A method for preparing a nano-silver powder with single particle dispersion

Abstract

The application provides a preparation method of nano silver powder with single particle dispersion. The method aims at solving the problems of easy agglomeration, high impurity and high cost of nano silver powder in the prior art. The method comprises the following steps: preparing an oxidizing agent solution containing a high molecular carboxylic acid or a salt thereof, a reducing agent solution, and a bottom solution containing a dispersant and a silver ion release regulator respectively; adjusting the pH of the bottom solution, and adding the oxidizing agent and the reducing agent solutions at the same flow rate to react; then, the target product is obtained through flocculant sedimentation purification, cleaning, drying and air grinding. The method controls the release of silver ions and the reaction rate through the synergistic effect of the high molecular carboxylic acid or the salt thereof, the silver ion release regulator and the like, and realizes the single particle dispersion of the nano silver powder without a large amount of dispersant, and is suitable for the fields of electronic information, biomedicine and the like.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, specifically relating to a method for preparing nano-silver powder with single-particle dispersion. Background Technology

[0002] In fields such as electronics, biomedicine, and catalysis, silver nanoparticles occupy an important position due to their unique properties. In the electronics industry, as electronic products become smaller and more high-performance, silver nanoparticles, due to their excellent conductivity, are widely used in ultrathin electrode materials, conductive adhesives, and optical functional materials. Especially with the trend towards high-power, high-density integrated circuits in microelectronic systems, there is an urgent need for novel conductive metal powder materials that can be sintered at low temperatures and applied at high temperatures. In the biomedical field, its antibacterial activity makes it promising for antibacterial dressings and biosensors. In the catalysis field, its large specific surface area and special surface activity can improve reaction efficiency and selectivity, showing potential value in organic synthesis and environmental protection.

[0003] The current main method for preparing nano-silver powder is chemical reduction. While this method is convenient, uses simple equipment, and is highly controllable, it has significant drawbacks. During the reaction, particles easily agglomerate, resulting in poor dispersibility and requiring large amounts of dispersant. However, dispersant coating increases impurity content, affecting the physical properties and functions of the nano-silver powder. Furthermore, some existing technologies are costly and difficult to industrialize. For example, CN112705726A uses ethanol as a reaction solvent and requires a high temperature of 130℃~160℃, leading to high reaction costs. Other methods do not meet green development requirements; for instance, CN118893216A uses silver ammonia solution as the silver source, which is costly, and uses formaldehyde solution as a reducing agent, which is biotoxic.

[0004] In summary, existing nano-silver powder preparation technologies struggle to simultaneously achieve good single-particle dispersion, precise control of particle size and morphology, and suffer from high costs, environmental impact, and difficulties in industrialization. Therefore, the industry urgently needs to develop a nano-silver powder preparation method that can effectively achieve single-particle dispersion, precise control of particle size and morphology, while also being environmentally friendly, simple in preparation, low-cost, and suitable for large-scale production. This would align with green development plans, promote its widespread application across various fields, and provide technical support for supply chain development. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. To this end, the present invention provides a method for preparing nano-silver powder with single-particle dispersion, achieving precise control of the nano-silver particles, solving the agglomeration problem, and simultaneously avoiding the use of large amounts of dispersant, thus reducing the impurity content.

[0006] The first aspect of the present invention provides a method for preparing nano-silver powder with single-particle dispersion, comprising the following steps:

[0007] (1) Prepare oxidizing agent solution, reducing agent solution and base liquid respectively;

[0008] (2) Adjust the pH of the base solution to 8-10, and add the oxidant solution and the reducing agent solution to the base solution at the same flow rate to obtain the first reaction solution;

[0009] (3) Add the flocculant solution to the first reaction solution, stir and coat it, the first reaction solution settles, and after centrifugation and filtration, crude nano silver powder is obtained;

[0010] (4) After washing the crude nano-silver powder, it is dried and air-milled to obtain the nano-silver powder with single particle dispersion.

[0011] The oxidant solution comprises silver nitrate and a solution of a high molecular weight carboxylic acid or its salt.

[0012] The components of the base liquid include a dispersant and a silver ion release regulator.

