Preparation method of silver-coated copper powder

Abstract

The invention provides a preparation method of silver-coated copper powder, and belongs to the technical field of conductive silver paste. The method comprises the following steps: S1, preparing a base solution containing copper powder: uniformly mixing the copper powder, a complexing agent and water to obtain the base solution; s2, a copper powder oxide layer is removed, specifically, the base solution is stirred, and the copper powder oxide layer is removed in the process of stirring the base solution; s3, silver-coated copper powder is prepared, specifically, a silver salt aqueous solution is added into the base solution, and stirring continues; after the reaction is finished, washing and drying to obtain silver-coated copper powder; the mass of silver ions in the silver salt aqueous solution is 1%-90% of the mass of the copper powder. According to the method, operation is simpler, coating is more uniform, the prepared silver-coated copper powder is lower in resistivity, the independent copper powder deoxidation step and the subsequent copper powder separation and washing step can be omitted, the copper powder deoxidation process is fused into the material mixing process, and the copper powder is prevented from being oxidized again in the separation and washing steps.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of conductive silver paste, and particularly relates to a preparation method of silver-coated copper powder. BACKGROUND

[0002] With the rise of silver price and the increase of industrial silver amount, the industry using conductive silver paste on a large scale begins to vigorously promote the conductive silver-coated copper paste to replace pure silver paste. The core conductive material of the conductive silver-coated copper paste is silver-coated copper powder, and the quality of the silver-coated copper powder affects the conductivity and stability of the silver-coated copper paste. The processing cost of the silver-coated copper powder also affects the price of the silver-coated copper paste. The reported preparation methods of the silver-coated copper powder include magnetron sputtering, spray pyrolysis, mechanical ball milling, and chemical method. The chemical method is the most widely used due to low preparation cost and good coating quality.

[0003] The preparation process of the existing chemical method silver-coated copper powder usually includes the following steps: copper powder deoxidation, copper powder separation, copper powder washing, silver shell coating, silver-coated copper powder separation, washing, and drying. The separate copper powder deoxidation step involves the subsequent copper powder separation and washing steps. This is because the copper powder deoxidation usually needs to use acid or alkali solution, and the copper powder needs to be washed to neutral before the silver shell coating. This not only increases the process flow and a large amount of wastewater, but also causes the loss of copper powder, cannot accurately estimate the silver content of the final silver-coated copper powder, and is difficult to produce the silver-coated copper powder with stable performance. In addition, in actual production, after the copper powder deoxidation, it is difficult to ensure that the copper powder surface is not oxidized again in the separation and washing process. If the copper powder surface is oxidized again in the process, not only the nucleation uniformity of the silver shell is affected, but also the resistivity of the finally prepared silver-coated copper powder is high.

[0004] It is particularly worth noting that micro-nano copper powder is very easy to oxidize in air. Because the copper oxide generated on the surface of the copper powder has high resistance, it will hinder the adhesion of silver on the surface of the copper core. Therefore, it is particularly necessary to remove the oxide layer on the surface of the copper powder before preparing silver-coated copper powder. However, in actual production, it is difficult to ensure that the surface of the copper powder is not oxidized again during the separation and washing process after the copper powder is deoxidized. For example, patent CN 120325965 A provides a preparation and surface modification method of silver-coated copper powder. The pretreatment step of the copper powder needs to mix the copper powder with a mixed acid solution, then perform ultrasonic stirring treatment, and then perform centrifugal separation to remove surface oxides and organic contaminants. The step needs to be repeated 3 times, and the copper powder is washed to neutral with deionized water. Finally, the copper powder is centrifugally separated. Patent CN 120286710 A provides a silver-coated copper powder for conductive paste and a preparation method thereof. The deoxidation step of the copper powder needs to use a citric acid aqueous solution to clean the copper powder, then use pure water to rinse the copper powder 3-5 times to obtain clean copper powder. In order to prevent the copper powder from being oxidized after washing, palm oil is also used to protect the copper powder. The palm oil is washed out with hot water before the silver-coated copper powder, and the pure water is also washed out with ethanol. The whole reaction process also needs to be protected by nitrogen. In short, in order to prevent the copper powder from being oxidized, a very complex process is adopted.

