Silver-coated copper powder with dense and smooth silver coating and preparation method thereof

Abstract

The present invention provides a silver-coated copper powder with a dense and smooth silver coating and a preparation method thereof, which belongs to the field of conductive slurry. The preparation method comprises the following steps: the first step is to remove the oxide on the surface of the copper powder; the second step is to prepare a silver-coated copper powder precursor; the third step is to mix the silver-coated copper powder precursor with a complexing agent, a dispersant and a reducing agent, and add deionized water to prepare a solution, slowly drip a silver salt solution of a certain concentration into the solution, and use a small amount of silver coating layer on the surface as a nucleation point to perform a reduction reaction to achieve dense coating of the silver-coated copper powder precursor. The present invention combines a chemical replacement method and a chemical reduction method to prepare silver-coated copper powder, first performs a small amount of replacement reaction, and then performs a reduction reaction to prepare the silver-coated copper powder, so as to achieve the purpose of high sphericity, small particle size, density and smoothness of the silver coating layer in the silver-coated copper powder.

Description

Technical Field

[0001] The invention belongs to the technical field of silver-coated copper powder, and particularly relates to silver-coated copper powder with dense and smooth silver plating layer and a preparation method thereof. Background Art

[0002] Silver-coated copper powder is a core-shell powder material with copper as the core and silver as the shell. It has the characteristics of excellent conductivity and strong oxidation resistance. Compared with silver powder, silver-coated copper powder is cheap and can effectively inhibit silver migration. Therefore, silver-coated copper powder is an ideal substitute for silver powder and has broad application prospects in the fields of electronic information, photovoltaic power generation, conductive paste, heterojunction battery, aerospace and mobile communications.

[0003] There are many methods for preparing silver-coated copper powder, including chemical plating, mechanical ball milling, melt physicochemical method, electrodeposition method, photoinduction method, etc. Among them, chemical plating is widely used in experimental research and industrial production due to its simple preparation process, low cost and stable performance of the prepared powder. Chemical plating is generally divided into a replacement process and a reduction process. The replacement process is to react the free silver ions with the copper atoms on the surface of the copper powder and deposit on the sample surface through the potential difference between silver and copper ions, but it has the disadvantages of thin silver coating, loose and porous, and low binding force with copper powder. The reduction method is to add a reducing agent so that the silver ions react on the surface of the copper powder and are wrapped on the surface of the copper powder, but it is easy to cause the phenomenon that the silver ions nucleate alone without coating the copper powder. Chemical plating is widely used in research and production, but there are still some problems with the silver-coated copper powder prepared by a single chemical plating method. Some manufacturers adopt the method of adding soluble silver salt in stages. First, a small amount of soluble silver salt is added to the suspension emulsion to undergo a replacement reaction with the copper powder to form silver crystal points on the surface of the copper powder. Then, most of the soluble silver salt and the reducing agent are added to the suspension emulsion. The silver ions are reduced to single silver under the action of the reducing agent with the above-mentioned silver crystal points as the center, thereby completing the encapsulation of the copper powder. However, the silver-coated copper powder prepared by this method has good antioxidant properties and unreasonable conductivity, which cannot meet market demand.

[0004] Therefore, how to use innovative methods to prepare silver-coated copper powder with high sphericity, dense packaging, continuity and smooth surface, low resistivity, excellent oxidation resistance and conductivity is still a problem to be solved in this field. Summary of the invention

[0005] The invention aims to provide a silver-coated copper powder with a dense and smooth silver plating layer and a preparation method thereof.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing silver-coated copper powder with a dense and smooth silver coating comprises the following steps:

[0008] (1) 200 parts by weight of copper powder, 3-6 parts by weight of a first dispersant, and 18,000-20,000 parts by weight of a sulfuric acid solution are mixed to obtain a first mixed solution, and the mixture is stirred at a speed of 300-500 r / min for 0.8-1.2 h to remove surface oxides, and then filtered, washed with water until neutral, and dried to obtain pretreated copper powder;

[0009] (2) 270-320 parts by weight of pretreated copper powder, 3000 parts by weight of deionized water, 28-34 parts by weight of a first complexing agent and 2-5 parts by weight of a second dispersant are mixed to obtain a second mixed solution, and 500 parts by weight of a silver nitrate solution having a concentration of 3.7-4.2 g / L is simultaneously prepared and dripped into the second mixed solution at a rate of 4-6 mL / min, and the dripping conditions are: a stirring speed of 360-420 r / min, a stirring time of 0.5-3 h, and a water bath constant temperature of 20-80° C.; after the silver nitrate solution is dripped, filtering, washing and drying are performed to obtain a silver-coated copper powder precursor in which a small amount of silver is coated on the surface of the copper powder;

