A monodisperse silver powder and its preparation method and application

Abstract

The present invention discloses a monodisperse silver powder and a preparation method and application thereof, and relates to the technical field of metal conductive powder. The D90 particle size, D50 particle size and D10 particle size of the monodisperse silver powder satisfy: X=(D90-D10) / D50, and X is 0.45-0.8. By limiting the particle size distribution width, the particle size distribution of the silver powder is narrow, the particle size distribution has high uniformity, and uniform dispersion can be achieved in the subsequent formation of slurry, which can meet the production requirements of high-density conductive patterns and thin-line electrodes, and is conducive to forming a conductive film with good conductivity.

Description

Technical Field

[0001] The present invention relates to the technical field of metal conductive powders, and in particular to monodisperse silver powder, a preparation method thereof, and applications thereof. Background Art

[0002] Silver powder is widely used in the photovoltaic field due to its excellent conductivity and oxidation resistance. Typically, it is mixed with glass frit to form a silver paste, which is then coated or printed onto electrodes or circuits on a substrate. The paste is then heated, cured, or calcined to sinter the silver particles together, forming a conductive film on the electrodes or circuits. The silver powder connects the silver particles, creating an electrical connection. However, current conductive films lack uniformity in both thickness and girth, which in turn affects their conductivity. This makes them unable to meet the demands of higher-density conductive patterns and thinner electrodes, driven by the shrinking size of electronic components. Summary of the Invention

[0003] The main purpose of the present invention is to provide a monodisperse silver powder and its preparation method and application, so as to solve the problem in the prior art that the silver powder has a wide particle size distribution, which makes it difficult to meet the requirements of high-density and fine-line production.

[0004] To achieve the above object, according to one aspect of the present invention, a monodisperse silver powder is provided, wherein the D90 particle size, D50 particle size and D10 particle size of the silver powder satisfy the following conditions: X = (D90-D10) / D50, where X is 0.45-0.8.

[0005] Furthermore, the D50 particle size of the monodisperse silver powder is 100 nm to 5 μm, the D90 particle size is 300 nm to 5 μm, and the D10 particle size is 90 nm to 500 nm.

[0006] Furthermore, the tap density of the monodisperse silver powder is 4~6g / cm 3 .

[0007] According to a second aspect of the present invention, there is provided a method for preparing monodisperse silver powder, comprising the following steps:

[0008] S1, mixing a first silver salt, a first ammonia solution, a first reducing agent and water to obtain a silver core solution;

[0009] S2, mixing the silver core solution, the first dispersant and the first solvent to obtain a first reaction solution;

[0010] S3, mixing a second silver salt, a second ammonia solution, a surfactant, and a second solvent to obtain a second reaction solution;

[0011] S4, mixing the second reducing agent, the second dispersant and the third solvent to obtain a third reaction solution;

[0012] S5, adding the second reaction liquid and the third reaction liquid to the first reaction liquid at the same rate to obtain a reaction liquid; wherein the first rate is equal to the second rate;

[0013] S6, filtering, washing, and drying the reaction liquid in sequence to obtain silver powder.

[0014] Furthermore, the second reaction liquid and the third reaction liquid are added to the first reaction liquid at a rate of 1% / min to 40% / min of the reaction liquid volume.

[0015] Furthermore, the molar ratio of the first silver salt, NH3 in the first ammonia water, and the first reducing agent is (0.1~1):(0.1~5):(1~5); and / or, the molar ratio of the first silver salt to the first dispersant is (5~50):(0.05~1); and / or, the molar ratio of the second silver salt, NH3 in the second ammonia water, the surfactant, the second reducing agent, and the second dispersant is (2.4~24):(2.4~120):(0.1~1):(24~120):(0.001~0.01); and / or, the molar ratio of the first silver salt to the second silver salt is (0.005~0.5):1.

[0016] Furthermore, the concentration of the first dispersant in the first reaction solution is 0.25×10 -4 ~1.25×10 -2 mol / L; and / or, the concentration of the second silver salt in the second reaction solution is 0.06~1.20mol / L; and / or, the concentration of the surfactant in the second reaction solution is 0.2×10 -3 ~0.12mol / L; and / or, the concentration of the second reducing agent in the third reaction solution is 0.6~3.0mol / L; and / or, the concentration of the second dispersant in the third reaction solution is 0.25×10 -4 ~1.25×10 -2 mol / L.

[0017] Further, the first silver salt and the second silver salt are each independently selected from at least one of silver nitrate, silver carbonate, silver oxalate, silver nitrite, silver chlorate, silver acetate, silver propionate, silver butyrate, silver lactate, silver bromide, silver chloride, and silver citrate; and / or, the first reducing agent and the second reducing agent are each independently selected from at least one of glucose, ascorbic acid, formaldehyde, hydrazine hydrate, sodium borohydride, sodium hypophosphite, hypophosphorous acid, citric acid, formic acid, and hydrazine hydrate; and / or, the first dispersant and the second dispersant are each independently selected from polyvinylpyrrolidone K1 0. at least one of polyvinyl pyrrolidone K30, polyvinyl pyrrolidone K90, polyethylene glycol, polyacrylic acid, polyvinyl alcohol, gelatin, and gum arabic; and / or, a surfactant selected from at least one of polyoxyethylene stearate-30, polyoxyethylene stearate-40, triethanolamine oleate, sorbitan laurate, polyoxyethylene lauryl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monopalmitate, and polyoxyethylene sorbitan stearate.

