JP5633045B2 - Silver powder and method for producing the same - Google Patents

Description

  The present invention relates to silver powder and a method for producing the same, and in particular, silver powder for conductive paste used for electronic components such as internal electrodes of multilayer capacitors and conductor patterns of circuit boards, electrodes and circuits of substrates for plasma display panels, and the like. It relates to a manufacturing method.

  Conventionally, silver powder is used together with glass frit in an organic vehicle as a conductive paste used for internal electrodes of multilayer capacitors, conductor patterns of circuit boards, electrodes of solar cells and plasma display panel (PDP) substrates, and circuits. In addition, a conductive paste produced by kneading is used. Silver powder for such conductive paste is required to have a reasonably small particle size and uniform particle size in order to cope with downsizing of electronic parts, high density of conductor patterns, fine lines, and the like. Yes.

  As a method for producing such silver powder for conductive paste, an alkali or complexing agent is added to a silver salt-containing aqueous solution to form a silver oxide-containing slurry or a silver complex-containing aqueous solution, and then a reducing agent is added. A method of reducing and precipitating silver powder and then drying it is known. In such a method, in order to produce a silver powder with less aggregation and excellent dispersibility, an alkali or complexing agent is added to the silver salt-containing aqueous solution to produce a silver oxide-containing slurry or a silver complex salt-containing aqueous solution, and a reducing agent And then reducing and precipitating silver particles, and then adding one or more of a fatty acid, a fatty acid salt, a surfactant, an organometallic compound, a chelating agent, and a polymer dispersant as a dispersing agent during the silver-containing slurry solution or filtration thereof Has been proposed to produce silver powder having a surface coated with a dispersant (see, for example, Patent Documents 1 and 2).

JP-A-10-88206 (paragraph numbers 0002-0004) Japanese Patent Laying-Open No. 2005-220380 (paragraph number 0013)

  A highly water-soluble organic solvent may be used as the solvent used in the conductive paste. However, if the silver powder used in the conductive paste is not compatible with the solvent, the silver powder does not disperse in the conductive paste and becomes a lump. Thus, when the conductive paste is applied to a substrate or the like, the conductive paste has a non-uniform film thickness, which deteriorates the conductivity and adhesive strength of the conductor formed by firing the conductive paste.

  Therefore, when using a highly water-soluble organic solvent as the solvent for the conductive paste, the silver powder used for the conductive paste is a silver powder with a relatively high surface moisture content that is compatible with a highly water-soluble organic solvent. Although desired, conventional silver powder production methods have failed to produce silver powder having a surface moisture content suitable for a conductive paste using an organic solvent having high water solubility.

  Accordingly, the present invention provides a silver powder production method capable of producing silver powder having a surface moisture content suitable for a conductive paste using an organic solvent having high water solubility in view of such conventional problems. For the purpose.

  As a result of earnest research to solve the above problems, the present inventors have added a reducing agent to an aqueous reaction system containing silver ions to reduce and precipitate silver particles. Alternatively, it is found that by adding two or more kinds of dispersants after reduction precipitation or during reduction precipitation, a silver powder having a surface water content suitable for a conductive paste using a highly water-soluble organic solvent can be produced. The present invention has been completed.

  That is, the silver powder production method according to the present invention is a silver powder production method in which silver particles are reduced and precipitated by adding a reducing agent to an aqueous reaction system containing silver ions, before or after reduction precipitation of silver particles or after reduction precipitation. Two or more kinds of dispersants are added therein. In this silver powder production method, each of the two or more dispersants is preferably a dispersant selected from the group consisting of fatty acids, fatty acid salts, surfactants, organometallic compounds, chelating agents, and polymer dispersants. Two or more kinds of dispersants preferably contain a hydrophilic dispersant and a hydrophobic dispersant. The hydrophilic dispersant is preferably gelatin or a collagen peptide, and the hydrophobic dispersant is preferably selected from the group consisting of benzotriazole, stearic acid, oleic acid and salts thereof. The reducing agent is preferably at least one reducing agent selected from the group consisting of ascorbic acid, alkanolamine, sodium borohydride, hydroquinone, hydrazine and formalin.

Further, the silver powder according to the present invention has a tap density of 2 g / cm ³ or more, an average particle size by laser diffraction method of 0.1 to 5 μm, a BET specific surface area of 0.1 to ⁵ m ² / g, and a surface moisture content of 3 to 3. It is characterized by 6 molecules / nm ² .