[0005] Patent CN 119927206 A provides a silver-coated copper powder with low silver content, a preparation method and application thereof. At least one of the deoxidation steps of the copper powder needs to be cleaned with acetone, dilute sulfuric acid, NaOH, EDTA, a mixed solution of ammonium sulfate and ammonia, ethanol, and deionized water. Patent CN 120115713 A provides a preparation method of smooth and dense silver-coated copper powder. The surface activation treatment of the copper powder is to disperse the copper powder in an alkaline or acidic solution to remove organic matter and oxide layer on the surface of the copper powder, or to remove organic matter and oxide layer on the surface of the copper powder in two steps in an alkaline or acidic solution. In order to prevent the deoxidized copper powder from being oxidized, the activated copper powder is also protected: the highly active copper powder obtained after acid washing or alkali washing is added to a protective reagent solution and stirred to reduce the oxidation rate of the copper powder in the solution and air.

[0006] Patent CN 110551995 A provides a method for preparing smooth and dense silver-coated copper powder by chemical plating. Sodium hydroxide solution is used to ultrasonically clean the copper powder, the upper clear liquid is poured out, and deionized water is continuously added to clean the copper powder to neutral. After completing the activation treatment step of the copper powder, the silver layer is coated. Patent CN 111304640 A provides silver-coated copper powder, a preparation method thereof, and electronic paste. In some embodiments, the copper powder is also pretreated after being obtained, including the steps of: sequentially cleaning the copper powder with octylphenol polyoxyethylene ether-10, deionized water, sulfuric acid with a concentration of 5-20%, and deionized water to obtain pretreated copper powder.

[0007] Patent CN 106148926 A provides a method for preparing silver-coated copper powder, which requires ultrasonically dispersing the copper powder to be silvered in a solvent, adding an alkaline reagent and a reducing agent, and then performing alkaline washing and reduction treatment on the copper powder. Patent CN106925774 A provides a method for preparing silver-coated copper powder. Although the specific embodiments do not include a copper powder deoxidation step, the copper powder deoxidation operation is performed in all the examples. In addition, patents CN111872376A, CN113020587A, CN120388777A, and CN 119057065A all have a separate copper powder deoxidation step and a subsequent copper powder washing step. Summary of the Invention

[0008] To address the aforementioned problems in existing technologies, this invention provides a method for preparing silver-coated copper powder. The method described in this invention is simpler to operate, produces more uniform coating, and yields silver-coated copper powder with lower resistivity. It eliminates the need for separate copper powder deoxidation steps and subsequent copper powder separation and washing steps, integrating the copper powder deoxidation process into the mixing process to prevent re-oxidation of the copper powder during separation and washing.

[0009] The technical solution of the present invention is as follows: A method for preparing silver-coated copper powder includes the following steps: S1. Prepare a base solution containing copper powder: Mix copper powder, complexing agent and water to obtain a base solution; the mass of the complexing agent is 1% to 300% of the copper powder; the mass ratio of water to copper powder is 4 to 150:1. S2. Removal of copper powder oxide layer: Stir the bottom liquid to remove the copper powder oxide layer during the stirring process. The stirring temperature is 0℃~90℃ and the stirring time is 1~60 min. S3. Preparation of silver-coated copper powder: Add silver salt aqueous solution to the base liquid and continue stirring. The stirring temperature is 0℃~90℃ and the stirring time is 2~60 min. After the reaction is completed, wash and dry to obtain silver-coated copper powder. The mass of silver ions in the silver salt aqueous solution is 1%~90% of the mass of copper powder.

[0010] Preferably, the copper powder in step S1 is at least one of copper powder containing an oxide layer or copper powder without an oxide layer.

[0011] Preferably, the copper powder in step S1 is spherical or near-spherical, with a D50 of 3-6 μm and a tap density of not less than 4.2 g / m³. 3 Specific surface area not greater than 0.45 m² 2 / g, oxygen content not greater than 1%.

[0012] Furthermore, the preferred particle size distribution D50 of the copper powder in step S1 is 3.5-5.5 μm, and the preferred tap density is not less than 4.7 g / m³. 3 The preferred specific surface area is no greater than 0.35 m². 2 / g, preferably with an oxygen content of no more than 0.2%.

[0013] Furthermore, the mass of the complexing agent in step S1 is preferably 10% to 200% of the copper powder, more preferably 80% to 150% of the copper powder mass.

[0014] Furthermore, the preferred mass ratio of water to copper powder in step S1 is 7~35:1; Preferably, the complexing agent in step S1 includes one or more of ammonia, ethylenediamine, alkanolamine complexing agents, ethyleneamine complexing agents, or succinimide.

