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

Abstract

The invention provides silver-coated copper powder, a preparation method and application thereof and a conductive material, and belongs to the technical field of metal powder preparation. The preparation method of the silver-coated copper powder comprises the following steps that a solution containing alkali and nitrate is adopted for conducting roughening treatment on copper powder, and the copper powder subjected to roughening treatment is prepared; the roughened copper powder and a passivating agent are subjected to passivating treatment, and the copper powder subjected to passivating treatment is prepared; after the passivated copper powder is subjected to a first reduction reaction, the passivated copper powder is mixed with a double-complexing-agent plating solution for reduction chemical silver plating, and the silver-coated copper powder is prepared; the passivating agent is prepared from benzotriazole; the double-complexing-agent plating solution comprises AgNO3, ethylene diamine tetraacetic acid disodium salt and ammonia water. By the adoption of the preparation method of the silver-coated copper powder, the combining capacity of silver and copper of the silver-coated copper powder can be improved, a compact and uniform silver layer is formed, and the silver-coated copper powder high in conductivity, stability and mechanical property is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal powder preparation, in particular to a silver-coated copper powder, a preparation method, application and conductive material thereof. BACKGROUND

[0002] The silver-coated copper powder is a kind of composite metal powder, taking copper powder as the core and wrapping a silver layer on the surface, which 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 contacting oxygen and moisture, delay the oxidation of copper and maintain the conductivity, and has wide application in the fields of electronics, conductive materials, electromagnetic shielding and catalysis.

[0003] In the preparation process of the silver-coated copper powder, uneven or too thin external silver layer may cause local corrosion, and the silver layer may fall off due to mechanical friction or thermal stress after long-term use; the oxidation layer on the surface of the copper powder will reduce the adhesion of the silver layer, resulting in interface voids; and too fast silver plating rate will cause loose silver layer with pores, cracks or non-dense crystals, resulting in increased resistivity, which seriously affects the application of the 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 to improve the conductivity of the silver-coated copper powder and ensure the reliability of long-term use, the preparation process of the silver-coated copper powder still needs to be further improved. SUMMARY

[0005] Therefore, the main purpose of the present application is to provide a silver-coated copper powder, a preparation method, application and conductive material thereof, 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 excellent mechanical properties.

[0006] In a first aspect, the present application provides a preparation method of a silver-coated copper powder, comprising the following steps:

[0007] Coarsening the copper powder by using a solution containing alkali and nitrate salt to prepare the coarsened copper powder;

[0008] Passivating the coarsened copper powder by using a passivation agent to prepare the passivated copper powder;

[0009] After the first reduction reaction, mixing the passivated copper powder with a double complexing agent plating solution for reduction chemical silver plating to prepare the silver-coated copper powder;

[0010] The passivation agent comprises benzotriazole;

[0011] The double complexing agent plating solution comprises AgNO3, disodium ethylenediaminetetraacetate and ammonia water.

[0012] In some embodiments, the alkali comprises NaOH and / or KOH;

[0013] The nitrate salt comprises sodium nitrate and / or potassium nitrate;

[0014] The concentration of the alkali in the alkali and nitrate salt-containing solution is 0.001 mM-0.1 mM, and the concentration of the nitrate salt is 5 mM-10 mM.

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

[0016] In some embodiments, the conditions of the roughening treatment comprise a temperature of 20℃-30℃ and a time of 1 min-30 min.

[0017] In some embodiments, the conditions of the passivation treatment comprise a concentration of the passivation agent of 1 mM-5 mM.

[0018] In some embodiments, the step of the first reduction reaction comprises treating the passivated copper powder with a solution containing an alkali complexing agent and a reducing agent, and a pH adjuster.

[0019] The alkali complexing agent comprises one or more of triethanolamine, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, and aqueous ammonia.

[0020] The reducing agent comprises 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.

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

[0022] In some embodiments, the conditions of the first reduction reaction comprise:

[0023] 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.

