A kind of high tap density silver powder and its preparation method and application

Abstract

The present invention discloses a high-tap-density silver powder, its preparation method, and application. The silver powder preparation method comprises the following steps: dispersing a silver salt in an alcoholamine solution, followed by reaction with an organic amine solution to produce the silver particles. The silver particle preparation method of the present invention can produce spherical powders of varying particle sizes. Silver paste prepared from spherical silver powders typically exhibits superior fluidity, with large and small silver particles filling each other, ensuring sufficient contact area between the silver powders and meeting the performance requirements of positive silver pastes.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a high-tap-density silver powder and a preparation method and application thereof. Background Art

[0002] Silver powder has excellent electrical, thermal, and corrosion resistance properties and is widely used in the electronics, aerospace, and materials industries. In recent years, the application of silver powder in the photovoltaic field has been increasing. Silver powder is used as a conductive material in heterojunction batteries. The application of high-temperature / low-temperature silver paste technology has made silver powder more widely used in this field. A series of parameters such as the morphology, particle size, and tap density of silver powder are related to the printing performance of the conductive paste, which in turn determines the photovoltaic conversion efficiency of solar cells. However, silver powder currently suffers from poor dispersibility and low tap density, resulting in poor printability after being made into silver paste. Therefore, the preparation of micron silver powder with good dispersibility and high tap density is one of the key factors in improving the photovoltaic conversion efficiency of solar cells.

[0003] At present, the only method for preparing silver powder that can be mass-produced in China is the liquid-phase reduction method, which uses a peristaltic pump to add reducing liquid and dispersing liquid to the silver salt solution in a timed and quantitative manner to prepare silver powder. The dispersion of the silver powder particles produced by this method is difficult to control, and the tap density is generally low. Summary of the Invention

[0004] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, the present invention aims to provide a silver powder with high tap density, a preparation method thereof, and an application thereof.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The first aspect of the present invention provides a method for preparing silver particles, comprising the following steps: dispersing a silver salt in an alcohol amine solution, and then reacting with an organic amine solution to obtain the silver particles.

[0007] In the present invention, the reduction rates of the silver salt by the alcoholamine solution and the organic amine solution are different, thereby producing silver powders of different particle sizes. The small-particle silver powder fills the gaps between the larger-particle silver powder, making the gaps between the silver powder particles smaller, resulting in a more compact overall structure of the silver powder, thereby increasing the tap density of the silver powder. At the same time, compared with large or small-particle silver powder alone, the silver powder of different particle sizes can accelerate sintering during the sintering process, while the larger-particle silver powder can still maintain a good shape at a higher temperature, thereby improving the structural stability of the sintered body and improving the overall sintering performance of the silver powder. On the other hand, the alcoholamine solution acts as a co-reducing agent and the organic amine acts as the main reducing agent. The combination of the two can increase the rate of the reduction reaction, thereby accelerating the generation rate of the silver powder. Furthermore, the alcoholamine solution itself is weakly alkaline. The first addition of the alcoholamine solution can provide an alkaline environment for the subsequent addition of the organic amine solution and its reaction with the silver salt, which is conducive to the reduction reaction of the organic amine and the silver salt.

[0008] In some embodiments of the present invention, the molar ratio of the alcoholamine compound in the alcoholamine solution to the silver ions in the silver salt is 0.05 to 5:1, such as 0.1:1, 0.5:1.0, 1:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, 4.5:1, etc.; if the silver ion concentration is too high, it may be difficult to effectively disperse; the addition of alcoholamine can increase the rate of the reduction reaction between the organic amine solution and the silver salt, accelerate the generation rate of silver powder, improve the purity of the silver powder, and reduce the occurrence of side reactions.

[0009] In some embodiments of the present invention, the molar concentration of the silver salt is controlled so that its molar concentration before adding the organic amine solution is 0.008-5.0 mol / L, such as 0.1 mol / L, 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, and 4.5 mol / L.

