Flaky silver-coated copper powder and preparation method thereof

Abstract

The invention relates to the technical field of silver-coated copper powder, in particular to flaky silver-coated copper powder and a preparation method thereof. Comprising the steps of copper powder pretreatment, flaky copper powder treatment, chemical replacement, cleaning treatment, electroplating enhancement, heat treatment enhancement and the like, oxidation can be prevented through inert atmosphere heat treatment on silver-coated copper powder, recrystallization of a silver layer is promoted, metallurgical bonding is formed through atomic diffusion, and internal stress is eliminated; the oxidation treatment can form a protective oxidation film on the surface of the silver layer, and the reduction treatment can eliminate excessive oxidation and recover conductivity, so that a stable surface state is formed, the high-temperature stability is improved, and the prepared silver-coated copper powder can be used for a long time under an extreme high-temperature condition to slow down oxidation.

Description

Technical Field

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

[0002] Silver-coated copper powder, as an excellent highly conductive filler, can be added to coatings (paints), adhesives, inks, polymer slurries, plastics, rubber, etc., to produce various conductive and electromagnetic shielding products. These products are widely used in conductive and electromagnetic shielding applications across various industrial sectors, including electronics, electromechanical, communications, printing, aerospace, and weaponry. Examples include conductive and electromagnetic shielding in electronic, electrical, and communication products such as computers, mobile phones, electronic medical equipment, and electronic instruments.

[0003] Silver-plated copper powder is produced using advanced chemical plating technology and specific molding and surface treatment processes to form silver plating layers of varying thicknesses on the surface of ultrafine copper powder. It overcomes the tendency of copper powder to oxidize easily while also possessing excellent conductivity, high chemical stability, resistance to oxidation, and low cost, making it a promising high-conductivity filler. Among these, the flake-shaped F-type silver-plated copper powder is suitable for conductive coatings, conductive inks, and conductive adhesives; it is also suitable for various high-temperature conductor sintering pastes, high-performance thick-film silver-based pastes, conductive rubber, conductive plastics, and other conductive composite materials.

[0004] For example, Chinese Patent Publication No. CN120243913A discloses a low-resistivity dendritic flake-shaped silver-coated copper powder. The copper powder is in the form of dendritic flakes, with a silver layer uniformly coated on the surface of the dendritic flake copper powder. A chelate layer is then coated on the surface of the silver layer, wherein the chelate layer includes cysteine ​​and glutathione. This invention also discloses a method for preparing the above-mentioned low-resistivity dendritic flake-shaped silver-coated copper powder, comprising the following steps: plating silver onto the surface of the dendritic flake-shaped copper powder to obtain an intermediate; washing the intermediate with an aminothiol solution, drying it, and then adding it to a mixture containing cysteine ​​and glutathione to carry out a chelation reaction, thereby obtaining the low-resistivity dendritic flake-shaped silver-coated copper powder. This low-resistivity dendritic flake-shaped silver-coated copper powder exhibits good dispersibility, antioxidant properties, and conductivity in coatings, and can improve the adhesion of the coating.

[0005] However, in high humidity or high temperature oxygen-containing environments, the surface of flake-shaped silver-coated copper powder will slowly oxidize. After oxidation, the conductivity decreases, and the color changes from bright to dark or yellowish. Under long-term high temperature conditions, silver and copper will interdiffusion will occur at the silver-copper interface, forming an alloy transition layer. This may change the material's conductivity and mechanical properties, and long-term high-temperature operation will lead to gradual performance degradation.

[0006] To address the above problems, this invention provides a flake-shaped silver-coated copper powder and its preparation method. Summary of the Invention

[0007] The purpose of this invention is to provide a flake-shaped silver-coated copper powder and its preparation method, so as to solve the problems mentioned in the background art.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing flake-shaped silver-coated copper powder, comprising the following steps:

[0009] S1, Copper powder pretreatment includes three steps: acid washing, alkaline washing, and acid washing again. During the first acid washing, the copper powder is immersed in a dilute sulfuric acid solution and stirred at room temperature for 10-15 minutes to remove surface oxides. After the first acid washing, the alkaline washing process begins, using sodium hydroxide solution to clean for 5-10 minutes to remove organic impurities. After the alkaline washing, the second acid washing process begins, where the copper powder is immersed in a dilute sulfuric acid solution again for 5-8 minutes. Finally, the copper powder is rinsed with deionized water until neutral.

