Silver powder with wide sintering window and preparation method thereof

Abstract

The present invention provides a silver powder with a wide sintering window and a preparation method thereof, which belongs to the technical field of metal powder preparation. The present application first controls the order of adding a reducing agent 1 and silver nitrate 1, the temperature of the reaction, and the amount of the reducing agent 1 and the silver nitrate 1 to prepare a spherical silver crystal mother liquor of a specific particle size, and then configures a reducing agent solution and a silver nitrate solution. With the silver crystal mother liquor as the base liquid, the reducing agent solution and the silver nitrate solution are added asynchronously, and the adding method of the reducing agent solution and the silver nitrate solution is controlled at the same time. Finally, after solid-liquid separation, washing, coating, drying and other process treatments, a series of silver powders with a median particle size of 100~800nm and a sintering temperature of 150~250℃ are obtained, and the generated silver powder has a regular crystal surface and a nearly spherical morphology. The silver powder prepared by the present application has a controllable particle size and a wide sintering window, and the preparation method is simple and environmentally friendly. It is not limited to laboratory synthesis and can be industrially scaled up.

Description

Technical Field

[0001] The present invention relates to the technical field of metal powder and preparation thereof, in particular to silver powder with a wide sintering window and a preparation method thereof. Background Art

[0002] As an important functional metal material, silver powder has irreplaceable application value in electronic packaging, conductive pastes, photovoltaic electrodes, flexible electronic devices, and other fields. Its core performance indicators include particle size distribution, morphology uniformity, sintering activity, and sintering temperature window. These indicators directly affect the conductivity, mechanical strength, and process adaptability of the final product.

[0003] At present, although traditional silver powder preparation technologies (such as chemical reduction, ball milling, spray pyrolysis, etc.) have achieved a certain degree of particle size control, they still have significant limitations: 1) The particle size control range is limited, and the particle size distribution of synthetic silver powder is relatively single, which makes it difficult to simultaneously meet the differentiated needs of ultrafine (<200nm) and submicron (>500nm) devices; 2) The sintering temperature window is narrow, and specific process conditions must be strictly matched, resulting in low production yield, high energy consumption, and inability to adapt to the co-firing requirements of different substrates (such as low-temperature polymer substrates and high-temperature ceramic substrates); 3) The existing process has insufficient control over the surface morphology and crystallinity of silver powder, resulting in the sintering densification process being sensitive to temperature, and prone to local unsintering or excessive melting.

[0004] In the prior art, patent publication number CN115780824A discloses a method for preparing and applying a silver powder with high sintering activity. The method comprises the following steps: adding a stabilizer to a reducing agent solution, followed by adding a silver nitrate solution, to obtain a nanosilver solution; weighing silver nitrate and water to mix to obtain solution A; weighing a reducing agent and water to mix, and then adding the nanosilver solution to obtain solution B; weighing a dispersant and water to mix to obtain solution C; rapidly adding solution A to solution B, and then adding solution C after a 1-30 second delay to obtain a reaction solution; adding a modifier to the reaction solution, surface treating it, and aging it to obtain a product; washing the product with deionized water, separating, and drying it. The present invention does not add a dispersant during the reaction process. Instead, by adding a dispersant after the reaction, the reaction instantly generates fine silver grains that grow in situ. After being combined into silver powder particles, the particles have good overall dispersibility, a small average particle size, and a small grain size, and exhibit high sintering activity. However, this patent mainly controls the state of generated silver powder by repeatedly adjusting the pH value of the solution. The preparation method is relatively complicated, and the average particle size of the generated silver powder is in the range of 1.4-2μm, which is large in particle size and has a small sintering window.

[0005] Patent publication number CN118926540A discloses a method for preparing nanosilver powder with high sintering activity. The method involves separating seed crystals from the mother liquor in a nucleus solution and then storing the seed crystals in a dispersant solution. To subsequently prepare the nanosilver powder, the dispersant solution containing the seed crystals is directly poured into a silver nitrate solution, a reducing agent solution is added dropwise, and the solution is heated in a water bath. After the reaction is complete, a flocculant is added, followed by washing, freeze-drying, and polishing. This method produces nanosilver powder with a particle size between 50 and 200 nm, good dispersibility, and excellent sintering activity. The silver powder prepared in this patent only meets the requirements of ultrafine (<200 nm) devices, not submicron (>500 nm) devices. Furthermore, the method is applicable only to low-temperature sintering nanosilver pastes, resulting in a narrow sintering temperature window. Summary of the Invention

[0006] In view of the technical problems existing in the background technology, the present application provides a silver powder with a wide sintering window and a preparation method thereof, aiming to solve the problems of the existing silver powder preparation process being complex, the narrow adjustable range of particle size, the narrow sintering temperature window, the inability to mass industrial production, and the difficulty in simultaneously meeting the differentiated needs of ultrafine and submicron devices.

