CN114850480B - Preparation method of high-conductivity flake silver powder for touch screen silver paste - Google Patents
Preparation method of high-conductivity flake silver powder for touch screen silver paste Download PDFInfo
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- CN114850480B CN114850480B CN202210593775.9A CN202210593775A CN114850480B CN 114850480 B CN114850480 B CN 114850480B CN 202210593775 A CN202210593775 A CN 202210593775A CN 114850480 B CN114850480 B CN 114850480B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
- B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
- B22F2009/043—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling by ball milling
Abstract
The invention discloses a preparation method of high-conductivity flake silver powder for touch screen silver paste, which comprises the steps of preparing precursor original spherical silver powder with high sphericity, high dispersibility and narrow particle size distribution from silver carbonate by a liquid phase chemical reduction method by taking an ascorbic acid aqueous solution as a reducing agent, and then utilizing ricinoleic acid, urotropine,NOne of- (2-hydroxy-2-phenethyl) -acetamide and benzophenone oxime yl acetic acid benzophenone oxime ester is used as a secondary dispersing agent, so that the precursor silver powder and zirconia balls are fully and uniformly dispersed in a ball milling solvent, no caking or powder wall sticking phenomenon exists, the silver powder slurry is subjected to mechanical ball milling treatment, and the silver powder slurry is subjected to treatment such as filtration, cleaning, drying, screening and packaging to obtain the flaky silver powder which has higher flakiness degree, lower apparent density, high dispersibility, narrow particle size distribution and high conductivity.
Description
Technical Field
The invention belongs to the field of new materials for chemically preparing electronic powder materials, and particularly relates to a preparation method of high-conductivity flake silver powder for touch screen silver paste.
Background
The touch screen is widely applied to the field of our daily life due to the characteristics of convenient operation, flexible use, strong man-machine interaction and the like, such as mobile phones, tablet computers, vehicle-mounted touch display equipment and the like. The touch screen is widely applied to the field of our daily life due to the characteristics of convenient operation, flexible use, strong man-machine interaction and the like, such as mobile phones, tablet computers, vehicle-mounted touch display equipment and the like. The silver paste for the touch screen is widely applied to the silver paste for the touch screen, and the sensing circuit made of the conductive silver paste of the touch screen transmits current to the chip so as to achieve the purpose of sensing the touch action of fingers and realize sensitive operation. The silver flake is used as an important core base material of silver paste for the touch screen, and the quality of the intelligent terminal is determined to a great extent by the comprehensive performance of the silver flake.
At present, the flake silver powder can be directly prepared into the flake silver powder in one step by a chemical reduction method, but the raw materials and the auxiliary materials are high in price, the batch production capacity is limited, and the method is not suitable for the production of the industrialized flake silver powder. The production of the flake silver powder is generally carried out by adopting a mechanical ball milling method at home, the precursor original silver powder is firstly prepared by adopting a chemical reduction method, and then the precursor original silver powder is ground by adopting a mechanical ball milling method, so that the flake silver powder is prepared, the process flow is complex, the product index performance is unstable, and the method is not suitable for industrialized mass production.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a preparation method of flake silver powder for touch screen silver paste, which has the advantages of higher flakiness degree, lower apparent density, high dispersibility, narrow particle size distribution and high conductivity.
The technical scheme adopted for solving the technical problems is as follows: the preparation method of the high-conductivity flake silver powder for the touch screen silver paste comprises the following steps in sequence:
(1) Reduction of precursor original silver powder: preparing silver nitrate and polyvinylpyrrolidone K90 water solution, and adding sodium carbonate water solution under stirring to prepare silver carbonate; adding an aqueous solution of a reducing agent ascorbic acid to prepare silver powder through liquid phase chemical reduction, and rapidly adding an absolute ethanol solution of a dispersing agent A under stirring, wherein the dispersing agent A is prepared from the following components in percentage by mass: 4-1: 1, washing, drying and crushing oleic acid and polyethylene glycol 8000 to obtain precursor silver powder;
(2) Ball milling of flake silver powder: firstly, precursor silver powder and zirconia grinding balls are soaked in absolute ethyl alcohol ball milling solvent, and absolute ethyl alcohol solution of dispersing agent B is added, wherein the dispersing agent B is ricinoleic acid, urotropine,NOne of- (2-hydroxy-2-phenethyl) -acetamide and benzophenone oxime yl acetic acid benzophenone oxime ester is subjected to premixing grinding treatment under the condition of lower rotating speed, so that precursor silver powder and zirconia grinding balls are fully and uniformly dispersed in an absolute ethyl alcohol ball milling solvent, no caking or powder wall sticking phenomenon exists, silver powder slurry is obtained, the rotating speed is increased, ball milling treatment is performed on the silver powder slurry, and the silver powder slurry is subjected to treatment such as filtering, cleaning, drying, screening and packaging to obtain the flaky silver powder.
