Flaky silver powder and preparation method thereof

Abstract

The invention discloses flake silver powder and a preparation method thereof, and belongs to the technical field of silver powder. The preparation method of the flaky silver powder comprises the following steps: mixing a reducing agent solution, a template agent solution and a reaction solvent to obtain a first mixed solution; mixing a silver nitrate solution with the first mixed solution to obtain a second mixed solution with initial flake silver powder; and mixing the sintering aid solution with the second mixed solution so as to coat the initial flake silver powder. According to the method, the reducing agent solution and the silver nitrate solution are subjected to one-step reduction reaction in the presence of the template agent solution, the flaky silver powder can be obtained within a short time, the production process is simple and environmentally friendly, and large-scale production is facilitated; after the initial flake silver powder is obtained, the sintering aid solution is combined, and the morphology and sintering activity of the flake silver powder can be effectively controlled. The flaky silver powder obtained through the method is narrow in particle size distribution and uniform in dispersion, the proportion of flaky silver powder is high, and the flaky silver powder can be applied to low-temperature sintering.

Description

Technical Field

[0001] The present invention relates to the technical field of silver powder, and more particularly, to a flaky silver powder and a preparation method thereof. Background Art

[0002] Most of the existing preparation methods of flaky silver powder adopt processes such as multiple reductions, multiple feedings, and ball milling, with many process steps and long time consumption. In terms of the use of reducing agents, highly toxic or highly harmful raw materials such as hydrazine hydrate, formaldehyde, and ferrous salts are usually used, which is not conducive to wastewater treatment and is not beneficial to the environment. In addition, there are usually obvious agglomeration problems between the flaky silver particles prepared by the existing technology, resulting in a large particle size distribution and poor dispersibility of the flaky silver particles.

[0003] In view of this, the present invention is specifically proposed. Summary of the Invention

[0004] The purpose of the present invention is to provide a flaky silver powder and a preparation method thereof to solve or improve the above technical problems.

[0005] The present invention can be implemented as follows:

[0006] In a first aspect, the present invention provides a preparation method of a flaky silver powder, including the following steps:

[0007] Mix a reducing agent solution, a templating agent solution, and a reaction solvent to obtain a first mixed solution;

[0008] Mix a silver nitrate solution with the first mixed solution to obtain a second mixed solution in which initial flaky silver powder is generated;

[0009] Mix a sintering aid solution with the second mixed solution to coat the initial flaky silver powder.

[0010] In an optional embodiment, the reducing agent solution includes an aqueous solution of ascorbic acid;

[0011] In an optional embodiment, based on the molar ratio of the number of electrons transferred in the oxidation-reduction chemical reaction, the dosage ratio of ascorbic acid to silver nitrate is 1.01:1 to 1.15:1.

[0012] In an optional embodiment, the concentration of the aqueous solution of ascorbic acid is 1.05 mol / L to 2.45 mol / L.

[0013] In an optional embodiment, the templating agent used in the templating agent solution includes a first templating agent and a second templating agent;

[0014] Among them, the first templating agent is an acid templating agent, and the second templating agent is a dispersant templating agent.

[0015] In an alternative embodiment, the first templating agent comprises at least one of nitric acid, formic acid, sulfuric acid, and their weak base salts.

[0016] In an alternative embodiment, the second templating agent comprises at least one of Darvan 811, Dispex AA4040, BYK-190, EFKA-4580, 731A, and Solsperse 32000.

[0017] In an alternative embodiment, the dosage of the first templating agent is 1% to 10% of the mass of silver nitrate.

[0018] In an alternative embodiment, the mass concentration of the first templating agent in the templating agent solution is 1% to 10%.

[0019] In an alternative embodiment, the dosage of the second templating agent is 0.2% to 1% of the mass of silver nitrate.

[0020] In an alternative embodiment, the mass concentration of the second templating agent in the templating agent solution is 0.1% to 10%.

[0021] In an alternative embodiment, the sintering aid solution comprises an organic carboxylic acid solution with a low number of carbon atoms.

[0022] In an alternative embodiment, the sintering aid comprises an organic carboxylic acid with 2 to 6 carbon atoms.

