Flaky silver powder and method for producing the same

Abstract

The application provides flaky silver powder and a preparation method thereof, and belongs to the technical field of metal powder, wherein the flaky silver powder is obtained by mixing two kinds of silver powder agglomerates with different single particle size distributions as base silver powder, ball milling with a ball milling medium and an additive solution in two stages; the rotation speed of the first stage ball milling is 30-80 rpm, and the time is 10-60 min; the rotation speed of the second stage ball milling is 120-150 rpm, and the time is 2-6 h; the two kinds of base silver powder are respectively a first base powder and a second base powder, the agglomerate particle size distribution is 1-150 mu m, and the silver content is greater than 99.9%; the single particle size distribution of the first base powder is 0.1-1.5 mu m, and the single particle size distribution of the second base powder is 0.5-3 mu m. The application realizes the synergistic optimization of the flaky silver powder morphology and performance by innovatively adopting two kinds of base silver powder with specific particle size distribution for combination and matching with the two-stage ball milling process with precise control. The preparation method is simple and controllable, and is easy to realize industrial large-scale production.

Description

Technical Field

[0001] This invention relates to the field of metal powder technology, specifically to a flake-shaped silver powder and its preparation method. Background Technology

[0002] As electronic components evolve towards high integration and miniaturization, higher demands are placed on silver powder, a key conductive material. It requires not only excellent conductivity but also high packing density, good dispersibility, and low sintering temperature. Existing technologies for preparing silver powder with different morphologies each have their limitations. Specifically, submicron spherical silver powder is typically prepared using chemical methods such as polyol reduction, with a particle size range of 20-100 nm. While this type of silver powder helps lower the sintering temperature of multilayer ceramic capacitors (MLCCs), its inherent spherical structure results in low packing density, and the nanoparticles are prone to agglomeration, making it difficult to meet the requirements for high-density filling. On the other hand, submicron sheet-like silver powder, such as silver sheets with a thickness of 5-20 nm and a diameter of 100-500 nm, can form a highly efficient conductive network through surface contact. However, mainstream preparation methods such as the CTAB template method suffer from high template agent residue and poor dispersibility; residual organic matter can severely affect the conductivity and long-term reliability of the sintered electrode. In addition, some technologies attempt to physically mix silver powders with different morphologies in order to obtain comprehensive performance. However, this method is prone to causing the stratification and re-agglomeration of powders with different morphologies, which cannot meet the requirements of high integration of electronic components.

[0003] In view of this, it is necessary to design a flake-shaped silver powder and its preparation method to solve the above problems. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a flake silver powder and its preparation method, aiming to solve the technical problems existing in the existing flake silver powder preparation process, such as high template agent residue, poor dispersibility, inability to achieve precise control of morphology ratio, and difficulty in industrial mass production.

[0005] In a first aspect, this application provides a method for preparing flake-shaped silver powder, comprising the following steps:

[0006] Two types of silver powder agglomerates with different single-particle size distributions were used as base silver powders. They were mixed with ball milling media and an additive solution and subjected to two-stage ball milling to obtain flake silver powder.

[0007] The first stage of ball milling involves a rotation speed of 30-80 rpm and a time of 10-60 min; the second stage involves a rotation speed of 120-150 rpm and a time of 2-6 h.

[0008] The two types of base silver powder are designated as the first base powder and the second base powder, respectively. Both have an aggregate particle size distribution of 1~150μm and a silver content greater than 99.9%.

[0009] The particle size distribution of the first base powder is 0.1~1.5μm, and the particle size distribution of the second base powder is 0.5~3μm.

[0010] As a further improvement of this application, the mass ratio of the first base powder to the second base powder is (0.02~50):1.

[0011] As a further improvement of this application, the additives in the additive solution are one or more of polyethylene glycol, lauric acid, butyl stearate, polyvinyl alcohol, stearic acid, and palmitic acid.

[0012] As a further improvement of this application, the amount of the additive is 1-3% of the total mass of the two basic silver powders, and the concentration of the additive solution is 50-200 g / L.

[0013] As a further improvement to this application, the milling media is a stainless steel ball or alloy ball with a diameter of 3 mm.

[0014] As a further improvement of this application, the mass ratio of the ball milling media to the total mass of the two basic silver powders is (5~8):1.