The preparation method of the absolute ethyl alcohol solution of the dispersant A specifically comprises the following steps: 60-64 g of dispersing agent A is weighed into a small 1000mL beaker, 500mL of absolute ethyl alcohol (analytically pure) is added, and the mixture is fully and uniformly stirred by a glass rod.
The preparation method of the absolute ethyl alcohol solution of the dispersant B specifically comprises the following steps: weighing 96-100 g of dispersing agent B in a 2500mL small beaker, adding 1000mL of absolute ethyl alcohol (analytically pure), and fully and uniformly stirring by using a glass rod.
The preparation method of the high-conductivity flake silver powder for the touch screen silver paste comprises the following steps of: pouring the sodium carbonate aqueous solution into the silver nitrate and polyvinylpyrrolidone K90 aqueous solution completely within 5min, and stirring for 3min at 300r/min after the addition is finished to prepare a silver carbonate suspension solution; pouring the ascorbic acid water solution into the mixture within 1min, stirring the mixture for 3min at 350r/min after the addition, pouring the absolute ethanol solution of the dispersing agent A into the mixture, stirring the mixture for 5min at 350r/min to ensure that the dispersing agent A is fully wrapped on the outer surfaces of the silver carbonate particles, and stopping stirring; pouring out supernatant after the flocculent powder is completely settled, and cleaning the powder with pure water for a small amount of times until the test conductivity is less than or equal to 20 mu S/cm; and drying the wet powder in a blast drying oven at 70 ℃ for 48 hours, crushing and sieving the dried powder, and obtaining the precursor original silver powder by the powder which is required to pass through a 200-mesh screen.
The preparation method of the high-conductivity flake silver powder for the touch screen silver paste comprises the following steps of: zirconia balls with the specification of 1mm are mixed according to the ball ratio of 1:8, adding the silver powder into a ball milling tank, wherein the mass of the zirconia balls is about 120Kg, the mass of the original silver powder of the precursor is about 15Kg, adding 5Kg of absolute ethyl alcohol and a dispersant B absolute ethyl alcohol solution into the ball milling tank, and carrying out low-speed ball milling for 120min according to 30r/min by a ball mill to fully infiltrate the silver powder into the auxiliary agent, so that the silver powder and the zirconia balls are fully and uniformly mixed, and no obvious agglomeration or powder wall sticking phenomenon of the powder occurs between the cylinder wall or the zirconia balls; after the silver powder and the zirconium balls are fully and uniformly mixed in an absolute ethyl alcohol system, the rotating speed is increased to 60r/min, sampling is carried out at regular time, ball milling is carried out once in the morning and evening respectively, the ball milling cover is opened for air release once, then ball milling is continued, and along with the extension of the ball milling time, the color of the silver powder slurry in the ball milling tank is changed from earthy yellow to silver gray; stopping ball milling when the index performance of the product meets the market demand, and then carrying out treatments such as filtering, cleaning, drying, screening, packaging and the like to obtain the flake silver powder.
The preparation method of the high-conductivity flake silver powder for the touch screen silver paste comprises the following specific steps of: 21000g of silver nitrate (analytically pure) and 25g of polyvinylpyrrolidone K90 are weighed, 75000mL of pure water is added, and stirring is carried out for 25min at 200r/min until the silver nitrate and the polyvinylpyrrolidone K90 are completely dissolved, and the temperature of the system is controlled at 25+/-1 ℃.
The preparation method of the high-conductivity flake silver powder for the touch screen silver paste comprises the following specific steps of: 6555g anhydrous sodium carbonate (analytically pure) was weighed, 75000mL pure water was added, and stirring was performed at 200r/min for 15min until sodium carbonate was completely dissolved, and the temperature of the system was controlled at 25.+ -. 1 ℃.
