Submicron silver powder and preparation method and application thereof

Abstract

The invention discloses submicron silver powder and a preparation method and application thereof, and belongs to the technical field of metal conductive powder. The preparation raw materials of the submicron silver powder comprise an oxidizing agent, a reducing agent, a dispersing agent, a coating settling agent and a twin crystal inhibitor. The oxidizing agent comprises at least one of silver nitrate, silver nitrite, silver carbonate and silver oxalate; the reducing agent comprises at least one of ascorbic acid, glucose, sodium borohydride, hydrazine hydrate and formaldehyde; the coating settling agent comprises at least one of lauric acid, myristic acid, palmitic acid and stearic acid; the twin crystal inhibitor comprises at least one of N, N-dimethylformamide, dimethyl sulfoxide, acetonitrile, hexamethylphosphoric triamide and dimethylacetamide, the dispersity of the submicron silver powder is effectively improved, meanwhile, co-crystal face growth of silver powder crystals is inhibited, the use amount of the organic dispersing agent is reduced, and the use performance of the silver powder at the paste end is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal conductive powder, and particularly relates to a sub-micron silver powder and a preparation method and application thereof. BACKGROUND

[0002] In the modern photovoltaic and electronic industry field, silver powder as a kind of key material, due to its excellent conductivity, chemical stability and other characteristics, plays an irreplaceable role in many application scenarios. Especially in electronic paste, especially the front silver paste of solar cells, silver powder as a conductive phase, its performance plays a decisive influence on the overall performance of the conductive paste. At present, there are various technical means for preparing sub-micron silver powder, including chemical liquid phase reduction method, plasma atomization method, high temperature pyrolysis method, etc. Among them, the chemical liquid phase reduction method has become the mainstream preparation process due to the advantages of easy control of product characteristic parameters, less equipment investment, and easy scale production.

[0003] However, the existing liquid phase reduction method has some problems in preparing ultra-fine silver powder, which need to be solved urgently. For example, the preparation process of the existing ultra-fine silver powder is more complex than that of micron-sized silver powder, and often needs to be prepared after multiple reduction reactions, which makes it difficult to industrialize and mass-produce. For example, a method for preparing nano-sized silver powder is disclosed, which comprises mixing a first silver salt, first ammonia water, a first reducing agent and water to obtain a silver core solution; mixing the silver core solution, a first dispersing agent and a first solvent to obtain a first reaction liquid; mixing a second silver salt, second ammonia water, a surfactant and a second solvent to obtain a second reaction liquid; mixing a second reducing agent, a second dispersing agent and a third solvent to obtain a third reaction liquid; adding the second reaction liquid and the third reaction liquid to the first reaction liquid at the same rate to obtain a reaction liquid; and after filtering, washing and drying the reaction liquid in sequence, obtaining silver powder. The preparation process is complex, requires multiple types of reagents, and multiple reduction reactions, which makes it difficult to industrialize and mass-produce.

[0004] On the other hand, the existing relatively simple micron-sized silver powder preparation process is relatively simple, but it does not solve the problem that bare ultra-fine silver particles are extremely easy to agglomerate due to high surface activity and are difficult to disperse after agglomeration. Therefore, in addition to using a surfactant, a high-molecular-weight organic polymer with a steric hindrance effect is usually used as a dispersant after using a sub-micron powder preparation process. The residual high-molecular-weight organic polymer dispersant on the surface of the silver ultra-fine powder will have a very adverse effect on the low-temperature sintering activity of the low-temperature silver paste, making it difficult to reduce the resistivity of the thick film body formed after low-temperature heating and curing to the ideal level, and the bonding force between the thick film body and the substrate will also be negatively affected.

[0005] Therefore, it is urgent to develop a sub-micron / nano silver powder preparation method with simple preparation process to prepare low-organic high-dispersibility sub-micron / nano silver powder. SUMMARY

[0006] The present application aims to solve the above technical problems in the prior art. To this end, the present application provides a sub-micron silver powder, a preparation method and application thereof, which effectively improves the dispersibility of the sub-micron silver powder, inhibits the growth of eutectic faces of silver powder crystals, reduces the amount of organic dispersant, and improves the performance of the silver powder in the slurry end.

