Block silver powder with excellent fluidity and high tap density and preparation method thereof

Abstract

The present invention provides a bulk silver powder with excellent fluidity and high tap density and a preparation method thereof. First, a silver salt solution and a reducing agent solution are prepared, and then a certain amount of reducing agent, a morphology regulator and pure water are mixed to obtain a base liquid. The silver salt solution and the reducing agent solution are simultaneously dropped into the base liquid under constant temperature stirring conditions to obtain a lamellar silver powder; finally, the lamellar silver powder is washed, solid-liquid separated, and dried, and then placed in a solid material processing device for shaping treatment to obtain a bulk silver powder with excellent fluidity and high tap density. The present invention achieves high tap density, high dispersibility and good morphology structure of silver powder through specific process steps and parameter regulation. The prepared bulk silver powder has good fluidity between particles, is more conducive to the sintering and densification of silver paste, and has better conductive properties; the preparation method not only simplifies the process flow and reduces production costs, but also the obtained silver powder has excellent performance and has industrial application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of metal powders, and in particular to blocky silver powder with excellent fluidity and high tap density and a preparation method thereof. Background Art

[0002] As an important micro-nano material, silver powder has been widely used in optical materials, electronic materials, medicine, catalysis and other fields due to its excellent electrical conductivity, thermal conductivity, high plasticity, low temperature sintering and oxidation resistance. With the rapid development of science and technology, especially the trend of electronic industrial products towards miniaturization and lightweight, higher requirements are placed on the performance of silver powder, especially its tap density has become one of the key factors affecting product quality.

[0003] Tap density is an important indicator to measure the tightness of the bonding between silver powder particles, which directly affects the application effect of silver powder in electronic paste, conductive film and other fields. Silver powder with high tap density has low porosity during the printing process, and the film layer formed after sintering is dense and uniform, with small and few pores, thus showing better conductive properties. However, the silver powder prepared on the current market generally has the problem of low tap density or large size, which to a certain extent limits its application in high-end fields.

[0004] In the prior art, the invention patent (application number CN 202410093440.X) discloses a method for preparing high tap density flaky silver powder, including preparing a silver nitrate solution, a reducing agent solution and a dispersant solution, wherein the reducing agent solution contains ascorbic acid and sodium ascorbate; then, adding the silver nitrate solution and the dispersant solution to the reducing agent solution, and obtaining spherical silver powder after sufficient reaction; shaping the spherical silver powder to obtain spherical silver powder; adding the spherical silver powder to ethanol, adding a grinding aid, and sand milling after sufficient mixing, and obtaining high tap density flaky silver powder after separation, washing and drying. This method first prepares spherical silver powder, then obtains spherical silver powder, and finally obtains flaky silver powder by sand milling. The preparation process is complicated and the cost is high. In addition, the particle size range of the obtained silver powder varies greatly due to the grinding from spherical to flaky, which makes the silver powder have lower fluidity and affects the subsequent application of the silver powder.

[0005] In order to overcome the shortcomings of the existing technology, researchers are constantly exploring new preparation methods and process optimization approaches. For example, some methods improve the dispersibility of silver powder and prevent agglomeration by adding dispersants or protective agents, but these methods often increase process complexity and cost. In addition, some patents also disclose the preparation of silver powder with high tap density by regulating reaction conditions (such as pH value, temperature, reducing agent, etc.), but these methods often find it difficult to simultaneously take into account high dispersibility, fluidity and tap density.

[0006] In view of this, it is necessary to design an improved bulk silver powder with excellent fluidity and high tap density and a preparation method thereof to solve the above problems. Summary of the invention

[0007] The object of the present invention is to provide a bulk silver powder with excellent fluidity and high tap density and a preparation method thereof, wherein a morphology regulator with a specific molecular weight is selected to participate in the reaction so that the silver powder forms a lamellar structure after the reduction reaction, and then the lamellar silver powder is cut and shaped by a solid material processing device with a high linear speed characteristic, thereby obtaining a micron-sized bulk silver powder with dispersed particles, excellent fluidity and high tap density.

