Preparation method of silver-coated copper powder

Abstract

The invention provides a preparation method of silver-coated copper powder, and relates to the technical field of metal powder preparation. The preparation method comprises the following steps: sequentially cleaning and activating copper powder, and mixing with a reducing agent solution to obtain a copper particle suspension; a silver-ammonia complexing solution is dropwise added into the copper particle suspension for silver plating, and silver-coated copper powder is obtained; in the dropwise adding process, the copper particle turbid liquid is subjected to ultrasonic oscillation and mechanical stirring at the same time, and holes appear in the copper particle turbid liquid through ultrasonic oscillation. The surfaces of the copper particles are negatively charged through activation, so that subsequent reaction of silver ions with positive charges with the copper particles is facilitated; the dispersion degree of copper and generated silver particles during plating is ensured through an external force field with enough strength under the action of ultrasonic oscillation and mechanical stirring, so that the surface of the silver-coated copper powder is smooth and compact. The silver-coated copper powder with the smooth and compact surface is prepared through a chemical method, the coating effect is good, operation steps are simplified, additives such as a dispersing agent and a defoaming agent do not need to be used, and temperature control does not need to be carried out.

Description

Technical Field

[0001] The invention relates to the technical field of metal powder preparation, and in particular to a method for preparing silver-coated copper powder. Background Art

[0002] Silver powder has excellent electrical conductivity and oxidation resistance, and is the main raw material for preparing electronic paste. However, silver, as a precious metal material, is expensive and is the main cost component of electronic paste. Silver-coated copper powder combines the excellent properties of silver and copper, not only overcoming the silver migration defect in silver conductive glue, but also retaining the high conductivity, oxidation resistance and thermal stability of silver. It can effectively replace the use of silver powder and reduce the production cost of enterprises.

[0003] At present, the mainstream methods for preparing silver-coated copper powder include atomized droplet deposition method, mechanical mixing method, chemical method and other methods. The atomized droplet deposition method has high production cost and complex process; the mechanical mixing method has large production investment and consumes a lot of silver; while the chemical reduction method has simple equipment investment, is easier to operate, and the reaction process is mild and easy to control. At present, chemical methods are widely used to prepare silver-coated copper powder, but this method still has problems such as incomplete surface coating of copper powder and poor coating effect. Patent CN116037920A discloses a method for preparing silver-coated copper powder, which uses a displacement method for the first time and a chemical reduction method for the second time for secondary plating. Due to the relatively intense displacement process, this method is prone to empty shell problems, and the surface of the silver-coated copper powder produced is not dense and smooth enough. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a method for preparing silver-coated copper powder. The silver-coated copper powder prepared by the present invention has a smooth and dense surface and is easy to prepare.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing silver-coated copper powder, comprising the following steps:

[0007] The copper powder is sequentially cleaned and activated, and then mixed with a reducing agent solution to obtain a copper particle suspension; the activation agent used in the activation is an alkaline solution, and the pH value of the copper particle suspension is 10-11;

[0008] A silver-ammine complex solution is added dropwise to the copper particle suspension to perform silver plating to obtain silver-coated copper powder; during the adding process, the copper particle suspension is simultaneously subjected to ultrasonic oscillation and mechanical stirring, and the ultrasonic oscillation causes cavities to appear in the copper particle suspension.

[0009] Preferably, the copper powder is spherical particles with a particle size of 0.2 to 10 μm.

[0010] Preferably, the cleaning includes alkaline washing and acid washing in sequence; the alkaline washing adopts a dilute alkaline solution, the alkali in the dilute alkaline solution is sodium hydroxide and / or potassium hydroxide, and the concentration of the dilute alkaline solution is 0.1-0.8 mol / L; the acid washing adopts a sulfuric acid solution, and the concentration of the sulfuric acid solution is 0.1-0.9 mol / L.

[0011] Preferably, the alkali in the alkaline solution is sodium hydroxide and / or potassium hydroxide, the concentration of the alkaline solution is 0.1-0.8 mol / L, and the activation time is 5-10 min.

[0012] Preferably, the reducing agent solution is a glucose aqueous solution, the concentration of the glucose aqueous solution is 0.15-1.5 mol / L, and the mass ratio of glucose to copper powder in the glucose aqueous solution is 1:(0.05-1).

[0013] Preferably, the silver-ammine complex solution is prepared from a silver nitrate solution and aqueous ammonia, and the concentration of the silver nitrate solution is 0.1-0.5 mol / L.

