WO2020106120A1 - Method for preparing monodispersed silver powder - Google Patents

Abstract

The method for preparing a silver powder according to the present invention relates to a method for preparing a silver powder, comprising: a reaction solution preparation step (S21) for preparing a first reaction solution comprising a silver ion, ammonia (NH3), and an organic acid alkali metal salt, and a second reaction solution comprising a reducing agent; and a salt reduction step (S2) comprising a deposition step (S22) for acquiring a silver powder by allowing the first reaction solution and the second reaction solution to free fall in the air and react, wherein a monodispersed silver powder having a SEM size of 0.3-1.3 μm can be acquired by depositing the silver powder through the mid-air free fall method.

Description

Manufacturing method of monodisperse silver powder

The present invention relates to a method for manufacturing silver powder contained in a conductive paste used in electronic components, such as an electrode for a solar cell, an internal electrode of a multilayer capacitor, and a conductor pattern of a circuit board, and a conductive paste containing silver powder.

Silver is widely used as an electrode material in the field of electrical and electronic due to its inherent high electrical conductivity and oxidation stability. In particular, in recent years, with the development of printed electronics technology that directly forms a desired type of circuit, an industry for conductive pastes in which silver is powdered and processed into a paste or ink form has been developed. Conductive pastes using silver powder have various uses such as plasma display panel (PDP), solar cell front electrode or rear electrode, and touch screen, as well as traditional conductive electrodes such as through-holes, die-bonding, and chip parts. This is an increasing trend.

Conventionally, in the production of silver powder, a wet reduction process in which an aqueous silver nitrate complex is prepared with an aqueous silver nitrate solution and ammonia water and an organic reducing agent is added thereto has been applied. These silver powders are used for forming electrodes or circuits such as chip parts, plasma display panels, and solar cells.

In particular, silver powder for solar cell electrodes often has non-uniform nucleation during synthesis, agglomeration of powders due to difference in reaction rate, and wide particle size distribution, which causes defects due to disconnection and short circuit between electrodes in the printing process after paste preparation. .

In general, in the reaction of the dumping method, heterogeneous growth is achieved due to the rate and composition of the reducing agent, mismatch between nucleation-growth, and the silver mirror reaction on the outer wall of the reactor.To compensate for this, dispersants such as PVP and gelatin are applied, but powder It has disadvantages such as problems such as an increase in the organic matter content and a decrease in electrode characteristics.

The present invention is to solve the above problems to solve the agglomeration of the silver powder and to provide an economical manufacturing method capable of mass-producing sub-micro grade fine powder.

However, the objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

The present invention is a reaction solution production step (S21) for preparing a first reaction solution containing a silver ion, ammonia (NH 3) and an organic acid alkali metal salt and a second reaction solution containing a reducing agent; And a silver salt reduction step (S2) including a precipitation step (S22) of reacting the first reaction solution and the second reaction solution while freely falling in the air to obtain silver powder.

In addition, in the precipitation step (S22), the first reaction solution and the second reaction solution are respectively supplied at a specific height of the reaction tank through a supply line capable of adjusting the flow rate while the first reaction solution and the second reaction solution are freely dropped. It is characterized by reacting.

In addition, the height (H) to which the first reaction solution and the second reaction solution are supplied is characterized in that the reaction tank and the reaction temperature of the reaction tank are 30 to 50 ° C.

In addition, the alkali metal salt of the organic acid is acetic acid (CH3COOH), formic acid (CH2O2), oxalic acid (C2H2O4), lactic acid (C3H6O3), citric acid (C6H8O7), fumaric acid (C4H4O4), citric acid (C6H8O7), butyric acid (C4H8O2), butyric acid (C4H8O2) ) And any one or more organic acids selected from the group consisting of uric acid (C5H4N4O3) and lithium (Li), sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg). Characterized in that it comprises a salt formed by any one or more metals.

In addition, when the silver ion is added as a 500 g / L silver nitrate (AgNO3) aqueous solution, the organic acid alkali metal salt is characterized in that it is added at a ratio of 300 to 600 g with respect to 1600 ml of the 500 g / L silver nitrate (AgNO3).

