Double-peak copper powder prepared through liquid phase reduction method and technology and application of double-peak copper powder

Abstract

The invention discloses double-peak copper powder prepared through a liquid phase reduction method and a process and application thereof, and relates to the technical field of double-peak copper powder preparation, the method comprises the steps that S1, a copper salt solution, a reducing agent solution, alkali liquor, a dispersing agent solution and a modifying agent solution are prepared; s2, the copper salt solution is mixed with at least two dispersing agent solutions, then alkali liquor is added, and the solution is adjusted to be weakly acidic or neutral or alkaline; s3, alkali liquor is added into the reducing agent solution, and the pH of the solution is adjusted to be weakly acidic or neutral or alkaline; s4, mixing the solutions treated in the step S2 and the step S3, and reacting to obtain a nano-micron double-peak copper powder suspension; s5, the suspension is left to stand, after supernate is removed, a modifier solution is added, stirring and filtering are conducted, and a modified double-peak copper powder crude product is obtained; and S6, the double-peak copper powder crude product is washed and dried, and the nanometer-micrometer double-peak copper powder is obtained and has good tap density and long anti-oxidation time, and the nanometer-micrometer double-peak copper powder can be applied to the fields of conductive paste and microelectronic devices.

Description

Technical Field

[0001] This invention relates to the field of bimodal copper powder preparation technology, specifically to a bimodal copper powder prepared by liquid-phase reduction method, its process, and its application. Background Technology

[0002] Copper has excellent electrical conductivity (59.6 × 10⁻⁶). 6 With its superior S / m (second only to silver), thermal conductivity (401 W / (m•K)), and resistance to electron migration, and at only 1-2% of the cost of silver, it has broad application prospects in photovoltaics, electronic packaging, integrated circuits, and other fields, and has already been widely used.

[0003] The performance of copper powder is closely related to its particle size. Traditional copper powder applications mainly use single particle sizes (micrometers or nanometers), but this has limitations in practical applications. For example, nanopowders have high specific surface area and high activity, but they are prone to agglomeration and oxidation, resulting in high costs and poor processability; micron powders have high mechanical strength and good oxidation resistance, but their activity is low, making it difficult to meet the needs of high-precision electronic devices.

[0004] The emergence of nano- to micron-scale bimodal copper powder, through gradient particle size design, combines the advantages of both scales to significantly optimize material properties. Especially in the field of electronic and microelectronic devices, single nanopowders often lack sufficient density after sintering, resulting in unsatisfactory electrical performance. Bimodal copper powder, using micron-scale copper powder as a framework and nanopowder filling the pores, can lower the sintering temperature and improve the density of the sintered electrode, thus enhancing electrical performance. However, conventional bimodal copper powder is usually prepared through a graded process. Whether synthesized using physical or chemical methods, the synthesized broad-distribution powder is graded and screened to prepare bimodal (nano and micron) copper powder. Such methods often suffer from the following problems: 1. The preparation process involves a large number of devices and is complex to operate, resulting in high costs; 2. When sieving powder, powders in the middle particle size range should not be filtered out; 3. When blending different nano-copper powders and micron-copper powders, the compatibility of the copper powders is required to be high, and the formulation is complex. 4. The prepared bimodal copper powder has poor coating properties, poor oxidation resistance, low density and tap density, and poor sintering activity.

[0005] For example, the patent application with publication number "CN112091208A" entitled "A thermally conductive copper powder with bimodal distribution characteristics and its preparation method and application", which uses this method to prepare bimodal copper powder, also has the above-mentioned defects. Summary of the Invention

[0006] The purpose of this invention is to provide a process for preparing bimodal copper powder by liquid-phase reduction, which can produce bimodal copper powder with good oxidation resistance, high density and tap density, and strong sintering activity. Moreover, the preparation method is convenient, and the crystal nucleation and reduction growth process can be controlled by the amount of dispersant added to obtain nano-micro bimodal copper powder of different specifications.

