A silver powder for solar positive silver and a method for preparing the same

Abstract

The application discloses a kind of silver powder of easy printing plasticity for solar positive silver and its preparation method, comprising the following steps: first, silver nitrate is added in reaction kettle, then deionized water is added for dissolution stirring, control in proper temperature, then quickly add dissolved vitamin C and dissolved dispersant and deionized water solution of precipitant, continue to carry out stirring reaction, continue to control this reaction temperature well, pour into vitamin C mixed solution reaction 10 minutes, continue to pour into the alcohol solution of proper dissolution of stearic acid in the process of stirring quickly, silver powder coating treatment is carried out, 3 minutes are carried out quickly separation of silver powder and solution, then silver powder is freeze-dried, then air grinding treatment is carried out, the final obtained silver powder tap density is greater than 6.5, silver powder particle size distribution is D10 1.2-1.4, D50 is 1.7-2.0, D90 is 2.3-2.5, and the particle size is very concentrated positive silver powder.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solar positive silver powder, and particularly relates to a silver powder easy to print and used for solar positive silver and a preparation method thereof. BACKGROUND

[0002] With the increasing demand for energy, solar energy as a clean energy is paid more and more attention. Solar energy is a green energy, and is paid more and more attention due to its advantages such as no pollution, inexhaustibility, and no limitation of regional resources, so solar cells emerge as the times require. The solar cell is a kind of semiconductor device capable of converting solar energy into electric energy. The solar cell will generate electric current under the condition of light, and the electric current is collected by the grid lines and electrodes and transmitted out. The front electrode and the grid lines of the solar cell are made of conductive silver paste through high-speed and high-precision screen printing, low-temperature drying, high-temperature sintering and other processes.

[0003] At present, there are related researches, for example, a preparation process of silver powder for printing paste in Chinese patent application No. CN201510852024.4, which comprises the following steps: step S100: taking silver nitrate crystals to prepare a silver nitrate solution; step S200: taking sodium carbonate crystals to prepare a sodium carbonate solution; step S300: respectively taking the silver nitrate solution and the sodium carbonate solution, and fully mixing to obtain solution A; step S400: adding a formaldehyde solution to the solution A until the reaction is complete to obtain solution B; and step S500: adding a nitric acid solution to the solution B to adjust the pH value, and continuing to stir to obtain silver powder. The silver powder prepared by the application has a narrow particle size distribution range and good morphology consistency, can be applied to printing paste of different application systems, and has a simple preparation process. However, it is found that the silver powder produced by the technical scheme of the patent has poor granularity, and the silver powder particle distribution shown in the SEM graph recorded in the patent is irregular, so it is difficult to make suitable solar positive silver paste.

[0004] The front silver paste of the solar cell mainly comprises four parts of silver powder, glass powder, additive and organic carrier. Among them, the performance of the silver powder is particularly important. The quality of the silver paste, the conductivity and the compactness of the conductive silver paste after film formation and other key technical indexes are determined by the performance of the silver powder. The shape and granularity of the micron silver powder will affect the performance of the silver paste, so the preparation of the silver powder is particularly important.

[0005] As an important material in the preparation process of solar cells, the quality and performance of silver powder have an important influence on the efficiency and service life of solar cells. At present, almost all silver powders at home and abroad have not improved the plasticity of fine line printing, resulting in that the existing silver powder is not suitable for solar positive silver paste, touch screen paste and 3D printer due to strong agglomeration, or the silver powder has wide particle size distribution range and inconsistent morphology, resulting in poor conductivity of the conductive silver paste using the silver powder.

[0006] Therefore, it is of great significance to develop a new type of easy-to-print plastic silver powder for solar positive silver, improve the printing performance of fine lines of subsequent solar positive silver paste, and improve the photoelectric conversion efficiency of the cell piece. SUMMARY

[0007] To solve the above technical problems, the application provides an easy-to-print plastic silver powder for solar positive silver and a preparation method thereof, which has great significance in improving the printing performance of fine lines of subsequent solar positive silver paste and improving the photoelectric conversion efficiency of the cell piece.

[0008] The object of the application is achieved by the following technical solutions.

