Silver powder for conductive paste with improved viscosity stability and method for producing the same

Abstract

The present invention provides a method for producing silver powder, the method comprising: a silver powder production step of producing a silver salt containing silver ions and then reducing the silver ions to precipitate silver particles; a silver powder recovery step of separating silver particles from an aqueous solution or slurry containing the precipitated silver particles, washing and drying the particles to recover silver powder; and a silver powder coating step of adding a pH adjuster to the recovered silver powder to adjust the pH, and then adding a coating agent to coat the silver powder. By adjusting the pH using the pH adjuster in the silver powder coating process, a conductive paste having a small viscosity increase rate over time and excellent viscosity stability can be provided when used in a conductive paste.

Description

Technical Field

[0001] The present invention relates to silver powder for conductive paste and a method for producing the same, and more particularly, to silver powder for improving the viscosity stability of conductive paste for forming electrodes in electronic components, such as electrodes for solar cell electrodes, internal electrodes of multilayer capacitors, and conductor patterns of circuit boards, and a method for producing the same.

Background Art

[0002] A conductive metal paste is a paste that has coating suitability enabling film formation and through which electricity flows in a dried coating film, and is a fluid composition in which a conductive filler (metal filler) is dispersed in a vehicle composed of a resin binder and a solvent, and is widely used for forming electric circuits and forming external electrodes of ceramic capacitors.

[0003] In particular, silver paste is the most chemically stable and has excellent conductivity among composite conductive pastes, so its application range in various fields such as conductive adhesion and coating and fine circuit formation is quite wide. In electronic components that particularly emphasize the reliability of PCBs (Printed Circuit Boards) and the like, silver paste is used in various ways such as for STH (Silver Through Hole), adhesives, or coating agents.

[0004] On the other hand, a solar cell is a device that obtains electric power using the photovoltaic effect in which electricity is generated when light is incident on a semiconductor substrate. Usually, a negative electrode is formed on the front surface (the surface irradiated with sunlight) of a semiconductor substrate made of p-type silicon or the like, and a positive electrode is formed on the back surface. A solar cell electrode is formed by screen-printing a conductive paste composition for electrode formation on a substrate and firing it. The conductive paste composition for electrode formation is composed of a conductive organic medium containing conductive powder, glass frit, an organic solvent, and a cellulose resin binder.

[0005] When the viscosity of the conductive paste changes over time, fluctuations in printability occur, making it impossible to obtain the appropriate film thickness and shape during printing. This leads to the problem of being unable to manufacture electrodes and other components with stable quality. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Korean Published Patent No. 10-2016-0016612 (February 15, 2016) [Patent Document 2] Korean Registered Patent No. 10-1775760 (August 31, 2017) [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to solve these problems, and its objective is to provide a silver powder and a method for producing the same that improve the viscosity stability of conductive pastes. However, the object of the present invention is not limited to the object described above, and other objections not mentioned above will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0008] The present invention provides a method for producing silver powder, comprising: a silver powder production step of producing a silver salt containing silver ions, then reducing the silver ions to precipitate silver particles; a silver powder recovery step of separating the silver particles from an aqueous solution or slurry containing the precipitated silver particles, washing and drying to recover the silver powder; and a silver powder coating step of adding a pH adjusting agent to the recovered silver powder to adjust its pH, and then adding a coating agent to coat it.

[0009] Furthermore, the silver powder coating step is characterized by including a pH adjustment step in which the recovered silver powder is added to pure water, stirred, and then a pH adjusting agent is added and stirred to adjust the pH of the silver powder solution, and a coating step in which a coating agent is added to the pH-adjusted silver powder solution to coat it.

[0010] Furthermore, the pH adjustment step is characterized by adding 200 to 400 parts by weight of pure water to 100 parts by weight of the recovered silver powder, stirring for 5 to 15 minutes, then adding the pH adjusting agent, and stirring for 5 to 15 minutes to adjust the pH to 8 to 12.

[0011] Furthermore, the pH adjustment step is characterized by including at least one selected from the group consisting of 2-amino-2-methyl-1-propanol, triethanolamine, and ammonium hydroxide as the pH adjusting agent.

[0012] Furthermore, the coating agent comprises a fatty acid or a salt thereof, wherein the fatty acid comprises at least one selected from the group consisting of stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, and linoleic acid.

[0013] Furthermore, the present invention relates to silver powder produced by the above method, wherein the silver powder has a specific surface area (m²). 2 The present invention provides a silver powder characterized in that the parameter value expressed as the amount of chemical bonding of the coating agent (%) relative to ( / g) is 0.3 or less.

[0014] Furthermore, the present invention provides a conductive paste comprising a metal powder containing silver powder produced by the above method, and an organic vehicle containing a solvent and an organic binder.

