Silver-plated copper powder of conductive slurry and preparation method of silver-plated copper powder

Abstract

The invention discloses silver-plated copper powder of conductive paste and a preparation method of the silver-plated copper powder, and relates to the technical field of electronic metal materials. The invention comprises 22-25 parts of copper sulfate pentahydrate; 24 to 30 parts of glucose; 22 to 24 parts of sodium hydroxide; 50 parts of palm oil; 11 to 14 parts of silver nitrate; 7-9 parts of a PVP solution; and 12-16 parts of mixed acid. After acid washing and alcohol washing of the copper powder, the copper powder is placed in molten palm oil at the temperature of 44 DEG C, and after cooling and solidification, the solidified palm oil and the copper powder are packaged in vacuum together and carried; before the copper powder is used for silver plating, the temperature is increased, palm oil is replaced with nitrogen, the copper powder is cleaned, and finally silver plating work is carried out, so that the oxidation rate of the copper powder can be greatly reduced, the oxidation rate of the copper powder is controlled within 0.5%, the coverage rate of silver on the surface of the copper powder during silver plating is increased, and high-level conductivity is achieved under the condition of low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic metal materials, and particularly relates to a silver-plated copper powder for conductive paste and a preparation method thereof. Background Art

[0002] As a good high-conductivity filler, silver-coated copper powder is often added to coatings (paints), adhesives, inks, polymer slurries, plastics, rubbers, etc., and various conductive and electromagnetic shielding products can be made, which are widely used in the conductive and electromagnetic shielding fields of various industrial sectors such as electronics, electromechanics, communication, printing, aerospace, and ordnance.

[0003] Conductive paste is a material that uniformly adds conductive powder to an adhesive and forms a conductor after curing. It is used for the formation of electronic circuits, the formation of electrodes of electronic components, the extraction of lead ends, the formation of circuit joints, etc. Conductive pastes are roughly divided into a high-temperature sintering type with glass powder added to the adhesive, a low-temperature sintering type using a synthetic resin adhesive, and a UV curing type cured by ultraviolet irradiation.

[0004] Silver-coated copper powder is often used in the preparation of conductive paste. For example, a Chinese patent with the publication number CN116890111A discloses a preparation method of silver-coated copper powder for conductive paste, and the preparation steps are as follows: Step 1: Grind copper powder and pour it into a beaker, add diluted copper cleaning solution, shake well and then put it into an ultrasonic cleaner for cleaning for more than 60 minutes; Step 2: After ultrasonic cleaning, centrifuge the mixture of copper powder and diluted copper cleaning solution to collect the copper powder precipitate.

[0005] Step 3: Add copper polishing solution to the copper powder, shake well and let it stand for a period of time, pour out the upper liquid, and continue to wash with deionized water and centrifuge 2 - 3 times; Step 4: Add the polished copper powder to copper silver plating solution, and the silver plating solution just covers the copper powder. Put it into a magnetic stirrer and stir. When the copper powder changes from red to silver-gray, pour out the silver plating solution, add deionized water for cleaning and centrifuge 2 - 3 times to obtain silver-coated copper powder.

[0006] This invention can prepare silver-coated copper powder with high silver coating rate, strong conductivity, and good antioxidant ability by using a polishing solution and a silver plating solution after activating the copper powder.

[0007] However, during the process from activating and polishing the copper powder to silver plating, the interval time is long and transportation is often required. Even with vacuum packaging, during the unpacking process, the copper powder is likely to contact oxygen and moisture in the air and form partial oxidation, and the oxidation rate is generally above 2%. This greatly affects the coverage rate of silver on the surface of the copper powder, resulting in a decrease in silver content and a reduction in the conductive efficiency of the silver-coated copper powder. At this time, to achieve the target conductivity, more silver needs to be covered, which greatly increases the production cost. Summary of the Invention

[0008] In view of the above technical problems and overcoming the shortcomings of the prior art, the present invention provides a silver-plated copper powder for conductive paste and a preparation method thereof.

