Preparation method of smooth and compact silver-coated copper powder

Abstract

The invention discloses a preparation method of smooth and compact silver-coated copper powder, which belongs to the technical field of conductive powder preparation, and is characterized in that an organic coating layer and an oxide layer on the surface of the copper powder can be effectively removed by carrying out proper acid-base surface activation treatment on the copper powder; then the activated copper powder is added into a protective reagent solution for anti-oxidation protection, the reaction between non-uniform active sites on the copper surface and oxygen in air and liquid is reduced, and it is guaranteed that an interface layer of the copper powder is uniform and free of the local oxidation phenomenon; and subsequently, a sensitization reduction coating method is adopted, so that the smooth low-silver silver-containing coated copper powder with high coating compactness is obtained. The low-silver powder-containing body has the characteristics of excellent oxidation resistance, low thermal gain, low resistivity, good conductivity and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive powder preparation, and specifically relates to a method for preparing smooth and dense silver-coated copper powder. Background Art

[0002] With the rapid development of the electrical era, the demand for excellent conductive materials by advanced electronic components is increasing day by day. In the fields of photovoltaic and electronic information, silver has stable and excellent conductive properties compared with copper. However, due to the high price of precious metals and the sharp increase in their use, the use cost of conductive metals has been greatly increased. Metal copper is relatively cheaper than silver, and its conductivity is slightly lower than that of silver, and it can be used as one of the alternative products of silver. The specific surface area of copper powder used in conductive powder is large, and its chemical properties are more active, and it is extremely easy to be continuously oxidized in the environment of slurry sintering and use, resulting in a sharp decrease in conductive performance. Therefore, silver-coated copper powder has been developed to solve the problems of high price of silver powder and easy oxidation of copper powder.

[0003] Due to the extremely easy oxidation property of copper powder, a certain degree of oxidation will occur after the synthesis of copper powder, which affects the displacement reaction between metallic copper and silver ions and makes it difficult to form silver nucleation sites. Therefore, chemical reagents such as acids and bases are used to pretreat copper powder when coating a silver layer on the surface of copper powder. Patent CN106148926B uses sodium hydroxide with a mass fraction of up to 50% of copper powder and hydrazine hydrate solvent for pretreatment, CN114101665B uses sulfuric acid and diethylene glycol butyl ether solvent for treatment, and patent CN110170650A uses 5wt% dilute sulfuric acid solution for treatment. These pretreatments highly activate the surface of copper powder, making the reactive sites on the surface of copper powder highly active and different, and it is difficult to accurately control a uniform reaction process. Whether the subsequent one-step method or multi-step method is used to form a silver-coated layer, it is very rough, the surface is not smooth enough, and defective positions where incomplete coating is likely to occur are easily generated. Although some other works (CN113020587B, CN110551995B, CN115156529B) can obtain powders with better coating density, their silver content is extremely high. The demand for reducing costs and low silver content makes it more challenging to prepare silver-coated copper powder with high coating density. Protecting the activated copper powder may solve the problem of uneven and dense coating caused by too high reaction activity of copper powder. Patent CN115365494B uses a lysozyme as a pre-protective layer for copper powder and controls the uniform growth of the silver layer, but lysozyme has a high price and is extremely susceptible to reaction temperature and pH. The present invention provides a method for pretreating and activating the surface of copper powder simply and pre-protecting it to obtain silver-coated copper powder with dense, uniform and smooth coating. Summary of the Invention

[0004] The present invention aims to solve the problems existing in the prior art and provides a method for preparing smooth and dense silver-coated copper powder. By appropriately treating the copper powder with acid and alkali on the surface, the organic coating layer and oxide layer on the surface of the copper powder can be effectively removed; then the activated copper powder is added to the protective reagent solution for antioxidant protection to reduce the reaction of the uneven active sites on the copper surface with oxygen in the air and liquid, so as to ensure that the interface layer of the copper powder is uniform and there is no local oxidation phenomenon; subsequently, the method of sensitization reduction coating is adopted to obtain smooth silver-coated copper powder with high coating density and low silver content. This low-silver-containing powder has excellent antioxidant properties, showing characteristics such as low thermal weight gain, low resistivity, and good electrical conductivity.

