A method for preparing silver powder for ultrafine line printing

Abstract

This application relates to the field of metal powder preparation technology, and in particular to a method for preparing silver powder for ultrafine line printing, comprising the following steps: preparing a silver ammonia solution and adding a dispersant, stirring to dissolve, adding a reducing agent solution, and aging to obtain nano-silver sol; forming a mixture of an initiator and deionized water, preparing aqueous solutions of acrylic acid and acrylamide separately, and adding them to the mixture for reaction, cooling and filtering to obtain an acrylic acid-acrylamide copolymer; weighing silver nitrate and deionized water, stirring to obtain solution A; weighing a reducing agent and deionized water, adjusting the pH to 1-2, and then adding the nano-silver sol and acrylic acid-acrylamide copolymer to obtain solution B; rapidly adding solution A to solution B, adding a surface modifier after the reaction is complete, aging, centrifuging, washing, and drying. The silver powder prepared by this application has the advantages of small average particle size, good overall uniformity, and small surface area, making it suitable for the field of ultrafine line printing.

Description

Technical Field

[0001] This application relates to the field of metal powder preparation technology, and in particular to a method for preparing silver powder for ultrafine line printing. Background Technology

[0002] High-speed screen printing is commonly used in the production of crystalline silicon solar cells. To achieve high conversion efficiency, the width of the grid electrodes must be reduced, resulting in increasingly narrower openings in the screen printing stencil. When the printing width of the fine grid needs to be reduced to below 15 micrometers, the stability of traditional front-side silver paste decreases significantly during high-speed printing, easily leading to problems such as grid breakage and screen clogging. However, reducing the printing speed leads to reduced production efficiency and increased costs, ultimately affecting the quality of crystalline silicon solar cells.

[0003] As the main material, silver powder directly affects the printing performance of the front-side silver paste, making the development of silver powder suitable for ultra-fine line printing particularly urgent. Generally speaking, the largest silver powder particle should be less than 1 / 3 of the screen printing plate aperture diameter, which requires the silver powder to have a small average particle size and good overall uniformity. In addition, the specific surface area of ​​the silver powder is also a key factor affecting the printing performance of the front-side silver paste. The larger the specific surface area of ​​the silver powder, the higher the viscosity of the resulting front-side silver paste, resulting in poor flowability and printing difficulties. Liquid-phase reduction is a common method for preparing silver powder. In order to reduce the average particle size and improve overall uniformity, a large amount of alkali and dispersant is usually added during the reaction process. This reaction method introduces more impurities, affecting the electrical properties of the silver powder. On the other hand, the prepared silver powder has a large specific surface area, resulting in high viscosity and poor printability after the front-side silver paste is made, which cannot meet the requirements of ultra-fine line printing.

[0004] Therefore, preparing a silver powder with small average particle size, good overall uniformity, and small specific surface area is of great significance for ultra-fine line printing. Summary of the Invention

[0005] In order to prepare a silver powder with small average particle size, good overall uniformity and small surface area to meet the requirements of the prepared silver paste for ultra-fine line printing, this application provides a method for preparing silver powder for ultra-fine line printing.

[0006] This application provides a method for preparing silver powder for ultra-fine line printing, using the following technical solution:

[0007] A method for preparing silver powder for ultra-fine line printing includes the following steps:

[0008] Preparation of nano-silver sol: Prepare silver ammonia solution, add dispersant to it, stir to dissolve, add reducing agent solution under stirring, and let it mature;

[0009] Preparation of acrylic acid-acrylamide copolymer: Initiator and deionized water are stirred and heated to form a mixture. Under nitrogen conditions, acrylic acid and acrylamide are separately prepared into aqueous solutions according to a certain monomer ratio and added to the mixture for reaction. After the reaction is completed, the mixture is cooled and filtered.

[0010] Preparation of silver powder for ultra-fine line printing: Weigh silver nitrate and deionized water, stir and dissolve to obtain solution A; weigh reducing agent and deionized water, stir the solution, add acid solution, adjust the pH value to 1-2, then add the nano silver sol and acrylic acid-acrylamide copolymer, stir to obtain solution B; under stirring conditions, rapidly add solution A to solution B with a feeding time of 1-20s, after the reaction is completed, add surface modifier, continue aging, centrifuge, wash and dry.

