Micron blocky and submicron spherical mixed silver powder and preparation method thereof

Abstract

The invention provides micron blocky and submicron spherical mixed silver powder and a preparation method thereof. The preparation method comprises the steps that firstly, a silver salt solution is prepared, a reducing agent, a dispersing agent and pure water are mixed to obtain a reducing agent solution, and nano-silver crystal suspension liquid and the dispersing agent are mixed to obtain a base solution; synchronously dropwise adding the silver salt solution and the reducing agent solution into the base solution to obtain a solution containing the mixed silver powder; and finally, the solution is subjected to washing, solid-liquid separation and drying and shaping treatment, and then the micron blocky and submicron spherical mixed silver powder is obtained. According to the preparation method, polyvinylpyrrolidone with low molecular weight is selected as a dispersing agent, and the adding process of the dispersing agent is controlled, so that nano-silver crystals and the dispersing agent play a synergistic role, the micron blocky and submicron spherical mixed silver powder with good dispersion uniformity and high tap density is obtained, and the mixed silver powder is better in stacking structure and high in conductivity after being formed into slurry; the preparation method provided by the invention simplifies the process steps, shortens the preparation time, and has industrial application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of metal powders, and in particular to a mixed silver powder of micron block and submicron spherical shape and a preparation method thereof. Background Art

[0002] With the rapid development of science and technology, silver powder, as an important conductive material, is increasingly used in photovoltaics, electronic information, 5G and other fields. Among them, silver powder is widely used as a conductive filler in low-temperature conductive paste because of its high conductivity and non-oxidative properties. In photovoltaic silver paste, silver powder is the main component of the conductive phase, and its morphology has an important influence on the conductive properties. Flake silver powder has become the main choice for conductive silver powder due to its large specific surface area and excellent conductivity. However, pure flake silver powder has limitations in certain application scenarios, such as printability and continuity of the conductive network. The combination of spherical silver powder and flake silver powder can form complementary advantages. Spherical silver powder can increase the tap density of silver powder, increase the conductive channel, further reduce the resistivity, and improve the conductivity; at the same time, the addition of spherical silver powder is also conducive to improving printability and refining the grid lines.

[0003] The methods for preparing silver powder in the prior art have many deficiencies in morphology control. Only silver powder with a single morphology can be prepared by chemical reduction. For example, an invention patent (publication number CN 110153441A) discloses a flaky silver powder prepared by a chemical reduction method and a preparation method thereof, and a flaky silver powder with a particle size of about 2 to 4 μm is prepared by a chemical reduction method; an invention patent (publication number CN 110586959A) discloses a method for preparing a high tap density flaky silver powder, firstly preparing micron-sized spherical silver powder by a chemical reduction method, and then using a ball milling process to ball-mill all the silver powder particles into sheets; the product prepared by this method has a single morphology, and the spherical silver powder needs to be further mixed with the flaky silver powder to achieve application in low-temperature slurry.

[0004] In view of this, it is necessary to design an improved micron block and submicron spherical mixed silver powder and a preparation method thereof to solve the above problems. Summary of the invention

[0005] The object of the present invention is to provide a micron block and submicron spherical mixed silver powder and a preparation method thereof, select a dispersant with a specific molecular weight, and control the dispersant addition process to ensure the generation of spherical silver powder and block silver powder, so as to obtain a mixed silver powder with a high tap density. After the mixed silver powder is prepared into a slurry, it has a good stacking structure and excellent conductivity.

[0006] To achieve the above-mentioned purpose of the invention, the present invention provides a micron block and submicron spherical mixed silver powder, wherein the micron block and submicron spherical mixed silver powder comprises a micron block silver powder with an average particle size of 2 to 30 μm and a thickness of 0.5 to 3 μm and a submicron spherical silver powder with a particle size of 0.1 to 1 μm; the micron block and submicron spherical mixed silver powder is prepared by a single chemical synthesis method.

[0007] As a further improvement of the present invention, the morphology of the micron-sized bulk silver powder includes one or more of a three-dimensional block, a flower ball or a crystal cluster.