[0005] The object of the present invention is achieved by the following technical solutions: A method for preparing smooth and dense silver-coated copper powder, comprising the following steps: Step 1. Surface activation treatment of copper powder: The copper powder is dispersed in an alkaline or acidic solution to wash away the organic matter and oxide layer on the surface of the copper powder, or it is washed away the organic matter and oxide layer on the surface of the copper powder in two steps successively in an alkaline or acidic solution; Step 2. Protection treatment of activated copper powder: The highly active copper powder obtained after pickling or alkali washing is added to the protective reagent solution and stirred and mixed to reduce the oxidation rate of the copper powder in the solution and air; Step 3. Coating a silver layer on the surface of the copper powder: In the copper powder suspension in the protective solution, a complexing agent, a metal salt solution, a reducing agent, and a silver solution are respectively added. After a certain temperature and reaction time, a silver-coated copper suspension is obtained; the suspension is washed, filtered, and dried to obtain silver-coated copper powder.

[0006] Preferably, in the step 1, the copper powder is spherical or quasi-spherical, and the average particle size of the copper powder is 0.5 - 5 μm.

[0007] Preferably, in the step 1, the alkaline solution uses at least one of sodium hydroxide, potassium hydroxide, and ammonia water; the alkaline solution is a solution with a mass fraction of 0.5% - 4%, the amount of the solution added is 3 - 10 times the mass of the copper powder, the treatment temperature is 40 - 80 °C, and the treatment time is 10 - 240 min.

[0008] Preferably, in the step 1, the acidic solution uses at least one of sulfuric acid, nitric acid, and ammonium bisulfate; the acidic solution is a solution with a mass fraction of 0.5% - 4%, the amount of the solution added is 3 - 10 times the mass of the copper powder, the treatment temperature is 40 - 80 °C, and the treatment time is 10 - 240 min.

[0009] Preferably, in the step 2, the protective reagent is at least one of nitric acid, formic acid, sodium formate, potassium formate, acetic acid, sodium acetate, potassium acetate, propionic acid, sodium propionate, potassium propionate, succinic acid, sodium succinate, potassium succinate, caproic acid, sodium caproate, and potassium caproate; the amount of the protective reagent added is 3-50% of the mass of the copper powder, and the treatment temperature is 20-80 °C.

[0010] Preferably, in the step 3, the complexing agent is at least one of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, triethylenetetramine, tetraethylenetriamine, and N-acetylsarcosine, and the amount of the complexing agent added is 10%-40% of the mass of the copper powder.

[0011] Preferably, in the step 3, the metal salt solution is at least one of silver nitrate, silver sulfate, silver acetate, stannous chloride, and palladium chloride; the amount of the metal salt added is 0.5-5% of the mass of the copper powder, the reaction temperature is 15-60 °C, and the reaction time is 1-15 min.

[0012] Preferably, in the step 3, the reducing agent is at least one of sodium borohydride, tartaric acid, glucose, ascorbic acid, citric acid, formic acid, formaldehyde, hydrazine hydrate, and metal salts of all the above reducing substances; the metal salts include sodium salts, potassium salts, sodium-potassium salts, calcium salts, and magnesium salts; the amount of the reducing agent added is 1.05 times the molar amount of the silver source, the reaction temperature is 10-40 °C, and the reaction time is 5-40 min.

[0013] Preferably, in the step 3, the silver solution is at least one of silver-ammonia complex solution, silver-ethylenediaminetetraacetic acid complex solution, silver-triethylenetetramine complex solution, and silver-diethylenetriamine; the amount of silver is 4%-27% of the mass of the copper powder, the reaction temperature is 15-60 °C, and the reaction time is 5-100 min.

[0014] Preferably, the total mass of silver in the metal salt solution and the silver reaction solution is less than 30% of the mass of the copper powder.

[0015] Preferably, the total mass of silver in the metal salt solution and the silver reaction solution is less than 10% of the mass of the copper powder.

[0016] The beneficial effects of this technical solution are as follows: First, a method for preparing smooth and dense silver-coated copper powder provided by the present invention, compared with the prior art, adds a protective treatment before silver plating of the copper powder. While protecting the copper powder from being oxidized in the reaction solution, it can also regulate the uneven reaction activity of the copper powder surface caused by factors such as structural morphology, pickling, and alkali washing, making the reaction rate of the copper powder surface more consistent in the subsequent reaction and ensuring the integrity of the coating.