[0009] A preparation method of an easy-to-print plastic silver powder for solar positive silver, comprising the following steps:

[0010] 1) uniformly mix silver nitrate and deionized water in a mass ratio of 1:(5-20), stir and dissolve in a reaction kettle A, control the temperature at (35±1) DEG C, and maintain for 5-10 min;

[0011] 2) add deionized water, vitamin C, a dispersing agent and a settling agent, and concentrated nitric acid with a mass concentration of 60-80% in a reaction kettle B, wherein the mass ratio of the added vitamin C to silver nitrate is (1-1.5):1, the added amount of the dispersing agent and the settling agent is 1-3‰ of the mass of silver nitrate, the mass ratio of the dispersing agent to the settling agent is (10-20):1, and the added amount of the concentrated nitric acid is 0.5-5% of the mass of the vitamin C, then stir and dissolve in the reaction kettle, control the temperature at (35±1) DEG C, and maintain for 5-10 min;

[0012] The dispersing agent is selected from modified polyether with phosphorus element or sulfonic acid group, and the settling agent is selected from piperazine derivatives;

[0013] 3) quickly add the solution in the reaction kettle B to the reaction kettle A and continuously stir, then add an alcohol solution with dissolved stearic acid equivalent to 1-2% of the mass of silver nitrate for silver powder coating treatment, and separate the silver powder and the solution after 3-5 min, wherein the mass concentration of the alcohol solution with dissolved stearic acid is 15-25%;

[0014] 4) The silver powder separated in the previous step is subjected to freeze-drying, followed by air milling, to obtain a printable plastic silver powder for solar positive silver, having a tap density greater than 6.5 and a very concentrated particle size distribution, with D10 of 1.2-1.4, D50 of 1.7-2.0, and D90 of 2.3-2.5.

[0015] In the present application:

[0016] The dispersant in step 2) is a phosphorus element or sulfonic acid group modified polyether, and the dispersant functions to make the generated silver powder have a high degree of spheroid shape and uniformity, and due to the modified phosphorus element and sulfonic acid group in the dispersant, it also adheres to the surface of the silver powder during the reaction to form a coating and plays a role in printing plasticity in the subsequent configuration of the positive silver paste, and also has a relatively good dispersion effect, so that the silver powder particles are separated from each other and do not form hard agglomerates; and the settling agent is selected from piperazine derivatives, and the settling agent functions to make the generated silver powder particles smaller and the surface energy larger, so that agglomerated particles are formed during the reaction, which can quickly settle, avoiding the use of PVP and gelatin systems to form a suspended state of the silver powder, which is not easy to separate the silver powder from the liquid phase, and the single-particle silver powder also does not form large-particle single-crystal states, which affects the printing performance of the subsequent silver paste.

[0017] The modified polyether in step 2) is preferably a sulfonic acid group modified polyether, and the type is modified polyether 5120 (Zhejiang Weiva New Material Technology Co., Ltd.); and the piperazine derivative is preferably one of methyl piperazine, ethyl piperazine, and 1,4-dimethyl piperazine.

[0018] The dispersant and the settling agent in step 2) are added in an amount of 1-3‰ of the weight of silver nitrate, and less than this proportion, the effect of the dispersant and the settling agent will not be obvious, and the silver powder will have problems such as particle size agglomeration, poor particle concentration, and poor plasticity; and more than this proportion, the particle size of the silver powder will be too small, and problems such as poor particle concentration and poor plasticity will also occur.

[0019] The ratio of the dispersant (phosphorus element or sulfonic acid group modified polyether) and the settling agent (piperazine derivative) in step 2) is 10:1 to 20:1. If the proportion of the modified polyether is too high, then too many large single-crystal particles will be produced during the synthesis of the silver powder, resulting in a decrease in particle size concentration and difficulty in separating the silver powder from the liquid phase, which can easily float in the water during the water washing process and cannot quickly settle down; and if the proportion of the piperazine derivative is too high, then the sphericity of the silver powder during the synthesis will decrease, the silver powder will agglomerate, the dispersibility will decrease, and the particle size of the silver powder produced during the reaction will also decrease, resulting in a decrease in the tap density and a significant decrease in the printing fine line plasticity of the subsequent positive silver paste.

[0020] The quick separation of step 3) is achieved by using the method of suction filtration to separate the silver powder from deionized water, and finally, the silver powder is cleaned twice using alcohol with a mass concentration of 10-30%, because alcohol has the functions of dehydration and rapid evaporation, and the subsequent quick drying of the silver powder can be achieved.