[0008] The present invention also provides a method for preparing a mixed silver powder of micron block and submicron spherical shape, comprising the following steps: S1, prepare silver salt solution; S2, mixing the reducing agent, dispersant and pure water in a certain proportion to obtain a reducing agent solution; S3, mixing the nano silver crystal suspension and the dispersant in a certain proportion to obtain a base liquid; S4, synchronously dropping the silver salt solution of step S1 and the reducing agent solution of step S2 into the base solution of step S3, and continuing stirring for 20 to 30 minutes after the dropping is completed to obtain a solution containing mixed silver powder; washing, solid-liquid separation, and drying and shaping the solution to obtain micron block and submicron spherical mixed silver powder.

[0009] As a further improvement of the present invention, in step S2 and step S3, the dispersant is polyvinyl pyrrolidone, and the molecular weight of the polyvinyl pyrrolidone is 8000-15000.

[0010] As a further improvement of the present invention, in step S2, the mass ratio of the dispersant to the silver salt in the silver salt solution of step S1 is 1:(1000~10000), and the mass ratio of the reducing agent to the silver salt is 1:(1~2).

[0011] As a further improvement of the present invention, in step S3, the mass ratio of the dispersant to the silver salt in the silver salt solution of step S1 is 1:(5~50).

[0012] As a further improvement of the present invention, in step S4, the dropping speed is 20-60 mL / min.

[0013] As a further improvement of the present invention, in step S3, the mass ratio of the nanosilver crystals in the nanosilver crystal suspension to the mass ratio of the silver salt in the silver salt solution is 1:(1000-10000), and the particle size of the nanosilver crystals is 2-40 nm.

[0014] As a further improvement of the present invention, in step S1, the concentration of the silver salt solution is 300-400 g / L.

[0015] As a further improvement of the present invention, in step S2, the reducing agent includes one or more of sodium borohydride, triethanolamine, hydrazine hydrate, hydroquinone, hydroxylamine, ascorbic acid, sodium citrate, hydrogen peroxide, hydrazine sulfate, glucose, formaldehyde, and potassium iodide.

[0016] The beneficial effects of the present invention are: 1. The micron block and submicron spherical mixed silver powder and the preparation method thereof of the present invention use low molecular weight polyvinyl pyrrolidone as a dispersant, so that the nano silver crystal and the dispersant play a synergistic role. On the one hand, polyvinyl pyrrolidone has amphiphilicity and can be selectively adsorbed on the crystal surface of some silver powder particles. Under the synergistic effect of nano silver crystals, the silver powder particles are promoted to be generated in a spherical shape. On the other hand, due to the low molecular weight and short molecular chain length of the dispersant, the steric hindrance is different from that of the dispersant with a higher molecular weight, so that the growth of the other part of the silver powder particles is less restricted, and a three-dimensional block structure with a size growth of more than ten microns and a certain thickness is obtained. The micron block and submicron spherical mixed silver powder obtained by the preparation method of the present invention has good dispersion uniformity and high tap density. After being prepared into slurry, the large-sized micron block particles have a better stacking structure, and the submicron particles can be filled into the stacking gaps of the block particles, so that the silver paste has excellent conductivity.

[0017] 2. The present invention adds a dispersant to the reducing agent solution and the nano silver crystal base solution respectively, and controls the dispersant addition process so that the dispersant ensures that the silver powder particles do not agglomerate during growth, which is beneficial to the generation of submicron spherical silver powder, and gradually drips the dispersant into the reducing agent to participate in the reaction process, so as to better play a synergistic role with the nano silver crystals and coordinately regulate the size and morphology of the silver powder. The present invention uses the synergistic effect of the dispersant and the nano silver crystals, so that there is no need to stand still during the preparation process, and realizes the preparation of micron block and submicron spherical mixed silver powder by a single chemical synthesis method, simplifies the process steps, shortens the preparation time, and has industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a microscopic morphology of the mixed silver powder of micron block and submicron spherical shape prepared in Example 1 of the present invention.

[0019] Figure 2 This is a microscopic morphology of the silver powder prepared in Comparative Example 1.

[0020] Figure 3 This is the microscopic morphology of the silver powder prepared in Comparative Example 2. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0023] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0024] A micron block and submicron spherical mixed silver powder, the micron block and submicron spherical mixed silver powder includes micron block silver powder with an average particle size of 2 to 30 μm and a thickness of 0.5 to 3 μm and submicron spherical silver powder with a particle size of 0.1 to 1 μm; the micron block and submicron spherical mixed silver powder is prepared by a single chemical synthesis method. The morphology of the micron block silver powder includes one or more of three-dimensional block, flower ball or crystal cluster. The micron block and submicron spherical mixed silver powder has good dispersion uniformity and high tap density. After being prepared into slurry, the large-sized micron block particles have a better stacking structure, and the submicron particles can be filled into the stacking gaps of the block particles, so that the silver paste has excellent conductivity.