[0010] In some embodiments of the present invention, the molar ratio of the organic amine compound in the organic amine solution to the silver ions in the silver salt is 0.005-0.15:1, such as 0.008:1, 0.01:1, 0.03:1, 0.05:1, 0.08:1, 0.1:1, 0.12:1, etc.

[0011] In some embodiments of the present invention, the silver salt includes at least one of silver sulfate, silver nitrate, silver oxide, silver acetate, silver oxalate, silver phosphate, silver hexafluorophosphate, silver tetrafluoroborate, silver hexafluoroarsenate, silver chromate, silver chloride, silver bromide, silver iodide, silver carbonate, silver bicarbonate, silver benzoate, silver tartrate, silver laurate, silver perchlorate, and silver perbromide.

[0012] In some embodiments of the present invention, the alcoholamine solution includes a solution of at least one of diethanolamine, methyldiethanolamine, ethanolamine, dimethylethanolamine, diglycolamine, isopropanolamine, triisopropanolamine, oleic acid diethanolamide, stearic acid diethanolamide, lauric acid diethanolamide and octadecyl diethanolamine.

[0013] In some embodiments of the present invention, the organic amine solution includes a solution of at least one of triethylamine, N,N-diisopropylethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, cyclohexylamine, N,N-dimethyloctylamine, N,N-dimethyldecylamine, tri(3,6-dioxaheptyl)amine, and octylamine.

[0014] In some embodiments of the present invention, the pH of the organic amine solution is controlled to be 10-13, such as 10.5, 11, 11.5, 12, 12.5, etc.; the pH value of the organic amine solution can be controlled within this range by using a pH regulator such as at least one of monoethanolamine, triethanolamine, and sodium hydroxide, so as to facilitate the reduction reaction. The particle size of the silver powder precipitated by the reduction decreases with the increase of the reaction pH.

[0015] In some embodiments of the present invention, the reaction is a hydrothermal reaction; the reaction temperature of the reaction is 75-235°C, such as 75-170°C, 90-210°C, 90-155°C, 100-200°C, 120-180°C, etc.; the reaction time of the reaction is 0.5-12h, such as 1-10h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, etc.; the temperature of the hydrothermal reaction can be controlled by methods known in the art, and a common method is to place the hydrothermal reactor in an oven for temperature control; to improve the uniformity of the reaction, the hydrothermal reaction can be carried out under stirring, and the stirring rate can be controlled at 200-500rpm.

[0016] In the method for producing silver powder of the present invention, the yield, purity, and particle size of the silver powder can be controlled by controlling the feed ratio of the reactants, such as the alcohol amine solution and the organic amine solution, in the hydrothermal reaction, or by controlling the temperature and time of the hydrothermal reaction, thereby regulating the tap density of the silver powder.

[0017] In the method for manufacturing silver powder of the present invention, the alcoholamine solution and the organic amine solution are used in combination, which can accelerate the reduction rate of the organic amine to the silver salt without causing the reaction rate to be too fast. Therefore, there is no need to strictly control the pH or temperature of the mixed solution or base solution of the alcoholamine solution and the silver salt; there is also no need to control the temperature of the organic amine solution. After the organic amine solution is added, the system does not immediately undergo a hydrothermal reaction or the reaction rate is too fast, resulting in an uncontrolled reaction process and difficulty in effectively controlling the particle size of the silver powder product in the initial stage. After the organic amine solution is added, an additional stirring procedure can be performed before the hydrothermal reaction to improve the reaction uniformity, thereby easily controlling the particle size of the silver powder product.

[0018] In the method for manufacturing silver powder of the present invention, in order to improve the uniformity of the silver salt reaction and the dispersibility of the reduced and precipitated silver powder, the silver salt dispersion and silver powder are treated with a dispersant. Specifically, the silver salt is dispersed in an alcoholamine solution, the dispersant is added, and then the silver salt is reacted with an organic amine solution. The mass ratio of the dispersant to the silver atoms in the silver salt is (0.05-8):1. As the dispersant, a hydrophobic dispersant is preferably used, and at least one of polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, sodium citrate, sodium lauryl sulfate, hexadecyltrimethylammonium bromide, gelatin, methylcellulose, citric acid, Tween 60, propionic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, acrylic acid, oleic acid, linoleic acid, arachidonic acid, and ricinoleic acid can be used. By using the above-mentioned dispersant, it is possible to balance the adsorption of the dispersant to silver and the dispersibility between silver particles, thereby preventing the agglomeration of silver powder particles.