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

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

[0026] In some embodiments, the molar ratio of AgNO3, disodium ethylenediaminetetraacetate and ammonia in the double 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, the application provides the silver-coated copper powder prepared by the method for preparing silver-coated copper powder according to the first aspect.

[0028] In a third aspect, the application provides the silver-coated copper powder prepared by the method for preparing silver-coated copper powder according to the first aspect or the silver-coated copper powder according to the second aspect for use in conductive materials.

[0029] In a fourth aspect, the application provides a conductive material comprising the silver-coated copper powder prepared by the method for preparing silver-coated copper powder according to the first aspect or the silver-coated copper powder according to the second aspect.

[0030] Compared with the conventional technology, the application has at least the following beneficial effects:

[0031] In the application, the copper is roughened by using a solution containing alkali and nitrate, and the oxidation of nitrate ions is used to form a controllable and rough oxide layer on the surface of the copper powder. Then, a passivation agent containing benzotriazole is added to passivate the formed oxide layer and form a passivation film on the surface, so as to avoid excessive oxidation and roughness and prevent secondary oxidation in the subsequent cleaning process of the copper powder. Before the reduction chemical silver plating, the passivation film and the oxide layer are removed to expose the rough surface and the multiple active sites of the roughened copper powder. The double complexing agent plating solution containing AgNO3, disodium ethylenediaminetetraacetate and ammonia is used for the reduction chemical silver plating. The use of disodium ethylenediaminetetraacetate and ammonia as the composite complexing agent can significantly improve the binding capacity of silver and copper in the silver-coated copper powder, form a dense and uniform silver layer, obtain a silver-coated copper powder with high conductivity, and significantly improve the stability and mechanical properties of the silver-coated copper powder. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to better describe and illustrate the embodiments or examples provided by the application, one or more drawings can be referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any one of the disclosed applications, the presently described embodiments or examples, and the best mode presently understood of these applications. In the drawings:

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

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

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

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

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

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

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

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

[0041] Figure 9 SEM image of silver-coated copper powder of Comparative Example 6. DETAILED DESCRIPTION

[0042] The present application will be further described with reference to the following embodiments and examples, which are intended to be purely exemplary of the present application and are not intended to limit the present application in any way. The purpose of these embodiments and examples is to provide a more thorough and complete understanding of the present application as well as to provide examples of the application to the skilled in the art. Further, in the following description of the embodiments various specific details are set forth in order to provide a thorough understanding of the present application. However, persons of ordinary skill in the art will readily appreciate that the application can be practiced without one or more of the specific details or with other methods, materials, etc. In other instances, well known structures, materials, and techniques have not been shown or described in order to avoid obscuring aspects of the application.

[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 in the description herein is for describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0044] The solvent of the solution in the present application is water, unless otherwise specified.

[0045] In view of the problems that the binding force between silver and copper, the uniformity and compactness of silver layer, and the conductivity of silver-coated copper powder still need to be further improved in the existing preparation process of silver-coated copper powder, the copper is roughened by using a solution containing alkali and nitrate, an oxidation layer of controllable nanoscale roughness is formed on the surface of copper powder by using the oxidation effect of nitrate ions, then the formed oxidation layer is passivated to form a passivation film on the surface to avoid excessive oxidation roughness, and then the passivation film and the oxidation layer are removed by a first reduction reaction, so that the copper powder surface obtains a rough surface structure after roughening and more active sites, and when reduction chemical silver plating is performed by using disodium ethylenediaminetetraacetate and ammonia water as a composite complexing agent, the binding capacity between silver and copper can be significantly improved, a compact and uniform silver layer is formed, and silver-coated copper powder with high conductivity is obtained.

