Nano-silver sol with low surface coating agent and preparation method of nano-silver sol

Abstract

The invention discloses nano-silver sol with a low surface coating agent and a preparation method of the nano-silver sol, and belongs to the technical field of nano-metal sol preparation.A dispersing agent solution is added into an oxidizing agent solution and a reducing agent solution respectively, control over nucleation and growth is achieved in combination with staged heating, the steric hindrance effect of a dispersing agent is better exerted, and the surface coating agent content is lowered; and finally, the dispersants which are weak in adsorption and free are washed off through the collecting, coiling and netting effects of the precipitant, the nano-silver sol with low burning loss, excellent dispersity and high stability is obtained, and the method is low in cost, high in collection rate and suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of nano metal sol preparation, and specifically relates to a nano silver sol with a low surface coating agent and a preparation method thereof. Background Art

[0002] Silver nanoparticles have an extremely important position in the field of microelectronics due to their good electrical conductivity, such as conductive inks used in chip packaging and printed electronic devices. In addition, the surface effects and quantum size effects of silver nanoparticles give them some special uses, such as surface enhanced Raman applications and medical applications.

[0003] As chip packaging moves toward low-temperature sintering, and printed electronic devices and circuits move toward thin lines, nano silver sols are required to have good dispersibility, stability, and low-temperature sintering properties. However, the initial temperature of the existing nano silver sol preparation method is mainly high temperature. In order to ensure the dispersibility and stability of the nano silver sol, a large amount of dispersant is often used for dispersion. The nano silver particles in the final nano silver sol contain a large amount of coating agent on the surface, which is difficult to completely remove under low-temperature sintering, resulting in poor electrical properties and appearance. In addition, the existing nano silver sol preparation method mainly uses high-speed centrifugation or reverse osmosis to wash the silver sol, which has the problems of complex process, incomplete collection of silver particles, high cost, and difficulty in redispersion.

[0004] Therefore, the preparation of a silver sol with low surface coating agent and uniform dispersion is of great significance for low-temperature sintering and fine-line printing. In addition, finding a simple and low-cost preparation method is of great practical significance for the preparation of nanopowder and nanosilver sol. Summary of the invention

[0005] In order to solve the problems of high surface coating agent content, high cost and complex process in the prior art, the present invention provides a nano silver sol with low surface coating agent and a preparation method thereof, wherein a dispersant solution is added to an oxidant solution and a reductant solution respectively, and the temperature is increased in stages to achieve control of nucleation and growth, and the steric hindrance of the dispersant is better exerted, and finally the weakly adsorbed and free dispersant is washed away by the collection and netting effect of the precipitant, so as to obtain a nano silver sol with low burning loss, excellent dispersibility and high stability. The method has low cost and high collection rate and is suitable for industrial production.

[0006] The objective of the present invention is achieved through the following technical solutions: A nano silver sol with a low coating agent on the surface comprises silver nano particles, a coating agent and a solvent; wherein the mass fraction of the silver nano particles is 0.5wt%-50wt%, and the mass fraction of the coating agent is less than 3wt%.

[0007] Preferably, the coating agent is polyvinyl pyrrolidone or polyethylene glycol.

[0008] A method for preparing a nano silver sol with a low surface coating agent comprises the following steps: Step 1: Add the regulator solution C to the reducing agent solution B under high-speed stirring, then add a portion of the dispersant solution D to the oxidant solution A, stir for 5-10 minutes, and obtain solution E; add another portion of the dispersant solution D to the reducing agent solution B, stir for 5-10 minutes, and obtain solution F; Step 2, under high-speed stirring, adding solution E to solution F through a flow meter, controlling the adding time of solution E to be 1 to 30 minutes, and controlling the temperature to be constant during the adding process; after solution E is added, starting to heat the reaction solution and ageing it to obtain a silver solution; Step 3, adding a precipitant and deionized water to the silver solution obtained in step 2, and repeatedly washing for 3-5 times, pouring out the supernatant for the last time, and collecting the silver powder for later use; Step 4: The silver powder collected in step 3 is dispersed in solution H by ultrasonic stirring using a dual-frequency ultrasonic cleaning machine, and stirred at a speed of 250 r / min. The total time of ultrasonic stirring is 10 to 30 minutes to form a silver sol, which is then tested.

[0009] Preferably, in step 1, the preparation of oxidant solution A is as follows: the oxidant is dissolved in solution G to a concentration of 0.01M-0.5M, and the solution temperature is controlled to be 10-30°C to obtain oxidant solution A; the oxidant is one or more of silver nitrate, silver ammonia and silver carbonate; and the solution G is one or more of deionized water, glycerol and ethylene glycol.

[0010] Preferably, in step 1, the reducing agent solution B is prepared by: dissolving the reducing agent in solution G, wherein the mass of the reducing agent is 0.25-4 times the mass of the oxidant, and the concentration is configured to be 0.04M-0.5M, and the solution temperature is controlled to be 10-30°C to obtain the reducing agent solution B; the solution G is one or more of deionized water, glycerol and ethylene glycol; the reducing agent is one or more of hydrazine hydrate, triethanolamine and sodium borohydride.