[0007] This invention is achieved through the following technical solution: A process for preparing bimodal copper powder by liquid-phase reduction includes the following steps: S1. Prepare copper salt solution, reducing agent solution, alkali solution, dispersant solution and modifier solution for later use; S2. At 60~85℃, a copper salt solution is mixed with at least two dispersant solutions, and then an alkaline solution is added to adjust the solution to a weakly acidic, neutral, or alkaline state. The dispersant is selected from at least two of polyvinylpyrrolidone, sodium dodecyl sulfate, methylcellulose, polyethylene glycol, or polyvinyl alcohol. S3. At 60~85℃, add alkaline solution to the reducing agent solution to adjust the pH of the solution to weakly acidic, neutral or alkaline. S4. Mix the solutions processed in steps S2 and S3 to obtain a nano-micro bimodal copper powder suspension. S5. Let the suspension in step S4 stand, remove the supernatant, add the modifier solution, stir and filter to obtain the modified bimodal copper powder crude product. S6. Wash and dry the crude bimodal copper powder from step S6 to obtain nano-micro bimodal copper powder.

[0008] Furthermore, in step S2, the amount of dispersant used is 0.1~10% of the mass of copper.

[0009] Furthermore, the copper salt is selected from one or more of copper sulfate pentahydrate, copper acetate monohydrate, copper nitrate, or copper chloride; the concentration of the copper salt is 1~2.5 mol / L.

[0010] Furthermore, the reducing agent is selected from one or more of ascorbic acid, glucose, hydrazine hydrate, sodium hypophosphite, or sodium borohydride; the concentration of the reducing agent is 1~5 mol / L.

[0011] Furthermore, the alkaline solution is selected from one or more of sodium hydroxide solution, ammonia solution, or sodium carbonate solution.

[0012] Furthermore, the amount of the modifier is 0.1-0.5% of the mass of copper, and the modifier includes one or more of benzotriazole, oleic acid, small molecule imidazole salts and thiazole salts or silane coupling agents.

[0013] Furthermore, in step S4, the solutions processed in steps S2 and S3 are mixed in a ratio of copper salt to reducing agent of 1:1 to 4.

[0014] A bimodal copper powder prepared by liquid-phase reduction method, which is obtained by any of the processes described above, wherein the nano-peak of the bimodal copper powder is 100~900nm and the micron-peak is 1~5μm.

[0015] Furthermore, during the stirring and dispersion process, the stirring speed is preferably controlled within the range of 300~500 rpm.

[0016] A bimodal copper powder prepared by liquid-phase reduction method, obtained by the process described in any of the preceding claims, wherein the bimodal copper powder meets the following specifications: tap density > 4.5 g / cm³. 3 .

[0017] An application of bimodal copper powder prepared by liquid-phase reduction method, wherein the bimodal copper powder is prepared by any of the processes described above, and the bimodal copper powder is used to prepare conductive pastes and microelectronic devices.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects: I. This invention innovatively proposes a liquid-phase reduction method for preparing bimodal copper powder. By controlling the crystal nucleation and reduction growth process with a dispersant, copper powder with a target nano- to micron bimodal distribution can be synthesized in one step. The preparation method is convenient and easy to control. Furthermore, the bimodal copper powder prepared by this method exhibits excellent oxidation resistance, high density and tap density, and strong sintering activity, making it applicable to the preparation of conductive pastes in the electronics and photovoltaic fields.

[0019] Second, in this invention, nano-micro bimodal copper powder is synthesized through an aqueous system. The post-treatment uses pure water sedimentation and washing, which effectively avoids the oxidation of the powder during the post-treatment process. In this solution, the bimodal copper powder is coated with a modifier, which increases the oxidation resistance time of the powder and is beneficial to the application of nano-micro bimodal copper powder in downstream fields. Attached Figure Description

[0020] Figure 1 This is an SEM image of the copper powder prepared in Example 1.