[0013] The present invention relates to a method for preparing nano-silver powder with single-particle dispersion, which has at least the following beneficial effects:

[0014] A solution of a high-molecular-weight carboxylic acid or its salt forms a homogeneous suspension of nano-carboxylic acid silver precursors in an oxidizing agent solution, which slows down the release of silver ions and controls the reaction rate. Simultaneously, the long-chain polymer can rapidly encapsulate the newly formed nano-silver crystal nuclei, inhibiting crystal growth and effectively controlling the morphology and particle size of the nano-silver particles.

[0015] Silver ion release regulators have a stronger binding affinity to silver ions than to carboxylate ions. By competing with carboxylate ions, they further control the release rate of silver ions, making nucleation of elemental silver the dominant process rather than grain growth, thus obtaining uniform silver nanoparticles with controllable morphology.

[0016] Furthermore, the reaction begins under alkaline conditions, with the pH gradually decreasing as the reaction proceeds. Under acidic conditions, the nanoscale silver salt dissolves, releasing silver ions which are then reduced. The reaction rate maintains a dynamic equilibrium with pH changes, lengthening the nucleation process and preventing the directional growth of silver crystal nuclei. Through the synergistic effect of these mechanisms, the preparation method of this invention achieves precise control over the nanoscale silver particles, solving the agglomeration problem while avoiding the use of large amounts of dispersants and reducing impurity content.

[0017] According to some embodiments of the present invention, in step (1), the concentration of the oxidant solution is 200-400 g / L.

[0018] According to some embodiments of the present invention, in step (1), the concentration of the oxidant solution is any value among 200g / L, 250g / L, 300g / L, 350g / L, and 400g / L, such as 250g / L, or any range formed by both, such as 300g / L and 350g / L.

[0019] The concentration of the oxidizing agent solution refers to the concentration of silver nitrate in the oxidizing agent solution.

[0020] According to some embodiments of the present invention, the concentration of the reducing agent solution is 60% of the concentration of the oxidizing agent solution.

[0021] According to some embodiments of the present invention, the high molecular weight carboxylic acid and its salts include at least one selected from polymethacrylic acid, polyacrylic acid, polymaleic acid, acrylic acid-maleic acid copolymer, carboxymethyl cellulose, hyaluronic acid, polyglutamic acid and pectin.

[0022] According to some embodiments of the present invention, the concentration of the polymeric carboxylic acid or its salt solution is 0.05-0.1 g / mL.

[0023] According to some embodiments of the present invention, the concentration of the polymeric carboxylic acid or its salt solution is any value selected from 0.05 g / mL, 0.06 g / mL, 0.07 g / mL, 0.08 g / mL, 0.09 g / mL, and 0.1 g / mL, such as 0.07 g / mL, or any range formed by both, such as 0.06 g / mL to 0.09 g / mL.

[0024] According to some embodiments of the present invention, the molecular weight of the polymeric carboxylic acid or its salt solution is ≤5000.

[0025] According to some embodiments of the present invention, the reducing agent solution includes at least one selected from sodium borohydride solution, sodium hypophosphite solution, hydrazine hydrate solution, ascorbic acid solution, and glucose solution.

[0026] According to some embodiments of the present invention, the dispersant includes at least one of PVP and gum arabic.

[0027] According to some embodiments of the present invention, the concentration of the dispersant is 10-20% of the concentration of the oxidant solution.

[0028] According to some embodiments of the present invention, the concentration of the dispersant is any one of 10%, 12%, 14%, 16%, 18%, and 20% of the concentration of the oxidant solution, such as 15%, or a range of any two, such as 13% to 17%.

[0029] According to some embodiments of the present invention, the mass ratio of the dispersant to the silver ion release regulator is (20~100):1.

[0030] According to some embodiments of the present invention, the mass ratio of the dispersant to the silver ion release regulator is any value among 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, and 100:1, such as 50:1, or any range formed by the two, such as 30:1 to 70:1.

[0031] According to some embodiments of the present invention, the silver ion release regulator comprises a soluble acid salt or a polyphosphate.

[0032] According to some embodiments of the present invention, the acid radical in the soluble acid salt combines with silver ions to form an insoluble precipitate.

[0033] According to some embodiments of the present invention, the soluble acid salt is selected from at least one of phosphates, carbonates, and chlorates.