[0011] Preferably, in step 1, the preparation of the regulator solution C is as follows: the regulator is dissolved in solution G, the concentration of the regulator is 0.01-0.05M, and the solution temperature is controlled to be 10-30°C; the solution G is one or more of deionized water, glycerol and ethylene glycol; the regulator is one or more of sodium hydroxide, ammonia water and sodium carbonate.

[0012] Preferably, in step one, the preparation of dispersant solution D is as follows: the dispersant is dissolved in solution G, the mass of the dispersant is 1-5 times that of the oxidant, the concentration is configured to be 50-500 g / L, and the solution temperature is controlled to be 10-30°C; the solution G is one or more of deionized water, propylene glycol and ethylene glycol; the dispersant is polyvinyl pyrrolidone or polyethylene glycol.

[0013] Preferably, the oxidant is one or more of silver nitrate, silver ammonia and silver carbonate; the solution G is one or more of deionized water, glycerol and ethylene glycol; the reducing agent is one or more of hydrazine hydrate, triethanolamine and sodium borohydride; the regulator is one or more of sodium hydroxide, ammonia water and sodium carbonate; the dispersant is one of polyvinyl pyrrolidone and polyethylene glycol.

[0014] Preferably, in step 1, the dispersant solution D is divided into two parts according to a ratio of 1-9:9-1, and added to the oxidant solution A and the reductant solution B respectively.

[0015] Preferably, in step 2, the constant temperature during the addition of solution E is 10-30°C. After the addition of solution E is completed, the temperature is increased to 130-160°C at a rate of 2°C / min-15°C / min, and the reaction aging time is 1-3h.

[0016] Preferably, in step three, the amount of the precipitant added is 50%-1000% of the mass of silver, prepared to a concentration of 100 g / L, and the amount of deionized water added is 10%-1000% of the mass of the silver solution; the precipitant is one or more of polyferric sulfate, alum and polyacrylamide.

[0017] Preferably, in step 4, the solution H is one of deionized water, ethanol, isopropanol, ethylene glycol and glycerol.

[0018] The beneficial effects of this technical solution are as follows: 1. The present invention provides a nano silver sol with a low surface coating agent. The average particle size of the silver particles in the nano silver sol is 20-200nm, the overall uniformity is good, the stability is good, and it can be stored for a long time without sedimentation. There will be no problem of network clogging during fine line printing.

[0019] 2. The present invention provides a nano silver sol with low surface coating agent, in which the amount of organic matter coated on the surface of silver particles is less than 3wt%, which can be completely removed at a curing temperature below 150°C, and is suitable for low-temperature sintering such as chip packaging.

[0020] 3. The present invention provides a method for preparing a nano silver sol with a low surface coating agent, in which a dispersant is added to an oxidant and a reductant respectively, and the temperature is increased in stages to control the speed of nucleation and growth well, so that the dispersant has sufficient time to combine with silver particles in the nucleation stage, and the steric hindrance effect of the dispersant is better exerted, thereby avoiding agglomeration caused by an excessively high initial reaction temperature.

[0021] Fourth, the present invention provides a method for preparing a nano silver sol with a low surface coating agent, wherein a precipitant is added to a silver solution, and the weakly adsorbed and free organic matter is removed by utilizing the collection and netting effect of the precipitant, and the precipitated silver particles do not form agglomerates and are easily redispersed. In addition, by utilizing sedimentation washing, the sedimentation and separation of particles in the silver sol is well achieved, which solves the problem of silver sol washing and separation difficulties, improves the silver sol collection rate, and reduces the production cost.

[0022] 5. The present invention provides a method for preparing a nano silver sol with a low surface coating agent. The silver particles in the silver sol are separated by a sedimentation method, and are dispersed in a low-boiling point organic solution by ultrasound or other means to obtain a silver sol with a high silver content of 50%.

[0023] 6. The present invention provides a method for preparing a nano silver sol with a low surface coating agent. The silver sol finally prepared has good dispersion, low burnout, can be stored for a long time, and can achieve low-temperature curing. The synthesized silver sol has a particle size D10 of 0.1-0.15um, D50 of 0.1-0.2 um, D90 of 0.2-0.5um, D95 of 0.3-1 um, an average size of 20-200nm in ZETA test, an absolute value of ZETA test potential of 8-30mv, and a burnout rate of 0.5%-3% at 550℃. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a SEM image of the silver sol in Example 1 of the present invention; Figure 2 is a SEM image of the silver sol in Example 2 of the present invention; Figure 3 is a SEM image of the silver sol in Example 3 of the present invention; Figure 4 is a SEM image of the silver sol in Example 4 of the present invention; Figure 5 is a SEM image of the silver sol in Example 5 of the present invention; Figure 6 is a SEM image of the silver sol in Example 6 of the present invention; Figure 7 is a SEM image of the silver sol in Example 7 of the present invention; Figure 8 is a SEM image of the silver sol in Comparative Example 3 of the present invention; Fig. 9 It is the SEM picture of the silver sol in Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0026] In Examples 1 to 7 and Comparative Examples 1 to 4, D10, D50, D90, and D95 ​​were measured using a laser diffraction particle size distribution tester, and the particle size and potential were measured using a Malvern ZETA potentiometer. The silver powder obtained by washing and drying the silver sol in a muffle furnace was kept at 550° C. for 1 h to measure the mass difference percentage before and after to obtain the content of the silver particle surface coating agent.

