Method for preparing spherical silver powder through semi-continuous method and spherical silver powder

Abstract

The invention provides a method for preparing spherical silver powder through a semi-continuous method and the spherical silver powder, and belongs to the technical field of photovoltaic silver powder preparation. The method comprises the following steps: preparing a base solution; silver powder nucleation; silver powder growth: a silver nitrate solution containing a dispersing agent and a reducing agent solution are added into the reaction kettle in a parallel flow mode and start to react, after the liquid level height of the reaction kettle reaches an expected value, the particle size of the spherical silver powder in the reaction kettle does not reach the target particle size, feed liquid in the reaction kettle overflows to an aging kettle while liquid is continuously sprayed to the reaction kettle, and the silver powder is obtained; and after the aging kettle is filled with the feed liquid to 20-75% of the volume of the aging kettle, the feed liquid in the aging kettle is discharged and concentrated and then flows back to the reaction kettle again to continue the reaction until the particle size of the spherical silver powder in the reaction kettle reaches the target particle size. According to the method, the material liquid in the reaction kettle is concentrated and then added into the reaction kettle again, meanwhile, the backflow speed of the slurry is controlled to be 0.5-2 times of the feeding speed, and the spherical silver powder with the better sphericity degree and the controllable particle size distribution can be obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of photovoltaic silver powder preparation, and in particular relates to a method for preparing spherical silver powder by a semi-continuous method and the spherical silver powder. Background Art

[0002] As we all know, solar energy is an inexhaustible renewable resource for human beings and occupies an important position in the long-term energy strategy. In recent years, with the continuous rise in global temperatures, it has seriously affected human survival, and the use and emission of fossil fuels have received more and more attention from various countries. As a clean energy, solar energy is safe and environmentally friendly during use, and is increasingly valued by people. Conductive silver paste is one of the important raw materials in the production process of solar cells, which has a serious impact on the photoelectric conversion efficiency of the battery. Conductive silver powder is the core component of conductive silver paste, and the performance of silver powder determines the performance of silver paste. At present, there is still a large gap between domestic silver powder and foreign countries in terms of morphology and structure, which has led to the current reliance on imports of high-quality conductive silver powder in my country, so the localization of high-quality silver powder is of great significance to my country.

[0003] The preparation methods of ultrafine silver powder mainly include gas phase method, liquid phase method and solid phase method. Liquid phase reduction method is currently a commonly used method for low-cost batch preparation of ultrafine silver powder. This method is simple to operate, with mild conditions and low equipment requirements. The applicant has previously applied for a method for preparing spherical silver powder by an intermittent method (application number: 202410272265.0) and a continuous method (application number: 202410811576.X), but these two inventions require the liquid to be divided into multiple reactors, which causes the number of silver powder nuclei in each reactor to drop sharply, and there is a risk of small nuclei again. The growth rate of silver powder particles is relatively fast, resulting in poor sphericity of silver powder, low output per unit reactor volume, and a large amount of reactors, which increases production costs. At the same time, the controllable distribution of silver powder particle size cannot be achieved. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a method for preparing spherical silver powder by a semi-continuous method and spherical silver powder. The present invention can continuously increase the solid content of the silver powder in the reactor by concentrating the feed liquid in the reactor and then adding it to the reactor again, thereby increasing the collision frequency between the silver powder particles and delaying the growth rate of the silver powder particles, thereby obtaining spherical silver powder with better sphericity; at the same time, by controlling the slurry reflux speed to 0.5-2 times the feed speed, spherical silver powders with different particle size distributions can be obtained.

[0005] The first aspect of the present invention discloses a method for preparing spherical silver powder by a semi-continuous method, the method comprising:

[0006] Step S1, adding pure water and dispersant into a reaction kettle to prepare a base liquid with a volume of 40% of the volume of the reaction kettle and stirring for a preset time;

[0007] Step S2, nucleation process: adding a silver nitrate solution containing a dispersant and a reducing agent solution into a reaction kettle to react, thereby completing the nucleation process of the silver powder;

[0008] Step S3, growth process: adding the silver nitrate solution containing the dispersant and the reducing agent solution into the reactor in parallel and starting the reaction, while continuously monitoring the liquid level in the reactor and the particle size of the spherical silver powder, until the particle size of the spherical silver powder in the reactor reaches the target particle size;

[0009] When the liquid level in the reactor reaches the expected value and the particle size of the spherical silver powder in the reactor reaches the target particle size, the reaction is terminated;

[0010] When the liquid level of the reactor reaches the expected value, but the particle size of the spherical silver powder in the reactor does not reach the target particle size, the liquid in the reactor overflows into the aging reactor while the liquid is continuously sprayed into the reactor. When the liquid in the aging reactor is filled to 20%-75% of the volume of the aging reactor, the liquid in the aging reactor is discharged and concentrated, and then refluxed into the reactor to continue the reaction until the particle size of the spherical silver powder in the reactor reaches the target particle size, and the reaction is terminated.