[0034] According to some embodiments of the present invention, the polyphosphate is selected from at least one of sodium hexametaphosphate, sodium tripolyphosphate, sodium tetrapolyphosphate, and sodium pyrophosphate.

[0035] Polyphosphate ions can not only control the release of silver ions, but their polymer chains can also further encapsulate the generated nanoparticles, thereby regulating their size and preventing aggregation.

[0036] According to some embodiments of the present invention, in step (2), the oxidant solution is first added to the base liquid, and after reacting for 5-10 seconds, the reducing agent solution is added to the base liquid at the same flow rate.

[0037] First, the oxidant solution is added to the base solution, and after reacting for 5-10 seconds, the reducing agent solution is added to the base solution at the same flow rate. This process optimizes the matching of silver ion release and reduction reaction through time-series control. Specifically, the base solution contains a silver ion release regulator, whose core function is to bind with silver ions (forming insoluble precipitates or complexes) to control the silver ion release rate. Adding the oxidant solution (containing silver nitrate) first and reacting for 5-10 seconds allows the silver ions in the oxidant to fully contact and initially bind with the silver ion release regulator in the base solution. For example, phosphates and silver ions initially form a small amount of silver phosphate precipitate, or sodium hexametaphosphate forms a complex with silver ions. Simultaneously, the high molecular weight carboxylic acids or their salts in the oxidant solution also form complexes with silver ions, competing with sodium hexametaphosphate for complexation, or promoting the dissolution and release of silver ions from insoluble silver salts, thereby maintaining the free silver ion concentration in the system at a "low and stable" level.

[0038] If oxidant and reducing agent are added simultaneously, a large number of free silver ions will be reduced by the reducing agent instantly, which can easily lead to explosive nucleation: too many crystal nuclei are generated in a short time, and the growth rate of crystal nuclei far exceeds the stabilizing ability of dispersant / regulator, which eventually leads to particle aggregation and uneven particle size. The 5-10 second pre-reaction window can be used to buffer the concentration of silver ions in advance by the regulator, laying the foundation for the smooth progress of the subsequent reduction reaction. The core is: (1) Sodium hexametaphosphate complexes with silver ions, or forms insoluble silver salts with chlorate, etc. (reducing the silver ion content in the solution and inhibiting the rate of silver ion reduction); (2) Under alkaline conditions, high molecular weight carboxylic acids or their salts will compete for complexation (competing with sodium hexametaphosphate for silver ions and promoting the release of silver ions), or promote the dissolution of insoluble silver salts and promote the release of silver ions. Mainly through the combined effect of 1 / 2, the concentration of silver ions is maintained at a "low and stable" level, which indirectly controls the reaction rate of silver ions and reducing agent, thereby avoiding the excessively rapid generation of silver ions and agglomeration or uncontrolled particle size. Secondly, high molecular weight carboxylic acids or their salts, as well as sodium hexapeptide, have a coating effect on silver powder, which helps improve its dispersibility. The intermittent addition of the reducing agent solution is to allow the silver ion release process to occur before the reduction reaction takes place.

[0039] Furthermore, the oxidant solution contains a high molecular weight carboxylic acid or its salt, whose function is to rapidly encapsulate newly formed silver nanocrystal nuclei, inhibiting nucleus growth and controlling morphology and particle size. After the oxidant solution is added first, silver ions are slowly released under the action of the regulator, initially forming a small number of initial silver nuclei. At this time, the long-chain structure of the high molecular weight carboxylic acid can quickly adsorb onto the surface of the initial nuclei, forming an encapsulation layer. This encapsulation layer can hinder the collision and fusion between nuclei, while also limiting the growth of specific crystal faces. If a reducing agent is added first, the silver ions in the subsequently added oxidant will be rapidly reduced directly under the action of the reducing agent. The initial nucleus formation rate is faster than the encapsulation rate of the high molecular weight carboxylic acid, causing some nuclei to remain unencapsulated and undergo secondary growth (i.e., small nuclei fuse into large particles), disrupting the dispersion of individual particles. A pre-reaction time of 5-10 seconds ensures the preferential encapsulation of the initial nuclei by the high molecular weight carboxylic acid, inhibiting aggregation and abnormal morphology from the source.

