Low-resistance branch-sheet-shaped silver-coated copper powder and preparation method and application thereof

Abstract

The invention discloses low-resistance branch-sheet-shaped silver-coated copper powder, the copper powder is in a branch sheet shape, the surface of the branch-sheet-shaped copper powder is uniformly coated with a silver layer, the surface of the silver layer is coated with a chelate layer, and the chelate layer comprises cysteine and glutathione. The invention further discloses a preparation method of the low-resistance branch-sheet-shaped silver-coated copper powder. The preparation method comprises the following steps: plating silver on the surface of the branch-sheet-shaped copper powder to obtain an intermediate; and cleaning the intermediate with an aminothiol solution, drying, and then adding the dried intermediate into a mixed solution containing cysteine and glutathione for chelation reaction to obtain the low-resistance dendritic sheet-shaped silver-coated copper powder. The invention further discloses application of the low-resistance branch-sheet-shaped silver-coated copper powder in a coating. The invention further discloses a coating which comprises a film forming substance and the low-resistance branch-sheet-shaped silver-coated copper powder. The low-resistance branch-sheet-shaped silver-coated copper powder has good dispersity, oxidation resistance and conductivity in a coating, and the adhesive force of the coating can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of silver-coated copper powder, and particularly to a low-resistance dendritic flaky silver-coated copper powder, a preparation method thereof, and an application thereof. Background Art

[0002] Since the 20th century, science and technology have made great progress. Many non-metallic materials with excellent properties have emerged one after another and have developed and been applied rapidly in the field of industrial coatings. However, while most non-metallic materials have many excellent properties, there are also some properties of the materials themselves that need to be avoided in the application process in different fields. The most important problem at present is to overcome the phenomenon of static electricity generation. In order to avoid the generation of static electricity, the method of adding conductive fillers is often adopted for optimization in the application production process. Among the conductive fillers commonly used in the current market, copper powder has the advantage of low price, but due to its poor stability, it is easily oxidized during the production and processing process, so its application prospect is not optimistic; silver powder has high conductivity, but is expensive, and silver migration may occur during use, and its application prospect is still unclear. Therefore, silver-coated copper powder with conductive properties made by coating copper powder with a silver layer has the high conductivity and stability of silver and is relatively low in price, so it has been widely used in conductive self-spray paint. However, the existing silver-coated copper powder still has problems such as insufficient antioxidant performance, low conductivity, easy agglomeration and uneven dispersion in the coating, and low coating adhesion. Summary of the Invention

[0003] Based on the technical problems existing in the background art, the present invention proposes a low-resistance dendritic flaky silver-coated copper powder, a preparation method thereof, and an application thereof. The low-resistance dendritic flaky silver-coated copper powder of the present invention has good dispersibility, antioxidant property, and conductivity in the coating, and can improve the adhesion of the coating.

[0004] The present invention proposes a low-resistance dendritic flaky silver-coated copper powder, wherein the copper powder is dendritic flaky, and a silver layer is uniformly coated on the surface of the dendritic flaky copper powder, and a chelate layer is coated on the surface of the silver layer, and the chelate layer includes: cysteine and glutathione.

[0005] Preferably, the dendritic flaky copper powder is obtained by processing dendritic copper powder into flakes.

[0006] Preferably, the particle size of the dendritic flaky copper powder is 8-20 μm; the thickness of the dendritic flaky copper powder is 0.4-2 μm.

[0007] The present invention also proposes a preparation method of the above-mentioned low-resistance dendritic flaky silver-coated copper powder, including the following steps: plating silver on the surface of the dendritic flaky copper powder to obtain an intermediate; cleaning the intermediate with an amino thiol solution, drying, and then adding it to a mixed solution containing cysteine and glutathione for chelation reaction to obtain the low-resistance dendritic flaky silver-coated copper powder.

[0008] Preferably, the solute of the amino thiol solution is at least one of cysteamine and acetylcysteine.

[0009] Preferably, the drying step includes: keeping warm at 35 - 45°C for 0.4 - 0.6 h in a vacuum environment, then keeping warm at 55 - 65°C for 1.5 - 2.5 h, and then naturally cooling to 20 - 25°C.

[0010] Preferably, the temperature of the chelation reaction is 50 - 80°C and the time is 2 - 8 h.

[0011] The present invention also proposes the application of the above-mentioned low-resistance dendritic flaky silver-coated copper powder in coatings.

