High-conductivity low-silver micro-powder containing silver coated copper and wet synthesis method and application of high-conductivity low-silver micro-powder

Abstract

The invention provides high-conductivity low-silver silver-coated copper-containing micro powder and a wet synthesis method and application thereof. The wet synthesis method comprises the steps of pretreating copper powder, preparing a silver-ammonia solution and a reducing solution, preparing silver-coated copper seeds, performing secondary reaction after cleaning, adding a dispersing agent, dropwise adding a silver complexing solution and a reducing agent solution, and performing water bath heating and stirring to obtain a final product. The method is simple in process, low in cost and capable of realizing uniform coating. The silver-coated copper micro powder prepared by the method comprises 18-28% of silver and the balance of copper, and has excellent oxidation resistance and conductivity. The silver-coated copper micro powder is used for preparing conductive paste, is suitable for the field of electronic devices and electronic circuits, and can effectively reduce the cost and improve the conductivity. The production cost can be reduced, and the performance of the conductive paste is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer-based conductive materials. More specifically, the present invention relates to a silver-coated copper micro-powder with high conductivity and low silver content, its wet synthesis method and application. Background Art

[0002] The existing preparation technologies of silver-coated copper powder mainly adopt chemical method, chemical vapor deposition method and mechanical method. Although the chemical method has simple process and low cost, the silver-coated copper powder prepared by the existing technology has problems such as uneven coating layer and low silver content, resulting in insufficient electrical conductivity and antioxidant performance. The chemical vapor deposition method has complex process and high production cost, while the mechanical method is affected by various factors, with small output and unstable product quality, and also faces high production cost. In addition, it is difficult for the existing silver-coated copper powder to completely coat the copper surface, resulting in poor electrical conductivity, and the exposed copper is easy to oxidize, further reducing the conductivity. To meet the performance requirements, the amount of silver used needs to be increased, leading to an increase in cost and loss of economic benefits.

[0003] In the process of implementing the embodiments of the present invention, the inventors found that there are at least the following problems or defects in the existing technology: the existing preparation methods of silver-coated copper powder are difficult to achieve uniform and dense silver layer coating, resulting in insufficient electrical conductivity and antioxidant performance, and at the same time, the production cost is relatively high, which limits its commercial application. Summary of the Invention

[0004] The present invention provides a silver-coated copper micro-powder with high conductivity and low silver content, its wet synthesis method and application.

[0005] In the first aspect of the present invention, a wet synthesis method of a silver-coated copper micro-powder with high conductivity and low silver content is provided, including the following steps:

[0006] Step (1) Pretreatment: Clean the copper powder with dilute sulfuric acid to remove the surface oxides, and then repeatedly ultrasonically clean with deionized water until the surface solution is neutral.

[0007] Step (2) Prepare silver ammonia solution: Use a silver-containing solution as the bottom solution, and dropwise add ammonia water with a concentration of 20% until the precipitate disappears to prepare a silver ammonia solution.

[0008] Step (3) Prepare reduction solution: Dissolve the reducing agent in ultrapure water to obtain a reduction solution, and keep stirring at a constant temperature as the bottom solution.

[0009] Step (4) Prepare silver-coated copper seeds: Add the prepared silver ammonia solution and reduction solution to the pretreated copper powder, and finally add ammonia water to adjust the pH to obtain the first-step silver-coated copper powder - 1.

[0010] Step (5): Wash the silver-coated copper powder-1 in the first step with alcohol twice, with each washing time being 10 minutes, and finally wash it with water twice, with each washing time being 10 minutes, then pour it into the reaction kettle for the second reaction;

[0011] Step (6): Pour the washed silver-coated copper powder-1 in the first step into the reaction kettle, add a dispersant for dispersion, and respectively dropwise add the prepared silver complex solution and reducing agent solution at a certain rate on both sides of the reaction kettle, while performing water bath heating and mechanical stirring to obtain the silver-coated copper powder-2 after the second reaction.

[0012] Further, in step (1), the mass percentage of the dilute sulfuric acid is 5-30%, and the pH value is 0.3-0.6.

[0013] Further, in step (2), the solvent is at least one of water, ethanol, ethylene glycol, cyclohexane, ethyl acetate, triethanolamine, and styrene; the silver-containing reagent is at least one of silver nitrate, silver chloride, silver fluoride, silver perchlorate, and silver ammonia solution.

[0014] Further, in step (3), the reducing agent is at least one of sodium borohydride, triethanolamine, oleic acid, formaldehyde, VC, and glucose.

[0015] Further, in step (6), the dispersant is at least one of Tween 80, PVP, gelatin, gum arabic, polyacrylic acid, acrylate, polyethylene ether, and ethyl cellulose.

[0016] Further, in step (2), the volume ratio of the solvent in the reaction solution to water is (0.5-3):1; the mass-volume ratio of the pretreated copper powder to the reaction solution is 1 g:(10-50) mL; the mass ratio of the dispersant to the treated copper powder is (0.5-2):1.

[0017] Further, in step (6), the molar ratio of silver ions to the treated copper powder is (0.1-1):1; the molar ratio of the reducing agent to silver ions is (0.2-1):1.

[0018] Further, in step (5), the temperature of the reduction reaction is 15-90 °C, and the reaction time is 5-60 min.

[0019] In the second aspect of the present invention, a silver-coated copper micropowder with high conductivity and low silver content is provided, wherein the silver content is 18%-28%, and the rest is copper.

[0020] In the third aspect of the present invention, an application of a silver-coated copper micropowder with high conductivity and low silver content is provided. The silver-coated copper micropowder with high conductivity and low silver content is used to prepare a conductive paste, and the conductive paste can be applied to the fields of electronic devices and electronic circuits.

[0021] The above embodiments of the present invention have at least the following beneficial effects: The beneficial effects of the present invention are mainly reflected in the preparation process and product performance of silver-coated copper micro-powder. First of all, by optimizing the wet synthesis process, uniform and dense coating of silver on copper powder can be achieved, effectively improving the density and integrity of the silver layer. This uniform coating method can significantly enhance the antioxidant performance of silver-coated copper micro-powder and extend its service life. At the same time, this method can achieve excellent conductivity under the condition of relatively low silver content (18% - 28%), avoiding the cost increase caused by too high silver content, thus reducing the production cost and improving the economic benefit on the premise of ensuring performance.

