TW201306967A - Silver powder and method for producing same - Google Patents

Abstract

In order to provide a silver powder which has excellent compatibility with a solvent, a resin, etc. in a silver paste, and excellent dispersibility, and a method for producing the same, a silver powder according to the invention has an organic coating layer formed on the surface thereof and has an internal friction angle of 20 or less and a contact angle with an aqueous solution of 50 vol% methanol of 100 or more.

Description

Silver powder and its manufacturing method

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 used silver paste when a wiring layer or an electrode of an electronic device is formed, and a method for producing the same.

The present application is based on Japanese Patent Application No. 2011-134337, filed on Jun. Application.

A silver paste such as a resin type silver paste or a calcined silver paste is widely used for formation of a wiring layer or an electrode of an electronic device. After the silver paste is applied or printed on various substrates, a conductive film such as a wiring layer or an electrode can be formed by heat curing or heating and firing.

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

Further, the calcined silver paste is formed of silver powder, glass, solvent, or the like, and is printed on a conductor pattern or a terminal, and then fired at 600 ° C to 800 ° C to form a conductive film to form a wiring layer or an electrode.

The wiring layer or the electrode formed by the silver paste is formed by the connection of the silver powder to form an electrically connected current path.

The silver powder used in these silver pastes has a particle size of 0.1 μm to several Μm, the particle size of the silver powder used may vary depending on the width of the wiring layer or the thickness of the electrode formed. Further, by uniformly dispersing the silver powder in the silver paste, a wiring layer having a uniform width and an electrode having a uniform thickness can be formed.

In general, a method of producing a silver paste is to measure and place each component in a predetermined container, and perform preliminary kneading using a universal stirrer or a kneading machine, and then perform main kneading using a triaxial roll or the like. In the preliminary kneading, it is important to sufficiently wet and disperse the respective constituent elements, and the preliminary kneading is sufficiently performed to prevent the occurrence of the silver foil in the main kneading, and the particle size of the silver powder in the silver paste is rapidly lowered. The particle size to the purpose makes it possible to uniformly disperse the silver powder in the silver paste.

Therefore, in the silver paste, it is required that not only the particle diameter is uniform but also agglomerated, and the vehicle is composed of a solvent or a resin, and the mixture is good in silver. The characteristics of high dispersibility in the paste. Such characteristics are not only due to the structural properties of the powder such as bulk density or particle size distribution, but also due to the sliding property of the powder surface or the chemical nature of the surface of the silver powder such as hydrophilicity and hydrophobicity.

In the case of the silver powder used in the silver paste, for example, Patent Document 1 discloses that the spherical silver powder has a specific bulk density and a molded body density, and the compatibility with the vehicle liquid or the resin is good. However, Patent Document 1 does not describe surface chemistry, and it is difficult to control the compatibility with a vehicle or a resin only by such a structural parameter. Further, in the method for producing silver powder in Patent Document 1, there is no description of a production method such as a crushing method of silver powder (which has a large influence on the surface chemistry described above).

On the other hand, Patent Document 2 describes that the particle size distribution will be adopted. The ratio D50/DIA of the measured D50 value to the particle diameter DIA obtained by image analysis is the basis of the degree of aggregation of the powder, and if it is below a specific value, it is low in cohesiveness. Indeed, the smaller the value, the less the number of aggregates in the cognitive powder. However, in Patent Document 2, similarly to Patent Document 1, the description relates to the description of the surface chemistry of the silver powder which affects the compatibility with the vehicle liquid or the resin during the paste formation, or the manufacturing method which affects the chemical properties. The records have not been revealed.

For the silver powder used in the silver paste, the bulk density, the density of the molded body, the degree of aggregation of the powder, etc., as in Patent Document 1 or Patent Document 2, cannot sufficiently improve the silver paste with the solvent or the resin only in terms of structural properties. Such as compatibility and dispersibility. Therefore, further improvement in compatibility and dispersibility is required for the silver powder.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 2006-097086

[Patent Document 2] Japanese Patent Publication No. 2004-100013

In view of the above-described conventional matters, the present invention has an object of providing a silver powder excellent in compatibility and dispersibility with a solvent or a resin of a silver paste, and a method for producing the same.

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

A method for producing a silver powder according to the present invention which achieves the above object is characterized in that, by subjecting silver particles to a surface treatment, an organic film layer is formed on the surface, and then the crushing treatment is sufficiently performed so as not to cause damage to the organic film layer.

In the present invention, the internal friction angle of the silver powder is 20° or less, and the contact angle of the 50% by volume aqueous solution of methanol is 100° or more, and the compatibility with the solvent or the resin is high, and the dispersibility is excellent, and the dispersibility is easy. Paste. Thereby, the present invention can improve the quality and productivity of the silver paste.

"Formation of Inventions"

Hereinafter, the silver powder to which the present invention is applied and a method for producing the same will be described in detail. Further, the present invention is not particularly limited, and the present invention is not limited to the following detailed description.

The 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 calcined silver paste composed of glass, a solvent, or the like. The resin type silver paste or the calcined type silver paste containing the silver powder 1 is used for formation of a wiring layer or an electrode. Therefore, in order to attempt to electrically continue, the silver powder 1 must have good compatibility with the solvent or resin of the silver paste. And uniformly dispersed in the paste. Silver powder 1 is particularly suitable for use with a silver paste of a hydrophobic solvent.