[0015] Secondly, this application provides a flake-shaped silver powder, which is prepared by the method for preparing flake-shaped silver powder described in the first aspect, wherein the particle size distribution of the flake-shaped silver powder is 0.1~30μm.

[0016] As a further improvement to this application, the flake silver powder comprises flake particles and submicron spherical particles.

[0017] As a further improvement of this application, the submicron spherical particles account for 5-20% of the total number of the flake-shaped silver powder particles.

[0018] As a further improvement of this application, the particle size distribution of the flake silver powder satisfies the following: D10 is 0.1~2μm, D50 is 2~7μm, and D90 is 6~15μm.

[0019] The beneficial effects of this application are as follows:

[0020] This application provides a method for preparing flake-shaped silver powder. The method involves using two silver powder aggregates with different single-particle size distributions as base silver powders, mixing them with ball milling media and an additive solution, and then performing a two-stage ball milling process to obtain flake-shaped silver powder. The first stage of ball milling is performed at a speed of 30–80 rpm for 10–60 min; the second stage is performed at a speed of 120–150 rpm for 2–6 h. The two base silver powders are designated as a first base powder and a second base powder, both with aggregate particle size distributions of 1–150 μm and silver content greater than 99.9%. The single-particle size distribution of the first base powder is 0.1–1.5 μm, and that of the second base powder is 0.5–3 μm. This application innovatively combines two base silver powders with specific particle size distributions and matches them with a precisely controlled two-stage ball milling process, achieving synergistic optimization of the morphology and properties of the flake-shaped silver powder. This method not only produces environmentally friendly flake silver powder with controllable morphology and proportion, excellent dispersibility, and no harmful template agent residue in a one-step process, effectively overcoming the defects of existing technologies such as agglomeration, layering, and impurity residue; at the same time, by adjusting the ratio of base powder and ball milling parameters, the product performance can be flexibly customized to meet the specific needs of different electronic components for conductive pastes, and the process is simple and controllable, making it easy to achieve large-scale industrial production.

[0021] This application uses two different types of silver powder with different agglomerates as raw materials, adds high-concentration additives, and ball mills them. By controlling the material and size of the grinding balls, the ball-to-material ratio, and the ball milling time, flake-shaped silver powder with a particle size distribution of 0.1~30μm is obtained. A first base powder with single particles of 0.1~1.5μm and agglomerates of 1~150μm is selected, along with a second base powder with single particles of 0.5~3μm and agglomerates of 1~150μm. The single particles of the two base powders have a gradient overlap, and the agglomerate structure is consistent, forming a synergistic effect and avoiding the defects of single raw materials. Through precise two-stage ball milling, the first stage matches the grinding ball speed and additive lubrication to efficiently destroy the agglomerate structure of the two base silver powders, fully deagglomerating them into single particles or small-sized aggregates. The second stage adjusts the ball milling time and kinetic energy so that the slightly larger particles in the deagglomerated powder form flakes, while retaining the fine particles of the first base powder as submicron spheres. This solves the technical problem that it is difficult to achieve deagglomeration and morphology control simultaneously in a one-time ball milling, ensuring the synergistic preservation of the two morphological powders. By combining basic silver powder property control with ball milling parameters, a breakthrough has been achieved in the stable preparation of flake-shaped silver powder with a particle size distribution of 0.1~30μm, which can be applied to conductive adhesives, electronic packaging and other fields.

[0022] 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

[0023] 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.

[0024] Figure 1 This is an electron microscope image of the flake-like silver powder obtained in Example 1 of this application;

[0025] Figure 2 The image shows an electron microscope image of the flake-like silver powder obtained in Comparative Example 1.

[0026] Figure 3 This is an electron microscope image of the flake-like silver powder obtained in Comparative Example 2. Detailed Implementation

[0027] 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.

[0028] 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.

[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 of this application, the term "multiple" 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).

[0032] Existing silver powder preparation technologies have significant limitations. For example, while submicron spherical silver powder can lower the sintering temperature of MLCCs, it suffers from low packing density and agglomeration. Submicron sheet-like silver powder, although capable of forming highly efficient conductive networks, generally relies on template methods such as CTAB, resulting in poor dispersibility and excessive organic residues, affecting product reliability. Physical mixing of silver powders with different morphologies easily leads to layering and agglomeration, failing to meet the high integration requirements of electronic components. Furthermore, existing technologies such as hydrothermal methods can only obtain single spherical structures, failing to achieve morphology synergy; and single-crystal silver powder preparation processes face challenges in industrial-scale scaling. Therefore, the market urgently needs a one-step preparation method for sheet-like silver powder with precise and controllable morphology ratios, environmentally friendly processes, and the ability to meet high-reliability application requirements, to overcome these technological bottlenecks.