[0046] In a first aspect, the application provides a preparation method of silver-coated copper powder, comprising the following steps:

[0047] The copper powder is roughened by using a solution containing alkali and nitrate to prepare roughened copper powder;

[0048] The roughened copper powder is passivated by using a passivation agent to prepare passivated copper powder;

[0049] The passivated copper powder is mixed with a double complexing agent plating solution after a first reduction reaction to perform reduction chemical silver plating and prepare the silver-coated copper powder;

[0050] The passivation agent comprises benzotriazole;

[0051] The double complexing agent plating solution comprises AgNO3, disodium ethylenediaminetetraacetate and ammonia water.

[0052] In the application, the copper is roughened by using a solution containing alkali and nitrate, an oxidation layer of controllable roughness is formed on the surface of copper powder by using the oxidation effect of nitrate ions, then a passivation agent comprising benzotriazole is used to passivate the formed oxidation layer to form a passivation film on the surface to avoid excessive oxidation roughness, and then the passivation film and the oxidation layer are removed by a first reduction reaction to obtain a roughened copper powder surface and more active sites, and when reduction chemical silver plating is performed by using a double complexing agent plating solution comprising AgNO3, disodium ethylenediaminetetraacetate and ammonia water, the binding capacity between silver and copper can be significantly improved, a compact and uniform silver layer is formed, and silver-coated copper powder with high conductivity is obtained.

[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] The copper powder is roughened by using an aqueous solution containing alkali and nitrate, and the nitrate is used as an oxidizing agent, under alkaline conditions, nitrate (NO3 - ) is reduced to nitrite (NO2- ), while releasing electrons, causing copper to be oxidized to form copper hydroxide, cuprous oxide, and further copper oxide, forming a controllable and rough oxide layer on the surface of copper. The surface of the oxide layer is rough, which increases the specific surface area. After removing the oxide layer, more active sites are provided for silver plating on the surface of the copper powder.

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

[0056] The concentration of the base in the solution containing the base and the nitrate is 0.001 mM-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. The concentration of the nitrate is 5 mM-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 the base and the nitrate is (100 g-200 g):1 L, which can be 100 g:1 L, 120 g:1 L, 150 g:1 L, 180 g:1 L, or 200 g:1 L.

[0058] In some embodiments, the conditions of the roughening treatment include a temperature of 20℃-30℃, which can be 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, or 30℃, and a time of 1 min-30 min, which can be 1 min, 2 min, 3 min, 4 min, 5 min, 10 min, 15 min, 20 min, 25 min, or 30 min. An appropriate increase in the temperature of the roughening treatment can accelerate the roughening treatment rate. The time of the roughening treatment is controlled to avoid excessive corrosion of the copper surface due to a long time.

[0059] The present application forms a uniform, controllable, and rough oxide layer on the surface of copper through roughening treatment. In order to prevent excessive oxidation, a passivation agent is used for passivation treatment to form a dense passivation film, preventing excessive roughening and secondary oxidation of the copper powder surface in the subsequent cleaning process of the copper powder.

[0060] In some embodiments, mechanical stirring or ultrasonic-assisted stirring is used for the roughening treatment to ensure uniform reaction.

[0061] In some embodiments, the roughening treatment employs mechanical stirring, and the mechanical stirring is performed at 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 is performed at a passivation agent concentration of 1 mM to 5 mM, which can be 1 mM, 2 mM, 3 mM, 4 mM or 5 mM.

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

[0064] In some embodiments, the passivation treatment employs mechanical stirring, and the mechanical stirring is performed at 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] The present application stops the roughening treatment by passivating the copper powder after the roughening treatment, and the passivation agent BTA is adsorbed on the surface of the copper powder after the roughening treatment to form a passivation layer with antioxidant effect, preventing further oxidation of the copper powder, thereby obtaining the passivated copper powder.

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

[0067] In some embodiments, the first reduction reaction step comprises 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 comprises one or more of triethanolamine (ETA), disodium ethylenediaminetetraacetate (EDTA-2Na), tetrasodium ethylenediaminetetraacetate (EDTA-4Na) and ammonia.

[0069] The reducing agent comprises 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.

