Preparation method of nano-silver

Abstract

The invention relates to the technical field of nano-silver preparation, and discloses a nano-silver preparation method which comprises the following steps: providing a base solution which comprises nano-silver particle seed crystals, a dispersing agent, a gel material and a solubilizer; a silver salt solution and a reducing agent solution are added into the base solution in a parallel flow mode, in the adding process, silver ions are reduced into silver simple substances, and after the silver salt solution is added, a metal chelating agent is added into a reaction system for full reaction; after the reaction is finished, slurry is obtained, and solid nano-silver is extracted from the slurry; the solubilizer is selected from at least one of sodium oleate, polysorbate 80 and propylene glycol. According to the method, the separation difficulty and purification difficulty of the prepared nano-silver can be reduced; the whole preparation process is simple. The particle size of the prepared nano-silver ranges from 200 nm to 500 nm, monodispersity is good, and the nano-silver has wide application prospects in the field of conductive paste.

Description

Technical Field

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

[0002] Nano-micron silver powder has attracted wide attention due to its unique physical and chemical properties and wide application prospects. Among the many methods for preparing nano-micron silver powder, the gel method, as an efficient and well-controllable preparation technology, has gradually shown its unique advantages. The basic principle of the gel method is a technology that converts a metal salt solution into a gel-state substance and then converts it into nano-micron particles under appropriate conditions. This method usually dissolves a silver salt (such as silver nitrate, silver chloride, etc.) in an appropriate solvent to form a uniform silver salt solution. Then it is necessary to select a suitable solvent and dissolution conditions to ensure that the silver salt can be completely dissolved and form a stable solution. Therefore, it is necessary to add a gelling agent such as polyvinyl alcohol, polyacrylic acid, etc., and then adjust the reaction conditions (such as pH value, temperature) to gradually convert the silver salt solution into a gel. The selection and dosage of the gelling agent are key factors affecting the formation and performance of the gel. After the gel network is formed, a reducing agent is added to form nano-micron silver powder.

[0003] Although the gel method has significant advantages in the preparation of nano-micron silver powder, it still faces some challenges. For example, how to further improve the yield and preparation efficiency of nano-micron silver powder, how to control the size and morphology consistency of the particles, etc., still need in-depth research and exploration. In addition, the industrial application of the gel method also needs to solve the problems that may be encountered during the scale-up production process, such as equipment design, process optimization, etc. At the same time, due to the large viscosity of the gel, it is difficult to separate and the purification process is cumbersome. Such as solvent washing, centrifugal separation, filtration, etc. These operations not only increase the complexity of the process, but may also lead to the loss or contamination of nano-micron silver powder.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing nano silver, aiming to improve at least one of the problems mentioned in the background technology.

[0006] The present invention is achieved in that:

[0007] The present invention provides a method for preparing nano silver, comprising:

[0008] Providing a base solution, which includes nano silver particle seed crystals, a dispersant, a gel material and a solubilizer;

[0009] Adding a silver salt solution and a reducing agent solution to the base liquid in parallel, during the adding process, the silver ions are reduced to silver element, and after the silver salt solution is added, adding a metal chelating agent to the reaction system for full reaction;

[0010] After the reaction is completed, a slurry is obtained, and solid nanosilver is extracted from the slurry;

[0011] In the base liquid, the particle size of the nano silver particles is 20 to 50 nm, and the mass ratio of the nano silver powder to the theoretical target is 0.1% to 5.0%; the mass ratio of the dispersant to the theoretical target is 1 to 3%, the mass ratio of the gel material to the theoretical target is 1 to 3.5%, and the mass ratio of the solubilizer to the theoretical target is 0.4 to 1%;

[0012] The solubilizing agent is selected from at least one of sodium oleate, polysorbate 80 and propylene glycol.

[0013] In an optional embodiment, the method for extracting solid nanosilver from the slurry comprises:

[0014] Add surfactant to the slurry and mix well;

[0015] The mixture was allowed to stand for sedimentation, the upper clear liquid was poured out, and the lower solid layer was washed and dried to obtain nanosilver.

[0016] In an optional embodiment, at least one of the following features (1) to (4) is also included:

[0017] (1) The surfactant is a long-chain carboxylic acid; optionally, the long-chain carboxylic acid is selected from at least one of stearic acid and lauric acid;

[0018] (2) The mass ratio of the amount of surfactant added to the theoretical target of generating nano silver powder is 0.1% to 2%;

[0019] (3) adding a surfactant to the slurry and mixing the slurry at a speed of 300 to 800 rpm for 2 to 6 minutes;

[0020] (4) The lower layer of solid is cleaned by using an ethanol solution.