[0025] A method for preparing a mixed silver powder of micron block and submicron spherical shape comprises the following steps: S1. Prepare silver salt solution; the concentration of the silver salt solution is 300~400 g / L.

[0026] S2, mixing the reducing agent, dispersant and pure water in a certain proportion to obtain a reducing agent solution; S3, mixing the nano silver crystal suspension and the dispersant in a certain proportion to obtain a base liquid; S4, synchronously adding the silver salt solution of step S1 and the reducing agent solution of step S2 to the base solution of step S3, and continuing stirring for 20 to 30 minutes after the addition is completed to obtain a solution containing mixed silver powder; washing, solid-liquid separation, and drying and shaping the solution to obtain micron block and submicron spherical mixed silver powder.

[0027] In particular, in step S2 and step S3, the dispersant is polyvinyl pyrrolidone, and the molecular weight of polyvinyl pyrrolidone is 8000-15000. In this way, by selecting low molecular weight polyvinyl pyrrolidone as the dispersant, the nano silver crystals and the dispersant play a synergistic role. On the one hand, polyvinyl pyrrolidone has amphiphilicity and can be selectively adsorbed on the crystal surface of some silver powder particles. Under the synergistic effect of the nano silver crystals, the silver powder particles are promoted to be generated in a spherical shape. On the other hand, due to the low molecular weight of the dispersant, the molecular chain length is short, and the steric hindrance is different from the dispersant with a higher molecular weight, so that the growth of another part of the silver powder particles is less restricted, and a three-dimensional block structure with a size growth of more than ten microns and a certain thickness is obtained.

[0028] In some specific embodiments, the dispersant is polyvinyl pyrrolidone K13-18.

[0029] Specifically, in step S2, the mass ratio of the dispersant to the silver salt in the silver salt solution of step S1 is 1:(1000-10000), and the mass ratio of the reducing agent to the silver salt is 1:(1-2). The reducing agent includes one or more of sodium borohydride, triethanolamine, hydrazine hydrate, hydroquinone, hydroxylamine, ascorbic acid, sodium citrate, hydrogen peroxide, hydrazine sulfate, glucose, formaldehyde, and potassium iodide.

[0030] In step S3, the mass ratio of the dispersant to the silver salt in the silver salt solution of step S1 is 1:(5-50); the mass ratio of the nanosilver crystals in the nanosilver crystal suspension to the silver salt in the silver salt solution is 1:(1000-10000), and the particle size of the nanosilver crystals is 2-40 nm. The use of nanosilver crystals can not only regulate the size of submicron silver powder, but also regulate the morphology of micron-sized silver powder and submicron-sized silver powder through the process of nanosilver crystals combined with dispersants and powder shaping treatment, thereby preparing silver powder with a mixed morphology of micron blocks and submicron spheres.

[0031] In some specific embodiments, in step S4, the shaping process includes one of ball milling and high-speed shearing.

[0032] In step S4, the dripping speed is 20-60 mL / min. The silver salt solution of step S1 and the reducing agent solution of step S2 are synchronously dripped into the base solution of step S3, and the dispersant is mixed into the reducing agent and gradually dripped into the reaction process to better play a synergistic role with the nano silver crystals and coordinately regulate the size and morphology of the silver powder.

[0033] The present invention uses the synergistic effect of the dispersant and the nano silver crystals to eliminate the need for standing during the preparation process, thereby achieving a one-time chemical synthesis method to prepare micron block and submicron spherical mixed silver powder, simplifying the process steps, shortening the preparation time, and having industrial application prospects.

[0034] Example 1 This embodiment provides a method for preparing a mixed silver powder of micron block and submicron spherical shape, comprising the following steps: S1. Prepare 400 mL of 350 g / L silver nitrate solution, and stir and dissolve it at a constant temperature of 25°C to obtain a silver salt solution.