[0021] The gas milling treatment of step 4) is specifically carried out by using a jet mill device for jet milling, and the gas milling process parameters are controlled as follows: the original powder thermal loss is less than 0.08%, the crushing pressure is 0.6 MPa, the feeding pressure is 0.3 MPa, and the feeding speed is 0.10-0.12 kg / min.

[0022] The present application also relates to a kind of silver powder for solar positive silver of easy printing plasticity, using the preparation method of the above-mentioned silver powder for solar positive silver of easy printing plasticity, the tap density of the silver powder is greater than 6.5, the particle size of the silver powder is very concentrated, and the distribution is D10 1.2-1.4, D50 is 1.7-2.0, and D90 is 2.3-2.5.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] 1、The preparation method of the silver powder for solar positive silver of easy printing plasticity, the reaction can be completed at room temperature without special adjustment of pH and temperature during production, which reduces the reaction energy consumption; in addition, compared with the traditional process, the process is relatively simple, the reaction time is relatively short, the production efficiency is greatly improved, and the production cost is saved.

[0025] 2、The preparation method of the silver powder for solar positive silver of easy printing plasticity, in the synthesis and distribution optimization of silver powder particles, the combination of dispersant and settling agent is used, wherein the dispersant of phosphorus element or sulfonic acid group modified polyether optimizes the concentration and particle size distribution range of the whole silver powder particles, the settling agent of piperazine derivative optimizes the particle state and surface condition of the silver powder, and the synthesized silver powder is easy to separate from the liquid phase, the silver powder particles produced by the method of the present application are well dispersed, and after synthesis in water, soft agglomeration is generated, so that the overall silver powder has a fast settling speed; the silver powder produced by the method of the present application can be washed to below 10 ppm during deionized water cleaning, and does not have the state that the silver powder is suspended in the solution and is not easy to separate as in other synthesis methods. The present application greatly optimizes the time required for the separation of silver powder and solution, so that the overall production process is extremely simple and easy to operate, and large-scale production can be achieved.

[0026] 3. The preparation method of the silver powder with easy printing plasticity for solar positive silver according to the application adopts the dispersing agent which is water-soluble and easy to dissolve and has a small amount, and compared with the dispersing agent such as PVP, gelatin and arabic resin used in the prior art, the dispersing agent is easy to clean and can be removed by washing with deionized water at ordinary temperature, and the production cost is lower.

[0027] 4. The silver powder with easy printing plasticity for solar positive silver according to the application can form soft agglomeration among multiple small silver powder particles into coarse silver powder particles in the preparation settlement process, so that the silver powder particles are more easily aggregated and precipitated in the reaction solution and are not easy to penetrate the centrifugal filter cloth, the proportion of the silver powder produced by the method is the highest, and there is basically no loss in continuous mass production, and the silver powder particles produced by the prior art method are in a suspended state, and some small silver powder particles are easy to penetrate the filter cloth and flow away during separation, so that not only the environment is polluted by heavy metal emissions, but also there is a big defect in the production cost. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is the SEM pattern of the silver powder with easy printing plasticity for solar positive silver prepared in the embodiment 1 of the application;

[0029] Figure 2 is the printing pattern of the positive silver paste of the silver powder with easy printing plasticity for solar positive silver prepared in the embodiment 1 of the application Figure 2 (a) is the top view of the printed circuit of the positive silver paste made of the silver powder in the embodiment 1 of the application; Figure 1 (b) is the side view of the printed circuit of the positive silver paste made of the silver powder in the embodiment 1 of the application; Figure 2 Figure 1

[0030] Figure 3 is the SEM pattern of the silver powder with easy printing plasticity for solar positive silver prepared in the embodiment 2 of the application;

[0031] Figure 4 is the printing pattern of the positive silver paste of the silver powder with easy printing plasticity for solar positive silver prepared in the embodiment 2 of the application Figure 4 (a) is the top view of the printed circuit of the positive silver paste made of the silver powder in the embodiment 2 of the application; Figure 3 (b) is the side view of the printed circuit of the positive silver paste made of the silver powder in the embodiment 2 of the application; Figure 4 Figure 3

[0032] Figure 5 is the SEM pattern of the silver powder with easy printing plasticity for solar positive silver prepared in the embodiment 3 of the application;

[0033] Figure 6 ​​​​is a printed pattern of a silver paste for solar positive silver prepared from the silver powder of Example 3 of the present application; Figure 6 (a) is a top view of a printed circuit prepared from the silver paste for solar positive silver; Figure 5 (b) is a side view of a printed circuit prepared from the silver paste for solar positive silver. Figure 6 (a) is a top view of a printed circuit prepared from the silver paste for solar positive silver; Figure 5 (b) is a side view of a printed circuit prepared from the silver paste for solar positive silver.