[0011] By adopting the above technical solution, the preparation method used in this application involves reacting under acidic conditions, using a self-made nano-silver sol to reduce the average particle size of the silver powder, and adding a very small amount of a self-made acrylic-acrylamide copolymer polymeric dispersant to improve overall uniformity. Simultaneously, the surface of the silver powder is adjusted to be smoother, effectively reducing the specific surface area. This yields silver powder suitable for ultra-fine line printing, with an average particle size between 0.5-1.5 μm, a maximum particle size <4.0 μm, and a specific surface area of ​​0.30-0.50 m². 2 With a particle size between / g and 100g, the average particle size is small, the overall uniformity is good, and the specific surface area is small, making it suitable for printing ultra-fine lines of silver paste on the front side.

[0012] Preferably, in the preparation process of the nano-silver sol, the concentration of the silver ammonia solution is 0.01-1 mmol / L; the mass ratio of ammonia to silver nitrate in the silver ammonia solution is (0.8-1):1; the mass ratio of the dispersant to silver nitrate is (1-100):1; and the molar ratio of the reducing agent to silver nitrate is (0.1-5):1.

[0013] By employing the above technical solution and selecting an ammoniacal solution of silver nitrate, a high silver reduction rate can be ensured. As the silver ion concentration decreases, the prepared silver nanoparticle sol becomes finer. With increasing silver ion concentration, the number of silver ions produced per unit time increases, leading to increased crystal nucleation and growth rates. However, since the silver reduction reaction is autocatalytic, the silver ions generated within the adsorption-diffusion layer accelerate the growth of silver crystals, resulting in a dominant growth rate and coarser particle size in the prepared silver nanoparticle sol. Simultaneously, the inhomogeneity within the solution increases with increasing silver ion concentration, causing irregular shapes on the surface of the prepared silver nanoparticle sol. Optimizing the mass ratio of silver nitrate to ammonia, dispersant, and reducing agent further refines the particle size of the prepared silver nanoparticle sol.

[0014] Preferably, the dispersant is one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, gelatin, gum arabic, and polyoxyethylene alkyl ether, more preferably polyethylene glycol; the reducing agent is one or more of hydrazine hydrate, sodium borohydride, glucose, sodium hypophosphite, ascorbic acid, and formaldehyde, more preferably hydrazine hydrate.

[0015] By adopting the above technical solution, a dispersant can be adsorbed onto the surface of silver particles to form a protective layer. When the silver particles approach each other, steric hindrance and vacancy effects can be generated in the region where the long chains of the dispersant overlap, thereby preventing the silver particles from approaching and agglomerating further. The use of polyethylene glycol as a dispersant can effectively improve the dispersion performance of silver colloidal solution, and improve colloidal stability by utilizing steric hindrance. The prepared silver sol is spherical and near-spherical with a narrow particle size distribution and high purity.

[0016] Silver powder produced by reducing silver nitrate solution with hydrazine hydrate has the characteristics of fine particle size and high purity. At the same time, the hydrazine hydrate reduction method has the advantages of short process flow, simple equipment, easy operation, high production efficiency and low cost.

[0017] Preferably, in the preparation process of the acrylic acid-acrylamide copolymer, the mass ratio of acrylic acid to acrylamide monomer is (0.1-1):1; the initiator is one or more of azobisisobutyramidine hydrochloride, potassium persulfate, sodium persulfate, and ammonium persulfate, and more preferably ammonium persulfate.

[0018] By adopting the above technical solution and optimizing the mass ratio of acrylic acid to acrylamide monomers, the polymerization reaction is stabilized, and the resulting copolymer has a moderate intrinsic viscosity. Adding an initiator can control the reaction rate and prevent gelation; ammonium persulfate can be used alone as an initiator. Its peroxy group (-OO-) breaks the -OO- bond upon heating, splitting into two corresponding free radicals, thereby initiating monomer polymerization.

[0019] Preferably, in the preparation process of the silver powder for ultrafine line printing, the concentration of solution A is 0.1-5 mol / L; the mass ratio of the reducing agent in solution B to the silver nitrate in solution A is (0.1-5):1; the mass ratio of the nano-silver sol added to solution B to the silver nitrate in solution A is (0.001-1):1; and the mass ratio of the acrylic acid-acrylamide copolymer added to solution B to the silver nitrate in solution A is (0.001-1):1.