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

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

[0072] The mass-volume ratio of the passivated copper powder to the solution containing the alkaline complexing agent and the reducing agent is (100-200g):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 the reducing agent is 0.01-0.1M, 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 0.01-0.1M, 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] The present application carries out the first reduction reaction in an alkaline and reducing environment by using an aqueous solution containing an alkaline complexing agent and a reducing agent, and a pH regulator, and carries out the de-passivation and removal of the surface oxide layer of the passivated copper powder, and the (-NH-) group in BTA is deprotonated to form BTA - under high-temperature alkaline conditions, BTA - is more easily desorbed from the copper surface into the solution, and the alkaline complexing agent competes with BTA for adsorption on the copper surface, accelerating the desorption of BTA from the copper surface.

[0074] Under this high-temperature condition, the adsorbate on the copper surface tends to be desorbed, and the oxides of the oxide layer in the copper powder are easily reduced by the reducing agent, and subsequent oxidation is inhibited.

[0075] By adjusting the pH value, the concentration of the alkaline complexing agent, the concentration of the reducing agent, the reduction temperature, the reaction time and other parameters, the present application realizes the removal of the passivation agent and the oxide layer on the surface of the copper powder, exposes the rough surface of the roughened copper powder, provides more active sites, and improves the adhesion between the copper and the subsequent silver coating. At the same time, the first reduction reaction also provides a reducing environment for the reduction chemical silver plating.

[0076] In some embodiments, the step of the first reduction reaction comprises: treating the passivated copper powder with a solution containing a basic complexing agent and a reducing agent, a pH adjusting agent; the basic complexing agent is triethanolamine, and the pH adjusting agent comprises potassium hydroxide and / or sodium hydroxide; the conditions of the first reduction reaction comprise: 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 step of the first reduction reaction comprises: treating the passivated copper powder with a solution containing a basic complexing agent and a reducing agent, a pH adjusting agent; the basic complexing agent is EDTA-2Na, and the pH adjusting agent comprises potassium hydroxide and / or sodium hydroxide; the conditions of the first reduction reaction comprise: 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 step of the first reduction reaction comprises: treating the passivated copper powder with a solution containing a basic complexing agent and a reducing agent, a pH adjusting agent; the basic complexing agent is EDTA-4Na, and the pH adjusting agent comprises potassium hydroxide and / or sodium hydroxide; the conditions of the first reduction reaction comprise: 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 by using a pH adjusting agent.

[0079] In some embodiments, the step of the first reduction reaction comprises: treating the passivated copper powder with a solution containing a basic complexing agent and a reducing agent, a pH adjusting agent; the basic complexing agent is ammonia, and the pH adjusting agent comprises potassium hydroxide and / or sodium hydroxide; the conditions of the first reduction reaction comprise: 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 the de-passivation and removal of the surface oxide layer of the passivated copper powder.

[0080] In some embodiments, the first reduction reaction uses mechanical stirring or ultrasonic-assisted stirring to ensure uniform reaction.

[0081] In some embodiments, the first reduction reaction employs mechanical stirring, and the mechanical stirring is performed at a rotation speed of 300 r / min-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 the passivation layer and the oxidation layer on the surface of the copper powder are removed by the first reduction reaction, a double complexing agent plating solution is added to the system, and the reduction chemical silver plating is performed.

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

[0084] In some embodiments, the molar ratio of AgNO3, disodium ethylenediaminetetraacetate and ammonia in the double complexing agent plating 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, and 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 a complexing agent, the conductivity, stability and mechanical properties of the silver-coated copper powder can be significantly improved.

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

[0086] In some embodiments, the reduction chemical silver plating employs mechanical stirring or ultrasonic-assisted stirring to ensure uniform reaction.

[0087] In some embodiments, the reduction chemical silver plating employs mechanical stirring, and the mechanical stirring is performed at 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 reduction chemical silver plating, the speed and time of adding the double complexing agent plating solution to the system after the first reduction reaction are controlled, the copper powder surface has a rough surface structure after roughening in the early stage of the reaction, the reaction speed of the reduction chemical silver plating is controlled and reduced to ensure the uniformity of the plating layer, and then the speed of adding the double complexing agent plating solution is increased to stabilize the reaction rate and deposition rate, so that the silver layer coated on the surface of the copper powder is uniform and dense.