[0015] Furthermore, the present invention provides a conductive paste for forming solar cell electrodes, comprising a metal powder containing silver powder produced by the above method, glass frit, and an organic vehicle containing a solvent and an organic binder. [Effects of the Invention]

[0016] The present invention relates to a silver powder used particularly in conductive pastes for forming front electrodes of solar cells. By adjusting the pH using a pH adjusting agent during the silver powder coating process, when used in a conductive paste, the viscosity increase or decrease rate over time is small, thus providing a conductive paste with excellent viscosity stability.

[0017] Furthermore, when manufacturing electrodes using the conductive paste containing the aforementioned silver powder, it is possible to minimize fluctuations in printability over time and obtain appropriate film thickness and shape during printing, thereby providing the effect of manufacturing electrodes and other components with stable quality. [Brief explanation of the drawing]

[0018] [Figure 1] This figure shows a method for analyzing the organic matter content of silver powder. [Modes for carrying out the invention]

[0019] Before describing the present invention in detail below, it should be understood that the terms used herein are merely for the purpose of describing specific embodiments and are not intended to limit the scope of the invention, which is limited solely by the appended claims. All technical and scientific terms used herein have the same meaning as commonly understood by those of the ordinary art, unless otherwise noted.

[0020] Throughout this specification and the claims as a whole, unless otherwise specified, the term "comprise", "comprises", or "comprising" means including the stated element, step, group of elements, or group of steps, and is not used in a sense of excluding any other element, step, group of elements, or group of steps.

[0021] On the other hand, various embodiments of the present invention can be combined with any other embodiments unless there is a clear indication to the contrary. Any feature indicated as particularly preferable or advantageous can be combined with any other feature indicated as preferable or advantageous. Hereinafter, embodiments of the present invention and the effects thereof will be described with reference to the accompanying drawings.

[0022] The present invention provides an effect that, by adjusting the pH using a pH adjuster in the coating step of the produced silver powder, the viscosity stability of the conductive paste containing the silver powder is improved, and when manufacturing an electrode using the conductive paste containing the silver powder, the variation in printability over time is minimized, and an appropriate film thickness and shape can be obtained during printing, so that an electrode with stable quality can be manufactured.

[0023] The method for manufacturing silver powder according to an embodiment of the present invention is composed of including a silver powder manufacturing step (S1), a silver powder recovery step (S2), and a silver powder coating step (S3). Hereinafter, each step will be specifically described. The silver powder manufacturing step (S1) according to an embodiment of the present invention includes a silver salt manufacturing step (S11) and a silver salt reduction step (S12).

[0024] The silver salt manufacturing step (S11) according to an embodiment of the present invention is a step of acid-treating ingot-shaped, granular, or particulate silver (Silver, Ag) to produce a silver salt solution containing silver ions (Ag + ) Although a silver powder can be directly manufactured by producing a silver salt solution through this step, subsequent steps can be performed using commercially available silver nitrate (AgNO3), a silver salt complex, or a silver intermediate solution.

[0025] A silver salt reduction step (S12) according to one embodiment of the present invention is a step of adding a reducing agent and ammonia to a silver salt solution to reduce silver ions and precipitate silver particles, and includes a reaction solution preparation step (S121) of producing a first reaction solution containing silver ions, ammonia and nitric acid, and a second reaction solution containing a reducing agent, and a precipitation step (S122) of reacting the first reaction solution and the second reaction solution to obtain silver powder.

[0026] In the reaction solution production step (S121) according to one embodiment of the present invention, ammonia and nitric acid are added to a silver salt solution containing silver ions, and the mixture is stirred to dissolve them, thereby producing a first reaction solution.

[0027] The aforementioned silver ions are not limited to any substance containing silver cations. Examples include silver nitrate (AgNO3), silver salt complexes, or silver intermediates. Preferably, silver nitrate (AgNO3) is used. The following explanation will use silver nitrate (AgNO3) containing silver ions at a concentration of 500 g / L as an example.

[0028] Ammonia (NH3) can be used in aqueous solution form. When using a 25% aqueous ammonia solution, it should be added at a rate of 100 to 150 parts by weight per 100 parts by weight of silver nitrate (AgNO3). If less than 100 parts by weight of aqueous ammonia solution is added, the reaction pH is low, which can result in incomplete reduction of silver ions or problems in forming a uniform particle distribution. If more than 150 parts by weight is added, there is a problem in that the organic matter content in the produced silver powder becomes too high. Preferably, 120 to 140 parts by weight of 25% aqueous ammonia solution should be added per 100 parts by weight of silver nitrate (AgNO3). The ammonia mentioned above includes its derivatives.

[0029] Nitric acid (HNO3) can be used in aqueous solution form. When using a 60% nitric acid aqueous solution, it is added at a rate of 40 to 120 parts by weight per 100 parts by weight of silver nitrate (AgNO3). If less than 40 parts by weight of nitric acid (HNO3) is added, it is difficult to adjust the size of the silver powder. If more than 120 parts by weight of nitric acid (HNO3) is added, there is a problem that the organic matter content increases significantly. Preferably, 80 to 100 parts by weight of a 60% nitric acid aqueous solution is added per 100 parts by weight of silver nitrate (AgNO3). The nitric acid mentioned above includes its derivatives.