[0018] Furthermore, the first solvent is selected from water or an alcohol solvent, and the alcohol solvent includes at least one of methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol, sec-butanol, pentanol, isopentanol, β-phenylethanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and propylene glycol monomethyl ether; and / or, the second solvent and the third solvent are each independently a diol solvent, and the diol solvent includes at least one of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,6-hexanediol, diethylene glycol, and dipropylene glycol.

[0019] Preferably, the first silver salt and the second silver salt are silver nitrate respectively; the first reducing agent and the second reducing agent are glucose respectively; the first dispersant and the second dispersant are polyvinyl alcohol respectively; the first solvent is water; the surfactant is polyoxyethylene lauryl ether; the second solvent and the third solvent are ethylene glycol respectively.

[0020] Furthermore, in S6, the reaction liquid is filtered and the solid phase is collected; the solid phase is washed with a fourth solvent, wherein the fourth solvent is selected from at least one of water, methanol, ethanol, isopropanol, ether, ethyl acetate, propylene oxide, hexane, toluene, xylene, styrene, chloroform, acetone, and methyl butyl ketone; and / or the drying temperature is 45-85° C. and the time is ≥10 h.

[0021] According to a third aspect of the present invention, a conductive silver paste is provided. The conductive silver paste comprises the silver powder provided by the first aspect or the silver powder prepared by the preparation method provided by the second aspect.

[0022] Furthermore, the conductive silver paste can be used to process metal wires ≥1μm, with the printed line width fluctuation being <5% and the printed line qualification rate being ≥99.0%.

[0023] According to a fourth aspect of the present invention, there is provided a conductive film, which is formed by treating the conductive silver paste of the third aspect with ≥150 o The resistivity of the conductive film is ≤0.5 mΩ·mm.

[0024] The implementation of the present invention has at least the following beneficial effects:

[0025] The silver powder provided by the present invention has a narrow particle size distribution and high particle size distribution uniformity by limiting the range of the particle size distribution width X. The silver powder can be uniformly dispersed in the subsequent slurry formation, meeting the production requirements of high-density conductive patterns and thin-line electrodes, improving the line qualification rate and reducing line width fluctuations, and facilitating the formation of a conductive film with good conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a SEM image of the silver powder in Example 1 of the present invention;

[0027] Figure 2 This is the SEM image of the silver powder in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0028] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0029] The existing silver powder suffers from a wide particle size distribution. To address this issue, the first aspect of the present invention provides a monodisperse silver powder, wherein the D90, D50, and D10 particle sizes of the monodisperse silver powder satisfy the following formula: X = (D90 - D10) / D50, where X is 0.45 to 0.8.

[0030] In the present invention, D10 particle size is the particle size corresponding to the 10% cumulative volume distribution percentage of the sample, D50 particle size is the particle size corresponding to the 50% cumulative volume distribution percentage of the sample, and D90 particle size is the particle size corresponding to the 90% cumulative volume distribution percentage of the sample. The particle size distribution width (SPAN) is denoted as X and is calculated according to the formula (D90 - D10) / D50.

[0031] X is in the range of 0.45 to 0.8, for example, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or any two thereof. By limiting the particle size distribution width SPAN value of the silver powder to an appropriate range, the particle size distribution width is more concentrated, the narrower the particle size distribution range, and the more uniform the particle size distribution.

[0032] The particle size distribution width range of silver powder is related to the qualified rate and line width fluctuation of the circuit formed by the slurry formed by it during the application process. If the particle size distribution width range is wide, it is easy to cause breakpoints in the product pattern during the screen printing process. The particle size distribution width range of silver powder is related to the dispersibility of the slurry formed by it, the density and width of the circuit and the conductivity of the conductive film. If the particle size distribution width range is wide, it is easy to cause breakpoints in the product pattern during the screen printing process, the qualified rate of the circuit is low, the line width fluctuation is large, and during the sintering process, large holes will appear, resulting in large contact resistance, affecting conductivity. The present invention limits the particle size distribution width to the above range, so that the particle size distribution of silver powder is narrower and the particle size distribution uniformity is high, which helps to improve its dispersibility in the slurry, can meet the requirements of high density of conductive patterns and thin line of electrodes, and form a conductive film with good conductivity.

[0033] According to the research of the present invention, by limiting the width of its particle size distribution, the silver powder particle size distribution is narrow and the particle size distribution uniformity is high. It can be evenly dispersed in the subsequent formation of slurry, which can meet the requirements of high density of conductive patterns and thin lines of electrodes, and also help to form a conductive film with good conductivity.