[0010] S2, flake copper powder treatment: the pretreated copper powder is mixed with ethylene glycol ether or propylene glycol ether, added to a ball mill and ground at low speed at 33℃ and 40rpm for 6h. After washing with deionized water and drying, flake copper powder with a particle size of 5~10 μm is screened out using an air classifier.

[0011] S3, Chemical Displacement: Take a measured amount of glucose, hydrazine hydrate, or ascorbic acid, mix it with a measured amount of deionized water, and stir until homogeneous to form a reducing solution; take a measured amount of silver nitrate, dissolve it in a measured amount of deionized water, add a measured amount of sodium citrate, and stir until homogeneous to form a silver stock solution; then disperse flake copper powder in a measured amount of ethanol, mix the dispersion with the reducing solution, and stir at 200 rpm for 15 minutes at a constant temperature of 30-35℃ to form a mixed solution with a pH of 9-10; finally, slowly add the silver stock solution dropwise into the mixed solution, maintaining a constant temperature of 28-32℃ during the dropwise addition process, with a dropwise addition time of 3.5-4 hours, simultaneously using ultrasonic stirring and mechanical stirring.

[0012] S4, cleaning treatment: the product is separated by centrifugation, washed with deionized water and acetone until neutral, and then vacuum dried at 60°C for 5-7 hours to obtain the initial copper powder.

[0013] S5, electroplating enhancement: a certain amount of silver nitrate, sodium thiosulfate and potassium metabisulfite are mixed to prepare an electroplating solution. The dried initial copper powder is immersed in the electroplating solution and electroplated at a constant temperature of 30~40℃ for 20~30 minutes. After separation, rinsing and drying, electroplated copper powder is obtained.

[0014] S6, heat treatment enhancement: place the electroplated copper powder in an argon, helium or nitrogen protective atmosphere and heat treat it at 700~850℃ for 2~2.5h. After natural cooling, place it in air at 200~250℃ for oxidation treatment for 30min, and then place it in hydrogen at 400~500℃ for reduction treatment for 1h. After natural cooling, the finished silver-coated copper powder is obtained.

[0015] In a more optimized manner, in step S1, the weight ratio of copper powder to ethanol is 1:22, the concentration of dilute sulfuric acid during the first pickling is 5%, the concentration of dilute sulfuric acid during the second pickling is 3%, the concentration of sodium hydroxide solution during alkaline washing is 5%, and the stirring speed is 300~500 rpm.

[0016] More optimally, in step S2, the ethylene glycol ether includes one or both of ethylene glycol butyl ether and diethylene glycol ethyl ether, and the propylene glycol ether includes one or both of propylene glycol methyl ether and dipropylene glycol methyl ether.

[0017] In a more optimized manner, in step S3, the weight ratio of glucose or hydrazine hydrate or ascorbic acid to deionized water is 1:22 to 1:25, and the weight ratio of silver nitrate to sodium citrate to deionized water is 1:2:150 to 5:1:120.

[0018] Ideally, the pH of the mixture is 10, the ultrasonic stirring frequency is 40kHz, and the mechanical stirring rate is 400rpm during the addition of the silver stock solution.

[0019] In a more optimized manner, in step S5, the concentration of silver nitrate is 30~50 g / L, the concentration of sodium thiosulfate is 80~120 g / L, the concentration of potassium metabisulfite is 20~30 g / L, and the current density during electroplating is 0.5~1.5 A / dm².

[0020] In a more optimized manner, in step S6, the temperature is 820°C during heat treatment in an inert gas atmosphere, 215°C during air oxidation, and 485°C under hydrogen conditions.

[0021] Ideally, the silver content of the finished silver-coated copper powder product prepared in step S6 is ≥20%.

[0022] The present invention also provides a flake-shaped silver-coated copper powder, which is prepared by any of the above-mentioned methods for preparing flake-shaped silver-coated copper powder.

[0023] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) In this invention, the main function of the first acid washing is to remove the oxide layer on the surface of the copper powder, expose the fresh copper surface, and improve the adhesion and uniformity of the subsequent silver coating; the main function of the alkaline washing is to remove organic impurities and grease on the surface of the copper powder, which will seriously affect the coating quality and uniformity of the silver layer; the function of the second acid washing is to neutralize the residual alkaline solution and further clean the surface of the copper powder, providing an ideal active surface for the subsequent silver coating.

[0024] (2) In this invention, the role of alcohol ether is to provide a suitable grinding environment, prevent copper powder from oxidizing and promote the formation of a sheet structure; low-speed ball milling can control the grinding energy to ensure that the copper powder is shaped into a sheet rather than broken; temperature control is to prevent overheating from causing copper powder to oxidize or solvent to evaporate, and long-term low-speed grinding can ensure sufficient deformation time to form a regular sheet structure.