[0021] In an optional embodiment, the metal chelator is selected from at least one of sodium ethylenediaminetetraacetate, aminotriacetic acid, and ethylenediaminetetraacetic acid;

[0022] Optionally, the dispersant is selected from at least one of polyvinyl pyrrolidone, gum arabic and gelatin, preferably polyvinyl pyrrolidone.

[0023] In an optional embodiment, at least one of the following features (1) to (3) is also included:

[0024] (1) The mass ratio of the added amount of the metal chelating agent to the theoretical target generated nano silver powder is 0.1% to 0.5%;

[0025] (2) The total mass of the solute in the base solution is less than or equal to 5% of the mass of the theoretical synthesized silver powder;

[0026] (3) In the base solution, the concentration of the nanosilver particle seed crystals is 0.009-0.455%wt, the concentration of the dispersant is 0.09-0.273%wt, the concentration of the gel material is 0.09-0.315%wt, and the concentration of the solubilizer is 0.036-0.09%wt.

[0027] In an optional embodiment, the silver salt in the silver salt solution is selected from at least one of silver nitrate, and;

[0028] Optionally, the silver salt solution is silver nitrate, and the mass concentration of the silver nitrate is 8 to 30%;

[0029] Optionally, the parallel addition time of the silver salt solution and the reducing agent solution is set to T, in units of min, T=(0.01-0.05) / C*60, where C is the mass concentration of the silver salt solution.

[0030] In an optional embodiment, the reducing agent in the reducing agent solution is selected from at least one of ascorbic acid, sodium ascorbate, glucose and sodium borohydride.

[0031] In an optional embodiment, the reaction time after adding the metal chelating agent is 30 to 90 seconds.

[0032] In an optional embodiment, the gel material is selected from at least one of gum arabic and gelatin;

[0033] Optionally, the gel material consists of 1.5 to 2 parts of gum arabic and 1 to 1.5 parts of gelatin, by weight.

[0034] In an optional embodiment, the preparation method of the base liquid includes:

[0035] The silver salt, oleylamine and polyethylene glycol 2000 are mixed and stirred to obtain a mixed solution;

[0036] The mixed solution is placed in an environment of 100 to 160° C. and aged for 25 to 35 minutes to obtain a seed solution containing nano silver particle seed crystals;

[0037] Mixing a dispersant, a gel material, a solubilizer and deionized water to obtain a dispersion;

[0038] Mixing the seed solution with the dispersion solution to obtain a base solution;

[0039] Optionally, the silver salt is silver nitrate;

[0040] Optionally, in the mixed solution, the mass percentage of silver ions is 0.1-5%, the mass percentage of oleylamine is 2-10%, and the mass percentage of polyethylene glycol 2000 is 85-97%;

[0041] Optionally, in the dispersion, the mass percentage of the dispersant is 0.1-0.3%, the mass percentage of the gel material is 0.1-0.35%, the mass percentage of the solubilizer is 0.04-0.1%, and the total mass percentage of the dispersant, gel material and solubilizer in the dispersion does not exceed 0.5%.

[0042] The present invention has the following beneficial effects:

[0043] The preparation method provided in the embodiment of the present invention greatly reduces the proportion of gel compared to the existing gel method for preparing nanosilver. If only the proportion of gel is reduced, the resistance to the migration of silver ions is reduced, and it is difficult to prepare nano-scale silver particles. To address this problem, the present invention improves the dispersibility of silver ions in the reaction system by adding a small amount of dispersant to the reaction system, and adds a solubilizing agent. These solubilizing agents are in the form of oil droplets after being added to the base liquid, so that the base liquid presents an emulsion state, forming a water-in-oil micro-interface; since the silver salt is added in the later stage of the reaction, it is easy to combine with the previously grown silver ions due to electrostatic adsorption and other reasons, thereby causing hard agglomeration and thus causing the D100 of the particles to become larger. The present application adds a metal chelating agent to bind small silver particles after the anion and the reducing agent are added, passivates the surface of the small silver particles, and reduces their agglomeration; therefore, the present invention can avoid the problem of large silver particle size caused by reducing the amount of gel, and the obtained silver particles have a particle size range of 200-500nm, and the particle size distribution has good uniformity; and the preparation method provided by the present invention reduces the amount of gel, so that the viscosity of the reaction system is significantly reduced, which can reduce the difficulty of separation and purification of the obtained nano silver; the whole preparation process is simple. The obtained nano silver particle size is between 200 and 500nm, with good monodispersity, and has broad application prospects in the field of conductive paste. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0045] Figure 1 is a SEM image of the nanosilver prepared in Example 1;