[0034] The D50 particle size of the monodisperse silver powder is related to the density of the formed conductive pattern and the thickness of the electrode. In some embodiments, D50 is 100nm~5μm. The present invention limits the D50 particle size of the monodisperse silver powder to 100nm~5μm, that is, the average particle size of the monodisperse silver powder is 100nm~5μm. The average particle size is suitable and can meet the production requirements of conductive patterns or electrodes of different thicknesses and thicknesses. By limiting the D50 particle size to 100nm~5μm, the present invention can select silver powders of different D50 particle sizes according to actual needs, realizing the production of conductive patterns with different densities and electrodes with different thicknesses, and in particular, can realize the production of high-density conductive patterns and thin-line electrodes. Preferably, D50 is 120 nm to 2 μm, that is, the D50 particle size of the silver powder is 120 nm to 2000 nm, for example, 120 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1500 nm, 2000 nm or a range consisting of any two thereof.

[0035] In some embodiments, the monodisperse silver powder has a D90 particle size of 300 nm to 5 μm and a D10 particle size of 90 nm to 500 nm, such as 90 nm, 100 nm, 120 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or a range consisting of any two thereof. Preferably, the monodisperse silver powder has a D90 particle size of 300 nm to 2.5 μm, such as 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1500 nm, 2000 nm, 2500 nm, or a range consisting of any two thereof.

[0036] The greater the tap density of the powder particles, the less likely they are to agglomerate. In some embodiments, the tap density of the monodisperse silver powder is 4-6 g / cm 3 , preferably 4.6~5.2g / cm 3 By limiting the tap density of the monodisperse silver powder to the above range, it is ensured that the silver powder does not agglomerate and has good dispersion, which is conducive to improving the dispersibility of the slurry formed therefrom.

[0037] A second aspect of the present invention provides a method for preparing monodisperse silver powder, comprising the following steps:

[0038] S1, mixing a first silver salt, a first ammonia solution, a first reducing agent and water to obtain a silver core solution;

[0039] S2, mixing the silver core solution, the first dispersant and the first solvent to obtain a first reaction solution;

[0040] S3, mixing a second silver salt, a second ammonia solution, a surfactant, and a second solvent to obtain a second reaction solution;

[0041] S4, mixing the second reducing agent, the second dispersant and the third solvent to obtain a third reaction solution;

[0042] S5, adding the second reaction liquid and the third reaction liquid to the first reaction liquid at the same rate to obtain a reaction liquid;

[0043] S6, filtering, washing, and drying the reaction liquid in sequence to obtain silver powder.

[0044] In the prior art, silver powder is mostly produced by adding a reducing agent dropwise to a silver precursor solution, or by mixing the reducing agent with the silver precursor solution in a single reaction. In these methods, silver salt reduction, nucleation, and growth occur simultaneously. Specifically, the method of producing silver powder by adding a reducing agent dropwise to a silver precursor solution is prone to localized agglomeration and growth of silver elemental particles due to the high concentration of silver salt in the initial reaction stage. The resulting particles are usually oversized, irregular in shape, and have an uneven particle size distribution. The surface is not effectively coated with the dispersant ligand, which has a significant impact on the dispersibility and stability of the conductive silver paste. The method of producing silver powder by mixing the reducing agent with the silver precursor solution in a single reaction stage, however, results in an uneven particle size distribution and poor particle morphology due to the excessively fast initial reaction rate, which is detrimental to the uniform dispersion of the conductive silver paste. The preparation method of silver powder provided by the present invention controls the growth of silver by controlling parameters such as the addition sequence and the addition speed, and by a method of first nucleating and then synchronously reducing and growing. The morphology, particle size and dispersibility of the silver powder can be controlled to obtain silver powder with uniform and controllable particle size, good dispersibility and few surface impurities. In addition, the reaction is mild and the yield is high, which can achieve mass production.

[0045] The agglomeration of ultrafine powders is mainly caused by the mutual attraction between particles, so to reduce agglomeration, the repulsive force between particles must be increased. The present invention introduces a surfactant into the preparation system, wherein the surfactant can be adsorbed on the surface of the particles and provide repulsive force through electrostatic repulsion or by means of steric hindrance. For example, the surfactant is coated on the surface of the newly generated particles to act as a coating film to isolate the particles from each other, or the ionic surfactant makes the particles have the same charge, repelling each other, inhibiting the occurrence of agglomeration and thus playing a dispersing role; this coating can also inhibit the growth of the particles, that is, controlling the size and morphology of the particles. In addition, the agglomerates in the reaction solution will produce microcracks under the action of mechanical force, which are easily healed by the action of their own molecular forces. The surfactant molecules can also automatically penetrate into the microcracks or be adsorbed on the crack walls to prevent the microcracks from healing, and can also enlarge the cracks or break the agglomerates into fragments by external force. The present invention introduces a surfactant into the preparation process of ultrafine powders to act as a protective agent or dispersant, and through the mutual cooperation between the various steps, it helps to prepare silver powder particles with good dispersibility and narrow particle size distribution.