[0023] In an alternative embodiment, the sintering aid comprises at least one of citric acid, sorbic acid, glycolic acid, lactic acid, and succinic acid.

[0024] In an alternative embodiment, the dosage of the sintering aid is 0.1% to 0.5% of the mass of silver nitrate.

[0025] In an alternative embodiment, the mass concentration of the sintering aid solution is 0.1% to 10%.

[0026] In an alternative embodiment, the reaction solvent comprises water and polyols.

[0027] In an alternative embodiment, the dosage of the reaction solvent is 10 to 40 times the mass of silver nitrate.

[0028] In an alternative embodiment, the polyols comprise at least one of ethylene glycol, glycerol, and diethylene glycol.

[0029] In an alternative embodiment, in the reaction solvent, the mass ratio of water to polyols is 1:2 to 1:4.

[0030] In an alternative embodiment, the silver nitrate solution and the first mixed solution are mixed under stirring conditions.

[0031] In an alternative embodiment, the stirring speed is 100 r / min to 600 r / min, preferably 200 r / min.

[0032] In an alternative embodiment, the mixing time is 5 min to 15 min, preferably 10 min.

[0033] In an alternative embodiment, the time for adding the sintering aid solution to the second mixed solution does not exceed 1 min.

[0034] In an alternative embodiment, after the sintering aid solution is added to the second mixed solution, the mixing time of the sintering aid solution and the second mixed solution is 2 min to 5 min.

[0035] In an alternative embodiment, it further includes: cleaning, centrifuging and drying the coated flaky silver powder.

[0036] In an alternative embodiment, the drying temperature is 40°C to 70°C, and the drying time is 2 h to 5 h.

[0037] In a second aspect, the present invention provides a flaky silver powder, which is prepared by the preparation method of any one of the foregoing embodiments.

[0038] In an alternative embodiment, the diameter of the flaky silver powder is 0.5 μm to 5 μm.

[0039] In an alternative embodiment, the specific surface area of the flaky silver powder is 1.05 m 2 / g to 1.95 m 2 / g.

[0040] The beneficial effects of the present invention include:

[0041] The preparation method provided by the present invention, through the one-step reduction reaction of the reducing agent solution and the silver nitrate solution in the presence of the templating agent solution, can obtain flaky silver powder through reaction in a short time. The production process is simple and environmentally friendly, which is conducive to large-scale production; after obtaining the initial flaky silver powder, combined with the sintering aid solution, the morphology and sintering activity of the flaky silver powder can be effectively controlled. The flaky silver powder obtained by this method has a narrow particle size distribution, is evenly dispersed, and has a high proportion of flakes, and can be applied in low-temperature sintering. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0043] Figure 1 SEM image of the flaky silver powder obtained in Example 1;

[0044] Figure 2 SEM image of the flaky silver powder obtained in Example 2;

[0045] Figure 3 SEM image of the flaky silver powder obtained in Example 3;

[0046] Figure 4 SEM image of the flaky silver powder obtained in Example 4;

[0047] Figure 5 SEM image of the flaky silver powder obtained in Example 5;

[0048] Figure 6 SEM image of the silver powder obtained in Comparative Example 1;

[0049] Figure 7 SEM image of the silver powder obtained in Comparative Example 2;

[0050] Figure 8 SEM image of the silver powder obtained in Comparative Example 3;

[0051] Figure 9 SEM image of the silver powder obtained in Comparative Example 4;

[0052] Figure 10 SEM image of the silver powder obtained in Comparative Example 6. Detailed implementation manners

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0054] The following specifically describes the flaky silver powder and its preparation method provided by the present invention.

[0055] The present invention provides a method for preparing flaky silver powder, including the following steps:

[0056] S1: Mix a reducing agent solution, a templating agent solution, and a reaction solvent to obtain a first mixed solution;

[0057] S2: Mix a silver nitrate solution with the first mixed solution to obtain a second mixed solution in which initial flaky silver powder is formed;

[0058] S3: Mix a sintering aid solution with the second mixed solution to coat the initial flaky silver powder.

[0059] In some optional embodiments, S1 is adding the reducing agent solution and the template solution into the reaction solvent, and stirring them uniformly to form a first mixed solution.

[0060] Wherein, the reducing agent solution includes an aqueous solution of ascorbic acid.