[0030] The first reaction solution, containing silver ions, ammonia, and nitric acid, can be prepared as an aqueous solution by adding silver ions, aqueous ammonia solution, and aqueous nitric acid solution to a solvent such as water, stirring, and dissolving them. It can also be prepared as a slurry. The reaction solution production step (S121) according to one embodiment of the present invention produces a second reaction solution containing a reducing agent.

[0031] The reducing agent is one or more selected from the group consisting of ascorbic acid, alkanolamine, hydroquinone, hydrazine, and formalin, and hydroquinone can be preferably selected from among these. The reducing agent is preferably contained in an amount of 10 to 20 parts by weight per 100 parts by weight of silver nitrate (AgNO3) contained in the first reaction solution. If less than 10 parts by weight is used, there is a risk that not all silver ions will be reduced, and if more than 20 parts by weight is used, there is a problem of increased organic matter content. Preferably, the second reaction solution is prepared by using 14 to 16 parts by weight of the reducing agent per 100 parts by weight of silver nitrate. The second reaction solution containing the reducing agent can be prepared as an aqueous solution by adding the reducing agent to a solvent such as water and stirring to dissolve it.

[0032] The precipitation step (S122) according to one embodiment of the present invention is a step in which a first reaction solution and a second reaction solution are reacted to obtain silver powder. The second reaction solution can be slowly added dropwise to the first reaction solution prepared in the reaction solution preparation step (S121) while stirring, or added all at once to allow the reaction to proceed. Preferably, after adding all at once, stirring for a further 5 to 10 minutes is performed to allow the particles to grow in the mixture. This allows the reduction reaction to be completed all at once in a short time, preventing aggregation of particles and improving dispersibility.

[0033] On the other hand, in embodiments of the present invention, in order to remove organic matter generated after the reaction, an alkaline washing solution such as caustic soda may be added in an amount of 80 to 160 parts by weight per 100 parts by weight of silver nitrate (AgNO3), and the mixture may be stirred for 5 to 20 minutes.

[0034] The silver powder recovery step (S2) according to one embodiment of the present invention is a step in which, after completing the silver particle deposition reaction via the silver powder manufacturing step (S1), the silver powder dispersed in the aqueous solution or slurry is separated by filtration or the like, washed, and dried.

[0035] The silver powder production method according to the present invention is suitably applicable to mass production processes in which approximately 100 kg or more are reacted in a single reaction. In contrast, conventional centrifugal separation methods do not allow for proper separation, and achieving complete separation requires large equipment or long separation times, reducing economic efficiency. Furthermore, the separated silver powder has a high moisture content, making it difficult to recover and thus unsuitable for mass production processes. Therefore, in the present invention, a filter press is used to recover the large quantities of silver powder produced.

[0036] In the silver powder recovery step (S2) according to one embodiment of the present invention, a slurry-like mixture containing the silver particles precipitated in the silver powder manufacturing step (S1) is introduced into a filter press chamber, and the filtrate is separated by squeezing to obtain cake-like silver powder (squeezing step (S21)). Subsequently, the cake-like silver powder is washed with a washing solution such as pure water (washing step (S22)). Compressed air is then introduced to adjust the moisture content while drying, thereby recovering the silver powder (drying step (S23)).

[0037] The squeezing step (S21) is a step in which a slurry-like mixture containing the manufactured silver powder is introduced into a filter press chamber, and the filtrate is separated by squeezing to obtain a cake-like silver powder. More preferably, the slurry introduced is made into a cake by removing the filtrate with a filter cloth in the chamber.

[0038] The aforementioned washing step (S22) is a step in which the filtered cake-like silver powder is washed with a washing solution such as pure water, and more preferably, the washing is continued until the conductivity of the waste liquid discharged after washing is 50 μS cm or less. The squeezing step (S21) and the washing step (S22) can be repeated.

[0039] The drying step (S23) is a step in which compressed air is introduced into the washed silver powder to adjust the moisture content while drying it, and more preferably, compressed air is introduced for 40 to 80 minutes until the moisture content becomes 10% to 20%, and the silver powder is recovered.

[0040] In the silver powder coating step (S3) according to the present invention, the viscosity stability of the silver powder can be improved by adding a pH adjusting agent to the recovered silver powder to adjust the pH (pH adjustment step (S31)), and then adding a coating agent to coat it (coating step (S32)).

[0041] The pH adjustment step (S31) is a step in which a pH adjusting agent is added to the recovered silver powder to adjust the pH for optimal coating in the coating step (S32), and is a step in which the recovered silver powder is added to pure water and stirred, then the pH adjusting agent is added and stirred.

[0042] The pH adjusting agent is at least one selected from the group consisting of 2-amino-2-methyl-1-propanol, triethanolamine, and ammonium hydroxide. Preferably, adjusting the pH using ammonium hydroxide is beneficial in terms of viscosity stability of the conductive paste described later.

