 to form the final product.

[0043] In one example, the external circulation dispersion device 20 includes at least one external circulation disperser 20, for example, it may include one external circulation disperser 20 or multiple external circulation dispersers 20 connected in series. That is, in the embodiment of the present invention, multiple external circulation dispersers 20 can be installed on the external pipe line of a synthesis reactor 10, so that the reaction liquid in the synthesis reactor 10 completes one cycle within 1-10 minutes, that is, to achieve a stable cycle.

[0044] In order to ensure that the metal powder is fully dispersed, at least one external circulation disperser 20 is connected in series outside the synthesis reactor 10. The external circulation disperser 20 is used to achieve a sufficient and efficient dispersion effect of the reaction liquid, so that the metal powder in the reaction liquid can be dispersed and deagglomerated in time, ensuring that the particles in the synthesis reactor grow in a monodisperse state.

[0045] The characteristic of the external circulation device 20 is to force the agglomerated powder in the reaction liquid to be dispersed in the device, mainly to disperse the agglomerated powder produced during the reaction to form a single particle state to participate in the next step of the reaction.

[0046] The volume of the external circulation dispersing device 20 is smaller than the synthesis reactor 10. Usually, the volume of each external circulation dispersing device 20 is 2L-50L, preferably 5L-20L. The volume of the external circulation dispersing device 20 needs to be controlled within a certain range. If the volume of the external circulation dispersing device 20 is too large or too small, the reaction liquid will not achieve the ideal dispersion effect when passing through the external circulation dispersing device 20 due to its too large or too small volume, causing the metal powder to easily agglomerate. The volume ratio of the external circulation dispersing device 20 to the synthesis reactor 10 is 1 to 2000, preferably 1 to 500. Of course, those skilled in the art can also make a selection according to actual needs. In one embodiment, an ultrasonic device 40 is arranged on the outer wall or inside of at least one external circulation dispersing device 20 of the external circulation dispersing device 20, and of course, a shearing disperser 40 can also be arranged inside it.

[0047] When an ultrasonic device or a shearing disperser 40 is provided, the bottom liquid is forcibly dispersed by the ultrasonic device or the shearing disperser 40 on the external circulation disperser 20 and then returns to the reaction liquid system along the tangent direction of the inner wall of the synthesis reactor 10 through the outlet of the external circulation disperser 20.

[0048] It should be noted that the external circulation disperser can adopt any principle for forced dispersion, and no limitation is made here. The ultrasonic device can be set in the form of an ultrasonic dispersion rod, and the external circulation disperser with a shearing disperser can be set as a high-speed dispersion homogenizer, for example, the ultrasonic dispersion rod or the shearing disperser can be set as an integrated or powdered one, and set at the center of the external circulation disperser.

[0049] In order to further enhance the dispersion of the metal powder in the reaction solution in the external circulation disperser, an ultrasonic device is installed on the external circulation disperser. When the ultrasonic vibration rod and / or the high-speed dispersion homogenizer are installed inside the external circulation disperser 20, the distance d from the outer wall of the ultrasonic vibration rod and / or the high-speed dispersion homogenizer to the inner wall of the external circulation disperser is 1-30 cm, preferably 2-10 cm.

[0050] In one example, the ultrasonic device 40 installed inside the external circulation disperser is in an elongated shape, such as an ultrasonic rod, and has an ultrasonic frequency of 20KHz-100KHz, preferably 40KHz-80KHz.

[0051] In addition, a high-speed dispersing homogenizer may be installed inside the external circulation disperser, and the rotation speed of the high-speed dispersing homogenizer is 3000rpm-5000rpm.

[0052] When performing forced external circulation, a combination of ultrasonic waves and high-speed dispersing homogenizers can also be used simultaneously to further achieve high dispersion of metal powders and concentrated distribution of particle sizes.

[0053] In one example, in order to ensure that the reaction liquid is fully dispersed in the external circulation dispersion device 20, the shape setting of the external circulation disperser or the dispersion device 20 is very important. The external circulation disperser itself cannot have a dead angle, and its joints should be connected at a certain curvature to ensure that the reaction liquid flows from bottom to top through the external circulation disperser in a piston-like manner without reflux. Therefore, the structure of the external circulation disperser 20 in the present invention is set to a (slender) cylindrical shape with curvature heads at both ends and a polished interior, and is connected to the synthesis reactor through a joint with a curvature.

