Silver-coated copper powder, preparation method thereof, application and conductive material

Abstract

The application provides a silver-coated copper powder and a preparation method, application and conductive material thereof, and belongs to the technical field of metal powder preparation. The preparation method of the silver-coated copper powder comprises the following steps: roughening treatment is performed on copper powder by using a solution containing alkali and nitrate salt to prepare roughened copper powder; the roughened copper powder is subjected to passivation treatment with a passivation agent to prepare passivated copper powder; and the passivated copper powder is subjected to a first reduction reaction, mixed with a double complexing agent plating solution for reduction chemical silver plating to prepare the silver-coated copper powder. The passivation agent comprises benzotriazole; and the double complexing agent plating solution comprises AgNO3, disodium ethylenediaminetetraacetate and ammonia. The preparation method of the silver-coated copper powder can improve the silver and copper binding capacity of the silver-coated copper powder, form a dense and uniform silver layer, and obtain silver-coated copper powder with high conductivity, stability and mechanical properties.

Description

Technical Field

[0001] This application relates to the field of metal powder preparation technology, and in particular to a silver-coated copper powder, its preparation method, application, and conductive material. Background Technology

[0002] Silver-coated copper powder is a composite metal powder with copper powder as the core and a silver layer on the surface. It combines the low cost and high conductivity of copper with the oxidation resistance and conductivity of silver. The outer silver layer can isolate the inner copper from contact with oxygen and moisture, delay copper oxidation, and maintain conductivity. It has wide applications in electronics, conductive materials, electromagnetic shielding, and catalysis.

[0003] In the preparation process of silver-coated copper powder, uneven or excessively thin external silver layer may lead to localized corrosion. After long-term use, the silver layer may fall off due to mechanical friction or thermal stress. The oxide layer on the surface of copper powder will reduce the adhesion of the silver layer and cause interface voids. Too fast a silver plating rate will cause the silver layer to be loose, with pores, cracks or non-dense crystals, resulting in increased resistivity and seriously affecting the application of silver-coated copper powder.

[0004] Therefore, in order to improve the bonding force between silver and copper, the uniformity and density of the silver layer, and thus improve the conductivity of silver-coated copper powder and ensure its long-term reliability, further improvements are still needed in the preparation process of silver-coated copper powder. Summary of the Invention

[0005] Based on this, the main objective of this application is to provide a silver-coated copper powder, its preparation method, application, and conductive material, so as to improve the bonding force between copper and silver, form a dense and uniform silver layer, improve the conductivity and stability of the silver-coated copper powder, and take into account its excellent mechanical properties.

[0006] The first aspect of this application provides a method for preparing silver-coated copper powder, comprising the following steps:

[0007] Copper powder was roughened by using a solution containing alkali and nitrates to prepare roughened copper powder;

[0008] The roughened copper powder is passivated with a passivating agent to prepare passivated copper powder.

[0009] The passivated copper powder is subjected to a first reduction reaction and then mixed with a double complexing agent plating solution for reduction chemical silver plating to prepare the silver-coated copper powder.

[0010] The passivating agent includes benzotriazole;

[0011] The dual-complexing agent plating solution includes AgNO3, disodium ethylenediaminetetraacetate, and ammonia.

[0012] In some embodiments, the base includes NaOH and / or KOH;

[0013] The nitrates include sodium nitrate and / or potassium nitrate;

[0014] In the solution containing alkali and nitrate, the concentration of alkali is 0.001 mM-0.1 mM, and the concentration of nitrate is 5 mM-10 mM;

[0015] The mass-to-volume ratio of the copper powder to the solution containing alkali and nitrate is (100g-200g):1L.

[0016] In some implementations, the roughening conditions include a temperature of 20°C-30°C and a time of 1 min-30 min.

[0017] In some embodiments, the passivation treatment conditions include a passivating agent concentration of 1 mM to 5 mM.

[0018] In some embodiments, the first reduction reaction step includes: treating the passivated copper powder with a solution containing an alkaline complexing agent and a reducing agent, and a pH adjuster;

[0019] The alkaline complexing agent includes one or more of triethanolamine, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, and ammonia water;

[0020] The reducing agent includes one or more of sodium borohydride, hydrazine hydrate, ascorbic acid, sodium ascorbate, glucose, sodium citrate, citric acid, potassium tartrate, sodium potassium tartrate, and sodium tartrate.

[0021] The pH adjuster includes one or more of tetraethylammonium hydroxide, potassium hydroxide, and sodium hydroxide.

[0022] In some implementations, the conditions for the first reduction reaction include:

[0023] Adjust the pH of the reaction system to 11-12; the temperature to 60℃-80℃; and the time to 10min-60min.

[0024] The mass-to-volume ratio of the passivated copper powder to the solution containing the alkaline complexing agent and the reducing agent is (100g-200g):1L; the concentration of the alkaline complexing agent in the solution containing the alkaline complexing agent and the reducing agent is 0.01M-0.1M, and the concentration of the reducing agent is 0.01M-0.1M.

