KR20180047529A - Silver powder and manufacturing method of the same - Google Patents

Abstract

The present invention relates to a manufacturing method of silver powder, comprising a silver salt reduction step (S2) including: a reaction solution manufacturing step (S21) of manufacturing a first reaction solution containing a silver ion, ammonia, and an organic acid alkali metal salt and a second reaction solution containing a reducing agent; and a precipitation step (S22) of obtaining silver powder by reacting the first reaction solution and the second reaction solution. The sintering properties of silver powder to be manufactured can be controlled by using an alkali metal salt.

Description

Silver powder and manufacturing method of the same < RTI ID = 0.0 >

The present invention relates to a silver powder and a method of manufacturing the same, and more particularly to a silver powder for conductive paste for forming an electrode in an electronic component such as an electrode for a solar cell, an internal electrode of a multilayer capacitor, and a conductor pattern of a circuit board.

The conductive metal paste is a paste in which a coating film is formed and has a coating property capable of forming a coating film. Electric paste flows through the dried coating film. The conductive metal paste is volatilized by the resin curing type and the high temperature sintering method in which the conductive filler is pressed by the resin, And a conductive filler is sintered to ensure conduction. Among them, the sintered conductive paste is generally a fluid composition in which a conductive filler (metal filler) is dispersed in a vehicle composed of a resin-based binder and a solvent, and is widely used for the formation of an electric circuit or the formation of an external electrode of a ceramic capacitor.

Generally, a well-dispersed silver powder of a uniform size among metal powders is highly conductive, chemically stable, and low in cost, and is used as conductive ink, pastes, and adhesive as important materials in various electronic industries . Silver powder is divided into spherical shape, flake shape, and cohesive shape depending on the shape, and silver powder suitable for the application field is applied.

As a conductive filler, a fine metal powder is used. It is easy to form an organic material by capping in the powder during the production of powder using a wet reduction method, which has a density lower than the theoretical density of the metal, There is a problem that the electric conductivity of a coated film produced by using a conductive paste due to xanthan also becomes low.

Meanwhile, in the case of forming the electrode of the solar cell by using the paste containing the metal powder, since the front electrode of the solar cell must minimize loss due to light absorption or reflection due to the metal electrode, the line width of the electrode must be reduced, Since the height of the electrode must be increased for the resistance, the electrode linewidth and the electrical conductivity, which are formed according to the shrinkage characteristics at the time of sintering the metal powder contained in the paste, are greatly influenced.

In the prior art (Korean Patent Laid-Open No. 10-2014-7025084), cavitation is generated by using ultrasonic waves to produce spherical silver powder having closed pores in the inside of the particles, so as to have the same particle size as that of the conventional silver powder Discloses a method for producing a silver powder capable of being fired at a lower temperature.

However, in the case of the prior art, since the pores are contained in the particles of the powder, the shrinkage ratio during sintering is high in the electrode forming process, which may be advantageous for fine pattern formation. However, the content of organic matters remaining in the pores in the silver powder production process increases, There is a problem that the electric conductivity is lowered in the application used as the silver powder and the ultrasonic wave equipment is introduced separately for forming the voids in the silver powder so that the manufacturing cost is increased and the process is complicated.

Accordingly, it is an object of the present invention to provide a method for manufacturing a silver powder which does not introduce any equipment and process, and which does not form pores, has a low organic matter content, and a high shrinkage ratio during sintering.

Korean Patent Publication No. 10-2014-0125418 (2014-10-28)

The present invention provides a silver powder suitable for use in a high-temperature sinterable conductive paste having a temperature of 600 ° C or higher, which is capable of rapidly shrinking at the beginning of sintering at a low temperature and exhibiting a high shrinkage ratio.

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

The present invention relates to a method for preparing a reaction solution (S21) for producing a second reaction solution comprising a first reaction solution containing silver ions, ammonia and an organic acid alkali metal salt and a reducing agent, and a step (S21) of reacting the first reaction solution and the second reaction solution And a silver salt reducing step (S2) including a precipitation step (S22) for obtaining a silver powder.

In addition, the organic acid alkali metal salt of 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)} , 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 ₅ H ₄ N ₄ O ₃ ) and one or more organic acids selected from the group consisting of lithium (Li), sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg) Characterized in that the metal comprises a salt.

Further, in the reaction solution preparation step (S21), the first reaction solution is added with 5 to 30 g of the organic acid alkali metal salt to 80 mL of 500 g / L silver nitrate (AgNO ₃ ) containing silver ions .

The pH of the first reaction solution is adjusted to 8 to 11 by adjusting the amount of ammonia added in the reaction solution preparation step (S21).