[0011] The flow rate of the silver nitrate solution containing the dispersant is 50-200 mL / min, the flow rate of the reducing agent solution is 75-300 mL / min, the reflux speed is 0.5-2 times the feed speed, the overflow speed is equal to the sum of the feed speed and the reflux speed, and the discharge speed of the feed liquid in the aging kettle is greater than or equal to the sum of the feed speeds;

[0012] Step S4, washing, centrifuging, dispersing and drying the spherical silver powder obtained in step S3 in sequence to obtain the target spherical silver powder.

[0013] According to the method for preparing spherical silver powder by a semi-continuous method according to the first aspect of the present invention, the method further comprises the following steps:

[0014] After the reaction, an alkali solution is added to the feed solution to make the pH of the feed solution equal to 12, and then a flocculant with a weight of 0.1% to 1% of the silver powder is added to the feed solution with a pH of 12 for flocculation and aging for 0.4 to 0.6 hours.

[0015] According to the method for preparing spherical silver powder by a semi-continuous method according to the first aspect of the present invention, the alkali solution is a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution;

[0016] The flocculant is one or more of oleic acid, stearic acid and polyacrylamide.

[0017] According to the method for preparing spherical silver powder by a semi-continuous process as described in the first aspect of the present invention, in the step S1, the concentration of the dispersant in the base liquid is 1.61-16.1 g / L.

[0018] According to the method for preparing spherical silver powder by a semi-continuous method according to the first aspect of the present invention, in the step S2, a silver nitrate solution containing a dispersant is first added to the reactor at a rate of 50-200 mL / min, and after the dropwise addition is completed, a reducing agent solution is then added to the reactor at a rate of 75-300 mL / min;

[0019] The dropwise addition time of the silver nitrate solution containing the dispersant and the reducing agent solution is 1-15 minutes.

[0020] According to the method for preparing spherical silver powder by a semi-continuous method described in the first aspect of the present invention, in step S2 and step S3, the molar ratio of silver nitrate to reducing agent added dropwise is 1:1.1-1:1.5.

[0021] According to the method for preparing spherical silver powder by a semi-continuous method as described in the first aspect of the present invention, the concentration of silver nitrate in the silver nitrate solution containing a dispersant is 0.5-2 mol / L, and the mass of the dispersant is 1%-10% of the mass of the silver nitrate;

[0022] The concentration of the reducing agent solution is 0.5-1.5 mol / L.

[0023] According to the method for preparing spherical silver powder by a semi-continuous method as described in the first aspect of the present invention, the reducing agent is one or more of ascorbic acid, glucose, hydrazine hydrate, hydrogen peroxide, and ferrous sulfate;

[0024] The dispersant is one or more of polyvinyl pyrrolidone K30, gum arabic, tannic acid, polyvinyl alcohol, gelatin, and polyethylene glycol.

[0025] According to the method for preparing spherical silver powder by the semi-continuous method described in the first aspect of the present invention, during the entire preparation process, the stirring speed is 200-400 r / min and the reaction temperature is 30-50°C.

[0026] The second aspect of the present invention discloses spherical silver powder prepared by the method for preparing spherical silver powder by the aforementioned semi-continuous method.

[0027] In summary, the solution proposed by the present invention has the following technical effects:

[0028] The present invention uses a method in which the feed liquid in the reactor is concentrated and then added back into the reactor, so that the solid content of the silver powder in the reactor can be continuously increased, thereby increasing the collision frequency between the silver powder particles and delaying the growth rate of the silver powder particles, thereby obtaining spherical silver powder with better sphericity; and at the same time, by controlling the slurry reflux speed to be 0.5-2 times the feed speed, spherical silver powders with different particle size distributions can be obtained.

[0029] In addition, the present invention adds alkali solution and flocculant to the reacted feed liquid before solid-liquid separation to remove the dispersant, thereby facilitating solid-liquid separation and improving the fluidity of the finished silver powder.