[0007] The present application also provides a preparation method of the sub-micron silver powder.

[0008] The present application also provides the application of the sub-micron silver powder in the photovoltaic field.

[0009] According to one aspect of the present application, a sub-micron silver powder is provided, and the preparation raw materials of the sub-micron silver powder include: an oxidizing agent, a reducing agent, a dispersant, and a coating settling agent and a twin crystal inhibitor.

[0010] The oxidizing agent includes at least one of silver nitrate, silver nitrite, silver carbonate and silver oxalate.

[0011] The reducing agent includes at least one of ascorbic acid, glucose, sodium borohydride, hydrazine hydrate and formaldehyde.

[0012] The coating settling agent includes at least one of lauric acid, myristic acid, palmitic acid and stearic acid.

[0013] The twin crystal inhibitor includes at least one of N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, hexamethylphosphoramide and dimethylacetamide.

[0014] The twin crystal inhibitor in the present application can form a strong complex with silver ions, effectively slow down the reduction speed of silver ions, avoid rapid nucleation and disordered growth of silver ions. At the same time, it can make the nano-silver crystal nucleus particles formed in the early stage of the reaction uniformly dispersed in the polar environment. And it can synergize with polyvinylpyrrolidone, after adsorbing on the surface of silver crystals, promote the growth of crystals to more regular spherical or cubic structure, and reduce the formation of long strip twin crystal organization.

[0015] The addition of the twin crystal inhibitor in the preparation process effectively improves the dispersibility of the sub-micron silver powder, inhibits the growth of eutectic faces of silver powder crystals, reduces the amount of organic dispersant, improves the performance of the silver powder in the slurry end, simplifies the existing preparation process of sub-micron powder / nano silver powder, and does not need to carry out multiple reduction reactions, and has strong industrialization conversion capacity.

[0016] The effects of the coating sedimentation agent on improving the dispersion of silver powder mainly include two aspects. Firstly, the coating sedimentation agent is combined with the surface of silver particles by chemical adsorption or physical adsorption to form a monolayer coating. Secondly, the long carbon chain (C12) extends outward to form a physical barrier to prevent the Van der Waals force between particles and inhibit agglomeration. The adsorption and steric hindrance effects form a stable coating layer on the surface of the sub-micron silver powder to prevent the sub-micron silver powder from agglomerating and hardening during drying and storage.

[0017] In some embodiments of the present application, the dispersant includes at least one of polyvinylpyrrolidone K10, polyvinylpyrrolidone K30, polyvinylpyrrolidone K90, polyethylene glycol, polyacrylic acid, polyvinyl alcohol, gelatin, and gum arabic.

[0018] In some embodiments of the present application, the dispersant includes polyvinylpyrrolidone K30.

[0019] In some embodiments of the present application, the coating agent is lauric acid.

[0020] In some embodiments of the present application, the D10 particle size of the sub-micron silver powder is 100-200 nm, the D50 particle size is 300-500 nm, and the D90 particle size is 700-1000 nm.

[0021] The tap density of the sub-micron silver powder is 5-7 g / cm 3 ;

[0022] The burn loss of the sub-micron silver powder is 0.5-0.7%.

[0023] The burn loss of the sub-micron silver powder refers to the percentage of the mass loss of the sample due to the volatilization of moisture, adsorbates, or residual organic matter after the silver powder sample is heated to about 600°C in an air atmosphere and maintained for about 1 hour. This value indicates that the silver powder has good purity and thermal stability.

[0024] According to the two aspects of the present application, a preparation method of the sub-micron silver powder is provided, which includes:

[0025] S1. Mixing a solution of a dispersant and a twin crystal inhibitor to obtain a reaction solution, and adjusting the pH of the reaction solution to 7.5-9.5;

[0026] S2. Mixing a solution of a reducing agent, a solution of an oxidizing agent, and the reaction solution to obtain a silver powder suspension;

[0027] S3. Mixing the silver powder suspension and a coating sedimentation agent to obtain the sub-micron silver powder.