The silver powder 1 has an internal friction angle of 20 or less, and has a contact angle of 100 or more in a 50% by volume aqueous solution of methanol. Further, the silver powder 1 preferably has a surface SP value of 18 or less by acetone titration. The silver powder 1 is improved in sliding by setting the surface chemical property of the powder to a low hydrophilicity, and is compatible with a solvent such as a solvent or a resin of a silver paste. In addition, the so-called silver powder 1 is also set to include secondary particles and aggregates in addition to primary particles. Here, as shown in FIG. 1(A), the primary particles refer to individual spherical silver particles 2; as shown in FIG. 1(B), primary particles are bonded by fusion or fixation. The silver particles 2 connected in plurality are referred to as secondary particles. As shown in FIG. 1(C), the primary particles or the secondary particles of the silver particles 2 are aggregated and referred to as aggregates.

In the silver powder 1, the average particle diameter of the primary particles is preferably in the range of 0.1 μm to 1.5 μm. When the average particle diameter of the primary particles is 0.1 μm or more, when a silver paste (conductive paste) is produced, electric resistance is not generated, and it is possible to obtain conductivity. In addition, by setting the average particle diameter of the primary particles to 1.5 μm or less, the dispersibility is not deteriorated, and silver flakes are not generated during kneading, and the printability is also improved. The average particle diameter of the primary particles can be measured by scanning electron microscope (SEM) observation. Further, the particle size of the silver powder 1 is D50 (volume accumulation 50% diameter) measured by a laser diffraction scattering method, preferably 0.5 μm to 5 μm, more preferably 1.0 μm to 4.0 μm. By setting D50 to this range, it is the best for use as a silver paste, and the internal friction angle is optimized to improve the paste. Dispersibility.

The internal friction angle of the silver powder 1 is a parameter indicating the easiness of sliding of the powder, and can be measured by a commercially available powder layer shear force measuring device. In the case of silver powder 1 for silver paste, when the internal friction angle exceeds 20°, the sliding between the particles (primary particles, secondary particles or aggregates which are independently present in the silver powder 1) is deteriorated. As a result, when the paste is formed, the solvent or the resin cannot enter between the particles of the silver powder 1, and only one part of the surface of the silver powder 1 can be wetted. In such a state, even if stirring is performed, the particles are not easily decomposed, and the dispersibility of the silver powder 1 is deteriorated. In the case of the silver powder 1 having poor dispersibility, it takes time not only to wet the components but also to prepare for the dispersion, and the coagulated silver powder 1 is also pressed when the main mixing is performed by a triaxial roll machine or the like. It is easy to produce silver flakes. Therefore, the silver powder 1 has an internal friction angle of 20 or less, and the sliding property is good, and the solvent or the resin enters between the particles, and since the compatibility is good, the dispersibility in the silver paste is good.

Further, the silver powder 1 is, after the manufacture, the internal friction angle is of course 20 or less, and it is preferable that the internal friction angle is maintained at 20 or less even after the production, and the paste is mixed even in a solvent or a resin. At the time of the transformation, it is also below 20°. For example, after the silver powder 1 is produced, even after passing through, for example, room temperature for one month, the internal friction angle of the silver powder 1 is 20 or less. The internal friction angle is a parameter which changes due to the aggregation of the particles. Even after the production, even if the powder has a low degree of aggregation, the internal friction angle is also increased by the temporal cohesion between the particles. When the internal friction angle is more than 20° over time, the dispersibility is lowered when the paste is formed, and the silver powder is lowered. 1 will cause a variety of problems such as cohesion. Here, as long as the internal friction angle of 20° or less can be maintained, since the progress of aggregation can be suppressed, it is possible to prevent the occurrence of problems during the paste formation.

Next, the contact angle of the silver powder 1 will be described. The 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 indicating the ease of wetting of the surface of the silver powder 1 with respect to the solvent, for example, the larger the contact angle with respect to water, the easier it is to be wetted by the hydrophobic paste solvent. Conversely, the smaller the contact angle with respect to water, the more hydrophilic it is, and the wetting with respect to the hydrophobic paste solvent is deteriorated. The contact angle of the silver powder 1 is generally measured on the surface to be formed. However, when the water is a large powder when measured by water, the water droplets become a true round shape on the surface of the formed powder due to water droplets. It will slide and it is difficult to measure accurately. Therefore, a method in which a solvent having a low polarity such as methanol is added to water and the polarity of the solvent is lowered is measured. At the time of making a silver paste, a hydrophobic solvent is generally used. Therefore, when the silver powder 1 is a hydrophilic surface having a contact angle of less than 100°, the compatibility of the paste with respect to the solvent or the resin is poor, and the silver powder 1 does not wet with the solvent or the resin, and is paste-formed. It will become difficult. Further, when the paste is forcibly mixed and re-agglomerated due to poor dispersion stability, separation of the paste is likely to occur.

Next, the surface SP value of the silver powder 1 will be described. The surface SP value of the silver powder 1 is 18 or less. The surface SP value is a parameter indicating the surface polarity of the silver powder 1, and the hydrophobicity is obtained as the case is smaller, and the hydrophilicity is made as the case is larger.

The surface SP value can be measured using a commercially available powder wettability tester or the like. The measurement can be carried out simply by using an acetone titration method as described in "Color material, 62 (9) 524-528". In this acetone titration method, a hydrophobic powder is added to water (A [ml]) and floated. The mixture was slowly stirred using a stirrer while dropping acetone in a burette, and the amount of acetone (B [ml]) required until the powder was wetted and settled was measured. The SP value of water is 23.43, and the SP value of acetone is 9.75. From the volume of water used and the volume of acetone used, the SP value of the settled acetone solution is calculated by the following formula 1, and this value is set as silver powder. 1 surface SP value.