[0033] To address the technical problems of high template agent residue, poor dispersibility, inability to accurately control morphology ratio, and difficulty in industrial-scale mass production in existing flake silver powder preparation processes, this application provides a flake silver powder and its preparation method. By using two silver powder aggregates with different single-particle size distributions as base silver powders and employing a two-stage ball milling process for physical shaping, a one-step method can be used to prepare environmentally friendly flake silver powder with controllable morphology ratio, high dispersibility, no harmful residues, and easy industrial scale-up, thus meeting the high reliability application requirements in the electronics field.

[0034] In a first aspect, embodiments of this application provide a method for preparing flake-shaped silver powder, comprising the following steps:

[0035] Two types of silver powder agglomerates with different single-particle size distributions were used as base silver powders. They were mixed with ball milling media and an additive solution and subjected to two-stage ball milling to obtain flake silver powder.

[0036] The first stage of ball milling involves a rotation speed of 30-80 rpm and a time of 10-60 min; the second stage involves a rotation speed of 120-150 rpm and a time of 2-6 h.

[0037] The two types of base silver powder are designated as the first base powder and the second base powder, respectively. Both have an aggregate particle size distribution of 1~150μm and a silver content greater than 99.9%.

[0038] The single particle size distribution of the first base powder is 0.1~1.5μm, and the single particle size distribution of the second base powder is 0.5~3μm.

[0039] In the technical solution of this application embodiment, two types of silver powder agglomerates with different single particle size distributions are used as base silver powders. A two-stage ball milling process is used to prepare flake silver powder. The first stage of ball milling uses a lower rotation speed and a shorter milling time, combined with the lubrication effect of the additive solution, to efficiently break down the agglomeration structure of the two base silver powders and fully deagglomerate them into single particles or small-sized aggregates. The second stage of ball milling increases the rotation speed and extends the milling time, so that the slightly larger particles in the deagglomerated powder become flakes, while retaining some fine particles as submicron spherical shapes, and finally obtaining flake silver powder with different morphologies and particle size distributions.

[0040] Furthermore, in some embodiments, the mass ratio of the first base powder to the second base powder is (0.02~50):1.

[0041] In the technical solution of this application embodiment, by adjusting the mass ratio of the first base powder and the second base powder, the morphology and particle size distribution of the flake silver powder can be further controlled. By selecting an appropriate mass ratio, the morphology and particle size distribution of the silver powder can be finely controlled to meet the needs of different application scenarios.

[0042] Furthermore, in some embodiments, the additives in the additive solution are one or more selected from polyethylene glycol, lauric acid, butyl stearate, polyvinyl alcohol, stearic acid, and palmitic acid. The amount of additive added is 1-3% of the total mass of the two base silver powders, and the concentration of the additive solution is 50-200 g / L.

[0043] In the technical solution of this application embodiment, the selected additives such as polyethylene glycol and lauric acid have molecular chains that can be adsorbed onto the surface of silver powder at one end and extend into the solvent at the other end, forming steric hindrance. This effectively prevents the deagglomerated particles from re-agglomerating during ball milling. Simultaneously, these additives act as lubricants, significantly reducing the coefficient of friction and impact force between the ball milling media and the silver powder, as well as between the silver powder particles. This avoids excessive particle breakage or cold welding due to excessive impact, creating favorable conditions for the plastic deformation of the particles in the second stage of ball milling. Controlling the additive addition amount to 1-3% of the total mass and the solution concentration to 50-200 g / L ensures sufficient protection and lubrication while preventing excessive additive coating of the silver powder surface, thus hindering its plastic deformation and ensuring ball milling efficiency and the excellent morphology of the final flake-shaped silver powder.

[0044] Furthermore, in some embodiments, the milling media are stainless steel balls or alloy balls with a diameter of 3 mm.