[0046] Figure 2 This is a SEM image of the nanosilver prepared in Example 2;

[0047] Figure 3 This is the SEM image of the nanosilver prepared in Example 3. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0049] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0050] The following is a detailed description of a method for preparing nano silver provided in an embodiment of the present invention.

[0051] The present invention provides a method for preparing nano silver, comprising:

[0052] Providing a base liquid, wherein the base liquid includes nano silver particle seed crystals, a dispersant, a gel material and a solubilizer;

[0053] Adding a silver salt solution and a reducing agent solution to the base liquid in parallel, during the adding process, the silver ions are reduced to silver element, and after the silver salt solution is added, adding a metal chelating agent to the reaction system for full reaction;

[0054] After the reaction is completed, a slurry is obtained, and solid nanosilver is extracted from the slurry;

[0055] In the base liquid, the particle size of the nano-silver particles is 20-50 nm, and the mass ratio of the nano-silver powder generated by the theoretical target is 0.1%-5.0%; the mass ratio of the dispersant to the nano-silver powder generated by the theoretical target is 1-3%, the mass ratio of the gel material to the nano-silver powder generated by the theoretical target is 1-3.5%, and the mass ratio of the solubilizer to the nano-silver powder generated by the theoretical target is 0.4-1%.

[0056] The preparation method provided in the embodiment of the present invention greatly reduces the proportion of gel compared to the existing gel method for preparing nanosilver. If only the proportion of gel is reduced, the resistance to the migration of silver ions is reduced, and it is difficult to prepare nano-scale silver particles. To address this problem, the present invention improves the dispersibility of silver ions in the reaction system by adding a small amount of dispersant to the reaction system, and adds a solubilizing agent. These solubilizing agents are in the form of oil droplets after being added to the base liquid, so that the base liquid presents an emulsion state, forming a water-in-oil micro-interface; since the silver salt is added in the later stage of the reaction, it is easy to combine with the previously grown silver ions due to electrostatic adsorption and other reasons, thereby causing hard agglomeration and thus causing the D100 of the particles to become larger. The present application adds a metal chelating agent after the anion and the reducing agent are added to bind the small silver particles, passivate the surface of the small silver particles, and reduce their agglomeration; therefore, the present invention can avoid the problem of large particle size of the obtained silver particles caused by reducing the amount of gel, by adding a small amount of dispersant and solubilizing agent in the reaction system, and adding a metal chelating agent in the post-reaction stage. The particle size range of the obtained silver particles is 200-500nm, and the particle size distribution is uniform; and the preparation method provided by the present invention reduces the amount of gel, so that the viscosity of the reaction system is significantly reduced, which can reduce the difficulty of separation and purification of the obtained nano silver; the whole preparation process is simple.

[0057] Specifically, the preparation method is:

[0058] S1. Preparation of seed solution

[0059] The silver salt, oleylamine and polyethylene glycol 2000 are mixed and stirred to obtain a mixed solution;

[0060] The mixed solution is placed in an environment of 100-160° C. (e.g., 100° C., 120° C., 140° C., or 160° C.) and aged for 25-35 min (e.g., 25 min, 30 min, or 35 min) to react and generate 20-50 nm nanosilver particles, thereby obtaining a seed solution containing nanosilver particle seed crystals.

[0061] Optionally, the mass percentage of the nanosilver particle seeds in the prepared seed solution is 0.1-5% (eg, 0.1%, 0.635%, 3.15% or 5%).

[0062] To obtain a seed solution with a mass percentage of 0.1-5% of nano silver particle seeds, optionally, in the mixed solution, the mass percentage of silver ions is 0.1-5%, the mass percentage of oleylamine is 2-10%, and the mass percentage of polyethylene glycol 2000 is 85-97%.

[0063] Optionally, the silver salt is silver nitrate.