[0019] In the silver powder manufacturing method of the present invention, after the hydrothermal reaction is completed to obtain a solid-liquid mixture, the solid-liquid mixture is washed and recovered. In the washing and recovery step, the slurry is dehydrated and the silver powder filter cake is washed. The washing in the washing and recovery step can be performed, for example, using pure water. Dehydration in the washing and recovery step can be performed, for example, by decantation or filter pressing. The end point of the washing can be determined using the conductivity of the washing water. Specifically, the washing can be determined to be complete when the conductivity of the washing water is below a specified value, such as when the conductivity reaches 0.5 mS / m or less.

[0020] After the cleaning and recovery process is completed, a drying process is performed to dry the recovered silver powder filter cake. A vacuum dryer or airflow dryer can be used for the drying process. During the drying process, the filter cake and the silver powder from the drying process can be blown with a high-pressure air stream, or the filter cake and the silver powder from the drying process can be added to a mixer with a stirring rotor or a grinder with a grinding rotor for stirring. This imparts a dispersing force to the filter cake and the silver powder from the drying process, thereby promoting dispersion and drying.

[0021] In the drying step, the temperature of the silver powder may be set to 70° C. or lower. If the temperature of the silver powder exceeds 70° C., the silver fine particles in the silver powder may be sintered.

[0022] During or after the drying process, crushing, pulverizing, or classification operations can be performed to adjust the particle size distribution of the silver powder. The pulverization operation can be performed using an air flow or mechanical pulverizer. The classification operation can be performed using a classification rotor, cyclonic air classification, inertial classification, or sieving.

[0023] The second aspect of the present invention provides silver powder produced by the method for preparing silver particles.

[0024] In some embodiments of the present invention, the average particle size of the silver powder is 1.0-3.1 μm, such as 1.1-2.99 μm, 1.1-2.5 μm, 1.1-2.2 μm, etc.

[0025] In some embodiments of the present invention, the silver powder has a cumulative 50% particle size (D50) of 3.0 μm or less, such as 2.5 μm or less, 2.0 μm or less, 1.8 μm or less, or 1.7 μm or less in the volume-based particle size distribution measured by a laser diffraction scattering particle size distribution measuring apparatus; and a cumulative 100% particle size (D100) of 20 μm or less, such as 18 μm or less, 15 μm or less, 12 μm or less, 10 μm or less, or 9 μm or less.

[0026] The volume-based particle size distribution of the silver powder adopts the particle size distribution measured by a laser diffraction scattering particle size distribution measuring device. In this embodiment, the following description is given of the case where the PSA particle size distribution measuring device PSA1090 (hereinafter simply referred to as the particle size distribution measuring device) manufactured by Anton Paar is used as the laser diffraction scattering particle size distribution measuring device. The particle size distribution of the silver powder can be obtained by dispersing it in a prescribed dispersion medium, i.e., by wet measurement. In this embodiment, 0.1 g of silver powder is added to 40 mL of isopropyl alcohol as a dispersion medium, and an ultrasonic homogenizer (manufactured by Nippon Seiki Co., Ltd., US-150T; 19.5 kHz, tip diameter 18 mm) is used to disperse it for 2 minutes to prepare a dispersion liquid, and then the dispersion liquid is provided to the particle size distribution measuring device to measure the particle size distribution of the silver powder.