[0030] In addition, in the whole process of the present invention, only two reaction kettles are needed to complete the batch production of spherical silver powder, which has lower cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 It is a schematic diagram of the process of the present invention.

[0033] Figure 2 This is a scanning electron microscope image of spherical silver powder with a particle size of 0.9 μm prepared in specific embodiment 1 of the present invention.

[0034] Figure 3 This is a scanning electron microscope image of spherical silver powder with a particle size of 1.3 μm prepared in specific embodiment 1 of the present invention.

[0035] Figure 4 is a scanning electron microscope image of the spherical silver powder prepared in specific embodiment 2 of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Semi-continuous process: The reactor is fed continuously. When the reactor is full, the material overflows into the aging reactor. The slurry in the aging reactor is pumped into the concentrator through a pneumatic diaphragm pump. The concentrator discharges part of the mother liquor through the internal filter element pipe, and the formed concentrated slurry flows back to the reactor.

[0038] The first aspect of this embodiment discloses a method for preparing spherical silver powder by a semi-continuous method. The process is as follows: Figure 1 The method comprises:

[0039] Step S1, adding pure water and dispersant into a reaction kettle to prepare a base liquid with a volume of 40% of the volume of the reaction kettle and stirring for a preset time.

[0040] Step S2, nucleation process: adding a silver nitrate solution containing a dispersant and a reducing agent solution into a reaction kettle to react, thereby completing the nucleation process of the silver powder;

[0041] Step S3, growth process: adding the silver nitrate solution containing the dispersant and the reducing agent solution into the reactor in parallel and starting the reaction, while continuously monitoring the liquid level in the reactor and the particle size of the spherical silver powder, until the particle size of the spherical silver powder in the reactor reaches the target particle size;

[0042] When the liquid level in the reactor reaches the expected value and the particle size of the spherical silver powder in the reactor reaches the target particle size, the reaction is terminated;

[0043] When the liquid level in the reactor reaches the expected value, but the particle size of the spherical silver powder in the reactor has not reached the target particle size, the liquid in the reactor overflows into the aging reactor while the liquid is continuously sprayed into the reactor. When the liquid in the aging reactor is filled to 20%-75% of the volume of the aging reactor, the liquid in the aging reactor is discharged and concentrated, and then refluxed into the reactor to continue the reaction until the particle size of the spherical silver powder in the reactor reaches the target particle size, and the reaction is terminated.

[0044] Among them, the flow rate of the silver nitrate solution containing the dispersant is 50-200mL / min, the flow rate of the reducing agent solution is 75-300mL / min, the reflux speed is 0.5-2 times the feed speed, the overflow speed is equal to the sum of the feed speed and the reflux speed, and the discharge speed of the liquid in the aging kettle is greater than or equal to the sum of the feed speeds.

[0045] Preferably, the expected value is any value greater than 50% of the volume of the reactor, more preferably, the expected value is 80-95% of the volume of the reactor, and more preferably, the expected value is 90%-95% of the volume of the reactor.

[0046] Preferably, a concentrator is used to concentrate the liquid in the aging kettle, and the filtration accuracy of the concentrator is 0.1-0.2 μm.

[0047] Step S4, washing, centrifuging, dispersing and drying the spherical silver powder obtained in step S3 in sequence to obtain the target spherical silver powder.

[0048] The present invention can realize the arbitrary regulation of different particle size distributions in a single reactor by adjusting the reflux speed of the concentrated feed liquid. At the same time, the increase of the solid content of the silver powder in the system and the increase of the material residence time can be achieved through continuous concentration control, thereby increasing the collision frequency between the silver powder particles and delaying the growth rate of the silver powder particles, thereby achieving the purpose of improving the sphericity, and obtaining spherical silver powder with better sphericity and controllable particle size distribution.

[0049] When it is necessary to control the sample with slightly wide particle size distribution, the reflux speed is set to the minimum, such as 0.5 times the feed speed, and the sample replacement time in the aging kettle is extended, and the particle size distribution can be appropriately widened in the end; when the sample with concentrated particle size distribution is required, the reflux speed is set to the maximum, such as 2 times the feed speed, that is, the replacement of the liquid in the aging kettle can be completed at the fastest speed, ensuring the uniformity of the particle size of the samples in the aging kettle and the reactor. Therefore, the particle size distribution can be adjusted by adjusting the reflux speed.