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 respect to the solvent or the resin is deteriorated, and the silver powder 1 and the solvent or the resin are not wetted, and the paste becomes difficult. Further, even if the paste is forcibly kneaded, the dispersion stability is re-agglomerated, and the separation of the paste is likely to occur. On the other hand, when the surface SP value of the silver powder 1 is 18 or less, the hydrophilicity of the silver powder 1 does not become excessively large, and the compatibility with a solvent or a resin becomes good, and the dispersibility is excellent, so the paste is changed. It's easy.

The silver powder 1 is subjected to surface treatment by the silver particles 2 obtained by the wet reduction method. As shown in FIG. 1, by forming the organic film layer 3 on the surface of the primary particles or secondary particles, the internal friction angle can be made The contact angle of the 50% by volume aqueous solution of methanol is set to 100° or more, and the surface SP value by the acetone titration method may be set to 18 or less. this The organic film layer 3 can be formed by a surfactant, a surfactant, and a dispersing agent.

The organic film layer 3 is preferably formed by a surfactant and a dispersing agent. In the case of the silver powder 1, the aggregation of the surfactant is suppressed by the adsorption of the surfactant to the silver particles 2 in the ionized state. However, when the aggregation is suppressed only by the surfactant, the amount of addition is excessive. Therefore, even if a good dispersion state is obtained in the silver paste, the conductivity of the wiring layer or the electrode may be insufficient. Here, in order to suppress the aggregation of the silver powder 1 and to make the conductivity of the wiring layer or the electrode sufficient, it is effective to use a surfactant and a dispersant in combination.

The organic film layer 3 is preferably formed by dispersing a dispersing agent at the time of adsorbing or adsorbing the silver particles 2 of the surfactant, and further forming a dispersing agent on the surfactant adsorbed on the silver particles 2. The organic film layer 3 is formed by adsorbing the dispersant on the surface of the silver particles 2 by the surfactant, and the organic film layer 3 is strongly adhered to the surface of the silver particles 2, and becomes a solvent or a resin. The compatibility is good. By this means, even if the silver powder 1 (the surface of the silver particles 2 is formed with almost the same organic film layer 3) is mixed in a solvent or a resin, peeling of the organic film layer 3 or the like can be suppressed.

For example, when silver powder 1 containing silver chloride as a starting material is used, a cationic surfactant is preferably used as the surfactant. Since the cationic surfactant is ionized into a positive ion without being affected by the pH, the effect of improving the adsorption property of the silver powder 1 can be obtained.

The cationic surfactant is not particularly limited, and is preferably selected from the group consisting of alkyl monoamine salts represented by monoalkylamine salts; and N-alkyl groups (C14 to C18). An alkyl diamine salt type represented by propylene diamine dioleate; an alkyl trimethyl ammonium salt type represented by alkyl trimethyl ammonium chloride; chlorinated with palm alkyl dimethyl benzyl An alkyl dimethyl benzyl ammonium salt type represented by ammonium; a 4-grade ammonium salt type represented by an alkyl dimer oxyethylene methyl ammonium chloride; an alkyl acridine salt type, dimethyl stearylamine The 3-grade amine type represented by polyoxypropylene. a polyoxyethylene alkylamine type represented by a polyoxyethylene alkylamine; a N,N',N'-parade (2-hydroxyethyl)-N-alkyl (C14-18) 1,3-diamine At least one of the oxyethylene addition molding of the diamine represented by the propane is more preferably any one of a quaternary ammonium salt type and a ternary amine salt type or a mixture thereof.

Further, the cationic surfactant preferably has at least one carbon number of C4 to C36 represented by methyl, butyl, hexadecyl, octadecyl, tallow, hardened tallow, and plant stearin. alkyl. The alkyl group is preferably one selected from the group consisting of polyoxyethylene, polyoxypropylene, polyoxyethylene polyoxypropylene, polyacrylic acid, and polycarboxylic acid. Since the adsorption of these alkyl groups with the fatty acid used as the dispersing agent is strong, when the dispersing agent is adsorbed to the silver particles 2 by the surfactant, the fatty acid can be strongly adsorbed.

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

As the dispersing agent, for example, a protective colloid such as a fatty acid, an organic metal or gelatin can be used. However, when it is considered that no impurities are mixed in and adsorbed with the surfactant, it is preferred to use a fatty acid or a salt. Still, the fatty acid or the salt can be added as an emulsion.

The fatty acid used as the dispersing agent is not particularly limited, but is preferably selected from at least stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, and linoleic acid. 1 species. Since these fatty acids have a relatively low boiling point, there is little adverse effect on the wiring layer or the electrode formed using the silver paste. The fatty acid is inherently hydrophobic, and the dispersing agent is adsorbed on the surface of the silver particle 2 by the surfactant, and most of it is present on the outer surface side of the organic film layer 3, and it is considered that the silver powder 1 becomes hydrophobic as it is. Sexually. It is particularly easy to adsorb to the silver particles 2, for example, by selecting a surfactant which is ionized by a charge opposite to the surface of the silver particles 2, so that the dispersant can be sufficiently used by the surfactant. Adsorption, silver powder 1 becomes fully hydrophobic.

