JPWO2012173245A1 - Silver powder and method for producing the same - Google Patents

Abstract

In order to provide a silver powder excellent in compatibility and dispersibility with a solvent or resin of the silver paste and a method for producing the same, the silver powder according to the present invention forms an organic coating layer on the surface of the silver powder and has an internal friction angle. The contact angle in an aqueous solution of 50% by volume of methanol is 20 ° or less, and the silver powder production method according to the present invention forms an organic film layer on the surface by performing surface treatment on silver particles. Thereafter, sufficient crushing treatment is performed so as not to damage the organic coating layer.

Description

The present invention relates to a silver powder and a method for producing the same, and more particularly to a silver powder which is a main component of a silver paste used for forming a wiring layer or an electrode of an electronic device and a method for producing the same.
This application claims priority on the basis of Japanese Patent Application No. 2011-134337 filed on June 16, 2011 in Japan. By referring to these applications, the present application Incorporated.

  Silver pastes such as resin-type silver paste and fired-type silver paste are frequently used for forming wiring layers, electrodes, and the like in electronic devices. After applying or printing these silver pastes on various substrates, a conductive film to be a wiring layer, an electrode, or the like can be formed by heat curing or heat baking.

  For example, a resin-type silver paste is made of silver powder, resin, curing agent, solvent, etc., printed on a conductor circuit pattern or terminal, and cured by heating at 100 ° C. to 200 ° C. to form a conductive film, wiring layer or electrode Form.

  Further, the fired silver paste is made of silver powder, glass, solvent, etc., printed on a conductor circuit pattern or terminal, and heated and fired at 600 ° C. to 800 ° C. to form a conductive layer, thereby forming a wiring layer or an electrode. .

  In wiring layers and electrodes formed of these silver pastes, electrically connected current paths are formed by continuous silver powder.

  The silver powder used in these silver pastes has a particle size of 0.1 μm to several μm, and the particle size of the silver powder used varies depending on the thickness of the wiring layer to be formed, the thickness of the electrode, and the like. Further, by uniformly dispersing silver powder in the silver paste, it is possible to form a wiring layer having a uniform thickness and an electrode having a uniform thickness.

  In general, in the method for producing a silver paste, each component is weighed and placed in a predetermined container, preliminarily kneaded using a universal stirrer, kneader, or the like, followed by main kneading with a three-roll or the like. In the preliminary kneading, it is important to sufficiently wet and disperse each component. By sufficiently performing this preliminary kneading, the occurrence of silver foil in the main kneading can be prevented, and the particle size of the silver powder in the silver paste can be reduced. It is possible to rapidly lower the particle size and uniformly disperse the silver powder in the silver paste.

  Therefore, the silver powder occupying most of the weight in the silver paste not only has a uniform particle size and little agglomeration, but also has good familiarity with vehicles made of solvents, resins, etc., and has high dispersibility in the silver paste. Such characteristics are required. Such characteristics vary depending not only on the structural properties of the powder such as bulk density and particle size distribution but also on the chemical properties of the silver powder surface such as the slipperiness of the powder surface, hydrophilicity and hydrophobicity.

  Regarding silver powder used for silver paste, for example, Patent Document 1 describes that spherical silver powder has a specific bulk density and compact density, thereby improving compatibility with a vehicle or a resin. Yes. However, in Patent Document 1, there is no description regarding the chemical properties of the surface, and it is difficult to control the compatibility with the vehicle or the resin only with such structural parameters. Patent Document 1 does not describe a method for producing silver powder, such as a method for crushing silver powder, which greatly affects the chemical properties of the surface.

  On the other hand, in Patent Document 2, the ratio D50 / DIA between the D50 value obtained by particle size distribution measurement and the particle size DIA obtained by image analysis is used as a measure of the agglomeration degree of the powder. It is described that it is. Certainly, if this value is small, the number of aggregates in the powder is considered to be small. However, in Patent Document 2, as in Patent Document 1, a description relating to the chemical properties of the silver powder surface affecting the compatibility with the vehicle and resin when making a paste and a description relating to the production method affecting the chemical properties. There is no.

  As for the silver powder used in the silver paste, as in Patent Document 1 and Patent Document 2, the structural properties such as the bulk density, the density of the molded body, the degree of aggregation of the powder, etc. are sufficient with the solvent or resin of the silver paste. Compatibility and dispersibility cannot be improved. For this reason, about silver powder, the further improvement of compatibility and a dispersibility is calculated | required.

JP 2006-097086 A JP 2004-100013 A

  Therefore, in view of the above-described conventional circumstances, an object of the present invention is to provide a silver powder excellent in compatibility and dispersibility with a solvent, a resin and the like of a silver paste, and a method for producing the same.

  The silver powder according to the present invention that achieves the above-described object is characterized in that an internal friction angle is 20 ° or less and a contact angle in a 50% by volume methanol aqueous solution is 100 ° or more.

  The method for producing a silver powder according to the present invention that achieves the above-described object is to perform a sufficient crushing treatment so as not to damage the organic coating layer after forming an organic coating layer on the surface by subjecting the silver particles to a surface treatment. It is characterized by performing.

  In the present invention, the internal friction angle of the silver powder is 20 ° or less, and the contact angle in the 50% by volume methanol aqueous solution is 100 ° or more, so that the compatibility with solvents and resins is high and the dispersibility is excellent. It can be easily pasted. Thereby, in this invention, the quality and productivity of a silver paste can be improved.

It is a figure which shows typically about a silver particle form and the surface-like body of a particle.

  Below, the manufacturing method of the silver powder and silver powder to which this invention is applied is demonstrated in detail. Note that the present invention is not limited to the following detailed description unless otherwise specified.