[0050] In addition, the present invention separates the nucleation and growth processes of silver powder preparation, and the growth process starts immediately after the nucleation is completed, and the nucleation process will not occur again due to subsequent reactions. At the same time, these two processes are not the traditional process of silver crystal nuclei swallowing each other, but slowly grow on the basis of the nuclei generated after nucleation, and there is no process of mutual swallowing.

[0051] In step S1, pure water and dispersant are added into a reaction kettle to prepare a base liquid having a volume of 40% of the volume of the reaction kettle and stirred for a preset time.

[0052] In some embodiments, the concentration of the dispersant in the base solution is 1.61-16.1 g / L, preferably 4-10 g / L.

[0053] In some embodiments, the preset time is 0.5-1.5 hours, preferably 1 hour.

[0054] In some embodiments, the stirring speed is 200-400 r / min and the reaction temperature is 30-50° C. to control the reaction rate during the nucleation process and the growth process. Too low a temperature is not conducive to nucleation and may lead to fewer nuclei and agglomeration in the later stage.

[0055] The present invention first prepares a dispersant solution of a certain concentration as a base liquid before preparing the silver powder, so as to ensure that the silver crystal nuclei can be uniformly dispersed in the solution during the silver powder nucleation process to avoid agglomeration. Therefore, before the reaction, the present invention controls the dispersant concentration of the base liquid to be 1.61-16.1 g / L, so that the dispersant amount in the reactor of the whole system remains unchanged per unit time, improves the dispersibility of the silver powder in the solution, and is conducive to the growth of the silver powder.

[0056] In step S2, the nucleation process: adding the silver nitrate solution containing the dispersant and the reducing agent solution into the reaction kettle to react and complete the nucleation process of the silver powder.

[0057] In some embodiments, in step S2, the silver nitrate solution containing the dispersant is first added to the reactor at a rate of 50-200 mL / min, and after the dropwise addition is completed, the reducing agent solution is then added to the reactor at a rate of 75-300 mL / min;

[0058] The dropwise addition time of the silver nitrate solution containing the dispersant and the reducing agent solution is 1-15 min, preferably 8-10 min.

[0059] During the nucleation process, the silver nitrate solution is added first and then the reducing agent solution. Adding the two separately (1) can prevent the initial particle size of the silver powder from being too large and causing serious agglomeration; (2) the amount of silver crystal nuclei can be accurately controlled; and (3) the nucleation and growth processes of the silver powder can be separated without affecting each other.

[0060] Preferably, during the nucleation and growth process, a particle size distribution instrument is used to monitor the particle size of the spherical silver powder in real time.

[0061] In some embodiments, the concentration of silver nitrate in the silver nitrate solution containing a dispersant is 0.5-2 mol / L, and the mass of the dispersant is 1%-10% of the mass of the silver nitrate, preferably 3%-5%;

[0062] The concentration of the reducing agent solution is 0.5-1.5 mol / L.

[0063] Different from the prior art in which the dispersant and silver nitrate are mixed during the reaction, the present invention mixes the dispersant and silver nitrate into a silver nitrate solution containing the dispersant before the reaction, which has the following advantages: (1) compared with single silver, the dispersant has better complexing property for silver ions, and mixing in advance makes it easier to control the reaction rate of the nucleation process and the amount of silver crystal nuclei in the reactor more accurately; (2) due to the mixing in advance, the solid content of silver powder in the reactor per unit time is higher than that in the mixing during the reaction process. In the equipment with the same volume, the equipment utilization rate is high, and less wastewater is generated, thereby saving costs.

[0064] In some embodiments, the reducing agent is one or more of ascorbic acid, glucose, hydrazine hydrate, hydrogen peroxide, and ferrous sulfate, preferably ascorbic acid.

[0065] In some embodiments, the dispersant is one or more of polyvinyl pyrrolidone K30, gum arabic, tannic acid, polyvinyl alcohol, gelatin, and polyethylene glycol, preferably one or more of polyvinyl pyrrolidone K30, gum arabic, and gelatin.

[0066] In some embodiments, in step S2 and step S3, the molar ratio of silver nitrate to reducing agent added dropwise is 1:1.1-1:1.5.

[0067] In the present invention, the molar amount of the reducing agent added must be greater than the molar amount of the silver nitrate added to ensure that the reducing agent is in an excessive state. The preparation process of silver powder belongs to an oxidation-reduction process, and the byproduct of the reaction is nitric acid. Excessive reducing agent will prevent the reaction between silver powder and nitric acid, and the excess is generally 10-50%. Therefore, the molar ratio of silver nitrate to reducing agent added in the present invention is 1:1.1-1:1.5.