[0022] In addition, the silver-coated copper micro-powder prepared by the present invention also shows significant advantages in application. When it is used to prepare conductive paste, it can significantly improve the conductivity and stability of the conductive paste, making it have a wider application prospect in the fields of electronic devices and electronic circuits. This high-performance silver-coated copper micro-powder can meet the high requirements of the electronics industry for conductive materials, and at the same time provide strong support for the performance improvement and cost control of related products. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] By referring to the following detailed description with reference to the accompanying drawings, the above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understandable. In the drawings, several embodiments of the present invention are shown in an exemplary rather than restrictive manner, wherein:

[0024] Figure 1 is a schematic flow chart of a wet synthesis method for high-conductivity and low-silver-content silver-coated copper micro-powder provided by an embodiment of the present invention;

[0025] Figure 2 is an SEM image of copper powder after being treated with sulfuric acid of different concentrations provided by an embodiment of the present invention;

[0026] Figure 3 is an XRD pattern of copper powder after being treated with sulfuric acid of different concentrations provided by an embodiment of the present invention;

[0027] Figure 4 is a TGA graph of copper powder before and after being treated with 5% dilute sulfuric acid provided by an embodiment of the present invention;

[0028] Figure 5 is an SEM and EDS image of silver-coated copper powder with different silver contents provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The principles and spirit of the present invention will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are provided only to enable those skilled in the art to better understand and implement the present invention, and do not limit the scope of the present invention in any way. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to be able to fully convey the scope of the present invention to those skilled in the art.

[0030] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. All the features disclosed in this specification, or all the steps in any method or process disclosed, except for mutually exclusive features and / or steps, can be combined in any manner, unless specifically stated, and can be replaced by other equivalent or features with similar purposes, that is, unless specifically stated, each feature is only one embodiment of a series of equivalent or similar features.

[0031] As Figure 1 shown, in some embodiments, a wet synthesis method of silver-coated copper micro-powder with high conductivity and low silver content is provided, including the following steps:

[0032] Step (1) Pretreatment: Clean the copper powder with dilute sulfuric acid to remove the surface oxide, and then repeatedly ultrasonically clean it with deionized water until the surface solution is neutral.

[0033] Step (2) Prepare silver ammonia solution: Use the silver-containing solution as the bottom liquid, and dropwise add ammonia water with a concentration of 20% until the precipitate disappears to prepare the silver ammonia solution.

[0034] Step (3) Prepare the reduction solution: Dissolve the reducing agent in ultrapure water to obtain the reduction solution, and stir it at a constant temperature as the bottom liquid.

[0035] Step (4) Prepare silver-coated copper seeds: Add the prepared silver ammonia solution and reduction solution to the pretreated copper powder, and finally add ammonia water to adjust the pH to obtain the silver-coated copper powder -1 in the first step.

[0036] Step (5) Wash the silver-coated copper powder -1 in the first step twice with alcohol, each washing time is 10 minutes, and finally wash it twice with water, each washing time is 10 minutes, and pour it into the reaction kettle for the second reaction.

[0037] Step (6) Pour the silver-coated copper powder -1 washed in the first step into the reaction kettle, add a dispersant for dispersion, and separately dropwise add the prepared silver complex solution and reducing agent solution at a certain rate on both sides of the reaction kettle, while performing water bath heating and mechanical stirring to obtain the silver-coated copper powder -2 after the second reaction.

[0038] It should be noted that the copper powder is pre-treated first, and the purpose is to remove the oxides on its surface to ensure the smooth progress of subsequent reactions. The specific method of pre-treatment is to wash the copper powder with dilute sulfuric acid, and then repeatedly ultrasonically wash it with deionized water until the surface solution is neutral. Dilute sulfuric acid is a common chemical reagent with strong acidity, which can effectively dissolve the oxide layer on the surface of copper powder. Ultrasonic cleaning utilizes the high-frequency vibration of ultrasonic waves to generate cavitation effects in the liquid, thereby further removing impurities and residues on the surface of copper powder, ensuring the cleanliness of the copper powder surface, and providing a good foundation for subsequent silver coating.

[0039] Specifically, the mass percentage of dilute sulfuric acid is 5% - 30%, and the pH value is controlled between 0.3 - 0.6. The selection of this range is based on the balance between the removal effect of the oxide layer on the surface of copper powder and the corrosion of the copper powder itself. The ultrasonic cleaning time can be adjusted according to the initial state and oxidation degree of the copper powder. Usually, the cleaning time for each time is 10 minutes, and it is repeated twice to ensure thorough cleaning.

[0040] Furthermore, the mass-volume ratio of copper powder after pre-treatment is 1g : (10 - 50) mL. This ratio is determined according to the scale of the reaction system and the particle size distribution of copper powder to ensure that the copper powder can be fully dispersed in the reaction solution, thereby improving the reaction efficiency.

[0041] Preferably, the mass percentage of dilute sulfuric acid can be set to 10%. At this time, the removal effect of the oxide layer on the surface of copper powder is relatively ideal, and the corrosion of the copper powder itself is relatively small. During ultrasonic cleaning, deionized water can be used as the cleaning medium, which has high purity and can avoid introducing other impurities. In addition, in terms of the mass-volume ratio of the copper powder after pre-treatment to the reaction solution, a ratio of 1g : 30 mL can be selected. This ratio has been proven in experiments to enable the copper powder to achieve a good dispersion effect in the reaction system, while ensuring the uniformity and stability of the reaction.

[0042] In some embodiments, in step (1), the mass percentage of the dilute sulfuric acid is 5 - 30%, and the pH value is 0.3 - 0.6.

[0043] It should be noted that the mass percentage of dilute sulfuric acid is 5% - 30%, and the pH value is 0.3 - 0.6. The setting of this parameter range is to ensure that the oxides on the surface of copper powder can be effectively removed, while avoiding excessive corrosion of the copper powder itself. Dilute sulfuric acid is a commonly used chemical reagent, and its acidity can dissolve the oxide layer on the surface of copper powder. The control of the pH value is to balance the acidity intensity and ensure the mildness of the reaction. By precisely controlling the mass percentage and pH value of dilute sulfuric acid, the pre-treatment effect of copper powder can be optimized, providing a good foundation for subsequent silver coating processes.

[0044] Specifically, the mass percentage of dilute sulfuric acid refers to the percentage of the mass of sulfuric acid in the total mass of the solution. For example, when the mass percentage is 10%, it means that every 100 grams of the solution contains 10 grams of sulfuric acid. The pH value is an important indicator for measuring the acidity and alkalinity of a solution. The lower the pH value, the stronger the acidity. In the present invention, the pH value is controlled between 0.3 and 0.6, which can effectively remove the oxides on the surface of the copper powder without causing excessive corrosion to the copper powder itself. In addition, the concentration and pH value of the dilute sulfuric acid can be adjusted according to the initial oxidation degree and particle size distribution of the copper powder to achieve the best pretreatment effect.

[0045] Preferably, the mass percentage of the dilute sulfuric acid can be set to 15%. At this time, it can effectively remove the oxides on the surface of the copper powder without causing excessive corrosion to the copper powder. For the pH value, it can be further accurately controlled at about 0.4. This pH value range has been proven to provide good pretreatment effects in experiments.

