KR102401091B1 - Silver powder for conductive paste with improved elasticity and method for producing the same - Google Patents

Abstract

The present invention is a silver powder coated with an organic material, wherein when the amount of physical adsorption and chemical bonding of the organic material is measured, the chemical bonding amount of the organic material is in the range of 0.06 wt% to 0.12 wt% based on the total weight of the coated silver powder, , The amount of chemical bonding relative to the total amount of the physical adsorption amount and the amount of chemical coating provides a silver powder, characterized in that 60% by weight or more.

Description

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

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

Conductive metal paste is a paste that has applicability to form a coating film and conducts electricity to a dried coating film. It is a fluid composition in which a conductive filler (metal filler) is dispersed in a vehicle consisting of a resin-based binder and a solvent. It is widely used in the formation of external electrodes of

In particular, silver paste is the most chemically stable and excellent in conductivity among composite conductive pastes, so its application range is quite wide in various fields such as conductive adhesion and coating and micro-circuit formation. In electronic components, such as printed circuit boards (PCBs), where reliability is particularly important, silver paste is used in various ways for STH (Silver Through Hole), adhesives, or coatings.

On the other hand, a solar cell is a device that obtains power by using the photovoltaic effect in which electricity is generated when light is incident on a semiconductor substrate. Typically, a front surface of a semiconductor substrate made of p-type silicon, etc. It has a structure in which the cathode electrode is formed on the (front, the surface on which sunlight is irradiated) and the anode electrode is formed on the rear surface. The solar cell electrode is formed by screen-printing and firing a conductive paste composition for forming an electrode on a substrate, and the conductive paste composition for forming an electrode is an electrically conductive powder, a glass frit, an organic solvent, and a cellulose resin binder. It consists of a conductive organic medium containing.

Recently, in order to reduce the consumption of silver contained in the paste composition when forming the front electrode of a solar cell and to increase the area of solar light integration, the line width has been gradually refined. For this purpose, techniques for controlling the viscosity of the electrically conductive paste have been developed. . However, when silver powder is surface-treated to improve the properties of the electrically conductive paste, there is a limitation in that the printed line width is spread even if the viscosity of the electrically conductive paste is controlled.

<Prior art literature>

Japanese Patent Laid-Open No. 2012-077372

Accordingly, it is an object of the present invention to provide a silver powder for improving the elasticity of a conductive paste and a method for manufacturing the same in order to solve the above problems.

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

In order to solve the above problem,

The present invention is a silver powder coated with an organic material. When the amount of physical adsorption and chemical bonding of the organic material is measured by the following method, the chemical bonding amount of the organic material is 0.06 wt% to 0.12 wt% based on the total weight of the coated silver powder. %, and the amount of chemical bonding relative to the total amount of the physical adsorption amount and the amount of chemical coating is 60% by weight or more.

In addition, the present invention provides a metal powder comprising the above-mentioned silver powder; and a glass vehicle including a solvent and an organic binder.

The present invention is a silver powder used in a conductive paste for forming a front electrode of a solar cell in particular, wherein the surface of the silver powder is coated with an organic material, for example, a fatty acid having 8 to 20 carbon atoms, and chemically bound fatty acid among the fatty acids coated on the surface. By controlling the content and the ratio of chemically bound fatty acids to the total coating amount, it is possible to provide a conductive paste having excellent elasticity.

In addition, when an electrode is manufactured using the conductive paste including the silver powder, a narrow line width can be easily printed, thereby providing an effect of manufacturing an electrode with stable quality.

1 is a graph showing an example of measuring a chemical adsorption amount and a physical adsorption amount according to TGA/DTA results for silver powder.

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

Throughout this specification and claims, unless stated otherwise, the term comprise, comprises, comprising is meant to include the stated object, step or group of objects, and steps, and any other object. It is not used in the sense of excluding a step or a group of objects or groups of steps.

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

The present invention includes a silver powder obtained by coating an organic material, for example, a fatty acid having 8 to 20 carbon atoms, with an organic material, for example, a fatty acid having 8 to 20 carbon atoms in the surface treatment process of the produced silver powder, and controlling the amount of chemical bonding among the organic material coated on the surface and the ratio to the total coating amount The elasticity of the conductive paste can be improved, and accordingly, when an electrode is manufactured using the conductive paste, even a narrow line width can be printed without smearing, thereby providing an effect of manufacturing an electrode with stable quality.