[0061] Ascorbic acid is used as a reducing agent, which is relatively safe and non-toxic compared to commonly used hydrazine hydrate, formaldehyde, etc. In addition, ascorbic acid has moderate reducibility and a relatively mild reaction rate, which can not only ensure that silver ions are effectively reduced to silver powder, but also facilitate the precise regulation of the reaction process by controlling parameters such as reaction temperature, concentration, and pH value, which is conducive to the preparation of silver powder with uniform particle size and regular morphology. However, hydrazine hydrate has strong reducibility, fast reaction speed with silver ions, and the reaction process is difficult to control, which easily leads to uneven growth of silver powder particles and a wide particle size distribution, making it difficult to obtain silver powder with uniform particle size and regular morphology. The reducibility of ferrous salts is relatively weak, the reaction rate is slow, and it is greatly affected by factors such as solution pH value and temperature. It is necessary to strictly control the reaction conditions to ensure the smooth progress of the reaction, otherwise problems such as incomplete reaction or impure product may occur. In addition, ascorbic acid usually does not introduce impurity ions that are difficult to remove during the reaction process, and can prepare silver powder with higher purity. And in some cases, ascorbic acid not only acts as a reducing agent, but also plays a certain role as a dispersant, which helps to improve the dispersibility of silver powder and make the prepared silver powder have better performance.

[0062] In some optional embodiments, the usage ratio of ascorbic acid to silver nitrate can be 1.01:1 to 1.15:1, such as 1.01:1, 1.05:1, 1.08:1, 1.1:1, 1.12:1 or 1.15:1, etc., based on the molar ratio of the number of electrons transferred in the redox chemical reaction, or other values ​​within the range of 1.01:1 to 1.15:1.

[0063] If the amount of reducing agent is too small, the silver ions in the silver source cannot be completely reduced to silver element, resulting in a decrease in the yield of silver powder. At the same time, unreacted silver ions may remain in the product, affecting the purity of the silver powder. In addition, since some silver ions are not reduced, the reduced silver atoms lack sufficient silver ion supplementation during the growth process, which will lead to insufficient growth of silver powder particles and uneven particle size distribution, with more small-particle silver powder and less large-particle silver powder, affecting the performance and application of the silver powder. If the amount of reducing agent is too large, the excess reducing agent may remain in the reaction system and become an impurity, affecting the purity of the silver powder. In addition, too much reducing agent will make the reduction reaction rate in the reaction system too fast, and the silver atom generation rate is too fast, which will easily lead to the agglomeration phenomenon between the silver powder particles to form larger agglomerates, affecting the dispersibility and particle size distribution of the silver powder, making it difficult to disperse evenly during the application process, reducing its performance.

[0064] As an example, the concentration of the ascorbic acid aqueous solution can be, but is not limited to, 0.5 mol / L to 1.02 mol / L, and the concentration of the ascorbic acid aqueous solution can be specifically adjusted according to actual needs.

[0065] In some alternative embodiments, the template used in the template solution includes a first template and a second template. The first template is an acid template, and the second template is a dispersant template.

[0066] The present invention uses a composite template including a first template and a second template, which can effectively control the nucleation and growth direction of silver atoms and prevent agglomeration. Among them, the acid template can inhibit the reduction ability of ascorbic acid and has a strong binding ability with the Ag(111) crystal plane, thereby slowing down the progress of the chemical reaction and ensuring the growth into a flaky structure in the one-dimensional direction. The dispersant template has a strong adsorption effect on silver atoms and prevents agglomeration between flake particles through steric hindrance and electrostatic hindrance effects, and a product with a narrow particle size distribution can be obtained.

[0067] As an example, the first template may include at least one of nitric acid, formic acid, sulfuric acid, and their weak base salts. The second template may include at least one of Darvan 811, Dispex AA4040, BYK-190, EFKA-4580, 731A, and Solsperse32000.

[0068] In some alternative embodiments, the dosage of the first template can be 1% to 10% of the mass of silver nitrate, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc., or other values within the range of 1% to 10%.