[0010] The second dispersant comprises polyethylene glycol, a homemade first dispersant and polyvinyl pyrrolidone in a weight ratio of 1: (1.2-1.4): (0.5-0.7);

[0011] The method for preparing the homemade first dispersant comprises the following steps:

[0012] S1: Under a nitrogen atmosphere, 2 parts by weight of 4,4′-diformic acid diphenyl ether, 0.12-0.15 parts by weight of dimethylformamide and 46-48 parts by weight of toluene are mixed, and 2.7-3.2 parts by weight of thionyl chloride are added dropwise. After the addition is complete, the temperature is raised to 70-75° C., the reaction is carried out for 5-6 hours, and the mixture is concentrated to dryness to obtain 4,4′-diformyl chloride diphenyl ether;

[0013] S2: dissolving 2.5-2.8 parts by weight of 4,4′-diformyl chloride diphenyl ether in 6-10 parts by weight of dichloromethane to obtain a dichloromethane solution of 4,4′-diformyl chloride diphenyl ether; mixing 12-15 parts by weight of alkylphenol polyoxyethylene ether OP-7 (Haian Petrochemical Plant, Jiangsu Province), 0.1-0.15 parts by weight of dimethylformamide, 2-2.3 parts by weight of triethylamine and 0.4-0.5 parts by weight of 2,6-di-tert-butyl-4-methylphenol, and adding 40-45 parts by weight of dichloromethane to dissolve; dropping the dichloromethane solution of 4,4′-diformyl chloride diphenyl ether, reacting at room temperature for 5-6 hours, adding water for separation after the reaction is completed, recovering the organic phase, using petroleum ether and ethyl acetate in a volume ratio of 10:1 as a solvent, using a silica gel column for purification, collecting the eluate, and rotating and concentrating to remove the solvent to obtain a self-made first dispersant;

[0014] (3) 270-320 parts by weight of a silver-coated copper powder precursor, 3000 parts by weight of deionized water, 28-32 parts by weight of a second complexing agent, 28-32 parts by weight of a reducing agent and 2-5 parts by weight of a third dispersant are mixed to obtain a third mixed solution, and 500 parts by weight of a silver nitrate solution with a concentration of 57-62 g / L is simultaneously prepared and dropwise added to the third mixed solution. During the dropwise addition process, the dropwise addition speed is 4-6 mL / min, the stirring speed is 300-500 r / min, the stirring time is 0.5-3 h, and the temperature is kept constant in a water bath at 20-80° C.; after the dropwise addition is completed, filtering, washing and drying are performed to obtain a silver-coated copper powder with a dense and smooth silver coating.

[0015] The present invention attempts to improve the coating effect of a silver-coated copper powder precursor in which a small amount of silver is coated on the surface of the copper powder by adding a commercially available second dispersant, but it is not ideal. The present invention can better reduce the resistivity of the silver-coated copper powder by compounding the commercially available second dispersant and the homemade first dispersant at a specific ratio. The compounded second dispersant contains second dispersants with different HLB values. These second dispersants behave differently in the water phase and the oil phase and can complement each other. The system of the present invention can reduce the interfacial tension between water and the surface of the copper powder, making the copper powder easier to disperse in the suspension emulsion, thereby increasing the contact opportunity between the silver ions and the surface of the copper powder. At the same time, the wettability of the copper powder can be improved, making it easier for the silver ions to be evenly distributed on the surface of the copper powder, promoting a uniform replacement reaction, and the second dispersant can be adsorbed on the surface of the silver crystal nucleus to inhibit the excessive growth of the crystal nucleus, thereby promoting the formation of smaller and more uniform silver crystal points; more nucleation sites can be provided, so that the silver crystal points are evenly distributed on the surface of the copper powder.

[0016] Furthermore, in step (1), the particle size of the copper powder is 2.5-4.0 μm, and the average particle size is 3.5 μm.

[0017] Furthermore, the concentration of the sulfuric acid solution in step (1) is 5%-40% by mass.

[0018] Furthermore, in step (1), the first dispersant is one or more of polyvinyl pyrrolidone, polyethylene glycol, polyacrylic acid, and polypropylene alcohol; and the concentration of the first dispersant in the first mixed solution is 0.001 mol / L-0.8 mol / L.

[0019] Furthermore, during the dropping process in step (3), the dropping speed is 4-6 mL / min, the stirring speed is 380-400 r / min, the stirring time is 0.8-1.2 h, and the temperature is kept constant in a water bath at 55-65° C.

