CN117862520B - Method for preparing flake silver powder by using shellac - Google Patents
Method for preparing flake silver powder by using shellac Download PDFInfo
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- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 title claims abstract description 227
- 238000000034 method Methods 0.000 title claims abstract description 48
- 229920001800 Shellac Polymers 0.000 title claims abstract description 34
- ZLGIYFNHBLSMPS-ATJNOEHPSA-N shellac Chemical compound OCCCCCC(O)C(O)CCCCCCCC(O)=O.C1C23[C@H](C(O)=O)CCC2[C@](C)(CO)[C@@H]1C(C(O)=O)=C[C@@H]3O ZLGIYFNHBLSMPS-ATJNOEHPSA-N 0.000 title claims abstract description 34
- 239000004208 shellac Substances 0.000 title claims abstract description 34
- 229940113147 shellac Drugs 0.000 title claims abstract description 34
- 235000013874 shellac Nutrition 0.000 title claims abstract description 34
- 239000000243 solution Substances 0.000 claims abstract description 159
- 229910052709 silver Inorganic materials 0.000 claims abstract description 71
- 239000004332 silver Substances 0.000 claims abstract description 71
- 239000000025 natural resin Substances 0.000 claims abstract description 69
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims abstract description 59
- 229910021642 ultra pure water Inorganic materials 0.000 claims abstract description 35
- 239000012498 ultrapure water Substances 0.000 claims abstract description 35
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 claims abstract description 32
- PLKATZNSTYDYJW-UHFFFAOYSA-N azane silver Chemical compound N.[Ag] PLKATZNSTYDYJW-UHFFFAOYSA-N 0.000 claims abstract description 32
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- 239000008103 glucose Substances 0.000 claims description 17
- LJCNRYVRMXRIQR-OLXYHTOASA-L potassium sodium L-tartrate Chemical compound [Na+].[K+].[O-]C(=O)[C@H](O)[C@@H](O)C([O-])=O LJCNRYVRMXRIQR-OLXYHTOASA-L 0.000 claims description 17
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- DBMJMQXJHONAFJ-UHFFFAOYSA-M Sodium laurylsulphate Chemical compound [Na+].CCCCCCCCCCCCOS([O-])(=O)=O DBMJMQXJHONAFJ-UHFFFAOYSA-M 0.000 claims description 12
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- NTIZESTWPVYFNL-UHFFFAOYSA-N Methyl isobutyl ketone Chemical compound CC(C)CC(C)=O NTIZESTWPVYFNL-UHFFFAOYSA-N 0.000 description 2
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- LQJBNNIYVWPHFW-UHFFFAOYSA-N 20:1omega9c fatty acid Natural products CCCCCCCCCCC=CCCCCCCCC(O)=O LQJBNNIYVWPHFW-UHFFFAOYSA-N 0.000 description 1
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- Manufacture Of Metal Powder And Suspensions Thereof (AREA)
- Powder Metallurgy (AREA)
Abstract
The invention relates to the technical field of metal powder preparation, and discloses a method for preparing flake silver powder by using shellac, which comprises the following steps: step S1: preparing a natural resin sacrificial template: coating the prepared lac solution on a flexible substrate, and curing; step S2: hydrophilic and sensitization treatment; step S3: preparing a silver film: spraying silver-ammonia solution and reducing solution on a natural resin sacrificial template for reaction, purging, flushing a silver film with ultrapure water, and purging at high temperature to obtain a bright silver film; step S4: immersing a natural resin sacrificial template plated with a silver film into an alcohol solution, a ketone solution or an alkaline solution, and stirring to obtain a flaky silver powder mother solution; step S5: crushing the flake silver powder mother liquor by adopting ultrasonic waves, and soaking and washing by ethanol, centrifuging and drying to obtain the flake silver powder. The prepared flake silver powder has uniform morphology and is flake; the surface is flat; the residue is little, and the conductive filler can produce very good conductive effect.
Description
Technical Field
The invention relates to the technical field of metal powder preparation, in particular to a method for preparing flake silver powder by using lac.
Background
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Silver powder is used as a conductive phase and has important application in conductive slurry, and the flake silver powder can form surface-to-surface contact in the process of forming a conductive path, so that the silver powder has better conductive performance compared with silver powder with other morphologies.
In recent years, research on preparing nano silver powder using green resources is increasing. The currently reported green synthesis method of nano silver is mainly to extract substances with reducing property from plant resources to reduce silver ions. However, the composition and dosage of the extract are difficult to control, the morphology and the particle size of the prepared nano silver powder are difficult to control, and the yield is low, so that the nano silver powder cannot be used as conductive filler.
At present, the preparation of commercial flake silver powder is mainly carried out by a mechanical ball milling method, but the mechanical ball milling method has high energy consumption. When preparing flake silver powder by a mechanical ball milling method, stearic acid is generally used as a ball milling medium, so that the surface of the silver powder prepared by the ball milling method is covered with a stearic acid film, and the silver powder is suitable for being used in traditional conductive slurry. With the development of wearable electronic materials, the matrix used in the flexible conductive composite material is not an oily system, but is mostly a hydrophilic system such as hydrogel, silver powder prepared by a ball milling method usually needs to be treated to be used in the flexible conductive composite material, and the conductive performance cannot be well exerted.
The chemical reduction method and the template method are also reported to prepare the flake silver powder, but the existing chemical reduction method has the problems that the morphology of the silver powder is not easy to control, the additives are more, the types of residual substances on the surface of the silver powder are complex, the mass production cannot be realized and the like; the template method introduces a large amount of synthetic resin in the preparation process, has the problems of complex post-treatment, large waste liquid discharge, higher overall production power consumption cost and the like, and is not beneficial to the green development of industry.