<Silver Powder>

According to an embodiment of the present invention, spherical particles having an average specific surface area of 0.4 to 0.6 m 2 /g may be coated with an organic material. The organic material is not limited, and may be, for example, a fatty acid. Coated with a fatty acid having 8 to 20 carbon atoms, the amount of chemically bound fatty acids in the coated fatty acid is 0.06 to 0.12% by weight based on the total weight of the coating silver powder, and the chemically bound amount is 60% by weight or more compared to the total of the amount of physical adsorption and the amount of chemical bonding silver powder. In addition, the amount of physical adsorption of the coated organic material is 0.01 to 0.08 wt % based on the total weight of the coated silver powder.

Specifically, the silver powder according to the present invention is preferably a pure silver powder. In addition, a silver-coated composite powder having at least a surface of a silver layer, an alloy containing silver as a main component, or the like may be used. In addition, other metal powders may be mixed and used. For example, aluminum, gold, palladium, copper, nickel, etc. are mentioned.

In addition, the shape of the silver powder is not particularly limited, but spherical particles may be preferably used.

In addition, the average particle size of the silver powder may be 0.5 to 5.0 μm, preferably 0.9 to 4.5 μm. In addition, the silver powder may satisfy two or more of the following conditions during particle size analysis:

[Condition 1] 0.60㎛ ≤ D10 ≤ 1.15㎛

[Condition 2] 2.00㎛ ≤ D50 ≤ 2.50㎛

[Condition 3] 3.60㎛ ≤ D90 ≤ 4.25㎛.

In the above [Condition 1], [Condition 2] and [Condition 3], D10, D50 and D90 are 10%, 50% and 90% of the cumulative volume of the cumulative curve in the cumulative particle size distribution according to the particle size distribution system, respectively. of particle size.

The silver powder according to the present invention is 0.95㎛ ≤ D10 ≤ 1.135㎛; At least two of [Condition 1], [Condition 2], and [Condition 3] may be satisfied with 2.05 µm ≤ D50 ≤ 2.45 µm, and 3.65 µm ≤ D90 ≤ 4.22 µm. When the silver powder satisfies the above conditions, when an electrode is manufactured using a conductive paste, a narrow line width can be easily printed, and thus an electrode with stable quality can be manufactured.

Furthermore, the silver powder according to the present invention is coated using a coating agent, and the coating agent may use a fatty acid having 8 to 20 carbon atoms.

In this case, the fatty acid having 8 to 20 carbon atoms may include at least one selected from the group consisting of stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, and linolenic acid.

In addition, in the present invention, the fatty acid is coated on the surface of the silver powder through chemical bonding and physical adsorption. Here, the chemical bond is formed through a chemical bond between the silver powder and the fatty acid, which is distinguished from the physical adsorption formed by the weak intermolecular force induced between the silver powder and the fatty acid, and the TGA/DTA analysis of the coated silver powder was performed. The amount of chemically bound can be confirmed through the change in the organic matter content. Specifically, as shown in FIG. 1, TGA/DTA analysis was performed from room temperature to 500° C. in air at a temperature increase rate of 10° C./min using SDT650 of TA instrument company to measure the organic matter content. , define the weight loss from 100°C to the exothermic start temperature of the DTA graph as the amount of physical adsorption (A) of the surface treatment agent, and the weight loss from the exothermic peak temperature of the DTA graph to the chemical bonding of the surface treatment agent It can be defined as quantity (B).

In this case, the amount of chemically bonded in the coated organic material may be 0.06 to 0.12 wt%, preferably 0.8 to 0.11 wt%, based on the total coated silver powder.

In addition, the chemically bound amount may be 60% or more of the total coating amount, preferably 60 to 90%, 65 to 85%, or 80% or more.

In addition, the physically adsorbed amount of the coated organic material may be 0.01 to 0.08 wt%, preferably 0.02 to 0.06 wt%, based on the total coated silver powder.

