Silver powder spheroidizing and shaping method based on surface modification pretreatment

Abstract

The invention discloses a silver powder spheroidizing and shaping method based on surface modification pretreatment, and belongs to the technical field of preparation of superfine spherical silver powder. The initial silver powder obtained through liquid phase reduction is subjected to gamma-mercaptopropyltrimethoxysilane surface modification treatment, so that harmful residues are removed, the surface property is improved, and the particle mechanical strength is enhanced. And the silver powder dispersion liquid subjected to effective pretreatment is transferred into a balling machine to be subjected to shaping treatment. The pretreatment step effectively overcomes the problems that the initial silver powder is easy to break, aggravated in agglomeration and low in shaping efficiency when being directly spheroidized, so that the subsequent spheroidizing and shaping can be efficiently carried out. By reasonably adjusting the frequency (40-75 Hz), the treatment time (10-15 minutes) and other process parameters of a spheroidizing machine and in combination with the pretreatment, the superfine spherical silver powder which is uniform in particle size, regular in shape and excellent in dispersity is finally obtained. The method provides an effective way for preparing the high-quality spherical silver powder through a liquid phase reduction method, and is suitable for the fields of electronics, conductive materials, catalysts and the like.

Description

Technical Field

[0001] This invention belongs to the field of preparation technology of ultrafine spherical silver powder, specifically relating to a method for spheroidizing and shaping silver powder based on surface modification pretreatment. Background Technology

[0002] Silver powder, due to its excellent electrical and thermal conductivity and catalytic properties, is widely used in electronics, conductive materials, catalysts, and other fields. Liquid-phase reduction is a common method for preparing silver powder due to its relatively simple process and low cost. However, this method has significant drawbacks: the surface of the resulting silver powder particles often retains reducing agents, dispersants, or byproducts; simultaneously, the initial particles are often irregular in shape, have low mechanical strength, and are prone to agglomeration. These surface defects and particle characteristics pose a significant challenge when liquid-phase reduced silver powder is directly subjected to mechanical shaping (such as spheroidization). Because existing liquid-phase reduction methods typically require complex post-processing or fail to directly produce ultrafine, high-sphericity products that meet the requirements of high-performance applications, developing a pre-treatment method that effectively addresses the surface and particle characteristic issues of liquid-phase reduced silver powder, enabling it to undergo efficient spheroidization shaping, is crucial for improving its quality. Summary of the Invention

[0003] To address the shortcomings of the prior art, this invention provides a method for spheroidizing and shaping silver powder based on surface modification pretreatment.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for spheroidizing and shaping silver powder based on surface modification pretreatment includes the following steps: (1) The reducing agent solution is added dropwise to a mixed solution containing a dispersant and silver nitrate to react and obtain an initial silver powder dispersion; (2) The initial silver powder dispersion was adjusted to pH 8-9 with an alkaline solution; (3) Add the ethanol solution of silane coupling agent dropwise to the initial silver powder dispersion obtained in step (2) after pH adjustment to react and obtain the silver powder dispersion after surface modification. Then wash, separate and dry to obtain the silver powder after surface modification. (4) The surface-modified silver powder is shaped by a spheroidizing machine to obtain spheroidized silver powder.

[0005] In a preferred embodiment of the present invention, the reducing agent is formaldehyde or hydrazine hydrate; the dispersant is polyvinylpyrrolidone with a molecular weight of 40,000-60,000; and the mass ratio of the reducing agent, dispersant and silver nitrate is 1-2:0.01-0.05:1-2.

[0006] In a preferred embodiment of the present invention, in step (1), the reaction temperature is 35-50°C and the time is 30-60 min.

[0007] In a preferred embodiment of the present invention, the alkaline solution is an ammonia solution or a sodium hydroxide solution.

[0008] In a preferred embodiment of the present invention, the silane coupling agent is γ-mercaptopropyltrimethoxysilane; the volume ratio of the silane coupling agent to ethanol in the silane coupling agent ethanol solution is 1:(5-10).