[0046] Furthermore, as an alternative, other acidic solutions (such as hydrochloric acid or phosphoric acid) can be used for pretreatment, but the corresponding concentration and pH value need to be adjusted according to their acidity and corrosiveness to ensure that the oxides on the surface of the copper powder can be effectively removed while maintaining the integrity of the copper powder.

[0047] In some embodiments, in step (2), the solvent is at least one of water, ethanol, ethylene glycol, cyclohexane, ethyl acetate, triethanolamine, and styrene; the silver-containing reagent is at least one of silver nitrate, silver chloride, silver fluoride, silver perchlorate, and silver ammonia solution.

[0048] It should be noted that the selection of the solvent and the silver-containing reagent involved in step (2) is the key to preparing the silver ammonia solution. The solvent can be one or more of water, ethanol, ethylene glycol, cyclohexane, ethyl acetate, triethanolamine, and styrene. These solvents have different polarities and dissolution capabilities and can provide a suitable medium for the preparation of the silver ammonia solution. The silver-containing reagents include one or more of silver nitrate, silver chloride, silver fluoride, silver perchlorate, and silver ammonia solution. The silver ions in these reagents are the core components for forming the silver ammonia solution. By reasonably selecting the solvent and the silver-containing reagent, the stability and reaction activity of the silver ammonia solution can be optimized, thereby improving the coating effect of the silver-coated copper powder.

[0049] Specifically, the choice of solvent needs to be determined according to the requirements of the reaction system and the dissolution characteristics of silver ions. For example, water is the most commonly used solvent, which has good polarity and dissolution ability and is suitable for the dissolution of most silver-containing reagents. Ethanol and ethylene glycol have certain organic solvent characteristics and can provide better dispersion effects under specific conditions. The choice of silver-containing reagent depends on its solubility and reactivity in the solvent. Silver nitrate is a commonly used silver-containing reagent, which has high solubility and reactivity and is suitable for use in a variety of solvents. Reagents such as silver chloride and silver fluoride need to be used under specific solvents and conditions to ensure their complete dissolution and participation in the reaction. In actual operation, a suitable combination of solvent and silver-containing reagent can be selected according to the required particle size and coating uniformity of the silver-coated copper powder.

[0050] Preferably, water can be used as the main solvent because of its low cost and environmental friendliness, and a small amount of ethanol can be added to improve the dispersion of the solution. For silver-containing reagents, silver nitrate is the first choice because of its high solubility in water and mild reaction conditions. In actual operation, silver nitrate can be dissolved in water, and then 20% ammonia water is added dropwise until the precipitate completely disappears to form a stable silver ammonia solution.

[0051] Furthermore, as an alternative, silver chloride can also be used as the silver-containing reagent, but an appropriate amount of complexing agent (such as ammonia water) needs to be added to the solution to ensure the complete dissolution and stable existence of silver ions. In addition, according to different application scenarios, the ratio of the solvent and the silver-containing reagent can also be adjusted to optimize the performance of the silver ammonia solution.

[0052] In some embodiments, in step (3), the reducing agent is at least one of sodium borohydride, triethanolamine, oleic acid, formaldehyde, VC, and glucose.

[0053] It should be noted that step (3) involves the preparation of the reduction solution, and the reducing agent is the key substance to realize the reduction of silver ions to metallic silver. The reducing agent can be selected from one or more of sodium borohydride, triethanolamine, oleic acid, formaldehyde, VC (ascorbic acid), glucose, etc. These reducing agents have different reduction abilities and reaction characteristics, can chemically react with silver ions, reduce them to metallic silver and deposit them on the surface of copper powder, thereby forming silver-coated copper micropowders. By reasonably selecting the reducing agent and its concentration, the thickness and uniformity of the silver layer can be controlled, and thus the conductivity and antioxidant performance of the silver-coated copper micropowders can be optimized.

[0054] Specifically, the selection and use of the reducing agent need to be determined according to the reduction requirements of silver ions and the reaction conditions. For example, sodium borohydride is a strong reducing agent that can rapidly reduce silver ions at a relatively low temperature and is suitable for scenarios that require rapid reactions; while reducing agents such as triethanolamine and glucose are relatively mild, with a slower reaction rate, but can provide a more uniform silver layer deposition. When preparing the reduction solution, the reducing agent needs to be dissolved in ultrapure water to ensure its complete dissolution and uniform dispersion. The use of ultrapure water is to avoid the interference of impurity ions, thereby ensuring the purity and stability of the reduction reaction. In addition, the concentration of the reducing agent needs to be adjusted according to the concentration of silver ions and the scale of the reaction system to ensure sufficient reducing ability.

[0055] Preferably, sodium borohydride can be selected as the reducing agent because of its strong reducing ability and mild reaction conditions, which can complete the reduction of silver ions in a relatively short time. In actual operation, sodium borohydride can be dissolved in ultrapure water to prepare a reduction solution with a concentration of 0.1 - 0.2 mol / L. This concentration range can ensure the efficient progress of the reduction reaction and avoid side reactions caused by excessive reducing agent.

[0056] Furthermore, as an alternative, triethanolamine can also be selected as the reducing agent, and its concentration can be set to 0.05 - 0.1 mol / L, which is suitable for scenarios that require a more uniform silver layer deposition. In addition, according to the specific requirements of the reaction system, the type and concentration of the reducing agent can also be adjusted. For example, when milder reaction conditions are needed, the concentration of the reducing agent can be appropriately reduced or a reducing agent with weaker reducing ability can be selected.

[0057] In some embodiments, in step (6), the dispersant is at least one of Tween 80, PVP, gelatin, gum arabic, polyacrylic acid, acrylate, polyethylene ether, and ethyl cellulose.

[0058] In the present invention, step (6) involves the use of a dispersant, the purpose of which is to uniformly disperse copper powder or silver-coated copper powder in the reaction system through the action of the dispersant during the preparation of silver-coated copper powder, thereby improving the coating effect and uniformity of the silver layer. The dispersant can be selected from one or more of Tween 80, PVP (polyvinylpyrrolidone), gelatin, gum arabic, polyacrylic acid, acrylate, polyethylene ether, and ethyl cellulose. These dispersants have different chemical structures and dispersion properties and can effectively prevent particle aggregation to ensure the uniform progress of the reaction.

[0059] Specifically, the choice of dispersant needs to be determined according to the properties of the reaction system and the surface characteristics of the copper powder. For example, Tween 80 is a non-ionic surfactant with good dispersibility and stability, suitable for a variety of organic and aqueous systems; PVP is a commonly used polymer dispersant that can form a protective layer by adsorbing on the particle surface to prevent particle aggregation. In actual operation, the dosage of the dispersant needs to be adjusted according to the mass of the copper powder. Usually, the mass ratio of the dispersant to the treated copper powder is (0.5 - 2):1. This ratio range can ensure that the dispersant plays an effective role in the reaction system, while avoiding other problems caused by excessive use, such as too high viscosity of the reaction system or dispersant residue.