[0068] In some embodiments, the method further comprises the steps of:

[0069] After the reaction, an alkali solution is added to the feed solution to make the pH of the feed solution equal to 12, and then a flocculant with a weight of 0.1% to 1% of the silver powder is added to the feed solution with a pH of 12 for flocculation and aging for 0.4 to 0.6 hours.

[0070] It should be noted that the mass of silver powder used as a control for the amount of flocculant is the theoretical mass of silver powder calculated based on the amount of silver nitrate in the raw material.

[0071] In some embodiments, the alkali solution is an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution;

[0072] The flocculant is one or more of oleic acid, stearic acid and polyacrylamide, preferably polyacrylamide.

[0073] The present invention adjusts the pH value of the reaction kettle liquid to 12 by adding alkali solution to remove the dispersant, facilitate solid-liquid separation and improve the fluidity of the finished silver powder. At the same time, the addition of flocculant can pseudo-agglomerate the silver powder, facilitate precipitation, further facilitate solid-liquid separation, and improve the washing efficiency; on the other hand, it can reduce the ignition loss rate.

[0074] The second aspect of the present invention discloses a spherical silver powder prepared by the above-mentioned preparation method.

[0075] Example 1 Semi-continuous method for preparing spherical silver powder

[0076] Firstly, a silver nitrate solution containing a dispersant with a silver nitrate concentration of 2 mol / L is prepared, wherein the mass of the dispersant is 3% of the mass of the silver nitrate; and an ascorbic acid solution with a concentration of 1 mol / L is prepared as a reducing agent solution.

[0077] In the first step, 40L of pure water was added to the 100L first reactor, stirring was started and the stirring intensity was controlled (200-400r / min), an appropriate amount of dispersant was added to adjust the concentration of the base liquid to 4.08g / L, and the reaction temperature was controlled to 40°C.

[0078] In the second step, the silver nitrate solution containing the dispersant is first added into the reactor at a rate of 100 ml / min, and the dropping time is controlled within 10 minutes. After the dropping is completed, the reducing agent solution is started to be added, and the rate of the reducing agent solution is controlled at 150 ml / min, and the dropping time is also controlled within 10 minutes. After the dropping is completed, the nucleation process of the silver powder is completed.

[0079] In the third step, the silver nitrate solution containing the dispersant (the flow rate is controlled at 100 mL / min) and the reducing agent solution (the flow rate is controlled at 150 mL / min) are turned on at the same time, added into the reactor in parallel through a peristaltic pump and the reaction is started, while the liquid level in the reactor and the particle size of the spherical silver powder are continuously monitored until the particle size of the spherical silver powder in the reactor reaches the target particle size, completing the growth stage of the spherical silver powder.

[0080] When the liquid level in the reactor reaches 90%-95% of the volume of the reactor, the particle size of the spherical silver powder in the reactor reaches the target particle size, and the reaction is terminated.

[0081] When the liquid level in the reactor reaches 90%-95% of the volume of the reactor, the particle size of the spherical silver powder in the reactor has not reached the target particle size, the liquid in the reactor overflows into the aging reactor while continuously spraying the liquid into the reactor. When the liquid in the aging reactor is filled to 20%-75% of the volume of the aging reactor, the liquid in the aging reactor is concentrated by a concentrator with a filtration accuracy of 0.2 μm and then re-added to the reactor to continue the reaction until the particle size of the spherical silver powder in the reactor reaches the target particle size, and the reaction is terminated.

[0082] Among them, the reflux speed is twice the feed speed, the overflow speed is equal to the sum of the feed speed and the reflux speed, and the discharge speed of the liquid in the aging kettle is greater than or equal to the sum of the feed speeds.

[0083] The whole process is as follows Figure 1 shown.

[0084] The fourth step is to add sodium hydroxide aqueous solution to the feed solution after the reaction is completed so that the pH of the feed solution is 12, and then add polyacrylamide with a weight percentage of 0.5% of the silver powder to the feed solution with a pH of 12, and stir and age for 0.5 hours.