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

The amount of the dispersant added is preferably in the range of 0.01% by mass to 3.00% by mass, more preferably 0.01% by mass to 1.00% by mass based on the silver particles 2. Although the amount of adsorption of the silver particles 2 varies depending on the type of the dispersing agent, when the amount added is less than 0.01% by mass, the silver particles 2 are dispersed without being adsorbed in an amount sufficient to suppress the aggregation effect of the silver particles 2. Agent situation. On the other hand, when the amount of the dispersant added exceeds 3.00% by mass, the amount of the dispersant adsorbed to the silver particles 2 increases, and the wiring layer or the electrode formed using the silver paste may not sufficiently obtain conductivity.

Since the silver powder 1 is a cationic surfactant, since the adsorbability of the surfactant to the silver particles 2 is greatly improved, the surfactant can be strongly adsorbed to the silver powder 1. More preferably, the adsorbent adsorbed on the silver particles 2 is stably adsorbed, whereby the silver powder 1 which further suppresses aggregation and is excellent in dispersibility in the paste can be obtained.

Next, a description will be given of each step of the method for producing the silver powder 1 of the present invention.

The method for producing the silver powder 1, for example, when silver chloride is used as a starting material, is as follows. First, the following steps are carried out: mixing a silver complex solution (which is obtained by dissolving silver chloride by a distoring agent) with a reducing agent solution, and reducing the silver complex. A silver particle slurry is produced by a wet reduction method in which silver particles 2 are deposited. In the step of producing a silver particle slurry, it is not necessary to provide a nitrous acid gas recovery device or a nitric acid nitrogen treatment device in a waste water in a conventional method using silver nitrate as a starting material, and also for the environment. The impact is a small process, so it is possible to try to reduce the manufacturing cost.

Specifically, in the step of producing a silver particle slurry, first, silver chloride is dissolved using a distoring agent, and a silver complex solution containing a silver complex is prepared. The distorting agent is not particularly limited, and it is preferred to use ammonia water which is easily formed into a complex with silver chloride and which does not contain a component as an impurity. Further, it is preferred that silver chloride be used in a high purity. As such a silver chloride, purity 99.9999% by mass of high-purity silver chloride is industrially stable.

As a method of dissolving silver chloride or the like, for example, when ammonia water is used as the distorting agent, ammonia water may be added after the slurry of silver chloride is produced, and in order to increase the concentration of the complex to improve productivity, chlorination is preferred. Silver is added to the ammonia water for dissolution. Ammonia water in which silver chloride is dissolved can be used by a general industrial user. However, in order to prevent impurities from being mixed, it is preferred to use ammonia water of the highest purity as possible.

Next, a reducing agent solution mixed with the silver complex solution is prepared. As the reducing agent, hydrazine or formalin or the like can be generally used. Since the reduction of ascorbic acid is slow, the crystal grains in the silver particles 2 tend to grow, which is particularly preferable. Since the reducing power of hydrazine or fumarin is strong, the crystal in the silver particles 2 tends to be small. Further, in order to control the uniformity of the reaction or the reaction rate, the reducing agent may be dissolved or diluted with pure water or the like to be used as a concentration-adjusted aqueous solution.

When the reduction reaction is carried out, it is preferred to add a water-soluble polymer. The water-soluble polymer to be added is not particularly limited, and at least one of polyethylene oxide, polyethylene glycol, polyvinyl alcohol or polyvinylpyrrolidone is preferred. When the silver complex 2 is precipitated and the silver particles 2 are precipitated, the water-soluble polymer is adsorbed on the surface of the silver particles 2 so as not to disperse the primary particles or the secondary particles of silver, and the silver particles 2 are dispersed. The role of the dispersant. When the water-soluble polymer is not added, the silver or the nucleus which is produced by the reduction of the silver complex is excessively aggregated, and thus the dispersibility is poor. Even in the case where a water-soluble polymer is not added, the particle size of the silver powder 1 can be adjusted to a level suitable for use as a silver paste by reducing conditions, but it can be adjusted by addition of a water-soluble polymer. Silver paste is used for better particle size. The amount of water-soluble polymer added is as long as it is in accordance with water-soluble polymer The type and the particle size of the silver powder 1 to be obtained may be appropriately determined, and it is preferably in the range of 1% by mass to 10% by mass based on the silver contained in the silver complex solution. By setting the content of the water-soluble polymer to 1% by mass to 10% by mass, excessive aggregation of primary particles or secondary particles of silver does not occur, and the particle size of the silver powder 1 is adjusted, and in the subsequent step, The organic film layer 3 is formed on the surface of the silver particles 2 moderately.

The water-soluble polymer may be added to either or both of the silver complex solution and the reducing agent solution. The water-soluble polymer may be added to both the silver complex solution and the reducing agent solution in advance, or may be added to the solution to be added before the reduction treatment, or may be used in the reduction treatment. The compound solution and the reducing agent solution are added as they are mixed. More preferably, the water-soluble polymer is previously mixed in a reducing agent solution. This case is an experimentally confirmed result. By mixing the reducing agent solution with the water-soluble polymer, the water-soluble polymer may be present in the case of nuclear generation or nuclear growth, since the water-soluble polymer will rapidly adsorb. On the surface of the generated core or silver particles 2, it is considered that excessive aggregation can be suppressed. Moreover, the concentration at the time of mixing the water-soluble polymer in the silver complex solution is more preferably set to more than 3% by mass and not more than 10% by mass. When the water-soluble polymer is added to the silver-containing complex solution in advance, the water-soluble polymer is hardly supplied to the nucleus or the nucleus, and the water-soluble polymer is not able to be appropriately adsorbed on the surface of the silver particle 2 Oh, so add more than 3 mass%.