[0008] To achieve the above-mentioned object of the invention, the present invention provides a method for preparing bulk silver powder with excellent fluidity and high tap density, comprising the following steps:

[0009] S1, prepare silver salt solution and reducing agent solution;

[0010] S2, mixing a certain amount of reducing agent, morphology regulator and pure water to obtain a base solution;

[0011] S3, under a constant temperature stirring condition of 30° C., the silver salt solution and the reducing agent solution of step S1 are simultaneously added dropwise to the base solution of step S2, and after the addition is completed, stirring is continued for 10 to 20 minutes to obtain flaky silver powder;

[0012] S4, washing, solid-liquid separation, and drying the flaky silver powder in step S3, and then placing it in a solid material processing device for shaping to obtain block silver powder with excellent fluidity and high tap density.

[0013] As a further improvement of the present invention, in step S2, the morphology regulator is polyvinyl pyrrolidone, and the molecular weight of the polyvinyl pyrrolidone is 8000-15000.

[0014] As a further improvement of the present invention, in step S4, the linear speed of the solid material processing device is 70-90 m / s, and the time of the shaping process is 5-10 min.

[0015] As a further improvement of the present invention, the mass ratio of the morphology regulator to the silver salt in the silver salt solution of step S1 is 1:(10~100).

[0016] As a further improvement of the present invention, in step S3, the silver salt solution and the reducing agent solution are simultaneously added dropwise at a speed of 60-90 mL / min.

[0017] As a further improvement of the present invention, in step S1, the mass ratio of the reducing agent in the reducing agent solution to the silver salt in the silver salt solution is 1:(1~2), and the mass ratio of the reducing agent in step S2 to the silver salt in the silver salt solution of step S1 is 1:(10~100).

[0018] As a further improvement of the present invention, in step S1, the concentration of the silver salt solution is 300-400 g / L, and the concentration of the reducing agent solution is 200-350 g / L; in step S2, the concentration of the base solution is 25-35 g / L.

[0019] As a further improvement of the present invention, the reducing agent is any one of sodium borohydride, triethanolamine, hydrazine hydrate, hydroquinone, hydroxylamine, ascorbic acid, sodium citrate, hydrogen peroxide, hydrazine sulfate, glucose, formaldehyde, and potassium iodide, or a mixture of several of them.

[0020] The present invention also provides a block silver powder with excellent fluidity and high tap density, which is prepared by any one of the preparation methods described above.

[0021] As a further improvement of the present invention, the particle size of the bulk silver powder is ≤10 μm, and the tap density is ≥6.1 g / cm 3 , angle of repose <35°.

[0022] The beneficial effects of the present invention are:

[0023] 1. The preparation method of the block silver powder with excellent fluidity and high tap density of the present invention is to select low molecular weight polyvinyl pyrrolidone as a morphology regulator to participate in the reaction. In the process of silver salt reduction, polyvinyl pyrrolidone is selectively adsorbed on the growing silver particle crystal surface. On the one hand, the steric hindrance formed by the polyvinyl pyrrolidone inhibits the growth of the reduced silver atoms on the adsorbed crystal surface, so that the silver powder particles continue to grow into a lamellar structure along a specific crystal surface; on the other hand, as the reaction proceeds, the concentration of the reduced silver atoms increases, and the steric hindrance of the low molecular weight polyvinyl pyrrolidone decreases. The silver powder particles are affected by the van der Waals force and the intermolecular adsorption force to form agglomeration, and a silver powder with a lamellar structure is obtained. The present invention also cuts the point-contact silver powder agglomerates by a solid material processing device with a high linear speed, and the energy of the high-speed rotation forces the cut silver powder particles to collide and rub against each other, and continuously reshapes, thereby obtaining a micron-sized block silver powder with dispersed particles, excellent fluidity and high tap density. The silver powder fully meets the application requirements of the high-end field.

