Preparation method of tablet and ball mixed silver powder

Abstract

The present invention discloses a method for preparing a mixed silver powder of flakes and balls, and relates to the technical field of metal powder metallurgy. The core of the present invention is to use pure water as a ball milling solvent and compounded zirconia balls and polyurethane balls as ball milling media during wet ball milling. Pure water as a ball milling solvent ensures that the properties and content of the organic coating on the surface of the silver powder remain unchanged, so that the silver powder has good dispersibility and alleviates the occurrence of lamination between flaky silver powders; while in the compounded ball milling medium, the zirconia balls are responsible for the ball milling of the silver powder into flakes, and the polyurethane balls are responsible for the ball milling dispersion of the silver powder, thereby synthesizing a mixed powder of flakes and balls in one step. The silver powders have good filling properties, improve the electrical properties of the silver powder, avoid the step of mixing flaky silver powder and spherical silver powder, and reduce costs.

Description

Technical Field

[0001] The invention relates to the technical field of metal powder metallurgy, in particular to the technical field of silver powder preparation, and more specifically to a method for preparing tablet-ball mixed silver powder. Background Art

[0002] Flake silver powder has a relatively large specific surface area, stable chemical properties, and surface or line contact between particles. It can effectively reduce the resistivity of the film and has excellent conductivity. It is widely used in the back of BSF-P type batteries, PERC batteries, HJT batteries, TOPCON batteries, as well as in conductive adhesives, varistors, flexible screens and other fields.

[0003] Studies have shown that adding an appropriate amount of flake silver powder to spherical silver powder can improve the performance of silver paste. This is primarily because the spherical silver powder fills the gaps between the flakes, resulting in a dense silver film after sintering, which in turn enhances the paste's adhesion and electrical properties. Currently reported methods for synthesizing two separate silver powders and then blending them suffer from long process times, high energy consumption, poor mixing uniformity, and poor cell density after sintering. However, there are few reports on a one-step method for synthesizing a blend of flake and spherical silver powders.

[0004] Currently, the industrial production of flaky silver powder mainly adopts wet or dry mechanical ball milling, which has a simple production process, low cost, and is easy to mass produce. When preparing flaky and ball mixed silver powder by dry ball milling, the addition of ball milling aids during the process will cause certain contamination to the silver powder. Moreover, the process is difficult to control, easily causing hardening, and it is difficult to achieve the required fineness. The preparation of flaky and ball mixed silver powder by wet ball milling is more controllable, but organic solvents such as ethanol are currently used as ball milling solvents. During the ball milling process, organic matter on the surface of the silver powder is easily dissolved, resulting in lamination and "cold welding". At the same time, because the silver powder can be well dispersed in the ethanol solution, it is easy to completely ball mill into flaks, but the degree of flaking is difficult to control. In addition, whether wet ball milling or dry ball milling, a single ball milling medium is often used, and the synthesized flaky and ball mixed silver powder has problems such as poor dispersibility and low filling capacity between the silver powders. Summary of the Invention

[0005] In order to overcome the defects and deficiencies in the above-mentioned prior art, the present invention provides a method for preparing a mixed silver powder of flakes and balls. The purpose of the present invention is to solve the problem that the synthesized mixed silver powder of flakes and balls has poor dispersibility and low filling capacity between silver powders due to the use of a single ball milling medium in the prior art. The core of the present invention is to use pure water as the ball milling solvent and compounded zirconia balls and polyurethane balls as the ball milling medium during wet ball milling. Pure water as the ball milling solvent ensures that the properties and content of the organic coating on the surface of the silver powder remain unchanged, so that the silver powder has good dispersibility and alleviates the occurrence of lamination between flaky silver powders; and in the compounded ball milling medium, the zirconia balls are responsible for the ball milling of the silver powder into flakes, and the polyurethane balls are responsible for the ball milling dispersion of the silver powder, so that the mixed powder of flakes and balls is synthesized in one step, with good filling capacity between silver powders, which improves the electrical properties of the silver powder, avoids the step of mixing flaky silver powder and spherical silver powder, and reduces costs.

[0006] In order to solve the above problems in the prior art, the present invention is implemented through the following technical solutions.

