Cleaning method for nanoscale silver powder

Abstract

The invention provides a method for cleaning nanoscale silver powder, which comprises the following steps of: adding a water repellent agent to carry out surface hydrophobization on the silver powder, filtering the silver powder by adopting microporous membrane equipment, reversely blowing the microporous membrane equipment by adopting compressed air and ethanol to reduce the escape amount of the silver powder, adding ethanol to carry out slurrying on the silver powder, and washing the surface of the silver powder by using a high-speed shearing machine. The surface free energy of silver powder agglomeration is broken through, finally, the silver powder is conveyed into the airflow drying machine in a self-flowing mode to be dried, automatic cleaning and drying of the silver powder are achieved, and the problems that an existing silver powder cleaning method is low in cleaning efficiency, high in silver powder escape amount and short in equipment filtering service life are solved.

Description

[Technical field]

[0001] The invention belongs to the technical field of precious metal cleaning, and in particular relates to a method for cleaning nano-scale silver powder. [Background technology]

[0002] In the field of electronic paste, ultrafine silver powder is widely used in the manufacture of various electronic components and circuits due to its excellent conductive properties, including traditional component electrode paste, hybrid integrated circuit paste, solar cell paste, RFID silver paste, PDP silver paste, etc. However, during the processing and reduction of silver powder, some chemical components may remain on the surface, resulting in a decrease in surface gloss, which not only affects the appearance of the silver powder, but also may affect its performance.

[0003] In order to solve this problem, the silver powder usually needs to be cleaned. However, most existing methods use manual cleaning and centrifugal filtration, which have low cleaning efficiency and silver powder easily escapes during the cleaning process, resulting in material loss. In addition, the centrifugal filtration method also has the problem of short filtration life, and the filter material needs to be replaced frequently, which increases production costs. [Summary of the invention]

[0004] The purpose of the present invention is to provide a method for cleaning nano-scale silver powder, so as to solve the problems of low cleaning efficiency, high silver powder escape and short equipment filtering life in the existing silver powder cleaning method.

[0005] The present invention is achieved by the following technical solutions:

[0006] A method for cleaning nano-scale silver powder comprises the following steps:

[0007] S1, hydrophobic treatment: while silver nitrate is replaced to generate silver powder, a hydrophobic agent is added to the reaction solution to hydrophobize the surface of the silver powder;

[0008] S2, sedimentation: after the reaction in step S1 is completed, the reaction solution is sedimented;

[0009] S3, washing: the supernatant of the reaction solution treated in step S2 is extracted, filtered once with a microporous filter membrane to obtain a silver powder residue, water is added to the silver powder residue for washing, sedimentation, and filtering with a microporous membrane device to obtain a coarse silver powder;

[0010] S4, slurrying: using compressed air and ethanol to back-blow the microporous membrane equipment, blowing the crude silver powder in step S3 into a high-speed shearing machine, and then adding ethanol to slurry the crude silver powder to obtain a silver powder slurry;

[0011] S5, high-speed shear washing: putting the silver powder slurry in step S4 into a high-speed disperser for stirring, and adding ethanol for stirring and washing;

[0012] S6, filtration: using a microporous membrane device to filter the silver powder slurry in step S5, and allowing the filtered silver powder to flow from the microporous membrane device to an air flow dryer for drying to obtain nano-scale silver powder.

[0013] First, by adding a hydrophobic agent, the surface of the generated silver powder is hydrophobized during the silver nitrate reaction to prevent powder agglomeration and adhesion, thereby improving the storage stability of the silver powder. Second, the silver powder is filtered using a microporous membrane device, which can effectively separate the silver powder from other substances and improve the efficiency and yield of silver powder cleaning. Third, compressed air and ethanol are used to back-blow the microporous membrane device to reduce the escape of silver powder and reduce powder loss. Ethanol is then added to slurry the silver powder, and the surface of the silver powder is washed by a high-speed shearing machine to break the surface free energy of the silver powder agglomeration, thereby reasonably improving the oil dispersibility of the silver powder and improving the conductive properties of the silver powder. Finally, by slurrying the silver powder, the slurry can be transported by gravity to the airflow dryer for drying, thereby quickly and evenly removing the moisture on the surface of the silver powder, and realizing the automatic cleaning and drying of the silver powder.