In addition, the present invention is a silver powder produced by the above manufacturing method, wherein the silver powder has a SEM size (DSEM) of 03 to 13 μm and a PSA size (D50) of 01 to 20 μm.

In addition, the silver powder is characterized in that the span value calculated by the following formula (span value) is 10 or less.

 Span value = (D90-D10) / D50

(Here, D90, D10, and D50 mean particle sizes corresponding to 90%, 10%, and 50% of the maximum value in the cumulative distribution of solid particle size, respectively.)

In addition, the silver powder is characterized in that the aggregation degree calculated by the ratio (D50 / DSEM) of PSA size (D50, μm) to SEM size (DSEM, μm) is 17 or less.

The present invention can obtain a monodispersed silver powder having a size of 03 to 13 μm (SEM size) by precipitating silver powder by an air-free fall method, and can prevent agglomeration from occurring, and the amount of organic acid alkali metal salt added and the reaction temperature By controlling the, even if a fine powder having a size of about 03 μm is manufactured, it is possible to maintain monodispersity and prevent aggregation from occurring.

Figure 1 shows a process schematic diagram of the precipitation step according to an embodiment of the present invention.

2 is a SEM photograph of the silver powder according to Example 1,

3 is a SEM photograph of the silver powder according to Example 2,

4 is a SEM photograph of the silver powder according to Example 3,

5 is a SEM photograph of the silver powder according to Example 4,

6 is a SEM photograph of the silver powder according to Comparative Example 1,

7 is a SEM photograph of the silver powder according to Comparative Example 1.

Before describing the present invention in detail below, it is understood that the terms used herein are only for describing specific embodiments and are not intended to limit the scope of the present invention, which is limited only by the scope of the appended claims. shall. All technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the art unless otherwise stated.

Throughout this specification and claims, unless otherwise stated, the terms comprise, comprises, comprising means referring to an article, step or group of articles, and steps, and any other article It is not intended to exclude a stage or group of things or a group of stages.

On the other hand, various embodiments of the present invention can be combined with any other embodiments, unless otherwise indicated. Any feature indicated as particularly preferred or advantageous may be combined with any other feature or features indicated as preferred or advantageous. Hereinafter, embodiments and effects according to the present invention will be described with reference to the accompanying drawings.

In the method of manufacturing a silver powder according to an embodiment of the present invention, a silver powder having a level of 0.3 to 1.3 μm can be obtained by preparing a silver powder by adjusting an air-free fall reaction and an input amount of oxalic acid.

The method for preparing silver powder according to an embodiment of the present invention includes a silver salt production step (S1); Silver salt reduction step (S2); Purification step such as filtration and washing (S3); Surface treatment step (S4); And a post-treatment step (S5). The method for preparing silver powder according to the present invention necessarily includes a silver salt reduction step (S2), and other steps can be omitted.

In the silver salt production step (S1) according to an embodiment of the present invention, silver salt solution containing silver ions (Ag +) is prepared by acid treatment of silver (Ag +) in the form of an ingot, a chip, or a granule. It is a step. In the present invention, a silver salt solution may be directly prepared through a silver salt preparation step (S1), and a subsequent step may be performed using a commercially available silver nitrate (AgNO3), silver salt complex, or silver intermediate solution.

The silver salt reduction step (S2) according to an embodiment of the present invention is a step of depositing silver particles by reducing silver ions by reacting the silver salt solution and the reduction solution in an air-free fall method. Specifically, the reaction solution production step (S21) for preparing a first reaction solution containing a silver salt solution, a first reaction solution containing ammonia and an alkali metal salt of an organic acid and a reducing agent (S21), and freely falling the first reaction solution and the second reaction solution It comprises a precipitation step (S22) to obtain a silver powder by reacting in a manner.