[0024] 2. The present invention achieves high tap density, high dispersibility and good morphology and structure of silver powder through specific process steps and parameter regulation. The prepared bulk silver powder has good fluidity between particles, is more conducive to the sintering and densification of silver paste, and has better conductivity. In addition, the preparation method of the present invention directly prepares silver powder with a lamellar structure, and then cooperates with shaping to obtain bulk silver powder, which not only simplifies the process flow, has fewer types of raw materials, is non-toxic, and reduces production costs, but also has excellent performance of the prepared silver powder and has prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a microscopic morphology of the bulk silver powder prepared in Example 1 of the present invention.

[0026] Figure 2 This is a microscopic morphology of the silver powder prepared in Comparative Example 1.

[0027] Figure 3 This is the microscopic morphology of the silver powder prepared in Comparative Example 2. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0030] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0031] A method for preparing bulk silver powder with excellent fluidity and high tap density comprises the following steps:

[0032] S1, prepare silver salt solution and reducing agent solution;

[0033] S2, mixing a certain amount of reducing agent, morphology regulator and pure water to obtain a base solution;

[0034] S3, under constant temperature stirring at 30°C, the silver salt solution and the reducing agent solution of step S1 are simultaneously added dropwise to the base solution of step S2, and stirring is continued for 10 to 20 minutes after the addition is completed to obtain flaky silver powder;

[0035] S4, washing, solid-liquid separation, and drying the flaky silver powder in step S3, and then placing it in a solid material processing device for shaping to obtain block silver powder with excellent fluidity and high tap density.

[0036] Specifically, in step S2, the morphology regulator is polyvinyl pyrrolidone, and the molecular weight of polyvinyl pyrrolidone is 8000-15000. By selecting low molecular weight polyvinyl pyrrolidone as a morphology regulator to participate in the reaction, during the reduction of the silver salt, polyvinyl pyrrolidone is selectively adsorbed on the growing crystal surface of the silver particles. On the one hand, the steric hindrance formed by it inhibits the growth of the reduced silver atoms on the adsorbed crystal surface, so that the silver powder particles continue to grow into a lamellar structure along a specific crystal surface; on the other hand, as the reaction proceeds, the concentration of the reduced silver atoms increases, the steric hindrance of the low molecular weight polyvinyl pyrrolidone decreases, and the silver powder particles are affected by the van der Waals force and the intermolecular adsorption force to form agglomeration, and a silver powder with a lamellar structure is obtained.

[0037] In some specific embodiments, the morphology regulator is polyvinyl pyrrolidone K13-18.

[0038] In step S4, the linear speed of the solid material processing device is 70-90 m / s, and the shaping time is 5-10 min. The point-contact lamellar silver powder agglomerates are cut by the solid material processing device with a high linear speed, and the energy of high-speed rotation forces the cut silver powder particles to collide and rub against each other, and continuously shape them, thereby obtaining micron-sized block silver powder with dispersed particles, excellent fluidity and high tap density, which fully meets the application requirements of high-end fields.

[0039] Specifically, in step S2, the mass ratio of the morphology regulator to the silver salt in the silver salt solution of step S1 is 1:(10-100), and the mass ratio of the reducing agent to the silver salt in the silver salt solution of step S1 is 1:(10-100). The concentration of the base solution is 25-35 g / L.

[0040] In step S1, the mass ratio of the reducing agent in the reducing agent solution to the silver salt in the silver salt solution is 1:(1-2), the concentration of the silver salt solution is 300-400 g / L, and the concentration of the reducing agent solution is 200-350 g / L; the reducing agent is any one of sodium borohydride, triethanolamine, hydrazine hydrate, hydroquinone, hydroxylamine, ascorbic acid, sodium citrate, hydrogen peroxide, hydrazine sulfate, glucose, formaldehyde, and potassium iodide, or a mixture of several of them.

