A preparation method for in-situ generated flaky mixed silver powder and flaky mixed silver powder

Abstract

The invention belongs to the technical field of metal powder preparation for the electronic industry, and specifically discloses a method for preparing a flaky mixed silver powder in situ and the mixed silver powder. The method comprises reacting a silver salt ammonia complex solution and a reducing agent solution in the presence of a mixed shape dispersant aqueous solution; the flaky silver powder shape control dispersant comprises one or more polysaccharides and / or thiol compounds; the granular silver powder shape control dispersant comprises one or more proteins and high molecular weight amino compounds; the temperature is 30-100°C, and the mixture is stirred for more than 2 hours to obtain a suspension of flaky mixed silver powder in situ, and ultrasonic cleaning, filtration separation, and drying are used to obtain a flaky mixed silver powder with a flaky silver powder content of 10-90% and a thickness of less than 300nm, and a granular silver powder content of 90-10% and a particle size of less than 300nm. The in-situ generation of flaky mixed silver powder process of the present invention is simple to operate, has low production cost, and can obtain a flaky silver powder mixed product without a grinding process, and is suitable for large-scale industrial preparation.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of metal powder for electronic industry, and specifically relates to flake mixed silver powder and a preparation method thereof, in particular to a mixed silver powder preparation method which can generate in situ and adjust the flake mixing ratio without the need for a flake silver powder mixing process and the corresponding flake mixed silver powder. Background Art

[0002] As an important conductive functional material, electronic silver paste is widely used in a variety of electronic products such as touch screens, membrane switches, and solar cell electrodes. Silver powder is the conductive phase in electronic silver paste, which accounts for a large proportion of the paste. As the demand for electronic silver paste increases rapidly, the demand for silver powder also increases rapidly.

[0003] Silver paste manufacturers use flaky silver powder to make low-temperature sintered silver paste, which can form surface contact and line contact in the paste, with a larger contact area, so that the paste has better conductive properties, but the fluidity of the flaky silver powder needs to be improved. In view of this, in order to improve the fluidity and welding tension, the flaky silver powder particles used should be added with spherical silver powder to make flaky spherical mixed silver powder. The flaky silver powder used in the prior art is generally first made into spherical silver powder by chemical reduction method, and then made by mechanical grinding method. For example, patent CN 116638094 A adopts chemical reduction method. Although it can make spherical silver powders of different sizes at the same time, it still needs mechanical grinding to make flaky spherical mixed silver powder, which is not easy to mass produce on a large scale. In addition, this method produces flaky silver powder, and there are problems such as grinding aid pollution, deformation between crystal lattices, and crack residual stress in the flaky silver powder, which leads to unsatisfactory conductive properties, and the production process is complicated and costly. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems in the prior art that the flake silver of spherical mixed silver powder needs to be completed by mechanical grinding of other process lines, has many steps, and is not easy to mass produce. A mixed silver powder preparation method and corresponding flake mixed silver powder are provided, which can generate in situ and adjust the flake mixing ratio, reduce the flake silver powder mixing steps.

[0005] In order to solve the above technical problems, the present invention provides a method for preparing in-situ generated flaky mixed silver powder, which comprises preparing a silver salt ammonia complex solution and a reducing agent solution respectively; reacting the silver salt ammonia complex solution and the reducing agent solution in the presence of a mixed shape dispersant aqueous solution;

[0006] The mixed shape dispersant aqueous solution includes a flaky silver powder shape-controlling dispersant and a granular silver powder shape-controlling dispersant, wherein the flaky silver powder shape-controlling dispersant includes one or two of a polysaccharide and / or a thiol compound; and the granular silver powder shape-controlling dispersant includes one or more of a protein and a high-molecular amino compound;

[0007] The mixture is stirred at a temperature of 30 to 100° C. for more than 2 hours to obtain a suspension of mixed silver powder in a flaky state in situ, and the suspension is cleaned by ultrasonic wave, and a silver powder cake is obtained by filtration and separation; the silver powder cake is then washed with an amphiphilic solution, and dried to obtain mixed silver powder in a flaky state;

[0008] In the prepared flaky and granular mixed silver powder, flaky silver powder accounts for 10-90% and its thickness is below 300nm, and granular silver powder accounts for 90-10% and its particle size is below 300nm.

