JP7069311B2 - How to make silver powder and conductive paste containing silver powder - Google Patents

Description

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

Silver is widely used as an electrode material in the field of electrical and electronic fields due to its inherent high electrical conductivity and oxidative stability. In particular, recently, with the development of printed electronics technology for directly forming a circuit having a desired form, an industry related to conductive paste, which is obtained by powdering silver and processing it into a paste or ink, has been developed. Conductive pastes in which silver powder is used include not only traditional conductive electrodes such as through holes, die bonding and chip components, but also plasma display panels (PDPs), front or back electrodes of solar cells, touch screens, etc. There are various uses, and the amount used tends to continue to increase.

Conventionally, in the production of silver powder, a wet reduction process has been applied in which a silver ammine complex aqueous solution is produced from an aqueous solution of silver nitrate and aqueous ammonia, and an organic reducing agent is added thereto. Such silver powder is used in the formation of electrodes or circuits such as chip components, plasma display panels, solar cells and the like.

When silver powder is used for the front electrode of a solar cell, the line width of the front electrode is reduced so that the loss due to shielding, scattering and reflection due to the formation area of the front electrode can be minimized and the efficiency can be improved. , The height is required to be increased. However, when the silver powder has a high shrinkage rate, the sintering start temperature is low, so that the compatibility with the glass frit may be low. That is, when the silver powder has a high shrinkage rate, sintering between the silver powders starts at a relatively low temperature, so that sintering may occur before the glass frit. This can result in undesired properties of etching and wettability of the conductive paste containing silver powder, which prevents glass frit acting on the atom transfer path of the substrate from moving to the bottom of the substrate. There is a risk. As a result, the contact resistance of the electrodes formed by using the conductive paste may increase and the efficiency of the solar cell may decrease, and the contact strength of the electrodes decreases, so that the electrodes may peel off in severe cases. There is a risk that the durability of the solar cell will decrease.

If the substance or composition of the binder or glass frit contained in the conductive paste is changed in order to improve this, there may be a problem that other properties of the conductive paste are undesirably changed.

The present invention has been made to solve such a problem, and an object thereof is a method for producing a silver powder capable of having a high shrinkage rate and a high sintering start temperature, and conductivity including the silver powder. The purpose is to provide a sex paste.

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

The method for producing silver powder according to the present invention is a reaction solution production step for producing a first reaction solution containing silver ion, ammonia (NH ₃ ), an organic acid alkali metal salt and ammonium nitrate, and a second reaction solution containing a reducing agent. (S21) and a silver salt reduction step (S2) including a precipitation step (S22) in which the first reaction solution and the second reaction solution are reacted to obtain a silver powder are included.

The first reaction solution can be produced by adding ammonium nitrate itself to a first solution containing silver ions, ammonia, and an organic acid alkali metal salt, or by producing ammonium nitrate by a reaction.

The first reaction solution can be produced by adding nitric acid to the first solution and reacting with the ammonia to produce the ammonium nitrate.

The nitric acid (HNO ₃ ) added to the first solution is used in the form of an aqueous solution, and the concentration of 60% of the nitric acid aqueous solution is 1 to 20 g with respect to 120 ml of the 500 g / L silver nitrate (AgNO ₃ ). Can be added.

The reducing agent may be one or more selected from the group consisting of alkanolamine, hydroquinone, hydrazine and formalin.

The precipitation step (S22) may be a step in which the second reaction solution is added dropwise or collectively added in a state where the first reaction solution is stirred to cause a reaction.

Further including a surface treatment step for making the hydrophilic surface of the silver powder hydrophobic, octadecylamine can be used as a surface treatment agent in the surface treatment step.

The conductive paste according to the present invention is a conductive paste containing silver powder, having an average particle size of 1.9 to 2.2 μm and a specific surface area of 0.3 to 0.5 m ² / g. The organic content is 0.5 to 0.7% and the sintering start temperature is 320 to 360 ° C.

In the silver powder according to the embodiment of the present invention, ammonium nitrate is added in the manufacturing process, and the sintering start temperature of the silver powder is increased while the shrinkage rate is maintained high at the time of sintering the conductive paste containing the same, and the glass frit is formed. Compatibility with and can be improved. When such a conductive paste is applied to the front electrode of a solar cell, the contact resistance of the front electrode can be lowered and the contact strength can be improved. At this time, since ammonium nitrate is added during the production of the silver powder to adjust the sintering start temperature, a desired sintering start temperature can be obtained by a simple process, and the binder and glass frit substances contained in the conductive paste can be obtained. And since it is not necessary to change the composition, it is possible to prevent problems such as changes in other characteristics associated therewith.

