Silver powder with low silver content and preparation method and application thereof

Abstract

The present invention belongs to the technical field of silver powder preparation, and specifically discloses a silver powder with a low silver content, a preparation method thereof, and an application thereof. The silver powder preparation method of the present invention comprises the following steps: S1, preparing a reaction system containing silver ions or silver complexes, adding a dispersant and a surfactant to the reaction system, and stirring and mixing; S2, adding a reducing agent solution, stirring and mixing for reaction, and adding a coating agent; S3, centrifuging to obtain a solid, drying, and crushing to obtain silver powder; wherein the surfactant comprises an ionic surfactant and a non-ionic surfactant. The silver powder prepared by the method of the present invention has a suitable particle size range and a low silver content, and has a relatively low grain size and degree of maturation and a high sintering activity, can be used for low-temperature rapid sintering, and has a good application prospect in the field of manufacturing electronic components.

Description

Technical Field

[0001] The invention relates to the technical field of silver powder preparation, and in particular to silver powder with low silver content and a preparation method and application thereof. Background Art

[0002] With the rapid development of electronic technology, especially the continuous innovation in the fields of stacked capacitors, solar cells and 5G communication technology, more stringent requirements are put forward for high-performance and low-cost electronic materials. Among them, silver powder materials, as a widely used conductive material in these technical fields, play a vital role in the metallization process of electronic components.

[0003] At present, although traditional silver powder materials show certain advantages in the sintering process, with the increasingly urgent demand for low silver content and low-temperature rapid sintering in the modern electronics industry, its performance bottleneck is becoming more and more obvious. In addition, in order to better adapt to the above-mentioned uses, the conductive paste needs to be able to adapt to the requirements of precision printing patterns, and the silver powder is also required to have a narrow particle size distribution and be well dispersed in organic solvents. Chemical reduction method is an important means of preparing silver powder. By precisely controlling the reaction conditions, silver powder with good sintering performance can be synthesized. However, how to further reduce the temperature of rapid sintering of silver powder, improve the performance of sintered silver powder, and reduce the production cost of silver powder materials are still urgent problems to be solved.

[0004] Therefore, there is an urgent need to improve the current silver powder material preparation technology, optimize the silver powder sintering performance, reduce production costs, and enable silver powder materials to be better used in electronic components. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a method for preparing silver powder. The scheme of the present invention achieves precise control of the non-silver content in the silver powder within the range of 1wt% to 3wt% by finely regulating the nucleation and agglomeration process of the silver powder, thereby preparing silver powder with a low silver content, and the silver powder has a relatively low grain size and degree of maturation, so that it has a high sintering activity, can achieve rapid sintering at a lower temperature, and the silver film prepared by sintering has a lower square resistance. The silver powder provided by the present invention not only meets the strict requirements of electronic components on sintering temperature and time, but also significantly reduces the consumption of silver and reduces production costs.

[0006] The invention also provides silver powder.

[0007] The invention also provides application of the silver powder.

[0008] A first aspect of the present invention provides a silver powder, wherein the silver content of the silver powder is 97wt% to 99wt% and the particle size ranges from 0.5 to 3μm.

[0009] The silver powder of the present invention is in a spherical shape with a particle size range of about 0.5 to 3 μm. The particle size range of the silver powder is suitable, which is conducive to printing after the silver powder is made into silver paste; and the silver content in the silver powder is 97wt% to 99wt%, and the non-silver content is 1wt% to 3wt%. The silver powder has a high sintering activity, can be quickly sintered at a lower temperature in an infrared sintering furnace, and the silver film prepared by sintering has a lower square resistance. The silver powder provided by the present invention meets the strict requirements of electronic components for sintering temperature and time, and has a good application prospect in electronic components such as internal electrodes of stacked capacitors, positive grid lines of solar cells, and 5G filters.

[0010] According to some embodiments of the present invention, the grain size of the silver powder is 20-27 nm.

[0011] According to some embodiments of the present invention, the sheet resistance of the silver film prepared from the silver powder is 2.2 to 3.1 mΩ / □.

[0012] According to some embodiments of the present invention, the sheet resistance of the silver film prepared from the silver powder is 2.3 to 3.0 mΩ / □.

[0013] A second aspect of the present invention provides a method for preparing silver powder, comprising the following steps:

[0014] S1, preparing a reaction system containing silver ions or silver complexes, adding a dispersant and a surfactant to the reaction system, and stirring and mixing;

[0015] S2, adding reducing agent solution, stirring and mixing to react, and adding coating agent;

[0016] S3, centrifuge to obtain a solid, dry it, and grind it to obtain silver powder;

[0017] The surfactants include ionic surfactants and nonionic surfactants.