[0007] On the one hand, embodiments of the present application provide a silver powder with a wide sintering window and a preparation method thereof, comprising the following steps:

[0008] S1. Under stirring, first add the dispersant to pure water, wait for the dispersant to dissolve, then add silver nitrate 1, wait for the silver nitrate 1 to dissolve, then add reducing agent 1, and after it is completely dissolved, obtain silver crystal mother liquor;

[0009] S2. Prepare reducing agent solution and silver nitrate solution respectively;

[0010] S3, asynchronously adding the reducing agent solution and the silver nitrate solution to the silver crystal mother liquor to obtain a solution containing silver powder;

[0011] S4. After solid-liquid separation, washing, coating and drying of the silver powder-containing solution, silver powder with a wide sintering window is obtained.

[0012] Wherein, when the temperature of the pure water is greater than or equal to 37°C and less than or equal to 40°C, the amount of the silver nitrate 1 is 1-2g, and the amount of the reducing agent 1 is 0.2-0.8g;

[0013] When the temperature of the pure water is greater than or equal to 34° C. and less than 37° C., the amount of the silver nitrate 1 is 0.4-0.6 g, and the amount of the reducing agent 1 is 0.06-0.32 g;

[0014] When the temperature of the pure water is greater than or equal to 30° C. and less than 34° C., the amount of the silver nitrate 1 is 0.05-0.2 g, and the amount of the reducing agent 1 is 0.02-0.04 g.

[0015] In the technical solution of the embodiment of the present application, the order of adding the reducing agent 1 and the silver nitrate 1, the reaction temperature and the amount of the reducing agent 1 and the silver nitrate 1 are first controlled. The reaction conditions can control the silver crystals to form a polyhedral morphology with a grain size of 5 to 30 nm. Then, the reducing agent solution and the silver nitrate solution are prepared, and the silver crystal mother liquor is used as the base liquid. The reducing agent solution and the silver nitrate solution are added asynchronously, and the addition method of the reducing agent solution and the silver nitrate solution is controlled at the same time. Finally, after solid-liquid separation, washing, coating, drying and other process treatments, silver powder with a wide adjustable particle size range and a wide sintering window is obtained, and the generated silver powder has a regular crystal surface and a nearly spherical morphology.

[0016] In some embodiments, in step S1, the reducing agent 1 is one or more of sodium citrate, sodium borohydride, L-ascorbic acid, formaldehyde, hydrazine hydrate, hydroquinone, hydroxylamine and hydrogen peroxide; the mass ratio of the reducing agent 1 to silver nitrate 1 is 1:10~4:5.

[0017] In this embodiment, the concentration of silver crystals is controlled by controlling the ratio of reducing agent 1 to silver nitrate 1.

[0018] In some embodiments, in step S2, the reducing agent solution and the silver nitrate solution are prepared as follows: reducing agent 2 and silver nitrate 2 are respectively added to deionized water, and stirred at a constant temperature of 28-30°C until completely dissolved; the reducing agent 2 in the reducing agent solution is one or more of sodium citrate, sodium borohydride, L-ascorbic acid, formaldehyde, hydrazine hydrate, hydroquinone, hydroxylamine and hydrogen peroxide; the concentration of the reducing agent solution is 78-82 g / L, and the concentration of the silver nitrate solution is 98-102 g / L; the mass ratio of the reducing agent 2 to silver nitrate 2 is (0.5-1):1.

[0019] In this embodiment, the reducing agent and silver nitrate are respectively prepared into solutions of certain concentrations, rather than directly adding the reducing agent and silver nitrate, thereby creating conditions for subsequently obtaining silver powder with a wide sintering window of adjustable size.