[0085] The fifth step is to wash the spherical silver powder obtained in the fourth step with deionized water at 50° C. and then centrifuge it, add 0.3-0.8% by mass of a surface coating agent and ethanol to the centrifuged spherical silver powder to obtain a spherical silver powder dispersion, use a high-speed disperser to high-speed disperse the spherical silver powder dispersion for 0.5-2h and then dry it to obtain the target spherical silver powder.

[0086] The surface coating agent is one or more of unsaturated higher fatty acids and amines with carbon atoms greater than or equal to 8. The drying temperature is 75-85°C and the drying time is 12-24 hours.

[0087] According to the process conditions of Example 1, the particle size of the silver powder is recorded as shown in Table 1, and the scanning electron microscope image of the silver powder is shown in Figure 2 shown.

[0088] Table 1

[0089]

[0090]

[0091] The silver powder obtained in Example 1 has a loss on ignition of 0.04%. The particle size distribution of the finished product is as follows: 10 :1.002d 50 :1.312d 90 :1.612.

[0092] As can be seen from Table 1, as the feeding begins, the crystal nuclei begin to grow rapidly, but as the solid content of the silver powder increases, the growth rate gradually slows down, and the collision of the silver powder particles increases. Figure 2 and Figure 3 It can be seen that the sphericity of the silver powder has become better.

[0093] Example 2 Semi-continuous method for preparing spherical silver powder

[0094] The difference from Example 1 is that in the third step: the reflux rate is 0.5 times the feed rate.

[0095] The silver powder obtained in Example 2 has a ignition loss of 0.03%. The particle size distribution of the finished product is as follows: d10: 0.65 d50: 1.54 d90: 2.60.

[0096] The particle size distribution data of the finished silver powder of the comparative example and example 2 and Figure 3 and Figure 4 It can be seen that the smaller the ratio of the reflux speed to the feed speed, the wider the particle size distribution of the finished silver powder.

[0097] Example 3 Semi-continuous method for preparing spherical silver powder

[0098] The difference from Example 1 is that in the third step: the reflux rate is 1 times the feed rate.

[0099] Example 4 Semi-continuous method for preparing spherical silver powder

[0100] The difference from Example 1 is that in the fourth step: polyacrylamide in an amount of 1% by weight of the silver powder is added to the liquid in the reactor, and the mixture is stirred and aged for 0.6 h.

[0101] Example 5 Semi-continuous method for preparing spherical silver powder

[0102] The difference from Example 1 is that in the fourth step: polyacrylamide in an amount of 0.1% by weight of the silver powder is added to the liquid in the reactor, and the mixture is stirred and aged for 0.4 h.

[0103] Example 6 Semi-continuous method for preparing spherical silver powder

[0104] The difference from Example 1 is that in the fourth step: the alkali solution is a potassium hydroxide aqueous solution.

[0105] Example 7 Semi-continuous method for preparing spherical silver powder

[0106] The difference from Example 1 is that in the first step: the concentration of the dispersant in the base liquid is 16.1 g / L, and the reaction temperature is 30°C.

[0107] Example 8 Semi-continuous method for preparing spherical silver powder

[0108] The difference from Example 1 is that in the first step: the concentration of the dispersant in the base liquid is 1.61 g / L, and the reaction temperature is 50°C.

[0109] Example 9 Semi-continuous method for preparing spherical silver powder

[0110] The difference from Example 1 is that the flow rate of the silver nitrate solution containing the dispersant is 50 mL / min, and the flow rate of the reducing agent solution is 75 mL / min.

[0111] Example 10 Semi-continuous method for preparing spherical silver powder

[0112] The difference from Example 1 is that the flow rate of the silver nitrate solution containing the dispersant is 200 mL / min, and the flow rate of the reducing agent solution is 300 mL / min.

[0113] In summary, the solution proposed by the present invention has the following technical effects:

[0114] The present invention uses a method in which the feed liquid in the reactor is concentrated and then added back into the reactor, so that the solid content of the silver powder in the reactor can be continuously increased, thereby increasing the collision frequency between the silver powder particles and delaying the growth rate of the silver powder particles, thereby obtaining spherical silver powder with better sphericity; and at the same time, by controlling the slurry reflux speed to be 0.5-2 times the feed speed, spherical silver powders with different particle size distributions can be obtained.

[0115] In addition, the present invention adds alkali solution and flocculant to the reacted feed liquid before solid-liquid separation to remove the dispersant, thereby facilitating solid-liquid separation and improving the fluidity of the finished silver powder.

[0116] In addition, in the whole process of the present invention, only two reaction kettles are needed to complete the batch production of spherical silver powder, which has lower cost.

