Preparation method of flake silver powder

Abstract

The invention discloses a preparation method of flaky silver powder. The preparation method comprises the following steps that S1, soluble silver salt, a complexing agent and water are mixed to obtain a solution A; mixing macromolecular organic acid, phosphate and water to form a solution B; s2, mixing the solution B with the solution A to obtain a mixed solution I; and S3, the mixed solution I and a weak oxidizing agent are mixed to obtain a mixed solution II, microspheres containing a reducing agent are dropwise added into the mixed solution II, and the flake silver powder is obtained. In the preparation method disclosed by the invention, the prepared silver powder has the characteristics of higher flake degree, uniform thickness and better dispersity.

Description

Technical Field

[0001] This invention relates to the field of silver powder preparation technology, and in particular to a method for preparing flake silver powder. Background Technology

[0002] Silver powder, as an important functional metallic material, is widely used in electronic components, conductive pastes, catalysts, antibacterial materials, and other fields. Among them, flake silver powder has unique application advantages in conductive adhesives, electromagnetic shielding coatings, and high-end electronic packaging due to its high specific surface area, good conductivity, and excellent reflective properties.

[0003] However, currently, the vast majority of flake silver powder used as conductive filler in flexible conductive composites is prepared by mechanical ball milling. However, mechanical ball milling is energy-intensive, has many influencing factors, is easily contaminated by impurities, and produces silver powder with uneven shape, surface roughness, uneven thickness, and low product stability. In flexible conductive composites prepared using this method, the contact between conductive filler particles is a rough surface-to-surface contact, leading to increased contact resistance between silver powder particles. Typically, a filling amount of 70-80 wt% is required to meet the conductivity requirements of industrial products.

[0004] Therefore, there is an urgent need to develop a method for preparing silver powder with higher flake density, uniform thickness, and better dispersibility. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the first aspect of the present invention proposes a method for preparing flake-shaped silver powder, wherein the silver powder prepared by the method has the characteristics of higher flake-likeness, uniform thickness, and better dispersibility.

[0006] A method for preparing flake silver powder according to a first aspect of the present invention includes the following steps: S1. Mix soluble silver salt, complexing agent and water to obtain solution A; mix high molecular weight organic acid, phosphate and water to form solution B; S2. Mix solution B with solution A to obtain mixture I; S3. Mix the mixture I and the weak oxidant to obtain mixture II, and then add microspheres containing a reducing agent to mixture II to obtain flake silver powder.

[0007] According to some embodiments of the present invention, the weak oxidizing agent includes at least one of p-benzoquinone, ferric sulfate, copper nitrate, or copper sulfate.

[0008] According to some embodiments of the present invention, the weak oxidant accounts for 0.01% to 1% of the mass percentage of the mixture I.

[0009] According to some embodiments of the present invention, the reducing agent includes at least one of ascorbic acid, glucose, hydrazine hydrate, or N,N-dimethylformamide.

[0010] According to some embodiments of the present invention, in step S1, the mass ratio of the soluble silver salt to the complexing agent is 1:(0.1~1).

[0011] According to some embodiments of the present invention, in step S1, the mass ratio of the soluble silver salt to the complexing agent is 1:(0.1~0.5).

[0012] According to some embodiments of the present invention, the mass ratio of the high molecular weight organic acid to the phosphate is 1:(0.2~0.8).

[0013] According to some embodiments of the present invention, the microspheres containing the reducing agent are prepared by the following method: The reducing agent is prepared by emulsion solvent evaporation, spray drying or thin-film hydration.

[0014] According to some embodiments of the present invention, the microspheres containing the reducing agent are prepared by an emulsification-solvent evaporation method, the steps of which are as follows: Polylactic acid, reducing agent and solvent are mixed and ultrasonically injected to obtain a primary emulsion; then the primary emulsion is mixed with a polyvinyl alcohol solution, emulsified by high-speed shearing, the solvent is removed, and centrifuged to obtain the final product.

[0015] According to some embodiments of the present invention, the mass ratio of the soluble silver salt, reducing agent and polylactic acid is 1:(0.3~0.6):(0.25~0.8).