[0020] More preferably, the concentration of solution A is 0.1-3 mol / L; the mass ratio of reducing agent in solution B to silver nitrate in solution A is (0.2-1):1; the mass ratio of nano-silver sol added to solution B to silver nitrate in solution A is (0.005-0.5):1; and the mass ratio of acrylic acid-acrylamide copolymer added to solution B to silver nitrate in solution A is (0.001-0.01):1.

[0021] By adopting the above technical solutions, the mass ratio of reducing agent to silver nitrate is optimized to maximize the yield of silver powder, while controlling the rate of chemical reaction, thereby controlling the particle size, morphology and dispersion of the obtained silver powder; by optimizing the mass ratio of nano-silver sol to silver nitrate, the average particle size of silver powder is further reduced; by optimizing the mass ratio of self-made acrylic acid-acrylamide copolymer polymeric dispersant to silver nitrate, the overall uniformity of silver powder is further improved.

[0022] Preferably, the reducing agent is one or more of glucose, ascorbic acid, hydrazine hydrate, sodium hypophosphite, triethanolamine, and formaldehyde; and the acid solution is one or more of formic acid, acetic acid, concentrated sulfuric acid, and concentrated nitric acid.

[0023] Preferably, in the preparation process of the silver powder for ultra-fine line printing, the surface modifier is one or more of oleic acid, ammonium oleate, and aliphatic carboxylic acids, and more preferably oleic acid.

[0024] By adopting the above technical solution, in order to obtain silver powder particles with specific physical properties, it is necessary to improve the dispersion effect of silver powder. Adding an appropriate amount of small molecule surfactant to the reaction system helps to further improve the dispersibility of silver powder. In the early stage of the reaction, silver crystal nuclei are generated, and the small molecule surfactant is immediately adsorbed on the surface, reducing the surface energy of the silver crystal nuclei, further improving the dispersibility and tap density of silver powder, facilitating subsequent cleaning, and making it suitable for widespread application.

[0025] Preferably, in the preparation process of the silver powder for ultra-fine line printing, the temperature during stirring is 10-50℃, and the feeding time is 1-20s.

[0026] By adopting the above technical solution, it is known from the nucleation and growth mechanism of crystals that the particle size and external shape of crystals are determined by multiple factors. When the feeding method is too fast, a large number of silver atoms are reduced and generated in a very short time, resulting in significant inhomogeneity. Agglomeration between crystal nuclei occurs simultaneously with crystal growth, and the crystal growth mechanism may follow a building block growth pattern. Therefore, the prepared silver powder has a large particle size and irregular shape. By optimizing the feeding time, the nucleation rate and growth rate of the crystals are both relatively equal, resulting in silver powder with good particle size uniformity and regular shape. Simultaneously, the silver atoms generated during reduction diffuse sufficiently under stirring, allowing for nucleation and growth. This method produces silver powder with a fine particle size, regular shape, and uniform particle size.

[0027] Higher reaction temperatures accelerate the reduction of silver, increasing the number of silver atoms produced per unit time. This leads to increased nucleation and growth rates. The reduction reaction also increases the number of silver atoms in the adsorption and diffusion layer on the nucleus surface, accelerating growth and resulting in a relatively higher crystal growth rate and coarser silver powder. Therefore, while ensuring a high powder generation rate, appropriately optimizing the reaction reduction temperature can help prepare fine-grained silver powder.

[0028] In summary, this application includes at least one of the following beneficial technical effects:

[0029] 1. The silver powder prepared in this application for ultra-fine line printing has an average particle size between 0.5-1.5 μm, a small average particle size, a maximum particle size of <4.0 μm, and good overall uniformity. It will not cause problems such as grid breakage or screen clogging when printing at high speed on a narrow-aperture screen printing plate.

[0030] 2. The silver powder prepared in this application for ultrafine line printing has a specific surface area of ​​0.30-0.50 m². 2 The formula is between / g, which solves the technical problem of large specific surface area of ​​small-particle silver powder. After being made into front silver paste, it has low viscosity and good printing stability, and is suitable for high-speed narrow-aperture ultra-fine line printing of front silver paste.