[0064] Furthermore, the mixed solution is prepared, for example, as follows:

[0065] Silver nitrate solution containing 0.1-0.5g of silver nitrate, 0.2-1.0g of oleylamine and polyethylene glycol 2000 are added into a container and stirred to obtain 10g of a mixed solution. The mixed solution is heated and aged to obtain a seed solution in which the mass percentage of the nano silver particle seed crystals is 0.635-3.18%.

[0066] Optionally, the heating method is oil bath heating.

[0067] S2. Preparation of dispersion

[0068] The dispersant, the gel material, the solubilizer and deionized water are mixed to obtain a dispersion.

[0069] Optionally, in the dispersion, the mass percentage of the dispersant is 0.1-0.3%, the mass percentage of the gel material is 0.1-0.35%, the mass percentage of the solubilizer is 0.04-0.1%, and the total mass percentage of the dispersant, gel material and solubilizer in the dispersion does not exceed 0.5%.

[0070] Optionally, the dispersant is selected from at least one of polyvinylpyrrolidone (PVP), gum arabic and gelatin.

[0071] Optionally, the gel material is selected from at least one of gum arabic (HLB value 8) and gelatin (HLB value 9.8).

[0072] Optionally, the gel material consists of 1.5 to 2 parts of gum arabic and 1 to 1.5 parts of gelatin, by weight.

[0073] Optionally, the solubilizing agent is selected from at least one of sodium oleate, polysorbate 80 and propylene glycol.

[0074] S3. Prepare base solution

[0075] Under stirring conditions of 350-450 rpm (eg, 350 rpm, 400 rpm, or 450 rpm), the seed solution and the dispersion solution are mixed and stirred for 25-35 s (eg, 25 s, 30 s, or 35 s) to obtain a base solution.

[0076] Specifically, the seed solution and the dispersion solution are prepared according to the following ingredients: the concentration of the nanosilver particle seed is 0.009-0.455%wt, the concentration of the dispersant is 0.09-0.273%wt, the concentration of the gel material is 0.09-0.315%wt, and the concentration of the solubilizer is 0.036-0.09%wt.

[0077] For example, 10 g of seed solution with a mass percentage of 0.1-5% of nano silver particle seed crystals and 100 g of the above dispersion solution are mixed to obtain a base solution, in which the mass fraction of the nano silver particle seed crystals is 0.009-0.455%.

[0078] S4. Reduction reaction

[0079] Dissolve the silver salt in deionized water to obtain a silver salt solution with a mass concentration of 10% to 30% (eg, 1%, 20% or 30%).

[0080] Optionally, the silver salt is selected from at least one of silver nitrate, silver nitrate, silver chloride and silver acetate;

[0081] The reducing agent is dissolved in deionized water to obtain a reducing agent solution with a concentration of 10% to 15% (eg, 10%, 12% or 15%).

[0082] Optionally, the reducing agent is selected from at least one of ascorbic acid, sodium ascorbate and glucose.

[0083] The silver salt solution and the reducing agent solution are injected into the bottom liquid in parallel through a peristaltic pump. During this process, the rotation speed of the reaction kettle is increased to 550-650 rpm (eg, 550 rpm, 600 rpm or 650 rpm).

[0084] Preferably, the silver salt is silver nitrate, and the mass concentration of silver nitrate is 8-12% (for example, 8%, 10% or 12%); when injecting, the parallel addition time of the silver nitrate solution and the reducing agent solution is set to T, in min, T=(0.01-0.05) / C*60, for example, 0.01 / C*60, 0.03 / C*60 or 0.05 / C*60, where C is the mass concentration of the silver salt solution.

[0085] After the silver salt solution is added, the metal chelating agent is added immediately, and the reaction is continued for 30 to 90 seconds (eg, 30 seconds, 60 seconds or 90 seconds) to terminate the reaction and obtain a slurry.

[0086] Optionally, the mass ratio of the added amount of the metal chelating agent to the theoretical target generated nano silver powder is 0.1% to 0.5% (eg, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%).

[0087] Optionally, the metal chelator is at least one of sodium ethylenediaminetetraacetate, aminotriacetic acid, and ethylenediaminetetraacetic acid (EDTA).

[0088] S5. Extraction of Nanosilver

[0089] Add a surfactant to the slurry, and continue stirring and mixing at a rotation speed of 300 to 800 rpm (eg, 300 rpm, 500 rpm, or 800 rpm) for 2 to 6 min (2 min, 4 min, or 6 min).