[0021] Figure 2 This is an SEM image of the copper powder prepared in Example 3.

[0022] Figure 3 This is an SEM image of the copper powder prepared in Example 6.

[0023] Figure 4 This is a SEM image of the copper powder prepared in Comparative Example 1.

[0024] Figure 5 This is a SEM image of the copper powder prepared in Comparative Example 3.

[0025] Figure 6This is a SEM image of the copper powder prepared in Comparative Example 4.

[0026] Figure 7 This is a SEM image of the copper powder after high-temperature sintering in Example 1.

[0027] Figure 8 This is a SEM image of the copper powder in Comparative Example 1 after high-temperature sintering. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0029] In this invention, the dispersant in the liquid-phase reduction process for preparing bimodal copper powder is selected from at least two of polyvinylpyrrolidone, sodium dodecyl sulfate, OP-10, methylcellulose, polyethylene glycol, or polyvinyl alcohol. Polyvinylpyrrolidone includes K30, K60, and K90, etc.; polyethylene glycol is preferably polyethylene glycol with a molecular weight of 200-1500; and methylcellulose is preferably methylcellulose with a viscosity of 5-200 mPa·s.

[0030] In this invention, the copper salt is selected from one or more of copper sulfate pentahydrate, copper acetate monohydrate, copper nitrate, or copper chloride; the concentration of the copper salt is 1~2.5 mol / L.

[0031] In this invention, the reducing agent is selected from one or more of ascorbic acid, glucose, hydrazine hydrate, sodium hypophosphite, or sodium borohydride; the concentration of the reducing agent is 1~5 mol / L.

[0032] In this invention, the alkaline solution is selected from one or more of sodium hydroxide solution, ammonia water, or sodium carbonate solution.

[0033] In this invention, the amount of the modifier is 0.1-0.5% of the mass of copper, and the modifier includes one or more of benzotriazole, fatty acids, small molecule imidazole salts and thiazole salts or silane coupling agents.

[0034] In this invention, the preparation of nano-micro bimodal copper powder is preferably carried out at 60-85°C. Within this temperature range, the higher the temperature, the faster the reaction rate. If the temperature in the preparation environment is too low, it is not conducive to the reduction of copper salt to copper; if the temperature is too high, the solvent water is easily evaporated, which is not conducive to the reaction.

[0035] Example 1 A process for preparing bimodal copper powder by liquid-phase reduction includes the following steps: S1. Prepare copper salt solution, reducing agent solution, alkali solution, dispersant solution and modifier solution according to the requirements in Table 1 below, and set them aside for later use; S2. At 75℃, the copper salt solution is mixed with the two dispersant solutions, and then an alkaline solution is added to adjust the pH of the solution to 5.0. S3. At 75℃, add alkali solution to the reducing agent solution to adjust the pH of the solution to 5.0; S4. Mix the solutions processed in steps S2 and S3 at a molar ratio of copper salt to reducing agent of 1:2 to obtain a nano-micro bimodal copper powder suspension. S5. Let the suspension in step S4 stand for 0.5 h, remove the supernatant, add 0.2 wt% modifier solution, stir and filter at 500 rpm to obtain the modified bimodal copper powder crude product. S6. Wash the crude bimodal copper powder from step S3 with deionized water and dry it under vacuum at 50°C to obtain nano-micro bimodal copper powder.

[0036] Table 1

[0037] Performance testing: The morphology of copper powder was observed using a scanning electron microscope; the particle size of copper powder was tested using a laser particle size analyzer; the carbon content was tested using a CS elemental analyzer; and the oxygen content was tested using an ONH elemental analyzer.

[0038] The nano-micron bimodal copper powder in this example was sintered at 500℃ under a nitrogen atmosphere. The resistivity of the sintered nano-micron bimodal copper powder was then measured, and the results are shown in Table 11. The morphology of the nano-micron bimodal copper powder before and after sintering was also observed. Figure 1 , 7 .