[0007] The present invention provides a method for preparing a mixed silver powder of tablets and balls, the preparation method comprising the following steps:

[0008] S1. Solution preparation: prepare silver-containing oxidant solution A and reducing agent solution B respectively; wherein the concentration of oxidant solution A is 0.5-2 mol / L, the mass of reducing agent is 0.5-2 times that of oxidant, and the reducing agent solution B is prepared with a concentration of 50-200 g / L; weigh dispersant and modifier; the mass of dispersant and modifier is 0.2-1 wt% of the mass of the reduced silver powder;

[0009] S2, reduction reaction, under high-speed stirring, adding the dispersant to the oxidant solution A, holding for a certain time, adding the reducing agent solution B to the oxidant solution A, controlling the addition flow of the reducing agent solution B; after the reducing agent solution B is added, react and age for a certain time;

[0010] S3, chemical modification of silver powder: after the aging time of step S2 is completed, the supernatant after the reaction is taken out by sedimentation, and the remaining part is added with a regulator to adjust the pH to > 10, and then the modifier is added, and the mixture is stirred and dispersed at high speed for 10-30 minutes;

[0011] S4, centrifugal washing, transfer the modified silver powder obtained in step S3 to a centrifuge, repeatedly wash with deionized water until the conductivity is less than 20 μs / cm, and collect for use;

[0012] S5, ball milling, transferring the silver powder collected in step S4 to a ball mill, adding compounded zirconium oxide balls and polyurethane balls at a ball-to-material ratio of (1-15):1, wherein the mass ratio of the compounded zirconium oxide balls to the polyurethane balls is (2-16):1; then adding pure water as a ball milling aid, the amount added being 30-100wt% of the mass of the reduced silver powder; first ball milling and dispersing at low frequency, and then ball milling into flakes and powder at a frequency of 10-40 Hz;

[0013] S6, drying, the ball-milled silver powder is dried in a forced air drying oven at 60-80°C;

[0014] S7. The silver powder dispersed by ball milling is passed through a 200-mesh sieve to obtain a mixed silver powder product of flakes and balls.

[0015] In step S1, the oxidant solution A is one or a mixture of silver oxide, silver nitrate, silver carbonate, and silver ammonia solution.

[0016] In step S1, the reducing agent solution B is a mixture of one or more of ascorbic acid, hydrazine hydrate, formaldehyde and glucose.

[0017] In step S1, the dispersant solution C is one or more of PVP, PVA, PEG, oleic acid, triethanolamine and sodium oleate.

[0018] In step S1, the regulator is sodium hydroxide, ammonia water or sodium bicarbonate.

[0019] In step S1, the modifier is one or a mixture of oleic acid, sodium oleate, and stearic acid.

[0020] In step S2, the reaction and aging for a certain period of time are carried out at a temperature of 25-60° C. and for a period of 2-10 minutes.

[0021] In step S3, it is only necessary to filter out the upper layer of the reaction solution and adjust the pH to > 10; the stirring speed is 150-400 rpm; and the speed of the dispersion disk is 300-1500 rpm.

[0022] In step S5, the size of the zirconia beads is 1 mm to 5 mm; the size of the polyurethane balls is 2 mm to 15 mm.

[0023] In step S5, the ball milling time is 0.5-4 h.

[0024] Compared with the prior art, the beneficial technical effects brought about by the present invention are as follows:

[0025] 1. The present invention uses pure water as a grinding aid solvent to ensure that the organic coating on the surface of the silver powder is not dissolved during the ball milling process. The burnout test (550°C) shows that the amount of organic coating remains basically unchanged before and after ball milling, which makes the silver powder have good dispersibility and alleviates the phenomenon of lamination between flaky silver powders. At the same time, since the modified silver powder has strong hydrophobicity, it can form certain agglomerates in the pure water solvent, and the agglomerates form flaky silver powder during ball milling.

[0026] 2. The present invention achieves the two effects of ball milling into flakes and ball milling dispersion by compounding ball milling media of different densities. The zirconia beads are responsible for ball milling the agglomerates into flakes, and the polyurethane balls are responsible for ball milling and dispersing the silver powder. In the silver powder after ball milling, the flake powder and the ball powder are evenly dispersed in the same powder.

[0027] 3. The flake and ball mixed silver powder prepared by the one-step method of the present invention has uniform dispersion of flakes and balls, avoiding the traditional steps of separately synthesizing flake powder and ball powder and then mixing them, solving the unevenness problem caused by the mixing of flake silver powder and ball powder, so that the spherical silver powder in the silver grid line is better filled in the gaps between the flake powder, thereby improving the tensile force and reducing the line resistance.

[0028] 4. The present invention can adjust the flake powder size and flake powder ratio by adjusting the ball milling frequency, ball milling time, ball milling medium compound ratio and ball milling medium size.

[0029] 5. The present invention adds a dispersant to the oxidizing solution in advance, so that the reduced silver powder is quickly coated by the dispersant, preventing its further growth and later agglomeration. The produced silver powder has good dispersibility and consistency, and the surface of the printed battery cell has good flatness, so that the tension and line resistance data on a single battery cell have good stability.