[0031] 3. The method for preparing silver powder for ultra-fine line printing in this application, under acidic conditions, allows the growth process of silver particles to be controlled by the presence of self-made nano silver sol, effectively reducing the average particle size of silver powder, eliminating the need to add a large amount of alkali solution and dispersant during the reaction process, and avoiding problems such as the introduction of impurities and separation difficulties.

[0032] 4. The method for preparing silver powder for ultra-fine line printing in this application uses a self-made acrylic acid-acrylamide copolymer with a large molecular weight. Only a very small amount needs to be added to form an adsorption layer of a certain thickness on the surface of silver particles, which increases the surface charge, prevents mutual adsorption and aggregation between particles, and improves the overall uniformity. Under the effect of steric hindrance, silver particles tend to form a more stable smooth surface, which reduces the specific surface area. The self-made polymeric dispersant has good water solubility and is easy to clean.

[0033] 5. The method for preparing silver powder for ultra-fine line printing described in this application controls the reaction process through self-made additives. It is highly innovative, easy to operate, has a large process window, is easy to achieve stable production, and is highly practical. Attached Figure Description

[0034] Figure 1 This is a SEM image of the silver powder prepared in Example 1 of this application.

[0035] Figure 2 This is a SEM image of the silver powder prepared in Example 10 of this application.

[0036] Figure 3 This is a SEM image of the silver powder prepared in Example 11 of this application.

[0037] Figure 4 This is a SEM image of the silver powder prepared in Comparative Example 1 of this application.

[0038] Figure 5 This is a SEM image of the silver powder prepared in Comparative Example 2 of this application. Detailed Implementation

[0039] The present application will be further described in detail below with reference to embodiments and accompanying drawings.

[0040] All raw materials used in the examples are commercially available.

[0041] Example 1

[0042] This embodiment discloses a method for preparing silver powder for ultrafine line printing, including the following steps:

[0043] S1, Preparation of nano-silver sol: At 25℃, prepare 1L of 0.1mmol / L silver ammonia solution, wherein the mass ratio of ammonia to silver nitrate is 0.9:1, add 0.5g of polyethylene glycol, stir to dissolve evenly, and then add 1L of 0.08mmol / L hydrazine hydrate solution under stirring, and let it mature for 30min to obtain nano-silver sol for later use.

[0044] S2, Preparation of acrylic acid-acrylamide copolymer: First, add 0.8g ammonium persulfate and 200g deionized water to the reaction vessel, stir and heat to 70℃, under nitrogen conditions, prepare 400g aqueous solutions of 90g acrylic acid and 210g acrylamide respectively, and add them dropwise at the same time. After reacting for 4 hours, cool and filter to obtain acrylic acid-acrylamide copolymer, which can be used as a polymeric dispersant for later use.

[0045] S3, the preparation of silver powder for ultra-fine line printing includes the following steps:

[0046] S31, Weigh 850g of silver nitrate and 10L of deionized water, stir until completely dissolved, to obtain solution A with a concentration of 0.5mol / L; S32, Weigh 680g of hydrazine hydrate and 10L of deionized water, stir until completely dissolved, add concentrated nitric acid to adjust the pH to 1.5, then add 42.5g of nano-silver sol and 5.1g of acrylic acid-acrylamide copolymer, stir evenly, to obtain solution B; In this embodiment, hydrazine hydrate is used as the reducing agent. In other embodiments, the reducing agent can also be one or more of hydrazine hydrate, glucose, sodium hypophosphite, ascorbic acid, triethanolamine, and formaldehyde; Concentrated nitric acid is used as the acid solution. In other embodiments, the acid solution can also be any one or more of formic acid, acetic acid, concentrated sulfuric acid, and concentrated nitric acid;

[0047] S33, under 45℃ and stirring conditions, solution A is rapidly added to solution B within 10 seconds. After the reaction is complete, oleic acid is added, and the mixture is allowed to mature for another 30 minutes. After centrifugation, washing, and drying, the finished product is obtained.

[0048] Example 2

[0049] This embodiment is basically the same as Example 1, except that, in S1, the preparation of the nano silver sol: at 25°C, 1L of 0.01mmol / L silver ammonia solution was prepared, wherein the mass ratio of ammonia to silver nitrate was 0.8:1. 0.01g of polyethylene glycol was added and stirred until dissolved. Then, 1L of 0.033mmol / L hydrazine hydrate solution was added under stirring and allowed to mature for 30min to obtain the nano silver sol for later use.