[0046] Specifically, in S1, the first silver salt can be mixed with the first part of water, and the silver salt (such as silver nitrate AgNO3) will dissolve in the water to form silver ions, thereby obtaining a silver salt solution; the first ammonia water can be mixed with the second part of water to form an ammonia solution; the reducing agent (such as glucose, formaldehyde, etc.) can be mixed with the third part of water to form a reducing agent solution; and then the ammonia solution can be added to the silver salt solution, and the ammonia water can react with the silver ions to form a silver ammonia complex ([Ag(NH3)2] +); a reducing agent solution is added thereto, where the reducing agent undergoes a redox reaction with the silver ammonia complex, reducing the silver ions to silver atoms; the silver atoms form silver nuclei in the solution, yielding a silver nucleus solution. The concentration of the first silver salt in the silver salt solution is 0.0006 to 0.06 mol / L, and the concentration of the first reducing agent in the reducing agent solution is 0.03 to 0.3 mol / L.

[0047] In the preparation method of the present invention, the first reaction liquid is a mother liquor, the second reaction liquid is a silver ion solution containing a surfactant, and the third reaction liquid is a reducing agent solution mainly composed of a reducing agent. In S1, the first silver salt reacts with ammonia water and the first reducing agent to form silver nuclei, which are then converted into the first reaction liquid. In this case, the first reaction liquid is the mother liquor. The second and third reaction liquids in S3 and S4 are added dropwise to the first reaction liquid at the same rate. At this time, the second silver salt in the second reaction liquid is reduced to silver atoms under the action of the reducing agent and simultaneously grows on the silver nuclei. The initial nucleation process in S1 can effectively control the number of nuclei formed in the early stage, and the subsequent addition at the same rate can effectively control the size uniformity during the growth process.

[0048] The present invention does not limit the specific numerical value of S5 rate.For example, in certain embodiments, the second reaction solution and the third reaction solution are respectively added to the first reaction solution at a rate of 1% / min~40% / min of reaction solution volume, it is understood that every 100 parts of the second reaction solution are added to the first reaction solution at a rate of 1 part / min~40 parts / min, and in like manner, every 100 parts of the third reaction solution are added to the first reaction solution at a rate of 1 part / min~40 parts / min. Further, every 1000 parts of the second reaction solution are added to the first reaction solution at a rate of 10 parts / min~400 parts / min, and in like manner, every 1000 parts of the third reaction solution are added to the first reaction solution at a rate of 10 parts / min~400 parts / min, and so on. By controlling the rate within the above range, different batches of silver powders with D50 particle sizes can be prepared.

[0049] Specifically, the second reaction liquid and the third reaction liquid are respectively added to the first reaction liquid at a rate of 1% / min to 40% / min of the volume of the reaction liquid. It can be understood that the addition rate of the second reaction liquid and the third reaction liquid is 1% / min to 40% / min of the volume of the reaction liquid, for example, 1% / min, 2% / min, 5% / min, 10% / min, 20% / min, 30% / min, 40% / min or a range consisting of any two of them.

[0050] By controlling the addition amount of each raw material, the D50 particle size of the silver powder can be effectively controlled. For example, in some embodiments, the molar ratio of the first silver salt, NH3 in the first ammonia water, and the first reducing agent is (0.1-1): (0.1-5): (1-5); and / or, the molar ratio of the first silver salt to the first dispersant is (5-50): (0.05-1); and / or, the molar ratio of the second silver salt, NH3 in the second ammonia water, the surfactant, the second reducing agent, and the second dispersant is (2.4-24): (2.4-120): (0.1-1): (24-120): (0.001-0.01); and / or, the molar ratio of the first silver salt to the second silver salt is (0.005-0.5): 1, for example, 0.005:1, 0.01:1, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, or a range consisting of any two thereof.

[0051] By adjusting the concentration of substances in each reaction solution, the reaction rate can be effectively increased. For example, in some embodiments, the concentration of the first dispersant in the first reaction solution is 0.25×10 -4 ~1.25×10 -2 mol / L; and / or, the concentration of the second silver salt in the second reaction solution is 0.06~1.20mol / L; and / or, the concentration of the surfactant in the second reaction solution is 0.2×10 -3 ~0.12mol / L; and / or, the concentration of the second reducing agent in the third reaction solution is 0.6~3.0mol / L; and / or, the concentration of the second dispersant in the third reaction solution is 0.25×10 -4 ~1.25×10 -2 mol / L.