[0016] According to some embodiments of the present invention, the soluble silver salt includes at least one of silver nitrate, silver acetate, silver fluoride, silver chlorate, or silver perchlorate.

[0017] According to some embodiments of the present invention, the complexing agent includes at least one of polyvinylpyrrolidone, polyethyleneimine, gelatin, or chitosan.

[0018] According to some embodiments of the present invention, the polymeric organic acid includes at least one of polyacrylic acid, polymethacrylic acid, or polymaleic acid.

[0019] According to some embodiments of the present invention, the phosphate includes at least one of potassium dihydrogen phosphate, diammonium hydrogen phosphate, sodium pyrophosphate, or sodium dihydrogen phosphate.

[0020] The preparation method according to embodiments of the present invention has at least the following beneficial effects: In the preparation method of this invention, the prepared silver powder has higher flake-likeness, uniform thickness, and better dispersibility. This is because solution A and solution B are first mixed to obtain mixture I. In this system, the silver ions are fixed in the sparingly soluble salt or polymer network, and their free concentration is effectively reduced. A weak oxidizing agent is then added to reduce the reduction rate of silver ions and inhibit explosive nucleation. Microspheres containing a reducing agent are then added dropwise. The reducing agent is slowly released from the microspheres and reacts with the silver ions slowly released from the sparingly soluble salt or polymer complex. Furthermore, under the action of the polymer complexing agent and the weak oxidizing agent, silver atoms preferentially grow along the (111) crystal plane, eventually forming flake-like silver powder. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a SEM image of the flake-shaped silver powder of Example 3 of the present invention; Figure 2 This is a SEM image of the flake-shaped silver powder of Comparative Example 1 of the present invention; Figure 3 This is a SEM image of the flake-shaped silver powder of Comparative Example 2 of the present invention; Figure 4 This is a SEM image of the flake silver powder of Comparative Example 3 of the present invention. Detailed Implementation

[0022] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0023] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0024] In some embodiments of the present invention, a method for preparing flake silver powder is provided, comprising the following steps: S1. Mix soluble silver salt, complexing agent and water to obtain solution A; mix high molecular weight organic acid, phosphate and water to form solution B; S2. Mix solution B with solution A to obtain mixture I; S3. Mix mixture I and a weak oxidizing agent to obtain mixture II. Then, add microspheres containing a reducing agent dropwise to mixture II to obtain flake silver powder.

[0025] It is understood that the silver powder prepared in the preparation method of the present invention has higher flake-likeness, uniform thickness, and better dispersibility. This is because solution A and solution B are first mixed to obtain mixture I. In this system, the silver ions are fixed in the sparingly soluble salt or polymer network, and their free concentration is effectively reduced. A weak oxidizing agent is then added to reduce the reduction rate of silver ions and inhibit explosive nucleation. Microspheres containing a reducing agent are then added dropwise. The reducing agent is slowly released from the microspheres and reacts with the silver ions slowly released from the sparingly soluble salt or polymer complex. Furthermore, under the action of the polymer complexing agent and the weak oxidizing agent, silver atoms preferentially grow along the (111) crystal plane, eventually forming flake-like silver powder.

[0026] In some embodiments of the present invention, the weak oxidizing agent includes at least one of p-benzoquinone, ferric sulfate, copper nitrate, or copper sulfate.

[0027] In some embodiments of the present invention, the weak oxidant accounts for 0.01% to 1% by mass in the mixture I. For example, it includes 0.01%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any sub-range consisting of any two of the above values.

[0028] In some embodiments of the present invention, the weak oxidant accounts for 0.1% to 1% by mass in the mixture I. For example, it includes 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any sub-range consisting of any two of the above values.

[0029] In some embodiments of the present invention, the reducing agent includes at least one of ascorbic acid, glucose, hydrazine hydrate, or N,N-dimethylformamide.

[0030] In some embodiments of the present invention, in step S1, the mass ratio of the soluble silver salt to the complexing agent is 1:(0.1~1). For example, it includes sub-ranges such as 1:0.1, 1:0.2, 1:0.4, 1:0.5, 1:0.6, 1:0.8, 1:1, or any two of the above ratios.