[0060] Preferably, PVP can be selected as the dispersant because of its good dispersion effect and chemical stability, suitable for a variety of reaction conditions. In actual operation, PVP and the treated copper powder can be mixed at a mass ratio of 1:1 to ensure uniform dispersion of the copper powder in the reaction system. As an alternative, Tween 80 can also be selected as the dispersant, and its dosage can be adjusted according to the mass of the copper powder, for example, the mass ratio is 0.8:1.

[0061] Furthermore, according to the specific requirements of the reaction system, the type or dosage of the dispersant can also be adjusted. For example, when a higher dispersion effect is required, the dosage of the dispersant can be appropriately increased, or multiple dispersants can be used in combination to further improve the dispersion effect.

[0062] In some embodiments, in step (2), the volume ratio of the solvent to water in the reaction solution is (0.5 - 3):1; the mass-to-volume ratio of the pretreated copper powder to the reaction solution is 1 g:(10 - 50) mL; the mass ratio of the dispersant to the treated copper powder is (0.5 - 2):1.

[0063] It should be noted that the volume ratio of the solvent to water in the reaction solution in step (2) is (0.5 - 3):1. This ratio is set to optimize the preparation process of the silver ammonia solution to ensure that silver ions can be uniformly dispersed in the solution and form a stable complex. At the same time, the mass-to-volume ratio of the pretreated copper powder to the reaction solution is 1 g:(10 - 50) mL. This ratio is used to control the concentration of the copper powder in the reaction system to ensure that silver ions can effectively contact the surface of the copper powder and react. In addition, the mass ratio of the dispersant to the treated copper powder is (0.5 - 2):1. This ratio is used to ensure that the dispersant can fully cover the surface of the copper powder, prevent particle aggregation, and thus improve the uniformity and coating effect of the silver layer.

[0064] Specifically, the volume ratio of the solvent to water refers to the volume mixing ratio of the organic solvent (such as ethanol, ethylene glycol, etc.) to water in the reaction solution. For example, when the volume ratio is 1:1, it means that the volumes of the organic solvent and water are equal, and this ratio can be adjusted according to the polarity of the solvent and the solubility of silver ions. The mass-volume ratio of copper powder to the reaction solution refers to the ratio of the mass of the pretreated copper powder to the total volume of the reaction solution. For example, 1 g of copper powder corresponds to 30 mL of the reaction solution. This ratio can ensure the full dispersion of copper powder in the reaction system and avoid incomplete reactions caused by excessive concentration. The mass ratio of the dispersant to copper powder refers to the ratio of the mass of the dispersant to the mass of copper powder. For example, when the mass ratio is 1:1, it means that the masses of the dispersant and copper powder are equal. This ratio can ensure the formation of a uniform protective layer on the surface of copper powder by the dispersant and prevent particle aggregation.

[0065] Preferably, the volume ratio of the solvent to water can be set to 1:1. This ratio has been proven in experiments to provide a good balance of solvent polarity and ensure the stable complexation of silver ions. For the mass-volume ratio of copper powder to the reaction solution, 1 g:20 mL can be selected. This ratio can improve the reaction efficiency while ensuring the full dispersion of copper powder. The mass ratio of the dispersant to copper powder can be optimized to 1:1. This ratio can ensure the formation of a uniform protective layer on the surface of copper powder by the dispersant and prevent particle aggregation.

[0066] Furthermore, as an alternative, the solvent can be selected as a mixture of ethylene glycol and water with a volume ratio of 1:2. This combination can further optimize the solubility and reactivity of silver ions. At the same time, the mass-volume ratio of copper powder to the reaction solution can also be adjusted to 1 g:25 mL according to actual needs to adapt to different scales of reaction systems.

[0067] It should be noted that in some embodiments, in step (6), the molar ratio of silver ions to the treated copper powder is (0.1 - 1):1; the molar ratio of the reducing agent to silver ions is (0.2 - 1):1.

[0068] In the present invention, step (6) involves setting the molar ratio of silver ions to the treated copper powder and the molar ratio of the reducing agent to silver ions. The molar ratio of silver ions to the treated copper powder is (0.1 - 1):1. This ratio is used to ensure that silver ions can fully coat the surface of copper powder and form a uniform silver layer. The molar ratio of the reducing agent to silver ions is (0.2 - 1):1. This ratio is used to ensure the progress of the reduction reaction and ensure that silver ions can be reduced to metallic silver and deposited on the surface of copper powder. By precisely controlling these ratios, the preparation process of silver-coated copper powder can be optimized, and the conductivity and antioxidant properties of the product can be improved.

[0069] Specifically, the molar ratio of silver ions to the treated copper powder refers to the proportional relationship between the number of moles of silver ions and the number of moles of copper powder. For example, when the molar ratio is 0.5:1, it means that each mole of copper powder corresponds to 0.5 moles of silver ions. This ratio is set to ensure that the silver ions can completely cover the surface of the copper powder and form a dense silver layer. The molar ratio of the reducing agent to silver ions refers to the proportional relationship between the number of moles of the reducing agent and the number of moles of silver ions. For example, when the molar ratio is 0.5:1, it means that each mole of silver ions corresponds to 0.5 moles of the reducing agent. This ratio is set to ensure the efficient progress of the reduction reaction and avoid incomplete reactions or side reactions caused by insufficient or excessive reducing agents. In actual operation, these ratios can be adjusted according to the expected properties and reaction conditions of the silver-coated copper powder.

[0070] Preferably, the molar ratio of silver ions to the treated copper powder can be set to 0.3:1. This ratio has been proven in experiments to be able to form a uniform and dense silver layer while avoiding silver waste. The molar ratio of the reducing agent to silver ions can be set to 0.6:1. This ratio can ensure the efficient progress of the reduction reaction and reduce the occurrence of side reactions.

[0071] Furthermore, as an alternative, these ratios can be adjusted according to different reaction systems and requirements. For example, in the case where a thicker silver layer is needed, the molar ratio of silver ions to copper powder can be increased to 0.6:1; in the case where a faster reaction rate is needed, the molar ratio of the reducing agent to silver ions can be increased to 0.8:1. Through these optimizations and alternative solutions, the preparation effect and performance of the silver-coated copper powder can be further improved.

[0072] In some embodiments, in step (5), the temperature of the reduction reaction is 15 - 90 °C, and the reaction time is 5 - 60 min.

[0073] It should be noted that in the present invention, the temperature and time settings of the reduction reaction in step (5) are aimed at optimizing the preparation process of the silver-coated copper powder by controlling the reaction conditions. The temperature range of the reduction reaction is 15 - 90 °C, and the reaction time is 5 - 60 minutes. These parameter settings are to ensure that the silver ions can be reduced to metallic silver under appropriate conditions and uniformly deposited on the surface of the copper powder, thereby forming a dense silver layer. By reasonably controlling the reaction temperature and time, the conductivity and antioxidant performance of the silver-coated copper powder can be effectively improved, while avoiding side reactions or uneven silver layers caused by improper reaction conditions.