[0040] The operation of adding the reducing agent and oxidizing agent at the same flow rate in step (2) is based on the premise that the concentration of silver ions in the system is stable. The pre-reaction of adding the oxidizing agent first is precisely to allow the system to enter a stable state of slow release of silver ions in advance. When the oxidizing agent and reducing agent are continuously added at the same flow rate, the amount of reducing agent will be precisely matched with the amount of silver ions slowly released by the regulator in the system: the amount of silver ions reduced per unit time is exactly equal to the amount of silver ions released at the same time, avoiding the excess of a certain reactant. This dynamic balance can ensure that the crystal nucleus generation rate and growth rate are always at a low rate and in a stable state, and finally form monodisperse particles with a very narrow particle size distribution. If there is no pre-reaction, and the two solutions are added directly at the same flow rate, the concentration of silver ions in the system will rise sharply in the initial stage due to the insufficient action of the regulator, resulting in an instantaneous excess of reducing agent when it is added, causing a violent local reduction reaction and generating a large number of fine crystal nuclei; after the silver ion concentration decreases, the reducing agent may be insufficient, resulting in slow crystal nucleus growth and eventually a mixture of large and small particles.

[0041] In summary, the timing operation in step (2) is not simply adding in sequence, but rather a deep synergy with the three core mechanisms of high molecular weight carboxylic acid encapsulation, silver ion release regulation, and feeding at the same flow rate. It ensures the dispersibility of single particles from three dimensions: concentration control, crystal nucleus stability, and reaction equilibrium. It is one of the key operations to solve the problems of agglomeration and uneven particle size in the existing technology.

[0042] According to some embodiments of the present invention, in step (3), the method for preparing the flocculant solution includes: dissolving the flocculant in an alcohol solvent, wherein the mass ratio of the flocculant to the alcohol solvent is (1~4):200.

[0043] According to some embodiments of the present invention, in step (3), when the flocculant solution is prepared, the mass ratio of flocculant to alcohol solvent is any one of 1:200, 1.5:200, 2:200, 2.5:200, 3:200, 3.5:200, or 4:200, such as 2.5:200, or any range formed by both, such as 1.5:200 to 3.5:200.

[0044] According to some embodiments of the present invention, in step (3), the flocculant includes at least one of lauric acid, oleic acid, myristic acid, palmitic acid and stearic acid. Attached Figure Description

[0045] Figure 1 This is a microscopic morphology diagram of the silver powder prepared in Example 1.

[0046] Figure 2 This is a microscopic morphology diagram of the silver powder prepared in Example 2.

[0047] Figure 3This is a microscopic morphology diagram of the silver powder prepared in Comparative Example 1.

[0048] Figure 4 This is a microscopic morphology diagram of the silver powder prepared in Comparative Example 2.

[0049] Figure 5 This is a microscopic morphology image of the silver powder prepared in Comparative Example 3. Detailed Implementation

[0050] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0051] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0052] Unless otherwise specified, "room temperature" in this invention means 25℃±5℃.

[0053] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0054] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products; analytical grade or higher is sufficient.

[0055] Polyacrylic acid was purchased from Sinopharm Reagent Co., Ltd., with a molecular weight of 5000.

[0056] Ascorbic acid was purchased from Luwei Pharmaceutical Co., Ltd.

[0057] Example 1

[0058] A method for preparing nano-silver powder with single-particle dispersion, comprising the following steps:

[0059] (1) Prepare the oxidizing agent solution, reducing agent solution and base liquid respectively:

[0060] Dissolve 2000g of silver nitrate in deionized water to obtain 10L of oxidant solution with a concentration of 0.05g / mL. Add 10mL of 0.05g / mL polyacrylic acid aqueous solution to the oxidant solution.

[0061] Dissolve 1200g of ascorbic acid in 10L of deionized water to obtain a reducing agent solution;

[0062] Dissolve 300g of polyvinylpyrrolidone in 20L of deionized water, and add 4g of sodium phosphate to dissolve and obtain the base solution;

[0063] (2) Add ammonia to the bottom solution to adjust the pH of the bottom solution to alkaline 9, and stir at 280 r / min; add the oxidant solution to the bottom solution at a flow rate of 3 L / min, and after 5 seconds, pump the reducing agent solution into the bottom solution at the same flow rate to obtain the first reaction solution.