[0017] II. A method for preparing smooth and dense silver-coated copper powder provided by the present invention is simple and easy to operate, and the protective reagent is inexpensive, which is suitable for large-scale production and preparation.

[0018] III. A method for preparing smooth and dense silver-coated copper powder provided by the present invention is simple and easy to operate, without the need to add additional operating equipment, and is suitable for large-scale production.

[0019] IV. A method for preparing smooth and dense silver-coated copper powder provided by the present invention can prepare low-silver-content silver-coated copper particles with smooth and dense coating. The silver content can be adjusted to 20% or less, especially 10% or less. The silver coating of this powder is complete and has excellent protection.

[0020] V. A method for preparing smooth and dense silver-coated copper powder provided by the present invention can prepare low-silver-content silver-coated copper particles with smooth and dense coating, which can replace silver powder in many application scenarios, has a significant cost reduction effect, and outstanding economic benefits. Description of the Drawings

[0021] Figure 1 SEM image of the silver-coated copper powder obtained in Example 1 of the present invention; Figure 2 SEM image of the silver-coated copper powder obtained in Example 14 of the present invention; Figure 3 SEM image of the silver-coated copper powder obtained in Example 20 of the present invention; Figure 4 SEM image of the silver-coated copper powder obtained in Comparative Example 1 of the present invention. Detailed Embodiments

[0022] The present invention will be further described in detail below in conjunction with embodiments, but the embodiments of the present invention are not limited thereto.

[0023] A method for preparing smooth and dense silver-coated copper powder includes the following steps: Step 1. Surface activation treatment of copper powder: Disperse the copper powder in an alkaline or acidic solution to wash away the organic matter and oxide layer on the surface of the copper powder, or wash away the organic matter and oxide layer on the surface of the copper powder in two steps in an alkaline or acidic solution; Step 2. Protection treatment of activated copper powder: Add the highly active copper powder obtained after pickling or alkali washing to the protective reagent solution and stir to mix, reducing the oxidation rate of the copper powder in the solution and air; Step 3. Coating a silver layer on the surface of copper powder: Add a complexing agent, a metal salt solution, a reducing agent, and a silver solution to the copper powder suspension in the protective solution respectively. After a certain temperature and reaction time, a silver-coated copper suspension is obtained; Wash and filter the suspension, and after drying, silver-coated copper powder is obtained.

[0024] Among them, in the said step 1, the copper powder is spherical or quasi-spherical, and the average particle size of the copper powder is 0.5 - 5 μm.

[0025] Among them, in the said step 1, the alkaline solution is at least one of sodium hydroxide, potassium hydroxide, and ammonia water; the alkaline solution is a solution with a mass fraction of 0.5% - 4%, the amount of the solution added is 3 - 10 times the mass of the copper powder, the treatment temperature is 40 - 80 °C, and the treatment time is 10 - 240 min.

[0026] Among them, in the said step 1, the acidic solution is at least one of sulfuric acid, nitric acid, and ammonium bisulfate; the acidic solution is a solution with a mass fraction of 0.5% - 4%, the amount of the solution added is 3 - 10 times the mass of the copper powder, the treatment temperature is 40 - 80 °C, and the treatment time is 10 - 240 min.

[0027] Among them, in the said step 2, the protective reagent is at least one of nitric acid, formic acid, sodium formate, potassium formate, acetic acid, sodium acetate, potassium acetate, propionic acid, sodium propionate, potassium propionate, succinic acid, sodium succinate, potassium succinate, hexanoic acid, sodium hexanoate, and potassium hexanoate; the amount of the protective reagent added is 3 - 50% of the mass of the copper powder, and the treatment temperature is 20 - 80 °C.

[0028] Among them, in the said step 3, the complexing agent is at least one of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, triethylenetetramine, tetraethylenetriamine, and N - acetylsarcosine, and the amount of the complexing agent added is 10% - 40% of the mass of the copper powder.

[0029] Among them, in the said step 3, the metal salt solution is at least one of silver nitrate, silver sulfate, silver acetate, stannous chloride, and palladium chloride; the amount of the metal salt added is 0.5% - 5% of the mass of the copper powder, the reaction temperature is 15 - 60 °C, and the reaction time is 1 - 15 min.