Even if the metal powder has the same or similar particle size range, the amount coated on the surface may vary greatly depending on the surface treatment process method or conditions, and accordingly, the physical properties of the powder may vary. The silver powder according to the present invention controls the amount of chemical bonding and the chemical bonding ratio of fatty acids coated on the surface to the above ranges, so that the paste prepared when manufacturing the conductive paste compared to the surface-treated silver powder having the same or similar particle size range may exhibit an excellent storage modulus.

<Method for producing silver powder>

The method for producing a silver powder according to the present invention includes a silver powder production step (S1), a silver powder recovery step (S2), and a silver powder coating step (S3). Hereinafter, each step will be described in detail.

In the present invention, the silver powder production step (S1) includes a silver salt production step (S11) and a silver salt reduction step (S12).

The silver salt preparation step (S11) is a step of preparing a silver salt solution containing silver ions (Ag ⁺ ) by acid-treating silver (silver, Ag). Through this step, the silver salt solution is directly prepared. Silver powder may be prepared by manufacturing, but the subsequent steps may be performed using commercially available silver nitrate (AgNO ₃ ), a silver salt complex, or a silver intermediate solution.

In addition, the silver salt reduction step (S12) is a step of reducing silver ions by adding a reducing agent and ammonia to the silver salt solution to precipitate silver particles, wherein the first reaction including silver ions, ammonia and nitric acid A reaction solution preparation step (S121) of preparing a second reaction solution including a solution and a reducing agent, and a precipitation step (S122) of obtaining silver powder by reacting the first reaction solution and the second reaction solution are included.

As an example, in the reaction solution preparation step (S121), a first reaction solution is prepared by adding a 25% aqueous ammonia solution and a 60% aqueous nitrate solution to a silver nitrate (AgNO ₃ ) solution containing silver ions and stirring to dissolve it.

In addition, the reaction solution preparation step (S121) prepares a second reaction solution containing a reducing agent.

In this case, the reducing agent may be at least one selected from the group consisting of ascorbic acid, alkanolamine, hydroquinone, hydrazine, and formalin, and hydroquinone may be preferably selected from among them. The content of the reducing agent is preferably included in an amount of 10 to 20 parts by weight based on 100 parts by weight of silver nitrate (AgNO ₃ ) included in the first reaction solution.

In addition, the precipitation step (S122) is a step of obtaining silver powder by reacting the first reaction solution and the second reaction solution. It is preferable to grow the particles in the mixed solution by stirring the reaction solution for 5 to 10 minutes after adding the reaction solution in batches to complete the reduction reaction within a short period of time to prevent aggregation of the particles and to increase the dispersibility.

On the other hand, in an embodiment of the present invention, 80 to 160 parts by weight of an alkali washing solution such as caustic soda is added based on 100 parts by weight of silver nitrate (AgNO ₃ ) in order to remove organic matter generated after the reaction, and further comprising the step of stirring for 5 to 20 minutes can do.

In addition, in the silver powder recovery step (S2), after the silver particle precipitation reaction is completed through the silver powder manufacturing step (S1), the silver powder dispersed in the aqueous solution or slurry is separated using filtration, etc., washed and dried am.

In the silver powder recovery step (S2), the mixture solution in a slurry state containing the silver particles precipitated in the silver powder production step (S1) is put into a filter press chamber, and the filtrate is separated through squeezing to separate the cake ( cake) to obtain a powder of silver (squeezing step (S21)). Thereafter, the silver powder in the cake state is washed using a washing solution such as pure water (washing step (S22)). The silver powder is recovered by introducing compressed air into it and drying it while controlling the moisture content (drying step (S23)).

The squeezing step (S21) is a step of injecting a slurry-state mixture containing the prepared silver powder into a filter press chamber and separating the filtrate through squeezing to obtain a cake-state silver powder. , more preferably, the input slurry is formed in a cake state by removing the filtrate from the filter cloth of the chamber.

The washing step (S22) is a step of washing the filtered silver powder in a cake state using a washing solution such as pure water, and more preferably, washing until the conductivity of the waste solution discharged after washing becomes 50 μScm or less.

The squeezing step (S21) and the washing step (S22) may be repeatedly performed.