[0027] Example 1 A preparation method of a nano silver sol with a low surface coating agent comprises the following steps: Step S1: Solution preparation Preparation of oxidant solution A Accurately weigh 15.77 g of silver nitrate and dissolve it in 9.18 L of ethylene glycol to prepare a 0.01 M silver nitrate solution. The solution temperature is controlled at 10° C. and stirred for 30 minutes to prepare an oxidant solution A.

[0028] Preparation of reducing agent solution B Accurately weigh 0.878 g of sodium borohydride and dissolve it in 568 mL of ethylene glycol to prepare a 0.04 M sodium borohydride solution. The solution temperature is controlled at 10° C. and stirred for 30 min to obtain a reducing agent solution B.

[0029] Preparation of Conditioner Solution C Accurately weigh 0.99 g of sodium hydroxide and dissolve it in 50 mL of ethylene glycol. The solution temperature is controlled at 10° C. and stirred for 30 minutes to prepare a regulator solution C.

[0030] Preparation of dispersant solution D Accurately weigh 10 g of PVP (K30) and dissolve it in 100 mL of ethylene glycol. The solution temperature is controlled at 10°C and stirred for 1 hour to obtain dispersant solution D.

[0031] Step S2: Adding dispersant and regulator At a stirring speed of 300 rpm, the regulator solution C was quickly added to the reducing agent solution B and stirred for 10 minutes. Then the dispersant solution D was divided into two parts by volume of 9:1 and added to the reducing agent solution B and the oxidant solution A respectively. The solution temperature was controlled at 10°C and stirred for 5 minutes respectively to obtain solution E and solution F.

[0032] Step S3: Reduction reaction Under stirring speed of 300 rpm, solution E was added to solution F at a rate of 306 mL / min for 30 min. The temperature during the addition process was controlled at 10-12 °C. After the addition was completed, the temperature was immediately raised to 150 °C at a rate of 2 °C / min. The reaction was completed after 2 h from the start of the dropwise addition.

[0033] Step S4: Sedimentation and washing Accurately weigh 5g of polyferric sulfate and add it to 200mL of deionized water, stir and dissolve to prepare a solution with a concentration of 100g / L, then add it to the final solution of step S3, then add 990mL of deionized water, stir for 10min, stop stirring and let settle for 30min, pour out the supernatant, then add 990mL of deionized water, stir for 10min, stop stirring and let settle for 30min, and repeat this washing process 3 times. (In this embodiment, the proportions of precipitant and deionized water are 50% and 10% respectively.) Step S5: Silver sol preparation The silver powder washed in step S4 was added to 100 g of ethylene glycol, ultrasonicated and stirred for 30 min to prepare a silver sol with a solid content of 10% and tested.

[0034] The test results in the above embodiment 1 are as follows: Figure 1 As shown, D10=0.13um, D50=0.16um, D90=0.21um, D95=0.27um, ZETA test size is 37nm, potential is -12mv, and coating agent content is 2.48% at 550℃. Figure 1 It can be seen that the synthesized silver powder has good dispersion and uniformity.

[0035] Example 2 A preparation method of a nano silver sol with a low surface coating agent comprises the following steps: Step S1: Solution preparation Preparation of oxidant solution A Accurately weigh 15.77 g of silver nitrate and dissolve it in 1.83 L of ethylene glycol to prepare a 0.05 M silver nitrate solution. The solution temperature is controlled at 10° C. and stirred for 30 min to prepare an oxidant solution A.

[0036] Preparation of reducing agent solution B Accurately weigh 1.756 g of sodium borohydride and dissolve it in 568 mL of ethylene glycol to prepare a 0.08 M sodium borohydride solution. The solution temperature is controlled at 10° C. and stirred for 30 min to obtain a reducing agent solution B.

[0037] Preparation of Conditioner Solution C Accurately weigh 0.99 g of sodium hydroxide and dissolve it in 50 mL of ethylene glycol. The solution temperature is controlled at 10° C. and stirred for 30 minutes to prepare a regulator solution C.

[0038] Preparation of dispersant solution D Accurately weigh 20 g of PVP (K30) and dissolve it in 100 mL of ethylene glycol. The solution temperature is controlled at 10°C and stirred for 1 hour to obtain dispersant solution D.