[0018] According to a specific embodiment of the present invention, the method for preparing silver powder provided by the present invention has at least the following beneficial effects:

[0019] The silver powder prepared by the scheme of the present invention is presented in a spherical shape with a particle size range of about 0.5 to 3 μm. The particle size range of the silver powder is suitable, which is conducive to the printing of the silver powder after it is made into silver paste; the preparation method of the present invention achieves accurate control of the non-silver content in the silver powder within the range of 1wt% to 3wt% by finely regulating the silver powder nucleation and the agglomeration process of silver microcrystalline particles, and makes the prepared silver powder have a relatively low grain size and degree of maturation, so that it has a high sintering activity. The silver powder prepared by the present invention is used for sintering, and can be sintered quickly at a lower temperature in an infrared sintering furnace, and the silver film prepared by sintering has a lower square resistance. The silver powder prepared by the preparation method provided by the present invention not only meets the strict requirements of electronic components for sintering temperature and time, but also significantly reduces the consumption of silver and reduces production costs. It has a good application prospect in electronic components such as internal electrodes of stacked capacitors, positive grid lines of solar cells, and 5G filters.

[0020] According to a specific embodiment of the present invention, the silver powder provided by the present invention has a higher content of non-silver substances and a lower content of silver. These non-silver substances are derived from organic matter in the process of preparing the silver powder and remain in the pores of the silver powder, which reduces the amount of silver used to a certain extent, thereby reducing the cost of the silver powder and expanding the economic benefits; these non-silver substances can also inhibit the aging of the silver powder and improve the sintering activity, and can achieve rapid sintering at low temperatures, greatly improving the production efficiency of the silver powder used in electronic components, and the sintered products such as silver films have relatively lower square resistance, thereby improving the performance of the prepared products.

[0021] According to some embodiments of the present invention, the concentration of silver in the reaction system described in step S1 is 0.1-1 mol / L.

[0022] The scheme of the present invention controls the concentration of silver in the reaction system to avoid excessively high concentration causing silver particles to explode and nucleate, resulting in serious agglomeration of silver particles, and excessively low concentration causing low economic efficiency, which is not suitable for industrial production.

[0023] According to some embodiments of the present invention, the concentration of silver in the reaction system described in step S1 is 0.15-0.5 mol / L.

[0024] According to some embodiments of the present invention, the concentration of silver in the reaction system described in step S1 is 0.15-0.3 mol / L.

[0025] According to some embodiments of the present invention, the concentration of silver refers to the molar volume concentration of silver ions or silver elements.

[0026] According to some embodiments of the present invention, the silver complex described in step S1 is generated by silver ions and at least one substance selected from ammonia, ammonium salts, sulfites, sulfates, amines or transition metal ions.

[0027] According to some embodiments of the present invention, the ionic surfactant comprises at least one of sulfonate, sulfate, phosphate or carboxylate; and / or the nonionic surfactant comprises at least one of Span or Tween.

[0028] The invention helps to control the nucleation and agglomeration process in the preparation process of silver powder by adding two types of surfactants, thereby controlling the content of non-silver organic matter in the silver powder and adjusting the aging process of the silver powder, so that the prepared silver powder has a low silver content and good sintering activity.

[0029] According to some embodiments of the present invention, the ionic surfactant includes at least one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfate or hexadecyltrimethylammonium bromide.

[0030] According to some embodiments of the present invention, the added amount of the surfactant is 2.5% to 4.5% of the theoretical mass of the generated silver powder.

[0031] The present invention explores the addition amount of the surfactant in the preparation method, and finds that the surfactant within the addition amount range can play an optimal role in regulating the nucleation and agglomeration processes, which helps to make the prepared silver powder have a lower grain size and degree of maturation, as well as a lower silver content and better sintering activity. At the same time, the addition amount of the surfactant is controlled to avoid increasing the raw material cost and cleaning cost, thereby improving the enterprise efficiency.

[0032] According to some embodiments of the present invention, the added amount of the surfactant is 2.8% to 4.5% of the theoretical mass of the generated silver powder.

[0033] According to some embodiments of the present invention, the mass ratio of the non-ionic surfactant to the ionic surfactant is 1:0.6-2.5.

[0034] According to some embodiments of the present invention, the mass ratio of the non-ionic surfactant to the ionic surfactant is 1:0.7-2.

[0035] According to some embodiments of the present invention, the dispersant includes at least one of gum arabic, gelatin, polyvinyl pyrrolidone, polyethylene glycol, polyacrylic acid, polycarboxylate, poly(meth)acrylic acid derivative, maleic anhydride copolymer or polyphosphate. The present invention uses a dispersant to prevent the agglomeration of silver powder particles.