Further, the present invention is a silver powder having an average particle size (D50) of 0.1 to 10 占 퐉, characterized in that the sintering initiation temperature is from 300 to 450 占 폚 and the shrinkage ratio is 20 to 30% at a temperature increase rate of 50 占 폚 / min and 800 占 폚 Silver powder.

The silver powder has a shrinking rate of 3 to 5% / min in a temperature raising condition of 50 ° C / min and 800 ° C in a range of 400 ° C to 600 ° C.

Also, the resistivity of the conductive film formed using the conductive paste containing the silver powder is 3.5 * 10 ^-6? M or less.

The silver powder having an average particle size (D50) of 0.1 to 10 占 퐉 according to the present invention has a particle size similar to that of the spherical silver powder produced by the conventional wet reduction method by adding an organic acid alkali metal salt in the preparation method, A shrinkage rate of 3 to 5% / min at a temperature rising temperature range of 400 to 600 ° C and a shrinkage rate of 20 to 30% in a temperature raising condition of 800 ° C / min and 800 ° C, A silver powder exhibiting a specific resistance of 3.5 * 10 < ^-6 > [Omega] m or less can be produced by using a paste containing the silver powder, and a conductive film baked at 750 deg.

FIGS. 1 to 4 show SEM images of silver powders prepared according to Examples and Comparative Examples of the present invention.

Before describing the present invention in detail, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention, which is defined solely by the appended claims. shall. All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise stated.

Throughout this specification and claims, the word "comprise", "comprises", "comprising" means including a stated article, step or group of articles, and steps, , Step, or group of objects, or a group of steps.

On the contrary, the various embodiments of the present invention can be combined with any other embodiments as long as there is no clear counterpoint. Any feature that is specifically or advantageously indicated as being advantageous may be combined with any other feature or feature that is indicated as being preferred or advantageous. Hereinafter, embodiments of the present invention and effects thereof will be described with reference to the accompanying drawings.

A method of manufacturing a silver powder according to an embodiment of the present invention includes: a silver salt producing step (S1); Silver salt reduction step (S2); Purification step such as filtration and washing (S3); And a surface treatment step (S4). The method for producing silver powder according to the present invention necessarily includes a silver salt reducing step (S2), and the other steps may be omitted.

One. (S1)

The silver salt preparation step S1 according to an embodiment of the present invention is a step of preparing silver salt solutions containing silver ions (Ag +) by acid treatment of silver, silver in the form of ingots, The silver salt solution may be directly produced through this step to prepare silver powder. However, the silver powder may be prepared by using commercially available silver nitrate silver salt complex or silver intermediate solution.

2. (S2)

The silver salt reducing step S2 according to an embodiment of the present invention is a step of adding a reducing agent and ammonia to a silver salt solution to reduce silver ions to precipitate silver particles, (S21) for producing a second reaction solution comprising a first reaction solution containing a metal salt and a reducing agent, and a precipitation step (S22) for obtaining a silver powder by reacting the first reaction solution and the second reaction solution .

In a reaction solution preparation step (S21) according to an embodiment of the present invention, an alkali metal organic acid salt is added to a silver salt solution containing silver ions, and the pH is adjusted with ammonia to prepare a first reaction solution by stirring and dissolving.

The silver ions are not limited as long as they are in the form of silver cations. For example, silver nitrate (AgNO ₃ ), silver salt complex or silver intermediate may be used. And the content of other ingredients based on 80 mL of silver (500 g / L) silver nitrate (AgNO ₃ ).

The present invention can produce a silver powder having a high shrinkage rate and a high shrinkage rate at a specific temperature range by starting the sintering at a low temperature by adding an alkali metal organic acid salt to the first reaction solution and adjusting the pH with ammonia.

The organic acid alkali metal salt of 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)} , 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 5 H 4 N 4 O} 3 (Short chain fatty acid) selected from the group consisting of lithium (Li), sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg) And at least one kind of metal forms a salt. 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 is added in an amount of 5 to 30 g to 80 mL of the 500 g / L silver nitrate (AgNO ₃ ). The organic acid alkali metal salt is added in the above range to lower the sintering initiation temperature and increase the shrinkage rate. When the amount is less than 5 g, the effect is insufficient. When the amount is more than 30 g, the effect is less than 30 g.

Ammonia (NH ₃ ) can be used in the form of an aqueous solution. For example, when 25% ammonia aqueous solution is used, 70 to 350 mL is added to 80 mL of 500 g / L silver nitrate (AgNO ₃ ). When ammonia is added in an amount exceeding 350 ml, the effect of reducing the heat shrinkage is insufficient. When ammonia is added in an amount of less than 70 ml, the size of the silver powder produced is decreased and the shape is varied. The ammonia includes a derivative thereof. By using ammonia, the pH condition at which reduction occurs in the precipitation step (S22) to be described later is adjusted to 8 to 11.