[0009] This invention utilizes the thiol group (-SH) of γ-mercaptopropyltrimethoxysilane (KH-590) to form a high-binding-energy Ag-S bond with silver atoms, replacing the surface residues of silver powder obtained by liquid-phase reduction. The propyl chain generated by the hydrolysis and condensation of γ-mercaptopropyltrimethoxysilane reduces the surface energy and inhibits aggregation through steric hindrance. Furthermore, this invention is carried out in a weakly alkaline environment (pH 8-9), which promotes the silanization reaction while protecting the silver matrix. Thorough washing ensures the purity of the coating layer and avoids byproducts interfering with subsequent shaping.

[0010] In a preferred embodiment of the present invention, the mass of the silane coupling agent is 0.5-2 wt% of the dry weight of the initial silver powder dispersion.

[0011] In a preferred embodiment of the present invention, in step (2), the reaction temperature is 30-50°C and the time is 30-60 min.

[0012] In a preferred embodiment of the present invention, the compressed air intake pressure for the spheroidizing machine is 0.4-0.8 MPa, and the time is 5-10 minutes.

[0013] The present invention also claims protection for the spherical silver powder prepared by the silver powder spheroidizing and shaping method based on surface modification pretreatment, wherein the sphericity of the spherical silver powder is ≥98% and the spheroidization rate is >95%.

[0014] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention provides a dedicated pretreatment method for silver powder obtained by liquid-phase reduction and its preparation process combined with spheroidization shaping, focusing on solving the problem that silver powder obtained by liquid-phase reduction cannot be directly and effectively spheroidized due to its surface residues, easy agglomeration, and fragile particles. Through the γ-mercaptopropyltrimethoxysilane surface-active modification treatment of this invention, harmful residues on the surface of silver powder are effectively removed, particle surface properties are improved, particle mechanical strength is enhanced, and agglomeration tendency is inhibited. The silver powder dispersion after surface-active modification pretreatment has the basic conditions for good mechanical shaping by a spheroidizer. Subsequent processing under optimized spheroidizer parameters (frequency 40-75 Hz, time 10-15 minutes) can efficiently transform irregular, easily agglomerated initial silver powder into spherical silver powder with uniform particle size (e.g., 1-2 μm) and highly regular morphology, significantly improving its dispersibility and application performance. Attached Figure Description

[0015] Figure 1 These are SEM images of the spheroidized silver powder prepared in Example 1 and Comparative Example 1 of the present invention. (a) is an SEM image of the spheroidized silver powder prepared in Comparative Example 1, and (b) is an SEM image of the spheroidized silver powder prepared in Example 1. Detailed Implementation

[0016] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0017] Example 1 A method for spheroidizing and shaping silver powder based on surface modification pretreatment includes the following steps: (1) Add 1L of 50g / L hydrazine hydrate solution dropwise to a mixture of 100ml of 5g / L PVP (molecular weight about 60000) solution and 1L of 50g / L silver nitrate solution and react at 35℃ for 30min to obtain a gray initial silver powder dispersion.

[0018] (2) The initial gray silver powder dispersion was adjusted to pH 8 with ammonia solution.

[0019] (3) 2.87 ml of γ-mercaptopropyltrimethoxysilane ethanol solution (the volume ratio of γ-mercaptopropyltrimethoxysilane to ethanol is 1:5) was added dropwise to the initial silver powder dispersion obtained in step (2) after pH adjustment. The mixture was reacted at 40 °C for 50 min to obtain the surface-modified silver powder dispersion. The amount of γ-mercaptopropyltrimethoxysilane used was 1 wt% of the mass of the gray initial silver powder dispersion (dry weight). The surface-modified silver powder dispersion was then centrifuged at 4000 rpm for 8 minutes. After discarding the supernatant, the precipitate was washed at least 3 times with anhydrous ethanol and deionized water to thoroughly remove unreacted silane monomers, hydrolysis byproducts and other residues. After washing, the precipitate was dried at 60 °C for 24 h to obtain the surface-modified silver powder.

[0020] (4) The surface-modified silver powder is fed into the feed port of the spheroidizer through the feeding system to obtain spheroidized silver powder. The compressed air intake pressure of the spheroidizer is 0.6 MPa and the time is 8 minutes.

[0021] The mechanical strength of the spheroidized silver powder in this embodiment meets the ASTM D3359 standard. The sphericity of the spheroidized silver powder is 98.1%, the sphericity rate is 96%, and the particle size ranges from 0.3 to 2.5 micrometers; there is no agglomeration.