[0025] In some embodiments, the step of reducing chemical silver plating includes: adding a double complexing agent plating solution at 30℃-60℃ at a rate of 10mL / min-15mL / min for 3min-5min, and then adding the double complexing agent plating solution at a rate of 15mL / min-30mL / min for 30min-60min to perform the reduction chemical silver plating.

[0026] In some embodiments, the molar ratio of AgNO3, disodium ethylenediaminetetraacetate, and ammonia in ammonia water in the dual complexing agent plating solution is (0.5-1):(0.5-1):(0.2-0.5), and the concentration of AgNO3 is 0.1M-0.3M.

[0027] In a second aspect of this application, silver-coated copper powder prepared by the method described in the first aspect is provided.

[0028] The third aspect of this application provides the application of silver-coated copper powder prepared by the method described in the first aspect or the silver-coated copper powder described in the second aspect in conductive materials.

[0029] In a fourth aspect of this application, a conductive material is provided, comprising silver-coated copper powder prepared by the method described in the first aspect or silver-coated copper powder described in the second aspect.

[0030] Compared with traditional technologies, this application has at least the following beneficial effects:

[0031] This application employs an alkaline and nitrate-containing solution to roughen copper, utilizing the oxidation effect of nitrate ions to form a controllable, rough oxide layer on the copper powder surface. Then, a passivating agent including benzotriazole is added to passivate the formed oxide layer, forming a passivation film on the surface. This prevents excessive oxidation and roughening, and also prevents secondary oxidation during subsequent copper powder cleaning. Before reduction electroless silver plating, the passivation film and oxide layer are removed, exposing the roughened surface and multiple active sites of the copper powder. A reduction electroless silver plating solution containing AgNO3, disodium ethylenediaminetetraacetate, and ammonia is used. Using disodium ethylenediaminetetraacetate and ammonia as a composite complexing agent significantly improves the bonding ability of silver and copper in the silver-coated copper powder, forming a dense and uniform silver layer, resulting in highly conductive silver-coated copper powder, and significantly improving the stability and mechanical properties of the silver-coated copper powder. Attached Figure Description

[0032] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. In the drawings:

[0033] Figure 1 Here is a SEM image of the silver-coated copper powder from Example 1;

[0034] Figure 2 Here is a SEM image of the silver-coated copper powder from Example 2;

[0035] Figure 3 Here is a SEM image of the silver-coated copper powder from Example 3;

[0036] Figure 4 SEM image of the silver-coated copper powder in Comparative Example 1;

[0037] Figure 5 SEM image of silver-coated copper powder in Comparative Example 2;

[0038] Figure 6 SEM image of silver-coated copper powder in Comparative Example 3;

[0039] Figure 7 SEM image of silver-coated copper powder in Comparative Example 4;

[0040] Figure 8 SEM image of silver-coated copper powder in Comparative Example 5;

[0041] Figure 9 This is a SEM image of the silver-coated copper powder in Comparative Example 6. Detailed Implementation

[0042] The present application will be further described in detail below with reference to the embodiments and examples. These embodiments and examples are only for illustrating the present application and are not intended to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the disclosure of the present application more thorough and comprehensive. It should also be understood that the present application can be implemented in many different forms and is not limited to the embodiments and examples described herein. Those skilled in the art can make various modifications or alterations without departing from the spirit of the present application, and the equivalent forms obtained also fall within the protection scope of the present application. In addition, numerous specific details are set forth in the following description to provide a fuller understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0043] 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 belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0044] Unless otherwise specified, the solvent for the solutions used in this application is water.

[0045] To address the shortcomings in existing silver-coated copper powder preparation processes, such as the need for further improvement in the bonding strength between silver and copper, the uniformity and density of the silver layer, and the conductivity of the silver-coated copper powder, this application employs a solution containing alkali and nitrates to roughen copper. The oxidation effect of nitrate ions is used to form a controllable nanoscale rough oxide layer on the copper powder surface. This oxide layer is then passivated to form a passivation film on the surface, preventing excessive oxidation and roughening. A first reduction reaction is then used to remove the passivation film and oxide layer, resulting in a roughened surface structure and more active sites on the copper powder surface. When using disodium ethylenediaminetetraacetate and ammonia as composite complexing agents for reduction electroless silver plating, the bonding strength between silver and copper can be significantly improved, forming a dense and uniform silver layer, resulting in highly conductive silver-coated copper powder.

[0046] The first aspect of this application provides a method for preparing silver-coated copper powder, comprising the following steps:

[0047] Copper powder was roughened by using a solution containing alkali and nitrates to prepare roughened copper powder;

[0048] The roughened copper powder is passivated with a passivating agent to prepare passivated copper powder.

[0049] The passivated copper powder is subjected to a first reduction reaction and then mixed with a double complexing agent plating solution for reduction chemical silver plating to prepare the silver-coated copper powder.

[0050] The passivating agent includes benzotriazole;

[0051] The dual-complexing agent plating solution includes AgNO3, disodium ethylenediaminetetraacetate, and ammonia.

