JP6791652B2 - Silver powder and its manufacturing method - Google Patents

Description

The present invention relates to spherical silver powder and a method for producing the same, and in particular, a spherical shape for a conductive paste used for an internal electrode of a multilayer capacitor, a conductor pattern of a circuit board, an electrode of a display panel or a substrate of a solar cell, or an electronic component such as a circuit. Regarding silver powder and its manufacturing method.

Conventionally, silver powder is added to an organic vehicle together with a glass frit and kneaded as a conductive paste used for electronic components such as internal electrodes of multilayer capacitors, conductor patterns of circuit boards, electrodes of substrates for solar cells and display panels, and circuits. The conductive paste produced by this is used. Such silver powder for conductive paste is required to have an appropriately small particle size and a uniform particle size in order to cope with miniaturization of electronic parts, high density of conductor patterns, fine line, etc. There is.

As a method for producing silver powder for such a conductive paste, an alkali or a complexing agent is added to a silver salt-containing aqueous solution to generate a silver oxide-containing slurry or a silver complex-containing aqueous solution, and then a reducing agent is added. A method is known in which silver powder is reduced and precipitated, and then dried. In such a method, in order to produce silver powder having less aggregation and excellent dispersibility, an alkali or a complexing agent is added to the silver salt-containing aqueous solution to generate a silver oxide-containing slurry or a silver complex salt-containing aqueous solution, and a reducing agent is used. Is added to reduce and precipitate silver particles, and then one or more of fatty acids, fatty acid salts, surfactants, organic metal compounds, chelating agents, and polymer dispersants as dispersants in the silver-containing slurry solution or its filtration. A method of producing silver powder whose surface is coated with a dispersant has been proposed by adding the above (see, for example, Patent Documents 1 and 2).

Further, when an organic solvent having high water solubility is used as the solvent used for the conductive paste, if the silver powder used for the conductive paste is not compatible with the solvent, the silver powder does not disperse in the conductive paste and becomes a lump. As a result, when the conductive paste is applied to a substrate or the like, the film thickness of the conductive paste becomes non-uniform, so that the conductivity and adhesive strength of the conductor formed by firing the conductive paste deteriorate.

Therefore, when a highly water-soluble organic solvent is used as the solvent for the conductive paste, the silver powder used for the conductive paste is a silver powder having a high surface moisture content that is compatible with the highly water-soluble organic solvent. Although it is desired, in the conventional method for producing silver powder such as the methods of Patent Document 1 and Patent Document 2, it is desired to produce silver powder having a surface moisture content suitable for a conductive paste using a highly water-soluble organic solvent. I couldn't.

In order to produce silver powder having a surface moisture content suitable for a conductive paste using such a highly water-soluble organic solvent, a reducing agent is added to an aqueous reaction system containing silver ions to reduce and precipitate silver particles. In the method for producing silver particles, as two or more kinds of dispersants, hydrophobic dispersants such as benzotriazole, stearic acid, and oleic acid, gelatin, collagen peptide, etc., are used before, after, or during the reduction precipitation of silver particles. A method of producing silver powder having a surface moisture content suitable for a conductive paste using a highly water-soluble organic solvent has been proposed by adding the hydrophilic dispersant of (see, for example, Patent Document 3).

Japanese Unexamined Patent Publication No. 10-88206 (paragraph number 0002-0004) JP-A-2005-22380 (paragraph number 0013) Japanese Unexamined Patent Publication No. 2008-88453 (paragraph number 0008-0009)

However, in the method of Patent Document 3, it is necessary to use a hydrophilic dispersant as well as a hydrophobic dispersant in order to obtain a silver powder having a surface moisture content suitable for a conductive paste using a highly water-soluble organic solvent. As the cost of the dispersant increases, the manufacturing cost increases. Further, in the conventional method for producing silver powder such as the methods of Patent Documents 1 to 3, the cake obtained by filtering the silver-containing slurry is heated and dried, so that the cost required for heating increases. The manufacturing cost is high. Further, by lowering the volume resistivity of the conductive film produced by using the conductive paste as compared with the conventional one, the characteristics of electronic parts and the like using the conductive paste can be improved, for example, the conductive paste can be used. It is desired to produce silver powder that can improve the power generation efficiency of a solar cell when used in a solar cell.

Therefore, in view of such conventional problems, the present invention provides silver powder capable of lowering the volume resistivity of the conductive film produced by using the conductive paste, and can reduce the volume resistivity of such silver powder. It is an object of the present invention to provide a method for producing silver powder which can be produced.

As a result of diligent research to solve the above problems, the present inventors obtained by filtering a silver-containing slurry obtained by adding a reducing agent to an aqueous reaction system containing silver ions to reduce and precipitate silver particles. By dehydrating the cake at room temperature, crushing it at room temperature, and classifying it at room temperature to obtain silver powder, silver powder that can reduce the volume resistivity of the conductive film produced by using it for a conductive paste is inexpensive. We have found that it can be manufactured in the above, and have completed the present invention.

That is, in the method for producing silver powder according to the present invention, a cake obtained by filtering a silver-containing slurry obtained by adding a reducing agent to an aqueous reaction system containing silver ions to reduce and precipitate silver particles is produced at room temperature. It is characterized by dehydration, crushing at room temperature, and classification at room temperature to obtain silver powder.