The preparation method of the high-conductivity flake silver powder for the touch screen silver paste comprises the following specific steps of: 13200g of ascorbic acid (analytically pure) was weighed, 150000mL of pure water was added, and stirred at 200r/min for 15min until the ascorbic acid was completely dissolved, and the temperature of the system was controlled at 25.+ -. 1 ℃.
The invention has the following advantages: the invention adopts the polyvinylpyrrolidone K90 with large molecular weight as the initial dispersant, mainly prevents the aggregation phenomenon of large area caused by the excessively fast growth of particles in the silver carbonate preparation process, ensures that the particle size of the silver carbonate particles is more uniform and the dispersibility is good, and simultaneously adopts the environment-friendly ascorbic acid as the reducing agent, so that the preparation system is nontoxic and pollution-free, and simultaneously has the following use mass ratio of 6: 4-1: the original silver powder is coated by a 1 oleic acid and polyethylene glycol 8000 compound system, and the precursor original silver powder has the characteristics of high sphericity, uniform particle size, narrow particle size distribution and the like.
According to the invention, one of ricinoleic acid, urotropine, N- (2-hydroxy-2-phenethyl) -acetamide and benzophenone oxime yl acetic acid benzophenone oxime ester is used as a secondary dispersing agent to further coat the surface of silver powder, so that the dispersibility of precursor original silver powder is better and the adhesiveness with the inner wall of roller stainless steel is poor as much as possible, a good basic condition is provided for the preparation of subsequent flaky silver powder with narrow particle size distribution, and meanwhile, the yield of silver powder can be obviously improved. Meanwhile, the silver paste is prepared by screening the secondary dispersing agent and utilizing the polyurethane organic polymer system, the influence of different dispersing agents on the conductivity of silver powder is analyzed, and the high-conductivity secondary dispersing agent is screened out, so that the matching property of the flake silver powder and the organic polymer system is better, and the realization of high dispersion and high conductivity is facilitated.
The preparation process of the invention is carried out at normal temperature and normal pressure, the reducing agent is ascorbic acid, and the used dispersing agent is nontoxic and pollution-free, thus the invention belongs to the environment-friendly preparation process, and the prepared flaky silver powder has higher flakiness degree, lower apparent density, high dispersibility, narrow particle size distribution and high conductivity, and the whole process flow is simple and easy to repeat, and the product index performance is stable, has stronger market competitiveness and is relatively suitable for industrial mass production.
Drawings
FIG. 1 is a scanning electron microscope image of an original spherical silver powder as a precursor of the present invention;
FIG. 2 is a focused ion beam-scanning electron microscope image of the original spherical silver powder of the precursor of the present invention;
FIG. 3 is a scanning electron microscope image of SF-YL-24;
FIG. 4 is a diagram showing the original spherical silver powder and plate-like silver powder SF-YL-24 according to the present invention in terms of wall sticking;
FIG. 5 is a physical diagram of SF-YL-24 product;
FIG. 6 is an X-ray diffraction pattern of SF-YL24 plate-like silver powder of the present invention;
FIG. 7 is a schematic illustration of the present inventionNAn infrared spectrum of- (2-hydroxy-2-phenethyl) -acetamide;
FIG. 8 is an infrared spectrum of benzophenone oxime acetate of the present invention;
FIG. 9 is an X-ray diffraction pattern of the original spherical silver powder and the plate-like silver powder as the precursor of the present invention.
Detailed Description
The technical scheme of the invention is clearly and completely described below with reference to the detailed description and the accompanying drawings.
The invention discloses a preparation method of high-conductivity flake silver powder for touch screen silver paste, which comprises the following steps:
(1) Reduction of precursor original silver powder: preparing silver nitrate and polyvinylpyrrolidone K90 water solution, and adding sodium carbonate water solution under stirring to prepare silver carbonate; adding a reducing agent ascorbic acid aqueous solution to prepare silver powder through liquid phase chemical reduction, and rapidly adding a dispersing agent A absolute ethanol solution under stirring, wherein the dispersing agent A is a compound system of oleic acid and polyethylene glycol 8000, and the mass ratio of the oleic acid to the polyethylene glycol 8000 is 6: 4-1: and 1, washing, drying and crushing to obtain the precursor silver powder.