[0014] Preferably, the dropping rate of the silver-ammine complex solution per gram of copper powder in the copper particle suspension is 0.4-20 mL / min.

[0015] Preferably, the ultrasonic oscillation has an ultrasonic frequency of 40 kHz and a power of 60 to 900 W.

[0016] Preferably, the rotation speed of the mechanical stirring is 100-300 r / min.

[0017] Preferably, the mass percentage of silver in the silver-coated copper powder is 5-50%.

[0018] The present invention provides a method for preparing silver-coated copper powder, comprising the following steps: washing and activating the copper powder in sequence, and then mixing it with a reducing agent solution to obtain a copper particle suspension; the activation agent used in the activation is an alkaline solution, and the pH value of the copper particle suspension is 10-11; silver ammonia complex solution is added dropwise to the copper particle suspension for silver plating to obtain the silver-coated copper powder; during the dropping process, the copper particle suspension is simultaneously subjected to ultrasonic oscillation and mechanical stirring, and the ultrasonic oscillation causes holes to appear in the copper particle suspension. The present invention makes the surface of the copper particles negatively charged by the activation, which is conducive to the subsequent reaction of positively charged silver ions with the copper particles; the present invention uses the ultrasonic oscillation and mechanical stirring to act on an external force field of sufficient strength to ensure the dispersion degree of the copper particles during the plating process, and refine the silver particles generated by the dispersion replacement reaction (the silver ions and copper will inevitably undergo a replacement reaction to generate silver particles during the silver plating process) and the reduction reaction, so as to prevent the silver particles from being too large and causing the surface coating to be rough and loose, thereby obtaining a silver-coated copper powder with a smooth and dense surface. The present invention prepares silver-coated copper powder with a smooth and dense surface through the above chemical method, has good coating effect, and has simplified operation steps. The chemicals used are common, and no additives such as dispersants and defoamers are required. The plating process is less sensitive to temperature and does not require temperature control. In addition, the chemical composition of the waste liquid after the preparation is simple, which is convenient for the recovery and treatment of the waste liquid and easy to realize industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a scanning electron microscope image of the silver-coated copper powder prepared in Example 1;

[0020] Figure 2 This is a scanning electron microscope image of the silver-coated copper powder prepared in Example 2;

[0021] Figure 3 This is a scanning electron microscope image of the silver-coated copper powder prepared in Example 3;

[0022] Figure 4 This is a scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 1. DETAILED DESCRIPTION

[0023] The present invention provides a method for preparing silver-coated copper powder, comprising the following steps:

[0024] The copper powder is sequentially cleaned and activated, and then mixed with a reducing agent solution to obtain a copper particle suspension; the activation agent used in the activation is an alkaline solution, and the pH value of the copper particle suspension is 10-11;

[0025] A silver-ammine complex solution is added dropwise to the copper particle suspension to perform silver plating to obtain silver-coated copper powder; during the adding process, the copper particle suspension is simultaneously subjected to ultrasonic oscillation and mechanical stirring, and the ultrasonic oscillation causes cavities to appear in the copper particle suspension.

[0026] In the present invention, unless otherwise specified, the raw materials involved are commercially available products well known to those skilled in the art.

[0027] The invention sequentially cleans and activates the copper powder, and then mixes it with a reducing agent solution to obtain a copper particle suspension.

[0028] In the present invention, the copper powder is preferably spherical particles, and the particle size is preferably 0.2 to 10 μm, more preferably 4 to 5 μm.

[0029] In the present invention, the cleaning preferably includes alkali washing and acid washing in sequence. In the present invention, the alkali washing preferably uses a dilute alkali solution, the alkali in the dilute alkali solution is preferably sodium hydroxide and / or potassium hydroxide, and the concentration of the dilute alkali solution is preferably 0.1-0.8 mol / L, more preferably 0.1-0.3 mol / L; the dilute alkali solution is specifically prepared by adding the alkali to deionized water. In the present invention, the dosage ratio of the dilute alkali solution to the copper powder is preferably 50mL:1g; the time of the alkali washing is preferably 5-10min, and the alkali washing is preferably carried out under ultrasonic oscillation. In the present invention, the acid washing preferably uses a sulfuric acid solution, and the concentration of the sulfuric acid solution (in terms of sulfate) is preferably 0.1-0.9 mol / L, more preferably 0.25-0.4 mol / L; the sulfuric acid solution is prepared by adding sulfuric acid to deionized water. In the present invention, the dosage ratio of the sulfuric acid solution to the copper powder is preferably 40mL:1g; the time of the acid washing is preferably 5-10min, and the acid washing is preferably carried out under ultrasonic oscillation.