[0028] In some embodiments of the present application, the solvent in the solution of the reducing agent includes water.

[0029] In some embodiments of the application, the solvent in the solution of the oxidizing agent comprises water.

[0030] In some embodiments of the application, the solvent in the solution of the dispersant comprises water.

[0031] In some embodiments of the application, the molar ratio of the twin crystal inhibitor to the oxidizing agent is 0.005-0.04:1.

[0032] First, the ratio range ensures that the strong polar aprotic solvent forms a moderate complex with silver ions, and at the preferred ratio, the twin crystal inhibitor works through the following synergistic mechanism: (1) the polar groups such as carbonyl groups in the molecule form dynamic coordination bonds with Ag + , controlling the reduction reaction rate in the ideal interval; (2) intermolecular forces are generated with the dispersant, forming a composite adsorption layer on the surface of the silver crystal nucleus, selectively inhibiting the excessive growth of the twin crystal face, and promoting the development of the crystal to isotropy.

[0033] In some embodiments of the application, the concentration of the solution of the oxidizing agent is 0.5-2 mol / L, and the amount used is 1-20 L.

[0034] The concentration of the solution of the reducing agent is 0.6-1.2 mol / L, and the amount used is 0.3-15 L.

[0035] The concentration of the solution of the dispersant is 1 x 10 -4 -5 x 10 -4 mol / L, and the amount used is 1-40 L.

[0036] The above concentration range ensures that the supply of silver ions is sufficient and stable, maintains a moderate ion concentration gradient, stabilizes the crystal growth rate, avoids explosive nucleation caused by local supersaturation, and ensures uniform particle size distribution.

[0037] In some embodiments of the application, the oxidizing agent comprises silver nitrate.

[0038] In some embodiments of the application, the concentration of the solution of the oxidizing agent specifically comprises about 0.8 mol / L, 1.2 mol / L, 1.5 mol / L, or 1.8 mol / L.

[0039] In some embodiments of the application, the concentration of the solution of the reducing agent is 0.6-1.2 mol / L.

[0040] The above concentration range ensures that the reduction of silver ions is complete, and maintains the stability of the pH of the reaction system.

[0041] In some embodiments of the present application, the concentration of the solution of the reducing agent specifically includes about 0.7 mol / L, 0.9 mol / L or 1.1 mol / L.

[0042] In some embodiments of the present application, the concentration of the solution of the dispersing agent is 1×10 -4 ~ 5×10 -4 mol / L.

[0043] With the above dispersing agent concentration, a complete adsorption layer is ensured to be formed on the surface of the silver particles, and the molecules are uniformly anchored to cooperatively control the anisotropy index of the crystal growth of the silver crystal surface and the twin crystal inhibitor.

[0044] In some embodiments of the present application, the concentration of the solution of the dispersing agent specifically includes about 2×10 -4 mol / L, 3×10 -4 mol / L or 4×10 -4 mol / L.

[0045] In some embodiments of the present application, the molar ratio of the coating settling agent to the oxidizing agent is 0.001-0.01:1.

[0046] In some embodiments of the present application, the molar ratio of the coating settling agent to the oxidizing agent is 0.002:1, 0.005:1 or 0.008:1.

[0047] In some embodiments of the present application, the molar ratio of the coating settling agent to the oxidizing agent is 0.001-0.01:1.

[0048] In some embodiments of the present application, in step S1, a pH adjusting agent is further added to adjust the pH of the reaction solution to 7.5-9.5.

[0049] Under the above circumstances, the pH adjusting agent forms a stable complex with silver ions, which reduces the rate of the reduction reaction and effectively avoids the common burst nucleation phenomenon.

[0050] In some embodiments of the present application, the pH adjusting agent includes at least one of ammonia, sodium hydroxide, nitric acid and formic acid.