The drying step (S23) is a step of drying while controlling the moisture content by introducing compressed air into the washed silver powder. More preferably, compressed air is introduced for 40 to 80 minutes so that the moisture content is 10% to 20%. It is better to recover the silver powder by drying it until it becomes

In the silver powder coating step (S3) according to the present invention, a pH adjusting agent is added to the recovered silver powder to adjust the pH (pH adjusting step (S31)), and then a coating agent is added (coating step (S32)). The coating agent coated on the powder, that is, the amount of chemical bonding of fatty acids can be effectively controlled.

The pH adjusting step (S31) is a step of adjusting the pH for optimal coating in the coating step (S32) by adding a pH adjusting agent to the recovered silver powder. The recovered silver powder is added to pure water and stirred. After that, a pH adjuster is added and stirred.

The pH adjusting agent may be any one or more selected from the group consisting of 2-amino-2-methylpropanol (2-Amino-2-Methyl-1-propanol), triethanolamine and ammonium hydroxide. and, preferably, adjusting the pH using ammonium hydroxide is good in terms of viscosity stability of the conductive paste, which will be described later.

The pH adjusting step (S31) is performed by adding 200 to 400 parts by weight of pure water based on 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. In the case of preparing a basic solution by adjusting the pH as described above, the coating agent is well dissociated and can be chemically bonded to the powder, and the powder thus prepared has excellent dispersion stability because the surface is well coated. In addition, chemical bonding exists only in an amount capable of bonding depending on the specific surface area of the powder to be coated. On the other hand, in the case of manufacturing with an acidic solution, since the coating agent is adsorbed to the surface of the powder without dissociation and may be removed depending on a solvent or other conditions, there is a problem in that the surface of the silver powder is exposed and the powder stability of the powder deteriorates. Preferably, it is good to adjust the pH so that the pH is 10 or more using the pH adjusting agent.

The coating step (S32) is a step of coating by adding a coating agent to the pH-adjusted silver powder solution, and the coating agent uses a coating agent containing fatty acids.

At this time, the fatty acid is not particularly limited, but is preferably at least one selected from the group consisting of stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid and linolenic acid.

In addition, the coating agent may be added as a coating solution with a concentration of 10% using an ethanol solution as a solvent, and 2 to 8 parts by weight of the coating agent is added based on 250 parts by weight of the reduced silver powder. When the coating agent is added in an amount of less than 2 parts by weight, there is a problem in suppressing aggregation of the silver powder or adsorption property of the coating agent is poor. There is a problem in that the conductivity of the wiring layer or the electrode formed using the is not sufficiently obtained. Preferably, the coating agent is added in an amount of 5 to 8 parts by weight based on 250 parts by weight of the reduced silver powder.

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 coating agent. In the coating step according to the present invention, since the silver powder is coated with reduced silver oxide, the amount of the coating agent adsorbed to the silver powder increases as compared to the case where the reduction step is not performed.

After the pH adjusting step (S31), even if the step of washing before the coating step (S32) is further included, the viscosity stability of the conductive paste containing the obtained silver powder is improved, but coating without washing after the pH adjusting step (S31) The viscosity stability of the conductive paste including the silver powder obtained by proceeding to step S32 provides a more excellent effect.

Thereafter, the silver powder is recovered by centrifugation and washed to obtain the final silver powder. The silver powder prepared by the method according to the present invention has a chemical binding amount of fatty acids coated on the silver powder of 0.06 to 0.12% by weight of the total fatty acids, as shown in Experimental Examples to be described later, and this value is 60% or more of the total coating amount has

Even if the particle size of the metal powder has the same or similar range, there may be a large deviation in the amount coated on the surface, and accordingly, the physical properties of the powder may vary. Specifically, in the present invention, TGA/DTA is checked under the condition of increasing the temperature by 10°C per minute to distinguish the amount of chemical bonding and the amount of physical adsorption. The ratio of the binding amount is lowered. Accordingly, even if the metal powder has the same particle size, when the pH is low or a compound other than a fatty acid is used during surface treatment, the amount of physical adsorption increases, resulting in a low chemical bonding ratio, and in this case, the storage elastic modulus of the conductive paste is significantly low.

<Conductive paste>

Furthermore, in one embodiment, the present invention provides a conductive paste comprising the silver powder according to the present invention as a metal powder.