[0027] In this specification, the term "cumulative 50% particle diameter" with respect to particle size distribution refers to the so-called median diameter. The cumulative 50% particle diameter is the diameter at which the volume-based accumulation of particles from the smaller particle size in the particle size distribution reaches 50%. Similarly, the cumulative 100% particle diameter is the diameter at which the volume-based accumulation of particles from the smaller particle size in the particle size distribution reaches 100%. Hereinafter, the cumulative 50% and cumulative 100% particle diameters, measured on a volume basis, may be referred to as D50 and D100, respectively.

[0028] In some embodiments of the present invention, in the volume-based particle size distribution of the silver powder, the ratio of the difference obtained by subtracting the cumulative 10% particle size from the cumulative 90% particle size to the cumulative 50% particle size (Span, particle size distribution width) can be 2.20 or less, such as less than 2.10, less than 2.08, less than 2.01, or less than 2.00. The smaller the Span and the smaller the difference, the narrower the particle size distribution of the silver powder, the better its dispersibility, and the higher the overall tap density of the formed silver powder.

[0029] In some embodiments of the present invention, the tap density of the silver powder is 5.80 g / cm3 Above, such as 5.85g / cm 3 Above, 6.00g / cm 3 Above, 6.30g / cm 3 Above, 6.50g / cm 3 Above, 6.60g / cm 3 Above, 6.60~7.10g / cm 3 , 6.60~7.0g / cm 3 The tap density of silver powder is the apparent density of the silver powder in a container after a predetermined amount of silver powder is weighed and placed in a container of a predetermined capacity, and the container is dropped a predetermined number of times at a predetermined height (hereinafter referred to as "after tapping"). It is calculated by dividing the weight of the silver powder in the container by the apparent volume of the silver powder in the container.

[0030] In some embodiments of the present invention, the tap density of the silver powder is a value obtained as follows: using a tap density measuring device (produced by Shibayama Scientific Co., Ltd., volume specific gravity measuring device SS-DA-2), 50 g of silver powder is weighed and placed in a container (50 mL test tube), and the container is tapped 3,000 times at a vibration frequency of 200 (i.e., 200 vibrations per minute). The weight of the silver powder (50 g) is divided by the apparent volume (cm) of the silver powder after tapping. 3 It should be noted that the unit of tap density is "g / cm 3 "express.

[0031] In some embodiments of the present invention, the silver powder is spherical silver powder, and spherical means that when the silver powder is observed under a scanning electron microscope (SEM), the particles are spherical or approximately spherical, and the sphericity of 100 particles is less than 1.5, wherein the sphericity refers to the ratio of the longest diameter to the shortest diameter when the particles are observed through SEM photos.

[0032] The third aspect of the present invention provides a conductive paste comprising silver powder produced by the above-mentioned method for preparing silver particles.

[0033] In some embodiments of the present invention, the conductive paste comprising the silver powder is prepared by dispersing the silver powder in a resin (binder) serving as a base material and a solvent.

[0034] In some embodiments of the present invention, the conductive paste includes the silver powder, a resin, and a solvent.

[0035] In some embodiments of the present invention, examples of resins used in preparing the conductive paste include epoxy resins, acrylic resins, polyester resins, polyimide resins, polyurethane resins, phenoxy resins, silicone resins, and ethyl cellulose. Two or more resins may be used simultaneously.

[0036] In some embodiments of the present invention, an example of a solvent, i.e., a dispersion medium, used to prepare the conductive paste is terpineol, butyl carbitol, butyl carbitol acetate, or texanol. Two or more solvents may be used simultaneously.

[0037] In some embodiments of the present invention, the conductive paste may contain ingredients other than those mentioned above, such as glass frit, a dispersant, a surfactant, and a viscosity modifier.

[0038] In some embodiments of the present invention, the conductive paste can be prepared, ie, dispersed and kneaded using ultrasonic dispersion, a disperser, a three-roll mill, a ball mill, a bead mill, a biaxial kneader, a rotary mixer, or the like.