[0043] In the pH adjustment step (S31), 100 parts by weight of the recovered silver powder is added to 200 to 400 parts by weight of pure water and stirred for 5 to 15 minutes, then the pH adjusting agent is added and stirred for 5 to 15 minutes to adjust the pH to 8 to 12. When the pH is adjusted as described above to produce a basic solution, the coating agent dissociates well and can chemically bind well to the powder, and the powder produced in this way has a well-coated surface and excellent dispersion stability. Moreover, there is only an amount that can be chemically bound according to the specific surface area of ​​the powder being coated. In contrast, when producing an acidic solution, the coating agent is adsorbed onto the surface of the powder in an undissociated state and can be removed by the solvent or other conditions, so the surface of the silver powder is left exposed, which has the problem of poor powder stability. Preferably, the pH is adjusted to 10 or higher using the pH adjusting agent.

[0044] The coating step (S32) is a step in which a coating agent is added to the pH-adjusted silver powder solution to coat it, and the coating agent used is a coating agent containing a fatty acid or a salt thereof.

[0045] The aforementioned fatty acid is not particularly limited, but it is preferably at least one selected from the group consisting of stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, and linoleic acid.

[0046] The coating agent can be added in a 10% coating solution using an ethanol solution as a solvent, with 2 to 8 parts by weight of the coating agent added per 250 parts by weight of the reduced silver powder. If less than 2 parts by weight of the coating agent is added, there is a problem that the ability to suppress aggregation of the silver powder and the adsorption of the coating agent will decrease. If more than 8 parts by weight of the coating agent is added, the amount adsorbed by the silver powder will be too large, resulting in a problem that sufficient conductivity cannot be obtained in wiring layers, electrodes, etc., formed using a conductive paste containing silver powder. Preferably, 5 to 8 parts by weight of the coating agent is added per 250 parts by weight of the reduced silver powder.

[0047] In the coating step (S32), the coating agent is added to the reduced silver powder solution and stirred for 10 to 30 minutes to coat the silver powder. In the coating step according to the present invention, since the silver powder is coated with reduced silver oxide, the amount of coating agent adsorbed onto the silver powder increases compared to when the reduction step is not performed.

[0048] Even if a washing step is further included after the pH adjustment step (S31) and before the coating step (S32), the viscosity stability of the resulting conductive paste containing silver powder is improved. However, the present invention provides the effect of even greater viscosity stability of the conductive paste containing silver powder obtained by performing the coating step (S32) without washing after the pH adjustment step (S31).

[0049] Subsequently, the silver powder is recovered using centrifugation and washed to obtain the final silver powder. The silver powder produced by the method according to the present invention has a specific surface area (m²) as shown in the experimental example described later. 2 It is characterized by a low parameter value of 0.3 or less, expressed as the amount of chemical bonding (%) of the coating agent relative to g.

[0050] In this invention, the amount of chemical bonding is classified by checking the TG / DTA ratio under conditions where the temperature is raised by 10°C per minute. However, when the coating amount is large, the amount of physical adsorption and the amount of chemical bonding overlap, and the amount of physical adsorption is included in the amount of chemical bonding. As a result, a high amount of chemical bonding is observed even under low pH conditions, so the parameter value expressed as the amount of chemical bonding of the coating agent relative to the specific surface area of ​​the powder (%) exceeds 0.3, and in this case, the dispersion stability and temporal changes of the paste are reduced. In other words, the amount of physical adsorption is a value that continues to increase regardless of the specific surface area, and when the parameter value expressed as the amount of chemical bonding of the coating agent relative to the specific surface area of ​​the powder (%) exceeds 0.3, it can be said that the amount of physical adsorption of the coating agent increases and the dispersion stability of the paste deteriorates. Furthermore, the present invention provides a conductive paste containing silver powder, manufactured by one embodiment of the present invention. The conductive paste comprises metal powder and an organic vehicle.

[0051] As the metal powder, silver powder manufactured by one embodiment of the present invention is used. The metal powder content is preferably 85 to 95% by weight of the total weight of the conductive paste composition, taking into account the thickness of the electrode formed during printing and the linear resistance of the electrode.

[0052] The organic vehicle is a mixture of a solvent and an organic binder in an amount of 5 to 15% by weight, and is preferably present in an amount of 5 to 15% by weight relative to the total weight of the conductive paste composition.

[0053] Examples of the organic binder include cellulose ester compounds such as cellulose acetate and cellulose acetate butyrate; cellulose ether compounds such as ethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, and hydroxyethylmethylcellulose; acrylic compounds such as polyacrylamide, polymethacrylate, polymethyl methacrylate, and polyethyl methacrylate; and vinyl compounds such as polyvinyl butyral, polyvinyl acetate, and polyvinyl alcohol. At least one of the organic binders can be selected and used.