[0035] S2. Weigh 90 g of ascorbic acid and 0.07 g of polyvinylpyrrolidone K13-18 respectively, add 400 mL of pure water, and stir and dissolve at a constant temperature of 25°C to obtain a reducing agent solution; S3, at a constant temperature of 25°C, 3 mL of a nanosilver crystal suspension containing 0.03 g of nanosilver crystals was mixed with 1 L of a solution containing 8 g of polyvinyl pyrrolidone K13-18 to obtain a base solution; S4. At a constant temperature of 25°C and a stirring speed of 300 r / min, use a peristaltic pump to synchronously add the silver salt solution prepared in step S1 and the reducing agent solution prepared in step S2 to the base solution in step S3 at a speed of 40 mL / min. After the addition is completed, continue to stir for 30 minutes to obtain a solution containing mixed silver powder; finally, wash the solution, perform solid-liquid separation, dry it, and perform ball milling to obtain a mixed silver powder of micron block and submicron spherical shape.

[0036] See also Figure 1 , which is a microscopic morphology of the mixed silver powder of micron block and submicron spherical prepared in Example 1. It can be seen from the figure that the mixed silver powder contains large-sized block particles and spherical particles, and the dispersion between the particles is good, which is conducive to the subsequent preparation of high-conductivity silver paste.

[0037] Comparative Example 1 Comparative Example 1 provides a method for preparing silver powder. Compared with Example 1, the difference is that in step S3, no nanosilver crystal suspension is used. The rest is substantially the same as Example 1 and will not be described again.

[0038] See also Figure 2 As shown, it is a microscopic morphology of the silver powder prepared in Comparative Example 1. It can be seen from the figure that the obtained silver powder particles are piled together and have poor dispersibility; because the nano silver crystal suspension is not used in the preparation process of Comparative Example 1, the nano silver crystal cannot play a role in regulating the morphology of the silver powder particles, and the synergistic effect of the nano silver crystal and the dispersant cannot be exerted.

[0039] Comparative Example 2 Comparative Example 2 provides a method for preparing silver powder. Compared with Example 1, the difference is that in step S2 and step S3, the dispersant is polyvinyl pyrrolidone K30, and the rest is substantially the same as Example 1, which will not be repeated here.

[0040] See also Figure 3 The figure shows the microscopic morphology of the silver powder prepared in Comparative Example 2. As can be seen from the figure, the silver powder structure is mostly spherical particles; this is because Comparative Example 2 uses a high molecular weight dispersant, which has a long molecular chain and large steric hindrance, affecting the growth of the silver powder particles.

[0041] Comparative Example 3 Comparative Example 3 provides a method for preparing silver powder. Compared with Example 1, the difference is that in step S2 and step S3, polyvinyl pyrrolidone K90 is used, and the rest is substantially the same as Example 1 and will not be described again.

[0042] Comparative Example 4 Comparative Example 4 provides a method for preparing silver powder. Compared with Example 1, the difference is that no dispersant is added to the reducing agent solution in step S2, the dispersant is completely mixed with the nanosilver crystal suspension and added to the base liquid, and the rest is roughly the same as Example 1 and will not be repeated here.

[0043] Comparative Example 5 Comparative Example 5 provides a method for preparing silver powder. Compared with Example 1, the difference is that in step S3, no dispersant is added, and the dispersant is all added to the reducing agent solution in step S2. The rest is roughly the same as Example 1 and will not be repeated here.

[0044] The silver powder size and tap density of Example 1 and Comparative Examples 1 to 5 were tested respectively, and the test results are shown in the following table.

[0045] Table 1 Test results of silver powder parameters in Example 1 and Comparative Examples 1 to 5 As shown in Table 1, Comparative Example 1 does not use nano silver crystals, and the prepared silver powder has no submicron spherical structure, and the silver powder is a block agglomerate. Comparative Examples 2 and 3 use high molecular weight polyvinyl pyrrolidone instead of low molecular weight polyvinyl pyrrolidone, and the block morphology of the obtained silver powder disappears, and most of them are quasi-spherical particles, and the size of the spherical particles changes under the influence of the dispersant. Comparative Example 3 uses polyvinyl pyrrolidone K90 to prepare silver powder particles with smaller particles, but due to the presence of agglomeration, the equipment test results are larger. Comparative Examples 4 and 5 respectively cancel the addition of the dispersant in step S2 and step S3, so that it cannot play a synergistic role with the nano silver crystals, so that the size of the spherical particles cannot be controlled when preparing the silver powder, and the spherical morphology particles disappear in Comparative Example 5.

