Silver-coated nickel powder and preparation method and application thereof

Abstract

The invention discloses silver-coated nickel powder and a preparation method and application thereof, and belongs to the technical field of conductive paste. The preparation method of the silver-coated nickel powder provided by the invention comprises the following steps: S1, nickel powder pretreatment: sequentially carrying out cleaning, coarsening and introduction of a catalytic active center; s2, chemical silver plating, wherein a product obtained in the step S1 and a silver precursor solution are mixed and dispersed and then subjected to a mixed reaction with a reducing agent solution; the silver precursor solution comprises a silver source and a complexing agent; the reducing agent solution comprises a reducing agent; the mixing reaction comprises a first stage, a second stage and a third stage which are sequentially carried out; the concentrations of the silver sources in the systems of the first stage, the second stage and the third stage are c1, c2 and c3 respectively according to the feeding amount; and c1 < c2 < c3. The silver-coated nickel powder prepared by the preparation method is tight in interlayer combination, stable in dispersion in conductive slurry and good in conductivity.

Description

Technical Field

[0001] This invention relates to the field of conductive paste technology, and in particular to a silver-coated nickel powder, its preparation method, and its application. Background Technology

[0002] With the rapid development of the electronics industry, the demand for conductive pastes is increasing. Silver, a precious metal, is the preferred material for preparing high-performance conductive pastes due to its excellent conductivity and oxidation resistance. However, the high price and volatility of silver lead to high costs for conductive pastes, limiting their large-scale application in low-cost electronic devices such as printed circuit boards, photovoltaic electrodes, and RFID tags.

[0003] To reduce costs, the industry has experimented with using inexpensive metal powders, such as copper and nickel powders, as conductive fillers. Nickel powder, in particular, has attracted attention due to its good oxidation resistance and low cost. However, nickel powder has two main drawbacks: Low intrinsic conductivity: Nickel's volume conductivity is approximately 1.43 × 10⁻⁶. 7 S / m, much lower than the conductivity of silver (6.30×10). 7 (S / m). Conductive pastes prepared directly using nickel powder cannot meet the conductivity requirements of high-end applications. To meet conductivity requirements, a high amount of filler is needed, resulting in conductive pastes with poor dispersibility and limited practicality.

[0004] High sintering temperature: Nickel has a high melting point (approximately 1455℃). During the heat treatment (sintering) of conductive paste, a high temperature (typically >800℃) is required to achieve effective bonding between particles and form conductive pathways. This does not meet the requirements of many flexible substrates (such as PET and PI) for low-temperature processes (typically <300℃) and also consumes a lot of energy.

[0005] To address these issues, researchers have developed core-shell structured materials such as silver-coated nickel powder, aiming to combine the excellent conductivity of silver with the low cost of inexpensive metals. However, existing silver-coated nickel powder preparation techniques (such as electroless plating) still have the following problems: Incomplete or non-dense silver coating: This makes the internal nickel core easy to be oxidized or corroded during the preparation or storage of the slurry, resulting in a decrease in overall conductivity.

[0006] The silver layer has weak bonding with the nickel core: the silver layer is prone to peeling during the slurry grinding or sintering process, resulting in unstable performance.

[0007] Poor control of silver layer thickness: Excessively increasing the silver layer thickness to ensure conductivity results in insignificant cost reduction; while an excessively thin silver layer cannot form an effective conductive network.

[0008] Therefore, developing a silver-coated nickel powder with complete, dense, and strong silver coating that can achieve high electrical conductivity at a relatively low sintering temperature is of great significance for promoting the development of low-cost conductive pastes. Summary of the Invention

[0009] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for preparing silver-coated nickel powder, which can effectively improve the interlayer bonding force of silver-coated nickel powder, avoid the generation of void defects at the silver-nickel interface, and also control the structure of the silver layer, which is beneficial to its practicality in subsequent application in conductive paste processes.

[0010] The present invention also provides silver-coated nickel powder prepared by the above preparation method.

[0011] The present invention also provides a conductive paste comprising the above-mentioned silver-coated nickel powder, and the application of the above-mentioned conductive paste.