[0009] To solve the above technical problems, the present invention provides a silver-plated copper powder for conductive paste and a preparation method thereof.

[0010] Technical effect: After pickling and alcohol washing the copper powder, the copper powder is placed in melted palm oil at 44 degrees Celsius. After cooling and solidifying, the solidified palm oil and the copper powder are vacuum-packed and transported together. Before silver-plating the copper powder, it is heated up and nitrogen is used to displace the palm oil and wash the copper powder. Finally, the silver-plating work is carried out, which can greatly reduce the oxidation rate of the copper powder, control the oxidation rate of the copper powder within 0.5%, increase the coverage rate of silver on the surface of the copper powder during silver-plating, and thus achieve a high level of conductivity at low cost.

[0011] The present invention provides a preparation method of a silver-plated copper powder for conductive paste, comprising the following steps:

[0012] S1, Take a certain amount of glucose as a reducing agent, a certain amount of sodium hydroxide as a pH regulator, and a certain amount of copper sulfate pentahydrate as a copper source. Slowly add copper sulfate pentahydrate to glucose under stirring conditions, and control the pH value of the solution between 5.9 and 6.3 with sodium hydroxide. After the reaction is completed, copper powder is obtained.

[0013] S2, Filter and collect the copper powder in a closed container. After washing the copper powder with a citric acid aqueous solution, rinse the copper powder with pure water 3 to 5 times to obtain clean copper powder.

[0014] S3, Add palm oil with a temperature above 50 degrees Celsius to the clean copper powder. After covering all the copper powder, cool it down to 22 degrees Celsius. After the palm oil solidifies, take out the solidified palm oil and copper powder mixture and vacuum-pack it.

[0015] S4, Unpack the mixture and put it into a reaction kettle. Replace the air in the reaction kettle with nitrogen, heat it up to 50 degrees Celsius, add pure water to the reaction kettle from the bottom, and use the characteristic that the density of palm oil is lower than that of water to discharge the palm oil from the top of the reaction kettle until only the mixture of pure water and copper remains in the reaction kettle. Then discharge the pure water and rinse the copper powder 3 times. The whole process is carried out under nitrogen protection.

[0016] S5, After the washing is completed, add ethanol to dehydrate the copper powder in the reaction kettle, and use the method of two-stage alcohol washing to ensure complete dehydration of the copper powder. The whole process is carried out under nitrogen protection.

[0017] S6. Take a fixed amount of pure water and silver nitrate to prepare a silver nitrate solution; prepare sulfuric acid and hydrochloric acid, and mix them to form a mixed acid solution; introduce pure water and a dispersant into the reaction kettle and mix them with copper powder. After ultrasonic dispersion, under the condition of constant temperature stirring, slowly dropwise add the silver nitrate solution to obtain a silver-coated copper powder suspension; the whole process is carried out under nitrogen protection.

[0018] S7. Filter and separate the silver-coated copper powder by pressure filtration. After washing the silver-coated copper powder with the mixed acid solution, then wash it with water and alcohol, filter it by pressure again and dry it to obtain a dried silver-coated copper powder product and package it. The whole process is carried out under nitrogen protection.

[0019] Further, in step S1, the reaction temperature is maintained at 45 °C and the dropping time is 10 h.

[0020] For the silver-coated copper powder for conductive paste and its preparation method as described above, in step S2, the concentration of the citric acid aqueous solution is 9-11%, and the moisture content of the clean copper powder is between 45-55%.

[0021] For the silver-coated copper powder for conductive paste and its preparation method as described above, in step S3, the palm oil used is 44-degree palm oil.

[0022] For the silver-coated copper powder for conductive paste and its preparation method as described above, in step S6, the reaction temperature is controlled at 70-80 °C, and the dropping time of the silver nitrate solution is 22 h.