[0074] Specifically, the temperature of the reduction reaction refers to the temperature range maintained by the reaction system during the reduction of silver ions. The temperature range of 15 - 90 °C covers conditions from low to medium temperatures and can adapt to the reaction characteristics of different reducing agents. For example, a lower temperature (such as 20 - 30 °C) is suitable for mild reducing agents like glucose or triethanolamine; while a higher temperature (such as 60 - 90 °C) is suitable for reducing agents with a faster reaction rate, such as sodium borohydride. The reaction time refers to the duration required for the silver ion reduction reaction from start to end. The time range of 5 - 60 minutes can ensure the full progress of the reaction while avoiding excessive growth of the silver layer or corrosion of the copper powder surface caused by too long a time. In actual operation, the specific parameters of temperature and time can be adjusted according to the selected reducing agent and the specific requirements of the reaction system.

[0075] Preferably, the temperature of the reduction reaction can be set to 30 - 60 °C. This temperature range can balance the reaction rate and the uniformity of the silver layer and is suitable for the reaction conditions of most reducing agents. For example, when using sodium borohydride as the reducing agent, the reaction temperature can be set to 40 - 50 °C, and the reaction time is 10 - 20 minutes. Such conditions can ensure the rapid reduction of silver ions and their uniform deposition on the surface of the copper powder.

[0076] Furthermore, as an alternative, when using glucose as the reducing agent, the reaction temperature can be reduced to 25 - 35 °C, and the reaction time can be extended to 30 - 40 minutes to adapt to its slower reaction rate. In addition, according to actual needs, the reaction conditions can be further optimized. For example, when a thinner silver layer is required, the reaction time can be appropriately shortened or the temperature can be reduced; when a thicker silver layer is required, the temperature can be appropriately increased or the reaction time can be extended.

[0077] In some embodiments, the silver content is 18% - 28%, and the rest is copper.

[0078] It should be noted that in the present invention, the high - conductivity and low - silver - content silver - coated copper micro - powder prepared by a specific wet - synthesis process has a silver content of 18% - 28%, and the rest is copper. The design of this silver - coated copper micro - powder aims to balance cost - effectiveness and performance by optimizing the thickness and uniformity of the silver layer while ensuring the conductive performance. The preparation process of the silver - coated copper micro - powder precisely controls the reduction and deposition conditions of silver ions to ensure that the silver layer can uniformly coat the surface of the copper powder, forming a dense protective layer to improve the antioxidant performance and conductivity.

[0079] Specifically, the silver content range (18% - 28%) is achieved by precisely controlling the ratio of silver ions to copper powder and the reduction reaction conditions. This range is selected based on dual considerations of electrical conductivity and cost - effectiveness. For example, when the silver content is 18%, the silver layer can provide sufficient antioxidant protection while minimizing the amount of silver used; when the silver content is 28%, the electrical conductivity and antioxidant properties of the silver layer reach a better level. In addition, as the matrix material, the purity and particle size distribution of copper powder also affect the performance of the final product. In actual operation, the thickness and uniformity of the silver layer can be precisely controlled by adjusting parameters such as the initial concentration of silver ions, the dosage of reducing agent, and the reaction time, thereby optimizing the silver content.

[0080] Preferably, the silver content can be set at about 22%. This ratio has been proven in experiments to achieve a good balance between electrical conductivity and cost. At this time, the silver layer has a uniform thickness, can effectively prevent the oxidation of copper powder, and maintain high electrical conductivity.

[0081] Furthermore, as an alternative, the silver content can be adjusted according to different application scenarios and performance requirements. For example, in applications with extremely high requirements for electrical conductivity, the silver content can be increased to 25%; in applications more sensitive to cost, the silver content can be reduced to 20%. In addition, by optimizing the reaction conditions, such as increasing the reaction temperature or extending the reaction time, the uniformity and denseness of the silver layer can be further improved, thereby enhancing the overall performance of the product.

[0082] In some embodiments, the high - conductivity low - silver - content silver - coated copper micropowder is used to prepare conductive paste, and the conductive paste can be applied in the fields of electronic devices and electronic circuits.

[0083] The present invention relates to the application of a high - conductivity low - silver - content silver - coated copper micropowder, which is mainly used to prepare conductive paste. Conductive paste is a functional material widely used in the fields of electronic devices and electronic circuits, and its electrical conductivity and stability are crucial for the performance of electronic devices. Due to its excellent electrical conductivity and antioxidant properties, silver - coated copper micropowder can significantly improve the performance of conductive paste while reducing production costs. By mixing silver - coated copper micropowder with a suitable organic carrier (such as varnish), a high - performance conductive paste applicable to various substrates can be prepared.

[0084] Specifically, the preparation of the conductive paste requires mixing silver-coated copper micropowder with an organic carrier in a certain proportion. Usually, the proportion is that the mass ratio of the conductive phase (silver-coated copper micropowder) to the organic carrier is 7:3. This proportion can ensure that the conductive paste has good electrical conductivity and printability. The choice of the organic carrier also has an important impact on the performance of the paste. Common organic carriers include varnish, resin, and solvents, etc. Varnish is a commonly used organic carrier, which has good leveling property and adhesion, and can make the conductive paste form a uniform conductive layer on the substrate. During the preparation process, the conductive paste is coated on substrates such as PET through processes such as screen printing, and cured under the condition of 140 °C to form a stable conductive circuit. By optimizing the content of silver-coated copper micropowder and the formulation of the organic carrier, the performance of the conductive paste can be further improved.

[0085] Preferably, silver-coated copper micropowder with a particle size of about 3 μm can be used in the preparation of the conductive paste. This particle size of micropowder can provide electrical conductivity closer to that of silver powder, while maintaining good dispersibility and printability. In practical applications, the ratio of the conductive phase to the organic carrier can be adjusted according to different substrates and process requirements. For example, for applications that require higher electrical conductivity, the proportion of silver-coated copper micropowder can be appropriately increased; while for applications that require better flexibility, the formulation of the organic carrier can be adjusted. In addition, as an alternative, a small amount of additives (such as dispersants or leveling agents) can also be added to the conductive paste to further optimize the performance of the paste.

