Preparation method of nanoscale silver-coated copper powder

Abstract

The invention relates to the technical field of silver-coated copper powder, in particular to a preparation method of nanoscale silver-coated copper powder. Comprising the steps of copper powder cleaning modification, continuous micro-flow precise silver plating, protective layer coating and post-treatment. By constructing a double-layer coating structure of'copper core-silver shell-silicon dioxide shell ', the problem of hard agglomeration among particles is solved, and excellent oxidation resistance and corrosion resistance superior to those of common silver coated copper powder and even pure silver powder are achieved; and meanwhile, through precise process control, excellent conductivity can still be maintained.

Description

Technical Field

[0001] This invention relates to the field of silver-coated copper powder technology, specifically a method for preparing nanoscale silver-coated copper powder. Background Technology

[0002] Silver-coated copper powder is a composite metal powder with copper powder as its core and a uniform silver coating on the surface. It combines the high conductivity of silver with the economic efficiency of copper, making it a cost-effective alternative to pure silver powder. It exhibits excellent conductivity, with a resistivity as low as 0.015–0.025 ohms / cm², and high chemical stability; the silver layer effectively prevents copper oxidation, maintaining long-term conductivity. Silver-coated copper powder comes in various shapes (e.g., spherical, granular, flake, dendritic) and has a controllable particle size (D50 range 5–25 micrometers), suitable for different process requirements.

[0003] Nano-silver-coated copper powder is a micro-nano-scale functional material. Its core copper particles are typically submicron to tens of micrometers in size, while the outer silver coating is nanometer-thick (tens to hundreds of nanometers). This precise core-shell structure design enables it to demonstrate key applications in multiple fields: in microelectronics, its micrometer-scale overall size combined with the nanometer-scale silver shell makes it an ideal material for preparing high-performance, low-cost conductive pastes and inks, used in printed circuits, flexible electronics, and electrodes for solar cells.

[0004] In the field of antibacterial applications, its nano-silver surface can exert efficient and long-lasting antibacterial properties, while the copper core reduces costs. It is often used in medical device coatings and antibacterial plastics. In addition, in the fields of catalysts and 3D printing, it can also be used to manufacture special catalysts and conductive composite materials due to its high specific surface area, high conductivity and oxidation resistance.

[0005] Currently, Chinese patent CN108080651A discloses a method for preparing nano-silver-coated copper powder for electronic pastes, which includes the following steps: adding a dispersant and a reducing agent to deionized water to form a mixed solution, and adjusting the mixed solution to neutral by adding an alkaline solution; taking copper salt and deionized water to form a copper salt solution, and adding a complexing agent to complex and obtain a copper ammonia solution; adding the copper ammonia solution dropwise to the mixed solution obtained in step one to obtain a reducing solution; taking silver nitrate and deionized water to form a silver salt solution, and adding a complexing agent to complex and obtain a silver ammonia solution, and adding the silver ammonia solution dropwise to the reducing solution; filtering the obtained solution and collecting the filter residue, washing the filter residue with deionized water and anhydrous ethanol and then drying it to obtain nano-silver-coated copper powder for electronic pastes.

[0006] In this invention, the raw material components and process steps are simple, easy to mass-produce, and are harmless, pollution-free, efficient and environmentally friendly; the resulting nano-silver-coated copper powder has low resistivity and high antioxidant capacity, which meets electrical performance requirements and reduces costs.

[0007] However, including the aforementioned patented technologies, the agglomeration of nanoscale silver-coated copper powder remains a core challenge in its preparation and application. Nanoparticles have a large specific surface area and high surface energy, making them highly prone to agglomeration. Agglomeration of nanoscale silver-coated copper powder directly leads to uneven coating, difficulty in dispersion, performance degradation, and poor stability of subsequent slurries or inks, severely impacting the dispersibility and performance of the final product.