[0014] In step S4, the compressed air and ethanol back-blowing microporous membrane device passes through the microporous filter element to filter the suspension through the membrane. At this time, the liquid and small solutes pass through the membrane and are collected as permeate, and the suspended particles are retained by the membrane and collected as concentrated retentate.

[0015] Specifically, the mechanism by which particles are retained depends on the properties of the membrane (including physical and chemical characteristics) and the nature of the interaction between the membrane and the particles. There are two main retention mechanisms:

[0016] a. Surface filtration or sieving mechanism: When the pore size of the membrane is smaller than the size of the suspended particles, the particles are blocked due to their geometric shape and cannot enter or pass through the membrane. Therefore, the particles are separated from the permeate.

[0017] b. Depth filtration mechanism: When the pore size of the membrane is larger than the size of the suspended particles, the particles can enter the membrane pores. When they come into contact with the pore wall and adhere to it, they are filtered out of the suspension. At this time, the filtration occurs deep in the pores of the membrane.

[0018] After the filtration is completed, the silver powder particles attached to the membrane are recovered by backblowing with compressed air or ethanol, thereby achieving efficient recovery of the silver powder.

[0019] Preferably, the hydrophobic agent in step S1 is stearic acid.

[0020] Preferably, the sedimentation time in step S2 is ≥ 30 min. In addition, during the sedimentation process, the clarity of the supernatant can be determined by visual observation and sampling.

[0021] Preferably, the specification of the microporous filtration membrane in step S3 is 0.1um*20M 2 .

[0022] Preferably, the conductivity of the coarse silver powder in step S3 is less than 20us / cm. First, in step S3, cleaning and sedimentation need to be performed according to the different characteristics of different silver powders. Specifically, the sedimentation time can be adjusted according to the change of the number of cleaning times, usually 5-60min. Secondly, in order to ensure the cleaning effect, it is necessary to detect the ion content in the silver powder, that is, to measure its conductivity. By detecting the conductivity, it can be determined whether the impurity ions on the surface of the silver powder are effectively removed during the cleaning process, thereby ensuring the quality and performance of the silver powder.

[0023] Preferably, the pressure of the compressed air in step S4 is less than 0.8 MPa.

[0024] Preferably, in step S4, the amount of ethanol added is 1.2 times the amount of the coarse silver powder. By adding ethanol, the silver powder can effectively transfer heat during high-speed shearing, ensuring uniform heating between the silver powders, thereby promoting self-friction and surface shaping of the silver powder. At the same time, ethanol can be used as a solvent to dissolve some soluble substances on the surface of the silver powder, further improving the quality of the silver powder.

[0025] Preferably, the stirring speed in step S5 is 1200-2000 rpm.

[0026] Preferably, the particle size range of the nano-scale silver powder in step S6 is 80-2000 nm.

[0027] The present invention provides a method for cleaning nano-scale silver powder, which has the following beneficial effects:

[0028] First, by adding a hydrophobic agent, the surface of the generated silver powder is hydrophobized during the silver nitrate reaction to prevent powder agglomeration and adhesion, thereby improving the storage stability of the silver powder. Second, the silver powder is filtered by a microporous membrane device, which can effectively separate the silver powder from other substances and improve the efficiency and yield of silver powder cleaning. Third, compressed air and ethanol are used to back-blow the microporous membrane device to reduce the escape amount of silver powder and reduce powder loss. Then, ethanol is added to slurry the silver powder, and the surface of the silver powder is washed by a high-speed shearing machine to break the surface free energy of silver powder agglomeration, thereby reasonably improving the oil dispersibility of the silver powder and improving the conductive performance of the silver powder. Finally, by slurrying the silver powder, the slurry can be transported by gravity to the airflow dryer for drying, thereby quickly and evenly removing the moisture on the surface of the silver powder, and realizing the automatic cleaning and drying of the silver powder. The present invention solves the problems of low cleaning efficiency, high escape amount of silver powder and short equipment filtration life of the existing silver powder cleaning method.