The first reaction solution containing silver ions, ammonia and alkali metal organic acid salts can be prepared in an aqueous solution state by adding silver ions, ammonia, or an organic acid alkali metal salt to a solvent such as water and stirring and dissolving them. .

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

The reducing agent may be at least one member selected from the group consisting of ascorbic acid, alkanolamine, hydroquinone, hydrazine and formalin, and among them, hydroquinone can be preferably selected. The content of the reducing agent is preferably 10 to 30 g per 80 mL of 500 g / L silver nitrate (AgNO ₃ ) contained in the first reaction solution. When less than 10 g is used, silver ions may not be reduced at all, and when it is used in excess of 30 g, organic matter content may increase, which may be a problem.

The second reaction solution containing a reducing agent can be prepared in an aqueous solution state by adding a reducing agent to a solvent such as water and dissolving it by stirring.

The precipitation step (S22) according to an embodiment of the present invention is a step of reacting the first reaction solution and the second reaction solution to obtain a silver powder, wherein the first reaction solution produced by the reaction solution production step (S21) The second reaction solution may be slowly added or the reaction may be performed in a batch. Preferably, the addition of the components in a batch may terminate the reduction reaction in a short period of time, thereby preventing agglomeration of particles and increasing dispersibility.

In the meantime, in the embodiment of the present invention, the addition of the above-mentioned dispersant is not excluded from the scope of right to improve the dispersibility of silver particles and to prevent agglomeration. Examples of the dispersing agent include fatty acids, fatty acid salts, surfactants, organic metals, chelating agents and protective colloids.

However, when the dispersant is added, it is preferable to control the particle diameter of the silver powder, the residual organic matter content and the crystallite diameter without adding the dispersant, since the residual organic matter content may increase and become a problem.

3. Purification step (S3)

In the refining step S3 according to an embodiment of the present invention, the silver powder dispersed in the aqueous solution or slurry is separated and washed by filtration after completing the silver particle precipitation reaction through the silver salt reducing step S2 Step S31. More specifically, after precipitating silver particles in the silver powder dispersion, the supernatant of the dispersion is discarded, filtered using a centrifugal separator, and the filter material is washed with pure water. The process of washing is done by completely removing the washing water from which the powder is washed. Thus reducing the water content to less than 10%. It is also possible to prevent agglomeration of the silver powder by optionally adding the above-mentioned dispersant to the reaction-completed solution before filtration.

Further, the purification step S3 according to an embodiment of the present invention may further include a post-cleaning drying and decoloring step (S34).

4. In the surface treatment step (S4)

The surface treatment step S4 according to an embodiment of the present invention is a step of hydrophobizing the hydrophilic surface of the silver powder, and may be selectively performed. More specifically, after adjusting the moisture content of the wet cake obtained after filtration to less than 10%, a surface treating agent may be added to the surface of the powder to adjust the water content to 70% to 85%. After that, the silver powder can be obtained through drying and decolorizing process. When the powder is surface-treated, the powder should be well dispersed to achieve sufficient surface treatment. If the water content is low, the dispersion efficiency is lowered.

The method for producing a silver powder according to the present invention is a method for producing a silver powder having an average particle size (D50) of 0.1 to 10 占 퐉 by adding an organic acid alkali metal salt to a silver powder of the same degree as a spherical silver powder produced by a conventional wet reduction method Min, a shrinkage rate of 3 to 5% / min in a temperature raising section of 400 to 600 ° C, a shrinkage rate of 20 to 30% % Phosphorus can be produced and a silver powder exhibiting a resistivity of 3.5 * 10 < ^-6 > [Omega] m or less can be produced by using a paste containing the silver powder, and a conductive film baked at 750 deg. have.

Examples and Comparative Examples

(One) Example 1

80 ml of 500 g / L silver nitrate, 10 g of potassium acetate and 70 ml of ammonia (concentration 25%) were added to 850 g of pure water at room temperature and dissolved by stirring to prepare a first reaction solution (see Table 1). Meanwhile, 20 g of hydroquinone was added to 1000 g of pure water at room temperature and dissolved by stirring to prepare a second reaction solution.

Subsequently, the first reaction solution was stirred, and the second reaction solution was added to the first reaction solution collectively, and the stirring was continued for 10 minutes from the completion of the addition, thereby growing particles in the mixed solution. Thereafter, stirring was stopped and the particles in the mixed solution were settled. Then, the supernatant of the mixed solution was discarded, and the mixed solution was filtered using a centrifugal separator. The filter material was washed with pure water and dried to obtain silver powder.