Wherein the preparation steps of the absolute ethanol solution of the dispersant A specifically comprise: wherein the preparation steps of the absolute ethanol solution of the dispersant A specifically comprise: 60-64 g of dispersing agent A is weighed into a small 1000mL beaker, 500mL of absolute ethyl alcohol (analytically pure) is added, and the mixture is fully and uniformly stirred by a glass rod. A Scanning Electron Microscope (SEM) of the precursor raw spherical silver powder is shown in fig. 1, and a focused ion beam-Scanning Electron Microscope (SEM) of the precursor raw spherical silver powder is shown in fig. 2.
(2) Ball milling of flake silver powder: firstly, grinding precursor silver powder and zirconiaSoaking the ball in absolute ethanol ball milling solvent, adding dispersant B absolute ethanol solution, wherein the dispersant B is ricinoleic acid, urotropine,NOne of- (2-hydroxy-2-phenethyl) -acetamide and benzophenone oxime yl acetic acid benzophenone oxime ester is subjected to premixing grinding treatment under the condition of lower rotating speed, so that precursor silver powder and zirconia grinding balls are fully and uniformly dispersed in an absolute ethyl alcohol ball milling solvent, no caking or powder wall sticking phenomenon exists, silver powder slurry is obtained, the rotating speed is increased, ball milling treatment is performed on the silver powder slurry, and the silver powder slurry is subjected to treatment such as filtering, cleaning, drying, screening and packaging to obtain the flaky silver powder.
Wherein the preparation steps of the absolute ethanol solution of the dispersant B specifically comprise: weighing 96-100 g of dispersing agent B in a 2500mL small beaker, adding 1000mL of absolute ethyl alcohol (analytically pure), and fully and uniformly stirring by using a glass rod.
The invention adopts ricinoleic acid, urotropine,NOne of- (2-hydroxy-2-phenethyl) -acetamide and benzophenone oxime yl acetic acid benzophenone oxime ester is used as a secondary dispersing agent to further coat the surface of silver powder, so that the dispersibility of the precursor original silver powder is better and the adhesiveness with the inner wall of roller stainless steel is poor as much as possible, a good basic condition is provided for the subsequent preparation of flake silver powder with narrow particle size distribution, and the yield of the silver powder can be obviously improved. The dispersing agent ensures good compatibility of the conductive silver powder and the organic polymer system, influences the particle size distribution of the silver powder, influences the wrapping degree of the silver powder in the system and the molecular chain shrinkage capability in the curing process, and further influences the conductivity of the conductive film layer.
The invention is usedNThe synthetic route for- (2-hydroxy-2-phenethyl) -acetamide is shown below:
。
Nthe infrared spectrum of the- (2-hydroxy-2-phenethyl) -acetamide is shown in figure 7: the infrared spectrum adopts KBr tabletting,N- (2-hydroxy-2-phenethyl) -acetamide infrared spectroscopic analysis: 3456cm -1 （ν OH —ν NH Association), 3048cm -1 (benzene ring v) =CH ），2945cm -1 (methyl), 1672cm -1 (amide I band v) C=O ），1621cm -1 (primary amine, m ~ s), 1574cm -1 (amide II band, m-w), 1305cm -1 (amide III band), 1446cm -1 (methylene, s) 1213cm -1 （ν C—N ），752cm -1 ，691cm -1 (benzene ring, monosubstituted).
The synthetic route pattern of the benzophenone oxime yl acetate used in the invention is shown as follows:
。
the infrared spectrum of the benzophenone oxime yl acetate with rigid planar structure is shown in figure 8: infrared spectrum analysis is carried out by KBr tabletting and benzophenone oxime yl acetate infrared spectrum analysis: 3464.53cm -1 （ν NO —ν -CH ），3046.28cm -1 ，3027.92cm -1 (benzene ring v) =CH ），1656.91cm -1 （ν C=O ) (carbonyl-linked benzophenone oxime group is an electron withdrawing group, which makes absorption red shift), 1491.53cm -1 （ν C=N ），1446.22cm -1 ，1417.39cm -1 (vibration of benzene ring skeleton).
The invention adopts ricinoleic acid, urotropine,NThe conductive performance index of the powder and the slurry coated by the original silver powder of the precursor by- (2-hydroxy-2-phenethyl) -acetamide and benzophenone oxime yl acetate is shown in the following table.