[0008] To address the above problems, this invention provides a method for preparing nanoscale silver-coated copper powder. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing nanoscale silver-coated copper powder to solve the problems mentioned in the background art.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0011] A method for preparing nanoscale silver-coated copper powder includes the following steps:

[0012] S1, Copper powder cleaning and modification: Under a nitrogen atmosphere, select a quantitative amount of spherical or granular copper powder with D50=500-700nm, transfer the copper powder to a reaction vessel, add dilute organic acid, ultrasonically stir at room temperature for 15min, centrifuge and filter, wash three times alternately with deionized water and anhydrous ethanol, then disperse the washed copper powder in a mixture of anhydrous ethanol and deionized water, add polyvinylpyrrolidone, mechanically stir for 45min to form a copper powder dispersion;

[0013] S2, continuous microflow precision silver plating: A quantitative amount of polyvinylpyrrolidone and reducing agent are dissolved in a water / ethanol mixture to form solution A; under light-protected conditions, silver nitrate solution and ammonia are slowly mixed to form a clear solution, solution B; copper powder dispersion is homogenized to ensure no sedimentation, forming solution C; solution A, solution B, and solution C are simultaneously injected into a continuous flow microreactor using a precision injection pump at a constant flow rate, and stirred at a constant temperature of 55°C. After reacting for 45-75 seconds, the silver plating dispersion is collected into a collection tank under a nitrogen atmosphere.

[0014] S3, Protective coating: The collected silver plating dispersion was transferred to a batch stirred reactor, ammonia was added to adjust the pH value, and ethanol solutions of tetraethyl orthosilicate and silane coupling agent were added slowly and simultaneously under mechanical stirring. The reaction was carried out at 38°C for 4.5 h. After the reaction was completed, stirring was maintained for 1.5 h, aminosilane was added, the temperature was raised to 60°C, and the reaction was carried out for 1 h to obtain a composite slurry with a SiO2 protective layer.

[0015] S4, post-processing: The composite slurry is centrifuged and filtered. After solid-liquid separation, it is washed four times with anhydrous ethanol to obtain a wet cake of nanoparticles. The wet cake is dispersed in cyclohexane to form a suspension. The suspension is poured into a freeze-drying tray and placed in a freeze dryer to freeze until completely solidified. The vacuum pump is turned on to lower the temperature to below -80℃ and sublimation is carried out for 36 hours to obtain the finished product of nano silver-coated copper powder.

[0016] In a more optimized manner, in step S1, the organic acid is citric acid or oxalic acid with a concentration of 1.5%; the volume ratio of anhydrous ethanol to deionized water is 1:1.

[0017] In a more optimized manner, in step S3, the silane coupling agent is KH-550 with a mass concentration of 0.15% (w / v).

[0018] In a more optimized manner, in step S2, the mass of polyvinylpyrrolidone is 66% of the total mass of copper powder and the target silver layer. When mixing silver nitrate solution and ammonia water, ammonia water is added dropwise to silver nitrate solution at a dropping rate of 0.62 mL / min.

[0019] Ideally, in step S2, the flow rate ratio of liquid A, liquid B, and liquid C is 2:1:1.

[0020] In a more optimized manner, in step S3, the pH value is adjusted to 10, and the thickness of the SiO2 protective layer is 2.5-3 nm.

[0021] In a more optimized manner, in step S3, the dropping rate of both the ethanol solution of tetraethyl orthosilicate and the ethanol solution of silane coupling agent is 0.8 mL / min, and the mechanical stirring rate is 150 rpm.

[0022] In a more optimized manner, in step S3, the amount of aminosilane used is 6.2% of the theoretical mass of the SiO2 protective layer, and before addition, the aminosilane is diluted with anhydrous ethanol to a 10% ethanol solution.

[0023] In a more optimized manner, in step S4, when the wet cake is dispersed in cyclohexane, the dispersed solids content is 11%.

[0024] This invention provides a nanoscale silver-coated copper powder, which is prepared by any of the above-mentioned methods for preparing nanoscale silver-coated copper powder.