[0089] In a second aspect, the application provides the silver-coated copper powder prepared by the preparation method of the first aspect.

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

[0091] In a third aspect, the application provides the silver-coated copper powder prepared by the preparation method of the first aspect or the silver-coated copper powder of the second aspect for use in conductive materials.

[0092] The silver-coated copper powder with tightly combined silver layer and copper and dense and uniform silver layer is used in the conductive materials, and has excellent conductivity.

[0093] In a fourth aspect, the application provides a conductive material comprising the silver-coated copper powder prepared by the preparation method of the first aspect or the silver-coated copper powder of the second aspect.

[0094] The silver-coated copper powder with tightly combined silver layer and copper and dense and uniform silver layer is used in the conductive materials, and can improve the conductivity.

[0095] The embodiments of the application will be described in detail below with reference to the examples. It should be understood that the examples are only used to illustrate the application and not to limit the scope of the application. The experimental methods in the following examples without specific conditions are preferred to refer to the instructions given in the application, and can also be carried out according to the experimental manuals or conventional conditions in the art, or according to the conditions suggested by the manufacturers, or according to the known experimental methods in the art.

[0096] Example 1

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

[0098] (1) 100 g of copper powder (average particle size 3 μm) was added into 1 L of an aqueous solution containing NaOH (0.008 mM) and NaNO3 (10 mM), and was subjected to roughening treatment at 20 °C, and was stirred at 500 r / min for 10 min to prepare the roughened copper powder;

[0099] (2) Then, BTA (benzotriazole) was added into the roughened copper powder, and was subjected to passivation treatment, and the concentration of BTA in the reaction system was 2 mM, and was stirred at 500 r / min for 10 min, and was washed by filtration until the washing water was neutral to obtain the passivated copper powder;

[0100] (3) The passivated copper powder was added into 1 L of an aqueous solution containing TEA (triethanolamine, 0.1 M) and glucose (0.08 M), NaOH was added to adjust the pH to 11.5, and the first reduction reaction was performed at 500 r / min for 40 min at 70°C to obtain a BTA desorption and deoxidized copper powder solution;

[0101] (4) A double complexing agent plating solution containing 0.2 M silver nitrate was prepared by mixing 0.6 M disodium ethylenediaminetetraacetate solution, 0.3 M aqueous ammonia solution and 0.6 M silver nitrate solution at a volume ratio of 1:1:1 and fully stirring; wherein the molar ratio of silver nitrate, disodium ethylenediaminetetraacetate and ammonia in the aqueous ammonia was 1:1:0.5;

[0102] The double complexing agent plating solution was added dropwise into the copper powder solution obtained in step (3) to perform reduction chemical silver plating, specifically, the double complexing agent plating solution was added dropwise into the copper powder solution at 45°C at a rate of 15 mL / min with stirring at a speed of 300 r / min, and after 5 min, the addition rate was increased to 25 mL / min for 30 min to obtain silver-coated copper powder.

[0103] Example 2

[0104] The silver-coated copper powder was prepared as follows:

[0105] (1) 100 g of copper powder (average particle size 3 μm) was added into 1 L of an aqueous solution containing NaOH (0.008 mM) and NaNO3 (10 mM), and roughening treatment was performed at 20°C with stirring at 500 r / min for 10 min to obtain roughened copper powder;

[0106] (2) Then BTA was added to the roughened copper powder to perform passivation treatment, and the concentration of BTA in the reaction system was 2 mM, and after stirring at 500 r / min for 10 min, the washing water was neutralized by washing and filtration to obtain passivated copper powder;