[0052] The present invention does not limit the specific types of each raw material, and can be adjusted according to actual needs. For example, in some embodiments, the first silver salt and the second silver salt are each independently selected from at least one of silver nitrate, silver carbonate, silver oxalate, silver nitrite, silver chlorate, silver acetate, silver propionate, silver butyrate, silver lactate, silver bromide, silver chloride, and silver citrate; and / or, the first reducing agent and the second reducing agent are each independently selected from at least one of glucose, ascorbic acid, formaldehyde, hydrazine hydrate, sodium borohydride, sodium hypophosphite, hypophosphorous acid, citric acid, formic acid, and hydrazine hydrate; and / or, the dispersant is selected from at least one of polyvinyl pyrrolidone K10, polyvinyl pyrrolidone K30, polyvinyl pyrrolidone K90, polyethylene glycol, polyacrylic acid, polyvinyl alcohol, gelatin, and gum arabic; and / or, the first solvent is selected from water or an alcohol solvent, and the alcohol solvent includes methanol, ethanol, propanol, isopropanol, butanol, etc. At least one of alcohol, isobutanol, tert-butanol, sec-butanol, amyl alcohol, isopentanol, β-phenylethanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and propylene glycol monomethyl ether; and / or, the surfactant is selected from at least one of polyoxyethylene stearate-30, polyoxyethylene stearate-40, triethanolamine oleate, sorbitan laurate, polyoxyethylene lauryl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monopalmitate, and polyoxyethylene sorbitan stearate; the second solvent and the third solvent are each independently selected from a diol solvent, and the diol solvent includes at least one of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,6-hexanediol, diethylene glycol, and dipropylene glycol.

[0053] In S6, the reaction liquid is filtered and the solid phase is collected; the solid phase is washed with a fourth solvent, wherein the fourth solvent is selected from at least one of water, methanol, ethanol, isopropanol, ether, ethyl acetate, propylene oxide, hexane, toluene, xylene, styrene, chloroform, acetone, and methyl butyl ketone; and / or the drying temperature is 45-85°C and the time is ≥10 hours, preferably 10-14 hours. The reaction liquid is filtered to separate the silver precipitate from the solution, the solid phase is collected, and the solid phase is washed with a fourth solvent to remove residual surfactant and dispersant, followed by centrifugation. The product after centrifugation is dried and ground to obtain silver powder.

[0054] Preferably, the first silver salt and the second silver salt are silver nitrate, the first reducing agent and the second reducing agent are glucose, the first dispersant and the second dispersant are polyvinyl alcohol, the first solvent is water, the surfactant is polyoxyethylene lauryl ether, and the second solvent and the third solvent are ethylene glycol. By limiting the above preparation parameters, optimal performance can be achieved.

[0055] A third aspect of the present invention provides a conductive silver paste, which comprises the silver powder provided by the first aspect or the silver powder prepared by the preparation method provided by the second aspect.

[0056] The inclusion of the uniform silver powder provides the conductive silver paste with advantages such as high dispersibility, high uniformity, and minimal agglomeration. If the silver powder in the conductive silver paste is unevenly dispersed, it is very likely to agglomerate, causing the silver powder to settle within the paste, resulting in an uneven conductive silver paste. When this conductive silver paste is used to form wiring layers and electrodes, the silver powder is unevenly distributed within the wiring layers and electrodes, resulting in areas where the silver powder is locally absent, preventing the formation of a conductive film with good conductivity. The inclusion of the narrow silver powder allows the silver powder to be evenly dispersed within the paste, resulting in the formation of a conductive film with uniform thickness and good conductivity, a high line pass rate, and low line width fluctuation.

[0057] In one embodiment of the present invention, the silver powder can be mixed with an organic polymer to form a conductive silver paste, which can then be dried or cured to form a film. In another embodiment of the present invention, the silver powder can be mixed with glass powder to form a conductive silver paste, which can then be directly sintered to form a film. Due to the inclusion of the silver powder, this conductive silver paste is particularly suitable for the production of high-density conductive patterns and thin-line electrodes, and the resulting conductive film exhibits excellent conductivity.

[0058] In some embodiments, the conductive silver paste can be used to process metal wires with a thickness of ≥1 μm, with a printed line width fluctuation of <5% and a printed line qualification rate of ≥99.0%.

[0059] The fourth aspect of the present invention provides a conductive film, which is made of the conductive silver paste of the third aspect after ≥150 o C temperature drying system.

[0060] Due to the inclusion of the conductive silver paste, the conductive film has advantages such as high stability, low resistivity, and good conductivity. In some embodiments, the resistivity of the conductive film is ≤0.5 mΩ·mm.

[0061] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0062] Example 1

[0063] The method for preparing the silver powder of this embodiment comprises the following steps:

[0064] S1, 0.05 g of silver nitrate, 0.08 g of ammonia water, 0.2 g of glucose and 10 mL of water were mixed to obtain a silver core solution; wherein the molar ratio of silver nitrate, NH3 in ammonia water and glucose was 0.295:1.173:1.109;

[0065] S2, mixing the silver core solution and 0.25 g of polyvinyl alcohol (molecular weight 75,000) with 100 mL to obtain a first reaction solution; the molar ratio of silver nitrate in S1 to polyvinyl alcohol in S2 is 44.3:0.5;

[0066] S3, 5 g of silver nitrate, 8 g of ammonia water, 0.5 g of polyoxyethylene lauryl ether (molecular weight 709) and 50 mL of ethylene glycol were mixed to obtain a second reaction solution; the molar ratio of the silver nitrate in S1 to the silver nitrate in S3 was 0.01:1;

