Nano silver powder, preparation method thereof and conductive paste

Abstract

The invention provides nano silver powder, a preparation method thereof and conductive paste, and belongs to the technical field of conductive materials. The preparation method of the nano silver powder comprises the following steps: mixing a compound dispersing agent with water to obtain a reaction base solution; under a stirring condition, adding a silver nitrate solution and a first solution containing a reducing agent into the reaction base solution, and reacting to obtain a first mixed solution; adding a coating agent into the first mixed solution to obtain a second mixed solution; carrying out solid-liquid separation on the second mixed solution, collecting a solid phase, and washing and drying the solid phase to obtain nano silver powder; wherein the compound dispersing agent comprises a high-molecular polymer dispersing agent, a nonionic polymer dispersing agent and a small-molecular dispersing agent. According to the preparation method, the particle size distribution of the silver powder is cooperatively regulated and controlled by adopting the matching of three specific types of dispersants, so that the nanoscale silver powder which is excellent in performance and relatively narrow in particle size distribution can be prepared.

Description

Technical Field

[0001] This invention relates to the field of conductive materials technology, specifically to a nano-silver powder, its preparation method, and a conductive paste. Background Technology

[0002] Nano-silver powder possesses properties such as high conductivity, high specific surface area, and surface effect, making it widely used in electronic packaging, conductive pastes (especially fine grids for photovoltaic HJT cells and silver pastes for 5G filters), antibacterial materials, and catalysts. Among these, spherical nano-silver powder, due to its excellent filling performance, high tap density, good dispersibility, and rheological properties, has become an ideal choice for high-end conductive pastes.

[0003] Particle size distribution is an important indicator for evaluating the quality of silver nanoparticles, as it directly affects their conductivity, dispersion stability, sintering activity, and other properties. Currently, the preparation of silver nanoparticles mainly employs a strategy of using a single type of dispersant. While this approach can suppress agglomeration, its ability to control particle size distribution is limited, resulting in silver nanoparticles with a relatively wide particle size distribution. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a nano silver powder, a preparation method thereof, and a conductive paste, aiming to provide a preparation method that can obtain nano silver powder with small particle size and narrow particle size distribution.

[0005] In a first aspect, embodiments of this application provide a method for preparing nano-silver powder, comprising the following steps: The compound dispersant was mixed with water to obtain the reaction base solution; Under stirring conditions, silver nitrate solution and a first solution containing a reducing agent are added to the reaction substrate, and then a coating agent is added to react and obtain a mixed solution. The mixed solution was subjected to solid-liquid separation, the solid phase was collected, and the solid phase was washed and dried to obtain nano silver powder; The compound dispersant includes high molecular weight polymer dispersants, nonionic polymer dispersants, and small molecule dispersants.

[0006] Optionally, in some embodiments of this application, the mass ratio of the polymeric dispersant, the nonionic polymeric dispersant, and the small molecule dispersant is a:b:c, wherein 6≤a≤32, 0<b≤1, and 0<c≤4.

[0007] Optionally, in some embodiments of this application, the polymeric dispersant includes one or more of gelatin, gum arabic, polyvinylpyrrolidone, and polyethylene glycol-2000; and is a nonionic polymer.

[0008] Optionally, in some embodiments of this application, the nonionic polymeric dispersant includes one or more of nonylphenol polyoxyethylene ether, Tween, and Triton.

[0009] Optionally, in some embodiments of this application, the small molecule dispersant includes one or more of sodium citrate, sodium tartrate, sodium oxalate, and sodium acetate.

[0010] Optionally, in some embodiments of this application, the reducing agent includes one or more of ascorbic acid, sodium ascorbate, hydrazine hydrate, and glucose.

[0011] Optionally, in some embodiments of this application, the mass ratio of silver nitrate in the silver nitrate solution, the reducing agent in the first solution, and the polymer dispersant is 100:(50~105):(6~32).

[0012] Optionally, in some embodiments of this application, the coating agent includes a first component, which includes one or more of oleic acid, lauric acid, and stearic acid.