It is a graph which shows the temperature and dimension change (dimension change) with time of the conductive paste containing silver powder which concerns on Example 1 and 3 by thermomechanical analysis (TMA). It is a photograph after sintering of the conductive paste containing silver powder which concerns on Example 1. FIG. It is a photograph after sintering of the conductive paste containing silver powder which concerns on Comparative Example 1.

Hereinafter, prior to describing the present invention in detail, the terms used in the present specification are merely for describing a specific embodiment, and the present invention is limited only by the appended claims. It should be understood that it does not attempt to limit the scope. All technical and scientific terms used herein have the same meaning as generally understood by those of ordinary skill in the art, unless otherwise stated.

Throughout the specification and claims, unless otherwise stated, the term Comprise, Complies, Comprising means to include the mentioned objects, steps, or groups of objects and steps. It is not used to exclude any other object, step, or group of objects or steps.

On the other hand, various embodiments of the present invention may be combined with several other different embodiments, unless expressly opposed. A feature that is particularly preferred or advantageous may be combined with any other feature and a plurality of features that are indicated as preferred or advantageous. Hereinafter, embodiments of the present invention and their effects will be described with reference to the accompanying drawings.

In the method for producing silver powder according to an embodiment of the present invention, ammonium nitrate is added to produce silver powder, and the conductive paste containing the silver powder is sintered in a state where the shrinkage rate is maintained high during sintering. The starting temperature can be increased to improve the compatibility with the glass frit. When such a conductive paste is applied to the front electrode of a solar cell, the contact resistance of the front electrode can be lowered and the contact strength can be improved.

The method for producing silver powder according to an embodiment of the present invention includes a silver salt production step (S1); a silver salt reduction step (S2); a purification step such as filtration and washing (S3); a surface treatment step (S4); and The post-processing step (S5) is included. The method for producing silver powder according to the present invention always includes a silver salt reduction step (S2), and other steps can be omitted.

In the silver salt production step (S1) according to the embodiment of the present invention, silver (silver, Ag) in the form of ingot, chip, or granule is acid-treated to contain silver ion (Ag ⁺ ). ) This is the step of producing a solution. In the present invention, the silver salt solution can be directly produced through the silver salt production step (S1), and the subsequent steps can be performed using a commercially available silver nitrate (AgNO ₃ ), silver salt complex or silver intermediate solution. can.

The silver salt reduction step (S2) according to an embodiment of the present invention is a step of precipitating silver particles by adding ammonia, a reducing agent, and ammonium nitrate to a silver salt solution to reduce silver ions. .. A reaction solution production step (S21) for producing a first reaction solution containing a silver salt solution, ammonia, an organic acid alkali metal salt and ammonium nitrate, and a second reaction solution containing a reducing agent, and a first reaction solution and a second reaction solution. And the precipitation step (S22) to obtain a silver powder by reacting with.

In the reaction solution production step (S21) according to the embodiment of the present invention, ammonium nitrate is added to a first solution formed by adding ammonia and an organic acid alkali metal salt to a silver salt solution containing silver ions, and this is added. The first reaction solution is produced by stirring and dissolving. At this time, in order to add ammonium nitrate to the first solution, ammonium nitrate itself can be added, or ammonium nitrate can be formed by the reaction of nitric acid and ammonia. At this time, rather than adding ammonium nitrate itself, producing ammonium nitrate by the reaction of nitric acid and ammonia is excellent in handling stability and it is easier to control the characteristics by pH control. For example, when the pH increases, monodispersity and spheroidization are possible, and apparent characteristics and the like can be effectively controlled. At this time, nitric acid and ammonia can be further added, respectively, and nitric acid can be added in a state where a sufficient amount of ammonia for adjusting the pH is added to produce ammonium nitrate.

More specifically, an organic acid alkali metal salt is added to a silver salt solution containing silver ions, and the pH is adjusted with ammonia to produce a first solution.

The silver ion is not limited as long as it is in the form of a silver cation. As an example, it can be silver nitrate (AgNO ₃ ), a silver salt complex or a silver intermediate. Preferably, silver nitrate (AgNO ₃ ) is used. Hereinafter, the use of silver nitrate (AgNO ₃ ) containing silver ions will be described as an example. Hereinafter, the content of other components and the like will be described with reference to 120 mL of silver nitrate (AgNO ₃ ) of 500 g / L.

