Micron silver powder, preparation method thereof and conductive paste

Abstract

The invention provides micron silver powder, a preparation method thereof and conductive paste, and belongs to the technical field of conductive materials. The micron silver powder comprises first silver powder, and the first silver powder comprises a sphere-like silver core and flaky silver adsorbed on the surface of the sphere-like silver core. According to the technical scheme, the micron silver powder is provided, the micron silver powder contains the first silver powder with the special morphology, the high stacking characteristic of flake silver powder is reserved, good conductivity is shown, the high specific surface area and flowability are achieved, and sintering activity and printability can be improved easily.

Description

Technical Field

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

[0002] With the development of social technology, the demand for flexible electronic devices is increasing. Flexible electronic devices typically use flexible materials as a substrate, on which circuit patterns are obtained through printing, spraying conductive paste, etc., and then sintered to form a dense conductive layer to achieve the required functions. The conductive paste mainly consists of conductive fillers and a carrier. The conductive fillers that play a conductive role are mostly metal powders or conductive ceramic powders. Silver powder has become the first choice for preparing conductive pastes due to its good stability and excellent conductivity.

[0003] Currently, the mainstream silver powder includes flake silver powder. Flake silver powder can be stacked to form surface and line contacts, and usually has good conductivity. However, due to the need for ball milling and other processes in the preparation process, the production cost is high, and flake silver powder usually has poor flowability, which is not conducive to printing. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a micron-sized silver powder, a method for preparing the same, and a conductive paste, aiming to provide a micron-sized silver powder with good flowability and a high specific surface area.

[0005] In a first aspect, embodiments of this application provide a micron-sized silver powder, comprising a first silver powder, the first silver powder comprising a quasi-spherical silver core and flake-shaped silver adsorbed on the surface of the quasi-spherical silver core.

[0006] Optionally, in some embodiments of this application, the specific surface area of ​​the first silver powder is 0.7~1.5m². 2 / g.

[0007] Optionally, in some embodiments of this application, the percentage of the first silver powder in the micron-sized silver powder is 50% to 80%.

[0008] Optionally, in some embodiments of this application, the D50 particle size of the first silver powder is 1.1~2μm.

[0009] Optionally, in some embodiments of this application, in the first silver powder, the flake silver extends radially outward from the surface of the quasi-spherical silver core.

[0010] Secondly, embodiments of this application propose a method for preparing micron-sized silver powder, comprising the following steps: The first reducing agent and the auxiliary agent are added to water to obtain the first reducing solution; Add silver nitrate to water to obtain silver nitrate solution. The spherical seed crystals are mixed with the first reducing solution to obtain a mixed solution; Under stirring conditions, the first silver nitrate solution was added to the mixed solution within 1 to 30 seconds, and then a coating agent was added to react and obtain a reaction mixture. The reaction mixture was subjected to solid-liquid separation, the solid phase was collected, and the solid phase was washed and dried to obtain micron-sized silver powder; The additives include one or more of gelatin, gum arabic, sodium citrate, and citric acid.

[0011] Optionally, in some embodiments of this application, the first reducing agent includes one or more of ascorbic acid, sodium borohydride, glucose, and formaldehyde.

[0012] Optionally, in some embodiments of this application, the coating agent includes one or more of lauric acid, stearic acid, palmitic acid, oleic acid, myristic acid, ethanolamine, and linolenic acid.

[0013] Optionally, in some embodiments of this application, the stirring speed is 500~1000 rpm.

[0014] Optionally, in some embodiments of this application, the molar ratio of the first reducing agent to the first silver nitrate is 0.4 to 1:1.

[0015] Optionally, in some embodiments of this application, the mass ratio of the auxiliary agent to the first silver nitrate is 0.05 to 1:1.

[0016] Optionally, in some embodiments of this application, the mass ratio of the coating agent to the first silver nitrate is 0.2 to 2:100.