[0012] According to an embodiment of the first aspect of the present invention, a method for preparing silver-coated nickel powder is provided, the method comprising the following steps: S1. Nickel powder pretreatment: The pretreatment includes sequential cleaning, roughening, and introduction of catalytic active centers; S2. Chemical silver plating: The product obtained in step S1 is mixed and dispersed with the silver precursor solution, and then mixed and reacted with the reducing agent solution. The silver precursor solution includes a silver source and a complexing agent; the reducing agent solution includes a reducing agent; the reducing agent includes glucose; The mixed reaction includes a first stage, a second stage, and a third stage performed sequentially; Based on the amount of feed, the concentrations of silver source in the first, second, and third stages of the system are c1, c2, and c3, respectively; and 5 g / L ≤ c1 ≤ 10 g / L, 10 g / L ≤ c1 ≤ 25 g / L, 20 g / L ≤ c1 ≤ 30 g / L, and c1 < c2 < c3.

[0013] The preparation method according to embodiments of the present invention has at least the following beneficial effects: Although those skilled in the art know that surface roughening may improve the bonding strength between the coating and the substrate to some extent, the core metal powder is usually not roughened in fields such as silver-coated nickel powder or silver-coated copper powder, because roughening can easily form pores between the silver layer and the core, and pores will reduce the electronic conductivity of the resulting product.

[0014] The preparation method provided by the present invention sets the concentration of the silver source in step S2 to ensure that the formation of the silver layer in the first stage is slower, thus making it easier to fill the pits. Combined with the roughening treatment in step S1, it can avoid the formation of interlayer pores while improving the interlayer bonding force.

[0015] The preparation method provided by this invention sets the concentration of the silver source in each stage in step S2, which saves the total time of silver plating on the one hand; on the other hand, the density of the silver formed in the first to third stages gradually decreases and the grain size gradually decreases, which reduces the sintering temperature of the silver-coated nickel powder in the subsequent use on the PCB board, so that a good conductive path can be obtained by sintering at the lowest possible temperature; furthermore, the surface silver layer with smaller grain size is also more conducive to improving the dispersion uniformity of the obtained silver-coated nickel powder in the later conductive paste and increasing its filling amount.

[0016] In summary, the preparation method provided by this invention, due to the synergistic effect between each step, can produce silver-coated nickel powder with high core-shell bonding force, easy sintering, and good dispersibility in conductive slurry.

[0017] According to some embodiments of the present invention, in step S1, the particle size of the nickel powder is 1~3μm. For example, it can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm; or a range of values ​​composed of any two of the above points.

[0018] According to some embodiments of the present invention, in step S1, the specific surface area of ​​the nickel powder is 0.5~1.5m². 2 / g. For example, it could be 0.5m. 2 / g, 0.8m 2 / g, 1.0m 2 / g, 1.2m 2 / g, 1.5m 2 / g; or the range of values ​​formed by any two of the above point values.

[0019] According to some embodiments of the present invention, in step S1, the cleaning includes cleaning with an alcohol-water mixture. The alcohol includes at least one of ethanol and methanol. The volume percentage of alcohol in the alcohol-water mixture is 30-70%. Specifically, it can be 30%, 40%, 50%, 60%, or 70%; or a range consisting of any two of the above values.

[0020] According to some embodiments of the present invention, in step S1, the cleaning time is 5 to 15 minutes. For example, it can be 5 minutes, 8 minutes, 10 minutes, 12 minutes, or 15 minutes; or a range of values ​​composed of any two of the above points.

[0021] According to some embodiments of the present invention, in step S1, the cleaning method includes ultrasonic cleaning. This can improve the cleaning depth and mass transfer rate.

[0022] According to some embodiments of the present invention, in step S1, the roughening process is to mix and react the nickel powder obtained from the cleaning with an acid aqueous solution.

[0023] According to some embodiments of the present invention, the concentration of the acidic aqueous solution is 0.1~0.5 wt%. For example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%; or a range of values ​​consisting of any two of the above points.

[0024] According to some embodiments of the present invention, the solute in the acidic aqueous solution includes at least one of HCl, HNO3, and acetic acid. Compared with other types of acids, nitric acid has a certain degree of oxidizing property and tends to roughen the surface rather than form uniform corrosion. Therefore, if conditions permit, nitric acid aqueous solution is preferred in actual production.