The soluble resin commonly used in the silver powder preparation process comprises water-soluble epoxy resin, water-soluble polyurethane resin, water-soluble acrylic resin, polyvinyl alcohol and the like. However, hydrophilic groups such as carboxyl, hydroxyl, amino, amido and the like are additionally introduced into the water-soluble resin in the synthesis process, and the preparation process is complex, so that the cost of the water-soluble resin is higher than that of the water-insoluble resin; acrylic resin is taken as an example, and the selling price of the acrylic resin is 4-5 ten thousand yuan/ton. As in the prior art CN104148655A, a green production method of plate-like silver powder is disclosed, which uses a vacuum evaporation plating method to produce plate-like silver powder using a water-soluble resin, and then dissolves the water-soluble resin in water so that the silver powder is detached. However, according to common knowledge in the art, even the water-soluble resin has good water resistance after self-crosslinking film formation, and further cannot be dissolved by pure water, and organic solvents are still needed for dissolution, which poses a threat to the environment; in addition, the high silver loss rate exists in the vacuum evaporation coating process, so that the preparation cost of the silver powder is increased again.
Shellac, also called shellac, is a natural resin produced by the shellac through the conversion of the plant juice absorbed by the shellac and secretion, has the characteristics of strong cohesiveness, insulation, moisture resistance, good film forming property and the like, is nontoxic and tasteless, and is commonly used in industries such as paint, medicine, food, fruit fresh keeping and the like. The "green industry", like the "green products", is becoming increasingly popular. And the lac in China has the advantages of rich resources, low price, lower cost, more convenient acquisition and the like compared with synthetic resin.
Disclosure of Invention
The invention aims at: aiming at the problems of high cost, long degradation period and increased environmental pressure existing in the preparation of the flake silver powder by using the existing synthetic resin, the method for preparing the flake silver powder by using the lac is provided, green resources can be continuously regenerated, the preparation process is green and pollution-free, the cost is lower, and the prepared flake silver powder is uniform in thickness and surface.
The technical scheme of the invention is as follows:
a method for preparing flake silver powder by using shellac, comprising the following steps:
step S1: preparing a natural resin sacrificial template: dissolving lac in ethanol to prepare a lac solution; coating the lac solution on a flexible PET substrate, and curing at 25-50 ℃ for 5-20 min;
Step S2: the natural resin sacrificial template is hydrophilized with Sodium Dodecyl Sulfate (SDS) solution. Sensitizing the sacrificial template by using SnCl 2 solution;
Step S3: preparing a silver film: preparing silver ammonia solution, spraying the silver ammonia solution and the reducing solution on a natural resin sacrificial template at the same time for reaction, uniformly purging by an air compressor, flushing a silver film by ultrapure water, and purging at a high temperature of 60-90 ℃ until the liquid on the surface of the silver film disappears, thereby obtaining a bright silver film on the natural resin sacrificial template;
step S4: immersing a natural resin sacrificial template plated with a silver film into an alcohol solution, a ketone solution or an alkaline solution, and stirring to obtain a flaky silver powder mother solution;
Step S5: crushing the flake silver powder mother solution by adopting ultrasonic, and soaking in ethanol, centrifuging and drying to obtain the nanometer flake silver powder.
The coating means in step S1 is screen printing or knife coating.
Preferably, the curing temperature is 50℃and the curing time is 10 min.
Preferably, the alcoholic solution is e.g. ethanol, methanol.
The production of plate-like silver powder using shellac has the following advantages over synthetic resins:
(1) Shellac is a natural biological resource and can be continuously regenerated. The cost is lower, the production process almost has no emission and waste generation, and the production process is more environment-friendly.
(2) Shellac can be naturally degraded by breaking the carbon chain, and the synthetic resin for the preparation of flake silver powder reported so far requires a considerable time to degrade.
(3) Shellac is widely used as a coating agent in paints, medicines and foods due to its good film forming property. According to the invention, the natural resin sacrificial template with good film forming property of lac is prepared, and the silver nano film is guided to grow orderly on the natural resin sacrificial template, so that the preparation of the flake silver powder with uniform thickness and surface is realized.
In addition, after the high-temperature blowing step is added, the silver film obtained on the natural resin sacrificial template is brighter, so that the generation of speckles or strip-shaped flaws on the surface of the silver film is effectively reduced, and the subsequent blackening and yellowing of the silver film are prevented.
According to a preferred embodiment, the shellac solution in step S1 is prepared from shellac and ethylcellulose in ethanol, the solid content of the shellac solution is 15 wt%, and the mass ratio of shellac to ethylcellulose is in the range of 9:1-7:3.
The lac solution coated on the PET substrate is solidified to form a lac film with a smooth surface, but the lac film is slowly dissolved under the action of the silver-ammonia solution and the reducing solution, so that the plated silver film layer is slightly uneven, and the quality of the prepared flake silver powder is reduced. After the ethylcellulose is added into the lac solution, the dissolution of the lac film is inhibited, so that the surface evenness of the lac film is further maintained, and the thickness uniformity of the prepared flaky silver powder is ensured.
Preferably, the mass ratio of lac to ethylcellulose is 7:3.
According to a preferred embodiment, in step S2, the concentration of the SDS solution is 0.35 mM; the SnCl 2 solution is prepared by mixing 10 mL/L hydrochloric acid and 44.3mM SnCl 2.
According to a preferred embodiment, in step S2, the hydrophilic treatment time is 5 minutes and the sensitizing treatment time is 5 minutes.
According to a preferred embodiment, in step S3, the reducing solution is one or a mixture of two of glucose and sodium potassium tartrate.
In step S3, when the reducing solution is a mixture of potassium sodium tartrate and glucose, the mass ratio of the reducing solution is as follows: 5:8-1:8. Preferably, it is: 1:7.
When the mass ratio of potassium sodium tartrate to glucose in the reducing solution is 1:8, the deposition speed of the silver film is too high, the flatness of the silver film can be reduced, and when the mass ratio is 5:8, the deposition speed of the silver film is too low, impurities are generated on the surface of the silver film, and the yellowing and blackening of the silver film affect the quality of the prepared flake silver powder. When the mass ratio of potassium sodium tartrate to glucose is 1:7, the deposition speed of the silver film is optimal, so that the surface evenness of the silver film can be ensured, and the quality of the flake silver powder can be ensured.
According to a preferred embodiment, in step S3, the reaction time for the reaction by spraying onto the sacrificial template of natural resin is between 5 and 8 minutes, preferably 6 minutes.
