Preparation method of high sintering active nano silver powder

Abstract

The present application provides a method for preparing a nano silver powder with high sintering activity, belonging to the technical field of nano silver powder preparation. The method separates the seed crystals from the mother liquor in the crystal nucleus solution, and then stores the seed crystals in a dispersant solution. When preparing the nano silver powder later, the dispersant solution containing the seed crystals is directly poured into a silver nitrate solution, and a reducing agent solution is added dropwise, and the water bath is heated at the same time. After the reaction is complete, a flocculant is added, and the solution is washed. After freeze drying and polishing, a nano silver powder with high sintering activity can be obtained. The present invention stores the seed crystals in a dispersant solution, and the seed crystals can be stored for a long time, and the volume of the seed crystals used in the subsequent reaction to prepare the nano silver powder can be greatly reduced, and the dispersant does not need to be added again when the nano silver powder is prepared later. The present invention prepares silver powder with a particle size between 50-200nm with a simple process, and the silver powder has good dispersibility, good sintering activity, and can be sintered at a low temperature of 180°C, which can be applied to the field of low-temperature sintering nano silver paste.

Description

Technical Field

[0001] The invention relates to the technical field of nano silver powder preparation, and in particular to a method for preparing nano silver powder with high sintering activity. Background Art

[0002] Nano silver powder is a metal powder with excellent conductivity and widely used in the electronics industry. It is an important raw material for the printed electronics industry. In the printed electronics industry, nano silver powder can be used as a conductive filler to prepare conductive inks for inkjet printing and conductive silver pastes for screen printing.

[0003] At present, the particle size D50 of silver powder used in conductive paste on the market is generally 1-3um. The silver powder has a large particle size and a small specific surface energy. It is not easy to sinter with each other, which prolongs the sintering time and has a high sintering temperature. In addition, the inter-ion gap is large, and the sintered layer is not dense enough. For photovoltaic front silver, the battery contact resistance is large and the electrode mechanical properties are not ideal. Studies have shown that excessively large particle size is likely to increase the reverse current and increase the possibility of PN junction burn-through. Nano silver powder is suitable for silver paste for the front electrode of solar cells. It has high sintering activity, can achieve low-temperature sintering, shorten the sintering time, and has strong antioxidant ability.

[0004] In the prior art, nano silver powder is generally prepared by a one-step or two-step synthesis method or a hydrothermal method.

[0005] The patent with publication number CN113547132A provides a method for preparing nano silver powder by a hydrothermal method and nano silver powder. During the preparation process, the reaction temperature needs to be controlled at 105-150°C and the reaction time is 5-8h. First, the reaction temperature is too high and the reaction time is too long to achieve large-scale production. Second, too high a temperature will cause the nano silver powder to agglomerate and have poor dispersibility, thereby affecting the application performance of the silver powder.

[0006] Patent No. CN 110238384 A provides a method for preparing single crystal nano silver powder, which adopts a one-step reduction method, first adjusting the pH of the formaldehyde solution and then reducing the silver nitrate solution. However, the silver powder prepared by this method has low sphericity and irregular morphology, and the morphology of the silver powder affects its sintering activity.

[0007] In view of this, it is necessary to design a method for preparing nano silver powder with high sintering activity to solve the above problems. Summary of the invention

[0008] The purpose of the present application is to provide a method for preparing a nano silver powder with high sintering activity. The method separates the seed crystals from the mother liquor in the crystal nucleus solution by high-speed centrifugation, and then stores the seed crystals in a dispersant solution of a certain concentration. When preparing the nano silver powder later, the dispersant solution containing the seed crystals is directly poured into the silver nitrate solution, and the reducing agent solution is added dropwise, and the water bath is heated at the same time. After the reaction is complete, a flocculant is added, and the nano silver powder with high sintering activity is obtained after being freeze-dried and polished. By storing the seed crystals in the dispersant solution, the seed crystals can be stored for a long time, and the volume of the seed crystals used in the subsequent reaction to prepare the nano silver powder can be greatly reduced, and the dispersant does not need to be added again when the nano silver powder is prepared later.