[0067] S4, mixing 20 g of glucose, 0.25 g of polyvinyl alcohol, and 50 mL of ethylene glycol to obtain a third reaction solution; wherein the molar ratio of silver nitrate, NH3 in ammonia water, polyoxyethylene lauryl ether, glucose, and polyvinyl alcohol in S3 and S4 is 8.81: 35.23: 0.212: 33.28: 0.001;

[0068] S5, adding the second reaction liquid and the third reaction liquid to the first reaction liquid at a rate of 0.5 mL / min respectively to obtain a reaction liquid;

[0069] S6, filtering the reaction liquid, collecting the solid phase, washing it with ethanol, drying it at 65° C. after centrifugation, and grinding it to obtain silver powder.

[0070] Example 2

[0071] The difference from Example 1 is that in S5, the second reaction liquid and the third reaction liquid are added to the first reaction liquid at a rate of 1 mL / min respectively.

[0072] Example 3

[0073] The difference from Example 1 is that in S5, the second reaction liquid and the third reaction liquid are added to the first reaction liquid at a rate of 5 mL / min respectively.

[0074] Example 4

[0075] The difference from Example 1 is that in S5, the second reaction liquid and the third reaction liquid are added to the first reaction liquid at a rate of 10 mL / min respectively.

[0076] Example 5

[0077] The difference from Example 1 is that in S5, the second reaction liquid and the third reaction liquid are added to the first reaction liquid at a rate of 20 mL / min respectively.

[0078] Example 6

[0079] The difference from Example 1 is that S3 replaces 0.5g of polyoxyethylene lauryl ether with 0.25g of polyoxyethylene lauryl ether, so that the mass ratio of silver nitrate, NH3 in ammonia water, polyoxyethylene lauryl ether, glucose, and polyvinyl alcohol in S3 and S4 is 8.81:35.23:0.106:33.28:0.001.

[0080] Example 7

[0081] The difference from Example 1 is that in S4, 20 g of glucose is replaced by 10 g of glucose, so that the mass ratio of silver nitrate, NH3 in ammonia water, polyoxyethylene lauryl ether, glucose, and polyvinyl alcohol in S3 and S4 is 8.81: 35.23: 0.212: 16.64: 0.001.

[0082] Example 8

[0083] The difference from Example 1 is that in S5, the second reaction liquid and the third reaction liquid are added to the first reaction liquid at a rate of 0.1 mL / min respectively.

[0084] Example 9

[0085] The difference from Example 1 is that in S5, the second reaction liquid and the third reaction liquid are added to the first reaction liquid at a rate of 30 mL / min respectively.

[0086] Comparative Example 1

[0087] The preparation method of the silver powder in this comparative example comprises the following steps:

[0088] S1, 5.05 g of silver nitrate, 8.08 g of ammonia water, 0.25 g of polyoxyethylene lauryl ether, 0.25 g of polyvinyl alcohol and 150 mL of water were mixed to obtain solution A;

[0089] S2, mix 20 g of glucose, 0.25 g of polyvinyl alcohol, and 50 mL of ethylene glycol to obtain solution B;

[0090] S3, adding solution B to solution A, heating to 70°C to obtain a reaction solution;

[0091] S4, filtering the reaction liquid, collecting the solid phase, washing it with ethanol, drying it at 65° C. after centrifugation, and grinding it to obtain the silver powder of this comparative example.

[0092] Comparative Example 2

[0093] The difference from Example 1 is that 0.5 g of polyoxyethylene lauryl ether is not added in S3, and ethanol is replaced by water in S4.

[0094] Comparative Example 3

[0095] The difference from Example 1 is that in S5, the second reaction liquid and the third reaction liquid are added to the first reaction liquid at one time.

[0096] Test example

[0097] 1. Particle size test

[0098] Particle size observation: The size and morphology of the silver powder were characterized using a Phenom scanning electron microscope. The specific operation was as follows: the silver powder was diluted in deionized water or an organic solvent at a mass ratio of 1:500 to obtain a dilution; the dilution was ultrasonically dispersed, a small amount was pipetted and dropped onto the surface of the silicon wafer and heated to remove the solvent; the sample was prepared by spraying gold, and then the size and morphology image information of the silver powder was obtained under a Phenom scanning electron microscope. The particle size distribution width SPAN was calculated according to the formula (D90-D10) / D50, where D10 is the particle size corresponding to the volume cumulative distribution percentage of the sample reaching 10%, D50 is the particle size corresponding to the volume cumulative distribution percentage of the sample reaching 50%, and D90 is the particle size corresponding to the volume cumulative distribution percentage of the sample reaching 90%.

[0099] 2. Tap density test

[0100] Use a tap density meter to measure the tap density of the powder: take an appropriate amount of silver powder and weigh it on an analytical balance to read the mass as m; put the silver powder into the measuring cylinder used by the tap density meter, with the surface of the silver powder level, place the measuring cylinder on the tap density meter, and vibrate it with an amplitude of 3 mm and a vibration frequency of 200 times / min until the volume of the silver powder no longer decreases. Read the volume at this time as v; according to the tap density formula ρ=m / v, obtain the tap density data of the silver powder.