[0012] The present invention also proposes a coating, comprising: a film-forming substance and the above-mentioned low-resistance dendritic flaky silver-coated copper powder. Description of the Drawings

[0013] Figure 1 It is the SEM image of the dendritic flaky copper powder.

[0014] Figure 2 It is the SEM image of the dispersion state of the silver-coated copper powder in the coating before and after chelation modification, where A is before chelation modification and B is after chelation modification. Detailed Embodiments

[0015] The present invention proposes a low-resistance dendritic flaky silver-coated copper powder, the copper powder is dendritic flaky, a silver layer is uniformly coated on the surface of the dendritic flaky copper powder, and a chelate layer is coated on the surface of the silver layer, wherein the chelate layer includes: cysteine and glutathione.

[0016] Preferably, the dendritic flaky copper powder is obtained by processing dendritic copper powder into flaky shape.

[0017] The above-mentioned dendritic copper powder can be purchased from the market.

[0018] The dendritic copper powder is processed into dendritic flaky copper powder by ball milling.

[0019] The edges of the above-mentioned dendritic flaky copper powder are irregular, and there are multiple protrusions and notches at the edges.

[0020] The technological steps of the above-mentioned ball milling include: mixing the dendritic copper powder and an auxiliary agent, and performing ball milling, wherein zirconia balls and steel balls are used in combination for ball milling.

[0021] Preferably, based on the dendritic copper powder, the ball-to-material ratio is 3:1.

[0022] Preferably, the weight ratio of zirconia balls to steel balls is 2:1.

[0023] Preferably, the diameter of the zirconia balls is 1.0 mm and 3.0 mm, and the weight ratio of the zirconia balls with diameters of 1.0 mm and 3.0 mm is 1:3.

[0024] Preferably, the diameter of the steel balls is 0.8 mm and 3.0 mm, and the weight ratio of the steel balls with diameters of 0.8 mm and 3.0 mm is 1:3.

[0025] Preferably, the auxiliary agent is at least one of stearic acid and oleic acid; preferably, the weight ratio of copper powder to the auxiliary agent is 1:0.001 - 0.02.

[0026] In the ball milling process of the present invention, adding auxiliary agents such as stearic acid and oleic acid can keep the thickness of the dendritic flake copper powder uniform during the process of grinding dendritic copper powder into dendritic flake copper powder, make its particle size span smaller and the particle size distribution uniform; and can make the copper powder evenly dispersed during the ball milling process, avoid the agglomeration of copper powder during the ball milling process, and improve the uniform dispersion of the dendritic flake copper powder after ball milling.

[0027] The ball milling process is as follows: ball milling at a speed of 40 r / min for 4 h, and during this period, an external heat preservation jacket is added to the ball mill, and a heat transfer medium at 50 °C (at least one of water and heat transfer oil) is introduced; then ball milling at a speed of 15 r / min for 2 h, and during this period, a heat transfer medium at 30 °C (at least one of water and heat transfer oil) is introduced.

[0028] Aiming at the problem of high hardness of copper powder, the present invention can effectively improve the dendritic flake structure after ball milling while ensuring the ball milling efficiency by adjusting the types of grinding balls, the diameter of grinding balls, the ball-to-material ratio, the ball milling process, the auxiliary agent, etc., so that it will not break and has a high specific surface area, which helps to improve the conduction amount; In addition, the irregular edges of the dendritic flake copper powder can increase the contact points between copper powders, further improve the conduction amount, and reduce the resistance.

[0029] The specific surface area of the above dendritic flake copper powder is 180 - 220 m 2 / kg, more preferably 202 m 2 / kg.

[0030] Preferably, the particle size of the dendritic flake copper powder is 8 - 20 μm; the thickness of the dendritic flake copper powder is 0.4 - 2 μm.

[0031] Preferably, the thickness of the silver layer is 20 - 120 nm.

[0032] The present invention also provides a method for preparing the above low-resistance dendritic flake silver-coated copper powder, which includes the following steps: plating silver on the surface of the dendritic flake copper powder to obtain an intermediate; cleaning the intermediate with an amino mercaptan solution, drying, and then adding it to a mixed solution containing cysteine and glutathione for chelation reaction to obtain the low-resistance dendritic flake silver-coated copper powder.