[0015] More preferably, the alkanolamine complexing agent includes, but is not limited to, monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, dimethylethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, or diethanolmonoisopropanolamine; the ethyleneamine complexing agent includes, but is not limited to, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, or polyethylenepolyamine.

[0016] Preferably, the complexing agent described in step S1 may further include one or more of the following: hypotriacetic acid and its salts, ethylenediaminetetraacetic acid and its salts, diethylenetriaminepentaacetic acid and its salts, or hydroxyethylethylenediaminetriacetic acid and its salts.

[0017] Preferably, step S1 may further include a reducing agent and / or a dispersant; the mass of the reducing agent is 10% to 100% of the mass of the copper powder, and the mass of the dispersant is 1% to 50% of the mass of the copper powder.

[0018] Furthermore, when a reducing agent and / or a dispersant are added in step S1, the mass of the reducing agent is preferably 30% to 60% of the mass of the copper powder, and the mass of the dispersant is preferably 2% to 20% of the mass of the copper powder.

[0019] Preferably, the reducing agent is one or more of hydrazine hydrate, ascorbic acid, glucose, or tartrate.

[0020] Preferably, the dispersant is one or more of the following: polyvinylpyrrolidone, polyoxyethylene ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, fatty acid polyol ester, polyethylene glycol, chitosan, sodium dodecyl sulfonate, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, or gelatin.

[0021] Furthermore, the stirring temperature in step S2 is preferably 10℃~50℃, more preferably 10℃~30℃.

[0022] Furthermore, the stirring time in step S2 is preferably 1 to 15 minutes, more preferably 8 to 10 minutes.

[0023] Furthermore, the stirring speed in step S2 is preferably 600~2000 rpm, more preferably 800-1000 rpm.

[0024] Preferably, the silver salt in step S3 includes one or more of silver nitrate, silver acetate, silver sulfate, or silver sulfamate; the mass concentration of the aqueous solution of the silver salt is 1% to 80%.

[0025] Furthermore, the mass of silver ions in the silver salt aqueous solution in step S3 is preferably 1% to 50% of the mass of copper powder, and more preferably 1% to 30% of the mass of copper powder.

[0026] Furthermore, the mass concentration of the silver salt aqueous solution in step S3 is preferably 20% to 60%.

[0027] Furthermore, the stirring temperature in step S3 is preferably 10℃~50℃, more preferably 10℃~30℃.

[0028] Furthermore, the stirring time in step S3 is preferably 5 to 20 minutes.

[0029] Furthermore, the stirring speed in step S3 is preferably 600-2000 rpm, more preferably 800-1000 rpm.

[0030] The beneficial technical effects of this invention are as follows: 1. This invention omits the separate copper powder deoxidation step and subsequent copper powder separation and washing steps, reducing the preparation process of silver-coated copper powder, simplifying the preparation process, and preventing the pollution and waste of large amounts of water resources during the copper powder washing process. This is because the complexing agent used in this invention can react with the copper oxide layer on the surface of the copper powder, removing the copper oxide layer.

[0031] Specifically, the necessary complexing agents selected in this invention, such as ammonia, ethylenediamine, alkanolamine complexing agents, ethyleneamine complexing agents, or succinimide, are all amine complexing agents with relatively strong alkalinity. They can remove oil stains from the copper surface and react with copper oxide to make the copper oxide on the surface of the copper core into an ionic state, which then dissolves in the solution.

[0032] In addition, the non-essential complexing agents selected in this invention, such as hypotriacetic acid and its salts, ethylenediaminetetraacetic acid and its salts, diethylenetriaminepentaacetic acid and its salts, or hydroxyethylethylenediaminetriacetic acid and its salts, are amine carboxylic acid complexing agents with relatively weak basicity. Their function is to regulate the deposition rate of silver ions on the surface of the copper core, making the silver shell more compact and increasing the tap density of the silver-coated copper powder.

[0033] There are no existing technologies that demonstrate the elimination of the copper powder cleaning step through systematic screening and adjustment of complexing agents. For example, patent CN 108356264 A uses ethylenediaminetetraacetic acid, thiourea, and citric acid as complexing agents. Ethylenediaminetetraacetic acid falls within the scope of non-essential complexing agents in this invention and is different from this invention. Similarly, patent CN 119035542 A uses EDTA.2Na.2H2O, EDTA.4Na.4H2O, or HEDTA as complexing agents, which also fall within the scope of non-essential complexing agents in this invention and are different from this invention.