[0013] Optionally, in some embodiments of this application, the step of mixing the compound dispersant with water to obtain the reaction base liquid includes: mixing the compound dispersant, pH adjuster and water to obtain the reaction base liquid with a pH of 7 to 11.

[0014] Optionally, in some embodiments of this application, the mass ratio of silver nitrate in the silver nitrate solution to the first component is 100:0.2~0.7.

[0015] Optionally, in some embodiments of this application, the coating agent further includes a second component, which includes one or more of ethyl laurate and oleamide, and the mass ratio of the first component to the second component is 10:1 to 5.

[0016] Optionally, in some embodiments of this application, the pH adjuster includes one or more of anhydrous sodium carbonate, ammonia, and sodium hydroxide.

[0017] Optionally, in some embodiments of this application, under stirring conditions, silver nitrate solution and a first solution containing a reducing agent are added to the reaction substrate, and then a coating agent is added to react and obtain a mixed solution. In this step, the temperature of the reaction substrate is controlled at 20~50°C and the reaction time is 5~30 min.

[0018] Optionally, in some embodiments of this application, in the step of adding silver nitrate solution and a first solution containing a reducing agent to the reaction substrate under stirring conditions, and then adding a coating agent to react and obtain a mixed solution, the stirring rate is 200~700 rpm.

[0019] Optionally, in some embodiments of this application, the silver nitrate solution and the first solution are added to the reaction substrate at a dropping rate greater than or equal to 50 g / s.

[0020] Optionally, in some embodiments of this application, the steps of performing solid-liquid separation on the second mixed solution, collecting the solid phase, and washing and drying the solid phase to obtain nano-silver powder include: The second mixed solution was subjected to vacuum filtration, and the solid phase was collected. The solid phase was washed with deionized water until the conductivity of the filtrate was less than 20 μS / cm. The solid phase was dried at 55-65℃ for 12-24 hours to obtain nano silver powder.

[0021] Secondly, this application provides a nano-silver powder prepared by the method described above.

[0022] Optionally, in some embodiments of this application, the D50 particle size of the nano-silver powder is 200~400nm.

[0023] Optionally, in some embodiments of this application, the tap density of the nano-silver powder is 2.5~5 g / cm³. 3 .

[0024] Optionally, in some embodiments of this application, the specific surface area of ​​the silver nanoparticles is 1~3m². 2 / g.

[0025] Thirdly, embodiments of this application propose a conductive paste, including the aforementioned nano-silver powder.

[0026] The technical solution proposed in this application has the following beneficial effects: By employing a combination of three specific types of dispersants to synergistically regulate the particle size distribution of silver powder, high-performance nanoscale silver powder with a narrow particle size distribution can be obtained, suitable for preparing high-end conductive pastes. Furthermore, this preparation method is simple, easy to operate, highly controllable, and reproducible. Specifically, the compound dispersants proposed in this application include a high-molecular-weight polymer dispersant, a nonionic polymer dispersant, and a small-molecule dispersant. When the reducing agent is added to initiate nucleation, the high-molecular-weight polymer dispersant, due to its high molecular weight and strong adsorption, can quickly anchor onto the newly formed microcrystal nuclei, providing immediate protection, effectively inhibiting ripening, and ensuring uniform initial nucleus size. The nonionic polymer dispersant continuously provides long-term steric hindrance during particle growth, preventing particle aggregation and helping to maintain system stability. Meanwhile, the small-molecule dispersant effectively regulates the silver powder particle size and nucleation process, achieving controllable preparation of small-particle-size, highly dispersible nanoscale silver powder, and imparting excellent dispersion stability and hydrophobicity through post-coating.