[0117] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all belong to the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A method for preparing spherical silver powder by a semi-continuous process, characterized in that: The method comprises: Step S1, adding pure water and dispersant into a reaction kettle to prepare a base liquid with a volume of 40% of the volume of the reaction kettle and stirring for a preset time; Step S2, nucleation process: adding a silver nitrate solution containing a dispersant and a reducing agent solution into a reaction kettle to react, thereby completing the nucleation process of the silver powder; Step S3, growth process: adding the silver nitrate solution containing the dispersant and the reducing agent solution into the reactor in parallel and starting the reaction, while continuously monitoring the liquid level in the reactor and the particle size of the spherical silver powder, until the particle size of the spherical silver powder in the reactor reaches the target particle size; When the liquid level in the reactor reaches the expected value and the particle size of the spherical silver powder in the reactor reaches the target particle size, the reaction is terminated; When the liquid level of the reactor reaches the expected value, but the particle size of the spherical silver powder in the reactor does not reach the target particle size, the liquid in the reactor overflows into the aging reactor while the liquid is continuously sprayed into the reactor. When the liquid in the aging reactor is filled to 20%-75% of the volume of the aging reactor, the liquid in the aging reactor is discharged and concentrated, and then refluxed into the reactor to continue the reaction until the particle size of the spherical silver powder in the reactor reaches the target particle size, and the reaction is terminated. The flow rate of the silver nitrate solution containing the dispersant is 50-200 mL / min, the flow rate of the reducing agent solution is 75-300 mL / min, the reflux speed is 0.5-2 times the feed speed, the overflow speed is equal to the sum of the feed speed and the reflux speed, and the discharge speed of the feed liquid in the aging kettle is greater than or equal to the sum of the feed speeds; Step S4, washing, centrifuging, dispersing and drying the spherical silver powder obtained in step S3 in sequence to obtain the target spherical silver powder.

2. The method for preparing spherical silver powder by a semi-continuous method according to claim 1, characterized in that: The method further comprises the steps of: After the reaction, an alkali solution is added to the feed solution to make the pH of the feed solution equal to 12, and then a flocculant with a weight of 0.1% to 1% of the silver powder is added to the feed solution with a pH of 12 to carry out flocculation aging for 0.4 to 0.6 hours.

3. The method for preparing spherical silver powder by a semi-continuous method according to claim 2, characterized in that: The alkali solution is a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution; The flocculant is one or more of oleic acid, stearic acid and polyacrylamide.

4. The method for preparing spherical silver powder by semi-continuous method according to claim 1, characterized in that: In the step S1, the concentration of the dispersant in the base liquid is 1.61-16.1 g / L.

5. The method for preparing spherical silver powder by a semi-continuous method according to claim 1, characterized in that: In the step S2, the silver nitrate solution containing the dispersant is first added to the reactor at a rate of 50-200 mL / min, and after the dropwise addition is completed, the reducing agent solution is then added to the reactor at a rate of 75-300 mL / min; The dropwise addition time of the silver nitrate solution containing the dispersant and the reducing agent solution is 1-15 minutes.

6. The method for preparing spherical silver powder by a semi-continuous method according to claim 1, characterized in that: In step S2 and step S3, the molar ratio of silver nitrate to reducing agent added dropwise is 1:1.1-1:1.

5.

7. The method for preparing spherical silver powder by a semi-continuous method according to claim 1, characterized in that: The concentration of silver nitrate in the silver nitrate solution containing a dispersant is 0.5-2 mol / L, and the mass of the dispersant is 1%-10% of the mass of the silver nitrate; The concentration of the reducing agent solution is 0.5-1.5 mol / L.

8. The method for preparing spherical silver powder by a semi-continuous method according to claim 1, characterized in that: The reducing agent is one or more of ascorbic acid, glucose, hydrazine hydrate, hydrogen peroxide, and ferrous sulfate; The dispersant is one or more of polyvinyl pyrrolidone K30, gum arabic, tannic acid, polyvinyl alcohol, gelatin, and polyethylene glycol.

9. The method for preparing spherical silver powder by a semi-continuous method according to claim 1, characterized in that: During the entire preparation process, the stirring speed is 200-400 r / min and the reaction temperature is 30-50°C.

10. A spherical silver powder prepared by the method for preparing spherical silver powder by the semi-continuous method according to any one of claims 1 to 9.

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