Microcrystalline silver powder and preparation method and application thereof

Abstract

The invention relates to microcrystalline silver powder and a preparation method and application thereof, and relates to the technical field of new materials. The preparation method comprises the following steps that a silver nitrate solution with the concentration larger than or equal to 2.0 g / mL and a dispersing agent solution are prepared, the silver nitrate solution and the dispersing agent solution are mixed, a conditioning agent is added, stirring is conducted, and a silver nitrate mixed solution is obtained; preparing a reducing agent solution and a reaction accelerator solution, and mixing the reducing agent solution and the reaction accelerator solution to obtain a reduced mixed solution; and the silver nitrate mixed solution is dropwise added into the reduction mixed solution, dropwise adding stirring, cleaning and solid-liquid separation are carried out, sediment is taken, a surface treating agent is added for surface treatment, drying, powdering and sieving are carried out, and the microcrystalline silver powder is obtained. According to the preparation method, on the basis of a liquid phase reduction method, the prepared microcrystalline silver powder is small in particle size and high in tap density, and has monodispersity, narrow particle size distribution and high adhesive force. The preparation method is simple in process, easy for batch production, good in stability and non-toxic in raw materials.

Description

Technical Field

[0001] The present invention relates to the technical field of new materials, and in particular to a microcrystalline silver powder and a preparation method and application thereof. Background Art

[0002] In the modern information society, the update of electronic products is changing people's living environment and lifestyle. In particular, the photovoltaic industry that has been launched at home and abroad in recent years has accelerated the development of electronic pastes, and ultrafine silver powder has been widely used in the electronics industry and has become a basic functional material for conductive electronic pastes. With the rapid development of the photovoltaic and electronics industries, the demand for silver powder has also greatly increased. Therefore, how to prepare high-performance ultrafine silver powder has become a hot topic in the current electronics industry.

[0003] The conductive functional phase in the conductive paste determines the electrical properties of the paste and affects the mechanical and physical properties of the sintered film. In the conductive paste, the functional phase is generally selected from precious metals with good conductivity such as gold, silver, copper, and palladium. Compared with other precious metals, silver is favored by the industry due to its electrical conductivity, thermal conductivity, and low price. Silver is the main material for the conductive phase in electronic paste due to its good electrical conductivity and physical and mechanical properties. Therefore, silver powder is used as the conductive phase in the photovoltaic industry and the electronics industry.

[0004] At present, the liquid phase chemical reduction method is used in the production of silver powder. The liquid phase chemical reduction method has a simple process flow and does not require high reaction equipment. It is suitable for both small-scale experiments and large-scale production. It can mass-produce most of the silver powders on the market, and the particle size can also be well controlled. However, the preparation of ultrafine silver powder using the liquid phase chemical reduction method is different from the preparation of spherical silver powder. Spherical silver powder with large particle size is easier to control and the dispersibility can be improved, while ultrafine silver powder has very strong adhesion. It is difficult to control the dispersibility during mass production. The surface cleanliness of the silver powder is not high, resulting in the silver powder particle size and specific surface area being difficult to control, low tap density, and high corrosion. The two major indicators for measuring the performance of ultrafine silver powder are dispersibility and tap density. The better the dispersibility and the higher the tap density, the conductive paste prepared by the ultrafine silver powder has the characteristics of non-stickiness, small shrinkage, easy de-screening when printing, and dense sintering. Therefore, there is an urgent need to develop a method with a simple process flow that can prepare silver powder with high dispersibility, high tap density, high sintering activity and easy industrialization, so as to solve the problems of poor sintering activity, high shrinkage rate, high corrosion, etc., and improve the electrical conductivity and photoelectric conversion capacity. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for preparing microcrystalline silver powder. The preparation method is based on a liquid phase reduction method. The prepared microcrystalline silver powder has small particle size, high tap density, monodispersity, narrow particle size distribution, and strong adhesion. The preparation method is simple and easy to mass produce, has good stability, and the raw materials are non-toxic, providing strong protection for production workers.