The organic acid alkali metal salts include acetic acid (CH ₃ COOH), formic acid (CH ₂ O ₂ ), oxalic acid (C ₂ H ₂ O ₄ ), lactic acid (C ₃ H ₆ O ₃ ), and citric acid (C ₆ H). ₈ O ₇ ), fumaric acid (C ₄ H ₄ O ₄ ), citric acid (C ₆ H ₈ O ₇ ), butyric acid (C ₄ H ₈ O ₂ ), propionic acid (CH ₃ CH ₂ COOH) and uric acid (C) At least one organic acid (short chain fatty acid) selected from the group consisting of ₅ H ₄ N ₄ O ₃ ) and lithium (Li), sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg). ) Salt is formed with at least one metal selected from the group consisting of. It is preferable to use at least one selected from the group consisting of potassium acetate (CH ₃ COOK), potassium formate (HCOOK) and potassium oxalate (C ₂ K ₂ O ₄ ).

The organic acid alkali metal salt can be added at a ratio of 8 to 32 g to 120 ml of the 500 g / L silver nitrate (AgNO ₃ ). The effect of increasing the shrinkage rate is provided by adding an organic acid alkali metal salt in the above range. When the organic acid alkali metal salt is added at a ratio of less than 8 g to 120 ml of 500 g / L silver nitrate (AgNO ₃ ), the effect is insignificant, and 120 ml of 500 g / L silver nitrate (AgNO ₃ ) is added. On the other hand, when the organic acid alkali metal salt is added at a ratio of more than 32 g, the effect may be similar to that when the organic acid alkali metal salt is added at a ratio of less than 32 g.

Ammonia (NH ₃ ) 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 can be added at a ratio of 96 ml to 234 ml to 120 ml of 500 g / L silver nitrate (AgNO ₃ ). As described above, in the present invention, ammonia can play a role of controlling pH and a role of producing ammonium nitrate together. With this in mind, an aqueous ammonia solution must be added to the extent that the role of controlling pH and the role of producing ammonium nitrate can be combined. When 25% aqueous ammonia solution is added at a ratio of less than 96 ml to 120 ml of 500 g / L silver nitrate (AgNO ₃ ), all the silver ions are not reduced or it is difficult to form a uniform particle distribution. Alternatively, the presence of nitric acid may not be suitable for producing ammonium nitrate. When 25% aqueous ammonia solution is added in a ratio of more than 234 ml to 120 ml of 500 g / L silver nitrate (AgNO ₃ ), the spheroidization or monodispersity of the powder improves as the pH increases. Since the organic content in the produced silver powder is higher than the desired standard, carbon may be accumulated after the production of the conductive paste and the conductivity may be lowered. The ammonia contains a derivative thereof.

The first reaction solution is produced by adding nitric acid to the first solution containing silver ions, an organic acid alkali metal salt and ammonia to generate ammonium nitrate. As an example, in the present embodiment, by adding nitric acid to the first solution, ammonium nitrate can be produced by reacting with the already added ammonia to produce ammonium nitrate, which can be used. Such ammonium nitrate can improve the sintering initiation temperature without altering other properties (eg, apparent properties) of the silver powder or the conductive paste containing it.

At this time, the nitric acid (HNO ₃ ) further added to the first solution can be used in the form of an aqueous solution. For example, when a nitric acid aqueous solution having a concentration of 60% is used, the amount of silver nitrate (AgNO ₃ ) is 500 g / L per 120 ml. , The aqueous nitric acid solution can be added at a ratio of 1 to 20 g. At this time, the ammonia further added to the first solution may be contained in a smaller amount than the ammonia for adjusting the pH. If the content of ammonia or nitric acid is less than the above range, the effect of raising the sintering start temperature may not be sufficient, and if it exceeds the above range, the total nitrogen concentration of the reaction waste liquid increases and wastewater treatment is performed. Increased costs can increase overall manufacturing costs.

The above-mentioned first reaction solution can be produced in the form of an aqueous solution by adding a nitrate aqueous solution to a first solution containing silver ions, an organic acid alkali metal salt, and an aqueous ammonia solution in a solvent such as water, and stirring and dissolving the solution. It can also be produced in the form of a slurry.