[0029] The method for cleaning nano silver powder of the present invention can improve the cleaning efficiency of nano silver powder while ensuring the cleaning effect by designing a new silver powder cleaning method, adopting chemical and physical means, and cooperating with reagents and equipment, and can realize the automated operation of silver powder cleaning and reduce production costs. [Specific implementation method]

[0030] The specific technical scheme of the present invention is described below in conjunction with Examples 1-3:

[0031] Example 1

[0032] A method for cleaning nano-scale silver powder comprises the following steps:

[0033] S1, hydrophobic treatment: while using 120 kg of silver nitrate to replace and generate silver powder, 2.5 kg of stearic acid is added to the reaction solution to hydrophobize the surface of the silver powder;

[0034] S2, sedimentation: after the reaction in step S1 is completed, the reaction solution is sedimented for 0.5h;

[0035] S3, cleaning: the supernatant of the reaction solution treated in step S2 is removed, and a 0.1um*20M 2 The silver powder residue was filtered once with a microporous membrane to obtain a silver powder residue, water was added to the silver powder residue for washing, the residue was settled for 5 minutes, and the residue was filtered with a microporous membrane device to obtain 90 kg of crude silver powder, the conductivity of which was 16.5 us / cm;

[0036] S4, slurrying: using compressed air and ethanol to back-blow the microporous membrane equipment, blowing the crude silver powder in step S3 into a high-speed shearing machine at 0.8 MPa, and then adding 18 kg of ethanol to slurry the crude silver powder to obtain 108 kg of silver powder slurry;

[0037] S5, high-speed shear washing: put the silver powder slurry in step S4 into a high-speed disperser and stir at 1200-2000 rpm. After stirring for 2 hours, add 140% ethanol and stir and wash;

[0038] S6, filtration: the silver powder slurry in step S5 is filtered by a microporous membrane device, and the filtered silver powder is flowed from the microporous membrane device to an air flow dryer for drying at 80 kg / h to obtain 76 kg of silver powder, the particle size of which is 1000 nm.

[0039] Example 2

[0040] A method for cleaning nano-scale silver powder comprises the following steps:

[0041] S1, hydrophobic treatment: while using 136 kg of silver nitrate to replace and generate silver powder, 2.8 kg of stearic acid is added to the reaction solution to hydrophobize the surface of the silver powder;

[0042] S2, sedimentation: after the reaction in step S1 is completed, the reaction solution is sedimented for 0.5h;

[0043] S3, cleaning: the supernatant of the reaction solution treated in step S2 is removed, and a 0.1um*20M 2 The silver powder residue was filtered once with a microporous membrane to obtain a silver powder residue, water was added to the silver powder residue for washing, the residue was settled for 5 minutes, and the residue was filtered with a microporous membrane device to obtain 103.7 kg of crude silver powder, the conductivity of which was 6.18 us / cm;

[0044] S4, slurrying: using compressed air and ethanol to back-blow the microporous membrane equipment, blowing the crude silver powder in step S3 into a high-speed shearing machine at 0.8 MPa, and then adding 15.5 kg of ethanol to slurry the crude silver powder to obtain 120 kg of silver powder slurry;

[0045] S5, high-speed shear washing: put the silver powder slurry in step S4 into a high-speed disperser and stir at 1200-2000 rpm. After stirring for 2 hours, add 140% ethanol and stir and wash;

[0046] S6, filtration: the silver powder slurry in step S5 is filtered by a microporous membrane device, and the filtered silver powder is flowed from the microporous membrane device into an air flow dryer for drying at 80 kg / h to obtain 85.86 kg of silver powder, the particle size of which is 100 nm.