[0064] (3) After the oxidizing agent and reducing agent solutions are added, 5g of lauric acid is dissolved in 500g of alcohol to obtain a flocculant solution. The flocculant solution is added to the first reaction solution, and after thorough stirring and coating, the silver powder settles naturally. After centrifugation and filtration, the crude nano silver powder is obtained.

[0065] (4) After cleaning the crude nano-silver powder with deionized water and alcohol, dry it and air-mill it (under normal conditions) to obtain nano-silver powder with single particle dispersion.

[0066] Example 2

[0067] A method for preparing nano-silver powder with single-particle dispersion, comprising the following steps:

[0068] (1) Prepare the oxidizing agent solution, reducing agent solution and base liquid respectively:

[0069] 2000g of silver nitrate was dissolved in deionized water to obtain 10L of oxidant solution with a concentration of 0.05g / ml. 10mL of aqueous solution of polyacrylic acid with a concentration of 0.05g / ml was added to the oxidant solution.

[0070] Dissolve 1200g of ascorbic acid in 10L of deionized water to obtain a reducing agent solution;

[0071] Dissolve 300g of polyvinylpyrrolidone in 20L of deionized water, and add 6g of sodium hexametaphosphate to dissolve and obtain the base solution;

[0072] (2) Add ammonia to the bottom solution to adjust the pH of the bottom solution to alkaline 9, and stir at 280 r / min; add the oxidant solution to the bottom solution at a flow rate of 3 L / min, and after 5 seconds, pump the reducing agent solution into the bottom solution at the same flow rate to obtain the first reaction solution.

[0073] (3) After the oxidizing agent and reducing agent solutions are added, 5g of lauric acid is dissolved in 500g of alcohol to obtain a flocculant solution. The flocculant solution is added to the first reaction solution, and after thorough stirring and coating, the silver powder settles naturally. After centrifugation and filtration, the crude nano silver powder is obtained.

[0074] (4) After cleaning the crude nano-silver powder with deionized water and alcohol, dry it and air-mill it (under normal conditions) to obtain nano-silver powder with single particle dispersion.

[0075] Compare with Example 1

[0076] The difference from Example 1 is that sodium phosphate is not added. Nano-silver particles cannot be obtained; the polyacrylic acid encapsulates the silver grains and hinders the growth of certain crystal faces, resulting in uneven morphology of the formed silver powder.

[0077] Compare with Example 2

[0078] The difference from Example 2 is that polyacrylic acid was not added. The secondary growth of the silver nanoparticles was severe, resulting in strip-shaped grains with eutectic planes.

[0079] Compare with Example 3

[0080] The difference from Example 2 is that polyacrylic acid and sodium hexametaphosphate are not added. This results in the formation of polycrystalline submicron silver powder.

[0081] Test case

[0082] Particle size, specific surface area, and tapping were all measured using conventional testing methods, and the instruments used were:

[0083] The particle size was measured using a Malvern particle size analyzer.

[0084] Specific surface area is measured using a specific surface area meter.

[0085] The tapped density was determined using a tapped density meter.

[0086] Electron microscopy was performed using a Thermo Fisher scanning electron microscope.

[0087] Fineness testing: A slurry was prepared from 89.6% silver powder, 8.2% organic carrier, and 2.2% plexiglass. The organic carrier consisted of 50% acrylic resin, 30% diethylene glycol butyl ether, 10% ethyl cellulose, 5% epoxy-modified polyamide, and 5% hydrogenated castor oil. The glass powder consisted of 35% SiO2, 20% B2O3, 30% Bi2O, and 15% Li2O. After thorough mixing using a three-roll mill, the fineness was measured using a scraper fineness meter. The results are shown in Table 1.

[0088] Table 1

[0089]

[0090] Table 1 compares the performance of nano-silver powder from Examples 1 and 2 of this invention with that from Control Examples 1, 2, and 3 using four key indicators: particle size (D0, D10, D50, D90, D100), dynamic specific surface area, tap density, and fineness. It can be seen that:

[0091] In terms of particle size uniformity, the examples are significantly better than the control examples.

[0092] Examples 1 and 2: The particle size distribution is extremely narrow, with D50 of 0.203 μm and 0.228 μm, respectively, and D100 of only 0.558 μm and 0.612 μm. Moreover, the difference between D0 (minimum particle size) and D100 (maximum particle size) is less than 0.5 μm, indicating that the particle size is highly uniform and meets the technical goal of single particle dispersion.