[0009] Preferably, the total weight of silver contained in 1L of synthetic system aqueous solution and the silver ammonia complex does not exceed 100g, the total weight of the reducing agent does not exceed 150g per 1L of synthetic system aqueous solution, and the total amount of ammonia is in the range of 2.3-6.0 times the amount of silver contained in the ammonia complex.

[0010] Preferably, a mixed shape dispersant aqueous solution of a flaky silver powder shape controlling dispersant and a granular silver powder shape controlling dispersant is added to an ammonia complex solution of a silver salt to prepare a mixed solution A, and the reducing agent solution is added to the mixed solution A in one batch or in batches, or the mixed solution A is added to the reducing agent solution in one batch or in batches.

[0011] Preferably, a mixed shape dispersant aqueous solution of a flaky silver powder shape controlling dispersant and a granular silver powder shape controlling dispersant is added to a reducing agent solution to prepare a reducing mixed solution B, and the reducing mixed solution B is added in batches or in batches to an ammine complex solution of a silver salt for reaction, or the ammine complex solution of a silver salt is added in batches to the reducing mixed solution B for reaction.

[0012] Preferably, an aqueous solution a of a dispersant for controlling the shape of flaky silver powder is prepared; an aqueous solution b of a dispersant for controlling the shape of granular silver powder is prepared; one of the aqueous solution a of a dispersant for controlling the shape of flaky silver powder or the aqueous solution b of a dispersant for controlling the shape of granular silver powder is added to an ammonia complex solution of a silver salt to prepare a mixed solution C; the aqueous solution b of a dispersant for controlling the shape of granular silver powder or the aqueous solution a of a dispersant for controlling the shape of flaky silver powder is added to an aqueous reducing agent solution to prepare a mixed solution D; the mixed solution C is added in a batch or in batches into the mixed solution D or the mixed solution D is added in batches into the mixed solution C.

[0013] Preferably, the silver salt is an inorganic acid silver salt or an organic acid silver salt.

[0014] Preferably, the silver salt is one of silver halide, silver nitrate and silver sulfate.

[0015] Preferably, the reducing agent solution is a water-soluble sulfite aqueous solution or a reducing phosphate aqueous solution or an aqueous solution of reducing sugar.

[0016] Preferably, the total weight of the mixed shape dispersant in 1 L of the synthetic system aqueous solution does not exceed 20 g.

[0017] Preferably, the reduction reaction time is 3 to 8 hours.

[0018] An in-situ generated flaky mixed silver powder is prepared by the above-mentioned preparation method.

[0019] Compared with the related art, the present invention has the following beneficial effects:

[0020] 1. The present invention adopts a liquid phase reduction preparation method to prepare flaky mixed silver powder in situ under the same process. The preparation process is different from the existing method of preparing flaky mixed silver powder by physical mixing and grinding of silver powders of different particle sizes, and preparing silver powder with polarized particle sizes by a liquid phase reduction process, and then obtaining flaky mixed silver powder by physical grinding. Instead, the present invention adopts a liquid phase reduction process to control the effects of different types of flaky silver powder shape control dispersants and granular silver powder shape control dispersants, and generates flaky mixed silver powder in situ in the liquid phase, thereby avoiding the problems of grinding aid pollution caused by subsequent physical grinding process, deformation between crystal lattices, crack residual stress in the flaky silver powder, etc., which lead to unsatisfactory conductive properties.