[0020] In some embodiments, in step S3, the specific operation steps of the asynchronous addition are: first add the reducing agent solution, and after adding 1 / 50 of the volume of the reducing agent solution, start adding the silver nitrate solution at the same time, and finally ensure that the reducing agent solution and the silver nitrate solution are added at the same time.

[0021] In this embodiment, a portion of the reducing agent solution is asynchronously and preferentially added to be adsorbed on the defect sites on the surface of the crystal nucleus to form a localized reduction micro-region. When the silver nitrate solution is added, the silver ions are preferentially directionally reduced on the surface of the pre-activated crystal nucleus, which effectively inhibits the random deposition behavior of the silver ions in the solution, significantly improves the orientation consistency of the crystal growth and the order of the surface atomic arrangement, and finally obtains silver particles with regular crystal faces and nearly spherical morphology.

[0022] In some embodiments, the reducing agent solution and the silver nitrate solution are added at a rate of 2 to 4 L / min.

[0023] In this embodiment, the specific feeding speeds of the reducing agent solution and the silver nitrate solution are used to ensure that the silver nitrate and the reducing agent can fully react and the reduced silver can grow stably.

[0024] In some embodiments, the mass ratio of silver nitrate 1 to silver nitrate 2 is 0.000008-0.00032:1.

[0025] In this embodiment, the particle size of the ultimately obtained series of silver powders is controlled by controlling the mass ratio of silver nitrate 1 to silver nitrate 2 and controlling the amount of silver nitrate solution added to the silver crystal mother liquor.

[0026] In some embodiments, the dispersant is one or more of triethanolamine, polyethylene glycol, polyvinyl alcohol, polyethylene propylamine, oleic acid, Tween 80, polyvinyl pyrrolidone, silane coupling agent, methyl cellulose, polyacrylic acid, gelatin and gum arabic, and the mass ratio of the dispersant to silver nitrate 2 is 1:10.

[0027] In this embodiment, by adding a dispersant to the solution, the silver powder subsequently reduced can be stably dispersed in the solution without agglomeration, which would affect the final morphology of the silver powder.

[0028] In a second aspect, an embodiment of the present application provides a silver powder prepared by the silver powder preparation method; the series particle size of the silver powder is 100~800nm, and the sintering temperature of the silver powder is 150~250℃.

[0029] In the technical solution of the embodiment of the present application, the silver powder has both a wide sintering temperature window and a wide adjustable range of particle size, breaking through the bottleneck of high-reliability electronic device manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0031] Figure 1 This is the SEM image of the silver powder with a wide sintering window prepared in Example 1.

[0032] Figure 2 This is the SEM image of the silver powder with a wide sintering window prepared in Comparative Example 2.

[0033] Figure 3 This is the SEM image of the silver powder with a wide sintering window prepared in Comparative Example 7. DETAILED DESCRIPTION

[0034] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0035] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0036] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0037] In order to solve the problems of complex existing silver powder preparation process, narrow adjustable particle size range, narrow sintering temperature window, inability to mass industrial production, and difficulty in simultaneously meeting the differentiated needs of ultrafine and submicron devices, the present application provides a method for preparing silver powder with a wide sintering window. First, the order of adding reducing agent 1 and silver nitrate 1, the reaction temperature and the amount of reducing agent 1 and silver nitrate 1 are controlled to prepare a spherical silver crystal mother liquor with a specific particle size, and then a reducing agent solution and a silver nitrate solution are prepared. The silver crystal mother liquor is used as the base liquid, and the reducing agent solution and the silver nitrate solution are added asynchronously, while the addition method of the reducing agent solution and the silver nitrate solution is controlled. Finally, after solid-liquid separation, washing, coating, drying and other process treatments, a series of silver powders with a particle size of 100~800nm and a sintering temperature of 150~250℃ are obtained, and the generated silver powder has a regular crystal surface and a nearly spherical morphology. The preparation method of the present invention is simple and easy, and is not limited to laboratory synthesis, and can be industrially scaled up; the prepared silver powder has a wide adjustable particle size range and a wide sintering window, which makes it possible to manufacture high-reliability electronic devices.