The conductive paste includes an organic vehicle including a solvent and an organic binder together with the metal powder.

As the metal powder, silver powder prepared according to an embodiment of the present invention is used. The content of the metal powder is preferably 85 to 95% by weight based on the total weight of the conductive paste composition in consideration of the thickness of the electrode formed during printing and the wire resistance of the electrode.

The organic vehicle is a solvent mixed with an organic binder in an amount of 5 to 15% by weight, and is preferably included in an amount of 5 to 15% by weight based on the total weight of the conductive paste composition.

The organic binder is a cellulose ester-based compound, and examples thereof include cellulose acetate and cellulose acetate butyrate. Examples of the cellulose ether compound include ethyl cellulose, methyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, and hydroxypropyl methyl cellulose. , hydroxyethyl methyl cellulose, etc., and examples of the acrylic compound include polyacrylamide, polymethacrylate, polymethyl methacrylate, and polyethyl methacrylate. ral, polyvinyl acetate, and polyvinyl alcohol. At least one organic binder may be selected and used.

As a solvent used for dilution of the composition, alpha-terpineol, texanol, dioctyl phthalate, dibutyl phthalate, cyclohexane, hexane, toluene, benzyl alcohol, dioxane, diethylene glycol, ethylene glycol monobutyl ether, ethylene It is preferable to use at least one selected from the group consisting of glycol monobutyl ether acetate, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, and the like.

The organic vehicle is required to maintain a uniformly mixed state of metal powder and the like. For example, when a conductive paste is applied to a substrate by screen printing, the conductive paste is homogenized to reduce blurring and flow of the printed pattern. It is required to suppress and improve the ejection properties of the conductive paste from the screen plate and the plate separation properties.

In addition, the conductive paste may further include a glass frit.

The composition, particle size, and shape of the glass frit are not particularly limited. Lead-free glass frit as well as lead-free glass frit can be used. Preferably, as a component and content of the glass frit, PbO is 5 to 29 mol%, TeO ₂ is 20 to 34 mol%, Bi ₂ O ₃ is 3 to 20 mol%, SiO ₂ 20 mol% or less, B ₂ O ₃ 10 mol% or less, alkali metals (Li, Na, K, etc.) and alkaline earth metals (Ca, Mg, etc.) preferably contain 10 to 20 mol%. By combining the organic content of each component, it is possible to prevent an increase in the electrode line width, to improve the contact resistance in high sheet resistance, and to improve short-circuit current characteristics.

The average particle diameter of the glass frit is not limited, but may have a particle diameter within the range of 0.5 to 10 μm, and various types of particles having different average particle diameters may be mixed and used. Preferably, at least one glass frit having an average particle diameter (D50) of 2 μm or more and 10 μm or less is used. Through this, the reactivity during firing is improved, damage to the n-layer can be minimized especially at high temperatures, adhesion is improved, and the open circuit voltage (Voc) can be excellent. In addition, it is possible to reduce an increase in the line width of the electrode during firing.

In addition, the content of the glass frit is preferably 1 to 5% by weight based on the total weight of the conductive paste composition. If it is less than 1% by weight, there is a risk that incomplete firing occurs to increase the electrical resistivity, and if it exceeds 5% by weight, the amount of silver powder There is a possibility that too much glass component in the adult body increases the electrical resistivity as well.

The conductive paste composition according to the present invention may further include, if necessary, commonly known additives, for example, a dispersant, a plasticizer, a viscosity modifier, a surfactant, an oxidizing agent, a metal oxide, a metal organic compound, and the like.

The conductive paste according to the present invention has an excellent storage modulus by containing silver powder, in which the content of chemically bound fatty acids among fatty acids coated on the surface and the ratio to the total coating amount are controlled as conductive metal powder. Specifically, the conductive paste may have a storage modulus of 1,000,000 Pa or more, more specifically, 1,000,000-1,500,000 Pa, measured under a shear stress of 1 to 800 Pa and a frequency of 1 rad/s at 25±1° C. there is.

Since the conductive paste can implement a high storage modulus of 1,000,000 Pa or more, it is possible to print in a narrow line width without smearing when manufacturing the front electrode of a solar cell, so it has excellent quality stability.