[0050] Example 3

[0051] This embodiment is basically the same as Example 1, except that, in S1, the preparation of the nano silver sol: at 25°C, 1L of 1mmol / L silver ammonia solution is prepared, wherein the mass ratio of ammonia to silver nitrate is 1:1. 1g of polyethylene glycol is added and stirred until dissolved. Then, under stirring, 1L of 0.067mmol / L hydrazine hydrate solution is added and allowed to mature for 30 minutes to obtain the nano silver sol for later use.

[0052] Example 4

[0053] This embodiment is basically the same as Example 1, except that in S2, the preparation of the acrylic acid-acrylamide copolymer is as follows: 0.8g of ammonium persulfate and 200g of deionized water are added to the reaction vessel, stirred and heated to 70°C. Under nitrogen conditions, 27g of acrylic acid and 270g of acrylamide are prepared into 400g aqueous solutions respectively and added dropwise. The reaction is carried out for 4 hours, cooled and filtered to obtain the acrylic acid-acrylamide copolymer, which is used as a polymeric dispersant for later use.

[0054] Example 5

[0055] This embodiment is basically the same as Example 1, except that in S2, the preparation of the acrylic acid-acrylamide copolymer is as follows: 0.8g of ammonium persulfate and 200g of deionized water are added to the reaction vessel, stirred and heated to 70°C. Under nitrogen conditions, 150g of acrylic acid and 150g of acrylamide are prepared into 400g aqueous solutions respectively and added dropwise. The reaction is carried out for 4 hours. After cooling and filtration, the acrylic acid-acrylamide copolymer can be obtained and used as a polymeric dispersant for later use.

[0056] Example 6

[0057] This embodiment is basically the same as Embodiment 1, except that: in S31, 170g of silver nitrate and 10L of deionized water are weighed and stirred until completely dissolved to obtain solution A with a concentration of 0.1mol / L; in S32, 17g of hydrazine hydrate and 10L of deionized water are weighed and stirred until completely dissolved, concentrated nitric acid is added to adjust the pH value to 1.5, and then 0.17g of nano silver sol and 0.17g of acrylic acid-acrylamide copolymer are added and stirred evenly to obtain solution B.

[0058] Example 7

[0059] This embodiment is basically the same as Embodiment 1, except that: in S31, 5100g of silver nitrate and 10L of deionized water are weighed and stirred until completely dissolved to obtain solution A with a concentration of 0.1mol / L; in S32, 1020g of hydrazine hydrate and 10L of deionized water are weighed and stirred until completely dissolved, concentrated nitric acid is added to adjust the pH to 1.5, and then 25.5g of nano silver sol and 51g of acrylic acid-acrylamide copolymer are added and stirred evenly to obtain solution B.

[0060] Example 8

[0061] This embodiment is basically the same as Embodiment 1, except that: in S31, 8500g of silver nitrate and 10L of deionized water are weighed and stirred until completely dissolved to obtain solution A with a concentration of 0.1mol / L; in S32, 8500g of hydrazine hydrate and 10L of deionized water are weighed and stirred until completely dissolved, concentrated nitric acid is added to adjust the pH value to 1.5, and then 4250g of nano silver sol and 8500g of acrylic acid-acrylamide copolymer are added and stirred evenly to obtain solution B.

[0062] Example 9

[0063] This embodiment is basically the same as Embodiment 1, except that: in S31, 850g of silver nitrate and 10L of deionized water are weighed and stirred until completely dissolved to obtain solution A with a concentration of 0.5mol / L; in S32, 4250g of hydrazine hydrate and 10L of deionized water are weighed and stirred until completely dissolved, concentrated nitric acid is added to adjust the pH to 1.5, and then 850g of nano silver sol and 85g of acrylic acid-acrylamide copolymer are added and stirred evenly to obtain solution B.