In the reaction solution preparation step (S21) according to an embodiment of the present invention, ammonia and an organic acid alkali metal salt are added to a silver salt solution containing silver ions and stirred and dissolved to prepare a first reaction solution. More specifically, a first reaction solution is prepared by adding an alkali metal salt of an organic acid to a silver salt solution containing silver ions and adjusting the pH with ammonia.

The silver ion is not limited as long as it is in the form of a silver cation. For example, it may be silver nitrate (AgNO3), a silver salt complex, or a silver intermediate. It is preferable to use silver nitrate (AgNO3). Hereinafter, the use of silver nitrate (AgNO3) containing silver ions will be described as an example. Hereinafter, the content of other components based on 1600 g / L silver nitrate (AgNO3) 1600 mL will be described.

The organic acid alkali metal salt is acetic acid (CH3COOH), formic acid (CH2O2), oxalic acid (C2H2O4), lactic acid (C3H6O3), citric acid (C6H8O7), fumaric acid (C4H4O4), citric acid (C6H8O7), butyric acid (C4H8O2), butyric acid (C4H8O2), And one or more organic acids (short-chain fatty acids) selected from the group consisting of uric acid (C5H4N4O3), lithium (Li), sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg). And salts formed by any one or more metals selected from the above. Preferably, potassium oxalate (C2K2O4) is used, and it is preferable to selectively use potassium sulfide.

The organic acid alkali metal salt may be added in a ratio of 300 to 600 g with respect to 1600 ml of the 500 g / L silver nitrate (AgNO3). It is possible to provide an effect of increasing the shrinkage rate by adding the organic acid alkali metal salt in the above range, and it is also possible to control the size of the precipitated silver powder as supported by the experimental examples to be described later. When the addition amount of the alkali metal salt of the organic acid is outside the above range, the pH of the first reaction solution is lowered, and thus, the reaction rate is significantly reduced. Therefore, it is difficult to secure the height for free falling in the air in the precipitation step, which will be described later. There is a problem that the silver particles can be grown non-uniformly with the same result as reacting. In addition, when the addition amount of the alkali metal salt of the organic acid is adjusted within the above range, the particle size of the precipitated silver powder can be controlled, and when added beyond the above range, the powder aggregates, and there is a problem in that a silver powder of uniform size cannot be obtained.

Ammonia (NH3) can be used in the form of an aqueous solution. For example, when a 25% aqueous ammonia solution is used, a 25% aqueous ammonia solution may be added at a rate of 2000 ml to 3000 ml with respect to 1600 ml of 500 g / L silver nitrate (AgNO3). As described above, in the present invention, ammonia serves to control the pH.

When a 25% aqueous ammonia solution is added in a proportion of less than 2000 ml with respect to 1600 ml of 500 g / L silver nitrate (AgNO3), all silver ions may not be reduced or it may be difficult to form a uniform particle distribution. When 25% ammonia aqueous solution is added in a proportion exceeding 3000 ml with respect to 1600 ml of 500 g / L silver nitrate (AgNO3), the spheroidization or monodispersity of the powder improves as the pH increases, but the organic content in the prepared silver powder After the conductive paste is higher than the desired standard, carbon may be accumulated and conductivity may be deteriorated. The ammonia includes its derivatives.

In the precipitation step, which will be described later, the reduction rate should be fast when reacting in the air free fall method. The ammonia serves to control the pH and the reduction rate, and when the ammonia is included below the content, the reduction rate is lowered and the reaction rate is slowed down. Therefore, there is a problem that particles are grown non-uniformly at the bottom of the reaction tank, and if it is included in excess of the above content, the reaction rate becomes too fast, and the second reaction liquids are captured in the powder, causing a slight increase in organic matter (~ 1.5%). Can occur.

The above-described first reaction solution may be prepared in an aqueous solution state by adding silver ions, an alkali metal salt of an organic acid and an aqueous ammonia solution to a solvent such as water and stirring it to dissolve, and may also be prepared in a slurry form.

The reaction solution preparation step (S21) according to an embodiment of the present invention also prepares a second reaction solution containing a reducing agent.