[0036] According to some embodiments of the invention, the dispersant is polyvinyl pyrrolidone.

[0037] According to some embodiments of the present invention, during the process of adding the reducing agent in step S2, the temperature of the mixed solution is controlled to be 5° C. to 55° C.

[0038] The present invention controls the temperature of the reaction system in the reduction reaction process more accurately, so as to avoid the temperature being too low, causing the nucleation rate to be too slow, resulting in the growth of silver particles, and the particle size being unsuitable for printing fine patterns; and to avoid the temperature being too high, causing the silver particles to be too small, and the particle size distribution to be uneven, which is not conducive to the preparation of silver paste.

[0039] According to some embodiments of the present invention, in the process of adding the reducing agent solution in step S2, the temperature of the mixed solution is preferably controlled at 10° C. to 40° C.

[0040] According to some embodiments of the present invention, the temperature of the mixed solution is more preferably controlled to be 20° C. to 30° C. during the process of adding the reducing agent solution in step S2.

[0041] According to some embodiments of the present invention, the reducing agent solution is added slowly in step S2, and the adding time is controlled to be 0.5 to 2 minutes.

[0042] According to some embodiments of the present invention, the temperature of the reducing agent solution in step S2 is 1 to 20° C. lower than the temperature of the reaction system in step S1.

[0043] In order to achieve temperature control, the present invention suppresses the temperature rise caused by the reaction heat by lowering the temperature of the reducing liquid and controlling the speed of adding the reducing liquid, or adding cold water for control, or cooling by external circulating water.

[0044] According to some embodiments of the present invention, the temperature of the reducing agent solution in step S2 is 2-5° C. lower than the temperature of the reaction system in step S1.

[0045] According to some embodiments of the present invention, the reducing agent is a substance containing an aldehyde group or a hydroxyl group.

[0046] According to some embodiments of the invention, the reducing agent comprises at least one of ascorbic acid, formaldehyde, acetaldehyde, ethylene glycol or glycerol.

[0047] According to some embodiments of the present invention, the reducing agent is preferably ascorbic acid or formaldehyde.

[0048] According to some embodiments of the present invention, the reducing agent solution is an aqueous solution or an alcohol solution of the reducing agent.

[0049] According to some embodiments of the present invention, the amount of the reducing agent added is 1.1 to 2.6 times the equivalent of the silver ion content in the solution.

[0050] The equivalent is the molar amount of silver ions that can be reduced by 1 mol of the reducing agent; for example, 1 mol of ascorbic acid can reduce 2 mol of silver ions, so 1 mol of ascorbic acid is twice the equivalent of 1 mol of silver ions; for another example, 1 mol of formaldehyde can reduce 2 mol of silver ions, so 1 equivalent of formaldehyde is 1 / 2 of the molar mass of silver ions.

[0051] The scheme of the present invention controls the reduction preparation of silver powder more finely. By controlling the type of reducing agent, the use of reducing agents such as sodium borohydride and hydrated hydrazine is avoided, and reducing agents such as ascorbic acid or formaldehyde are used, so that the reduction reaction can be avoided to be too violent, thereby making it easy to control the temperature of the reaction system and avoid the silver powder particle size distribution being too wide, which is not conducive to production and subsequent application of the silver powder. At the same time, the amount of reducing agent added is controlled to avoid too little addition leading to too long a reaction time and too much addition leading to instantaneous release of reaction heat, which is not conducive to temperature control.

[0052] According to some embodiments of the present invention, the amount of the reducing agent added is 1.2 to 1.8 times the molar equivalent of the silver ion content in the solution.

[0053] According to some embodiments of the invention, the coating agent comprises at least one of lauric acid, oleic acid, stearic acid or n-decanoic acid.

[0054] According to some embodiments of the present invention, step S3 further comprises washing with pure water.

[0055] According to some embodiments of the present invention, the drying in step S3 is performed by using an oven at 40° C. to 80° C. for 8 to 16 hours.

[0056] The third aspect of the present invention provides application of the silver powder described in the first aspect of the present invention in the field of electronic component manufacturing.

[0057] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0059] Figure 1 This is a SEM image of the silver powder prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0060] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0061] A first aspect of the present invention provides a silver powder, wherein the silver content of the silver powder is 97wt% to 99wt% and the particle size ranges from 0.5 to 3μm.

[0062] According to some embodiments of the present invention, the grain size of the silver powder is 20-27 nm.

[0063] According to some embodiments of the present invention, the grain size of the silver powder is 21-27 nm.

[0064] According to some embodiments of the present invention, the sheet resistance of the silver film prepared from the silver powder is 2.2 to 3.1 mΩ / □.