[0017] Optionally, in some embodiments of this application, before the step of mixing the spherical seed crystals with the first reducing solution to obtain a mixed solution, the method further includes: The dispersant is dissolved in water to obtain a dispersion; The second reducing agent is dissolved in water to obtain the second reducing solution; The second silver nitrate is dissolved in water to obtain a second silver nitrate solution; The second silver nitrate solution was added to the dispersion, and after stirring to dissolve it, the second reducing solution was added, and the reaction yielded spherical seed crystals.

[0018] Optionally, in some embodiments of this application, the dispersant includes one or more of gelatin, gum arabic, polyvinylpyrrolidone, sodium citrate, polyethylene glycol, and polyvinyl alcohol.

[0019] Optionally, in some embodiments of this application, the second reducing agent includes one or more of ascorbic acid, sodium borohydride, glucose, and formaldehyde.

[0020] Optionally, in some embodiments of this application, the mass ratio of the dispersant, the second reducing agent, and the second silver nitrate is 10~1000:0.1~2:1.

[0021] Thirdly, embodiments of this application propose a conductive paste comprising the micron-sized silver powder described above.

[0022] The technical solution proposed in this application has the following beneficial effects: This application proposes a micron-sized silver powder containing a first silver powder with a special morphology. This first silver powder consists of a spherical silver core and flake-like silver adsorbed on the surface of the spherical silver core. It retains the high stacking characteristics of the flake-like silver powder, exhibiting good conductivity, and also has a high specific surface area, which helps to improve sintering activity. In addition, it has good fluidity, and no breakage of the flake-like silver will occur during the printing process, which helps to improve printability.

[0023] 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, specific embodiments of this application are given below. Attached Figure Description

[0024] 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.

[0025] Figure 1 The images show SEM images of the micron-sized silver powder prepared in Example 1 at low and high magnification. Figure 2 SEM images of the micron-sized silver powder prepared in Example 2 at low and high magnification. Figure 3 SEM images of the micron-sized silver powder prepared in Comparative Example 1 at low and high magnification. Figure 4 SEM images of the micron-sized silver powder prepared in Comparative Example 3 at low and high magnification. Figure 5 The images show SEM images of the micron-sized silver powder prepared in Comparative Example 4 at low and high magnification. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] In a first aspect, embodiments of this application propose a micron-sized silver powder, which includes a first silver powder having a specific morphology, such as... Figure 1 and Figure 2 As shown, the first silver powder includes a spherical silver core and flake-like silver adsorbed on the surface of the spherical silver core.

[0034] This application proposes a micron-sized silver powder containing a first silver powder with a special morphology. This first silver powder consists of a spherical silver core and flake-like silver adsorbed on the surface of the spherical silver core. It retains the high stacking characteristics of flake-like silver powder, exhibiting good conductivity, and also has a high specific surface area, which helps to improve sintering activity. It also has good flowability, and no breakage of flake-like silver will occur during the printing process, which helps to improve printability. In addition, the special morphology of the micron-sized silver powder of this application allows it to have a larger contact area than regular spherical silver powder when they come into contact with each other. As a result, when using this micron-sized silver powder to prepare conductive paste and cure it, the problem of tensile breakage is not likely to occur.

[0035] Furthermore, in some embodiments, in the first silver powder, flake-like silver extends radially outward from the surface of the quasi-spherical silver core, resulting in the first silver powder having an extremely high specific surface area.

[0036] In some embodiments, the specific surface area of ​​the first silver powder is 0.7~1.5m². 2 / g; The first silver powder proposed in this application has a large effective contact area and an extremely high specific surface area due to its special morphology and structure, thus exhibiting good sintering activity. As a preferred embodiment, the first silver powder has a distinct lamellar structure on its surface, extending outwards in a clearly defined thin sheet shape and distributed extensively on the surface of the spherical silver core, with a specific surface area reaching 0.9~1.5m². 2 / g.

[0037] In some embodiments, the D50 particle size of the first silver powder is 1.1~2μm.

[0038] In some embodiments, the percentage of the first silver powder in the micron-sized silver powder is 50% to 80%. The first silver powder with a special morphological structure accounts for more than 50% of the micron-sized silver powder, which enables the micron-sized silver powder to stably possess the high sintering activity brought by the first silver powder.