[0090] After stirring, the mixture is allowed to stand for at least 30 minutes to allow the nanosilver ions to settle in the reaction container. The supernatant in the container is discarded, and then an ethanol solution is added to the container to clean the nanosilver in the reaction container. After repeating the operation at least twice, the wet powder obtained by cleaning is placed in an oven at 30 to 40° C. (e.g., 30° C., 35° C. or 40° C.) and dried to obtain nano-scale silver powder.

[0091] Optionally, the surfactant is a long-chain carboxylic acid; optionally, the long-chain carboxylic acid is selected from at least one of stearic acid and lauric acid.

[0092] Optionally, the mass ratio of the added amount of the surfactant to the theoretically synthesized nano-silver powder is 0.1% to 2% (eg, 0.1%, 0.5%, 1%, 1.5% or 2%).

[0093] Since the proportion of gel in the slurry is low and the viscosity is low, in this step, the surfactant stearic acid is added to the slurry so that the nanosilver generated by the reaction can be smoothly settled to the bottom of the container. The process is simple to operate and realizes the convenient separation of nanosilver. After separation, the nanosilver can be purified by washing with an ethanol solution. The purification method is also simple, and there will be no pollution to the nanosilver and no loss of nanosilver.

[0094] It should be noted that in this step, if a surfactant is not added, it is difficult to achieve automatic precipitation of nanosilver. The nanosilver in the slurry can only be extracted by high-speed centrifugation, which reduces the convenience.

[0095] Example 1

[0096] Take 0.5 g of silver nitrate, add 1.0 g of oleylamine, and then add 8.5 g of PEG 2000 solution, heat and ripen in a constant temperature oil bath at 120° C. for 30 min to obtain 10.0 g of brown seed solution containing nano-silver for standby use, and the mass percentage of nano-silver seeds in the seed solution is 3.175%;

[0097] Weigh 15.8 g of silver nitrate and 142.2 g of deionized water, stir until completely dissolved, and obtain 158 g of 10% silver nitrate solution, theoretically generating 10 g of silver powder;

[0098] Weigh 10.0 g of sodium ascorbate and 90.0 g of deionized water, stir until completely dissolved, and obtain 100 g of a reducing agent solution with a mass fraction of 10%;

[0099] Weigh 0.2 g of dispersant PVP K30 powder, 0.15 g of gum arabic, 0.1 g of gelatin, and 0.05 g of sodium oleate, which together account for 5% of the theoretically generated silver powder, of which PVP, gum arabic, gelatin, and sodium oleate account for 2%, 1.5%, 1%, and 0.5%, respectively, and then add 99.5 g of deionized water, stir until completely dissolved, and obtain 100 g of a solution with a mass fraction of 0.2% of the dispersant, and then disperse it by high-speed shearing in a disperser, and fully mix to obtain a dispersion;

[0100] At a rotation speed of 400 rpm, 10 g of the seed solution was added to the dispersion and mixed and stirred for 30 seconds to obtain a base solution, in which the mass fraction of the nanosilver particle seed in the base solution was 0.289%;

[0101] The silver nitrate solution and the reducing agent solution are added to the bottom solution in parallel through a peristaltic pump, and the speed is increased to 600 rpm at the same time, and the parallel addition time is set to 10 minutes;

[0102] After the silver nitrate solution is added, 0.05 g of metal chelating agent sodium ethylenediaminetetraacetate (sodium EDTA) is immediately added, which is 0.5% of the theoretical mass of the generated silver powder, and the reaction is continued for 1 min to obtain a slurry;

[0103] Add 0.5 g of surfactant long-chain stearic acid to the slurry, which is 5% of the theoretical mass of the generated silver powder, and continue stirring for 4 min;

[0104] After stirring, the mixture was allowed to stand for 30 minutes. After the nano-sized silver particles settled by themselves, the supernatant was discarded. A 70% ethanol solution was added to the obtained solid for washing. The operation was repeated twice to obtain a wet powder. The wet powder was placed in an oven at 35°C and dried to obtain nano-sized silver powder.

[0105] Example 2

[0106] This embodiment is basically the same as Embodiment 1, except that:

[0107] Weigh 0.1 g of dispersant PVP K30 powder, 0.2 g of gum arabic, 0.15 g of gelatin, and 0.05 g of sodium oleate, totaling 5% of the theoretical mass of the generated silver powder, of which PVP, gum arabic, gelatin, and sodium oleate account for 1%, 2%, 1.5%, and 0.5%, respectively. Add 99.5 g of deionized water and stir until completely dissolved to obtain a solution with a dispersant mass fraction of 0.1%. Disperse the solution by high-speed shearing in a disperser and mix thoroughly to obtain a dispersion.