[0025] According to some embodiments of the present invention, in the roughening process, the mass ratio of the nickel powder (dry weight) obtained from the cleaning to the acid aqueous solution is 1:5 to 8; for example, it can be 1:5, 1:6, 1:7, 1:8; or a range of values ​​composed of any two of the above points.

[0026] According to some embodiments of the present invention, in step S1, the roughening temperature is 35~45℃. For example, it can be 35℃, 38℃, 40℃, 42℃, 45℃; or a range of values ​​composed of any two of the above points.

[0027] According to some embodiments of the present invention, in step S1, the coarsening time is 5 to 30 minutes. For example, it can be 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes; or a range of values ​​composed of any two of the above point values.

[0028] According to some embodiments of the present invention, step S1 further includes washing between the roughening and the introduction of the catalytic active centers. The washing ends when the washing solution is nearly neutral (pH=7±0.2).

[0029] According to some embodiments of the present invention, in step S1, the introduction of the catalytic active center includes sequential impregnation in an aqueous solution of stannous chloride and an aqueous solution of palladium chloride. The concentration of the stannous chloride solution is 0.02~0.05 mol / L; for example, it can be 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L; or a range of values ​​consisting of any two of the above points.

[0030] The immersion time in the stannous chloride aqueous solution is 5 to 10 minutes. For example, it can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes; or a range of values ​​composed of any two of the above points.

[0031] The concentration of the palladium chloride solution is 0.02~0.05 mol / L; for example, it can be 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L; or a range of values ​​consisting of any two of the above points.

[0032] The immersion time in the palladium chloride aqueous solution is 5 to 10 minutes. For example, it can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes; or a range of values ​​composed of any two of the above points.

[0033] According to some embodiments of the present invention, step S1 further includes water washing after the introduction of the catalytic active center. The number of water washes is ≥2. The solid-liquid mass ratio of each water wash is ≤1:5.

[0034] According to some embodiments of the present invention, in step S2, the concentration of the reducing agent in the mixed reaction system is 10~50 g / L. For example, it can specifically be 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L; or a range of values ​​consisting of any two of the above points.

[0035] According to some embodiments of the present invention, in step S2, the pH of the mixing reaction is 10.5 to 12. For example, it can specifically be 10.5, 11, 11.5, 12; or a range of values ​​composed of any two of the above points. The pH of the first stage, the second stage, and the third stage are selected from any value within the above range, and the three can be the same, can be the same in pairs, or can be completely different.

[0036] According to some embodiments of the present invention, in step S2, the silver source includes silver nitrate.

[0037] According to some embodiments of the present invention, in step S2, the complexing agent includes at least one of potassium sodium tartrate and EDTA or its derivatives. Specifically, The complexing agent is a combination of potassium sodium tartrate and EDTA-2Na in a mass ratio of 2.5 to 3.5:1.

[0038] The complexing agent in the mixing reaction system described in step S2 has a concentration of 30-50 g / L; specifically, it can be 30 g / L, 35 g / L, 40 g / L, 45 g / L, or 50 g / L; or a range of any two of the above values. According to some embodiments of the present invention, in step S2, the silver precursor solution in the second stage further includes a dispersant. The dispersant includes PVP.

[0039] The concentration of the dispersant in the system during the second stage of step S2 is 1~5 g / L; for example, it can be 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L; or a range of values ​​composed of any two of the above points.

[0040] According to some embodiments of the present invention, in step S2, the silver precursor solution in the third stage further includes a grain refiner. The grain refiner includes bismuth nitrate. This further refines the grains, making it easier to form conductive pathways after subsequent sintering.

[0041] The concentration of the grain refiner in the system of the third stage of step S2 is 0.01~0.05 g / L; for example, it can be 0.01 g / L, 0.02 g / L, 0.03 g / L, 0.04 g / L, 0.05 g / L; or a range of values ​​composed of any two of the above points.

[0042] According to some embodiments of the present invention, in step S2, the solvent of the solution used includes water.