[0069] If the dosage of the first template is too small, it is difficult to obtain silver powder with a flaky structure. If the dosage of the first template is too large, it is easy to affect the production efficiency and output of silver powder, increasing the production cost; in addition, if the first template is in excess, it may also cause certain corrosion or chemical changes on the surface of the silver powder, instead reducing the stability of the silver powder and making it more likely to oxidize or undergo other chemical reactions during storage and use.

[0070] In some alternative embodiments, the dosage of the second template can be 0.2% to 1% of the mass of silver nitrate, such as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%, etc., or other values within the range of 0.2% to 1%.

[0071] If the amount of the second templating agent is too small, it is likely to result in poor dispersion effect, and the silver powder is prone to agglomeration, leading to a relatively wide particle size distribution of the prepared silver powder and poor uniformity and stability of the silver powder in the reaction system; if the amount of the second templating agent is too large, the silver powder is likely to be spherical rather than flaky.

[0072] As an example, the mass concentration of the first templating agent in the templating agent solution can be, by way of example but not limitation, 1% to 10%, and the mass concentration of the second templating agent in the templating agent solution can be, by way of example but not limitation, 0.1% to 10%. Specifically, the concentrations of the first templating agent and the second templating agent in the templating agent solution can be adjusted according to actual needs.

[0073] In some alternative embodiments, the reaction solvent includes water and polyols, and the polyols can exemplarily include at least one of ethylene glycol, glycerol, and diethylene glycol. The introduction of polyols can play a role in increasing the viscosity of the system.

[0074] In some alternative embodiments, in the reaction solvent, the mass ratio of water to polyols can be 1:2 to 1:4, such as 1:2, 1:2.5, 1:3, 1:3.5, or 1:4, etc., or other values within the range of 1:2 to 1:4.

[0075] By combining water and polyols in the above mass ratio, the viscosity of the system can be controlled to 2 mPa·s to 200 mPa·s. In this viscosity range, it is beneficial to the transport, diffusion, and reaction of substances in the reaction system, and provides the reaction rate and the formation rate of silver powder.

[0076] In some alternative embodiments, the amount of the reaction solvent can be 10 times to 40 times the mass of silver nitrate, such as 10 times, 15 times, 20 times, 25 times, 30 times, 35 times, or 40 times, etc., or other values within the range of 10 times to 40 times.

[0077] In some alternative embodiments, S2 is to add the silver nitrate solution to the first mixed solution, mix and react under stirring conditions to obtain a second mixed solution in which initial flaky silver powder is formed.

[0078] Among them, the silver nitrate solution is prepared from silver nitrate and water, and its concentration can be 1.05 mol / L to 2.45 mol / L.

[0079] The stirring speed can be 100 r / min to 600 r / min, such as 100 r / min, 200 r / min, 300 r / min, 400 r / min, 500 r / min, or 600 r / min, etc., or other values within the range of 100 r / min to 600 r / min. Preferably, 200 r / min is adopted.

[0080] The mixing time (reaction time) can be 5 min to 15 min, such as 5 min, 8 min, 10 min, 12 min or 15 min, etc., or other values ​​within the range of 5 min to 15 min, preferably 10 min.

[0081] In some optional embodiments, S3 is to add the sintering aid solution into the second mixed solution having the initial flaky silver powder, and continue stirring to perform the surface coating treatment.

[0082] The sintering aid solution includes an organic carboxylic acid solution with a low carbon number. For example, the sintering aid includes an organic carboxylic acid with a carbon number of 2 to 6. For example, the sintering aid may include at least one of citric acid, sorbic acid, glycolic acid, lactic acid and succinic acid.

[0083] The present invention uses the above-mentioned sintering aid to coat the silver surface. The low boiling point property of the sintering aid can promote surface sintering during the sintering process of flaky silver powder, which is beneficial to constructing a conductive path during low-temperature sintering.

[0084] In some optional embodiments, the amount of the sintering aid can be 0.1% to 0.5% of the mass of silver nitrate, such as 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45% or 0.5%, etc., or other values ​​within the range of 0.1% to 0.5%.

[0085] For example, the mass concentration of the sintering aid solution may be 0.1% to 10% by way of example but not limitation. The concentration of the sintering aid solution may be adjusted according to actual needs.