[0025] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0026] (1) This invention fundamentally reconstructs the stability logic of nano-silver-coated copper powder by constructing a double-layer coating structure of "copper core-silver shell-silica shell". Its primary effect is to completely solve the problem of hard agglomeration between particles, which is due to two synergistic mechanisms: first, the outermost rigid silica shell provides insurmountable physical steric hindrance, preventing particles from directly contacting each other during drying and storage; second, the final freeze-drying process completely eliminates capillary forces during the drying process, keeping the powder in a fluffy, porous, and easily redispersible flocculent morphology. This absolute physical isolation ensures that the material maintains excellent monodispersity throughout the entire process from preparation to application.

[0027] (2) This invention achieves superior anti-oxidation and anti-corrosion properties compared to ordinary silver-coated copper powder or even pure silver powder. The dense, non-porous amorphous silica layer acts like an inert "armor" for each particle, effectively blocking the penetration of corrosive media such as water vapor, oxygen, and sulfides. This provides double protection for the internal silver layer, enabling the material to maintain stable performance in harsh environments such as high temperature and high humidity for a long time, solving the fundamental weakness of traditional silver-coated copper powder caused by copper core oxidation due to silver layer defects.

[0028] (3) The present invention uses a silicon dioxide insulating shell to construct a reliable ion migration barrier between adjacent particles, completely cutting off the migration path of silver and copper ions driven by electric field and humidity. This makes the material particularly critical in high-density, high-reliability circuit interconnection, and can pass rigorous reliability tests such as 85°C / 85% relative humidity with applied bias voltage, significantly extending the service life of the device.

[0029] (4) This invention maintains excellent conductivity through precise process control. The key lies in controlling the thickness of the silicon dioxide layer to the nanometer level (typically <5nm). During the final sintering or pressing process, this ultrathin shell can conduct current through the tunneling effect or undergo local rupture under pressure, thereby forming a highly efficient conductive path. Therefore, its bulk resistivity can still approach the level of high-quality silver-coated copper powder. Attached Figure Description

[0030] Figure 1 This is an electron microscope image of Example 1. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] This invention provides a method for preparing nanoscale silver-coated copper powder, comprising the following steps:

[0033] S1. Copper powder cleaning and modification: Under a nitrogen atmosphere, select a quantitative amount of spherical or granular copper powder with a D50 of 500-700 nm, transfer the copper powder to a reaction vessel, add a dilute organic acid (citric acid or oxalic acid) at a concentration of 1.5%, ultrasonically stir at room temperature for 15 min, centrifuge and filter, and wash three times alternately with deionized water and anhydrous ethanol (volume ratio of anhydrous ethanol to deionized water is 1:1). Then disperse the washed copper powder in a mixture of anhydrous ethanol and deionized water, add polyvinylpyrrolidone at a mass concentration of 0.15% (w / v), and mechanically stir for 45 min to form a copper powder dispersion.

[0034] This step removes the oxide layer and impurities from the copper powder surface, resulting in a clean and active metal surface, laying the foundation for subsequent uniform silver plating. The addition of ethanol helps improve wettability and inhibit oxidation, and also pre-constructs a layer of molecular anchoring sites on the copper core surface, which not only further prevents copper oxidation but also enhances the adhesion to the subsequent silver layer.

[0035] S2, continuous microfluidic precision silver plating: A measured amount of polyvinylpyrrolidone and reducing agent are dissolved in a water / ethanol mixture to form solution A; under light-protected conditions, silver nitrate solution and ammonia are slowly mixed to form a clear solution, solution B; the copper powder dispersion is homogenized to ensure no sedimentation, forming solution C; solutions A, B, and C are simultaneously injected into the continuous flow microreactor at a constant flow rate using a precision injection pump, with a flow rate ratio of 2:1:1. The mixture is stirred at a constant temperature of 55°C, and after reacting for 45-75 seconds, the silver plating dispersion is collected into a nitrogen-atmospheric collection tank; the mass of polyvinylpyrrolidone is 66% of the total mass of copper powder and the target silver layer; when mixing silver nitrate solution and ammonia, ammonia is added dropwise to the silver nitrate solution at a dropping rate of 0.62 mL / min.