  A silver powder 1 shown in FIG. 1 is contained in a resin-type silver paste composed of a curing agent, a resin, a solvent, or the like, or a fired silver paste composed of glass, a solvent, or the like. The resin-type silver paste and the fired-type silver paste containing the silver powder 1 are used for forming wiring layers and electrodes. For this reason, the silver powder 1 has good compatibility with the solvent and resin of the silver paste so that electrical connection can be achieved, and it is necessary to disperse the paste without unevenness in the paste. The silver powder 1 is particularly suitable for a silver paste using a hydrophobic solvent.

  Silver powder 1 has an internal friction angle of 20 ° or less and a contact angle in a 50% by volume aqueous methanol solution of 100 ° or more. Further, the silver powder 1 preferably has a surface SP value of 18 or less by the acetone titration method. This silver powder 1 has good compatibility with a vehicle such as a solvent or resin of the silver paste by making the chemical properties of the powder surface low hydrophilic and improving the slip. Silver powder 1 includes secondary particles and aggregates in addition to primary particles. Here, as shown in FIG. 1 (A), the primary particles mean individual spherical silver particles 2, and as shown in FIG. 1 (B), a plurality of primary particles are connected by fusion, fixation, or the like. The silver particles 2 are referred to as secondary particles. As shown in FIG. 1C, the aggregate of these primary particles and secondary particles of silver particles 2 is called an aggregate.

  In the silver powder 1, the primary particles are preferably in the range of an average particle size of 0.1 μm to 1.5 μm. When the average particle diameter of the primary particles is 0.1 μm or more, when the silver paste (conductive paste) is used, resistance is not generated and the conductivity can be improved. Further, when the average particle size of the primary particles is 1.5 μm or less, silver flakes are not generated during kneading without deteriorating the dispersibility, and the printability is improved. The average particle size of the primary particles can be measured by observation with a scanning electron microscope (SEM). The particle size of the silver powder 1 is preferably D50 (volume integrated 50% diameter) measured using a laser diffraction scattering method, and is preferably 0.5 μm to 5 μm, and more preferably 1.0 μm to 4.0 μm. preferable. By setting D50 within this range, it becomes preferable for the silver paste, the internal friction angle is optimized, and the dispersibility in the paste is improved.

  The internal friction angle of the silver powder 1 is a parameter representing the slipperiness of the powder, and can be measured by a commercially available powder layer shear force measuring device. In the case of the silver powder 1 for silver paste, when the internal friction angle exceeds 20 °, the slip between the particles (primary particles, secondary particles or aggregates present independently in the silver powder 1) is deteriorated. As a result, when forming a paste, the solvent or resin cannot be split between the particles of the silver powder 1 and only a part of the surface of the silver powder 1 can be wetted. In such a state, even if agitation is performed, the particles are difficult to loosen and the dispersibility of the silver powder 1 is poor. The silver powder 1 with poor dispersibility not only takes time for pre-kneading to wet and disperse each component, but the silver powder 1 aggregated during the main kneading by a three-roll mill or the like is crushed and silver flakes are easily generated. Become. Therefore, since the silver powder 1 has an internal friction angle of 20 ° or less, the slipping is improved, the solvent and the resin enter between the particles, and the compatibility is improved, so that the dispersibility in the silver paste is improved.

  The silver powder 1 has an internal friction angle of 20 ° or less immediately after production, and also maintains an internal friction angle of 20 ° or less even after production. Even in the case of conversion, it is preferably 20 ° or less. For example, after the silver powder 1 is manufactured, for example, even after one month has passed at room temperature, the internal friction angle of the silver powder 1 is 20 ° or less. The internal friction angle is a parameter that varies depending on the aggregation of particles. Even if the powder has a low degree of aggregation immediately after production, the internal friction angle increases as the aggregation of particles progresses over time. There is. If the internal friction angle changes over time and exceeds 20 °, the dispersibility is lowered when forming a paste, and various problems such as aggregation of the silver powder 1 are caused. Therefore, if the internal friction angle of 20 ° or less can be maintained, the progress of aggregation can be suppressed, so that a problem can be prevented from occurring during pasting.

  Next, the contact angle of the silver powder 1 will be described. Silver powder 1 has a contact angle of 100 ° or more in a 50% by volume aqueous solution of methanol. The contact angle is a parameter representing the wettability of the surface of the silver powder 1 with respect to the solvent. For example, the greater the contact angle with water, the easier the wet with the hydrophobic paste solvent. Conversely, the smaller the contact angle with water is, the more hydrophilic it is and the wettability with the hydrophobic paste solvent becomes worse. The contact angle of the silver powder 1 is generally measured on the molded surface. However, when measuring with water, when the powder is highly hydrophobic, the water droplets become spherical on the surface of the molded powder. Since water drops slide and move, it is difficult to measure accurately. For this reason, a method of performing measurement by adding a low polarity solvent such as methanol to water and lowering the polarity of the solvent is performed. In producing a silver paste, generally a hydrophobic solvent is often used. Therefore, when the silver powder 1 has a hydrophilic surface with a contact angle of less than 100 °, the paste is poorly compatible with the solvent or the resin, and the silver powder 1 does not wet with the solvent or the resin and can be made into a paste. It becomes difficult. In addition, when the mixture is forcibly kneaded into a paste, the dispersion stability is poor and the paste is likely to be separated by reaggregation.

  Next, the surface SP value of the silver powder 1 will be described. The silver powder 1 has a surface SP value of 18 or less. The surface SP value is a parameter representing the polarity of the surface of the silver powder 1, and the smaller the surface SP value, the more hydrophobic the surface SP value.

  The surface SP value can be measured by a commercially available powder wettability tester or the like, but simply, an acetone titration method as described in “Coloring Materials, 62 (9) 524-528”. But measurement is possible. In this acetone titration method, a hydrophobic powder is added to water (A [ml]) and suspended. While gently stirring with a stirrer, acetone is dropped with a burette, and the dripping amount of acetone (B [ml]) required until the powder wets and settles is measured. The SP value of water 23.43, the SP value of acetone 9.75, the volume of water used and the SP value of the acetone solution settled from the volume of acetone used were calculated from the following formula 1, and these values were calculated for silver powder 1. The surface SP value is used.