[0034] The complexing agent in patent CN 110551995 A is one or more of thiourea, thioaminourea, sodium thiosulfate, ammonia, EDTA, citric acid, 8-hydroxyquinoline, DTPA, triethylenetetramine, or ethylenediaminetetrapropionic acid. In particular, the use of thiourea, thioaminourea, or sodium thiosulfate as the complexing agent results in a new complexation system with alkali-treated copper powder that has a smaller complexation constant, making the complexed ions more stable. Therefore, the desired effect can be achieved without the need for a stabilizer. Although there is some overlap with the complexing agents selected in this invention, it does not emphasize that ammonia or triethylenetetramine are necessary complexing agents, and this patent tends to favor thiourea, thioaminourea, or sodium thiosulfate as complexing agents.

[0035] The complexing agents in patent CN 106925774 A include one or more of ammonia, ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, and tetrasodium ethylenediaminetetraacetate. Although there is some overlap with the complexing agents selected in this invention, it does not emphasize that ammonia, ethylenediamine, diethylenetriamine, triethylenetetraamine, and tetraethylenepentamine are necessary complexing agents. In the embodiments of that patent, any of the proposed complexing agents can be used, and the dosage and function of the complexing agents differ from those of this invention. In fact, weakly alkaline amine carboxylic acid complexing agents such as disodium ethylenediaminetetraacetate have low solubility in water, especially at higher concentrations, where they form a white precipitate with silver ions, which is detrimental to the uniform deposition of silver ions on the copper core surface. Adding NaOH or the stronger alkaline necessary amine complexing agent of this invention is necessary to improve solubility. Therefore, the stronger alkaline necessary amine complexing agent of this invention also helps to improve the solubility of the auxiliary complexing agent, thereby improving the quality of the silver shell.

[0036] The complexing agent in the reducing solution of patent CN 115156529 A is one or more of ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid salt, triethanolamine, polyethylenepolyamine, triethylenetetraamine, diethylenetriamine, ammonia, ethylenediamine, thiourea, succinimide, hydantoin, imidazole, and citric acid. Similar to patents CN 110551995 A and CN 106925774 A, it does not emphasize that the overlapping complexing agents triethanolamine, polyethylenepolyamine, triethylenetetraamine, diethylenetriamine, ammonia, ethylenediamine, and succinimide are necessary complexing agents. In the embodiments of this patent, any of the proposed complexing agents can be selected, and the dosage and function of the complexing agents are different from those of this invention. That is, the initial intention of this patent in selecting these complexing agents is different from that of this invention.

[0037] 2. This invention not only omits the steps of copper powder deoxidation, separation, and washing, but also prevents the regeneration of an oxide layer on the surface of the copper powder during separation and washing. This is because this invention first mixes the copper powder with a complexing agent, a reducing agent, etc., and stirs for a certain period of time. During this process, the complexing agent can remove the oxide layer on the surface of the copper powder and inhibit the formation of an oxide layer. It should be noted that the reducing agent and dispersant are unnecessary in this invention; they can be added as needed or not.

[0038] 3. The complexing agent of this invention can both remove the copper oxide layer and act as a complexing agent for silver ions. Therefore, after stirring to remove the copper oxide layer, it is not necessary to separate and wash the copper powder; instead, the silver salt aqueous solution can be directly poured in to prepare silver-coated copper powder. This avoids the formation of a new copper oxide layer on the surface of the copper powder during subsequent separation and washing, and greatly simplifies the operation process.

[0039] 4. Unlike most other silver-coated copper powder technologies, this invention does not require the preparation of a silver ammonia solution (also known as a silver complexing solution). Instead, the silver salt solution is directly poured into the copper powder base solution. Since silver ammonia solution is usually alkaline, it readily decomposes in air, producing silver oxide, which easily turns brown or black. The quality of silver-coated copper powder prepared from the self-decomposed silver ammonia solution is unstable. This invention avoids the preparation of the silver ammonia solution, resulting in more stable quality silver-coated copper powder.