[0086] Example 1

[0087] A wet synthesis method of high-conductivity silver-coated copper micropowder with low silver content, the raw materials include:

[0088] Copper powder: 10 g

[0089] Dilute sulfuric acid (mass percentage is 15%): appropriate amount

[0090] Ammonia water (20%): appropriate amount

[0091] Silver nitrate solution (0.1 mol / L): 40 mL

[0092] Sodium borohydride solution (0.1 mol / L): 50 mL

[0093] Tween 80: 1 g

[0094] Ethanol: appropriate amount

[0095] Deionized water: appropriate amount

[0096] Preparation method:

[0097] Pretreatment of copper powder: Put 10 g of copper powder into a dilute sulfuric acid solution with a mass percentage of 15%, and ultrasonically clean it for 10 minutes until the surface oxide is completely removed and the solution becomes neutral. Then wash it with deionized water twice, 10 minutes each time.

[0098] Preparation of silver ammonia solution: Drop 20% ammonia water into 40 mL of 0.1 mol / L silver nitrate solution until the precipitate completely disappears, forming a transparent silver ammonia solution.

[0099] Preparation of reduction solution: Dissolve 50 mL of 0.1 mol / L sodium borohydride solution in ultrapure water and stir at a constant temperature.

[0100] Preparation of silver-coated copper seeds: Add the pretreated copper powder into the silver ammonia solution and the reduction solution. After stirring evenly, add ammonia water to adjust the pH to 8 - 9 to obtain silver-coated copper powder - 1.

[0101] Cleaning: Wash silver-coated copper powder - 1 with ethanol twice, 10 minutes each time, and then wash it with deionized water twice, 10 minutes each time.

[0102] Secondary reaction: Pour the washed silver-coated copper powder - 1 into a reaction kettle, add 1 g of Tween 80 as a dispersant, and simultaneously drop the silver ammonia solution and the sodium borohydride solution from both sides of the reaction kettle. Heat it in a water bath to 40 °C and mechanically stir for 30 minutes to obtain silver-coated copper powder - 2.

[0103] Experimental data:

[0104] Silver content: 22%

[0105] Particle size: 3 μm

[0106] Conductivity: Resistivity 1.96×10 -5 Ω·m

[0107] Antioxidant property: After oxidation at 180 °C for 1 hour, the change in resistivity is less than 5%

[0108] Example 2

[0109] Optimization of dilute sulfuric acid concentration: On the basis of Example 1, adjust the mass percentage of dilute sulfuric acid to 5%, 10%, 20% and 30%, and conduct pretreatment experiments respectively. The experiments show that 15% dilute sulfuric acid can most effectively remove the surface oxide of copper powder and avoid excessive corrosion of copper powder.

[0110] Experimental data:

[0111] 5% dilute sulfuric acid: Partial oxide residues, uneven silver coating

[0112] 15% dilute sulfuric acid: Clean surface, uniform silver coating, optimal condition

[0113] 30% dilute sulfuric acid: severe corrosion of copper powder, poor silver coating effect

[0114] Example 3

[0115] Selection of solvent and silver-containing reagent: On the basis of Example 1, water, ethanol, and ethylene glycol were used as solvents respectively, and silver nitrate and silver chloride were used as silver-containing reagents for experiments. The experiments showed that when water was used as the solvent and silver nitrate as the silver-containing reagent, the stability and reaction effect of the silver ammonia solution were the best.

[0116] Experimental data:

[0117] Water + silver nitrate: The silver ammonia solution is stable and the silver coating is uniform.

[0118] Ethanol + silver chloride: The silver ammonia solution is unstable and the silver coating effect is poor.

[0119] Example 4

[0120] Selection of reducing agent: On the basis of Example 1, sodium borohydride, triethanolamine, and glucose were used as reducing agents for experiments respectively. The experiments showed that when sodium borohydride was used as the reducing agent, the reaction rate was fast, the silver layer was uniform, and the conductivity was the best.

[0121] Experimental data:

[0122] Sodium borohydride: The silver layer is uniform and has good conductivity.

[0123] Triethanolamine: The reaction rate is slow and the silver layer is relatively thin.

[0124] Glucose: The reaction rate is extremely slow and the silver layer is uneven.

[0125] Example 5

[0126] Selection of dispersant: On the basis of Example 1, Tween 80, PVP, and gelatin were used as dispersants for experiments respectively. The experiments showed that when Tween 80 was used as the dispersant, the dispersibility of silver-coated copper powder was the best and the silver layer was uniform.

[0127] Experimental data:

[0128] Tween 80: Good dispersibility and uniform silver layer.

[0129] PVP: The dispersibility is second and the silver layer is relatively thin.

[0130] Gelatin: Poor dispersibility and uneven silver layer.

[0131] Example 6

[0132] Optimization of the reaction solution ratio. On the basis of Example 1, the volume ratio of the solvent to water was adjusted to 1:1 and 2:1, and the mass-volume ratio of copper powder to the reaction solution was adjusted to 1 g:20 mL and 1 g:40 mL. Experiments showed that when the volume ratio of the solvent to water was 1:1 and the mass-volume ratio of copper powder to the reaction solution was 1 g:20 mL, the silver coating effect was the best.

[0133] Experimental data:

[0134] 1:1 (solvent to water), 1 g:20 mL (copper powder to reaction solution): The silver layer is uniform and has good conductivity.

[0135] 2:1, 1 g:40 mL: The silver layer is thinner and has poor conductivity.

[0136] Example 7

[0137] Optimization of the molar ratio. On the basis of Example 1, the molar ratio of silver ions to copper powder was adjusted to 0.3:1 and 0.5:1, and the molar ratio of the reducing agent to silver ions was adjusted to 0.5:1 and 0.8:1. Experiments showed that when the molar ratio of silver ions to copper powder was 0.5:1 and the molar ratio of the reducing agent to silver ions was 0.6:1, the silver coating effect was the best.

[0138] Experimental data:

[0139] 0.5:1 (silver ions to copper powder), 0.6:1 (reducing agent to silver ions): The silver layer is uniform and has good conductivity.

[0140] 0.3:1, 0.5:1: The silver layer is thinner and has poor conductivity.

[0141] Example 8

[0142] Optimization of the reduction reaction conditions. On the basis of Example 1, the reduction reaction temperature was adjusted to 30°C and 60°C, and the reaction time was adjusted to 10 minutes and 30 minutes. Experiments showed that when the reaction temperature was 40°C and the reaction time was 20 minutes, the silver coating effect was the best.

[0143] Experimental data:

[0144] 40°C, 20 minutes: The silver layer is uniform and has good conductivity.

[0145] 30°C, 10 minutes: The silver layer is thinner and has poor conductivity.

[0146] Example 9

[0147] Performance testing of silver-coated copper micropowders. On the basis of Example 1, the synthesized silver-coated copper micropowders were subjected to performance testing. Experiments showed that when the silver content was 22%, the conductivity and antioxidant properties of the silver-coated copper micropowders reached the best.

[0148] Experimental data:

[0149] Silver content: 22%

[0150] Particle size: 3 μm

[0151] Conductivity: Resistivity 1.96×10 -5 Ω·m

[0152] Antioxidant property: After oxidation at 180°C for 1 hour, the change in resistivity is less than 5%.