  When the surface SP value of the silver powder 1 is larger than 18, the hydrophilicity is too large, the compatibility of the paste with the solvent or resin is deteriorated, and the silver powder 1 is not wetted with the solvent or resin, and the paste is formed. It becomes difficult. Moreover, even if it is kneaded forcibly to make a paste, the dispersion stability is poor and the paste is likely to be separated by reaggregation. On the other hand, since the surface SP value of the silver powder 1 is 18 or less, the hydrophilicity of the silver powder 1 does not become too large, the compatibility with the solvent and the resin becomes good, and the dispersibility becomes excellent. Becomes easier.

  Silver powder 1 is obtained by subjecting silver particles 2 obtained by a wet reduction method to surface treatment, and forming organic coating layer 3 on the surface of primary particles or secondary particles as shown in FIG. Can be made 20 ° or less, the contact angle in a 50% by volume aqueous methanol solution can be made 100 ° or more, and the surface SP value by the acetone titration method can also be made 18 or less. The organic coating layer 3 can be formed of a surfactant or a surfactant and a dispersant.

  The organic coating layer 3 is preferably formed of a surfactant and a dispersant. In the silver powder 1, it is possible to suppress aggregation by adsorbing the surfactant to the silver particles 2 in an ionized state, but the amount added is too large to suppress aggregation only with the surfactant. . Therefore, even if a good dispersion state is obtained in the silver paste, the conductivity of the wiring layer and the electrode may not be sufficient. Therefore, it is effective to use a surfactant and a dispersant in combination in order to suppress the aggregation of the silver powder 1 and to make the wiring layer and the electrode sufficiently conductive.

  In particular, the organic coating layer 3 is formed by further adsorbing the dispersing agent to the surfactant adsorbed on the silver particles 2 by adding a dispersing agent during or after the adsorption of the surfactant to the silver particles 2. preferable. The organic coating layer 3 is strongly attached to the surface of the silver particles 2 by adsorbing the dispersant to the surface of the silver particles 2 through a surfactant to form the organic coating layer 3, while the solvent or resin The compatibility with is good. Thereby, even if it mix | blends the silver powder 1 in which the organic coating layer 3 was formed in the surface of the silver particle 2 substantially uniformly with a solvent or resin, it can suppress that the organic coating layer 3 peels.

  For example, in the case of silver powder 1 using silver chloride as a starting material, it is preferable to use a cationic surfactant as the surfactant. Since the cationic surfactant is ionized into positive ions without being affected by pH, the effect of improving the adsorptivity to the silver powder 1 can be obtained.

  The cationic surfactant is not particularly limited, but is an alkyl monoamine salt type represented by a monoalkylamine salt, an alkyl diamine salt represented by an N-alkyl (C14 to C18) propylenediamine dioleate. Type, alkyltrimethylammonium salt type represented by alkyltrimethylammonium chloride, alkyldimethylbenzylammonium salt type represented by cocoalkyldimethylbenzylammonium chloride, quaternary ammonium salt type represented by alkyldipolyoxyethylenemethylammonium chloride , Alkylpyridinium salt type, tertiary amine type typified by dimethylstearylamine, polyoxyethylene alkylamine type typified by polyoxypropylene / polyoxyethylene alkylamine, N ′, N′-tris (2-hydroxyethyl) -N-alkyl (C14-18) 1,3-diaminopropane is preferably at least one selected from oxyethylene addition types of diamines represented by 4 Any of a quaternary ammonium salt type, a tertiary amine salt type, or a mixture thereof is more preferable.

  The cationic surfactant preferably has at least one alkyl group having a carbon number of C4 to C36 represented by methyl group, butyl group, cetyl group, stearyl group, beef tallow, hard beef tallow, and plant stearyl. Moreover, as an alkyl group, it is preferable that at least 1 sort (s) selected from polyoxyethylene, polyoxypropylene, polyoxyethylene polyoxypropylene, polyacrylic acid, and polycarboxylic acid is added. Since these alkyl groups are strongly adsorbed with the fatty acid used as the dispersant, the fatty acid can be strongly adsorbed when the dispersant is adsorbed on the silver particles 2 through the surfactant.

  The cationic surfactant is not particularly limited, but is preferably at least one selected from fluoride, bromide, iodide, chloride, sulfate, nitrate, and phosphate. These are preferable because they are generally contained as a main component of the surfactant and are easily available.

  As the dispersant, for example, protective colloids such as fatty acids, organometallics, and gelatins can be used. However, in view of adsorbability with a surfactant without fear of contamination with impurities, fatty acids or salts thereof may be used. preferable. In addition, you may add a fatty acid or its salt as an emulsion.

  The fatty acid used as the dispersant is not particularly limited, but is preferably at least one selected from stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, and linolenic acid. This is because these fatty acids have a relatively low boiling point and thus have little adverse effect on the wiring layer and electrodes formed using the silver paste. Fatty acids are inherently hydrophobic, and a large amount of fatty acid is present on the outer surface side of the organic coating layer 3 by adsorbing a dispersing agent on the surface of the silver particles 2 via a surfactant. It is thought that it will have sex. In particular, by selecting a surfactant that is easily adsorbed on the silver particles 2, for example, a charge that is ionized to a charge opposite to the surface of the silver particles 2, the dispersant can be sufficiently adsorbed via the surfactant. And the silver powder 1 becomes sufficiently hydrophobic.