[0052] This application uses a solution containing alkali and nitrate to roughen copper. The oxidation of nitrate ions forms a controllable, rough oxide layer on the surface of the copper powder. Then, a passivating agent including benzotriazole is used to passivate the formed oxide layer, forming a passivation film on the surface to avoid excessive oxidation and roughness. The passivation film and oxide layer are then removed by a first reduction reaction, resulting in a roughened copper powder surface with more active sites. When a reduction electroless silver plating solution containing AgNO3, disodium ethylenediaminetetraacetate, and ammonia is used, the bonding ability between silver and copper can be significantly improved, forming a dense and uniform silver layer, resulting in highly conductive silver-coated copper powder.

[0053] In some embodiments, the average particle size of the copper powder is 1-5 μm, which can be 1 μm, 2 μm, 3 μm, 4 μm or 5 μm.

[0054] Copper powder is roughened using an aqueous solution containing alkali and nitrate. The nitrate acts as an oxidizing agent; under alkaline conditions, nitrate ions (NO3) are released. - ) is reduced to nitrite (NO2)- At the same time, electrons are released, which promotes the oxidation of copper to form copper hydroxide and cuprous oxide, and further to form copper oxide. A controllable and rough oxide layer is formed on the copper surface. The rough surface of the oxide layer not only increases the specific surface area, but also provides more active sites for silver plating on the copper powder surface after the oxide layer is removed.

[0055] In some embodiments, the base includes NaOH and / or KOH; the nitrate includes sodium nitrate and / or potassium nitrate;

[0056] In the solution containing alkali and nitrate, the concentration of alkali is 0.001 mM to 0.1 mM, which can be 0.001 mM, 0.002 mM, 0.003 mM, 0.004 mM, 0.005 mM, 0.006 mM, 0.007 mM, 0.008 mM, 0.009 mM, 0.01 mM, 0.02 mM, 0.03 mM, 0.04 mM, 0.05 mM, 0.06 mM, 0.07 mM, 0.08 mM, 0.08 mM, or 0.1 mM, and the concentration of nitrate is 5 mM to 10 mM, which can be 5 mM, 6 mM, 7 mM, 8 mM, 9 mM, or 10 mM.

[0057] The mass-to-volume ratio of the copper powder to the solution containing alkali and nitrate is (100g-200g):1L, which can be 100g:1L, 120g:1L, 150g:1L, 180g:1L or 200g:1L.

[0058] In some embodiments, the roughening treatment conditions include: a temperature of 20℃-30℃ (e.g., 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, or 30℃), and a time of 1min-30min (e.g., 1min, 2min, 3min, 4min, 5min, 10min, 15min, 20min, 25min, or 30min). Appropriately increasing the roughening temperature can accelerate the roughening rate. Controlling the roughening time is crucial to avoid excessive corrosion of the copper surface due to prolonged treatment.

[0059] This application uses a roughening process to form a uniform, controllable, and rough oxide layer on the copper surface. To prevent excessive oxidation, a passivating agent is used for passivation treatment to form a dense passivation film, preventing excessive roughening and secondary oxidation of the copper powder surface during subsequent copper powder cleaning processes.

[0060] In some implementations, the roughening process employs mechanical stirring or ultrasonic-assisted stirring to ensure a uniform reaction.

[0061] In some embodiments, the roughening process employs mechanical stirring, and the conditions for mechanical stirring include a rotation speed of 300 r / min to 800 r / min, which can be 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min or 800 r / min.

[0062] In some embodiments, the passivation treatment conditions include: the concentration of the passivating agent is 1mM-5mM, which can be 1mM, 2mM, 3mM, 4mM or 5mM.

[0063] In some implementations, the passivation process employs mechanical stirring or ultrasonic-assisted stirring to ensure a uniform reaction.

[0064] In some embodiments, the passivation treatment employs mechanical stirring, and the conditions for mechanical stirring include a rotation speed of 300 r / min to 800 r / min, which can be 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min or 800 r / min.

[0065] This application involves passivating roughened copper powder with a passivating agent to stop the roughening process. The passivating agent BTA is adsorbed on the surface of the roughened copper powder to form a passivation layer with anti-oxidation properties, preventing further oxidation of the copper powder, thus obtaining passivated copper powder.

[0066] In some embodiments, after passivation, a cleaning step is also included, which includes rinsing the passivated copper powder with pure water multiple times until the pH is neutral.

[0067] In some embodiments, the first reduction reaction step includes: treating the passivated copper powder with a solution containing an alkaline complexing agent and a reducing agent, and a pH adjuster;

[0068] The alkaline complexing agent includes one or more of triethanolamine (ETA), disodium ethylenediaminetetraacetate (EDTA-2Na), tetrasodium ethylenediaminetetraacetate (EDTA-4Na), and ammonia water;

[0069] The reducing agent includes one or more of sodium borohydride, hydrazine hydrate, ascorbic acid, sodium ascorbate, glucose, sodium citrate, citric acid, potassium tartrate, sodium potassium tartrate, and sodium tartrate.

[0070] The pH adjuster includes one or more of tetraethylammonium hydroxide, potassium hydroxide, and sodium hydroxide.

[0071] In some embodiments, the conditions for the first reduction reaction include: adjusting the pH of the reaction system to 11-12; the temperature to 60°C-80°C, which can be 60°C, 65°C, 70°C, 75°C or 80°C; and the time to 10 min-60 min, which can be 10 min, 20 min, 30 min, 40 min, 50 min or 60 min.