[0020] When the reduction reaction is carried out in the present invention, the dripping conditions have a great influence on the performance parameters of the silver-coated copper powder. Under specific dripping conditions, the particle size of the silver-coated copper powder is smaller and the tap density is higher. Analysis shows that the dripping conditions have a great influence on the performance parameters of the silver-coated copper powder, especially in terms of particle size and tap density. The dripping speed, stirring speed, stirring time and temperature all need to be within a suitable range to ensure that silver ions are uniformly deposited on the surface of the copper powder to form a dense and smooth silver coating.

[0021] Furthermore, in step (2), the first complexing agent includes one or more of EDTA, EDTA2Na, EDTA4Na, ammonia water, ethylenediamine, diethylenetriamine, triethylenetetramine and tetraethylenepentamine, and the concentration of the first complexing agent in the second mixed solution is 0.01g / L-10g / L.

[0022] Furthermore, in step (3), the third dispersant is one or more of polyvinyl pyrrolidone, polyethylene glycol, polyacrylic acid, and polypropylene alcohol; and the concentration of the first dispersant in the first mixed solution is 0.001 mol / L-0.8 mol / L.

[0023] Furthermore, in the step (3), the third dispersant is a mixture of polyethylene glycol, polyacrylic acid and a homemade third dispersant in a weight ratio of (1.5-1.7):1:(0.2-0.4).

[0024] Furthermore, the preparation method of the homemade third dispersant comprises the following steps:

[0025] (1) Under a nitrogen atmosphere, the reactor was evacuated to -0.09 MPa, 100 parts by weight of isooctyl alcohol polyoxyethylene ether and 0.3 parts by weight of sodium hydroxide were mixed, the temperature was raised to 100-105° C., and heated for 1-2 h to obtain dehydrated isooctyl alcohol polyoxyethylene ether.

[0026] (2) Add 23-25 ​​parts by weight of styrene oxide to the dehydrated isooctyl alcohol polyoxyethylene ether, react at 100-105° C. for 3-4 hours, add acetic acid to make the pH neutral, and obtain a self-made third dispersant.

[0027] The present invention uses a single dispersant, and the anti-oxidation effect of the obtained silver-coated copper powder is not good. The effect is also not ideal when compounded with commercially available dispersants. The present invention can improve the anti-oxidation effect of the silver-coated copper powder by compounding a commercially available dispersant and a homemade third dispersant in a specific ratio. Analysis shows that the dispersant of the present invention can prevent the agglomeration of the silver-coated copper powder particles and maintain the uniform dispersion of the particles. At the same time, the compounded dispersant forms a dense protective layer on the surface of the silver-coated copper powder to isolate the contact between silver and oxygen and reduce the occurrence of oxidation reactions; PEG, PAA and the homemade third dispersant can form a multi-layer protective structure on the surface of the silver-coated copper powder, each layer has different functions, and the anti-oxidation performance is improved together.

[0028] Furthermore, in step (3), the second complexing agent includes one or more of EDTA, EDTA2Na, EDTA4Na, ammonia water, ethylenediamine, diethylenetriamine, triethylenetetramine and tetraethylenepentamine, and the concentration of the second complexing agent in the third mixed solution is 0.01g / L-10g / L.

[0029] Furthermore, in step (3), the reducing agent comprises at least one of hydrazine hydrate, sodium borohydride, gum arabic, glucose, ascorbic acid, L-histidine, and glutamic acid; and the concentration of the reducing agent in the third mixed solution is 0.2 g / L-50 g / L.

[0030] The invention also provides silver-coated copper powder with dense and smooth silver plating layer obtained by the preparation method.

[0031] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0032] 1. The present invention adopts a chemical replacement method plus a chemical reduction method to prepare silver-coated copper powder: first, the copper powder is pretreated and mixed with a dispersant and a complexing agent, and then a small amount of silver nitrate solution is added to the mixed solution, a small amount of replacement reaction occurs in the system, and a silver-coated copper powder precursor is prepared; then the silver-coated copper powder precursor is mixed with a complexing agent, a dispersant, a reducing agent and deionized water, and a silver nitrate solution is added to the mixed solution to cause a reduction reaction, so that the silver generated by the reduction forms a small amount of silver on the surface of the high-energy precursor as a nucleation point for nucleation growth, thereby achieving a tight coating of the high-energy precursor powder. The silver-coated copper powder prepared by the present invention has good sphericity and a dense and smooth silver coating layer.

[0033] 2. The present invention can effectively reduce the resistivity of silver-coated copper powder by compounding the commercially available second dispersant and the homemade first dispersant in a specific ratio.

[0034] 3. Under specific dropping conditions, the particle size of silver-coated copper powder is smaller and the tap density is higher.