  The addition amount of the surfactant is preferably in the range of 0.002% by mass to 1.000% by mass with respect to the silver particles 2. Since almost the entire amount of the surfactant is adsorbed on the silver particles 2, the added amount of the surfactant and the adsorbed amount are almost equal. When the addition amount of the surfactant is less than 0.002% by mass, the effect of suppressing aggregation of the silver particles 2 and improving the adsorptivity of the dispersant may not be obtained. On the other hand, when the addition amount exceeds 1.000 mass%, the conductivity of the wiring layer or electrode formed using the silver paste is not preferable.

  The addition amount of the dispersing agent is preferably in the range of 0.01% by mass to 3.00% by mass with respect to the silver particles 2, and more preferably 0.01% by mass to 1.00% by mass. Although the amount adsorbed on the silver particles 2 varies depending on the type of the dispersant, when the added amount is less than 0.01% by mass, the amount of the dispersant that can sufficiently obtain the effect of suppressing aggregation of the silver particles 2 is the silver particles. 2 may not be adsorbed. On the other hand, when the added amount of the dispersant exceeds 3.00% by mass, the dispersant adsorbed on the silver particles 2 increases, and the conductivity of the wiring layer and the electrode formed using the silver paste is sufficient. It may not be obtained.

  In the silver powder 1, by using a cationic surfactant, the adsorptivity of the surfactant to the silver particles 2 is greatly improved, so that the surfactant can be firmly adsorbed to the silver powder 1. More preferably, by stably adsorbing the surfactant adsorbed on the silver particles 2, it is possible to obtain the silver powder 1 that is further suppressed in aggregation and excellent in dispersibility in the paste.

  Next, the manufacturing method of the silver powder 1 of this invention is demonstrated for every process.

  The method for producing silver powder 1 is as follows in the case of using silver chloride as a starting material, for example. First, a silver complex solution containing a silver complex obtained by dissolving silver chloride with a complexing agent is mixed with a reducing agent solution, and a silver particle slurry is prepared by a wet reduction method in which the silver complex is reduced and silver particles 2 are precipitated. A process of generating is performed. In the process of producing the silver particle slurry, it is not necessary to install a nitrite gas recovery device and a treatment device for nitrate nitrogen in wastewater, which are required in the conventional method using silver nitrate as a starting material. Since the process has little influence, the manufacturing cost can be reduced.

  Specifically, in the step of producing a silver particle slurry, first, silver chloride is dissolved using a complexing agent to prepare a silver complex solution containing a silver complex. Although it does not specifically limit as a complexing agent, It is preferable to use the ammonia water which is easy to form a complex with silver chloride and does not contain the component which remains as an impurity. Moreover, it is preferable to use a high purity silver chloride. As such silver chloride, high-purity silver chloride having a purity of 99.9999% by mass is stably produced for industrial use.

  As a method for dissolving silver chloride, for example, when ammonia water is used as a complexing agent, a slurry of silver chloride may be prepared and ammonia water may be added. However, in order to increase the complex concentration and increase productivity, ammonia may be added. It is preferable to dissolve by adding silver chloride in water. Ammonia water that dissolves silver chloride may be a normal one that is used industrially, but is preferably as highly pure as possible in order to prevent contamination with impurities.

  Next, a reducing agent solution to be mixed with the silver complex solution is prepared. As the reducing agent, general hydrazine, formalin and the like can be used. Ascorbic acid is particularly preferable because it has a moderate reducing action and thus the crystal grains in the silver particles 2 are easy to grow. Since hydrazine and formalin have a strong reducing power, the crystals in the silver particles 2 tend to be small. Moreover, in order to control the uniformity or reaction rate of the reaction, the reducing agent may be used as an aqueous solution whose concentration is adjusted by dissolving or diluting with pure water or the like.

  When performing the reduction reaction, it is preferable to add a water-soluble polymer. Although it does not specifically limit as a water-soluble polymer to add, It is preferable that it is at least 1 sort (s) of polyethylene oxide, polyethyleneglycol, polyvinyl alcohol, or polyvinylpyrrolidone. The water-soluble polymer is adsorbed on the surface of the silver particles 2 so that the primary particles or secondary particles of the silver are not excessively aggregated when the silver complex is reduced and the silver particles 2 are precipitated. It acts as a dispersing agent to disperse. When the water-soluble polymer is not added, the nuclei generated by the reduction of the silver complex and the silver particles 2 on which the nuclei have grown may aggregate excessively, resulting in poor dispersibility. Even if the water-soluble polymer is not added, the particle size of the silver powder 1 can be adjusted to a degree preferable for the silver paste depending on the reduction conditions. However, the addition of the water-soluble polymer can make the particle size more preferable for the silver paste. It becomes possible to adjust. The addition amount of the water-soluble polymer may be appropriately determined depending on the type of the water-soluble polymer and the particle size of the silver powder 1 to be obtained, but is 1% by mass to 10% by mass with respect to the silver contained in the silver complex solution. % Is preferable. By adjusting the content of the water-soluble polymer to 1% by mass to 10% by mass, excessive aggregation of the primary particles or secondary particles of silver does not occur, and the particle size of the silver powder 1 is adjusted and the silver particles 2 are added in a later step. The organic coating layer 3 can be appropriately formed on the surface.

  The water-soluble polymer can be added to both or one of the silver complex solution and the reducing agent solution. The addition of the water-soluble polymer to either or both of the silver complex solution and the reducing agent solution may be added in advance to the solution to be added prior to the reduction treatment, and the silver complex-containing solution for the reduction treatment And may be added when the reducing agent solution is mixed. More preferably, it is better to mix a water-soluble polymer in the reducing agent solution in advance. This is a result confirmed experimentally. By mixing the reducing agent solution and the water-soluble polymer, the water-soluble polymer is present in the nucleation or nucleation field. It is considered that excessive aggregation is suppressed because the water-soluble polymer is rapidly adsorbed on the surface of the particle 2. The concentration when the water-soluble polymer is mixed with the silver complex solution is more preferably more than 3% by mass and 10% by mass or less. When the water-soluble polymer is added to the silver complex-containing solution in advance, it is difficult to supply the water-soluble polymer to the nucleation or nucleation site, and the water-soluble polymer is adsorbed to the surface of the silver particles 2 appropriately. Since there is a possibility that it cannot be performed, more than 3% by mass is added.