The present invention provides a method for forming an electrode of a solar cell, characterized in that the conductive paste is applied on a substrate, dried and fired, and a solar cell electrode manufactured by the method. Except for using the conductive paste containing the silver powder of the above characteristics in the method for forming the solar cell electrode of the present invention, methods commonly used for manufacturing the solar cell may be used for the substrate, printing, drying and firing. am. For example, the substrate may be a silicon wafer.

Examples and Comparative Examples - Preparation of silver powder

production example

In 6.6 kg of pure water at room temperature, 1.28 kg of silver nitrate of 500 g/L concentration, 1.57 kg of ammonia (concentration of 25%), and 1.26 kg of nitric acid (concentration of 60%) were added and dissolved by stirring to prepare a first aqueous solution. On the other hand, 0.2 kg of hydroquinone was added to 10 kg of pure water at room temperature and dissolved by stirring to prepare a second aqueous solution. Next, the first aqueous solution was stirred, and the second aqueous solution was added to the first aqueous solution at once, and the mixture was further stirred for 5 minutes after the addition was completed to grow particles in the mixed solution. After the reaction, 0.8 kg of caustic soda was added to remove organic matter and stirred for 10 minutes.

The silver powder in the mixed solution is recovered using a filter press, and pure water is additionally flowed so that the conductivity of the waste solution is 50 μScm or less. Then, compressed air was flowed for 1 hour and dried until the moisture content was about 10-20% to obtain silver powder.

Example 1.

250 g of the silver powder obtained in Preparation Example was put into 750 g of pure water at 60° C. of pH 10, stirred for 10 minutes with a homo-mixer, 7.5 g of a 10% stearic acid ethanol solution was added, and coating was performed for 20 minutes. Thereafter, it was recovered by centrifugation and washed to obtain a conductivity of 50 μScm or less to obtain a silver powder.

After drying the obtained silver powder at 80° C. for 12 hours, it was pulverized in a food mixer and pulverized in a jet-mill to obtain a final silver powder.

Example 2.

250 g of the silver powder obtained in Preparation Example was put into 750 g of pure water at 40° C. of pH 10, stirred for 10 minutes with a homo-mixer, 15 g of 10% ethanol stearate solution was added, and coating was performed for 20 minutes. Thereafter, it was recovered by centrifugation and washed to obtain a conductivity of 50 μScm or less to obtain a silver powder.

After drying the obtained silver powder at 80° C. for 12 hours, it was pulverized in a food mixer and pulverized in a jet-mill to obtain a final silver powder.

Example 3.

250 g of the silver powder obtained in Preparation Example was put into 750 g of pure water at 40° C. of pH 12, stirred for 10 minutes with a homo-mixer, 15 g of a 10% ethanol stearate solution was added, and coating was performed for 20 minutes. Thereafter, it was recovered by centrifugation and washed to obtain a conductivity of 50 μScm or less to obtain a silver powder.

After drying the obtained silver powder at 80° C. for 12 hours, it was pulverized in a food mixer and pulverized in a jet-mill to obtain a final silver powder.

Comparative Example 1.

250 g of the silver powder obtained in Preparation Example was put into 750 g of pure water at 40° C. of pH 7, stirred for 10 minutes with a homo-mixer, 7.5 g of a 10% ethanol stearate solution was added, and coating was performed for 20 minutes. Thereafter, it was recovered by centrifugation and washed to obtain a conductivity of 50 μScm or less to obtain a silver powder.

After drying the obtained silver powder at 80° C. for 12 hours, it was pulverized in a food mixer and pulverized in a jet-mill to obtain a final silver powder.

Comparative Example 2.

Put 250 g of the silver powder obtained in Preparation Example into 750 g of pure water at 40° C. of pH 10, stir with a homo-mixer for 10 minutes, add 3.75 g of 10% stearic acid ethanol solution and 3.75 g of octadecylamine, and coat for 20 minutes. did Thereafter, it was recovered by centrifugation and washed to obtain a conductivity of 50 μScm or less to obtain a silver powder.

After drying the obtained silver powder at 80° C. for 12 hours, it was pulverized in a food mixer and pulverized in a jet-mill to obtain a final silver powder.

Comparative Example 3.