[0043] According to some embodiments of the present invention, in step S2, the reaction at each stage involves dispersing the solid from the previous stage in the silver precursor solution of the corresponding stage, and introducing the reducing agent solution into it, controlling the pH during the process; after the reducing agent solution has been completely added, the reaction continues. In each stage, the addition time of the reducing agent solution is 0.5~1.5h; specifically, it can be 0.5h, 1h, 1.5h; or any range of two of the above values. Alternatively, the addition rate of the reducing agent solution is 1~5mL / min; specifically, it can be 1mL / min, 2mL / min, 3mL / min, 4mL / min, 5mL / min; or any range of two of the above values. In actual production, the addition method with the shorter addition time is selected according to the experimental scale.

[0044] In each stage, the volume ratio of the silver precursor solution to the reducing agent solution is 1:0.5 to 1.5. For example, it can be 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5; or a range of values ​​consisting of any two of the above points.

[0045] According to some embodiments of the present invention, in step S2, the concentration of the silver source in the system of the first stage is 5~15 g / L. For example, it can be 5 g / L, 8 g / L, 10 g / L, 12 g / L, 15 g / L; or a range of values ​​composed of any two of the above points.

[0046] The solid-liquid ratio in the first stage is 1g:8~12mL; for example, it can be 1g:8mL, 1g:9mL, 1g:10mL, 1g:11mL, 1g:11mL, or a range of values ​​composed of any two of the above points.

[0047] The reaction temperature in the first stage is 40~50℃; for example, it can be 40℃, 42℃, 44℃, 45℃, 46℃, 48℃, 50℃; or a range of values ​​composed of any two of the above points.

[0048] The reaction time of the first stage is 10 to 60 minutes. For example, it can be 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 60 minutes; or a range of values ​​composed of any two of the above points.

[0049] The reaction temperature and duration mentioned here refer to the reaction conditions after the reducing agent solution has been added; the reaction condition restrictions for the second and third stages are explained in the same way.

[0050] According to some embodiments of the present invention, in step S2, the concentration of the silver source in the system of the second stage is 10~25 g / L. For example, it can be 10 g / L, 15 g / L, 20 g / L, 25 g / L; or a range of values ​​composed of any two of the above points.

[0051] The solid-liquid ratio in the second stage is 1g:15~25mL; for example, it can be 1g:15mL, 1g:18mL, 1g:20mL, 1g:22mL, 1g:25mL, or a range of values ​​composed of any two of the above points.

[0052] The reaction temperature in the second stage is 50~60℃; for example, it can be 50℃, 52℃, 54℃, 55℃, 56℃, 58℃, 60℃; or a range of values ​​composed of any two of the above points.

[0053] The reaction time for the second stage is 10 to 60 minutes. For example, it can be 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 60 minutes; or a range of values ​​consisting of any two of the above points.

[0054] According to some embodiments of the present invention, in step S2, the concentration of the silver source in the third stage system is 20~30 g / L. For example, it can be 20 g / L, 22 g / L, 24 g / L, 26 g / L, 28 g / L, 30 g / L; or a range of values ​​consisting of any two of the above points.

[0055] The solid-liquid ratio in the third stage is 1g:8~12mL; for example, it can be 1g:8mL, 1g:9mL, 1g:10mL, 1g:11mL, 1g:11mL, or a range of values ​​composed of any two of the above points.

[0056] The reaction temperature of the third stage is 55~65℃; for example, it can be 55℃, 56℃, 58℃, 60℃, 62℃, 64℃, 65℃; or a range of values ​​composed of any two of the above points.

[0057] The reaction time of the third stage is 10 to 60 minutes. For example, it can be 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 60 minutes; or a range of values ​​composed of any two of the above points.

[0058] According to some embodiments of the present invention, the preparation method further includes the following steps after step S2: S3. Drying and / or passivation treatment.

[0059] According to some embodiments of the present invention, in step S3, if both drying and passivation are performed, their order is not strictly limited. That is, in actual production, drying can be performed first followed by passivation, or passivation can be performed first followed by drying.

[0060] According to some embodiments of the present invention, step S3 further includes annealing after drying.

[0061] The annealing temperature is 120~180℃. For example, it can be 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃; or a range of values ​​consisting of any two of the above points.

[0062] The annealing atmosphere is at least one of nitrogen and argon. The annealing time is 10-30 minutes. For example, it can be 10 minutes, 12 minutes, 14 minutes, 16 minutes, 18 minutes, 20 minutes, 25 minutes, or 30 minutes; or a range of any two of the above values.