[0065] According to some embodiments of the present invention, the sheet resistance of the silver film prepared from the silver powder is 2.3 to 3.0 mΩ / □.

[0066] A second aspect of the present invention provides a method for preparing silver powder, comprising the following steps:

[0067] S1, preparing a reaction system containing silver ions or silver complexes, adding a dispersant and a surfactant to the reaction system, and stirring and mixing;

[0068] S2, adding reducing agent solution, stirring and mixing to react, and adding coating agent;

[0069] S3, centrifuge to obtain a solid, dry it, and grind it to obtain silver powder;

[0070] The surfactants include ionic surfactants and nonionic surfactants.

[0071] According to some embodiments of the present invention, the concentration of silver in the reaction system described in step S1 is 0.1-1 mol / L.

[0072] According to some embodiments of the present invention, the concentration of silver in the reaction system described in step S1 is 0.15-0.5 mol / L.

[0073] According to some embodiments of the present invention, the concentration of silver in the reaction system described in step S1 is 0.15-0.3 mol / L.

[0074] According to some embodiments of the present invention, the concentration of silver refers to the molar volume concentration of silver ions or silver elements.

[0075] According to some embodiments of the present invention, the silver complex described in step S1 is generated by silver ions and at least one substance selected from ammonia, ammonium salts, sulfites, sulfates, amines or transition metal ions.

[0076] According to some embodiments of the present invention, the ionic surfactant comprises at least one of sulfonate, sulfate, phosphate or carboxylate; and / or the nonionic surfactant comprises at least one of Span or Tween.

[0077] According to some embodiments of the present invention, the ionic surfactant includes at least one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfate or hexadecyltrimethylammonium bromide.

[0078] According to some embodiments of the present invention, the added amount of the surfactant is 2.5% to 4.5% of the theoretical mass of the generated silver powder.

[0079] According to some embodiments of the present invention, the added amount of the surfactant is 2.8% to 4.5% of the theoretical mass of the generated silver powder.

[0080] According to some embodiments of the present invention, the mass ratio of the non-ionic surfactant to the ionic surfactant is 1:0.6-2.5.

[0081] According to some embodiments of the present invention, the mass ratio of the non-ionic surfactant to the ionic surfactant is 1:0.7-2.

[0082] According to some embodiments of the present invention, the dispersant includes at least one of gum arabic, gelatin, polyvinyl pyrrolidone, polyethylene glycol, polyacrylic acid, polycarboxylate, poly(meth)acrylic acid derivative, maleic anhydride copolymer or polyphosphate. The present invention uses a dispersant to prevent the agglomeration of silver powder particles.

[0083] According to some embodiments of the invention, the dispersant is polyvinyl pyrrolidone.

[0084] According to some embodiments of the present invention, during the process of adding the reducing agent in step S2, the temperature of the mixed solution is controlled to be 5° C. to 55° C.

[0085] According to some embodiments of the present invention, in the process of adding the reducing agent solution in step S2, the temperature of the mixed solution is preferably controlled at 10° C. to 40° C.

[0086] According to some embodiments of the present invention, the temperature of the mixed solution is more preferably controlled to be 20° C. to 30° C. during the process of adding the reducing agent solution in step S2.

[0087] According to some embodiments of the present invention, the reducing agent solution is added slowly in step S2, and the adding time is controlled to be 0.5 to 2 minutes.

[0088] According to some embodiments of the present invention, the temperature of the reducing agent solution in step S2 is 1 to 20° C. lower than the temperature of the reaction system in step S1.

[0089] According to some embodiments of the present invention, the temperature of the reducing agent solution in step S2 is 2-5° C. lower than the temperature of the reaction system in step S1.

[0090] According to some embodiments of the present invention, the reducing agent is a substance containing an aldehyde group or a hydroxyl group.

[0091] According to some embodiments of the invention, the reducing agent comprises at least one of ascorbic acid, formaldehyde, acetaldehyde, ethylene glycol or glycerol.

[0092] According to some embodiments of the present invention, the reducing agent is preferably ascorbic acid or formaldehyde.

[0093] According to some embodiments of the present invention, the reducing agent solution is an aqueous solution or an alcohol solution of the reducing agent.

[0094] According to some embodiments of the present invention, the amount of the reducing agent added is 1.1 to 2.6 times the equivalent of the silver ion content in the solution.

[0095] The equivalent is the molar amount of silver ions that can be reduced by 1 mol of the reducing agent; for example, 1 mol of ascorbic acid can reduce 2 mol of silver ions, so 1 mol of ascorbic acid is twice the equivalent of 1 mol of silver ions; for another example, 1 mol of formaldehyde can reduce 2 mol of silver ions, so 1 equivalent of formaldehyde is 1 / 2 of the molar mass of silver ions.