[0051] In some embodiments of the present application, the step of step S2 includes: adding the solution of the reducing agent, the solution of the oxidizing agent and the solution of the dispersing agent into the reaction solution to mix the reaction to obtain a silver powder suspension.

[0052] In some embodiments of the present application, in step S2, the feeding speed of the solution of the reducing agent is 40%-60% of the volume of the reaction solution per minute.

[0053] In step S2, the feeding speed of the solution of the oxidizing agent is 40%-60% of the reaction liquid volume per minute.

[0054] In some embodiments of the present application, in step S2, the feeding time of the solution of the reducing agent, the solution of the oxidizing agent and the solution of the dispersing agent is 1-10 minutes.

[0055] In some embodiments of the present application, in step S3, the post-treatment includes sedimentation, filtration, washing, drying and crushing.

[0056] According to the three aspects of the present application, the application of the sub-micron silver powder in the photovoltaic field is provided. BRIEF DESCRIPTION OF DRAWINGS

[0057] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the following drawings, in which:

[0058] Figure 1 is a SEM image of the silver powder of Example 1;

[0059] Figure 2 is a SEM image of the silver powder of Example 2;

[0060] Figure 3 is a SEM image of the silver powder of Example 3;

[0061] Figure 4 is a SEM image of the silver powder of Comparative Example 1;

[0062] Figure 5 is a SEM image of the silver powder of Comparative Example 2;

[0063] Figure 6 is a SEM image of the silver powder of Comparative Example 3.

[0064] Figure 7 is a SEM image of the silver powder of Comparative Example 4.

[0065] Figure 8 is a SEM image of the silver powder of Comparative Example 5. DETAILED DESCRIPTION

[0066] The concept and the technical effects of the present application will be described clearly and completely in the following embodiments, so as to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0067] In the description of the application, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In this specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in one or more embodiments or examples.

[0068] Embodiment 1

[0069] The embodiment provides a sub-micron silver powder, and the specific steps are as follows:

[0070] 200g of silver nitrate is dissolved in 1L of pure water, and the temperature of the solution is controlled to be 20°C to obtain an oxidizing agent solution;

[0071] 120g of ascorbic acid is dissolved in 1L of pure water, and the temperature of the solution is controlled to be 20°C to obtain a reducing agent solution;

[0072] S1. 20g of polyvinylpyrrolidone K30 is dissolved in 1.25L of pure water, the temperature of the solution is controlled to be 20°C, 2g of nitric acid, 3g of ammonia water, and 3.4g of N, N-dimethylformamide are added to obtain a reaction solution;

[0073] S2. Under the condition that the reaction solution is continuously stirred at a speed of 440rpm / min, the reducing agent solution and the oxidizing agent solution are simultaneously added to the reaction solution at a rate of 60% of the volume of the solution per minute, and after the addition is completed, a silver powder suspension is obtained;

[0074] S3. After 0.5g of lauric acid is dissolved in 20ml of ethanol, the silver powder suspension is added, and after continuous stirring, the solid phase is collected, washed with pure water and ethanol respectively, and dried and ground to obtain the final product silver powder.

[0075] The SEM diagram of the silver powder prepared in the embodiment is as shown in Figure 1 .

[0076] Figure 1 It can be seen from the diagram that the silver particles are highly monodisperse spherical / cubic structures, the D50 particle size is stably in the range of 300-500nm, and the surface is smooth without twin crystal defects. The morphology confirms that the synergistic effect of N, N-dimethylformamide and polyvinylpyrrolidone effectively inhibits the growth of eutectic surfaces, and the lauric acid coating layer avoids particle agglomeration, which meets the index requirements of tap density 5-7g / cm 3 , and specific surface area 1.7-2.2m 2 / g.

[0077] Embodiment 2

[0078] The difference between this example and Example 1 is that the amount of N,N-dimethylformamide is 0.4 g, and the reducing agent solution and the oxidizing agent solution are simultaneously added to the reaction solution at a rate of 40% per minute of the solution volume.