[0033] Before silver plating, the dendrite-like copper powder must be cleaned to remove oil and oxide layer; the specific cleaning steps include: first cleaning with an alkaline solution (such as sodium hydroxide aqueous solution, etc.) to remove oil, and then cleaning with an acidic solution (such as dilute sulfuric acid, etc.) to remove the oxide layer on the surface of the copper powder to obtain pure copper powder.

[0034] The silver plating step comprises: mixing the dendrite-shaped copper powder with the silver plating solution, performing silver plating treatment, and obtaining an intermediate.

[0035] The silver plating solution includes: 40-170 g / L of silver nitrate, 50-250 g / L of reducing agent, and the solvent is water.

[0036] The silver plating solution also contains a pH adjuster, so that the pH of the silver plating solution is 10.2-10.6.

[0037] Stir and silver plate at 40-60°C for 0.5-4h.

[0038] The reducing agent may be formaldehyde, ethylene glycol, etc., and the pH adjusting agent may be ethylenediamine, ammonium carbonate, etc.

[0039] The invention selects a suitable silver plating solution and process and adjusts a suitable pH value, so as to control the silver deposition rate and the uniformity of the silver layer and improve the adhesion of the silver layer.

[0040] In the above intermediate, the thickness of the silver layer is 20-120nm, and the silver content is 5-40wt%.

[0041] Preferably, the solute of the aminothiol solution is at least one of cysteamine and acetylcysteine.

[0042] In the aminothiol solution, the solute concentration is 0.08-0.15 mol / L, preferably 0.1 mol / L.

[0043] The aminothiol solution is used to ultrasonically clean the intermediate; preferably, the ultrasonic frequency is 35-45 kHz, more preferably 30 kHz.

[0044] The present invention has been found through research that after silver plating, the intermediate surface adsorbs complex, and there are still free impurity metal ions (such as Fe 2+ Cr 3+ The intermediate is ultrasonically cleaned with aminothiol solution. Aminothiol can chelate with free impurity metal ions and be removed from the surface of the intermediate by ultrasound. In addition, the thiol group in aminothiol can reduce the silver ammonia complex ions to generate silver element and attach to the surface of the intermediate, thereby achieving removal. The complex is prepared for the later chelation reaction; and the appropriate type of aminothiol is selected, which has a low activation energy and will not chelate with the intermediate.

[0045] Preferably, the drying step includes: keeping warm at 35 - 45 °C for 0.4 - 0.6 h in a vacuum environment, then keeping warm at 55 - 65 °C for 1.5 - 2.5 h, and then naturally cooling to 20 - 25 °C.

[0046] Preferably, the pressure of the vacuum environment is -0.06 ~ -1 kPa.

[0047] The present invention adopts a vacuum gradient drying process, which can avoid the agglomeration of intermediate powder and retain the active sites on the surface of the intermediate, preparing for the later chelation reaction.

[0048] The vacuum gradient drying process described in the present invention follows Fick's second law. By regulating the temperature gradient (ΔT = 20 °C) and pressure gradient (ΔP = 80 kPa), the water diffusion coefficient is increased, so that the water diffusion coefficient is greater than the Hamaker constant of dendritic silver-coated copper powder, which can avoid the agglomeration of dendritic silver-coated copper powder caused by van der Waals force and retain the active sites on the surface of the intermediate at the same time.

[0049] Preferably, the temperature of the chelation reaction is 50 - 80 °C and the time is 2 - 8 h.

[0050] In the above mixed solution containing cysteine and glutathione, the concentration of cysteine is 0.03 - 0.08 mol / L, and the concentration of glutathione is 0.04 - 0.10 mol / L.

[0051] The present invention finds that although both cysteine and glutathione contain sulfhydryl and carboxyl groups, their coordination behaviors are different: 1. The adsorption energy of the carboxyl group in cysteine with Ag is weak, significantly weaker than that of the sulfhydryl group; the HOMO (highest occupied molecular orbital) in cysteine is mainly localized on the S atom, which matches the LUMO (lowest unoccupied molecular orbital) energy level of Ag, promoting the electron transfer from S to Ag; the perpendicular coordination of the sulfhydryl group in cysteine with the Ag surface is the most stable configuration; 2. When the sulfhydryl group in glutathione coordinates with Cu, the adsorption energy is low, while when the carboxyl group and amino group in glutathione coordinate with Cu synergistically, the total energy of the system can be reduced to form a stable five-membered ring configuration; the HOMO in glutathione is distributed on the carboxylic acid O and amino N atoms, and the energy level difference between it and the LUMO of Cu is significantly smaller than the energy level difference between the sulfhydryl - SH and the LUMO of Cu, indicating that the coordination of carboxylic acid / amino group is more optimal; the bidentate chelation of the carboxyl group and amino group with the Cu atom is the most stable configuration; 3. Steric hindrance effect The tripeptide backbone (γ - Glu - Cys - Gly) of glutathione produces significant steric hindrance on the Ag surface, resulting in a reduced contact probability between the sulfhydryl group and Ag; on the Cu surface, the flexible chain segment of glutathione allows the carboxylic acid and amino group to adjust their conformations to form a chelation ring with low strain.