[0039] Secondly, this application provides a method for preparing micron-sized silver powder, which can prepare the micron-sized silver powder described above. The preparation method includes the following steps: S10, the first reducing agent and auxiliary agent are added to water to obtain the first reducing solution.

[0040] The additives include one or more of gelatin, gum arabic, sodium citrate, and citric acid.

[0041] S20, add the first silver nitrate to water to obtain the first silver nitrate solution.

[0042] S30, mix the spherical seed crystals with the first reducing solution to obtain a mixed solution.

[0043] S40, under stirring conditions, the first silver nitrate solution is added to the mixed solution within 1~30s, and then a coating agent is added to react and obtain a reaction mixture.

[0044] S50, the reaction mixture is subjected to solid-liquid separation, the solid phase is collected and washed and dried to obtain micron-sized silver powder.

[0045] The method described in this application is simple, fast-responding, easy to operate, and produces products with stable quality, ensuring that the proportion of first silver powder is as high as 50% or more, making it suitable for mass production.

[0046] Specifically, in the method of this application, a first silver nitrate solution is added to a mixed solution at an extremely rapid pace, which promotes the rapid generation of a large number of silver atoms. These silver atoms grow to form a large number of plate-like single-crystal silver particles. By selecting specific additives, the crystal growth orientation of the silver atoms can be selectively controlled, promoting their growth into plate-like structures. Simultaneously, stirring is applied, causing the plate-like silver particles to selectively adhere to spherical seed crystals and aggregate to form the first silver powder. Through the combined control of multiple conditions, the stable formation of the morphology of the first silver powder is ensured.

[0047] In step S10: By adding the additive to the first reducing solution and then mixing it with the spherical seed crystals, compared to mixing the additive with the spherical seed crystals first and then adding the first reducing agent, the seed crystals can be protected from damage caused by stirring and dissolving the additive, which helps to control the morphology and size of the product.

[0048] The first reducing agent may be one or more of ascorbic acid, sodium borohydride, glucose, and formaldehyde, including but not limited to ascorbic acid, sodium borohydride, glucose, and formaldehyde.

[0049] The addition amounts of the first reducing agent and the auxiliary agent can meet the following conditions: the molar ratio of the first reducing agent to the first silver nitrate is 0.4~1:1; the mass ratio of the auxiliary agent to the first silver nitrate is 0.05~1:1, wherein the concentration of the auxiliary agent in the first reducing solution can be 0.1~40g / L.

[0050] In step S20, the concentration of the silver nitrate solution can be 0.5~2.5 mol / L. In steps S10 and S20, the water used can be deionized water.

[0051] In step S30: The near-spherical seed crystals can be purchased or prepared by oneself. Specifically, before step S30, the preparation step of the near-spherical seed crystals may also be included: dissolving the dispersant in water to obtain a dispersion; dissolving the second reducing agent in water to obtain a second reducing solution; dissolving the second silver nitrate in water to obtain a second silver nitrate solution; adding the second silver nitrate solution to the dispersion, stirring to dissolve it, then adding the second reducing solution, and reacting to obtain the near-spherical seed crystals.

[0052] The dispersant may include, but is not limited to, one or more of gelatin, gum arabic, polyvinylpyrrolidone, sodium citrate, polyethylene glycol, and polyvinyl alcohol; the second reducing agent may include, but is not limited to, one or more of ascorbic acid, sodium borohydride, glucose, and formaldehyde. The mass ratio of the dispersant, the second reducing agent, and the second silver nitrate may be 10~1000:0.1~2:1.

[0053] It is understood that the preparation steps of the above-mentioned spherical seed crystals, as well as steps S10 and S20, do not have a specific order. They can be carried out simultaneously or in any order depending on the actual situation.

[0054] When mixing the spherical seed crystals with the first reducing solution, the amount of spherical seed crystals added can meet the following condition: the mass ratio of the spherical seed crystals to the first silver nitrate is 0.0001~1:100. When preparing spherical seed crystals, the amount of seed solution added can also be adjusted according to the amount of second silver nitrate used in seed preparation. For example, the mass ratio of second silver nitrate to first silver nitrate can be 1×10⁻⁶. -10 ~1×10 -6 Mix an appropriate volume of seed solution with the first reducing solution at a ratio of 1:1.