[0021] 2. The present invention selects different types of flaky silver powder shape control dispersants and granular silver powder shape control dispersants, coordinates and regulates a longer reaction time and reaction temperature, regulates the reaction speed, and regulates the growth experience of different particles. Spontaneous nucleation of silver will form a densely packed structure. The reaction system under the action of the flaky silver powder shape control dispersant, by adding a suitable flaky silver powder shape control dispersant, makes it easy to combine with the surface with a smaller free energy after the monomer nucleation, further hinders the growth of the crystal face, and other crystal faces will further grow. Combined with the core that has enough time and raw materials to grow up, the growth mode tends to be mainly crystal growth, and the final particles are easy to form into regular polyhedral flakes or cakes. Select a suitable granular silver powder shape control dispersant, coordinate and regulate a longer reaction time and reaction temperature, and regulate the reaction speed. The colloidal system formed improves the stability and dispersibility of nanosilver, and at the same time affects the specific surface free energy of the crystal nucleus, reduces the formation success of the spherical crystal nucleus, and helps to increase the nucleation speed. Excessive nucleation under the rapid nucleation system increases the probability of particle collision, and spherical particles are easily formed.

[0022] 3. The present invention uses a method for preparing flaky and granular mixed silver powder in situ in liquid phase. According to the screening and use of different flaky silver powder shape control dispersants and granular silver powder shape control dispersants and the ratio control of the two dispersants, combined with temperature control and reaction time regulation, 10-90% of flaky silver powder with a thickness below 300nm and 90-10% of granular silver powder with a particle size below 300nm can be produced in situ. The in-situ generation process of the present application is simple to operate and has low production cost. The final product can be obtained without converting other processes. It is suitable for large-scale industrial preparation, which solves the problem that the prior art requires process flow combined with mechanical grinding production line to make flaky and spherical mixed silver powder, which is not convenient for large-scale industrial preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is one of the SEM images of silver powder 1# obtained in Example 1 of the present invention;

[0024] Figure 2 This is the second SEM image of silver powder 1# obtained in Example 1 of the present invention;

[0025] Figure 3 This is the third SEM image of silver powder 1# obtained in Example 1 of the present invention;

[0026] Figure 4 This is one of the SEM images of silver powder 2# obtained in Example 2 of the present invention;

[0027] Figure 5 This is the second SEM image of silver powder 2# obtained in Example 2 of the present invention;

[0028] Figure 6 This is one of the SEM images of silver powder 3# obtained in Example 3 of the present invention;

[0029] Figure 7 This is the second SEM image of silver powder 3# obtained in Example 3 of the present invention;

[0030] Figure 8 This is the third SEM image of silver powder 3# obtained in Example 3 of the present invention;

[0031] Fig. 9 This is the fourth SEM image of silver powder 3# obtained in Example 3 of the present invention;

[0032] Fig.10 This is the fifth SEM image of silver powder 3# obtained in Example 3 of the present invention;

[0033] Fig.11 This is a particle distribution diagram of silver powder 3# obtained in Example 3 of the present invention;

[0034] Fig.12 This is one of the SEM images of silver powder 4# obtained in Example 4 of the present invention;

[0035] Fig.13 This is the second SEM image of silver powder 4# obtained in Example 4 of the present invention;

[0036] Fig.14 is a particle distribution diagram of silver powder 4# obtained in Example 4 of the present invention;

[0037] Fig.15 This is one of the SEM images of silver powder 5# obtained in Example 5 of the present invention;

[0038] Fig.16 This is the second SEM image of silver powder 5# obtained in Example 5 of the present invention. DETAILED DESCRIPTION

[0039] The objectives, technical solutions and beneficial effects of the present invention are further described in detail below in conjunction with the accompanying drawings and implementation examples.

[0040] The following detailed descriptions are exemplary and are intended to provide further explanation of the claimed invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs.

