Silver powder, method for producing silver powder, device for producing silver powder, and resin-curable conductive paste

Abstract

To provide a silver powder capable of imparting excellent volume resistivity and fine line printability to a conductive paste.SOLUTION: The present invention relates to a silver powder having a volume-based cumulative 50% diameter D50 of 0.1-1.0 μm as measured by laser diffraction, a ratio of D50 to BET diameter DBET of 1.3 or less, and a shrinkage rate of at least 1% at 200°C as measured by thermomechanical analysis.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to silver powder, a method for manufacturing silver powder, a silver powder manufacturing apparatus, and a resin-curing type conductive paste.

Background Art

[0002] Conventionally, in order to form electrodes and wirings of electronic components by a printing method or the like, a conductive paste prepared by blending a metal powder such as silver powder with a solvent, a resin, a dispersant, etc. has been used.

[0003] In recent years, heterojunction (HJT) type solar cells have attracted attention. In HJT type solar cells and the like, generally, a resin-curing type conductive paste using silver powder is fired and cured at a relatively low temperature of about 200°C in an air atmosphere to form electrodes and conductor patterns.

[0004] For example, in Patent Document 1, silver fine particles having an average particle diameter (D SEM ) of 30 to 100 nm and a tap density of 3.0 g / cm 3 or more, obtained by a predetermined manufacturing method, have been proposed, and it is described that the silver fine particles are used in a resin-curing type conductive paste or the like.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Here, when the firing temperature at the time of forming electrodes, conductor patterns, etc. is lowered to, for example, 150°C to 200°C, there may occur a problem that the volume resistivity increases. Therefore, it is desirable that the conductive paste containing silver powder can suppress an increase in the volume resistivity even when the firing temperature is lowered.

[0007] In recent years, electrodes, conductor patterns, etc. have been made finer. Therefore, when forming electrodes, conductor patterns, etc. using a conductive paste containing silver powder, it is desirable that the conductive paste is less likely to break even when printed with a finer line width than in the past and is also less likely to break after firing, that is, it has excellent fine line printability.

[0008] Therefore, an object of the present invention is to provide silver powder and a method for producing the same that can impart excellent volume resistivity and fine line printability even when fired at a low temperature when made into a conductive paste. Another object of the present invention is to provide a silver powder production apparatus capable of producing the above silver powder. Another object of the present invention is to provide a resin-cured conductive paste having excellent volume resistivity and fine line printability even when fired at a low temperature.

Means for Solving the Problems

[0009] As a result of intensive research to solve the above problems, the present inventor has completed the present invention described below.

[0010] That is, the gist configuration of the present invention for solving the above problems is as follows.

[0011] [1] Silver powder having a volume-based cumulative 50% diameter D by the laser diffraction method of 0.1 μm or more and 1.0 μm or less, 50 wherein the ratio of the D to the BET diameter D is 1.3 or less, and the shrinkage rate at 200 °C in thermomechanical analysis is 1% or more. BET for the D 50 is 1.3 or less, and the shrinkage rate at 200 °C in thermomechanical analysis is 1% or more.

[0012] [2] The silver powder according to [1], wherein the shrinkage rate at 150 °C in thermomechanical analysis is 0.6% or more.

[0013] [3] The BET specific surface area is 0.90 m 2 / g or more and 2.50 m 2The silver powder according to claim [1] or [2], which is below / g.

[0014] The silver powder according to any one of [1] to [3], which is used for a resin-curing type conductive paste.

[0015] [5] A method for producing silver powder, comprising flowing a silver-containing solution through a flow path, adding a pH adjuster to the flow path at a pH adjuster addition position in the middle of the flow path, adding a complexing agent to the flow path at a complexing agent addition position downstream of the pH adjuster addition position, adding a hydrazine-based reducing agent to the flow path at a reducing agent addition position downstream of the complexing agent addition position, and reducing and depositing silver powder in the flow path.

[0016] [6] The method for producing silver powder according to [5], wherein the time required for the silver-containing solution to flow from the complexing agent addition position to the reducing agent addition position is 0.1 second or more and 10 seconds or less.

[0017] [7] The method for producing silver powder according to [5] or [6], wherein a surface treatment agent is added to the flow path between the complexing agent addition position and the reducing agent addition position or on the downstream side of the reducing agent addition position.

[0018] [8] A silver powder production apparatus for adding a pH adjuster, a complexing agent, and a hydrazine-based reducing agent as a reducing agent to a silver-containing solution to reduce and deposit silver powder, comprising a tube forming a flow path of the silver-containing solution, a pH adjuster addition part connected to the tube, and a complexing agent addition part, and having a reducing agent addition part connected to the tube on the downstream side of the pH adjuster addition section and the complexing agent addition part.