[0054] In the present invention, the morphology of the metal powder is spherical or quasi-spherical. In the present invention, an external circulation dispersion device is added, and its forced dispersion effect makes the prepared metal powder have high dispersibility and uniformity. In addition, the metal powder prepared by the present invention also has a narrow distribution width, and the particle size distribution width (D90-D10 / D50) of the metal powder is less than 1.0; the metal powder includes any one of silver, copper, tin and nickel or any combination thereof.

[0055] Characterization method of particle size distribution width: Test the particle size D10, D50, and D90 on a laser diffraction particle size analyzer, and then calculate according to the following formula:

[0056] Particle size distribution width = (D90-D10) / D50

[0057] The smaller the particle size distribution width value, the better the dispersion and uniformity of the metal powder (such as silver powder); the larger the value, the worse the dispersion and uniformity of the silver powder.

[0058] Returning to the method for preparing highly dispersed metal powder of the present invention, after the above operation reaches the required stability, the oxidizing liquid and the reducing liquid are added to the synthesis reactor 10 for synthesis reaction. During the entire synthesis reaction, the reaction liquid is continuously sent to the external circulation disperser 20 by the circulation pump 30 at the bottom of the synthesis reactor 10 for strong dispersion without dead angles and without distinction, and then sent to the synthesis reactor 10 for synthesis reaction. Sampling analysis and testing are carried out during the reaction process. When the particle size of the metal powder reaches the requirement, the addition of the oxidizing liquid and the reducing liquid is stopped to stop the synthesis reaction. Finally, after the synthesis reaction liquid is discharged from the synthesis reactor 10, it is subjected to solid-liquid separation, cleaning, post-treatment, drying and other processes to obtain highly dispersed metal powder.

[0059] It should be noted that the reaction liquid is also sent into the external circulation disperser 20 in a plug flow state for forced dispersion.

[0060] The method and device for preparing highly dispersed metal powder of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0061] Example 1

[0062] 1. Add 800g of silver nitrate to 5000g of pure water at 15℃-45℃, stir and dissolve to obtain an oxidizing solution;

[0063] 2. Add 600 g of ascorbic acid to 5000 g of pure water at 15°C-45°C, and stir to dissolve to obtain a reducing solution;

[0064] 3. Add 100 g of polyvinyl pyrrolidone to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a dispersion.

[0065] 4. Add the dispersion as the reaction liquid (base liquid) into the synthesis reactor 10, and start the agitator 11 in the synthesis reactor 10.

[0066] 5. The reaction liquid is forced to pass through the external circulation disperser 20 through the circulation pump 30 for forced internal and external circulation. The volume of the external circulation disperser 20 is 5L. An ultrasonic vibrating rod 40 is installed in the external circulation disperser 20. The frequency of the ultrasonic rod 40 is adjusted to 20kHz, the power is 2000W, and the distance d from the ultrasonic rod 40 to the inner wall of the external circulation disperser 20 is 3cm. The flow rate is adjusted so that the bottom liquid flows from bottom to top in the external circulation disperser 20 in a piston flow state and completes one cycle within 2 minutes;

[0067] 6. Add the oxidizing liquid and reducing liquid dropwise into the synthesis reactor 10 for synthesis reaction, and continuously send them into the external circulation disperser 20 in a piston flow state for forced dispersion, and then recirculate them into the synthesis reactor 10 for reaction. Sampling analysis and testing are performed during the reaction. When the particle size of the metal powder reaches the requirement, the dropwise addition is stopped, and the stirring and circulation are continued for 10 minutes to stop the reaction. After the synthesized reaction liquid is processed by solid-liquid separation, cleaning, post-treatment, drying and other processes, a highly dispersed, narrowly distributed and uniform silver powder with a D50 of 1.48um and a distribution width of 0.73 is obtained.

[0068] The particle size and particle size distribution of the silver powder prepared in Example 1 are shown in Table 1.

[0069] The scanning electron microscope image of the silver powder prepared in Example 1 is shown in Figure 3 The silver powder is basically spherical, with the characteristics of uniform morphology, excellent dispersion and high crystallinity.

[0070] Example 2

[0071] 1. Add 800g of silver nitrate to 5000g of pure water at 15℃-45℃, stir and dissolve to obtain an oxidizing solution;

[0072] 2. Add 600 g of ascorbic acid to 5000 g of pure water at 15°C-45°C, and stir to dissolve to obtain a reducing solution;

[0073] 3. Add 50 g of polyvinyl alcohol and 50 g of fatty acid salt to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a dispersion.