[0055] In step S40, the coating agent may be one or more of lauric acid, stearic acid, palmitic acid, oleic acid, myristic acid, ethanolamine, and linolenic acid. The coating agent can form a protective layer on the surface of the silver powder particles to regulate particle growth and reduce disordered particle growth.

[0056] The amount of coating agent added can meet the following conditions: the mass ratio of the coating agent to the first silver nitrate is 0.2~2:100.

[0057] In step S40, the stirring speed is 500~1000 rpm. High-speed stirring can promote the selective adhesion of the formed flake-shaped silver particles to the seed crystal to aggregate and form the first silver powder. When the speed is too high, the strong lateral shear force will cause the particles to tend to be spherical, and the increased probability of collision between particles will lead to agglomeration. At the same time, it will also lead to an increase in equipment cost. When the speed is too low, it is easy to cause insufficient and uneven reaction, resulting in non-uniform particle size, and will also increase agglomeration.

[0058] Furthermore, in some embodiments, the preparation method of this application can be carried out at room temperature, for example, at 21~25°C, with a lower requirement for reaction temperature.

[0059] Furthermore, embodiments of this application also propose a conductive paste, which includes the micron-sized silver powder described above.

[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: Dissolve 40g of polyvinylpyrrolidone in 200ml of deionized water to obtain a dispersion; dissolve silver nitrate in deionized water to prepare a second silver nitrate solution with a concentration of 0.1g / ml; dissolve sodium borohydride in deionized water to prepare a second reducing solution with a concentration of 0.01g / ml. Add the first silver nitrate solution to the dispersion at a mass ratio of 133:0.1:1, followed by the second reducing solution. Stir the reaction for 10 min to obtain a yellow seed crystal solution.

[0062] Step 2: Dissolve 160g of silver nitrate in 600ml of deionized water to obtain the first silver nitrate solution; dissolve 86g of ascorbic acid and 10g of gelatin in 1.6L of deionized water to obtain the first reducing solution (equivalent to a mass ratio of auxiliary agent to first silver nitrate of 0.0625:1 and a molar ratio of first reducing agent to first silver nitrate of 0.52:1).

[0063] Step 3: According to the mass ratio of seed solution to first reducing solution of 0.2:200 (equivalent to the mass ratio of second silver nitrate to first silver nitrate of the same mass of seed solution of 0.00000125:1), take the seed solution and add it to the first reducing solution. After stirring evenly, continue stirring at 700 rpm and add silver nitrate solution within 5 seconds. Then add 0.5g of lauric acid dissolved in 10ml of alcohol (equivalent to the mass ratio of coating agent to first silver nitrate of 0.3:100) and stir for 10 minutes.

[0064] Step four: After the reaction solution is washed with deionized water until the conductivity is below 20 μS / cm, it is dried in an oven at 60°C and then pulverized to obtain the finished powder.

[0065] Example 2 Step 1: Dissolve 40g of polyvinylpyrrolidone in 200ml of deionized water to obtain a dispersion; dissolve silver nitrate in deionized water to prepare a second silver nitrate solution with a concentration of 0.1g / ml; dissolve sodium borohydride in deionized water to prepare a second reducing solution with a concentration of 0.01g / ml. Add the first silver nitrate solution to the dispersion at a mass ratio of 133:0.1:1, followed by the second reducing solution. Stir the reaction for 10 min to obtain a yellow seed crystal solution.

[0066] Step 2: Dissolve 200g of silver nitrate in 750ml of deionized water to obtain the first silver nitrate solution; dissolve 126.6g of ascorbic acid and 10g of gelatin in 1.6L of deionized water to obtain the first reducing solution (equivalent to a mass ratio of auxiliary agent to first silver nitrate of 0.05:1 and a molar ratio of first reducing agent to first silver nitrate of 0.61:1).