The reducing agent may be at least one selected from the group consisting of alkanolamine, hydroquinone, hydrazine and formalin, and among them, hydroquinone may be preferably selected. At this time, the reducing agent may be included in 300 to 500g with respect to 1600ml of 500g / L nitric acid contained in the first reaction solution. 500g / L silver nitrate may reduce all of the silver ions when the reducing agent is less than 300g for 1600ml, and 500g / L silver nitrate may increase the organic content when reducing agent exceeds 500g for 1600ml. there is a problem.

When the reducing agent is included below the above range, there is a problem that all silver ions cannot be reduced. The reducing agent should be included in an amount capable of reducing all of the silver ions, and by adjusting the concentration of the reducing agent included in the second reaction solution. The reduction rate can be adjusted.

For example, the reduction rate may be increased by increasing the concentration of the reducing agent or increasing the reduction rate or decreasing the concentration of the reducing agent. The second reaction solution containing the reducing agent may be prepared by adding a reducing agent to a solvent such as water, stirring and dissolving it to form an aqueous solution having a concentration of 5% or less.

Precipitation step (S22) according to an embodiment of the present invention is a step of obtaining a silver powder by reacting the first reaction solution and the second reaction solution, the first reaction solution and the preparation prepared by the reaction solution production step (S21) 2 The reaction solution can be reacted in a free-falling manner. When a silver powder is obtained by reacting in the free-falling manner as described above, an appropriate amount of the reaction solution reacts uniformly and continuously during the free-fall of the reaction solutions to prevent aggregation between particles and increase dispersibility.

More specifically, in the precipitation step (S22) according to the present invention, silver particles may be precipitated in a free-falling manner using a reaction liquid tank and a reaction tank as shown in FIG. 1. In the reaction liquid production step (S21), the first reaction liquid and the second reaction liquid may be prepared in a first reaction liquid production tank and a second reaction liquid production tank, respectively.

The reaction liquids prepared in each tank are respectively supplied to the reaction tanks through a supply line capable of adjusting the flow rate. When the reaction liquid is injected through a nozzle having a diameter of 15Ф to the reaction tank, it is preferable to be supplied at a flow rate of 3.8L / min to 4.5L / min.

After the reaction liquids are transferred to the reaction tank, the first reaction liquid and the second reaction liquid react while being supplied to the reaction tank through a nozzle and dropping in the air. The height (H) at which the first reaction solution and the second reaction solution are supplied is dropped from the height of 3 m or more relative to the bottom of the reaction tank. There is a problem in that aggregation of silver powder produced when falling in the air below 3 m occurs. Preferably, monodisperse particles having better air-falling at a height of 5 m to 7 m can be obtained.

The reaction temperature of the reaction tank is adjusted to 30 to 50 ° C to react. The size of the precipitated silver powder can be controlled by controlling the reaction temperature to the above range, as supported by the experimental examples described later. When the reaction temperature is increased, it is possible to increase the density of the powder surface, increase the crystallinity, and affect the coating degree of the coating agent, and increase the reaction temperature when the content of the organic acid alkali metal salt added to the first reaction solution is the same. The particle size of the precipitated silver powder can be reduced.

Through the precipitation step (S22) according to the present invention, 0.3-1.3 μm size (SEM size) monodispersed silver powder can be obtained, aggregation can be prevented from occurring, and the amount of organic acid alkali metal salt added and the reaction temperature. By adjusting, even if a fine powder having a size of about 0.3 μm is produced, it is possible to maintain monodispersity and prevent aggregation from occurring.

Purification step (S3) according to an embodiment of the present invention is a step of separating and washing the silver powder dispersed in the silver powder dispersion obtained at the bottom of the reaction tank through filtration through silver salt (S31) (S31) ). More specifically, after the silver particles in the silver powder dispersion are precipitated, the supernatant of the dispersion is discarded, filtered using a centrifuge, and the filter medium is washed with pure water. The washing process can completely remove the washing water from washing the powder.

In addition, the purification step (S3) according to an embodiment of the present invention may further include a drying and disintegration step (S32) after washing. Here, the water content may be 10% or less, but the present invention is not limited thereto.