[0025] (3) In this invention, sodium thiosulfate and potassium metabisulfite can provide a stable electroplating environment, control the current density can adjust the silver deposition rate and density, and control the temperature can maintain the stability of the electroplating solution, thereby filling the gaps and pores of the silver layer on the surface of the copper powder during chemical replacement, and increasing the silver content of the finished product of sheet silver-coated copper powder while ensuring a more uniform and dense finish.

[0026] (4) In this invention, inert atmosphere heat treatment can prevent oxidation, promote recrystallization of silver layer, form metallurgical bond through atomic diffusion, and eliminate internal stress; oxidation treatment can form a protective oxide film on the surface of silver layer, and reduction treatment can eliminate excessive oxidation, restore conductivity, thereby forming a stable surface state and improving high temperature stability, so that the silver-coated copper powder prepared by this invention can be used for a long time under extreme high temperature conditions while slowing down oxidation. Attached Figure Description

[0027] Figure 1 is an electron microscope image of flake-shaped silver-coated copper powder. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] This invention provides a method for preparing flake-shaped silver-coated copper powder, comprising the following steps:

[0030] S1, Copper powder pretreatment includes three steps: acid washing, alkali washing, and acid washing again. During the first acid washing, the copper powder is immersed in a dilute sulfuric acid solution and stirred at room temperature for 10-15 minutes to remove surface oxides. After the first acid washing, the alkali washing process begins, using sodium hydroxide solution to clean for 5-10 minutes to remove organic impurities. After the alkali washing, the second acid washing begins, where the copper powder is immersed in a dilute sulfuric acid solution again for 5-8 minutes. Finally, the copper powder is rinsed with deionized water until neutral.

[0031] In this step, the weight ratio of copper powder to ethanol is 1:22, the concentration of dilute sulfuric acid during the first pickling is 5%, the concentration of dilute sulfuric acid during the second pickling is 3%, the concentration of sodium hydroxide solution during alkaline washing is 5%, and the stirring speed is 300~500 rpm.

[0032] The main purpose of the first acid pickling is to remove the oxide layer on the surface of the copper powder, exposing a fresh copper surface and improving the adhesion and uniformity of the subsequent silver coating. The main purpose of the alkaline pickling is to remove organic impurities and grease from the surface of the copper powder, which can seriously affect the coating quality and uniformity of the silver layer. The purpose of the second acid pickling is to neutralize the residual alkaline solution and further clean the surface of the copper powder, providing an ideal active surface for the subsequent silver coating.

[0033] S2, flake copper powder treatment: The pretreated copper powder is mixed with ethylene glycol ether or propylene glycol ether, and then ground at low speed for 6 hours at 33℃ and 40 rpm in a ball mill. After washing with deionized water and drying, the flake copper powder with a particle size of 5~10μm is screened out using an air classifier. In this step, the ethylene glycol ether includes one or both of ethylene glycol butyl ether or diethylene glycol ethyl ether, and the propylene glycol ether includes one or both of propylene glycol methyl ether and dipropylene glycol methyl ether.

[0034] In this step, the role of alcohol ether is to provide a suitable grinding environment, prevent copper powder oxidation, and promote the formation of a lamellar structure. Low-speed ball milling can control the grinding energy to ensure that the copper powder is shaped into a lamellar shape rather than breaking. Temperature control is used to prevent overheating that could lead to copper powder oxidation or solvent evaporation. Long-term low-speed grinding can ensure sufficient deformation time to form a regular lamellar structure.

[0035] S3, Chemical Displacement: Take a measured amount of glucose, hydrazine hydrate, or ascorbic acid, mix it with a measured amount of deionized water, and stir until homogeneous to form a reducing solution; take a measured amount of silver nitrate, dissolve it in a measured amount of deionized water, and add a measured amount of sodium citrate, stirring until homogeneous to form a silver stock solution; then disperse flake copper powder in a measured amount of ethanol, mix the dispersion with the reducing solution, and stir at 200 rpm for 15 minutes at a constant temperature of 30-35℃ to form a mixed solution with a pH of 9-10; finally, slowly add the silver stock solution dropwise into the mixed solution, maintaining a constant temperature of 28-32℃ during the dropwise process, with a dropwise time of 3.5-4 hours, simultaneously using ultrasonic stirring and mechanical stirring.