[0072] The mass-to-volume ratio of the passivated copper powder to the solution containing the alkaline complexing agent and reducing agent is (100g-200g):1L, which can be 100g:1L, 120:1L, 150:1L, 180:1L, or 200:1L; the concentration of the alkaline complexing agent in the solution containing the alkaline complexing agent and reducing agent is 0.01M-0.1M, which can be 0.01M, 0.02M, 0.03M, 0.04M, 0.05M, 0.06M, 0.07M, 0.08M, 0.09M, or 0.1M; the concentration of the reducing agent is 0.01M-0.1M, which can be 0.01M, 0.02M, 0.03M, 0.04M, 0.05M, 0.06M, 0.07M, 0.08M, 0.09M, or 0.1M.

[0073] This application employs an aqueous solution containing an alkaline complexing agent and a reducing agent, along with a pH adjuster, to conduct a first reduction reaction under alkaline and reducing conditions. This process depassivates the copper powder after passivation treatment and removes the surface oxide layer. Under high-temperature alkaline conditions, the (-NH-) groups within BTA are deprotonated to form BTA. - BTA - It is easier to desorb from the copper surface into the solution, and at the same time, the alkaline complexing agent competes with BTA for adsorption on the copper surface, accelerating the desorption of BTA from the copper surface.

[0074] Under these high-temperature conditions, the adsorbates on the copper surface tend to desorb, and the oxides in the oxide layer of the copper powder are easily reduced by the reducing agent, thus inhibiting subsequent oxidation.

[0075] This application achieves the removal of passivating agents and oxide layers from the surface of copper powder by controlling parameters such as pH value, alkaline complexing agent concentration, reducing agent concentration, reduction temperature, and reaction time. This exposes the roughened surface of the copper powder, providing more active sites and improving the adhesion between copper and the subsequent silver coating layer. Simultaneously, the first reduction reaction also provides a reducing environment for the reduction of electroless silver plating.

[0076] In some embodiments, the first reduction reaction step includes: treating the passivated copper powder with a solution containing an alkaline complexing agent and a reducing agent, and a pH adjuster; wherein the alkaline complexing agent is triethanolamine, and the pH adjuster includes potassium hydroxide and / or sodium hydroxide; the conditions for the first reduction reaction include: the concentration of triethanolamine is 0.01M-0.1M, which can be 0.01M, 0.02M, 0.03M, 0.04M, 0.05M, 0.06M, 0.07M, 0.08M, 0.09M, or 0.1M.

[0077] In some embodiments, the first reduction reaction step includes: treating the passivated copper powder with a solution containing an alkaline complexing agent and a reducing agent, and a pH adjuster; the alkaline complexing agent is EDTA-2Na, and the pH adjuster includes potassium hydroxide and / or sodium hydroxide; the conditions for the first reduction reaction include: the concentration of EDTA-2Na is 0.01M-0.1M, which can be 0.01M, 0.02M, 0.03M, 0.04M, 0.05M, 0.06M, 0.07M, 0.08M, 0.09M, or 0.1M.

[0078] In some embodiments, the first reduction reaction step includes: treating the passivated copper powder with a solution containing an alkaline complexing agent and a reducing agent, and a pH adjuster; the alkaline complexing agent is EDTA-4Na, and the pH adjuster includes potassium hydroxide and / or sodium hydroxide; the conditions for the first reduction reaction include: the concentration of EDTA-4Na is 0.01M-0.1M, which can be 0.01M, 0.02M, 0.03M, 0.04M, 0.05M, 0.06M, 0.07M, 0.08M, 0.09M, or 0.1M. The pH value is adjusted using a pH adjuster.

[0079] In some embodiments, the first reduction reaction step includes: treating the passivated copper powder with a solution containing an alkaline complexing agent and a reducing agent, and a pH adjuster; the alkaline complexing agent is ammonia; the pH adjuster includes potassium hydroxide and / or sodium hydroxide; the conditions for the first reduction reaction include: the concentration of ammonia is 0.01M-0.1M, which can be 0.01M, 0.02M, 0.03M, 0.04M, 0.05M, 0.06M, 0.07M, 0.08M, 0.09M, or 0.1M. The first reduction reaction can achieve depassivation and removal of the surface oxide layer from the passivated copper powder.

[0080] In some implementations, the first reduction reaction is carried out by mechanical stirring or ultrasonic-assisted stirring to ensure uniform reaction.

[0081] In some embodiments, the first reduction reaction is carried out by mechanical stirring, and the conditions for mechanical stirring include a rotation speed of 300 r / min to 800 r / min, which can be 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min or 800 r / min.

[0082] After removing the passivation layer and oxide layer on the surface of the copper powder through the first reduction reaction, a double complexing agent plating solution is added to the system to perform reduction chemical silver plating.

[0083] In some embodiments, the step of reducing chemical silver plating includes: adding a double complexing agent plating solution at 30℃-60℃ at a rate of 10mL / min-15mL / min for 3min-5min, and then adding the double complexing agent plating solution at a rate of 15mL / min-30mL / min for 30min-60min to perform the reduction chemical silver plating.