[0064] Example 10

[0065] This embodiment is basically the same as Embodiment 1, except that: in S31, 850g of silver nitrate and 10L of deionized water are weighed and stirred until completely dissolved to obtain solution A with a concentration of 0.5mol / L; in S32, 680g of hydrazine hydrate and 10L of deionized water are weighed and stirred until completely dissolved, concentrated nitric acid is added to adjust the pH to 1.5, and then 51g of nano silver sol and 5.1g of acrylic acid-acrylamide copolymer are added and stirred evenly to obtain solution B.

[0066] Example 11

[0067] This embodiment is basically the same as Embodiment 1, except that: in S31, 850g of silver nitrate and 10L of deionized water are weighed and stirred until completely dissolved to obtain solution A with a concentration of 0.5mol / L; in S32, 680g of hydrazine hydrate and 10L of deionized water are weighed and stirred until completely dissolved, concentrated nitric acid is added to adjust the pH value to 1.5, and then 42.5g of nano silver sol and 6.8g of acrylic acid-acrylamide copolymer are added and stirred evenly to obtain solution B.

[0068] Example 12

[0069] This embodiment is basically the same as embodiment 10, except that in S33, under the conditions of 10°C and stirring, solution A is rapidly added to solution B within 30 seconds. After the reaction is completed, oleic acid is added and the mixture is allowed to mature for another 30 minutes. After centrifugation, washing and drying, the finished product can be obtained.

[0070] Example 13

[0071] This embodiment is basically the same as embodiment 10, except that in S33, under the conditions of 30°C and stirring, solution A is rapidly added to solution B within 20 seconds. After the reaction is completed, oleic acid is added and the mixture is allowed to mature for another 30 minutes. After centrifugation, washing and drying, the finished product can be obtained.

[0072] Example 14

[0073] This embodiment is basically the same as embodiment 10, except that in S33, under the conditions of 50°C and stirring, solution A is rapidly added to solution B within 1 second. After the reaction is completed, oleic acid is added, and the product is further aged for 30 minutes. After centrifugation, washing and drying, the finished product can be obtained.

[0074] Comparative Example

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 10 is that S1 is omitted and nano-silver sol is not added in S3, while the remaining steps are the same as in Example 10.

[0077] Comparative Example 2

[0078] The difference between this comparative example and Example 10 is that S2 is omitted, and in S3, the acrylic acid-acrylamide copolymer is replaced with an equal amount of gum arabic. The remaining steps are the same as in Example 9.

[0079] Performance testing

[0080] 1. Particle size detection

[0081] The silver powder in each example and comparative example was tested using a Malvern 2000 particle size analyzer to determine the average and maximum particle size of the silver powder.

[0082] 1. Specific surface area

[0083] The specific surface area of ​​the silver powder in each embodiment and comparative example was measured using a HORIBA SA-9600 Series specific surface area analyzer.

[0084] Table 1 Performance test data of Examples 1-14 and Comparative Examples 1-2

[0085]

[0086] Refer to Table 1 and combine with Figure 1-5 , Figure 1-5 According to the scanning electron microscope (SEM) of JEOL JSM-7800, compared with Examples 1-14 and Comparative Examples 1-2, the silver powder prepared in this application has a small average particle size, a maximum particle size of <3.05μm, good overall uniformity, and a small specific surface area. In Comparative Example 1, no self-made nano-silver sol was added during the preparation process, and the growth process of silver particles was uncontrollable, resulting in larger average and maximum particle sizes of silver powder. In Comparative Example 2, gum arabic was used instead of the self-made polymeric dispersant during the preparation process. The silver particles were affected by the gum arabic, resulting in inconsistent growth in various directions, forming a rough surface with a large surface area.

[0087] Silver powder obtained from Examples 1, 10, and 11 and Comparative Examples 1-2 was used to prepare silver paste for the front side of crystalline silicon solar cells. 94% silver powder and 6% organic carrier by weight were mixed evenly and then milled using a three-roll mill to obtain six kinds of silver paste for the front side of crystalline silicon solar cells. The pastes were then printed on monocrystalline silicon solar cells at high speed using a screen printing plate with 12μm openings. The printing performance of the silver paste was evaluated, and the test results are shown in Table 2.

[0088] Table 2. Detection data of the front silver paste prepared in Examples 1, 10, 11 and Comparative Examples 1-2.