[0093] The D50 of control example 1 (without sodium phosphate) increased sharply to 2.391 μm, and the D100 reached 28.649 μm. The particle size distribution spanned more than 28 μm, and the particle size difference was huge. This directly confirms the technical principle that the lack of soluble acid salt (sodium phosphate) leads to uncontrolled release of silver ions and severe particle aggregation.

[0094] The D50 of control example 2 (without polyacrylic acid) was 0.401 μm (1.7-1.9 times that of the example) and the D100 was 0.893 μm. The poor particle size uniformity reflects the problem that the lack of high molecular weight carboxylic acid (polyacrylic acid) cannot effectively encapsulate the crystal nucleus, leading to the secondary growth of particles.

[0095] Compared with Example 3 (without polyacrylic acid + sodium hexametaphosphate), the D50 was 0.795 μm and the D100 was 1.838 μm, indicating further coarsening of particle size. This shows that the combination of silver ion release regulator and high molecular weight carboxylic acid is crucial for controlling particle size. The absence of both will lead to the superposition of particle agglomeration and coarsening.

[0096] Regarding dynamic specific surface area, the examples and the control examples show an inverse correlation.

[0097] The dynamic specific surface areas of Examples 1 and 2 are 3.18 m², respectively. 2 / g, 3.01m 2 / g is within a reasonably high range because the particle size is small and the dispersion is good, resulting in a larger surface area per unit mass of particles, which is consistent with the core characteristics of nanomaterials.

[0098] Although the specific surface area of ​​Example 1 reached 3.72 m² 2 / g (slightly higher than in the example), but combined with the particle size data, it can be seen that it is an abnormally high value caused by the mixture of large and ultrafine particles, and is not a normal characteristic of monodisperse particles, so it has no practical application significance.

[0099] Compared with Examples 2 and 3, the specific surface area decreased to 1.33 m².2 / g, 0.82m 2 / g showed a significant decreasing trend with increasing particle size, further proving that the control example had severe particle agglomeration and a significant reduction in surface activity.

[0100] Regarding tap density, the examples take into account both dispersibility and packing properties.

[0101] The tap density of Examples 1 and 2 was 3.42 g / cm³, respectively. 3 3.48 g / cm 3 The density is at a moderate level, which avoids both excessive agglomeration leading to excessively high density (affecting subsequent processing) and excessive dispersion leading to excessively low density (affecting the material's mechanical / conductive properties), thus meeting the application requirements of the electronic information field for easy processing and high performance of nano-silver powder.

[0102] Compared with Examples 2 and 3: the tap density increased to 4.90 g / cm³. 3 5.13 g / cm 3 Because the particles agglomerate and form a dense mass, it is difficult to disperse them evenly during the subsequent preparation of conductive paste, thus affecting the conductivity; the tap density of control example 1 is 3.98 g / cm³. 3 (Higher than the example), the poor packing properties are also due to uneven particle size.

[0103] In terms of fineness, the embodiments meet the standards for industrial applications.

[0104] The fineness of Examples 1 and 2 is 3 μm, which is much lower than that of the control examples (12 μm for Control Example 1, 10 μm for Control Example 2, and 6 μm for Control Example 3). This indicates that the nano-silver powder prepared in the examples has no obvious large particle impurities when it is subsequently made into a slurry, and can directly meet the process requirements of electronic components (such as ultra-thin electrodes and conductive adhesives) for low fineness and high uniformity. On the other hand, the fineness of the control examples exceeds the standard, which will lead to uneven slurry coating and affect the stability of product performance.

[0105] As can be seen from the data in Table 1, the core innovation of this invention (adding a high molecular weight carboxylic acid to the oxidant solution and adding a silver ion release regulator to the base solution) is the key to achieving single-particle dispersed silver nanoparticles. The synergistic effect of the two can precisely control the silver ion release rate, avoid particle agglomeration and secondary growth, and finally obtain silver nanoparticles with uniform particle size, reasonable specific surface area and fineness, thus solving the core pain points of poor dispersibility and unstable performance of existing technologies.