[0067] Step 3: According to the mass ratio of seed solution to first reducing solution of 0.2:200 (equivalent to the mass ratio of second silver nitrate to first silver nitrate of the same mass of seed solution of 0.00000125:1), take the seed solution and add it to the first reducing solution. After stirring evenly, continue stirring at 700 rpm and add silver nitrate solution within 10 seconds. Then add 0.5g of lauric acid dissolved in 10ml of alcohol (equivalent to the mass ratio of coating agent to first silver nitrate of 0.3:100) and stir for 10 minutes.

[0068] Step four: After the reaction solution is washed with deionized water until the conductivity is below 20 μS / cm, it is dried in an oven at 60°C and then pulverized to obtain the finished powder.

[0069] Example 3 Step 1: Dissolve 40g of polyvinylpyrrolidone in 200ml of deionized water to obtain a dispersion; dissolve silver nitrate in deionized water to prepare a second silver nitrate solution with a concentration of 0.1g / ml; dissolve sodium borohydride in deionized water to prepare a second reducing solution with a concentration of 0.01g / ml. Add the first silver nitrate solution to the dispersion at a mass ratio of 133:0.1:1, followed by the second reducing solution. Stir the reaction for 10 min to obtain a yellow seed crystal solution.

[0070] Step 2: Dissolve 160g of silver nitrate in 600ml of deionized water to obtain the first silver nitrate solution; dissolve 86g of ascorbic acid and 10g of gelatin in 1.6L of deionized water to obtain the first reducing solution (equivalent to a mass ratio of 1:16 between the auxiliary agent and the first silver nitrate, and a molar ratio of 0.52:1 between the first reducing agent and the first silver nitrate).

[0071] Step 3: According to the mass ratio of seed solution to first reducing solution of 0.4:200 (equivalent to the mass ratio of second silver nitrate to first silver nitrate of the same mass of seed solution of 0.0000025:1), take the seed solution and add it to the first reducing solution. After stirring evenly, continue stirring at 700 rpm and add silver nitrate solution within 5 seconds. Then add 0.5g of lauric acid dissolved in 10ml of alcohol (equivalent to the mass ratio of coating agent to first silver nitrate of 0.3:100) and stir for 10min.

[0072] Step four: After the reaction solution is washed with deionized water until the conductivity is below 20 μS / cm, it is dried in an oven at 60°C and then pulverized to obtain the finished powder.

[0073] Example 4 The scheme in this embodiment is basically the same as that in embodiment 1, except that the addition time of silver nitrate solution in step 3 of this embodiment is changed from 5s to 30s.

[0074] Example 5 The scheme in this embodiment is basically the same as that in embodiment 1, except that the auxiliary agent is changed from gelatin to gum arabic.

[0075] Example 6 Step 1: Dissolve 40g of polyvinylpyrrolidone in 200ml of deionized water to obtain a dispersion; dissolve silver nitrate in deionized water to prepare a second silver nitrate solution with a concentration of 0.1g / ml; dissolve sodium borohydride in deionized water to prepare a second reducing solution with a concentration of 0.01g / ml. Add the first silver nitrate solution to the dispersion at a mass ratio of 10:0.5:1, followed by the second reducing solution. Stir the reaction for 10 min to obtain a yellow seed crystal solution.

[0076] Step 2: Dissolve 160g of silver nitrate in 600ml of deionized water to obtain the first silver nitrate solution; according to the mass ratio of the auxiliary agent to the first silver nitrate being 1:1 and the molar ratio of the first reducing agent to the first silver nitrate being 0.4:1, dissolve formaldehyde and sodium citrate in 1.6L of deionized water to obtain the first reducing solution.

[0077] Step 3: According to the mass ratio of seed solution to first reducing solution of 0.2:200 (equivalent to the mass ratio of second silver nitrate to first silver nitrate of the same mass of seed solution of 0.00000125:1), take the seed solution and add it to the first reducing solution. After stirring evenly, continue stirring at 1000 rpm and add silver nitrate solution within 5 seconds. Then add 0.32g of oleic acid dissolved in 10ml of alcohol (equivalent to the mass ratio of coating agent to first silver nitrate of 0.2:100) and stir for 10 minutes.

