Method for preparing scaly silver powder through dry mechanical ball milling

Abstract

The invention discloses a method for preparing scaly silver powder through dry mechanical ball milling, and belongs to the technical field of conductive materials.The method comprises the steps that large-particle metal silver powder, a solid grinding auxiliary and a grinding medium are put into a grinding bin of a horizontal high-energy stirring ball mill, and after vacuumizing and inert gas filling are conducted alternately, the large-particle metal silver powder, the solid grinding auxiliary and the grinding medium are subjected to ball milling under the protection of inert gas; stirring for 2-5 minutes at the temperature of 25 DEG C and the rotating speed of 270-330 revolutions per minute to obtain mixed powder; under the protection of inert gas, the mixed powder is subjected to ball milling at the alternating rotating speed for 20-60 minutes, and scaly silver powder is obtained; and under the protection of inert gas, continuously ball-milling the scaly silver powder for 4-8 minutes at the rotating speed of 270-330 revolutions per minute, and then carrying out ball-material separation. The scaly silver powder is low in oxygen content, uniform in particle size distribution, good in conductivity, capable of meeting the conductivity requirement of electronic elements, short in technological process, high in safety and free of pollution to the environment.

Description

Technical Field

[0001] The invention belongs to the technical field of conductive materials, and in particular relates to a method for preparing flaky silver powder by dry mechanical ball milling. Background Art

[0002] With the rapid development of the electronics industry, the performance requirements for conductive materials are constantly increasing. Flake silver powder has better conductivity than other forms of silver powder such as spherical silver powder due to its unique flake structure. In the field of electronic pastes, such as conductive pastes and electrode pastes, flake silver powder can form a good conductive network, reduce the resistivity of the paste, and improve the conductive properties of electronic components.

[0003] At present, the preparation method of flaky silver powder mainly includes mechanical ball milling. For example, the Chinese patent document with application number 200810231718.6 discloses "a method for preparing flaky silver powder". The method achieves the technical goal through the following steps: unsaturated fatty acid is used as a dispersant in the preparation process of precursor silver powder, and also as a dispersant in the ball milling process. The prepared silver nitrate solution and oleic acid ethanol solution are mixed, stirred evenly at a set temperature and time, and a reducing agent is added to the silver nitrate mixed solution to reduce silver ions to obtain precursor silver powder; the precursor silver powder is ball milled in a ball mill to obtain flaky silver powder, and then the flaky silver powder is immersed in an alkyd solution, the alkyd solution is filtered out, and the silver powder is dried to finally obtain a flaky silver powder with a high silver content. The ball milling process of this method is to add the dried precursor silver powder into the ball mill according to a certain material ball water ratio, and the process is wet milling. In addition, the use of stainless steel balls for grinding balls will introduce iron impurities. The silver powder after ball milling needs to be soaked in an alkyd solution, filtered and dried to obtain flaky silver powder. This process will produce alkyd filtrate, and the volatile gases produced during the drying process will pollute the environment. The Chinese patent document with application number 202310805605.7 announced "a method for preparing flaky silver powder with good dispersibility". Polyvinyl pyrrolidone is stirred and dissolved as a polymer protective agent, and then silver nitrate solution and reducing agent ascorbic acid solution are dripped into it at the same time, the system temperature and pH value are adjusted, and the ultrafine silver powder precursor is obtained by washing, filtering and drying. It is moved to a stainless steel ball mill, and zirconium balls and steel balls are added in a 1:1 ratio. Stearic acid and oleic acid are dissolved in anhydrous ethanol as protective agents for the ball milling process. After the ball milling is completed, it is washed and dried to obtain flaky silver powder. The anhydrous ethanol, stearic acid and oleic acid added in the ball milling stage of this process will produce a large amount of filtrate in the future, which is difficult to recover. At the same time, anhydrous ethanol poses a safety risk. In addition, the process involves two drying cycles. The prepared flaky silver powder with a high specific surface area is easily oxidized to form silver oxide during the drying process, thereby affecting the conductivity of the entire material.