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

The reducing agent is one or more selected from the group consisting of alkanolamine, hydroquinone, hydrazine and formalin, and hydroquinone can be preferably selected from these. At this time, the reducing agent may be contained in an amount of 20 to 30 g with respect to 120 ml of 500 g / L of silver nitrate contained in the first reaction solution. When the ratio of the reducing agent to 120 ml of 500 g / L silver nitrate is less than 20 g, all the silver ions may not be reduced, and the ratio of the reducing agent to 120 ml of 500 g / L silver nitrate exceeds 30 g. When used, there is a problem that the organic substance content increases.

The second reaction solution containing the reducing agent can be produced in the form of an aqueous solution by adding the reducing agent to a solvent such as water and stirring to dissolve the second reaction solution.

The precipitation step (S22) according to the embodiment of the present invention is a step of reacting the first reaction liquid and the second reaction liquid to obtain silver powder, and is the first step produced by the reaction liquid production step (S21). The second reaction solution can be slowly added dropwise or collectively added in a state where the first reaction solution is agitated to cause the reaction. Preferably, after the batch addition, the particles are further stirred for 10 to 20 minutes to grow the particles in the mixed solution, so that the reduction reaction is completed in a short time, the aggregation of the particles is prevented, and the dispersibility is improved. You can let me do it.

On the other hand, in the embodiment of the present invention, it is not excluded from the scope of rights that a dispersant is further added and reacted in order to improve the dispersibility of the silver particles and prevent aggregation. Examples of dispersants include fatty acids, fatty acid salts, surfactants, organic metals, chelate-forming agents and protective colloids. However, the present invention is not limited to this, and may not include a dispersant.

In the purification step (S3) according to the embodiment of the present invention, after the silver particle precipitation reaction is completed via the silver salt reduction step (S2), the silver powder dispersed in the aqueous solution or the slurry is filtered or the like. The step (S31) of separating and washing is included. More specifically, after the silver particles in the silver powder dispersion are settled, 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 which the powder has been washed. It is also possible to selectively add the above dispersant to the reaction-completed solution prior to filtration to prevent agglomeration of the silver powder.

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

The surface treatment step (S4) according to the embodiment of the present invention is a step of hydrophobizing the hydrophilic surface of the silver powder, and can be selectively performed. This is because if the silver powder has a hydrophilic surface, its properties may change due to moisture and surface oxidation during long-term storage, and it is highly compatible with organic solvents and final printing properties when it is produced into a conductive paste. This is because it may affect it. At this time, as the surface treatment agent, a salt or an emulsion form alone or various compounds can be used.

As an example, a surface treatment agent containing octadecylamine can be added to the silver powder obtained after filtration to impart hydrophobicity to the silver powder. As an example, octadecylamine can be contained in an amount of 0.01 to 0.1 parts by weight (for example, 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 the processes of filtration, washing, drying and crushing. When the silver powder is surface-treated, the surface treatment is sufficiently performed only when the powder is well dispersed, and when the water content is low, the dispersion efficiency is inferior. Therefore, it is better to surface-treat a certain amount with the water content. ..

The post-treatment step (S5) according to the embodiment of the present invention includes a drying step of the silver powder obtained after the surface treatment, a crushing step for dispersing the aggregated powder, and a classification step for removing the coarse powder. be able to. As an example, a crushing process can be carried out 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. Not limited to.

The silver powder produced by the method for producing a silver powder according to an embodiment of the present invention has an average particle size (D50) of 1.9 to 2.2 μm and a specific surface area of 0.3 to 0.5 m ² /. It is g, the organic matter content is 0.5 to 0.7%, and the sintering start temperature of the conductive paste containing this can be 320 to 360 ° C. (for example, 330 to 360 ° C.).

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

The conductive paste composition according to the present invention may contain, if necessary, commonly known additives such as dispersants, plasticizers, viscosity modifiers, surfactants, oxidizing agents, metal oxides, metal organic compounds and the like. Can be further included.

The present invention also provides a method for forming an electrode of a solar cell, which comprises applying the conductive paste onto a substrate, drying and firing, and a solar cell electrode manufactured by this method. In the method for forming electrodes of a solar cell of the present invention, except for using a conductive paste containing silver powder having the above-mentioned characteristics, the method usually used for manufacturing a solar cell is used for the substrate, printing, drying and firing. Of course you can. As an example, the substrate may be a silicon wafer.