[0084] In some embodiments, the molar ratio of AgNO3, disodium ethylenediaminetetraacetate, and ammonia in the ammonia solution is (0.5-1):(0.5-1):(0.2-0.5), which can be 1:1:0.2, 1:1:0.3, 1:1:0.4, or 1:1:0.5. The concentration of AgNO3 is 0.1M-0.3M, which can be 0.1M, 0.2M, or 0.3M. By using disodium ethylenediaminetetraacetate and ammonia as composite complexing agents, the conductivity, stability, and mechanical properties of silver-coated copper powder can be significantly improved.

[0085] In some embodiments, the conditions for reducing chemical silver plating include a temperature of 30°C-60°C, which can be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C.

[0086] In some implementations, the reduction of electroless silver plating is achieved by mechanical stirring or ultrasonic-assisted stirring to ensure a uniform reaction.

[0087] In some embodiments, the reduction of electroless silver plating is performed by mechanical stirring. The conditions for mechanical stirring include a rotation speed of 100-500 r / min, which can be 100 r / min, 200 r / min, 300 r / min, 400 r / min or 500 r / min.

[0088] In the step of reducing electroless silver plating, this application controls the rate and time of adding the double complexing agent plating solution to the system after the first reduction reaction. In the early stage of the reaction, the copper powder surface has a roughened surface structure. By controlling and reducing the reaction rate of reducing electroless silver plating, the uniformity of the plating layer is ensured. Subsequently, by increasing the rate of adding the double complexing agent plating solution, the reaction rate and deposition rate are stabilized, so that the silver layer coated on the copper powder surface is uniform and dense.

[0089] In a second aspect of this application, silver-coated copper powder prepared by the preparation method described in the first aspect is provided.

[0090] In the silver-coated copper powder prepared in this application, the silver layer and copper are tightly bonded, and the silver layer is dense and uniform.

[0091] The third aspect of this application provides the application of silver-coated copper powder prepared by the method described in the first aspect or the silver-coated copper powder described in the second aspect in conductive materials.

[0092] This application utilizes silver-coated copper powder, which has a tight bond between the silver layer and copper and a dense and uniform silver layer, in conductive materials, resulting in excellent conductivity.

[0093] In a fourth aspect of this application, a conductive material is provided, comprising silver-coated copper powder prepared by the method described in the first aspect or silver-coated copper powder described in the second aspect.

[0094] The conductive material of this application uses silver-coated copper powder with a tight bond between silver and copper and a dense and uniform silver layer, which can improve its conductivity.

[0095] The embodiments of this application will be described in detail below with reference to examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this application, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0096] Example 1

[0097] The preparation method of silver-coated copper powder is as follows:

[0098] (1) Take 100g of copper powder (average particle size 3μm), add it to 1L of aqueous solution containing NaOH (0.008mM) and NaNO3 (10mM), and roughen it at 20℃. Stir at 500r / min for 10min to prepare the roughened copper powder.

[0099] (2) Then BTA (benzotriazole) was added to the roughened copper powder for passivation treatment. The concentration of BTA in the reaction system was 2mM. After stirring at 500r / min for 10min, the mixture was filtered and washed until the washing water was neutral to obtain the passivated copper powder.

[0100] (3) Add the passivated copper powder to 1L of aqueous solution containing TEA (triethanolamine, 0.1M) and glucose (0.08M), add NaOH, adjust the pH to 11.5, stir at 500r / min for 40min to carry out the first reduction reaction. The temperature of the first reduction reaction is 70℃ to obtain copper powder solution with BTA desorption and deoxidation.

[0101] (4) Mix 0.6M disodium ethylenediaminetetraacetate solution, 0.3M ammonia solution and 0.6M silver nitrate solution in a volume ratio of 1:1:1 and stir thoroughly to prepare a double complexing agent plating solution containing 0.2M silver nitrate; wherein the molar ratio of silver nitrate, disodium ethylenediaminetetraacetate and ammonia in ammonia solution is 1:1:0.5;

[0102] The double complexing agent plating solution was added dropwise into the copper powder solution obtained in step (3) and stirred to carry out reduction chemical silver plating. Specifically, at 45°C, the double complexing agent plating solution was added dropwise into the copper powder solution at a rate of 15 mL / min and stirred at a speed of 300 r / min. After adding for 5 min, it was added dropwise again at a rate of 25 mL / min for 30 min to prepare silver-coated copper powder.

[0103] Example 2

[0104] The preparation method of silver-coated copper powder is as follows:

[0105] (1) Take 100g of copper powder (average particle size 3μm), add it to 1L of aqueous solution containing NaOH (0.008mM) and NaNO3 (10mM), and roughen it at 20℃. Stir at 500r / min for 10min to prepare the roughened copper powder.

[0106] (2) Then BTA is added to the roughened copper powder for passivation treatment. The concentration of BTA in the reaction system is 2mM. After stirring at 500r / min for 10min, the mixture is filtered and washed until the washing water is neutral to obtain the passivated copper powder.