According to a preferred embodiment, in step S3, the silver-ammonia solution preparation method comprises the following steps: 28wt% ammonia was added dropwise to a 58.8mM AgNO 3 solution, the solution was observed to change from clear to turbid, and the dropwise addition was continued until the solution became clear. At this time, 1M of NaOH solution was added to make the solution cloudy again, and then 28wt% aqueous ammonia was added to obtain a transparent silver ammonia solution.
According to a preferred embodiment, in step S4, the natural resin sacrificial template coated with the silver film is immersed in an alcoholic solution of ethanol for 1 to 5 minutes, preferably 2 minutes, with a stirring speed of 500 to 1000 r/min, preferably 700 r/min.
The dissolution rate of the ultraviolet film can be controlled by controlling the immersion time and the stirring speed, and the slow dissolution of the ultraviolet film can prolong the dissolution time of the ultraviolet film, so that the problem that part of the ultraviolet film is adhered to the surface of the flake silver powder again in the dissolution process can exist. Through experiments, the applicant of the application finds that the dissolution rate of the ultraviolet film is most suitable under the condition that the stirring speed is 700 r/min and the immersion time is 2 minutes, and the prepared flaky silver film has almost no residue on the surface.
The ethanol has good eluting effect and less impurity residue, as shown in figure 5, and is environment-friendly and recyclable.
According to a preferred embodiment, in step S3, the temperature of the high temperature purge is preferably 80-85 ℃, more preferably 85 ℃.
According to a preferred embodiment, in step S5, the ultrasonic power is 480W, the ultrasonic time is 10-50 minutes, and the ultrasonic time can be adjusted according to the requirements of the particle size of the silver powder in the subsequent application.
The application also provides an application of the lac in preparing flake silver powder.
Compared with the prior art, the invention has the beneficial effects that:
1. a method for preparing flake silver powder by using lac, wherein the surface of the flake silver powder prepared by using the lac is not covered by stearic acid, so that the flake silver powder can be well dispersed in a flexible matrix and has excellent conductivity. In the process for preparing the flake silver powder by using the natural resin, a shellac material is used as a plating base material, so that a powerful guarantee is provided for subsequent large-scale roll-to-roll continuous mass preparation. The mature chemical deposition technology used in the process also ensures the large-scale production of the silver nano film, and reduces the waste of silver;
2. A method for preparing flake silver powder by using lac utilizes good film forming property of the lac to prepare a smooth and flat natural resin sacrificial template, so that flake silver powder with uniform thickness and uniform surface is prepared, the size of the prepared flake silver powder is controllable by the preparation process, the surface is uniform, and the flake silver powder is suitable for playing a good conductive role in conductive filler;
3. The method for preparing the flake silver powder by using the lac replaces synthetic resin, so that the cost is saved in industry, the overall surface quality of the prepared silver powder can be improved, and the use scene of the silver powder is widened; in the environment, natural renewable resources are utilized, natural rapid degradation can be realized, the preparation process is simple to operate, and organic solvents such as acetone and the like are not needed, so that the pressure on the environment is avoided, and the method belongs to a real green process method for preparing the flake silver powder.
Drawings
FIG. 1 is a comparative SEM image of the plate-like silver powders (a), (b) prepared in example 1 of the present invention and commercial plate-like silver powders (c), (d); FIG. 1 (a) is a general morphology view of the plate-like silver powder produced according to the present invention, and FIG. 1 (b) is a side cross-sectional view of the plate-like silver powder produced according to the present invention; FIG. 1 (c) is a general morphology diagram of a commercial plate-like silver powder, and FIG. 1 (d) is a side interface diagram of a commercial plate-like silver powder;
FIG. 2 is a graph showing the comparison of the particle size distribution of the plate-like silver powder prepared in examples 1 to 5 of the present invention under different ultrasonic time periods;
FIG. 3 is an XRD pattern of the plate-like silver powder prepared in example 1 of the present invention;
FIG. 4 is an AFM image of the plate-like silver powder prepared in example 1 of the present invention;
FIG. 5 is a TGA graph of the plate-like silver powder prepared in example 1 of the present invention;
FIG. 6 is a graph showing the comparison of the effect of silver plating on a sacrificial template of natural resin prepared in examples 1,2 and 5 of the present invention using different shellac and ethylcellulose;
FIG. 7 is a golden phase diagram of flake silver powder prepared at different purge temperatures in the present invention;
FIG. 8 is a graph showing the surface resistance of the plate-like silver powder prepared at different purge temperatures in the present invention;
FIG. 9 is an SEM image of the plate-like silver powder prepared in example 7 and comparative example 1 according to the present invention;
Fig. 10 is an SEM image of the spherical silver powder prepared in comparative example 2 of the present invention;
fig. 11 is an SEM image of the plate-like silver powder prepared in comparative example 2 of the present invention.
Detailed Description
The examples set forth below are merely basic illustrations of the inventive concepts to facilitate a further understanding of the application by those skilled in the art and are not intended to limit the scope of the application. The method adopted in the application is a conventional method without special description. The experimental materials used in the present application are all commercially available without any particular explanation. Commercial flake silver powder was purchased from Zhongyuxin shield alloy limited.
The features and capabilities of the present invention are described in further detail below in connection with examples.
Example 1
A method for preparing flake silver powder by using shellac, comprising the following steps:
step S1: preparing a natural resin sacrificial template:
step S1.1: preparing a lac solution, namely dissolving lac and ethyl cellulose in the mass ratio of 7:3 into an ethanol solution, and preparing the lac solution with the solid content of 15 wt%;
Step S1.2: printing the lac solution on a flexible PET substrate in a screen printing mode, and placing the flexible PET substrate in a 50 ℃ oven for curing for 10 min to form the natural resin sacrificial template.
Step S2:
step S2.1: hydrophilic treatment: placing the natural resin sacrificial template in 0.35 mM SDS solution, taking out after 5: 5 min, and flushing with ultrapure water;
step S2.2: sensitization: placing the natural resin sacrificial template processed in the step S2.1 into an acidic SnCl 2 solution, taking out after 5: 5 min, and flushing with ultrapure water; the SnCl 2 solution is prepared by mixing 10 mL/L hydrochloric acid and 44.3mM SnCl 2.