In the silver powder according to the embodiment of the present invention, ammonium nitrate is added in the manufacturing process, and the sintering start temperature of the silver powder is increased while the shrinkage rate is maintained high at the time of sintering the conductive paste containing the same, and the glass frit is formed. Compatibility with and can be enhanced. When such a conductive paste is applied to the front electrode of a solar cell, the contact resistance of the front electrode can be lowered and the contact strength can be improved. At this time, since ammonium nitrate is added during the production of the silver powder to adjust the sintering start temperature, a desired sintering start temperature can be obtained in a simple process, and the binder and glass frit substances contained in the conductive paste can be obtained. And since it is not necessary to change the composition, it is possible to prevent problems such as change of other characteristics due to this.
Examples and Comparative Examples

(1) Example 1
Add 4 g of an aqueous nitric acid solution (concentration 60%) to a first solution containing 720 g of pure water at room temperature, 120 ml of silver nitrate of 500 g / L, 22 g of potassium oxalate and 210 ml of ammonia (concentration 25%), and stir at 25 ° C. for 30 minutes. The first reaction solution was prepared. On the other hand, 24 g of hydroquinone was added to 800 g of pure water at room temperature and stirred at 25 ° C. for 30 minutes to prepare a second reaction solution.

Next, the second reaction solution was collectively added to the first reaction solution, and after the addition was completed, the particles were further stirred for 10 minutes to grow particles in the mixed solution. Then, stirring is stopped, the particles in the mixture are settled, the supernatant of the mixture is discarded, the mixture is filtered using a centrifuge, the filter medium is washed with pure water, and the mixture is washed with pure water at 70 ° C.12. A silver powder was obtained by performing a purification step of drying for hours.

Subsequently, in a state where the silver powder obtained in the purification step was added to 300 g of pure water and stirred, 0.18 g of octadecylamine was dissolved in ethanol using an ultrasonic cleaner, and then added and stirred for 10 minutes. bottom. After obtaining the coated silver powder using a centrifuge, a surface treatment step of drying at 70 ° C. for 12 hours was performed.

Then, in order to remove the agglomerated substances in the post-treatment step, the final crushing was carried out by treating with a jet mill manufactured by Nissin of Japan at an air pressure of 0.04 kg and a feeding rate of 30 g / min. Obtained the silver powder.

(2) Examples 2 and 3

A silver powder was obtained in the same manner as in Example 1 except that the contents of ammonia and nitric acid added to the first solution were changed as shown in Table 1 below.

(3) Comparative Example 1
In Comparative Example 1, since ammonia and nitric acid were not added to the first solution, silver powder was obtained in the same manner as in Example 1 except that the first solution itself was used as the first reaction solution.

Experimental example (1) Measurement of particle size of silver powder

After adding 50 mg of silver powder produced by Examples and Comparative Examples of the present invention to 30 ml of ethanol and dispersing in an ultrasonic washing machine for 3 minutes, a particle size distribution measuring device (S3500, manufactured by Microtrac) by a laser diffraction method is used. The average particle size (D50) was measured by measuring the particle size using. The results are shown in Table 2 below.

(2) Measurement of specific surface area

The silver powder produced according to the examples and comparative examples of the present invention is dried at 100 ° C. for 1 hour, and then the specific surface area is measured by nitrogen adsorption using a specific surface measuring device (BELSORP mini-II, manufactured by BEL Japan). bottom. The results are shown in Table 2 below.

(3) Measurement of organic matter content (ignition loss)

The silver powder produced according to the examples and comparative examples of the present invention was subjected to TG / DTA EXART6600 manufactured by Seiko Instruments Inc. in air at a heating rate of 10 ° C./min at room temperature. The organic content was measured by thermogravimetric analysis (TGA) analysis in the range from to 500 ° C. The results are shown in Table 2 below.

(4) Measurement of sintering start temperature

Manufactured by Examples and Comparative Examples of the Invention in 10 g of an organic vehicle in which 7.7 wt% of ethyl cellulose resin (STD200, manufactured by The Dow Chemical Company) and 92.3 wt% of butyl carbitol acetate (manufactured by Oi Kakin Co., Ltd.) are mixed. 90 g of the silver powder was mixed with a self-rotating idling vacuum stirring and unpacking device, and then kneaded with a 3-roll mill to produce a paste.

The produced paste is applied onto an alumina substrate having a thickness of 200 μm and a size of 1 cm × 1 cm, dried at 80 ° C. for 2 hours, sliced, and then via TMA (Thermomechanical Analysis). While raising the temperature to 800 ° C. at a heating rate of 50 ° C./min, the thickness change (dimension change) of the dried body due to the temperature was confirmed, and the sintering start temperature was measured. Here, the sintering start temperature was measured using the signal change maximum technique. FIG. 1 shows the temperature and dimension change of the conductive paste containing silver powder according to Examples 1 and 3, and Table 2 contains silver powder according to Examples 1 to 3 and Comparative Example 1. The sintering start temperature of the conductive paste is shown.