[0030] 6. After the reaction is completed and the silver powder is filtered, the present invention adds modifiers such as oleic acid, sodium oleate, and oleylamine, so that the silver powder has strong hydrophobicity, which is convenient for washing and avoids operational errors. At the same time, due to the good hydrophobicity, the powder is not easy to agglomerate during washing, and the final powder obtained has good dispersibility and consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain examples of the present invention and should not be regarded as limiting the scope.

[0032] Figure 1 This is an electron microscope image of the first group of tablet-ball mixed silver powder in Example 1 of the present invention;

[0033] Figure 2 This is an electron microscope image of the fourth group of tablet-ball mixed silver powder in Example 1 of the present invention;

[0034] Figure 3 This is an electron microscope image of the fifth group of tablet-ball mixed silver powder in Example 1 of the present invention;

[0035] Figure 4 This is an electron microscope image of the eighth group of tablet-ball mixed silver powder in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] The technical solutions of the present invention are further described in detail below in conjunction with the accompanying drawings and specific embodiments. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0037] Example 1

[0038] The invention discloses a method for preparing a mixed silver powder of tablets and balls, which comprises the following steps:

[0039] S1. Solution preparation

[0040] Preparation of oxidant solution A

[0041] Accurately weigh 1.5 kg of silver nitrate and prepare a 1 mol / L silver nitrate solution. Control the solution temperature at 30-32°C and stir for 30 minutes to prepare silver nitrate solution A.

[0042] Preparation of reducing agent solution B

[0043] Accurately weigh 0.75 kg of ascorbic acid and prepare a 1 mol / L solution. Control the solution temperature at 30-32°C and stir for 30 minutes to prepare reducing agent solution B.

[0044] Preparation of dispersant solution C

[0045] Accurately weigh 10 g of PVP and add it directly into oxidant solution A in powder form;

[0046] Preparation of modifier solution E

[0047] Accurately weigh 7 g of sodium oleate, dissolve it in 200 ml of water, heat it to 55-60°C, and stir to dissolve it to prepare a modifier solution E;

[0048] S2. Reduction reaction

[0049] At a stirring speed of 400 rpm, the dispersant solution was quickly added to the silver nitrate solution A and stirred for 10 minutes; the reducing agent solution B was added to the silver nitrate solution A at a rate of 200 ml / min, aged for 2 minutes after addition, and the supernatant was filtered;

[0050] S3, chemical modification of silver powder, adjust the pH of the filtered silver powder to 10-11 with ammonia water, add modifier solution E, and then stir for 15 minutes.

[0051] S4, centrifugal washing, silver powder filtering, washing until the conductivity is less than 20us / cm, ensuring the moisture content is 30-45%, and then taking it out for use;

[0052] S5, ball milling

[0053] The synthesized silver powder was subjected to the following 8 experiments:

[0054] In the first group, 100 g of silver powder was added to a polyurethane ball mill, followed by 400 g of zirconia beads with a diameter of 1 mm, 200 g of 5 mm polyurethane balls, and then 60 g of pure water. The ball mill frequency was 15 Hz and the milling was carried out for 4 h.

[0055] In the second group, 100 g of silver powder was added to a polyurethane ball mill, followed by 600 g of zirconia beads with a diameter of 1 mm, 100 g of 5 mm polyurethane balls, and then 60 g of pure water. The ball mill frequency was 15 Hz and the milling was carried out for 4 h.

[0056] In the third group, 100 g of silver powder was added to a polyurethane ball mill, followed by 800 g of zirconia beads with a diameter of 1 mm, 50 g of 5 mm polyurethane balls, and then 60 g of pure water. The ball mill frequency was 15 Hz and the milling was carried out for 4 h.

[0057] The fourth group added 100 g of silver powder into a polyurethane ball mill, added 600 g of 2 mm zirconia beads, added 100 g of 5 mm polyurethane balls, and then added 60 g of pure water. The ball mill frequency was 15 Hz and the milling was carried out for 4 h.

[0058] The fifth group added 100 g of silver powder into a polyurethane ball mill, added 600 g of 3 mm zirconia beads, added 100 g of 5 mm polyurethane balls, and then added 60 g of pure water. The ball mill frequency was 15 Hz and the milling was carried out for 4 h.

[0059] The sixth group added 100 g of silver powder into a polyurethane ball mill, added 600 g of 5 mm zirconium oxide beads, added 100 g of 5 mm polyurethane balls, and then added 60 g of pure water. The ball mill frequency was 15 Hz and the milling was carried out for 4 h.

[0060] In the seventh group, 100 g of silver powder was added to a polyurethane ball mill, followed by 600 g of 3 mm zirconia beads, 100 g of 5 mm polyurethane balls, and then 60 g of pure water. The ball mill frequency was set at 20 Hz and the milling was performed for 4 h.