[0040] 5. The resistivity of copper at room temperature is approximately 1.75 × 10⁻⁶. -6The resistivity of copper oxide is 3 to 12 orders of magnitude higher than that of copper, while the resistivity of copper oxide is Ω·cm. Therefore, to ensure the low resistivity of silver-coated copper powder, the oxide on the surface of the copper powder must be removed. Otherwise, the current will tend to flow from the silver shell instead of the copper core with higher resistivity, thus defeating the purpose of silver-coated copper technology. This invention eliminates the formation of oxides on the surface of the copper core during the preparation process, thereby improving the conductivity of the silver-coated copper powder. In addition, since there are no copper oxides on the surface of the copper powder during the preparation process, the silver shell nucleation is uniform, resulting in a high uniformity of silver shell coating in the silver-coated copper powder prepared by this invention. Conductive pastes usually contain acidic substances. If the silver shell coating is uneven, the exposed copper areas will be corroded by the acidic substances, causing the paste to turn green. Uneven coating can also lead to dehydration of the silver shell in the exposed copper areas and areas with thinner silver shells during the thermal curing process of the paste, failing to protect the copper core from oxidation during heating. Attached Figure Description

[0041] Figure 1 Scanning electron microscope image of the product prepared in Example 1; Figure 2 Scanning electron microscope image of the product prepared in Example 2; Figure 3 Scanning electron microscope image of the product prepared in Example 3; Figure 4 Scanning electron microscope image of the product prepared in Example 4; Figure 5 Scanning electron microscope image of the product prepared in Example 5; Figure 6 Scanning electron microscope image of the product prepared in Comparative Example 1; Figure 7 The scanning electron microscope image of the product prepared in Comparative Example 2; Figure 8 Scanning electron microscope image of the product prepared in Comparative Example 3; Figure 9 The image shows a scanning electron microscope (SEM) image of the product prepared in Comparative Example 4. Figure 10 Scanning electron microscope image of the product prepared in Comparative Example 5; Figure 11 Scanning electron microscope image of the product prepared in Comparative Example 6; Figure 12 The images show silver-coated copper powder after being soaked in oleic acid for one day. Number 1 represents silver-coated copper powder of Comparative Example 1, number 2 represents silver-coated copper powder of Example 1, number 3 represents silver-coated copper powder of Example 2, and number 4 represents silver-coated copper powder of Example 3. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0043] Unless otherwise specified, all raw materials used in the examples are commercially available products. The copper powder may or may not have an oxide layer, is spherical or near-spherical in shape, has a D50 of 4-6 μm, and a tap density of approximately 4.5-4.9 g / m³. 3 Specific surface area less than 0.4 m² 2 / g, oxygen content less than 0.5%.

[0044] Example 1: S1: Prepare copper-containing foundation liquid: Mix 136g of spherical copper powder with oxide layer and D50 of 4.0 μm, 120g of complexing agent ammonia water, 15g of complexing agent disodium ethylenediaminetetraacetate, 30g of reducing agent ascorbic acid, 10g of dispersant polyvinylpyrrolidone, and 1600g of water.

[0045] S2: Stir the copper-containing bottom liquid at 10℃ for 10 min at a stirring speed of 1000 rpm.

[0046] S3: Add silver nitrate aqueous solution to the copper-containing powder solution under stirring. Stop the reaction after stirring at 1000 rpm for 20 minutes at 10°C. After washing and drying, silver-coated copper powder is obtained. The silver nitrate aqueous solution contains 27.35 g of silver nitrate and 60 g of water.

[0047] Silver content calculation: The mass of silver in silver nitrate is 63.5% of the mass of silver nitrate, which is about 17.37g, accounting for 11.3% of the mass of the prepared silver-coated copper powder; considering the replacement loss of copper, the actual silver content of the product is 12%.

[0048] Example 2: S1: Prepare copper-containing foundation liquid: Mix 140 g of spherical copper powder with oxide layer and D50 of 4.0 μm, 110 g of complexing agent ethylenediamine, 5 g of complexing agent sodium hypotriacetate, 30 g of reducing agent ascorbic acid, 8 g of dispersant polyvinylpyrrolidone, 2 g of dispersant polyethylene glycol, and 2600 g of water.

[0049] S2: Stir the copper-containing foundation liquid at 15℃ for 9 minutes at a stirring speed of 850 rpm.

[0050] S3: Add silver sulfate aqueous solution to the copper-containing powder solution under stirring. Stop the reaction after stirring at 15℃ for 20 min at a stirring speed of 850 rpm. After washing and drying, silver-coated copper powder is obtained. The silver sulfate aqueous solution contains 20.2 g of silver sulfate and 60 g of water.