[0107] (3) The passivated copper powder was added into 1 L of an aqueous solution containing EDTA-2Na (0.05 M) and sodium ascorbate (0.02 M), NaOH was added to adjust the pH to 11.5, and the first reduction reaction was performed at 500 r / min for 30 min at 60°C to obtain a BTA desorption and deoxidized copper powder solution;

[0108] (4) A double complexing agent plating solution containing 0.2 M silver nitrate was prepared by mixing 0.6 M disodium ethylenediaminetetraacetate solution, 0.3 M aqueous ammonia solution and 0.6 M silver nitrate solution at a volume ratio of 1:1:1 and fully stirring; wherein the molar ratio of silver nitrate, disodium ethylenediaminetetraacetate and ammonia in the aqueous ammonia was 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 perform reduction chemical silver plating. Specifically, the double complexing agent plating solution was added dropwise into the copper powder solution at a rate of 15 mL / min at 45°C while stirring was started at a speed of 300 r / min. After 5 min, the addition was continued at a rate of 25 mL / min for 30 min to prepare the silver-coated copper powder.

[0110] Example 3

[0111] The silver-coated copper powder was prepared as follows:

[0112] (1) 100 g of copper powder (average particle size 3 μm) was added to 1 L of an aqueous solution containing NaOH (0.008 mM) and NaNO3 (10 mM) and roughened at 20°C for 10 min with stirring at 500 r / min to prepare roughened copper powder.

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

[0114] (3) The passivated copper powder was added to 1 L of an aqueous solution containing EDTA-4Na (0.04 M) and potassium sodium tartrate (0.1 M), and NaOH was added to adjust the pH to 11.5. The mixture was stirred at 500 r / min for 60 min at 80°C to perform a first reduction reaction, thereby obtaining a copper powder solution from which BTA was detached and deoxidized.

[0115] (4) A double complexing agent plating solution containing 0.2 M silver nitrate was prepared by mixing 0.6 M disodium ethylenediaminetetraacetate solution, 0.3 M aqueous ammonia solution and 0.6 M silver nitrate solution in a volume ratio of 1:1:1 and stirring thoroughly. The molar ratio of silver nitrate, disodium ethylenediaminetetraacetate and ammonia in the aqueous ammonia was 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 perform reduction chemical silver plating. Specifically, the double complexing agent plating solution was added dropwise into the copper powder solution at a rate of 15 mL / min at 45°C while stirring was started at a speed of 300 r / min. After 5 min, the addition was continued at a rate of 25 mL / min for 30 min to prepare the silver-coated copper powder.

[0117] Comparative Example 1

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

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

[0120] Comparative Example 2

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

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

[0123] Comparative Example 3

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

[0126] Comparative Example 4

[0127] The difference between Comparative Example 4 and Example 1 is that the "0.6 M disodium ethylenediaminetetraacetate solution, 0.3 M aqueous ammonia solution, and 0.6 M silver nitrate solution are mixed in a volume ratio of 1:1:1, and a double complexing agent plating solution containing 0.2 M silver nitrate is prepared by stirring thoroughly; wherein the molar ratio of silver nitrate, disodium ethylenediaminetetraacetate, and ammonia in aqueous ammonia is 1:1:0.5" is replaced by "0.6 M aqueous ammonia solution and 0.4 M silver nitrate solution are mixed in a volume ratio of 1:1, and a complexing agent plating solution containing 0.2 M silver nitrate is prepared by stirring thoroughly; wherein the molar ratio of silver nitrate and ammonia in aqueous ammonia is 1:1.5";

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

[0129] Comparative Example 5

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

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

[0132] Comparative Example 6

[0133] Comparative Example 6 differs from Example 1 in that "BTA" is replaced by "PVP (polyvinylpyrrolidone, average molecular weight 55000)";

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

[0135] Test Example 1

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

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

[0138] The shell-core structure of the silver-coated copper powder of Examples 1-3 and Comparative Examples 1-6 is shown in order as Figures 1-9 It can be seen that: Figures 1-3 In the silver-coated copper powder of Examples 1-3, the silver layer wrapped around the copper core is tightly combined and no gap is present, and the silver layer is evenly wrapped; while Figures 4-9 In the silver-coated copper powder of Comparative Examples 1-6, there are many gaps between the silver layer wrapped around the copper core, and the uniformity and tightness of the silver layer are reduced. This shows that, compared with Comparative Examples 1-6, the reaction active sites in the silver-coated copper powder of Examples 1-3 are fully exposed, the silver layer is evenly coated, and the tiny rough surface makes the silver-copper layer combination more tightly.