[0009] The present invention provides a method for preparing a nano silver powder with high sintering activity, comprising the following steps:

[0010] S1, preparing a crystal nucleus solution: pouring a reducing agent solution and a dispersant solution into a silver nitrate solution at the same time, stirring, to obtain a crystal nucleus solution;

[0011] S2, centrifuging the crystal nucleus solution with a high-speed centrifuge to separate the seed crystals from the mother solution;

[0012] S3, storing the separated seed crystals in a dispersant solution to obtain a seed crystal dispersant solution having a silver concentration of 2 to 10 g / L for standby use;

[0013] S4, preparing silver nitrate solution and reducing agent solution respectively;

[0014] S5, adding the dispersant solution containing the seed crystals into the silver nitrate solution, and then dropping the reducing agent solution, the reaction temperature is 40-60° C., and stirring;

[0015] S6, adding the prepared flocculant to the solution prepared in step S5, stirring for 5-10 minutes, fully flocculating, removing the supernatant after precipitation, washing the precipitated silver powder with deionized water, freeze-drying, and grinding to obtain high sintering active nano silver powder with a particle size between 50-200nm.

[0016] Preferably, in step S5, the ratio of the mass of the dispersant in the dispersant solution to the mass of the silver nitrate in the silver nitrate solution is (0.05-0.1):1.

[0017] Preferably, in step S5, the ratio of the mass of the reducing agent in the reducing agent solution to the mass of the silver nitrate in the silver nitrate solution is (0.5-0.8):1.

[0018] Preferably, in step S5, the dispersant solution containing seed crystals is added to the silver nitrate solution, and then the reducing agent solution is dripped into the aforementioned solution, the stirring speed is 200-300 r / min, and the dripping speed of the reducing agent solution is 50-100 ml / min.

[0019] Preferably, in step S6, the mass of the flocculant is 0.03-0.1 wt % of the mass of the silver powder.

[0020] Preferably, the reducing agent in the crystal nucleus solution is sodium borohydride, and the dispersing agent is polyvinyl pyrrolidone; the mass ratio of sodium borohydride, polyvinyl pyrrolidone and silver nitrate in the crystal nucleus solution is (0.1~0.3):(0.08~0.2):1.

[0021] Preferably, in step S3, the dispersant is one or two of gum arabic, polyvinyl pyrrolidone, gelatin and methyl cellulose.

[0022] Preferably, in step S4, the reducing agent is ascorbic acid.

[0023] Preferably, in step S4, the concentration of the silver nitrate solution is 100-400 g / L.

[0024] Preferably, in step S6, the flocculant is a mixture of one amine and one acid selected from triethanolamine, trimethylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine, oleylamine, stearic acid, 12-hydroxystearic acid, lauric acid, ricinoleic acid, elaeisoleic acid, and octanoic acid.

[0025] Preferably, in step S2, the rotation speed of the centrifuge is 15000-20000 r / min, and the centrifugation time is 10-20 min.

[0026] The beneficial effects of the present invention are:

[0027] 1. The method for preparing nano silver powder with high sintering activity provided by the present invention comprises the following steps: separating the seed crystals from the mother liquor in the prepared crystal nucleus solution by high-speed centrifugation, and then storing the seed crystals in a dispersant solution of a certain concentration; when preparing the nano silver powder, pouring the dispersant solution containing the seed crystals into a silver nitrate solution, and then dripping a reducing agent solution, while heating in a water bath, adding a flocculant after the reaction is complete, washing with deionized water, and obtaining the nano silver powder with high sintering activity after freeze drying and grinding.

[0028] By separating the seed crystals from the mother liquor and storing the seed crystals in the dispersant solution, on the one hand, it is beneficial to the long-term storage of the seed crystals and the seed crystals are not easy to deteriorate; on the other hand, the method of separating the seed crystals from the mother liquor can greatly reduce the volume of the seed crystals used in the subsequent reaction to prepare the nano silver powder, which is of great help to the subsequent expansion experiment, and there is no need to add the dispersant again in the subsequent preparation of the nano silver powder.

[0029] 2. The preparation method of high sintering activity nano silver powder provided by the present invention, the flocculation process makes the surface of the silver powder coated with a layer of organic matter, can improve the wettability and affinity of the silver powder and the organic carrier, improve the printing performance of the silver paste, the prepared nano-scale silver powder has good dispersibility, high sphericity, high sintering activity, can achieve low-temperature sintering at 180°C, and the sintered layer is dense, and can be applied to the field of low-temperature sintering nano silver paste, such as solar photovoltaic positive electrode silver paste and nano sintering silver paste, which has high sintering activity, can achieve low-temperature sintering, shorten the sintering time, and has strong antioxidant ability.