[0034] Figure 7 is a SEM pattern of a silver powder for solar positive silver prepared in Comparative Example 1 of the present application;

[0035] Figure 8 is a printed pattern of a silver paste for solar positive silver prepared from the silver powder of Comparative Example 1 of the present application; Figure 8 (a) is a top view of a printed circuit prepared from the silver paste for solar positive silver; Figure 7 (b) is a side view of a printed circuit prepared from the silver paste for solar positive silver. Figure 8 (a) is a top view of a printed circuit prepared from the silver paste for solar positive silver; Figure 7 (b) is a side view of a printed circuit prepared from the silver paste for solar positive silver.

[0036] Figure 9 is a SEM pattern of a silver powder for solar positive silver prepared in Comparative Example 2 of the present application;

[0037] Figure 10 is a printed pattern of a silver paste for solar positive silver prepared from the silver powder of Comparative Example 2 of the present application; Figure 10 (a) is a top view of a printed circuit prepared from the silver paste for solar positive silver; Figure 9 (b) is a side view of a printed circuit prepared from the silver paste for solar positive silver. Figure 10 (a) is a top view of a printed circuit prepared from the silver paste for solar positive silver; Figure 9 (b) is a side view of a printed circuit prepared from the silver paste for solar positive silver. DETAILED DESCRIPTION

[0038] The present application will be further described in detail by the following examples, but these examples should not be considered as limiting the present application. The raw materials and equipment in the examples of the present application are all commercially available unless otherwise specified, and the methods in the examples are all conventional methods in the art unless otherwise specified.

[0039] Example 1:

[0040] A method for preparing a silver powder for solar positive silver with easy printing plasticity, comprising the following steps:

[0041] Firstly, 48 kilograms of silver nitrate and 100 liters of deionized water are mixed and stirred to dissolve in a reaction kettle A, and the water temperature is controlled at 35°C;

[0042] In the second step, 32 kg of vitamin C was added to 100 L of deionized water in reactor B. 96 g of modified polyether 5120 (Zhejiang Weifa New Material Technology Co., Ltd.) and 9 g of methylpiperazine (Aladdin Company) were also added. The solution was stirred and the water temperature was controlled at 35°C.

[0043] In the third step, the solution in the B reactor was quickly added to the A reactor while stirring continuously. After the solution in the B reactor was poured in, the stirring reaction was continued for 10 minutes. Then, a 1 kg stearic acid solution dissolved in hot alcohol was quickly poured into the A reactor for coating. After 3 minutes, the silver powder and the solution were quickly separated. The silver powder was then freeze-dried and then air-milled to obtain silver powder A.

[0044] Its SEM images are as follows Figure 1 As shown, the front silver paste printing pattern is as follows Figure 2 As shown, the silver powder effect test data is shown in Table 1:

[0045] Loose density Tapped density D10 D50 D90 Specific surface 4.17 6.51 1.50 1.82 2.23 0.218

[0046] You can see Figure 1 The silver powder particles are evenly distributed and the particle size is uniform.

[0047] Figure 2 (a) Figure 2 (b) shows that the printed lines of the solar front silver paste made with this silver powder are continuous, uniform and well shaped.

[0048] Figure 2 It shows that the configured front silver paste has continuous fine printing and good shaping.

[0049] Example 2:

[0050] A method for preparing easily printable plastic silver powder for solar front silver comprises the following steps:

[0051] In the first step, 48 kg of silver nitrate and 100 liters of deionized water were mixed and dissolved in reactor A, and the water temperature was controlled at 35°C.

[0052] In the second step, 32 kg of vitamin C was added to 150 L of deionized water in reactor B. 150 g of modified polyether 5120 (Zhejiang Weifa New Material Technology Co., Ltd.) and 10 g of ethylpiperazine (Aladdin Company) were also added. The solution was stirred and the water temperature was controlled at 35°C.