  Furthermore, the conductive paste according to the present invention is characterized by using the above silver powder as a conductor.

  According to the present invention, ketones such as acetone and dimethyl ketone, esters such as ethyl acetate and diethylene glycol ethyl ether acetate, alcohols such as ethanol and isopropyl alcohol, glycols such as ethylene glycol and propylene glycol, ethyl cellosolve And silver powder having a surface water content suitable for a conductive paste using a highly water-soluble organic solvent such as glycol ethers such as methyl cellosolve can be produced.

  In the embodiment of the method for producing silver powder according to the present invention, the surface of the aqueous reaction system containing silver ions is added by adding two or more kinds of dispersants before or after reducing particles are precipitated by adding a reducing agent. Is coated with a dispersant to produce a silver powder having a desired surface moisture content and good dispersibility in a highly water-soluble organic solvent.

  As an aqueous reaction system containing silver ions, an aqueous solution or slurry containing silver nitrate, a silver complex or a silver intermediate can be used. An aqueous solution containing a silver complex can be produced by adding aqueous ammonia, ammonium salt, chelate compound or the like to the aqueous silver nitrate solution. A slurry containing a silver intermediate can be produced by adding sodium hydroxide, sodium chloride, sodium carbonate or the like to an aqueous silver nitrate solution. Among these, in order to make the silver powder have an appropriate particle size and spherical shape, it is preferable to use an ammine complex aqueous solution obtained by adding ammonia water to a silver nitrate aqueous solution. Since the coordination number of ammonia in the ammine complex is 2, 2 mol or more of ammonia is added per 1 mol of silver. Further, if the amount of ammonia added is too large, the complex becomes too stable and the reduction is difficult to proceed. Therefore, the amount of ammonia added is preferably 8 moles or less per mole of silver. If adjustments such as increasing the amount of reducing agent added are made, it is possible to obtain spherical silver powder having an appropriate particle size even if the amount of ammonia added exceeds 8 mol.

  As a reducing agent, ascorbic acid, sulfite, alkanolamine, hydrogen peroxide solution, formic acid, ammonium formate, sodium formate, glyoxal, tartaric acid, sodium hypophosphite, sodium borohydride, hydroquinone, hydrazine, hydrazine compound, pyrogallol, Glucose, gallic acid, formalin, anhydrous sodium sulfite, Rongalite and the like can be used. Among these, it is preferable to use at least one selected from the group consisting of ascorbic acid, alkanolamine, sodium borohydride, hydroquinone, hydrazine and formalin, and it is particularly preferable to use formalin because it is inexpensive. preferable. If these reducing agents are used, silver particles having an appropriate particle size can be obtained. In order to increase the reaction yield of silver, the addition amount of the reducing agent needs to be 1 equivalent or more with respect to silver. When a reducing agent having a weak reducing power is used, a reducing agent of 2 equivalents or more, for example, 10 to 20 equivalents of reducing agent may be added to silver. Moreover, about the addition method of a reducing agent, in order to prevent aggregation of silver powder, it is preferable to add at a speed | rate of 1 equivalent / min or more. The reason for this is not clear, but by introducing the reducing agent in a short time, reduction precipitation of silver particles occurs at once, the reduction reaction is completed in a short time, and aggregation of the generated nuclei is difficult to occur, It is thought that dispersibility is improved. Therefore, it is preferable that the addition time of the reducing agent is as short as possible. For example, the reducing agent may be added at a rate of 100 equivalents / minute or more, and the reaction is completed in a shorter time during the reduction. It is preferable to stir the reaction solution.