[0045] In the technical solution of this application embodiment, the stainless steel ball or alloy ball has high hardness, which can effectively break up silver powder agglomerates, causing them to deagglomerate into single particles or small aggregates; the moderate diameter can provide sufficient crushing force without causing excessive crushing of the silver powder. By selecting a suitable ball milling media, the crushing efficiency and morphological evolution of the silver powder during the ball milling process can be effectively controlled, thereby obtaining the desired flake-shaped silver powder.

[0046] Furthermore, in some embodiments, the mass ratio of the ball milling media to the total mass of the two base silver powders is (5~8):1.

[0047] In the technical solution of this application embodiment, a higher ball-to-material ratio can increase the number of collisions between the ball milling media and the silver powder, thereby improving the crushing efficiency and making the silver powder subject to a more uniform crushing force between the ball milling media, thereby obtaining a more uniform particle size distribution and morphology.

[0048] Secondly, embodiments of this application provide a flake-shaped silver powder, which is prepared by the method for preparing flake-shaped silver powder described in the first aspect, and the particle size distribution of the flake-shaped silver powder is 0.1~30μm.

[0049] By using two silver powder agglomerates with specific particle size distributions as raw materials and precisely controlling a two-stage ball milling process, a composite morphology silver powder with a particle size distribution of 0.1~30μm was finally obtained. This silver powder product simultaneously contains submicron spherical, submicron flake, and micron flake morphologies, solving the technical challenge of simultaneously achieving deagglomeration and morphology control in a single ball milling process. This flake-shaped silver powder can be applied to key components such as internal electrodes of multilayer ceramic capacitors (MLCCs), conductive pastes, conductive adhesives for electronic packaging, and flexible electronic circuits.

[0050] Furthermore, in some embodiments, the flake silver powder comprises flake particles and submicron spherical particles. The submicron spherical particles account for 5-20% of the total number of flake silver powder particles.

[0051] In the technical solution of this application embodiment, the proportion of submicron spherical particles ensures that they can fully fill the gaps between the sheet particles, thereby significantly improving the bulk density of the powder and the sintering density of the conductive slurry, while avoiding weakening the ability of the sheet particles to build an efficient conductive network due to excessive spherical particles.

[0052] Furthermore, in some embodiments, the particle size distribution of the flake silver powder satisfies the following: D10 is 0.1~2μm, D50 is 2~7μm, and D90 is 6~15μm.

[0053] In the technical solution of this application embodiment, the flake silver powder has a moderate particle size range, which ensures that enough fine particles fill the gaps and improve the bulk density, while avoiding excessively large particles from affecting the uniformity and leveling of the slurry. This application improves the batch stability and performance controllability of the product by synergistically controlling the raw material ratio and two-stage ball milling parameters, and can better meet the strict requirements of high-end electronic slurries for powder particle size distribution.

[0054] 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.

[0055] Example 1

[0056] This embodiment provides a method for preparing flake silver powder, including the following steps:

[0057] S1. Weigh 1 kg of the first base powder, weigh 4 kg of the second base powder, and weigh 120 g of lauric acid; wherein, the single particle size distribution of the first base powder is 0.1~1.5 μm, and the aggregate particle size distribution is 1~150 μm; the single particle size distribution of the second base powder is 0.5~3 μm, and the aggregate particle size distribution is 1~150 μm;

[0058] S2. Mix the two base powders thoroughly;

[0059] S3. Dissolve lauric acid in 1.1L of anhydrous ethanol to form a lauric acid ethanol solution;

[0060] S4. Pour the lauric acid ethanol solution into the ball milling equipment. The ball milling media is stainless steel balls with a diameter of 3 mm. The mass ratio of the ball milling media to the two base powders is 20:3. Start the milling speed at 50 rpm. Pour the two base powders into the ball milling equipment and stir for 30 minutes. Then increase the speed to 130 rpm and mill for 2.5 hours.

[0061] S5. Clean the silver powder with anhydrous ethanol, place it in an oven and dry at 50°C for 10 hours to obtain flake silver powder.

[0062] Example 2

[0063] This embodiment provides a method for preparing flake silver powder. Compared with Example 1, the only difference is that the first base powder is 0.1 kg and the second base powder is 4.9 kg. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here.

[0064] Example 3

[0065] This embodiment provides a method for preparing flake silver powder. Compared with Example 1, the only difference is that the first base powder is 4.9 kg and the second base powder is 0.1 kg. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here.