[0063] According to some embodiments of the present invention, the passivation treatment involves impregnating the solid obtained in the previous step in a benzotriazole ethanol solution. This avoids oxidation or other forms of deterioration of the silver-coated nickel powder during later storage and use. The concentration of the benzotriazole ethanol solution is 0.1~0.3wt%. For example, it can be 0.1%, 0.2%, 0.3%; or a range of any two of the above values.

[0064] The temperature of the benzotriazole ethanol solution is 45~55℃. For example, it can be 45℃, 50℃, 55℃; or a range of values ​​consisting of any two of the above points.

[0065] The passivation treatment duration is 3 to 8 minutes. For example, it can be 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, or 8 minutes; or a range of values ​​composed of any two of the above points.

[0066] According to some embodiments of the present invention, in the preparation method, due to the reasonable step setting, there is no need to perform solid product drying treatment between two adjacent steps / operations; it is only necessary to reduce the liquid content to below 10wt%.

[0067] According to an embodiment of the second aspect of the present invention, a silver-coated nickel powder prepared by the preparation method described in the first aspect of the present invention is provided, wherein the silver-coated nickel powder comprises nickel powder and a silver layer coated on the surface of the nickel powder; The thickness of the silver layer is 50~300nm.

[0068] Since the silver-coated nickel powder adopts all the technical solutions of the preparation methods described in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments. Furthermore, By controlling the coating thickness, the core nickel powder can be avoided during the sintering process while minimizing the investment in silver plating. This ensures that the subsequent calcination temperature is only required for the calcination of the pure silver powder conductive paste.

[0069] According to some embodiments of the present invention, the thickness of the silver layer is 150~200nm. For example, it can be 150nm, 160nm, 170nm, 180nm, 190nm, 200nm; or a range of values ​​composed of any two of the above points.

[0070] According to some embodiments of the present invention, the D50 particle size of the silver-coated nickel powder is 1~3.5μm. For example, it can be 1μm, 2μm, 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2.9μm, 3μm, 3.5μm; or a range of values ​​composed of any two of the above points.

[0071] According to some embodiments of the present invention, the specific surface area of ​​the silver-coated nickel powder is 0.6~2m². 2 / g. For example, it could be 0.6m. 2 / g, 0.7m 2 / g, 1.0m 2 / g, 1.5m 2 / g、2m 2 / g; or the range of values ​​formed by any two of the above point values.

[0072] According to an embodiment of a third aspect of the present invention, a conductive paste is provided, wherein the raw materials for preparing the conductive paste include silver-coated nickel powder obtained by the preparation method described in the first aspect of the present invention, or include silver-coated nickel powder described in the second aspect of the present invention.

[0073] Since the conductive paste adopts all the technical solutions of the silver-coated nickel powder or preparation method of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments.

[0074] According to some embodiments of the present invention, the conductive paste further includes an organic carrier and a curing agent.

[0075] According to some embodiments of the present invention, the composition of the conductive paste, by mass percentage, is as follows: The silver-plated nickel powder content is 70-80%; for example, it can be 70%, 72%, 74%, 76%, 78%, 80%; or a range of values ​​consisting of any two of the above points.

[0076] Organic carrier 18~32%; for example, it can be 18%, 19%, 20%, 25%, 30%, 32%; or a range of values ​​composed of any two of the above points.

[0077] Hardener 0.1~0.5%. For example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%; or a range of values ​​consisting of any two of the above points.

[0078] According to some embodiments of the present invention, the organic carrier comprises ethyl cellulose and terpineol. The mass ratio of ethyl cellulose to terpineol is 1:8 to 10. Specifically, it can be 1:8, 1:9, 1:10; or a range of values ​​consisting of any two of the above points.

[0079] According to some embodiments of the present invention, the curing agent includes at least one of polyetheramine, polyamide and acid anhydride.

[0080] According to an embodiment of a fourth aspect of the present invention, an application of the conductive paste described in the third aspect of the present invention in the electronics industry is provided.

[0081] Since the application adopts all the technical solutions of the conductive paste of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments.

[0082] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0083] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a SEM image of the silver-coated nickel powder obtained in Example 1 of the present invention.