  As the dispersant, fatty acids, fatty acid salts, surfactants, organometallic compounds, chelating agents, polymer dispersants and the like can be used. Examples of fatty acids include propionic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, acrylic acid, oleic acid, linoleic acid, arachidonic acid and the like. Examples of fatty acid salts include lithium, sodium, potassium, barium, magnesium, calcium, aluminum, iron, cobalt, manganese, lead, zinc, tin, strontium, zirconium, silver, copper, and other fatty acids and salts formed. Things can be mentioned. Examples of surfactants include anionic surfactants such as alkylbenzene sulfonates and polyoxyethylene alkyl ether phosphates, cationic surfactants such as aliphatic quaternary ammonium salts, and amphoteric compounds such as imidazolinium betaine. Nonionic surfactants such as surfactants and polyoxyethylene alkyl ethers and polyoxyethylene fatty acid esters can be mentioned. Examples of organometallic compounds include acetylacetone tributoxyzirconium, magnesium citrate, diethylzinc, dibutyltin oxide, dimethylzinc, tetra-n-butoxyzirconium, triethylindium, triethylgallium, trimethylindium, trimethylgallium, monobutyltin oxide, tetra Examples include isocyanate silane, tetramethyl silane, tetramethoxy silane, polymethoxy siloxane, monomethyl triisocyanate silane, silane coupling agent, titanate coupling agent, aluminum coupling agent and the like. Examples of chelating agents include imidazole, oxazole, thiazole, selenazole, pyrazole, isoxazole, isothiazole, 1H-1,2,3-triazole, 2H-1,2,3-triazole, 1H-1,2,4. -Triazole, 4H-1,2,4-triazole, 1,2,3-oxadiazole, 1,2,4-oxadiazole, 1,2,5-oxadiazole, 1,3,4-oxa Diazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,2,5-thiadiazole, 1,3,4-thiadiazole, 1H-1,2,3,4-tetrazole, 1,2 , 3,4-oxatriazole, 1,2,3,4-thiatriazole, 2H-1,2,3,4-tetrazole, 1,2,3,5-oxatriazole, , 3,5-thiatriazole, indazole, benzimidazole and benzotriazole and their salts, or oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecane Diacid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, glycolic acid, lactic acid, oxybutyric acid, glyceric acid, tartaric acid, malic acid, tartronic acid, hydroacrylic acid, mandelic acid, citric acid, ascorbic acid, etc. Can be mentioned. Examples of the polymer dispersant include peptides, gelatin, collagen peptides, albumin, gum arabic, protalbic acid, lysalbic acid and the like.

Two or more kinds of dispersants are appropriately selected from the above-mentioned dispersants, and added to a slurry-like reaction system before or after reduction precipitation of silver particles or during reduction precipitation, thereby obtaining silver powder having a desired surface moisture content. Can be manufactured. When a highly water-soluble organic solvent is used as the solvent for the conductive paste, if the surface moisture content of the silver powder used for the conductive paste is less than 3 molecules / nm ² , the silver powder may not be dispersed in the paste and may be agglomerated. Alternatively, force is applied to the bulk silver powder to form a flaky silver powder, and when it exceeds 6 molecules / nm ² , there is a problem such as deterioration of the storage stability of the paste. Therefore, it is preferable that the surface water content of the silver powder used for the conductive paste using an organic solvent having high water solubility is 3 to 6 molecules / nm ² . If two or more kinds of dispersants are appropriately selected from the above-mentioned dispersants and added to the slurry-like reaction system before or after the reduction precipitation of the silver particles or during the reduction precipitation, the surface moisture content is 3 to 6 molecules. / Nm ² silver powder can be produced. In particular, in order to produce silver powder having a surface moisture content of 3 to 6 molecules / nm ² , a hydrophobic dispersant selected from benzotriazole, stearic acid, oleic acid, and salts thereof, gelatin, collagen peptides, and the like It is preferable to use a combination of hydrophilic dispersants. In addition, what is necessary is just to adjust the addition amount of each dispersing agent so that silver powder may become a desired characteristic between 0.05-2 mass% with respect to the silver with which an aqueous reaction system is prepared, and also each dispersion | distribution. What is necessary is just to adjust the ratio of the addition amount of an agent so that silver powder may become a desired characteristic.

  The obtained silver-containing slurry is filtered and washed with water, whereby a lump cake containing 1 to 200% by mass of water with little fluidity is obtained. In order to accelerate the drying of the cake or prevent aggregation at the time of drying, the water in the cake may be replaced with a lower alcohol or a polyol. The cake is dried by a dryer such as a forced circulation air dryer, vacuum dryer, airflow dryer, etc., and then crushed to obtain silver powder. Instead of crushing, silver particles are put into an apparatus that can mechanically fluidize the particles, and the particles are mechanically collided with each other, thereby smoothing the irregularities and corners of the silver powder particles. Surface smoothing treatment may be performed. Moreover, you may perform a classification process after crushing and a smoothing process. In addition, you may dry, grind | pulverize, and classify | categorize using the integrated apparatus (Drymeister made from Hosokawa Micron Corporation, a micron dryer etc.) which can perform drying, grinding | pulverization, and classification.