[0074] 4. The subsequent reaction steps are the same as those in Example 1. Example 2 The frequency of the ultrasonic rod 40 is adjusted to 40 kHz.

[0075] 5. The D50 of the prepared silver powder is 1.46um, and the distribution width of the silver powder is 0.88, so it is a highly dispersed, narrowly distributed and uniform silver powder.

[0076] The particle size and particle size distribution results of the silver powder prepared in Example 2 of the present invention are shown in Table 1.

[0077] The scanning electron microscope image of the silver powder prepared in Example 2 of the present invention is shown in Figure 4 The silver powder is spherical, has uniform morphology, excellent dispersion, no agglomeration and high crystallinity.

[0078] Example 3

[0079] 1. Add 1000g of silver nitrate to 5000g of pure water at 15℃-45℃, stir and dissolve to obtain an oxidizing solution;

[0080] 2. Add 700 g of ammonium formate to 5000 g of pure water at 15°C-45°C, and stir to dissolve to obtain a reducing solution;

[0081] 3. Add 150 g of polyvinyl pyrrolidone to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a dispersion.

[0082] 4. The subsequent reaction steps are the same as those in Example 1. However, the base liquid completes one cycle in 2 minutes through the circulating disperser; and the frequency of the ultrasonic rod is adjusted to 60 kHz.

[0083] 5. The D50 of the prepared silver powder is 1.58um, and the distribution width of the silver powder is 0.91.

[0084] The particle size and particle size distribution of the silver powder prepared in Example 3 of the present invention are shown in Table 1.

[0085] The scanning electron microscope image of the silver powder prepared in Example 3 of the present invention is shown in Figure 5 The silver powder is spherical, with the characteristics of relatively uniform morphology, excellent dispersion, no agglomeration, and high crystallinity.

[0086] Example 4

[0087] 1. Add 2.4 kg of silver nitrate to 15 kg of pure water at 15°C-45°C, stir and dissolve to obtain an oxidizing solution;

[0088] 2. Add 15 kg of hydrazine hydrate to 15 kg of pure water at 15°C-45°C, stir and dissolve to obtain a reducing solution;

[0089] 3. Add 150g of PVP K30 to 5kg of pure water at 15℃-45℃, stir and dissolve to obtain a dispersion;

[0090] 4. The subsequent reaction steps are the same as those in Example 1. The external circulation disperser 20 is replaced by a high-speed dispersion homogenizer, the distance d from the outer edge of the dispersion head of the high-speed dispersion homogenizer to the inner wall of the external circulation disperser is 5 cm, and the speed of the high-speed dispersion homogenizer is 4000 rpm. The bottom liquid completes one cycle through the external circulation disperser 20 within 2 minutes;

[0091] 5. The D50 of the prepared silver powder is 1.56um, and the distribution width of the silver powder is 0.88.

[0092] The particle size and particle size distribution results of the silver powder prepared in Example 4 of the present invention are shown in Table 1.

[0093] The scanning electron microscope image of the silver powder prepared in Example 4 of the present invention is shown in Figure 6 The silver powder is spherical, with uniform morphology, excellent dispersion, no agglomeration and high crystallinity.

[0094] Example 5

[0095] 1. Add 800g of silver nitrate to 5000g of pure water at 15℃-45℃, stir and dissolve to obtain an oxidizing solution;

[0096] 2. Add 500 g of ascorbic acid to 5000 g of pure water at 15°C-45°C, and stir to dissolve to obtain a reducing solution;

[0097] 3. Add 100 g of polyvinyl pyrrolidone to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a dispersion.

[0098] 4. The subsequent reaction steps are the same as those in Example 1. The external circulation disperser 20 is replaced by a high-speed dispersion homogenizer, the distance d from the outer edge of the dispersion head of the high-speed dispersion homogenizer to the inner wall of the container of the external circulation disperser is 3 cm, the rotation speed of the high-speed dispersion homogenizer is 3500 rpm, and the bottom liquid completes one cycle within 1 minute through the external circulation disperser 20;

[0099] 5. Prepare silver powder with a D50 of 1.57um and a distribution width of 0.9;

[0100] The particle size and particle size distribution results of the silver powder prepared in Example 5 of the present invention are shown in Table 1.

[0101] The scanning electron microscope image of the silver powder prepared in Example 5 of the present invention is shown in Figure 7 The silver powder is spherical, with uniform morphology, excellent dispersion, no agglomeration and high crystallinity.