  When a water-soluble polymer is added, foaming may occur during the reduction reaction. Therefore, an antifoaming agent may be added to the silver complex solution or the reducing agent mixed solution. The antifoaming agent is not particularly limited, and may be usually used at the time of reduction. However, in order not to inhibit the reduction reaction, the addition amount of the antifoaming agent is preferably set to a minimum level at which an antifoaming effect can be obtained.

  In addition, about the water used when preparing a silver complex solution and a reducing agent solution, in order to prevent mixing of an impurity, it is preferable to use the water from which the impurity was removed, and it is especially preferable to use a pure water.

  In the step of generating the silver particle slurry, the silver complex solution prepared as described above and the reducing agent solution are mixed, the silver complex is reduced, and silver particles 2 are precipitated by a wet reduction method. This reduction reaction may be performed by a batch method or a continuous reduction method such as a tube reactor method or an overflow method. The particle size of the silver particles 2 can be controlled by the mixing rate of the silver complex solution and the reducing agent solution and the reduction rate of the silver complex, and can be easily controlled to the target particle size. And the obtained silver particle slurry is filtered with a filter etc., and the silver particle 2 is solid-liquid separated.

  Silver particles 2 obtained in this step have a large amount of chlorine ions and excess water-soluble polymer adsorbed on the surface. Therefore, in order to make the wiring layer and electrode formed using the silver paste sufficiently conductive, the obtained slurry of the silver particles 2 is washed in the next washing step, and these surface adsorbed materials are removed. It must be removed by washing.

  Although it does not specifically limit as a washing | cleaning method, after putting the silver particle 2 solid-liquid-separated from the slurry into a washing | cleaning liquid and stirring using a stirrer or an ultrasonic cleaner, it separates into solid and liquid again. A method of collecting the silver particles 2 is generally used. In addition, in order to sufficiently remove the surface adsorbate, it is preferable to repeat the operations consisting of charging into the cleaning liquid, stirring and washing, and solid-liquid separation as appropriate several times.

  The cleaning liquid may use water, but an alkaline aqueous solution may be used in order to efficiently remove chlorine. Although it does not specifically limit as an alkaline solution, It is preferable to use the sodium hydroxide aqueous solution with few remaining impurities and cheap. In the case of using an aqueous sodium hydroxide solution as the cleaning liquid, it is desirable to further wash the silver particles 2 or a slurry thereof with water in order to remove sodium after washing with the aqueous sodium hydroxide solution.

  The concentration of the aqueous sodium hydroxide solution used for washing is preferably 0.01 mol / l to 1 mol / l. If it is less than 0.01 mol / l, the cleaning effect is insufficient, and if it exceeds 1 mol / l, sodium may remain in the silver particles 2 beyond tolerance. The water used for the cleaning liquid is preferably water that does not contain an impurity element harmful to the silver particles 2, and pure water is particularly preferable.

  Further, a surface treatment process for forming the organic coating layer 3 on the surface of the silver particles 2 is performed. In the surface treatment step for the silver particles 2, the silver particles 2 are treated with a surfactant, or more preferably with a surfactant and a dispersant. This surface treatment may be performed at any stage as long as the silver particles 2 are not dried, but when the chlorine and the water-soluble polymer are completely removed, the silver particles 2 are aggregated. Since uniform surface treatment on the surface of the particles 2 may be difficult, the surface treatment is performed immediately after the reduction or immediately after the reduction, after the silver particles 2 are solid-liquid separated from the silver particle slurry, and before the cleaning step. It is preferable to perform the surface treatment simultaneously with the treatment or the cleaning step.

  In the surface treatment step, for example, the surface treatment is performed after solid-liquid separation of the silver particles 2 from the silver particle slurry, thereby preventing the adsorption of the surfactant and the dispersant due to residual organic substances caused by the reducing agent. The surface treatment can be performed efficiently. For this reason, sufficient organic coating layer 3 is formed, and compatibility and dispersibility with a solvent, resin, etc. are secured.

  In addition, when the cleaning is repeated a plurality of times, the surface treatment may be performed at any time of cleaning, but the chlorine remaining in the silver particles 2 and the excess water-soluble polymer do not affect the surface treatment. It is preferable to perform the surface treatment after removing the silver particles 2 to the extent that the aggregation of the silver particles 2 does not proceed, for example, after washing once or more.

  For example, as a specific method of preferable surface treatment using a surfactant and a dispersant, when performing the surface treatment before washing, the silver particles 2 obtained by solid-liquid separation from the silver particle slurry are separated from the surfactant and What is necessary is just to add and stir, after throwing in the water which added the dispersing agent, stirring after throwing in the water which added the surfactant. Moreover, you may perform washing | cleaning and surface treatment simultaneously by adding surfactant and a dispersing agent to a washing | cleaning liquid simultaneously, or adding a dispersing agent after addition of surfactant. In order to improve the adsorptivity of the surfactant and the dispersant to the silver particles 2, the silver particles 2 are added to the water or cleaning liquid to which the surfactant is added and stirred, and then the dispersant is further added and stirred. It is preferable.

  In addition, the apparatus used for washing | cleaning and surface treatment may be an apparatus normally used for washing | cleaning and surface treatment, for example, the reaction tank with a stirrer etc. can be used.

  Next, the collection process which collect | recovers the silver particle 2 which formed the organic coating layer 3 on the surface is performed. In this recovery step, the silver particles 2 are recovered by solid-liquid separation after surface treatment and washing. The apparatus used for solid-liquid separation may be a commonly used apparatus such as a centrifuge, a suction filter, a filter press, or the like.