[0108] Example 3

[0109] This embodiment is basically the same as Embodiment 1, except that:

[0110] Take 0.1g of silver nitrate, add 0.2g of oleylamine, and then add 9.7g of PEG 2000 solution, heat and ripen in a constant temperature oil bath at 120°C for 30min to obtain 10.0g of brown seed solution containing nano-micron silver for standby use, wherein the mass fraction of nano silver particle seed crystals is 0.635%;

[0111] Weigh 15.8 g of silver nitrate and 142.2 g of deionized water, stir until completely dissolved, and obtain 158 g of 10% silver nitrate solution, theoretically generating 10 g of silver powder;

[0112] Weigh 10.0 g of sodium ascorbate and 90.0 g of deionized water, stir until completely dissolved, and obtain 100 g of a reducing agent solution with a mass fraction of 10%;

[0113] Weigh 10.0 g of sodium ascorbate and 90.0 g of deionized water, stir until completely dissolved, and obtain 100 g of a reducing agent solution with a mass fraction of 10%;

[0114] Weigh 0.2 g of dispersant PVP K30 powder, 0.15 g of gum arabic, 0.1 g of gelatin, and 0.05 g of sodium oleate, which together account for 5% of the theoretical target of generating nano-silver powder, wherein PVP, gum arabic, gelatin, and sodium oleate account for 2%, 1.5%, 1%, and 0.5%, respectively, and then add 99.5 g of deionized water, stir until completely dissolved, and obtain 100 g of a solution with a mass fraction of 0.2% of the dispersant, and then disperse it by high-speed shearing in a disperser, and fully mix to obtain a dispersion;

[0115] At a rotation speed of 400 rpm, the seed solution was added to the dispersion solution and mixed and stirred for 30 seconds to obtain a base solution, in which the mass fraction of the nanosilver particle seed was 0.058%;

[0116] The silver nitrate solution and the reducing agent solution are added to the bottom solution in parallel through a peristaltic pump, and the speed is increased to 600 rpm at the same time, and the parallel addition time is set to 10 minutes;

[0117] After the silver nitrate solution is added, 0.05 g of metal chelating agent sodium ethylenediaminetetraacetate (sodium EDTA) is immediately added, which is 0.5% of the theoretical mass of the generated silver powder, and the reaction is continued for 1 min to obtain a slurry;

[0118] Add 0.5 g of surfactant long-chain stearic acid to the slurry, which is 5% of the theoretical mass of the generated silver powder, and continue stirring for 4 min;

[0119] After stirring, the mixture was allowed to stand for 30 minutes. After the nano-sized silver ions settled by themselves, the supernatant was discarded. A 70% ethanol solution was added to the obtained solid for washing. The operation was repeated twice to obtain a wet powder. The wet powder was placed in an oven at 35°C and dried to obtain nano-sized silver powder.

[0120] Example 4

[0121] This embodiment is substantially the same as embodiment 1, except that the metal chelating agent is replaced by aminotriacetic acid instead of sodium EDTA.

[0122] Example 5

[0123] This embodiment is substantially the same as embodiment 1, except that the solubilizing agent is replaced by polysorbate 80 instead of sodium oleate.

[0124] Example 6

[0125] This embodiment is basically the same as Embodiment 1, except that:

[0126] Take 0.0157g of silver nitrate, add 0.2g of oleylamine, and then add 9.7853g of PEG 2000 solution, heat and ripen in a constant temperature oil bath at 120°C for 30min to obtain 10.0g of brown seed solution containing nano-silver for standby use, and the mass percentage of nano-silver seeds in the seed solution is 0.1%;

[0127] Weigh 0.1 g of dispersant PVP K30 powder, 0.05 g of gum arabic, 0.05 g of gelatin, and 0.1 g of sodium oleate, which together account for 3% of the theoretically generated silver powder, of which PVP, gum arabic, gelatin, and sodium oleate account for 1%, 0.5%, 0.5%, and 1%, respectively, and then add 99.7 g of deionized water, stir until completely dissolved, and obtain 100 g of a solution with a dispersant mass fraction of 0.1%, and then disperse it through a disperser with high-speed shearing, and fully mix to obtain a dispersion;

[0128] In the prepared base solution, the concentration of the nano silver particle seed crystals is 0.009%wt, the concentration of the dispersant is 0.09%wt, the concentration of the gel material is 0.09%wt, and the concentration of the solubilizer is 0.09%wt.