[0086] In the present invention, the time for adding the sintering aid solution to the second mixed solution does not exceed 1 min, such as 1 min, 0.5 min or 0.1 min, etc., or other values ​​within the range of not more than 1 min.

[0087] By controlling the addition time of the sintering aid solution within the above range, it is beneficial to form a carboxylic acid coating effect on the surface of the flaky silver powder.

[0088] In the present invention, after the sintering aid solution is added to the second mixed solution, the mixing time of the sintering aid solution and the second mixed solution is controlled to be 2min to 5min, such as 2min, 2.5min, 3min, 3.5min, 4min, 4.5min or 5min, etc., and can also be other values ​​within the range of 2min to 5min.

[0089] If the mixing time of the sintering aid solution and the second mixed solution is too short, it is not conducive to the coating process and affects the sintering of the flaky silver powder; if the mixing time of the sintering aid solution and the second mixed solution is too long, it is easy to cause low reaction efficiency.

[0090] Further, after S3, S4 may also be included: cleaning, centrifuging, and drying the coated flaky silver powder.

[0091] Among them, the drying temperature can be 40°C to 70°C, such as 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, or 70°C, etc. The drying time can be 2h to 5h, such as 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, or 5h, etc.

[0092] Correspondingly, the present invention also provides a kind of flaky silver powder, which is prepared by the above preparation method.

[0093] This flaky silver powder has a narrow particle size distribution, is evenly dispersed, has a high proportion of flaky shape, and can be applied in low-temperature sintering.

[0094] In some alternative embodiments, the diameter of the flaky silver powder is 0.5μm to 5μm. In some alternative embodiments, the D 10 is 1.129μm to 1.541μm, the D 50 is 1.988μm to 2.894μm, the D 90 is 2.935μm to 4.732μm, and the D 100 is 5μm to 6μm. In alternative embodiments, the specific surface area of the flaky silver powder is 1.05m 2 / g to 1.95m 2 / g, such as 1.289m 2 / g to 1.832m 2 / g.

[0095] The features and properties of the present invention will be further described in detail below in conjunction with embodiments.

[0096] Example 1

[0097] This example provides a kind of flaky silver powder, and its preparation method includes:

[0098] S1: Add the reducing agent solution and the templating agent solution into the reaction solvent, and stir evenly to form the first mixed solution.

[0099] S2: Add the silver nitrate solution into the first mixed solution, mix and react for 10 min under stirring conditions (200 r / min) to obtain the second mixed solution in which initial flaky silver powder is formed.

[0100] S3: Add all the sintering aid solution into the second mixed solution in which initial flaky silver powder is formed within 1 min, and continue to stir for 2 min for surface coating treatment.

[0101] S4: Centrifuge and wash the product after coating treatment, and dry it at 50 °C for 3 h to obtain about 32 g of flaky silver powder.

[0102] Based on the molar ratio of the number of electrons transferred in the redox chemical reaction, the dosage ratio of ascorbic acid to silver nitrate is 1.06:1. The dosage of dilute nitric acid is 1.0% of the mass of silver nitrate, the dosage of Dispex AA4040 is 0.5% of the mass of silver nitrate. The dosage of glycolic acid is 0.15% of silver nitrate, and the mass of the reaction solvent is 21.76 times that of silver nitrate.

[0103] The solution preparation method is as follows. Specifically, when in use, the prepared solutions are adaptively added according to the above dosage relationship (the same applies to the following examples and comparative examples):

[0104] The reducing agent solution is an aqueous solution of ascorbic acid with a concentration of 0.75 mol / L, which is specifically prepared by adding water to 27.8 g of ascorbic acid.

[0105] The template agent solution consists of the following: 5.0 g of dilute nitric acid with a mass concentration of 10%, and 2.5 g of Dispex AA4040 with a mass concentration of 10%.

[0106] The reaction solvent is prepared from 328 g of glycerol, 400 g of ethylene glycol, and 360 g of deionized water (the mass ratio of water to polyol is about 1:2.02).

[0107] The concentration of the silver nitrate solution is 2.2 mol / L, which is specifically prepared by adding water to 50 g of silver nitrate.

[0108] The concentration of the co-firing agent solution is 1.5%, which is specifically prepared by adding deionized water to 0.075 g of glycolic acid.