[0079] Figure 2 The SEM image of the silver powder morphology of Example 2 is shown, corresponding to a halving of the amount of N,N-dimethylformamide. The particle dispersion remains good, and some particles show a slight tendency to be angular, indicating that when the amount of twinning inhibitor is insufficient, the crystal growth orientation begins to appear. This result confirms the linear regulation of the concentration of N,N-dimethylformamide on the growth of silver crystal faces, and an addition amount of 1% or more is required to achieve optimal morphology control.

[0080] Example 3

[0081] The difference between this example and Example 1 is that 3.4 g of N,N-dimethylformamide is replaced by 2 g of dimethylacetamide, and the reducing agent solution and the oxidizing agent solution are simultaneously added to the reaction solution at a rate of 50% per minute of the solution volume.

[0082] Figure 3 The SEM image of the silver powder morphology of Example 3 is shown, corresponding to a comparison experiment in which dimethylacetamide is used instead of N,N-dimethylformamide. The particles still maintain regular geometric shapes, but the particle size distribution is slightly wider.

[0083] Comparative Example 1

[0084] This comparative example provides a sub-micron silver powder, which differs from Example 1 in that the amount of N,N-dimethylformamide is 0.1 g.

[0085] The above Comparative Example 1 exhibits typical twinning defects: the amount of twinning inhibitor is insufficient, generating long, flocculent twinning crystals, and there is hard agglomeration between particles, causing silver atoms to be randomly stacked along the crystal faces, affecting the conductivity of the paste.

[0086] Comparative Example 2

[0087] This comparative example provides a sub-micron silver powder, which differs from Example 1 in that the amount of N,N-dimethylformamide is 8 g.

[0088] In this comparative example, the amount of N,N-dimethylformamide added exceeds the limit, and a lamellar abnormal structure appears. Excessive N,N-dimethylformamide passivates the active sites on the crystal faces, causing two-dimensional directional growth to dominate. This structure significantly reduces the tap density.

[0089] Comparative Example 3:

[0090] This comparative example provides a sub-micron silver powder, which differs from Example 1 in that no lauric acid is added, and only ethanol is used for treatment.

[0091] The comparative example lacks lauric acid coating, and the particles form a dense and hard compact body due to Van der Waals force, verifying the dual function of the coating settling agent: the long chain not only prevents agglomeration through steric hindrance, but also promotes rapid solid-liquid separation.

[0092] Comparative Example 4

[0093] The comparative example strictly maintains all the raw material formulations and process parameters of Example 1 unchanged, only changing the feeding speed: the reducing agent solution and the oxidizing agent solution are simultaneously added to the reaction solution at a rate of 20% per minute of the solution volume.

[0094] The comparative example feeds too slowly, resulting in too long a crystal nucleus growth time, and the twinning inhibitor has limited effect, and the silver powder shows a polycrystalline growth trend and agglomeration.

[0095] Comparative Example 5

[0096] The comparative example strictly maintains all the raw material formulations and process parameters of Example 1 unchanged, only changing the feeding speed: the reducing agent solution and the oxidizing agent solution are simultaneously added to the reaction solution at a rate of 70% per minute of the solution volume.

[0097] The comparative example feeds too slowly, and the silver nitrate is reduced too quickly, resulting in rapid nucleation, and the silver powder particle size is within 0.3 um (visual observation, no particle size measurement was performed), and there is local agglomeration, and the experiment fails.