The silver powder obtained in this method for producing silver powder preferably has a water content of 5 to 40 ppm by the Karl Fischer method. The room temperature may be higher than 0 ° C. and lower than 40 ° C., and is preferably 5 to 35 ° C. The dry weight loss of the crushed powder obtained by crushing is preferably 1 to 6.5%, and the dry weight loss of the cake is preferably 15% or less. Further, it is preferable to add the dispersant before the reduction precipitation of the silver particles, after the reduction precipitation, or during the reduction precipitation. This dispersant is preferably a hydrophobic dispersant, and preferably a dispersant composed of fatty acids. Further, the dispersant is preferably a dispersant selected from the group consisting of stearic acid, oleic acid, palmitic acid, myristic acid and salts thereof.

The silver powder according to the present invention is characterized by having a water content of 5 to 40 ppm by the Karl Fischer method and a crystallite diameter of 30.0 to 31.5 nm. The surface water content of this silver powder is preferably 0.4 to 2.9 molecules / nm ² . Further, the average particle size by the laser diffraction method is preferably 0.1 to 5 μm, and the BET specific surface area is preferably 0.1 to ⁵ m ² / g. Further, when the silver powder is pelletized and heated from room temperature to 900 ° C. at a heating rate of 10 ° C./min in an air atmosphere, the peak value of thermal expansion at the temperature of the peak value of the coefficient of thermal expansion is + 0.4% or less. It is preferable to have it.

Further, the conductive paste according to the present invention is characterized in that the above-mentioned silver powder is used as a conductor.

In the present specification, "dry weight loss" refers to the amount of weight loss of a sample after 10 g of the sample is placed in a weighing bottle, dried at 110 ° C. for 3 hours, and allowed to cool for 40 minutes or more. It is a value obtained by multiplying the value obtained by dividing by the weight (10 g) of the above by 100.

According to the present invention, it is possible to inexpensively produce silver powder capable of lowering the volume resistivity (higher conductivity) of the conductive film produced by using it for a conductive paste.

It is a figure which shows the coefficient of thermal expansion when the silver powder of Examples and Comparative Examples was pelletized and heated from room temperature to 900 ° C. at a heating rate of 10 ° C./min in an air atmosphere. It is an enlarged view around 250 degreeC in FIG.

In the embodiment of the method for producing silver powder according to the present invention, the silver-containing slurry obtained by adding a reducing agent to an aqueous reaction system containing silver ions to reduce and precipitate silver particles was filtered and washed with water. The cake is dehydrated at room temperature, crushed at room temperature, and classified at room temperature to obtain silver powder.

As the aqueous reaction system containing silver ions, an aqueous solution or slurry containing silver nitrate, a silver complex or a silver intermediate can be used. The aqueous solution containing the silver complex can be produced by adding aqueous ammonia, an ammonium salt, a 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 for the silver powder to have an appropriate particle size and a spherical shape, it is preferable to use an aqueous solution of an ammine complex obtained by adding aqueous ammonia to an aqueous solution of silver nitrate. 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 reduction does not proceed easily. Therefore, the amount of ammonia added is preferably 8 mol or less per 1 mol of silver. By making adjustments such as increasing the amount of the reducing agent added, it is possible to obtain spherical silver powder having an appropriate particle size even if the amount of ammonia added exceeds 8 mol.

Reducing agents include ascorbic acid, sulfite, alkanolamine, hydrogen peroxide, formic acid, ammonium formate, sodium formate, glyoxal, tartaric acid, sodium hypophosphite, sodium sulfite, hydroquinone, hydrazine, hydrazine compounds, pyrogallol, Glucose, formic acid, formic acid, anhydrous sodium sulfite, longalite and the like can be used. Among these, it is preferable to use one or more selected from the group consisting of ascorbic acid, alkanolamine, sodium boron hydride, hydroquinone, hydrazine and formalin, and in particular, formalin is used because it is inexpensive. preferable. By using these reducing agents, silver particles having an appropriate particle size can be obtained. The amount of the reducing agent added must be 1 equivalent or more with respect to silver in order to increase the reaction yield of silver. When a reducing agent having a weak reducing power is used, 2 equivalents or more of the reducing agent, for example, 10 to 20 equivalents of the reducing agent may be added to silver. As for the method of adding the reducing agent, it is preferable to add the reducing agent at a rate of 1 equivalent / min or more in order to prevent agglomeration of the silver powder. The reason for this is not clear, but when the reducing agent is added in a short time, the reduction precipitation of silver particles occurs all at once, the reduction reaction is completed in a short time, and the generated nuclei are unlikely to aggregate. It is thought that the dispersibility will improve. Therefore, it is preferable that the addition time of the reducing agent is short. For example, the reducing agent may be added at a rate of 100 equivalents / minute or more, and the reaction may be 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 are metals such as lithium, sodium, potassium, barium, magnesium, calcium, aluminum, iron, cobalt, manganese, lead, zinc, tin, strontium, zirconium, silver and copper, and fatty acids forming salts. I can mention things. 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 imidazolinium betaine. Examples include surfactants and nonionic surfactants such as polyoxyethylene alkyl ethers and polyoxyethylene fatty acid esters. Examples of organometallic compounds include acetylacetone tributoxyzincene, magnesium citrate, diethylzinc, dibutyltin oxide, dimethylzinc, tetra-n-butoxyzincoxide, triethylindium, triethylgallium, trimethylindium, trimethylgallium, monobutyltinoxide, tetra. Examples thereof include isocyanatesilane, tetramethylsilane, tetramethoxysilane, polymethoxysiloxane, monomethyltriisocyanatesilane, silane coupling agent, titanate-based coupling agent, and aluminum-based coupling agent. 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-thiazol, 1,2,4-thiazol, 1,2,5-thiazyl, 1,3,4-thiazol, 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, 1,2,3,5- Thiatriazole, indazole, benzoimidazole and benzotriazole and their salts, or oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelli acid, suberic acid, azelaic acid, sebacic acid, dodecanedic acid, maleic acid , Fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, glycolic acid, lactic acid, oxybutyric acid, glyceric acid, tartrate acid, malic acid, tartronic acid, hydroacrylic acid, mandelic acid, citric acid, ascorbic acid and the like. .. Examples of the polymer dispersant include peptides, gelatin, collagen peptides, albumin, gum arabic, protalbic acid, lithalbic acid and the like.