[0041] In step S3, the silver salt solution and the reducing agent solution are added dropwise at a speed of 60 to 90 mL / min. The purpose of adding the morphology control agent to the base solution and limiting the silver salt solution and the reducing agent to be mixed in the base solution by dropwise addition is to ensure that the silver powder first grows into a sheet and then agglomerates into a lamellar structure, that is, more morphology control agents are present in the initial reduction reaction environment of the silver salt, and the morphology control agents can use their steric hindrance to inhibit the growth of silver atoms on the adsorbed crystal surface, and the silver powder then continues to grow into a lamellar structure. In the later stage of the reaction, the regulating effect of the morphology control agent is weakened, so that the already generated lamellar structure is agglomerated by the van der Waals force and the intermolecular adsorption force, and a silver powder with a lamellar structure is obtained.

[0042] The preparation method of the present invention directly prepares silver powder with a lamellar structure, and then obtains block silver powder by shaping, which not only simplifies the process flow, reduces the types of raw materials, is non-toxic, and reduces production costs, but also the prepared silver powder has excellent performance and has industrial application prospects.

[0043] A bulk silver powder with excellent fluidity and high tap density is prepared by the above preparation method. The particle size of the bulk silver powder is ≤10 μm and the tap density is ≥6.1 g / cm 3 , the angle of repose is less than 35°. The present invention realizes high tap density, high dispersibility and good morphology structure of silver powder through specific process steps and parameter regulation. The prepared bulk silver powder has good fluidity between particles, is more conducive to the sintering and densification of silver paste, and has better conductive performance.

[0044] Example 1

[0045] This embodiment provides a bulk silver powder with excellent fluidity and high tap density and a preparation method thereof, comprising the following steps:

[0046] S1, prepare 500 ml, 400 g / L silver nitrate solution, stir and dissolve at a constant temperature of 30°C to obtain a silver salt solution, prepare 500 ml, 280 g / L ascorbic acid solution, stir and dissolve at a constant temperature of 30°C to obtain a reducing agent solution;

[0047] S2. Weigh 10 g of ascorbic acid and 14 g of polyvinylpyrrolidone K13-18 respectively, add 800 mL of pure water, and stir to dissolve at a constant temperature of 30°C to obtain a base solution;

[0048] S3, under the conditions of constant temperature of 30°C and stirring at a speed of 300 r / min, using a peristaltic pump to synchronously add the silver salt solution and the reducing agent solution of step S1 to the base solution of step S2 at a speed of 60 mL / min, and continue stirring for 20 minutes after the addition is completed to obtain flaky silver powder;

[0049] S4, washing, solid-liquid separation, drying and placing the flaky silver powder in step S3 in a solid material processing device for shaping, with a linear speed of 70 m / s and a processing time of 5 min to obtain a bulk silver powder with excellent fluidity and high tap density.

[0050] See also Figure 1 , which is a microscopic morphology of the bulk silver powder prepared in Example 1. It can be seen from the figure that the silver powder is in bulk, with a particle size of ≤10 μm, and the particles are well dispersed.

[0051] Comparative Example 1

[0052] Comparative Example 1 provides a method for preparing silver powder. Compared with Example 1, the difference is that in step S4, the shaping device used is a ball milling device, and the rest is the same as Example 1 and will not be repeated here.

[0053] See also Figure 2 The figure shows the microscopic morphology of the silver powder prepared in Comparative Example 1. As can be seen from the figure, the obtained silver powder is in block form, but the particle size distribution is wide, and the largest particle exceeds 30 μm. Because the ball mill used in Comparative Example 1 has a grinding effect on the agglomerated particles, the cutting and crushing effect is weak, and it is difficult to crush the large silver powder particles.

[0054] Comparative Example 2

[0055] Comparative Example 2 provides a method for preparing silver powder. Compared with Example 1, the difference is that in step S2, the morphology regulator used is polyvinyl pyrrolidone K90, and the rest is the same as Example 1 and will not be repeated here.

[0056] See also Figure 3 As shown, it is a microscopic morphology of the silver powder prepared in Comparative Example 2. It can be seen from the figure that the obtained silver powder is submicron silver powder particles. Because the morphology regulator used in Comparative Example 2 is polyvinyl pyrrolidone K90, which has a large mass fraction, a corresponding molecular chain length, and a strong steric hindrance, the generated silver powder particles are small, and the solid material processing equipment cannot play a role in crushing and shaping.