[0084] Figure 2 This is a SEM image of the silver-coated nickel powder obtained in Example 1 of the present invention.

[0085] Figure 3 This is a SEM image of the silver-coated nickel powder obtained in Example 1 of the present invention.

[0086] Figure 4 This is a SEM image of the silver-coated nickel powder obtained in Example 1 of the present invention. Detailed Implementation

[0087] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0088] Example 1 This example demonstrates the preparation of a silver-coated nickel powder. The specific preparation method is as follows: S1. Nickel powder pretreatment: sequentially performing cleaning, roughening, and introduction of catalytic active centers; The nickel powder D50 used in this example has a particle size of 2.5 μm and a specific surface area of ​​0.8 m². 2 / g; Custom-made by Xianfeng Nano, using carbonyl nickel synthesis method.

[0089] Cleaning: Ultrasonically clean the nickel powder in an ethanol-water solution (ethanol:water = 1:1 volume ratio) for 10 minutes to remove water-soluble and alcohol-soluble impurities, mainly oil stains. After cleaning, simply filter to reduce the liquid content to below 10%; no additional drying is required.

[0090] Coarsening: The washed nickel powder (filter cake) is mixed with 0.3 wt% HNO3 aqueous solution, with a solid-liquid mass ratio of 1:6 based on the mass of the dried nickel powder. The mixing conditions are 40℃ and stirring for 10 min. During stirring, it is only necessary to prevent the nickel powder from settling to the bottom; there is no need to strictly limit the stirring speed. After the reaction is complete, wash with water until the washing solution is nearly neutral, reducing the liquid content to below 10%.

[0091] Introduction of catalytic active centers: The roughened nickel powder (filter cake) was first soaked in a 0.03 mol / L stannous chloride aqueous solution for 8 min, then removed and soaked in a 0.003 mol / L palladium chloride aqueous solution for 8 min; then solid-liquid separation and washing (washed 3 times with water, each time with a solid-liquid ratio of 1:5) was carried out until the liquid content dropped to below 10%.

[0092] S2. Chemical silver plating: The reaction proceeds in three stages in sequence: the first stage, the second stage, and the third stage.

[0093] The silver precursor solution used in the first stage is: silver nitrate 20 g / L, potassium sodium tartrate 60 g / L, EDTA-2Na 20 g / L, and water as the solvent. The silver precursor solution used in the second stage consists of: silver nitrate 40 g / L, potassium sodium tartrate 60 g / L, EDTA-2Na 20 g / L, PVP (weight-average molecular weight approximately 40,000) 4 g / L, and water as the solvent. The silver precursor solution used in the third stage consists of: silver nitrate 55 g / L, potassium sodium tartrate 60 g / L, EDTA-2Na 20 g / L, bismuth nitrate 0.04 g / L, and water as the solvent. Reducing agent solution: 60 g / L glucose aqueous solution; pH adjuster: 2M sodium hydroxide aqueous solution.

[0094] The reaction process of chemical silver plating: First stage: Disperse the nickel powder obtained in step S1 into the silver precursor solution used in the first stage according to the mass-volume ratio of 1g:10mL. After the dispersion is uniform, introduce a reducing agent solution of the same volume as the silver precursor solution in the first stage into the solution and control the introduction time to 1h. During the introduction process, use a pH adjuster to control the pH to 11. After the introduction is completed, continue the reaction for 20min. The temperature of the entire first stage is controlled at 45℃.

[0095] Second stage: Disperse the nickel powder obtained in the first stage into the silver precursor solution used in the second stage according to the mass-volume ratio of 1g:20mL. After uniform dispersion, introduce a reducing agent solution of the same volume as the silver precursor solution in the first stage into the solution and control the introduction time to 1h. During the introduction process, use a pH adjuster to control the pH at 11.5. After the introduction is completed, continue the reaction for 30min. The temperature of the entire first stage is controlled at 55℃.

[0096] Third stage: Disperse the nickel powder obtained in the second stage into the silver precursor solution used in the third stage according to the mass-volume ratio of 1g:10mL. After the dispersion is uniform, introduce a reducing agent solution with the same volume as the silver precursor solution in the first stage into the solution and control the introduction time to 1h. During the introduction process, use a pH adjuster to control the pH at 12. After the introduction is completed, continue the reaction for 20min. The temperature of the entire first stage is controlled at 60℃.