[0078] Step four: After the reaction solution is washed with deionized water until the conductivity is below 20 μS / cm, it is dried in an oven at 60°C and then pulverized to obtain the finished powder.

[0079] Example 7 Step 1: Dissolve 40g of polyvinylpyrrolidone in 200ml of deionized water to obtain a dispersion; dissolve silver nitrate in deionized water to prepare a second silver nitrate solution with a concentration of 0.1g / ml; dissolve sodium borohydride in deionized water to prepare a second reducing solution with a concentration of 0.01g / ml. Add the first silver nitrate solution to the dispersion at a mass ratio of 1000:0.1:1, followed by the second reducing solution. Stir the reaction for 10 min to obtain a yellow seed crystal solution.

[0080] Step 2: Dissolve 160g of silver nitrate in 600ml of deionized water to obtain the first silver nitrate solution; according to the mass ratio of the auxiliary agent to the first silver nitrate being 1:16 and the molar ratio of the first reducing agent to the first silver nitrate being 1:1, dissolve glucose and citric acid in 1.6L of deionized water to obtain the first reducing solution.

[0081] Step 3: According to the mass ratio of seed solution to first reducing solution of 0.2:200 (equivalent to the mass ratio of second silver nitrate to first silver nitrate of the same mass of seed solution of 0.00000125:1), take the seed solution and add it to the first reducing solution. After stirring evenly, continue stirring at 500 rpm and add silver nitrate solution within 5 seconds. Then add 3.2g of stearic acid dissolved in 10ml of alcohol (equivalent to the mass ratio of coating agent to first silver nitrate of 2:100) and stir for 10 minutes.

[0082] Step four: After the reaction solution is washed with deionized water until the conductivity is below 20 μS / cm, it is dried in an oven at 60°C and then pulverized to obtain the finished powder.

[0083] Comparative Example 1 This comparative example is basically the same as Example 1, except that step one is omitted, and correspondingly, no seed solution is added in step three. All other parameters and conditions remain unchanged.

[0084] Comparative Example 2 This comparative example is essentially the same as Example 1, except that the auxiliary agent is changed from gelatin to polyvinylpyrrolidone. All other parameters and conditions remain unchanged.

[0085] Comparative Example 3 This comparative example is basically the same as Example 1, except that the addition time of the silver nitrate solution in step three is changed from 5s to 150s. All other parameters and conditions remain unchanged.

[0086] Comparative Example 4 This comparative example is basically the same as Example 1, except that the addition time of the silver nitrate solution in step three is changed from 5s to 45s. All other parameters and conditions remain unchanged.

[0087] II. Testing Methods The micron-sized 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 5 As shown in Tables 1 and 2.

[0088] 1. Morphology test: SEM was used to test the morphology of the micron-sized silver powder.

[0089] 2. Particle size test: The particle size of silver powder was measured using a Malvern laser particle size analyzer.

[0090] 3. Loose packing density test: GB / T 1479.1-2011 Loose packing density meter / funnel method.

[0091] 4. Tap density test: GB / T 5162-2021 Tap density meter / tap method.

[0092] 5. Specific surface area test: GB / T13390-2008 Specific surface area analyzer / nitrogen adsorption method.

[0093] III. Analysis of Test Results for Each Embodiment and Comparative Example Table 1

[0094] Table 2

[0095] As can be seen from the test results in Table 1 and the electron micrographs in the attached figures, each embodiment can produce first silver powder by adding seed crystals, selecting a suitable dispersant, and controlling the feeding rate. This first silver powder has a spherical silver core and multiple flake-like silver adsorbed on its surface, with a D50 distribution in the range of 1.1~2.01 μm and an extremely high specific surface area, exhibiting good bulk density and tap density. Furthermore, the percentage of first silver powder in each embodiment shows that the preparation method of this application can stably and directionally form the morphology of the first silver powder, obtaining micron-sized silver powder with a high percentage of first silver powder.