[0036] In this step, the weight ratio of glucose, hydrazine hydrate, or ascorbic acid to deionized water is 1:22 to 1:25, and the weight ratio of silver nitrate, citric acid, and deionized water is 1:2:150 to 5:1:120. The pH of the mixture is preferably 10, the ultrasonic stirring frequency is 40 kHz, and the mechanical stirring rate is 400 rpm during the addition of the silver stock solution.

[0037] Ethanol is used as the dispersion medium, glucose, hydrazine hydrate, or ascorbic acid as the reducing agent, and CTAB, CTAC, or SDBS as the dispersant to prevent copper powder agglomeration and ensure uniform silver deposition. Silver nitrate provides the silver source, and sodium citrate acts as a complexing agent to control the silver ion release rate. Slow dropwise addition controls the reaction rate and prevents rapid agglomeration of silver particles. Temperature and pH control maintain suitable reaction kinetics, optimize the reduction reaction environment, and ensure the quality of the silver layer. After this step, a relatively dense silver layer is formed on the copper powder surface, but it cannot completely cover the surface. Therefore, electroplating is required to reinforce and ensure a dense and uniform silver layer covering the copper powder surface.

[0038] S4, cleaning treatment: the product is separated by centrifugation, washed with deionized water and acetone until neutral, and then vacuum dried at 60°C for 5-7 hours to obtain the initial copper powder. S5, Electroplating Enhancement: Prepare an electroplating solution by mixing a certain amount of silver nitrate, sodium thiosulfate, and potassium metabisulfite. Immerse the dried initial copper powder in the electroplating solution and electroplat at a constant temperature of 30-40℃ for 20-30 minutes. After separation, rinsing, and drying, obtain electroplated copper powder. In this step, the concentration of silver nitrate is 30-50 g / L, the concentration of sodium thiosulfate is 80-120 g / L, and the concentration of potassium metabisulfite is 20-30 g / L. During the electroplating process, the current density is 0.5-1.5 A / dm².

[0039] Sodium thiosulfate and potassium metabisulfite can provide a stable electroplating environment. Controlling the current density can regulate the silver deposition rate, and controlling the temperature can maintain the stability of the electroplating solution. This fills the gaps and pores of the silver layer on the copper powder surface during chemical replacement, ensuring a more uniform and dense finish while increasing the silver content of the finished flake silver-coated copper powder.

[0040] S6, Heat Treatment Enhancement: The electroplated copper powder is placed in an argon, helium, or nitrogen protective atmosphere and heat-treated at 700~850℃ for 2~2.5h. After natural cooling, it is oxidized in air at 200~250℃ for 30min, and then reduced in hydrogen at 400~500℃ for 1h. After natural cooling, flake-shaped silver-coated copper powder with a silver content ≥20% is obtained. In this step, the preferred temperature for heat treatment in an inert gas atmosphere is 820℃; the preferred temperature for oxidation in air is 215℃; and the preferred temperature under hydrogen conditions is 485℃.

[0041] Inert atmosphere heat treatment can prevent oxidation, promote recrystallization of the silver layer, form metallurgical bonding through atomic diffusion, and eliminate internal stress; oxidation treatment can form a protective oxide film on the surface of the silver layer, while reduction treatment can eliminate excessive oxidation and restore conductivity, thereby forming a stable surface state and improving high-temperature stability. This allows the silver-coated copper powder prepared by this invention to be used for a long time under extreme high-temperature conditions while slowing down oxidation.

[0042] This invention provides several embodiments and uses commercially available silver-coated copper powder as a comparative example. Resistivity, silver content, oxidation resistance temperature, and tap density were tested. The specific formulations of the embodiments are shown in Table 1, and the results are shown in Table 2.

[0043] Table 1. Ingredient ratios in each embodiment

[0044] Table 2 Test Results of Each Embodiment and Comparative Example

[0045] As shown in Table 2, the preparation formula of Example 2 can produce the best-performing flake silver-coated copper powder with an oxidation resistance temperature of 344°C, which is much higher than that of commercially available ordinary silver-coated copper powder. Therefore, it can be used for a long time under extreme high temperature conditions while slowing down the oxidation process.