[0030] Among them, in the said step 3, the reducing agent is at least one of sodium borohydride, tartaric acid, glucose, ascorbic acid, citric acid, formic acid, formaldehyde, hydrazine hydrate, and metal salts of all the above reducing substances; the metal salts include sodium salts, potassium salts, sodium - potassium salts, calcium salts, and magnesium salts; the amount of the reducing agent added is 1.05 times the molar amount of the silver source (the silver source includes silver in the metal salt solution and silver solution), the reaction temperature is 10 - 40 °C, and the reaction time is 5 - 40 min.

[0031] Among them, in the said step 3, the silver solution is at least one of silver - ammonia complex solution, silver - ethylenediaminetetraacetic acid complex solution, silver - triethylenetetramine complex solution, and silver - diethylenetriamine, the amount of silver is 4% - 27% of the mass of the copper powder, the reaction temperature is 15 - 60 °C, and the reaction time is 5 - 100 min.

[0032] Among them, the total mass of silver in the metal salt solution and the silver reaction solution is less than 30% of the mass of the copper powder.

[0033] Among them, the total mass of silver in the metal salt solution and the silver reaction solution is less than 10% of the mass of the copper powder.

[0034] The evaluation implementation method of the silver-coated copper powder is as follows: use a wet laser particle size analyzer to detect the particle size of the silver-coated copper powder; use a simultaneous differential thermal and differential thermogravimetric determination device (TG-DTA device) to heat the above silver-coated copper powder from room temperature to 500 °C in the atmosphere, and evaluate its antioxidant performance and stability according to the weight increase rate of the silver-coated copper powder; mix the silver-coated copper powder with nano silver powder to prepare a slurry (mass ratio 7:3), the slurry formula includes epoxy resin, phthalic anhydride as a curing agent, and diethylene glycol butyl ether acetate as a solvent, and the solid content is not less than 93%. After curing at 200 °C, test its electrical conductivity.

[0035] Example 1 A method for preparing smooth and dense silver-coated copper powder, comprising the following steps: Step 1: Disperse 100 g of spherical copper powder with an average particle size of 2.5 μm in 300 g of sodium hydroxide solution with a mass concentration of 0.5%, and treat it at 80 °C for 30 min. After suction filtration and washing, transfer it to 300 g of nitric acid solution with a mass fraction of 4%, treat it at 80 °C for 30 min, and then suction filter and wash to remove the acid solution and residual anions.

[0036] Step 2: Transfer the pickled and washed copper powder to 200 mL containing 5 g of sodium formate, treat it at 40 °C for 120 min, and then suction filter and wash.

[0037] Step 3: Add 900 g of deionized water so that the mass fraction of copper powder in the suspension is 10%. Then add 20 g of disodium ethylenediaminetetraacetate, adjust the temperature of the suspension to 35 °C, the stirring rate of mechanical stirring is 300 rpm, and pump in 100 mL of silver nitrate solution with a mass fraction of 5% of the copper powder at a rate of 30 mL / min, and the reaction time is 10 min.

[0038] Step 4: Use a fast pump to pump in 150 mL of a reducing solution containing 27.48 g of potassium sodium tartrate, keep the reaction temperature at 35 °C, and the reaction time is 10 min; then pump in 100 mL of a silver solution containing 8.98 g of silver-ammonia complex solution at a rate of 30 mL / min, and the mass fraction of silver contained is 10% of the copper powder. After the reaction is completed, suction filter, wash with pure water, vacuum dry at 50 °C overnight, and pulverize to obtain the silver-coated copper target powder, and the specific morphology is as shown in the appendix Figure 1 as shown.

[0039] Example 2 The difference between this example and Example 1 is that the average particle size of the copper powder is 0.5 μm.

[0040] Example 3 The difference between this example and Example 1 is that the average particle size of the copper powder is 5 μm.

[0041] Example 4 The difference between this example and Example 1 is that the copper powder is dispersed in 1000 g of sodium hydroxide solution with a mass concentration of 1%.

[0042] Example 5 The difference between this example and Example 1 is that the copper powder is dispersed in 500 g of sodium hydroxide solution with a mass concentration of 4%.

[0043] Example 6 The difference between this example and Example 1 is that after suction filtration and washing, it is transferred to 1000 g of nitric acid solution with a mass fraction of 0.5%.

