Preparation and surface modification method of oversized silver-coated copper powder

Abstract

The invention relates to the technical field of silver-coated copper powder, in particular to a preparation and surface modification method of oversized silver-coated copper powder. Comprising the steps of pretreatment, electroplating, cleaning and surface modification treatment, a surface modifier is used for optimizing the structure of a silver plating layer, the silver plating layer is more compact, a protection layer can be formed on the surface of silver-coated copper powder, corrosive substances in the environment are further isolated, and therefore contact between a copper core and oxygen and water is effectively isolated, the oxidation process is delayed, and the corrosion resistance of the copper core is improved. And the compatibility of the silver-coated copper powder and organic slurry can be greatly improved, and the application effect of the silver-coated copper powder in aqueous slurry is improved.

Description

Technical Field

[0001] This invention relates to the field of silver-coated copper powder technology, specifically to a method for preparing and surface modifying ultra-large size silver-coated copper powder. Background Technology

[0002] Silver-coated copper powder is a composite metal powder with copper (Cu) as its core and a uniform silver coating on its surface. It combines the excellent conductivity and oxidation resistance of silver with the economic benefits of copper. Through techniques such as chemical plating, a silver coating is formed on the surface of the copper powder, overcoming the tendency of copper powder to oxidize while maintaining good conductivity and chemical stability.

[0003] Currently, most silver-coated copper powder has a particle size between 3 and 5 micrometers. Ultra-large particle size silver-coated copper powder generally refers to silver-coated copper powder with a particle size of 7.5 micrometers or larger. Ultra-large particle size silver-coated copper powder can be used as a core component of thermal conductive pastes, replacing some pure silver powder and reducing silver usage by more than 50%, significantly lowering production costs.

[0004] Chinese patent CN120516004A discloses an ultra-large diameter silver-coated copper powder particle and its preparation process, relating to the field of electronic metal materials technology. The process includes steps such as atomization preparation of copper powder particles, acid washing, alkaline washing, silver plating, and cleaning and drying. This invention prepares copper powder particles using atomization technology, precisely controlling the atomization pressure and medium flow rate to break molten copper liquid into droplets of suitable particle size, which are then rapidly condensed into copper powder particles. The resulting copper powder particles have a stable particle size between 7.5 and 8 micrometers, are uniform in size, have a high yield, and exhibit excellent production speed. Furthermore, the silver-coated copper powder particles prepared by this invention have a dense and uniform silver layer covering the surface, with an average thickness controlled below 100 nm, ensuring particle performance while reducing costs.

[0005] However, ultra-large silver-coated copper powder is generally used in water-based slurries. When it is in a harsh environment with high humidity or high temperature and oxygen, its surface is prone to oxidation. Oxidation not only affects its conductivity but also causes the color to change from bright to dark or yellow, which greatly affects the performance and service life.

[0006] To address the aforementioned problems, this invention provides a method for preparing and surface modifying ultra-large silver-coated copper powder. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing and surface modifying ultra-large silver-coated copper powder, so as to solve the problems mentioned in the background art.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing ultra-large size silver-coated copper powder, comprising the following steps:

[0009] S1, Pretreatment: Take a certain amount of copper powder, place the copper powder in an alkaline washing solution, soak it at 60℃ for 45 minutes, ultrasonically treat it for 5 minutes, filter it and wash it with deionized water, immerse it in an acid-removing washing solution, mechanically stir it for 2 hours, filter it and wash it repeatedly with deionized water until neutral, dry it and mechanically grind the copper powder to obtain pretreated copper powder.

[0010] S2, electroplating, take a certain amount of potassium thiocyanate and silver nitrate, add brightener, prepare electroplating solution, place pretreated copper powder in electroplating tank as cathode, silver plate as anode, add electroplating additive and dispersant, after energizing, silver ions will be reduced and deposited on the surface of copper powder.

[0011] S3, filter the electroplated copper powder and wash it with deionized water to remove residual electroplating solution;

[0012] S4. The obtained copper powder is subjected to surface modification treatment to obtain ultra-large size silver-coated copper powder finished product.