[0097] S3. The product obtained from post-processing step S2: water washing, passivation, drying, and annealing; Passivation: The filter cake after washing with water is immersed in a 0.2wt% benzotriazole ethanol solution at 50℃ for 5 minutes and then taken out. The drying temperature is 60℃, and the environment is a nitrogen atmosphere.

[0098] The annealing temperature was 150℃, the duration was 15 minutes, and the environment was a nitrogen atmosphere.

[0099] Example 2 This example prepares a silver-coated nickel powder, which differs from Example 1 in that: In step S2, bismuth nitrate is not added to the silver precursor solution in the third stage.

[0100] Example 3 This example prepares a silver-coated nickel powder, which differs from Example 1 in that: Step S3 does not include the final annealing step.

[0101] Comparative Example 1 This example prepares a silver-coated nickel powder, which differs from Example 1 in that: Step S1 does not include a coarsening step.

[0102] Comparative Example 2 This example prepares a silver-coated nickel powder, which differs from Example 1 in that: In step S2, the concentration of the silver precursor solution used in all three stages is the same, which is 39 g / L.

[0103] Comparative Example 3 This example prepares a silver-coated nickel powder, which differs from Example 1 in that: The electroless silver plating is not divided into three stages. Instead, the silver aqueous solution from all stages of the example is mixed and then mixed with an equal amount of nickel powder used in step S2 of Example 1. Then, an equal amount of reducing agent solution as in Example 1 is introduced into the mixture. The process is controlled at pH 11.5 and temperature 55°C. After the introduction is completed in 3 hours, the reaction continues for 30 minutes.

[0104] Application Example 1 This example demonstrates the preparation of a conductive paste, the specific components of which, by mass percentage, are as follows: 80wt% silver-plated nickel powder; Organic carrier 19.8 wt%; Curing agent 0.2wt%; The silver-coated nickel powder is from the examples or comparative examples; The organic carrier is a 1:9 mass ratio mixture of ethyl cellulose and terpineol; The curing agent is polyetheramine D. 230.

[0105] The preparation process involves grinding, mixing, and dispersing all raw materials.

[0106] Application Example 2 This example uses the conductive paste obtained in Application Example 1 to print a pattern. Specifically, The material is screen-printed onto the surface of a PI board, then cured at 150℃ for 2 hours, followed by annealing at 250℃ under an argon atmosphere for 20 minutes.

[0107] The dry film thickness of the printed pattern obtained in this example is approximately 20 μm.

[0108] Test case The first aspect of this example tested the particle size, specific surface area, silver layer thickness, and morphology of the silver-coated nickel powder obtained in the examples and comparative examples. Particle size was measured using a laser particle size analyzer, and the D50 value was recorded. Specific surface area was measured using BET analysis. Silver layer thickness was measured under a transmission electron microscope (TEM), with ≥50 samples taken and the average value recorded. Morphology was measured using a scanning electron microscope (SEM).

[0109] The second aspect of this example tests the resistivity of the printed pattern obtained in Example 2, specifically using a resistance meter for measurement.

[0110] The third aspect of this example tested the storage performance of the conductive paste obtained in Example 1. The specific test method was as follows: the paste was stored at room temperature in the absence of air for 60 days; visual inspection was conducted to determine if the paste had settled or separated into layers; and the resistivity was tested using the method described in the second aspect of this example, recorded as the resistivity after storage.

[0111] The test results are shown in Table 1 and... Figures 1-4 As shown.

[0112] Table 1. Performance of silver-coated nickel powder obtained in the examples and comparative examples

[0113] Scanning electron microscopy (SEM) results showed that the silver-coated nickel powder obtained in the examples had a near-spherical structure with virtually no broken particles within the field of view, and the overall particle size was mainly between 2 and 3 μm, consistent with the results of laser particle size analysis. The products obtained in the comparative examples also had a near-spherical structure, but there may have been some small particles within the field of view, with the largest number in Comparative Example 3 and the second largest in Comparative Example 1.