[0096] According to some embodiments of the present invention, the amount of the reducing agent added is 1.2 to 1.8 times the molar equivalent of the silver ion content in the solution.

[0097] According to some embodiments of the invention, the coating agent comprises at least one of lauric acid, oleic acid, stearic acid or n-decanoic acid.

[0098] According to some embodiments of the present invention, step S3 further comprises washing with pure water.

[0099] According to some embodiments of the present invention, the drying in step S3 is performed by using an oven at 40° C. to 80° C. for 8 to 16 hours.

[0100] The third aspect of the present invention provides application of the silver powder described in the first aspect of the present invention in the field of electronic component manufacturing.

[0101] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0102] Example 1

[0103] This embodiment provides a method for preparing silver powder with low silver content, and the specific steps are as follows:

[0104] 1) 574 g of silver nitrate was dissolved in 18000 g of distilled water, 514 g of ammonia solution with a mass concentration of 30% was added, and then 54 g of polyvinyl pyrrolidone (PVP-K30), 6 g of Span and 4.5 g of sodium dodecyl sulfate were added, and the mixture was stirred to obtain a silver complex solution, and the mixed solution was poured into a double-layer glass beaker, and 25° C. water was passed into the interlayer of the beaker to maintain a constant temperature;

[0105] 2) adding 5000 g of a solution containing 388 g of ascorbic acid at 23° C. to the mixed solution of step 1) at a rate of 5000 g / min at a stirring rate of 400 r / min, and maintaining the temperature change of the mixed solution in the whole process less than 2° C.;

[0106] 3) continuing to stir the mixed solution for 30 min, adding 20 g of an ethanol solution containing 30 wt % oleic acid for surface coating to obtain a suspension containing silver particles;

[0107] 4) The suspension is washed with pure water until the conductivity of the precipitated solution is greater than 0.2 ms, and then dispersed by centrifugation. The obtained solid is placed in an oven and dried at 60° C. for 12 h to obtain a dry powder, which is then crushed to obtain silver powder.

[0108] Example 2

[0109] This embodiment provides a method for preparing silver powder with low silver content, and the specific steps are as follows:

[0110] 1) 574 g of silver nitrate was dissolved in 18000 g of distilled water, 514 g of ammonia solution with a mass concentration of 30% was added, and then 54 g of polyvinyl pyrrolidone (PVP-K30), 6 g of Span and 6 g of sodium dodecyl sulfate were added, and the mixture was stirred to obtain a silver complex solution, and the mixed solution was poured into a double-layer glass beaker, and 25° C. water was passed into the interlayer of the beaker to maintain a constant temperature;

[0111] 2) adding 5000 g of a solution containing 388 g of ascorbic acid at 23° C. to the mixed solution of step 1) at a rate of 5000 g / min at a stirring rate of 400 r / min, and maintaining the temperature change of the mixed solution in the whole process less than 2° C.;

[0112] 3) continuing to stir the mixed solution for 30 min, adding 20 g of an ethanol solution containing 30 wt % oleic acid for surface coating to obtain a suspension containing silver particles;

[0113] 4) The suspension is washed with pure water until the conductivity of the precipitated solution is greater than 0.2 ms, and then dispersed by centrifugation. The obtained solid is placed in an oven and dried at 60° C. for 12 h to obtain a dry powder, which is then crushed to obtain silver powder.

[0114] Example 3

[0115] This embodiment provides a method for preparing silver powder with low silver content, and the specific steps are as follows:

[0116] 1) 574 g of silver nitrate was dissolved in 18000 g of distilled water, 514 g of ammonia solution with a mass concentration of 30% was added, 54 g of polyvinyl pyrrolidone (PVP-K30), 6 g of Span and 9 g of sodium dodecylbenzene sulfonate were added, and the mixture was stirred to obtain a silver complex solution, and the mixed solution was poured into a double-layer glass beaker, and 25° C. water was passed into the interlayer of the beaker to maintain a constant temperature;

[0117] 2) adding 5000 g of a solution containing 388 g of ascorbic acid at 23° C. to the mixed solution of step 1) at a rate of 5000 g / min at a stirring rate of 400 r / min, and maintaining the temperature change of the mixed solution in the whole process less than 2° C.;

[0118] 3) continuing to stir the mixed solution for 30 min, adding 20 g of an ethanol solution containing 30 wt % oleic acid for surface coating to obtain a suspension containing silver particles;

[0119] 4) The suspension is washed with pure water until the conductivity of the precipitated solution is greater than 0.2 ms, and then dispersed by centrifugation. The obtained solid is placed in an oven and dried at 60° C. for 12 h to obtain a dry powder, which is then crushed to obtain silver powder.

