A high-volume flake silver powder and its preparation method

Abstract

This invention discloses a high-bulk-density flake silver powder and its preparation method, belonging to the field of conductive materials technology. The preparation method includes: adding a compound dispersant solution to a reaction vessel under stirring; then adding a silver ammonia solution at a flow rate of 1.47–1.96 L / min; followed by adding a compound reducing agent solution at the same flow rate; then adding the remaining silver ammonia solution and compound reducing agent solution to a reactor at the same flow rate; heating and reacting to obtain spherical silver powder; washing the spherical silver powder with water until the conductivity is ≤20 μS / cm; then coating the surface of the washed spherical silver powder with saturated fatty acids; drying the surface-coated spherical silver powder and spheroidizing it; stirring the spheroidized spherical silver powder, unsaturated fatty acids, and alcohol; adding grinding balls for milling; filtering, washing, and drying. The flake silver powder of this invention has high bulk density, high conductivity, good filling properties, excellent printability, and low production cost.

Description

Technical Field

[0001] This invention belongs to the field of conductive materials technology, and particularly relates to a highly porous flake-shaped silver powder and its preparation method. Background Technology

[0002] As a material with good conductivity, flake silver powder, compared to spherical silver powder, uses line and surface contact instead of point contact, which results in lower contact resistance and stronger conductivity. Therefore, it is widely used in electronic paste industries such as membrane switches, heterojunctions, and conductive adhesives.

[0003] Silver powder is a material with good conductivity, typically exhibiting both line and surface contact conductivity. It has low contact resistance and high conductivity. Flake silver powder is widely used in electronic paste industries such as membrane switches, heterojunctions, and conductive adhesives.

[0004] The preparation methods for flake silver powder mainly include chemical and physical methods. Chemically prepared flake silver powder is difficult to control, has poor stability, and the degree of flake formation required for product application needs further research. Therefore, it is limited to experimental research. The main reason behind this is that the silver powder is too thin, and shrinkage occurs after sintering, leading to increased resistance and limited practical value. In contrast, the physical ball milling method offers high flatness, good stability, and is conducive to industrial production. As an important component of conductive silver paste, the physical properties of flake silver powder directly determine whether the paste has good conductivity, density, reliability, and printability. High bulk density flake silver powder is more conducive to improving the conductivity, density, reliability, and printability of conductive silver paste. Therefore, the bulk density of flake silver powder plays an important role in improving the electrical properties of conductive silver paste.

[0005] Currently, high bulk density silver powder is mainly concentrated in spherical silver powder, with a bulk density reaching 3.0–4.0 g / cm³. 3 The bulk density of flake silver powder is around 0.5–1.6 g / cm³, while that of flaky silver powder is low due to the degree of flake formation and the preparation process. 3 The bulk density of the silver powder prepared by these two patents is only around 0.6–0.8 g / cm³. For example, national patent CN118023512A discloses a method for preparing low-bulk-density flake silver powder, which mainly achieves low bulk density by mixing zirconia balls of different particle sizes and then wet-milling them. National patent CN110026564A discloses another method for preparing low-bulk-density flake silver powder, which involves preparing spherical silver powder using a chemical method and then grinding it into low-bulk-density flake silver powder using a wet rod mill. 3The reason is that during the grinding process of flake silver powder, as the degree of flake formation increases, the loose packing density continuously decreases, resulting in a lower loose packing density. In other words, it is quite difficult to obtain high-bulk-density flake silver powder, but high-bulk-density flake silver powder has better conductivity, filling properties, printability, and lower cost than low-bulk-density flake silver powder. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for preparing high-bulk-density flake silver powder. The flake silver powder prepared by this method has high bulk density, high conductivity, good filling properties, excellent printing performance, and low production cost.

[0007] The second objective of this invention is to provide a highly porous, flake-shaped silver powder.