[0035] 4. The present invention can improve the oxidation resistance of silver-coated copper powder by compounding a commercially available dispersant and a homemade third dispersant in a specific ratio. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The raw materials used in the following examples are all commercially available products:

[0038] The particle size of the copper powder is 2.5-4.0 μm, and the average particle size is 3.5 μm.

[0039] Polyethylene glycol, Nantong Arches Chemical Co., Ltd., polyethylene glycol 400.

[0040] Polyvinyl pyrrolidone, Rongsheng New Materials Technology (Nantong, Jiangsu) Co., Ltd., industrial grade PVPK30.

[0041] Polyacrylic acid, Hubei Kemaidi Chemical Co., Ltd., molecular weight 100,000.

[0042] 2-Ethylene glycol ether, Nantong Yongle Chemical Co., Ltd.

[0043] C16-18 alcohol polyoxyethylene ether, O-10, Hai'an Petrochemical Plant, Jiangsu Province.

[0044] Example 1

[0045] This embodiment provides a silver-coated copper powder with a dense and smooth silver plating layer, and the preparation method thereof comprises the following steps:

[0046] (1) 200 parts by weight of copper powder, 5 parts by weight of a first dispersant, and 19,000 parts by weight of a sulfuric acid solution were mixed to obtain a first mixed solution, which was stirred at a speed of 400 r / min for 1 hour to remove surface oxides, and then filtered, washed with water until neutral, and dried to obtain pretreated copper powder; the concentration of the sulfuric acid solution was 20% by mass. The first dispersant was polyvinyl pyrrolidone; and the concentration of the first dispersant in the first mixed solution was 0.2 mol / L.

[0047] (2) 300 parts by weight of pretreated copper powder, 3000 parts by weight of deionized water, 30 parts by weight of a first chelating agent and 4 parts by weight of a second dispersant are mixed to obtain a second mixed solution, and 500 parts by weight of a silver nitrate solution with a concentration of 4 g / L is prepared and added dropwise to the second mixed solution at a rate of 5 mL / min. The conditions for the addition are: a stirring speed of 400 r / min, a stirring time of 1 h, and a constant temperature of 60°C in a water bath. After the addition of the silver nitrate solution, the mixture is filtered, washed, and dried to obtain a silver-coated copper powder precursor in which a small amount of silver is coated on the surface of the copper powder. The first chelating agent is EDTA, and the concentration of the first chelating agent in the second mixed solution is 2 g / L.

[0048] The second dispersant comprises polyethylene glycol, a homemade first dispersant and polyvinyl pyrrolidone in a weight ratio of 1:1.3:0.6;

[0049] The method for preparing the homemade first dispersant comprises the following steps:

[0050] S1: Under a nitrogen atmosphere, 2 parts by weight of 4,4′-diformic acid diphenyl ether, 0.14 parts by weight of dimethylformamide and 47 parts by weight of toluene were mixed, and 3 parts by weight of thionyl chloride were added dropwise. After the addition was completed, the temperature was raised to 72° C., the reaction was carried out for 5.5 hours, and the mixture was concentrated to dryness to obtain 4,4′-diformyl chloride diphenyl ether;

[0051] S2: Dissolve 2.7 parts by weight of 4,4′-diformyl chloride diphenyl ether in 8 parts by weight of dichloromethane to obtain a dichloromethane solution of 4,4′-diformyl chloride diphenyl ether; mix 13 parts by weight of alkylphenol polyoxyethylene ether OP-7 (Haian Petrochemical Plant, Jiangsu Province), 0.12 parts by weight of dimethylformamide, 2.2 parts by weight of triethylamine and 0.45 parts by weight of 2,6-di-tert-butyl-4-methylphenol, and add 42 parts by weight of dichloromethane to dissolve; dropwise add the dichloromethane solution of 4,4′-diformyl chloride diphenyl ether, react at room temperature for 5.5 hours, and after the reaction is completed, add water for liquid separation, recover the organic phase, use petroleum ether and ethyl acetate in a volume ratio of 10:1 as solvent, use a silica gel column for column purification, collect the eluate, and rotate and concentrate to remove the solvent to obtain a self-made first dispersant;

[0052] (3) 300 parts by weight of a silver-coated copper powder precursor, 3000 parts by weight of deionized water, 30 parts by weight of a second complexing agent, 30 parts by weight of a reducing agent, and 4 parts by weight of a third dispersant are mixed to obtain a third mixed solution. At the same time, 500 parts by weight of a 60 g / L silver nitrate solution is prepared and added dropwise to the third mixed solution. During the addition process, the addition speed is 5 mL / min, the stirring speed is 390 r / min, the stirring time is 1 h, and the temperature is kept constant in a water bath at 60°C. After the addition is completed, the mixture is filtered, washed, and dried to obtain a silver-coated copper powder with a dense and smooth silver coating.