[0039] Step S2: Adding dispersant and regulator At a stirring speed of 300 rpm, the regulator solution C was quickly added to the reducing agent solution B and stirred for 10 minutes. Then the dispersant solution D was divided into two parts by volume of 7:3 and added to the reducing agent solution B and the oxidant solution A respectively. The solution temperature was controlled at 10°C and stirred for 10 minutes respectively to obtain solution E and solution F.

[0040] Step S3: Reduction reaction Under stirring speed of 300 rpm, solution E was added to solution F at a rate of 92 mL / min for 20 min. The temperature during the addition process was controlled at 10-12 °C. After the addition was completed, the temperature was immediately raised to 150 °C at a rate of 5 °C / min. The reaction was completed after 2 h from the start of the dropwise addition.

[0041] Step S4: Sedimentation and washing Accurately weigh 10g of polyferric sulfate and add it to 100mL of deionized water, stir and dissolve to prepare a solution with a concentration of 100g / L, then add it to the final solution of step S3, then add 2.54L of deionized water, stir for 10min, stop stirring and let settle for 30min, pour out the supernatant, then add 2.54L of deionized water, stir for 10min, stop stirring and let settle for 30min, and repeat this washing process 3 times. (In this embodiment, the proportions of precipitant and deionized water are 100% and 100% respectively.) Step S5: Silver sol preparation The silver powder washed in step S4 was added to 50 g of ethylene glycol, and ultrasonicated and stirred for 30 min to prepare a silver sol with a solid content of 20% and tested.

[0042] The test results in the above Example 2 are as follows: Figure 2 As shown, D10=0.12um, D50=0.15um, D90=0.25um, D95=0.29um, ZETA test size is 68nm, potential is -20.2mv, and coating agent content is 2.72% at 550℃. Figure 2 It can be seen that the synthesized silver powder has good dispersion and uniformity.

[0043] Example 3 A preparation method of a nano silver sol with a low surface coating agent comprises the following steps: Step S1: Solution preparation Preparation of oxidant solution A Accurately weigh 15.77 g of silver nitrate and dissolve it in 0.93 L of ethylene glycol to prepare a 0.1 M silver nitrate solution. The solution temperature is controlled at 10° C. and stirred for 30 minutes to prepare an oxidant solution A.

[0044] Preparation of reducing agent solution B Accurately weigh 3.512 g of sodium borohydride and dissolve it in 568 mL of ethylene glycol to prepare a 0.16 M sodium borohydride solution. The solution temperature is controlled at 10° C. and stirred for 30 min to prepare a reducing agent solution B.

[0045] Preparation of Conditioner Solution C Accurately weigh 0.99 g of sodium hydroxide and dissolve it in 50 mL of ethylene glycol. The solution temperature is controlled at 10° C. and stirred for 30 minutes to prepare a regulator solution C.

[0046] Preparation of dispersant solution D Accurately weigh 30 g of PVP (K30) and dissolve it in 100 mL of ethylene glycol. The solution temperature is controlled at 10°C and stirred for 1 hour to obtain dispersant solution D.

[0047] Step S2: Adding dispersant and regulator At a stirring speed of 500 rpm, the regulator solution C was quickly added to the reducing agent solution B and stirred for 10 minutes. Then the dispersant solution D was divided into two parts by volume of 5:5 and added to the reducing agent solution B and the oxidant solution A respectively. The solution temperature was controlled at 10°C and stirred for 5 minutes respectively to obtain solution E and solution F.

[0048] Step S3: Reduction reaction Under stirring speed of 500 rpm, solution E was added to solution F at a rate of 93 mL / min for 10 min. The temperature during the addition process was controlled at 10-12 °C. After the addition was completed, the temperature was immediately raised to 150 °C at a rate of 5 °C / min. The reaction was completed after 2 h from the start of the dropwise addition.

[0049] Step S4: Sedimentation and washing Accurately weigh 20g of polyferric sulfate and add it to 200mL of deionized water, stir and dissolve to prepare a solution with a concentration of 100g / L, then add it to the final solution of step S3, then add 3.29L of deionized water, stir for 10min, stop stirring and let settle for 30min, pour out the supernatant, then add 3.29L of deionized water, stir for 10min, stop stirring and let settle for 30min, and repeat this washing process 3 times. (In this embodiment, the proportions of precipitant and deionized water are 200% and 200% respectively.) Step S5: Silver sol preparation The silver powder washed in step S4 was added to 40 g of ethylene glycol, and ultrasonicated and stirred for 30 min to prepare a silver sol with a solid content of 25% and tested.

[0050] The test results in the above Example 3 are as follows: Figure 3 As shown, D10=0.14um, D50=0.16um, D90=0.22um, D95=0.26um, ZETA test size is 97nm, potential is -30mv, and coating agent content is 2.10% at 550℃. Figure 3 It can be seen that the synthesized silver powder has good dispersibility and contains large and small particles.