[0023] For the silver-coated copper powder for conductive paste and its preparation method as described above, in step S6, the concentration of sulfuric acid is 1.44% and the concentration of hydrochloric acid is 0.83%.

[0024] For the silver-coated copper powder for conductive paste and its preparation method as described above, in steps S5 and S7, two-stage alcohol washing is used. After the first-stage alcohol washing, the water content in the ethanol solution is greater than 30%.

[0025] For the silver-coated copper powder for conductive paste and its preparation method as described above, in step S6, the dispersant used is a PVP solution.

[0026] The present invention also provides a silver-coated copper powder for conductive paste, which is prepared by using the preparation method of the silver-coated copper powder for any one of the above conductive pastes, and includes the following components:

[0027]

[0028]

[0029] The beneficial effects of the present invention are:

[0030] (1) In the present invention, the melting point of 44-degree palm oil is 44 degrees Celsius. That is, when the temperature is below 44 °C, the palm oil solidifies. Utilizing this property, copper powder can be placed in the palm oil at a relatively high temperature and then cooled to room temperature. As the palm oil solidifies, it encapsulates the copper powder, isolating the copper powder from oxygen and moisture in the air, facilitating the storage and handling of the copper powder, and greatly reducing the possibility of copper powder oxidation.

[0031] (2) In the present invention, after the temperature is raised to 50 °C, the palm oil melts, and pure water is added from bottom to top. Since the density of palm oil is lower than that of water, the palm oil can be discharged and reused after the water level rises. The copper powder is rinsed three times to ensure that the palm oil on the copper powder is completely removed.

[0032] (3) In the present invention, after the copper powder is pickled and alcohol-washed, the copper powder is placed in the melted 44-degree palm oil. After cooling and solidifying, the solidified palm oil and the copper powder are vacuum-packed and transported together. Before using the copper powder for silver plating, the temperature is raised, nitrogen is used to displace the palm oil, and the copper powder is cleaned. Finally, the silver plating work is carried out, which can greatly reduce the oxidation rate of the copper powder, control the oxidation rate of the copper powder within 0.5%, increase the coverage rate of silver on the surface of the copper powder during silver plating, and thus achieve a high level of conductivity at low cost. Specific Embodiments

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the following provides a detailed description of the specific embodiments. Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0035] A silver-plated copper powder for conductive paste and its preparation method provided in this embodiment include the following steps:

[0036] S1, taking a quantitative amount of glucose as a reducing agent, a quantitative amount of sodium hydroxide as a pH regulator, and a quantitative amount of copper sulfate pentahydrate as a copper source. Under stirring conditions, copper sulfate pentahydrate is slowly added dropwise to glucose, and the pH value of the solution is controlled between 5.9 and 6.3 with sodium hydroxide. After the reaction is completed, copper powder is obtained.

[0037] In this step, the reaction temperature is maintained at 45 °C and the dropping time is 10 h. Slowly drop copper sulfate pentahydrate into glucose, which can enable copper sulfate pentahydrate to fully contact with the reducing agent, improve the quality and shape regularity of the copper powder prepared by reduction, and thus improve the covering uniformity of the subsequent silver-coated copper.

[0038] S2. Filter and collect the copper powder in a closed container. After washing the copper powder with a citric acid aqueous solution, rinse the copper powder with pure water 3 - 5 times to obtain clean copper powder; in this step, the concentration of the citric acid aqueous solution is 9 - 11%, and the moisture content of the clean copper powder is between 45 - 55%.

[0039] S3. Add palm oil with a temperature above 50 °C to the clean copper powder. After covering all the copper powder, cool it down to 22 °C. After the palm oil solidifies, take out the mixture of solidified palm oil and copper powder and vacuum package it. In this step, the palm oil used is 44-degree palm oil.