[0030] In the present invention, the specific operation of the cleaning is preferably: adding the dilute alkali solution to the copper powder, ultrasonically oscillating for 5 to 10 minutes, and discarding the supernatant; then adding the sulfuric acid solution, ultrasonically oscillating for 5 to 10 minutes, and discarding the supernatant.

[0031] The present invention removes organic matter (such as oil stains) on the surface of the copper powder by the alkali washing, and removes the oxide layer on the surface of the copper powder by the acid washing.

[0032] In the present invention, the activation reagent used in the activation is an alkaline solution, and the concentration of the alkaline solution is preferably 0.1-0.8 mol / L, more preferably 0.1-0.3 mol / L; the alkali in the alkaline solution is preferably sodium hydroxide and / or potassium hydroxide, and the alkaline solution is specifically prepared by adding the alkali to deionized water. In the present invention, the dosage ratio of the activation reagent to the copper powder is preferably 40 mL: 1 g. The present invention preferably adds the alkaline solution to the cleaned copper powder for activation. In the present invention, the activation time is preferably 5-10 min, and the activation is preferably carried out under the condition of ultrasonic oscillation. In the present invention, the role of ultrasonic oscillation in the alkaline washing, acid washing and activation is to make the solution fully contact with the copper particles, so that they react fully and improve the reaction efficiency. The present invention has no special requirements for the conditions of ultrasonic oscillation in the alkaline washing, acid washing and activation, and the conditions of ultrasonic cleaning well known to those skilled in the art can be used. After the activation, the supernatant is poured off to obtain surface-activated copper powder. Through the activation, the present invention makes the surface of the copper particles negatively charged, which is conducive to the subsequent reaction of positively charged silver ions with them.

[0033] In the present invention, the reducing agent solution is preferably a glucose aqueous solution, specifically a solution of glucose and deionized water, the concentration of the glucose aqueous solution is preferably 0.15-1.5 mol / L, more preferably 0.15-0.3 mol / L, and the mass ratio of glucose to copper powder in the glucose aqueous solution is preferably 1:(0.05-1), more preferably 1:(0.5-0.85). The present invention preferably adds a glucose aqueous solution to the surface-activated copper powder to obtain a copper particle suspension. In the present invention, the pH value of the copper particle suspension is 10-11. When the pH value of the copper particle suspension is less than the range value, additional alkali can be added for adjustment.

[0034] After obtaining the copper particle suspension, the present invention drips a silver-ammine complex solution into the copper particle suspension to perform silver plating to obtain silver-coated copper powder.

[0035] In the present invention, the silver ammonia complex solution is prepared from a silver nitrate solution and ammonia water, specifically, ammonia water is added dropwise to the silver nitrate solution until the initially generated precipitate is just dissolved, thereby obtaining the silver ammonia complex solution. In the present invention, the concentration of the silver nitrate solution is preferably 0.1-0.5 mol / L, more preferably 0.1-0.2 mol / L, and the silver nitrate solution is prepared by adding deionized water to solid silver nitrate or high-concentration silver nitrate solution; the mass fraction of the ammonia water is preferably 20-25%.

[0036] During the dropping process, the present invention simultaneously performs ultrasonic oscillation and mechanical stirring on the copper particle suspension, and the ultrasonic oscillation causes holes to appear in the copper particle suspension. During the plating process, the present invention applies an external force field of a combination of ultrasonic oscillation and mechanical stirring to the copper particle suspension, providing sufficient external force field strength to ensure the dispersion degree of copper and generated silver particles, wherein mechanical stirring suspends the copper particles to prevent the copper particles from sinking to the bottom, and ultrasonic oscillation makes them more dispersed. If mechanical stirring is omitted, the copper particles will sink to the bottom and fail to achieve the desired dispersion effect. In the present invention, the ultrasonic oscillation is required to cause holes to appear in the suspension, that is, obvious cavities (bubbles) appear inside and on the surface of the suspension to meet the requirements, so as to ensure that the replaced and reduced silver particles are small and highly dispersed. In order to maintain the appearance of cavitation and ensure the dispersion of copper particles, in the present invention, the ultrasonic frequency of the ultrasonic oscillation is preferably 40kHz, the power is preferably 60-900W, more preferably 100-600W, and further preferably 200-600W (the intensity of the external force field is related to the amount of copper powder processed in a single time, and the appearance of cavitation in the suspension is the standard). In the present invention, the cavitation is the macroscopic manifestation of the effect of ultrasonic oscillation on the suspension. In the present invention, the rotation speed of the mechanical stirring is preferably 100-300r / min, more preferably 200-300r / min.