[0031] In some embodiments of the present invention, in step S1, the mass ratio of the soluble silver salt to the complexing agent is 1:(0.1~0.5). For example, it includes sub-ranges such as 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, or any two of the above ratios.

[0032] In some embodiments of the present invention, the mass ratio of the high molecular weight organic acid to the phosphate is 1:(0.2~0.8). For example, it includes sub-ranges of 1:0.2, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8 or any two of the above ratios.

[0033] In some embodiments of the present invention, the microspheres containing the reducing agent are prepared by the following method: The reducing agent is prepared by emulsion solvent evaporation, spray drying or thin-film hydration.

[0034] In some embodiments of the present invention, the microspheres containing the reducing agent are prepared by an emulsification-solvent evaporation method, the steps of which are as follows: Polylactic acid, reducing agent and solvent are mixed and ultrasonically injected to obtain a primary emulsion; then the primary emulsion is mixed with a polyvinyl alcohol solution, emulsified by high-speed shearing, the solvent is removed, and centrifuged to obtain the final product.

[0035] In some embodiments of the present invention, the mass ratio of the soluble silver salt, reducing agent and polylactic acid is 1:(0.3~0.6):(0.25~0.8).

[0036] In some embodiments of the present invention, the soluble silver salt includes at least one of silver nitrate, silver acetate, silver fluoride, silver chlorate, or silver perchlorate.

[0037] In some embodiments of the present invention, the complexing agent includes at least one of polyvinylpyrrolidone, polyethyleneimine, gelatin, or chitosan.

[0038] In some embodiments of the present invention, the high molecular weight organic acid includes at least one of polyacrylic acid, polymethacrylic acid, or polymaleic acid.

[0039] In some embodiments of the present invention, the phosphate includes at least one of potassium dihydrogen phosphate, sodium dihydrogen phosphate, diammonium hydrogen phosphate, sodium pyrophosphate, or sodium dihydrogen phosphate.

[0040] In this invention, high molecular weight organic acids refer to organic compounds that can dissociate into protons in aqueous solution, exhibiting acidity, and have a high molecular weight (typically >10,000 g / mol). Their molecular structure contains multiple acidic functional groups attached to a polymer backbone.

[0041] In this invention, soluble silver salt refers to silver salt with a solubility ≥ 1g / 100g water at room temperature (generally 20°C).

[0042] Some of the raw materials used in the embodiments and comparative examples of this invention are as follows: Microspheres containing a reducing agent are prepared by the following method: The emulsification-solvent evaporation method was used: 0.5 g PLA was dissolved in 10 mL of acetonitrile, and then 0.935 g ascorbic acid was added. The mixture was sonicated to form a primary emulsion. This primary emulsion was poured into 100 mL of an aqueous solution containing 1% polyvinyl alcohol, and emulsified at high speed to form a W / O / W complex emulsion. The mixture was stirred overnight to allow the acetonitrile to evaporate. The ascorbic acid / PLA microspheres were collected by centrifugation and redispersed in 50 mL of deionized water for later use.

[0043] Example 1 This example provides a method for preparing flake-shaped silver powder, including the following steps: S1. Dissolve 1.7g silver nitrate and 0.34g PVP (K30) in 200mL of deionized water at 60℃ to obtain solution A; dissolve 0.5g polyacrylic acid (PAA, Mw~2000) and 0.2g sodium dihydrogen phosphate in 50mL of deionized water to obtain solution B; S2. While stirring at 400 rpm, add solution B dropwise to solution A at a rate of 1 mL / min. After the addition is complete, continue stirring for 1 hour to obtain mixture I. S3. Place the above mixture I in a 500 mL three-necked flask, maintain the water bath temperature at 50 °C, and stir at 300 rpm. Dissolve p-benzoquinone (p-benzoquinone mass percentage relative to mixture I is 0.05%) in 10 mL of ethanol and add it to the above mixture I. Slowly add microspheres containing the reducing agent dropwise over 3 hours. After the addition is complete, continue the reaction for 1 hour. Allow the reaction solution to cool naturally to room temperature, and centrifuge to obtain silver powder precipitate. Wash twice with 0.1 mol / L dilute nitric acid solution to remove any trace impurities that may be introduced, and then wash three times each with deionized water and anhydrous ethanol alternately. Dry the washed silver powder in a vacuum drying oven at 50 °C for 12 hours to obtain flake silver powder.