[0019] [9] A resin-curing type conductive paste containing the silver powder according to any one of [1] to [3].

Advantages of the Invention

[0020] According to the present invention, there are provided a silver powder capable of imparting excellent volume resistivity and fine line printability even when fired at a low temperature when made into a conductive paste, a method for producing the silver powder, a silver powder production apparatus capable of producing such silver powder, and a resin-cured conductive paste having excellent volume resistivity and fine line printability even when fired at a low temperature.

Brief Description of the Drawings

[0021]

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Mode for Carrying Out the Invention

[0022] (Terms and Measurement Methods) First, prior to the description of the embodiments, terms and measurement methods in this specification will be described.

[0023] <Shrinkage Rate of Silver Powder> The shrinkage rate of the silver powder was measured as follows. First, 0.3 g of silver powder was weighed. Next, the silver powder was put into a predetermined mold with a diameter of 5 mmφ, and using a press machine, it was pressed firmly at a load of 50 kg for 1 minute to prepare a cylindrical measurement sample. This measurement sample was set in the sample holder of a thermomechanical analysis (TMA) apparatus (Thermo plus EVO 2 series TMA8311), and a load of 98 mN was applied by the measurement probe. Then, the temperature was raised from room temperature (25°C ± 5) to 900°C at a rate of 10°C / minute, and thermomechanical analysis (TMA) of the measurement sample was carried out. The "shrinkage rate at 200°C in thermomechanical analysis" and the "shrinkage rate at 150°C in thermomechanical analysis" were calculated by the following formulas (1) and (2), respectively. Shrinkage rate at 200°C in thermomechanical analysis (%) = (L RT - L 200 ) / L RT × 100 ··· (1) Shrinkage rate at 150°C in thermomechanical analysis (%) = (L RT - L 150 ) / L RT × 100 ··· (2) Here, L RT is the length (mm) of the cylindrical measurement sample in the axial direction at room temperature (25°C ± 5), L 200 is the length (mm) of the cylindrical measurement sample in the axial direction at a temperature of 200°C, L 150 is the length (mm) of the cylindrical measurement sample in the axial direction at a temperature of 150°C.

[0024] <BET specific surface area> In this specification, the "BET specific surface area" was measured by the BET one-point method using nitrogen adsorption with a Macsorb HM-model 1210 (manufactured by MOUNTECH). The measurement of the BET specific surface area was carried out with a sample weight of 3.0 g, using an N 2 / He (30 / 70) mixed gas, with a gas flow rate of 25 mL / min, and the degassing conditions before measurement were 60 °C for 10 minutes.

[0025] <True density measurement> A 10 cc platinum crucible was filled with silver powder, and the mass of the filled silver powder was precisely measured. Then, using a dry automatic densitometer (manufactured by Micromeritics, apparatus name: AccuPyc II 1340), the volume of the silver powder whose mass had been measured was measured by the constant volume expansion method (the "gas pycnometer method" in the Japanese Pharmacopoeia), and the density was calculated. In the measurement of the true density, the closed voids inside the silver particles not connected to the outside are measured in a form included in the density.

[0026] <BET diameter D BET > The BET diameter D BET (hereinafter sometimes simply referred to as "D BET ") (unit: μm) is the particle diameter converted from the BET specific surface area (unit: m 2 / g) and the true density (unit: g / cm 3 ) measured by the BET one-point method, and was obtained by the following formula (3). D BET = 6 / (BET specific surface area × true density) ··· (3)

[0027] <Average primary particle diameter D SEM > The average primary particle diameter D SEM (hereinafter sometimes simply referred to as "D SEM ") was obtained by measuring the equivalent circle diameter (Heywood diameter) of 100 or more arbitrary silver particles in the SEM image of the silver powder and calculating the average value. D SEMFor example, it can be obtained by using an image taken at 10,000 times magnification and image shape measurement software such as Mac-View (manufactured by Mounttech Co., Ltd.).

[0028] <Particle size distribution> In this specification, the volume-based cumulative 10% particle diameter D of silver powder 10 , the cumulative 50% particle diameter D 50 , and the cumulative 90% particle diameter D 90 were measured by a laser diffraction / scattering particle size distribution measuring device (manufactured by Microtrac Bell Co., Ltd., Microtrac MT-3300 EXII). In the measurement, 0.1 g of the sample (silver powder) was added to 40 mL of isopropyl alcohol (IPA) and dispersed. For the dispersion, an ultrasonic homogenizer (manufactured by Nippon Seiki Co., Ltd., device name: US-150T; 19.5 kHz, chip tip diameter 18 mm) was used. The dispersion time was 2 minutes. The dispersed sample was applied to the above device, and the particle size distribution was determined using the attached analysis software. Note that hereinafter, the volume-based cumulative 10% particle diameter D by the laser diffraction method 10 , the cumulative 50% particle diameter D 50 , and the cumulative 90% particle diameter D 90 will be simply referred to as "D 10 ", "D 50 ", and "D 90 ", respectively.