。
According to the practical production experience of the low-temperature cured conductive silver paste, the influence of precursor original silver powder coated by different dispersing agents on the conductivity of the silver paste is explored on the basis of (conductive silver powder: organic carrier=65:35), wherein the organic carrier is 12% of Henschel 5836P resin, and the organic carrier is fully stirred and dispersed in 88% of dibasic ester solution.
Screen printing and curing conditions: a PET film (thickness 75 μm) is used as a base material, and standard circuits (line width 0.4 mm, line distance 1.01 mm and line length 1000 mm) are printed on the PET film (PET) through a 300-mesh polyester screen, and baking conditions are 135 ℃/30 min.
As shown in the table above, the precursor original silver powder coated by the secondary dispersing agent is not added, and the oleic acid and the polyethylene glycol 8000 have long straight chains, so that the compound dispersing agent has functional groups such as olefin, carboxyl, hydroxyl and the like, and the particle size distribution is narrower than that of the traditional original silver powder (D90 is smaller than 2.5 mu m).
The X-ray diffraction pattern of the original spherical silver powder and the flaky silver powder of the precursor of the invention is shown in fig. 9.
The particle size distribution of the precursor original silver powder coated by the ricinoleic acid is also narrower, but the particle size distribution has the characteristic of wall sticking, and the characteristics of lump formation, cold welding, poor dispersibility and the like are easy to exist in the ball milling process, so that the conductivity and the stability of the flake silver powder are further affected. Urotropine,NThe original silver powder of the precursor coated by the- (2-hydroxy-2-phenethyl) -acetamide has narrower particle size distribution, probably because the urotropine self structure is a rigid structure and is similar to a cage structure, has stronger steric hindrance effect,Nthe structure of- (2-hydroxy-2-phenethyl) -acetamide also has benzene rings, hydroxy groups, amide bonds, and the like. The original silver powder of the precursor coated by the benzophenone oxime yl acetate benzophenone oxime ester has narrower particle size distribution, and because the precursor has 4 benzene ring rigid plane structures, the precursor can be fully adsorbed and coated on the outer surface of the silver powder due to a plurality of nitrogen atoms, oxime ether and oxime ester groups, benzene ring structures and the like, and the silver powder has better dispersibility and narrower particle size distribution due to stronger steric hindrance effect, and the prepared silver paste has stronger hydrogen bonding effect with resin molecules in an organic polymerization system in the curing shrinkage process, so the curing shrinkage arrangement is tidy, and the high conductivity is shown.
In conclusion, the original silver powder of the precursor coated by the benzophenone oxime yl acetate benzophenone oxime ester has better dispersibility, the modified silver powder and the inner wall of the roller stainless steel show non-sticky characteristics, good basic conditions are provided for the subsequent preparation of the platy silver powder with narrow particle size distribution, meanwhile, the yield of the silver powder can be obviously improved and improved, and the benzophenone oxime yl acetate benzophenone oxime ester is selected as a secondary dispersing agent to continue the subsequent ball milling.
Example 1
Zirconia balls with the specification of 1mm are mixed according to the ball ratio of 1:8, adding the powder into a ball milling tank, wherein the mass of zirconia balls is about 120Kg, the mass of original silver powder of a precursor is about 15Kg, adding 5Kg of absolute ethyl alcohol into the powder, adding benzophenone oxime yl acetate benzophenone oxime ester ethanol solution (wherein the mass of a dispersing agent is about 96 g), and performing low-speed (30 r/min) ball milling for 120min through a ball mill to fully infiltrate the silver powder into an auxiliary agent, wherein the silver powder and the zirconia balls are fully and uniformly mixed, and no obvious agglomeration or powder wall sticking phenomenon occurs between the cylinder wall or the zirconia balls; after the silver powder and the zirconium balls are fully and uniformly mixed in an absolute ethyl alcohol system, the rotating speed is increased to 60r/min, sampling is carried out at regular time, ball milling is carried out once in the morning and evening respectively, the ball milling cover is opened for air release once, then ball milling is continued, and along with the extension of the ball milling time, the color of the silver powder slurry in the ball milling tank is changed from earthy yellow to silver gray; ball milling for 6h, sampling, analyzing and detecting: taking 1000mL of slurry in a ball milling tank, carrying out suction filtration by using a Buchner funnel, and putting a silver powder filter cake into a vacuum drying oven for drying treatment to obtain about 140g of flake silver powder, which is named as SF-YL6.