250 g of the silver powder obtained in Preparation Example was put into 750 g of pure water at 60° C. of pH 7, stirred with a homo-mixer for 10 minutes, 15 g of a 10% stearic acid ethanol solution was added, and coating was performed for 20 minutes. Thereafter, it was recovered by centrifugation and washed to obtain a conductivity of 50 μScm or less to obtain a silver powder.

After drying the obtained silver powder at 80° C. for 12 hours, it was pulverized in a food mixer and pulverized in a jet-mill to obtain a final silver powder.

coating process pure fatty acid pH temperature ingredient Consumption compared to silver powder Example 1 10 60℃ stearic acid 0.3% by weight Example 2 10 40℃ stearic acid 0.6 wt% Example 3 12 40℃ stearic acid 0.6 wt% Comparative Example 1 7 40℃ stearic acid 0.3% by weight Comparative Example 2 10 40℃ Stearic acid + octadecyl amine 0.3% by weight Comparative Example 3 7 60℃ stearic acid 0.6 wt%

Experimental Example 1. Analysis of specific surface area, particle size distribution and organic matter content

For the silver powders prepared in Examples and Comparative Examples, after removing moisture at 100° C. for 1 hour, the specific surface area by nitrogen adsorption was analyzed using a specific surface area measuring device (BELSORP mini-II, BEL Japan). The results (BET) are shown in Table 2 below.

In addition, the particle size distribution by laser diffraction method was measured using a particle size distribution measuring device (S3500, Microtrac) after adding 50 mg of silver powder to 30 ml of ethanol and dispersing it in an ultrasonic washing machine for 3 minutes, and the results (D10, D50) , D90) are shown in Table 2 below.

D10 (μm) D50 (μm) D90 (μm) BET (m ² /g) Example 1 0.995 2.164 3.86 0.51 Example 2 1.134 2.404 4.21 0.43 Example 3 0.964 2.080 3.66 0.51 Comparative Example 1 1.070 2.198 3.82 0.49 Comparative Example 2 1.074 2.193 3.82 0.42 Comparative Example 3 0.983 2.018 3.85 0.50

In addition, the silver powders prepared in Examples and Comparative Examples were subjected to TGA/DTA analysis in the range from room temperature to 500°C in air at a temperature increase rate of 10°C/min using SDT650 of TA instrument company to conduct organic matter The content was measured. As shown in FIG. 1, the weight loss from 100° C. to the temperature at which exotherm starts in the DTA graph is regarded as the physical adsorption amount (A) of the surface treatment agent, and the weight loss from the temperature at which exotherm in the DTA graph starts to the exothermic peak temperature is measured on the surface. It was measured as the amount of chemical binding (B) of the treatment agent, and the results are shown in Table 3 below.

Physical adsorption amount (A) [wt%] Chemical bonding amount (B) [wt%] Total coating amount (C=A+B) [wt%] Chemical bonding ratio (B/C*100) Example 1 0.021 0.106 0.127 83.5 Example 2 0.059 0.09 0.149 60.4 Example 3 0.053 0.102 0.155 65.8 Comparative Example 1 0.174 0.115 0.289 39.8 Comparative Example 2 0.121 0.330 0.451 73.0 Comparative Example 3 0.363 0.169 0.532 31.8

As shown in Tables 2 and 3, the silver powders prepared in Examples and Comparative Examples had similar particle size distributions and specific surface areas. However, the silver powder prepared in Examples has a chemical bonding amount of 0.06 to 0.12 wt% of the coated fatty acid, which is 60% or more of the total coating amount, whereas in the case of the silver powder prepared in Comparative Example, the chemical bonding amount of the coating agent and It can be seen that both the physical adsorption amount is very high, and the chemical bonding ratio does not have a constant tendency.

Preparation Example - Preparation of conductive paste

ETHOCELTM Std200 Ethylcellulose (The Dow Chemical Company) 7.7 wt% and diethylene glycol monoethyl ether acetate (Daejeonghwageum) 92.3 wt% binder 10g mixed and 90g silver powder prepared according to Examples and Comparative Examples were degassed by rotating vacuum stirring After mixing with the device, a conductive paste was prepared using a sambon roll.