[0029] <D BET ratio of D 50 to D 50 (D BET / D 50 Silver powder may be in a state where individual particles are not completely separated and a plurality of particles are aggregated. In the measurement of the particle size by the laser diffraction method, the particle size of the aggregated particles is measured for the aggregated particles. On the other hand, the BET single-point method measures the specific surface area using the amount of gas adsorbed on the particles, and the BET diameter converted from this specific surface area indicates the particle size (particle diameter) of the particles assuming that the measured particles are true spheres. In the case of a state with less aggregation and close to monodispersion, the value of the ratio (D BET / D 1 ) tends to be close to 1.

[0030] <Ignition loss value> In this specification, the "ignition loss (Ig-loss) value" indicates the amount of change in mass when heated from room temperature to 800 °C. Specifically, it serves as an indicator of the amount of composition other than silver in the silver powder, and is an indicator showing the amount of residual components in the silver powder, such as the amount of residual components of the treatment agent and additives used in the manufacturing process of the silver powder. And in this specification, the "ignition loss (Ig-loss) value" is obtained by precisely weighing (weighing value: w 1 ) the silver powder sample, putting it into a magnetic crucible, heating it to 800 °C, and holding it at 800 °C for 30 minutes as a sufficient time to reach a constant weight. Then, it is cooled and weighed again (weighing value: w 2 ), and calculated from "ignition loss (Ig-loss) value (mass %) = (w 1 - w 2 ) / w 1 × 100".

[0031] <Quantification of surface treatment agent> In this specification, for example, when the surface treatment agent of the silver powder is a fatty acid, the content of the fatty acid was measured according to the quantitative analysis method of fatty acids described in Japanese Patent No. 5622543. Specifically, first, after dissolving the silver powder in nitric acid, an organic solvent (n-hexane) is mixed, and then the entire amount of the surface treatment agent is extracted into the organic solvent phase. After that, a predetermined amount of the organic solvent phase is aliquoted, the solvent is evaporated to dryness, and the remaining solid (the surface treatment agent that did not evaporate and solidified) is determined by measuring the carbon content with a carbon-sulfur analyzer and calculating.

[0032] For example, when the surface treatment agent is specified as stearic acid and it is assumed that no carbon source other than stearic acid is contained in the silver powder, the measurement method of the stearic acid content is as described in the above publication.

[0033] Also, in this specification, for example, when the surface treatment agent of the silver powder is benzotriazole, the content of the benzotriazole was measured according to the quantitative analysis method of benzotriazole and benzotriazole salts described in Japanese Patent No. 5523153. Specifically, first, the silver powder was washed with an aqueous hydrochloric acid solution, and quantitative analysis by spectrophotometry was performed on the washing solution to obtain it.

[0034] Note that the type of the surface treatment agent can be specified by qualitative analysis by gas chromatography of the surface treatment agent that volatilized when the silver powder was heated.

[0035] <Crystallite size> The crystallite size Dx was determined by using an X-ray diffractometer (SmartLab manufactured by Rigaku Corporation) according to Scherrer's formula (D hkl = Kλ / βcosθ). Here, in Scherrer's formula, D hkl means the size of the crystallite (the size of the crystallite in the direction perpendicular to (hkl)) (unit: nm), λ means the wavelength of the measured X-ray (0.15405 nm when using a Cu target), β means the broadening of the diffraction line due to the size of the crystallite (rad) (expressed using the half-value width), θ means the Bragg angle of the diffraction angle (rad) (the angle when the incident angle and the reflection angle are equal, and the angle at the peak top is used), and K means the Scherrer constant (K = 0.94). Note that peak data of the (111) plane of the Miller index may be used for the calculation.