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

[0140] Silver-coated copper powder coating tightness: 1 g of silver-coated copper powder was soaked in 5 mL of 99% glacial acetic acid solution, and the time (min) for the copper green to start dissolving was observed. The better the silver layer coating, the longer the time for the copper green to start dissolving;

[0141] The resistivity and tensile force measurement method is as follows: 5 parts of bisphenol F type epoxy resin, 0.5 parts of 2-ethyl-4-methylimidazole, 1 part of polyamide, 1.5 parts of butyl carbitol acetate and 2 parts of tripropylene glycol monomethyl ether are uniformly stirred, added into 90 parts of silver-coated copper powder, stirred by a homogenizer, ground by a three-roll mill, and vacuumized to obtain silver-coated copper paste; the silver-coated copper paste is printed on a solar blue film sheet, the pattern width is 300 um, the length is 2 cm, and after curing at 200 DEG C for 20 min, a cured grid line is obtained, the line shape is measured, and the volume resistivity (μΩ·cm) is obtained according to the volume resistivity = resistance x width x height / length; the end of the grid line is bonded with a metal tab, and the tensile force test is carried out on a universal testing machine with the upper clamp vertically fixed, the peeling force curve is recorded, and the average peeling force (N) is extracted, and the results are shown in Table 1.

[0142] Table 1 Properties of silver-coated copper powder of 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 of Examples 1-3 is 19-20 μΩ·cm, the copper green start dissolution time is 11-17 min, and the tensile force is 1.6-1.7 N, compared with Comparative Examples 1-6, the silver-coated copper powder of Examples 1-3 has excellent conductivity, stability and mechanical properties.

[0145] Compared with Comparative Example 1 which uses an aqueous solution containing H2SO4 (0.1 M) for roughening treatment of copper powder, Example 1 uses an aqueous solution containing NaOH (0.08 mM) and NaNO3 (10 mM) for roughening treatment of copper powder, and the resistivity of the silver-coated copper powder is reduced by 58%, the copper green start dissolution time is reduced by 14 times, and the tensile force is increased by 78%, which shows that compared with roughening treatment of copper powder using more H2SO4, the application of roughening treatment of copper powder using NaOH and NaNO3 can significantly improve the conductivity, stability and mechanical properties of the silver-coated copper powder.

[0146] Compared with Comparative Example 2 which uses a solution containing NaClO2 and NaOH for roughening treatment, Example 1 uses a solution containing NaNO3 and NaOH for roughening treatment, and the resistivity of the silver-coated copper powder is reduced by 88%, the copper green start dissolution time is reduced by 14 times, and the tensile force is increased by 129%, which shows that compared with roughening treatment of copper powder using a solution containing NaClO2 and NaOH, the application of roughening treatment of copper powder using a solution containing NaOH and NaNO3 can significantly improve the conductivity, stability and mechanical properties of the silver-coated copper powder.

[0147] Compared with the complexing agent plating solution of Comparative Example 3-4 using only disodium ethylenediaminetetraacetate or ammonia, the silver-coated copper powder of Example 1 using the double complexing agent plating solution containing disodium ethylenediaminetetraacetate and ammonia has a resistivity reduced by 49-56%, a copper green dissolution start time reduced by 2-4 times, and a drawing force increased by 0.4N-0.6N, which shows that, compared with the complexing agent plating solution using only disodium ethylenediaminetetraacetate or ammonia, the application using disodium ethylenediaminetetraacetate and ammonia in combination can significantly improve the conductivity and stability of the silver-coated copper powder, and give consideration to excellent mechanical properties.