Step S3.1: the silver-ammonia solution is prepared according to the following preparation method: 28wt% ammonia was added dropwise to a 58.8mM AgNO 3 solution, the solution was observed to change from clear to turbid, and the dropwise addition was continued until the solution became clear. At this time, 1M NaOH solution was added to make the solution cloudy again, and then 28wt% aqueous ammonia was added to obtain a transparent silver ammonia solution;
Step S3.2: and (3) dissolving potassium sodium tartrate and glucose with the mass ratio of 1:7 into ultrapure water, spraying the solution and the silver ammonia solution onto the natural resin sacrificial template at the same time with the volume ratio of 1:1, and simultaneously, uniformly purging by an air compressor. After the reaction is carried out for 6 minutes, the bright silver film is obtained by flushing with ultrapure water for 3 times and then blowing with hot air at 85 ℃;
step S4: immersing the silver film obtained in the step S3.2 in ethanol solution for 2 minutes, and stirring at the speed of 700 r/min to obtain flake silver powder mother liquor;
Step S5: and (3) placing the flake silver powder mother liquor into a high-energy ultrasonic pulverizer to pulverize, setting ultrasonic power to be 480W, and setting ultrasonic time to be 20 minutes to obtain flake silver powder with average particle size of 12.5 mu m.
As can be seen from comparison of FIG. 1 (a) and FIG. 1 (c), the SEM image of the flake silver powder prepared in this example and the SEM image of commercial flake silver powder (purchased from Zhongxin shield alloy Co., ltd.) are shown in FIG. 1, the flake silver powder prepared in this example has a uniform morphology, is of a flake structure, has a relatively uniform particle size, has no lubricant layer covering the surface, has a non-uniform morphology, and has other morphologies in which silver powder is doped. As can be seen by comparing FIGS. 1 (b) and (d), the silver flake prepared according to the present invention has a uniform thickness of about 55nm; and the commercial flake silver powder has unclear side edges and uneven thickness.
The XRD pattern of the silver flake prepared in the embodiment is shown in fig. 3, and thus, the graph shows that one strong peak appears at 38.12 degrees, and four weak peaks appear at 44.40 degrees, 64.5 degrees, 77.40 degrees and 81.6 degrees respectively. These five diffraction peaks represent the (111), (200), (220), (311) and (222) crystal planes of the silver face-centered cubic structure, respectively. Besides the five diffraction peaks, the spectrum has no other diffraction peaks, which are completely matched with the diffraction peaks on the silver standard card, so that the powder prepared by the method is very pure silver powder. The strong diffraction peak of the sample at 38.12 degrees shows that the silver powder prepared by the method is in an ideal sheet structure from the other side surface.
The AFM image of the plate-like silver powder prepared in this example is shown in fig. 4, from which it can be seen that the surface of the plate-like silver powder prepared in the invention is relatively flat and has low roughness. This is advantageous for the subsequent preparation of the conductive composite material, and can form better surface-to-surface contact when constructing the conductive channel, thereby improving the transmission rate of electrons.
The TGA profile of the plate-like silver powder prepared in this example is shown in fig. 5, from which it can be seen that the mass loss of the silver plate is small, only 1.52wt% during the whole heating process, indicating that almost no other substances remain on the surface of the plate-like silver powder prepared in this way.
Example 2
A method for preparing flake silver powder by using shellac, comprising the following steps:
Step S1: preparing a natural resin sacrificial template:
step S1.1: preparing a lac solution, namely dissolving lac and ethyl cellulose in an ethanol solution according to the mass ratio of 8:2, and preparing the lac solution with the solid content of 15 wt%;
Step S1.2: printing the lac solution on a flexible PET substrate in a screen printing mode, and placing the flexible PET substrate in a 50 ℃ oven for curing for 10 min to form the natural resin sacrificial template.
Step S2.1: hydrophilic treatment: placing the natural resin sacrificial template in 0.35 mM SDS solution, taking out after 5: 5 min, and flushing with ultrapure water;
step S2.2: sensitization: placing the natural resin sacrificial template processed in the step S2.1 into an acidic SnCl 2 solution, taking out after 5: 5 min, and flushing with ultrapure water; the SnCl 2 solution is prepared by mixing 10 mL/L hydrochloric acid and 44.3mM SnCl 2.
Step S3.1: the silver-ammonia solution is prepared according to the following preparation method: 28wt% ammonia was added dropwise to a 58.8mM AgNO 3 solution, the solution was observed to change from clear to turbid, and the dropwise addition was continued until the solution became clear. At this time, 1M NaOH solution was added to make the solution cloudy again, and then 28wt% aqueous ammonia was added to obtain a transparent silver ammonia solution;
in the step S3.2, potassium sodium tartrate and glucose with the mass ratio of 1:4 are dissolved in ultrapure water, and are sprayed onto a natural resin sacrificial template at the same time with silver-ammonia solution in the volume ratio of 1:1, and meanwhile, the natural resin sacrificial template is uniformly purged by an air compressor. After 7 minutes of reaction, the film was rinsed 3 times with ultrapure water and then purged with hot air at 90℃to obtain a bright silver film.
Step S4: the bright silver film obtained in the step 3.2 is immersed in NaOH solution at 50 ℃ and 1M for 10 minutes, and stirred at the speed of 500 r/min, so as to obtain flake silver powder mother liquor.
Step S5: and (3) placing the flake silver powder mother liquor into a high-energy ultrasonic pulverizer to pulverize, setting ultrasonic power to be 480W, and setting ultrasonic time to be 40 minutes to obtain flake silver powder with average particle size of 9 mu m.
The SEM pattern, XRD pattern, AFM pattern and TGA pattern of the plate-like silver powder prepared in this example were similar to those of example 1.
Example 3
Example 3 is a further modification of example 1; a method for preparing flake silver powder by using shellac, comprising the following steps:
Step S1: preparing a natural resin sacrificial template:
step S1.1: preparing a lac solution, namely dissolving lac and ethyl cellulose in the mass ratio of 7:3 into an ethanol solution, and preparing the lac solution with the solid content of 15 wt%;
Step S1.2: printing the lac solution on a flexible PET substrate in a screen printing mode, and placing the flexible PET substrate in a 50 ℃ oven for curing for 10 min to form the natural resin sacrificial template.