[0047] Example 3

[0048] A method for cleaning nano-scale silver powder comprises the following steps:

[0049] S1, hydrophobic treatment: while using 120 kg of silver nitrate to replace and generate silver powder, 2.5 kg of stearic acid is added to the reaction solution to hydrophobize the surface of the silver powder;

[0050] S2, sedimentation: after the reaction in step S1 is completed, the reaction solution is sedimented for 0.5h;

[0051] S3, cleaning: the supernatant of the reaction solution treated in step S2 is removed, and a 0.1um*20M 2 The silver powder residue was filtered once with a microporous membrane to obtain a silver powder residue, water was added to the silver powder residue for washing, the residue was settled for 5 minutes, and the residue was filtered with a microporous membrane device to obtain 83.2 kg of crude silver powder, the conductivity of which was 16.7 us / cm;

[0052] S4, slurrying: using compressed air and ethanol to back-blow the microporous membrane equipment, blowing the crude silver powder in step S3 into a high-speed shearing machine at 0.8 MPa, and then adding 12.5 kg of ethanol to slurry the crude silver powder to obtain 95.7 kg of silver powder slurry;

[0053] S5, high-speed shear washing: put the silver powder slurry in step S4 into a high-speed disperser and stir at 1200-2000 rpm. After stirring for 2 hours, add 140% ethanol and stir and wash;

[0054] S6, filtration: the silver powder slurry in step S5 is filtered by a microporous membrane device, and the filtered silver powder is flowed from the microporous membrane device to an air flow dryer for drying at 80 kg / h to obtain 74.7 kg of silver powder, the particle size of which is 1500 nm.

[0055] Comparative Example 1

[0056] A method for cleaning silver powder comprises the following steps:

[0057] S1, hydrophobic treatment: while using 2.5 kg of silver nitrate to replace and generate silver powder, 0.55 kg of stearic acid is added to the reaction solution to hydrophobize the surface of the silver powder;

[0058] S2, sedimentation: after the reaction in step S1 is completed, the reaction solution is sedimented for 0.5h;

[0059] S3, cleaning: the supernatant of the reaction solution treated in step S2 is removed, filtered once with a filter membrane to obtain a silver powder residue, water is added to the silver powder residue for cleaning, settled for 5 minutes, and filtered with a suction filtration device to obtain 2.169 kg of crude silver powder;

[0060] S4, slurrying: using a high-speed shearing machine, adding 0.325 kg of ethanol to slurry the crude silver powder to obtain 2.495 kg of silver powder slurry;

[0061] S5, high-speed shear washing: put the silver powder slurry described in step S4 into a high-speed disperser, add 140% ethanol and stir at 2000 rpm for 15 minutes;

[0062] S6. Filtration: Filter the silver powder slurry in step S5 using a suction filtration device, and dry the filtered silver powder for 4 hours to obtain 1.494 kg of silver powder, the particle size of which is 100 nm.

[0063] Comparative Example 2

[0064] A method for cleaning silver powder comprises the following steps:

[0065] S1, hydrophobic treatment: while using 136 kg of silver nitrate to replace and generate silver powder, 2.8 kg of stearic acid is added to the reaction solution to hydrophobize the surface of the silver powder;

[0066] S2, sedimentation: after the reaction in step S1 is completed, the reaction solution is sedimented for 0.5h;

[0067] S3, cleaning: the supernatant of the reaction solution treated in step S2 is removed, and filtered once using a 10000 mesh centrifuge to obtain a silver powder residue, water is added to the silver powder residue for cleaning, and the residue is settled for 5 minutes, and filtered using a 10000 mesh centrifuge to obtain 91.8 kg of crude silver powder, the conductivity of which is 7.19 us / cm;

[0068] S4, slurrying: put the centrifuged silver powder into a high-speed shearing machine, and then add 13.8 kg of ethanol to slurry the crude silver powder to obtain 105.6 kg of silver powder slurry;

[0069] S5, high-speed shear washing: put the silver powder slurry in step S4 into a high-speed disperser and stir at 1200-2000 rpm. After stirring for 2 hours, add 140% ethanol and stir and wash;

[0070] S6, filtration: centrifugally dehydrate the silver powder in step S5, and dry the filtered silver powder by forced air drying at 60° C. for 5 h to obtain 68.85 kg of silver powder, the particle size of which is 100 nm.

[0071] The silver powders of Examples 1-3 and Comparative Example 1 were tested, and the test data are shown in Table 1.