[0008] To achieve one of the above objectives, the present invention employs the following technical solution:

[0009] A method for preparing high-density, sheet-like silver powder, characterized in that the preparation method includes:

[0010] Step S1: Under stirring, a compound dispersant solution with a mass concentration of 15-25 g / L is added to the reaction vessel. Then, a silver ammonia solution with a molar concentration of 1-2 mol / L is added at a flow rate of 1.47-1.96 L / min. Next, a compound reducing agent solution with a molar concentration of 0.5-1.5 mol / L is added at the same flow rate. Then, the remaining silver ammonia solution and compound reducing agent solution are added to the reactor at the same flow rate. The temperature is raised to 45-50℃, and the reaction time is 10-30 min to obtain spherical silver powder with a mass concentration of 1.6-2.5 micrometers.

[0011] In step S1, the volume ratio of the silver ammonia solution to the compound reducing agent solution is 1:1;

[0012] In step S1, the mass ratio of the compound dispersant in the compound dispersant solution to the silver nitrate in the silver ammonia solution is 1:6.8-23;

[0013] Step S2: Wash the spherical silver powder with water until the conductivity is ≦20μs / cm, and then use saturated fatty acids to coat the surface of the washed spherical silver powder.

[0014] In step S2, the mass ratio of the saturated fatty acid to the spherical silver powder is 0.002 to 0.008:1;

[0015] Step S3: After drying the spherical silver powder coated on the surface, sphericalize it for 3-8 minutes;

[0016] Step S4: After stirring the spheroidized spherical silver powder, unsaturated fatty acid grinding aid and alcohol for 8-12 minutes, add grinding balls and grind for 12-18 hours. Filter, wash and dry to obtain high-loose flake silver powder.

[0017] In step S4, the mass ratio of the unsaturated fatty acid grinding aid, grinding balls, alcohol, and spherical silver powder is 0.8–1.0: 4.5–5.0: 0.6–0.8: 1.

[0018] Furthermore, in step S1, the volume ratio of the silver ammonia solution added first to the silver ammonia solution added later is 1:15 to 20.

[0019] The volume ratio of the first added compound reducing agent solution to the last added compound reducing agent solution is 1:15-20.

[0020] Furthermore, in step S1, the solute in the compound reducing agent solution is a mixture of ascorbic acid and formaldehyde with a concentration of 37%;

[0021] In step S1, the compound dispersant is a mixture of polyvinylpyrrolidone K30 and gum arabic, or a mixture of polyvinylpyrrolidone K30 and gelatin.

[0022] Furthermore, the mass ratio of ascorbic acid to formaldehyde is 1:1 to 2;

[0023] The mass ratio of polyvinylpyrrolidone K30 to gum arabic is 3.5–4.5:1;

[0024] The mass ratio of polyvinylpyrrolidone K30 to gelatin is 3.5–4.5:1.

[0025] Furthermore, in step S1, the stirring speed in the stirring state is 250-350 r / min.

[0026] Furthermore, in step S2, the conductivity is 15–18 μS / cm.

[0027] Furthermore, in step S2, the saturated fatty acid is one of palmitic acid, stearic acid, lauric acid, and myristic acid.

[0028] Furthermore, in step S4, the diameter of the grinding ball is 1.2 to 1.6 mm;

[0029] The grinding balls are steel balls or zirconium balls.

[0030] Furthermore, in step S4, the unsaturated fatty acid grinding aid is one of oleic acid, linolenic acid, linoleic acid, arachidonic acid, and docosenoic acid.

[0031] The conductivity in this invention is preferably 15-18 μs / cm.

[0032] To achieve the second objective mentioned above, the present invention employs the following technical solution:

[0033] A highly porous flake silver powder, which is prepared by the method described above.

[0034] In summary, the technical solution of the present invention has the following technical effects:

[0035] This invention ensures the formation of a large number of crystal nuclei by sequentially adding a portion of silver ammonia solution and a portion of the compound reducing agent solution to the compound dispersant solution at the same flow rate, which is beneficial for the subsequent growth of silver powder. Then, the remaining silver ammonia solution and compound reducing agent solution are added at the same flow rate, improving the dispersibility of the silver ammonia solution and compound reducing agent solution and ensuring their complete reaction. The compound reducing agent solution increases the particle size of the spherical silver powder, which is beneficial for obtaining spherical silver powder with high bulk density. Controlling the reaction temperature of the silver ammonia solution and compound reducing agent solution at 45–50°C ensures the formation of a large number of crystal nuclei in a short time, which is beneficial for the slow growth of silver powder in the later stage. Surface coating is performed using saturated fatty acids, utilizing the hydrophilic carboxyl groups and hydrophobic groups of saturated fatty acids. The long CH2 group gives the silver powder both hydrophilic and hydrophobic properties, thereby improving the dispersibility of spherical silver powder and facilitating the production of high bulk density in flake silver powder. By compounding dispersants and spheroidizing, the tap density and bulk density of the spherical silver powder are improved, resulting in flake silver powder with high bulk density. The use of unsaturated fatty acids in the grinding process ensures that the unsaturated fatty acids and the substances coating the silver powder surface (saturated fatty acids) do not repel each other, and utilizes the fact that the carbon-carbon double bonds of the unsaturated fatty acids do not rotate, thus hindering the stacking and agglomeration of silver powder to a certain extent, thereby improving the dispersibility of the flake powder and further increasing the bulk density of the flake silver powder. The flake silver powder of this invention has high bulk density, high conductivity, good filling properties, excellent printability, and low production cost. Attached Figure Description

[0036] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0037] Figure 1 Photograph of the spherical silver powder appearance shape in Example 1;

[0038] Figure 2Photographs showing the appearance of the flake-shaped silver powder in Example 1;

[0039] Figure 3 Photograph of the spherical silver powder appearance shape in Example 2;

[0040] Figure 4 This is a photograph of the appearance of the flake-shaped silver powder in Example 2. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1:

[0043] 1. Prepare a silver ammonia solution with a molar concentration of 2 mol / L using silver nitrate.

[0044] Ascorbic acid and formaldehyde with a concentration of 37% were mixed in a 1:1 mass ratio to prepare a compound reducing agent solution with a molar concentration of 1 mol / L.

[0045] A compound dispersant solution with a mass concentration of 15 g / L was prepared by mixing polyvinylpyrrolidone K30 and gum arabic at a mass ratio of 4:1.

[0046] The volume ratio of the prepared silver ammonia solution to the compound reducing agent solution is 1:1. The mass ratio of polyvinylpyrrolidone K30 and gum arabic in the prepared compound dispersant solution to silver nitrate in the silver ammonia solution is 1:23.

[0047] 2. Under stirring at 300 r / min, first add the prepared compound dispersant solution to the reaction vessel, then add 1 / 15 of the silver ammonia solution at a flow rate of 1.47 L / min, then add 1 / 15 of the compound reducing agent solution at a flow rate of 1.47 L / min, and then add the remaining silver ammonia solution and compound reducing agent solution to the reactor at a flow rate of 1.47 L / min. The temperature is raised to 50℃, and the reaction time is 20 min to obtain 1.6 micrometer spherical silver powder.

[0048] 3. The spherical silver powder is washed with water until the conductivity reaches 20 μS / cm. Then, hexadecanoic acid is used to coat the surface of the washed spherical silver powder. The mass ratio of hexadecanoic acid to spherical silver powder is 0.003:1.

[0049] 4. After drying the surface-coated spherical silver powder, spheroidize it for 5 minutes to obtain a solid density of 5.5 g / cm³. 3 The loose bulk density is 3.32 g / cm³. 3 Spherical silver powder, such as Figure 1 As shown.

[0050] 5. After stirring the spheroidized silver powder, oleic acid, and alcohol for 10 minutes, zirconium balls with a diameter of 1.4 mm were added, and the mixture was ground for 15 hours. The mixture was then filtered, washed, and dried to obtain 3.1 g / cm³ silver powder. 3 High-quality, sheet-like silver powder, such as Figure 2 As shown. The mass ratio of oleic acid, zirconium spheres, alcohol, and spheroidized silver powder is 0.8:4.5:0.6:1.

[0051] Example 2:

[0052] 1. Prepare a silver ammonia solution with a molar concentration of 1 mol / L using silver nitrate.

[0053] Ascorbic acid and formaldehyde with a concentration of 37% were mixed at a mass ratio of 1:2 to prepare a compound reducing agent solution with a molar concentration of 0.5 mol / L.