[0061] In the eighth group, 100 g of silver powder was added to a polyurethane ball mill, followed by 600 g of 3 mm zirconia beads, 100 g of 5 mm polyurethane balls, and then 60 g of pure water. The ball mill frequency was set at 25 Hz and the milling was performed for 4 h.

[0062] Silver powder drying, sieving and testing

[0063] The wet silver powder, zirconium oxide beads, and polyurethane balls were dried together at 60°C overnight. After drying, the silver powder and ball milling medium were separated with a coarse screen, and the silver powder was then passed through a 200-mesh sieve to obtain a mixed powder of tablets and balls. The silver powder was tested for tap density, surface area, particle size, and SEM. Finally, the battery cell was printed at the downstream end to test the silver powder adhesion, line resistance, PL and other properties.

[0064] For the sake of comparison, the current density changes and results of the eight groups of ball milling experiments are listed in Table 1:

[0065] Table 1 Effects of different ball milling conditions on silver powder parameters.

[0066]

[0067] The results of the first to third group comparisons show that as the mass ratio of zirconia balls to polyurethane increases, the silver powder flake effect becomes more obvious, the proportion of sheet silver powder increases, D50, D90, and D95 ​​gradually increase, and the sheet powder size gradually increases; the results of the second, fourth, fifth, and sixth group comparisons show that as the size of the zirconia balls increases, the flake effect becomes more obvious, the sheet silver powder size increases, and D90, D95, and the specific table increase as the size of the zirconia balls increases; the results of the fifth, seventh, and eighth group comparisons show that as the ball milling frequency increases, D10, D50, D90, D95, and the specific table gradually increase, and the flake effect becomes more obvious.

[0068] Example 2

[0069] The invention discloses a method for preparing a mixed silver powder of tablets and balls, which comprises the following steps:

[0070] S1. Solution preparation

[0071] Preparation of oxidant solution A

[0072] Accurately weigh 315 g of silver nitrate and prepare a 2 mol / L silver nitrate solution. Control the solution temperature at 39-41°C and stir for 30 minutes to prepare silver nitrate solution A.

[0073] Preparation of Conditioner Solution D

[0074] Accurately weigh 100 g of sodium hydroxide and prepare a 2 mol / L solution. Control the solution temperature at 39-41°C and stir for 30 minutes to prepare a regulator solution D.

[0075] Preparation of reducing agent solution B

[0076] Accurately weigh 630 g of ascorbic acid and prepare a 1 mol / L solution. Control the solution temperature at 39-41°C and stir for 30 minutes to prepare reducing agent solution B.

[0077] Preparation of dispersant solution C

[0078] Accurately weigh 2 g of PVP (K30) and add it directly into reducing agent solution B in powder form and stir for 30 min;

[0079] Preparation of modifier solution E

[0080] Accurately weigh 2 g of sodium oleate, dissolve it in 50 ml of water, heat it to 55-60°C, and stir to dissolve it to prepare a modifier solution E;

[0081] S2. Reduction reaction

[0082] At a stirring speed of 400 rpm, the dispersant was quickly added to the reducing agent solution B and stirred for 10 minutes; the reducing agent solution was added to the silver nitrate solution A at a rate of 200 ml / min, aged for 2 minutes after addition, and the supernatant was filtered;

[0083] S3, chemical modification of silver powder, add modifier solution E, then stir for 15 minutes, filter the silver powder, and wash until the conductivity is less than 20us / cm, and ensure the moisture content is 30-45%.

[0084] S4, centrifugal washing, silver powder filtering, washing until the conductivity is less than 20us / cm, ensuring the moisture content is 30-45%, and then taking it out for use;

[0085] S5, ball milling

[0086] The obtained silver powder was added to a polyurethane ball mill, 1200 g of zirconia beads with a diameter of 3 mm, 200 g of 5 mm polyurethane balls, and then 200 g of pure water. The ball mill frequency was 20 Hz and the ball milling was carried out for 2 h.

[0087] Silver powder drying, sieving and testing

[0088] The wet silver powder, zirconium oxide beads, and polyurethane balls were dried together at 60°C overnight. After drying, the silver powder and ball milling medium were separated with a coarse screen, and the silver powder was then passed through a 200-mesh sieve to obtain a mixed powder of tablets and balls. The silver powder was tested for tap density, surface area, particle size, and SEM. Finally, the battery cell was printed at the downstream end to test the silver powder adhesion, line resistance, PL and other properties.

[0089] The test results in Example 2 are as follows: D10 = 0.24 μm, D50 = 1.35 μm, D90 = 7.78 μm, D95 = 11.84 μm, and the specific surface area is 1.23 m 2 / g, tap density 5.2g / cm 3 , the burn-in loss at 550℃ is 1.12%. The higher the concentration of oxidant solution A, the larger the synthesized silver powder particles are, the easier it is to form sheets, and the larger the D90 and D95 ​​are.