The silver powder thus obtained has a tap density of 2 g / cm ³ or more, preferably 3 g / cm ³ or more, more preferably 3.5 g / cm ³ or more, and an average particle size by laser diffraction method of 0.1 to 0.1 g. 5 [mu] m, preferably 0.5 to 3 [mu] m, BET specific surface area of 0.1 to 5 m ² / g, preferably 0.1~2m ² / g, the surface moisture content is 3-6 molecules / nm ^2, a water-soluble Dispersibility with respect to organic solvents having high viscosity is good. When the tap density is less than 2 g / cm ³ , the silver particles are agglomerated and it becomes difficult to cope with fine lines. Also, if the average particle diameter by laser diffraction method is smaller than 0.1 μm, it is possible to cope with fine lines, but the activity of the particles is high, and when silver powder is used as a baking paste, baking is performed at 500 ° C. or higher. Not suitable for. On the other hand, when the average particle diameter by laser diffraction method is larger than 5 μm, the dispersibility is inferior, and it becomes difficult to cope with the fine line. Furthermore, when the BET specific surface area exceeds 5 m ² / g, the viscosity of the paste is too high, and the printability is deteriorated. On the other hand, if the BET specific surface area is less than 0.1 m ² / g, the particles are too large, and it becomes difficult to cope with fine lines.

  Hereinafter, the Example of the silver powder by this invention and its manufacturing method is described in detail.

[Example 1]
To 4300 kg of silver nitrate aqueous solution containing 54 kg of silver, 203 kg of 25% by mass of ammonia water and 18 kg of 25% by mass of sodium hydroxide aqueous solution were added to obtain a silver ammine complex salt aqueous solution. After the liquid temperature of this silver ammine complex salt aqueous solution was 20 ° C., an aqueous solution of 0.2 mass% collagen peptide (NCG-10 manufactured by Zerais Co., Ltd.) was added to the amount of silver, and then 18.5 mass% formalin. 480 kg of an aqueous solution was added to precipitate silver particles. After the addition of the formalin aqueous solution was completed, an aqueous solution of 0.3 mass% benzotriazole Na salt relative to the amount of silver was added, and the resulting silver-containing slurry was filtered and washed with water to obtain a cake. .

  11.3 kg of the obtained cake was dried at 75 ° C. for 16 hours by a vacuum dryer having an internal volume of 100 L to obtain 10.0 kg of dried powder. It was confirmed with an infrared moisture meter that the dried powder was dry. The obtained dry powder was crushed and classified to obtain silver powder having a desired particle size.

About the obtained silver powder, the tap density, the average particle diameter by a laser diffraction method, the maximum particle diameter, the BET specific surface area, and the surface moisture content were calculated | required. Tap density is measured using a tap density measuring device (Casa specific gravity measuring device SS-DA-2 manufactured by Shibayama Kagaku Co., Ltd.), 15 g of a silver powder sample is weighed and placed in a 20 mL test tube, and tapped 1000 times with a drop of 20 mm. Calculated from tap density = sample weight (15 g) / sample volume after tapping (cm ³ ). The average particle diameter D50 (cumulative 50 mass% particle diameter) and the maximum particle diameter Dmax by laser diffraction method are as follows: 0.3 g of silver powder sample is added to 30 mL of isopropyl alcohol and dispersed for 5 minutes by an ultrasonic cleaner with an output of 50 W. It measured using the particle size distribution measuring apparatus (Honeywell-Macrotrack particle size distribution measuring apparatus 9320-HRA (X-100) by Nikkiso Co., Ltd.). The BET specific surface area was measured by the BET single point method using a BET specific surface area measuring device (Monosorb manufactured by Quanta Chrome). The surface moisture content was measured by using a coulometric titration type automatic moisture measuring device (CA-100 (vaporizer VA-100) manufactured by Mitsubishi Chemical Co., Ltd.) and the moisture content (ppm) at a vaporization temperature of 100 ° C. ) Surface water content (H ₂ O molecule / nm ² ) = water content (ppm) from 1 g of silver powder sample ÷ 10 ⁶ ÷ 18.0 × (6.02 × 10 ²³ ) ÷ BET specific surface area ( m ² / g) × 10 ¹⁸ . As a result, the tap density was 4.3 g / cm ³ , the average particle size by laser diffraction method was 1.4 μm, the maximum particle size was 5.5 μm, the BET specific surface area was 0.74 m ² / g, and the surface moisture content was 3. It was 5 molecules / nm ² .