[0098] Table 1. Performance test

[0099] D10 (nm) D50 (nm) D90 (nm) Tap density Specific surface Burn-off Example 1 112 310 845 6.3 2.10 0.68 Example 2 152 376 823 6.8 1.95 0.55 Example 3 195 487 850 6.9 1.87 0.57 Comparative Example 1 293 674 1012 / / Comparative Example 2 / / / / / Comparative Example 3 / / / / /

[0100] The test data of the examples and comparative examples in Table 1 are analyzed: the submicron silver powder prepared in Examples 1-3 exhibits excellent performance indicators, wherein the D50 particle size of Example 1 is 310 nm, the D10-D90 distribution is 112-845 nm, the tap density reaches 6.3 g / cm 3 , the specific surface area is 2.10 m 2 / g, and the burn loss is only 0.68%, and all parameters meet the technical index requirements. In contrast, Comparative Example 1 has insufficient N,N-dimethylformamide (0.1 g), resulting in an increase in D50 particle size to 674 nm, and obvious twinning defects and particle agglomeration can be seen from the SEM image; the excessive addition of N,N-dimethylformamide (8 g) in Comparative Example 2 causes a lamellar abnormal structure, and effective measurement data cannot be obtained; the absence of lauric acid in Comparative Example 3 results in severe compaction of the particles, verifying the key role of the coating settling agent in preventing silver powder agglomeration.

[0101] The above has described the embodiments of the present application in detail, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the present application. In addition, the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

Claims

1. A submicron silver powder, characterized in that, The raw materials for preparing the submicron silver powder include: oxidant, reducing agent, dispersant, coating and settling agent, and twinning inhibitor; The oxidizing agent includes at least one of silver nitrate, silver nitrite, silver carbonate, and silver oxalate; The reducing agent includes at least one of ascorbic acid, glucose, sodium borohydride, hydrazine hydrate, and formaldehyde; The coating settling agent includes at least one of lauric acid, myristic acid, palmitic acid and stearic acid; The twinning inhibitor includes at least one of N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, hexamethylphosphoric triamine, and dimethylacetamide.

2. The submicron silver powder according to claim 1, characterized in that, The dispersant includes at least one of polyvinylpyrrolidone K10, polyvinylpyrrolidone K30, polyvinylpyrrolidone K90, polyethylene glycol, polyacrylic acid, polyvinyl alcohol, gelatin, and gum arabic.

3. The submicron silver powder according to claim 2, characterized in that, The submicron silver powder has a D10 particle size of 100-200 nm, a D50 particle size of 300-500 nm, and a D90 particle size of 700-1000 nm. The tap density of the submicron silver powder is 5–7 g / cm³. 3 ; The burn-off rate of the submicron silver powder is 0.5% to 0.7%.

4. A method for preparing submicron silver powder as described in any one of claims 1 to 3, characterized in that, include: S1. The dispersant solution and the twinning inhibitor are mixed to obtain a reaction solution, and the pH of the reaction solution is adjusted to 7.5-9.5; S2. Mix the reducing agent solution, the oxidizing agent solution, and the reaction solution to obtain a silver powder suspension; S3. The silver powder suspension and the coating sedimentation agent are mixed and reacted, and then post-treated to obtain submicron silver powder.

5. The preparation method according to claim 4, characterized in that, The molar ratio of the twinning inhibitor to the oxidant is 0.005 to 0.04:

1.

6. The preparation method according to claim 4, characterized in that, The concentration of the oxidant solution is 0.5–2 mol / L, and the amount used is 1–20 L; The concentration of the reducing agent solution is 0.6–1.2 mol / L, and the amount used is 0.3–15 L; The concentration of the dispersant solution is 1×10⁻⁶. -4 ~5×10 -4 mol / L, dosage is 1-40L.

7. The preparation method according to claim 4, characterized in that, In step S2, the feeding rate of the reducing agent solution is 40%-60% / min of the reaction liquid volume; In step S2, the feeding rate of the oxidant solution is 40%-60% / min of the reaction liquid volume.

8. The preparation method according to claim 4, characterized in that, In step S2, the feeding time of the reducing agent solution, the oxidizing agent solution, and the dispersant solution is 1 to 10 minutes.

9. The preparation method according to claim 4, characterized in that, The molar ratio of the coating settling agent to the oxidant is 0.001 to 0.01:

1.

10. An application of submicron silver powder as described in any one of claims 1 to 3 in the photovoltaic field.

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