[0090] Example 3

[0091] The invention discloses a method for preparing a mixed silver powder of tablets and balls, which comprises the following steps:

[0092] S1. Solution preparation

[0093] Preparation of oxidant solution A

[0094] Accurately weigh 315 g of silver nitrate to prepare a 1.3 mol / L silver nitrate solution. Control the solution temperature between 39 and 41°C and stir for 30 minutes to prepare silver nitrate solution A.

[0095] Preparation of Conditioner Solution D

[0096] Accurately weigh 100 g of sodium hydroxide and prepare a 2 mol / L solution. Control the solution temperature at 39-41°C and stir for 30 minutes to prepare a regulator solution D.

[0097] Preparation of reducing agent solution B

[0098] Accurately weigh 400 g of ascorbic acid and prepare a 1 mol / L solution. Control the solution temperature at 39-41°C and stir for 30 minutes to prepare reducing agent solution B.

[0099] Preparation of dispersant solution C

[0100] Accurately weigh 1g of PVP (K30) and add it directly into reducing agent solution B in powder form and stir for 30min;

[0101] Preparation of modifier solution E

[0102] Accurately weigh 1 g of sodium oleate, dissolve it in 50 ml of water, heat it to 55-60°C, and stir to dissolve it to prepare a modifier solution E;

[0103] S2. Reduction reaction

[0104] At a stirring speed of 400 rpm, the dispersant was quickly added to the reducing agent solution B and stirred for 10 minutes; the reducing agent solution was added to the silver nitrate solution A at a rate of 200 ml / min, aged for 2 minutes after addition, and the supernatant was filtered;

[0105] S3, chemical modification of silver powder, add modifier solution E, then stir for 15 minutes, filter the silver powder, and wash until the conductivity is <20us / cm, and ensure the moisture content is 30-45%.

[0106] S4, centrifugal washing, silver powder filtering, washing until the conductivity is <20us / cm, ensuring the moisture content is 30-45%, and then taking it out for use;

[0107] S5, ball milling

[0108] The obtained silver powder was added to a polyurethane ball mill, 1200 g of zirconia beads with a diameter of 3 mm, 200 g of 5 mm polyurethane balls, and then 120 g of pure water. The ball mill frequency was 20 Hz and the ball milling was carried out for 2 h.

[0109] Silver powder drying, sieving and testing

[0110] The wet silver powder, zirconium oxide beads and polyurethane balls were dried together at 60°C overnight. After drying, the silver powder and ball milling medium were separated with a coarse screen, and then the silver powder was passed through a 200-mesh sieve to obtain a mixed powder of tablets and balls. The silver powder was tested for tap density, surface area, particle size and SEM. Finally, it was printed into battery cells at the downstream end to test the silver powder adhesion, line resistance, PL and other properties.

[0111] The test results in Example 3 are as follows: D10 = 0.2 μm, D50 = 1.02 μm, D90 = 5.25 μm, D95 = 8.16 μm, and the specific surface area is 1.63 m 2 / g, tap density 5.8g / cm 3 , burn loss of 0.73% at 550℃.

[0112] Example 4

[0113] The invention discloses a method for preparing a mixed silver powder of tablets and balls, which comprises the following steps:

[0114] S1. Solution preparation

[0115] Preparation of oxidant solution A

[0116] Accurately weigh 315 g of silver nitrate and prepare a 2 mol / L silver nitrate solution. Control the solution temperature at 39-41°C and stir for 30 minutes to prepare silver nitrate solution A.

[0117] Preparation of Conditioner Solution D

[0118] Accurately weigh 250 g of 28% ammonia water and control the solution temperature at 39-41°C to prepare a regulator solution D.

[0119] Preparation of reducing agent solution B

[0120] Accurately weigh 170 g of ascorbic acid and prepare a 1 mol / L solution. Control the solution temperature at 39-41°C and stir for 30 minutes to prepare reducing agent solution B.

[0121] Preparation of dispersant solution C

[0122] Accurately weigh 1g of PVP (K30) and add it directly into reducing agent solution B in powder form and stir for 30min;

[0123] Preparation of modifier solution E

[0124] Accurately weigh 1 g of sodium oleate, dissolve it in 50 ml of water, heat it to 55-60°C, and stir to dissolve it to prepare a modifier solution E;

[0125] S2. Reduction reaction

[0126] At a stirring speed of 400 rpm, the dispersant was quickly added to the reducing agent solution B and stirred for 10 minutes; the reducing agent solution was added to the silver nitrate solution A at a rate of 200 ml / min, aged for 2 minutes after addition, and the supernatant was filtered;

[0127] S3, chemical modification of silver powder, add modifier solution E, then stir for 15 minutes, filter the silver powder, and wash until the conductivity is <20us / cm, and ensure the moisture content is 30-45%.