[0036] This step enables uniform, dense, and controllable deposition of silver atoms, yielding a dispersion of copper-silver core-shell structured nanoparticles. The continuous flow process ensures unparalleled batch consistency and extremely high product uniformity. The flow rate ratio of solutions A, B, and C determines the stoichiometric ratio of the reactants, directly affecting the silver layer thickness, while temperature influences the reaction rate and the crystallinity of the silver layer.

[0037] S3, Protective Layer Coating: The collected silver-plated dispersion was transferred to a batch-type stirred reactor. Ammonia was added to adjust the pH to 10. Under mechanical stirring, an ethanol solution of tetraethyl orthosilicate and an ethanol solution of silane coupling agent were simultaneously and slowly added dropwise. The dropping rate of both the ethanol solutions of tetraethyl orthosilicate and silane coupling agent was 0.8 mL / min. The mechanical stirring speed was 150 rpm, and the reaction was carried out at 38℃ for 4.5 h. After the reaction, stirring was maintained for 1.5 h, aminosilane was added, and the temperature was raised to 60℃. The reaction was carried out for 1 h to obtain a composite slurry with a SiO2 protective layer. The thickness of the SiO2 protective layer was 2.5-3 nm. The amount of aminosilane used was 6.2% of the theoretical mass of the SiO2 protective layer. Before addition, the aminosilane was diluted with anhydrous ethanol to a 10% ethanol solution. The silane coupling agent was KH-550 with a mass concentration of 0.15% (w / v).

[0038] This step enables the in-situ growth of an amorphous, dense SiO2 shell layer on the surface of the copper-silver core-shell structure. Aminosilane end-capping converts the silanol groups on the SiO2 surface into amino groups, significantly improving the compatibility and dispersion stability of the powder in organic resins, thus forming the final copper-silver-silica composite structure.

[0039] S4, Post-processing: The composite slurry is centrifuged and filtered. After solid-liquid separation, it is washed four times with anhydrous ethanol to obtain a wet cake of nanoparticles. The wet cake is dispersed in cyclohexane to form a suspension. The dispersed solids content of the wet cake in cyclohexane is 11%. The suspension is poured into a freeze-drying tray and placed in a freeze dryer to freeze until completely solidified. The vacuum pump is turned on to lower the temperature to below -80℃ and sublimate for 36 hours to obtain the finished product of nano-silver-coated copper powder.

[0040] This step yields a high-purity wet cake of copper-silver-silica nanoparticles. Simultaneously, by removing the solvent through sublimation, it completely avoids hard agglomeration caused by capillary forces during the drying process, perfectly preserving the original dispersion state of the nanoparticles in the solution.

[0041] The performance of the silver-coated copper powder particles obtained by the present invention is verified through examples and comparative examples.

[0042] Example 1 uses the complete process of the present invention to prepare nano-silver-coated copper powder; Example 2 differs from Example 1 in that freeze drying is replaced by oven drying.

[0043] Comparative Example 1 is ordinary nano-silver-coated copper powder prepared by traditional chemical plating method. The difference between Comparative Example 2 and Comparative Example 1 is that a silica coating layer is added, but it is dried in an ordinary oven.

[0044] The test results are shown in Table 1.

[0045] Table 1 Test Results of Comparative Examples and Specific Examples

[0046]

[0047] Example 1 exhibited the lowest tap density and the best slurry stability, demonstrating that the synergistic effect of "SiO2 coating" and "freeze-drying" is the core solution to hard agglomeration and the achievement of perfect dispersion. Example 1 also showed significantly better oxidation initiation temperature and electrical resistance stability than the other groups, proving that the uniform coating ensured by the "continuous flow process" and the structural integrity maintained by "freeze-drying" together endowed it with top-tier oxidation resistance. Example 1 demonstrated an order-of-magnitude advantage in resistance to electrochemical migration. This verifies that the dense, continuous, and defect-free SiO2 insulating layer produced by the complete strategy is key to completely blocking ion migration.