[0030] 3. The method for preparing high sintering active nano silver powder provided by the present invention can prepare silver powder with a particle size between 50-200 nm in a simple process, and the size of the prepared nanoparticles can be controlled by adjusting the amount of the dispersant solution containing the seed crystals.

[0031] 4. The nano silver powder of the present invention is freeze-dried. Since the nano particles are very small, air drying or vacuum drying will cause the nano particles to agglomerate, and the size of the agglomerates will increase, which will affect the sintering activity of the nano powder.

[0032] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 This is a real picture of the dispersant solution containing seed crystals in Example 1 after being left for 7 days.

[0035] Figure 2 This is a SEM image of the nano silver powder prepared in Example 1 of the present invention.

[0036] Figure 3 This is the SEM image of the nano silver powder prepared in Example 1 after low temperature sintering.

[0037] Figure 4 This is a SEM image of the nano silver powder prepared in Example 2 of the present invention.

[0038] Figure 5 This is a SEM image of the nano silver powder prepared in Example 3 of the present invention.

[0039] Figure 6 This is a real picture of the crystal nucleus solution after being left for 7 days without separation of seed crystals and mother liquor.

[0040] Figure 7 This is the SEM image of the silver powder prepared in Comparative Example 1.

[0041] Figure 8 This is the SEM image of the silver powder prepared in Comparative Example 2. DETAILED DESCRIPTION

[0042] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0044] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0045] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0046] The present invention provides a method for preparing nano silver powder with high sintering activity, comprising the following steps:

[0047] S1, preparing a crystal nucleus solution: pouring a reducing agent solution and a dispersant solution into a silver nitrate solution at the same time, stirring, to obtain a crystal nucleus solution;

[0048] Specifically, the reducing agent in the crystal nucleus solution is sodium borohydride, and the dispersing agent is polyvinyl pyrrolidone.

[0049] The mass ratio of sodium borohydride, polyvinyl pyrrolidone and silver nitrate in the crystal nucleus solution is (0.1~0.3):(0.08~0.2):1.

[0050] S2, centrifuging the crystal nucleus solution with a high-speed centrifuge to separate the seed crystals from the mother solution;

[0051] Among them, the rotation speed of the centrifuge is 15000~20000r / min, and the centrifugation time is 10~20min.

[0052] S3, storing the separated seed crystals in a dispersant solution of a certain concentration, wherein the seed crystal dispersant solution contains silver at a concentration of 2 to 10 g / L, for later use;

[0053] The dispersant is one or two of gum arabic, polyvinyl pyrrolidone, gelatin and methyl cellulose.

[0054] S4, preparing silver nitrate solution and reducing agent solution respectively;

[0055] Among them, the concentration of silver nitrate solution is 100~400g / L.

[0056] The reducing agent is ascorbic acid, and its concentration is 50~230g / L.

[0057] S5, adding the dispersant solution containing the seed crystals into the silver nitrate solution, and then dropping the reducing agent solution, the reaction temperature is 40-60° C., and stirring;

[0058] Specifically, a dispersant solution containing seed crystals is added to a silver nitrate solution, and then a reducing agent solution is dripped into the aforementioned solution, with a stirring speed of 200-300 r / min and a dripping speed of the reducing agent solution of 50-100 ml / min.

[0059] Among them, the ratio of the mass of the dispersant in the dispersant solution to the mass of the silver nitrate in the silver nitrate solution is (0.05~0.1):1.

[0060] The ratio of the mass of the reducing agent in the reducing agent solution to the mass of the silver nitrate in the silver nitrate solution is (0.5~0.8):1.

[0061] S6, adding the prepared flocculant to the solution prepared in step S5, stirring for 5-10 minutes, fully flocculating, removing the supernatant after precipitation, washing the precipitated silver powder with deionized water, freeze-drying, and grinding to obtain high sintering active nano silver powder with a particle size between 50-200nm.

[0062] Specifically, the mass of the flocculant is 0.03-0.1 wt % of the mass of the silver powder.

[0063] The flocculant is a mixture of one of each of amines and acids selected from triethanolamine, trimethylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine, oleylamine, stearic acid, 12-hydroxystearic acid, lauric acid, ricinoleic acid, elaeistolic acid and octanoic acid.

[0064] The flocculation process coats the surface of the silver powder with a layer of organic matter, which can enhance the wettability and affinity between the silver powder and the organic carrier and improve the printing performance of the silver paste.