When a water-soluble polymer is added, an antifoaming agent may be added to the silver complex solution or the reducing agent mixture because of foaming during the reduction reaction. The antifoaming agent is not particularly limited as long as it is a user who is usually reduced. . However, in order not to hinder the reduction reaction, the amount of the antifoaming agent added is preferably minimized to obtain a defoaming effect.

Further, in order to prevent the incorporation of impurities in the water used for preparing the silver complex solution and the reducing agent solution, it is preferred to use the impurities as the removed water, and it is particularly preferable to use pure water.

In the step of forming a silver particle slurry, the silver complex solution prepared as described above is mixed with a reducing agent solution to reduce the silver complex and precipitate the silver particles 2 by a wet reduction method. This reduction reaction can be carried out in a batch process or can be carried out using a continuous reduction process such as a tubular reactor process or an overflow process. Further, the particle diameter of the silver particles 2 can be easily controlled by controlling the mixing speed of the silver complex solution and the reducing agent solution or the reduction rate of the silver complex. Then, the obtained silver particle slurry is filtered using a filter or the like, and the silver particles 2 are solid-liquid separated.

The silver particles 2 obtained in this step have a large amount of chloride ions and the remaining water-soluble polymer adsorbed on the surface. Therefore, in order to set the conductivity of the wiring layer or the electrode formed using the silver paste to be sufficient, the obtained slurry of the silver particles 2 is washed in the subsequent washing step, and it is necessary to adsorb the surface. The matter is removed by washing.

The washing method is not particularly limited, and generally, the silver particles 2 separated from the slurry by solid-liquid separation are put into the washing liquid, stirred by a stirrer or an ultrasonic cleaner, and then subjected to solid-liquid separation to recover the silver particles 2 The method. Moreover, in order to sufficiently remove the surface adsorbate, it is preferable to repeat the operation which is performed by the washing liquid, the stirring washing, and the solid-liquid separation.

Water can be used as the washing liquid, but in order to remove chlorine efficiently, an aqueous alkali solution can be used. The alkali solution is not particularly limited, and it is preferred to use an anhydrous sodium hydroxide solution which is low in residual impurities. When a sodium hydroxide aqueous solution is used as the cleaning liquid, it is preferred to wash the silver particles 2 or the slurry with water in order to remove sodium after washing with an aqueous sodium hydroxide solution.

The concentration of the aqueous sodium hydroxide solution used for washing is preferably from 0.01 mol/l to 1 mol/l. If it is less than 0.01 mol/l, the washing effect may be insufficient; if it exceeds 1 mol/l, the sodium of the allowable value or more may remain in the silver particles 2. Further, the water used in the cleaning liquid preferably contains no impurity element which is harmful to the silver particles 2, and particularly preferably pure water.

Further, a surface treatment step of forming the organic film 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 used for the use of a surfactant, or more preferably a surfactant and a dispersant are used for the treatment. This surface treatment can be carried out at any stage before the silver particles 2 are dried. However, when the chlorine and the water-soluble polymer are completely removed, the silver particles 2 aggregate, and it is difficult to apply silver particles to the surface after the removal. Since the surface of 2 is subjected to the same surface treatment, it is preferred to carry out surface treatment at the same time as or after reduction, or to perform surface treatment after the silver particles 2 are separated from the silver particle slurry by solid-liquid separation and before the washing step. Or surface treatment at the same time as the washing step.

In the surface treatment step, for example, by subjecting the silver particles 2 to solid phase separation from the silver particle slurry and then performing surface treatment, it is possible to prevent adsorption of the surfactant or the dispersant due to the residual organic matter or the like of the reducing agent. Therefore, a sufficient organic film layer 3 can be formed and can be secured with a solvent or a resin Such as compatibility and dispersibility.

Further, when the washing is repeated for a plurality of times, the surface treatment can be performed at any of the washings, and the chlorine remaining in the silver particles 2 and the remaining water-soluble polymer can be removed without affecting the surface treatment. To the extent that the silver particles 2 are not aggregated, for example, it is preferable to perform surface treatment after one or more washes.

For example, as a specific method of preferably surface treatment using a surfactant and a dispersant, when the surface treatment before washing is performed, the silver particles 2 obtained by solid-liquid separation of the silver particle slurry are added to the surfactant and added thereto. The water of the dispersing agent may be stirred or added to the water to which the surfactant is added, and then the dispersing agent may be further added and stirred. Further, by adding the surfactant and the dispersing agent to the cleaning liquid at the same time or after adding the surfactant, the dispersing agent is added to carry out the washing and the surface treatment simultaneously. In order to improve the adsorptivity of the surfactant and the dispersant to the silver particles 2, it is preferred to introduce the silver particles 2 into the water or the washing liquid to which the surfactant is added, and then add the dispersing agent to stir the mixture. .

In addition, the apparatus used for washing and surface treatment may be any apparatus used for usual washing or surface treatment, and for example, a reaction tank equipped with a stirrer or the like can be used.

Next, a recovery step of recovering the silver particles 2 on which the organic film layer 3 has been formed is performed. This recovery step is carried out by subjecting the surface treatment and washing to solid-liquid separation to recover the silver particles 2. Moreover, as long as it is a normal user, the apparatus used for solid-liquid separation can be used, for example, a centrifuge, suction. Filter filter, filter press, etc.