[0036] (Silver powder) The silver powder of the present invention has a volume-based D 50 of 0.1 μm or more and 1.0 μm or less by the laser diffraction method, and the ratio of D BET to D 50 (D 50 / D BET ) is 1.3 or less, and the shrinkage rate at 200 °C in thermomechanical analysis is 1% or more. For silver powder as described above, even when fired at a low temperature (150 to 200 °C) in a conductive paste, an excellent volume resistivity can be imparted. The reason is that D 50 / D BETSilver powder with a shrinkage rate of 1.3 or less and close to monodispersion has a shrinkage rate of a predetermined ratio or more at 200 °C. Therefore, in electrodes, conductor patterns, etc. obtained using a conductive paste containing the silver powder, it is presumed that silver particles can form a better conductive network during firing compared to silver powder with a lower shrinkage rate at 200 °C. In this specification, even when fired at a low temperature (150 to 200 °C), it is also described that the volume resistivity and disconnection rate are small as "having low-temperature firing property". Also, silver powder as described above can impart excellent fine-line printability to the conductive paste. The reason is that by setting D 50 within a predetermined range, it is presumed that the deterioration of fine-line printability due to large particle size and the excessive increase in the viscosity of the conductive paste containing the silver powder can be effectively suppressed.

[0037] The shrinkage rate at 200 °C in thermomechanical analysis is 1.0% or more, preferably 1.1% or more, and more preferably 1.3% or more. If the shrinkage rate at 200 °C in thermomechanical analysis is 1.0% or more, the low-temperature firing property can be improved. On the other hand, since D 50 / D BET is 1.3 or less, the shrinkage rate does not exceed 5.0%. The shrinkage rate at 200 °C in thermomechanical analysis is preferably, for example, 5.0% or less, and more preferably 3.0% or less.

[0038] The shrinkage rate at 150 °C in thermomechanical analysis is preferably 0.6% or more, more preferably 0.7% or more, and even more preferably 0.8% or more. If the shrinkage rate at 150 °C in thermomechanical analysis is 0.6% or more, the above-mentioned low-temperature firing property can be obtained more effectively. On the one hand, the shrinkage rate at 150 °C in thermomechanical analysis is preferably, for example, 3.0% or less, more preferably 1.5% or less, and even more preferably 1.3% or less. Further, for the conductive film obtained by firing the resin-cured conductive paste using the silver powder of the present invention at a low temperature, when emphasis is placed on obtaining high conductivity, the shrinkage rate at 150 °C in the thermomechanical analysis of the present invention can be 1.05% or more and 1.5% or less, and further, it can be 1.05% or more and 1.4% or less.

[0039] D 50 / D BET is preferably 1.3 or less, more preferably 1.27 or less, and even more preferably 1.20 or less. D 50 / D BET If it is 1.3 or less, excellent dispersibility can be obtained, and thus excellent fine line printability can be imparted. In addition, D 50 / D BET is often 1.0 or more, but may be less than 1.0 as in this example. In this case, the value of D 50 / D BET is preferably 0.8 or more.

[0040] D 50 is 0.1 μm or more, preferably 0.2 μm or more, more preferably 0.25 μm or more, even more preferably 0.35 μm or more, 1.0 μm or less, preferably 0.9 μm or less, and more preferably 0.8 μm or less. If D 50 is within the above range, the fine line printability of the conductive paste can be improved. Further, for the conductive film obtained by firing the resin-cured conductive paste using the silver powder of the present invention at a low temperature, when emphasis is placed on obtaining high conductivity, D 50 of the silver powder of the present invention can be 0.1 μm or more and 0.5 μm or less, and further, it can be 0.2 μm or more and 0.4 μm or less.

[0041] D 10is preferably 0.05 μm or more, more preferably 0.10 μm or more, preferably 0.40 μm or less, and more preferably 0.35 μm or less. D 10 If it is within the above range, the fine line printability of the conductive paste can be improved.

[0042] D 90 is preferably 0.5 μm or more, more preferably 0.55 μm or more, still more preferably 0.6 μm or more, preferably 1.2 μm or less, more preferably 1.1 μm or less, and still more preferably 1.0 μm or less. D 90 If it is within the above range, the fine line printability of the conductive paste can be improved. Also, regarding the conductive film obtained by firing the resin-curing type conductive paste using the silver powder of the present invention at a low temperature, when emphasizing obtaining high conductivity, the D of the silver powder of the present invention 90 can be 0.5 μm or more and 0.9 μm or less, and further can be 0.55 μm or more and 0.85 μm or less.

[0043] D BET is preferably 0.22 μm or more, more preferably 0.25 μm or more, even more preferably 0.28 μm or more, and particularly preferably 0.30 μm or more. Also, BET is preferably 0.68 μm or less, more preferably 0.61 μm or less, and even more preferably 0.58 μm or less. D BET If it is within the above range, the fine line printability of the conductive paste can be improved.