[0044] Example 2 This example provides a method for preparing flake silver powder, which is the same as that in Example 1, except that the mass percentage of p-benzoquinone relative to mixture I is 0.01%.

[0045] Example 3 This example provides a method for preparing flake silver powder, which is the same as that in Example 1, except that the mass percentage of p-benzoquinone relative to mixture I is 0.1%.

[0046] Example 4 This example provides a method for preparing flake silver powder, which is the same as that in Example 1, except that the mass percentage of p-benzoquinone relative to mixture I is 0.5%.

[0047] Example 5 This example provides a method for preparing flake silver powder, which is the same as that in Example 1, except that the mass percentage of p-benzoquinone relative to mixture I is 1%.

[0048] Example 6 This example provides a method for preparing flake silver powder, which is the same as that in Example 1, except that the mass percentage of p-benzoquinone relative to mixture I is 1.5%.

[0049] Example 7 This example provides a method for preparing flake silver powder, which is the same as that in Example 1, except that the mass ratio of silver nitrate to PVP is 1:0.5.

[0050] Example 8 This example provides a method for preparing flake silver powder, which is the same as that in Example 1, except that the mass ratio of silver nitrate to PVP is 1:0.8.

[0051] Example 9 This example provides a method for preparing flake silver powder, which is the same as that in Example 1, except that p-benzoquinone is replaced with copper nitrate.

[0052] Comparative Example 1 Comparative Example 1 provides a method for preparing flake silver powder, which is the same as that in Example 1, except that it does not contain p-benzoquinone.

[0053] Comparative Example 2 Comparative Example 2 provides a method for preparing flake silver powder, which is the same as that in Example 1, except that ascorbic acid is added directly instead of preparing microspheres containing a reducing agent.

[0054] Comparative Example 3 The traditional method involves mixing silver nitrate solution with PVP aqueous solution, then directly and rapidly adding ascorbic acid aqueous solution and stirring vigorously to react.

[0055] Performance testing The flake-shaped silver powder prepared in Example 3 of this invention was tested using a scanning electron microscope (SEM), and the results are as follows: Figure 1 As shown, SEM observation revealed that the sheet-like structure had smooth and regular edges, was mainly hexagonal, had good dispersibility, and did not stack. The fineness of the slurry made from the sample was 2.5 μm. Analysis by a sheet-like laser particle size analyzer showed that the D50 of the product in Example 3 was 2.5 μm.

[0056] Furthermore, the flake silver powder structure prepared in Example 1 has smooth and regular edges, is mainly hexagonal, has good dispersibility, does not stack, and the fineness of the slurry is 2.5. The D50 of the product in Example 1 is 3.5 μm.

[0057] Furthermore, the flake silver powder structure prepared in Example 2 has smooth and regular edges, is mainly hexagonal, has good dispersibility, does not stack, and the fineness of the slurry is 3.5. The D50 of the product in Example 2 is 3 μm.

[0058] Furthermore, the flake silver powder structure prepared in Example 4 has smooth and regular edges, is mainly hexagonal, has good dispersibility, does not stack, and the fineness of the slurry is 3. The D50 of the product in Example 4 is 2 μm.

[0059] Furthermore, the flake silver powder structure prepared in Example 5 has smooth and regular edges, is mainly hexagonal, has good dispersibility, does not stack, and the fineness of the slurry is 3.5. The D50 of the product in Example 5 is 1.5 μm.

[0060] Furthermore, the flake silver powder prepared in Example 6 was mainly hexagonal in structure, with general dispersibility and a small amount of stacking. The fineness of the slurry made from the sample was 4.5, and the D50 of the product in Example 6 was 4 μm.