Next, the washing and the surface treatment are completed, and the drying step of evaporating the water of the silver particles 2 obtained by the solid-liquid separation and drying is performed. As a drying method, for example, the silver particles 2 recovered after the washing and surface treatment are placed on a stainless steel liner, and a commercially available drying device such as an air oven or a vacuum dryer is used, as long as it is 40 to 80 ° C. The temperature can be heated.

Then, the dried silver particles 2 are sufficiently crushed to have a sufficiently weak energy to the extent that the organic film layer 3 formed on the surface is not damaged, and is preferably used as a silver paste. The crushing and classification steps of the classification treatment are carried out to obtain silver powder 1. The crushing method is not particularly limited as long as it does not cause damage to the organic film layer 3, and it is preferable to use a device having a weak crushing force such as a jet motor or a high-speed mixer. When the crushing force is strong, not only the organic film layer 3 is damaged, but also the silver powder 1 is deformed, so it is not suitable. The classification device is not particularly limited, and an air flow classifier, a sieve, or the like can be used.

The term "crushing treatment" refers to an operation of decomposing the dried agglomerated powder into the state of primary particles or secondary particles before surface treatment. As a means of crushing, a ball type machine or a conflict type air flow type pulverizer, a punch type pulverizer, a barrel type high speed mixer, or the like can be used, but when the energy of crushing is too weak, it cannot be sufficiently wet-treated. The aggregate formed by the middle or drying process is decomposed, and the internal friction angle cannot be made 20 or less. On the other hand, when the energy of the crushing is too strong, the surface of the organic powder layer 3 of the silver powder 1 may be damaged, or the joint of the primary particles in the secondary particles may be destroyed, and the surface of the silver powder 1 will be new. Exposed to the new face of metal silver, thus the watch The hydrophilicity of the surface becomes large, so that the contact angle of the 50% by volume aqueous solution of methanol is less than 100°, or the surface SP value by the acetone titration method becomes larger than 18. Further, the exposed new surface becomes an active point, and re-aggregation occurs during storage, and the internal friction angle is also increased over time.

Therefore, it is possible to adjust the crushing conditions and suppress the breakage of the joint of the primary particles with each other while confirming the parameters such as the internal friction angle, the contact angle, and the surface SP value, regardless of the type of the crusher. It is necessary to apply a crushing treatment such that the organic film layer 3 on the surface of the silver powder 1 is not damaged, that is, the organic film layer 3 is not peeled off and the silver particles 2 are 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 or the state of the silver powder 1 to be produced.

For example, when a high-speed agitator is used, the conditions vary depending on the capacity of the agitator. However, the peripheral speed and the stirring time of the agitator are adjusted so that the organic coating layer 3 is not damaged in response to the amount of the silver particles 2 to be supplied. . As the crushing conditions when the high-speed mixer is used, for example, the peripheral speed is set to 10 m/sec to 40 m/sec, and it is preferable to set the crushing time to the extent of 10 minutes to 60 minutes.

Further, after the crushing treatment, the silver particle agglomerates formed or mixed in the step of forming the silver particles or the crushing and classifying step are removed, and it is preferred to carry out air flow or sieve type. Hierarchical processing.

In the method for producing the silver powder 1 described above, the organic film layer 3 is formed on the surface of the silver particles 2 obtained by the step of forming the silver particle slurry, and then the new surface of the metal silver in the silver particles 2 is suppressed. Regenerate By crushing, a low-hydrophilic silver powder 1 having an internal friction angle of 20 or less and a contact angle of 100 or more in a methanol 50% by volume aqueous solution was obtained. Further, the silver powder 1 had a surface SP value of 18 or less by acetone titration. Therefore, in this manufacturing method, the internal friction angle of the silver powder 1 is 20° or less, and the contact angle of the 50% by volume aqueous solution of methanol is 100° or more, because of the wettability of the silver paste with respect to a solvent or a resin. It is excellent, so the dispersibility is good, and it is easy to paste and make a silver paste.

Further, since the silver powder 1 produced by the production method is subjected to sufficient surface treatment, the internal rubbing angle is 20° even when the silver paste is mixed with the resin or the solvent, not only after the manufacture, but also when the silver paste is mixed with the resin or the solvent. In the case where it is temporarily mixed with a solvent after the production, the compatibility with a solvent or a resin is good, and since it is excellent in dispersibility, it can be easily paste-formed.

Therefore, since the silver powder 1 is uniformly dispersed in the silver paste, electrical connection can be made good by forming a wiring layer or an electrode using a silver paste.

[Examples]

Specific embodiments to which the present invention is applied will be described below. However, the invention is not limited by the examples.

<Example 1>

In Example 1, first, in a warm bath at 38 ° C, while maintaining the liquid temperature In 36 L of 25% ammonia water at 36 ° C, 2490 g of silver chloride (manufactured by Sumitomo Metal Mine Co., Ltd.) was charged while stirring to prepare a silver complex solution, which was kept at 36 ° C in a warm bath.

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

Next, 187.5 g of a water-soluble polymer polyvinyl alcohol (manufactured by Kuraray, PVA 205, 10.0% by mass based on the silver particles) was fractionated, and a solution of 4.6 L of pure water dissolved at 36 ° C was mixed to the above reduction. In the solution.