[0037] In actual operation, before the silver-ammine complex solution is added dropwise, the copper particle suspension is first subjected to ultrasonic oscillation alone (i.e., without mechanical stirring) to determine the ultrasonic oscillation conditions that can cause cavitation in the copper particle suspension. When the silver-ammine complex solution is added dropwise, the copper particle suspension is subjected to ultrasonic oscillation and mechanical stirring simultaneously according to the determined ultrasonic oscillation conditions.

[0038] In the present invention, the drop rate of the silver-ammine complex solution corresponding to each gram of copper powder in the copper particle suspension is preferably 0.4-20 mL / min, more preferably 1-5 mL / min, and further preferably 1-2 mL / min. The present invention preferably uses a pump to drip the silver-ammine complex solution. In the present invention, the drop rate of the silver-ammine complex solution is related to the specific surface area of ​​copper and the amount of the reducing agent, and the amount of the reducing agent is related to the amount of the silver-ammine complex solution added, that is, it is related to the silver content of the silver-coated copper powder. In order to ensure that the surface of the silver-coated copper powder is smooth and dense and to achieve simple operation of the chemical plating method, the influence of the specific surface area can be ignored. The present invention controls the drop rate of the silver-ammine complex solution, which is conducive to obtaining a smooth and dense surface of the silver-coated copper powder. If the drop rate is too fast, the generated silver particles will grow too large, the silver layer of the prepared silver-coated copper particles will be rough and attached with raised silver particles, and the coating effect will be poor; if the drop rate is too slow, the surface effect of the prepared silver-coated copper powder will not be significantly improved, but the cost of the reaction will be increased.

[0039] In the present invention, the volume ratio of the total added volume of the silver ammonia complex solution to the reducing agent solution is preferably 37:33, and the reducing agent may be excessive. In the present invention, when the addition is completed (i.e., the silver plating is completed), the effects of the ultrasonic oscillation and mechanical stirring external force field are simultaneously terminated.

[0040] After the silver plating is completed, the present invention preferably sequentially performs solid-liquid separation, solid phase water washing and drying on the obtained suspension to obtain the silver-coated copper powder. The present invention has no special requirements for the solid-liquid separation method, and a solid-liquid separation method well known to those skilled in the art can be used; the number of water washing is preferably 2 times, and the residual liquid on the surface is removed by water washing; the drying temperature is preferably 80°C, and the time is preferably 2 to 6 hours.

[0041] In the present invention, the mass percentage of silver in the silver-coated copper powder is preferably 5 to 50%, more preferably 15 to 30%, and further preferably 20 to 25%.

[0042] The present invention prepares silver-coated copper powder with a smooth and dense surface by a chemical method, has simplified operation steps, uses common chemicals, ensures the dispersion of copper particles during plating by acting on an external force field of sufficient intensity, thereby eliminating the use of additives such as dispersants and defoamers, and has low temperature sensitivity during the plating process, without the need for temperature control. The chemical composition of the waste liquid after the preparation is simple, which is convenient for the recovery and treatment of the waste liquid and easy to realize industrial production.

[0043] In order to further illustrate the present invention, the preparation method of the silver-coated copper powder provided by the present invention is described in detail below in combination with examples, but they should not be construed as limiting the protection scope of the present invention.

[0044] Example 1

[0045] Weigh 5 g of copper powder (spherical) with an average particle size of 4 μm in a glass beaker, add 250 mL of 5 g / L sodium hydroxide solution, ultrasonically treat (60 W (1 oscillator)) for 5 min, then pour out the supernatant, add 200 mL of 0.4 mol / L sulfuric acid solution, ultrasonically treat (60 W (1 oscillator)) for 5 min, then pour out the supernatant, add 200 mL of 4 g / L sodium hydroxide solution, ultrasonically treat (60 W (1 oscillator)) for 5 min for activation, then pour out the supernatant, add 165 mL of 35.5 g / L glucose solution, and obtain a copper particle suspension (pH 5.3). 11); then, ultrasonic oscillation and mechanical stirring are applied, wherein the ultrasonic oscillation (frequency 40kHz, power 240W (4 oscillators)) can cause cavities (obvious cavities) to appear in the suspension, the speed of mechanical stirring is 100r / min, and 185mL of 0.1mol / L silver ammonia complex solution (prepared with 0.1mol / L silver nitrate solution and 25% ammonia water by mass fraction) is dripped at a rate of 5mL / min by a pump. When the dripping is completed, the external force field is stopped, and the solution temperature is about 45°C. After solid-liquid separation, the solution is washed with water twice, placed in a drying oven at 80°C for 6h, and then the powder is collected, i.e., silver-coated copper powder.