[0022] Example 2 A method for spheroidizing and shaping silver powder based on surface modification pretreatment includes the following steps: (1) Add 1L of 50g / L formaldehyde solution dropwise to a mixture of 200ml of 10g / L PVP (molecular weight about 40000) solution and 1L of 100g / L silver nitrate solution and react at 40℃ for 40min to obtain a gray initial silver powder dispersion.

[0023] (2) The initial gray silver powder dispersion was adjusted to pH 9 with ammonia solution.

[0024] (3) 2.87 ml of γ-mercaptopropyltrimethoxysilane ethanol solution (the volume ratio of γ-mercaptopropyltrimethoxysilane to ethanol is 1:8) was added dropwise to the initial silver powder dispersion obtained in step (2) after pH adjustment. The mixture was reacted at 30 °C for 60 min to obtain a surface-modified silver powder dispersion. The amount of γ-mercaptopropyltrimethoxysilane used was 0.5 wt% of the mass of the gray initial silver powder dispersion (dry weight). The surface-modified silver powder dispersion was then centrifuged at 3000 rpm for 10 min. After discarding the supernatant, the precipitate was washed at least 3 times with anhydrous ethanol and deionized water alternately to thoroughly remove unreacted silane monomers, hydrolysis byproducts and other residues. After washing, the precipitate was dried at 60 °C for 24 h to obtain the surface-modified silver powder.

[0025] (4) The surface-modified silver powder is fed into the feed port of the spheroidizer through the feeding system to obtain spheroidized silver powder. The compressed air intake pressure of the spheroidizer is 0.4 MPa and the time is 10 minutes.

[0026] The spherical silver powder prepared in this embodiment has mechanical strength that meets ASTM D3359 standard. The sphericity of the spherical silver powder is 98%, the sphericity rate is 95.3%, and the particle size range is 0.5-3 micrometers; there is no agglomeration.

[0027] Example 3 A method for spheroidizing and shaping silver powder based on surface modification pretreatment includes the following steps: (1) Add 1L of 60g / L hydrazine hydrate solution dropwise to a mixture of 250ml of 5g / L PVP (molecular weight about 50,000) solution and 1L of 50g / L silver nitrate solution and react at 50℃ for 50min to obtain a gray initial silver powder dispersion.

[0028] (2) The initial gray silver powder dispersion was adjusted to pH 8.5 with ammonia solution.

[0029] (3) 5.74 ml of γ-mercaptopropyltrimethoxysilane ethanol solution (the volume ratio of γ-mercaptopropyltrimethoxysilane to ethanol is 1:10) was added dropwise to the initial silver powder dispersion obtained in step (2) after pH adjustment. The mixture was reacted at 50 °C for 30 min to obtain a surface-modified silver powder dispersion. The amount of γ-mercaptopropyltrimethoxysilane used was 2 wt% of the mass of the gray initial silver powder dispersion (dry weight). The surface-modified silver powder dispersion was then centrifuged at 5000 rpm for 5 min. After discarding the supernatant, the precipitate was washed at least 3 times with anhydrous ethanol and deionized water alternately to thoroughly remove unreacted silane monomers, hydrolysis byproducts and other residues. After washing, the precipitate was dried at 60 °C for 24 h to obtain the surface-modified silver powder.

[0030] (4) The surface-modified silver powder is fed into the feed port of the spheroidizer through the feeding system to obtain spheroidized silver powder. The compressed air intake pressure of the spheroidizer is 0.8 MPa and the time is 5 minutes.

[0031] The spherical silver powder prepared in this embodiment has mechanical strength that meets ASTM D3359 standard. The sphericity of the spherical silver powder is 98.5%, the sphericity rate is 96.4%, and the particle size range is 0.3-2 micrometers; there is no agglomeration.

[0032] Comparative Example 1 A method for spheroidizing and shaping silver powder based on surface modification pretreatment includes the following steps: (1) Add 1L of 50g / L hydrazine hydrate solution dropwise to a mixture of 100ml of 5g / L PVP (molecular weight about 60000) solution and 1L of 50g / L silver nitrate solution and react at 35℃ for 30min to obtain a gray initial silver powder dispersion.

[0033] (2) The initial gray silver powder dispersion was adjusted to pH 8 with ammonia solution.