[0051] Example 4 A preparation method of a nano silver sol with a low surface coating agent comprises the following steps: Step S1: Solution preparation Preparation of oxidant solution A Accurately weigh 15.77 g of silver nitrate and dissolve it in 309 mL of ethylene glycol to prepare a 0.3 M silver nitrate solution. The solution temperature is controlled at 10° C. and stirred for 30 minutes to prepare an oxidant solution A.

[0052] Preparation of reducing agent solution B Accurately weigh 7.024 g of sodium borohydride and dissolve it in 568 mL of ethylene glycol to prepare a 0.32 M sodium borohydride solution. The solution temperature is controlled at 10° C. and stirred for 30 min to prepare a reducing agent solution B.

[0053] Preparation of Conditioner Solution C Accurately weigh 0.99 g of sodium hydroxide and dissolve it in 50 mL of ethylene glycol. The solution temperature is controlled at 10° C. and stirred for 30 minutes to prepare a regulator solution C.

[0054] Preparation of dispersant solution D Accurately weigh 40 g of PVP (K30) and dissolve it in 100 mL of ethylene glycol. The solution temperature is controlled at 10°C and stirred for 1 hour to obtain dispersant solution D.

[0055] Step S2: Adding dispersant and regulator At a stirring speed of 700 rpm, the regulator solution C was quickly added to the reducing agent solution B and stirred for 10 minutes. Then the dispersant solution D was divided into two parts by volume of 3:7 and added to the reducing agent solution B and the oxidant solution A respectively. The solution temperature was controlled at 10°C and stirred for 10 minutes respectively to obtain solution E and solution F.

[0056] Step S3: Reduction reaction Under stirring speed of 700 rpm, solution E was added to solution F at a rate of 62 mL / min for 5 min. The temperature during the addition process was controlled at 10-12 °C. After the addition was completed, the temperature was immediately raised to 150 °C at a rate of 10 °C / min. The reaction was completed after 2 h from the start of the dropwise addition.

[0057] Step S4: Sedimentation and washing Accurately weigh 50g of polyferric sulfate and add it to 500mL of deionized water, stir and dissolve to prepare a solution with a concentration of 100g / L, then add it to the final solution of step S3, then add 5.13L of deionized water, stir for 10min, stop stirring and let settle for 30min, pour out the supernatant, then add 5.13L of deionized water, stir for 10min, stop stirring and let settle for 30min, and repeat this washing process 3 times. (In this embodiment, the proportions of precipitant and deionized water are 500% and 500% respectively.) Step S5: Silver sol preparation The silver powder washed in step S4 was added to 25 g of ethylene glycol, and ultrasonicated and stirred for 30 min to prepare a silver sol with a solid content of 40% and tested.

[0058] The test results in the above Example 4 are as follows: Figure 4 As shown, D10=0.13um, D50=0.17um, D90=0.26um, D95=0.37um, ZETA test size is 121nm, potential is -20mv, and coating agent content is 1.89% at 550℃. Figure 4 It can be seen that the synthesized silver powder has good dispersibility and consistency.

[0059] Example 5 A preparation method of a nano silver sol with a low surface coating agent comprises the following steps: Step S1: Solution preparation Preparation of oxidant solution A Accurately weigh 15.77 g of silver nitrate and dissolve it in 186 mL of ethylene glycol to prepare a 0.5 M silver nitrate solution. The solution temperature is controlled at 10° C. and stirred for 30 minutes to prepare an oxidant solution A.

[0060] Preparation of reducing agent solution B Accurately weigh 14.047 g of sodium borohydride and dissolve it in 743 mL of ethylene glycol to prepare a 0.5 M sodium borohydride solution. The solution temperature is controlled at 10° C. and stirred for 30 min to prepare a reducing agent solution B.

[0061] Preparation of Conditioner Solution C Accurately weigh 0.99 g of sodium hydroxide and dissolve it in 50 mL of ethylene glycol. The solution temperature is controlled at 10° C. and stirred for 30 minutes to prepare a regulator solution C.

[0062] Preparation of dispersant solution D Accurately weigh 50 g of PVP (K30) and dissolve it in 100 mL of ethylene glycol. The solution temperature is controlled at 10°C and stirred for 1 hour to obtain dispersant solution D.

[0063] Step S2: Adding dispersant and regulator At a stirring speed of 250 rpm, the regulator solution C was quickly added to the reducing agent solution B and stirred for 7 minutes. Then the dispersant solution D was divided into two parts by volume of 1:9 and added to the reducing agent solution B and the oxidant solution A respectively. The solution temperature was controlled at 10°C and stirred for 10 minutes respectively to obtain solution E and solution F.

[0064] Step S3: Reduction reaction Under stirring speed of 300 rpm, solution E was added to solution F at a rate of 186 mL / min. The addition time was 1 min. The temperature during the addition process was controlled at 10-12 °C. After the addition was completed, the temperature was immediately raised to 150 °C at a rate of 15 °C / min. The reaction was completed after 2 h from the start of the dropwise addition.