[0046] Figure 1 This is a scanning electron microscope image of the silver-coated copper powder prepared in Example 1. The surface of the silver-coated copper powder is smooth and dense. The mass percentage of silver in the silver-coated copper powder is 28.5%.

[0047] Example 2

[0048] 2 g of copper powder (spherical) with an average particle size of 5 μm was weighed into a glass beaker, 100 mL of 8 g / L potassium hydroxide solution was added, and the supernatant was poured out after ultrasonic treatment (60 W (1 oscillator)) for 5 min, 80 mL of 0.25 mol / L sulfuric acid solution was added, and the supernatant was poured out after ultrasonic treatment (60 W (1 oscillator)) for 5 min, 80 mL of 8 g / L potassium hydroxide solution was added, and the supernatant was poured out after ultrasonic treatment (60 W (1 oscillator)) for 5 min for activation treatment, and then the supernatant was poured out, and 66 mL of 35.5 g / L glucose solution was added to obtain a copper particle suspension (pH 11); ultrasonic oscillation and mechanical stirring were then applied, and ultrasonic oscillation (frequency 40 kHz, power 120 W (2 oscillators)) was performed. ， The suspension can be made to have holes (obvious holes), the speed of mechanical stirring is 100r / min, and 21mL of 0.2mol / L silver ammonia complex solution (prepared with 0.2mol / L silver nitrate solution and 25% ammonia water by mass) is added dropwise by a pump at a speed of 2mL / min, and the external force field is stopped after the addition is completed. Since the external force field action time is short and the temperature is room temperature, the solid and liquid are separated and washed twice, and the powder is collected after being placed in a drying box at 80°C for 2h, i.e., silver-coated copper powder.

[0049] Figure 2 This is a scanning electron microscope image of the silver-coated copper powder prepared in Example 2. The surface of the silver-coated copper powder is smooth and dense. The mass percentage of silver in the silver-coated copper powder is 18.5%.

[0050] Example 3

[0051] Weigh 50g of copper powder (spherical) with an average particle size of 5μm into a glass beaker, add 2.5L of a 10g / L mixed solution of sodium hydroxide and potassium hydroxide (the mass ratio of sodium hydroxide and potassium hydroxide in the mixed solution is 1:1), and ultrasonically treat (120W (2 oscillators)) for 10min, then pour out the supernatant. Add 2L of a 0.1mol / L sulfuric acid solution, ultrasonically treat (120W (2 oscillators)) for 10min, then pour out the supernatant, add 2L of a 10g / L mixed solution of sodium hydroxide and potassium hydroxide (the mass ratio of sodium hydroxide and potassium hydroxide in the mixed solution is 1:1), and ultrasonically treat (120W (2 oscillators)) for 5min for activation, then pour out the supernatant. 1000mL of 50g / L glucose solution is added to obtain a copper particle suspension (pH value of 10); then ultrasonic oscillation and mechanical stirring are applied, wherein the ultrasonic oscillation (frequency of 40kHz, power of 600W (10 oscillators)) can cause holes (obvious cavities) to appear in the suspension, the mechanical stirring speed is 300r / min, and 1160mL of 0.1mol / L silver ammonia complex solution (prepared with 0.1mol / L silver nitrate solution and ammonia water with a mass fraction of 25%) is dripped at a rate of 20mL / min by a pump machine, the external force field is stopped when the dripping is completed, the reaction process temperature is about 40°C, the solid-liquid separation is followed by washing twice, the mixture is placed in a drying oven at 80°C for insulation for 6h, and then powder is collected, i.e., silver-coated copper powder.

[0052] Figure 3 This is a scanning electron microscope image of the silver-coated copper powder prepared in Example 3. The surface of the silver-coated copper powder is smooth and dense. The mass percentage of silver in the silver-coated copper powder is 20%.