[0052] 4. According to Pearson's hard and soft acid-base theory (HSAB), silver belongs to soft acid and has a strong coordination tendency with the soft base of the mercapto group of cysteine, while copper as a borderline acid can form stable chelates with the carboxyl and amino groups of glutathione.

[0053] In summary, cysteine and glutathione are based on the principles of coordination chemistry and colloidal stability, and improve performance by constructing a double-ligand organic-inorganic hybrid interface; cysteine, due to its small molecular size and high HOMO energy level of the mercapto group, preferentially forms covalent bonds with Ag; glutathione reduces the chelate ring strain energy through multi-functional groups in cooperation, driving the coordination of carboxylic acid and amino groups with Cu; steric hindrance and orbital matching degree jointly determine the coordination selectivity.

[0054] The present invention also proposes the application of the above low-resistance dendritic silver-coated copper powder in coatings.

[0055] The present invention also proposes a coating, comprising: a film-forming substance and the above low-resistance dendritic silver-coated copper powder.

[0056] The above film-forming substance can be acrylic resin, epoxy resin, epoxy-acrylic composite resin, etc.

[0057] In the above coating, the volume fraction of the low-resistance dendritic silver-coated copper powder can be 40-80 vol%.

[0058] The above coating can also include: antioxidants, dispersants, flame retardants, fillers, etc.

[0059] The double-layer repulsive potential energy of the silver-coated copper powder after chelation modification in the present invention is significantly higher than the van der Waals attractive potential energy, which can greatly improve the colloidal stability parameter and effectively inhibit agglomeration. From this, it can be seen that: the silver-coated copper powder after chelation modification (i.e., the low-resistance dendritic silver-coated copper powder) has good dispersion stability and can be evenly dispersed in the coating.

[0060] In addition, the amino group in the chelation layer can form a hydrogen bond network with the resin matrix. When the resin matrix contains a benzene ring, it can also produce stacking effect with the benzene ring structure. The two cooperate to increase the interfacial binding energy between the dendritic silver-coated copper powder and the resin by 40%, thereby improving the adhesion of the entire coating.

[0061] In summary, the present invention uses cysteine and glutathione with good biocompatibility as a double-ligand system. The mercapto group of cysteine forms an Ag-S covalent bond with silver atoms, and at the same time, the carboxylic acid and amino groups of glutathione chelate with the uncoated copper core to form an organic-inorganic hybrid interface with a double-anchoring structure on the surface of the silver-coated copper powder to obtain a chelation layer; Compared with the traditional method of modifying silver-coated copper powder with silane coupling agent, the present invention forms a denser chelating layer through the synergistic action of dual ligands, improves its coverage rate, enhances the antioxidant performance of dendritic silver-coated copper powder, and enables the dendritic silver-coated copper powder to have good dispersion stability, avoiding agglomeration and making it uniformly dispersed in the coating. In addition, it can enable the dendritic silver-coated copper powder to form a three-dimensional conductive network in the coating, reduce the coating resistivity, and improve the coating conductivity. And the chelating layer also contains amino groups and mercapto groups. On the one hand, it can construct a dynamic disulfide bond network to achieve stress self-adaptive adjustment during the coating curing process. On the other hand, it can provide hydrogen bond network formation and conjugation with the resin matrix, improve the interfacial binding energy, and enhance the adhesion of the coating.

[0062] In addition, the preparation process of the low-resistance dendritic silver-coated copper powder described in the present invention does not contain VOCs and complies with the RoHS environmental protection standard. This green and efficient preparation method provides a new idea for the development of high-performance conductive coatings.

[0063] Next, the technical solution of the present invention will be described in detail through specific examples. However, it should be clearly stated that these examples are for illustrative purposes only and are not construed as limiting the scope of the present invention.