[0054] It is preferable to select and use at least one compound from the following as a solvent for diluting the composition: alcohols such as methanol, ethanol, n-propanol, benzyl alcohol, and terpineol; ketones such as acetone, methyl ethyl ketone, cyclohexanone, isophorone, and acetylacetone; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; ethers such as tetrahydrofuran, dioxane, methyl cellosolve, diglym, and butyl carbitol; esters such as methyl acetate, ethyl acetate, diethyl carbonate, TXIB (1-isopropyl-2,2-dimethyltrimethylenediisobutyrate), carbitol acetate, and butyl carbitol acetate; sulfoxides and sulfones such as dimethyl sulfoxide and sulfolane; aliphatic halogenated hydrocarbons such as methylene chloride, chloroform, carbon tetrachloride, and 1,1,2-trichloroethane; and aromatics such as benzene, toluene, o-xylene, p-xylene, m-xylene, monochlorobenzene, and dichlorobenzene. Furthermore, when used for forming solar cell electrodes, the conductive paste according to the present invention comprises metal powder, glass frit, and an organic vehicle.

[0055] As the metal powder, silver powder manufactured according to one embodiment of the present invention is used. The metal powder content is preferably 85 to 95% by weight of the total weight of the conductive paste composition, taking into account the thickness of the electrodes formed during printing and the linear resistance of the electrodes.

[0056] There are no particular restrictions on the composition, particle size, or shape of the glass frit. Lead-free glass frit can be used as well as leaded glass frit. Preferably, the glass frit contains, on an oxide basis, 5-29 mol% of PbO, 20-34 mol% of TeO2, 3-20 mol% of Bi2O3, 20 mol% or less of SiO2, 10 mol% or less of B2O3, and 10-20 mol% of alkali metals (Li, Na, K, etc.) and alkaline earth metals (Ca, Mg, etc.). By combining the organic content of each component, it is possible to prevent an increase in electrode wire width, achieve high surface resistance and excellent contact resistance, and achieve excellent short-circuit current characteristics.

[0057] The average particle size of the glass frit is not limited, but can be in the range of 0.5 to 10 μm, and a mixture of various particles with different average particle sizes can be used. Preferably, at least one type of glass frit should have an average particle size (D50) of 2 μm or more and 10 μm or less. This results in excellent reactivity during firing, minimizing damage to the n-layer, especially at high temperatures, improving adhesion, and achieving excellent open-circuit voltage (Voc). It also reduces the increase in electrode line width during firing.

[0058] Furthermore, the glass frit content is preferably 1 to 5% by weight relative to the total weight of the conductive paste composition. However, if it is less than 1% by weight, incomplete firing may occur, potentially leading to a high electrical resistivity. If it exceeds 5% by weight, the amount of glass component in the fired silver powder may increase, also potentially leading to a high electrical resistivity.

[0059] The organic vehicle may include, but is not limited to, an organic binder or a solvent. In some cases, the solvent can be omitted. The organic vehicle is preferably included in an amount of 1 to 10% by weight relative to the total weight of the conductive paste composition.

[0060] Organic vehicles are required to maintain a uniform mixture of metal powder and glass frit, etc. For example, when conductive paste is applied to a substrate by screen printing, they are required to homogenize the conductive paste, suppress blurring and flow of the printed pattern, and further improve the discharge and separation of the conductive paste from the screen plate.

[0061] The organic binders contained in the organic vehicle are not limited, but examples of cellulose ester compounds include cellulose acetate and cellulose acetate butyrate; examples of cellulose ether compounds include ethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, and hydroxyethylmethylcellulose; examples of acrylic compounds include polyacrylamide, polymethacrylate, polymethyl methacrylate, and polyethyl methacrylate; and examples of vinyl compounds include polyvinyl butyral, polyvinyl acetate, and polyvinyl alcohol. At least one of the above organic binders can be selected and used.

[0062] As a solvent used to dilute the composition, it is preferable to select and use at least one compound from among those consisting of α-terpineol, texanol, dioctyl phthalate, dibutyl phthalate, cyclohexane, hexane, toluene, benzyl alcohol, dioxane, diethylene glycol, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether, and diethylene glycol monobutyl ether acetate.

[0063] The conductive paste composition according to the present invention may further contain, if necessary, commonly known additives such as dispersants, plasticizers, viscosity modifiers, surfactants, oxidizing agents, metal oxides, metal-organic compounds, and the like.

[0064] The conductive paste according to the present invention has a viscosity sensitization rate of ±12% or less after 24 hours and a viscosity sensitization rate of ±17% or less after 48 hours, and it can be confirmed in the examples and experimental cases described below that it has excellent viscosity stability.