[0044] Example 7 The difference between this example and Example 1 is that after suction filtration and washing, it is transferred to 500 g of nitric acid solution with a mass fraction of 1%.

[0045] Example 8 The difference between this example and Example 1 is that the copper powder is dispersed in 300 g of potassium hydroxide and ammonia water with a mass concentration of 0.5%.

[0046] Example 9 The difference between this example and Example 1 is that after suction filtration and washing, it is transferred to 300 g of sulfuric acid and ammonium bisulfate with a mass fraction of 4%.

[0047] Example 10 The difference between this example and Example 1 is that the temperature in Step 1 is 40 °C and the treatment time is 240 min.

[0048] Example 11 The difference between this example and Example 1 is that the temperature in Step 1 is 60 °C and the treatment time is 10 min.

[0049] Example 12 The difference between this example and Example 1 is that 100 g of spherical copper powder with an average particle size of 2.5 μm is dispersed in 300 g of sodium hydroxide solution with a mass concentration of 0.5%, treated at 80 °C for 30 min, and then suction filtered and washed to remove residual anions.

[0050] Example 13 The difference between this example and Example 1 is as follows: 100 g of spherical copper powder with an average particle size of 2.5 μm is dispersed in 300 g of nitric acid solution with a mass fraction of 4%, treated at 80 °C for 30 min, and then filtered and washed to remove residual anions.

[0051] Example 14 A method for preparing smooth and dense silver-coated copper powder includes the following steps: Step 1: Disperse 100 g of quasi-spherical copper powder with an average particle size of 3 μm in 300 g of sodium hydroxide solution with a mass concentration of 0.5%, and treat it at 80 °C for 30 min. After filtration and washing, transfer it to 300 g of nitric acid solution with a mass fraction of 4%, treat it at 80 °C for 30 min, and then filter and wash to remove the acid solution and residual anions.

[0052] Step 2: Transfer the pickled and washed copper powder to 200 mL containing 3 g of formic acid, treat it at 60 °C for 120 min, and then filter and wash.

[0053] Step 3: Add 250 g of deionized water to make the mass fraction of copper powder in the suspension 40%. Then add 10 g of ethylenediaminetetraacetic acid, adjust the temperature of the suspension to 35 °C, the stirring rate of mechanical stirring is 300 rpm, pump in 100 mL of silver nitrate solution with a mass fraction of 5% of copper powder at a rate of 30 mL / min, and the reaction time is 10 min.

[0054] Step 4: Quickly pump in 150 mL of reducing solution containing 27.48 g of potassium sodium tartrate, keep the reaction temperature at 35 °C, and the reaction time is 10 min; then pump in 100 mL of silver solution containing 8.98 g of silver-ammonia complex solution at a rate of 30 mL / min, and the mass fraction of silver contained is 10% of copper powder. After the reaction, filter, wash with pure water, dry in vacuum at 50 °C overnight, and pulverize to obtain the silver-coated copper target powder, and the specific morphology is as shown in the appendix. Figure 2 as shown.

[0055] Example 15 The difference between this example and Example 14 is as follows: In Step 2, transfer the pickled and washed copper powder to 1000 mL containing 50 g of formic acid.

[0056] Example 16 The difference between this example and Example 14 is as follows: In Step 2, transfer the pickled and washed copper powder to 200 mL containing 3 g of nitric acid.

[0057] Example 17 The difference between this example and Example 14 is that in Step 2, the pickled and cleaned copper powder is transferred to 200 mL containing 3 g of acetic acid, sodium acetate, propionic acid, and sodium propionate.

[0058] Example 18 The difference between this example and Example 14 is that in Step 2, the pickled and cleaned copper powder is transferred to 200 mL containing 3 g of succinic acid, sodium succinate, hexanoic acid, and sodium hexanoate.

[0059] Example 19 The difference between this example and Example 14 is that in Step 2, it is treated at 80 °C for 10 min.

[0060] Example 20 A method for preparing smooth and dense silver-coated copper powder, comprising the following steps: Step 1: Disperse 100 g of spherical copper powder with an average particle size of 2.5 μm in 300 g of sodium hydroxide solution with a mass concentration of 0.5%, and treat it at 80 °C for 30 min. After suction filtration and cleaning, transfer it to 300 g of nitric acid solution with a mass fraction of 4%, and treat it at 80 °C for 30 min, then perform suction filtration and cleaning to remove the acid solution and residual anions.