[0120] Comparative Example 1

[0121] This comparative example provides a method for preparing silver powder, and the specific steps are as follows:

[0122] 1) 574 g of silver nitrate was dissolved in 18000 g of distilled water, 514 g of ammonia solution with a mass concentration of 30% was added, 54 g of polyvinyl pyrrolidone (PVP-K30), 2 g of Span and 1 g of sodium dodecyl sulfate were added, and the mixture was stirred to obtain a silver complex solution, and the mixed solution was poured into a double-layer glass beaker, and 25° C. water was introduced into the interlayer of the beaker to maintain a constant temperature;

[0123] 2) adding 5000 g of a solution containing 388 g of ascorbic acid at 23° C. to the mixed solution of step 1) at a rate of 5000 g / min at a stirring rate of 400 r / min, and maintaining the temperature change of the mixed solution in the whole process less than 2° C.;

[0124] 3) continuing to stir the mixed solution for 30 min, adding 20 g of an ethanol solution containing 30 wt % oleic acid for surface coating to obtain a suspension containing silver particles;

[0125] 4) The suspension is washed with pure water until the conductivity of the precipitated solution is greater than 0.2 ms, and then dispersed by centrifugation. The obtained solid is placed in an oven and dried at 60° C. for 12 h to obtain a dry powder, which is then crushed to obtain silver powder.

[0126] Comparative Example 2

[0127] This comparative example provides a method for preparing silver powder, and the specific steps are as follows:

[0128] 1) 574 g of silver nitrate was dissolved in 18000 g of distilled water, 514 g of ammonia solution with a mass concentration of 30% was added, 54 g of polyvinyl pyrrolidone (PVP-K30) and 10 g of sodium dodecyl sulfate were added, and the mixture was stirred to obtain a silver complex solution. The mixed solution was poured into a double-layer glass beaker, and 25° C. water was introduced into the interlayer of the beaker to maintain a constant temperature;

[0129] 2) adding 5000 g of a solution containing 388 g of ascorbic acid at 23° C. to the mixed solution of step 1) at a rate of 5000 g / min at a stirring rate of 400 r / min, and maintaining the temperature change of the mixed solution in the whole process less than 2° C.;

[0130] 3) continuing to stir the mixed solution for 30 min, adding 20 g of an ethanol solution containing 30 wt % oleic acid for surface coating to obtain a suspension containing silver particles;

[0131] 4) The suspension is washed with pure water until the conductivity of the precipitated solution is greater than 0.2 ms, and then dispersed by centrifugation. The obtained solid is placed in an oven and dried at 60° C. for 12 h to obtain a dry powder, which is then crushed to obtain silver powder.

[0132] Comparative Example 3

[0133] This comparative example provides a method for preparing silver powder, and the specific steps are as follows:

[0134] 1) 574 g of silver nitrate was dissolved in 18000 g of distilled water, 514 g of ammonia solution with a mass concentration of 30% was added, and then 54 g of polyvinyl pyrrolidone (PVP-K30), 6 g of Span and 12 g of sodium dodecyl sulfate were added, and the mixture was stirred to obtain a silver complex solution, and the mixed solution was poured into a double-layer glass beaker, and 25° C. water was passed into the interlayer of the beaker to maintain a constant temperature;

[0135] 2) adding 5000 g of a solution containing 388 g of ascorbic acid at 23° C. to the mixed solution of step 1) at a rate of 5000 g / min at a stirring rate of 400 r / min, and maintaining the temperature change of the mixed solution in the whole process less than 2° C.;

[0136] 3) continuing to stir the mixed solution for 30 min, adding 20 g of an ethanol solution containing 30 wt % oleic acid for surface coating to obtain a suspension containing silver particles;

[0137] 4) The suspension is washed with pure water until the conductivity of the precipitated solution is greater than 0.2 ms, and then dispersed by centrifugation. The obtained solid is placed in an oven and dried at 60° C. for 12 h to obtain a dry powder, which is then crushed to obtain silver powder.