[0072] Table 1 Silver powder detection data of Examples 1-3 and Comparative Example 1

[0073] Silver powder Example 1 Example 3 Example 3 Comparative Example 1 Comparative Example 2 Theoretical weight (kg) 76.2 86.36 76.20 1.5875 86.36 Actual weight (kg) 76.0 85.86 74.70 1.4940 68.85 Particle size (nm) 1000 100 1500 100 100 Conductivity(us / cm) 16.5 6.18 16.7 5.49 4.94 Filtration time (h) 5 7 6 8 6 Yield (%) 99.74 99.42 98.03 94.11 79.72

[0074] Note: The actual weight does not include the equipment residue, and the conductivity is the conductivity of the final product.

[0075] The silver powder escape amount of Examples 1-3 and Comparative Example 1 was calculated, and the results are shown in Table 2. Wherein, silver powder escape amount = (theoretical weight - actual weight) / theoretical weight * 100%.

[0076] Table 2 Silver powder escape amount of Examples 1-3 and Comparative Example 1

[0077]

[0078] As shown in Table 1, compared with the cleaning method using a suction filtration device in Comparative Example 1, the cleaning methods of Examples 1-3 have a higher yield and a shorter filtration time, and compared with the cleaning method using a 10000 mesh centrifuge in Comparative Example 2, the cleaning methods of Examples 1-3 have a higher yield and the filtration time is not much different.

[0079] As shown in Table 2, compared with Comparative Examples 1-2, the cleaning methods of Examples 1-3 have lower silver powder escape amounts.

[0080] The above examples are only used to further illustrate the technical content of the present invention, so that readers can understand it more easily, but they do not mean that the implementation of the present invention is limited to this. Any technical extension or re-creation made according to the present invention is protected by the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A method for cleaning nano-scale silver powder, characterized in that: The following steps are involved: S1, hydrophobic treatment: while silver nitrate is replaced to generate silver powder, a hydrophobic agent is added to the reaction solution to hydrophobize the surface of the silver powder; S2, sedimentation: after the reaction in step S1 is completed, the reaction solution is sedimented; S3, washing: the supernatant of the reaction solution treated in step S2 is extracted, filtered once with a microporous filter membrane to obtain a silver powder residue, water is added to the silver powder residue for washing, sedimentation, and filtering with a microporous membrane device to obtain a coarse silver powder; S4, slurrying: using compressed air and ethanol to back-blow the microporous membrane equipment, blowing the crude silver powder in step S3 into a high-speed shearing machine, and then adding ethanol to slurry the crude silver powder to obtain a silver powder slurry; S5, high-speed shear washing: putting the silver powder slurry in step S4 into a high-speed disperser for stirring, and adding ethanol for stirring and washing; S6, filtration: using a microporous membrane device to filter the silver powder slurry in step S5, and allowing the filtered silver powder to flow from the microporous membrane device to an air flow dryer for drying to obtain nano-scale silver powder.

2. The method for cleaning nano-scale silver powder according to claim 1, characterized in that: The hydrophobic agent in step S1 is stearic acid.

3. The method for cleaning nano-scale silver powder according to claim 1, characterized in that: The sedimentation time in step S2 is ≥30 min.

4. The method for cleaning nano-scale silver powder according to claim 1, characterized in that: The specification of the microporous filtration membrane in step S3 is 0.1um*20M 2 .

5. The method for cleaning nano-scale silver powder according to claim 1, characterized in that: The conductivity of the coarse silver powder in step S3 is less than 20 us / cm.

6. The method for cleaning nano-scale silver powder according to claim 1, characterized in that: The pressure of the compressed air in step S4 is less than 0.8 MPa.

7. The method for cleaning nano-scale silver powder according to claim 1, characterized in that: Step S4: adding ethanol to 1.2 times the amount of the crude silver powder.

8. The method for cleaning nano-scale silver powder according to claim 1, characterized in that: The stirring speed in step S5 is 1200-2000 rpm.

9. The method for cleaning nano-scale silver powder according to claim 1, characterized in that: The particle size range of the nano-scale silver powder in step S6 is 80-2000 nm.

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