[0041] The present invention aims to provide a method for preparing mixed silver powder of flakes, which can generate in situ and adjust the mixing ratio of flakes, and reduce the flake silver powder mixing process. The preparation process is different from the existing method of preparing mixed silver powder of flakes by mixing and grinding silver powders of different particle sizes, and preparing spherical silver powder with polarized particle sizes by liquid phase reduction process, and then physically grinding to obtain mixed silver powder of flakes. By adopting a liquid phase reduction process, regulating the effects of different types of flaky silver powder shape controlling dispersants and granular silver powder shape controlling dispersants, and coordinating and controlling a longer reaction time and reaction temperature, regulating the reaction rate, and regulating different particle growth experiences, the reaction system under the action of the flaky silver powder shape controlling dispersant makes it difficult for the particles to aggregate after the monomer nucleates through the steric effect or interaction with the surface of the nanoparticles. There is enough time and core for the raw materials to grow, and the growth mode tends to be mainly crystal growth. Finally, the particles are easily formed into regular polyhedral flakes or cakes; the granular silver powder shape controlling dispersant is combined with the control of a longer reaction time and reaction temperature, and the reaction rate. The colloidal system formed improves the stability and dispersibility of nanosilver, while affecting the specific surface free energy of the crystal nucleus, reducing the success of forming spherical crystal nuclei, and helping to increase the nucleation rate. Excessive nucleation in a rapid nucleation system increases the probability of collision between particles, making it easy to form spherical particles, thereby generating in situ mixed silver powder with different proportions of flaky particles.

[0042] The technical solution of the present invention can be further summarized as follows:

[0043] S01. Prepare the silver salt ammonia complex solution and the reducing agent solution respectively.

[0044] S01-1: The preparation of the silver salt ammonia complex solution is to dissolve the silver salt in ion exchange water, stir it thoroughly to dissolve, then add a certain amount of ammonia water, stir it at a constant temperature of 30-100°C to obtain a silver ammonia complex aqueous solution, wherein the total weight of silver contained in the silver ammonia complex does not exceed 100g for 1L of the synthetic system aqueous solution, and the total amount of ammonia is within the range of 2.3-6.0 times the amount of silver contained in the ammonia complex. The silver salt used can be an inorganic acid silver salt or an organic acid silver salt, and the inorganic acid silver salt can be one of silver halide, silver nitrate, and silver sulfate.

[0045] S01-2: Prepare a reducing agent solution by dissolving the reducing agent in ion exchange water and stirring at a constant temperature of 30-100°C, wherein the total weight of the reducing agent does not exceed 150g for 1L of the synthetic system aqueous solution. The selected reducing agent can be listed as at least one of a water-soluble sulfite, a reducing phosphate, or a reducing sugar.

[0046] S02: Maintain the temperature of the silver salt ammonia complex solution and the reducing agent solution at 30-100°C, react the silver salt ammonia complex solution and the reducing agent solution in the presence of two different types of mixed shape dispersant aqueous solutions, the reaction process is carried out under a stirring state of 100-1000rpm, and is fully stirred for more than 2 hours, specifically 3-8 hours, to obtain a suspension of flaky mixed silver powder in situ. The mixed shape dispersant includes a flaky silver powder shape-controlling dispersant and a granular silver powder shape-controlling dispersant, the synthetic system aqueous solution is 1L, and the total weight of the flaky silver powder shape-controlling dispersant and the granular silver powder shape-controlling dispersant does not exceed 20g.