[0061] Step 2: Transfer the pickled and cleaned copper powder to 200 mL containing 5 g of sodium formate, treat it at 40 °C for 120 min, and then perform suction filtration and cleaning.

[0062] Step 3: Add 900 g of deionized water to make the mass fraction of copper powder in the suspension 10%. Then add 20 g of tetrasodium ethylenediaminetetraacetate, adjust the temperature of the suspension to 35 °C, the stirring rate of mechanical stirring is 300 rpm, pump in 100 mL of silver nitrate solution with a mass fraction of 5% of copper powder at a rate of 30 mL / min, and the reaction time is 10 min.

[0063] Step 4: Use a rapid pump to pump in 150 mL of a reducing solution containing 27.48 g of potassium sodium tartrate, keep the reaction temperature at 35 °C, and the reaction time is 10 min; then pump in 100 mL of a silver solution containing 8.98 g of silver-ammonia complex solution at a rate of 30 mL / min, and the mass fraction of silver contained is 10% of copper powder. After the reaction, perform suction filtration, wash with pure water, vacuum dry at 50 °C overnight, and pulverize to obtain the silver-coated copper target powder, and the specific morphology is as shown in the appendix Figure 3 as shown.

[0064] Example 21 The difference between this example and Example 20 is that in Step 3, 20 g of triethylenetetramine and tetraethylenetriamine are added.

[0065] Example 22 The difference between this example and Example 20 is that in step 3, 20 g of N-acetyl sarcosine is added.

[0066] Example 23 The difference between this example and Example 20 is that in step 3, a silver nitrate solution with a mass fraction of 0.5% of copper powder is pumped in at a rate of 30 mL / min for 100 mL; step 4: Subsequently, a silver solution containing 12.74 g of silver-ammonia complex solution is pumped in at a rate of 30 mL / min for 100 mL, and the mass fraction of silver contained is 10% of copper powder.

[0067] Example 24 The difference between this example and Example 20 is that in step 3, a silver nitrate solution with a mass fraction of 2% of copper powder is pumped in at a rate of 30 mL / min for 100 mL; step 4: Subsequently, a silver solution containing 11.49 g of silver-ammonia complex solution is pumped in at a rate of 30 mL / min for 100 mL, and the mass fraction of silver contained is 10% of copper powder.

[0068] Example 25 The difference between this example and Example 20 is that in step 3, a silver sulfate solution and a silver acetate solution with a mass fraction of 5% of copper powder are pumped in at a rate of 30 mL / min for 100 mL.

[0069] Example 26 The difference between this example and Example 20 is that in step 3, a stannous chloride solution and a palladium chloride solution with a mass fraction of 5% of copper powder are pumped in at a rate of 30 mL / min for 100 mL.

[0070] Example 27 The difference between this example and Example 20 is that in step 4, a reducing solution containing 3.68 g of sodium borohydride is quickly pumped in for 150 mL.

[0071] Example 28 The difference between this example and Example 20 is that in step 4, a reducing solution containing 17.54 g of glucose is quickly pumped in for 150 mL.

[0072] Example 29 The difference between this example and Example 20 is that in step 4, a reducing solution containing 4.87 g of hydrazine hydrate is quickly pumped in for 150 mL.

[0073] Example 30 The difference between this example and Example 20 lies in: Step 4: Rapidly pump in 150 mL of a reducing solution containing 13.44 g of ascorbic acid, citric acid, and formic acid (ascorbic acid:citric acid:formic acid = 1:1:1).

[0074] Example 31 The difference between this example and Example 20 lies in: Step 4: Rapidly pump in 150 mL of a reducing solution containing 27.48 g of potassium sodium tartrate, maintain the reaction temperature at 35°C, and the reaction time at 10 min; then pump in 100 mL of a silver solution containing 25.32 g of silver-ethylenediaminetetraacetic acid complex solution at a rate of 30 mL / min, and the mass fraction of silver contained is 10% of the copper powder.