[0013] In step S2, the electroplating current density is 1 A / dm², the electroplating temperature is 55°C, and the duration is 5 min. More preferably, the alkaline washing solution includes either sodium hydroxide or sodium carbonate at a concentration of 5%; the acid washing solution includes either hydrochloric acid or dilute sulfuric acid at a concentration of 6%.

[0014] In a more optimized manner, the electroplating solution comprises, by weight, the following components:

[0015] Silver nitrate 20-40 parts; free potassium thiocyanate 90-150 parts; potassium hydroxide 5-10 parts; brightener one 40 parts; brightener two 10 parts.

[0016] Ideally, brightener one is Ag-935 cyanide brightener, and brightener two is cyanide-free electroplating silver brightener. Ideally, the potassium thiocyanate content is 140 g / L, and the free potassium thiocyanate content is 22 g / L. Ideally, the electroplating additives include one of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol.

[0017] More preferably, the dispersant includes one of polymethyl acrylate type superdispersant, sodium dodecyl sulfate (SDS), and polyacrylate (PAA).

[0018] This invention provides a surface modification method for ultra-large size silver-coated copper powder, applicable to any of the above-mentioned methods for preparing ultra-large size silver-coated copper powder, comprising the following steps:

[0019] Step 1: Place the silver-coated copper powder particles obtained in step S3 into a hydrogen reduction furnace for low-temperature heat treatment. The hydrogen pressure is 3.5 MPa, the heat treatment temperature is 125°C, and the duration is 4.5 h.

[0020] Step 2: Place the silver-coated copper powder in deionized water, add a surface modifier, and ultrasonically stir at 85°C for 3 hours. Filter and dry. Then immerse it in a 75% ethanol solution for 4 hours, filter and dry to obtain the finished silver-coated copper powder.

[0021] In a more optimized manner, the surface modifier is one of the following: silane coupling agent, sodium stearate, or glyceryl stearate, at a concentration of 6.9 g / L.

[0022] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0023] (1) In this invention, the dense silver layer formed by electroplating can effectively protect the copper core. Even in a humid environment, the conductivity will not decrease after long-term use, and the stability is comparable to that of silver powder. The dispersant can improve the dispersibility of silver-coated copper powder in the organic carrier, reduce agglomeration, and improve the stability and oxidation resistance of the slurry. The electroplating additive can optimize the uniformity and density of the silver coating, reduce the risk of copper core exposure, effectively isolate oxygen and sulfides, and delay oxidation.

[0024] (2) The present invention can improve the density of the coating on the surface of silver-copper powder by low-temperature heat treatment with hydrogen. This denser silver coating can more effectively isolate the copper powder from the outside air, thereby delaying the oxidation process; it can also effectively remove the oxide layer that has formed on the surface of the silver-coated copper powder, so that the surface of the copper powder is restored to a clean metallic state, laying the foundation for further improving its oxidation resistance and conductivity.

[0025] (3) The present invention uses surface modifiers to optimize the structure of the silver plating layer, making it denser, and can also form a protective layer on the surface of the silver-coated copper powder, further isolating corrosive substances in the environment, thereby effectively isolating the copper core from contact with oxygen and moisture, delaying the oxidation process, and also greatly improving the compatibility of the silver-coated copper powder with organic slurry, and improving the application effect of the silver-coated copper powder in water-based slurry. Attached Figure Description

[0026] Figure 1 This is an electron microscope image of the ultra-large silver-coated copper powder particles in Example 1. Detailed Implementation

[0027] 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.

[0028] This invention provides a method for preparing and modifying ultra-large size silver-coated copper powder, comprising the following steps:

[0029] S1, Pretreatment: Take a measured amount of copper powder, immerse it in an alkaline washing solution at 60℃ for 45 minutes, ultrasonically treat for 5 minutes, filter, wash with deionized water, immerse in an acid washing solution, mechanically stir for 2 hours, filter again, repeatedly wash with deionized water until neutral, dry, and mechanically grind the copper powder to obtain pretreated copper powder. This step removes various contaminants from the surface of the copper powder, effectively removing grease, oxides, rust, and other contaminants, exposing a clean metal surface, making its surface clean and activated, thereby ensuring that the silver layer can uniformly and densely coat the surface of the copper particles.