[0057] The silver powders prepared in Example 1 and Comparative Examples 1-2 were tested for relevant parameters, and the results are shown in the following table.

[0058] Table 1 Test results of silver powder parameters in Example 1 and Comparative Examples 1-2

[0059]

[0060] As shown in Table 1, the silver powder prepared in Example 1 has a relatively uniform particle size and a good morphology and structure, and the silver powder has a high tap density and good fluidity between particles, which is more conducive to the sintering and densification of the silver paste and has better conductive properties when used. The silver powder prepared in Comparative Example 1 has a wide particle size distribution and poor fluidity. The silver powder prepared in Comparative Example 2 has a poor tap density and a large repose angle, indicating that the generated silver powder particles are small and have poor fluidity.

[0061] Comparative Example 3

[0062] Comparative Example 3 provides a method for preparing silver powder. Compared with Example 1, the difference is that in step S3, the silver salt solution of step S1 and the base solution of step S2 are simultaneously added dropwise to the reducing agent solution, and the rest is the same as Example 1 and will not be repeated here.

[0063] Comparative Example 4

[0064] Comparative Example 4 provides a method for preparing silver powder. Compared with Example 1, the difference is that in step S2, the morphology regulator is a silane coupling agent, and the rest is roughly the same as Example 1, which will not be repeated here.

[0065] Comparative Example 5

[0066] Comparative Example 5 provides a method for preparing silver powder. Compared with Example 1, the difference is that in step S4, no shaping treatment is performed, and the rest is roughly the same as Example 1, which will not be repeated here.

[0067] Comparative Example 6

[0068] Comparative Example 6 provides a method for preparing silver powder. Compared with Example 1, the difference is that in step S3, the silver salt solution and reducing agent solution of step S1 are directly mixed with the base solution of step S2, and the rest is the same as Example 1 and will not be repeated here.

[0069] The silver powders prepared in Comparative Examples 3 to 6 were tested for relevant parameters, and the results are shown in the following table.

[0070] Table 2 Test results of silver powder parameters of comparative examples 3 to 6

[0071]

[0072] As can be seen from Table 2, in Comparative Example 3, the order of adding reagents was changed to prepare silver powder in the form of granular agglomerates with larger size. In Comparative Example 4, the morphology regulator was replaced with a silane coupling agent, and the morphology of the silver powder particles was highly crystalline irregular blocks. After being shaped by the solid material processing device, the morphology did not change significantly. In Comparative Example 5, the silver powder was not shaped by the solid material processing device after synthesis, and the powder particles were still lamellar structures with a size greater than 10 μm. In Comparative Example 6, the silver salt solution and the reducing agent solution of step S1 were directly mixed with the base liquid of step S2, and the reagents reacted quickly. The silver powder particles grew too fast to form block-like agglomerated particles, and no lamellar morphology was generated. The solid material processing device had no obvious effect on its morphology shaping. In the above comparative examples, the silver powder had a low tap density and poor fluidity because its morphology was mostly irregular agglomerated.