Step S2.1: hydrophilic treatment: placing the natural resin sacrificial template in 0.35 mM SDS solution, taking out after 5: 5 min, and flushing with ultrapure water;
step S2.2: sensitization: placing the natural resin sacrificial template processed in the step S2.1 into an acidic SnCl 2 solution, taking out after 5: 5 min, and flushing with ultrapure water; the SnCl 2 solution is prepared by mixing 10 mL/L hydrochloric acid and 44.3mM SnCl 2.
Step S3.1: the silver-ammonia solution is prepared according to the following preparation method: 28wt% ammonia was added dropwise to a 58.8mM AgNO 3 solution, the solution was observed to change from clear to turbid, and the dropwise addition was continued until the solution became clear. At this time, 1M NaOH solution was added to make the solution cloudy again, and then 28wt% aqueous ammonia was added to obtain a transparent silver ammonia solution;
Step S3.2: and (3) dissolving potassium sodium tartrate and glucose with the mass ratio of 1:6.5 into ultrapure water, spraying the solution and the silver ammonia solution onto the natural resin sacrificial template at the same time with the volume ratio of 1:1, and uniformly blowing by an air compressor. After 7 minutes of reaction, flushing with ultrapure water for 3 times, and then blowing with 80 ℃ hot air to obtain a bright silver film;
step S4: immersing the silver film obtained in the step S3.2 in ethanol solution for 2 minutes, and stirring at the speed of 600 r/min to obtain flake silver powder mother liquor;
step S5: and (3) placing the flake silver powder mother liquor into a high-energy ultrasonic pulverizer to pulverize, setting ultrasonic power to be 480W, and setting ultrasonic time to be 30 minutes to obtain flake silver powder with average particle size of 10 mu m.
SEM images, XRD images and AFM images of the plate-like silver powder prepared in this example were similar to those of example 1.
Example 4
Example 4 is a further modification of example 3; a method for preparing flake silver powder by using shellac, comprising the following steps:
Step S1: preparing a natural resin sacrificial template:
step S1.1: preparing a lac solution, namely dissolving lac and ethyl cellulose in the mass ratio of 7:3 into an ethanol solution, and preparing the lac solution with the solid content of 15 wt%;
step S1.2: printing the lac solution on a flexible PET substrate in a knife coating mode, and placing the substrate in a 50 ℃ oven for curing for 10 min to form the natural resin sacrificial template.
Step S2.1: hydrophilic treatment: placing the natural resin sacrificial template in 0.35 mM SDS solution, taking out after 5: 5 min, and flushing with ultrapure water;
step S2.2: sensitization: placing the natural resin sacrificial template processed in the step S2.1 into an acidic SnCl 2 solution, taking out after 5: 5 min, and flushing with ultrapure water; the SnCl 2 solution is prepared by mixing 10 mL/L hydrochloric acid and 44.3mM SnCl 2.
Step S3.1: the silver-ammonia solution is prepared according to the following preparation method: 28wt% ammonia was added dropwise to a 58.8mM AgNO 3 solution, the solution was observed to change from clear to turbid, and the dropwise addition was continued until the solution became clear. At this time, 1M NaOH solution was added to make the solution cloudy again, and then 28wt% aqueous ammonia was added to obtain a transparent silver ammonia solution;
Step S3.2 is: and (3) dissolving potassium sodium tartrate and glucose with the mass ratio of 5:8 into ultrapure water, spraying the solution and the silver ammonia solution onto the natural resin sacrificial template at the same time with the volume ratio of 1:1, and uniformly purging by an air compressor. After the reaction for 6 minutes, the film was rinsed 3 times with ultrapure water and then purged with hot air at 85℃to obtain a bright silver film.
Step S4: immersing the silver film obtained in the step S3.2 into ethyl acetate solution for 2 minutes, and stirring at the speed of 900 r/min to obtain flake silver powder mother liquor;
The step S5 is as follows: and (3) placing the flake silver powder mother liquor into a high-energy ultrasonic pulverizer to pulverize, setting ultrasonic power to be 480W, and setting ultrasonic time to be 50 minutes to obtain flake silver powder with average particle size of 6 mu m.
The SEM pattern, XRD pattern, AFM pattern and TGA pattern of the plate-like silver powder prepared in this example were similar to those of example 1.
Example 5
A method for preparing flake silver powder by using shellac, comprising the following steps:
Step S1: preparing a natural resin sacrificial template:
step S1.1: preparing a lac solution, namely dissolving lac and ethyl cellulose in the mass ratio of 9:1 into an ethanol solution, and preparing the lac solution with the solid content of 15 wt%;
Step S1.2: printing the lac solution on a flexible PET substrate in a knife coating mode, and placing the substrate in a 40 ℃ oven for curing 15min to form the natural resin sacrificial template.
Step S2.1: hydrophilic treatment: placing the natural resin sacrificial template in 0.35 mM SDS solution, taking out after 5: 5 min, and flushing with ultrapure water;
step S2.2: sensitization: placing the natural resin sacrificial template processed in the step S2.1 into an acidic SnCl 2 solution, taking out after 5: 5 min, and flushing with ultrapure water; the SnCl 2 solution is prepared by mixing 10 mL/L hydrochloric acid and 44.3mM SnCl 2.
Step S3.1: the silver-ammonia solution is prepared according to the following preparation method: 28wt% ammonia was added dropwise to a 58.8mM AgNO 3 solution, the solution was observed to change from clear to turbid, and the dropwise addition was continued until the solution became clear. At this time, 1M NaOH solution was added to make the solution cloudy again, and then 28wt% aqueous ammonia was added to obtain a transparent silver ammonia solution;
Step S3.2 is: and (3) dissolving potassium sodium tartrate and glucose with the mass ratio of 1:7 into ultrapure water, spraying the solution and the silver ammonia solution onto the natural resin sacrificial template at the same time with the volume ratio of 1:1, and simultaneously, uniformly purging by an air compressor. After the reaction for 6 minutes, the film was rinsed 3 times with ultrapure water and then purged with hot air at 60℃to obtain a bright silver film.