[0053] In the step (3), the third dispersant is polyvinyl pyrrolidone; the concentration of the first dispersant in the first mixed solution is 0.2 mol / L. The second complexing agent is EDTA, and the concentration of the second complexing agent in the third mixed solution is 2 g / L. The reducing agent is hydrazine hydrate; the concentration of the reducing agent in the third mixed solution is 10 g / L.

[0054] The third dispersant in step (3) is a mixture of polyethylene glycol, polyacrylic acid and a homemade third dispersant in a weight ratio of 1.6:1:0.3.

[0055] The preparation method of the self-made third dispersant comprises the following steps:

[0056] (1) Under a nitrogen atmosphere, the reactor was evacuated to -0.09 MPa, 100 parts by weight of isooctyl alcohol polyoxyethylene ether and 0.3 parts by weight of sodium hydroxide were mixed, the temperature was raised to 102° C., and heated for 1.5 h to obtain dehydrated isooctyl alcohol polyoxyethylene ether.

[0057] (2) 24 parts by weight of styrene oxide was introduced into the dehydrated isooctyl alcohol polyoxyethylene ether, and the mixture was reacted at 102° C. for 3.5 h. Acetic acid was added to make the pH neutral to obtain a self-made third dispersant.

[0058] Example 2

[0059] This embodiment provides a silver-coated copper powder with a dense and smooth silver plating layer, and the preparation method thereof comprises the following steps:

[0060] (1) 200 parts by weight of copper powder, 3 parts by weight of a first dispersant, and 18,000 parts by weight of a sulfuric acid solution were mixed to obtain a first mixed solution, which was stirred at a speed of 500 r / min for 0.8 h to remove surface oxides, and then filtered, washed with water until neutral, and dried to obtain a pretreated copper powder; the concentration of the sulfuric acid solution was 15% by mass. The first dispersant was polyethylene glycol; the concentration of the first dispersant in the first mixed solution was 0.8 mol / L.

[0061] (2) 270 parts by weight of pretreated copper powder, 3000 parts by weight of deionized water, 34 parts by weight of a first chelating agent and 2 parts by weight of a second dispersant are mixed to obtain a second mixed solution, and 500 parts by weight of a silver nitrate solution with a concentration of 4.2 g / L is prepared and added dropwise to the second mixed solution at a rate of 4 mL / min. The conditions for the addition are: a stirring speed of 420 r / min, a stirring time of 3 h, and a constant temperature of 80° C. in a water bath. After the addition of the silver nitrate solution, the mixture is filtered, washed and dried to obtain a silver-coated copper powder precursor in which a small amount of silver is coated on the surface of the copper powder. The first chelating agent is EDTA2Na, and the concentration of the first chelating agent in the second mixed solution is 10 g / L.

[0062] The second dispersant comprises polyethylene glycol, a homemade first dispersant and polyvinyl pyrrolidone in a weight ratio of 1:1.2:0.5;

[0063] The method for preparing the homemade first dispersant comprises the following steps:

[0064] S1: Under a nitrogen atmosphere, 2 parts by weight of 4,4′-diformic acid diphenyl ether, 0.15 parts by weight of dimethylformamide and 48 parts by weight of toluene were mixed, and 2.7 parts by weight of thionyl chloride were added dropwise. After the addition was completed, the temperature was raised to 75° C., the reaction was carried out for 5 hours, and the mixture was concentrated to dryness to obtain 4,4′-diformyl chloride diphenyl ether;

[0065] S2: Dissolve 2.8 parts by weight of 4,4′-diformyl chloride diphenyl ether in 10 parts by weight of dichloromethane to obtain a dichloromethane solution of 4,4′-diformyl chloride diphenyl ether; mix 15 parts by weight of alkylphenol polyoxyethylene ether OP-7 (Haian Petrochemical Plant, Jiangsu Province), 0.1 parts by weight of dimethylformamide, 2.3 parts by weight of triethylamine and 0.4 parts by weight of 2,6-di-tert-butyl-4-methylphenol, and add 45 parts by weight of dichloromethane to dissolve; dropwise add the dichloromethane solution of 4,4′-diformyl chloride diphenyl ether, react at room temperature for 5 hours, and after the reaction is completed, add water for liquid separation, recover the organic phase, use petroleum ether and ethyl acetate in a volume ratio of 10:1 as solvent, use a silica gel column for column purification, collect the eluate, and rotate and concentrate to remove the solvent to obtain a self-made first dispersant;

[0066] (3) 270 parts by weight of a silver-coated copper powder precursor, 3000 parts by weight of deionized water, 32 parts by weight of a second complexing agent, 32 parts by weight of a reducing agent, and 2 parts by weight of a third dispersant were mixed to obtain a third mixed solution. At the same time, 500 parts by weight of a 62 g / L silver nitrate solution was prepared and added dropwise to the third mixed solution. During the addition process, the addition speed was 6 mL / min, the stirring speed was 380 r / min, the stirring time was 1.2 h, and the temperature was kept constant in a water bath at 55°C. After the addition was completed, the mixture was filtered, washed, and dried to obtain a silver-coated copper powder with a dense and smooth silver coating.