[0040] The melting point of 44-degree palm oil is 44 °C, that is, when the temperature is below 44 °C, the palm oil solidifies into a solid state. Utilizing this property, the copper powder can be placed in the palm oil at a higher temperature state and then cooled down to room temperature. The palm oil solidifies and wraps the copper powder inside, isolating the copper powder from oxygen and moisture in the air, facilitating the storage and handling of the copper powder, and greatly reducing the possibility of copper powder oxidation.

[0041] S4. Unpack the mixture and put it into the reaction kettle. Replace the air in the reaction kettle with nitrogen, heat up to 50 °C, add pure water to the reaction kettle from the bottom, and utilize the property that the density of palm oil is lower than that of water to discharge the palm oil from the top of the reaction kettle until only the mixture of pure water and copper remains in the reaction kettle; then discharge the pure water and rinse the copper powder with pure water 3 times. The whole process is carried out under nitrogen protection.

[0042] After heating up to 50 °C, the palm oil melts. Then add pure water from bottom to top. Since the density of palm oil is lower than that of water, the palm oil can be discharged and reused after the water level rises. Repeat rinsing the copper powder three times to ensure that the palm oil on the copper powder is completely removed.

[0043] S5. After washing, add ethanol to the reaction kettle for dehydration, and adopt a two-stage alcohol washing method to ensure complete dehydration of the copper powder. The whole process is carried out under nitrogen protection.

[0044] S6. Take a certain amount of pure water and silver nitrate to make a silver nitrate solution; prepare sulfuric acid and hydrochloric acid and mix them to form a mixed acid solution; introduce pure water and a dispersant into the reaction kettle to mix with the copper powder. After ultrasonic dispersion, under the condition of constant temperature stirring, slowly drop the silver nitrate solution to obtain a silver-coated copper powder suspension; the whole process is carried out under nitrogen protection; in this step, the concentration of sulfuric acid is 1.44%, the concentration of hydrochloric acid is 0.83%, and the dispersant used is a PVP solution.

[0045] In S7, the silver-coated copper powder is filtered and separated by pressure filtration. After washing the silver-coated copper powder with a mixed acid solution, it is further washed with water and alcohol, then pressure-filtered again and dried to obtain the finished product of dry silver-coated copper powder, which is then packaged. The whole process is carried out under nitrogen protection.

[0046] In steps S5 and S7, two-stage alcohol washing is used. After the first-stage alcohol washing, the water content in the ethanol solution is greater than 30%.

[0047] The present invention prepares silver-coated copper powder through a number of examples and comparative examples. The specific examples and comparative examples are shown in Table 1.

[0048] Table 1 Component content table in each example and comparative example

[0049] Project Example 1 Example 2 Example 3 Example 4 Comparative Example Copper sulfate pentahydrate (parts) 22.5 22 25 23 22.5 Glucose (parts) 28 24 30 27 28 Sodium hydroxide (parts) 23.3 22 24 23 23.3 Palm oil (parts) 50 50 50 50 - Silver nitrate (parts) 16.3 11 14 13 16.3 PVP solution (parts) 8 7 9 8 8 Mixed acid (parts) 14 12 16 14 14

[0050] The present invention tests the oxidation rate of copper powder before replacement, and the particle size, conductivity and silver coverage rate of silver-coated copper powder after replacement. The test results are shown in Table 2.

[0051] Table 2 Test result table of each example and comparative example

[0052]

[0053]

[0054] Combining the data in Table 1 and Table 2, it can be seen that Example 1 is the best preparation scheme, which can control the oxidation rate of copper powder before silver replacement at 0.1%, greatly reducing the interference of copper oxide on silver coverage. Compared with the comparative examples, under the condition of the same particle size, the silver content of the silver-coated copper powder prepared in Example 1 increases slightly, but the silver coverage rate increases significantly, indicating that the uniformity of silver coating on the surface of copper powder in Example 1 is much greater than that in the comparative examples. Therefore, Example 1 obtains a lower resistivity and meets the higher requirement of conductive efficiency.