As the above-mentioned dispersant, it is preferable to use a hydrophobic dispersant, and it is preferable to use a dispersant composed of fatty acids. As the dispersant composed of this fatty acid, it is preferable to use a dispersant selected from the group consisting of stearic acid, oleic acid, palmitic acid, myristic acid and salts thereof. In addition, after producing silver powder whose surface is coated with a dispersant composed of these fatty acids having a large carbon number, the surface of the silver powder is mixed by dissolving the silver powder in a solvent together with fatty acids having a carbon number smaller than those of these fatty acids. The fatty acid having a large number of carbon atoms may be replaced with a fatty acid having a small number of carbon atoms.

The obtained silver-containing slurry is filtered by a filter press or the like and washed with water to obtain a lumpy cake containing 1 to 200% by mass of water with respect to silver and having almost no fluidity. The drying weight loss of this cake is preferably 15% or less, more preferably 12% or less.

The cake thus obtained is dehydrated at room temperature (without heating) to obtain dehydrated powder. Although the amount of water is reduced by this dehydration (drying at room temperature), it is preferable to dehydrate to the extent that there is no problem in crushing as a subsequent step. This dehydration can be performed by a dryer such as a forced circulation air dryer, a vacuum dryer, or an air flow dryer, and is preferably performed by a vacuum dryer.

The dehydrated powder thus obtained is crushed at room temperature to obtain crushed powder. The water content is further reduced by this crushing, and the drying weight loss of the crushed powder is preferably 1 to 6.5%, more preferably 2 to 5%. By crushing the dehydrated powder obtained by dehydration at room temperature in this way at room temperature, crushed powder that is not completely dried can be obtained. This crushing process can be performed by a stirrer such as a coffee mill. Further, as this crushing process, silver particles are put into a device (for example, Henschel mixer) capable of mechanically fluidizing the particles, and the particles are mechanically collided with each other to cause unevenness on the particle surface. A surface smoothing treatment may be performed to smooth the angular portion. A vacuum stirrer such as a vacuum Henschel mixer may be used to simultaneously dehydrate and crush the cake to obtain crushed powder from the cake.

The crushed powder thus obtained is classified at room temperature to obtain silver powder. This classification can be performed by combining a collision crusher using a high-pressure air stream such as a jet mill and a wind power classifier. By this classification, the water content is further reduced, and the drying weight loss of the silver powder after the classification is preferably less than 0.01%, and a silver powder similar to a normal (almost completely) dried silver powder can be obtained. By dehydrating the cake at room temperature and crushing the dehydrated powder obtained at room temperature and classifying the cake at room temperature in this way, a silver powder having a dry weight loss almost the same as that obtained by heating and drying the cake is obtained. Therefore, classification at room temperature plays a role as a final drying step. The water content of the silver powder after this classification by the Karl Fischer method is preferably 5 to 40 ppm, more preferably 8 to 38 ppm. The water content of the silver powder after the classification by the Karl Fischer method is larger than the water content of the silver powder obtained by heating and drying the cake obtained by filtering the silver-containing slurry. The surface water content of this silver powder is preferably 0.4 to 2.9 molecules / nm ² , and more preferably 0.5 to 2.5 molecules / nm ² . The amount of water on the surface of the silver powder (the amount of water molecules adsorbed on the surface of the silver powder due to the binding between the functional group of the dispersant on the surface of the silver powder and the water molecules) determines the amount of water molecules adsorbed on the surface of the silver powder by heating the cake obtained by filtering the silver-containing slurry. It is different from the water content of the silver powder obtained by drying.

The temperature at which the dehydration, filtration, crushing, and classification are performed is room temperature, which may be higher than 0 ° C. and lower than 40 ° C., but is preferably 5 to 35 ° C.

When the silver powder is produced in this manner, the silver particles are precipitated and then dried stepwise without applying extra heat, so that the production cost of the silver powder can be reduced.

According to the embodiment of the method for producing silver powder described above, silver powder having a water content of 5 to 40 ppm, preferably 8 to 38 ppm and a crystallite diameter of 30.0 to 31.5 nm by the Karl Fischer method can be produced. .. The surface water content of this silver powder is preferably 0.4 to 2.9 molecules / nm ² , and more preferably 0.5 to 2.5 molecules / nm ² .

The average particle size of this silver powder by laser diffraction is preferably 0.1 to 5 μm, more preferably 0.5 to 3 μm. If the average particle size by the laser diffraction method is smaller than 0.1 μm, it is possible to make fine lines, but the activity of the particles is high, and when silver powder is used for a baking paste, it is suitable for firing at 500 ° C or higher. Is not suitable. On the other hand, if the average particle size by the laser diffraction method is larger than 5 μm, the dispersibility becomes inferior, and it is also difficult to cope with fine line formation.

BET specific surface area of the silver powder is preferably 0.1 to 5 m ² / g, more preferably 0.1~2m ² / g. If 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 line formation.

When this silver powder is pelletized and heated in an air atmosphere from room temperature to 900 ° C. at a heating rate of 10 ° C./min, the peak value of thermal expansion at the peak value of the coefficient of thermal expansion is + 0.4% or less. It is preferable to have it.