[0039] Example 2 The difference between this embodiment and Example 1 is that the pH value and the amount of dispersant are different in step S2, while the other steps are the same. The process conditions are shown in Table 2.

[0040] Further investigation was conducted into the impact of the above conditions on bimodal copper powder products. The results are shown in Table 2.

[0041] Table 2

[0042] As shown in Table 2, the amount of different dispersants and pH values ​​will affect the particle size distribution of bimodal copper powder. By adjusting the dispersant ratio and the pH value in the system, bimodal copper powder products of different specifications can be obtained.

[0043] Example 3 A process for preparing bimodal copper powder by liquid-phase reduction includes the following steps: S1. Prepare copper salt solution, reducing agent solution, alkali solution, dispersant solution and modifier solution according to the requirements in Table 3 below, and set them aside for later use; S2. At 75℃, the copper salt solution is mixed with the two dispersant solutions, and then an alkaline solution is added to adjust the pH of the solution to 5.0. S3. At 75℃, add alkali solution to the reducing agent solution to adjust the pH of the solution to 5.0; S4. Mix the solutions processed in steps S2 and S3 at a molar ratio of copper salt to reducing agent of 1:3 to obtain a nano-micro bimodal copper powder suspension. S5. Let the suspension in step S4 stand for 0.5 h, remove the supernatant, add 0.2 wt% modifier solution, stir and filter at 500 rpm to obtain the modified bimodal copper powder crude product. S6. Wash the crude bimodal copper powder from step S3 with deionized water and dry it under vacuum at 50°C to obtain nano-micro bimodal copper powder.

[0044] Table 3

[0045] Performance testing: The morphology of copper powder was observed using a scanning electron microscope; the particle size of copper powder was tested using a laser particle size analyzer; the carbon content was tested using a CS elemental analyzer; and the oxygen content was tested using an ONH elemental analyzer.

[0046] The morphology of nano-micro bimodal copper powder is shown in Figure 2 The nano-micro bimodal copper powder in this example was sintered at 500℃ under a nitrogen atmosphere, and the resistivity of the sintered nano-micro bimodal copper powder was then tested. The test results are shown in Table 11.

[0047] The results of the above investigation show that increasing the amount of ascorbic acid (compared to Example 1, the concentration of ascorbic acid in the system was increased from 2 mol / L to 3 mol / L) can reduce the particle size of copper powder to a certain extent.

[0048] Example 4 A process for preparing bimodal copper powder by liquid-phase reduction includes the following steps: S1. Prepare copper salt solution, reducing agent solution, alkali solution, dispersant solution and modifier solution according to the requirements in Table 4 below, and set them aside for later use; S2. At 75℃, the copper salt solution is mixed with the two dispersant solutions, and then an alkaline solution is added to adjust the pH of the solution to 5.0. S3. At 75℃, add alkali solution to the reducing agent solution to adjust the pH of the solution to 5.0; S4. Mix the solutions processed in steps S2 and S3 at a molar ratio of copper salt to reducing agent of 1:3 to obtain a nano-micro bimodal copper powder suspension. S5. Let the suspension in step S4 stand for 0.5 h, remove the supernatant, add 0.3 wt% modifier solution, stir and filter at 500 rpm to obtain the modified bimodal copper powder crude product. S6. The crude bimodal copper powder from step S6 is dried under vacuum at 50°C after being treated with deionized water three times to obtain nano-micro bimodal copper powder.

[0049] Table 4

[0050] Performance testing: The morphology of copper powder was observed using a scanning electron microscope; the particle size of copper powder was tested using a laser particle size analyzer; the carbon content was tested using a CS elemental analyzer; and the oxygen content was tested using an ONH elemental analyzer.