[0061] Furthermore, the flake-shaped silver powder prepared in Example 7 has regular edges, is mainly hexagonal, has good dispersibility, does not stack, and the fineness of the slurry is 3.5. The D50 of the product in Example 7 is 4.0 μm.

[0062] Furthermore, the flake silver powder prepared in Example 8 was mainly hexagonal in structure, with general dispersibility and a small amount of stacking. The fineness of the slurry made from the sample was 4.5 μm, and the D50 of the product in Example 8 was 4.5 μm.

[0063] Furthermore, the flake silver powder structure prepared in Example 9 has smooth and regular edges, is mainly hexagonal, has good dispersibility, does not stack, and the fineness of the slurry is 3.5. The D50 of the product in Example 9 is 1.5 μm.

[0064] Furthermore, Comparative Example 1 was tested using a scanning electron microscope, and the results are as follows: Figure 2 As shown, observations revealed that the sample contained no p-benzoquinone, the platy structure was reduced, and polyhedral silver powder was the main component, proving that p-benzoquinone can enable silver powder to grow towards specific crystal faces. The fineness of the slurry prepared from the sample was 7.

[0065] Furthermore, comparative example 2 was analyzed using scanning electron microscopy (SEM), and the results are as follows: Figure 3 As shown, observations revealed that: directly adding ascorbic acid without preparing microspheres containing a reducing agent resulted in poor sample dispersibility, and the fineness of the slurry prepared from the sample was 15.

[0066] Furthermore, comparative example 3 was tested using a scanning electron microscope, and the results are as follows: Figure 4 As shown, observations revealed that when silver nitrate solution and PVP aqueous solution were mixed using the traditional method, ascorbic acid aqueous solution was directly and rapidly added and the reaction was carried out with vigorous stirring. The sample was mainly composed of flake silver powder and polyhedrons, and the fineness of the slurry was 6.

[0067] The present invention has been described in detail above with reference to the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing flake-shaped silver powder, characterized in that, Includes the following steps: S1. Mix soluble silver salt, complexing agent and water to obtain solution A; mix high molecular weight organic acid, phosphate and water to form solution B; S2. Mix solution B with solution A to obtain mixture I; S3. Mix the mixture I and the weak oxidant to obtain mixture II, and then add microspheres containing a reducing agent to mixture II to obtain flake silver powder.

2. The method for preparing flake silver powder according to claim 1, characterized in that, The weak oxidizing agent includes at least one of p-benzoquinone, ferric sulfate, copper nitrate, or copper sulfate.

3. The method for preparing flake silver powder according to claim 1, characterized in that, The weak oxidant accounts for 0.01% to 1% of the mass of the mixture I.

4. The method for preparing flake silver powder according to claim 1, characterized in that, In step S1, the mass ratio of the soluble silver salt to the complexing agent is 1:(0.1~1).

5. The method for preparing flake silver powder according to claim 1, characterized in that, The reducing agent includes at least one of ascorbic acid, glucose, hydrazine hydrate, or N,N-dimethylformamide.

6. The method for preparing flake silver powder according to claim 1, characterized in that, The microspheres containing the reducing agent are prepared by the following method: The reducing agent is prepared by emulsion solvent evaporation, spray drying or thin-film hydration.

7. The method for preparing flake silver powder according to claim 1, characterized in that, The soluble silver salt includes at least one of silver nitrate, silver acetate, silver fluoride, silver chlorate, or silver perchlorate.

8. The method for preparing flake silver powder according to claim 1, characterized in that, The complexing agent includes at least one of polyvinylpyrrolidone, polyethyleneimine, gelatin, or chitosan.

9. The method for preparing flake silver powder according to claim 1, characterized in that, The high molecular weight organic acid includes at least one of polyacrylic acid, polymethacrylic acid, or polymaleic acid.

10. The method for preparing flake silver powder according to claim 1, characterized in that, The phosphate includes at least one of potassium dihydrogen phosphate, diammonium hydrogen phosphate, sodium pyrophosphate, or sodium dihydrogen phosphate.

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