[0039] In some embodiments of the present invention, the conductive paste using the silver powder of the present invention is suitable for forming a conductive film, that is, forming a conductive pattern or an electrode on a substrate. For example, it can be applied directly on various substrates such as silicon wafers for solar cells, films for touch panels, and glass for EL elements, or on a film further provided with a transparent conductive film as needed to form a conductive film. The conductive film obtained using the conductive paste of the present invention is suitable for use in, for example, collector electrodes of solar cell units, external electrodes of chip-type electronic components, RFID, electromagnetic wave shielding, vibrator bonding, membrane switches, electroluminescence, and other electrodes or electrical wiring applications.

[0040] In some embodiments of the present invention, the conductive paste is printed on the substrate by, for example, screen printing, offset printing, photolithography, etc., so that a conductive film having a desired shape can be formed.

[0041] The beneficial effects of the present invention are:

[0042] 1. The preparation method of silver particles of the present invention can produce spherical powders of different particle sizes. The silver paste prepared from spherical silver powder usually has better fluidity. Large-size and small-size silver particles fill each other, ensuring sufficient contact area between the silver powders, which can meet the requirements of the positive silver paste for the performance of the silver powder.

[0043] 2. The preparation method of silver particles of the present invention can produce spherical powders of different particle sizes, which can be applied to high and low temperature sintering silver paste. When sintering, compared with single large particles or small particles, silver powders of different particle sizes can cooperate with each other during the sintering process. Small particles can accelerate the sintering process, while large particles can better maintain their shape at higher temperatures, thereby improving structural stability and improving the overall sintering performance. Therefore, compared with single large powder and single small powder, mixed large and small powders have sintering advantages and are suitable for solar cell manufacturing.

[0044] 3. The method for preparing silver particles of the present invention is an environmentally friendly method that can be carried out at relatively low temperature and pressure, and the by-products are generally easy to handle. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a SEM image of the silver powder obtained in Example 1 of the present invention.

[0046] Figure 2 This is a SEM image of the silver powder obtained in Example 2 of the present invention.

[0047] Figure 3 This is a SEM image of the silver powder prepared in Example 3 of the present invention.

[0048] Figure 4 This is a SEM image of the silver powder obtained in Example 4 of the present invention.

[0049] Figure 5 This is a SEM image of the silver powder obtained in Example 5 of the present invention.

[0050] Figure 6 This is the SEM image of the silver powder obtained in Example 6 of the present invention.

[0051] Figure 7 This is the SEM image of the silver powder obtained in Comparative Example 1 of the present invention.

[0052] Figure 8 This is the SEM image of the silver powder obtained in Comparative Example 2 of the present invention.

[0053] Figure 9 This is the SEM image of the silver powder obtained in Comparative Example 3 of the present invention.

[0054] Figure 10 This is the SEM image of the silver powder prepared in Comparative Example 4 of the present invention.

[0055] Figure 11 This is the SEM image of the silver powder obtained in Comparative Example 5 of the present invention. DETAILED DESCRIPTION

[0056] The present invention is further described in detail below using specific examples. Unless otherwise specified, the raw materials, reagents, and apparatus used in the examples and comparative examples are available from conventional commercial sources or by conventional methods. Unless otherwise specified, all experimental or testing methods are conventional in the art.

[0057] Example 1

[0058] This embodiment prepares silver particles, and the specific process is as follows:

[0059] 1. Preparation before the experiment:

[0060] The alcohol amine solution uses dimethylethanolamine with an active ingredient content of 98%, and the molar ratio of dimethylethanolamine to Ag is 2.25:1;

[0061] The dispersant used was 98.5% oleic acid, the mass of which was 6.14% of the mass of silver ions;

[0062] The organic amine solution selected octylamine with an active ingredient content of 98%, and the molar ratio of octylamine to Ag was 0.0798:1;

[0063] Preparation of pH adjuster solution: 40% mass fraction of sodium hydroxide solution, the molar number of sodium hydroxide is approximately 0.58% of the molar number of silver ions

[0064] 2. Weigh 2 g of silver carbonate (silver ion molar weight is 0.0145 mol) and add it to the inner container of the hydrothermal reactor. Then add 2.468 g of dimethylethanolamine and 0.1246 g of oleic acid. Place the inner container on a magnetic stirrer and stir at 300 rpm until it is evenly stirred to obtain a base solution.