[0065] The invention separates the seed crystals from the mother liquor in the prepared crystal nucleus solution by high-speed centrifugation, and then stores the seed crystals in a dispersant solution of a certain concentration; when preparing the nano silver powder, the dispersant solution containing the seed crystals is poured into a silver nitrate solution, and then a reducing agent solution is added dropwise, and water bath heating is performed at the same time, and after the reaction is complete, a flocculant is added, and the solution is washed with deionized water, and the nano silver powder with high sintering activity is obtained after freeze drying and grinding processes.

[0066] The nano-scale silver powder prepared by this patented method has good dispersibility, high sphericity, and high sintering activity. It can achieve low-temperature sintering at 180°C, and the sintered layer is dense. It can be applied to the field of low-temperature sintering nano silver paste, such as solar photovoltaic positive electrode silver paste and nano sintering silver paste.

[0067] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used without specifying the manufacturer are all conventional products that can be obtained commercially.

[0068] Example 1

[0069] This embodiment provides a method for preparing a high sintering active nano silver powder, comprising the following steps:

[0070] S1, preparation of nucleus solution:

[0071] Prepare silver nitrate solution by weighing 0.051 g of silver nitrate and dissolving it in 240 ml of deionized water;

[0072] Prepare the reducing agent solution by weighing 0.0085 g of sodium borohydride and dissolving it in 45 ml of deionized water;

[0073] To prepare the dispersant solution, weigh 0.007 g of polyvinyl pyrrolidone and dissolve it in 15 ml of deionized water.

[0074] Pour the reducing agent solution and the dispersant solution into the silver nitrate solution at the same time, stir for 10 minutes and then stop to obtain a crystal nucleus solution.

[0075] S2, centrifuging in a high-speed centrifuge to separate the seed crystals from the mother liquor in the crystal nucleus solution, the centrifuge speed is 15000r / min, and the centrifugation is performed for 20min;

[0076] S3, weigh 3.75g of polyvinyl pyrrolidone, dissolve it in 20ml of deionized water to obtain a dispersant solution, store the seed crystals separated in step S2 in the dispersant solution, and obtain a seed crystal dispersant solution with a silver concentration of 2.55g / L.

[0077] Wherein, the concentration of polyvinyl pyrrolidone solution is 75g / L.

[0078] S4, prepare a silver nitrate solution, weigh 70g of silver nitrate and dissolve it in 200ml of deionized water;

[0079] Prepare the reducing agent solution by weighing 40 g of ascorbic acid and dissolving it in 180 ml of deionized water.

[0080] S5, take 40 ml of the dispersant solution containing seed crystals obtained in step S3 and pour it directly into the silver nitrate solution, then drop the reducing agent solution into the aforementioned solution, the reaction temperature is 60°C water bath, the stirring speed is 300 r / min, and the dropping speed is 100 ml / min.

[0081] At this time, the ratio of the mass of the dispersant in the dispersant solution, the mass of the reducing agent in the reducing agent solution, and the mass of the silver nitrate in the silver nitrate solution was 0.054:0.57:1.

[0082] S6, prepare a flocculant, weigh 0.1 g of 12-hydroxystearic acid and 0.1 g of hexadecylamine and dissolve them in 10 ml of anhydrous ethanol, and obtain a flocculant solution after all of them are dissolved.

[0083] The prepared flocculant solution was added to the solution prepared in step S5, and stirred for 10 minutes to fully flocculate. After precipitation, the supernatant was removed, and the silver powder was washed with deionized water until the conductivity was below 20 us / cm.

[0084] The precipitated silver powder is washed with deionized water, freeze-dried, and polished to obtain high sintering active nano silver powder with a particle size between 50-200 nm.

[0085] Figure 1 This is a real picture of the dispersant solution containing seed crystals in Example 1 after being placed for 7 days. It can be seen that after being placed for 7 days, the inner wall of the beaker is not covered with a silver mirror, the seed crystal concentration has not changed, and it is still a uniform solution.

[0086] After testing, the SEM image of the silver powder prepared in this embodiment is as follows Figure 2As shown in the figure, the particle size range is about 100-200nm. Nano silver powder is suitable for silver paste in the field of low-temperature sintering. It has good sintering activity and can be sintered at a low temperature of 180℃. The SEM picture of the silver powder after sintering is shown in the figure below. Figure 3 shown.

[0087] Example 2-3

[0088] Compared with Example 1, the main difference is that the amount of the seed dispersant solution in step S5 is changed, and other experimental parameters and conditions are basically the same as those in Example 1, which will not be repeated here. The details are shown in the following table.