[0065] Furthermore, the present invention provides a method for forming electrodes for a solar cell, characterized by applying the conductive paste onto a substrate, drying and firing, and a solar cell electrode manufactured by the said method. In the method for forming electrodes for a solar cell of the present invention, except for the use of a conductive paste containing the silver powder having the aforementioned properties, it goes without saying that the substrate, printing, drying and firing can be carried out using methods generally used in the manufacture of solar cells. For example, the substrate may be a silicon wafer. [Examples]

[0066] Examples and Comparative Examples - Production of Silver Powder (1) Example 1 A first aqueous solution was prepared by adding 1.28 kg of silver nitrate (500 g / L concentration), 1.57 kg of ammonia (25% concentration), and 1.26 kg of nitric acid (60% concentration) to 6.6 kg of pure water at room temperature and stirring until dissolved. Meanwhile, a second aqueous solution was prepared by adding 0.2 kg of hydroquinone to 10 kg of pure water at room temperature and stirring until dissolved. Next, the first aqueous solution was stirred, and the second aqueous solution was added all at once. After the addition was complete, the mixture was stirred for another 5 minutes to allow the particles to grow in the mixture. To remove the organic matter generated after the reaction, 0.8 kg of caustic soda was added and the mixture was stirred for 10 minutes.

[0067] The silver powder in the mixture was recovered using a filter press, and pure water was then passed through to reduce the conductivity of the waste liquid to 50 μS cm or less. After that, compressed air was passed through for 1 hour to dry the mixture until the moisture content was approximately 10-20%, and the silver powder was recovered.

[0068] 250 g of the recovered silver powder was placed in 750 g of pure water and stirred in a homo-mixer for 10 minutes. Then, 4.7 g of 90% 2-amino-2-methyl-1-propanol was added and stirred for 10 minutes. After that, 7.5 g of 10% stearate ethanol solution was added and the mixture was coated for 20 minutes. The mixture was then recovered by centrifugation and washed to obtain silver powder with a conductivity of 50 μS cm or less. The obtained silver powder was dried at 80°C for 12 hours, then ground in a food mixer, and finally crushed in a jet mill to obtain the final silver powder.

[0069] (2) Example 2 A first aqueous solution was prepared by adding 1.28 kg of silver nitrate (500 g / L concentration), 1.57 kg of ammonia (25% concentration), and 1.26 kg of nitric acid (60% concentration) to 6.6 kg of pure water at room temperature and stirring until dissolved. Meanwhile, a second aqueous solution was prepared by adding 0.2 kg of hydroquinone to 10 kg of pure water at room temperature and stirring until dissolved. Next, the first aqueous solution was stirred, and the second aqueous solution was added all at once. After the addition was complete, the mixture was stirred for another 5 minutes to allow the particles to grow in the mixture. To remove the organic matter generated after the reaction, 0.8 kg of caustic soda was added and the mixture was stirred for 10 minutes.

[0070] The silver powder in the mixture was recovered using a filter press, and pure water was then passed through to reduce the conductivity of the waste liquid to 50 μS cm or less. After that, compressed air was passed through for 1 hour to dry the mixture until the moisture content was approximately 10-20%, and the silver powder was recovered.

[0071] 250g of the recovered silver powder was placed in 750g of pure water and stirred in a homo-mixer for 10 minutes. Then, 50g of triethanolamine (98%) was added and stirred for 10 minutes. After that, 7.5g of 10% stearate ethanol solution was added and the mixture was coated for 20 minutes. The mixture was then recovered by centrifugation and washed to obtain silver powder with a conductivity of 50 μS cm or less. The obtained silver powder was dried at 80°C for 12 hours, then ground in a food mixer, and finally crushed in a jet mill to obtain the final silver powder.

[0072] (3) Example 3 A first aqueous solution was prepared by adding 1.28 kg of silver nitrate (500 g / L concentration), 1.57 kg of ammonia (25% concentration), and 1.26 kg of nitric acid (60% concentration) to 6.6 kg of pure water at room temperature and stirring until dissolved. Meanwhile, a second aqueous solution was prepared by adding 0.2 kg of hydroquinone to 10 kg of pure water at room temperature and stirring until dissolved. Next, the first aqueous solution was stirred, and the second aqueous solution was added all at once. After the addition was complete, the mixture was stirred for another 5 minutes to allow the particles to grow in the mixture. To remove the organic matter generated after the reaction, 0.8 kg of caustic soda was added and the mixture was stirred for 10 minutes.

[0073] The silver powder in the mixture was recovered using a filter press, and pure water was then passed through to reduce the conductivity of the waste liquid to 50 μS cm or less. After that, compressed air was passed through for 1 hour to dry the mixture until the moisture content was approximately 10-20%, and the silver powder was recovered.

[0074] 250 g of the recovered silver powder was placed in 750 g of pure water and stirred in a homo-mixer for 10 minutes. Then, 0.23 g of ammonium hydroxide (25%) was added and stirred for another 10 minutes. Finally, 7.5 g of 10% stearate ethanol solution was added and the mixture was coated for 20 minutes. After that, the mixture was recovered by centrifugation and washed to obtain silver powder with an conductivity of 50 μS cm or less. The obtained silver powder was dried at 80°C for 12 hours, then pulverized in a food mixer and crushed in a jet mill to obtain the final silver powder.