[0102] Comparative Example 1

[0103] 1. Add 800g of silver nitrate to 5000g of pure water at 15℃-45℃, stir and dissolve to obtain an oxidizing solution;

[0104] 2. Add 600 g of ascorbic acid to 5000 g of pure water at 15°C-45°C, and stir to dissolve to obtain a reducing solution;

[0105] 3. Add 100 g of polyvinyl alcohol to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a dispersion.

[0106] 4. Close valves 53 and 57, and do not perform forced external circulation. Under stirring, add the dispersion into the synthesis reactor 10, and then add the oxidizing liquid and reducing liquid. After the reaction is completed, stop adding the oxidizing liquid and reducing liquid. Finally, after the synthesis reaction liquid is subjected to solid-liquid separation, cleaning, post-treatment, drying and other processes, a silver powder with a D50 of 1.61 um and a distribution width of 1.11 is obtained, which has poor dispersion and wide particle size distribution.

[0107] The particle size and particle size distribution of the silver powder prepared in Comparative Example 1 are shown in Table 1.

[0108] The scanning electron microscope image of the silver powder prepared in Comparative Example 1 is shown in Figure 8 The silver powder has irregular and spherical shapes, poor dispersion and serious agglomeration.

[0109] Comparative Example 2

[0110] 1. Add 800g of silver nitrate to 5000g of pure water at 15℃-45℃, stir and dissolve to obtain an oxidizing solution;

[0111] 2. Add 300 g of hydrazine hydrate to 5000 g of pure water at 15°C-45°C, and stir to dissolve to obtain a reducing solution;

[0112] 3. Add 200 g of polyvinyl pyrrolidone to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a dispersion.

[0113] 4. Close valves 53 and 57, and do not perform forced external circulation. Under stirring, add the dispersion into the synthesis reactor, and then add the oxidizing solution and reducing solution. After the reaction is completed, stop adding the oxidizing solution and reducing solution. Finally, after the synthesis reaction solution is subjected to solid-liquid separation, cleaning, post-treatment, drying and other processes, a silver powder with poor dispersion and wide particle size distribution is obtained, with a D50 of 1.45 um and a distribution width of the silver powder (D90-D10) / D50 of 1.08.

[0114] The particle size and particle size distribution of the silver powder prepared in Comparative Example 2 are shown in Table 1.

[0115] The scanning electron microscope image of the silver powder prepared in Comparative Example 2 is shown in Fig. 9 The silver powder has an irregular, spherical shape, poor dispersion, and serious agglomeration.

[0116] Table 1 Comparison of results of Examples 1-5 and Comparative Examples 1-2

[0117]

[0118]

[0119] The silver powders of Examples 1-5 and Comparative Examples 1 and 2 were prepared into slurries in the same manner and tested in the same manner, and the results obtained are shown in Table 2. According to the data, the silver powders of Examples 1-5 were forced to disperse the reaction liquid without dead angles and without distinction during the synthesis process, and the soft agglomerated silver powders produced during the synthesis process were broken up. The silver powders after the final synthesis were well dispersed and had a narrow particle size distribution. After the silver powders were made into slurries, the viscosity was low and the resistivity was good, which was basically around 2.8Ω.cm. However, the silver powders synthesized without the forced external circulation dispersion device for the reaction liquid had a relatively high viscosity of the slurry prepared by the silver powders, and the resistivity reached more than 3.5Ω.cm, which was about 30% higher than the silver powders prepared by the forced external circulation dispersion device.

[0120] Table 2 Comparison of slurry performance data of implementation results

[0121]

[0122] The method and device for preparing highly dispersed metal powder according to the embodiments of the present invention have at least one of the following advantages or part of one of the advantages:

[0123] 1. The present invention adopts a method in which the reaction liquid is continuously fed into an external circulation dispersion device outside the synthesis reactor for efficient dispersion during the synthesis reaction, so that the metal powder that may agglomerate in the synthesis reactor is dispersed in time, thereby solving the defect that only using the agitator of the synthesis reactor cannot solve the dispersion problem in time and effectively; the present invention can ensure that the particles in the entire synthesis reactor are always in a monodisperse state for uniform growth, thereby solving the problem of uniform dispersion of metal powder.

[0124] 2. While the oxidizing liquid, reducing liquid and dispersing liquid are added to the synthesis reactor for synthesis, the reaction liquid is sent to an external circulation disperser with high dispersing function of an ultrasonic device and / or a shearing disperser for cyclic shearing dispersion to complete the synthesis of highly dispersed and highly uniform metal powder. This method has good repeatability and strong operability. The metal powder prepared by this method has the advantages of high dispersion, narrow particle size distribution and high uniformity, which solves the shortcomings of existing metal powders such as poor dispersibility, wide particle size distribution and poor uniformity. It is suitable for conductive slurries, conductive adhesives and other fields that have high requirements for the dispersibility, particle size distribution and uniformity of metal powders.