[0128] S4, centrifugal washing, silver powder filtering, washing until the conductivity is <20us / cm, ensuring the moisture content is 30-45%, take out and divide into 10 parts for use;

[0129] S5, ball milling

[0130] The obtained silver powder was added to a polyurethane ball mill, 1200 g of zirconia beads with a diameter of 3 mm, 200 g of 5 mm polyurethane balls, and then 120 g of pure water. The ball mill frequency was 20 Hz and the ball milling was carried out for 2 h.

[0131] Silver powder drying, sieving and testing

[0132] The wet silver powder, zirconium oxide beads and polyurethane balls were dried together at 60°C overnight. After drying, the silver powder and ball milling medium were separated with a coarse screen, and then the silver powder was passed through a 200-mesh sieve to obtain a mixed powder of tablets and balls. The silver powder was tested for tap density, surface area, particle size and SEM. Finally, it was printed into battery cells at the downstream end to test the silver powder adhesion, line resistance, PL and other properties.

[0133] The test results in Example 4 are as follows: D10 = 0.17 μm, D50 = 0.76 μm, D90 = 2.51 μm, D95 = 3.68 μm, and the specific surface area is 1.53 m 2 / g, tap density 4.3g / cm3 , burn loss of 0.62% at 550℃.

[0134] Example 5

[0135] The invention discloses a method for preparing a mixed silver powder of tablets and balls, which comprises the following steps:

[0136] S1. Solution preparation: prepare silver-containing oxidant solution A and reducing agent solution B respectively; wherein the concentration of oxidant solution A is 0.5 mol / L, the mass of reducing agent is 1 times that of oxidant, and reducing agent solution B is prepared with a concentration of 0.5 mol / L. Weigh a dispersant and a modifier, the mass of which is 0.2 wt% of the mass of the reduced silver powder;

[0137] S2, reduction reaction, under high-speed stirring, adding the dispersant to the oxidant solution A, holding for a certain time, then adding the reducing agent solution B to the oxidant solution A, controlling the addition flow of the reducing agent solution B; after the reducing agent solution B is added, react and age for a certain time; the ageing temperature is 60 ° C, and the ageing time is 2 minutes;

[0138] S3, chemical modification of silver powder. After the aging time of step S2 is completed, the supernatant after the reaction is removed by sedimentation, and the remaining portion is added with a regulator to adjust the pH to > 10, and then the modifier is added and dispersed with high-speed stirring for 10-30 minutes; the stirring speed is 150 rpm; the dispersion disk speed is 300 rpm.

[0139] S4, centrifugal washing, transfer the modified silver powder obtained in step S3 to a centrifuge, repeatedly wash with deionized water until the conductivity is less than 20 μs / cm, and collect for use;

[0140] S5, ball milling, transferring the silver powder collected in step S4 to a ball mill, adding compounded zirconia balls and polyurethane balls at a ball-to-material ratio of 1:1, wherein the mass ratio of the compounded zirconia balls to the polyurethane balls is 2:1; then adding pure water as a ball milling aid, the amount added is 30wt% of the mass of the reduced silver powder; first ball milling and dispersion at a low frequency of 10 Hz, and then ball milling at a frequency of 20 Hz to form a ball powder;

[0141] S6, drying, the ball-milled silver powder is dried in a forced air drying oven at 60-80°C;

[0142] S7, the silver powder dispersed by ball milling is passed through a 200-mesh sieve to obtain a mixed silver powder product of flakes and balls;

[0143] The oxidant solution A is a mixture of one or more of silver oxide, silver nitrate, silver carbonate, and silver ammonia solution. The reducing agent solution B is a mixture of one or more of ascorbic acid, hydrazine hydrate, formaldehyde, and glucose. The dispersant solution C is one or more of PVP, PVA, PEG, oleic acid, triethanolamine, and sodium oleate. The regulator is sodium hydroxide, ammonia water, or sodium bicarbonate. The modifier is a mixture of one or more of oleic acid, sodium oleate, and stearic acid.