[0089]

[0090] The SEM images of the silver powders prepared in Example 2 and Example 3 are as follows: Figure 4 and Figure 5 shown.

[0091] from Figure 4 It can be seen that when the amount of the dispersant solution containing the seed crystals decreases, the particle size of the silver powder increases, and the particle size range is about 200-300 nm.

[0092] from Figure 5 It can be obtained that when the amount of the dispersant solution containing the seed crystal increases, the particle size of the silver powder decreases, and the particle size range is about 50-100 nm.

[0093] That is, the preparation method of the present invention can control the particle size of the silver powder by controlling the amount of the solution containing the seed crystal dispersant.

[0094] Comparative Example 1

[0095] This comparative example provides a method for preparing nano silver powder. Compared with Example 1, the main difference is that the crystal nucleus solution is not separated from the mother solution, and the crystal seed solution is not stored in the dispersant solution. The specific steps are as follows:

[0096] S1. Preparation of crystal nucleus solution:

[0097] Prepare silver nitrate solution by weighing 0.051 g of silver nitrate and dissolving it in 240 ml of deionized water;

[0098] Prepare the reducing agent solution by weighing 0.0085 g of sodium borohydride and dissolving it in 45 ml of deionized water;

[0099] To prepare the dispersant solution, weigh 0.007 g of polyvinyl pyrrolidone and dissolve it in 15 ml of deionized water.

[0100] Pour the reducing agent solution and the dispersant solution into the silver nitrate solution at the same time, stir for 10 minutes and then stop to obtain a crystal nucleus solution.

[0101] S2. Weigh 3.75 g of polyvinyl pyrrolidone and dissolve it in 20 ml of deionized water to obtain a dispersant solution.

[0102] S3, prepare silver nitrate solution, weigh 70g of silver nitrate and dissolve it in 200ml of deionized water;

[0103] Prepare the reducing agent solution by weighing 40 g of ascorbic acid and dissolving it in 180 ml of deionized water.

[0104] S4. Pour 300 ml of the crystal nucleus solution and the dispersant solution prepared in step S1 directly into the silver nitrate solution, and then drop the reducing agent solution into the above solution. The reaction temperature is 60° C. in a water bath, the stirring speed is 300 r / min, and the dropping speed is 100 ml / min.

[0105] S5. Prepare a flocculant. Weigh 0.1 g of 12-hydroxystearic acid and 0.1 g of hexadecylamine and dissolve them in 10 ml of anhydrous ethanol. After all of them are dissolved, a flocculant solution is obtained.

[0106] The prepared flocculant was added to the solution prepared by S5, stirred for 10 minutes, and fully flocculated. After precipitation, the supernatant was removed, and the silver powder was washed with deionized water until the conductivity was below 20us / cm.

[0107] The precipitated silver powder is washed with deionized water, freeze-dried, and polished to obtain silver powder.

[0108] Figure 6 This is a real picture of the crystal nucleus solution after being left for 7 days without separation of seed crystals and mother liquor.

[0109] It can be seen that after 7 days, the inner wall of the beaker is covered with a layer of silver mirror. This is due to the gradual precipitation of crystal seeds, which will also cause the concentration of crystal seeds to change.

[0110] After testing, the SEM image of the silver powder prepared in this comparative example is as follows Figure 7 As shown, compared with Example 1, the silver powder prepared in Comparative Example 1 has a slightly larger particle size of about 300-400nm, and the sphericity is not high, with more flake morphology. This is mainly because the volume of the added crystal nucleus solution is large (300ml), which dilutes the concentration of the silver nitrate solution, causing the silver powder particle size to grow, thereby affecting the sintering performance of the silver powder. Experiments show that when the volume of the crystal nucleus solution is increased to 800ml, silver powder with a size of less than 200nm can be obtained. Compared with Example 1, only 40ml of dispersant solution containing seed crystals is used, and the volume of the crystal nucleus solution in the comparative example is significantly increased.

[0111] Comparative Example 2

[0112] Comparative Example 2 provides a method for preparing silver powder, which is different from Example 1 in that the addition method of silver nitrate and reducing agent solution in step S4 is different; specifically, silver nitrate and reducing agent solution are simultaneously added dropwise to the dispersant solution containing seed crystals. The remaining steps are consistent with Example 1 and are not described in detail here.