[0054] A compound dispersant solution with a mass concentration of 25 g / L was prepared by mixing polyvinylpyrrolidone K30 and gum arabic at a mass ratio of 4.5:1.

[0055] The volume ratio of the prepared silver ammonia solution to the compound reducing agent solution is 1:1. The mass ratio of polyvinylpyrrolidone K30 and gum arabic in the prepared compound dispersant solution to silver nitrate in the silver ammonia solution is 1:6.8.

[0056] 2. Under stirring at 350 r / min, first add the prepared compound dispersant solution to the reaction vessel, then add 1 / 20 of the silver ammonia solution at a flow rate of 1.96 L / min, then add 1 / 20 of the compound reducing agent solution at a flow rate of 1.96 L / min, and then add the remaining silver ammonia solution and compound reducing agent solution to the reactor at a flow rate of 1.96 L / min. The temperature is raised to 45℃ and the reaction time is 10 min to obtain 2.5 micrometer spherical silver powder.

[0057] 3. The spherical silver powder is washed with water until the conductivity reaches 18 μS / cm. Then, stearic acid is used to coat the surface of the washed spherical silver powder. The mass ratio of stearic acid to spherical silver powder is 0.008:1.

[0058] 4. After drying the surface-coated spherical silver powder, sphericalize it for 8 minutes to obtain a solid density of 5.7 g / cm³. 3 The loose bulk density is 3.42 g / cm³.3 Spherical silver powder, such as Figure 3 As shown.

[0059] 5. After stirring the spheroidized silver powder, linolenic acid, and alcohol for 8 minutes, steel balls with a diameter of 1.2 mm were added, and the mixture was ground for 18 hours. The mixture was then filtered, washed, and dried to obtain 3.28 g / cm³ silver powder. 3 High-quality, sheet-like silver powder, such as Figure 4 As shown. The mass ratio of linolenic acid, steel balls, alcohol, and spherical silver powder is 1.0:5.0:0.8:1.

[0060] Example 3:

[0061] 1. Prepare a silver ammonia solution with a molar concentration of 1.5 mol / L using silver nitrate.

[0062] Ascorbic acid and formaldehyde with a concentration of 37% were mixed at a mass ratio of 1:1.5 to prepare a compound reducing agent solution with a molar concentration of 1.5 mol / L.

[0063] A compound dispersant solution with a mass concentration of 20 g / L was prepared by mixing polyvinylpyrrolidone K30 and gelatin at a mass ratio of 3.5:1.

[0064] The volume ratio of the prepared silver ammonia solution to the compound reducing agent solution is 1:1. The mass ratio of polyvinylpyrrolidone K30 and gelatin in the prepared compound dispersant solution to silver nitrate in the silver ammonia solution is 1:12.7.

[0065] 2. Under stirring at 250 r / min, first add the prepared compound dispersant solution to the reaction vessel, then add 1 / 18 of the silver ammonia solution at a flow rate of 1.75 L / min, then add 1 / 18 of the compound reducing agent solution at a flow rate of 1.75 L / min, and then add the remaining silver ammonia solution and compound reducing agent solution to the reactor at a flow rate of 1.75 L / min. The temperature is raised to 48℃ and the reaction time is 30 min to obtain 2.0 micrometer spherical silver powder.

[0066] 3. The spherical silver powder is washed with water until the conductivity reaches 15 μS / cm. Then, lauric acid is used to coat the surface of the washed spherical silver powder. The mass ratio of lauric acid to spherical silver powder is 0.002:1.

[0067] 4. After drying the surface-coated spherical silver powder, sphericalize it for 3 minutes to obtain a solid density of 5.6 g / cm³. 3 The loose bulk density is 3.37 g / cm³. 3 Spherical silver powder.

[0068] 5. After stirring the spheroidized silver powder, linoleic acid, and alcohol for 12 minutes, steel balls with a diameter of 1.6 mm were added, and the mixture was ground for 128 hours. The mixture was then filtered, washed, and dried to obtain 3.16 g / cm³ silver powder. 3 High-density flake silver powder. The mass ratio of linoleic acid, steel balls, alcohol and spheroidized silver powder is 0.9:4.8:0.7:1.