[0067] In step (3), the third dispersant is polyethylene glycol; the concentration of the first dispersant in the first mixed solution is 0.8 mol / L. The second complexing agent is EDTA2Na, and the concentration of the second complexing agent in the third mixed solution is 10 g / L. The reducing agent is sodium borohydride; the concentration of the reducing agent in the third mixed solution is 30 g / L.

[0068] The third dispersant in step (3) is a mixture of polyethylene glycol, polyacrylic acid and a homemade third dispersant in a weight ratio of 1.5:1:0.2.

[0069] The preparation method of the self-made third dispersant comprises the following steps:

[0070] (1) Under a nitrogen atmosphere, the reactor was evacuated to -0.09 MPa, 100 parts by weight of isooctyl alcohol polyoxyethylene ether and 0.3 parts by weight of sodium hydroxide were mixed, the temperature was raised to 105° C., and heated for 2 h to obtain dehydrated isooctyl alcohol polyoxyethylene ether.

[0071] (2) 25 parts by weight of styrene oxide was introduced into the dehydrated isooctyl alcohol polyoxyethylene ether, and the mixture was reacted at 105° C. for 3 h. Acetic acid was added to make the pH neutral to obtain a self-made third dispersant.

[0072] Comparative Example 1

[0073] The difference between this comparative example and Example 1 is that the second dispersant comprises polyethylene glycol, a homemade first dispersant and polyvinyl pyrrolidone in a weight ratio of 1:1:1, and the preparation method of the homemade first dispersant is the same as that of Example 1.

[0074] Comparative Example 2

[0075] The difference between this comparative example and Example 1 is that the second dispersant comprises polyethylene glycol, Tween 60 and polyvinyl pyrrolidone in a weight ratio of 1:1.3:0.6.

[0076] Comparative Example 3

[0077] The difference between this comparative example and Example 1 is that alkylphenol polyoxyethylene ether OP-7 (from Hai'an Petrochemical Plant, Jiangsu Province) is replaced by alkylphenol polyoxyethylene ether OP-10 (from Hai'an Petrochemical Plant, Jiangsu Province).

[0078] The method for preparing the homemade first dispersant comprises the following steps:

[0079] S1: Under a nitrogen atmosphere, 2 parts by weight of 4,4′-diformic acid diphenyl ether, 0.14 parts by weight of dimethylformamide and 47 parts by weight of toluene were mixed, and 3 parts by weight of thionyl chloride were added dropwise. After the addition was completed, the temperature was raised to 72° C., the reaction was carried out for 5.5 hours, and the mixture was concentrated to dryness to obtain 4,4′-diformyl chloride diphenyl ether;

[0080] S2: Dissolve 2.7 parts by weight of 4,4′-diformyl chloride diphenyl ether in 8 parts by weight of dichloromethane to obtain a dichloromethane solution of 4,4′-diformyl chloride diphenyl ether; mix 13 parts by weight of alkylphenol polyoxyethylene ether OP-10 (Haian Petrochemical Plant, Jiangsu Province), 0.12 parts by weight of dimethylformamide, 2.2 parts by weight of triethylamine and 0.45 parts by weight of 2,6-di-tert-butyl-4-methylphenol, and add 42 parts by weight of dichloromethane to dissolve; dropwise add the dichloromethane solution of 4,4′-diformyl chloride diphenyl ether, react at room temperature for 5.5 hours, and after the reaction is completed, add water for liquid separation, recover the organic phase, use petroleum ether and ethyl acetate in a volume ratio of 10:1 as solvent, use a silica gel column for column purification, collect the eluate, and rotate and concentrate to remove the solvent to obtain a self-made first dispersant;

[0081] Comparative Example 4

[0082] The difference between this comparative example and Example 1 is that during the dropping process in step (3), the dropping speed is 8 mL / min, the stirring speed is 350 r / min, the stirring time is 2 h, and the temperature is kept constant in a water bath at 45°C.