[0113] The SEM image of the final silver powder is as follows: Figure 8 It can be seen that the silver powder prepared in Comparative Example 2 has poor dispersibility, agglomeration, and irregular morphology.

[0114] Comparative Example 3

[0115] Comparative Example 3 provides a method for preparing silver powder, which is different from Example 1 in that the reducing agent ascorbic acid in step S4 is replaced by glucose. The remaining steps are basically the same as those in Example 1 and will not be described in detail.

[0116] Experiments show that due to the slow reduction of glucose, the final silver powder has a small particle size and irregular morphology.

[0117] In summary, the present invention provides a method for preparing a high sintering active nano silver powder. By adjusting the amount of seed dispersion solution, the size of silver powder nanoparticles can be controlled. By separating the seed from the mother liquor, the seed can be stored for a long time and is not easy to deteriorate. In addition, the method of separating the seed from the mother liquor can significantly reduce the amount of seed solution used in the reaction process, which is of great help to subsequent expansion experiments.

[0118] In this application, nano silver powder is freeze-dried. Since the particle size of nanoparticles is very small, the use of blast drying or vacuum drying will cause the nanoparticles to agglomerate, and the size of the agglomerates will increase, affecting the sintering activity of the nanopowder. Freeze drying solves this problem. The flocculation process coats the surface of the silver powder with a layer of organic matter, which can improve the wettability and affinity of the silver powder and the organic carrier, and improve the printing performance of the silver paste. The nano-scale silver powder prepared by the method of the present invention has good dispersibility, high sphericity, and high sintering activity. It can achieve low-temperature sintering at 180°C, and the sintered layer is dense.

[0119] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing high sintering active nano silver powder, characterized in that: The following steps are involved: S1, preparing a crystal nucleus solution: pouring a reducing agent solution and a dispersing agent solution into a silver nitrate solution at the same time, stirring, to obtain a crystal nucleus solution; the reducing agent in the crystal nucleus solution is sodium borohydride, and the dispersing agent is polyvinyl pyrrolidone; the mass ratio of sodium borohydride, polyvinyl pyrrolidone, and silver nitrate in the crystal nucleus solution is (0.1-0.3):(0.08-0.2):1; S2, centrifuging the crystal nucleus solution with a high-speed centrifuge to separate the seed crystals from the mother solution; S3, storing the separated seed crystals in a dispersant solution to obtain a seed crystal dispersant solution having a silver concentration of 2-10 g / L for standby use; wherein the dispersant is one or two of gum arabic, polyvinyl pyrrolidone, gelatin, and methyl cellulose; S4, preparing a silver nitrate solution and a reducing agent solution respectively; the reducing agent is ascorbic acid; S5, adding the dispersant solution containing the seed crystals into the silver nitrate solution, and then dropping the reducing agent solution, the reaction temperature is 40-60° C., and stirring; S6, adding the prepared flocculant to the solution prepared in step S5, stirring for 5-10 minutes, fully flocculating, removing the supernatant after precipitation, washing the precipitated silver powder with deionized water, freeze-drying, and grinding to obtain high sintering active nano silver powder with a particle size between 50-200nm; wherein the mass of the flocculant is 0.03~0.1wt% of the mass of the silver powder.

2. The method for preparing high sintering active nano silver powder according to claim 1, characterized in that: In step S5, the ratio of the mass of the dispersant in the dispersant solution to the mass of the silver nitrate in the silver nitrate solution is (0.05-0.1):

1.

3. The method for preparing high sintering active nano silver powder according to claim 1, characterized in that: In step S5, the ratio of the mass of the reducing agent in the reducing agent solution to the mass of the silver nitrate in the silver nitrate solution is (0.5-0.8):

1.

4. The method for preparing high sintering active nano silver powder according to claim 1, characterized in that: In step S5, the dispersant solution containing seed crystals is added to the silver nitrate solution, and then the reducing agent solution is dripped into the aforementioned solution, with a stirring speed of 200-300 r / min and a dripping speed of the reducing agent solution of 50-100 ml / min.

5. The method for preparing high sintering active nano silver powder according to claim 1, characterized in that: In step S4, the concentration of the silver nitrate solution is 100-400 g / L.

6. The method for preparing high sintering active nano silver powder according to claim 1, characterized in that: In step S6, the flocculant is a mixture of one of each of amines and acids selected from triethanolamine, trimethylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine, oleylamine, stearic acid, 12-hydroxystearic acid, lauric acid, ricinoleic acid, elaeisoleic acid, and octanoic acid.

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