When a conductive film is produced by using such silver powder as a conductive paste, the volume resistivity of the conductive film can be made lower than before, and when the conductive paste is used for a solar cell, the solar cell The power generation efficiency can be improved.

Hereinafter, examples of the silver powder according to the present invention and the method for producing the same will be described in detail.

[Example 1]
To 3600 mL of a silver nitrate aqueous solution containing 12 g / L of silver ions, 180 mL of 25 mass% ammonia water and 16 mL of a 75 g / L 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 set to 40 ° C., and 192 mL of a 37 mass% formalin aqueous solution was added to precipitate silver particles. After the addition of the formalin aqueous solution was completed, 0.2% by mass of stearic acid emulsion was added as stearic acid with respect to the amount of silver, and the obtained silver-containing slurry was filtered under reduced pressure and washed with water to obtain a cake. .. When the dry weight loss of this cake was calculated, it was 9.7%.

Next, 47 g of the obtained cake was dehydrated at room temperature (25 ° C.) for 3 hours by a vacuum dryer having an internal volume of 27 L to obtain 42 g of dehydrated powder.

Next, the obtained dehydrated powder (powder containing water after dehydration) was crushed with a coffee mill at room temperature for 1 minute to obtain 40 g of crushed powder. When the dry weight loss of this crushed powder was determined, it was 4.5%.

Next, the obtained crushed powder was classified by a jet mill at room temperature to obtain silver powder having a desired particle size. When the dry weight loss of this silver powder was determined, it was less than 0.01%.

In addition, the water content in the obtained silver powder was measured, and the surface water content of the silver powder was calculated.

The water content in the silver powder was measured by the Karl Fischer method using a coulometric titration type automatic water content measuring device (CA-100 (vaporizer VA-100) manufactured by Mitsubishi Chemical Corporation). As a result, the water content in the silver powder was measured. Was 35.1 ppm.

The surface water content of the silver powder is determined by using a coulometric titration method automatic water content measuring device (CA-100 (vaporizer VA-100) manufactured by Mitsubishi Chemical Corporation) and the water content from 1 g of the silver powder sample at a vaporization temperature of 100 ° C. the (ppm) was measured, the surface moisture content _{(H 2} O molecules / ^nm 2) = amount of water leaving the silver powder sample ^{1g (ppm) ÷ 10 6 ÷} 18.0 × (6.02 × 10 23) ÷ BET specific It was calculated from the surface area (m ² / g) × 10 ¹⁸ . As a result, the surface water content of the silver powder was 2.19 molecules / nm ² .

Further, regarding the obtained silver powder, the cumulative 10% by mass particle size (D ₁₀ ), the cumulative 50% by mass particle size (average particle size D ₅₀ ), the cumulative 90% by mass particle size (D ₉₀ ), and the maximum grain size by the laser diffraction method. The diameter (Dmax) was determined, and the BET specific surface area, tap density, thermal expansion rate, and crystallite diameter were determined.

The cumulative 10% by mass particle size (D ₁₀ ), the cumulative 50% by mass particle size (average particle size D ₅₀ ), the cumulative 90% by mass particle size (D ₉₀ ), and the maximum particle size (Dmax) of silver powder by the laser diffraction method are 0.3 g of silver powder sample was added to 30 mL of isopropyl alcohol and dispersed for 5 minutes with an ultrasonic washer with an output of 50 W. Macrotrack particle size distribution measuring device (Honeywell-Macrotrack particle size distribution measuring device 9320-HRA manufactured by Nikkiso Co., Ltd. (X-100)) was used for measurement. As a result, the cumulative 10% by mass particle size (D ₁₀ ) by the laser diffraction method is 1.2 μm, the cumulative 50% by mass particle size (average particle size D ₅₀ ) is 1.9 μm, and the cumulative 90% by mass particle size (D ₉₀ ). Was 3.1 μm, and the maximum particle size (Dmax) was 7.8 μm.

The BET specific surface area of the silver powder was measured by the BET 1-point method using a BET specific surface area measuring device (a monosorb manufactured by Quanta Chrome). As a result, the BET specific surface area was 0.53 m ² / g.

For the tap density (TAP) of silver powder, weigh 30 g of silver powder, put it in a 20 mL test tube, tap it 1,000 times with a head of 20 mm, and tap density = sample mass (30 g) / sample volume after tapping (cm ³ ). Calculated from. As a result, the tap density was 4.9 g / cm ³ .

The crystallite diameter of the silver powder was determined by Scherrer's formula (Dhkl = Kλ / βcosθ). In this equation, Dhkl is the size of the crystallite diameter (size of the crystallite in the direction perpendicular to hkl) (Angstrom), and λ is the wavelength of the measured X-ray (Angstrom) (1.5405 Angstrom when using a Cu target). β is the spread (rad) of the diffraction line according to the size of the crystallite (expressed using the half-value width), and θ is the Bragg angle (rad) of the diffraction angle (the angle when the incident angle and the reflection angle are equal, and the peak. (Use the top angle), K is a Scherrer constant (depending on the definition of D or β, K = 0.94 when using the half-value range for β). A powder X-ray diffractometer was used for the measurement, and the peak data of the (200) plane was used for the calculation. As a result, the crystallite diameter (Dx) of the silver powder was 31.2 nm.