[0055] In addition to the above examples, the present invention may have other embodiments. Any technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A preparation method of silver-plated copper powder for conductive paste, characterized in that, It includes the following steps: S1, Take a quantitative amount of glucose as a reducing agent, a quantitative amount of sodium hydroxide as a pH regulator, and a quantitative amount of copper sulfate pentahydrate as a copper source. Slowly add the copper sulfate pentahydrate to the glucose under stirring conditions, and control the pH value of the solution between 5.9 and 6.3 with sodium hydroxide. After the reaction is completed, copper powder is obtained; S2, Filter and collect the copper powder in a closed container. After washing the copper powder with a citric acid aqueous solution, rinse the copper powder with pure water 3 to 5 times to obtain clean copper powder; S3, Add palm oil with a temperature above 50 °C to the clean copper powder. After covering all the copper powder, cool it down to 22 °C. After the palm oil solidifies, take out the mixture of solidified palm oil and copper powder and vacuum package it; S4, Unpackage the mixture and put it into a reaction kettle. Replace the air in the reaction kettle with nitrogen, heat it up to 50 °C, add pure water to the reaction kettle from the bottom, and utilize the property that the density of palm oil is lower than that of water to discharge the palm oil from the top of the reaction kettle until only the mixture of pure water and copper remains in the reaction kettle; then discharge the pure water and rinse the copper powder with pure water 3 times. The whole process is carried out under nitrogen protection; S5, After the cleaning is completed, add ethanol to the reaction kettle for dehydration, and adopt a two-step alcohol washing method to ensure complete dehydration of the copper powder. The whole process is carried out under nitrogen protection; S6, Take a quantitative amount of pure water and silver nitrate to make a silver nitrate solution; Prepare sulfuric acid and hydrochloric acid and mix them to form a mixed acid solution; Pass pure water and a dispersant into the reaction kettle and mix them with the copper powder. After ultrasonic dispersion, keep the constant temperature stirring condition and slowly add the silver nitrate solution to obtain a silver-coated copper powder suspension; The whole process is carried out under nitrogen protection; S7, Filter and separate the silver-coated copper powder by pressure filtration. After washing the silver-coated copper powder with the mixed acid solution, then wash it with water and alcohol, filter it by pressure again and dry it to obtain a dry silver-coated copper powder product and package it. The whole process is carried out under nitrogen protection.

2. The preparation method of silver-plated copper powder for conductive paste according to claim 1, characterized in that: In the step S1, the reaction temperature is maintained at 45 °C and the dropping time is 10 h.

3. The preparation method of silver-plated copper powder for conductive paste according to claim 1, characterized in that: In the step S2, the concentration of the citric acid aqueous solution is 9 to 11%, and the moisture content of the clean copper powder is between 45 and 55%.

4. The preparation method of silver-plated copper powder for conductive paste according to claim 1, characterized in that: In the step S3, the palm oil used is 44-degree palm oil.

5. The preparation method of silver-plated copper powder for conductive paste according to claim 1, characterized in that: In the step S6, the reaction temperature is controlled between 70 and 80 °C, and the dropping time of the silver nitrate solution is 22 h.

6. The preparation method of silver-plated copper powder for conductive paste according to claim 1, characterized in that: In the step S6, the concentration of sulfuric acid is 1.44% and the concentration of hydrochloric acid is 0.83%.

7. The preparation method of silver-plated copper powder for conductive paste according to claim 1, characterized in that: In the steps S5 and S7, two-step alcohol washing is used. After the first-step alcohol washing, the water content in the ethanol solution is greater than 30%.

8. The preparation method of silver-plated copper powder for conductive paste according to claim 1, characterized in that: In the step S6, the dispersant used is a PVP solution.

9. A silver-plated copper powder for conductive paste, prepared by using the preparation method of the silver-plated copper powder for any one of the conductive pastes described in claims 1 to 8, characterized in that, By weight, it includes the following components:

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