[0051] The nano-micro bimodal copper powder in this example was sintered at 500℃ under a nitrogen atmosphere, and the resistivity of the sintered nano-micro bimodal copper powder was then tested. The test results are shown in Table 11.

[0052] Example 5 A process for preparing bimodal copper powder by liquid-phase reduction includes the following steps: S1. Prepare copper salt solution, reducing agent solution, alkali solution, dispersant solution and modifier solution according to the requirements in Table 5 below, and set them aside for later use; S2. At 75℃, the copper salt solution is mixed with the two dispersant solutions, and then an alkaline solution is added to adjust the pH of the solution to 5.0. S3. At 75℃, add alkali solution to the reducing agent solution to adjust the pH of the solution to 5.0; S4. Mix the solutions processed in steps S2 and S3 at a molar ratio of copper salt to reducing agent of 1:3 to obtain a nano-micro bimodal copper powder suspension. S5. Let the suspension in step S4 stand for 0.5 h, remove the supernatant, add 0.2 wt% modifier solution, stir and filter at 500 rpm to obtain the modified bimodal copper powder crude product. S6. The crude bimodal copper powder from step S6 is dried under vacuum at 50°C after being treated with deionized water three times to obtain nano-micro bimodal copper powder.

[0053] Table 5

[0054] Performance testing: The morphology of copper powder was observed using a scanning electron microscope; the particle size of copper powder was tested using a laser particle size analyzer; the carbon content was tested using a CS elemental analyzer; and the oxygen content was tested using an ONH elemental analyzer.

[0055] The morphology of nano-micro bimodal copper powder is shown in Figure 3 The nano-micron bimodal copper powder in this example was sintered at 500℃ under a nitrogen atmosphere, and the resistivity of the sintered nano-micron bimodal copper powder was then tested. The test results are shown in Table 11.

[0056] The test results above show that using different types of dispersants can affect the particle size distribution of bimodal copper powder.

[0057] Example 6 A process for preparing bimodal copper powder by liquid-phase reduction includes the following steps: S1. Prepare copper salt solution, reducing agent solution, alkali solution, dispersant solution and modifier solution according to the requirements in Table 6 below, and set them aside for later use; S2. At 75℃, the copper salt solution is mixed with the two dispersant solutions, and then an alkaline solution is added to adjust the pH of the solution to 5.0. S3. At 75℃, add alkali solution to the reducing agent solution to adjust the pH of the solution to 5.0; S4. Mix the solutions processed in steps S2 and S3 at a molar ratio of copper salt to reducing agent of 1:3 to obtain a nano-micro bimodal copper powder suspension. S5. Let the suspension in step S4 stand for 0.5 h, remove the supernatant, add 0.5 wt% modifier solution, stir and filter at 500 rpm to obtain the modified bimodal copper powder crude product. S6. The crude bimodal copper powder from step S6 is dried under vacuum at 50°C after being treated with deionized water three times to obtain nano-micro bimodal copper powder.

[0058] Table 6

[0059] Performance testing: The morphology of copper powder was observed using a scanning electron microscope; the particle size of copper powder was tested using a laser particle size analyzer; the carbon content was tested using a CS elemental analyzer; and the oxygen content was tested using an ONH elemental analyzer.

[0060] The morphology of nano-micro bimodal copper is shown in Figure 3 The nano-micro bimodal copper powder in this example was sintered at 500℃ under a nitrogen atmosphere, and the resistivity of the sintered nano-micro bimodal copper powder was then tested. The test results are shown in Table 11.

[0061] The test results above show that by using a combination of multiple dispersants and controlling the amount of dispersant, copper powder with high tap density and good electrical properties can be obtained.

[0062] Comparative Example 1 The only difference between this comparative example and Example 1 is that this example uses only one dispersant.