[0064] The water used in the following examples and comparative examples is deionized water.

[0065] Example 1

[0066] A preparation method of low-resistance dendritic silver-coated copper powder includes the following steps: Ball milling: Take dendritic copper powder with a particle size of 18 μm and stearic acid and mix them evenly at a weight ratio of 1:0.01. Transfer them to a ball mill, adjust the ball-to-material ratio to 3:1 based on the dendritic copper powder, ball mill at a speed of 40 r / min for 4 h, and during this period, add a heat-insulating jacket to the ball mill and introduce water at 50 °C. Then ball mill at a speed of 15 r / min for 2 h, and introduce water at 30 °C during this period. After ball milling, take out to obtain dendritic silver-coated copper powder with a specific surface area of 202 m 2 / kg (the SEM diagram of the dendritic silver-coated copper powder is as Figure 1 shown. It can be seen that the edges of the dendritic silver-coated copper powder are irregular, with multiple protrusions and notches at the edges; the particle size D 50 of the dendritic silver-coated copper powder is 19.18 μm; the thickness of the dendritic silver-coated copper powder is 400 nm); among them, the grinding balls are composed of zirconia balls and steel balls at a weight ratio of 2:1; The diameter of the zirconia balls is 1.0 mm and 3.0 mm, and the weight ratio of the zirconia balls with diameters of 1.0 mm and 3.0 mm is 1:3; The diameters of the steel balls are 0.8 mm and 3.0 mm, and the weight ratio of the steel balls with diameters of 0.8 mm and 3.0 mm is 1:3; Silver plating: Take the above-mentioned dendritic flaky copper powder, first clean it with an aqueous sodium hydroxide solution to remove oil stains, and then clean it with dilute sulfuric acid. Utilize the reaction mechanism of sulfuric acid with oxides to remove the oxide layer on the surface of the copper powder to obtain pure dendritic flaky copper powder; then mix it with a silver plating solution (the silver plating solution includes: 40 g / L of silver nitrate, 60 g / L of ethylene glycol, adjust its pH to 10.3 with ammonium carbonate, and the solvent is water), stir and silver plate at 45 °C for 30 min, wash with water to obtain an intermediate product, and the thickness of the silver layer is detected to be 70 nm; Surface modification: Add the intermediate product to a 0.1 mol / L aqueous solution of cysteamine, adjust the ultrasonic frequency to 40 kHz for ultrasonic cleaning, then transfer it to a vacuum drying oven, adjust the pressure to -0.08 kPa to maintain a vacuum environment, keep it at 40 °C for 0.5 h, then keep it at 60 °C for 2 h, and then naturally cool to 25 °C to balance the water content; Then add it to a mixed solution containing cysteine and glutathione (the concentration of cysteine is 0.05 mol / L, the concentration of glutathione is 0.08 mol / L, and the solvent is water) and mix well, stir and carry out chelation reaction at 80 °C for 2 h, take it out, wash with water and ethanol, and dry it to obtain low-resistance dendritic flaky silver-coated copper powder.

[0067] The silver-coated copper powder before chelation modification (i.e., the intermediate product of Example 1) and the silver-coated copper powder after chelation modification (i.e., the low-resistance dendritic flaky silver-coated copper powder of Example 1) are used in an epoxy-acrylic composite system coating (the coating is composed of an epoxy / acrylic composite resin containing a benzene ring, a solvent propyl ester, and an additive polyvinylpyrrolidone in a weight ratio of 30:5:4) in the same amount for testing. The results are as Figure 2 shown.

[0068] Figure 2 SEM images of the dispersion states of the silver-coated copper powder before and after chelation modification in the coating, where A is before chelation modification and B is after chelation modification.

[0069] It can be seen from Figure 2 that: before and after chelation modification, the agglomeration index of the silver-coated copper powder in the coating decreased from 23.7% to 6.5%; this is because after chelation modification, the surface potential of the silver-coated copper powder changed, and the double-layer repulsive potential energy of the silver-coated copper powder was significantly higher than the van der Waals attractive potential energy, effectively inhibiting the van der Waals gravitational aggregation between particles through electrostatic repulsion; More importantly, amino and mercapto groups are grafted on the surface of the silver-coated copper powder after chelation modification, which can provide hydrogen bond networks and conjugation effects with the resin matrix (the interfacial binding energy is increased by about 40%), increasing the peel strength of the coating from 1.2 N / mm to 2.8 N / mm; The present invention also found that the chelation-modified silver-coated copper powder forms a three-dimensional conductive network in the coating. Compared with the silver-coated copper powder before chelation modification, its percolation threshold decreases from 12 vol% to 7.5 vol%.