[0066] Example 4

[0067] This embodiment provides a method for preparing flake silver powder. Compared with Example 1, the only difference is that the first stage of ball milling is performed at a speed of 30 rpm for 10 min, and the second stage of ball milling is performed at a speed of 120 rpm for 2 h. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here.

[0068] Example 5

[0069] This embodiment provides a method for preparing flake silver powder. Compared with Example 1, the only difference is that the first stage of ball milling is performed at a speed of 80 rpm for 60 min, and the second stage of ball milling is performed at a speed of 150 rpm for 6 h. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here.

[0070] Comparative Example 1

[0071] Comparative Example 1 provides a method for preparing flake silver powder. Compared with Example 1, the only difference is that the first base powder and the second base powder are both monodisperse silver powders with a particle size distribution of 1~6μm. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0072] Comparative Example 2

[0073] Comparative Example 2 provides a method for preparing flake silver powder. Compared with Example 1, the only difference is that the rotation speed is not adjusted during ball milling, and the ball milling speed is 130 rpm. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0074] Comparative Example 3

[0075] Comparative Example 3 provides a method for preparing flake silver powder. Compared with Example 1, the only difference is that the base silver powder is 5 kg of the first base powder and no second base powder is added. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0076] Comparative Example 4

[0077] Comparative Example 4 provides a method for preparing flake silver powder. Compared with Example 1, the only difference is that the base silver powder is 5 kg of second base powder and no first base powder is added. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0078] The test results of the flake silver powder prepared in the examples and comparative examples are shown in Table 1.

[0079] Table 1. Silver powder detection results obtained from the examples and comparative examples.

[0080]

[0081] From Table 1 and Figures 1 to 3 It can be seen that the particle size distribution of the flake-like silver powder prepared in this application meets the following requirements: D10 is 0.1~2μm, D50 is 2~7μm, and D90 is 6~15μm. The silver powder prepared in Example 1 has a uniform particle size distribution and exhibits morphological structures such as submicron spheres, submicron flakes, and micron flakes. The silver powder prepared in Comparative Example 1 has a narrow particle size distribution and only has a flake-like morphology. The silver powder prepared in Comparative Example 2 has too wide a particle size distribution, and the micron flake size is too large, affecting the slurry-forming performance. Comparative Examples 3 and 4 use only one type of base powder, which cannot achieve morphological synergy, and the proportion of spherical particles is not ideal.

[0082] 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 producing a flaky silver powder, characterized by, The method comprises the following steps: Agglomerates of two kinds of silver powder with different single particle size distribution are mixed with ball milling medium and an additive solution to obtain flaky silver powder by two-stage ball milling; the flaky silver powder comprises flaky particles and sub-micron spherical particles; The first-stage ball milling is performed at a speed of 30-80 rpm for 10-60 min, and the second-stage ball milling is performed at a speed of 120-150 rpm for 2-6 h; The two kinds of base silver powder are a first base powder and a second base powder, and the particle size distribution of the agglomerates is 1-150 μm, and the silver content is greater than 99.9%; The single particle size distribution of the first base powder is 0.1-1.5 μm, and the single particle size distribution of the second base powder is 0.5-3 μm; The mass ratio of the first base powder to the second base powder is (0.02-50):1; The additive in the additive solution is one or more of polyethylene glycol, lauric acid, butyl stearate, polyvinyl alcohol, stearic acid and palmitic acid; The additive is added in an amount of 1-3% of the total mass of the two kinds of base silver powder, and the concentration of the additive solution is 50-200 g / L.

2. The method of claim 1, wherein the silver flake is prepared by the process of claim 1. The ball milling medium is stainless steel ball or alloy ball with a diameter of 3 mm.

3. The method of claim 2, wherein the silver flake is prepared by the process of claim 1. The mass ratio of the ball milling medium to the total mass of the two kinds of base silver powder is (5-8):

1.

4. A flaky silver powder, characterized by, The flaky silver powder prepared by the method of any one of claims 1-3 has a particle size distribution of 0.1-30 μm.

5. The flake-shaped silver powder according to claim 4, characterized in that, The sub-micron spherical particles account for 5-20% of the total number of the flaky silver powder particles.

6. The flaky silver powder according to claim 4, characterized by The particle size distribution of the flaky silver powder satisfies: D10 is 0.1-2 μm, D50 is 2-7 μm, and D90 is 6-15 μm.

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