  Next, after the cleaning and the surface treatment are completed, a drying process is performed in which the moisture of the silver particles 2 obtained by solid-liquid separation is evaporated and dried. As a drying method, for example, the silver particles 2 collected after the completion of the cleaning and surface treatment are placed on a stainless steel pad, and a commercially available drying apparatus such as an atmospheric oven or a vacuum dryer is used at a temperature of 40 ° C. to 80 ° C. What is necessary is just to heat.

  Next, a pulverization / classification step of sufficiently pulverizing and classifying to a preferred particle size for silver paste with sufficiently weak energy that does not damage the organic coating layer 3 on which the dried silver particles 2 are formed. And silver powder 1 is obtained. The crushing method is not particularly limited as long as it does not damage the organic coating layer 3, and it is preferable to use a device having a weak crushing force such as a jet mill or a high-speed stirrer. An apparatus having a strong crushing force is not preferable because not only the organic coating layer 3 is damaged but also the silver powder 1 is deformed. The classifying device is not particularly limited, and an airflow classifier, a sieve, or the like can be used.

  The crushing treatment refers to an operation of breaking up the aggregated powder after drying into a state of primary particles or secondary particles before the surface treatment. Various means such as a ball mill, a collision-type airflow pulverizer, an impact-type pulverizer, and a cylindrical high-speed stirrer can be used as the pulverization means, but if the pulverization energy is too weak In addition, the agglomerates generated during the wet process or the drying process cannot be sufficiently unraveled, and the internal friction angle cannot be reduced to 20 ° or less. On the other hand, when the energy of pulverization is excessively increased, the organic coating layer 3 on the surface of the silver powder 1 is damaged, or the bond between primary particles in the secondary particles is destroyed, A newly exposed surface of metallic silver is newly exposed on the surface of the silver powder 1, so that the hydrophilicity of the surface is increased, the contact angle in a 50% by volume aqueous solution of methanol is less than 100 °, and the surface SP value by the acetone titration method is 18 It will be bigger. Furthermore, the exposed new surface may become an active point and re-aggregate during storage, and the internal friction angle may increase with time.

  Therefore, even when using any crusher, the crushing conditions are adjusted while checking parameters such as the internal friction angle, contact angle, and surface SP value, and the destruction of the bonded portion where primary particles are bonded to each other is suppressed. At the same time, it is necessary to add a crushing treatment that does not damage the organic coating layer 3 on the surface of the silver powder 1, that is, the organic coating layer 3 is peeled off and the silver particles 2 are not exposed. The crushing conditions are such that the number of revolutions of the crushing device, the crushing time, the temperature, and the like are appropriately determined depending on the size of the crushing device, the state of the produced silver powder 1, and the like.

  For example, when a high-speed stirrer is used, the conditions vary depending on the capacity of the stirrer, but the peripheral speed and stirring time of the stirrer are adjusted according to the input amount of the silver particles 2 so that the organic coating layer 3 is not damaged. . As crushing conditions when a high-speed stirrer is used, for example, it is preferable that the peripheral speed is 10 m / sec to 40 m / sec and the crushing time is about 10 minutes to 60 minutes.

  In addition, after the pulverization treatment, classification treatment such as an air flow method or a sieving method is performed for the purpose of removing agglomerated silver powder aggregates that have been generated or mixed in the silver particle slurry generation step or the pulverization / classification step. It is preferable.

  In the manufacturing method of the silver powder 1 mentioned above, after forming the organic coating layer 3 on the surface of the silver particle 2 obtained by the silver particle slurry production | generation process, it suppresses that the new surface of metallic silver newly produces | generates in the silver particle 2. By crushing in this manner, it is possible to obtain a low hydrophilic silver powder 1 having an internal friction angle of 20 ° or less and a contact angle in a 50% by volume methanol aqueous solution of 100 ° or more. Furthermore, this silver powder 1 has a surface SP value of 18 or less by the acetone titration method. Thereby, in this manufacturing method, when the internal friction angle of the silver powder 1 is 20 ° or less and the contact angle in a 50% by volume aqueous solution of methanol is 100 ° or more, the wettability of the silver paste to the solvent, resin, etc. Is excellent in dispersibility and can be easily pasted to produce a silver paste.

  Moreover, since the silver powder 1 manufactured by this manufacturing method has been subjected to sufficient surface treatment, the internal friction angle is 20 ° or less not only immediately after the manufacture but also when mixed with the resin or solvent of the silver paste. Therefore, even when mixed with a solvent after a while after production, it has good compatibility with solvents and resins, etc., and is excellent in dispersibility, so it can be easily pasted. .

  Therefore, since the above-described silver powder 1 is dispersed evenly in the silver paste, electrical connection can be improved when a wiring layer or an electrode is formed with the silver paste.

  Specific examples to which the present invention is applied will be described below, but the present invention is not limited to these examples.

<Example 1>
In Example 1, first, 2490 g of silver chloride (manufactured by Sumitomo Metal Mining Co., Ltd.) was added to 36 L of 25 mass% ammonia water maintained at a liquid temperature of 36 ° C. in a 38 ° C. bath while stirring, and a silver complex solution And kept at 36 ° C. in a warm bath.

  On the other hand, 1318 g of a reducing agent, ascorbic acid (manufactured by Kanto Chemical Co., Ltd., reagent) was dissolved in 10 L of pure water at 36 ° C. to prepare a reducing agent solution.

  Next, a solution of 187.5 g of water-soluble polymer polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA205, 10.0% by mass with respect to silver particles) was taken and dissolved in 4.6 L of 36 ° C. pure water. Was mixed with the reducing agent solution.