[0027] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0029] Figure 1 Here is a SEM image of the silver nanopowder prepared in Example 1; Figure 2 Here is a SEM image of the silver nanopowder prepared in Example 3; Figure 3 This is a SEM image of the silver nanoparticles prepared in Comparative Example 1. Detailed Implementation

[0030] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0032] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0033] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0034] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0035] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0036] In the description of the embodiments of this application, the term "at least one" refers to one or more, "more than one" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces). "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0037] This application provides a method for preparing nano-silver powder, the method comprising the following steps: S10, the compound dispersant is mixed with water to obtain the reaction base liquid; S20, under stirring conditions, silver nitrate solution and a first solution containing a reducing agent are added to the reaction substrate, and then a coating agent is added to react and obtain a mixed solution; S30, the mixed solution is subjected to solid-liquid separation, the solid phase is collected, and the solid phase is washed and dried to obtain nano silver powder; The compound dispersant includes high molecular weight polymer dispersants, nonionic polymer dispersants, and small molecule dispersants.

[0038] In the technical solution proposed in this application, by using three specific types of dispersants in combination to synergistically regulate the particle size distribution of silver powder, nanoscale silver powder with superior performance and a narrow particle size distribution can be obtained, which is suitable for preparing high-end conductive pastes. Moreover, the preparation method has a simple process flow, is easy to operate, has strong controllability, and good reproducibility. Specifically, the compound dispersants proposed in this application include polymeric dispersants, nonionic polymeric dispersants, and small molecule dispersants. When the reducing agent is added to initiate nucleation, the polymeric dispersant, due to its high molecular weight and strong adsorption, can quickly anchor onto the newly formed microcrystal nuclei, providing immediate protection, effectively inhibiting ripening, and ensuring uniform initial crystal nucleus size. The nonionic polymeric dispersant continuously provides long-term steric hindrance during particle growth, preventing particle aggregation and helping to maintain system stability. During this period, the small molecule dispersant effectively regulates the silver powder particle size and nucleation process, realizing the controllable preparation of small-particle-size, highly dispersible nanoscale silver powder, and imparting excellent dispersion stability and hydrophobicity through post-coating.

[0039] The polymeric dispersant may include, but is not limited to, one or more of gelatin, gum arabic, polyvinylpyrrolidone, and polyethylene glycol-2000; and is a nonionic polymer. The nonionic polymeric dispersant may include, but is not limited to, one or more of nonylphenol polyoxyethylene ether, Tween, and Triton. The small molecule dispersant may include, but is not limited to, one or more of sodium citrate, sodium tartrate, sodium oxalate, and sodium acetate.

[0040] In some embodiments, the mass ratio of the polymeric dispersant, the nonionic polymeric dispersant, and the small molecule dispersant is a:b:c, where 6 ≤ a ≤ 32, 0 < b ≤ 1, and 0 < c ≤ 4. That is, the mass ratio of the three is (6~32):(0~1):(0~4). It should be noted that the ranges 0~1 and 0~4 do not include the endpoint value of 0. Controlling the proportions of the three within the above range helps to coordinate their relative weights in the dispersion system and better exert their synergistic effect.

[0041] Furthermore, in some embodiments, the mass ratio of silver nitrate in the silver nitrate solution, the reducing agent in the first solution, and the polymer dispersant is 100:(50~105):(6~32).

[0042] In some embodiments, the mass of water added to the reaction substrate for every 50g of the polymer dispersant is 300~800mL.

[0043] The silver nitrate solution refers to an aqueous solution of silver nitrate. The amount of water added is 500-1000 mL for every 160 g of silver nitrate.

[0044] In some embodiments, the solvent of the first solution is water, wherein the mass of water added corresponds to 500~1000mL for every 86.4g of reducing agent.

[0045] In some embodiments, the reducing agent may include, but is not limited to, one or more of ascorbic acid, sodium ascorbate, hydrazine hydrate, and glucose; this application improves the dispersibility of the reaction system by using a combination of three types of dispersants and utilizing their synergistic effect, so that a relatively mild reducing agent can react under relatively mild conditions to obtain nano-silver powder.

[0046] In some embodiments, the coating agent includes a first component, which may be one or more of oleic acid, lauric acid, stearic acid, ethyl laurate, and oleamide. The amount of the first component added may meet the following ratio: the mass ratio of silver nitrate in the silver nitrate solution to the first component is 100:0.2~0.7. The first component can form a protective layer on the surface of the silver powder particles, thereby regulating particle growth, preventing agglomeration, and improving dispersibility.