[0004] In summary, the existing flaky silver powder has a high oxygen content, uneven particle size distribution, and poor conductivity, which cannot meet the conductivity requirements of electronic components. In addition, the process is long, the safety risk is high, and the environmental pollution is serious. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing flaky silver powder by dry mechanical ball milling. The flaky silver powder prepared by the method has low oxygen content, uniform particle size distribution, high conductivity, can meet the conductivity performance requirements of electronic components, and has a short process flow, high safety, and no pollution to the environment.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing flaky silver powder by dry mechanical ball milling, the method comprising:

[0008] Step S1, loading large-particle metallic silver powder, solid grinding aid and grinding medium into the grinding chamber of a horizontal high-energy stirring ball mill, alternately evacuating and filling with inert gas, and then stirring for 2 to 5 minutes at a temperature of 25° C. and a speed of 270 to 330 rpm under the protection of inert gas to obtain a mixed powder;

[0009] Step S2, under the protection of inert gas, ball milling the mixed powder at an alternating speed for 20 to 60 minutes to obtain flaky silver powder;

[0010] In step S2, the specific process of the alternating speed ball milling is as follows:

[0011] In the alternating speed range of 500 to 1200 rpm, the alternating speed is changed every 1 to 4 minutes;

[0012] Step S3, under the protection of inert gas, the flaky silver powder is continuously ball-milled at a speed of 270 to 330 rpm for 4 to 8 minutes, and then the ball-milled material is separated.

[0013] Furthermore, in the step S1, the particle size of the large-particle metallic silver powder is 8 to 12 microns, and the purity is greater than or equal to 99.99%.

[0014] Furthermore, in step S1, the vacuuming and the filling with inert gas are alternately performed 3 to 4 times until the vacuum degree is 150 to 250 Pa and the pressure reaches 0.7 to 0.9×10 5 Pa.

[0015] Furthermore, in the step S1, the amount of the solid grinding aid added is 0.5-0.8wt% of the mass of the large-particle metallic silver powder, that is, the mass ratio of the solid grinding aid to the large-particle metallic silver powder is 0.5-0.8:100.

[0016] Furthermore, in step S1, the solid grinding aid is one or a mixture of two or more of stearic acid, hexadecanoic acid, and polyethylene glycol.

[0017] Furthermore, in the step S1, the ball-to-material ratio of the alternating speed ball mill is 5 to 25:1, that is, the amount of grinding medium used is 5 to 25 times the total mass of the large-particle metallic silver powder and the solid grinding aid.

[0018] Furthermore, in the step S1, the ball-to-material ratio of the alternating speed ball mill is 10-20:1, that is, the amount of grinding medium used is 10-20 times the total mass of the large-particle metallic silver powder and the solid grinding aid.

[0019] Further, in the step S1, the grinding medium is one of stainless steel, zirconium oxide and bearing steel;

[0020] The diameter of the grinding medium is 2 to 5 mm.

[0021] Furthermore, the inner lining material of the grinding chamber and the stirring shaft blades of the horizontal high-energy stirring ball mill are both zirconia ceramics.

[0022] In summary, the technical solution of the present invention has the following technical effects:

[0023] The horizontal high-energy stirring ball mill of the present invention adopts an alternating speed operation mode. Different ball milling speeds during operation change the running trajectory of the grinding medium, improve the ball milling efficiency, ensure the uniformity of particle size distribution, and realize the efficient preparation of flaky silver powder.

[0024] The present invention adopts dry mechanical ball milling, reduces the processes of cleaning and drying, has low production energy consumption, short process flow, and can realize efficient preparation of flaky silver powder. In addition, the process does not involve anhydrous ethanol and alkyd solution, is highly safe and environmentally friendly.

[0025] The entire ball milling process of the present invention is carried out under an inert protective atmosphere, which largely avoids the contact between the high specific surface area and high activity metal silver powder and the air, inhibits the introduction of oxygen, and avoids the decrease in conductivity caused by the generation of silver oxide.