[0109] Example 2

[0110] This example provides a kind of flaky silver powder, and its preparation method includes:

[0111] S1: Add the reducing agent solution and the template agent solution into the reaction solvent, and stir evenly to form the first mixed solution.

[0112] S2: Add the silver nitrate solution into the first mixed solution, mix and react for 15 min under stirring conditions (100 r / min) to obtain the second mixed solution in which initial flaky silver powder is formed.

[0113] S3: Add all the co-firing agent solution into the second mixed solution in which initial flaky silver powder is formed within 0.5 min, and continue to stir for 3 min for surface coating treatment.

[0114] S4: Centrifuge and wash the product after coating treatment, and dry it at 40 °C for 5 h to obtain flaky silver powder.

[0115] In terms of the molar ratio of the number of electrons transferred in the redox chemical reaction, the dosage ratio of ascorbic acid to silver nitrate is 1.15:1. The dosage of formic acid is 2.0% of the mass of silver nitrate, the dosage of BYK-190 is 0.2% of the mass of silver nitrate, the dosage of citric acid is 0.5% of silver nitrate, and the mass of the reaction solvent is 30.6 times that of silver nitrate.

[0116] The method for preparing the solution is as follows: The reducing agent solution is an aqueous solution of 0.5 mol / L ascorbic acid.

[0117] The template agent solution is composed of the following: an aqueous solution of formic acid with a mass concentration of 10%, and BYK-190 with a mass concentration of 0.2%.

[0118] The reaction solvent is prepared from 630 g of glycerol, 390 g of diethylene glycol, and 510 g of deionized water (the mass ratio of water to polyol is approximately 1:2).

[0119] The concentration of the silver nitrate solution is 1.05 mol / L, and the dosage of silver nitrate is 50 g.

[0120] The concentration of the co-firing agent (citric acid) solution is 0.1%.

[0121] Example 3

[0122] This example provides a flaky silver powder, and its preparation method includes:

[0123] S1: Add the reducing agent solution and the template agent solution to the reaction solvent, and stir evenly to form a first mixed solution.

[0124] S2: Add the silver nitrate solution to the first mixed solution, mix and react under stirring conditions (600 r / min) for 5 min to obtain a second mixed solution in which initial flaky silver powder is formed.

[0125] S3: Add all of the co-firing agent solution to the second mixed solution in which initial flaky silver powder is formed within 0.1 min, and continue to stir for 5 min for surface coating treatment.

[0126] S4: Centrifuge and wash the product after the coating treatment, and dry it at 70 °C for 2 h to obtain flaky silver powder.

[0127] In terms of the molar ratio of the number of electrons transferred in the redox chemical reaction, the dosage ratio of ascorbic acid to silver nitrate is 1.08:1. The dosage of sulfuric acid is 8% of the mass of silver nitrate, the dosage of Solsperse 32000 is 1.0% of the mass of silver nitrate, the dosage of lactic acid is 0.2% of silver nitrate, and the mass of the reaction solvent is 23.8 times that of silver nitrate.

[0128] The method for preparing the solution is as follows: the reducing agent solution is an aqueous solution of ascorbic acid with a concentration of 1.02 mol / L.

[0129] The template agent solution is composed of sulfuric acid with a mass concentration of 5% and Solsperse 32000 with a mass concentration of 5%.

[0130] The reaction solvent is prepared from 476 g of ethylene glycol, 476 g of diethylene glycol and 238 g of deionized water (the mass ratio of water to polyol is about 1:4).

[0131] The concentration of the silver nitrate solution is 2.45 mol / L, and the amount of silver nitrate used is 50 g.

[0132] The concentration of the co - firing agent (lactic acid) solution is 10%.

[0133] Example 4

[0134] The difference between this example and Example 1 is that the mass ratio of the reaction solvent to silver nitrate is 40:1.

[0135] Example 5

[0136] The difference between this example and Example 1 is that the amount of dilute nitric acid used as the first template agent is 6% of the mass of silver nitrate.

[0137] Comparative Example 1

[0138] The difference between this comparative example and Example 1 is that the template agent solution is not used in S1.

[0139] The silver powder obtained in this comparative example has no flaky structure, and its SEM image is as Figure 6 shown.