[0006] In order to achieve the above object, the present invention provides a preparation method of microcrystalline silver powder, comprising the following steps: preparing a silver nitrate solution with silver nitrate, preparing a dispersant solution, mixing the silver nitrate solution and the dispersant solution, adding a regulator, stirring, and obtaining a silver nitrate mixed solution; preparing a reducing agent solution and a reaction accelerator solution, mixing the reducing agent solution and the reaction accelerator solution, and obtaining a reduced mixed solution; dropping the silver nitrate mixed solution into the reduced mixed solution, performing dropwise stirring, washing, solid-liquid separation, taking a precipitate, adding a surface treatment agent for surface treatment, drying, powdering, and sieving to obtain microcrystalline silver powder;

[0007] The concentration of silver nitrate in the silver nitrate solution is ≥2.0 g / mL.

[0008] In the above preparation method, after silver nitrate is prepared into a silver ion solution with a high concentration, a pH regulator solid is directly added, and a reaction accelerator is added to make the silver powder rapidly nucleate. At the same time, a dispersant is added to inhibit the nucleation crystal growth, and the silver powder particle size is controlled between 1.0-1.5 to improve the tap density. The silver powder obtained by this preparation method is microcrystalline silver powder, which has a small particle size and a high tap density, and is suitable for crystalline silicon solar cells and various types of conductive silver pastes; and the higher the tap density of the silver powder, the greater the content of active conductive substances in the monomer volume, and the better the thick film density, so that the volume resistivity of the slurry made of the microcrystalline silver powder as the raw material is smaller after curing, and the contact resistance between the conductive oxide is also smaller, thereby improving the photoelectric conversion rate of the solar cell. The preparation method is based on the liquid phase redox method, with a simple process, a small dispersant content, non-toxicity, high production efficiency, easy batch production, good stability, and non-toxic raw materials, providing strong protection for production staff.

[0009] In one embodiment, the dispersant includes at least one of tannin, guar gum, and gum guar, and the mass of the dispersant is 0.15-1.5% of the mass of the silver nitrate.

[0010] The above raw materials can effectively control the nucleation of silver powder and inhibit the nucleation growth process as a dispersant, so that the particle size of the silver powder is controlled within a smaller range and the tap density is increased. The dispersant used in the preparation method is relatively small and easy to clean, which improves the dispersibility and is simple to clean. It is applied to the rear end of the slurry, and silver is used as a conductive phase. The ultimate goal is to reduce the resistance of the series circuit, and the resistivity is low. The conductivity of silver is guaranteed.

[0011] In one embodiment, the reaction accelerator includes at least one of triphenylphosphine and urea, and the mass of the reaction accelerator is 0.05-0.2% of the mass of the silver nitrate.

[0012] The above reaction accelerator and its dosage, in combination with the dispersant, can enable the silver powder to rapidly nucleate while preventing the nucleus crystals from growing excessively.

[0013] In one embodiment, the regulator includes at least one of sodium carbonate, ammonia water, sodium hydroxide and potassium hydroxide, and the mass of the regulator is 8-20% of the mass of the silver nitrate.

[0014] The above-mentioned adjusting agent is used to adjust the pH value.

[0015] In one embodiment, the reducing agent includes at least one of ascorbic acid, glycerol, triethanolamine, and glucose, and the amount of the reducing agent used is 0.35-1.0 times the silver content in the silver nitrate.

[0016] In one embodiment, the surface treatment agent includes at least one of oleic acid, dodecanoic acid, tetradecanoic acid, and boric acid, and the mass of the surface treatment agent is 0.25-1.0% of the mass of the silver nitrate.

[0017] In one embodiment, the temperature of the step of preparing the silver nitrate solution is 20-40°C, the temperature of the step of preparing the reducing agent solution is 35-45°C; the time of the dropping is 0.5-1.5h, the speed of the dropping and stirring is 150-300rp / min, the temperature of the dropping and stirring is 35-45°C, and the time of the dropping and stirring is 60-120min.