[0106] The performance degradation of Control Example 1 (lacking silver ion release regulator), Control Example 2 (lacking high molecular weight carboxylic acid), and Control Example 3 (lacking both) indirectly confirms the irreplaceable nature of the combination of high molecular weight carboxylic acid and silver ion release regulator, further supporting the novelty of the technical solution of this invention.

[0107] Performance data for Examples 1 and 2 (D50 0.203-0.228 μm, fineness 3 μm, tap density 3.42-3.48 g / cm³) 3 It perfectly meets the needs of the electronic information field for low-temperature sintering and highly conductive nano-silver powder, while avoiding the problems of high cost and high toxicity of existing technologies, and has the potential for industrial promotion.

[0108] Figure 1 This is a scanning electron microscope (SEM) image of the silver powder prepared in Example 1. From... Figure 1 As can be directly observed, the nano-silver powder particles are uniform in shape, either spherical or regular, with no obvious adhesion or agglomeration between particles. The outline of each particle is clear, and the particle size difference is extremely small (as shown in Table 1, D50 = 0.203 μm, indicating that the particle size is concentrated around 0.2 μm). There are no ultra-large particles (such as D100 of only 0.558 μm) or fine debris mixed in, and the overall dispersion state meets the technical goal of single particle dispersion, which is completely consistent with the performance data of uniform particle size and fineness of 3 μm in Table 1.

[0109] Figure 2 This is a scanning electron microscope (SEM) image of the silver powder prepared in Example 2. From... Figure 2 As can be directly observed, the nano-silver powder particles also have a regular shape, without agglomeration or adhesion, and the particle size distribution is concentrated (corresponding to D50=0.228μm in Table 1). There are only slight differences from Example 1 in the edge details of individual particles (because Example 2 uses sodium hexametaphosphate instead of sodium phosphate in Example 1, which is a different choice of "silver ion release regulator"). However, the overall dispersibility and particle size uniformity are not affected, proving that the combination of high molecular weight carboxylic acid + different silver ion release regulators in the technical solution of this invention can stably achieve the single particle dispersion effect.

[0110] Figure 3 This is a scanning electron microscope (SEM) image of the silver powder prepared in Comparative Example 1. From... Figure 3 As can be directly observed, the nano-silver powder particles exhibit extremely irregular morphology, including both ultra-large blocky aggregates (corresponding to D100=28.649μm in Table 1) and fine fragments. The particles adhere to each other to form cluster-like structures, with no obvious individual particle outlines. Some particles even exhibit abnormal morphologies such as needle-like or sheet-like shapes, which contrasts sharply with the regular morphology of the examples. This directly confirms the technical principle that when soluble acid salts (sodium phosphate) are missing, the release of silver ions becomes uncontrolled, leading to disordered particle growth and severe agglomeration. This is consistent with the deterioration performance of particles with a size range exceeding 28μm and a fineness of 12μm in Table 1.

[0111] Figure 4 This is a scanning electron microscope (SEM) image of the silver powder prepared in Comparative Example 2. From... Figure 4It can be directly observed that although the nano-silver powder particles do not have the super-large aggregates of Control Example 1, they exhibit obvious strip-like eutectic phenomena. Multiple particles grow and connect along the same direction, forming chain-like or columnar structures. The boundaries of individual particles are blurred, and the particle size varies greatly (corresponding to D50 = 0.401 μm in Table 1, which is more than 1.7 times that of the example). Without the encapsulation effect of high molecular weight carboxylic acid (polyacrylic acid), the newly formed silver crystal nuclei cannot be stabilized in time, leading to secondary growth and the formation of eutectic planes, which corresponds to "specific surface area reduced to 1.33 m²" in Table 1. 2 The reasons for the performance degradation of / g and fineness of 10μm are completely matched.

[0112] Figure 5 This is a scanning electron microscope (SEM) image of the silver powder prepared in Comparative Example 3. From... Figure 5 As can be directly observed, the silver nanoparticles exhibit a polycrystalline agglomeration, with significantly coarsened particle size (corresponding to D50 = 0.795 μm in Table 1, approaching the submicron level). Multiple small particles fuse to form large, blocky particles, with rough surfaces and irregular shapes. Due to the simultaneous absence of the nucleation encapsulation effect of high-molecular-weight carboxylic acids and the silver ion release regulation effect of polyphosphates, silver ions are rapidly reduced and grow disorderly, ultimately forming polycrystalline submicron-sized particles, which corresponds to the "specific surface area of ​​only 0.82 m²" mentioned in Table 1. 2 / g, tap density reaches 5.13g / cm³ 3 The severe clustering characteristics are consistent.