[0047] It should be noted that in order to achieve effective control of the size and proportion of silver flakes and silver spheres in silver powder, in the preparation process, it is necessary to further select specific dispersants from the above-mentioned flaky silver powder shape control dispersants and granular silver powder shape control dispersants for combination, and according to the dosage of different dispersant combinations, the formation and proportion of silver flakes and silver spheres can be controlled. Specifically, starting from the selection and different combinations of flaky silver powder shape control dispersants and granular silver powder shape control dispersants, the synthesis of mixed powders of silver flakes and silver spheres can be achieved in the liquid phase reduction process. Usually, the flaky silver powder shape control dispersant uses one or two of polysaccharides and / or thiol compounds, and cooperates with the control of a longer reaction time such as 3 to 8 hours and a reaction temperature such as 30 to 100 ° C to control the reaction rate, and the monomer nucleation is not easy to aggregate between the particles through the steric effect or the interaction with the surface of the nanoparticles, so that there is enough time and raw material to grow the core, and the growth mode tends to be mainly crystal growth, and the final particles are easily formed into regular polyhedral flakes or cakes. The granular silver powder shape-controlling dispersant includes one or more of proteins and polymer amino compounds, and is coordinated with a longer reaction time such as 3 to 8 hours and a reaction temperature such as 30 to 100°C to control the reaction speed, affect the specific surface free energy of the crystal nucleus, reduce the success of forming a spherical crystal nucleus, and help increase the nucleation speed. Excessive nucleation under a rapid nucleation system increases the probability of particles colliding with each other, which helps to form spherical particles. Therefore, the amount of different types of flaky silver powder shape-controlling dispersants and granular silver powder shape-controlling dispersants is regulated, and a longer reaction time and reaction temperature are coordinated to control the reaction speed, and the growth experience of different particles is regulated, so that some particles are formed into regular polyhedral flakes or cakes, and some are formed into spherical particles. The control method is simple and easy to operate. It should be noted that, generally speaking, silver powders of 100 nm or less than 50 nm are very easy to agglomerate in a liquid phase reaction system because the surface potential energy of extremely small particles is relatively large even when dispersed by a dispersant. Therefore, it is very difficult to produce silver powders with a particle size of less than 100 nm or less than 50 nm. However, in the experiments of the present invention, it was found that by adding two different types of flaky silver powder shape-controlling dispersants and granular silver powder shape-controlling dispersants, the flaky silver powder that has been generated serves as a spatial barrier to the subsequent growth of silver powder, thereby reducing the subsequent nucleation success of silver particles and the specific surface free energy of the crystal nucleus, so that silver powders with an average particle size of 100 nm and 50 nm in the system of the present invention for in-situ generation of flaky mixed silver powder do not agglomerate. Therefore, the present invention can also be used to in-situ generate ultrafine silver powders with an average particle size of 100 nm and 50 nm, such as Figures 8 to 10 shown.

[0048] The mixing method in step S02 can be listed as follows:

[0049] S02-1: Add a mixed shape dispersant aqueous solution of a flaky silver powder shape controlling dispersant and a granular silver powder shape controlling dispersant to the ammonia complex solution of the silver salt to prepare a mixed solution A, add the reducing agent solution into the mixed solution A all at once or in batches, or add the mixed solution A into the reducing agent solution in one batch or in batches.

[0050] S02-2: Add a mixed shape dispersant aqueous solution of a flaky silver powder shape controlling dispersant and a granular silver powder shape controlling dispersant to a reducing agent solution to obtain a reducing mixed solution B, and add the reducing mixed solution B into an ammine complex solution of a silver salt in one batch or in batches for reaction, or add the ammine complex solution of a silver salt into the reducing mixed solution B at one time or in batches for reaction.

[0051] S02-3: Prepare an aqueous solution a of a dispersant for controlling the shape of flaky silver powder; prepare an aqueous solution b of a dispersant for controlling the shape of granular silver powder; add either the aqueous solution a of a dispersant for controlling the shape of flaky silver powder or the aqueous solution b of a dispersant for controlling the shape of granular silver powder to an amino complex solution of a silver salt to prepare a mixed solution C; add the aqueous solution b of a dispersant for controlling the shape of granular silver powder or the aqueous solution a of a dispersant for controlling the shape of flaky silver powder to an aqueous reducing agent solution to prepare a mixed solution D; add the mixed solution C into the mixed solution D at once or in batches, or add the mixed solution D into the mixed solution C at once or in batches.