[0063] A process for preparing copper powder by liquid-phase reduction includes the following steps: S1. Prepare copper salt solution, reducing agent solution, alkali solution, dispersant solution and modifier solution according to the requirements in Table 7 below, and set them aside for later use; S2. At 75℃, the copper salt solution is mixed with the dispersant-sodium dodecyl sulfate solution, and then an alkali solution is added to adjust the pH of the solution to 5.0. S3. At 75℃, add alkali solution to the reducing agent solution to adjust the pH of the solution to 5.0; S4. Mix the solutions processed in steps S2 and S3 at a molar ratio of copper salt to reducing agent of 1:2 to obtain a copper powder suspension. S5. Let the suspension in step S4 stand for 0.5 h, remove the supernatant, add 0.2 wt% modifier solution, stir and filter at 500 rpm to obtain the modified crude copper powder. S6. The crude copper powder from step S6 is dried under vacuum at 50°C after being treated with deionized water three times.

[0064] Table 7

[0065] Performance testing: The morphology of copper powder was observed using a scanning electron microscope; the particle size of copper powder was tested using a laser particle size analyzer; the carbon content was tested using a CS elemental analyzer; and the oxygen content was tested using an ONH elemental analyzer.

[0066] The copper powder in this comparative example was sintered at 500℃ under a nitrogen atmosphere, and the resistivity of the sintered copper powder was then measured. The test results are shown in Table 11. The morphology of the copper powder before and after sintering was also observed for reference. Figure 4 , 8 .

[0067] Compared to Example 1, this comparative example used the same mass of dispersant—sodium dodecyl sulfate—instead of dispersants methylcellulose and K30, resulting in copper powder with a unimodal distribution. Furthermore, as shown in Table 11, the copper powder prepared using a single dispersant exhibited lower tap density and higher resistivity.

[0068] Comparative Example 2 The only difference between this comparative example and Example 1 is that only one conventional dispersant was used.

[0069] A process for preparing copper powder by liquid-phase reduction includes the following steps: S1. Prepare copper salt solution, reducing agent solution, alkali solution, dispersant solution and modifier solution according to the requirements in Table 8 below, and set them aside for later use; S2. At 75℃, mix the copper salt solution with the dispersant-K30 solution, then add alkali solution to adjust the pH of the solution to 5.0. S3. At 75℃, add alkali solution to the reducing agent solution to adjust the pH of the solution to 5.0; S4. Mix the solutions processed in steps S2 and S3 at a molar ratio of copper salt to reducing agent of 1:3 to obtain a copper powder suspension. S5. Let the suspension in step S4 stand for 0.5 h, remove the supernatant, add 0.2 wt% modifier solution, stir and filter at 500 rpm to obtain the modified crude copper powder. S6. The crude copper powder from step 2 is dried under vacuum at 50°C after being treated with deionized water three times to obtain micron-sized copper powder.

[0070] Table 8

[0071] Performance testing: The morphology of copper powder was observed using a scanning electron microscope; the particle size of copper powder was tested using a laser particle size analyzer; the carbon content was tested using a CS elemental analyzer; and the oxygen content was tested using an ONH elemental analyzer.

[0072] The copper powder in this example was sintered at 500°C under a nitrogen atmosphere, and the resistivity of the sintered copper powder was then tested. The test results are shown in Table 11.

[0073] Compared to Example 1, this comparative example used the same mass of dispersant K30 instead of dispersant methylcellulose and K30, and also obtained copper powder with a unimodal distribution. This shows that a single dispersant has a limited impact on the morphology and particle size of the copper powder, making it difficult to control the formation of copper powder with different particle sizes during the nucleation and growth stages. The prepared copper powder is mostly copper powder with a narrow single-size distribution. Since the obtained copper powder has a unimodal distribution, compared to Example 1, this means that its tap density and electrical properties are reduced.

[0074] Comparative Example 3 The only difference between this comparative example and Example 1 is that the pH of the reaction system was adjusted to alkaline.