(2) Example 2

80 g of silver nitrate, 80 g of silver nitrate, 10 g of potassium acetate and 10 g of potassium oxalate, and 90 ml of ammonia (25% of concentration) were added to 830 g of pure water at room temperature to dissolve with stirring to prepare a first reaction solution. Meanwhile, 20 g of hydroquinone was added to 1000 g of pure water at room temperature and dissolved by stirring to prepare a second reaction solution.

Subsequently, the first reaction solution was stirred, and the second reaction solution was added to the first reaction solution collectively, and the stirring was continued for 10 minutes from the completion of the addition, thereby growing particles in the mixed solution. Thereafter, stirring was stopped and the particles in the mixed solution were settled. Then, the supernatant of the mixed solution was discarded, and the mixed solution was filtered using a centrifugal separator. The filter material was washed with pure water and dried to obtain silver powder.

(3) Example 3

80 g of silver nitrate, 19 g of potassium oxalate and 128 ml of ammonia (25% in concentration) were added to 792 g of purified water at room temperature, and dissolved by stirring to prepare a first reaction solution. Meanwhile, 20 g of hydroquinone was added to 1000 g of pure water at room temperature and dissolved by stirring to prepare a second reaction solution (see Table 1).

Subsequently, the first reaction solution was stirred, and the second reaction solution was added to the first reaction solution collectively, and the stirring was continued for 10 minutes from the completion of the addition, thereby growing particles in the mixed solution. Thereafter, stirring was stopped and the particles in the mixed solution were settled. Then, the supernatant of the mixed solution was discarded, and the mixed solution was filtered using a centrifugal separator. The filter material was washed with pure water and dried to obtain silver powder.

(4) Comparative Example

80 ml of 500 g / L silver nitrate, 71 ml of ammonia (25% in concentration) and 12 ml of nitric acid were added to 837 g of pure water at room temperature, and dissolved by stirring to prepare a first reaction solution (see Table 1). Meanwhile, 20 g of hydroquinone was added to 1000 g of pure water at room temperature and dissolved by stirring to prepare a second reaction solution.

Subsequently, the first reaction solution was stirred, and the second reaction solution was added to the first reaction solution collectively, and the stirring was continued for 10 minutes from the completion of the addition, thereby growing particles in the mixed solution. Thereafter, stirring was stopped and the particles in the mixed solution were settled. Then, the supernatant of the mixed solution was discarded, and the mixed solution was filtered using a centrifugal separator. The filter material was washed with pure water and dried to obtain silver powder.

The first aqueous solution pure
(g) lunar caustic
(ml) ammonia
(ml) Potassium acetate
(g) Potassium acetate & potassium oxalate
(g) Potassium oxalate
(g) nitric acid
(ml) Example 1 850 80 70 10 Example 2 830 80 90 20 Example 3 792 80 128 19 Comparative Example 1 837 80 71 12

Experimental Example

(One) SEM size measurement

Silver powders prepared according to the Examples and Comparative Examples were measured by SEM size (μm) after measuring the diameters of each of 100 powders using a scanning electron microscope (JEOL) The results are shown in Table 2, and the SEM images taken are shown in Figs. Fig. 1 shows a silver powder of Example 1, Fig. 2 shows a silver powder of Example 2, Fig. 3 shows a silver powder of Example 3, and Fig. 4 shows an SEM image of silver powder of Comparative Example 1.

(2) XRD

Powder X-ray diffraction was performed on the silver powder prepared according to the above Examples and Comparative Examples using X-ray diffractometer manufactured by PANalytical Company. Powder X-ray diffraction was carried out. From the diffraction angle peak position and half value width of the obtained [111] And the crystallite diameter (A) was measured using the method described in Table 2 below.

(3) Organic matter content (heat loss, Ignition loss)

The TGA / DTA EXART 6600 manufactured by Seiko Instruments Inc. was subjected to TGA analysis in the range of room temperature to 500 ° C at a temperature raising rate of 10 ° C / min in the air to measure the organic content. The results are shown in Table 2 below.

(4) TMA (thermogravimetric analyzer) and resistivity

To evaluate the sintering property and conductivity of the silver powder according to the present invention, 87 g of silver powder prepared according to the above Examples and Comparative Examples, 1 g of ethyl cellulose resin (STD200), 1 g of an organic solvent (diethylene glycol monoethyl ether acetate) Were mixed and kneaded by 3-roll mill to prepare a paste.