[0101] 3. Print circuit test

[0102] A Nordson EFD dispensing machine was used to test the slurry printing process: 17g of silver powder, 1g of polyurethane, 1g of isophorone, and 1g of diethylene glycol butyl ether acetate were mixed to form a conductive slurry. The prepared conductive slurry was placed in a 3mL material tube and fitted with a 25μm glass needle. The entire device was placed in a booster pen and connected to the dispensing machine. The pressure was adjusted to 20psi, and each line was 100mm long and 40μm wide. The test was considered qualified if 3mL of slurry was printed without any open circuits or blockages. The qualified rate was calculated as the number of qualified lines / total number of lines. A qualified rate of 99.0% or above indicated the performance test passed, while a qualified rate below 99.0% indicated the test failed.

[0103] 4. Line width stability test

[0104] A microscope was used to read the line width data during the printed circuit test. Fifty lines were randomly selected for line width testing, and the line width at three different locations on each line was measured and the average was taken. A line with a width fluctuation of ≤5.0% across the 50 lines was considered stable, while a width fluctuation of >5.0% was considered unstable.

[0105] 5. Conductivity test

[0106] The resistivity of the slurry was tested using a Ruike Weiye FT-340 four-probe square resistance tester: the prepared conductive slurry was coated on a glass substrate using a coating machine and sintered at 200°C for 1 hour under a nitrogen atmosphere to obtain a conductive film with a thickness of 15μm. The thickness of the conductive film sample after high-temperature sintering was measured using a step profiler. The corresponding parameters were set in the square resistance tester, and the four probes were adjusted to press vertically down on the sample and touch lightly. After the reading stabilized, the resistivity data was recorded.

[0107] The test results are shown in Table 1.

[0108] serial number D50 particle size D90 particle size D10 particle size SPAN Tap density Line qualification rate Linewidth fluctuation Resistivity Example 1 250 nm 320 nm 180 nm 0.56 <![CDATA[4.8 g / cm 3 ]]> 99.4% 3.2% 0.09 mΩ·mm Example 2 300 nm 400 nm 200 nm 0.67 <![CDATA[5.0 g / cm 3 ]]> 99.3% 3.7% 0.08 mΩ·mm Example 3 500 nm 600 nm 375 nm 0.45 <![CDATA[4.9 g / cm 3 ]]> 99.5% 3.4% 0.13 mΩ·mm Example 4 800 nm 950 nm 500 nm 0.56 <![CDATA[5.1 g / cm 3 ]]> 99.8% 3.0% 0.07 mΩ·mm Example 5 950 nm 1100 nm 450 nm 0.68 <![CDATA[4.8 g / cm 3 ]]> 99.6% 4.0% 0.13 mΩ·mm Example 6 400 nm 560 nm 250 nm 0.78 <![CDATA[4.7 g / cm 3 ]]> 99.5% 3.9% 0.10 mΩ·mm Example 7 350 nm 450 nm 200 nm 0.71 <![CDATA[4.7 g / cm 3 ]]> 99.4% 4.2% 0.15 mΩ·mm Example 8 120 nm 200 nm 90 nm 0.92 <![CDATA[4.6 g / cm 3 ]]> 99.2% 4.8% 0.24 mΩ·mm Example 9 2000 nm 2500 nm 500 nm 1.00 <![CDATA[4.6 g / cm 3 ]]> 99.1% 4.8% 0.27 mΩ·mm Comparative Example 1 3000 nm 4500 nm 200 nm 1.43 <![CDATA[3.2 g / cm 3 ]]> 63.3% 20.6% 1.06 mΩ·mm Comparative Example 2 2600 nm 3500 nm 450 nm 1.17 <![CDATA[3.4 g / cm 3 ]]> 71.4% 18.9% 0.86 mΩ·mm Comparative Example 3 2200 nm 3300 nm 320 nm 1.22 <![CDATA[4.0 g / cm 3 ]]> 80.9% 15.4% 0.69 mΩ·mm .

[0109] according to Figure 1 It can be seen that the silver powder particles in Example 1 are uniform in size, well dispersed, and have no obvious agglomeration phenomenon. Figure 2 As can be seen, the silver powder in Comparative Example 1 exhibited agglomeration and poor dispersibility. Table 1 shows that the preparation method of the present invention effectively improves the uniformity of the silver powder particle size distribution. The slurry formed from the silver powder can produce a conductive film with a resistivity of 0.5 mΩ·mm or less, and further, a conductive film with a resistivity of 0.27 mΩ·mm or less. Furthermore, the qualified rate of printed circuits using the slurry is 99.1% or higher, and the line width fluctuation is less than 5%. This meets the requirements for higher density conductive patterns and thinner electrodes as electronic components are reduced in size.