[0046] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the content of the present invention under the inventive concept of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing flake-shaped silver-coated copper powder, characterized in that, Includes the following steps: S1, Copper powder pretreatment includes three steps: acid washing, alkaline washing, and acid washing again. During the first acid washing, the copper powder is immersed in a dilute sulfuric acid solution and stirred at room temperature for 10-15 minutes to remove surface oxides. After the first acid washing, the alkaline washing process begins, in which the copper powder is cleaned with sodium hydroxide solution for 5-10 minutes to remove organic impurities. After the alkaline washing, the second acid washing process begins, in which the copper powder is soaked and cleaned again in a dilute sulfuric acid solution for 5-8 minutes. Finally, the copper powder is rinsed with deionized water until it is neutral. S2, flake copper powder treatment: the pretreated copper powder is mixed with ethylene glycol ether or propylene glycol ether, added to a ball mill and ground at low speed at 33℃ and 40rpm for 6h. After washing with deionized water and drying, flake copper powder with a particle size of 5~10μm is screened out using an air classifier. S3, Chemical Displacement: Take a measured amount of glucose, hydrazine hydrate, or ascorbic acid, mix it with a measured amount of deionized water, and stir until homogeneous to form a reducing solution; take a measured amount of silver nitrate, dissolve it in a measured amount of deionized water, and add a measured amount of sodium citrate, stirring until homogeneous to form a silver stock solution; then disperse flake copper powder in a measured amount of ethanol, mix the dispersion with the reducing solution, and stir at 200 rpm for 15 minutes at a constant temperature of 30-35℃ to form a mixed solution with a pH of 9-10; finally, slowly add the silver stock solution dropwise into the mixed solution, maintaining a constant temperature of 28-32℃ during the dropwise addition process, with a dropwise addition time of 3.5-4 hours, simultaneously using ultrasonic stirring and mechanical stirring. S4, cleaning treatment: the product is separated by centrifugation, washed with deionized water and acetone until neutral, and then vacuum dried at 60°C for 5-7 hours to obtain the initial copper powder. S5, electroplating enhancement: a certain amount of silver nitrate, sodium thiosulfate and potassium metabisulfite are mixed to prepare an electroplating solution. The dried initial copper powder is immersed in the electroplating solution and electroplated at a constant temperature of 30~40℃ for 20~30 minutes. After separation, rinsing and drying, electroplated copper powder is obtained. S6, heat treatment enhancement: place the electroplated copper powder in an argon, helium or nitrogen protective atmosphere and heat treat it at 700~850℃ for 2~2.5h. After natural cooling, place it in air at 200~250℃ for oxidation treatment for 30min, and then place it in hydrogen at 400~500℃ for reduction treatment for 1h. After natural cooling, the finished silver-coated copper powder is obtained.

2. The method for preparing flake-shaped silver-coated copper powder according to claim 1, characterized in that: In step S1, the weight ratio of copper powder to ethanol is 1:22, the concentration of dilute sulfuric acid during the first pickling is 5%, the concentration of dilute sulfuric acid during the second pickling is 3%, the concentration of sodium hydroxide solution during alkaline washing is 5%, and the stirring speed is 300~500 rpm.

3. The method for preparing flake-shaped silver-coated copper powder according to claim 1, characterized in that: In step S2, the ethylene glycol ether includes one or both of ethylene glycol butyl ether and diethylene glycol ethyl ether, and the propylene glycol ether includes one or both of propylene glycol methyl ether and dipropylene glycol methyl ether.

4. The method for preparing flake-shaped silver-coated copper powder according to claim 1, characterized in that: In step S3, the weight ratio of glucose, hydrazine hydrate, or ascorbic acid to deionized water is 1:22 to 1:25, and the weight ratio of silver nitrate, sodium citrate, and deionized water is 1:2:150 to 5:1:

120.

5. The method for preparing flake-shaped silver-coated copper powder according to claim 4, characterized in that: The pH value of the mixture is 10, the frequency of the ultrasonic stirring is 40kHz, and the mechanical stirring rate is 400rpm during the addition of the silver stock solution.

6. The method for preparing flake-shaped silver-coated copper powder according to claim 1, characterized in that: In step S5, the concentration of silver nitrate is 30~50 g / L, the concentration of sodium thiosulfate is 80~120 g / L, the concentration of potassium metabisulfite is 20~30 g / L, and the current density during electroplating is 0.5~1.5 A / dm².

7. The method for preparing flake-shaped silver-coated copper powder according to claim 1, characterized in that: In step S6, the temperature is 820°C during inert gas atmosphere heat treatment; 215°C during air oxidation; and 485°C under hydrogen conditions.

8. The method for preparing flake-shaped silver-coated copper powder according to claim 1, characterized in that: The silver content of the finished silver-coated copper powder product prepared in step S6 is ≥20%.

9. A flake-shaped silver-coated copper powder, characterized in that: It is prepared by any one of the methods described in claims 1-8 for preparing flake-shaped silver-coated copper powder.

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