Next, the silver complex solution and the reducing agent solution were supplied to the barrel at 2.44 L/min and 0.90 L/min using a Mohno Pump (manufactured by Bingshen Co., Ltd.) to separate the silver complex. reduction. The reduction rate at this time was 127 g/min in terms of the amount of silver. Further, the above-mentioned crucible is a tube made of vinyl chloride having an inner diameter of 25 mm and a length of 725 mm. The slurry containing the silver particles obtained by the reduction of the silver complex is received in the receiving tank while stirring. After the end of the acceptance, stirring was continued for 60 minutes in the receiving tank. The silver particle slurry after the completion of the stirring was filtered using a filter press, and the silver particles were solid-liquid separated.

Thereafter, the silver particles after the solid-liquid separation are subjected to surface treatment. 0.90 g of a polyoxyethylene addition-grade ammonium salt of a commercially available cationic surfactant as a surface treatment agent (manufactured by Croda Japan Co., Ltd., trade name Cirrasol G-265, 0.048% by mass based on silver particles) and Dispersing agent stearic acid emulsion 16.87g (made by Zhongjing Oil & Fat Co., Ltd., SELOSOL 920, relative 20 L of pure water was added to the silver particles, and the surface of the silver particles was surface-treated by stirring. Thereafter, NaOH was added at a concentration of 0.05 mol/L, stirred for 15 minutes, washed, and then filtered using a filter press to recover silver particles.

Next, before the recovered silver particles were dried, the silver particles were placed in a 0.05 mol/L NaOH aqueous solution, stirred for 15 minutes, washed, and then filtered and collected by a filter press. Thereafter, the solid-liquid separation operation by this washing operation and filtration was repeated three times.

The silver particles after solid-liquid separation were placed in 20 L of pure water, stirred and filtered, and then the silver particles were transferred to a stainless steel liner, and dried at 60 ° C for 10 hours using a vacuum dryer.

After drying, it is crushed and classified. 1.5 kg of silver particles after drying were weighed and placed in a 5 L high-speed mixer (FM5C/I made by Japan Coke), and rotated for 30 minutes at a peripheral speed of 15 m/sec. Perform crushing treatment. Further, the crushed silver particles were subjected to classification treatment using a gas flow classifier (Japan Mining Co., Ltd. EJ-3 type) at a classification point of 7 μm to obtain silver powder. The obtained silver powder was observed by SEM, and the average particle diameter of the primary particles was 0.98 μm, and the particle size (D50) measured by the laser diffraction scattering method was 2.35 μm.

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

The internal friction angle was measured by using a powder layer shear force measuring device (NS-S300 type manufactured by Nano Seeds Co., Ltd.). After filling 18 g of silver powder into a cell of SUS having an inner diameter of 15 mm at normal temperature, the set value of the press-in load was set to 20 N, and the load was applied at a press-in speed of 0.2 mm/sec. After the set load was reached, the transverse shear was started at 100 μm/sec after 100 seconds. Still, the sampling frequency is set to 10 Hz. The value of the press-in load at the start of the transverse shear divided by the cross-sectional area of the cell is set to the vertical stress σ (N/cm ² ), and the maximum shear force measured after the transverse shear is obtained. The value obtained by dividing the sectional area of the cell is set as the shear stress τ (N/cm ² ).

Next, the set value of the press-in load was set to 40 N, and the vertical stress σ and the shear stress τ were measured in the same manner. Further, the set value of the press-in load was set to 60 N, and the vertical stress σ and the shear stress τ were measured in the same manner. The vertical stress σ obtained in the above three conditions is taken as the horizontal axis, the shear stress τ is plotted as the vertical axis, and the slope (degree) of the approximate straight line obtained by the least squares method is set. For the internal friction angle.

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

The contact angle of the methanol 50% by volume aqueous solution was measured using a contact angle measuring device (CA-X150 manufactured by Kyowa Interface Science Co., Ltd.). The silver powder was press-formed at a normal temperature at a load of about 1 MPa, and the silver powder was obtained into a flat-packed test body which was pressure-filled. The contact angle formed by the methanol 50% by volume aqueous solution was measured for this test body. The contact angle of the silver powder of Example 1 measured by this method was 110°.

The measurement of the surface SP value by the acetone titration method was carried out as follows. 0.5 g of silver powder was added to 50 ml of water while stirring slowly. Acetone was continuously dropped in water containing silver powder, and when the silver particles floating on the water surface were dispersed and the solution became cloudy, the end point was set. The surface SP value of the aqueous acetone solution calculated from the added volume of acetone at this time was set 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, the obtained silver powder was used for evaluation of paste formation. For the evaluation of pasteification, first, 9.2 g of silver powder was weighed in a small stainless steel plate, and a medium liquid of epoxy resin (manufactured by Mitsubishi Chemical Corporation, JER 819) and terpineol was 1:7. 0.8g. At this time, it was observed that the surface of the silver powder was quickly wetted by the vehicle liquid. Next, when mixing using a metal spatula, it is easy to mix and disperse, and it can become paste shape. Further, this paste was kneaded at 2000 rpm for 5 minutes using a self-transformation kneading machine (manufactured by Thinky ARE-250 type), and a uniform silver paste was obtained. As a result of evaluation of the dispersibility of the obtained silver paste using a mortar fine gauge, the maximum particle diameter Dmax was 7 μm small and exhibited excellent dispersibility.