[0065] 3. Add 0.0084 g of sodium hydroxide solution to 0.152 g of octylamine and adjust the pH of the octylamine to 12 to obtain a reducing agent solution;

[0066] 4. Pour the reducing agent solution into the inner container of the hydrothermal reactor and mix it with the base liquid. Turn on the magnetic stirring at 300 rpm and stir for 10 minutes. Then put the inner container into the hydrothermal reactor and place it in a 105°C oven for 3 hours.

[0067] 5. After the reaction, wait until the hydrothermal kettle cools to room temperature (25°C), add deionized water and alcohol to the inner tank of the hydrothermal kettle after the reaction, wash and dry (drying temperature is 55°C, drying time is 2.5h) to obtain silver particles.

[0068] Example 2

[0069] Silver particles were prepared in this embodiment. The preparation method thereof was different from that in embodiment 1 in that the molar ratio of dimethylethanolamine to Ag was 4:1.

[0070] Example 3

[0071] In this embodiment, silver particles were prepared. The preparation method thereof was different from that in Example 1 in that the initial molar amount of silver ions was 4.5 mol, that is, the molar ratio of dimethylethanolamine to Ag was 0.00725:1, and the molar ratio of octylamine to Ag was 0.00025:1.

[0072] Example 4

[0073] Silver particles were prepared in this embodiment. The preparation method thereof was different from that in embodiment 1 in that the mass of oleic acid was 1.8% of the mass of silver ions.

[0074] Example 5

[0075] Silver particles were prepared in this embodiment. The preparation method thereof was different from that in embodiment 1 in that the molar ratio of octylamine to Ag was 0.12:1.

[0076] Example 6

[0077] Silver particles were prepared in this embodiment. The difference between the preparation method and that in embodiment 1 is that the molar ratio of dimethylethanolamine to Ag is 8:1.

[0078] Example 7

[0079] Silver particles were prepared in this embodiment. The preparation method thereof differed from that in embodiment 1 in that the organic amine solution used was cyclohexylamine having an active ingredient content of 99%, and the molar ratio of cyclohexylamine to Ag was 0.0926:1.

[0080] Example 8

[0081] Silver particles were prepared in this embodiment. The preparation method thereof was different from that in Example 1 in that the alcoholamine solution used was triisopropanolamine with an active ingredient content of 95%, and the molar ratio of triisopropanolamine to Ag was 2:1.

[0082] Comparative Example 1

[0083] This comparative example prepared a silver powder, and the specific process was as follows:

[0084] 1. Preparation before the experiment is the same as in Example 1;

[0085] 2. Weigh 2 g of silver carbonate (silver ion molar amount is 0.0145 mol) and add it to the inner liner of the hydrothermal reactor. Then add 2.468 g of dimethylethanolamine and 0.1246 g of oleic acid. Place the inner liner on a magnetic stirrer and stir at 300 rpm until it is evenly stirred to obtain a base liquid. After stirring at 300 rpm for 10 minutes, the inner liner is placed in the hydrothermal reactor and placed in an oven at 105°C for 3 hours.

[0086] 3. After the reaction, wait until the hydrothermal kettle cools to room temperature (25°C), add deionized water and alcohol to the inner tank of the hydrothermal kettle after the reaction, wash and dry (drying temperature is 55°C, drying time is 2.5h) to obtain silver powder.