[0047] Furthermore, in some other embodiments, the coating agent may also include a second component, which includes one or more of ethyl laurate and oleamide, and the mass ratio of the first component to the second component is 10:1 to 5; the second component, as an auxiliary component, can improve the fusion performance of silver powder in the subsequent preparation of conductive paste.

[0048] The coating agent can be added in the form of a solution. For example, anhydrous ethanol can be used as a solvent to disperse the first component or a mixture of the first and second components into the solvent to form a coating agent solution, which is then added to the reaction substrate. This helps the coating agent to be mixed in more evenly and quickly.

[0049] In some embodiments, a pH adjuster may be added to the reaction substrate to regulate its acidity or alkalinity, making it suitable for silver powder formation. Accordingly, step S10 can be implemented as follows: the compound dispersant, pH adjuster and water are mixed to obtain a reaction substrate with a pH of 7-11.

[0050] The pH adjuster may include, but is not limited to, one or more of anhydrous sodium carbonate, ammonia, and sodium hydroxide. It is understood that the amount of pH adjuster added is adjusted according to the pH of the reaction substrate.

[0051] Furthermore, in some embodiments, the pH adjuster is preferably anhydrous sodium carbonate, as the amount of anhydrous sodium carbonate added and its effect on the pH adjustment of the reaction substrate are easier to control. The ratio of anhydrous sodium carbonate to the polymer can be controlled within the range of 0.5 to 1.5:50, thus maintaining the pH of the reaction substrate within a suitable range.

[0052] In step S20, the temperature of the reaction substrate is controlled at 20~50℃. This preparation method has low requirements for reaction temperature and can be carried out at a lower temperature, resulting in a mild reaction process.

[0053] In addition, in step S20, the reaction time is 5 to 30 minutes; the stirring rate is 200 to 700 rpm.

[0054] In some embodiments, the silver nitrate solution and the first solution are added at a relatively rapid rate to promote explosive nucleation and improve production efficiency. Specifically, the silver nitrate solution and the first solution can be added to the reaction substrate at a dropping rate greater than or equal to 50 g / s.

[0055] In addition, step S30 may specifically include: S31, the second mixed solution is subjected to reduced pressure filtration to collect the solid phase; S32, the solid phase is washed with deionized water until the conductivity of the filtrate is less than 20 μS / cm; S33, the solid phase is dried at 55~65℃ for 12~24h to obtain nano silver powder.

[0056] Furthermore, this application also proposes a nano-silver powder, which is prepared by the method described above. The nano-silver powder prepared by the above method has the characteristics of small particle size and narrow distribution, and exhibits a good spherical morphology.

[0057] In some embodiments, the D50 particle size of the nano-silver powder is 200~400nm.

[0058] In some embodiments, the nano-silver powder has a favorable tap density and specific surface area; specifically, the tap density of the nano-silver powder is 2.5~5 g / cm³. 3 The specific surface area of ​​the nano-silver powder is 1~3m². 2 / g.

[0059] Furthermore, embodiments of this application also propose a conductive paste, which includes the aforementioned nano-silver powder.

[0060] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0061] Example 1 Step 1: Add 160g of silver nitrate to 600ml of deionized water to obtain a silver nitrate solution; add 86.4g of ascorbic acid to 600ml of deionized water and dissolve completely to obtain the first solution; dissolve 1g of anhydrous sodium carbonate, 50g of polyethylene glycol-2000, 0.75g of Tween-80, and 5g of sodium tartrate in 880ml of deionized water as the reaction base solution, with a pH of 10; dissolve 0.5g of lauric acid in 10ml of anhydrous ethanol to obtain the coating agent solution.

[0062] Step 2: Set the stirring speed to 500 rpm, and add the silver nitrate solution and the first solution to the reaction base liquid at a dropping rate greater than 50 g / s at a uniform rate of 30°C. After the addition is complete, pour in the coating agent solution and react for 30 minutes.

[0063] Step 3: The nano-silver powder is separated by vacuum filtration, washed with deionized water until the conductivity of the filtrate is <20μS / cm, then washed with anhydrous ethanol, and dried in a drying oven at 60℃ for 12h. The dried nano-silver powder is then milled by air to obtain the finished powder.