[0053] Thirdly, the solution in the B reactor was quickly added to the A reactor with continuous stirring, and after the solution in the B reactor was poured in, the stirring was continued for 10 minutes, then 1 kg of stearic acid solution dissolved in hot alcohol was quickly poured into the A reactor for coating treatment, and the silver powder was quickly separated from the solution after 3 minutes, then the silver powder was freeze-dried and then air-milled, and finally the silver powder B was obtained;

[0054] The SEM image thereof is shown in Figure 3 The printed image of the prepared silver paste is shown in Figure 4 The silver powder effect test data are shown in Table 2:

[0055] Loose density Tapped density D10 D50 D90 Specific surface

[0056] It can be seen that the silver powder particles in Figure 3 are uniformly distributed, and the particle size uniformity is good.

[0057] Figure 4 (a) and Figure 4 (b) show that the solar silver paste printed lines made of the silver powder are continuous, uniform and have good plasticity.

[0058] Figure 4 It is shown that the prepared silver paste is continuously printed and has good plasticity.

[0059] Example 3:

[0060] A method for preparing a silver powder with easy printing plasticity for solar silver, comprising the following steps:

[0061] Firstly, 48 kg of silver nitrate and 150 liters of deionized water were mixed and stirred to dissolve in the A reactor, and the water temperature was controlled at 35℃;

[0062] Secondly, 32 kg of vitamin C was added to 120 L of deionized water in the B reactor, and 120 g of modified polyether 5120 (Zhejiang Weiva New Material Technology Co., Ltd.) and 8 g of 1,4-dimethylpiperazine (Araldite) were added at the same time, and the solution was stirred, and the water temperature was controlled at 35℃;

[0063] Thirdly, the solution in the B reactor was quickly added to the A reactor with continuous stirring, and after the solution in the B reactor was poured in, the stirring was continued for 10 minutes, then 1 kg of stearic acid solution dissolved in hot alcohol was quickly poured into the A reactor for coating treatment, and the silver powder was quickly separated from the solution after 3 minutes, then the silver powder was freeze-dried and then air-milled, and finally the silver powder C was obtained;

[0064] The SEM image thereof is shown in Figure 5 The printed image of the prepared silver paste is shown in Figure 6The silver powder effect test data are shown in Table 3:

[0065] Loose density Tapped density D10 D50 D90 Specific surface 3.95 6.56 1.49 1.92 2.31 0.265

[0066] It can be seen that Figure 5 the silver powder particle distribution is uniform, and the particle size uniformity is good.

[0067] Figure 6 (a), Figure 6 (b) indicates that the solar silver paste printed lines made of the silver powder are continuous, uniform and have good shape.

[0068] Figure 6 It indicates that the configured silver paste is printed continuously and has good shape.

[0069] Comparative Example 1:

[0070] The difference between Comparative Example 1 and Examples 1-3 is that the overall dispersant and settling agent addition ratio is reduced to one-tenth of the examples, which is lower than the dosage range of the examples.

[0071] The steps of the silver powder preparation method for solar silver are as follows:

[0072] First, 48 kg of silver nitrate and 100 liters of deionized water are mixed and stirred to dissolve in the A reaction kettle, and the water temperature is controlled at 35°C;

[0073] Second, 32 kg of vitamin C is added to 100 L of deionized water in the B reaction kettle, and 10 g of modified polyether 5120 (Zhejiang Weifan New Material Technology Co., Ltd.) and 1 g of methylpiperazine (Araladin Company) are added at the same time. Stir the solution and control the water temperature at 35°C;

[0074] Third, the solution in the B reaction kettle is quickly added to the A reaction kettle and continuously stirred. After the solution in the B reaction kettle is poured in and stirred for 10 minutes, 1 kg of stearic acid solution dissolved in hot alcohol is quickly poured into the A reaction kettle for coating treatment. After 3 minutes, the silver powder and the solution are quickly separated. Then the silver powder is freeze-dried, followed by air milling treatment. Finally, the silver powder D1 is obtained.

[0075] The SEM pattern is shown in Figure 7 The silver paste printing pattern is shown in Figure 8 The silver powder effect test data are shown in Table 4:

[0076] Loose density Tapped density D10 D50 D90 Specific surface 3.55 6.03 1.31 2.22 2.92 0.193

[0077] It can be seen that Figure 7The silver powder particle distribution uniformity in Comparative Example 2 is slightly worse than that of the examples, and due to the decrease in the amount of the overall dispersant, the generated silver powder particles are also slightly larger, and there are agglomeration phenomena in local areas, and local larger single-crystal silver powder particles, resulting in a larger final powder particle size, and the apparent density of the overall silver powder is significantly reduced, while Figure 8 (a), Figure 8 (b) indicates that the solar silver paste printed lines made of the silver powder have obvious broken grids, and the line uniformity is poor.