A photograph of the conductive paste containing silver powder according to Example 1 after sintering is attached to FIG. 2, and a photograph of the conductive paste containing silver powder according to Comparative Example 1 after sintering is attached to FIG.

実施例１乃至３による銀粉末を含む導電性ペーストは、図１および表２に示されるように、焼結開始温度が３２０℃以上（一例として、３２０℃以上）であって比較例１に比べて高いことが分かる。このとき、銀粉末の平均粒径、比表面積、有機物含有量などの他の特性（特に、比表面積）は変化せずに、導電性ペーストの焼結開始温度のみが効果的に調節できることが分かる。

As shown in FIGS. 1 and 2, the conductive paste containing the silver powder according to Examples 1 to 3 has a sintering start temperature of 320 ° C. or higher (for example, 320 ° C. or higher) as compared with Comparative Example 1. It turns out that it is expensive. At this time, it can be seen that only the sintering start temperature of the conductive paste can be effectively adjusted without changing other characteristics (particularly, the specific surface area) such as the average particle size, the specific surface area, and the organic matter content of the silver powder. ..

Referring to FIGS. 2 and 3, the conductive paste containing silver powder according to Example 1 was fired uniformly as a whole, whereas the conductive paste containing silver powder according to Comparative Example 1 was sintered. It can be seen that there are areas that have not been created.

The features, structures, effects, etc. exemplified in each of the above-described embodiments can be combined or modified with respect to other embodiments by a person having ordinary knowledge in the field to which the embodiment belongs. Therefore, the contents related to these combinations and modifications should be construed as being included in the scope of the present invention.

Claims (4)

A reaction solution production step (S21) for producing a first reaction solution containing silver ion, ammonia (NH ₃ ), an organic acid alkali metal salt and ammonium nitrate, and a second reaction solution containing a reducing agent.
A silver salt reduction step (S2) including a precipitation step (S22) in which the first reaction solution and the second reaction solution are reacted to obtain a silver powder is included.
Silver nitrate was used as the one containing the silver ion, and
The organic acid alkali metal salt was added at a ratio of 8 to 32 g to 120 ml of the silver nitrate (AgNO ₃ ) at 500 g / L.
The organic acid alkali metal salts include acetic acid (CH ₃ COOH), formic acid (CH ₂ O ₂ ), oxalic acid (C ₂ H ₂ O ₄ ), lactic acid (C ₃ H ₆ O ₃ ), and citric acid (C ₆ H ). ₈ O ₇ ), fumaric acid (C ₄ H ₄ O ₄ ), citric acid (C ₆ H ₈ O ₇ ), butylic acid (C ₄ H ₈ O ₂ ), propionic acid (CH ₃ CH ₂ COOH) and uric acid (C) At least one organic acid (short chain fatty acid) selected from the group consisting of ₅ H ₄ N ₄ O ₃ ) and lithium (Li), sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg). ) Formed a salt with at least one metal selected from the group consisting of.
The first reaction solution is produced by adding nitric acid to a first solution containing silver ions, ammonia, and an organic acid alkali metal salt to produce ammonium nitrate by reaction with the ammonia.
Nitric acid (HNO ₃ ) added to the first solution is used in the form of an aqueous solution.
An aqueous solution of the nitric acid having a concentration of 60% by mass was added at a ratio of 1 to 20 g to 120 ml of the silver nitrate (AgNO ₃ ) of 500 g / L.
A method for producing silver powder, wherein a 25% aqueous ammonia solution is added at a ratio of 96 ml to 234 ml to 120 ml of the silver nitrate (AgNO ₃ ) of 500 g / L. The method for producing a silver powder according to claim 1, wherein the reducing agent is at least one selected from the group consisting of alkanolamine, hydroquinone, hydrazine and formalin. The first aspect of the present invention is characterized in that the precipitation step (S22) is a step in which the second reaction solution is added dropwise or collectively added in a state where the first reaction solution is stirred to cause a reaction. How to make silver powder. The method for producing silver powder according to claim 1, further comprising a surface treatment step for making the hydrophilic surface of the silver powder hydrophobic, and using octadecylamine as a surface treatment agent in the surface treatment step.

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