[0065] Step S4: Sedimentation and washing Accurately weigh 100g of polyferric sulfate and add it to 1L of deionized water, stir and dissolve to prepare a solution with a concentration of 100g / L, add it to the final solution of step S3, then add 10.79L of deionized water, stir for 10min, stop stirring and let settle for 30min, pour out the supernatant, then add 10.79L of deionized water, stir for 10min, stop stirring and let settle for 30min, and repeat this washing process 4 times. (In this embodiment, the proportions of precipitant and deionized water are 1000% and 1000% respectively.) Step S5: Silver sol preparation The silver powder washed in step S4 was added to 20 g of ethylene glycol, and ultrasonicated and stirred for 30 min to prepare a silver sol with a solid content of 50% and tested.

[0066] The test results in the above Example 5 are as follows: Figure 5As shown, D10=0.13um, D50=0.15um, D90=0.39um, D95=0.87um, ZETA test size is 187nm, potential is -16mv, and coating agent content is 2.56% at 550℃. Figure 5 It can be seen that the particle size distribution of the synthesized silver powder is relatively wide and the consistency is slightly poor.

[0067] Example 6 A preparation method of a nano silver sol with a low surface coating agent comprises the following steps: Step S1: Solution preparation Preparation of oxidant solution A Silver ammonia was weighed and dissolved in deionized water to prepare a concentration of 0.1 M. The solution temperature was controlled at 20° C. and stirred for 30 minutes to prepare an oxidant solution A.

[0068] Preparation of reducing agent solution B Weigh hydrazine hydrate and dissolve it in deionized water to prepare a concentration of 0.1 M. The solution temperature is controlled at 20° C. and stirred for 30 minutes to prepare a reducing agent solution B.

[0069] Preparation of Conditioner Solution C Ammonia water was weighed and dissolved in deionized water to prepare a concentration of 0.05 M. The solution temperature was controlled at 20° C. and stirred for 30 minutes to prepare a regulator solution C.

[0070] Preparation of dispersant solution D Weigh polyethylene glycol and dissolve it in deionized water to prepare a concentration of 100 g / L. The solution temperature is controlled at 20° C. and stirred for 1 hour to prepare a dispersant solution D.

[0071] Step S2: Adding dispersant and regulator At a stirring speed of 300 rpm, the regulator solution C was quickly added to the reducing agent solution B and stirred for 5 minutes. Then the dispersant solution D was divided into two parts by volume of 1:9 and added to the reducing agent solution B and the oxidant solution A respectively. The solution temperature was controlled at 20°C and stirred for 7 minutes respectively to obtain solution E and solution F.

[0072] Step S3: Reduction reaction With stirring at 300 rpm, solution E was added to solution F for about 1 min. The temperature during the addition process was controlled at 20-22°C. After the addition was completed, the temperature was immediately raised to 160°C at a rate of 8°C / min. The reaction was completed after 1 h from the start of the dropwise addition.

[0073] Step S4: Sedimentation and washing Weigh polyacrylamide and add it to deionized water, the polyacrylamide is 1000% of the mass of silver, stir and dissolve to prepare a solution with a concentration of 100 g / L, add it to the final solution of step S3, and then add deionized water 1000% of the total volume of the silver solution, stir for 10 minutes, stop stirring and let settle for 30 minutes, pour out the supernatant, and repeat this washing process 5 times.

[0074] Step S5: Silver sol preparation The silver powder washed in step S4 was added to 2000 g of ethylene glycol, ultrasonicated and stirred for 30 min to prepare a silver sol with a solid content of 0.5% and tested.

[0075] The test results in the above Example 6 are as follows: Figure 6 As shown, D10=0.13um, D50=0.16um, D90=0.25um, D95=0.32um, ZETA test size is 151nm, potential is -18.7mv, and coating agent content is 1.56% at 550℃. Figure 6 It can be seen that the synthesized silver powder has a wide particle size distribution and contains large and small powders.

[0076] Example 7 A preparation method of a nano silver sol with a low surface coating agent comprises the following steps: Step S1: Solution preparation Preparation of oxidant solution A Silver nitrate and silver carbonate were weighed and dissolved in propylene glycol and ethylene glycol to prepare a concentration of 0.1 M. The solution temperature was controlled at 30° C. and stirred for 30 minutes to prepare an oxidant solution A.

[0077] Preparation of reducing agent solution B Weigh triethanolamine and hydrazine hydrate and dissolve them in propylene glycol and ethylene glycol to prepare a concentration of 0.1 M. The solution temperature is controlled at 30° C. and stirred for 30 minutes to prepare a reducing agent solution B.

[0078] Preparation of Conditioner Solution C Sodium hydroxide and sodium carbonate were weighed and dissolved in propylene glycol and ethylene glycol to prepare a concentration of 0.05 M. The solution temperature was controlled at 30° C. and stirred for 30 minutes to prepare a regulator solution C.