[0044] The BET specific surface area is preferably 0.90 m 2 / g or more, more preferably 1.00 m 2 / g or more, still more preferably 1.05 m 2 / g or more, preferably 2.50 m 2 / g or less, more preferably 2.25 m 2 / g or less, and even more preferably 2.00 m2 It is more preferably below / g, and more preferably below 1.80 m 2 / g. If the BET specific surface area is 0.90 m 2 / g or more, appropriate particle activity can be obtained, which is advantageous in terms of the volume resistivity of the wiring pattern formed using the conductive paste even in firing at low temperature. Also, it is easy to cope with high density and the like. On the other hand, if the BET specific surface area is 2.50 m 2 / g or less, it is advantageous in terms of the ease of handling of the paste when it is a conductive paste. Also, regarding the conductive film obtained by firing the resin-curing type conductive paste using the silver powder of the present invention at low temperature, when emphasizing obtaining high conductivity, the specific surface area of the silver powder of the present invention is 1.35 m 2 / g or more and 2.50 m 2 / g or less, and further, 1.40 m 2 / g or more and 2.50 m 2 / g or less.

[0045] Here, the true density of silver is 10.49 g / cm 3 However, the true density of the silver powder of the present invention is, for example, 9.7 g / cm 3 or more, preferably 9.8 g / cm 3 or more, more preferably 9.9 g / cm 3 or more, still more preferably 10.49 g / cm 3 or less. Also, regarding the conductive film obtained by firing the resin-curing type conductive paste using the silver powder of the present invention at low temperature, when emphasizing obtaining high conductivity, the bulk density of the silver powder of the present invention is 9.7 g / cm 3 or more and 9.95 g / cm 3 or less, and further, 9.7 g / cm 3 or more and 9.9 g / cm 3 or less.

[0046] D SEMis preferably 0.10 μm or more, more preferably 0.20 μm or more, still more preferably 0.25 μm or more, even more preferably 0.35 μm or more, preferably 1.00 μm or less, more preferably 0.90 μm or less, and even more preferably 0.80 μm or less. D SEM If it is within the above range, the fine line printability of the conductive paste can be improved. Further, regarding the conductive film obtained by firing the resin-curing type conductive paste using the silver powder of the present invention at a low temperature, when importance is attached to obtaining high conductivity, the D of the silver powder of the present invention SEM can be 0.10 μm or more and 0.4 μm or less, and further can be 0.15 μm or more and 0.35 μm or less.

[0047] The ignition loss (Ig-loss) value is preferably 0.3 mass% or more, more preferably 0.35 mass% or more. Also, it is preferably 1.2 mass% or less, more preferably 1.1 mass% or less, and still more preferably 0.8 mass% or less. If the ignition loss value is 0.3 mass% or more, aggregation of the silver powder can be suppressed and dispersibility can be improved. On the other hand, if the ignition loss value is 1.2 mass% or less, deterioration of the resistance value due to excessive impurities can be prevented. Further, regarding the conductive film obtained by firing the resin-type conductive paste using the silver powder of the present invention at a low temperature, when importance is attached to obtaining high conductivity, the ignition loss value of the silver powder of the present invention can be 0.65 mass% or more and 1.2 mass% or less, and further can be 0.70 mass% or more and 1.2 mass% or less.

[0048] The crystallite size is preferably 25 nm or more, more preferably 30 nm or more, or may be 30 nm or more, still more preferably 32 nm or more, or may be 32 nm or more, and preferably 38 nm or less.

[0049] Here, the silver powder of the present invention preferably contains a surface treatment agent. If the silver powder contains a surface treatment agent, the dispersibility of the silver powder can be improved. Specific examples of the surface treatment agent will be described in the section on "Method for Producing Silver Powder" described later.

[0050] Here, the silver powder of the present invention preferably contains a surface treatment agent. If the silver powder contains a surface treatment agent, the dispersibility of the silver powder can be improved. Specific examples of the surface treatment agent will be described in the section on "Method for Producing Silver Powder" described later.

[0051] The silver powder of the present invention is not particularly limited and can be used in conductive pastes such as resin-curing type conductive pastes and sintering type conductive pastes. However, since the silver powder of the present invention has excellent volume resistivity and fine line printability even when fired at a low temperature when made into a conductive paste, it can be suitably used in resin-curing type conductive pastes.