The surface treatment step (S4) according to an embodiment of the present invention is a step of hydrophobicizing the hydrophilic surface of the silver powder, and may be selectively performed. This is because if the silver powder has a hydrophilic surface, properties may change due to moisture and surface oxidation during long-term storage, and may have a great influence on compatibility with organic solvents and final printing properties when prepared with a conductive paste. At this time, as the surface treatment agent, a single or multiple compounds in the form of a salt or emulsion may be used.

For example, hydrophobicity may be imparted to the silver powder by adding a surface treatment agent containing octadecylamine to the silver powder obtained after filtration. As an example, octadecylamine may contain 0.01 to 0.1 parts by weight (eg, 0.03 parts by weight) with respect to 100 parts by weight of silver nitrate. After that, the silver powder can be obtained again through filtration, washing, drying, and crushing. When the silver powder is surface-treated, the powder must be well dispersed, so that the surface treatment is sufficiently achieved. If the water content is low, the dispersion efficiency decreases, so that the surface treatment is performed with a certain amount of water content (for example, 70 to 85%). good.

The post-treatment step (S5) according to an embodiment of the present invention may include a crushing process for dispersing the agglomerated powder and drying the silver powder obtained after the surface treatment, and a classification process for removing the coarse powder. For example, the crushing process may be performed at a constant air pressure (for example, 0.4 kgf) and a feeding speed (for example, 30 to 60 g / min) using a jet mill or the like, but the present invention is limited thereto. It does not work.

The silver powder prepared according to the method of manufacturing a silver powder according to an embodiment of the present invention has a SEM size (DSEM) of 0.3 to 1.3 μm, a PSA size (D50) of 1.0 to 2.0 μm, and is measured in an experimental example to be described later. The resulting span value is 1.0 or less, and the degree of aggregation (D50 / DSEM) measured in the experimental examples to be described later is 1.7 or less.

According to the manufacturing method of the present invention, even as shown in the examples to be described below, the SEM size is less than 0.3 μm, and even fine silver powder, which appears to be monodisperse on the SEM image, can be manufactured.

The present invention also provides a conductive paste comprising silver powder prepared according to one embodiment of the present invention. More specifically, the conductive paste according to the present invention can be suitably used for forming a solar cell electrode, including silver powder, glass frit, and organic vehicle prepared according to the present invention.

The conductive paste composition according to the present invention may further include additives commonly known as necessary, for example, dispersants, plasticizers, viscosity modifiers, surfactants, oxidizing agents, metal oxides, metal organic compounds, and the like.

The present invention also provides a method for forming an electrode of a solar cell, characterized in that the conductive paste is applied onto a substrate, dried and fired, and a solar cell electrode produced by the method. Except for using the conductive paste containing the silver powder of the above characteristics in the method for forming a solar cell electrode of the present invention, substrates, printing, drying and firing can be used, as well as methods commonly used in the manufacture of solar cells. to be. In one example, the substrate may be a silicon wafer.

Examples and comparative examples

(1) Example 1

A first reaction solution was prepared by adding and stirring 1600 ml of silver nitrate (500 g / L), 380 g of potassium oxalate, and 2560 ml of ammonia (concentration 25%) in 15840 g of pure water at room temperature in the first reaction solution tank. Meanwhile, in the second reaction liquid tank, 400 g of hydroquinone was added to 20000 g of pure water at room temperature and stirred to prepare a second reaction liquid.

Subsequently, the flow rate was controlled at 3.8L / min 4.5L / min using a chemical pump from WILO, and the reaction solution was transferred to the reaction tank, respectively, and then sprayed from the nozzle (air-dropping method) to generate the first reaction solution and the second reaction solution. The silver powder dispersion liquid containing silver powder that reacted and precipitated while falling in the air was recovered from the bottom of the reaction tank. At this time, the reaction temperature of the reaction tank was 35 ° C, and the drop heights of the first reaction solution and the second reaction solution were 6 m.