[0079] Preparation of dispersant solution D Weigh polyvinyl pyrrolidone and polyethylene glycol and dissolve them in glycerol and ethylene glycol to prepare a concentration of 100 g / L. The solution temperature is controlled at 30° C. and stirred for 1 hour to prepare a dispersant solution D.

[0080] Step S2: Adding dispersant and regulator At a stirring speed of 300 rpm, the regulator solution C was quickly added to the reducing agent solution B and stirred for 5 minutes. Then the dispersant solution D was divided into two parts by volume of 1:9 and added to the reducing agent solution B and the oxidant solution A respectively. The solution temperature was controlled at 30°C and stirred for 7 minutes respectively to obtain solution E and solution F.

[0081] Step S3: Reduction reaction With stirring at 300 rpm, add solution E to solution F for about 1 min. Control the temperature during the addition process at 28-30 °C. After the addition is completed, immediately raise the temperature to 130 °C at a rate of 2 °C / min. The reaction is timed to end after 3 h from the start of the addition.

[0082] Step S4: Sedimentation and washing Weigh polyacrylamide and add it to deionized water, the polyacrylamide is 1000% of the mass of silver, stir and dissolve to prepare a solution with a concentration of 100 g / L, add it to the final solution of step S3, and then add deionized water 1000% of the total volume of the silver solution, stir for 10 minutes, stop stirring and let settle for 30 minutes, pour out the supernatant, and repeat this washing process 5 times.

[0083] Step S5: Silver sol preparation The silver powder washed in step S4 was added to 2000 g of ethylene glycol, ultrasonicated and stirred for 30 min to prepare a silver sol with a solid content of 0.5% and tested.

[0084] The test results in the above Example 7 are as follows: Figure 7 As shown, D10=0.14um, D50=0.23um, D90=0.36um, D95=0.65um, ZETA test size is 62nm, potential is -23.1mv, and coating agent content is 1.76% at 550℃. Figure 7 It can be seen that the particle size distribution of the synthesized silver powder is concentrated and the morphology of the silver powder is uneven.

[0085] Comparative Example 1 The difference between this comparative example and Example 1 is that in step S4, washing is repeated once.

[0086] The test results in the above comparative example 1 are as follows: the electron microscope image of the silver sol and Figure 1 The results are consistent, D10=0.13um, D50=0.16um, D90=0.22um, D95=0.23um, the ZETA test size is 37nm, the potential is -16mv, and the coating agent content is 16.7% at 550℃. It can be seen from the test data that the free organic matter in the silver sol was not completely washed away due to insufficient washing times.

[0087] Comparative Example 2 The difference between this comparative example and Example 1 is that no sedimentation washing is performed, the silver powder is directly collected by centrifugation, and the process proceeds to step S5 for preparing silver sol.

[0088] The test results in the above comparative example 2 are as follows: the electron microscope image of the silver sol and Figure 1 The results are consistent, D10=0.13um, D50=0.16um, D90=0.22um, D95=0.24um, the ZETA test size is 37nm, the potential is -25mv, and the coating agent content is 78.6% at 550℃. It can be seen from the test data that the surface of the unwashed silver sol contains more organic matter, which is difficult to remove completely during low-temperature sintering.

[0089] Comparative Example 3 The difference between this comparative example and Example 2 is that: Step S2: Adding dispersant and regulator At a stirring speed of 300 rpm, the regulator solution C was quickly added to the reducing agent solution B and stirred for 5 minutes. Then, the dispersant solution D was added to the reducing agent solution B. The solution temperature was controlled at 30° C. and stirred for 7 minutes to obtain a solution E.

[0090] With stirring at 300 rpm, add solution E to solution A for about 20 minutes. Control the temperature during the addition process at 10-12°C. After the addition is completed, immediately raise the temperature to 150°C at a rate of 5°C / min. The reaction is timed to end at 2 hours from the start of the dropwise addition.

[0091] The test results in the above comparative example 3 are as follows: Figure 8 As shown, D10=0.13um, D50=0.21um, D90=0.37um, D95=0.53um, ZETA test size is 83nm, potential is -10.3mv, and coating agent content is 2.93% at 550℃. Figure 8 It can be seen that the synthesized silver powder has poor consistency.

[0092] Comparative Example 4 The difference between this comparative example and Example 2 is that: Step S2: Adding dispersant and regulator At a stirring speed of 300 rpm, the regulator solution C was quickly added to the reducing agent solution B, stirred for 5 minutes, the solution temperature was controlled at 30°C, and stirred for 7 minutes to obtain solution E; the dispersant solution D was added to the oxidant solution A, the solution temperature was controlled at 30°C, and stirred for 7 minutes to obtain solution F.

[0093] With stirring at 300 rpm, add solution E to solution F for about 20 min. Control the temperature during the addition process at 10-12 °C. After the addition is completed, immediately raise the temperature to 150 °C at a rate of 5 °C / min. The reaction is timed to end at 2 h from the start of the dropwise addition.