[Example 2]
To 4100 kg of silver nitrate aqueous solution containing 68 kg of silver, 253 kg of 25 mass% aqueous ammonia and 22 kg of 25 mass% sodium hydroxide aqueous solution were added to obtain an aqueous silver ammine complex salt solution. After the liquid temperature of this silver ammine complex salt aqueous solution was 20 ° C., an aqueous solution of 0.2 mass% collagen peptide (NCG-10 manufactured by Zerais Co., Ltd.) was added to the amount of silver, and then 18.5 mass% formalin. 600 kg of an aqueous solution was added to precipitate silver particles. After the addition of the formalin aqueous solution was completed, an ethanol solution of 0.3% by mass of benzotriazole with respect to the amount of silver was added, and the resulting silver-containing slurry was filtered and washed with water to obtain a cake.

  Of the obtained cake, 75.5 kg was dried with a 500 L vacuum dryer at 70 ° C. for 24 hours to obtain 63.5 kg of dried powder. It was confirmed with an infrared moisture meter that the dried powder was dry. The obtained dry powder was crushed and classified to obtain silver powder having a desired particle size.

About the obtained silver powder, the tap density, the average particle diameter by the laser diffraction method, the maximum particle diameter, the BET specific surface area, and the surface moisture content were determined in the same manner as in Example 1. As a result, the tap density was 4.3 g / cm ³ , the average particle size by laser diffraction method was 1.4 μm, the maximum particle size was 5.5 μm, the BET specific surface area was 0.69 m ² / g, and the surface moisture content was 5. 2 molecules / nm ² .

[Example 3]
To 4500 kg of silver nitrate aqueous solution containing 54 kg of silver, 203 kg of 25 mass% aqueous ammonia and 18 kg of 25 mass% sodium hydroxide aqueous solution were added to obtain an aqueous silver ammine complex salt solution. The liquid temperature of this silver ammine complex salt aqueous solution was 20 degreeC, and 240 kg of 37 mass% formalin aqueous solution was added, and silver particle was deposited. After the addition of the formalin aqueous solution, 0.5% by mass of an ethanol solution of benzotriazole with respect to the amount of silver was added, and then 0.2% by mass of collagen peptide with respect to the amount of silver (manufactured by Zelice) Of NCG-10) was added and the resulting silver-containing slurry was filtered and washed with water to give a cake.

17.1 kg of the obtained cake was subjected to an air flow dryer (flash jet dryer FJD-4 manufactured by Seishin Enterprise Co., Ltd.) set at an air flow rate of 15 m ³ / min, an inlet temperature of 90 ° C., and an outlet temperature of 60 ° C. It was dried for 10 minutes to obtain 15.8 kg of dry powder. It was confirmed with an infrared moisture meter that the dried powder was dry. The obtained dry powder was crushed and classified to obtain silver powder having a desired particle size.

About the obtained silver powder, it calculated | required about the tap density, the average particle diameter by a laser diffraction method, the maximum particle diameter, the BET specific surface area, and the surface moisture content by the method similar to Example 1. FIG. As a result, the tap density was 4.3 g / cm ³ , the average particle size by laser diffraction method was 1.4 μm, the maximum particle size was 4.6 μm, the BET specific surface area was 0.80 m ² / g, and the surface moisture content was 5. It was 6 molecules / nm ² .

[Example 4]
To 4550 kg of silver nitrate aqueous solution containing 54 kg of silver, 169 kg of 25 mass% aqueous ammonia and 16 kg of 25 mass% sodium hydroxide aqueous solution were added to obtain an aqueous silver ammine complex salt solution. The liquid temperature of this silver ammine complex salt aqueous solution was 20 degreeC, and 240 kg of 37 mass% formalin aqueous solution was added, and silver particle was deposited. After completion of the addition of the formalin aqueous solution, 0.5% by mass of an ethanol solution of benzotriazole based on the amount of silver was added, and then 0.2% by mass of gelatin (manufactured by Zelice Co. E-200) was added and the resulting silver-containing slurry was filtered and washed with water to give a cake.

  17.1 kg of the obtained cake was dried at 70 ° C. for 24 hours by a 100 L vacuum dryer to obtain 14.0 kg of dried powder. It was confirmed with an infrared moisture meter that the dried powder was dry. The obtained dry powder was crushed and classified to obtain silver powder having a desired particle size.