After separating the silver particles in the obtained silver powder dispersion, the supernatant of the dispersion is discarded, filtered using a centrifuge, and the filter medium is washed with pure water. Thereafter, the washing water was removed to a water content of less than 10%. After this, a surface treatment agent was added, and the water content was adjusted to 70 to 85%, and the final silver powder was obtained through drying and crushing.

(2) Example 2

Silver powder was obtained in the same manner as in Example 1, except that the drop heights of the first reaction solution and the second reaction solution were 3 m.

(3) Example 3

Silver powder was obtained in the same manner as in Example 1, except that the reaction tank had a reaction temperature of 50 ° C.

(4) Example 4

570 g of potassium oxalate was added to the first reaction solution, and silver powder was obtained in the same manner as in Example 1, except that the reaction temperature of the reaction tank was 50 ° C.

(5) Comparative Example 1

Silver powder was obtained in the same manner as in Example 1, except that the drop heights of the first reaction solution and the second reaction solution were 2 m.

(6) Comparative Example 2

 It was carried out except that the second reaction solution was added to the first reaction solution in a beaker at a reaction temperature of 35 ° C (dumping method) and stirred for 10 minutes after the addition was completed to obtain a silver powder dispersion solution containing precipitated silver particles. Silver powder was obtained in the same manner as in Example 1.

division	First reaction solution				Second reaction solution		Reaction method	Temperature (℃)	Height (m)
	Pure (g)	Silver nitrate (ml)	Potassium oxalate (g)	Ammonia (ml)	Pure (g)	Hydroquinone (g)
Example 1	15480	1600	380	2560	20000	400	Airdrop	35	6
Example 2	15480	1600	380	2560	20000	400	Airdrop	35	3
Example 3	15480	1600	380	2560	20000	400	Airdrop	50	6
Example 4	15480	1600	570	2560	20000	400	Airdrop	50	6
Comparative Example 1	15480	1600	380	2560	20000	400	Airdrop	35	2
Comparative Example 2	15480	1600	380	2560	20000	400	Airdrop	35	-

Experimental Example

(1) SEM size measurement of silver powder

The silver powder prepared according to the Examples and Comparative Examples of the present invention was measured using a scanning electron microscope manufactured by JEOL, and the diameter of each of the 100 powders was measured and averaged to measure the SEM size (μm). It is shown in Table 2 below. In addition, SEM images of silver powders prepared according to Examples and Comparative Examples are shown in FIGS. 2 to 7.

(2) Particle size analysis (PSA) measurement of silver powder

50 mg of silver powder prepared according to Examples and Comparative Examples of the present invention was added to 30 ml of ethanol and dispersed in an ultrasonic washer for 3 minutes, and then a particle size distribution measurement apparatus (S3500, Microtrac) by a laser diffraction method was used to measure PSA size ( μm) was measured. The results are shown in Table 2 below.

(3) Span value measurement

Using the particle size distribution measured for the silver powder prepared according to the Examples and Comparative Examples of the present invention, a span value defined as follows was calculated.

Span value = (D90-D10) / D50

(Here, D90, D10, and D50 mean particle sizes corresponding to 90%, 10%, and 50% of the maximum value in the cumulative distribution of solid particle size, respectively.)

If the span value is small, it means that the distribution of the particle size is narrow, and it can be seen that a silver powder of uniform size was produced.

(4) Measurement of cohesion

In order to evaluate the degree of aggregation of the prepared silver powder, the ratio (D50 / DSEM) of PSA size (D50, μm) to SEM size (DSEM, μm) was calculated. It means that the PSA particle size, in which particle size analysis of particles dispersed by light scattering into one particle, is smaller than the particle size measured by SEM imaging, has better dispersion.

division	SeMsize	PSA			Span value	Cohesion
		D10	D50	D90
Example 1	1.08	0.93	1.37	2.11	0.86	1.27
Example 2	1.15	0.98	1.72	2.42	0.84	1.50
Example 3	1.22	0.98	1.45	2.20	0.84	1.19
Example 4	0.29	0.42	0.99	1.88	1.47	3.41
Comparative Example 1	3.81	-	-	-	-	-
Comparative Example 2	1.18	1.25	2.15	3.59	1.09	1.82