[0087] Comparative Example 2

[0088] This comparative example prepared a silver powder, and the specific process was as follows:

[0089] 1. Preparation before the experiment is the same as in Example 1;

[0090] 2. Weigh 2 g of silver carbonate (silver ion molar weight 0.0145 mol) and add it to the inner container of the hydrothermal reactor; add 0.0084 g of sodium hydroxide solution to 0.152 g of octylamine and adjust the pH value of octylamine to 12 to obtain a reducing agent solution; add the reducing agent solution and 0.1246 g of oleic acid to the inner container of the hydrothermal reactor; start magnetic stirring at 300 rpm and stir for 10 minutes, then place the inner container in the hydrothermal reactor and place it in a 105°C oven for 3 hours;

[0091] 3. After the reaction, wait until the hydrothermal kettle cools to room temperature (25°C), add deionized water and alcohol to the inner tank of the hydrothermal kettle after the reaction, wash and dry (drying temperature is 55°C, drying time is 2.5h) to obtain silver powder.

[0092] Comparative Example 3

[0093] In this comparative example, a silver powder was prepared. The difference between the preparation method and that of Example 1 lies in that hydrazine hydrate was used to replace the octylamine in Example 1, and the molar ratio of hydrazine hydrate to Ag was 0.0798:1.

[0094] Comparative Example 4

[0095] In this comparative example, a silver powder was prepared. The difference between the preparation method and that of Example 1 lies in that cyclohexylamine was used to replace the dimethylethanolamine in Example 1, and the molar ratio of cyclohexylamine to Ag was 2.25:1.

[0096] Comparative Example 5

[0097] In this comparative example, a silver powder was prepared. The preparation method thereof was different from that of Example 1 in that diethanolamine was used instead of octylamine in Example 1, and the molar ratio of diethanolamine to Ag was 0.0798:1.

[0098] Test Case

[0099] The obtained silver powder was characterized, and the results are shown in Table 1:

[0100] Table 1

[0101] Group Average particle size (μm) D50(μm) D100(μm) Span <![CDATA[Tap density (g / cm 3 )]]> Example 1 1.332 1.12 5.3 1.84 6.95 Example 2 1.13 0.9962 4 1.852 6.92 Example 3 1.2947 1.088 5.4 1.865 6.65 Example 4 1.87 1.41 8 1.997 6.85 Example 5 2.11 1.63 8 1.95 6.62 Example 6 3.06 2.426 15 2.13 5.89 Comparative Example 1 0.71 0.48 3 2.21 5.68 Comparative Example 2 1.88 1.68 12 2.08 5.87 Comparative Example 3 10.032 8.487 36 1.628 5.08 Comparative Example 4 4.428 3.286 21 2.231 5.47 Comparative Example 5 3.577 2.681 18 2.254 5.48

[0102] Figures 1 to 11 The SEM images of the silver powders obtained in Examples 1 to 6 and Comparative Examples 1 to 5 are shown in Table 1 and Figures 1 to 11 It can be seen that the silver powders of Examples 1 to 6 have good dispersibility, a narrow particle size distribution width (Span), good particle fluidity, and a high tap density. Although the silver powder in Example 6 is slightly agglomerated and the overall tap density of the silver powder is reduced, there is still enough small-sized silver powder to fill between the large silver powder particles, and the tap density can still reach 5.89 g / cm 3 , and it is not easy to agglomerate in the subsequent conductive paste preparation process; Comparative Example 1 Figure 7 There is no big or small powder in the middle, all are small powder, and the tap density is low; Comparative Example 2 Figure 8 It shows that there is too much large powder and almost no small powder. In the process of preparing the slurry, due to the lack of small powder filling, the large powder is easy to agglomerate, its fluidity is poor, and its performance is reduced; in Comparative Example 3, the reducing property of the reducing agent used is very strong, resulting in a significant increase in the average particle size, D50, and D100 of the product silver powder, and a decrease in the overall tap density of the silver powder; in Comparative Examples 4 and 5, only organic amine solution or alcohol amine solution is used for reduction before and after. Although large and small powders are also produced in the product silver powder, the particle size of both small and large powders is significantly enlarged, the particles are obviously agglomerated, the powder dispersibility is poor, and the tap density is also low.