Step S4: immersing the silver film obtained in the step S3.2 into ethanol solution for 4 minutes, and stirring at the speed of 500 r/min to obtain flake silver powder mother liquor;
The step S5 is as follows: and (3) placing the flake silver powder mother liquor into a high-energy ultrasonic pulverizer to pulverize, setting ultrasonic power to be 480W, and setting ultrasonic time to be 10 minutes to obtain flake silver powder with average particle size of 13 mu m.
The SEM pattern, XRD pattern, AFM pattern and TGA pattern of the plate-like silver powder prepared in this example were similar to those of example 1.
Example 6
A method for preparing flake silver powder by using shellac, comprising the following steps:
Step S1: preparing a natural resin sacrificial template:
step S1.1: preparing a lac solution, namely dissolving lac and ethyl cellulose in the mass ratio of 7:3 into an ethanol solution, and preparing the lac solution with the solid content of 15 wt%;
Step S1.2: printing the lac solution on a flexible PET substrate in a knife coating mode, and placing the substrate in a 25 ℃ oven for curing 20 min to form the natural resin sacrificial template.
Step S2.1: hydrophilic treatment: placing the natural resin sacrificial template in 0.35 mM SDS solution, taking out after 5: 5 min, and flushing with ultrapure water;
step S2.2: sensitization: placing the natural resin sacrificial template processed in the step S2.1 into an acidic SnCl 2 solution, taking out after 5: 5 min, and flushing with ultrapure water; the SnCl 2 solution is prepared by mixing 10 mL/L hydrochloric acid and 44.3mM SnCl 2.
Step S3.1: the silver-ammonia solution is prepared according to the following preparation method: 28wt% ammonia was added dropwise to a 58.8mM AgNO 3 solution, the solution was observed to change from clear to turbid, and the dropwise addition was continued until the solution became clear. At this time, 1M NaOH solution was added to make the solution cloudy again, and then 28wt% aqueous ammonia was added to obtain a transparent silver ammonia solution;
Step S3.2 is: and (3) dissolving potassium sodium tartrate and glucose with the mass ratio of 1:3 into ultrapure water, spraying the solution and the silver ammonia solution onto the natural resin sacrificial template at the same time with the volume ratio of 1:1, and uniformly purging by an air compressor. After the reaction for 6 minutes, the film was rinsed 3 times with ultrapure water and then purged with hot air at 85℃to obtain a bright silver film.
Step S4: immersing the silver film obtained in the step S3.2 in an acetone solution for 2 minutes, and stirring at the speed of 1000 r/min to obtain a flaky silver powder mother solution;
the step S5 is as follows: and (3) placing the flake silver powder mother liquor into a high-energy ultrasonic pulverizer to pulverize, setting ultrasonic power to be 480W, and setting ultrasonic time to be 40 minutes to obtain flake silver powder with average particle size of 9 mu m.
The SEM pattern, XRD pattern, AFM pattern and TGA pattern of the plate-like silver powder prepared in this example were similar to those of example 1.
Fig. 2 is a graph showing the particle size distribution of the silver flake prepared in examples 1 to 5 of the present invention, and it can be seen from fig. 2 that the particle size of the silver flake can be controlled by the ultrasonic time, and the particle size distribution of the silver flake shows a tendency to gradually decrease as the ultrasonic treatment time increases. When the ultrasonic treatment time is 50 minutes, the average particle size of the silver flakes is about 6 mu m.
FIG. 6 shows the effect of silver plating on a sacrificial template of natural resin made of lac solution in different proportions of lac and ethylcellulose in examples 5, 2 and 1 of the present application; as shown in fig. 6, when the ratio of shellac to ethylcellulose is 9:1, the plating is not uniform enough, and the surface has little reflection effect; when the ratio of the lac to the ethyl cellulose is 8:2, the uniformity of the coating is improved, the surface has a certain reflection effect, but the surface of the coating is flawed. When the ratio of lac to ethyl cellulose is 7:3, the plating layer is very uniform, the silver film on the surface is very bright, the whole surface has a reflection effect, and the surface has no visible flaws and concave-convex, which indicates that when the ratio of lac to ethyl cellulose is 7:3, the prepared natural resin sacrificial template is most suitable for the uniform growth of the silver film on the natural resin sacrificial template, and the flat and bright silver film can be prepared by using the natural resin sacrificial template.
As shown in FIG. 7, which is a golden phase diagram of a silver film obtained at 60 ℃,70 ℃, 80 ℃, 85 ℃ and 90 ℃ sweeping temperature in the application, as can be seen from FIG. 7, flaws exist on the surface of the unswept silver film, and the flaws on the surface of the silver film are reduced after sweeping. The silver film surface condition is best at temperatures of 85 ℃ and 90 ℃. As a result of performing surface resistance test on the silver film by using the four-probe tester, as shown in fig. 8, as can be seen from fig. 8, the surface resistance of the silver film which is not purged is higher, and as the purging temperature increases, the surface resistance of the silver film gradually decreases. After the temperature reaches 80 ℃, the surface resistance of the silver film reaches the minimum value and basically remains unchanged. It can be seen that the optimum purge temperature is 85 ℃.
Example 7
A method for preparing flake silver powder by using shellac, comprising the following steps:
Step S1: preparing a natural resin sacrificial template:
step S1.1: preparing a lac solution, namely dissolving lac and ethyl cellulose in the mass ratio of 9:1 into an ethanol solution, and preparing the lac solution with the solid content of 15 wt%;
Step S1.2: printing the lac solution on a flexible PET substrate in a screen printing mode, and placing the flexible PET substrate in a 25 ℃ oven for curing 20min to form the natural resin sacrificial template.
Step S2.1: hydrophilic treatment: placing the natural resin sacrificial template in 0.35 mM SDS solution, taking out after 5: 5 min, and flushing with ultrapure water;
Step S2.2: sensitization: placing the natural resin sacrificial template processed in the step S2.1 into an acidic SnCl 2 solution, taking out after 5:5 min, and flushing with ultrapure water; the SnCl 2 solution is prepared by mixing 10 mL/L hydrochloric acid and 44.3mM SnCl 2.