[0070] When the volume fraction of the chelation-modified silver-coated copper powder in the coating reaches 15 vol%, the volume resistivity of the coating is , which is reduced by one order of magnitude compared with the volume resistivity of the silver-coated copper powder before chelation modification.

[0071] The chelation-modified silver-coated copper powder is made into a slurry, subjected to 2000h of damp heat aging treatment, and then its conductivity is tested. It is found that it can still maintain 86% of its initial conductivity, showing excellent antioxidant, corrosion-resistant, and environmental stability.

[0072] Example 2

[0073] A preparation method of low-resistance dendritic silver-coated copper powder includes the following steps: Take the intermediate product of Example 1 and add it to a 0.1mol / L cysteamine aqueous solution. Adjust the ultrasonic frequency to 40kHz for ultrasonic cleaning, then transfer it to a vacuum drying oven, adjust the pressure to -0.06kPa to maintain a vacuum environment, keep it at 40°C for 0.5h, then keep it at 60°C for 2h, and then naturally cool it to 25°C to balance the water content; Then add it to a mixed solution containing cysteine and glutathione (the concentration of cysteine is 0.05mol / L, the concentration of glutathione is 0.04mol / L, and the solvent is water), mix well, stir and chelate at 75°C for 2.5h, take it out, wash it with water and ethanol, and dry it to obtain low-resistance dendritic silver-coated copper powder.

[0074] Example 3

[0075] A preparation method of low-resistance dendritic silver-coated copper powder includes the following steps: Take the intermediate product of Example 1 and add it to a 0.1mol / L acetylcysteine aqueous solution. Adjust the ultrasonic frequency to 40kHz for ultrasonic cleaning, then transfer it to a vacuum drying oven, adjust the pressure to -0.1kPa to maintain a vacuum environment, keep it at 40°C for 0.5h, then keep it at 60°C for 2h, and then naturally cool it to 25°C to balance the water content; Then add it to a mixed solution containing cysteine and glutathione (the concentration of cysteine is 0.03mol / L, the concentration of glutathione is 0.08mol / L, and the solvent is water), mix well, stir and chelate at 60°C for 3h, take it out, wash it with water and ethanol, and dry it to obtain low-resistance dendritic silver-coated copper powder.

[0076] Comparative Example 1 A preparation method of dendritic silver-coated copper powder includes the following steps: Replace the "mixed solution containing cysteine and glutathione (the concentration of cysteine is 0.05 mol / L, the concentration of glutathione is 0.08 mol / L, and the solvent is water)" with "an aqueous solution of cysteine with a concentration of 0.05 mol / L", and the others are the same as in Example 1.

[0077] Comparative Example 2 A method for preparing dendritic silver-coated copper powder includes the following steps: Replace the "mixed solution containing cysteine and glutathione (the concentration of cysteine is 0.05 mol / L, the concentration of glutathione is 0.08 mol / L, and the solvent is water)" with "an aqueous solution of glutathione with a concentration of 0.08 mol / L", and the others are the same as in Example 1.

[0078] Comparative Example 3 A method for preparing dendritic silver-coated copper powder includes the following steps: Replace the "dendritic flaky copper powder" with "dendritic copper powder with a particle size of 18 μm", and prepare dendritic silver-coated copper powder according to the silver plating and surface modification process of Example 1.

[0079] Comparative Example 4 A method for preparing low-resistance dendritic silver-coated copper powder includes the following steps: Take the intermediate of Example 1 and directly add it to the mixed solution containing cysteine and glutathione (the concentration of cysteine is 0.05 mol / L, the concentration of glutathione is 0.08 mol / L, and the solvent is water), mix well, stir and chelate at 80 °C for 2 h, take out, wash with water, and dry to obtain low-resistance dendritic silver-coated copper powder.

[0080] Comparative Example 5 A method for preparing low-resistance dendritic silver-coated copper powder includes the following steps: Take the intermediate of Example 1 and add it to an aqueous solution of 0.1 mol / L cysteamine, adjust the ultrasonic frequency to 40 kHz for ultrasonic cleaning, then transfer it to a vacuum drying oven, adjust the pressure to -0.08 kPa to maintain a vacuum environment, and keep it at 40 °C for 2 h; Then add it to the mixed solution containing cysteine and glutathione (the concentration of cysteine is 0.05 mol / L, the concentration of glutathione is 0.08 mol / L, and the solvent is water), mix well, stir and chelate at 80 °C for 2 h, take out, wash with water, and dry to obtain low-resistance dendritic silver-coated copper powder.