[0034] (3) The initial silver powder dispersion after pH adjustment was centrifuged at 4000 rpm for 8 minutes. After discarding the supernatant, the precipitate was washed at least 3 times with anhydrous ethanol and deionized water to thoroughly remove unreacted silane monomers, hydrolysis byproducts and other residues. After washing, the precipitate was dried at 60°C for 24 h to obtain silver powder.

[0035] (4) The silver powder is fed into the feed port of the baller through the feeding system to obtain the ballered silver powder. The compressed air intake pressure of the baller is 0.6 MPa and the time is 8 minutes.

[0036] The silver powder prepared in this comparative example, lacking surface activation, exhibited poor spheroidization during the spheroidization process due to insufficient mechanical strength, resulting in particles that were more prone to breakage. The spheroidization degree of the spheroidized silver powder was only 91%, and the spheroidization rate was 93%, which is far from achieving the spheroidization degree and spheroidization rate of the silver powder prepared in Examples 1-3. Furthermore, the spheroidized silver powder prepared in Comparative Example 1 had a particle size range of 1.5-6 micrometers. Large particle sizes and uneven particle size distribution may make it difficult to disperse uniformly during use, leading to inconsistent material properties and affecting the quality of the final product.

[0037] Figure 1 The images show a SEM comparison of the spheroidized silver powder prepared in Example 1 and Comparative Example 1. As can be seen from the images, the unactivated silver powder particles have irregular shapes, many sharp edges and corners, and exhibit significant agglomeration, with the particles tightly packed together. In contrast, the silver powder particles prepared in Example 1 after surface modification have significantly more regular shapes, exhibiting a more rounded and spherical morphology. Agglomeration is significantly reduced, and the dispersion between particles is greatly improved.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for spheroidizing and shaping silver powder based on surface modification pretreatment, characterized in that, Includes the following steps: (1) The reducing agent solution is added dropwise to a mixed solution containing a dispersant and silver nitrate to react and obtain an initial silver powder dispersion; (2) The initial silver powder dispersion was adjusted to pH 8-9 with an alkaline solution; (3) Add the ethanol solution of silane coupling agent dropwise to the initial silver powder dispersion obtained in step (2) after pH adjustment to react and obtain the silver powder dispersion after surface modification. Then wash, separate and dry to obtain the silver powder after surface modification. (4) The surface-modified silver powder is shaped by a spheroidizing machine to obtain spheroidized silver powder.

2. The method for spheroidizing and shaping silver powder based on surface modification pretreatment as described in claim 1, characterized in that, The reducing agent is formaldehyde or hydrazine hydrate; the dispersant is polyvinylpyrrolidone with a molecular weight of 40,000-60,000; the mass ratio of the reducing agent, dispersant and silver nitrate is 1-2:0.01-0.05:1-2.

3. The method for spheroidizing and shaping silver powder based on surface modification pretreatment as described in claim 1, characterized in that, In step (1), the reaction temperature is 35-50℃ and the time is 30-60min.

4. The method for spheroidizing and shaping silver powder based on surface modification pretreatment as described in claim 1, characterized in that, The alkaline solution is an ammonia solution or a sodium hydroxide solution.

5. The method for spheroidizing and shaping silver powder based on surface modification pretreatment according to claim 1, characterized in that: The silane coupling agent is γ-mercaptopropyltrimethoxysilane; the volume ratio of the silane coupling agent to ethanol in the ethanol solution of the silane coupling agent is 1:(5-10).

6. The method for spheroidizing and shaping silver powder based on surface modification pretreatment as described in claim 1, characterized in that, The mass of the silane coupling agent is 0.5-2 wt% of the initial dry weight of the silver powder dispersion.

7. The method for spheroidizing and shaping silver powder based on surface modification pretreatment as described in claim 1, characterized in that, In step (2), the reaction temperature is 30-50℃ and the time is 30-60min.

8. The method for spheroidizing and shaping silver powder based on surface modification pretreatment as described in claim 1, characterized in that, The compressed air intake pressure for the spheroidizing machine is 0.4-0.8 MPa, and the time is 5-10 minutes.

9. The spherical silver powder prepared by the silver powder spheroidizing and shaping method based on surface modification pretreatment as described in claim 1, wherein the sphericity of the spherical silver powder is ≥98% and the spheroidization rate is >95%.

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