For the coefficient of thermal expansion of silver powder, a pellet-shaped silver powder sample prepared by applying a load of 50 kgf to 0.15 g of silver powder placed in a mold having a diameter of 5 mm was used with an expansion rate measuring device (DILATOMETER manufactured by NETZSCH JAPAN). The length of the sample when heated from room temperature to 900 ° C. at a heating rate of 10 ° C./min in an air atmosphere was measured and determined. The results are shown in FIGS. 1 and 2. As shown in FIGS. 1 and 2, in this example, when the pellet-shaped silver powder sample was heated from room temperature to 900 ° C. at a heating rate of 10 ° C./min in an air atmosphere, it did not expand (FIG. 1). And in FIG. 2, it can be seen that it contracts (without becoming positive (+)). The peak value of thermal expansion at the temperature of the peak value of the coefficient of thermal expansion (244 ° C.) was −0.1%.

In addition, 88 parts by weight of the obtained silver powder, diethylene glycol monobutyl ether acetate (manufactured by Wako Pure Chemical Industries, Ltd.) and 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (manufactured by Chisso Co., Ltd.) were added. 4 parts by weight of a vehicle in which 30% by weight of ethyl cellulose (manufactured by Wako Pure Chemical Industries, Ltd.) is dissolved in a solvent mixed at a weight ratio of 1: 1 and monobutyl ether acetate (manufactured by Wako Pure Chemical Industries, Ltd.). 2.25 parts by weight of an organic solvent mixed with 2,4-trimethyl-1,3-pentanediol monoisobutyrate (manufactured by Chisso Co., Ltd.) at a weight ratio of 1: 1 and glass frit (ASF1898B manufactured by Asahi Glass Co., Ltd.) 1.6 parts by weight of tellurium dioxide (manufactured by Wako Pure Chemical Industries, Ltd.) as a penetrant, 3.4 parts by weight of magnesium stearate (manufactured by Wako Pure Chemical Industries, Ltd.) as a thixo agent, and 0.25 parts by weight. Weigh 0.5 parts by weight of oleic acid (manufactured by Wako Pure Chemical Industries, Ltd.) as a dispersant with an electronic balance, and use a self-revolving stirring defoaming device (AR250 manufactured by Shinky Co., Ltd.) (revolving 1400 rpm x rotating). After performing the mixing operation for 30 seconds (at 700 rpm) twice, the mixture is kneaded by passing it through a roll gap of 100 μm to 20 μm using a three-roll mill (EXAKT80S manufactured by Otherman) to contain 85% by weight of silver. A silver paste was prepared. At the time of this kneading, the above-mentioned organic solvent was further added (the amount of the organic solvent after the addition was 2.73 parts by weight) to adjust the viscosity of the silver paste.

When the viscosity of this silver paste was measured with a viscometer (DV-III Ultra manufactured by Brookfield) at 25 ° C. at 1 rpm and 5 rpm, it was 445 (Pa · s) and 140 (Pa · s), respectively, and the Ti value. (Tixo ratio = viscosity of 1 rpm to viscosity of 5 rpm (viscosity of 1 rpm / viscosity of 5 rpm)) was 3.2.

Next, the obtained silver paste was placed on a 96% alumina substrate (1 inch size) with a screen printing machine (MT-320T manufactured by Microtech) and a screen plate (250 mesh, wire diameter 23 μm, emulsion 20 μm). Was screen-printed so as to form a linear coating film having a width of 500 μm and a length of 37.5 mm at a squeegee pressure of 180 MPa and a printing speed of 300 mm / sec, and dried at 200 ° C. for 10 minutes using a hot air dryer. After that, the temperature was raised in the air at a heating rate of 10 ° C./min by a small electric furnace (KBF-008H manufactured by Koyo Thermo System Co., Ltd.), and the temperature was maintained at 600 ° C., 780 ° C., and 820 ° C. for 10 minutes, respectively. A conductive film was produced by firing.

The film thickness and line width of the conductive film fired at each temperature are measured with a contact type surface roughness meter (SE-30D manufactured by Kosaka Laboratory Co., Ltd.), and the line resistivity is measured with a digital multimeter (R6551 manufactured by Advantest Co., Ltd.). ) = Volume resistivity (Ω · cm) = line resistivity (Ω) x film thickness (cm) x line width (cm) / line length (cm). 28 μm, 19.2 μm, 17.8 μm, line widths are 500.7 μm, 499.7 μm, 500.4 μm, respectively, line resistors are 0.237 Ω, 0.120 Ω, 0.112 Ω, respectively, and volume resistivity is 8, respectively. It was .86 μΩ · cm, 3.07 μΩ · cm, and 2.66 μΩ · cm.

In addition, a silicon wafer (80Ω / □, 6-inch single crystal manufactured by E & M Co., Ltd.) was prepared, and aluminum paste (Toyo Aluminum Co., Ltd.) was used on the back surface of this silicon wafer using a screen printing machine (MT-320T manufactured by Microtech Co., Ltd.). After printing the company's Alsolar 14-7021 (with Pb) in a solid pattern with a length of 154 mm, it is dried at 200 ° C. for 10 minutes with a hot air dryer, and a screen printing machine (Microtech) is printed on the surface of the silicon wafer. The above paste was printed on 100 finger electrode shapes with a width of 50 μm and 3 bus bar electrode shapes with a width of 1.3 mm using MT-320T) manufactured by Co., Ltd., and then dried at 200 ° C. for 10 minutes using a hot air dryer. Then, a solar cell was produced by firing at a peak temperature of 820 ° for 21 seconds in-out of a high-speed firing IR press (high-speed firing test 4-chamber furnace manufactured by Nippon Gaishi Co., Ltd.).

When the film thickness, line width and cross-sectional area of the three bus bar electrodes of this solar cell were measured with a contact type surface roughness meter (SE-30D manufactured by Kosaka Laboratory Co., Ltd.), the average film thickness was 14. It was 6 μm, the average line width was 62.3 μm, the average cross-sectional area was 503 μm ² , and the aspect ratio (film thickness / line width) of the cross section was 0.24. The weight of the silver paste applied to form the finger electrode and the bus bar electrode was 0.130 g.