[0052] S03: using ultrasonic cleaning to clean the C suspension, and filtering and separating to obtain silver powder cake;

[0053] S04: washing the silver powder cake with amphiphilic solution ethanol to prevent agglomeration;

[0054] S05: Drying to obtain flaky and granular mixed silver powder; in the obtained flaky and granular mixed silver powder, flaky silver powder accounts for 10-90% and its thickness is below 300nm, and granular silver powder accounts for 90-10% and its particle size is below 300nm.

[0055] The present invention provides a method for in-situ preparing flaky and granular mixed silver powder in liquid phase. According to the screening and use of different flaky silver powder shape controlling dispersants and granular silver powder shape controlling dispersants, combined with temperature control and reaction time regulation, the flaky and granular mixed silver powder with a thickness of 10-90% and a particle size of less than 300nm and a granular silver powder of 90-10% and a particle size of less than 300nm can be produced in-situ. The preparation process is simple and the production cost is low, which solves the problem that the prior art needs to use mechanical grinding to make flaky and spherical mixed silver powder.

[0056] The flaky mixed silver powder produced in situ by the preparation method of the present invention can adjust the thickness of the flaky particles and the diameter of the spherical particles, such as: Figure 8As shown, the sheet thickness and ball diameter tend to be close, and it is more conducive to the regulated preparation of large-area silver sheets and small-size silver balls, making the conductive network distribution in the conductive paste more uniform and forming a closer sheet-ball contact, which helps to reduce the local concentration of current during transmission, reduce resistance, and improve overall conductivity.

[0057] Several typical embodiments are listed below to illustrate the specific implementation of the present invention. Of course, the protection scope of the present invention is not limited to the following embodiments.

[0058] Example 1: Preparation of spherical mixed silver powder 1#

[0059] Mixed liquid A: Dissolve 1.5g of silver nitrate in 30g of ion exchange water, and add 4g of 10% ammonia water to prepare a silver-ammine complex aqueous solution. Dissolve 0.15g of agar in 40g of ion exchange water and add to the silver-ammine complex aqueous solution.

[0060] Reducing solution B: Dissolve 1.8 g potassium sulfite in 30 g ion exchange water.

[0061] The reducing solution B is injected into the mixed liquid A and stirred with a stirrer. After reacting at 35℃~40℃ for 4 hours, the generated silver-containing suspension is filtered under reduced pressure, washed with ionized water, and finally washed with ethanol solvent to obtain a silver powder cake. The silver powder cake is dried under reduced pressure and crushed to obtain anhydrous mixed silver powder. The thickness is less than 50nm; the maximum flake diameter is more than 3μm.

[0062] Example 2: Preparation of spherical mixed silver powder 2#

[0063] Silver ammonia complex aqueous solution A: Dissolve 1.5 g of silver nitrate in 30 g of ion exchange water, and add 4 g of 10% ammonia water to prepare a silver ammonia complex aqueous solution.

[0064] Mixed liquid B: Dissolve 1.8 g of potassium sulfite in 30 g of ion exchange water to prepare a reducing solution. Dissolve 0.15 g of agar in 40 g of ion exchange water and add the reducing solution to prepare a mixed liquid.

[0065] The mixed liquid B is injected into the silver-ammine complex aqueous solution A and stirred with a stirrer. After reacting at 35°C to 40°C for 4 hours, the generated silver-containing suspension is filtered under reduced pressure, washed with ionized water, and finally washed with ethanol solvent to obtain a silver powder cake. The silver powder cake is dried under reduced pressure and crushed to obtain anhydrous mixed silver powder. The thickness is less than 50nm; the maximum flake size (diameter) is 2.5μm or more (2500nm).

[0066] Example 3: Preparation of spherical mixed silver powder 3#

[0067] Mixed liquid A: Dissolve 50g of silver nitrate in 100g of ion exchange water, and add 46g of 25% ammonia water to prepare a silver-ammine complex aqueous solution. Dissolve 4.75g of agar and 0.25g of collagen peptide in 300g of ion exchange water and add them to the silver-ammine complex aqueous solution.