[0107] (3) Add the passivated copper powder to 1L of an aqueous solution containing EDTA-2Na (0.05M) and sodium ascorbate (0.02M), add NaOH, adjust the pH to 11.5, stir at 500r / min for 30min to carry out the first reduction reaction. The temperature of the first reduction reaction is 60℃ to obtain a copper powder solution with BTA desorption and deoxidation.

[0108] (4) Mix 0.6M disodium ethylenediaminetetraacetate solution, 0.3M ammonia solution and 0.6M silver nitrate solution in a volume ratio of 1:1:1 and stir thoroughly to prepare a double complexing agent plating solution containing 0.2M silver nitrate; wherein the molar ratio of silver nitrate, disodium ethylenediaminetetraacetate and ammonia in ammonia solution is 1:1:0.5;

[0109] The double complexing agent plating solution was added dropwise into the copper powder solution obtained in step (3) and stirred to carry out reduction chemical silver plating. Specifically, at 45°C, the double complexing agent plating solution was added dropwise into the copper powder solution at a rate of 15 mL / min and stirring was started. The stirring speed was 300 r / min. After adding for 5 min, the solution was added dropwise again at a rate of 25 mL / min for 30 min to prepare silver-coated copper powder.

[0110] Example 3

[0111] The preparation method of silver-coated copper powder is as follows:

[0112] (1) Take 100g of copper powder (average particle size 3μm), add it to 1L of aqueous solution containing NaOH (0.008mM) and NaNO3 (10Mm), and roughen it at 20℃. Stir at 500r / min for 10min to prepare the roughened copper powder.

[0113] (2) Then BTA (benzotriazole) was added to the roughened copper powder for passivation treatment. The concentration of BTA in the reaction system was 2mM. After stirring at 500r / min for 10min, the mixture was filtered and washed until the washing water was neutral to obtain the passivated copper powder.

[0114] (3) Add the passivated copper powder to 1L of an aqueous solution containing EDTA-4Na (0.04M) and potassium sodium tartrate (0.1M), add NaOH, adjust the pH to 11.5, stir at 500r / min for 60min to carry out the first reduction reaction. The temperature of the first reduction reaction is 80℃ to obtain a copper powder solution with BTA desorption and deoxidation.

[0115] (4) Mix 0.6M disodium ethylenediaminetetraacetate solution, 0.3M ammonia solution and 0.6M silver nitrate solution in a volume ratio of 1:1:1 and stir thoroughly to prepare a double complexing agent plating solution containing 0.2M silver nitrate; wherein the molar ratio of silver nitrate, disodium ethylenediaminetetraacetate and ammonia in ammonia solution is 1:1:0.5;

[0116] The double complexing agent plating solution was added dropwise into the copper powder solution obtained in step (3) and stirred to carry out reduction chemical silver plating. Specifically, at 45°C, the double complexing agent plating solution was added dropwise into the copper powder solution at a rate of 15 mL / min and stirring was started. The stirring speed was 300 r / min. After adding for 5 min, it was added dropwise again at a rate of 25 mL / min for 30 min to prepare silver-coated copper powder.

[0117] Comparative Example 1

[0118] The difference between Comparative Example 1 and Example 1 is that "aqueous solution containing NaOH (0.08mM) and NaNO3 (10mM)" is replaced with "aqueous solution containing H2SO4 (0.1M)";

[0119] Silver-coated copper powder was prepared according to the method in Example 1.

[0120] Comparative Example 2

[0121] The difference between Comparative Example 2 and Example 1 is that "aqueous solution containing NaOH (0.08mM) and NaNO3 (10mM)" is replaced with "aqueous solution containing NaOH (0.08mM) and NaClO2 (10mM)";

[0122] Silver-coated copper powder was prepared according to the method in Example 1.

[0123] Comparative Example 3

[0124] The difference between Comparative Example 3 and Example 1 is that the phrase "mixing 0.6M disodium ethylenediaminetetraacetate solution, 0.3M ammonia solution, and 0.6M silver nitrate solution in a volume ratio of 1:1:1 and stirring thoroughly to prepare a double complexing agent plating solution containing 0.2M silver nitrate; wherein the molar ratio of silver nitrate, disodium ethylenediaminetetraacetate, and ammonia in the ammonia solution is 1:1:0.5" is replaced with "mixing 0.6M disodium ethylenediaminetetraacetate solution and 0.4M silver nitrate solution in a volume ratio of 1:1 and stirring thoroughly to prepare a complexing agent plating solution containing 0.2M silver nitrate; wherein the molar ratio of silver nitrate and disodium ethylenediaminetetraacetate is 1:1.5".

[0125] Silver-coated copper powder was prepared according to the method in Example 1.

[0126] Comparative Example 4

[0127] The difference between Comparative Example 4 and Example 1 is that the phrase "mixing equal volumes of 0.6M disodium ethylenediaminetetraacetate solution, 0.3M ammonia solution, and 0.6M silver nitrate solution in a volume ratio of 1:1:1 and stirring thoroughly to prepare a double complexing agent plating solution containing 0.2M silver nitrate; wherein the molar ratio of silver nitrate, disodium ethylenediaminetetraacetate, and ammonia in ammonia solution is 1:1:0.5" is replaced with "mixing 0.6M ammonia solution and 0.4M silver nitrate solution in a volume ratio of 1:1 and stirring thoroughly to prepare a complexing agent plating solution containing 0.2M silver nitrate; wherein the molar ratio of silver nitrate and ammonia in ammonia solution is 1:1.5".