[0148] Compared with Comparative Example 5 without passivation treatment, the silver-coated copper powder of Example 1 after passivation treatment using BTA has a resistivity reduced by 79%, a copper green dissolution start time reduced by 14 times, and a drawing force increased by 78%, which shows that, compared with no passivation treatment, the application using BTA for passivation treatment can significantly improve the conductivity, stability and mechanical properties of the silver-coated copper powder.

[0149] Compared with Comparative Example 6 using PVP as a passivation agent, the silver-coated copper powder of Example 1 using BTA as a passivation agent has a resistivity reduced by 71%, a copper green dissolution start time reduced by 4 times, and a drawing force increased by 60%, which shows that, compared with other passivation agents (PVP), the application using BTA as a passivation agent for passivation treatment can significantly improve the conductivity, stability and mechanical properties of the silver-coated copper powder.

[0150] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, but as long as the combinations of the technical features do not contradict, they should be considered within the scope of the present disclosure.

[0151] The above-described embodiments only express several implementation manners of the application, and the description is more specific and detailed, but it should not be understood as a limitation on the patent scope of the application. It should be noted that, for those skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made, which are within the scope of the application. Therefore, the patent protection scope of the application should be subject to the appended claims.

Claims

1. A method for preparing silver-coated copper powder, characterized in that, Includes the following steps: Copper powder was roughened by using a solution containing alkali and nitrates to prepare roughened copper powder; The roughened copper powder is passivated with a passivating agent to prepare passivated copper powder. 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. The alkali includes NaOH; the nitrate includes sodium nitrate. 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; The mass-to-volume ratio of the copper powder to the solution containing alkali and nitrate is (100g-200g):1L; The passivating agent includes benzotriazole; The dual-complexing agent plating solution includes AgNO3, disodium ethylenediaminetetraacetate, and ammonia.

2. The method for preparing silver-coated copper powder according to claim 1, characterized in that, The conditions for roughening treatment include: temperature of 20℃-30℃ and time of 1min-30min.

3. The method for preparing silver-coated copper powder according to claim 1, characterized in that, The passivation treatment conditions include a passivating agent concentration of 1 mM to 5 mM.

4. The method for preparing silver-coated copper powder according to claim 1, characterized in that, The first reduction reaction 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 includes one or more of triethanolamine, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, and ammonia water; 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. The pH adjuster includes one or more of tetraethylammonium hydroxide, potassium hydroxide, and sodium hydroxide.

5. The method for preparing silver-coated copper powder according to claim 4, characterized in that, The conditions for the first reduction reaction include: Adjust the pH of the reaction system to 11-12; the temperature to 60℃-80℃; and the time to 10min-60min. 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; In the solution containing the alkaline complexing agent and the reducing agent, the concentration of the alkaline complexing agent is 0.01M-0.1M, and the concentration of the reducing agent is 0.01M-0.1M.

6. The method for preparing silver-coated copper powder according to claim 1, characterized in that, The steps for reducing chemical silver plating include: adding the double complexing agent plating solution at a rate of 10 mL / min to 15 mL / min for 3 min to 5 min at 30℃-60℃, and then adding the double complexing agent plating solution at a rate of 15 mL / min to 30 mL / min for 30 min to 60 min to perform the reduction chemical silver plating.

7. The method for preparing silver-coated copper powder according to claim 1, characterized in that, In the dual-complexing agent plating solution, the molar ratio of AgNO3, disodium ethylenediaminetetraacetate, and ammonia in ammonia water is (0.5-1):(0.5-1):(0.2-0.5), and the concentration of AgNO3 is 0.1M-0.3M.

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

9. The application of 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 in conductive materials.

10. A conductive material, characterized in that, This includes the silver-coated copper powder prepared by the method described in any one of claims 1-7, or the silver-coated copper powder described in claim 8.

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