[0075] S1. Prepare copper salt solution, reducing agent solution, alkali solution, dispersant solution and modifier solution according to the requirements in Table 9 below, and set them aside for later use; S2. At 75℃, the copper salt solution is mixed with the two dispersant solutions, and then an alkaline solution is added to adjust the pH of the solution to 8.5. S3. At 75℃, add alkali solution to the reducing agent solution to adjust the pH of the solution to 8.5; S4. Mix the solutions processed in steps S2 and S3 at a molar ratio of copper salt to reducing agent of 1:2 to obtain a nano-micro bimodal copper powder suspension. S5. Let the suspension in step S4 stand for 0.5 h, remove the supernatant, add 0.2 wt% dispersant solution, stir and filter at 500 rpm to obtain the modified bimodal copper powder crude product. S6. The crude bimodal copper powder from step S6 is dried under vacuum at 50°C after being treated with deionized water three times to obtain nano-micro bimodal copper powder.

[0076] Table 9

[0077] Performance testing: The morphology of copper powder was observed using a scanning electron microscope; the particle size of copper powder was tested using a laser particle size analyzer; the carbon content was tested using a CS elemental analyzer; and the oxygen content was tested using an ONH elemental analyzer.

[0078] The morphology of nano-micro bimodal copper powder is shown in Figure 5 The nano-micron bimodal copper powder in this example was sintered at 500℃ under a nitrogen atmosphere, and the resistivity of the sintered nano-micron bimodal copper powder was then tested. The test results are shown in Table 11.

[0079] The test results above show that when the pH value of the reaction system is too high, the particle size distribution of the generated copper powder is extremely skewed, with a large difference between nano and micron sizes, which will also lead to a decrease in its tap density and electrical properties.

[0080] Comparative Example 4 The only difference between this comparative example and Example 1 is that the pH value in step S3 is adjusted to be strongly acidic.

[0081] S1. Prepare copper salt solution, reducing agent solution, alkali solution, dispersant solution and modifier solution according to the requirements in Table 10 below, and set them aside for later use; S2. At 75℃, the copper salt solution is mixed with the two dispersant solutions, and then an alkaline solution is added to adjust the pH of the solution to 5.0. S3. At 75℃, add acid to the reducing agent solution to adjust the pH of the solution to 3.0; S4. Mix the solutions processed in steps S2 and S3 at a molar ratio of copper salt to reducing agent of 1:2 to obtain a copper powder suspension. S5. Let the suspension in step S4 stand for 0.5 h, remove the supernatant, add 0.2 wt% dispersant solution, stir and filter at 500 rpm to obtain the modified crude copper powder. S6. The crude copper powder from step S6 is dried under vacuum at 50°C after being treated with deionized water three times.

[0082] Table 10

[0083] Performance testing: The morphology of copper powder was observed using a scanning electron microscope; the particle size of copper powder was tested using a laser particle size analyzer; the carbon content was tested using a CS elemental analyzer; and the oxygen content was tested using an ONH elemental analyzer.

[0084] The morphology of copper powder is shown in Figure 6 The copper powder in this comparative example was sintered at 500℃ under a nitrogen atmosphere, and the resistivity of the sintered copper powder was then tested. The test results are shown in Table 11.

[0085] The test results above show that when the pH value of the reaction system is too low (strongly acidic), the prepared copper powder has a single-peak distribution, large particle size and irregular shape, and the tap density and electrical properties of the copper powder decrease significantly.

[0086] Table 11

[0087] As shown in Table 11, Comparative Examples 1 and 2, which used a single dispersant, did not obtain bimodal copper powder. Investigation revealed that the effect of a single dispersant on the morphology and particle size of copper powder was limited. However, when using dual dispersants (such as Examples 1-6), bimodal copper powder was obtained. The method of this invention not only effectively improves the tap density and reduces the resistivity of copper powder, but also significantly enhances the density of the sintered copper powder. See [link to relevant documentation]. Figure 7 , Figure 8 .