[0083] Comparative Example 5

[0084] The difference between this comparative example and Example 1 is that the third dispersant in step (3) is a mixture of polyethylene glycol, polyacrylic acid and a self-made third dispersant in a weight ratio of 1:1:1. The preparation method of the self-made third dispersant is the same as that of Example 1.

[0085] Comparative Example 6

[0086] The difference between this comparative example and Example 1 is that the third dispersant in step (3) is polyethylene glycol, polyacrylic acid and polypropylene alcohol in a weight ratio of 1.6:1:0.3.

[0087] Comparative Example 7

[0088] The difference between this comparative example and Example 1 is that the preparation method of the homemade third dispersant comprises the following steps:

[0089] (1) Under a nitrogen atmosphere, the reactor was evacuated to -0.09 MPa, 100 parts by weight of C16-18 alcohol polyoxyethylene ether and 0.3 parts by weight of sodium hydroxide were mixed, the temperature was raised to 102° C., and heated for 1.5 h to obtain dehydrated C16-18 alcohol polyoxyethylene ether.

[0090] (2) 24 parts by weight of styrene oxide was introduced into the dehydrated C16-18 alcohol polyoxyethylene ether, and the mixture was reacted at 102° C. for 3.5 hours. Acetic acid was added to make the pH neutral to obtain a self-made third dispersant.

[0091] Performance Testing

[0092] The silver-coated copper powders prepared in Examples 1-2 and Comparative Examples 1-7 were subjected to performance tests.

[0093] 1. Use a laser particle size analyzer to measure the particle size of the silver-coated copper powder. Use a tap density meter to measure the tap density.

[0094] 2. Resistivity test

[0095] Test method: Compact the silver-coated copper powder in a 1 cm long cylindrical plastic tube and use a digital multimeter (20 to 2×10 6 Ω) Determine the resistance value of the silver-coated copper powder and calculate the volume resistivity of the silver-coated copper powder according to the following formula: ρ = Rπr 2 / L.

[0096] Wherein, ρ is the volume resistivity; R is the measured resistance value; r is the radius of the plastic tube; and L is the length of the plastic tube.

[0097] 3. Antioxidant test:

[0098] Silver-coated copper powder is mainly used in low-temperature environments. The present invention conducts an antioxidant test on the powder at 300°C, which is higher than the use temperature of the powder slurry, to examine the antioxidant performance of the powder. A muffle furnace can be set at 300°C for 1h to detect the mass m1 (unit: g) of the silver-coated copper powder, and the total mass m2 (unit: g) of the powder after the temperature treatment condition is measured. The weight gain percentage is calculated by the ratio of the weight gain difference to the powder mass (m2-m1) / m1 to characterize the antioxidant property of the silver-coated copper powder. The greater the weight gain of this data, the more the powder is oxidized and the worse the antioxidant property.

[0099] The performance test results are shown in Table 1.

[0100] Table 1 Performance test results

[0101]

[0102] From the above performance test results, it can be seen that the silver-coated copper powder of Examples 1-2 has a small particle size, a high tap density, a strong antioxidant ability, and good electrical conductivity, especially the comprehensive performance of Example 1 is the most outstanding.

[0103] However, the comparative examples are significantly inferior to the embodiments in the corresponding performance tests because they do not adopt the necessary technical solutions. The composition of the second dispersant in comparative examples 1-2 is different, and the preparation method of the homemade first dispersant in comparative example 3 is different. From the results, it can be seen that the resistivity of the silver-coated copper powder increases and the conductivity deteriorates. The dropping conditions in the reduction process of comparative example 4 are different, the particle size of the silver-coated copper powder becomes larger, and the tap density decreases. The composition of the third dispersant in comparative examples 5-6 is different, and the preparation method of the homemade third dispersant in comparative example 7 is different, and the antioxidant property of the silver-coated copper powder decreases. The above experimental results further prove the importance of the technical solution defined in the present invention for its technical effect.