[0144] Example 6

[0145] The invention discloses a method for preparing a mixed silver powder of tablets and balls, which comprises the following steps:

[0146] S1. Solution preparation: prepare silver-containing oxidant solution A and reducing agent solution B respectively; wherein the concentration of oxidant solution A is 1 mol / L, the mass of reducing agent is 0.5 times that of oxidant, and reducing agent solution B is prepared with a concentration of 0.5 mol / L. Weigh a dispersant and a modifier, the mass of which is 0.5 wt% of the mass of the reduced silver powder;

[0147] S2, reduction reaction, under high-speed stirring, adding the dispersant to the oxidant solution A, holding for a certain time, then adding the reducing agent solution B to the oxidant solution A, controlling the addition flow of the reducing agent solution B; after the reducing agent solution B is added, react and age for a certain time; the ageing temperature is 50 ° C, and the ageing time is 5 minutes;

[0148] S3, chemical modification of silver powder. After the aging time of step S2 is completed, the supernatant after the reaction is removed by sedimentation, and the remaining portion is added with a regulator to adjust the pH to > 10, and then the modifier is added and dispersed with high-speed stirring for 10-30 minutes; the stirring speed is 250 rpm; the dispersion disk speed is 800 rpm.

[0149] S4, centrifugal washing, transfer the modified silver powder obtained in step S3 to a centrifuge, repeatedly wash with deionized water until the conductivity is less than 20 μs / cm, and collect for use;

[0150] S5, ball milling, transferring the silver powder collected in step S4 to a ball mill jar, adding compounded zirconia balls and polyurethane balls at a ball-to-material ratio of 8:1, wherein the mass ratio of the compounded zirconia balls to the polyurethane balls is 8:1; then adding pure water as a ball milling aid, the amount added is 60wt% of the mass of the reduced silver powder; first ball milling and dispersion at a low frequency of 10Hz, and then ball milling at a frequency of 30Hz to form a ball powder;

[0151] S6, drying, the ball-milled silver powder is dried in a forced air drying oven at 60-80°C;

[0152] S7, the silver powder dispersed by ball milling is passed through a 200-mesh sieve to obtain a mixed silver powder product of flakes and balls;

[0153] The oxidant solution A is a mixture of one or more of silver oxide, silver nitrate, silver carbonate, and silver ammonia solution. The reducing agent solution B is a mixture of one or more of ascorbic acid, hydrazine hydrate, formaldehyde, and glucose. The dispersant solution C is one or more of PVP, PVA, PEG, oleic acid, triethanolamine, and sodium oleate. The regulator is sodium hydroxide, ammonia water, or sodium bicarbonate. The modifier is a mixture of one or more of oleic acid, sodium oleate, and stearic acid.

[0154] Example 7

[0155] The invention discloses a method for preparing a mixed silver powder of tablets and balls, which comprises the following steps:

[0156] S1. Solution preparation: prepare silver-containing oxidant solution A and reducing agent solution B respectively; wherein the concentration of oxidant solution A is 2 mol / L, and the amount of reducing agent is twice that of oxidant, and the reducing agent solution B is configured with a concentration of 2 mol / L. Weigh a dispersant and a modifier, and the mass of the dispersant and modifier is 1 wt% of the mass of the reduced silver powder;

[0157] S2, reduction reaction, under high-speed stirring, adding the dispersant to the oxidant solution A, holding for a certain time, then adding the reducing agent solution B to the oxidant solution A, controlling the addition flow of the reducing agent solution B; after the reducing agent solution B is added, react and age for a certain time; the ageing temperature is 25 ° C, and the ageing time is 10 minutes;

[0158] S3, chemical modification of silver powder. After the aging time of step S2 is completed, the supernatant after the reaction is removed by sedimentation, and a regulator is added to the remaining portion to adjust the pH to > 10. Then, a modifier is added and the mixture is stirred and dispersed at high speed for 10-30 minutes; the stirring speed is 400 rpm; and the speed of the dispersion plate is 1500 rpm.

[0159] S4, centrifugal washing, transfer the modified silver powder obtained in step S3 to a centrifuge, repeatedly wash with deionized water until the conductivity is less than 20 μs / cm, and collect for use;

[0160] S5, ball milling, transferring the silver powder collected in step S4 to a ball mill, adding compounded zirconia balls and polyurethane balls at a ball-to-material ratio of 15:1, wherein the mass ratio of the compounded zirconia balls to the polyurethane balls is 16:1; then adding pure water as a ball milling aid, the amount added being 100wt% of the mass of the reduced silver powder; first ball milling and dispersing at a low frequency of 10 Hz, and then ball milling at a frequency of 40 Hz to form a ball powder;

[0161] S6, drying, the ball-milled silver powder is dried in a forced air drying oven at 60-80°C;

[0162] S7, the silver powder dispersed by ball milling is passed through a 200-mesh sieve to obtain a mixed silver powder product of flakes and balls;

[0163] The oxidant solution A is a mixture of one or more of silver oxide, silver nitrate, silver carbonate, and silver ammonia solution. The reducing agent solution B is a mixture of one or more of ascorbic acid, hydrazine hydrate, formaldehyde, and glucose. The dispersant solution C is one or more of PVP, PVA, PEG, oleic acid, triethanolamine, and sodium oleate. The regulator is sodium hydroxide, ammonia water, or sodium bicarbonate. The modifier is a mixture of one or more of oleic acid, sodium oleate, and stearic acid.