[0018] The temperature range of the silver nitrate solution and the reducing agent solution is also an important factor to be considered in the experimental design. Different temperatures combined with the type and amount of dispersant will affect the physical parameters such as the tap density and dispersibility of the silver powder as well as the sintering activity.

[0019] In one embodiment, the cleaning comprises: cleaning the product obtained after dripping and stirring until the conductivity is lower than 20 μs / cm; the solid-liquid separation is achieved by natural sedimentation; and the drying temperature is 65-85°C.

[0020] The present invention also provides microcrystalline silver powder obtained by the preparation method, wherein the microcrystalline silver powder is a microcrystalline silver powder with a high tap density, wherein the tap density of the microcrystalline silver powder is 4.5-6.0 g / ml, the particle size D50 is 0.8-2.0 μm, and the specific surface area is 1.0-2.0 m 2 / g.

[0021] The above-mentioned microcrystalline silver powder has small particle size, high tap density, uniform morphology, monodispersity, narrow particle size distribution, and strong adhesion. It is an ultra-fine microcrystalline silver powder. Compared with conventional microcrystalline silver powder, it has higher activity and higher photoelectric conversion rate. The electrode prepared by using this microcrystalline silver powder can reduce contact attenuation, provide strong electrode connection ability and strong drought resistance.

[0022] The present invention also provides application of the microcrystalline silver powder in preparing electrodes and conductive slurries.

[0023] The invention also provides an electronic paste, which is prepared by using the microcrystalline silver powder.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention discloses a microcrystalline silver powder and a preparation method and application thereof. The preparation method is based on a liquid phase reduction method, and the prepared microcrystalline silver powder has small particle size, high tap density, monodispersity, narrow particle size distribution, and strong adhesion. The preparation method is simple and easy to mass produce, has good stability, and the raw materials are non-toxic, providing strong protection for production staff. The prepared silver powder is microcrystalline silver powder, which has small particle size, high tap density, uniform morphology, monodispersity, and narrow particle size distribution. It is an ultrafine microcrystalline silver powder, which has higher activity and higher photoelectric conversion rate than conventional microcrystalline silver powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the morphology of the microcrystalline silver powder prepared in Example 1;

[0027] Figure 2 This is a morphology diagram of the microcrystalline silver powder prepared in Comparative Example 1;

[0028] Figure 3 This is a morphology diagram of the microcrystalline silver powder prepared in Example 2;

[0029] Figure 4 This is a morphology diagram of the microcrystalline silver powder prepared in Comparative Example 2;

[0030] Figure 5 This is the morphology of the microcrystalline silver powder prepared in Example 3;

[0031] Figure 6 This is a morphology diagram of the microcrystalline silver powder prepared in Comparative Example 3;

[0032] Figure 7 This is the morphology of the microcrystalline silver powder prepared in Comparative Example 4. DETAILED DESCRIPTION

[0033] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0035] source:

[0036] Unless otherwise specified, the reagents, materials, and equipment used in this example are all commercially available; the experimental methods are all conventional experimental methods in the art unless otherwise specified.

[0037] Example 1

[0038] (1) Dissolve 1 kg of silver nitrate in 5 L of deionized water in a mixing kettle to prepare a silver nitrate solution (silver nitrate concentration is 0.2 g / mL) and control the solution temperature to 30 ± 2 °C.

[0039] (2) Weigh 1.5 g of tannin (dispersant) and dissolve it in 20 ml of deionized water to prepare a dispersant solution, and control the solution temperature to be 30° C. In this embodiment, the mass of the dispersant is 0.15% of the mass of silver nitrate.

[0040] (3) Weigh 0.5 g of triphenylphosphine (reaction accelerator) and dissolve it in 20 ml of deionized water to prepare a reaction accelerator solution, and control the solution temperature to be 30° C. In this embodiment, the mass of the reaction accelerator is 0.05% of the mass of silver nitrate.