[0064] Example 2 Step 1: Add 160g of silver nitrate to 600ml of deionized water to obtain a silver nitrate solution; add 86.4g of ascorbic acid to 600ml of deionized water and dissolve it completely to obtain the first solution; dissolve 1g of anhydrous sodium carbonate, 15g of gelatin, 0.5g of nonylphenol polyoxyethylene ether, and 10g of sodium citrate in 880ml of deionized water as the reaction base solution, with a pH of 10; dissolve 0.5g of lauric acid and 0.1g of ethyl laurate in 10ml of anhydrous ethanol to obtain the coating agent solution.

[0065] Step 2: Set the stirring speed to 500 rpm, and add the silver nitrate solution and the first solution to the reaction base liquid at a dropping rate greater than 50 g / s at a uniform rate of 30°C. After the addition is complete, pour in the coating agent solution and react for 30 minutes.

[0066] Step 3: The nano-silver powder is separated by vacuum filtration, washed with deionized water until the conductivity of the filtrate is <20μS / cm, then washed with anhydrous ethanol, and dried in a drying oven at 60℃ for 12h. The dried nano-silver powder is then milled by air to obtain the finished powder.

[0067] Example 3 Step 1: Add 160g of silver nitrate to 600ml of deionized water to obtain a silver nitrate solution; add 86.4g of ascorbic acid to 600ml of deionized water and dissolve thoroughly to obtain the first solution; dissolve 1g of anhydrous sodium carbonate, 10g of polyvinylpyrrolidone K90, 1g of Triton, 0.5g of sodium citrate and 0.5g of sodium tartrate in 880ml of deionized water as the reaction base solution, with a pH of 10; dissolve 0.5g of lauric acid and 0.1g of ethyl laurate in 10ml of anhydrous ethanol as the coating agent solution.

[0068] Step 2: Set the stirring speed to 500 rpm, and add the silver nitrate solution and the first solution to the reaction base liquid at a dropping rate greater than 50 g / s at a uniform rate of 30°C. After the addition is complete, pour in the coating agent solution and react for 30 minutes.

[0069] Step 3: The nano-silver powder is separated by vacuum filtration, washed with deionized water until the conductivity of the filtrate is <20μS / cm, then washed with anhydrous ethanol, and dried in a drying oven at 60℃ for 12h. The dried nano-silver powder is then milled by air to obtain the finished powder.

[0070] Example 4 Step 1: Add 160g of silver nitrate to 600ml of deionized water to obtain a silver nitrate solution; add 86.4g of ascorbic acid to 600ml of deionized water and dissolve it completely to obtain the first solution; dissolve 1g of anhydrous sodium carbonate, 10g of polyvinylpyrrolidone K90, 1g of Tween-80, and 2g of sodium citrate in 880ml of deionized water as the reaction base solution, with a pH of 10; dissolve 0.5g of oleic acid in 10ml of anhydrous ethanol as the coating agent solution.

[0071] Step 2: Set the stirring speed to 500 rpm, and add the silver nitrate solution and the first solution to the reaction base liquid at a dropping rate greater than 50 g / s at a uniform rate of 30°C. After the addition is complete, pour in the coating agent solution and react for 30 minutes.

[0072] Step 3: The nano-silver powder is separated by vacuum filtration, washed with deionized water until the conductivity of the filtrate is <20μS / cm, then washed with anhydrous ethanol, and dried in a drying oven at 60℃ for 12h. The dried nano-silver powder is then milled by air to obtain the finished powder.

[0073] Comparative Example 1 This comparative example is essentially the same as Example 1, except that the nonionic polymeric dispersant Tween-80 and the small molecule dispersant sodium tartrate are not added. All other parameters and conditions remain unchanged.

[0074] Comparative Example 2 This comparative example is essentially the same as Example 2, except that gelatin, a polymeric dispersant, is not added. All other parameters and conditions remain unchanged.