[0075] (4) Example 4 A first aqueous solution was prepared by adding 1.28 kg of silver nitrate (500 g / L concentration), 1.57 kg of ammonia (25% concentration), and 1.26 kg of nitric acid (60% concentration) to 6.6 kg of pure water at room temperature and stirring until dissolved. Meanwhile, a second aqueous solution was prepared by adding 0.2 kg of hydroquinone to 10 kg of pure water at room temperature and stirring until dissolved. Next, the first aqueous solution was stirred, and the second aqueous solution was added all at once. After the addition was complete, the mixture was stirred for another 5 minutes to allow the particles to grow in the mixture. To remove the organic matter generated after the reaction, 0.8 kg of caustic soda was added and the mixture was stirred for 10 minutes.

[0076] The silver powder in the mixture was recovered using a filter press, and pure water was then passed through to reduce the conductivity of the waste liquid to 50 μS cm or less. After that, compressed air was passed through for 1 hour to dry the mixture until the moisture content was approximately 10-20%, and the silver powder was recovered.

[0077] 250g of the recovered silver powder was placed in 750g of pure water and stirred for 10 minutes using a homo-mixer. Then, 0.46g of ammonium hydroxide (25%) was added and stirred for another 10 minutes. Finally, 7.5g of a 10% stearate ethanol solution was added and the mixture was coated for 20 minutes. After that, the mixture was recovered by centrifugation and washed to obtain silver powder with an conductivity of 50 μS cm or less. The obtained silver powder was dried at 80°C for 12 hours, then pulverized in a food mixer and crushed in a jet mill to obtain the final silver powder.

[0078] (5) Example 5 A first aqueous solution was prepared by adding 1.28 kg of silver nitrate (500 g / L concentration), 1.57 kg of ammonia (25% concentration), and 1.26 kg of nitric acid (60% concentration) to 6.6 kg of pure water at room temperature and stirring until dissolved. Meanwhile, a second aqueous solution was prepared by adding 0.2 kg of hydroquinone to 10 kg of pure water at room temperature and stirring until dissolved. Next, the first aqueous solution was stirred, and the second aqueous solution was added all at once. After the addition was complete, the mixture was stirred for another 5 minutes to allow the particles to grow in the mixture. To remove the organic matter generated after the reaction, 0.8 kg of caustic soda was added and the mixture was stirred for 10 minutes.

[0079] The silver powder in the mixture was recovered using a filter press, and pure water was then passed through to reduce the conductivity of the waste liquid to 50 μS cm or less. After that, compressed air was passed through for 1 hour to dry the mixture until the moisture content was approximately 10-20%, and the silver powder was recovered.

[0080] 250 g of the recovered silver powder was placed in 750 g of pure water and stirred in a homomixer for 10 minutes. Then, 4.6 g of ammonium hydroxide (25%) was added and stirred for another 10 minutes. After that, 7.5 g of 10% stearate ethanol solution was added and the mixture was coated for 20 minutes. The mixture was then recovered by centrifugation and washed to obtain silver powder with an conductivity of 50 μS cm or less. The obtained silver powder was dried at 80°C for 12 hours, then pulverized in a food mixer and crushed in a jet mill to obtain the final silver powder.

[0081] (6) Comparative Example 1 A first aqueous solution was prepared by adding 1.28 kg of silver nitrate (500 g / L concentration), 1.57 kg of ammonia (25% concentration), and 1.26 kg of nitric acid (60% concentration) to 6.6 kg of pure water at room temperature and stirring until dissolved. Meanwhile, a second aqueous solution was prepared by adding 0.2 kg of hydroquinone to 10 kg of pure water at room temperature and stirring until dissolved. Next, the first aqueous solution was stirred, and the second aqueous solution was added all at once. After the addition was complete, the mixture was stirred for another 5 minutes to allow the particles to grow in the mixture. After that, stirring was stopped, the particles in the mixture were allowed to settle, the supernatant of the mixture was discarded, the mixture was filtered using a centrifuge, the filter media was washed with pure water, and dried to recover the silver powder.

[0082] 250 g of the recovered silver powder was placed in 750 g of pure water and stirred in a homo-mixer for 10 minutes. Then, 7.5 g of a 10% stearate ethanol solution was added and the mixture was coated for 20 minutes. After that, it was recovered by centrifugation and washed to obtain silver powder with an conductivity of 50 μS cm or less. The obtained silver powder was dried at 80°C for 12 hours, then ground in a food mixer, and finally crushed in a jet mill to obtain the final silver powder.

[0083] [Table 1]

[0084] Experimental Example (1) - Analysis of specific surface area, particle size distribution, and organic matter content After removing moisture from the silver powder produced in the above examples and comparative examples at 100°C for 1 hour, the specific surface area due to nitrogen adsorption was analyzed using a specific surface area analyzer (BELSORP mini-II, manufactured by Bell Japan). The results (BET) are shown in Table 2 below.

[0085] The particle size distribution was determined by laser diffraction by adding 50 mg of silver powder to 30 ml of ethanol, dispersing it in an ultrasonic cleaner for 3 minutes, and then measuring it using a particle size distribution analyzer (S3500, Microtrac). The results (D10, D50, D90) are shown in Table 2 below.