[0078] Figure 8 It indicates that the solar silver paste printed lines have obvious broken grids and poor plasticity.

[0079] Comparative Example 2:

[0080] The difference between Comparative Example 2 and Examples 1-3 is that the amount of the piperazine derivative in the settling agent is increased.

[0081] The steps of the silver powder preparation method for solar silver are as follows:

[0082] First, 48 kg of silver nitrate and 100 liters of deionized water are mixed and stirred to dissolve in the A reaction kettle, and the water temperature is controlled at 35°C;

[0083] Second, 32 kg of vitamin C is added to 100 L of deionized water in the B reaction kettle, and 10 g of modified polyether 5120 (Zhejiang Weifan New Material Technology Co., Ltd.) and 5 g of methyl piperazine (Araladin Company) are added at the same time, the solution is stirred, and the water temperature is controlled at 35°C;

[0084] Third, the solution in the B reaction kettle is quickly added to the A reaction kettle, and stirring is continuously performed. After the solution in the B reaction kettle is poured in, the stirring is continued for 10 minutes, and then 1 kg of stearic acid solution dissolved in hot alcohol is quickly poured into the A reaction kettle for coating treatment. After 3 minutes, the silver powder and the solution are quickly separated, and then the silver powder is freeze-dried and then subjected to air milling treatment, and finally the silver powder D2 is obtained.

[0085] The SEM pattern thereof is shown in Figure 9 The silver paste printing pattern configured is shown in Figure 10 The silver powder effect test data are shown in Table 5:

[0086] Loose density Tapped density D10 D50 D90 Specific surface 3.63 6.11 1.11 1.56 2.42 0.356

[0087] It can be seen that Figure 9 The sphericity of the silver powder particles in Comparative Example 2 is obviously decreased compared with the examples, and the generated silver powder particles are small, resulting in a small overall silver powder apparent density, while Figure 10 (a), Figure 10(b) indicates that the solar silver paste printed lines made of this silver powder also have obvious broken grids, and the line uniformity is very poor.

[0088] Figure 10 It indicates that the configured silver paste is printed with obvious broken grids and poor shaping.

[0089] Results and discussion:

[0090] 1. Compared with the prior art, for example, Chinese Patent Application No. CN201910201743.8 Single-dispersed conductive silver powder suitable for high and low temperature silver paste and its preparation method and Chinese Patent Application No. CN201711458387.5 Preparation method of spherical silver powder for photovoltaic positive silver electrode, the synthesis methods mentioned in them are relatively simple, but the separation of silver powder and solution is very difficult. These two documents only mention the advantages of their own synthesis, but avoid the time and tedious steps required in the separation process of silver powder and solution.

[0091] In Examples 1-3, special dispersants and settling agents are used to optimize the synthesis and distribution of silver powder particles. The dispersants of phosphorus element or sulfonic acid group modified polyether optimize the concentration and particle size distribution range of the overall silver powder particles, and the settling of piperazine derivatives optimizes the surface state and particle size of the silver powder, and makes the synthesized silver powder easy to separate from the liquid phase. The silver powder particles produced by the method of the present application are well dispersed, and after synthesis in water, soft agglomeration occurs, making the overall silver powder settle quickly. The silver powder produced by the method of the present application can be washed to below 10 ppm during deionized water washing, and does not appear in the state that the silver powder is suspended in the solution and is not easy to separate. The present patent application greatly optimizes the separation process of silver powder and solution, making the overall production process extremely simple and easy to operate for large-scale production.

[0092] 2. Compared with the prior art, for example, Chinese Patent Application No. CN201811139986.5 Conductive positive silver paste and its preparation method and Chinese Patent Application No. CN201711458387.5 Preparation method of spherical silver powder for photovoltaic positive silver electrode, PVP and gelatin, arabic resin and other dispersants used in these two patents.

[0093] Compared with Comparative Example 1, it is shown that the dispersants used in the present patent application are water-soluble dispersants that are easily soluble and have a small amount, and are easy to clean. They can be easily removed by washing with ordinary temperature deionized water. If the amount of dispersant and settling agent added is too low, large single crystal particles will be produced during the synthesis of silver powder, and agglomeration will occur in some parts, resulting in a large particle size of the overall silver powder and a decrease in the tap density of the silver powder, thereby affecting the subsequent positive silver paste preparation and printing test.