<Example 2>

In Example 2, the same as in Example 1, except that the amount of polyvinyl alcohol was set to 75 g (4.00% by mass with respect to the silver particles), and the rotary wing of the high-speed mixer was rotated at a peripheral speed of 28 m/sec. The method of obtaining silver powder is evaluated at the same time. The primary particle of the obtained silver powder had an average particle diameter of 1.01 μm and a particle size (D50) of 2.73 μm.

The internal friction angle of the silver powder of Example 2 was 10.4°, and it was placed at room temperature. The internal friction angle after 1 month 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, the same paste evaluation as in Example 1 was carried out using the obtained silver powder. It was observed that the surface of the silver powder was quickly wetted by the vehicle. When this is mixed using a metal spatula, it can be easily mixed and dispersed, and it can be in the form of a paste. Further, this paste was kneaded using a self-transition kneading machine in the same manner as in Example 1 to obtain a uniform silver paste. As a result of evaluation of the dispersibility of the obtained silver paste using a mortar scale, the maximum particle diameter Dmax was 6 μm small and exhibited excellent dispersibility.

<Comparative Example 1>

In Comparative Example 1, silver powder was obtained in the same manner as in Example 1 except that the rotary blade of the high-speed mixer was rotated at a peripheral speed of 42 m/sec, and evaluation was simultaneously performed. The primary particles of the obtained silver powder had an average particle diameter of 0.99 μm and a particle size (D50) of 1.82 μm. Further, the internal friction angle of the silver powder of Comparative Example 1 was 20.8°, which was considerably higher than that of the examples. Further, the contact angle of the silver powder of Comparative Example 1 was 85°, and the surface SP value was 18.7.

Next, the same paste evaluation as in Example 1 was carried out using the obtained silver powder. The surface of the silver powder was hardly observed due to the wetting of the vehicle. Moreover, when this metal stirring blade is used for stirring, it is in a large clay state, and it cannot be made into a paste shape. Further, this silver paste was kneaded in the same manner as in Example 1 using a self-transition kneading machine to obtain a paste. As a result of evaluation of the dispersibility of the obtained silver paste using a mortar scale, the maximum particle diameter Dmax was 20 μm large, and the dispersibility was poor.

<Comparative Example 2>

In Comparative Example 2, silver powder was obtained in the same manner as in Example 2 except that the rotary vane of the high-speed mixer was rotated at a peripheral speed of 7 m/sec, and evaluation was simultaneously performed. The primary particle of the obtained silver powder had an average particle diameter of 1.00 μm and a particle size (D50) of 3.52 μm. Further, the internal friction angle of the silver powder of Comparative Example 2 was 25.8°, which was considerably higher than that of the examples. Further, the contact angle of the silver powder of Comparative Example 2 was 110°, and the surface SP value was 17.4.

Next, the same paste evaluation as in Example 1 was carried out using the obtained silver powder. The surface of the silver powder was hardly observed due to the wetting of the vehicle. Moreover, when this metal stirring blade is used for stirring, it is in a large clay state, and it cannot be made into a paste shape. Further, this paste was kneaded in the same manner as in Example 1 using a self-transition kneading machine to obtain a paste. As a result of evaluation of the dispersibility of the obtained silver paste using a mortar scale, the maximum particle diameter Dmax was 18 μm large, and the dispersibility was poor.

According to the above examples and comparative examples, even in the case of the silver powder produced by the same method, the first embodiment was sufficiently crushed to the extent that the film formed on the surface of the silver powder was not damaged. In the second embodiment, the internal friction angle is 20° or less, and the contact angle of the 50% by volume aqueous solution of methanol is 100° or more, and silver powder having good compatibility with the vehicle liquid and excellent dispersibility is obtained. Further, in Example 1 and Example 2, the surface SP value by the acetone titration method was 18 or less. Further, in Example 1 and Example 2, even after the silver powder was allowed to stand at room temperature for one month, the internal rubbing angle was 20 or less, and the progress of aggregation was suppressed.

On the other hand, in Comparative Example 1, since the crushing conditions were too strong and the organic film layer formed on the surface of the silver powder was damaged, the internal rubbing angle was larger than 20°, and the contact angle was also smaller than 100°. Furthermore, the surface SP value also becomes larger than 18 . Further, in Comparative Example 2, since the crushing conditions were weak, the aggregates could not be sufficiently decomposed, and the internal friction angle was 25.8°, which was considerably large. In Comparative Example 1 and Comparative Example 2, the compatibility with the vehicle liquid was poor, and the dispersibility of the silver powder was deteriorated.

1‧‧‧Silver powder

2‧‧‧Silver particles

3‧‧‧Organic coating

[Fig. 1] A simulation showing a graph of the morphology of silver particles and the surface state of particles.

Claims (5)

A silver powder characterized by an internal friction angle of 20 or less and a contact angle of 100 or more in a 50% by volume aqueous solution of methanol. The silver powder of the first aspect of the patent application, wherein the surface SP value by the acetone titration method is 18 or less. The silver powder according to claim 1 or 2, wherein the internal friction angle is 20 or less when mixed with a solvent of the silver paste. A method for producing a silver powder characterized by subjecting a silver particle synthesized by a wet reduction method to surface treatment, and forming an organic film layer on a surface thereof, and then sufficiently crushing the organic film layer without causing damage to the organic film layer The silver powder having an internal friction angle of 20 or less and a contact angle of 100 or more in a methanol 50% by volume aqueous solution was produced. The method for producing a silver powder according to the fourth aspect of the invention, wherein the method of crushing is a high-speed agitator, and the peripheral speed of the stirring blade is 10 m/sec or more and 40 m/sec or less.