[0026] The flaky silver powder of the present invention has low oxygen content, uniform particle size distribution and good electrical conductivity, and can meet the electrical conductivity requirements of electronic components. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are some implementations of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 This is a SEM photo of the powder prepared in Example 1 (2000 times);

[0029] Figure 2 This is the SEM photograph (2000 times) of the powder prepared in Example 2. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention is clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Embodiment 1:

[0032] Step S1, put large-particle silver powder with a particle size of 10 microns and a purity of 99.99%, stearic acid and zirconium oxide balls with a diameter of 2 mm into the grinding chamber of the horizontal high-energy stirring ball mill, and then connect the mechanical pump and the Roots pump to the inlet and outlet of the grinding chamber in sequence, turn on the vacuum system, open the exhaust valve, and when the vacuum degree in the grinding chamber drops to 200 Pa, close the exhaust valve and the vacuum system. Open the charging valve and charge argon gas until the pressure in the grinding chamber reaches 0.9×10 5 After Pa, close the inflation valve. Continue to evacuate and inflate according to the above operation, and cycle for more than 4 times. The entire ball milling process is carried out under argon protection. Open the coolant circulation system, and circulate the coolant between the zirconia ceramic of the horizontal high-energy ball mill and the outer wall to ensure that the entire ball milling is carried out at a temperature of 25°C. At a speed of 270 rpm, the ball mill is stirred for 5 minutes to obtain a mixed powder.

[0033] The amount of stearic acid added is 0.8wt% of the mass of the large-particle silver powder, and the amount of zirconium oxide balls is 10 times the total mass of the large-particle silver powder and stearic acid, and the ball-to-material ratio is 10:1.

[0034] Step S2, continue to ball mill at a speed of 900 rpm for 2 minutes and then at a speed of 1100 rpm for 2 minutes under the protection of inert gas while ensuring that other conditions remain unchanged, and repeat the following operation until ball milling for 30 minutes to obtain flaky silver powder.

[0035] Step S3, continue to ball-mill the flaky silver powder at a speed of 270 rpm under the protection of inert gas for 5 minutes and then separate the ball and material.

[0036] The median diameter D50 of the flaky silver powder prepared in this embodiment is 12.51 μm, and the bulk density is 1.15 g / cm 3 , the microscopic appearance is Figure 1 As shown, the particle size distribution of the flaky silver powder is uniform, and subsequent verification shows that its sheet resistance is 16.81 mΩ / □.

[0037] Embodiment 2:

[0038] Step S1, large-particle silver powder with a particle size of 12 microns and a purity of 99.99%, hexadecanoic acid and a stainless steel ball with a diameter of 3 mm are loaded into the grinding chamber of the horizontal high-energy stirring ball mill, and then the mechanical pump and the Roots pump are connected to the inlet and outlet of the grinding chamber in sequence, the vacuum system is turned on, the air extraction valve is opened, and when the vacuum degree in the grinding chamber drops to 250 Pa, the air extraction valve is closed, and the vacuum system is turned off. The air filling valve is opened, and argon gas is filled in, and the pressure in the grinding chamber reaches 0.7×10 5 After Pa, close the inflation valve. Continue to evacuate and inflate according to the above operation, and cycle for more than 3 times. The entire ball milling process is carried out under argon protection. Open the coolant circulation system, and circulate the coolant between the zirconia ceramic of the horizontal high-energy ball mill and the outer wall to ensure that the entire ball milling is carried out at a temperature of 25°C. At a speed of 330 rpm, the ball mill is stirred for 2 minutes to obtain a mixed powder.

[0039] The amount of hexadecanoic acid added is 0.7wt% of the mass of the large-particle silver powder, and the amount of stainless steel balls is 25 times the total mass of the large-particle silver powder and hexadecanoic acid, that is, the ball-to-material ratio is 25:1.

[0040] Step S2, continue to ball mill at a speed of 500 rpm for 1 minute, then at a speed of 1000 rpm for 3 minutes under the protection of inert gas while ensuring that other conditions remain unchanged, and repeat the following operation until the ball milling is continued for 60 minutes to obtain flaky silver powder.

[0041] Step S3, continue to ball-mill the flaky silver powder at a speed of 330 rpm for 8 minutes under the protection of inert gas, and then separate the ball and material.

[0042] The median diameter D50 of the flaky silver powder prepared in this embodiment is 15.34 μm, and the bulk density is 1.24 g / cm 3 , the microscopic appearance is Figure 2 As shown, the particle size distribution is uniform, and subsequent verification shows that its square resistance is 16.17 mΩ / □.