[0073] In summary, the present invention provides a bulk silver powder with excellent fluidity and high tap density and a preparation method thereof. A morphology regulator with a specific molecular weight is selected to participate in the reaction, so that the silver powder forms a lamellar structure after the reduction reaction, and then the lamellar silver powder is cut and shaped by a solid material processing device with a high linear speed characteristic, thereby obtaining a micron-sized bulk silver powder with dispersed particles, excellent fluidity and high tap density. The present invention selects low molecular weight polyvinyl pyrrolidone as a morphology regulator to participate in the reaction. In the process of silver salt being reduced, polyvinyl pyrrolidone is selectively adsorbed on the growing crystal plane of silver particles. On the one hand, the steric hindrance formed by the polyvinyl pyrrolidone inhibits the growth of reduced silver atoms on the adsorbed crystal plane, so that the silver powder particles continue to grow into a lamellar structure along a specific crystal plane; on the other hand, as the reaction proceeds, the concentration of reduced silver atoms increases, the steric hindrance effect of the low molecular weight polyvinyl pyrrolidone decreases, and the silver powder particles are affected by van der Waals forces and intermolecular adsorption forces to form agglomerations, so as to obtain silver powder with a lamellar structure; finally, the point-contact silver powder agglomerates are cut by a solid material processing device with a high linear speed, and the energy of high-speed rotation forces the cut silver powder particles to collide and rub against each other, and continuously reshape, so as to obtain micron-level block silver powder with dispersed particles, excellent fluidity and high tap density, and the silver powder fully meets the application requirements of high-end fields. The invention realizes high tap density, high dispersibility and good morphology structure of silver powder through specific process steps and parameter regulation. The prepared bulk silver powder has good fluidity between particles, is more conducive to the sintering and densification of silver paste, and has better conductive performance. The preparation method not only simplifies the process flow and reduces the production cost, but also the prepared silver powder has excellent performance and has industrial application prospects.

[0074] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing bulk silver powder with excellent fluidity and high tap density, characterized in that: The following steps are involved: S1, prepare silver salt solution and reducing agent solution; S2, mixing a reducing agent, a morphology regulator and pure water to obtain a base solution; the morphology regulator is polyvinyl pyrrolidone, and the molecular weight of the polyvinyl pyrrolidone is 8000-15000; S3, under a constant temperature stirring condition of 30° C., the silver salt solution and the reducing agent solution of step S1 are simultaneously added dropwise to the base solution of step S2, and after the addition is completed, stirring is continued for 10 to 20 minutes to obtain flaky silver powder; S4, washing, solid-liquid separation, and drying the flaky silver powder in step S3, and then placing it in a solid material processing device for shaping treatment, wherein the solid material processing device cuts the point-contact flaky silver powder agglomerates at a linear speed of 70-90 m / s, and the shaping time is 5-10 min to obtain block silver powder with excellent fluidity and high tap density.

2. The method for preparing bulk silver powder with excellent fluidity and high tap density according to claim 1, characterized in that: The mass ratio of the morphology regulator to the silver salt in the silver salt solution of step S1 is 1:(10-100).

3. The method for preparing bulk silver powder with excellent fluidity and high tap density according to claim 1, characterized in that: In step S3, the silver salt solution and the reducing agent solution are simultaneously added dropwise at a speed of 60-90 mL / min.

4. The method for preparing bulk silver powder with excellent fluidity and high tap density according to claim 1, characterized in that: In step S1, the mass ratio of the reducing agent in the reducing agent solution to the silver salt in the silver salt solution is 1:(1-2), and the mass ratio of the reducing agent in step S2 to the silver salt in the silver salt solution of step S1 is 1:(10-100).

5. The method for preparing bulk silver powder with excellent fluidity and high tap density according to claim 1, characterized in that: In step S1, the concentration of the silver salt solution is 300-400 g / L, and the concentration of the reducing agent solution is 200-350 g / L; in step S2, the concentration of the base solution is 25-35 g / L.

6. The method for preparing bulk silver powder with excellent fluidity and high tap density according to claim 4, characterized in that: The reducing agent is any one of sodium borohydride, triethanolamine, hydrazine hydrate, hydroquinone, hydroxylamine, ascorbic acid, sodium citrate, hydrogen peroxide, hydrazine sulfate, glucose, formaldehyde, and potassium iodide, or a mixture of several of them.

7. A bulk silver powder with excellent fluidity and high tap density, characterized in that: The silver powder is prepared by the method for preparing a bulk silver powder with excellent fluidity and high tap density as described in any one of claims 1 to 6.

8. The bulk silver powder with excellent fluidity and high tap density according to claim 7, characterized in that: The particle size of the bulk silver powder is ≤10 μm, and the tap density is ≥6.1 g / cm 3 , angle of repose <35°.

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