[0052] (Method for Producing Silver Powder) The method for producing the silver powder of the present invention (hereinafter, may be simply referred to as the "production method") includes flowing a silver-containing solution through a flow path, adding a pH adjuster to the flow path at a pH adjuster addition position in the middle of the flow path, adding a complexing agent to the flow path at a complexing agent addition position downstream of the pH adjuster addition position, adding a hydrazine-based reducing agent to the flow path at a reducing agent addition position downstream of the complexing agent addition position, and reducing and depositing silver powder in the flow path. By the method as described above, silver powder capable of imparting excellent volume resistivity and fine line printability to a conductive paste can be obtained even when fired at a low temperature. Further, by the production method of the present invention, the silver powder of the present invention described above can be obtained. In the production method of the present invention, a silver-containing solution, a pH adjuster, a complexing agent, and a hydrazine-based reducing agent are continuously supplied in this order, and these are quantitatively mixed to keep the rate of formation of the silver complex and the rate of reduction and precipitation of the silver powder constant, and thus a predetermined silver powder can be obtained quantitatively and continuously.

[0053] The silver-containing solution is a solution that reacts with a complexing agent to form a silver complex, and a solution containing a silver salt can be used. For example, aqueous solutions of silver nitrate, silver chloride, silver formate, silver oxalate, silver sulfate, etc. can be mentioned, and an aqueous solution of silver nitrate is preferred from the viewpoint of easy availability.

[0054] From an economic perspective, the silver concentration in the silver-containing solution is preferably 0.01 mol / L or more, more preferably 0.05 mol / L or more, and even more preferably 0.10 mol / L or more. On the other hand, from the viewpoint of ensuring the interparticle distance of the particles after reduction precipitation and suppressing aggregation, the silver concentration in the silver-containing solution is preferably 0.5 mol / L or less, more preferably 0.3 mol / L or less.

[0055] The flow rate in this embodiment is a value obtained by dividing the flow rate of the solution by the cross-sectional area of the tube, assuming that the tube is filled with liquid. Also, the elapsed time between a specific position and a specific position is obtained by dividing the length between the positions by the flow rate. From the viewpoints of productivity and formation of monodisperse particles, the flow rate of the silver-containing solution is preferably 0.45 m / s or more, more preferably 0.65 m / s or more, and even more preferably 1.00 m / s or more. Also, from the viewpoints of suppressing aggregation and forming monodisperse particles, it is preferably 3.20 m / s or less, more preferably 2.70 m / s or less, and even more preferably 2.00 m / s or less.

[0056] In the production method of the present invention, the pH of the silver-containing solution is adjusted by flowing the silver-containing solution through a flow path and adding a pH adjuster to the flow path at a pH adjuster addition position in the middle of the flow path. Thereby, the particle size of the silver powder can be effectively adjusted. As the pH adjuster, general alkaline and acidic pH adjusters such as sodium hydroxide, potassium hydroxide, sodium carbonate, and nitric acid can be used. Note that the pH adjuster is usually added to the flow path in the state of an aqueous solution of the pH adjuster. The addition amount of the pH adjuster is appropriately adjusted according to the particle size of the silver powder to be produced.

[0057] In the production method of the present invention, a silver complex is formed by adding a complexing agent to the flow path at a complexing agent addition position downstream of the pH adjuster addition position. Note that the complexing agent is usually added to the flow path in the state of an aqueous solution of the complexing agent.

[0058] Examples of the complexing agent include ammonia, ammonium salts, citric acid, acetic acid, etc., among which ammonia is preferred. Ammonia can be added as aqueous ammonia. For example, when aqueous ammonia is added as the complexing agent, a silver ammine complex is formed. The silver ammine complex is preferred because it can be easily reduced by hydrazine.

[0059] From an economic perspective, the concentration of aqueous ammonia is preferably 0.35 mol / L or more, more preferably 0.50 mol / L or more, preferably 16.2 mol / L or less, more preferably 15.1 mol / L or less, and still more preferably 10.0 mol / L or less.

[0060] The addition amount of ammonia per 1 mol of silver is preferably 2.10 mol or more, and more preferably 2.20 mol or more. On the other hand, the addition amount of ammonia per 1 mol of silver is preferably 10.00 mol or less, and more preferably 8.00 mol or less.

[0061] The flow rate of the complexing agent added at the complexing agent addition position is preferably 0.40 m / s or more, more preferably 0.60 m / s or more, still more preferably 1.00 m / s or more, preferably 3.20 m / s or less, more preferably 2.70 m / s or less, and still more preferably 2.00 m / s or less.

[0062] Even when a complexing agent other than ammonia is used, the concentration, addition amount, and flow rate can be made in accordance with the above, taking into account the amount of the complexing agent relative to the amount of silver required to form the complex.