A battery characteristic test was conducted by irradiating the above solar cell with pseudo-sunlight having a light irradiation energy of 100 mW cm ² using a xenon lamp of a solar simulator (manufactured by Wacom Denso Co., Ltd.). As a result, the current (short-circuit current) Isc flowing between both terminals when the output terminal of the solar cell is short-circuited is 8.590 mA, and the voltage (open-circuit voltage) Voc between both terminals when the output terminal of the solar cell is opened. Is 0.626V, the current density Jsc (short-circuit current Isc per 1cm ² ) is 0.0360mA / cm ² , and the maximum output Pmax (= Imax · Vmax) is divided by the product of the open circuit voltage Voc and the current density Jsc (curve). Factor) FF (= Pmax / Voc · Isc) is 76.50, and power generation efficiency Eff (value obtained by dividing the maximum output Pmax by the irradiation light amount (W) (per 1 cm ² ) multiplied by 100) is 17.22. %, The series resistance Rs was 0.0072Ω / □.

[Example 2]
The dry weight loss of the obtained cake was determined by the same method as in Example 1 except that pressure filtration was performed instead of vacuum filtration, and it was 7.0%. 47 g of this cake was dehydrated at room temperature (25 ° C.) for 3 hours by a vacuum dryer having an internal volume of 27 L to obtain 42 g of dehydrated powder. This dehydrated powder was crushed with a coffee mill at room temperature for 1 minute to obtain 40 g of crushed powder. The dry weight loss of this crushed powder was determined and found to be 2.3%. Next, the obtained crushed powder was classified by a jet mill at room temperature to obtain silver powder having a desired particle size. When the dry weight loss of this silver powder was determined, it was less than 0.01%.

Moreover, when the water content in the silver powder was measured by the same method as in Example 1, it was 8.9 ppm. Moreover, when the surface water content of the silver powder was calculated by the same method as in Example 1, it was 0.60 molecules / nm ² .

Further, with respect to the obtained silver powder, the cumulative 10% by mass particle size (D ₁₀ ), the cumulative 50% by mass particle size (average particle size D ₅₀ ), and the cumulative 90% by mass by the laser diffraction method were carried out by the same method as in Example 1. The particle size (D ₉₀ ) and the maximum particle size (Dmax) were determined, and the BET specific surface area, tap density, thermal expansion rate, and crystallite diameter were determined. As a result, the cumulative 10% by mass particle size (D ₁₀ ) by the laser diffraction method is 1.3 μm, the cumulative 50% by mass particle size (average particle size D ₅₀ ) is 2.1 μm, and the cumulative 90% by mass particle size (D ₉₀ ). Was 3.6 μm, and the maximum particle size (Dmax) was 9.3 μm. The BET specific surface area was 0.49 m ² / g, the tap density was 5.0 g / cm ³ , and the crystallite diameter was 30.3 nm. The coefficient of thermal expansion is shown in FIGS. 1 and 2. As shown in FIGS. 1 and 2, in this embodiment, when the pellet-shaped silver powder sample is heated from room temperature to 900 ° C. at a heating rate of 10 ° C./min in an air atmosphere, it expands slightly at around 250 ° C. It can be seen that the sample shrinks after it has been (slightly positive (+) in FIGS. 1 and 2). The peak value of thermal expansion at the temperature of the peak value of the coefficient of thermal expansion (244 ° C.) was 0.35%.

Further, using the obtained silver powder, a silver paste containing 85% by mass of silver was prepared by the same method as in Example 1, and the viscosity of this silver paste was determined by the same method as in Example 1. 254 (Pa · s) at 1 rpm and 90 (Pa · s) at 5 rpm at 25 ° C., the ratio of the viscosity of 1 rpm to the viscosity of 5 rpm measured at 25 ° C. (viscosity of 1 rpm / viscosity of 5 rpm) (Ti value) Was 2.8.

Further, using the obtained silver paste, a conductive film was prepared by the same method as in Example 1, the film thickness, line width and line resistivity thereof were measured, and the volume resistivity was calculated. The film thickness is 29 μm, 19.2 μm, 19.6 μm, the line width is 499.2 μm, 500.2 μm, 499.7 μm, respectively, and the line resistivity is 0.237 Ω, 0.114 Ω, 0.103 Ω, respectively, and the volume resistivity. The resistivity was 9.15 μΩ · cm, 2.92 μΩ · cm, and 2.69 μΩ · cm, respectively.

Further, using the obtained silver paste, a solar cell was produced by the same method as in Example 1, the film thickness, line width and cross-sectional area of the three bus bar electrodes were measured, and the aspect ratio was determined. The average film thickness was 18.0 μm, the average line width was 76.9 μm, the cross-sectional area was 691 μm ² , and the aspect ratio was 0.23. To form each bus bar electrode. The amount of silver paste applied was 0.139 g. In addition, when the battery characteristics of this solar cell were tested, the short-circuit current Isc was 8.519 mA, the open circuit voltage Voc was 0.627 V, the current density Jsc was 0.0357 mA / cm ² , the curve factor FF was 77.11, and power generation. The efficiency Eff was 17.26% and the series resistance Rs was 0.071Ω / □.

[Comparative Example 1]
47 g of the cake obtained by the same method as in Example 1 was dried at 70 ° C. for 10 hours by a vacuum dryer having an internal volume of 27 L to obtain 42 g of dry powder. This dried powder was crushed with a coffee mill at room temperature for 1 minute to obtain 40 g of crushed powder. When the dry weight loss of this crushed powder was determined, it was less than 0.01%. Next, the obtained crushed powder was classified by a jet mill at room temperature to obtain silver powder having a desired particle size. When the dry weight loss of this silver powder was determined, it was less than 0.01%.