[0068] Reducing solution B: Dissolve 50 g of potassium sulfite in 150 g of ion exchange water.

[0069] The reducing solution B is injected into the liquid A and stirred with a stirrer. After reacting at 50℃~60℃ for 4 hours, the generated silver-containing suspension is filtered under reduced pressure, washed with plasma water, and finally washed with ethanol solvent to obtain a silver powder cake. The silver powder cake is dried under reduced pressure and crushed to obtain anhydrous mixed silver powder. Among them, the 200nm granular silver powder accounts for less than 3%, the flaky silver powder accounts for more than 97%, and the thickness is less than 100nm.

[0070] Example 4: Preparation of spherical mixed silver powder 4#

[0071] Mixed solution A: Dissolve 50g of silver nitrate in 100g of ion exchange water, and add 46g of 25% ammonia water to prepare a silver-ammine complex aqueous solution. Dissolve 2.5g of agar in 150g of ion exchange water and add to the silver-ammine complex aqueous solution.

[0072] Reduction mixed solution B: Dissolve 50 g of potassium sulfite in 150 g of ion exchange water to prepare a reduction solution. Dissolve 2.5 g of collagen peptide in 150 g of ion exchange water and add the reduction solution to prepare a mixed reduction solution.

[0073] Pour liquid A into liquid B and stir with a stirrer.

[0074] After reacting at 50℃~60℃ for 4 hours, the generated silver-containing suspension is filtered under reduced pressure, washed with plasma water, and finally washed with ethanol solvent to obtain a silver powder cake. The silver powder cake is dried under reduced pressure and crushed to obtain anhydrous mixed silver powder. Among them, the 220nm granular silver powder accounts for more than 73%, the flaky silver powder accounts for less than 27%, and the thickness is less than 100nm.

[0075] Example 5: Preparation of spherical mixed silver powder 5#

[0076] Solution A: Dissolve 50 g of silver nitrate in 100 g of ion exchange water, and add 46 g of 25% ammonia water to prepare a silver ammonia complex aqueous solution.

[0077] Reduction mixed solution B: Dissolve 50 g of potassium sulfite in 150 g of ion exchange water to prepare a reduction solution. Dissolve 0.25 g of agar and 4.75 g of collagen peptide in 300 g of ion exchange water and add to the reduction solution to prepare a mixed reduction solution B.

[0078] Liquid B was injected into liquid A three times at 10-minute intervals and stirred with a stirrer.

[0079] After reacting at 50℃~60℃ for 4 hours, the generated silver-containing suspension is filtered under reduced pressure, washed with plasma water, and finally washed with ethanol solvent to obtain a silver powder cake. The silver powder cake is dried under reduced pressure and crushed to obtain anhydrous mixed silver powder. Among them, the flaky silver powder accounts for less than 10% and the thickness is less than 100nm; the granular silver powder accounts for more than 90% and the particle size is less than 100nm.

[0080] Analysis of the above specific embodiments and the electron microscope images and partial particle size distribution curves of the corresponding mixed silver powders 1# to 5# shows that by adding a flaky silver powder shape control dispersant, flaky silver powder is produced in the silver powder. Analysis of embodiments 3 to 5 and the electron microscope images and partial particle size distribution curves of the corresponding mixed silver powders 3# to 5# shows that adding different types of flaky silver powder shape control dispersants and granular silver powder shape control dispersants can respectively control the in-situ production of flaky silver powder and spherical silver powder, and the proportion and particle size ratio of flaky silver powder and spherical silver powder in the mixed silver powder can be adjusted by the type, amount, addition method, reaction temperature, reaction time, etc. of the dispersant.