[0129] Example 7

[0130] This embodiment is basically the same as Embodiment 1, except that:

[0131] Take 0.785g of silver nitrate, add 1.0g of oleylamine, and then add 8.215g of PEG 2000 solution, heat and ripen in a constant temperature oil bath at 120°C for 30min to obtain 10.0g of brown seed solution containing nano-silver for standby use, and the mass percentage of nano-silver seeds in the seed solution is 5%;

[0132] Weigh 0.3 g of dispersant PVP K30 powder, 0.1 g of gum arabic, 0.05 g of gelatin, and 0.04 g of sodium oleate, which together account for 4.9% of the theoretically generated silver powder, of which PVP, gum arabic, gelatin, and sodium oleate account for 3%, 1%, 0.5%, and 0.4%, respectively, and then add 99.51 g of deionized water, stir until completely dissolved, and obtain 100 g of a solution with a mass fraction of 0.2% of the dispersant, and then disperse it by high-speed shearing in a disperser, and fully mix to obtain a dispersion;

[0133] In the prepared base solution, the concentration of the nano silver particle seed crystals was 0.455%wt, the concentration of the dispersant was 0.273%wt, the concentration of the gel material was 0.137%wt, and the concentration of the solubilizer was 0.036%wt.

[0134] Comparative Example 1

[0135] This comparative example is substantially the same as Example 1, except that the dispersion does not include a dispersant.

[0136] Comparative Example 2

[0137] This comparative example is substantially the same as Example 1, except that the dispersion does not include sodium oleate.

[0138] Comparative Example 3

[0139] This comparative example is substantially the same as Example 1, except that no metal chelating agent is added after the silver nitrate solution is added.

[0140] Comparative Example 4

[0141] This comparative example is basically the same as Example 1, except that the amount of sodium oleate added to the dispersion is too high, 0.15 g, and the mass ratio of the theoretical target nano silver powder is 1.5%, which exceeds the range required by the present application.

[0142] Experimental example

[0143] (1) Take SEM images of the nanosilver prepared in each embodiment, such as Figures 1 to 3 As shown in the figure, it can be seen that the nanosilver prepared in each embodiment of the present application is all nanometer-scale, with good uniformity of particle size distribution, good monodispersity, and almost no agglomeration.

[0144] (2) The particle size of the products obtained in each embodiment and comparative example was measured and recorded in Table 1 and Table 2.

[0145] Table 1 Particle size of the products obtained in each embodiment

[0146]

[0147] Table 2 Particle size of the products obtained in each comparative example

[0148] Group Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Particle size μm 1.35 1.65 2.18 4.24

[0149] It can be seen from the particle size data in Table 1 and Table 2 that the particle size of the particles prepared in each embodiment is in the range of 200 to 500 nm.

[0150] Comparing Comparative Example 1 and Comparative Example 2 with Example 1, the particle sizes of Comparative Example 1 and Comparative Example 2 are obviously larger, exceeding the nanometer level, indicating that the dispersant and solubilizer are indispensable in the base liquid;

[0151] Comparing Comparative Example 3 with Example 1, the particle size of Comparative Example 3 is obviously larger, indicating that if the metal chelating agent is not added after the silver salt is dissolved and added, the particle size of the obtained particles will be larger;

[0152] Comparing Comparative Example 4 with Example 1, Comparative Example 4 has the largest average particle size, indicating that adding too much solubilizer in the base liquid will cause powder agglomeration, resulting in larger particle size.

[0153] In summary, the preparation method provided in the embodiment of the present invention reduces the amount of gel used, so that the viscosity of the reaction system is significantly reduced, and the difficulty of separation and purification of the obtained nanosilver can be reduced; the entire preparation process is simple. The average particle size of the obtained nanosilver is between 200-500nm, the monodispersity is good, and it has broad application prospects in the field of conductive paste.