About the obtained silver powder, it calculated | required about the tap density, the average particle diameter by a laser diffraction method, the maximum particle diameter, the BET specific surface area, and the surface moisture content by the method similar to Example 1. FIG. As a result, the tap density was 4.3 g / cm ³ , the average particle size by laser diffraction method was 1.3 μm, the maximum particle size was 5.5 μm, the BET specific surface area was 0.69 m ² / g, and the surface moisture content was 3. It was 7 molecules / nm ² .

[Comparative Example 1]
To 4450 kg of silver nitrate aqueous solution containing 108 kg of silver, 214 kg of 25 mass% aqueous ammonia and 40 kg of 25 mass% aqueous sodium hydroxide were added to obtain an aqueous silver ammine complex salt solution. The liquid temperature of this silver ammine complex salt aqueous solution was 30 ° C., and 264 kg of a 37% by mass formalin aqueous solution was added to precipitate silver particles. After the addition of the formalin aqueous solution was completed, 0.4% by mass of oleic acid was added to the amount of silver, and the resulting silver-containing slurry was filtered and washed with water to obtain a cake.

  10.1 kg of the obtained cake was dried at 60 ° C. for 24 hours with a 100 L vacuum dryer to obtain 8.2 kg of dried powder. It was confirmed with an infrared moisture meter that the dried powder was dry. The obtained dry powder was crushed and classified to obtain silver powder having a desired particle size.

About the obtained silver powder, it calculated | required about the tap density, the average particle diameter by a laser diffraction method, the maximum particle diameter, the BET specific surface area, and the surface moisture content by the method similar to Example 1. FIG. As a result, the tap density was 3.8 g / cm ³ , the average particle size by laser diffraction method was 2.4 μm, the maximum particle size was 7.8 μm, the BET specific surface area was 0.47 m ² / g, and the surface moisture content was 1. 1 molecule / nm ² .

[Comparative Example 2]
To 4500 kg of an aqueous silver nitrate solution containing 54 kg of silver, 225 kg of 25 mass% ammonia water was added to obtain an aqueous silver ammine complex salt solution. After the liquid temperature of this silver ammine complex salt aqueous solution was set to 40 ° C. and 0.3% by mass of polyoxyethylene alkyl ether (Neugen ET-80 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added to the aqueous solution, 240 kg of a 37% by mass formalin aqueous solution was added to precipitate silver particles. The silver-containing slurry thus obtained was filtered and washed with water to obtain a cake.

  46.5 kg of the obtained cake was dried at 80 ° C. for 16 hours with a 500 L vacuum dryer to obtain 41.6 kg of dried powder. It was confirmed with an infrared moisture meter that the dried powder was dry. The obtained dry powder was crushed and classified to obtain silver powder having a desired particle size.

About the obtained silver powder, it calculated | required about the tap density, the average particle diameter by a laser diffraction method, the maximum particle diameter, the BET specific surface area, and the surface moisture content by the method similar to Example 1. FIG. As a result, the tap density was 3.6 g / cm ³ , the average particle size by laser diffraction method was 4.7 μm, the maximum particle size was 9.3 μm, the BET specific surface area was 0.30 m ² / g, and the surface moisture content was 2. It was 7 molecules / nm ² .

[Comparative Example 3]
To 4550 kg of silver nitrate aqueous solution containing 54 kg of silver, 203 kg of 25% by mass of aqueous ammonia and 18 kg of 25% by mass of sodium hydroxide aqueous solution were added to obtain a silver ammine complex salt aqueous solution. The liquid temperature of this silver ammine complex salt aqueous solution was 40 ° C., and 240 kg of a 37% by mass formalin aqueous solution was added to precipitate silver particles. After the addition of the formalin aqueous solution was completed, 0.2 mass% of stearic acid emulsion was added as stearic acid to the amount of silver, and the resulting silver-containing slurry was filtered and washed with water to obtain a cake.

Of the obtained cake, 18.8 kg was subjected to an airflow dryer (flash jet dryer FJD-4 manufactured by Seishin Enterprise Co., Ltd.) in which the air flow used was 6 m ³ / min, the inlet temperature was 230 ° C., and the outlet temperature was 170 ° C. It was dried for 25 minutes to obtain 17.0 kg of dried powder. It was confirmed with an infrared moisture meter that the dried powder was dry. The obtained dry powder was crushed and classified to obtain silver powder having a desired particle size.