[0041] (4) Weigh 80 g of solid sodium carbonate as a regulator. In this embodiment, the mass of the regulator is 8% of the mass of silver nitrate.

[0042] (5) Add the tannin solution (dispersant solution) to the silver nitrate solution and stir to obtain solution A.

[0043] (6) Add sodium carbonate solid into the A solution batching kettle at one time, start stirring at a stirring speed of 350 rpm to obtain B solution (silver nitrate mixed solution).

[0044] (7) Weigh 0.22 kg of glucose (reducing agent) into a reactor, add water to dissolve and prepare 1 L of reducing agent solution, heat to 40°C; add triphenylphosphine solution (reaction accelerator solution), stir at a stirring speed of 200 rp / min to obtain C solution (reducing mixed solution).

[0045] (8) Add solution B (silver nitrate mixed solution) dropwise into solution C (reduced mixed solution) to start the reaction, and perform the dropping and stirring at a stirring speed of 200 rp / min for 1 hour while maintaining the temperature in the reactor at 35-45°C. After the dropping is completed, stir for 10 minutes until the reaction is complete. After the reaction is completed, wash the silver powder obtained by the reaction until the conductivity is less than 20 μs / cm, and allow it to settle naturally for solid-liquid separation.

[0046] (9) After separation, 5 g of tetradecanoic acid (surface treatment agent) was added to the silver powder for surface treatment, dried at 65°C until the material had a constant weight, ground into powder and sieved to obtain microcrystalline silver powder with a high tap density. In this embodiment, the mass of the surface treatment agent was 0.5% of the mass of silver nitrate. Figure 1 ), with a specific surface area of ​​1.0-2.0m 2 / g.

[0047] Example 2

[0048] (1) Dissolve 1 kg of silver nitrate in 5 L of deionized water in a mixing kettle to prepare a silver nitrate solution (silver nitrate concentration is 0.2 g / mL) and control the solution temperature to 30 ± 2 °C.

[0049] (2) Weigh 1.5 g of tannin (dispersant) and dissolve it in 20 ml of deionized water to prepare a dispersant solution, and control the solution temperature to be 30° C. In this embodiment, the mass of the dispersant is 0.15% of the mass of silver nitrate.

[0050] (3) Weigh 0.5 g of triphenylphosphine (reaction accelerator) and dissolve it in 20 ml of deionized water to prepare a reaction accelerator solution, and control the solution temperature to be 30° C. In this embodiment, the mass of the reaction accelerator is 0.05% of the mass of silver nitrate.

[0051] (4) Weigh 80 g of solid sodium hydroxide as a regulator. In this embodiment, the mass of the regulator is 8% of the mass of silver nitrate.

[0052] (5) Add the tannin solution (dispersant solution) to the silver nitrate solution and stir to obtain solution A.

[0053] (6) Add sodium hydroxide solid into the A solution batching kettle at one time, start stirring at a stirring speed of 350 rpm to obtain B solution (silver nitrate mixed solution).

[0054] (7) Weigh 0.22 kg of glucose (reducing agent) into a reactor, add water to dissolve and prepare 1 L of reducing agent solution, heat to 40°C; add triphenylphosphine solution (reaction accelerator solution), stir at a stirring speed of 200 rp / min to obtain C solution (reducing mixed solution).

[0055] (8) Add solution B (silver nitrate mixed solution) dropwise into solution C (reduced mixed solution) to start the reaction, and perform the dropping and stirring at a stirring speed of 200 rp / min for 1 hour while maintaining the temperature in the reactor at 35-45°C. After the dropping is completed, stir for 10 minutes until the reaction is complete. After the reaction is completed, wash the silver powder obtained by the reaction until the conductivity is less than 20 μs / cm, and allow it to settle naturally for solid-liquid separation.

[0056] (9) After separation, 5 g of tetradecanoic acid (surface treatment agent) was added to the silver powder for surface treatment, dried at 65°C until the material had a constant weight, ground into powder and sieved to obtain microcrystalline silver powder with a high tap density. In this embodiment, the mass of the surface treatment agent was 0.5% of the mass of silver nitrate. Figure 3 ), with a specific surface area of ​​1.0-2.0m 2 / g.