[0038] The present invention provides a method for preparing silver powder with a wide sintering window, comprising the following steps:

[0039] S1. Under stirring, first add the dispersant to pure water, wait for the dispersant to dissolve, then add silver nitrate 1, wait for the silver nitrate 1 to dissolve, then add reducing agent 1, and after it is completely dissolved, obtain silver crystal mother liquor;

[0040] S2. Prepare reducing agent solution and silver nitrate solution respectively;

[0041] S3, asynchronously adding the reducing agent solution and the silver nitrate solution to the silver crystal mother liquor to obtain a solution containing silver powder;

[0042] S4. After solid-liquid separation, washing, coating and drying of the silver powder-containing solution, silver powder with a wide sintering window is obtained.

[0043] In the technical solution of the embodiment of the present application, the order of adding the reducing agent 1 and the silver nitrate 1, the reaction temperature and the amount of the reducing agent 1 and the silver nitrate 1 are first controlled to prepare a spherical silver crystal mother liquor of a specific particle size, and then the reducing agent solution and the silver nitrate solution are prepared. The silver crystal mother liquor is used as the base liquid, and the reducing agent solution and the silver nitrate solution are added asynchronously. At the same time, the addition method of the reducing agent solution and the silver nitrate solution is controlled. Finally, after solid-liquid separation, washing, coating, drying and other process treatments, silver powder with a wide adjustable particle size range and a wide sintering window is obtained, and the generated silver powder has a regular crystal surface and a nearly spherical morphology.

[0044] Furthermore, in some embodiments, in step S1, when the temperature of the pure water is greater than or equal to 37° C. and less than or equal to 40° C., the amount of the silver nitrate 1 is 1-2 g, and the amount of the reducing agent 1 is 0.2-0.8 g; further, under this condition, the particle size range of the prepared silver powder is 100-400 nm;

[0045] When the temperature of the pure water is greater than or equal to 34° C. and less than 37° C., the amount of the silver nitrate 1 is 0.4-0.6 g, and the amount of the reducing agent 1 is 0.06-0.32 g. Furthermore, under this condition, the particle size range of the prepared silver powder is 100-600 nm.

[0046] When the temperature of the pure water is greater than or equal to 30°C and less than 34°C, the amount of the silver nitrate 1 is 0.05-0.2g, and the amount of the reducing agent 1 is 0.02-0.04g; further, under this condition, the particle size range of the prepared silver powder is 200-800nm.

[0047] Furthermore, within the corresponding pure water temperature range, as the pure water temperature increases, the amounts of silver nitrate 1 and reducing agent 1 increase accordingly.

[0048] In the technical solution of the embodiment of the present application, under various reaction conditions, the silver crystals can be controlled to form a polyhedral morphology with a grain size of 5 to 30 nm.

[0049] Furthermore, in some embodiments, in step S1, the reducing agent 1 is one or more of sodium citrate, sodium borohydride, L-ascorbic acid, formaldehyde, hydrazine hydrate, hydroquinone, hydroxylamine and hydrogen peroxide; the mass ratio of the reducing agent 1 to silver nitrate 1 is 1:10~4:5.

[0050] In the technical solution of the embodiment of the present application, the concentration of silver crystals generated is controlled by controlling the ratio of the reducing agent 1 and the silver nitrate 1.

[0051] Furthermore, in some embodiments, in step S2, the reducing agent solution and the silver nitrate solution are prepared as follows: reducing agent 2 and silver nitrate 2 are respectively added to deionized water, and stirred at a constant temperature of 28-30°C until completely dissolved; the reducing agent 2 in the reducing agent solution is one or more of sodium citrate, sodium borohydride, L-ascorbic acid, formaldehyde, hydrazine hydrate, hydroquinone, hydroxylamine and hydrogen peroxide; the concentration of the reducing agent solution is 78-82 g / L, and the concentration of the silver nitrate solution is 98-102 g / L; the mass ratio of the reducing agent 2 to silver nitrate 2 is (0.5-1):1.

[0052] In the technical solution of the embodiment of the present application, the reducing agent and silver nitrate are respectively configured as solutions of a certain concentration, rather than directly adding the reducing agent and silver nitrate, thereby creating conditions for subsequently obtaining silver powder with a wide sintering window with adjustable size.