Example 2
The difference from example 1 is the ball milling 12h sample analysis test: taking 1000mL of slurry in a ball milling tank, carrying out suction filtration by using a Buchner funnel, and putting a silver powder filter cake into a vacuum drying oven for drying treatment to obtain about 140g of flake silver powder, which is named as SF-YL12.
Example 3
The difference from example 1 is the ball milling 18h sample analysis test: the slurry in the 1000mL ball milling tank is filtered by suction through a Buchner funnel, and the silver powder filter cake is put into a vacuum drying oven for drying treatment, so that about 140g of flake silver powder is prepared and named SF-YL18.
Example 4
The difference from example 1 is ball milling 24h sample analysis detection: taking slurry in a 1000mL ball milling tank, carrying out suction filtration by using a Buchner funnel, and putting a silver powder filter cake into a vacuum drying oven for drying treatment to obtain about 140g of flaky silver powder, which is named as SF-YL24; the scanning electron microscope diagram of SF-YL-24 is shown in fig. 3, the physical diagram of the original spherical silver powder and flake silver powder SF-YL-24 of the invention with the wall sticking condition is shown in fig. 4, and the physical diagram of the SF-YL-24 product is shown in fig. 5.
Example 5
The difference from example 1 is ball milling 30h sample analysis detection: the slurry in the 1000mL ball milling tank is filtered by suction through a Buchner funnel, and the silver powder filter cake is put into a vacuum drying oven for drying treatment, so that about 140g of flake silver powder is prepared and named SF-YL30.
According to the practical production experience of the low-temperature cured conductive silver paste, the influence of different ball milling time on the conductivity of the silver paste is explored on the basis of (conductive silver powder: organic carrier=65:35), wherein the organic carrier is 12% of hensmal 5836P resin, and the resin is fully stirred and dispersed in 88% of dibasic ester solution. Screen printing and curing conditions: a PET film (thickness 75 μm) is used as a base material, and standard circuits (line width 0.4 mm, line distance 1.01 mm and line length 1000 mm) are printed on the PET film (PET) through a 300-mesh polyester screen, and baking conditions are 135 ℃/30 min.
The results of the sheet property tests for different ball milling times of examples 1 to 5 are shown in the following table:
。
as can be seen from FIG. 6, the SF-YL24 plate-like silver powders were each at 2θStrong diffraction peaks exist near =38.1 °, 44.3 °, 64.5 °, 77.5 ° and 81.6 °, the corresponding diffraction planes are (111), (200), (220), (311) and (222), respectively, and each diffraction peak coincides with a peak on a standard silver card (JCPD, 04-0783). The diffraction pattern does not show other impurity diffraction peaks, which indicates that the silver in the prepared flake silver powder is simple substance silver with a face-centered cubic structure and has higher purity. Each diffraction peak in the graph is sharp in capping, which indicates that the silver powder has better crystallinity, and the particles of the flake silver powder consist of silver grains with good crystallinityA kind of electronic device. From the intensity of diffraction peaks of each crystal face, the intensities of the diffraction peaks of the (111) crystal faces are different, the peak of the (111) crystal face is higher, and the intensities of diffraction peaks of other crystal faces are lower, so that the silver powder has obvious preferred orientation growth in the growth process.
It can be found from the above table that the particle size distribution of the flake silver powder prepared in examples 1 to 5 is narrower, especially the D50 of the flake silver powder prepared in examples 1 to 4 is smaller than 2 μm, the conductivity is enhanced along with the extension of the ball milling time, when the ball milling is carried out for 24 hours, the flake silver powder becomes the lowest sheet resistance, along with the continuing of the ball milling, the conductivity is reduced, and the edge of the flake silver powder is possibly curled locally, the compactness of stacking layers during the curing of the conductive film layer is affected, so that the conductivity is reduced.