[0164] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that, with the exception of the listed oxidizing agents silver nitrate, silver oxide, and silver ammonia solution, the reducing agent ascorbic acid, the dispersant PVP, and the modifier sodium oleate, the remaining systems silver carbonate, hydrazine hydrate, formaldehyde, and glucose all have the same effect as the tablet-shaped mixed silver powder synthesized from the listed silver nitrate, silver ammonia, and silver oxide. Furthermore, those skilled in the art will be able to make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a pellet-ball mixed silver powder, characterized in that: The preparation method comprises the following steps: S1. Solution preparation: prepare silver-containing oxidant solution A and reducing agent solution B respectively; wherein the concentration of oxidant solution A is 0.5-2 mol / L, the mass of reducing agent is 0.5-2 times that of oxidant, and the reducing agent solution B is prepared with a concentration of 50-200 g / L; weigh dispersant and modifier; the mass of dispersant and modifier is 0.2-1 wt% of the mass of the reduced silver powder; S2, reduction reaction, under high-speed stirring, adding the dispersant to the oxidant solution A, holding for a certain time, adding the reducing agent solution B to the oxidant solution A, controlling the addition flow of the reducing agent solution B; after the reducing agent solution B is added, react and age for a certain time; S3, chemical modification of silver powder: after the aging time of step S2 is completed, the supernatant after the reaction is taken out by sedimentation, and the remaining part is added with a regulator to adjust the pH to > 10, and then the modifier is added, and the mixture is stirred and dispersed at high speed for 10-30 minutes; S4, centrifugal washing, transfer the modified silver powder obtained in step S3 to a centrifuge, repeatedly wash with deionized water until the conductivity is less than 20 μs / cm, and collect for use; S5, ball milling, transferring the silver powder collected in step S4 to a ball mill, adding compounded zirconium oxide balls and polyurethane balls at a ball-to-material ratio of (1-15):1, wherein the mass ratio of the compounded zirconium oxide balls to the polyurethane balls is (2-16):1; then adding pure water as a ball milling aid, the amount added being 30-100wt% of the mass of the reduced silver powder; first ball milling and dispersing at low frequency, and then ball milling into flakes and powder at a frequency of 10-40 Hz; S6, drying, the ball-milled silver powder is dried in a forced air drying oven at 60-80°C; S7. The silver powder dispersed by ball milling is passed through a 200-mesh sieve to obtain a mixed silver powder product of flakes and balls.

2. The method for preparing a mixed silver powder of tablets and balls as claimed in claim 1, characterized in that: In step S1, the oxidant solution A is one or a mixture of silver oxide, silver nitrate, silver carbonate, and silver ammonia solution.

3. The method for preparing a mixed silver powder of tablets and balls as claimed in claim 1 or 2, characterized in that: In step S1, the reducing agent solution B is a mixture of one or more of ascorbic acid, hydrazine hydrate, formaldehyde and glucose.

4. The method for preparing a mixed silver powder of tablets and balls as claimed in claim 3, characterized in that: In step S1, the dispersant solution C is one or more of PVP, PVA, PEG, oleic acid, triethanolamine and sodium oleate.

5. The method for preparing a mixed silver powder of tablets and balls as claimed in claim 1 or 2, characterized in that: In step S1, the regulator is sodium hydroxide, ammonia water or sodium bicarbonate.

6. The method for preparing a mixed silver powder of tablets and balls according to claim 1 or 2, characterized in that: In step S1, the modifier is one or a mixture of oleic acid, sodium oleate, and stearic acid.

7. The method for preparing a pellet-ball mixed silver powder according to claim 1 or 2, characterized in that: In step S2, the reaction and aging for a certain period of time are carried out at a temperature of 25-60° C. and for a period of 2-10 minutes.

8. The method for preparing a mixed silver powder of tablets and balls according to claim 1 or 2, characterized in that: In step S3, it is only necessary to filter out the upper layer of the reaction solution and adjust the pH to > 10; the stirring speed is 150-400 rpm; and the speed of the dispersion disk is 300-1500 rpm.

9. The method for preparing a mixed silver powder of tablets and balls according to claim 1 or 2, characterized in that: In step S5, the size of the zirconia beads is 1 mm to 5 mm; the size of the polyurethane balls is 2 mm to 15 mm.

10. The method for preparing a pellet-ball mixed silver powder according to claim 1 or 2, characterized in that: In step S5, the ball milling time is 0.5-4 h.

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