[0086] Using TA Instrument's SDT650, TG / DTA analysis was performed in air at a heating rate of 10°C / min in the range of room temperature to 500°C to measure the organic matter content. As shown in Figure 1, the weight loss from 100°C to the exothermic onset temperature in the DTA graph was measured as the physical adsorption amount of the surface treatment agent, and the weight loss from the exothermic onset temperature to the exothermic peak temperature in the DTA graph was measured as the chemical bonding amount (Chemical-IGL) of the surface treatment agent. The results (C-IGL) are shown in Table 2 below.

[0087] [Table 2]

[0088] As shown in Table 2 above, when the pH was adjusted to 8 or higher before coating, the particle size distribution and specific surface area were similar to when the pH was not adjusted, but the amount of chemically bonded coating agent (C-IGL) decreased. It can be confirmed that the amount of chemical bonding of the coating agent relative to the specific surface area of ​​the silver powder (C-IGL / BET) is 0.3 or less in the example.

[0089] Manufacturing Example - Manufacturing of Conductive Paste A binder consisting of 7.7% by weight of ETHOCEL™ Std200 ethylcellulose (manufactured by The Dow Chemical Company) and 92.3% by weight of diethylene glycol monoethyl ether acetate (manufactured by Oi Chemicals Co., Ltd.) was mixed with 90g of silver powder produced according to the examples and comparative examples. This mixture was then combined in a rotary-orbiting vacuum stirring and degassing apparatus, and a conductive paste was produced using a three-roll machine.

[0090] Experimental Example (2) - Analysis of Viscosity Change Over Time The viscosity of the obtained conductive paste was measured at 25°C and 30 RPM using a Brookfield DV2T digital viscometer. A small sample adapter and a No. 14 spindle were used.

[0091] To analyze the change in viscosity over time, the viscosity of the conductive paste was measured immediately after manufacturing, and then measured again after being stored in a 50°C oven for 24 hours and 48 hours.

[0092] [Table 3]

[0093] From the results above, it can be confirmed that the conductive pastes from Examples 1 to 5 have a viscosity sensitization rate of ±12% or less after 24 hours and a viscosity sensitization rate of ±17% or less after 48 hours. In particular, the conductive paste from Example 5, in which the pH was adjusted to 11 or higher using ammonium hydroxide as a pH adjuster, has a viscosity sensitization rate of ±2% after 24 hours and a viscosity sensitization rate of ±3% after 48 hours, demonstrating that it can ensure the best viscosity stability.

[0094] In Comparative Example 1, the viscosity sensitization rate of the conductive paste after 24 hours was ±15%, and after 48 hours it was ±21%, confirming that it is difficult to ensure viscosity stability.

[0095] The features, structures, and effects exemplified in each of the above-described embodiments can be combined or modified and implemented in other embodiments by a person with ordinary skill in the art to which the embodiments belong. Therefore, the content related to such combinations and modifications should be interpreted as being within the scope of the present invention.

Claims

1. After producing a silver salt containing silver ions, a silver powder production step is taken in which the silver ions are reduced to precipitate silver particles, A silver powder recovery step involves separating the silver particles from the aqueous solution or slurry containing the precipitated silver particles, washing and drying them to recover the silver powder. A method for producing silver powder, comprising a silver powder coating step in which a pH adjusting agent is added to the recovered silver powder to adjust its pH, and then a coating agent is added to coat the silver powder, The silver powder coating step includes a pH adjustment step in which the recovered silver powder is added to pure water, stirred, and then a pH adjusting agent is added and stirred to adjust the pH of the silver powder solution, and a coating step in which a coating agent is added to the pH-adjusted silver powder solution to coat it. The pH adjusting agent is ammonium hydroxide. The silver powder has a specific surface area (m²). ２ The parameter value expressed as the amount of chemical bonding of the coating agent (%) relative to ( / g) is 0.142 to 0.

300. The aforementioned specific surface area is the specific surface area due to nitrogen adsorption, and m ２ It is represented as / g, The chemical bonding amount of the coating agent is expressed in percentage, and is determined as follows: TG / DTA analysis is performed in air at a heating rate of 10°C / min from room temperature to 500°C, the weight loss from 100°C to the exothermic onset temperature on the DTA graph is considered as the physical adsorption amount of the coating agent, and the weight loss from the exothermic onset temperature to the exothermic peak temperature on the DTA graph is measured as the chemical bonding amount (Chemical-IGL) of the coating agent. A method for producing silver powder.

2. The pH adjustment step is as follows: The method for producing silver powder according to claim 1, characterized by the step of adding 200 to 400 parts by weight of pure water to 100 parts by weight of the recovered silver powder and stirring for 5 to 15 minutes, then adding the pH adjusting agent and stirring for 5 to 15 minutes to adjust the pH to 8 to 12.

3. The coating agent comprises a fatty acid or a salt thereof. The method for producing silver powder according to claim 1, characterized in that the fatty acid comprises at least one selected from the group consisting of stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, and linoleic acid.

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