[0075] Example 32 The difference between this example and Example 20 lies in: Step 4: Rapidly pump in 150 mL of a reducing solution containing 27.48 g of potassium sodium tartrate, maintain the reaction temperature at 35°C, and the reaction time at 10 min; then pump in 100 mL of a silver solution containing 16.08 g of silver-triethylenetetramine complex solution at a rate of 30 mL / min, and the mass fraction of silver contained is 10% of the copper powder.

[0076] Example 33 The difference between this example and Example 20 lies in: Step 4: Rapidly pump in 150 mL of a reducing solution containing 27.48 g of potassium sodium tartrate, maintain the reaction temperature at 35°C, and the reaction time at 10 min; then pump in 100 mL of a silver solution containing 13.36 g of silver-diethylenetriamine solution at a rate of 30 mL / min, and the mass fraction of silver contained is 10% of the copper powder.

[0077] Example 34 The difference between this example and Example 20 lies in: Step 4: Rapidly pump in 150 mL of a reducing solution containing 19.71 g of potassium sodium tartrate, maintain the reaction temperature at 35°C, and the reaction time at 10 min; then pump in 100 mL of a silver solution containing 5.26 g of silver-ammonia complex solution at a rate of 30 mL / min, and the mass fraction of silver contained is 7.175% of the copper powder.

[0078] Example 35 The difference between this example and Example 20 lies in: Step 4: Rapidly pump in 500 mL of a reducing solution containing 95.49 g of potassium sodium tartrate, maintain the reaction temperature at 35°C, and the reaction time at 10 min; then pump in 100 mL of a silver solution containing 31.58 g of silver-ammonia complex solution at a rate of 30 mL / min, and the mass fraction of silver contained is 30.175% of the copper powder.

[0079] Comparative Example 1 Step 1: Disperse 100 g of spherical copper powder with an average particle size of 3.0 μm in 200 mL of 0.05 mol / L sodium hydroxide solution and treat it at 60 °C for 30 min. After suction filtration and washing, transfer it to 200 mL of acidic solution with a mass fraction of 1% and treat it at 60 °C for 20 min, then perform suction filtration and washing to remove the acid solution and residual anions.

[0080] Step 2: Transfer the pickled copper powder to 200 mL of pure water and treat it at 60 °C for 30 min, then perform suction filtration and washing.

[0081] Step 3: Add 900 g of deionized water to make the mass fraction of copper powder in the suspension 10%. Then add 20 g of disodium ethylenediaminetetraacetate, adjust the temperature of the suspension to 35 °C, the stirring rate of mechanical stirring is 300 rpm, and pump in 100 mL of silver nitrate solution with a mass fraction of 3% of copper powder at a rate of 30 mL / min, and the mass of silver nitrate is 4.00 g.

[0082] Step 4: Use a rapid pump to pump in 100 mL of reducing solution containing 17.68 g of potassium sodium tartrate, keep the reaction temperature at 35 °C, and the stirring rate of mechanical stirring is between 300 rpm. Pump in the silver-ammonia complex solution prepared with 12.01 g of silver nitrate at a rate of 30 mL / min, and the mass fraction of silver contained is 9% of copper powder. After the reaction, perform suction filtration, wash with pure water, vacuum dry at 50 °C overnight, and pulverize to obtain the silver-coated copper target powder, and the specific morphology is as shown in the appendix Figure 4 as follows.

[0083] The data of the silver-coated copper powder and the test data of the above examples and comparative examples are shown in Tables 1 and 2 in the appendix. It can be seen from Example 14 and Comparative Example 1 that after using the protective agent to protect the copper powder, the surface of the formed silver-coated copper powder is denser and smoother, the specific surface area is lower, the thermal weight gain is lower, and the resistivity is lower. It can be seen from Examples 1-35 that pickling, sensitization, and silver reduction all affect the coating effect. Since pickling and alkali washing activation will affect the surface activity of the copper powder before protection, and protection changes the surface reaction activity of the copper powder, it is necessary to regulate sensitization and reduction after protection.

[0084] Table 1 Table 2 The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any simple modification and equivalent change made to the above embodiments based on the technical essence of the present invention all fall within the protection scope of the present invention.