[0128] Silver-coated copper powder was prepared according to the method in Example 1.

[0129] Comparative Example 5

[0130] The difference between Comparative Example 5 and Example 1 is that no passivation treatment was performed;

[0131] Silver-coated copper powder was prepared according to the method in Example 1.

[0132] Comparative Example 6

[0133] The difference between Comparative Example 6 and Example 1 is that “BTA” is replaced with “PVP (polyvinylpyrrolidone, average molecular weight 55,000)”.

[0134] Silver-coated copper powder was prepared according to the method in Example 1.

[0135] Experimental Example 1

[0136] (1) Observe the coating of silver-coated copper powder in Examples 1-3 and Comparative Examples 1-6.

[0137] Sample preparation: The silver-coated copper powders of Examples 1-3 and Comparative Examples 1-6 were fixed on the sample stage, and the silver-coated copper powder particles were sliced ​​using focused ion beam (FIB) and the cross-sectional shell-core structure of the silver-coated copper particles was observed using SEM.

[0138] The core-shell structures of the silver-coated copper powders in Examples 1-3 and Comparative Examples 1-6 are as follows: Figures 1-9 As shown, it can be seen that: Figures 1-3 In the silver-coated copper powder of Examples 1-3, the silver layer and the copper core are tightly bonded without gaps, and the silver layer is evenly coated; while Figures 4-9 In the silver-coated copper powders of Comparative Examples 1-6, there were many gaps between the coated silver layer and the copper core, and the uniformity and tightness of the silver coating were reduced. This indicates that, compared with Comparative Examples 1-6, in the silver-coated copper powders of Examples 1-3 of this application, the reactive sites are fully exposed, the silver coating is uniform, and the slightly rough surface makes the silver-copper layer bond more tightly.

[0139] (2) The coating density, silver-copper bonding force and resistivity of the silver-coated copper powders in Examples 1-3 and Comparative Examples 1-6 were determined, and the results are shown in Table 1.

[0140] The density of silver-coated copper powder coating: 1g of silver-coated copper powder was soaked in 5mL of 99% glacial acetic acid solution, and the time (min) for patina to begin to dissolve was observed. The better the silver coating, the longer the time for patina to begin to dissolve.

[0141] Methods for determining resistivity and tensile strength: By mass, 5 parts of bisphenol F epoxy resin, 0.5 parts of 2-ethyl-4-methylimidazolium, 1 part of polyamide, 1.5 parts of butyl carbitol acetate, and 2 parts of tripropylene glycol monomethyl ether were thoroughly mixed and added to 90 parts of silver-coated copper powder. The mixture was then homogenized, ground in a three-roll mill, and vacuum-sealed to obtain silver-coated copper paste. The silver-coated copper paste was printed onto a solar blue film with a pattern width of 300 μm and a length of 2 cm. After curing at 200 °C for 20 min, the cured grid lines were obtained. The line shape was measured, and the volume resistivity (μΩ·cm) was obtained according to the formula: volume resistivity = resistance × width × height / length. A metal tab was attached to the end of the grid lines, and the tensile strength was tested on a universal testing machine with the clamps vertically fixed. The peel force curve was recorded, and the average peel force (N) was extracted. The results are shown in Table 1.

[0142] Table 1. Performance of silver-coated copper powder in Examples 1-3 and Comparative Examples 1-6

[0143]

[0144] The results in Table 1 show that the resistivity of the silver-coated copper powder in Examples 1-3 of this application is 19-20 μΩ·cm, the time for the patina to begin dissolving is 11-17 min, and the pull-out force is 1.6-1.7 N. Compared with Comparative Examples 1-6, the silver-coated copper powder in Examples 1-3 has excellent conductivity, stability, and mechanical properties.

[0145] Compared with Comparative Example 1, which used an aqueous solution containing H2SO4 (0.1M), Example 1 used an aqueous solution containing NaOH (0.08mM) and NaNO3 (10mM) to roughen the copper powder. The resistivity of the silver-coated copper powder decreased by 58%, the time for patina to begin dissolving decreased by 14 times, and the pull-out force increased by 78%. This shows that compared with using more H2SO4 for roughening, the use of NaOH and NaNO3 in this application to roughen the copper powder can significantly improve the conductivity, stability, and mechanical properties of the silver-coated copper powder.

[0146] Compared with Comparative Example 2, which used a solution containing NaClO2 and NaOH for roughening treatment, Example 1 used a solution containing NaNO3 and NaOH for roughening treatment. The resistivity of the silver-coated copper powder was reduced by 88%, the time for patina to begin dissolving was reduced by 14 times, and the pull-out force was increased by 129%. This shows that, compared with the roughening treatment using a solution containing NaClO2 and NaOH, the roughening treatment of copper powder using a solution containing NaOH and NaNO3 in this application can significantly improve the conductivity, stability, and mechanical properties of the silver-coated copper powder.