[0053] Furthermore, in some embodiments, in step S3, the specific operation steps of the asynchronous addition are: first add the reducing agent solution, and after adding 1 / 50 of the volume of the reducing agent solution, start adding the silver nitrate solution at the same time, and finally ensure that the reducing agent solution and the silver nitrate solution are added at the same time.

[0054] In the technical solution of the embodiment of the present application, a portion of the reducing agent solution is asynchronously and preferentially added to be adsorbed on the defect sites on the surface of the crystal nucleus to form a localized reduction micro-region. When the silver nitrate solution is added, the silver ions are preferentially directionally reduced on the surface of the pre-activated crystal nucleus, which effectively inhibits the random deposition behavior of the silver ions in the solution, significantly improves the orientation consistency of the crystal growth and the order of the surface atomic arrangement, and finally obtains silver particles with regular crystal faces and nearly spherical morphology.

[0055] Furthermore, in some embodiments, the reducing agent solution and the silver nitrate solution are added at a rate of 2 to 4 L / min.

[0056] In the technical solution of the embodiment of the present application, the specific adding speeds of the reducing agent solution and the silver nitrate solution are used to enable the silver nitrate and the reducing agent to fully react, and the reduced silver can grow stably.

[0057] Furthermore, in some embodiments, the mass ratio of silver nitrate 1 to silver nitrate 2 is 0.000008~0.00032:1.

[0058] In the technical solution of the embodiment of the present application, the particle size of the final series of silver powders is controlled by controlling the mass ratio of silver nitrate 1 and silver nitrate 2 and controlling the amount of silver nitrate solution added to the silver crystal mother liquor.

[0059] Furthermore, in some embodiments, the dispersant is one or more of triethanolamine, polyethylene glycol, polyvinyl alcohol, polyethylene propylamine, oleic acid, Tween 80, polyvinyl pyrrolidone, silane coupling agent, methyl cellulose, polyacrylic acid, gelatin and gum arabic, and the mass ratio of the dispersant to silver nitrate 2 is 1:10.

[0060] In the technical solution of the embodiment of the present application, by adding a dispersant to the solution, the silver powder subsequently reduced can be stably dispersed in the solution without agglomeration, which affects the final morphology of the silver powder.

[0061] In a second aspect, an embodiment of the present application provides a silver powder prepared by the silver powder preparation method; the series particle size of the silver powder is 100~800nm, and the sintering temperature of the silver powder is 150~250℃.

[0062] In the technical solution of the embodiment of the present application, the silver powder has both a wide sintering temperature window and a wide adjustable range of particle size, breaking through the bottleneck of high-reliability electronic device manufacturing.

[0063] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0064] Examples 1-3 and Comparative Examples 1-2

[0065] Examples 1-3 and Comparative Examples 1-2 respectively provide a method for preparing silver powder with a wide sintering window, comprising the following steps:

[0066] S1. Weigh sodium borohydride, silver nitrate, and polyvinyl pyrrolidone; add 50 L of pure water to a reactor, control the pure water temperature, start stirring, and then add weighed polyvinyl pyrrolidone in sequence. After the polyvinyl pyrrolidone is dissolved, weighed silver nitrate is added. After the silver nitrate is dissolved, weighed sodium borohydride is added. After the silver nitrate is completely dissolved, a silver crystal mother liquor is obtained. The amounts of sodium borohydride and silver nitrate and the corresponding pure water temperatures in Examples 1 to 3 and Comparative Examples 1 to 2 are shown in Table 1.

[0067] S2. Weigh 2160 g of L ascorbic acid, add it to 27 L of pure water, and stir and dissolve it at a constant temperature of 30 ° C to obtain an L ascorbic acid solution; weigh 2500 g of silver nitrate, add it to 25 L of pure water, and stir and dissolve it at a constant temperature of 30 ° C to obtain a silver nitrate solution;

[0068] S3. Add L ascorbic acid solution and silver nitrate solution to the silver crystal mother liquor: First, start the feeding pump of L ascorbic acid solution and add it at a rate of 2 L / min. After 1 minute, start the feeding pump of silver nitrate solution and add it at a rate of 2 L / min. After the addition is completed, a solution containing silver powder is obtained;

[0069] S4. The silver powder-containing solution is filtered, washed, coated, dried, and other processes to obtain silver powder with a wide sintering window.