Experimental Example 2. Analysis of viscosity and elasticity

Viscosity of the obtained conductive paste was measured at 25° C. at 10 rpm and 30 rpm using a Brookfield viscometer, DV2T (Digital viscometer). In this case, a small sample adapter and a No.14 spindle were used.

In addition, the storage modulus of the obtained conductive paste was measured through an amplitude sweep at 25°C using a rotational rheometer, HAAKE RheoStress1. At this time, the measuring sensor was PP35Ti, the gap size was 1.0 mm, the shear stress was 1-800 Pa, and each frequency was 1 rad/s.

The measured results are shown in Table 4 below.

Viscosity Elasticity G'
(50~100 Pa) 10 rpm
[Pas] 30 rpm
[Pas] Example 1 469 237 1,116,833 Example 2 435 204 1,048,801 Example 3 446 197 1,018,200 Comparative Example 1 433 195 717,856 Comparative Example 2 484 230 814,104 Comparative Example 3 488 220 782,025

As shown in the above results, it was found that the conductive pastes using silver powder prepared in Examples and Comparative Examples had viscosity ranges of 430 to 490 Pas and 190 to 240 Pas at 10 rpm and 3 rpm, respectively. However, all the examples satisfying the chemical bonding amount and the chemical bonding amount ratio of the silver powder according to the present invention have an elasticity of 1,000,000 Pa or more, whereas the conductive paste using the silver powder of the comparative example has an elasticity of less than 850,000 Pa. You can check what you have.

From these results, the silver powder according to the present invention can improve the elasticity of the conductive paste including the coated fatty acid by controlling the chemical bonding amount and the chemical bonding ratio, and through this, the front electrode of the solar cell using the conductive paste It can be seen that narrow line width printing can be easily performed without smearing.

Features, structures, effects, etc. exemplified in each of the above-described embodiments may be combined or modified for other embodiments by those of ordinary skill in the art to which the embodiments belong. Accordingly, the contents related to such combinations and modifications should be interpreted as being included in the scope of the present invention.

Claims (8)

A silver powder coated with an organic material,
When the amount of physical adsorption and chemical bonding of the organic material is calculated by the following calculation method,
The amount of chemical bonding of the organic material is in the range of 0.06 wt% to 0.12 wt% based on the total weight of the coated silver powder,
The amount of physical adsorption in the coated organic material is in the range of 0.01 to 0.08 wt% based on the total weight of the coated silver powder,
The silver powder, characterized in that the amount of chemical bonding relative to the total amount of the physical adsorption amount and the amount of chemical coating is 60% by weight or more.

<Calculation method>
Using SDT650 of TA Instruments, when TGA/DTA analysis was performed in the range from room temperature to 500°C in air at a temperature increase rate of 10°C/min and the organic matter content was measured, the temperature at which the heat of the DTA graph starts from 100°C The weight loss is calculated by defining the amount of physical adsorption (A) of the surface treatment agent, and the weight loss from the exothermic start temperature to the exothermic peak temperature in the DTA graph is defined as the chemical bonding amount (B) of the surface treatment agent. .
delete With respect to paragraph 1,
The average particle size of the coated silver powder is 0.5 μm to 5 μm.
With respect to paragraph 3,
The coated silver powder is a silver powder that satisfies at least two of the following conditions during particle size analysis:
[Condition 1] 0.60㎛ ≤ D10 ≤ 1.15㎛
[Condition 2] 2.00㎛ ≤ D50 ≤ 2.50㎛
[Condition 3] 3.60㎛ ≤ D90 ≤ 4.25㎛.
With respect to paragraph 1,
The organic material is a fatty acid, and silver powder comprising at least one selected from the group consisting of stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid and linolenic acid.
A metal powder comprising the silver powder according to claim 1; and
A conductive paste comprising a; a glass vehicle containing a solvent and an organic binder.
7. The method of claim 6,
The conductive paste is a conductive paste, characterized in that the storage elastic modulus measured under 25 ± 1 ℃, 1 rad/s frequency condition is 1,000,000 Pa or more.
7. The method of claim 6,
The conductive paste has a viscosity of 10 rpm and 3 rpm at 25° C., respectively, in the range of 430 to 490 Pas and 190 to 240 Pas.

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