[0057] Example 3

[0058] (1) Dissolve 1 kg of silver nitrate in 5 L of deionized water in a mixing kettle to prepare a silver nitrate solution (silver nitrate concentration is 0.2 g / mL) and control the solution temperature to 30 ± 2 °C.

[0059] (2) Weigh 1.5 g of tannin (dispersant) and dissolve it in 20 ml of deionized water to prepare a dispersant solution, and control the solution temperature to be 30° C. In this embodiment, the mass of the dispersant is 0.15% of the mass of silver nitrate.

[0060] (3) Weigh 0.5 g of triphenylphosphine (reaction accelerator) and dissolve it in 20 ml of deionized water to prepare a reaction accelerator solution, and control the solution temperature to be 30° C. In this embodiment, the mass of the reaction accelerator is 0.05% of the mass of silver nitrate.

[0061] (4) Weigh 80 g of potassium hydroxide solid as a regulator. In this embodiment, the mass of the regulator is 8% of the mass of silver nitrate.

[0062] (5) Add the tannin solution (dispersant solution) to the silver nitrate solution and stir to obtain solution A.

[0063] (6) Add potassium hydroxide solid into the A solution batching kettle at one time, start stirring at a stirring speed of 350 rp / min, and obtain B solution (silver nitrate mixed solution).

[0064] (7) Weigh 0.22 kg of glucose (reducing agent) into a reactor, add water to dissolve and prepare 1 L of reducing agent solution, heat to 40°C; add triphenylphosphine solution (reaction accelerator solution), stir at a stirring speed of 200 rp / min to obtain C solution (reducing mixed solution).

[0065] (8) Add solution B (silver nitrate mixed solution) dropwise into solution C (reduced mixed solution) to start the reaction, and perform the dropping and stirring at a stirring speed of 200 rp / min for 1 hour while maintaining the temperature in the reactor at 35-45°C. After the dropping is completed, stir for 10 minutes until the reaction is complete. After the reaction is completed, wash the silver powder obtained by the reaction until the conductivity is less than 20 μs / cm, and allow it to settle naturally for solid-liquid separation.

[0066] (9) After separation, 5 g of tetradecanoic acid (surface treatment agent) was added to the silver powder for surface treatment, dried at 65°C until the material had a constant weight, ground into powder and sieved to obtain microcrystalline silver powder with a high tap density. In this embodiment, the mass of the surface treatment agent was 0.5% of the mass of silver nitrate. Figure 5 ), with a specific surface area of ​​1.0-2.0m 2 / g.

[0067] Comparative Example 1

[0068] A silver powder, the preparation method of which is substantially the same as that of Example 1, except that the temperature of the silver nitrate solution in step (1) is 60°C.

[0069] This comparative example prepared various irregular mixed silver powders with various shapes (see Figure 2 ).

[0070] Comparative Example 2

[0071] A silver powder, the preparation method of which is substantially the same as that of Example 1, except that no reaction accelerator is added.

[0072] This comparative example prepared a relatively cohesive spherical silver powder with a morphology (see Figure 4 ).

[0073] Comparative Example 3

[0074] A silver powder, the preparation method of which is basically the same as that of Example 1, except that in step (4), the regulator is configured into a solution.

[0075] This comparative example prepared a relatively large block of crystalline silver powder with a morphology (see Figure 6 ).

[0076] Comparative Example 4

[0077] A silver powder, the preparation method of which is basically the same as that of Example 1, except that in step (2), the dispersant is replaced by a common rosin dispersant.

[0078] This comparative example prepared a silver powder with very small particle size, poor dispersibility and low tapping density. Figure 7 ).