[0075] Comparative Example 3 This comparative example is essentially the same as Example 2, except that the polymeric dispersant gelatin is not added, and the pH of the first solution is adjusted to 9. All other parameters and conditions remain unchanged.

[0076] Comparative Example 4 This comparative example is essentially the same as Example 1, except that the amount of polyethylene glycol-2000 added is 75g. All other parameters and conditions remain unchanged.

[0077] Comparative Example 5 This comparative example is essentially the same as Example 1, except that the nonionic polymeric dispersant Tween-80 is not added. All other parameters and conditions remain unchanged.

[0078] Comparative Example 6 This comparative example is basically the same as Example 1, except that the amount of Tween-80 added is changed to 10g. All other parameters and conditions remain unchanged.

[0079] Comparative Example 7 This comparative example is essentially the same as Example 1, except that the small molecule dispersant sodium tartrate is not added. All other parameters and conditions remain unchanged.

[0080] II. Testing Methods The nano-silver powders prepared in each example and comparative example were tested according to the following method, and the results are as follows. Figures 1 to 3 As shown in Tables 1 and 2.

[0081] 1. Morphology test: SEM was used to test the morphology of the nano silver powder.

[0082] 2. Particle size test: GB / T 19077-2016 "Particle size analysis by laser diffraction".

[0083] 3. Burn-off test: Take a sample of nano-silver powder (accurate to 0.1 mg) and record the initial mass (m0); place the sample in nitrogen and calcine it at 538℃ for 1 hour at a heating rate of 10℃ / min to simulate the high-temperature exposure conditions in actual processes; after cooling, weigh the mass of the calcined sample (m1) and calculate the burn-off rate: Burn-off rate (%) = (m0-m1) / m0×100%.

[0084] 4. Loose packing density test: GB / T 1479.1-2011 Loose packing density meter / funnel method.

[0085] 5. Tap density test: GB / T 5162-2021 Tap density meter / tap method.

[0086] 6. Specific surface area test: GB / T13390-2008 Specific surface area analyzer / nitrogen adsorption method.

[0087] III. Analysis of Test Results for Each Embodiment and Comparative Example Table 1

[0088] Table 2

[0089] Data from the Malvern laser particle size analyzer and electron microscopy images show that the D50 particle size distribution of the silver nanoparticles prepared in each embodiment is between 200 and 400 nm, exhibiting a narrow particle size distribution, reflecting high dispersibility. Meanwhile, Table 2 shows that the silver nanoparticles in each embodiment have a large specific surface area (>1 m²). 2 / g), and a relatively high tap density (≥2.5 g / cm³). 3 The small burn-off rate (<0.70%) indicates that the nano-silver powder prepared in this application can balance particle size, better morphology and high dispersibility. Furthermore, the preparation method in this application has mild reaction conditions and strong controllability. The silver powder quality shown in each embodiment is relatively stable and has good reproducibility.

[0090] Furthermore, Example 1 is compared with Comparative Examples 1, 3 to 6, and Example 2 is compared with Comparative Example 2: Comparative Example 1 showed larger particle size and wider particle size distribution, indicating that when there is no synergistic effect between nonionic polymer dispersant and small molecule dispersant, and only a single polymer dispersant is used, it is not conducive to controlling the size and uniformity of the particles.

[0091] In Comparative Example 2, only nonionic polymeric dispersants and small molecule dispersants were used in combination. The particle size distribution was wide and the D50 particle size was larger. This indicates that without the participation of polymeric dispersants, the steric hindrance effect they provide would be lacking, which would lead to an increase in particle size and a decrease in dispersibility.

[0092] Comparative Example 3, based on Comparative Example 2, significantly increased the pH value of the first solution by synergistically adding nonionic polymeric dispersants and small molecule dispersants, enabling nucleation to occur during the reaction stage and reducing particle size. However, it still could not achieve the effect of adding polymeric dispersants, resulting in poor dispersibility.