[0069] The flake silver powders from Examples 1, 2, and 3 were fused with an organic carrier in an epoxy system, with the silver content controlled at approximately 40%. The prepared silver paste was then rolled three times. Finally, the rolled silver paste was screen-printed onto a PET sheet with a line width of 0.8 mm and a line length of 1 m. The drying temperature was 150°C for 50 minutes. The line resistance was tested as follows: the D50 of the flake silver powders from Examples 1, 2, and 3 were 2.1 μm, 3.1 μm, and 2.7 μm, respectively, and the bulk density was 3.1 g / cm³. 3 3.28g / cm 3 and 3.16 g / cm 3 The resistance values ​​were 75Ω, 70Ω and 72Ω, respectively, and the flake silver powder of Examples 1, 2 and 3 had good density.

[0070] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing high-density, sheet-like silver powder, characterized in that, The preparation method includes: Step S1: Under stirring, add a compound dispersant solution with a mass concentration of 15~25 g / L to the reaction vessel, then add a silver ammonia solution with a molar concentration of 1~2 mol / L at a flow rate of 1.47~1.96 L / min, and then add a compound reducing agent solution with a molar concentration of 0.5~1.5 mol / L at the same flow rate. Next, add the remaining silver ammonia solution and compound reducing agent solution to the reactor at the same flow rate, heat to 45~50℃, and react for 10~30 min to obtain spherical silver powder with a mass concentration of 1.6~2.5 micrometers. In step S1, the volume ratio of the silver ammonia solution to the compound reducing agent solution is 1:1; In step S1, the mass ratio of the compound dispersant in the compound dispersant solution to the silver nitrate in the silver ammonia solution is 1:6.8~23; In step S1, the solute in the compound reducing agent solution is a mixture of ascorbic acid and formaldehyde at a concentration of 37%; In step S1, the compound dispersant is a mixture of polyvinylpyrrolidone K30 and gum arabic, or a mixture of polyvinylpyrrolidone K30 and gelatin; Step S2: Wash the spherical silver powder with water until the conductivity is ≦20μs / cm, and then use saturated fatty acids to coat the surface of the washed spherical silver powder. In step S2, the mass ratio of the saturated fatty acid to the spherical silver powder is 0.002~0.008:1; In step S2, the saturated fatty acid is one of palmitic acid, stearic acid, lauric acid, and myristic acid; Step S3: After drying the spherical silver powder coated on the surface, sphericalize it for 3-8 minutes; Step S4: After stirring the spheroidized spherical silver powder, unsaturated fatty acid grinding aid and alcohol for 8-12 minutes, add grinding balls and grind for 12-18 hours. Filter, wash and dry to obtain high-loose flake silver powder. In step S4, the mass ratio of the unsaturated fatty acid grinding aid, grinding balls, alcohol, and spherical silver powder is 0.8~1.0:4.5~5.0:0.6~0.8:1; In step S4, the unsaturated fatty acid grinding aid is one of oleic acid, linolenic acid, linoleic acid, arachidonic acid, and docosenoic acid.

2. The preparation method according to claim 1, characterized in that, In step S1, the volume ratio of the silver ammonia solution added first to the silver ammonia solution added later is 1:15~20. The volume ratio of the first added compound reducing agent solution to the last added compound reducing agent solution is 1:15~20.

3. The preparation method according to claim 2, characterized in that, The mass ratio of ascorbic acid to formaldehyde is 1:1~2; The mass ratio of polyvinylpyrrolidone K30 to gum arabic is 3.5~4.5:1; The mass ratio of polyvinylpyrrolidone K30 to gelatin is 3.5~4.5:

1.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step S1, the stirring speed during the stirring state is 250~350 r / min.

5. The preparation method according to claim 4, characterized in that, In step S2, the conductivity is 15~18 μs / cm.

6. The preparation method according to claim 5, characterized in that, In step S4, the diameter of the grinding ball is 1.2~1.6mm; The grinding balls are steel balls or zirconium balls.

7. A high-volume, flake-shaped silver powder, characterized in that, The high-density flake silver powder is prepared by the method described in any one of claims 1 to 6.

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