[0053] Comparative Example 1

[0054] Weigh 50g of copper powder (spherical) with an average particle size of 5μm into a glass beaker, add 2.5L of a 10g / L mixed solution of sodium hydroxide and potassium hydroxide (the mass ratio of sodium hydroxide and potassium hydroxide in the mixed solution is 1:1), and ultrasonically treat (120W (2 oscillators)) for 10min, then pour out the supernatant. Add 2L of a 0.1mol / L sulfuric acid solution, ultrasonically treat (120W (2 oscillators)) for 10min, then pour out the supernatant, add 2L of a 10g / L mixed solution of sodium hydroxide and potassium hydroxide (the mass ratio of sodium hydroxide and potassium hydroxide in the mixed solution is 1:1), and ultrasonically treat (120W (2 oscillators)) for 5min for activation, then pour out the supernatant. 1000mL of 50g / L glucose solution was added to obtain a copper particle suspension (pH value 10); then ultrasonic oscillation and mechanical stirring were applied, the ultrasonic machine working power was adjusted to 300W (5 oscillators), the frequency was 40kHz, no cavitation occurred in the copper particle suspension, the mechanical stirring speed was 300r / min, and 1160mL of 0.1mol / L silver ammonia complex solution was added dropwise at a rate of 20mL / min by a pump machine. The external force field was stopped when the addition was completed. The temperature of the reaction process was about 40°C. After solid-liquid separation, the mixture was washed with water twice, placed in a drying oven at 80°C for 6h, and then powder was collected, i.e., silver-coated copper powder.

[0055] Figure 4 This is a scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 1. Compared with Example 3, most of the silver-coated copper particles prepared in Comparative Example 1 have rough surfaces and defects similar to pits appear on the surface.

[0056] It can be seen from the above embodiments that the present invention utilizes a chemical method (including replacement and reduction) for plating, and applies a strong external force field of ultrasonic oscillation and mechanical stirring during the plating process to prepare silver-coated copper powder with a smooth and dense surface.

[0057] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing silver-coated copper powder, characterized in that: The following steps are involved: The copper powder is sequentially cleaned and activated, and then mixed with a reducing agent solution to obtain a copper particle suspension; the activation agent used in the activation is an alkaline solution, and the pH value of the copper particle suspension is 10-11; A silver-ammine complex solution is added dropwise to the copper particle suspension to perform silver plating to obtain silver-coated copper powder; during the adding process, the copper particle suspension is simultaneously subjected to ultrasonic oscillation and mechanical stirring, and the ultrasonic oscillation causes cavities to appear in the copper particle suspension.

2. The preparation method according to claim 1, characterized in that The copper powder is spherical particles with a particle size of 0.2 to 10 μm.

3. The preparation method according to claim 1, characterized in that The cleaning comprises sequentially performing alkali washing and acid washing; the alkali washing adopts a dilute alkali solution, the alkali in the dilute alkali solution is sodium hydroxide and / or potassium hydroxide, and the concentration of the dilute alkali solution is 0.1 to 0.8 mol / L; the acid washing adopts a sulfuric acid solution, and the concentration of the sulfuric acid solution is 0.1 to 0.9 mol / L.

4. The preparation method according to claim 1, characterized in that The alkali in the alkaline solution is sodium hydroxide and / or potassium hydroxide, the concentration of the alkaline solution is 0.1-0.8 mol / L, and the activation time is 5-10 minutes.

5. The preparation method according to claim 1, characterized in that The reducing agent solution is a glucose aqueous solution, the concentration of the glucose aqueous solution is 0.15-1.5 mol / L, and the mass ratio of glucose to copper powder in the glucose aqueous solution is 1:(0.05-1).

6. The preparation method according to claim 1, characterized in that The silver ammonia complex solution is prepared from a silver nitrate solution and ammonia water, and the concentration of the silver nitrate solution is 0.1-0.5 mol / L.

7. The preparation method according to claim 1 or 6, characterized in that The dropping rate of the silver ammonia complex solution corresponding to each gram of copper powder in the copper particle suspension is 0.4 to 20 mL / min.

8. The preparation method according to claim 1, characterized in that The ultrasonic oscillation has an ultrasonic frequency of 40 kHz and a power of 60 to 900 W.

9. The preparation method according to claim 1 or 8, characterized in that The rotation speed of the mechanical stirring is 100-300 r / min.

10. The preparation method according to claim 1, characterized in that The mass percentage of silver in the silver-coated copper powder is 5-50%.

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