It will be apparent that the embodiments described above are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Claims (6)
1. A preparation method of high-conductivity flake silver powder for touch screen silver paste is characterized by comprising the following steps: the method comprises the following steps:
(1) Reduction of precursor original silver powder: pouring the sodium carbonate aqueous solution into the silver nitrate and polyvinylpyrrolidone K90 aqueous solution completely within 5min, and stirring for 3min at 300r/min after the addition is finished to prepare a silver carbonate suspension solution; pouring all the aqueous solution of ascorbic acid into the container within 1min, stirring for 3min at 350r/min, pouring the absolute ethanol solution of the dispersing agent A into the container, stirring for 5min at 350r/min, enabling the dispersing agent A to fully wrap the outer surfaces of the silver carbonate particles, and stopping stirring; wherein the mass ratio of the dispersant A is 6: 4-1: 1, pouring out supernatant after flocculent powder is completely settled, and cleaning the powder with pure water for a small amount of times until the conductivity is less than or equal to 20 mu S/cm; drying wet powder in a blast drying oven at 70 ℃ for 48 hours, crushing and sieving the dried powder, and obtaining precursor silver powder by the powder which is required to pass through a 200-mesh screen;
(2) Ball milling of flake silver powder: firstly, zirconia balls with the specification of 1mm are mixed according to the ball ratio of 1:8, adding the mixture into a ball milling tank, wherein the mass of zirconia balls is 120Kg, the mass of precursor original silver powder is 15Kg, adding 5Kg of absolute ethyl alcohol into the mixture, and adding a dispersing agent B, namely absolute ethyl alcohol solution, wherein the dispersing agent B is ricinoleic acid, urotropine,NOne of- (2-hydroxy-2-phenethyl) -acetamide and benzophenone oxime yl acetate benzophenone oxime ester, zirconia balls with the specification of 1mm are mixed according to the ball ratio of 1:8, adding the silver powder into a ball milling tank, wherein the mass of zirconia balls is 120Kg, the mass of original silver powder of a precursor is 15Kg, adding 5Kg of absolute ethyl alcohol into the ball milling tank, ball milling the absolute ethyl alcohol solution of a dispersing agent B by a ball mill for 120min at 30r/min, so that the silver powder is fully soaked in the auxiliary agent, the silver powder and the zirconia balls are fully and uniformly mixed, and no obvious agglomeration or powder wall sticking phenomenon exists; and (3) after the silver powder and the zirconium balls are fully and uniformly mixed in an absolute ethyl alcohol system, increasing the rotating speed to 60r/min, sampling at regular time, closing the ball milling for one time in the morning and evening respectively, opening the ball milling cover for discharging air for one time, continuing ball milling, changing the color of the silver powder slurry from earthy yellow to silver gray, and stopping ball milling to obtain the flaky silver powder.
2. The method for preparing the high-conductivity flake silver powder for the touch screen silver paste according to claim 1, wherein the preparation step of the absolute ethanol solution of the dispersing agent A is specifically as follows: 60-64 g of dispersing agent A is weighed into a small 1000mL beaker, 500mL of absolute ethyl alcohol is added, and the mixture is fully and uniformly stirred by a glass rod.
3. The method for preparing the high-conductivity flake silver powder for the touch screen silver paste according to claim 1, wherein the preparation step of the absolute ethyl alcohol solution of the dispersing agent B is specifically as follows: weighing 96-100 g of dispersing agent B in a 2500mL small beaker, adding 1000mL of absolute ethyl alcohol, and fully and uniformly stirring by using a glass rod.
4. The method for preparing the high-conductivity flake silver powder for the silver paste of the touch screen according to claim 1, 2 or 3, wherein the preparation steps of the silver nitrate and polyvinylpyrrolidone K90 aqueous solution are as follows: 21000g of silver nitrate and 25g of polyvinylpyrrolidone K90 are weighed, 75000mL of pure water is added, stirring is carried out for 25min at 200r/min until the silver nitrate and the polyvinylpyrrolidone K90 are completely dissolved, and the temperature of the system is controlled at 25+/-1 ℃.
5. The method for preparing high conductivity flake silver powder for touch screen silver paste according to claim 4, wherein the preparation step of the sodium carbonate aqueous solution comprises the following steps: 6555g anhydrous sodium carbonate is weighed, 75000mL pure water is added, stirring is carried out for 15min at 200r/min until the sodium carbonate is completely dissolved, and the temperature of the system is controlled at 25+/-1 ℃.
6. The method for preparing high conductivity flake silver powder for touch screen silver paste according to claim 5, wherein the step of preparing the ascorbic acid aqueous solution comprises the following steps: 13200g of ascorbic acid is weighed, 150000mL of pure water is added, stirring is carried out for 15min at 200r/min, the temperature of the system is controlled at 25+/-1 ℃.
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