Step S3.1: the silver-ammonia solution is prepared according to the following preparation method: 28wt% ammonia was added dropwise to a 58.8mM AgNO 3 solution, the solution was observed to change from clear to turbid, and the dropwise addition was continued until the solution became clear. At this time, 1M NaOH solution was added to make the solution cloudy again, and then 28wt% aqueous ammonia was added to obtain a transparent silver ammonia solution;
Step S3.2: and (3) dissolving potassium sodium tartrate and glucose with the mass ratio of 1:4 into ultrapure water, spraying the solution and the silver ammonia solution onto the natural resin sacrificial template at the same time with the volume ratio of 1:1, and uniformly purging by an air compressor. After the reaction for 6 minutes, the film was rinsed 3 times with ultrapure water and then purged with hot air at 80℃to obtain a bright silver film.
Step S4: immersing the silver film obtained in the step S3.2 in ethanol solution for 5 minutes, and stirring at the speed of 500 r/min to obtain flake silver powder mother liquor;
step S5: and (3) placing the flake silver powder mother liquor into a high-energy ultrasonic pulverizer to pulverize, setting ultrasonic power to be 480W, and setting ultrasonic time to be 10 minutes to obtain flake silver powder with average particle size of 13 mu m.
Example 8
A method for preparing flake silver powder by using shellac, comprising the following steps:
Step S1: preparing a natural resin sacrificial template:
step S1.1: preparing a lac solution, namely dissolving lac and ethyl cellulose in an ethanol solution according to the mass ratio of 8:2, and preparing the lac solution with the solid content of 15 wt%;
Step S1.2: printing the lac solution on a flexible PET substrate in a screen printing mode, and placing the flexible PET substrate in a 30 ℃ oven for curing for 10 min to form the natural resin sacrificial template.
Step S2.1: hydrophilic treatment: placing the natural resin sacrificial template in 0.35 mM SDS solution, taking out after 5: 5 min, and flushing with ultrapure water;
Step S2.2: sensitization: placing the natural resin sacrificial template processed in the step S2.1 into an acidic SnCl 2 solution, taking out after 5:5 min, and flushing with ultrapure water; the SnCl 2 solution is prepared by mixing 10 mL/L hydrochloric acid and 44.3mM SnCl 2.
Step S3.1: the silver-ammonia solution is prepared according to the following preparation method: 28wt% ammonia was added dropwise to a 58.8mM AgNO 3 solution, the solution was observed to change from clear to turbid, and the dropwise addition was continued until the solution became clear. At this time, 1M NaOH solution was added to make the solution cloudy again, and then 28wt% aqueous ammonia was added to obtain a transparent silver ammonia solution;
Step S3.2: and (3) dissolving potassium sodium tartrate and glucose with the mass ratio of 1:3 into ultrapure water, spraying the solution and the silver ammonia solution onto the natural resin sacrificial template at the same time with the volume ratio of 1:1, and uniformly purging by an air compressor. After 5 minutes of reaction, the film was rinsed 3 times with ultrapure water and then purged with hot air at 85℃to obtain a bright silver film.
Step S4: the bright silver film obtained in the step 3.2 is immersed in NaOH solution at 50 ℃ and 1M for 10 minutes, and stirred at the speed of 500 r/min, so as to obtain flake silver powder mother liquor.
Step S5: and (3) placing the flake silver powder mother liquor into a high-energy ultrasonic pulverizer to pulverize, setting ultrasonic power to be 480W, and setting ultrasonic time to be 40 minutes to obtain flake silver powder with average particle size of 9.1 mu m.
Step S6.1: 0.162g of the silver powder in S5, 0.164g of polydimethylsiloxane (main agent: curing agent=10:1) and 0.09 g of 4-methyl-2-pentanone were mechanically mixed 30min.
Step S6.2: a conductive elastomer film was deposited on the polydimethylsiloxane substrate through a mask and evacuated at-8 kPa a for 20 minutes to eliminate bubbles and cured at 145 c for 4 h to give a conductive composite with a solids content of 49.7 wt%.
Step S6.3: and (3) testing the conductive composite material obtained in the step S6.2 by a four-probe tester to obtain the conductive composite material with the conductivity of 9353.1S/cm.
Comparative example 1
This comparative example differs from example 7 in that:
step S1: preparation of an acrylic sacrificial template:
Step S1.1: dissolving heat-shrinkable acrylic resin in cyclohexanone solution, and diluting to 15 wt%;
Step S1.2: printing diluted acrylic resin on a flexible PET substrate in a screen printing mode, and placing the flexible PET substrate into an oven at 80 ℃ to be cured for 1h so as to form the acrylic resin sacrificial template.
Step S4: immersing the silver film obtained in the step S3.2 into an acetone solution for 15 minutes to obtain a flaky silver powder mother solution;
Step S5: and (3) placing the flake silver powder mother liquor into a high-energy ultrasonic pulverizer to pulverize, setting ultrasonic power to be 480W, and setting ultrasonic time to be 50 minutes to obtain flake silver powder with average particle size of 7.5 mu m.
The rest of the procedure was the same as in example 7.
SEM tests were performed on the silver powders prepared in example 7 and comparative example 1, and as a result, as shown in fig. 9, fig. 9a, 9b are the silver powders prepared in example 7, and fig. 9c, 9d are the silver powders prepared in comparative example 1. As can be seen from comparing fig. 9a, 9b and 9c, 9d, when the magnification is the same, the silver powder prepared in example 7 has smooth and flat surface, while the silver powder prepared in comparative example 1 has rough surface, uneven surface, and more remarkable after the comparison and magnification. The silver powder has large surface roughness and rugged surface, so that fluctuation of the thickness of the silver powder and uniformity reduction can be caused.
From the comparison of the material level used in example 7 and comparative example 1, it can be found that shellac, ethylcellulose and ethanol used in example 7 are all environment-friendly materials or reagents; in the corresponding process, reagents such as acrylic resin, acetone and the like are used in comparative example 1. The curing temperature was 25℃and the curing time was 20 min in example 7; in comparative example 1, the curing temperature was 80℃and the curing time was 1 h. Example 7 the curing using the oven was performed at a lower temperature and for a shorter time, and therefore less energy consuming.