[0125] 3. By utilizing the characteristics of the external circulation disperser, which is small in size and does not have a dead angle during stirring, the agglomerated powder inevitably formed during the synthesis process of the large-sized synthesis reactor for production due to the existence of a dead angle in stirring is continuously and completely dispersed. In the present invention, the particles forcibly dispersed by the small external circulation disperser are continuously returned to the large-sized synthesis reactor to continue to participate in the reaction until the particle size of the silver particles meets the requirements. During the reaction process, various reaction liquid parameters can be conveniently adjusted on the large-sized synthesis reactor.

[0126] 4. The silver particles formed after the mixed reaction of the oxidizing solution and the reducing solution will continue to participate in the next cycle of synthesis reaction as seeds. The newly generated silver particles will grow and adjust the microcrystalline morphology on the original silver particles, and this cycle will be repeated until the particle size of the silver powder meets the requirements. When using this method, in addition to controlling the particle size of the silver powder by adjusting the parameters of the oxidizing solution and the reducing solution during the synthesis of silver powder, the particle size and morphology of the silver powder can also be controlled by controlling the amount of silver source during the reaction cycle.

[0127] 5. In the present invention, a small disperser is used in conjunction with a large synthesis reactor to achieve large-scale production while reducing the amplification effect of production. The small disperser is used mainly to fully ensure the dispersion and particle size uniformity of the silver powder by utilizing its small size and the absence of a stirring dead angle.

[0128] The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiment. Those skilled in the art will understand that these embodiments can be changed without departing from the principles and spirit of the overall concept of the present invention, and these changes should also be regarded as falling within the protection scope of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing highly dispersed metal powder, the method comprising the following steps: Step (1) adding the bottom liquid into the synthesis reactor, and performing internal and external circulation of the synthesis reactor through an external circulation dispersion device connected to the synthesis reactor to achieve stable circulation; Step (2) After the stable circulation meets the predetermined requirements, the oxidizing liquid and the reducing liquid are continuously added into the synthesis reaction kettle to mix with the bottom liquid to form a reaction liquid, and a synthesis reaction is performed. During the synthesis reaction, the reaction liquid is continuously forced to disperse through the external circulation dispersing device and is fed into the synthesis reaction kettle, wherein at least one of the external circulation dispersing devices is provided with an ultrasonic device on the outer wall or inside; and / or at least one of the external circulation dispersing devices is provided with a shearing disperser inside, and the volume ratio of the external circulation dispersing device to the synthesis reaction kettle is 1:2000 to 1:500; Step (3) sampling, analyzing and testing are performed during the synthesis reaction. When the particle size of the metal powder generated by the synthesis reaction meets the requirements, the addition of the oxidizing liquid and the reducing liquid is stopped to stop the synthesis reaction; Step (4) After the reaction liquid is discharged from the synthesis reactor, it is subjected to solid-liquid separation, washing, post-treatment, and drying to obtain highly dispersed metal powder; Wherein, in step (1), the bottom liquid enters the external circulation dispersion device from bottom to top in a piston flow state, and after being forcibly dispersed by the external circulation dispersion device, flows into the synthesis reactor along the tangent direction of the reactor wall of the synthesis reactor, and achieves a stable circulation; The volume of the at least one external circulation disperser is 5L-20L, The external circulation disperser can ensure that the reaction liquid flows through the external circulation disperser from bottom to top in a piston-like manner without backflow.

2. The method for preparing highly dispersed metal powder according to claim 1, characterized in that: The bottom liquid circulates continuously between the synthesis reactor and the external circulation dispersion device and completes a cycle within a period of 1-10 minutes to achieve a stable cycle.

3. The method for preparing highly dispersed metal powder according to claim 2, characterized in that: The external circulation dispersing device and the synthesis reactor are connected in series through a pipeline, and the volume of the external circulation dispersing device is smaller than the volume of the synthesis reactor; The external circulation dispersion device comprises at least one external circulation disperser, The volume of the external circulation disperser is 2L-50L.

4. The method for preparing highly dispersed metal powder according to claim 3, characterized in that: The at least one external circulation disperser is cylindrical with curved ends at both ends and a polished interior. The synthetic reactor pipeline is connected via a curved joint.