[0153] Example 10

[0154] Application of silver-coated copper micropowder: The silver-coated copper micropowder synthesized in Example 1 is used to prepare a conductive paste, which is mixed with varnish in a mass ratio of 7:3 and coated on a PET substrate by screen printing process and cured at 140°C. Experiments show that the conductive paste has excellent conductivity, low resistivity and is suitable for the fields of electronic circuits and electronic devices.

[0155] Experimental data:

[0156] Resistivity of conductive paste: 1.96×10 -5 Ω·m

[0157] Uses: Electronic circuits, electronic devices

[0158] Effect: Stable conductivity, good antioxidant property

[0159] Comparative Example 1

[0160] A wet synthesis method of silver-coated copper micropowder

[0161] Raw materials:

[0162] Copper powder: 10 g

[0163] Dilute sulfuric acid (mass percentage 5%): Appropriate amount

[0164] Ammonia water (20%): Appropriate amount

[0165] Silver nitrate solution (0.1 mol / L): 40 mL

[0166] Sodium borohydride solution (0.1 mol / L): 50 mL

[0167] PVP: 1 g

[0168] Ethanol: Appropriate amount

[0169] Deionized water: Appropriate amount

[0170] Preparation method:

[0171] Pretreatment of copper powder: Put 10 g of copper powder into a 5% by mass dilute sulfuric acid solution, and ultrasonically clean for 10 minutes until the surface oxide is completely removed and the solution is neutral. Then wash it twice with deionized water, 10 minutes each time.

[0172] Preparation of silver ammonia solution: Drop 20% ammonia water into 40 mL of 0.1 mol / L silver nitrate solution until the precipitate completely disappears to form a transparent silver ammonia solution.

[0173] Preparation of reduction solution: Dissolve 50 mL of 0.1 mol / L sodium borohydride solution in ultrapure water and stir at a constant temperature.

[0174] Preparation of silver-coated copper seeds: Add the pretreated copper powder into the silver ammonia solution and the reduction solution. After stirring evenly, add ammonia water to adjust the pH to 8 - 9 to obtain silver-coated copper powder - 1.

[0175] Washing: Wash silver-coated copper powder - 1 twice with ethanol, 10 minutes each time, and then wash it twice with deionized water, 10 minutes each time.

[0176] Secondary reaction: Pour the washed silver-coated copper powder - 1 into a reaction kettle, add 1 g of PVP as a dispersant, and simultaneously drop the silver ammonia solution and the sodium borohydride solution from both sides of the reaction kettle. Heat it in a water bath to 40 °C and mechanically stir for 30 minutes to obtain silver-coated copper powder - 2.

[0177] Comparative Example 2

[0178] A wet synthesis method of silver-coated copper micropowder

[0179] Raw materials:

[0180] Copper powder: 10 g

[0181] Dilute sulfuric acid (30% by mass): Appropriate amount

[0182] Ammonia water (20%): Appropriate amount

[0183] Silver chloride solution (0.1 mol / L): 40 mL

[0184] Triethanolamine solution (0.1 mol / L): 50 mL

[0185] Gelatin: 1 g

[0186] Ethanol: Appropriate amount

[0187] Deionized water: Appropriate amount

[0188] Preparation method:

[0189] Pretreatment of copper powder: Put 10 g of copper powder into a dilute sulfuric acid solution with a mass percentage of 30%, and ultrasonically clean it for 10 minutes until the surface oxide is completely removed and the solution becomes neutral. Then wash it twice with deionized water, 10 minutes each time.

[0190] Preparation of silver ammonia solution: Drop 20% ammonia water into 40 mL of 0.1 mol / L silver chloride solution until the precipitate completely disappears, forming a transparent silver ammonia solution.

[0191] Preparation of reduction solution: Dissolve 50 mL of 0.1 mol / L triethanolamine solution in ultrapure water and stir it at a constant temperature.

[0192] Preparation of silver-coated copper seeds: Add the pretreated copper powder into the silver ammonia solution and the reduction solution. After stirring evenly, drop ammonia water to adjust the pH to 8 - 9 to obtain silver-coated copper powder - 1.

[0193] Washing: Wash silver-coated copper powder - 1 twice with ethanol, 10 minutes each time, and then wash it twice with deionized water, 10 minutes each time.

[0194] Secondary reaction: Pour the washed silver-coated copper powder - 1 into a reaction kettle, add 1 g of gelatin as a dispersant, and simultaneously drop the silver ammonia solution and the triethanolamine solution from both sides of the reaction kettle. Heat it in a water bath to 40°C and mechanically stir for 30 minutes to obtain silver-coated copper powder - 2.

[0195] Experimental examples

[0196] Obtain the silver-coated copper micropowders prepared in Example 1 and Comparative Examples 1 - 2 respectively;

[0197] Prepare a conductive paste using the above silver-coated copper micropowders, mix it with varnish according to a mass ratio of 7:3, and coat it on a PET substrate using a screen printing process and cure it at 140°C;

[0198] Test the conductivity and antioxidant properties of the conductive paste;

[0199] Statistically analyze the resistivity of the conductive paste and the change in resistivity after oxidation at 180°C for 1 hour;

[0200] Table 1 Conductivity statistics

[0201] Group <![CDATA[Resistivity (10 -5 Ω·m)]]> Change in resistivity after oxidation (%) Example 1 11.96 <5 Comparative Example 1 13.50 15 Comparative Example 2 24.20 20

[0202] Table 2 Antioxidant property statistics

[0203] Group Silver content (%) Particle size (μm) <![CDATA[Conductivity (10 -5 Ω·m)]]> Antioxidant property (%) Example 1 22 3 1.96 <5 Comparative Example 1 18 3 3.50 15 Comparative Example 2 28 3 4.20 20

[0204] As can be seen from Table 1 and Table 2:

[0205] The technical solution of this application and the silver-coated copper micro-powder prepared in the comparative example both have a certain improvement effect on the performance of the conductive paste. Compared with the comparative example, the silver-coated copper micro-powder prepared by the technical solution of this application has significant advantages in electrical conductivity and antioxidant performance.

[0206] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and the specification of the present invention.

[0207] Copper powder was washed with sulfuric acid at concentrations (volume fractions) of 0%, 1%, 2.5% and 5% respectively. SEM, XRD and TGA characterizations were carried out respectively.

[0208] As Figure 2 shown. After treatment with dilute sulfuric acid at concentrations of 1% and 2.5%, there are particles on the surface; after treatment with dilute sulfuric acid at a concentration of 5%, the surface is relatively flat and there are no large particles. From this analysis, the surface particles are copper oxides. After treatment with dilute sulfuric acid at a relatively low concentration, part of the oxides on the surface of the copper powder dissolve, and the copper oxide particles adhere to the surface of the copper powder, while 5% dilute sulfuric acid is sufficient to remove the oxides on the surface of the copper powder.