About the obtained silver powder, it calculated | required about the tap density, the average particle diameter by a laser diffraction method, the maximum particle diameter, the BET specific surface area, and the surface moisture content by the method similar to Example 1. FIG. As a result, the tap density was 4.4 g / cm ³ , the average particle size by laser diffraction method was 2.4 μm, the maximum particle size was 9.3 μm, the BET specific surface area was 0.47 m ² / g, and the surface moisture content was 2. It was 6 molecules / nm ² .

[Comparative Example 4]
To 4400 kg of silver nitrate aqueous solution containing 65 kg of silver, 229 kg of 25 mass% aqueous ammonia and 8 kg of 25 mass% sodium hydroxide aqueous solution were added to obtain an aqueous silver ammine complex salt solution. The liquid temperature of this silver ammine complex salt aqueous solution was 20 ° C., and 317 kg of a 37% by mass formalin aqueous solution was added to precipitate silver particles. After the addition of the formalin aqueous solution, 1.0% by mass of an ethanol solution of benzotriazole with respect to the amount of silver was added, and the resulting silver-containing slurry was filtered and washed with water to obtain a cake.

15 kg of the obtained cake was subjected to an air flow dryer (flash jet dryer FJD-4 manufactured by Seishin Enterprise Co., Ltd.) in which the air flow used was 12.5 m ³ / min, the inlet temperature was 130 ° C., and the outlet temperature was 80 ° C. It was dried for 10 minutes to obtain 12.6 kg of dried powder. It was confirmed with an infrared moisture meter that the dried powder was dry. The obtained dry powder was crushed and classified to obtain silver powder having a desired particle size.

About the obtained silver powder, it calculated | required about the tap density, the average particle diameter by a laser diffraction method, the maximum particle diameter, the BET specific surface area, and the surface moisture content by the method similar to Example 1. FIG. As a result, the tap density was 4.4 g / cm ³ , the average particle size by laser diffraction method was 1.3 μm, the maximum particle size was 5.5 μm, the BET specific surface area was 0.75 m ² / g, and the surface moisture content was 1. It was 6 molecules / nm ² .

[Comparative Example 5]
To 4600 kg of silver nitrate aqueous solution containing 54 kg of silver, 122 kg of 25 mass% aqueous ammonia and 8 kg of 25 mass% sodium hydroxide aqueous solution were added to obtain an aqueous silver ammine complex salt solution. The liquid temperature of this silver ammine complex salt aqueous solution was 25 ° C., and 264 kg of a 37% by mass formalin aqueous solution was added to precipitate silver particles. After the addition of the formalin aqueous solution was completed, an aqueous solution of Na salt of 0.5% by mass of benzotriazole with respect to the amount of silver was added, and the resulting silver-containing slurry was filtered and washed with water to obtain a cake. .

  10.0 kg of the obtained cake was dried with a 50 L vacuum dryer at 90 ° C. for 18 hours to obtain 8.2 kg of dried powder. It was confirmed with an infrared moisture meter that the dried powder was dry. The obtained dry powder was crushed and classified to obtain silver powder having a desired particle size.

About the obtained silver powder, it calculated | required about the tap density, the average particle diameter by a laser diffraction method, the maximum particle diameter, the BET specific surface area, and the surface moisture content by the method similar to Example 1. FIG. As a result, the tap density was 4.0 g / cm ³ , the average particle size by laser diffraction method was 1.4 μm, the maximum particle size was 5.5 μm, the BET specific surface area was 0.70 m ² / g, and the surface moisture content was 2. It was 0 molecule / nm ² .

[Comparative Example 6]
To 4000 kg of silver nitrate aqueous solution containing 81 kg of silver, 253 kg of 25 mass% ammonia water and 27 kg of 25 mass% sodium hydroxide aqueous solution were added to obtain an aqueous silver ammine complex salt solution. The liquid temperature of this silver ammine complex salt aqueous solution was 20 ° C., and 720 kg of an 18.5% by mass formalin aqueous solution was added to precipitate silver particles. After the addition of the formalin aqueous solution is completed, an aqueous solution of 0.2% by mass gelatin (E-200 manufactured by Zerais Co.) is added to the amount of silver, and the resulting silver-containing slurry is filtered and washed with water. And got a cake.