[0138] Comparative Example 4

[0139] This comparative example provides a method for preparing silver powder, and the specific steps are as follows:

[0140] 1) 574 g of silver nitrate was dissolved in 18000 g of distilled water, 514 g of a 30% ammonia solution was added, 54 g of polyvinyl pyrrolidone (PVP-K30), 12 g of Span and 6 g of sodium dodecyl sulfate were added, and the mixture was stirred to obtain a silver complex solution. The mixed solution was poured into a double-layer glass beaker, and 25° C. water was introduced into the interlayer of the beaker to maintain a constant temperature;

[0141] 2) adding 5000 g of a solution containing 388 g of ascorbic acid at 23° C. to the mixed solution of step 1) at a rate of 5000 g / min at a stirring rate of 400 r / min, and maintaining the temperature change of the mixed solution in the whole process less than 2° C.;

[0142] 3) continuing to stir the mixed solution for 30 min, adding 20 g of an ethanol solution containing 30 wt % oleic acid for surface coating to obtain a suspension containing silver particles;

[0143] 4) The suspension is washed with pure water until the conductivity of the precipitated solution is greater than 0.2 ms, and then dispersed by centrifugation. The obtained solid is placed in an oven and dried at 60° C. for 12 h to obtain a dry powder, which is then crushed to obtain silver powder.

[0144] Comparative Example 5

[0145] This comparative example provides a method for preparing silver powder with low silver content, and the specific steps are as follows:

[0146] 1) 574 g of silver nitrate was dissolved in 18000 g of distilled water, 514 g of ammonia solution with a mass concentration of 30% was added, and then 54 g of polyvinyl pyrrolidone (PVP-K30), 6 g of Span and 3 g of sodium dodecyl sulfate were added, and the mixture was stirred to obtain a silver complex solution, and the mixed solution was poured into a double-layer glass beaker, and 25° C. water was passed into the interlayer of the beaker to maintain a constant temperature;

[0147] 2) adding 5000 g of a solution containing 388 g of ascorbic acid at 23° C. to the mixed solution of step 1) at a rate of 5000 g / min at a stirring rate of 400 r / min, and maintaining the temperature change of the mixed solution in the whole process less than 2° C.;

[0148] 3) continuing to stir the mixed solution for 30 min, adding 20 g of an ethanol solution containing 30 wt % oleic acid for surface coating to obtain a suspension containing silver particles;

[0149] 4) The suspension is washed with pure water until the conductivity of the precipitated solution is greater than 0.2 ms, and then dispersed by centrifugation. The obtained solid is placed in an oven and dried at 60° C. for 12 h to obtain a dry powder, which is then crushed to obtain silver powder.

[0150] Performance Test:

[0151] 1. The silver powder prepared in each Example 1 was observed using a scanning electron microscope (SEM). The results are as follows: Figure 1 shown.

[0152] From the SEM image of the silver powder prepared in Example 1, it can be seen that the silver powder prepared in this scheme is in a spherical shape with a particle size range of about 0.5 to 3 μm.

[0153] 2. In order to evaluate the effect of the scheme of the present invention on inhibiting the aging of silver powder, the grain sizes of the silver powder samples of each embodiment and comparative example and the commercially available silver powder were tested. The silver powder of the embodiment and comparative example was tested using X-ray diffraction (XRD), and the grain size of the peak corresponding to the 111 crystal plane was calculated using the Scherrer formula. The smaller the grain size, the smaller the aging degree of the silver powder, and the silver powder is more inclined to agglomerate;

[0154] In order to evaluate the silver content in the low-silver content silver powder prepared by the scheme of the present invention, the non-silver content in each silver powder was tested: a certain mass of each embodiment and comparative silver powder and commercially available silver powder were heated to 538° C., kept warm for 30 minutes, and the remaining mass was measured. The ratio of the reduced mass to the original mass was the non-silver content;

[0155] In order to evaluate the sintering activity of silver powder, a certain mass of the silver powder of each embodiment and comparative example and commercially available silver powder were mixed with an organic solvent and coated on an alumina ceramic substrate by screen printing, and heated at 250° C. for 5 min to obtain a silver film, and the square resistance of the silver film was tested.

[0156] The test results are shown in Table 1, which compares the grain size, non-silver content and square resistivity of the silver film after sintering of the silver powders of the embodiments and comparative examples and commercially available silver powders.

[0157] Table 1 Grain size, non-silver content and square resistance of silver film after sintering of each silver powder sample

[0158] Silver powder sample Grain size (nm) Non-silver content (wt%) Square resistance (mΩ / □) Example 1 27 1.12 2.87 Example 2 24 1.67 2.65 Example 3 22 2.31 2.48 Comparative Example 1 32 0.67 3.32 Comparative Example 2 29 0.87 3.19 Comparative Example 3 22 2.34 2.49 Comparative Example 4 23 1.71 2.63 Comparative Example 5 28 0.73 3.14 Commercially available silver powder 1 29 0.69 3.21 Commercially available silver powder 2 40 0.68 3.54

[0159] It can be seen from the above test results that the silver powder prepared by the scheme of the present invention has a relatively small grain size and low silver content, and the silver film prepared by sintering has a lower square resistance. It can be seen from the preparation method and test results of the silver powder samples of each embodiment that with the increase in the amount of ionic surfactant used in the preparation process, the grain size of the silver powder shows a decreasing trend, which also shows that its degree of maturation continues to decrease, and the silver powder is more inclined to form agglomeration of silver microcrystalline particles, and the agglomerated part accounts for a higher proportion in the preparation process; the sintering activity of the silver powder is evaluated by the square resistance of the silver film after printing and sintering of each silver powder sample, and it is found that with the increase of the content of non-silver organic matter in the silver powder and the decrease of the degree of maturation, the square resistance of the silver film after sintering decreases, indicating that the sintering activity of the silver powder is improved.