[0096] Furthermore, comparing Example 1 with Comparative Examples 1 to 4, it can be seen that: Comparative Example 1, without the addition of seed crystals, yielded silver powder with poor morphology and was unable to form the first silver powder morphology structure; Comparative Example 2, using polyvinylpyrrolidone as a dispersant, resulted in silver powder that could not re-aggregate into spherical shapes, leading to a significant decrease in specific surface area; Comparative Example 3, using a traditional slow feeding method, showed that due to the inability to quickly generate a large amount of flake-like silver powder aggregates, and because the dispersant gelatin restricted the uniform growth of the powder, the resulting silver powder was basically amorphous particles; In Comparative Example 4, the feeding speed was extended to 45s. Compared with the fast feeding method in Example 1, the resulting silver powder particles still had a flake-like structure, but the morphology was closer to spherical powder, the flake-like morphology was not prominent enough, and the specific surface area also decreased significantly.

[0097] 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 micron-sized silver powder, characterized in that, It includes a first silver powder, which comprises a spherical silver core and flake-like silver adsorbed on the surface of the spherical silver core.

2. The micron-sized silver powder according to claim 1, characterized in that, The specific surface area of ​​the first silver powder is 0.7~1.5m². 2 / g; and / or, In the micron-sized silver powder, the percentage of the first silver powder is 50% to 80%.

3. The micron-sized silver powder according to claim 2, characterized in that, The first silver powder has a D50 particle size of 1.1~2μm; and / or, In the first silver powder, the flake-like silver extends radially outward from the surface of the quasi-spherical silver core.

4. A method for preparing micron-sized silver powder according to any one of claims 1 to 3, characterized in that, Includes the following steps: The first reducing agent and the auxiliary agent are added to water to obtain the first reducing solution; Add silver nitrate to water to obtain silver nitrate solution. The spherical seed crystals are mixed with the first reducing solution to obtain a mixed solution; Under stirring conditions, the first silver nitrate solution was added to the mixed solution within 1 to 30 seconds, and then a coating agent was added to react and obtain a reaction mixture. The reaction mixture was subjected to solid-liquid separation, the solid phase was collected, and the solid phase was washed and dried to obtain micron-sized silver powder; The additives include one or more of gelatin, gum arabic, sodium citrate, and citric acid.

5. The preparation method according to claim 4, characterized in that, The first reducing agent includes one or more of ascorbic acid, sodium borohydride, glucose, and formaldehyde; and / or, The coating agent includes one or more of lauric acid, stearic acid, palmitic acid, oleic acid, myristic acid, ethanolamine, and linolenic acid.

6. The preparation method according to claim 4, characterized in that, The stirring speed is 500~1000 rpm; and / or, The molar ratio of the first reducing agent to the first silver nitrate is 0.4~1:1; and / or, The auxiliary agent is mixed with the first silver nitrate in a ratio of 0.05 to 1:1; and / or, The mass ratio of the coating agent to the first silver nitrate is 0.2~2:

100.

7. The preparation method according to claim 4, characterized in that, Before the step of mixing the spherical seed crystals with the first reducing solution to obtain a mixed solution, the method further includes: The dispersant is dissolved in water to obtain a dispersion; The second reducing agent is dissolved in water to obtain the second reducing solution; The second silver nitrate is dissolved in water to obtain a second silver nitrate solution; The second silver nitrate solution was added to the dispersion, and after stirring to dissolve it, the second reducing solution was added, and the reaction was carried out to obtain spherical seed crystals.

8. The preparation method according to claim 7, characterized in that, The dispersant includes one or more of gelatin, gum arabic, polyvinylpyrrolidone, sodium citrate, polyethylene glycol, and polyvinyl alcohol; and / or, The second reducing agent includes one or more of ascorbic acid, sodium borohydride, glucose, and formaldehyde.

9. The preparation method according to claim 7, characterized in that, The mass ratio of the dispersant, the second reducing agent, and the second silver nitrate is 10~1000:0.1~2:

1.

10. A conductive paste, characterized in that, Includes the micron-sized silver powder as described in any one of claims 1 to 3.

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