  14.5 kg of the obtained cake was dried at 75 ° C. for 20 hours with a 100 L vacuum dryer to obtain 11.6 kg of dried powder. It was confirmed with an infrared moisture meter that the dried powder was dry. The obtained dry powder was crushed and classified to obtain silver powder having a desired particle size.

About the obtained silver powder, it calculated | required about the tap density, the average particle diameter by a laser diffraction method, the maximum particle diameter, the BET specific surface area, and the surface moisture content by the method similar to Example 1. FIG. As a result, the tap density was 4.0 g / cm ³ , the average particle size by laser diffraction method was 1.8 μm, the maximum particle size was 7.8 μm, the BET specific surface area was 0.73 m ² / g, and the surface moisture content was 7. It was 7 molecules / nm ² .

[Comparative Example 7]
To 4500 kg of silver nitrate aqueous solution containing 54 kg of silver, 225 kg of 25% by mass of ammonia water and 2 kg of 25% by mass of sodium hydroxide aqueous solution were added to obtain a silver ammine complex salt aqueous solution. After the liquid temperature of this silver ammine complex salt aqueous solution was set to 40 ° C., 240 kg of a 37 mass% formalin aqueous solution was added to precipitate silver particles. After the addition of the formalin aqueous solution was completed, 0.1% by mass of lauric acid was added to the amount of silver, and the resulting silver-containing slurry was filtered and washed with water to obtain a cake.

  65.3 kg of the obtained cake was dried at 75 ° C. for 20 hours with a 500 L vacuum dryer to obtain 49.7 kg of dried powder. It was confirmed with an infrared moisture meter that the dried powder was dry. The obtained dry powder was crushed and classified to obtain silver powder having a desired particle size.

About the obtained silver powder, it calculated | required about the tap density, the average particle diameter by a laser diffraction method, the maximum particle diameter, the BET specific surface area, and the surface moisture content by the method similar to Example 1. FIG. As a result, the tap density was 4.3 g / cm ³ , the average particle size by laser diffraction method was 3.8 μm, the maximum particle size was 15.6 μm, the BET specific surface area was 0.27 m ² / g, and the surface moisture content was 2. It was 7 molecules / nm ² .

[Comparative Example 8]
To 4500 kg of silver nitrate aqueous solution containing 54 kg of silver, 225 kg of 25% by mass of ammonia water and 2 kg of 25% by mass of sodium hydroxide aqueous solution were added to obtain a silver ammine complex salt aqueous solution. The liquid temperature of this silver ammine complex salt aqueous solution was 40 ° C., and 240 kg of a 37% by mass formalin aqueous solution was added to precipitate silver particles. After the addition of the formalin aqueous solution, 0.1% by mass of linolenic acid was added to the amount of silver, and the resulting silver-containing slurry was filtered and washed with water to obtain a cake.

  62.5 kg of the obtained cake was dried at 70 ° C. for 20 hours with a 500 L vacuum dryer to obtain 50.0 kg of dried powder. It was confirmed with an infrared moisture meter that the dried powder was dry. The obtained dry powder was crushed and classified to obtain silver powder having a desired particle size.

About the obtained silver powder, it calculated | required about the tap density, the average particle diameter by a laser diffraction method, the maximum particle diameter, the BET specific surface area, and the surface moisture content by the method similar to Example 1. FIG. As a result, the tap density was 5.0 g / cm ³ , the average particle size by laser diffraction method was 3.3 μm, the maximum particle size was 13.1 μm, the BET specific surface area was 0.30 m ² / g, and the surface moisture content was 1. It was 8 molecules / nm ² .

  The results of Examples 1 to 4 and Comparative Examples 1 to 8 are shown in Table 1.

Claims (3)

Surface is gelatin or collagen peptide hydrophilic dispersing agent and benzotriazole, stearic acid, is coated with a dispersant comprising a hydrophobic dispersant selected from oleic acid, and the group consisting of salts, tap density 2 g / cm Silver powder characterized by ³ or more, an average particle diameter by laser diffraction method of 0.1 to 5 μm, a BET specific surface area of 0.1 to ⁵ m ² / g, and a surface moisture content of 3 to 6 molecules / nm ² . The silver powder according to claim 1, wherein the silver powder is a silver powder for fired conductive paste. Characterized by using as the conductor the silver powder according to claim 1 or 2, a conductive paste.