[0088] As can be seen from Example 1 and Comparative Example 4, when the pH value of the reaction system is too low (strongly acidic), the prepared copper powder still exhibits a single-peak distribution characteristic, with not only a large particle size but also an irregular morphology, ultimately leading to a significant decrease in the tap density and electrical properties of the copper powder.

[0089] In addition, the bimodal copper powder obtained by the liquid-phase reduction method of the present invention maintains a relatively low carbon (C) content and oxygen (O) content. After being sealed and stored at room temperature for 90 days, the increase in carbon (C) content and oxygen (O) content is small. It can be seen that the bimodal copper powder obtained by this method has excellent antioxidant effect.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A process for preparing bimodal copper powder by liquid-phase reduction, characterized in that, Includes the following steps: S1. Prepare copper salt solution, reducing agent solution, alkali solution, dispersant solution and modifier solution for later use; S2. At 60~85℃, a copper salt solution is mixed with at least two dispersant solutions, and then an alkaline solution is added to adjust the solution to a weakly acidic, neutral, or alkaline state. The dispersant is selected from at least two of polyvinylpyrrolidone, sodium dodecyl sulfate, methylcellulose, polyethylene glycol, or polyvinyl alcohol. S3. At 60~85℃, add alkaline solution to the reducing agent solution to adjust the pH of the solution to weakly acidic, neutral or alkaline. S4. Mix the solutions processed in steps S2 and S3 to obtain a nano-micro bimodal copper powder suspension. S5. Let the suspension in step S4 stand, remove the supernatant, add the modifier solution, stir and filter to obtain the modified bimodal copper powder crude product. S6. Wash and dry the crude bimodal copper powder from step S6 to obtain nano-micro bimodal copper powder.

2. The process for preparing bimodal copper powder by liquid-phase reduction according to claim 1, characterized in that: In step S2, the amount of dispersant used is 0.1~10% of the mass of copper.

3. The process for preparing bimodal copper powder by liquid-phase reduction according to claim 1, characterized in that: The copper salt is selected from one or more of copper sulfate pentahydrate, copper acetate monohydrate, copper nitrate, or copper chloride; the concentration of the copper salt is 1~2.5 mol / L.

4. The process for preparing bimodal copper powder by liquid-phase reduction according to claim 1, characterized in that: The reducing agent is selected from one or more of ascorbic acid, glucose, hydrazine hydrate, sodium hypophosphite, or sodium borohydride; the concentration of the reducing agent is 1~5 mol / L.

5. The process for preparing bimodal copper powder by liquid-phase reduction according to claim 1, characterized in that: The alkaline solution is selected from one or more of sodium hydroxide solution, ammonia water, or sodium carbonate solution.

6. The process for preparing bimodal copper powder by liquid-phase reduction according to claim 1, characterized in that: The amount of the modifier is 0.1-0.5% of the mass of copper, and the modifier includes one or more of benzotriazole, oleic acid, small molecule imidazole salts and thiazole salts or silane coupling agents.

7. The process for preparing bimodal copper powder by liquid-phase reduction according to claim 1, characterized in that: In step S4, the solutions processed in steps S2 and S3 are mixed in a ratio of copper salt to reducing agent of 1:1 to 4.

8. A bimodal copper powder prepared by liquid-phase reduction, characterized in that: The bimodal copper powder is prepared using the process described in any one of claims 1 to 7, wherein the nano-peak of the bimodal copper powder is 100 to 900 nm and the micro-peak is 1 to 5 μm.

9. A bimodal copper powder prepared by liquid-phase reduction, characterized in that: The bimodal copper powder, prepared using the process described in any one of claims 1 to 7, meets the following specifications: tap density > 4.5 g / cm³. 3 .

10. An application of a bimodal copper powder prepared by a liquid-phase reduction method, characterized in that: The bimodal copper powder is prepared by the process described in any one of claims 1 to 7, and is used to prepare conductive pastes and microelectronic devices.

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