Claims

1. A method for preparing smooth and dense silver-coated copper powder, characterized in that: The following steps are involved: Step 1, copper powder surface activation treatment: dispersing the copper powder in an alkaline or acidic solution to clean and remove organic matter and an oxide layer on the copper powder surface, or cleaning and removing organic matter and an oxide layer on the copper powder surface in an alkaline or acidic solution in two steps; Step 2, protection treatment of activated copper powder: adding the highly active copper powder obtained after acid washing or alkali washing into the protection reagent solution and stirring and mixing, so as to reduce the oxidation rate of the copper powder in the solution and the air; Step 3, coating the surface of the copper powder with a silver layer: in the copper powder suspension in the protective solution, a complexing agent, a metal salt solution, a reducing agent and a silver solution are added in sequence, and after a certain temperature and reaction time, a silver-coated copper suspension is obtained; the suspension is washed, filtered, and dried to obtain the silver-coated copper powder.

2. The method for preparing a smooth and dense silver-coated copper powder according to claim 1, characterized in that: In the step 1, the copper powder is spherical or quasi-spherical, and the average particle size of the copper powder is 0.5-5 μm.

3. The method for preparing a smooth and dense silver-coated copper powder according to claim 2, characterized in that: In step 1, the alkaline solution is at least one of sodium hydroxide, potassium hydroxide and ammonia water; the alkaline solution is a 0.5%-4% mass fraction solution, the amount of the solution added is 3-10 times the mass of the copper powder, the treatment temperature is 40-80°C, and the treatment time is 10-240min.

4. The method for preparing a smooth and dense silver-coated copper powder according to claim 3, characterized in that: In step 1, the acidic solution is at least one of sulfuric acid, nitric acid, and ammonium bisulfate; the acidic solution is a 0.5%-4% mass fraction solution, the amount of the solution added is 3-10 times the mass of the copper powder, the treatment temperature is 40-80° C., and the treatment time is 10-240 min.

5. The method for preparing a smooth and dense silver-coated copper powder according to claim 4, characterized in that: In step 2, the protective agent is at least one of nitric acid, formic acid, sodium formate, potassium formate, acetic acid, sodium acetate, potassium acetate, propionic acid, sodium propionate, potassium propionate, succinic acid, sodium succinate, potassium succinate, hexanoic acid, sodium hexanoate and potassium hexanoate; the amount of the protective agent added is 3-50% of the mass of the copper powder, and the treatment temperature is 20-80°C.

6. The method for preparing a smooth and dense silver-coated copper powder according to claim 5, characterized in that: In the step 3, the complexing agent is at least one of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, triethylenetetramine, tetraethylenetriamine, and N-acetylsarcosine, and the amount of the complexing agent added is 10%-40% of the mass of the copper powder.

7. The method for preparing a smooth and dense silver-coated copper powder according to claim 6, characterized in that: In step 3, the metal salt solution is at least one of silver nitrate, silver sulfate, silver acetate, stannous chloride, and palladium chloride; the amount of metal salt added is 0.5-5% of the mass of the copper powder, the reaction temperature is 15-60° C., and the reaction time is 1-15 min.

8. The method for preparing a smooth and dense silver-coated copper powder according to claim 7, characterized in that: In the step 3, the reducing agent is at least one of sodium borohydride, tartaric acid, glucose, ascorbic acid, citric acid, formic acid, formaldehyde, hydrazine hydrate and metal salts of all the reducing substances above; the metal salts include sodium salts, potassium salts, sodium potassium salts, calcium salts and magnesium salts; the amount of the reducing agent added is 1.05 times the molar amount of the silver source, the reaction temperature is 10-40°C, and the reaction time is 5-40min.

9. The method for preparing a smooth and dense silver-coated copper powder according to claim 8, characterized in that: In step 3, the silver solution is at least one of a silver-ammonia complex solution, a silver-ethylenediaminetetraacetic acid complex solution, a silver-triethylenetetramine complex solution, and a silver-diethylenetriamine complex solution, the amount of silver is 4%-27% of the mass of the copper powder, the reaction temperature is 15-60° C., and the reaction time is 5-100 min.

10. The method for preparing a smooth and dense silver-coated copper powder according to claim 9, characterized in that: The total mass of silver in the metal salt solution and the silver reaction solution is less than 30% of the mass of the copper powder.

11. The method for preparing a smooth and dense silver-coated copper powder according to claim 9, characterized in that: The total mass of silver in the metal salt solution and the silver reaction solution is less than 10% of the mass of the copper powder.

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