[0094] 3、Compared with the prior art, for example, a conductive positive silver paste and a preparation method thereof, Chinese patent application No. CN201811139986.5, a preparation method of spherical silver powder for photovoltaic positive silver electrode, Chinese patent application No. CN201711458387.5, the silver powder particles produced by them are in a suspended state, and some fine silver powder particles are easily lost through the filter cloth during separation. This not only pollutes the environment with heavy metal emissions, but also has a large defect in production cost.

[0095] Compared with Comparative Example 2, it is illustrated that too much addition of the settling agent can cause the formation of serious agglomeration between multiple small silver powder particles into coarse silver powder particles, the fraction performance between silver powder particles is reduced, the overall silver powder particle accumulation is not dense, the tap density of the silver powder is reduced, thereby affecting the subsequent positive silver paste preparation printing test. The preparation method of the present patent application can form soft agglomeration between multiple small silver powder particles into coarse silver powder particles during the settling process, so that the silver powder particles are more easily aggregated and settled in the reaction solution and are not easily passed through the centrifugal filter cloth. The proportion of the silver powder produced by such a method is the highest, and there is basically no loss in continuous mass production.

[0096] 4、Through the comparison of the basic properties of the examples and the comparative examples, the formula and silver powder preparation process of the examples are obviously superior to the comparative examples.

[0097] The above examples of the present application are only examples for clearly illustrating the present application, and are not limitations on the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the embodiments are not required to be exhausted. Any modification, equivalent replacement and improvement made within the spirit and principles of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A method for preparing easily printable plastic silver powder for solar front silver, characterized by: The steps include: 1) Mix silver nitrate and deionized water in a mass ratio of 1:(5-20) and dissolve in reactor A with stirring. The temperature is controlled at (35±1)℃ for 5-10 minutes. 2) Add deionized water, vitamin C, a dispersant and a precipitant, and concentrated nitric acid with a mass concentration of 60-80% to reactor B, wherein the mass ratio of the added vitamin C to the silver nitrate is (1-1.5):1, the added amount of the dispersant and precipitant is 1-3‰ of the mass of the silver nitrate, wherein the mass ratio of the dispersant to the precipitant is (10-20):1, and the added amount of concentrated nitric acid is 0.5-5% of the mass of the vitamin C. Stir and dissolve in the reactor, control the temperature at (35±1)°C, and maintain the temperature for 5-10 minutes; The dispersant is selected from phosphorus or sulfonic acid modified polyether, and the sedimentation agent is selected from piperazine derivatives; 3) The solution in reactor B is quickly added to reactor A while stirring continuously. An alcohol solution containing stearic acid at a concentration of 1-2% by mass of silver nitrate is then added to coat the silver powder. After 3-5 minutes, the silver powder and the solution are quickly separated. The concentration of the alcohol solution containing stearic acid is 15-25%. 4) The silver powder separated in the previous step is freeze-dried and then subjected to airflow milling to obtain easily printable plastic silver powder for solar front silver. The silver powder has a very concentrated particle size distribution, with a D10 of 1.2-1.4 μm, a D50 of 1.7-2.0 μm, and a D90 of 2.3-2.5 μm.

2. The method for preparing an easily printable plastic silver powder for solar front silver according to claim 1, characterized in that: The modified polyether in step 2) is selected from sulfonic acid modified polyether; the piperazine derivative is selected from methylpiperazine, ethylpiperazine, and 1,4-dimethylpiperazine.

3. The method for preparing an easily printable plastic silver powder for solar front silver according to claim 1, characterized in that: The rapid separation in step 3) is to achieve rapid separation of the silver powder from deionized water by suction filtration, and the final two washings are performed using alcohol with a mass concentration of 10-30%.

4. The method for preparing an easily printable plastic silver powder for solar front silver according to claim 1, characterized in that: In the air flow mill process, the heat loss of the raw powder is less than 0.08%, the crushing pressure is 0.6MPa, the feeding pressure is 0.3MPa, and the feeding speed is 0.10~0.12kg / min.

5. An easily printable plastic silver powder for solar front silver, characterized by: The silver powder is obtained by the preparation method of the easy-to-print plastic silver powder for solar front silver according to any one of claims 1 to 4. The particle size of the silver powder is very concentrated, with a distribution of D10 of 1.2-1.4 μm, D50 of 1.7-2.0 μm, and D90 of 2.3-2.5 μm.

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