Comparative example 2
The comparative example uses a mechanical ball milling method to prepare the plate-like silver powder.
Step S1: preparing spherical silver powder as a precursor:
step S1.1: weighing 4g of polyvinylpyrrolidone, dissolving in 200 ml ethylene glycol, adding 1g of AgNO 3, and fully stirring and dissolving to obtain a precursor solution;
step S1.2: transferring the precursor solution into a 500 ml flask, putting a magnet, putting into 160 ℃ oil bath, setting stirring speed to be 300 r/min, and reacting for 60min at constant temperature.
Step S1.3: washing the silver powder obtained after the reaction in the step S1.2 with ethanol three times, centrifugally separating at the rotating speed of 8000 r/min, and vacuum drying at 40 ℃ for 3 h to obtain spherical silver powder, and carrying out SEM (scanning electron microscope) test on the morphology of the spherical silver powder, wherein the result is shown in figure 10.
Step S2.1: the ball mill pot of 100 ml was filled with 25 g stainless steel balls, and 2.5 g spherical silver powder, 0.05 g calcium stearate, 0.05 ml oleic acid, and 3 ml ethanol were sequentially put into the ball mill pot as ball milling media. Then closing the ball milling tank;
Step S2.2: 2 ball milling tanks are directly opposite to and fixed on a ball mill, and ball milling is performed for 0.5h at a rotating speed of 50 r/min;
Step S2.3: the ball mill rotational speed was reset to 250 r/min and ball mill 24: 24 h.
Step S3: and (3) washing the ball-milled material in the step (2.3) with ethanol for 3 times. And (3) carrying out vacuum drying on 2h at 50 ℃ to obtain flake silver powder with the particle size of 2-6 mu m, and carrying out SEM (scanning electron microscope) test on the morphology of the flake silver powder, wherein the result is shown in FIG. 11.
Step S4.1: 0.651 g of silver powder in S3, 0.202 g g of polydimethylsiloxane (main agent: curing agent=10:1) and 0.20 g of 4-methyl-2-pentanone were mechanically mixed 30: 30 min.
Step S4.2: a conductive elastomer film was deposited on the polydimethylsiloxane substrate through a mask and evacuated at-8 kPa a for 20 minutes to eliminate bubbles and cured at 145 c for 4 h a resulting in a conductive composite with a solids content of 76.2 wt%.
Step S4.3: and (3) testing the conductive composite material obtained in the step S4.2 by using a four-probe tester to obtain the conductive composite material with the conductivity of 7486.3S/cm.
The comparison of the conductivity shows that: the conductivity of the conductive composite prepared in example 8 was as high as 9353.1S/cm at a silver powder solids content of 49.7 wt%, and the conductivity of the conductive composite prepared in comparative example 2 was 7486.3S/cm at a silver powder solids content of 76.2 wt%. It can be seen that the conductivity of the conductive composite material is greatly improved when the solid content of the silver powder prepared in the embodiment 8 of the invention is reduced by about 34 wt%. It is known that the cost of the conductive composite material is mainly derived from the price of silver powder, and the use of the flake silver powder prepared by the method as the conductive filler can improve the conductive performance and reduce the production cost by about 34 percent.
The above examples merely illustrate specific embodiments of the application, which are described in more detail and are not to be construed as limiting the scope of the application. It should be noted that it is possible for a person skilled in the art to make several variants and modifications without departing from the technical idea of the application, which fall within the scope of protection of the application.
Claims (7)
1. A method for preparing flake silver powder by using lac, which is characterized by comprising the following steps:
step S1: preparing a natural resin sacrificial template: dissolving lac in ethanol to prepare a lac solution; coating the lac solution on a flexible PET substrate, and curing at 25-50 ℃ for 5-20 min;
Wherein the lac solution is prepared by dissolving lac and ethyl cellulose in ethanol, the solid content of the lac solution is 15 wt percent, and the mass ratio of the lac to the ethyl cellulose is 9:1-7:3;
Step S2: carrying out hydrophilic treatment on the natural resin sacrificial template by using a sodium dodecyl sulfate solution; sensitizing the sacrificial template by using SnCl 2 solution;
Step S3: preparing a silver film: preparing silver-ammonia solution, spraying the silver-ammonia solution and the reducing solution on a natural resin sacrificial template at the same time for reaction for 5-8 minutes, uniformly purging, flushing the silver film with ultrapure water, and performing high-temperature purging at 60-90 ℃ to obtain a bright silver film on the natural resin sacrificial template;
step S4: immersing a natural resin sacrificial template plated with a silver film into an alcohol solution, a ketone solution or an alkaline solution, and stirring to obtain a flaky silver powder mother solution;
Step S5: crushing the silver flake mother solution by adopting ultrasonic, and soaking in ethanol, centrifuging and drying to obtain the silver flake.
2. The method for preparing plate-like silver powder using shellac according to claim 1, wherein the mass ratio of shellac to ethylcellulose in step S1 is 7:3.
3. The method for preparing flake silver powder by using shellac according to claim 1, wherein in the step S3, the reducing solution is one or a mixture of two of glucose and potassium sodium tartrate, and when the reducing solution is a mixture of potassium sodium tartrate and glucose, the mass ratio of potassium sodium tartrate to glucose is 5:8-1:8.
4. The method according to claim 3, wherein in the step S3, the reducing solution is a mixture of potassium sodium tartrate and glucose, and the mass ratio of potassium sodium tartrate to glucose is 1:7.
5. The method for preparing plate-like silver powder using shellac according to claim 1, wherein in step S4, the natural resin sacrificial template coated with the silver film is immersed in an ethanol solution for 1 to 5 minutes at a stirring speed of 500 to 1000 r/min.
6. The method for preparing plate-like silver powder using shellac according to claim 5, wherein the immersion time of the natural resin sacrificial template coated with the silver film in the ethanol solution is 2 minutes and the stirring speed is 700 r/min in step S4.
7. The method for preparing plate-like silver powder using shellac according to claim 1, wherein the high-temperature purging is performed at 80 to 85 ℃ in step S3.
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