[0160] In the silver powder preparation process of Comparative Example 1, the dosage of both types of surfactants is low, making it difficult to control the content of non-silver organic matter in the prepared silver powder, and it is difficult to adjust the degree of maturation of the silver powder, resulting in a larger grain size of the silver powder, a lower non-silver content, and a higher square resistance of the silver film prepared by sintering the silver powder. Comparative Example 5 increases the dosage of the two types of surfactants, and the silver powder obtained has appropriately reduced the silver powder grain size, silver content and square resistance of the silver film compared to Comparative Example 1, but still does not achieve the superior performance of the silver powder prepared in the example. Comparative Example 2 lacks the use of non-ionic surfactants in the preparation process, and it is also difficult to obtain a silver powder with better technical effects.

[0161] Comparative Examples 3 and 4 continue to increase the dosage of ionic surfactants and non-ionic surfactants, respectively, but the performance improvements are not obvious, especially the excessive dosage of non-ionic surfactants has an adverse effect; the results show that when the surfactant is added to a certain amount, the continued addition of surfactants has no obvious improvement effect on the silver powder, and will also increase the raw material cost and subsequent cleaning cost, so it is necessary to control the amount of surfactant added within an appropriate range.

[0162] In summary, the silver powder prepared by the scheme of the present invention is in a spherical shape with a particle size range of about 0.5 to 3 μm. The present invention achieves precise control of the non-silver content in the silver powder within the range of 1wt% to 3wt% by finely regulating the silver powder nucleation and agglomeration process, and enables the prepared silver powder to have a relatively low grain size and degree of maturation, so that it has a high sintering activity. The silver powder prepared by the present invention is used for sintering, and can be rapidly sintered at a lower temperature in an infrared sintering furnace, and the silver film prepared by sintering has a lower square resistance. The silver powder provided by the present invention not only meets the strict requirements of electronic components for sintering temperature and time, but also significantly reduces the consumption of silver and reduces production costs. It has a good application prospect in electronic components such as internal electrodes of stacked capacitors, positive grid lines of solar cells, and 5G filters.

[0163] The above is a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A method for preparing silver powder, characterized in that: The following steps are involved: S1, preparing a reaction system containing silver ions or silver complexes, adding a dispersant and a surfactant to the reaction system, and stirring and mixing; S2, adding reducing agent solution, stirring and mixing to react, and adding coating agent; S3, centrifuge to obtain a solid, dry it, and grind it to obtain silver powder; The surfactants include ionic surfactants and nonionic surfactants; The ionic surfactant includes at least one of sulfonate, sulfate, phosphate or carboxylate; The nonionic surfactant includes at least one of Span or Tween; The amount of the surfactant added is 2.5% to 4.5% of the theoretical mass of the generated silver powder; The mass ratio of the nonionic surfactant to the ionic surfactant is 1:0.6-2.5; The reducing agent is a substance containing an aldehyde group or a hydroxyl group.

2. The preparation method according to claim 1, characterized in that: The concentration of silver in the reaction system described in step S1 is 0.1-1 mol / L.

3. The preparation method according to claim 1, characterized in that: The silver complex described in step S1 is generated by silver ions and at least one substance selected from ammonia, ammonium salts, sulfites, sulfates, amines or transition metal ions.

4. The preparation method according to claim 1, characterized in that: The dispersant comprises at least one of gum arabic, gelatin, polyvinyl pyrrolidone, polyethylene glycol, polyacrylic acid, polycarboxylate, poly(meth)acrylic acid derivative, maleic anhydride copolymer or polyphosphate.

5. The preparation method according to claim 1, characterized in that: In step S2, the temperature of the mixed solution is controlled to be 5° C. to 55° C. during the process of adding the reducing agent.

6. A silver powder, characterized in that: The silver powder is prepared by the preparation method according to any one of claims 1 to 5, the silver content of the silver powder is 97wt% to 99wt%, and the particle size ranges from 0.5 to 3μm.

7. Use of the silver powder as claimed in claim 6 in the field of electronic component manufacturing.

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