  Next, the silver complex solution and the reducing agent solution are fed into a bowl at 2.44 L / min and 0.90 L / min using a MONO pump (Hyojin Equipment Co., Ltd.), respectively, Reduced. The reduction rate at this time is 127 g / min in terms of silver. In addition, a PVC pipe having an inner diameter of 25 mm and a length of 725 mm was used for the above-mentioned rod. The slurry containing silver particles obtained by reduction of the silver complex was received in a receiving tank while stirring. After completion of reception, stirring in the receiving tank was continued for 60 minutes. The silver particle slurry after stirring was filtered with a filter press to separate the silver particles into solid and liquid.

  Next, surface treatment was performed on the solid-liquid separated silver particles. 0.90 g of a polyoxyethylene-added quaternary ammonium salt (trade name: Silasol, 0.048% by mass with respect to silver particles), which is a commercially available cationic surfactant as a surface treatment agent, and a dispersant A stearic acid emulsion 16.87 g (manufactured by Chukyo Yushi Co., Ltd., Cellosol 920, 0.90% by mass with respect to silver particles) is put into 20 L of pure water and stirred to surface-treat the surface of the silver particles. did. Thereafter, NaOH was added to a concentration of 0.05 mol / L, and the mixture was stirred and washed for 15 minutes, and then filtered through a filter press to collect silver particles.

  Subsequently, before drying the collected silver particles, the silver particles were put into a 0.05 mol / L NaOH aqueous solution, washed by stirring for 15 minutes, and then collected by filtration with a filter press. Thereafter, this washing operation and solid-liquid separation operation by filtration were repeated three times.

  The silver particles separated into solid and liquid were put into 20 L of pure water, stirred and filtered, and then the silver particles were transferred to a stainless steel pad and dried at 60 ° C. for 10 hours in a vacuum dryer.

  After drying, crushing and classification were performed. For crushing, 1.5 kg of silver particles after drying is taken, put into a 5 L high speed stirrer (FM5C / I manufactured by Nippon Coke Co., Ltd.), and the rotating blade is rotated at a peripheral speed of 15 m / sec for 30 minutes. The crushing process was performed. Furthermore, the silver particles after pulverization were classified at a classification point of 7 μm using an airflow classifier (Japan Mining Co., Ltd. EJ-3 type) to obtain silver powder. The average particle diameter of the primary particles by SEM observation of the obtained silver powder was 0.98 μm, and the particle size (D50) measured using a laser diffraction scattering method was 2.35 μm.

  The silver powder of Example 1 was obtained as described above. About the obtained silver powder, the internal friction angle, the contact angle, and the surface SP value were measured.

For the measurement of the internal friction angle, a powder layer shear force measuring device (NS-S300 type manufactured by Nano Seeds Co., Ltd.) was used. After filling 18 g of silver powder into a 15 mm inner diameter SUS cell at room temperature, the indentation load was set to 20 N, and the load was applied at an indentation speed of 0.2 mm / sec. After reaching the set load, side sliding started at a speed of 10 μm / second 100 seconds later. The sampling frequency was 10 Hz. The value obtained by dividing the indentation load at the start of side-sliding by the cell cross-sectional area is taken as the vertical stress σ (N / cm ² ), and the maximum shearing force measured after side-sliding is divided by the cell cross-sectional area. The value obtained was defined as the shear stress τ (N / cm ² ).

  Next, the setting value of the indentation load was 40 N, and the normal stress σ and the shear stress τ were measured in the same manner. Further, the vertical stress σ and the shear stress τ were measured in the same manner with the indentation load set value set to 60N. The vertical stress σ obtained under the above three conditions is plotted on the horizontal axis and the shear stress τ is plotted on the vertical axis, and the slope (degree) of the approximate straight line obtained using the least square method is defined as the internal friction angle.

  The internal friction angle of the silver powder of Example 1 measured by the above method was 7.1 °. After this silver powder was allowed to stand at room temperature for 1 month, the internal friction angle was measured by the same method as described above, and it was 7.8 °.

  The contact angle was measured with a 50% by volume aqueous solution of methanol using a contact angle measuring device (CA-X150 manufactured by Kyowa Interface Science Co., Ltd.). Silver powder was press-molded at a load of about 1 MPa at room temperature to obtain a flat test specimen filled with silver powder. The contact angle formed by a 50% by volume methanol aqueous solution was measured on this test specimen. The contact angle of the silver powder of Example 1 measured by this method was 110 °.

  The surface SP value was measured by the acetone titration method as follows. Add 50 ml of water to 0.5 g of silver powder, add acetone continuously to the water containing silver powder while stirring gently, and the silver particles floating on the water surface are dispersed and the solution becomes cloudy. It was. The surface SP value of the acetone aqueous solution calculated from the added volume of acetone at this time was defined as the surface SP of the silver powder. The surface SP value of the silver particles of Example 1 measured by this method was 16.7.

  Next, paste formation was evaluated using the obtained silver powder. For evaluation of pasting, first, 9.2 g of silver powder, 0.8 g of a vehicle having a weight ratio of epoxy resin (Mitsubishi Chemical Co., Ltd., JER 819) and terpineol in a 1: 7 weight were weighed in a stainless steel small dish. At this time, it was observed that the surface of the silver powder was quickly wetted by the vehicle. Next, when this was mixed using a metal spatula, mixing and dispersion proceeded easily, and a paste could be formed. Furthermore, this paste was kneaded at 2000 rpm for 5 minutes using a self-revolving kneading machine (ARE-250, manufactured by Shinky Corporation) to obtain a uniform silver paste. When the dispersibility of the obtained silver paste was evaluated using a grind gauge, the maximum particle size Dmax was as small as 7 μm and showed excellent dispersibility.

<Example 2>
In Example 2, the amount of polyvinyl alcohol was 75 g (4.00% by mass with respect to silver particles), and the rotating blades of the high-speed stirrer were rotated at a peripheral speed of 28 m / sec. Silver powder was obtained and evaluated in the same manner. The average particle size of the primary particles of the obtained silver powder was 1.01 μm, and the particle size (D50) was 2.73 μm.