[0103] The silver particles of the present invention can be applied to conductive silver paste. First, the tap density has an important influence on the thick film microstructure of the conductive silver paste. The silver powder particles with high tap density in Examples 1 to 6 are more likely to form a uniformly dispersed state in the slurry, which can reduce the aggregation between the silver powder particles, thereby obtaining a better microstructure. When preparing a thick film, the uniform dispersion of the silver powder particles can make the film layer denser, reduce the porosity, and improve the conductive performance. However, the silver powder particles with low tap density in Comparative Examples 1 to 5 are easy to aggregate together to form an uneven microstructure, resulting in an increase in the porosity of the film layer, thereby reducing the conductive performance. Secondly, the tap density will also affect the electrical properties of the conductive silver paste. The silver powder particles with high tap density in Examples 1 to 6 have better conductivity because a high tap density means a larger contact area between the silver powder particles and a shorter electron conduction path. In addition, silver powder particles with high tap density are also more likely to form a connected network in the film layer, which can provide more conductive paths and further improve the conductive performance. The tap density of the silver powder will also affect the rheological properties of the conductive silver paste. Rheological properties refer to the physical characteristics of the conductive silver paste during processing, such as viscosity and fluidity. The silver powder particles with high tap density in Examples 1-6 disperse more evenly in the paste, reducing the paste's viscosity, improving fluidity, and facilitating processing and molding. In contrast, the silver powder particles with low tap density in Comparative Examples 1-5 tend to aggregate, resulting in higher viscosity, reducing the paste's fluidity and increasing processing difficulty.

[0104] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing silver particles, characterized in that: The following steps are involved: Dispersing the silver salt in an alcohol amine solution, adding a dispersant, and then reacting with an organic amine solution to obtain the silver particles; The molar ratio of the alcoholamine compound in the alcoholamine solution to the silver ions in the silver salt is 0.05 to 5:1; The molar ratio of the organic amine compound in the organic amine solution to the silver ions in the silver salt is 0.005-0.15:1; Controlling the pH of the organic amine solution to be 10-13; The alcoholamine solution includes a solution of at least one of diethanolamine, methyldiethanolamine, ethanolamine, dimethylethanolamine, diglycolamine, isopropanolamine, triisopropanolamine, oleic acid diethanolamide, stearic acid diethanolamide, lauric acid diethanolamide and octadecyl diethanolamine; The organic amine solution includes a solution of at least one of triethylamine, N-ethyldiisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, cyclohexylamine, dimethyloctylamine, dimethyldecylamine, tri(3,6-dioxaheptyl)amine, and octylamine; The silver particles meet the following conditions: (I) an average particle size of 1.0 to 3.1 μm; (II) a D50 of 3.0 μm or less; (III) a D100 of 20 μm or less; (IV) a Span of 2.20 or less; and (V) a tap density of 5.80 g / cm 3 above.

2. The method for preparing silver particles according to claim 1, wherein: The dispersant includes at least one of polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, sodium citrate, sodium lauryl sulfate, cetyltrimethylammonium bromide, gelatin, methylcellulose, citric acid, Tween 60, propionic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, acrylic acid, oleic acid, linoleic acid, arachidonic acid, and ricinoleic acid.

3. The method for preparing silver particles according to claim 1, wherein: The reaction is a hydrothermal reaction.

4. The method for preparing silver particles according to claim 1, wherein: The reaction temperature of the reaction is 75-235°C.

5. The method for preparing silver particles according to claim 1, wherein: The reaction time of the reaction is 0.5 to 12 hours.

6. The method for preparing silver particles according to claim 1, wherein: The reaction is carried out under stirring at a stirring rate of 200-500 rpm.

7. Silver particles obtained by the method for preparing silver particles according to any one of claims 1 to 6.

8. The silver particles according to claim 7, wherein: The silver particles meet the following conditions: (I) Average particle size of 1.0 to 3.1 μm; (II) D50 is less than 3.0 μm; (III) D100 is less than 20 μm; (IV) Span is less than 2.20; (V) Tap density is 6.00g / cm 3 above.

9. A conductive paste comprising silver particles produced by the method for producing silver particles according to any one of claims 1 to 6; or the silver particles according to claim 7 or 8.

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