[0094] The test results in the above comparative example 4 are as follows: Fig. 9 As shown, D10=0.14um, D50=0.28um, D90=0.52um, D95=0.75um, ZETA test size is 212nm, potential is -5.6mv, and coating agent content is 2.63% at 550℃. Fig. 9 It can be seen that the synthesized silver powder is larger in size.

[0095] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A nano silver sol with low surface coating agent, characterized in that: It comprises silver nanoparticles, a coating agent and a solvent; wherein the mass fraction of the silver nanoparticles is 0.5wt%-50wt%, and the mass fraction of the coating agent is less than 3wt%.

2. The nano silver sol with low surface coating agent according to claim 1, characterized in that: The coating agent is polyvinyl pyrrolidone or polyethylene glycol.

3. A method for preparing a nano silver sol with a low surface coating agent, characterized in that: The following steps are involved: Step 1: Add the regulator solution C to the reducing agent solution B under high-speed stirring, then add a portion of the dispersant solution D to the oxidant solution A, stir for 5-10 minutes, and obtain solution E; add another portion of the dispersant solution D to the reducing agent solution B, stir for 5-10 minutes, and obtain solution F; Step 2, under high-speed stirring, adding solution E to solution F through a flow meter, controlling the adding time of solution E to be 1 to 30 minutes, and controlling the temperature to be constant during the adding process; after solution E is added, starting to heat the reaction solution and ageing it to obtain a silver solution; Step 3, adding a precipitant and deionized water to the silver solution obtained in step 2, and repeatedly washing for 3-5 times, pouring out the supernatant for the last time, and collecting the silver powder for later use; Step 4: The silver powder collected in step 3 is dispersed in solution H by ultrasonic stirring using a dual-frequency ultrasonic cleaning machine, and stirred at a speed of 250 r / min. The total time of ultrasonic stirring is 10 to 30 minutes to form a silver sol, which is then tested.

4. The method for preparing a nano silver sol with low surface coating agent according to claim 3, characterized in that: In the step 1, the preparation of oxidant solution A is as follows: the oxidant is dissolved in solution G to a concentration of 0.01M-0.5M, and the solution temperature is controlled to be 10-30°C to obtain oxidant solution A; the oxidant is one or more of silver nitrate, silver ammonia and silver carbonate; and the solution G is one or more of deionized water, glycerol and ethylene glycol.

5. The method for preparing a nano silver sol with low surface coating agent according to claim 4, characterized in that: In the step 1, the reducing agent solution B is prepared by dissolving the reducing agent in the solution G, wherein the reducing agent mass is 0.25-4 times the mass of the oxidant, and the concentration is configured to be 0.04M-0.5M, and the solution temperature is controlled to be 10-30°C to obtain the reducing agent solution B; the solution G is one or more of deionized water, glycerol and ethylene glycol; the reducing agent is one or more of hydrazine hydrate, triethanolamine and sodium borohydride.

6. The method for preparing a nano silver sol with low surface coating agent according to claim 5, characterized in that: In the step 1, the preparation of the regulator solution C is as follows: the regulator is dissolved in the solution G, the concentration of the regulator is 0.01-0.05M, and the solution temperature is controlled to be 10-30°C; the solution G is one or more of deionized water, glycerol and ethylene glycol; the regulator is one or more of sodium hydroxide, ammonia water and sodium carbonate.

7. The method for preparing a nano silver sol with low surface coating agent according to claim 6, characterized in that: In the step 1, the preparation of dispersant solution D is as follows: the dispersant is dissolved in solution G, the mass of the dispersant is 1-5 times that of the oxidant, the concentration is configured to be 50-500 g / L, and the solution temperature is controlled to be 10-30°C; the solution G is one or more of deionized water, glycerol and ethylene glycol; the dispersant is polyvinyl pyrrolidone or polyethylene glycol.

8. The method for preparing a nano silver sol with low surface coating agent according to claim 7, characterized in that: In the step 1, the dispersant solution D is divided into two parts according to the ratio of 1-9:9-1, and added into the oxidant solution A and the reductant solution B respectively.

9. The method for preparing a nano silver sol with low surface coating agent according to claim 8, characterized in that: In the step 2, the constant temperature during the addition of solution E is 10-30°C. After the addition of solution E is completed, the temperature is increased to 130-160°C at a rate of 2°C / min-15°C / min, and the reaction aging time is 1-3h.

10. The method for preparing a nano silver sol with low surface coating agent according to claim 9, characterized in that: In the step three, the amount of the precipitant added is 50% to 1000% of the theoretical mass of the silver particles, and the concentration is prepared to be 100 g / L; the amount of deionized water added is 10% to 1000% of the mass of the silver solution; and the precipitant is one or more of polyferric sulfate, alum and polyacrylamide.

11. The method for preparing a nano silver sol with low surface coating agent according to claim 10, characterized in that: In the step 4, the solution H is one of deionized water, ethanol, isopropanol, ethylene glycol and glycerol.

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