  The internal friction angle of the silver powder of Example 2 was 10.4 °, and the internal friction angle after standing for 1 month at room temperature was 10.6 °. Further, the contact angle of the silver powder of Example 2 was 109 °, and the surface SP value was 17.4.

  Next, evaluation of pasting similar to Example 1 was performed using the obtained silver powder. It was observed that the surface of the silver powder was quickly wetted by the vehicle. When this was mixed using a metal spatula, mixing and dispersion proceeded easily and a paste could be formed. Further, this paste was kneaded with a self-revolving kneader in the same manner as in Example 1 to obtain a uniform silver paste. When the dispersibility of the obtained silver paste was evaluated using a grind gauge, the maximum particle size Dmax was as small as 6 μm and showed excellent dispersibility.

<Comparative Example 1>
In Comparative Example 1, silver powder was obtained and evaluated in the same manner as in Example 1 except that the rotating blades of the high-speed stirrer were rotated at a peripheral speed of 42 m / sec. The average particle size of the primary particles of the obtained silver powder was 0.99 μm, and the particle size (D50) was 1.82 μm. The internal friction angle of the silver powder of Comparative Example 1 was 20.8 °, which was considerably higher than that of the example. Moreover, the contact angle of the silver powder of the comparative example 1 was 85 degrees, and surface SP value was 18.7.

  Next, evaluation of pasting similar to Example 1 was performed using the obtained silver powder. Little wetting by the vehicle on the surface of the silver powder was observed. Moreover, when this was stirred using a metal spatula, it remained in a large clay state and could not be made into a paste. Further, this silver paste was kneaded in a self-revolving kneader in the same manner as in Example 1 to obtain a paste. When the dispersibility of the obtained silver paste was evaluated using a grind gauge, the maximum particle size Dmax was as large as 20 μm and the dispersibility was poor.

<Comparative example 2>
In Comparative Example 2, silver powder was obtained and evaluated in the same manner as in Example 2 except that the rotating blades of the high-speed stirrer were rotated at a peripheral speed of 7 m / sec. The average particle size of the primary particles of the obtained silver powder was 1.00 μm, and the particle size (D50) was 3.52 μm. Moreover, the internal friction angle of the silver powder of the comparative example 2 was 25.8 degrees, and was quite high compared with the Example. Moreover, the contact angle of the silver powder of Comparative Example 2 was 110 °, and the surface SP value was 17.4 °.

  Next, evaluation of pasting similar to Example 1 was performed using the obtained silver powder. Little wetting by the vehicle on the surface of the silver powder was observed. Moreover, when this was stirred using a metal spatula, it remained in a large clay state and could not be made into a paste. Further, this paste was kneaded in a self-revolving kneader in the same manner as in Example 1 to obtain a paste. When the dispersibility of the obtained silver paste was evaluated using a grind gauge, the maximum particle size Dmax was as large as 18 μm and the dispersibility was poor.

  From the above examples and comparative examples, even in the case of silver powder produced by the same method, as compared with the comparative example, the examples 1 and examples were sufficiently crushed so as not to damage the coating formed on the surface of the silver powder. In No. 2, the internal friction angle was 20 ° or less, the contact angle in a 50% by volume aqueous methanol solution was 100 ° or more, and a silver powder having good compatibility with the vehicle and excellent dispersibility was obtained. Moreover, in Example 1 and Example 2, the surface SP value by acetone titration method was 18 or less. Furthermore, in Example 1 and Example 2, even after the silver powder was left at room temperature for 1 month, the internal friction angle was 20 ° or less, and aggregation was suppressed.

  On the other hand, in Comparative Example 1, the crushing conditions were too strong, the organic coating layer formed on the surface of the silver powder was damaged, the internal friction angle was larger than 20 °, and the contact angle was also smaller than 100 °. . Furthermore, the surface SP value was also larger than 18. Moreover, in the comparative example 2, since the crushing conditions were weak and the aggregate could not be sufficiently loosened, the internal friction angle was considerably large as 25.8 °. Thereby, in the comparative example 1 and the comparative example 2, compatibility with a vehicle was bad and the dispersibility of silver powder became bad.

The silver powder according to the present invention that achieves the above-mentioned object has an organic coating layer formed of a cationic surfactant and a fatty acid or a salt thereof on the surface, has an internal friction angle of 20 ° or less, and methanol. The contact angle in a 50% by volume aqueous solution is 100 ° or more.

The silver powder production method according to the present invention that achieves the above-described object is to form an organic coating layer formed of a cationic surfactant and a fatty acid or a salt thereof on the surface by subjecting the silver particles to a surface treatment. , using a high speed stirrer, the peripheral speed of the stirring blade is 10 m / sec or more, the following conditions 40 m / sec, and performing a sufficient disintegration treatment so as not to damage the organic coating layer.

Claims (5)

  A silver powder having an internal friction angle of 20 ° or less and a contact angle in a 50% by volume aqueous methanol solution of 100 ° or more.   Furthermore, the surface SP value by an acetone titration method is 18 or less, Silver powder of Claim 1 characterized by the above-mentioned.   The silver powder according to claim 1 or 2, wherein the internal friction angle when mixed with a solvent of silver paste is 20 ° or less. After forming the organic coating layer on the surface by performing surface treatment on the silver particles synthesized using the wet reduction method, perform sufficient crushing treatment to the extent that the organic coating layer is not damaged,
A method for producing silver powder, comprising producing a silver powder having an internal friction angle of 20 ° or less and a contact angle in a 50% by volume aqueous methanol solution of 100 ° or more.   5. The method for producing silver powder according to claim 4, wherein the pulverization method is performed using a high-speed stirrer and the peripheral speed of the stirring blade is 10 m / second or more and 40 m / second or less.

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