[0079] Experimental example

[0080] The following tests were performed on the silver powders of the embodiments and comparative examples:

[0081] (1) The particle size of the silver powder was determined by using a Malvern laser particle size analyzer, using anhydrous ethanol as the solvent, and ultrasonically dispersing for 10 minutes;

[0082] (2) Silver powder tap density, measured by using a tap density meter;

[0083] (3) The conventional micropowder A in Table 1 below is C-01 produced by Guangdong Lingguang New Materials Co., Ltd., and is prepared by reducing silver oxide with triethanolamine.

[0084] The test results are shown in Table 1:

[0085] Table 1 Particle size and tap density of each embodiment and comparative example

[0086] Particle size (D10) μm Particle size (D50) μm Particle size (D90) μm Tap density(g / ml) Conventional micro powder A 0.52 1.73 5.97 2.62 Example 1 0.71 1.09 4.43 5.08 Example 2 0.40 1.16 4.86 4.63 Example 3 0.55 1.27 5.77 4.55 Comparative Example 1 0.76 1.18 5.03 4.57 Comparative Example 2 0.86 1.56 7.10 3.32 Comparative Example 3 0.46 1.88 6.33 3.80 Comparative Example 4 0.23 0.81 3.49 2.26

[0087] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing microcrystalline silver powder, characterized in that: The following steps are involved: Silver nitrate is used to prepare a silver nitrate solution, a dispersant solution is prepared, the silver nitrate solution and the dispersant solution are mixed, a regulator is added, and the mixture is stirred to obtain a silver nitrate mixed solution; a reducing agent solution and a reaction accelerator solution are prepared, the reducing agent solution and the reaction accelerator solution are mixed to obtain a reduced mixed solution; the silver nitrate mixed solution is added dropwise to the reduced mixed solution, the mixture is stirred dropwise, washed, solid-liquid separated, a precipitate is taken, a surface treatment agent is added for surface treatment, drying, powdering, sieving, and obtaining microcrystalline silver powder; The concentration of silver nitrate in the silver nitrate solution is ≥2.0 g / mL.

2. The preparation method according to claim 1, characterized in that: The dispersant includes at least one of tannin, guar gum and gum, and the mass of the dispersant is 0.15-1.5% of the mass of the silver nitrate.

3. The preparation method according to claim 1, characterized in that: The reaction accelerator comprises at least one of triphenylphosphine and urea, and the mass of the reaction accelerator is 0.05-0.2% of the mass of the silver nitrate.

4. The preparation method according to claim 1, characterized in that: The regulator includes at least one of sodium carbonate, ammonia water, sodium hydroxide and potassium hydroxide, and the mass of the regulator is 8-20% of the mass of the silver nitrate.

5. The preparation method according to claim 1, characterized in that: The reducing agent comprises at least one of ascorbic acid, glycerol, triethanolamine and glucose, and the amount of the reducing agent used is 0.35-1.0 times the silver content in the silver nitrate.

6. The preparation method according to claim 1, characterized in that: The surface treatment agent includes at least one of oleic acid, dodecanoic acid, tetradecanoic acid and boric acid, and the mass of the surface treatment agent is 0.25-1.0% of the mass of the silver nitrate.

7. The preparation method according to any one of claims 1 to 6, characterized in that The temperature of the step of preparing the silver nitrate solution is 20-40°C, and the temperature of the step of preparing the reducing agent solution is 35-45°C; the time of the dropping is 0.5-1.5h, the speed of the dropping and stirring is 150-300rp / min, the temperature of the dropping and stirring is 35-45°C, and the time of the dropping and stirring is 60-120min.

8. The microcrystalline silver powder obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The microcrystalline silver powder is a microcrystalline silver powder with high tap density, wherein the tap density of the microcrystalline silver powder is 4.5-6.0 g / ml, the particle size D50 is 0.8-2.0 μm, and the specific surface area is 1.0-2.0 m 2 / g.

9. Use of the microcrystalline silver powder according to claim 8 in the preparation of electrodes and conductive pastes.

10. A conductive paste, characterized in that: The microcrystalline silver powder is prepared by using the microcrystalline silver powder described in claim 8.

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