[0030] S2, electroplating: Take a certain amount of potassium thiocyanate and silver nitrate, add brightener, and prepare an electroplating solution. Place the pretreated copper powder in the electroplating tank as the cathode and the silver plate as the anode. Add electroplating additives and dispersants. After energizing, silver ions are reduced and deposited on the surface of the copper powder. The current density during electroplating is 1A / dm2, the electroplating temperature is 55℃, and the duration is 5min.

[0031] Copper powder has poor oxidation resistance and easily forms an oxide film on its surface, losing its conductivity. The dense silver layer formed by electroplating effectively protects the copper core. Even in humid environments, its conductivity does not decrease with long-term use, and its stability is comparable to that of silver powder. Dispersants can improve the dispersibility of silver-coated copper powder in organic carriers, reduce agglomeration, and enhance the stability and oxidation resistance of the slurry. Electroplating additives can optimize the uniformity and density of the silver coating, reduce the risk of copper core exposure, effectively isolate oxygen and sulfides, and delay oxidation.

[0032] During electroplating, controlling the current density and temperature can ensure that the silver layer is uniform and dense, and achieves efficient anti-oxidation through the "copper core silver armor" structure.

[0033] S3. The electroplated copper powder is filtered and washed with deionized water to remove residual plating solution. Finally, surface modification is performed, specifically as follows:

[0034] Step 1: Place the silver-coated copper powder particles obtained in step S3 into a hydrogen reduction furnace for low-temperature heat treatment. The hydrogen pressure is 3.5 MPa, the heat treatment temperature is 125°C, and the duration is 4.5 h.

[0035] Step 2: Place the silver-coated copper powder in deionized water, add a surface modifier, and ultrasonically stir at 85°C for 3 hours. Filter and dry. Then immerse it in a 75% ethanol solution for 4 hours, filter and dry to obtain the finished silver-coated copper powder.

[0036] Low-temperature heat treatment with hydrogen can improve the density of the coating on the surface of silver-copper powder. This denser silver coating can more effectively isolate the copper powder from the outside air, thereby slowing down the oxidation process; it can also effectively remove the oxide layer that has formed on the surface of the silver-coated copper powder, restoring the copper powder surface to a clean metallic state, laying the foundation for further improving its oxidation resistance and conductivity.

[0037] Surface modifiers optimize the structure of the silver plating layer, making it denser, and can also form a protective layer on the surface of silver-coated copper powder, further isolating it from corrosive substances in the environment. This effectively isolates the copper core from contact with oxygen and moisture, slows down the oxidation process, and can also significantly improve the compatibility of silver-coated copper powder with organic slurries, thereby enhancing the application effect of silver-coated copper powder in water-based slurries.

[0038] The present invention includes examples and several comparative examples to test the antioxidant properties of the prepared ultra-large silver-coated copper powder. The specific steps are shown in Table 1, and the test results are shown in Table 2.

[0039] The testing method is as follows:

[0040] 1. Thermogravimetric analysis: In an air or oxygen atmosphere, the temperature is increased at a rate of 5-10℃ / min, and the initial oxidation temperature and mass gain curve are recorded.

[0041] 2. Weight gain under constant temperature: Weigh 2g of copper powder and spread it evenly on a ceramic boat. Keep it at 200℃ for 2 hours and calculate the weight gain rate.

[0042] 3. Rapid screening by nitric acid drop: Prepare nitric acid at a standard ratio of 1:1 (volume ratio), and drop 0.05 mL onto the surface of the powder bed at 25°C. Record the time required for obvious bubbles to appear or for the color to turn green.

[0043] Table 1 Comparison of each embodiment with the comparative example.

[0044] Table 2. Test results for each embodiment and comparative example.