The sintering initiation temperature (° C.) and the shrinkage rate (400 ° C. to 600 ° C.) in the range of 400 ° C. to 600 ° C. were obtained when the paste prepared above was applied on an alumina substrate in an area of 200 μm ² and heated at 50 ° C./min and 800 ° C. by TMA (Thermomechanical Analysis) % / min) and area shrinkage (%) were measured and are shown in Table 2 below.

The paste thus prepared was printed on an alumina substrate and fired to 750 DEG C using a belt simulating apparatus to obtain a conductive film. The resistivity (Ωm) of the obtained conductive film was measured by a 4-probe method using a resistivity meter (Loresta-GX MCP-T700 from MITSUBISHI) and is shown in Table 2 below.

SEM size
(탆) XRD (A) IGL (%) Sintering initiation temperature (캜) Shrinkage rate (% / min) Shrinkage (%) Resistivity (Ωm) Example 1 1.39 280 1.07 375 3.25 24 3.38 * 10 -6 Example 2 1.20 301 0.55 350 4.5 26 3.28 * 10 -6 Example 3 1.20 327 0.63 360 3.75 24 3.26 * 10 -6 Comparative Example 1 1.38 247 0.71 500 2.5 16 3.88 * 10 -6

As shown in Table 2, the silver powder prepared according to the present invention has the same particle size as that of the silver powder prepared according to the conventional method, and the organic matter content is also comparable to that of the comparative example (Example 1), or the residual organic matter content was low (Examples 2 and 3).

In addition, since the sintering initiation temperature of the silver powder according to the present invention is lower than that of the comparative example and exhibits a rapid shrinking rate in a temperature rising range of 400 to 600 ° C, the conductive paste containing silver powder When the electrode is formed, the final shrinkage ratio after firing is high and the plastic density is high, so that the electric conductivity of the solar cell is excellent.

Also, as shown in Figs. 1 to 3, it is preferable that the voids exist in the inside of the powder particles (here, the voids refer to voids having a shortest diameter of 50 nm or more in the SEM image as voids) The resistivity of the conductive film formed is low and the electrical conductivity is excellent. It can be suitably used to form a fine pattern of 40 μm or less when the front electrode of the solar cell is formed due to its high shrinkage ratio, and the resistance of the manufactured electrode can be lowered.

The features, structures, effects, and the like illustrated in the above-described embodiments can be combined and modified in other embodiments by those skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

Claims (10)

A reaction solution preparation step (S21) of producing a second reaction solution containing a first reaction solution containing silver ions, ammonia and an organic acid alkali metal salt and a reducing agent, and
And a silver salt reducing step (S2) comprising a precipitation step (S22) of reacting the first reaction solution and the second reaction solution to obtain a silver powder.
The method according to claim 1,
The organic acid alkali metal salt of 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)} , 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 5 H 4 N 4 O} 3 And at least one selected from the group consisting of lithium (Li), sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg) Lt; RTI ID = 0.0 > Silver powder.
The method according to claim 1,
Wherein the pH of the first reaction solution is adjusted to be 8 to 11 by adjusting the amount of ammonia added in the reaction solution preparation step (S21).
The method according to claim 1,
Wherein the first reaction solution is prepared by adding 5 to 30 g of the organic acid alkali metal salt to 80 mL of 500 g / L silver nitrate (AgNO ₃ ) containing silver ions in the reaction solution preparation step (S21) Powder.
The method according to claim 1,
Wherein the first reaction solution is prepared by adding 70 to 350 mL of the ammonia to 80 mL of 500 g / L silver nitrate (AgNO ₃ ) containing the silver ion in the reaction solution preparation step (S21). Way.
The method according to claim 1,
Wherein the reducing agent is at least one selected from the group consisting of ascorbic acid, alkanolamine, hydroquinone, hydrazine and formalin.
The method according to claim 1,
Wherein the precipitation step (S22) is a step of adding or collectively adding the second reaction solution in a state of stirring the first reaction solution to react.
As a silver powder having an average particle size (D50) of 0.1 to 10 占 퐉,
Wherein the silver powder has a sintering initiation temperature of 300 to 450 DEG C at a temperature increase rate of 50 DEG C / min and 800 DEG C, and a shrinkage ratio of 20 to 30%.
9. The method of claim 8,
Wherein the silver powder has a shrinking rate of 3 to 5% / min in a temperature raising condition of 50 占 폚 / min and 800 占 폚 in a range of 400 占 폚 to 600 占 폚.
9. The method of claim 8,
Wherein a resistivity of the conductive film formed using the conductive paste containing silver powder is 3.5 * 10 < ^-6 > OM or less.

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