[0048] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for preparing nanoscale silver-coated copper powder, characterized in that, Includes the following steps: S1, Copper powder cleaning and modification: Under a nitrogen atmosphere, select a quantitative amount of spherical or granular copper powder with D50=500-700nm, transfer the copper powder to a reaction vessel, add dilute organic acid, ultrasonically stir at room temperature for 15min, centrifuge and filter, wash three times alternately with deionized water and anhydrous ethanol, then disperse the washed copper powder in a mixture of anhydrous ethanol and deionized water, add polyvinylpyrrolidone, mechanically stir for 45min to form a copper powder dispersion; S2, continuous microfluidic precision silver plating: a quantitative amount of polyvinylpyrrolidone and reducing agent are dissolved in a water / ethanol mixture to form solution A; under light-protected conditions, silver nitrate solution and ammonia are slowly mixed to form a clear solution, solution B; the copper powder dispersion is homogenized to ensure no sedimentation, forming solution C; Using a precision injection pump, liquids A, B, and C are simultaneously injected into a continuous flow microreactor at a constant flow rate. The mixture is stirred at a constant temperature of 55°C. After reacting for 45-75 seconds, the silver-plated dispersion is collected into a collection tank under a nitrogen atmosphere. S3, Protective coating: The collected silver plating dispersion was transferred to a batch stirred reactor, ammonia was added to adjust the pH value, and ethanol solutions of tetraethyl orthosilicate and silane coupling agent were added slowly and simultaneously under mechanical stirring. The reaction was carried out at 38°C for 4.5 h. After the reaction was completed, stirring was maintained for 1.5 h, aminosilane was added, the temperature was raised to 60°C, and the reaction was carried out for 1 h to obtain a composite slurry with a SiO2 protective layer. S4, post-processing: The composite slurry is centrifuged and filtered. After solid-liquid separation, it is washed four times with anhydrous ethanol to obtain a wet cake of nanoparticles. The wet cake is dispersed in cyclohexane to form a suspension. The suspension is poured into a freeze-drying tray and placed in a freeze dryer to freeze until completely solidified. The vacuum pump is turned on to lower the temperature to below -80℃ and sublimation is carried out for 36 hours to obtain the finished product of nano silver-coated copper powder.

2. The method for preparing nanoscale silver-coated copper powder according to claim 1, characterized in that: In step S1, the organic acid is citric acid or oxalic acid with a concentration of 1.5%; the volume ratio of anhydrous ethanol to deionized water is 1:

1.

3. The method for preparing nanoscale silver-coated copper powder according to claim 1, characterized in that: In step S3, the silane coupling agent is KH-550 with a mass concentration of 0.15% (w / v).

4. The method for preparing nanoscale silver-coated copper powder according to claim 1, characterized in that: In step S2, the mass of polyvinylpyrrolidone is 66% of the total mass of copper powder and target silver layer. When mixing silver nitrate solution and ammonia water, ammonia water is added dropwise to silver nitrate solution at a dropping rate of 0.62 mL / min.

5. The method for preparing nanoscale silver-coated copper powder according to claim 4, characterized in that: In step S2, the flow rate ratio of liquid A, liquid B, and liquid C is 2:1:

1.

6. The method for preparing nanoscale silver-coated copper powder according to claim 1, characterized in that: In step S3, the pH value is adjusted to 10, and the thickness of the SiO2 protective layer is 2.5-3 nm.

7. The method for preparing nanoscale silver-coated copper powder according to claim 1, characterized in that: In step S3, the dropping rate of both the ethanol solution of tetraethyl orthosilicate and the ethanol solution of silane coupling agent is 0.8 mL / min, and the mechanical stirring rate is 150 rpm.

8. The method for preparing nanoscale silver-coated copper powder according to claim 1, characterized in that: In step S3, the amount of aminosilane used is 6.2% of the theoretical mass of the SiO2 protective layer. Before adding it, the aminosilane is diluted with anhydrous ethanol to a 10% ethanol solution.

9. The method for preparing nanoscale silver-coated copper powder according to claim 1, characterized in that: In step S4, when the wet cake is dispersed in cyclohexane, the dispersed solids content is 11%.

10. A nanoscale silver-coated copper powder, characterized in that: It is prepared by any one of the preparation methods of nanoscale silver-coated copper powder as described in claims 1-9.

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