[0113] The electron micrographs of Examples 1 and 2 directly demonstrate that the core technical solution of this invention, "adding a high molecular weight carboxylic acid to the oxidant solution and adding a silver ion release regulator to the base solution", can effectively achieve the regular morphology and single particle dispersion of nano-silver powder, solve the agglomeration problem of the prior art, and the effect is stable (both silver ion release regulators are applicable).

[0114] The electron micrographs of Comparative Example 1 (lacking silver ion release regulator), Comparative Example 2 (lacking high molecular weight carboxylic acid), and Comparative Example 3 (lacking both) demonstrate, from the three dimensions of "disordered morphology," "eutectic growth," and "polycrystalline coarsening," that high molecular weight carboxylic acid and silver ion release regulator are a necessary combination to achieve monodispersity. The former is responsible for encapsulating the crystal nucleus and inhibiting secondary growth, while the latter is responsible for controlling the release of silver ions and avoiding disordered nucleation. The synergistic effect of the two is indispensable.

[0115] The differences in microstructure of the five figures (such as regular single particles / agglomerates / eutectic strips) correspond perfectly with the macroscopic performance data (particle size, specific surface area, fineness) in Table 1, forming a complete chain of evidence from "microstructure → macroscopic performance". This further supports the scientific validity and practicality of the technical solution of this invention and provides a visualized technical basis for the preparation of "monodisperse nano silver powder".

[0116] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for producing a nano silver powder having a single particle dispersion, characterized by, The method comprises the following steps: (1) preparing an oxidant solution, a reducing agent solution and a base solution respectively; (2) adjusting the pH of the base solution to 8-10, adding the oxidant solution into the base solution, after 5-10 seconds, adding the reducing agent solution into the base solution at the same flow rate, to obtain a first reaction solution; (3) adding a flocculating agent solution into the first reaction solution, stirring and coating, then settling the first reaction solution, and centrifugal filtering to obtain a crude nano-silver powder; (4) cleaning the crude nano-silver powder, and drying and air-milling to obtain the nano-silver powder with single-particle dispersion. The components of the oxidant solution include silver nitrate and a high-molecular carboxylic acid or salt solution, the solute of the high-molecular carboxylic acid or salt solution includes at least one of polymethyl methacrylate, polyacrylic acid, polymaleic acid, acrylic acid-maleic acid copolymer, carboxymethyl cellulose, hyaluronic acid, polyglutamic acid and pectin; The components of the base solution include a dispersant and a silver ion release regulator, the silver ion release regulator includes a soluble acid salt or a polyphosphate salt, the soluble acid salt is selected from at least one of phosphate, carbonate and chlorate, and the polyphosphate salt is selected from at least one of sodium hexametaphosphate, sodium tripolyphosphate, sodium tetraphosphate and sodium pyrophosphate.

2. The production method according to claim 1, characterized by, The concentration of the oxidant solution is 200-400 g / L.

3. The preparation method according to claim 2, characterized in that, The concentration of the reducing agent solution is 60% of the concentration of the oxidant solution.

4. The production method according to claim 1, characterized by, The concentration of the high-molecular carboxylic acid or salt solution is 0.05-0.1 g / mL; and / or, the molecular weight of the solute of the high-molecular carboxylic acid or salt solution is ≤5000.

5. The method of claim 1, wherein, The reducing agent solution includes at least one of sodium borohydride solution, sodium hypophosphite solution, hydrazine hydrate solution, ascorbic acid solution and glucose solution.

6. The method of claim 1, wherein, The dispersant includes at least one of PVP and gum arabic; and / or, the concentration of the dispersant is 10-20% of the concentration of the oxidant solution; and / or, the mass ratio of the dispersant to the silver ion release regulator is (20-100):

1.

7. The preparation method according to claim 1, characterized in that, In step (3), the preparation method of the flocculating agent solution includes: dissolving a flocculating agent in an alcohol solvent, and the mass ratio of the flocculating agent to the alcohol solvent is (1-4):200.

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