[0089]

[0090] Referring to Table 2, it can be seen that the silver powder prepared in this application example, when used to make silver paste for the front side of crystalline silicon solar cells, exhibits significantly better printing performance than the silver powder prepared in the comparative example and the silver paste made from commercially available silver powder when printed at high speed on a screen printing plate with 12-micron apertures. This indicates that the lower specific surface area of ​​the silver powder ensures that the prepared front side silver paste has low viscosity, small average particle size, and good overall uniformity, making it easier for the silver powder to pass through the mesh without causing problems such as screen clogging or grid breakage. Therefore, it has good printing performance and is suitable for ultra-fine line printing. The silver powder prepared in Comparative Example 1 has a large average particle size and a large maximum particle size, resulting in poor overall uniformity and easy screen clogging. The silver powder prepared in Comparative Example 2 has a large specific surface area, resulting in high viscosity and poor flowability after being made into front side silver paste. The silver powder prepared in the comparative examples all exhibited screen clogging and grid breakage, failing to meet the requirements of ultra-fine line printing.

[0091] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing silver powder for ultrafine line printing, characterized in that: Includes the following steps: Preparation of nano-silver sol: Prepare a silver ammonia solution, add a dispersant, stir to dissolve, then add a reducing agent solution under stirring and allow to mature; Preparation of acrylic acid-acrylamide copolymer: Stir and heat an initiator and deionized water to form a mixture. Under nitrogen conditions, prepare aqueous solutions of acrylic acid and acrylamide in a certain monomer ratio, and add them to the mixture for reaction. After the reaction is complete, cool and filter; Preparation of silver powder for ultrafine line printing: Weigh silver nitrate and deionized water, stir to dissolve, and obtain solution A; Weigh a reducing agent and deionized water, stir the solution, add acid to adjust the pH to 1-2, then add the nano-silver sol and acrylic acid-acrylamide copolymer, and stir to obtain solution B; Under stirring conditions, rapidly add solution A to solution B with a feeding time of 1-30 seconds. After the reaction is complete, add a surface modifier, continue maturation, and then centrifuge, wash, and dry. In the preparation of the nano-silver sol, the concentration of the silver ammonia solution is 0.01-1 mmol / L; the mass ratio of ammonia to silver nitrate in the silver ammonia solution is (0.8-1):1; the mass ratio of the dispersant to silver nitrate is (1-100):1; and the molar ratio of the reducing agent to silver nitrate is (0.1-5):

1. In the preparation process of the acrylic acid-acrylamide copolymer, the mass ratio of acrylic acid to acrylamide monomer is (0.1-1):1; The concentration of solution A is 0.1-3 mol / L; the mass ratio of reducing agent in solution B to silver nitrate in solution A is (0.2-1):1; the mass ratio of nano-silver sol added to solution B to silver nitrate in solution A is (0.005-0.5):1; the mass ratio of acrylic acid-acrylamide copolymer added to solution B to silver nitrate in solution A is (0.001-0.01):

1.

2. The method for preparing silver powder for ultrafine line printing according to claim 1, characterized in that: The dispersant is one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, gelatin, gum arabic, and polyoxyethylene alkyl ether; the reducing agent is one or more of hydrazine hydrate, sodium borohydride, glucose, sodium hypophosphite, ascorbic acid, and formaldehyde.

3. The method for preparing silver powder for ultrafine line printing according to claim 1, characterized in that: The initiator is one or more of azobisisobutyramidine hydrochloride, potassium persulfate, sodium persulfate, and ammonium persulfate.

4. The method for preparing silver powder for ultrafine line printing according to claim 1, characterized in that: The reducing agent is one or more of glucose, ascorbic acid, hydrazine hydrate, sodium hypophosphite, triethanolamine, and formaldehyde; the acid solution is one or more of formic acid, acetic acid, concentrated sulfuric acid, and concentrated nitric acid.

5. The method for preparing silver powder for ultrafine line printing according to claim 1, characterized in that: In the preparation process of the silver powder used for ultra-fine line printing, the surface modifier is one or more of oleic acid, ammonium oleate, and aliphatic carboxylic acids.

6. The method for preparing silver powder for ultrafine line printing according to claim 1, characterized in that: In the preparation process of the silver powder used for ultra-fine line printing, the temperature during stirring is 10-50℃, and the feeding time is 1-20s.

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