[0093] Comparative Example 4 showed increased particle size and a significantly wider particle size distribution, but also decreased tap density and increased burn-off. Comparative Example 5 showed increased particle size and somewhat weakened dispersibility. Comparative Example 6 showed increased particle size and a wider particle size distribution, but also decreased tap density and increased burn-off. Comparative Example 7 showed a slightly increased particle size. This indicates that the lack of synergistic effects from nonionic polymer dispersants or small molecule dispersants reduces the precise control of particle size distribution and size. When the dosage of polymeric dispersants or nonionic polymer dispersants exceeds the range of (6~32):(0~1):(0~4), it is detrimental to the improvement of dispersibility and size control.

[0094] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing nano-silver powder, characterized in that, The method comprises the following steps: mixing the compound dispersant with water to obtain a reaction base solution; under stirring, adding a silver nitrate solution and a first solution containing a reducing agent into the reaction base solution, and then adding a coating agent to obtain a mixed solution; performing solid-liquid separation on the mixed solution, collecting a solid phase, and performing washing and drying on the solid phase to obtain nano silver powder; the compound dispersant comprises a high molecular polymer dispersant, a non-ionic polymer dispersant, and a small molecule dispersant.

2. The production method according to claim 1, characterized by, The mass ratio of the high molecular polymer dispersant, the non-ionic polymer dispersant, and the small molecule dispersant is a:b:c, wherein 6≤a≤32, 0 3. The preparation method according to claim 1, characterized in that, The high molecular polymer dispersant comprises one or more of gelatin, gum arabic, polyvinylpyrrolidone, and polyethylene glycol-2000; is a non-ionic polymer; and / or, The non-ionic polymer dispersant comprises one or more of nonylphenol polyoxyethylene ether, Tween, and triton; and / or, The small molecule dispersant comprises one or more of sodium citrate, sodium tartrate, sodium oxalate, and sodium acetate.

4. The method of claim 1, wherein, The reducing agent comprises one or more of ascorbic acid, sodium ascorbate, hydrazine hydrate, and glucose; and / or, The mass ratio of silver nitrate in the silver nitrate solution, the reducing agent in the first solution, and the high molecular polymer dispersant is 100:(50-105):(6-32); and / or, The coating agent comprises a first component, and the first component comprises one or more of oleic acid, lauric acid, and stearic acid; and / or, The step of mixing the compound dispersant with water to obtain a reaction base solution comprises the following steps: mixing the compound dispersant, a pH regulator, and water to obtain a reaction base solution with a pH of 7-11.

5. The preparation method according to claim 4, characterized in that, The mass ratio of silver nitrate in the silver nitrate solution and the first component is 100:0.2-0.7; and / or, The coating agent further comprises a second component, and the second component comprises one or more of ethyl laurate and oleic acid amide; and / or, The pH regulator comprises one or more of anhydrous sodium carbonate, ammonia water, and sodium hydroxide.

6. The method of claim 1, wherein, In the step of adding the silver nitrate solution and the first solution containing the reducing agent into the reaction base solution under stirring, and then adding the coating agent to obtain a mixed solution, the temperature of the reaction base solution is controlled to be 20-50°C, and the reaction time is 5-30 min; and / or, The stirring rate is 200-700 rpm; and / or, The silver nitrate solution and the first solution are added into the reaction base solution at a dropping rate of greater than or equal to 50 g / s.

7. The preparation method according to claim 1, characterized in that, The step of performing solid-liquid separation on the second mixed solution, collecting a solid phase, and performing washing and drying on the solid phase to obtain nano silver powder comprises the following steps: performing vacuum filtration on the second mixed solution to collect a solid phase; washing the solid phase with deionized water until the conductivity of the filtrate is less than 20 μS / cm; drying the solid phase at 55-65°C for 12-24 h to obtain nano silver powder.

8. A nano-silver powder, characterized in that, The method for preparing the silver nanoparticles according to any one of claims 1 to 7.

9. The nano-silver powder according to claim 8, characterized in that, The D50 particle size of the silver nanoparticles is 200-400 nm; and / or, The tap density of the nano-silver powder is 2.5-5 g / cm 3 ; and / or, The specific surface area of the nano-silver powder is 1-3 m 2 / g.

10. An electrically conductive paste, characterized by, The silver nanoparticles according to claim 8 or 9.

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