[0070] Table 1 The amount of sodium borohydride and silver nitrate used and the corresponding pure water temperature in Examples 1 to 3 and Comparative Examples 1 to 2

[0071]

[0072] The SEM image of the silver powder prepared in Example 1 is as follows: Figure 1 shown.

[0073] Depend on Figure 1 It can be seen that the silver powder prepared in this embodiment has good dispersibility, presents a regular polyhedral spherical shape, and has a particle size of 100-400 nm.

[0074] Examples 4 to 6 and Comparative Examples 3 to 4

[0075] Examples 4 to 6 and Comparative Examples 3 to 4 respectively provide a method for preparing silver powder with a wide sintering window. Compared with Example 1, the difference is that the amounts of sodium borohydride and silver nitrate in step S1 are different, as shown in Table 2. The other steps are roughly the same as those in Example 1 and are not repeated here.

[0076] Table 2 The amount of sodium borohydride and silver nitrate used and the corresponding pure water temperature in Examples 4 to 6 and Comparative Examples 3 to 4

[0077]

[0078] Examples 7-9 and Comparative Examples 5-6

[0079] Examples 7 to 9 and Comparative Examples 5 to 6 respectively provide a method for preparing silver powder with a wide sintering window. Compared with Example 1, the difference lies in the different amounts of sodium borohydride and silver nitrate used in step S1, as shown in Table 3. The other steps are substantially the same as those in Example 1 and are not described again here.

[0080] Table 3 The amount of sodium borohydride and silver nitrate used and the corresponding pure water temperature in Examples 7 to 9 and Comparative Examples 5 to 6

[0081]

[0082] Comparative Examples 7-8

[0083] Comparative Examples 7 and 8 provide a method for preparing silver powder with a wide sintering window. Compared with Example 1, the difference is that the L ascorbic acid solution and the silver nitrate solution are added in different ways in step S3. In Comparative Example 7, the L ascorbic acid solution is added first, and then the silver nitrate solution is added. In Comparative Example 8, the L ascorbic acid solution and the silver nitrate solution are added simultaneously. The other steps are substantially the same as in Example 1 and are not repeated here.

[0084] The particle size and sintering temperature of the silver powders prepared in Examples 1 to 9 and Comparative Examples 1 to 8 were tested, and the results are shown in Table 4.

[0085] Table 4 Particle size and sintering temperature of silver powder obtained in Examples 1 to 9 and Comparative Examples 1 to 8

[0086]

[0087] It can be seen from the test results of Examples 1 to 9 in Table 4 that, in the silver crystal mother liquor prepared by this scheme, the corresponding amount of reducing agent and silver nitrate is matched with the appropriate reaction temperature, and finally a silver powder with a particle size distribution in the range of 100 to 800 nm can be obtained, which has a wide sintering temperature range, and the generated silver powder has a regular crystal surface and a nearly spherical morphology; while in Comparative Examples 1 to 6, the amount of silver nitrate 1 and reducing agent 1 is outside the scope required by this patent, and the prepared silver powder has a widened particle size distribution, D (10) is less than 100 nm or D (90) exceeds 800 nm, and the prepared silver powder has a more flaky morphology. Figure 2 This is the SEM image of the silver powder prepared in Comparative Example 2; in Comparative Example 7, a large amount of silver powder agglomerates. Figure 3 This is the SEM image of the silver powder prepared in Comparative Example 7. In Comparative Example 8, the initial reaction lacked the reducing agent to adsorb the local reduction micro-regions formed on the surface of the silver crystal. The added silver nitrate generated a large number of new crystal nuclei, resulting in a smaller silver powder particle size and a more flaky morphology.

[0088] In summary, the present invention first controls the order of adding the reducing agent 1 and silver nitrate 1, the reaction temperature, and the ratio of the reducing agent 1 to the silver nitrate 1 to prepare a spherical silver crystal mother liquor of a specific particle size, then prepares a reducing agent solution and a silver nitrate solution, uses the silver crystal mother liquor as the base liquid, asynchronously adds the reducing agent solution and the silver nitrate solution, and simultaneously controls the addition method of the reducing agent solution and the silver nitrate solution. Finally, after solid-liquid separation, washing, coating, drying and other process treatments, a series of silver powders with a particle size of 100 to 800 nm and a sintering temperature of 150 to 250°C are obtained, and the generated silver powder has a regular crystal surface and a nearly spherical morphology. The preparation method of the present invention is simple and easy to implement, and is not limited to laboratory synthesis and can be industrially scaled up. The obtained silver powder has a wide adjustable particle size range and a wide sintering window, which provides the possibility for the manufacture of high-reliability electronic devices.