[0043] Embodiment 3:

[0044] Step S1, load large-particle silver powder with a particle size of 8 microns and a purity of 99.99%, polyethylene glycol and bearing steel with a diameter of 5 mm into the grinding chamber of the horizontal high-energy stirring ball mill, then connect the mechanical pump and the Roots pump to the inlet and outlet of the grinding chamber in sequence, turn on the vacuum system, open the air extraction valve, and when the vacuum degree in the grinding chamber drops to 150Pa, close the air extraction valve and the vacuum system. Open the charging valve and charge argon gas until the pressure in the grinding chamber reaches 0.8×10 5 After Pa, close the inflation valve. Continue to evacuate and inflate according to the above operation, and cycle for more than 3 times. The entire ball milling process is carried out under argon protection. Open the coolant circulation system, and circulate the coolant between the zirconia ceramic of the horizontal high-energy ball mill and the outer wall to ensure that the entire ball milling is carried out at a temperature of 25°C. At a speed of 300 rpm, the ball mill is stirred for 4 minutes to obtain a mixed powder.

[0045] The amount of polyethylene glycol added is 0.5wt% of the mass of the large-particle silver powder, and the amount of bearing steel used is 5 times the total mass of the large-particle silver powder and polyethylene glycol, that is, the ball-to-material ratio is 5:1.

[0046] Step S2, continue to ball mill at a speed of 600 rpm for 4 minutes and then at a speed of 1200 rpm for 1 minute under the protection of inert gas while ensuring that other conditions remain unchanged, and repeat the following operation until the ball milling is completed for 20 minutes to obtain flaky silver powder.

[0047] Step S3, continue to ball-mill the flaky silver powder at a speed of 300 rpm for 4 minutes under the protection of inert gas, and then separate the ball and material.

[0048] The median diameter D50 of the flaky silver powder prepared in this embodiment is 11.37 μm, and the bulk density is 1.08 g / cm 3 The particle size distribution is uniform, and after subsequent verification, its square resistance is 17.06mΩ / □.

[0049] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not 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. The above embodiments only express several implementation methods of the present application, and their descriptions 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, without departing from the concept of the present application, several variations and improvements can be made, which all belong to the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A method for preparing flaky silver powder by dry mechanical ball milling, characterized in that: The method comprises: Step S1, loading large-particle metallic silver powder, solid grinding aid and grinding medium into the grinding chamber of a horizontal high-energy stirring ball mill, alternately evacuating and filling with inert gas, and then stirring for 2 to 5 minutes at a temperature of 25° C. and a speed of 270 to 330 rpm under the protection of inert gas to obtain a mixed powder; Step S2, under the protection of inert gas, ball milling the mixed powder at an alternating speed for 20 to 60 minutes to obtain flaky silver powder; In step S2, the specific process of the alternating speed ball milling is as follows: In the alternating speed range of 500 to 1200 rpm, the alternating speed is changed every 1 to 4 minutes; Step S3, under the protection of inert gas, the flaky silver powder is continuously ball-milled at a speed of 270 to 330 rpm for 4 to 8 minutes, and then the ball-milled material is separated.

2. The method according to claim 1, characterized in that In the step S1, the particle size of the large-particle metallic silver powder is 8 to 12 microns, and the purity is greater than or equal to 99.99%.

3. The method according to claim 2, characterized in that In step S1, the vacuuming and the filling with inert gas are alternately performed 3 to 4 times until the vacuum degree is 150 to 250 Pa and the pressure reaches 0.7 to 0.9×10 5 Pa.

4. The method according to claim 3, characterized in that In the step S1, the solid grinding aid is added in an amount of 0.5-0.8 wt % of the mass of the large-particle metallic silver powder.

5. The method according to any one of claims 1 to 4, characterized in that: In the step S1, the solid grinding aid is one of stearic acid, hexadecanoic acid, polyethylene glycol, or a mixture of two or more thereof.

6. The method according to claim 5, characterized in that In the step S1, the ball-to-material ratio of the alternating speed ball mill is 5 to 25:

1.

7. The method according to claim 6, characterized in that In the step S1, the ball-to-material ratio of the alternating speed ball mill is 10-20:

1.

8. The method according to claim 7, characterized in that In the step S1, the grinding medium is one of stainless steel, zirconium oxide and bearing steel; The diameter of the grinding medium is 2 to 5 mm.

9. The method according to claim 8, characterized in that The inner lining material of the grinding chamber and the stirring shaft blades of the horizontal high-energy stirring ball mill are both zirconia ceramics.

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