[0104] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a silver-coated copper powder with a dense and smooth silver coating, characterized in that: The following steps are involved: (1) 200 parts by weight of copper powder, 3-6 parts by weight of a first dispersant, and 18000-20000 parts by weight of a sulfuric acid solution are mixed to obtain a first mixed solution, and the mixture is stirred at a speed of 300-500 r / min for 0.8-1.2 h to remove surface oxides, and then filtered, washed with water until neutral, and dried to obtain pretreated copper powder; wherein the copper powder has a particle size of 2.5-4.0 μm and an average particle size of 3.5 μm; the first dispersant is one or more of polyvinyl pyrrolidone and polyethylene glycol; and the concentration of the first dispersant in the first mixed solution is 0.001 mol / L-0.8 mol / L; (2) 270-320 parts by weight of pretreated copper powder, 3000 parts by weight of deionized water, 28-34 parts by weight of a first complexing agent and 2-5 parts by weight of a second dispersant are mixed to obtain a second mixed solution, and 500 parts by weight of a silver nitrate solution with a concentration of 3.7-4.2 g / L is prepared and added dropwise to the second mixed solution at a rate of 4-6 mL / min, and the conditions for the addition are: a stirring speed of 360-420 r / min, a stirring time of 0.5-3 h, and a water bath constant temperature of 20-80° C. After the silver nitrate solution is added dropwise, the mixture is filtered, washed, and dried to obtain a silver-coated copper powder precursor in which a small amount of silver is coated on the surface of the copper powder; wherein the first complexing agent includes one or more of EDTA, EDTA2Na, and EDTA4Na, and the concentration of the first complexing agent in the second mixed solution is 0.01 g / L-10 g / L; The second dispersant comprises polyethylene glycol, a homemade first dispersant and polyvinyl pyrrolidone in a weight ratio of 1: (1.2-1.4): (0.5-0.7); The method for preparing the homemade first dispersant comprises the following steps: S1: Under a nitrogen atmosphere, 2 parts by weight of 4,4′-diformic acid diphenyl ether, 0.12-0.15 parts by weight of dimethylformamide and 46-48 parts by weight of toluene are mixed, and 2.7-3.2 parts by weight of thionyl chloride are added dropwise. After the addition is complete, the temperature is raised to 70-75° C., the reaction is carried out for 5-6 hours, and the mixture is concentrated to dryness to obtain 4,4′-diformyl chloride diphenyl ether; S2: dissolving 2.5-2.8 parts by weight of 4,4′-diformyl chloride diphenyl ether in 6-10 parts by weight of dichloromethane to obtain a dichloromethane solution of 4,4′-diformyl chloride diphenyl ether; mixing 12-15 parts by weight of alkylphenol polyoxyethylene ether OP-7, 0.1-0.15 parts by weight of dimethylformamide, 2-2.3 parts by weight of triethylamine and 0.4-0.5 parts by weight of 2,6-di-tert-butyl-4-methylphenol, and adding 40-45 parts by weight of dichloromethane to dissolve; dropping the dichloromethane solution of 4,4′-diformyl chloride diphenyl ether, reacting at room temperature for 5-6 hours, adding water for separation after the reaction is completed, recovering the organic phase, purifying it through a silica gel column, collecting the eluate, and rotating and concentrating to remove the solvent to obtain a self-made first dispersant; (3) 270-320 parts by weight of a silver-coated copper powder precursor, 3000 parts by weight of deionized water, 28-32 parts by weight of a second complexing agent, 28-32 parts by weight of a reducing agent and 2-5 parts by weight of a third dispersant are mixed to obtain a third mixed solution, and 500 parts by weight of a silver nitrate solution with a concentration of 57-62 g / L is simultaneously prepared and dripped into the third mixed solution. During the dripping process, the dripping speed is 4-6 mL / min, the stirring speed is 380-400 r / min, the stirring time is 0.8-1.2 h, and the temperature is kept constant in a water bath at 55-65° C. After the dripping is completed, the mixture is filtered, washed and dried to obtain a silver-coated copper powder with a dense and smooth silver coating. The third dispersant is a mixture of polyethylene glycol, polyacrylic acid and a homemade third dispersant in a weight ratio of (1.5-1.7):1:(0.2-0.4); The preparation method of the self-made third dispersant comprises the following steps: under a nitrogen atmosphere, vacuumizing a reaction kettle, mixing 100 parts by weight of isooctyl alcohol polyoxyethylene ether and 0.3 parts by weight of sodium hydroxide, heating to 100-105° C., and heating for 1-2 hours to obtain dehydrated isooctyl alcohol polyoxyethylene ether; introducing 23-25 ​​parts by weight of styrene oxide into the dehydrated isooctyl alcohol polyoxyethylene ether, reacting at 100-105° C. for 3-4 hours, and adding acetic acid to make the pH neutral to obtain the self-made third dispersant.

2. The method for preparing a silver-coated copper powder having a dense and smooth silver coating according to claim 1, wherein: The concentration of the sulfuric acid solution in step (1) is 5%-40% by mass.

3. The method for preparing a silver-coated copper powder having a dense and smooth silver coating according to claim 1, wherein: In step (3), the reducing agent comprises at least one of hydrazine hydrate, sodium borohydride, gum arabic, glucose, ascorbic acid, L-histidine, and glutamic acid; and the concentration of the reducing agent in the third mixed solution is 0.2 g / L-50 g / L.

4. A silver-coated copper powder having a dense and smooth silver coating, obtained by the preparation method according to any one of claims 1 to 3.

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