[0063] In the production method of the present invention, silver powder is reduced and precipitated by adding a hydrazine-based reducing agent to the flow path at the reducing agent addition position downstream of the complexing agent addition position. In addition, examples of the hydrazine-based reducing agent in the present invention include hydrazine, hydrazine hydrate, carbohydrazide, hydrazine sulfate, phenylhydrazine, etc. Among them, hydrazine and carbohydrazide are preferred, and hydrazine is more preferred. By using hydrazine, silver powder with a desired particle size can be stably obtained. Usually, the hydrazine-based reducing agent is added to the flow path in an aqueous solution state.

[0064] From the viewpoint of a uniform reduction reaction, the concentration of hydrazine in the hydrazine aqueous solution is preferably 0.025 mol / L or more, more preferably 0.05 mol / L or more, still more preferably 0.10 mol / L or more, preferably 3.3 mol / L or less, more preferably 2.0 mol / L or less, and still more preferably 1.0 mol / L or less. Also, from the viewpoint of a uniform reduction reaction, the concentration of the hydrazine-based reducing agent in the hydrazine-based reducing agent aqueous solution is preferably 0.025 mol / L or more, more preferably 0.05 mol / L or more, still more preferably 0.10 mol / L or more, preferably 3.3 mol / L or less, more preferably 2.0 mol / L or less, and still more preferably 1.0 mol / L or less.

[0065] The addition amount of hydrazine relative to 1 mol of silver is preferably such that substantially no unreacted silver is generated, preferably 0.26 mol or more, and more preferably 0.28 mol or more. On the other hand, the addition amount of hydrazine relative to 1 mol of silver is preferably 0.88 mol or less, more preferably 0.75 mol or less, and still more preferably 0.50 mol or less in order not to add an excessive amount of the reducing agent. In addition, the addition amount of the hydrazine-based reducing agent relative to 1 mol of silver is preferably such that substantially no unreacted silver is generated, preferably 0.26 mol or more, and more preferably 0.28 mol or more. On the other hand, in order not to add more reducing agent than necessary, the addition amount of the hydrazine-based reducing agent with respect to 1 mol of silver is preferably 0.88 mol or less, more preferably 0.75 mol or less, and even more preferably 0.50 mol or less.

[0066] In the production method of the present invention, from the viewpoint of productivity, the flow rate of the silver complex solution immediately before adding the reducing agent to the flow path is preferably 0.50 m / sec or more, more preferably 0.75 m / sec or more, and even more preferably 1.0 m / sec or more. Also, from the viewpoint of suppressing aggregation and forming monodisperse particles, it is preferably 3.5 m / sec or less, more preferably 3.0 m / sec or less, and even more preferably 2.0 m / sec or less.

[0067] When adding the reducing agent to the flow path, the flow rate of the reducing agent is preferably 0.5 times or more, more preferably 0.8 times or more, with respect to the flow rate of the silver complex solution immediately before the reducing agent. Also, from the viewpoint of suppressing the increase in the liquid flow to the pipe wall surface and the decrease in the mixing efficiency, it is preferably 2.5 times or less, more preferably 2.0 times or less, and even more preferably 1.5 times or less.

[0068] In the production method of the present invention, since the hydrazine-based reducing agent is added where the silver complex is formed, the time required for the silver-containing solution to flow from the complexing agent addition position to the reducing agent addition position (the elapsed time obtained by dividing the length from the complexing agent addition position to the reducing agent addition position by the flow rate of the silver complex solution immediately before the reducing agent addition) is preferably 0.1 second or more, and more preferably 0.5 second or more. On the other hand, if the elapsed time after forming the complex becomes long, the stability of the silver complex may increase and the reduction reaction may be difficult to proceed. Therefore, in order to improve the freshness of the silver complex at the time of adding the reducing agent, the elapsed time is preferably within 10.0 seconds, and more preferably within 5.0 seconds.

[0069] In the production method of the present invention, a surface treatment agent can be added to the flow path between the complexing agent addition position and the reducing agent addition position or on the downstream side of the reducing agent addition position. The addition of the surface treatment agent is advantageous in suppressing the aggregation of the silver powder reduced and deposited. The addition is preferably carried out at a point between the complexing agent addition position and the reducing agent addition position.

[0070] Examples of the surface treatment agent include fatty acids, fatty acid salts, surfactants, organometals, chelating agents, protective colloids, etc. The surface treatment agent can be used in an amount of 0.3 mass% or more and 1.3 mass% or less based on the silver in the silver-containing solution. The surface treatment agent may be used in the form of an emulsion, a solution, or the like.

[0071] (1) Fatty acids Examples of the 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, ricinoleic acid, etc.