[0081] Take the silver-coated copper powders prepared in the above Examples 1-3 and Comparative Examples 1-5, and mix them with an acrylic resin coating (the acrylic resin coating is composed of acrylic resin, solvent propyl ester, and additive polyvinylpyrrolidone in a weight ratio of 30:5:4) to obtain a conductive coating. The volume fraction of silver-coated copper powder in each group of conductive coatings is 40 vol%.

[0082] Prepare the conductive coatings of each group into coatings according to their respective methods. The coating drying conditions are all drying at 65°C for 30 min, and perform performance testing on the coatings. The results are shown in Table 1.

[0083] Detect the corrosion resistance according to the ASTM D2247 damp heat cycle test.

[0084] Detect the adhesion according to GB / T9286-2021-1C-1.

[0085]

[0086] It can be seen from Example 1 and Comparative Examples 1-2 that when cysteine or glutathione is used alone for modification, the corrosion resistance of dendritic flake silver-coated copper powder in the coating is lower than that of Example 1 with the combined modification of cysteine and glutathione, and its conductivity is also lower than that of Example 1; It can be seen from Example 1 and Comparative Example 3 that the dendritic flake silver-coated copper powder in Example 1 has better conductivity, adhesion and corrosion resistance than the dendritic silver-coated copper powder in Comparative Example 3; It can be seen from Example 1 and Comparative Example 4 that without cleaning with an aqueous solution of amino mercaptan and vacuum gradient drying treatment, and directly performing chelation modification, the obtained dendritic flake silver-coated copper powder has lower conductivity and corrosion resistance than Example 1; It can be seen from Example 1 and Comparative Example 5 that after chelation modification after constant temperature vacuum drying treatment, the obtained dendritic flake silver-coated copper powder has lower conductivity and corrosion resistance than Example 1.

[0087] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A low-resistance dendritic flaky silver-coated copper powder, characterized in that, The copper powder is dendritic and flaky, and a silver layer is uniformly coated on the surface of the dendritic and flaky copper powder, and a chelate layer is coated on the surface of the silver layer, wherein the chelate layer includes: cysteine and glutathione.

2. The low-resistance dendritic flaky silver-coated copper powder according to claim 1, wherein The dendritic and flaky copper powder is obtained by processing dendritic copper powder into flakes.

3. The low-resistance dendritic flaky silver-coated copper powder according to claim 1, wherein The particle size of the dendritic and flaky copper powder is 8 - 20 μm.

4. The low-resistance dendritic flaky silver-coated copper powder according to claim 1, wherein The thickness of the dendritic and flaky copper powder is 0.4 - 2 μm.

5. A method for preparing the low-resistance dendritic flaky silver-coated copper powder according to any one of claims 1-4, characterized in that, It includes the following steps: silver plating on the surface of the dendritic and flaky copper powder to obtain an intermediate; cleaning the intermediate with an amino thiol solution, drying, and then adding it to a mixed solution containing cysteine and glutathione for chelation reaction to obtain low-resistance dendritic and flaky silver-coated copper powder.

6. The preparation method of the low-resistance dendritic flaky silver-coated copper powder according to claim 5, wherein, The solute of the amino thiol solution is at least one of cysteamine and acetylcysteine.

7. The preparation method of the low-resistance dendritic flaky silver-coated copper powder according to claim 5, characterized in that, The drying step includes: keeping warm at 35 - 45 °C for 0.4 - 0.6 h in a vacuum environment, then keeping warm at 55 - 65 °C for 1.5 - 2.5 h, and then naturally cooling to 20 - 25 °C.

8. The preparation method of the low-resistance dendritic flaky silver-coated copper powder according to claim 5, characterized in that, The temperature of the chelation reaction is 50 - 80 °C, and the time is 2 - 8 h.

9. Application of the low-resistance dendritic and flaky silver-coated copper powder according to any one of claims 1 - 4 in coatings.

10. A coating, characterized in that, It includes: A film-forming substance and the low-resistance dendritic and flaky silver-coated copper powder according to any one of claims 1 - 4.

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