[0045] Combining the data in Tables 1 and 2, it can be seen that the brightener, dispersant, low-temperature heat treatment method, and surface modifier in the formulation all affect the antioxidant performance of ultra-large silver-coated copper powder. The order of influence from largest to smallest is: surface modifier, low-temperature heat treatment, dispersant, and brightener. Furthermore, the ultra-large silver-coated copper powder prepared in Example 1 exhibits excellent antioxidant properties, with a very high initial oxidation temperature, a isothermal weight gain rate far lower than the standard, and a rapid nitric acid droplet screening time far exceeding industry standard levels.

[0046] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing ultra-large size silver-coated copper powder, characterized in that, Includes the following steps: S1, Pretreatment: Take a certain amount of copper powder, place the copper powder in an alkaline washing solution, soak it at 60℃ for 45 minutes, ultrasonically treat it for 5 minutes, filter it and wash it with deionized water, immerse it in an acid-removing washing solution, mechanically stir it for 2 hours, filter it and wash it repeatedly with deionized water until neutral, dry it and mechanically grind the copper powder to obtain pretreated copper powder. S2, electroplating, take a certain amount of potassium thiocyanate and silver nitrate, add brightener, prepare electroplating solution, place pretreated copper powder in electroplating tank as cathode, silver plate as anode, add electroplating additive and dispersant, after energizing, silver ions will be reduced and deposited on the surface of copper powder. S3, filter the electroplated copper powder and wash it with deionized water to remove residual electroplating solution; S4, perform surface modification treatment on the obtained copper powder to obtain ultra-large size silver-coated copper powder finished product. In step S2, the current density during electroplating is 1A / dm2, the electroplating temperature is 55℃, and the duration is 5min.

2. The method for preparing ultra-large size silver-coated copper powder according to claim 1, characterized in that: The alkaline washing solution includes one of sodium hydroxide and sodium carbonate, with a concentration of 5%; the acid washing solution includes one of hydrochloric acid and dilute sulfuric acid, with a concentration of 6%.

3. The method for preparing ultra-large size silver-coated copper powder according to claim 1, characterized in that, The electroplating solution comprises the following components by weight: Silver nitrate 20-40 parts; free potassium thiocyanate 90-150 parts; potassium hydroxide 5-10 parts; brightener one 40 parts; brightener two 10 parts.

4. The method for preparing ultra-large size silver-coated copper powder according to claim 3, characterized in that: The first brightener is Ag-935 cyanide brightener, and the second brightener is a cyanide-free electroplating silver brightener.

5. The method for preparing ultra-large size silver-coated copper powder according to claim 3, characterized in that: The content of potassium thiocyanate is 140 g / L, and the content of free potassium thiocyanate is 22 g / L.

6. The method for preparing ultra-large size silver-coated copper powder according to claim 1, characterized in that: The electroplating additives include one of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol.

7. The method for preparing ultra-large size silver-coated copper powder according to claim 1, characterized in that: The dispersant includes one of polymethyl acrylate type superdispersant, sodium dodecyl sulfate (SDS), and polyacrylic acid (PAA).

8. A surface modification method for ultra-large size silver-coated copper powder, applied in any one of the preparation methods of ultra-large size silver-coated copper powder according to claims 1-7, characterized in that, Includes the following steps: Step 1: Place the silver-coated copper powder particles obtained in step S3 into a hydrogen reduction furnace for low-temperature heat treatment. The hydrogen pressure is 3.5 MPa, the heat treatment temperature is 125°C, and the duration is 4.5 h. Step 2: Place the silver-coated copper powder in deionized water, add a surface modifier, and ultrasonically stir at 85°C for 3 hours. Filter and dry. Then immerse it in a 75% ethanol solution for 4 hours, filter and dry to obtain the finished silver-coated copper powder.

9. The surface modification method for ultra-large size silver-coated copper powder according to claim 8, characterized in that: The surface modifier is one of silane coupling agent, sodium stearate, and glyceryl stearate, with a concentration of 6.9 g / L.

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