[0147] Compared with the complexing agent plating solutions of Comparative Examples 3-4, which only used disodium ethylenediaminetetraacetate or ammonia, Example 1 used a dual complexing agent plating solution containing disodium ethylenediaminetetraacetate and ammonia. The resistivity of the silver-coated copper powder was reduced by 49-56%, the time for the patina to begin dissolving was reduced by 2-4 times, and the pull-out force was increased by 0.4N-0.6N. This shows that compared with the complexing agent plating solutions that only used disodium ethylenediaminetetraacetate or ammonia, the combination of disodium ethylenediaminetetraacetate and ammonia in this application can significantly improve the conductivity and stability of the silver-coated copper powder, while also taking into account excellent mechanical properties.

[0148] Compared with Comparative Example 5 without passivation treatment, Example 1, after passivation treatment with BTA, showed a 79% reduction in resistivity of its silver-coated copper powder, a 14-fold reduction in the time for patina to begin dissolving, and a 78% increase in pull-out force. This indicates that, compared with no passivation treatment, the use of BTA for passivation treatment in this application can significantly improve the conductivity, stability, and mechanical properties of the silver-coated copper powder.

[0149] Compared with Comparative Example 6, which uses PVP as a passivating agent, Example 1 uses BTA as a passivating agent. The resistivity of its silver-coated copper powder is reduced by 71%, the time for patina to begin dissolving is reduced by 4 times, and the pull-out force is increased by 60%. This shows that, compared with other passivating agents (PVP), the use of BTA as a passivating agent in this application can significantly improve the conductivity, stability and mechanical properties of silver-coated copper powder.

[0150] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0151] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for producing silver-coated copper powder, characterized by, The method comprises the following steps: The copper powder is roughened by a solution containing alkali and nitrate, to prepare roughened copper powder; The roughened copper powder is passivated by a passivation agent, to prepare passivated copper powder; The passivated copper powder is reduced by a first reduction reaction, and then mixed with a double complex plating solution to perform reduction chemical silver plating, to prepare the silver-coated copper powder; The alkali includes NaOH; and the nitrate includes sodium nitrate. The concentration of the alkali in the solution containing alkali and nitrate is 0.001 mM-0.1 mM, and the concentration of the nitrate is 5 mM-10 mM. The mass-volume ratio of the copper powder to the solution containing alkali and nitrate is (100 g-200 g):1 L. The passivation agent includes benzotriazole. The double complex plating solution includes AgNO3, disodium ethylenediaminetetraacetate and ammonia.

2. The method of claim 1, wherein the silver-coated copper powder is prepared by the steps of: The roughening conditions include a temperature of 20℃-30℃ and a time of 1 min-30 min.

3. The method of claim 1, wherein the silver-coated copper powder is prepared by the steps of: The passivation conditions include a concentration of the passivation agent of 1 mM-5 mM.

4. The method of claim 1, wherein the silver-coated copper powder is prepared by the steps of: The first reduction reaction comprises treating the passivated copper powder by a solution containing an alkaline complexing agent and a reducing agent, and a pH adjuster; The alkaline complexing agent includes one or more of triethanolamine, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate and ammonia. The reducing agent includes one or more of sodium borohydride, hydrazine hydrate, ascorbic acid, sodium ascorbate, glucose, sodium citrate, citric acid, potassium tartrate, potassium sodium tartrate and sodium tartrate. The pH adjuster includes one or more of tetraethylammonium hydroxide, potassium hydroxide and sodium hydroxide.

5. The method of claim 4, wherein the silver-coated copper powder is prepared by the steps of: The first reduction reaction conditions include: The pH value of the reaction system is adjusted to 11-12, the temperature is 60℃-80℃, and the time is 10 min-60 min. The mass-volume ratio of the passivated copper powder to the solution containing an alkaline complexing agent and a reducing agent is (100 g-200 g):1 L. The concentration of the alkaline complexing agent in the solution containing an alkaline complexing agent and a reducing agent is 0.01 M-0.1 M, and the concentration of the reducing agent is 0.01 M-0.1 M.

6. The method of claim 1, wherein the silver-coated copper powder is prepared by the steps of: The reduction chemical silver plating comprises adding the double complex plating solution at a speed of 10 mL / min-15 mL / min for 3 min-5 min, and then adding the double complex plating solution at a speed of 15 mL / min-30 mL / min for 30 min-60 min, at 30℃-60℃, to perform reduction chemical silver plating.

7. The method of claim 1, wherein the silver-coated copper powder is prepared by the steps of: In the double complex plating solution, the molar ratio of AgNO3, disodium ethylenediaminetetraacetate and ammonia is (0.5-1):(0.5-1):(0.2-0.5), and the concentration of AgNO3 is 0.1 M-0.3 M.

8. The silver-coated copper powder prepared by the method of any one of claims 1-7.

9. The silver-coated copper powder prepared by the method of any one of claims 1-7 or the silver-coated copper powder of claim 8, for use in conductive materials.

10. An electrically conductive material, characterized in that, The silver-coated copper powder prepared by the method of any one of claims 1-7 or the silver-coated copper powder of claim 8.

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