[0046] In summary, the present invention provides a micron block and submicron spherical mixed silver powder and a preparation method thereof. By selecting low molecular weight polyvinyl pyrrolidone as a dispersant, the nano silver crystals and the dispersant play a synergistic role, promote the silver powder particles to be generated in a spherical shape, and obtain a three-dimensional block structure with a size of more than ten microns and a certain thickness; at the same time, the dispersant is added to the reducing agent solution and the nano silver crystal base solution respectively, and the dispersant addition process is controlled to promote the dispersant and the nano silver crystal to play a better synergistic role, and coordinately regulate the size and morphology of the silver powder. The micron block and submicron spherical mixed silver powder obtained by the preparation method of the present invention has good dispersion uniformity and high tap density. After being prepared into slurry, the large-sized micron block particles have a better stacking structure, and the submicron particles can be filled into the stacking gaps of the block particles, so that the silver paste has excellent conductivity. The present invention realizes the preparation of micron block and submicron spherical mixed silver powder by a one-time chemical synthesis method through the synergistic effect of the dispersant and the nano silver crystal, simplifies the process steps, shortens the preparation time, and has industrial application prospects.

[0047] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A mixed silver powder of micron block and submicron spherical shape, characterized in that: The micron block and submicron spherical mixed silver powder comprises micron block silver powder with an average particle size of 2-30 μm and a thickness of 0.5-3 μm and submicron spherical silver powder with a particle size of 0.1-1 μm; the micron block and submicron spherical mixed silver powder is prepared by a single chemical synthesis method.

2. The micron block and submicron spherical mixed silver powder according to claim 1, characterized in that: The morphology of the micron-sized bulk silver powder includes one or more of a three-dimensional block, a flower ball or a crystal cluster.

3. A method for preparing a mixed silver powder of micron block and submicron spherical shape according to any one of claims 1 or 2, characterized in that: The following steps are involved: S1, prepare silver salt solution; S2, mixing the reducing agent, dispersant and pure water in a certain proportion to obtain a reducing agent solution; S3, mixing the nano silver crystal suspension and the dispersant in a certain proportion to obtain a base liquid; S4, synchronously dropping the silver salt solution of step S1 and the reducing agent solution of step S2 into the base solution of step S3, and continuing stirring for 20 to 30 minutes after the dropping is completed to obtain a solution containing mixed silver powder; washing, solid-liquid separation, and drying and shaping the solution to obtain micron block and submicron spherical mixed silver powder.

4. The method for preparing the mixed silver powder of micron block and submicron spherical according to claim 3, characterized in that: In step S2 and step S3, the dispersant is polyvinyl pyrrolidone, and the molecular weight of the polyvinyl pyrrolidone is 8000-15000.

5. The method for preparing the mixed silver powder of micron block and submicron spherical according to claim 3, characterized in that: In step S2, the mass ratio of the dispersant to the silver salt in the silver salt solution of step S1 is 1:(1000-10000), and the mass ratio of the reducing agent to the silver salt is 1:(1-2).

6. The method for preparing the mixed silver powder of micron block and submicron spherical according to claim 5, characterized in that: In step S3, the mass ratio of the dispersant to the silver salt in the silver salt solution of step S1 is 1:(5-50).

7. The method for preparing the mixed silver powder of micron block and submicron spherical according to claim 3, characterized in that: In step S4, the dropping speed is 20-60 mL / min.

8. The method for preparing the mixed silver powder of micron block and submicron spherical according to claim 3, characterized in that: In step S3, the mass ratio of the nano-silver crystals in the nano-silver crystal suspension to the mass ratio of the silver salt in the silver salt solution is 1:(1000-10000), and the particle size of the nano-silver crystals is 2-40 nm.

9. The method for preparing the mixed silver powder of micron block and submicron spherical according to claim 3, characterized in that: In step S1, the concentration of the silver salt solution is 300-400 g / L.

10. The method for preparing the mixed silver powder of micron block and submicron spherical according to claim 3, characterized in that: In step S2, the reducing agent includes one or more of sodium borohydride, triethanolamine, hydrazine hydrate, hydroquinone, hydroxylamine, ascorbic acid, sodium citrate, hydrogen peroxide, hydrazine sulfate, glucose, formaldehyde, and potassium iodide.

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