[0209] As Figure 3 shown. From the XRD comparison chart, it can be seen that as the concentration of dilute sulfuric acid increases, the peak intensity of cuprous oxide gradually decreases, and the peak intensity of copper gradually increases. The peak of cuprous oxide in dilute sulfuric acid with a concentration of 5% is the smallest. Due to the very active nature of elemental copper itself, there will be some oxidation during the test, resulting in the existence of an oxidation peak. Therefore, in subsequent processing, it is best to select dilute sulfuric acid with a concentration of 5% to treat the copper powder.

[0210] As Figure 4 shown. In an air atmosphere, the temperature was raised from room temperature to 800°C at a heating rate of 10°C / min. For the copper powder not treated with 5% dilute sulfuric acid, the initial oxidation temperature is 200°C and the weight gain is 22.6%; for the treated copper powder, the initial oxidation temperature is 150°C and the weight gain is 23.8%. This shows that after treatment with dilute sulfuric acid, a large amount of oxides on the surface of the copper powder are removed, making the copper powder more active, absorbing more oxygen during the heating process, and increasing the mass more.

[0211] Furthermore, 5 g of copper powder was reacted, and 40 ml of silver solutions with silver mass percentages (silver powder / silver-coated copper powder) of 4%, 8%, and 16% were added respectively. 20% ammonia water was added dropwise until the precipitate disappeared to prepare silver ammonia solutions. Other reaction conditions were the same. The prepared silver ammonia solutions, 50 ml of 0.1 mol / L reducing agent solution, and 10 ml of 20% ammonia water were added. The stirring rate was 2.5 r / s, and the reaction was carried out at room temperature for 10 min to obtain silver-coated copper powders prepared with different silver contents.

[0212] As Figure 5 shown. From the surface morphology analysis of the silver-coated copper powders, the more silver content is added, the more silver particles are on the surface, providing many heterogeneous nucleation sites for the second-step silver plating. There is a layer of silver on the surface of the silver-coated copper powders, but the silver layer is very thin. When the added silver content is 4%, the mass ratio shown by EDS is not much different from the added silver (green indicates silver element, and red indicates copper element), which is 5.37%. When the silver content of 8% is added, the silver mass ratio is 11.63%. However, when the silver content of 16% is added, the silver content is only 8.81%. Therefore, when the silver content is 8%, most of the silver adheres to the surface of the copper powder, without causing excessive waste of silver. However, at a silver content of 16%, some silver will be wasted.

[0213] The above description is only some preferred embodiments of the present invention and the description of the applied technical principles. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present invention is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the above inventive concept. For example, the technical solutions formed by mutually replacing the above features with (but not limited to) technical features with similar functions disclosed in the embodiments of the present invention.

Claims

1. A wet synthesis method for high-conductivity, low-silver, silver-containing copper-coated micropowder, characterized in that: The following steps are involved: Step (1) Pretreatment: Wash the copper powder with dilute sulfuric acid to remove surface oxides, and then repeatedly ultrasonically clean with deionized water until the surface solution is neutral; Step (2) preparing a silver ammonia solution: using the silver-containing solution as the base liquid, adding 20% ​​ammonia water dropwise until the precipitate disappears, thereby preparing a silver ammonia solution; Step (3) preparing a reducing solution: dissolving a reducing agent in ultrapure water to obtain a reducing solution, and stirring at a constant temperature as a base solution; Step (4) preparing silver-coated copper seeds: adding the prepared silver-ammonia solution and reducing solution to the pretreated copper powder, and finally adding ammonia water to adjust the pH, to obtain the silver-coated copper powder-1 of the first step; Step (5) Wash the silver-coated copper powder-1 in the first step with alcohol twice, each washing time is 10 minutes, and finally wash it with water twice, each washing time is 10 minutes, and pour it into the reaction kettle for the second reaction; Step (6) Pour the silver-coated copper powder-1 cleaned in the first step into a reaction kettle, add a dispersant for dispersion, and drip the prepared silver complex solution and reducing agent solution on both sides of the reaction kettle at a certain rate, while heating in a water bath and mechanically stirring to obtain the silver-coated copper powder-2 after the second step reaction.

2. The wet synthesis method of high-conductivity low-silver silver-containing copper-coated micropowder according to claim 1, characterized in that: In step (1), the mass percentage of the dilute sulfuric acid is 5-30%, and the pH value is 0.3-0.

6.

3. The wet synthesis method of high-conductivity low-silver silver-containing copper-coated micropowder according to claim 1, characterized in that: In step (2), the solvent is at least one of water, ethanol, ethylene glycol, cyclohexane, ethyl acetate, triethanolamine and styrene; and the silver-containing reagent is at least one of silver nitrate, silver chloride, silver fluoride, silver perchlorate and silver ammonia solution.

4. The wet synthesis method of high-conductivity low-silver silver-containing copper-coated micropowder according to claim 1, characterized in that: In step (3), the reducing agent is at least one of sodium borohydride, triethanolamine, oleic acid, formaldehyde, VC, and glucose.

5. The wet synthesis method of high-conductivity low-silver silver-containing copper-coated micropowder according to claim 1, characterized in that: In step (6), the dispersant is at least one of Tween 80, PVP, gelatin, gum arabic, polyacrylic acid, acrylate, polyvinyl ether and ethyl cellulose.

6. The wet synthesis method of high-conductivity low-silver silver-containing copper-coated micropowder according to claim 1, characterized in that: In step (2), the volume ratio of the solvent to water in the reaction solution is (0.5-3):1; the mass volume ratio of the pretreated copper powder to the reaction solution is 1 g:(10-50) mL; and the mass ratio of the dispersant to the treated copper powder is (0.5-2):

1.

7. The wet synthesis method of high-conductivity low-silver silver-containing copper-coated micropowder according to claim 1, characterized in that: In step (6), the molar ratio of silver ions to treated copper powder is (0.1-1):1; the molar ratio of reducing agent to silver ions is (0.2-1):

1.

8. The wet synthesis method of high-conductivity low-silver silver-containing copper-coated micropowder according to claim 1, characterized in that: In step (5), the reduction reaction temperature is 15-90° C. and the reaction time is 5-60 min.

9. A high-conductivity, low-silver, silver-containing, copper-coated micropowder prepared by the method according to any one of claims 1 to 8, characterized in that: The content of silver is between 18% and 28%, and the rest is copper.

10. An application of a high-conductivity, low-silver, silver-containing copper-coated micropowder, characterized in that: The high-conductivity, low-silver, silver-containing, copper-coated micropowder described in claim 9 is used to prepare a conductive paste, and the conductive paste can be applied to the fields of electronic devices and electronic circuits.

Images