[0051] Example 3: S1: Prepare copper-containing foundation liquid: Mix 136 g of spherical copper powder with oxide layer and D50 of 5.5 μm, 150 g of complexing agent tetraethylenepentamine, 50 g of reducing agent glucose, 10 g of dispersant polyoxyethylene ether, 2 g of dispersant chitosan, and 3600 g of water.

[0052] S2: Stir the copper-containing foundation liquid at 20℃ for 8 minutes at a stirring speed of 950 rpm.

[0053] S3: Add silver nitrate aqueous solution to the copper-containing powder solution under stirring. Stop the reaction after stirring at 20℃ for 12 min at a stirring speed of 950 rpm. After washing and drying, silver-coated copper powder is obtained. The silver nitrate aqueous solution contains 25.6 g of silver nitrate and 80 g of water.

[0054] Example 4: S1: Prepare copper-containing foundation liquid: Mix 136g of spherical copper powder with no oxide layer and a D50 of 5.5 μm, 150g of complexing agent triethanolamine, 5g of complexing agent succinimide, 30g of reducing agent ascorbic acid, 10g of dispersant gelatin, 2g of dispersant sodium dodecyl sulfonate, and 1600g of water.

[0055] S2: Stir the copper-containing foundation liquid at 20℃ for 10 min at a stirring speed of 800 rpm.

[0056] S3: Add silver nitrate aqueous solution to the copper-containing powder solution under stirring. Stop the reaction after stirring at 20℃ for 15 min at a stirring speed of 800 rpm. After washing and drying, silver-coated copper powder is obtained. The silver nitrate aqueous solution contains 26 g of silver nitrate and 70 g of water.

[0057] Example 5: S1: Prepare copper-containing foundation liquid: Mix 140 g of spherical copper powder with oxide layer and D50 of 5.5 μm, 80 g of complexing agent ethylenediamine, 60 g of complexing agent triisopropanolamine, and 1800 g of water.

[0058] S2: Stir the copper-containing foundation liquid at 25℃ for 10 min at a stirring speed of 1000 rpm.

[0059] S3: Add silver nitrate aqueous solution to the copper-containing powder solution under stirring. Stop the reaction after stirring at 1000 rpm for 18 minutes at 25°C. After washing and drying, silver-coated copper powder is obtained. The silver nitrate aqueous solution contains 20 g of silver nitrate and 50 g of water.

[0060] Example 6: The preparation method of Example 5 was followed, except that the type of complexing agent was changed to only 140 g of succinimide, thus obtaining Example 6.

[0061] Comparative Example 1: Comparative Example 1 is a commercially available silver-coated copper powder with superior performance, containing the same silver content as in Example 1, with a D50 of 4.8 μm and a tap density of 5.19 g / m³. 3 The specific surface area is 0.341 m². 2 / g, with an oxygen content of 0.115%.

[0062] Comparative Example 2: The preparation method of Example 1 was followed, except that the copper powder was replaced with spherical copper powder containing an oxide layer, with a D50 of 2-3 μm and a tap density of approximately 3.6 g / m³. 3 Its specific surface area is approximately 0.81 m². 2 / g, oxygen content less than 0.5%.

[0063] Comparative Example 3: The preparation method of Example 5 was followed, except that the complexing agent was replaced with 20 g of ethylenediamine and 15 g of triisopropanolamine.

[0064] Comparative Example 4: The preparation method of Example 5 was followed, except that the complexing agent was replaced with 120 g of ethylenediamine and 90 g of triisopropanolamine.

[0065] Comparative Example 5: The preparation method of Example 5 was followed, except that the complexing agent was replaced with 140 g of disodium ethylenediaminetetraacetate.

[0066] Comparative Example 6: The preparation method of Example 5 was followed, except that the complexing agent was replaced with 140 g of hypotriacetic acid.

[0067] Test Example 1: Product Form The products obtained in Examples 1-5 and Comparative Examples 1-6 were scanned by electron microscopy, as shown below. Figures 1-11As shown in the figures, the silver-coated copper powders of Examples 1-5 have relatively smooth surfaces and complete coatings, similar in morphology to Comparative Example 1. Comparative Example 2, due to the smaller particle size of the copper powder, also has smaller silver-coated copper powder particles, distributed in the range of 1-3 μm. Comparative Example 3, due to the use of less complexing agent, failed to completely remove the oxide layer on the surface of the copper powder, and the silver ion deposition rate was faster, resulting in a rough surface of the silver-coated copper powder. Comparative Example 4 used more complexing agent, which completely removed the oxide layer on the surface of the copper powder, resulting in a smoother silver shell, but rougher than Example 5. In fact, within the same reaction time, due to the excessive amount of complexing agent used in Comparative Example 4, the silver ions in the reaction solution were not completely converted into a silver shell. Comparative Examples 5 and 6 both used only non-essential complexing agents, resulting in silver-coated copper powders with rough silver shell surfaces and obvious gaps. The surface morphology of the silver-coated copper powder obtained in Example 6 is similar to that of Example 5.