[0110] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing monodisperse silver powder, characterized in that: The following steps are involved: S1, mixing a first silver salt, a first ammonia solution, a first reducing agent and water to obtain a silver core solution; S2, mixing the silver core solution, the first dispersant and the first solvent to obtain a first reaction solution; S3, mixing a second silver salt, a second ammonia water, a surfactant and a second solvent to obtain a second reaction solution; S4, mixing the second reducing agent, the second dispersing agent and the third solvent to obtain a third reaction solution; S5, adding the second reaction liquid and the third reaction liquid to the first reaction liquid at the same rate to obtain a reaction liquid; S6, filtering, washing and drying the reaction liquid in sequence to obtain silver powder; In step S5, the second reaction liquid and the third reaction liquid are added to the first reaction liquid at a rate of 1% / min to 40% / min of the reaction liquid volume; The D90 particle size, D50 particle size and D10 particle size of the monodisperse silver powder satisfy the following conditions: X = (D90-D10) / D50, where X is 0.45-0.8; The surfactant is selected from at least one of polyoxyethylene stearate-30, polyoxyethylene stearate-40, sorbitan laurate, polyoxyethylene lauryl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monopalmitate, and polyoxyethylene sorbitan stearate.

2. The preparation method according to claim 1, characterized in that: The D50 particle size of the monodisperse silver powder is 100nm~5μm, the D90 particle size is 300nm~5μm, and the D10 particle size is 90nm~500nm.

3. The preparation method according to claim 1, characterized in that: The tap density of the monodisperse silver powder is 4-6 g / cm 3 .

4. The preparation method according to claim 1, characterized in that: The molar ratio of the first silver salt, NH3 in the first ammonia water, and the first reducing agent is (0.1-1): (0.1-5): (1-5); and / or, the molar ratio of the first silver salt to the first dispersant is (5-50): (0.05-1); and / or, the molar ratio of the second silver salt, NH3 in the second ammonia water, the surfactant, the second reducing agent, and the second dispersant is (2.4-24): (2.4-120): (0.1-1): (24-120): (0.001-0.01); and / or, the molar ratio of the first silver salt to the second silver salt is (0.005-0.5):

1.

5. The preparation method according to claim 1, characterized in that: The concentration of the first dispersant in the first reaction solution is 0.25×10 -4 ~1.25×10 -2 mol / L; and / or, the concentration of the second silver salt in the second reaction solution is 0.06-1.20 mol / L; and / or, the concentration of the surfactant in the second reaction solution is 0.2×10 -3 ~0.12mol / L; and / or, the concentration of the second reducing agent in the third reaction solution is 0.6~3.0mol / L; and / or, the concentration of the second dispersant in the third reaction solution is 0.25×10 -4 ~1.25×10 -2 mol / L.

6. The preparation method according to claim 1, characterized in that: The first silver salt and the second silver salt are each independently selected from at least one of silver nitrate, silver carbonate, silver oxalate, silver nitrite, silver chlorate, silver acetate, silver propionate, silver butyrate, silver lactate, silver bromide, silver chloride, and silver citrate; and / or, the first reducing agent and the second reducing agent are each independently selected from at least one of glucose, ascorbic acid, formaldehyde, hydrazine hydrate, sodium borohydride, sodium hypophosphite, hypophosphorous acid, citric acid, formic acid, and hydrazine hydrate; and / or, the first dispersant and the second dispersant are each independently selected from at least one of polyvinyl pyrrolidone K10, polyvinyl pyrrolidone K30, polyvinyl pyrrolidone K90, polyethylene glycol, polyacrylic acid, polyvinyl alcohol, gelatin, and gum arabic.

7. The preparation method according to claim 1, characterized in that: The first solvent is selected from water or an alcohol solvent, and the alcohol solvent includes at least one of methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol, sec-butanol, amyl alcohol, isopentanol, β-phenylethanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and propylene glycol monomethyl ether; and / or the second solvent and the third solvent are each independently a diol solvent, and the diol solvent includes at least one of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,6-hexanediol, diethylene glycol, and dipropylene glycol.

8. The preparation method according to claim 1, characterized in that: In step S6, the reaction liquid is filtered to collect the solid phase; the solid phase is washed with a fourth solvent, wherein the fourth solvent is selected from at least one of water, methanol, ethanol, isopropanol, ether, ethyl acetate, propylene oxide, hexane, toluene, xylene, styrene, chloroform, acetone, and methyl butyl ketone; and / or the drying temperature is 45-85° C. and the time is ≥10 h.

9. A conductive silver paste, characterized in that: The conductive silver paste comprises silver powder prepared by the preparation method according to any one of claims 1 to 8.

10. The conductive silver paste according to claim 9, characterized in that: The conductive silver paste is used for processing metal wires with a diameter of ≥1 μm, the printed line width fluctuation is <5%, and the printed line qualification rate is ≥99.0%.

11. A conductive film, characterized in that: The conductive film is prepared by drying the conductive silver paste according to claim 9 or 10 at a temperature of ≥150° C., and the resistivity of the conductive film is ≤0.5 mΩ·mm.

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