[0154] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing nano silver, characterized in that: include: Providing a base liquid, wherein the base liquid includes nano silver particle seed crystals, a dispersant, a gel material and a solubilizer; Adding a silver salt solution and a reducing agent solution to the base liquid in parallel, during the adding process, the silver ions are reduced to silver element, and after the silver salt solution is added, adding a metal chelating agent to the reaction system for full reaction; After the reaction is completed, a slurry is obtained, and solid nanosilver is extracted from the slurry; In the base liquid, the particle size of the nano-silver particles is 20-50 nm, and the mass ratio of the nano-silver powder to the theoretical target is 0.1%-5.0%; the mass ratio of the dispersant to the theoretical target is 1-3%, the mass ratio of the gel material to the theoretical target is 1-3.5%, and the mass ratio of the solubilizer to the theoretical target is 0.4-1.0%; The solubilizing agent is selected from at least one of sodium oleate, polysorbate 80 and propylene glycol.

2. The preparation method according to claim 1, characterized in that: The method for extracting solid nanosilver from the slurry comprises: adding a surfactant to the slurry and mixing; The solution was allowed to settle, the upper clear liquid was poured out, and the lower solid layer was washed and dried to obtain the nano silver.

3. The preparation method according to claim 2, characterized in that: Also includes at least one of the following features (1) to (4): (1) The surfactant is a long-chain carboxylic acid; optionally, the long-chain carboxylic acid is selected from at least one of stearic acid and lauric acid; (2) The mass ratio of the added amount of the surfactant to the theoretical target of generating nano silver powder is 0.1% to 2%; (3) adding a surfactant to the slurry and mixing the slurry at a speed of 300 to 800 rpm for 2 to 6 minutes; (4) The lower layer of solid is cleaned by using an ethanol solution.

4. The preparation method according to claim 1, characterized in that: The metal chelating agent is selected from at least one of sodium ethylenediaminetetraacetate, aminotriacetic acid, and ethylenediaminetetraacetic acid; Optionally, the dispersant is selected from at least one of polyvinyl pyrrolidone, gum arabic and gelatin, preferably polyvinyl pyrrolidone.

5. The preparation method according to claim 1, characterized in that: Also includes at least one of the following features (1) to (3): (1) The mass ratio of the added amount of the metal chelating agent to the theoretical target generated nano silver powder is 0.1% to 0.5%; (2) The total mass of the solute in the base solution is less than or equal to 5% of the mass of the theoretically synthesized silver powder; (3) The concentration of the nanosilver particle seed crystals in the base liquid is 0.009-0.455%wt, the concentration of the dispersant is 0.09-0.273%wt, the concentration of the gel material is 0.09-0.315%wt, and the concentration of the solubilizer is 0.036-0.09%wt.

6. The preparation method according to claim 1, characterized in that: The silver salt in the silver salt solution is selected from at least one of silver nitrate, and; Optionally, the silver salt solution is silver nitrate, and the mass concentration of the silver nitrate is 8-30%; Optionally, the parallel addition time of the silver salt solution and the reducing agent solution is set to T, in units of min, T=(0.01-0.05) / C*60, wherein C is the mass concentration of the silver salt solution.

7. The preparation method according to claim 1, characterized in that The reducing agent in the reducing agent solution is selected from at least one of ascorbic acid, sodium ascorbate, glucose and sodium borohydride.

8. The preparation method according to claim 1, characterized in that: The reaction time after adding the metal chelating agent is 30 to 90 seconds.

9. The preparation method according to claim 1, characterized in that: The gel material is selected from at least one of gum arabic and gelatin; Optionally, the gel material consists of 1.5 to 2 parts of gum arabic and 1 to 1.5 parts of gelatin, by weight.

10. The preparation method according to claim 1, characterized in that: The preparation method of the base liquid comprises: The silver salt, oleylamine and polyethylene glycol 2000 are mixed and stirred to obtain a mixed solution; placing the mixed solution in an environment of 100 to 160° C. and ripening for 25 to 35 minutes to obtain a seed solution containing the nano-silver particle seed crystals; Mixing the dispersant, the gel material, the solubilizer and deionized water to obtain a dispersion; Mixing the seed solution with the dispersion solution to obtain the base solution; Optionally, the silver salt is silver nitrate; Optionally, in the mixed solution, the mass percentage of silver ions is 0.1-5%, the mass percentage of oleylamine is 2-10%, and the mass percentage of polyethylene glycol 2000 is 85-97%; Optionally, in the dispersion, the mass percentage of the dispersant is 0.1-0.3%, the mass percentage of the gel material is 0.1-0.35%, the mass percentage of the solubilizer is 0.04-0.1%, and the total mass percentage of the dispersant, the gel material and the solubilizer in the dispersion does not exceed 0.5%.

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