[0068] Figure 12 The images show different silver-coated copper powders after being soaked in oleic acid for one day. Number 1 represents a commercially available comparative silver-coated copper powder, number 2 represents the silver-coated copper powder prepared in Example 1, number 3 represents the silver-coated copper powder prepared in Example 2, and number 4 represents the silver-coated copper powder prepared in Example 3. The silver-coated copper powder in number 1 turns blue after soaking in oleic acid, while numbers 2-4 do not. This indicates that the silver-coated copper powder prepared in the examples of this invention has a completely encapsulated copper core in its silver shell, and there is no copper leakage.

[0069] Test Example 2: Product Oxygen Content Table 1 shows the oxygen content of the copper powder used in Examples 1 and 2, the copper powder used in Examples 3-5 and Comparative Examples 2-6, the silver-coated copper powder prepared in Examples 1-5, and the silver-coated copper powder prepared in Comparative Examples 1-6.

[0070] Table 1 As shown in Table 1, the oxygen content of the silver-coated copper powder prepared in Examples 1 and 2 was 0.075% and 0.053% lower than that of the copper powder used in Examples 1 and 2, respectively. The oxygen content of the silver-coated copper powder prepared in Examples 3, 4, and 5 was 0.146%, 0.145%, and 0.141% lower than that of the copper powder used in Examples 1 and 2, respectively, indicating that the present invention has a better deoxidation effect on copper powder. The oxygen content of the silver-coated copper powder obtained in Example 6 was similar to that in Example 5.

[0071] The oxygen content of the silver-coated copper powder prepared in Comparative Example 2 was 0.137% higher than that of the silver-coated copper powder prepared in Example 1, but 0.139% lower than that of the copper powder used in Comparative Example 2. This indicates that the silver-coated copper powder prepared from copper powder with smaller particle size has a thinner silver shell and weaker oxidation resistance, resulting in partial oxidation of the copper core during the powder heating and drying process. The oxygen content of the silver-coated copper powder prepared in Comparative Example 3 was 0.259% higher than that of the silver-coated copper powder prepared in Example 5, indicating that the amount of necessary complexing agent used in this invention plays an important role in removing oxides from the surface of the copper powder and preventing oxidation during subsequent separation and washing.

[0072] The oxygen content of the silver-coated copper powder prepared in Comparative Example 4 was 0.013% higher than that of the silver-coated copper powder prepared in Example 5. This indicates that the amount of necessary complexing agent used in this invention was too large. Although it can ensure that the copper core of the silver-coated copper powder does not oxidize during the preparation process, due to the complexing process, the silver ions are not completely converted into silver shells and deposited on the surface of the copper cores. Therefore, the silver shells are thinner, and the oxygen content will increase slightly during the drying process of the powder.

[0073] The oxygen content of the silver-coated copper powder prepared in Comparative Examples 5 and 6 was 0.296% and 0.181% higher than that in Example 5, respectively. This indicates that the non-essential complexing agent in this invention alone cannot remove the oxide layer on the copper surface. On the contrary, due to the non-dense silver coating, the oxygen content of the silver-coated copper powder increased compared to the original copper powder during the reaction and powder heating and drying process.

[0074] Test Example 3: Product Resistivity Because the silver-coated copper powder particles are relatively large, nano-silver powder is needed to fill the gaps between them in actual use. For applications in silicon-based solar cells, nano-silver powder is also needed to contact the substrate of the solar cell. Therefore, the silver-coated copper powder obtained in the examples and comparative examples was mixed with 25% nano-silver powder to prepare a low-temperature conductive silver-copper paste, which was then cured at 200°C for 7 min to obtain an electrode. Its resistivity was then tested, and the test results are shown in Table 2.