Moreover, when the water content in the silver powder was measured by the same method as in Example 1, it was 22.2 ppm. Moreover, when the surface water content of the silver powder was calculated by the same method as in Example 1, it was 1.72 molecules / nm ² .

Further, with respect to the obtained silver powder, the cumulative 10% by mass particle size (D ₁₀ ), the cumulative 50% by mass particle size (average particle size D ₅₀ ), and the cumulative 90% by mass by the laser diffraction method were carried out by the same method as in Example 1. The particle size (D ₉₀ ) and the maximum particle size (Dmax) were determined, and the BET specific surface area, tap density, thermal expansion rate, and crystallite diameter were determined. As a result, the cumulative 10% by mass particle size (D ₁₀ ) by the laser diffraction method is 1.1 μm, the cumulative 50% by mass particle size (average particle size D ₅₀ ) is 2.0 μm, and the cumulative 90% by mass particle size (D ₉₀ ). Was 3.1 μm, and the maximum particle size (Dmax) was 6.5 μm. The BET specific surface area was 0.43 m ² / g, the tap density was 5.2 g / cm ³ , and the crystallite diameter was 31.8 nm. The coefficient of thermal expansion is shown in FIGS. 1 and 2. As shown in FIGS. 1 and 2, in this comparative example, unlike Example 1, when the pellet-shaped silver powder sample was heated from room temperature to 900 ° C. at a heating rate of 10 ° C./min in an air atmosphere, 250 It can be seen that it expands near ° C. (becomes positive (+) in FIGS. 1 and 2) and then contracts. The peak value of thermal expansion at the temperature of the peak value of the coefficient of thermal expansion (244 ° C.) was 0.54%.

Further, using the obtained silver powder, a silver paste containing 85% by mass of silver was prepared by the same method as in Example 1, and the viscosity of this silver paste was determined by the same method as in Example 1. 361 (Pa · s) at 1 rpm and 125 (Pa · s) at 5 rpm at 25 ° C., the ratio of the viscosity of 1 rpm to the viscosity of 5 rpm measured at 25 ° C. (viscosity of 1 rpm / viscosity of 5 rpm) (Ti value) Was 2.9.

Further, using the obtained silver paste, a conductive film was prepared by the same method as in Example 1, the film thickness, line width and line resistivity thereof were measured, and the volume resistivity was calculated. The film thickness is 30 μm, 20.2 μm, 18.6 μm, the line width is 486.4 μm, 499.7 μm, 500.4 μm, respectively, and the line resistivity is 0.257 Ω, 0.120 Ω, 0.110 Ω, respectively, and the volume resistivity. Was 10.03 μΩ · cm, 3.23 μΩ · cm, and 2.73 μΩ · cm, respectively.

Further, using the obtained silver paste, a solar cell was produced by the same method as in Example 1, the film thickness, line width and cross-sectional area of the three bus bar electrodes were measured, and the aspect ratio was determined. The average value of the film thickness was 15.1 μm, the average value of the line width was 64.2 μm, the cross-sectional area was 574 μm ² , and the aspect ratio was 0.24. The amount of silver paste applied to form each bus bar electrode was 0.139 g. In addition, when the battery characteristics of this solar cell were tested, the short-circuit current Isc was 8.578 mA, the open circuit voltage Voc was 0.627 V, the current density Jsc was 0.0359 mA / cm ² , the curve factor FF was 75.49, and power generation. The efficiency Eff was 17.01% and the series resistance Rs was 0.076Ω / □.

[Comparative Example 2]
The dry weight loss of the obtained cake was determined by the same method as in Comparative Example 1 except that pressure filtration was performed instead of vacuum filtration, and it was 7.0%. 47 g of this cake was dried at 70 ° C. for 390 hours in a vacuum dryer having an internal volume of 27 L to obtain 42 g of dry powder. This dried powder was crushed with a coffee mill at room temperature for 1 minute to obtain 40 g of crushed powder. When the dry weight loss of this crushed powder was determined, it was less than 0.01%. Next, the obtained crushed powder was classified by a jet mill at room temperature to obtain silver powder having a desired particle size. When the dry weight loss of this silver powder was determined, it was less than 0.01%.

Moreover, when the water content in the silver powder was measured by the same method as in Example 1, it was 3.6 ppm. Moreover, when the surface water content of the silver powder was calculated by the same method as in Example 1, it was 0.32 molecules / nm ² .

Further, with respect to the obtained silver powder, the cumulative 10% by mass particle size (D ₁₀ ), the cumulative 50% by mass particle size (average particle size D ₅₀ ), and the cumulative 90% by mass by the laser diffraction method were carried out by the same method as in Example 1. The particle size (D ₉₀ ) and the maximum particle size (Dmax) were determined, and the BET specific surface area, tap density, thermal expansion rate, and crystallite diameter were determined. As a result, the cumulative 10% by mass particle size (D ₁₀ ) by the laser diffraction method is 1.2 μm, the cumulative 50% by mass particle size (average particle size D ₅₀ ) is 2.0 μm, and the cumulative 90% by mass particle size (D ₉₀ ). Was 3.2 μm, and the maximum particle size (Dmax) was 9.3 μm. The BET specific surface area was 0.37 m ² / g, the tap density was 6.0 g / cm ³ , and the crystallite diameter was 32.2 nm. The coefficient of thermal expansion is shown in FIGS. 1 and 2. As shown in FIGS. 1 and 2, in this comparative example, unlike Example 1, when the pellet-shaped silver powder sample was heated from room temperature to 900 ° C. at a heating rate of 10 ° C./min in an air atmosphere, 250 It can be seen that it expands near ° C. (becomes positive (+) in FIGS. 1 and 2) and then contracts. The peak value of thermal expansion at the temperature of the peak value of the coefficient of thermal expansion (244 ° C.) was 0.51%.