[0140] Comparative Example 2

[0141] The difference between this comparative example and Example 1 is that the template agent solution only contains dilute nitric acid and does not contain Dispex AA4040.

[0142] Comparative Example 3

[0143] The difference between this comparative example and Example 1 is that the template agent solution only contains Dispex AA4040 and does not contain dilute nitric acid.

[0144] Comparative Example 4

[0145] The difference between this comparative example and Example 1 is that the amount of dilute nitric acid used is 0.5% of the mass of silver nitrate.

[0146] The silver powder obtained in this comparative example has a weak flaky structure, and its SEM image is as Figure 9 shown.

[0147] Comparative Example 5

[0148] The difference between this comparative example and Example 1 lies in that the dosage of glycolic acid is 0.05% of the mass of silver nitrate.

[0149] The coating effect of this comparative example is average, and the resistance is large when the finally obtained flaky silver powder is used as the conductive phase during the sintering of the paste.

[0150] Comparative Example 6

[0151] The difference between this comparative example and Example 1 lies in that the mass ratio of water to polyol in the reaction solvent is 1:1.

[0152] In this comparative example, the dosage of polyol is small, the viscosity of the system is low, the proportion of flakes in the obtained flaky silver powder decreases, and there is a granular silver powder structure. Its SEM image is as Figure 10 shown.

[0153] Test Example 1

[0154] ①. The silver powders obtained in Examples 1 to 5, Comparative Examples 1 to 4, and Comparative Example 6 were observed by scanning electron microscopy. The results are respectively as Figures 1 to 10 shown. It can be seen from Figures 1 to 10 that: Flaky silver powders were successfully obtained in Examples 1 to 5. The silver powders obtained in Comparative Examples 1 to 4 and Comparative Example 6 do not have a flaky structure or the proportion of the flaky structure is too low.

[0155] ②. The particle size distributions of the silver powders obtained in Examples 1 to 5 and Comparative Examples 1 to 4 were tested by a laser particle size analyzer. The results are shown in Table 1.

[0156] ③. The specific surface areas of the silver powders obtained in Examples 1 to 5 and Comparative Example 1 were tested by a specific surface area analyzer. The results are shown in Table 1.

[0157] Table 1 Test Results

[0158] <![CDATA[D 10 (μm)]]> <![CDATA[D 50 (μm)]]> <![CDATA[D 90 (μm)]]> <![CDATA[D 100 (μm)]]> <![CDATA[Specific surface area (m 2 / g)]]> Example 1 1.301 2.179 3.397 6.0 1.558 Example 2 1.541 2.894 4.732 8.0 1.289 Example 3 1.409 2.541 3.887 6.0 1.575 Example 4 1.129 1.988 2.935 5.0 1.832 Example 5 1.398 2.769 4.193 6.0 1.487 Comparative Example 1 0.816 1.467 2.951 6.0 0.873 Comparative Example 2 1.612 3.311 12.313 30.0 / Comparative Example 3 1.195 2.481 5.507 12.0 / Comparative Example 4 0.625 1.089 1.990 4.0 /

[0159] It can be seen from Table 1 that the silver powders prepared by the methods provided in Examples 1 to 5 of the present invention are flaky, have a narrow particle size distribution, and a suitable specific surface area. When the preparation conditions are not controlled properly, it will lead to problems such as the inability to obtain flaky silver powder, obvious agglomeration of flaky silver powder, or wide distribution of silver powder.

[0160] Test Example 2

[0161] The silver powders obtained in Examples 1 to 5, Comparative Example 1, Comparative Example 4, and Comparative Example 6 were used as the conductive phase, supplemented with an organic solvent, vinyl chloride-vinyl acetate resin and polyurethane as the binder phase, and were configured into a conductive paste by stirring with a three-roll mill. The sheet resistance of each printed paste after curing (200 °C, 30 min) was measured by a four-probe resistance tester. The results are shown in Table 2.