[0075] Table 2 As shown in Table 1, the resistivity of the 12% silver-containing copper-coated powder prepared in Example 1 of this invention is lower than that of the silver-coated copper-coated powder in Comparative Example 1 with the same silver content. This is because the silver-coated copper-coated powder prepared in this invention has a uniform coating and a lower oxygen content. Examples 2-4 have slightly higher resistivity than Examples 1 and Comparative Example 1 because their silver content is lower. The resistivity of the silver-coated copper-coated powder obtained in Example 6 is similar to that of Example 5.

[0076] The smaller copper powder particle size in Comparative Example 2 resulted in a thinner silver shell in the silver-coated copper powder with the same silver content, leading to weaker oxidation resistance compared to Example 1. Therefore, the resistivity of the silver-coated copper powder prepared in Comparative Example 3 was higher than that in Example 1. The insufficient amount of complexing agent in Comparative Example 3 failed to completely remove the oxide layer on the copper powder surface, and the rough silver shell resulted in a higher resistivity of the silver-coated copper powder prepared in Comparative Example 4 compared to Example 5. Excessive use of complexing agent in Comparative Example 4 resulted in incomplete conversion of silver ions and a thinner silver shell, leading to a higher resistivity of the silver-coated copper powder prepared in Comparative Examples 5 and 6. The use of inappropriate complexing agents resulted in a rough surface with obvious gaps in the silver shell of the prepared silver-coated copper powder, leading to poor oxidation resistance and thus higher resistivity.

[0077] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, and for those of ordinary skill in the art, various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. Therefore, the present invention is not limited to the specific details without departing from the general concept defined by the claims and their equivalents.

Claims

1. A method for preparing silver-coated copper powder, characterized in that, Includes the following steps: S1. Prepare a base solution containing copper powder: Mix copper powder, complexing agent and water to obtain a base solution; the mass of the complexing agent is 1% to 300% of the copper powder; the mass ratio of water to copper powder is 4 to 150:

1. S2. Removal of copper powder oxide layer: Stir the bottom liquid to remove the copper powder oxide layer during the stirring process. The stirring temperature is 0℃~90℃ and the stirring time is 1~60 min. S3. Preparation of silver-coated copper powder: Add silver salt aqueous solution to the base liquid and continue stirring. The stirring temperature is 0℃~90℃ and the stirring time is 2~60 min. After the reaction is completed, wash and dry to obtain silver-coated copper powder. The mass of silver ions in the silver salt aqueous solution is 1%~90% of the mass of copper powder.

2. The method according to claim 1, characterized in that, The copper powder mentioned in step S1 is at least one of copper powder containing an oxide layer or copper powder without an oxide layer.

3. The method according to claim 1, characterized in that, The copper powder mentioned in step S1 is spherical or near-spherical, with a D50 of 3-6 μm and a tap density of not less than 4.2 g / m³. 3 Specific surface area not greater than 0.45 m² 2 / g, oxygen content not greater than 1%.

4. The method according to claim 1, characterized in that, The complexing agent mentioned in step S1 includes one or more of ammonia, ethylenediamine, alkanolamine complexing agents, ethyleneamine complexing agents, or succinimide.

5. The method according to claim 4, characterized in that, The alkanolamine complexing agents include, but are not limited to, monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, dimethylethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, or diethanolmonoisopropanolamine; the ethyleneamine complexing agents include, but are not limited to, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, or polyethylenepolyamine.

6. The method according to claim 3, characterized in that, The complexing agent described in step S1 may also include one or more of the following: hypotriacetic acid and its salts, ethylenediaminetetraacetic acid and its salts, diethylenetriaminepentaacetic acid and its salts, or hydroxyethylethylenediaminetriacetic acid and its salts.

7. The method according to claim 1, characterized in that, Step S1 may also include a reducing agent and / or a dispersant; the mass of the reducing agent is 10% to 100% of the mass of the copper powder, and the mass of the dispersant is 1% to 50% of the mass of the copper powder.

8. The method according to claim 7, characterized in that, The reducing agent is one or more of hydrazine hydrate, ascorbic acid, glucose, or tartrate.

9. The method according to claim 7, characterized in that, The dispersant is one or more of the following: polyvinylpyrrolidone, polyoxyethylene ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, fatty acid polyol ester, polyethylene glycol, chitosan, sodium dodecyl sulfonate, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, or gelatin.

10. The method according to claim 1, characterized in that, The silver salt mentioned in step S3 includes one or more of silver nitrate, silver acetate, silver sulfate, or silver sulfamate; the mass concentration of the aqueous solution of the silver salt is 1% to 80%.

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