5. The method for preparing highly dispersed metal powder according to claim 4, characterized in that: An ultrasonic device is disposed on the outer wall or inside of the at least one external circulation disperser; and / or The at least one external circulation disperser is provided with a shear disperser inside. When at least one of the ultrasonic device and / or the shearing disperser is arranged in the at least one external circulation disperser, the distance from the outer wall of at least one of the ultrasonic device and the shearing disperser to the inner wall of the at least one external circulation disperser is in the range of 1-30 cm, and the ultrasonic frequency of the ultrasonic device is in the range of 20 KHz-100 KHz.

6. The method for preparing highly dispersed metal powder according to claim 5, characterized in that: The distance between the outer wall of the ultrasonic device and the shearing disperser and the inner wall of at least one external circulation disperser is in the range of 2-10 cm; The ultrasonic frequency range is 40KHz-80KHz; The rotation speed of the shear disperser ranges from 3000 rpm to 5000 rpm.

7. The method for preparing highly dispersed metal powder according to claim 6, characterized in that: The metal powder has a spherical or quasi-spherical shape; The particle size distribution width of the metal powder is less than 1.0; The metal powder includes powder of any one of silver, copper, tin and nickel or any combination thereof.

8. The method for preparing highly dispersed metal powder according to any one of claims 1 to 7, characterized in that: The base liquid is pure water or a dispersion liquid, the dispersion liquid is an aqueous solution containing any one of polyvinyl alcohol, guar gum, arabic resin, polyvinyl pyrrolidone, fatty acid, copper nitrate, magnesium nitrate or any combination thereof, and the concentration of the dispersion liquid is 10-100 g / L; Preparation of the oxidizing solution: Add the metal salt into pure water, stir and dissolve, and keep the temperature at 15°C-45°C. The metal salt in the oxidizing solution includes any one of oxalate, carbonate, sulfate, citrate, nitrate, metal oxide, and metal ammonia complex, or any combination thereof, and the concentration of the metal salt is 30 g / L-300 g / L. When the metal salt is silver nitrate, the oxidizing solution is a silver ammonia complex solution prepared by adding ammonia water to silver nitrate. Preparation of the reducing solution: adding a reducing agent into pure water, stirring and dissolving, and maintaining a constant temperature at 15° C.-45° C., wherein the reducing agent comprises any one of hydrazine hydrate, formaldehyde, formic acid, ammonium formate, ascorbic acid, hydrogen peroxide, triethanolamine, glycerol, glucose, and hydroxylamine, or any combination thereof, and the concentration of the reducing agent is 20 g / L-200 g / L.

9. A device for preparing highly dispersed metal powder using the method for preparing highly dispersed metal powder according to any one of claims 1 to 8, comprising: Synthesis reactor; An external circulation dispersing device, which is connected to the pipeline of the synthesis reactor, and the bottom liquid or the reaction liquid is forcibly dispersed in the external circulation dispersing device; A circulation device, wherein the circulation device is connected to the synthesis reaction kettle and the external circulation dispersion device pipeline respectively, so that the base liquid or the reaction liquid is continuously circulated in the high-dispersion metal powder preparation device; An ultrasonic device is arranged on the outer wall or inside of at least one of the external circulation dispersers in the external circulation disperser; and / or The at least one external circulation disperser is provided with a shear disperser inside. wherein when at least one of the ultrasonic device and / or the shearing disperser is disposed in the at least one external circulation disperser, the distance from the outer wall of at least one of the ultrasonic device and the shearing disperser to the inner wall of the external circulation disperser is in the range of 1-30 cm; The ultrasonic frequency ranges from 40KHz to 80KHz, and the rotation speed of the shearing disperser ranges from 3000rpm to 5000rpm.

10. The device for preparing highly dispersed metal powder according to claim 9, characterized in that: The at least one external circulation disperser is a cylindrical shape with curved ends at both ends and a polished interior, and is connected to the synthesis reactor pipeline via a curved joint.

11. The device for preparing highly dispersed metal powder according to claim 10, characterized in that: The outlet of the synthesis reactor is connected to a first pipeline, the first pipeline is branched into two flow paths, the first flow path of the two flow paths passes through the first valve, the circulation device, the second valve, the external circulation dispersion device in sequence and is connected to the inlet of the synthesis reactor; A third valve is arranged on the second flow path of the two flow paths to discharge the reaction liquid after the synthesis reaction is stopped.

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