[0089] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing silver powder with a wide sintering window, characterized in that: The steps include: S1. Under stirring, first add the dispersant to pure water, wait for the dispersant to dissolve, then add silver nitrate 1, wait for the silver nitrate 1 to dissolve, then add reducing agent 1, and after it is completely dissolved, obtain silver crystal mother liquor; S2. Prepare reducing agent solution and silver nitrate solution respectively; S3, asynchronously adding the reducing agent solution and the silver nitrate solution to the silver crystal mother liquor to obtain a solution containing silver powder; S4, separating the silver powder-containing solution into solid and liquid, washing, coating and drying to obtain silver powder with a wide sintering window; Wherein, when the temperature of the pure water is greater than or equal to 37°C and less than or equal to 40°C, the amount of the silver nitrate 1 is 1-2g, and the amount of the reducing agent 1 is 0.2-0.8g; When the temperature of the pure water is greater than or equal to 34° C. and less than 37° C., the amount of the silver nitrate 1 is 0.4-0.6 g, and the amount of the reducing agent 1 is 0.06-0.32 g; When the temperature of the pure water is greater than or equal to 30° C. and less than 34° C., the amount of the silver nitrate 1 is 0.05-0.2 g, and the amount of the reducing agent 1 is 0.02-0.04 g.

2. The method for preparing silver powder with a wide sintering window according to claim 1, characterized in that: In step S1, the reducing agent 1 is one or more of sodium citrate, sodium borohydride, L-ascorbic acid, formaldehyde, hydrazine hydrate, hydroquinone, hydroxylamine and hydrogen peroxide; and the mass ratio of the reducing agent 1 to silver nitrate 1 is 1:10 to 4:

5.

3. The method for preparing silver powder with a wide sintering window according to claim 1, characterized in that: In step S2, the reducing agent solution and the silver nitrate solution are prepared by adding the reducing agent 2 and the silver nitrate 2 into deionized water respectively, and stirring at a constant temperature of 28-30°C until they are completely dissolved.

4. The method for preparing silver powder with a wide sintering window according to claim 3, characterized in that: The reducing agent 2 in the reducing agent solution is one or more of sodium citrate, sodium borohydride, L-ascorbic acid, formaldehyde, hydrazine hydrate, hydroquinone, hydroxylamine and hydrogen peroxide; the concentration of the reducing agent solution is 78-82 g / L, and the concentration of the silver nitrate solution is 98-102 g / L; the mass ratio of the reducing agent 2 to the silver nitrate 2 is (0.5-1):

1.

5. The method for preparing silver powder with a wide sintering window according to claim 1, characterized in that: In step S3, the specific operation steps of the asynchronous addition are: first add the reducing agent solution, and after adding 1 / 50 of the volume of the reducing agent solution, start adding the silver nitrate solution at the same time, and finally ensure that the reducing agent solution and the silver nitrate solution are added at the same time.

6. The method for preparing silver powder with a wide sintering window according to claim 5, characterized in that: The adding speed of the reducing agent solution and the silver nitrate solution is 2-4 L / min.

7. The method for preparing silver powder with a wide sintering window according to claim 4, characterized in that: The mass ratio of the silver nitrate 1 to the silver nitrate 2 is 0.000008-0.00032:

1.

8. The method for preparing silver powder according to claim 1, wherein In step S1, the dispersant is one or more of triethanolamine, polyethylene glycol, polyvinyl alcohol, polyethylene propylamine, oleic acid, Tween 80, polyvinyl pyrrolidone, silane coupling agent, methyl cellulose, polyacrylic acid, gelatin and gum arabic, and the mass ratio of the dispersant to silver nitrate 2 is 1:

10.

9. A silver powder, characterized in that: The silver powder is prepared by the preparation method of the silver powder according to any one of claims 1 to 8, wherein the series particle size of the silver powder is 100 to 800 nm, and the sintering temperature of the silver powder is 150 to 250°C.

Images