[0081] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing in-situ generated flaky mixed silver powder, characterized in that: preparing a silver salt ammonia complex solution and a reducing agent solution respectively; Wherein, in 1L of the synthetic system aqueous solution, the total weight of silver contained in the silver ammonia complex does not exceed 100g, the total weight of the reducing agent does not exceed 150g, and the total amount of ammonia is in the range of 2.3-6.0 times the amount of silver contained in the ammonia complex; reacting a silver salt ammonia complex solution and a reducing agent solution in the presence of a mixed shape dispersant; The mixed shape dispersant includes a flaky silver powder shape-controlling dispersant and a granular silver powder shape-controlling dispersant, wherein the flaky silver powder shape-controlling dispersant includes one or more of polysaccharides and / or thiol compounds; and the granular silver powder shape-controlling dispersant includes one or more of proteins and / or high-molecular amino compounds; The mixture is stirred at a temperature of 30 to 100° C. for more than 2 hours, and the reduction reaction time is 3 to 8 hours to obtain a suspension of mixed silver powder in situ in a flaky state. The suspension is cleaned by ultrasonic wave, and a silver powder cake is obtained by filtration and separation. The silver powder cake is then washed with an amphiphilic solution, and dried to obtain mixed silver powder in a flaky state. In the prepared flaky and granular mixed silver powder, flaky silver powder accounts for 10-90% and its thickness is below 300nm, and granular silver powder accounts for 90-10% and its particle size is below 300nm.

2. The method for preparing in-situ generated flaky mixed silver powder according to claim 1, characterized in that: A mixed shape dispersant aqueous solution of a flaky silver powder shape controlling dispersant and a granular silver powder shape controlling dispersant is added to the ammonia complex solution of the silver salt to prepare a mixed solution A, and the reducing agent solution is added to the mixed solution A in one batch or in batches, or the mixed solution A is added to the reducing agent solution in one batch or in batches.

3. The method for preparing in-situ generated flaky mixed silver powder according to claim 1, characterized in that: A mixed shape dispersant aqueous solution of a flaky silver powder shape controlling dispersant and a granular silver powder shape controlling dispersant is added to a reducing agent solution to prepare a reducing mixed solution B, and the reducing mixed solution B is added in batches or in parts to an ammine complex solution of a silver salt for reaction, or the ammine complex solution of a silver salt is added in batches or in parts to a reducing mixed solution B for reaction.

4. The method for preparing in-situ generated flaky mixed silver powder according to claim 1, characterized in that: Prepare an aqueous solution a of a dispersant for controlling the shape of flaky silver powder; prepare an aqueous solution b of a dispersant for controlling the shape of granular silver powder; add one of the aqueous solution a of the dispersant for controlling the shape of flaky silver powder or the aqueous solution b of the dispersant for controlling the shape of granular silver powder to an ammonia complex solution of a silver salt to prepare a mixed solution C; add the aqueous solution b of the dispersant for controlling the shape of granular silver powder or the aqueous solution a of the dispersant for controlling the shape of flaky silver powder to an aqueous reducing agent solution to prepare a mixed solution D; add the mixed solution C in one batch or in batches to the mixed solution D or add the mixed solution D in one batch or in batches to the mixed solution C.

5. The method for preparing in-situ generated flaky mixed silver powder according to claim 1, characterized in that: The silver salt is an inorganic acid silver salt or an organic acid silver salt, and the reducing agent solution is a water-soluble sulfite aqueous solution or a reducing phosphate aqueous solution or a reducing sugar aqueous solution.

6. The method for preparing in-situ generated flaky mixed silver powder according to claim 1, characterized in that: The silver salt is one of silver halide, silver nitrate and silver sulfate.

7. The method for preparing in-situ generated flaky mixed silver powder according to claim 1, characterized in that: The total weight of the synthetic system aqueous solution 1L and the mixed shape dispersant does not exceed 20g.

8. An in-situ generated flaky mixed silver powder, characterized in that: The method is obtained by the preparation method according to any one of claims 1 to 7.

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