Further, using the obtained silver powder, a silver paste containing 85% by mass of silver was prepared by the same method as in Example 1, and the viscosity of this silver paste was determined by the same method as in Example 1. It is 325 (Pa · s) at 1 rpm and 103 (Pa · s) at 5 rpm at 25 ° C., and the ratio of the viscosity of 1 rpm to the viscosity of 5 rpm measured at 25 ° C. (viscosity of 1 rpm / viscosity of 5 rpm) (Ti value). Was 3.2.

Further, using the obtained silver paste, a conductive film was prepared by the same method as in Example 1, the film thickness and line resistivity thereof were measured, and the volume resistivity was calculated. They are 30 μm, 24.4 μm and 22.4 μm, respectively, line widths are 499.5 μm, 500.2 μm and 500.6 μm, respectively, line resistors are 0.250 Ω, 0.110 Ω and 0.105 Ω, respectively, and volume resistivity is each. It was 9.99 μΩ · cm, 3.58 μΩ · cm, and 3.14 μΩ · cm.

Further, using the obtained silver paste, a solar cell was produced by the same method as in Example 1, the film thickness, line width and cross-sectional area of the three bus bar electrodes were measured, and the aspect ratio was determined. The average value of the film thickness was 18.2 μm, the average value of the line width was 75.6 μm, the cross-sectional area was 640 μm ² , and the aspect ratio was 0.24. The amount of silver paste applied to form each bus bar electrode was 0.127 g. When the battery characteristics of this solar cell were tested, the short-circuit current Isc was 8.535 mA, the open circuit voltage Voc was 0.626 V, the current density Jsc was 0.0357 mA / cm ² , the curve factor FF was 75.20, and power generation. The efficiency Eff was 16.81% and the series resistance Rs was 0.080Ω / □.

The results of these examples and comparative examples are shown in Tables 1 to 6.

The yield of silver powder in Comparative Example 2 in which the dry weight loss of silver powder after crushing (before classification) was less than 0.01% (almost completely dried) (the amount of silver powder which is a good product with respect to the amount of silver powder input excluding water) The yield of silver powder in Example 2 after crushing (before classification) was 1 to 6.5% (not yet completely dried), although the ratio) was only 68%. The yield was as high as 92%, and as in Example 2, the yield of silver powder was obtained by dehydrating the cake obtained from the silver-containing slurry at room temperature, crushing the dehydrated powder obtained at room temperature, and classifying at room temperature. It turned out that it can be raised.

Claims (17)

The cake obtained by filtering the silver-containing slurry obtained by adding a reducing agent to an aqueous reaction system containing silver ions and reducing and precipitating silver particles was dehydrated at room temperature and crushed at room temperature to obtain the obtained product. A method for producing silver powder, which comprises classifying crushed powder having a dry weight loss of 1 to 6.5% to obtain silver powder having a dry weight loss of less than 0.01% . The method for producing silver powder according to claim 1, wherein the classification is carried out at room temperature. The method for producing silver powder according to claim 2 , wherein the room temperature is higher than 0 ° C. and lower than 40 ° C. The method for producing silver powder according to claim 2 , wherein the room temperature is a temperature of 5 to 35 ° C. The method for producing silver powder according to any one of claims 1 to 4 , wherein the water content of the silver powder by the Karl Fischer method is 5 to 40 ppm. The method for producing silver powder according to any one of claims 1 to 5 , wherein the dry weight loss of the crushed powder obtained by the crushing is 1 to 6.5%. The method for producing silver powder according to any one of claims 1 to 6 , wherein the drying weight loss of the cake is 15% or less. The method for producing silver powder according to any one of claims 1 to 7 , wherein the dispersant is added before, after the reduction precipitation, or during the reduction precipitation of the silver particles. The method for producing silver powder according to claim 8 , wherein the dispersant is a hydrophobic dispersant. The method for producing silver powder according to claim 8 or 9 , wherein the dispersant is a dispersant composed of fatty acids. The method for producing silver powder according to any one of claims 8 to 10 , wherein the dispersant is a dispersant selected from the group consisting of stearic acid, oleic acid, palmitic acid, myristic acid and salts thereof. .. A silver powder having a water content of 5 to 40 ppm by the Karl Fischer method and a crystallite diameter of 30.0 to 31.5 nm. The silver powder according to claim 12 , wherein the surface water content of the silver powder is 0.4 to 2.9 molecules / nm ² . The silver powder according to claim 12 or 13 , wherein the average particle size of the silver powder by laser diffraction is 0.1 to 5 μm. The silver powder according to any one of claims 12 to 14 , wherein the silver powder has a BET specific surface area of 0.1 to ⁵ m ² / g. A pellet-shaped silver powder sample prepared by placing 0.15 g of the silver powder in a mold having a diameter of 5 mm and applying a load of 50 kgf to the silver powder was prepared in an air atmosphere at a heating rate of 10 ° C./min from room temperature to 900 ° C. The silver powder according to any one of claims 12 to 15 , wherein the peak value of thermal expansion at the temperature of the peak value of the coefficient of thermal expansion when heated is + 0.4% or less. A conductive paste using the silver powder according to any one of claims 12 to 16 as a conductor.

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