As shown in the results of Table 2 and Figs. 2 to 5, when silver particles are precipitated by a free-falling method at a height of 3 m or more (Examples 1 to 3), monodispersed silver powders having low span values and cohesion are obtained It is possible to increase the reaction temperature and increase the input amount of potassium oxalate (Example 4) to obtain a monodisperse powder at a level of 300 μm. In the case of Example 4, since the particle size is very fine and the surface energy is high, aggregation between powders may occur during the particle size analysis measurement, and thus the span value and the degree of aggregation are measured rather high, but as shown in FIG. 5, Examples 1 to As in 3, it can be confirmed that mass production is possible. In addition, when the drop height was less than 3 m (Comparative Example 1), as shown in FIG. 6, the powder was aggregated, and thus PSA size, span value, and degree of aggregation could not be measured, and silver powder was precipitated by dumping in a beaker (Comparison) Example 2) As shown in Table 2 and the results of Table 2, it was confirmed that a silver powder having high span value and degree of aggregation and aggregation occurred was obtained.

The features, structures, effects, and the like exemplified in each of the above-described embodiments may be combined or modified for other embodiments by a person having ordinary knowledge in the field to which the embodiments belong. Therefore, the contents related to such combinations and modifications should be interpreted as being included in the scope of the present invention.

Claims (9)

1. A reaction liquid preparation step (S21) of preparing a first reaction liquid containing a silver ion, ammonia (NH3) and an alkali metal salt of an organic acid and a second reaction liquid containing a reducing agent; And

   A silver salt reduction step (S2) comprising a precipitation step (S22) to obtain a silver powder by reacting while freely dropping the first reaction solution and the second reaction solution in the air.
2. According to claim 1,

   In the precipitation step (S22), the first reaction solution and the second reaction solution are respectively supplied at a specific height of the reaction tank through a supply line capable of adjusting the flow rate, and the first reaction solution and

   A method for producing silver powder, wherein the second reaction solution is allowed to react while falling freely.
3. According to claim 2,

   The height (H) of supplying the first reaction solution and the second reaction solution is 3 m or more from the bottom of the reaction tank, the method for producing silver powder.
4. According to claim 2,

   The reaction tank has a reaction temperature of 30 to 50 ℃, characterized in that the production method of the silver powder.
5. According to claim 4,

   The alkali metal salt of the organic acid is acetic acid (CH3COOH), formic acid (CH2O2), salic acid (C2H2O4), lactic acid (C3H6O3), citric acid (C6H8O7), fumaric acid (C4H4O4), citric acid (C6H8O7), butyric acid (C4H8O2), propionic acid (C4H8O2) And one or more organic acids selected from the group consisting of uric acid (C5H4N4O3) and lithium (Li), sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg). Method of producing a silver powder, characterized in that it comprises one or more metal salts.
6. The method of claim 5,

   When the silver ion is added as an aqueous solution of 500 g / L silver nitrate (AgNO3), the alkali metal salt of the organic acid is prepared at a ratio of 300 to 600 g with respect to 1600 ml of 500 g / L silver nitrate (AgNO3). Way.
7. A silver powder produced by the method of any one of claims 1 to 6, wherein the silver powder has a SEM size (DSEM) of 0.3 to 1.3 μm and a PSA size (D50) of 0.1 to 2.0 μm. Method for producing silver powder.
8. The method of claim 7,

   The silver powder is a method for producing a silver powder, characterized in that the span value (span value) calculated by the following formula is 1.0 or less.

   Span value = (D90-D10) / D50

   (Here, D90, D10, and D50 mean particle sizes corresponding to 90%, 10%, and 50% of the maximum value in the cumulative distribution of solid particle size, respectively.)
9. The method of claim 7,

   The silver powder is a method of manufacturing a silver powder, characterized in that the aggregation degree calculated by the ratio (D50 / DSEM) of PSA size (D50, μm) to SEM size (DSEM, μm) is 1.7 or less.

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