[0162] Table 2 Test Results

[0163] Sheet Resistance (mΩ / □) Example 1 81.77 Example 2 98.21 Example 3 78.64 Example 4 86.13 Example 5 92.08 Comparative Example 1 152.33 Comparative Example 4 116.50 Comparative Example 6 99.11

[0164] As can be seen from Table 2, the sheet resistance of the silver powder provided in Examples 1 to 5 of the present invention is lower and the sintering activity is higher after being made into a paste than that of the silver powder provided in Comparative Example 1, Comparative Example 4, and Comparative Example 6.

[0165] In summary, the preparation method provided by the present invention reacts an ascorbic acid solution and a silver nitrate solution through a one-step reduction method under the cooperation of a composite template agent solution and a specific reaction solvent to obtain flaky silver powder within a short reaction time. The production process is simple and environmentally friendly, which is conducive to large-scale production. After obtaining the initial flaky silver powder, combined with a sintering aid solution, the morphology and sintering activity of the flaky silver powder can be effectively controlled. The flaky silver powder obtained by this method has a narrow particle size distribution, is evenly dispersed, and has a high proportion of flakes, and can be applied in low-temperature sintering.

[0166] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing flaky silver powder, characterized in that: The following steps are involved: Mixing the reducing agent solution, the template solution and the reaction solvent to obtain a first mixed solution; Mixing the silver nitrate solution with the first mixed solution to obtain a second mixed solution having initial flaky silver powder; The sintering aid solution is mixed with the second mixed solution to coat the initial flaky silver powder.

2. The preparation method according to claim 1, characterized in that: The reducing agent solution includes an aqueous solution of ascorbic acid; Preferably, the amount ratio of ascorbic acid to silver nitrate is 1.01:1 to 1.15:1, calculated on the molar ratio of the number of electrons transferred in the redox chemical reaction.

3. The preparation method according to claim 1, characterized in that: The template used in the template solution includes a first template and a second template; Wherein, the first template is an acid template, and the second template is a dispersant template; Preferably, the first template comprises at least one of nitric acid, formic acid, sulfuric acid and weak base salts thereof; Preferably, the second template comprises at least one of Darvan 811, Dispex AA4040, BYK-190, EFKA-4580, 731A and Solsperse 32000; Preferably, the amount of the first template agent is 1% to 10% of the mass of silver nitrate; Preferably, the amount of the second template agent is 0.2% to 1% of the mass of silver nitrate.

4. The preparation method according to claim 1, characterized in that: The sintering aid solution includes an organic carboxylic acid solution with a low carbon number; Preferably, the sintering aid comprises an organic carboxylic acid having 2 to 6 carbon atoms; Preferably, the burning aid comprises at least one of citric acid, sorbic acid, glycolic acid, lactic acid and succinic acid; Preferably, the amount of the sintering aid is 0.1% to 0.5% of the mass of silver nitrate.

5. The preparation method according to claim 1, characterized in that: The reaction solvent includes water and polyol; Preferably, the mass of the reaction solvent is 10 to 40 times the mass of silver nitrate; Preferably, the polyol comprises at least one of ethylene glycol, glycerol and diethylene glycol; Preferably, in the reaction solvent, the mass ratio of water to polyol is 1:2 to 1:

4.

6. The preparation method according to claim 1, characterized in that: The silver nitrate solution and the first mixed solution are mixed under stirring conditions; Preferably, the stirring speed is 100 r / min to 600 r / min, more preferably 200 r / min; Preferably, the mixing time is 5 min to 15 min, more preferably 10 min.

7. The preparation method according to claim 1, characterized in that: The time for adding the sintering aid solution into the second mixed solution does not exceed 1 minute.

8. The preparation method according to claim 7, characterized in that: After the sintering aid solution is added to the second mixed solution, the sintering aid solution and the second mixed solution are mixed for 2 minutes to 5 minutes.

9. The preparation method according to any one of claims 1 to 8, characterized in that: Also includes: The coated flaky silver powder is washed, centrifuged and dried; Preferably, the drying temperature is 40° C. to 70° C., and the drying time is 2 h to 5 h.

10. A flaky silver powder, characterized in that: The flaky silver powder is prepared by the preparation method according to any one of claims 1 to 9; Preferably, the diameter of the flaky silver powder is 0.5 μm to 5 μm; Preferably, the specific surface area of ​​the flaky silver powder is 1.05 m 2 / g~1.95m 2 / g.

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