[0114] Comparing Examples 1 and 2, it can be seen that adding a grain refiner to the silver precursor solution in the third stage can refine the particle size of silver deposited on the surface of nickel powder, thereby making it easier to form a uniform silver layer. Therefore, the resistivity of the printed pattern obtained by preparing conductive paste with silver-coated nickel powder obtained in Example 1 is lower, and the storage stability of the conductive paste is higher.

[0115] Comparing Examples 1 and 3, it can be seen that annealing treatment can further improve the bonding strength between nickel powder and silver layer, preventing the silver layer from peeling off during later use and testing. Therefore, compared with Example 3, the overall performance of Example 1 is improved.

[0116] Comparing Example 1 and Comparative Example 1, it can be seen that the roughening step can significantly improve the adhesion between nickel powder and silver layer. Without the roughening step, the subsequent silver layer peels off severely, especially after a certain storage time, the resistivity of the slurry increases significantly.

[0117] Comparing Example 1 and Comparative Examples 2-3, it can be seen that the present invention, by setting three stages of silver deposition and further limiting the parameters of each step, can significantly improve the dispersion uniformity of silver-coated nickel powder in conductive paste and reduce the sintering difficulty of printed patterns. It should be noted that the reason for the significant decrease in particle size of the product obtained in Comparative Example 3 is that the silver aggregates individually to form silver particles, rather than fully coating the surface of the nickel powder; therefore, the resulting conductive paste is prone to stratification.

[0118] In summary, the preparation method of silver-coated nickel powder provided by this invention exhibits significant synergistic effects among its various steps, improving coating uniformity, bonding strength between the silver layer and nickel powder, dispersion uniformity and filling amount of silver-coated nickel powder in the conductive paste, and sinterability of the printed pattern. For these reasons, the silver-coated nickel powder prepared by this invention is expected to find wide application in the electronics industry.

[0119] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for preparing silver-coated nickel powder, characterized in that, The preparation method includes the following steps: S1. Nickel powder pretreatment: The pretreatment includes sequential cleaning, roughening, and introduction of catalytic active centers; S2. Chemical silver plating: The product obtained in step S1 is mixed and dispersed with the silver precursor solution, and then mixed and reacted with the reducing agent solution. The silver precursor solution includes a silver source and a complexing agent; the reducing agent solution includes a reducing agent; the reducing agent includes glucose; The mixed reaction includes a first stage, a second stage, and a third stage performed sequentially; Based on the amount of feed, the concentrations of silver source in the first, second, and third stages of the system are c1, c2, and c3, respectively; and 5 g / L ≤ c1 ≤ 10 g / L, 10 g / L ≤ c1 ≤ 25 g / L, 20 g / L ≤ c1 ≤ 30 g / L, and c1 < c2 < c3.

2. The preparation method according to claim 1, characterized in that, In step S1, the roughening process involves mixing and reacting the nickel powder obtained from the cleaning process with an acidic aqueous solution.

3. The preparation method according to claim 2, characterized in that, The concentration of the acid aqueous solution is 0.1~0.5wt%; and / or the solute in the acid aqueous solution includes at least one of HNO3 and acetic acid.

4. The preparation method according to claim 1, characterized in that, In step S2, the concentration of the reducing agent in the mixed reaction system is 10~50 g / L.

5. The preparation method according to claim 1, characterized in that, In step S2, the silver precursor solution in the second stage further includes a dispersant; and / or, in step S2, the silver precursor solution in the third stage further includes a grain refiner.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The preparation method further includes the following steps after step S2: S3. Drying and / or passivation treatment.

7. A silver-coated nickel powder prepared by the preparation method according to any one of claims 1 to 6, characterized in that, The silver-coated nickel powder includes nickel powder and a silver layer coating the surface of the nickel powder; The thickness of the silver layer is 50~300nm.

8. The silver-coated nickel powder according to claim 7, characterized in that, The D50 particle size of the silver-coated nickel powder is 1~3.5μm; and / or, the specific surface area of ​​the silver-coated nickel powder is 0.6~2m². 2 / g.

9. A conductive paste, characterized in that, The raw materials for preparing the conductive paste include silver-coated nickel powder prepared by the preparation method according to any one of claims 1 to 6, or include silver-coated nickel powder according to any one of claims 7 to 8.

10. The application of the conductive paste as described in claim 9 in the electronics industry.

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