[0072] (2) Fatty acid salts Examples of the fatty acid salts include metal salts of the fatty acids in (1) above, and examples of the metal include lithium, sodium, potassium, barium, magnesium, calcium, aluminum, iron, cobalt, manganese, lead, zinc, tin, strontium, zirconium, silver, copper, etc.

[0073] (3) Surfactants Examples of the surfactants include anionic surfactants such as alkylbenzene sulfonates and polyoxyethylene alkyl ether phosphates, cationic surfactants such as aliphatic quaternary ammonium salts, amphoteric surfactants such as imidazolinium betaines, and nonionic surfactants such as polyoxyethylene alkyl ethers and polyoxyethylene fatty acid esters.

[0074] Examples of the organometal include acetylacetone tributoxyzirconium, magnesium citrate, diethylzinc, dibutyltin oxide, dimethylzinc, tetra-n-butoxyzirconium, triethylindium, triethylgallium, trimethylindium, trimethylgallium, monobutyltin oxide, tetraisocyanate silane, tetramethylsilane, tetramethoxysilane, monomethyltriisocyanate silane, silane coupling agent, titanate coupling agent, aluminum coupling agent, and the like.

[0075] (5) Chelating agent Examples of the chelating agent 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-oxadiazole, 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, 1,2,3,5-thiatriazole, indazole, benzimidazole, benzotriazole, etc., and salts of these chelating agents and polycarboxylic acids such as dicarboxylic acids including succinic acid, malonic acid, glutaric acid, adipic acid, etc.

[0076] (6) Protective colloid Examples of the protective colloid include peptide, gelatin, albumin, gum arabic, protalbinate, resalbinate, glue, and the like.

[0077] As the surface treatment agent, from the viewpoint of ease of modification of the silver particle surface, (1) fatty acids are preferred, and among them, stearic acid is preferred. (1) The fatty acid is preferably in the form of an emulsion, and examples thereof include stearic acid emulsion.

[0078] In the production method of the present invention, from the viewpoint of the reactivity of the reduction reaction, the temperature of the silver complex solution immediately before the addition of the reducing agent is preferably 20°C or higher, more preferably 30°C or higher. On the other hand, from the viewpoint of operability, the temperature of the liquid flowing through the flow path is preferably 65°C or lower, more preferably 60°C or lower.

[0079] In the production method of the present invention, a mixer may be used to apply a spiral rotation in the axial direction of the flow path to perform liquid mixing.

[0080] In the production method of the present invention, the silver powder can be obtained by discharging the liquid containing the reduced and precipitated silver powder (hereinafter also referred to as "silver powder-containing liquid") outside the flow path and recovering it. The silver powder-containing liquid is usually obtained in the state of a slurry or a dispersion.

[0081] From the viewpoint of expecting the completion of the reduction reaction, the time from the addition of the reducing agent until the silver powder-containing liquid is discharged outside the flow path is preferably 1 second or more, more preferably 2 seconds or more. On the other hand, from the viewpoint of suppressing deposition in the piping, the time from the addition of the reducing agent until the silver powder-containing liquid is discharged outside the flow path is preferably 10 seconds or less, more preferably 5 seconds or less.

[0082] By filtering and washing the silver powder-containing liquid discharged outside the flow path, a cake-like substance containing silver powder and water and having almost no fluidity is obtained. The silver powder of the present invention is obtained by drying this cake with a dryer such as a forced circulation type atmospheric dryer, a vacuum dryer, or an air flow drying device. By replacing the moisture in the cake with a lower alcohol or the like, drying can be accelerated. For the cake, dry crushing treatment, surface smoothing treatment, etc. can be performed. The dry crushing treatment can be carried out using, for example, a sample mill, a blender, a coffee mill, a multi-pass mixer, etc. Also, the surface smoothing treatment can be performed by mechanically colliding particles with each other using a high-speed stirrer. Thereafter, by classification treatment, aggregates of silver powder larger than a predetermined particle size may be removed. Furthermore, for the cake, drying, crushing, and classification may be performed using an integrated device (such as a dry micronizer or micron dryer manufactured by Hosokawa Micron Corporation) capable of performing drying, crushing, and classification on the cake.

[0083] (Silver powder manufacturing apparatus) The silver powder manufacturing apparatus of the present invention is a silver powder manufacturing apparatus for reducing and depositing silver powder by adding a pH adjuster, a complexing agent, and a hydrazine-based reducing agent as a reducing agent to a silver-containing solution, and includes a tube forming a flow path of the silver-containing solution, a pH adjuster addition part connected to the tube, and a complexing agent addition part. pH adjuster addition section And it has a reducing agent addition part connected to the tube downstream of the complexing agent addition part. pH adjuster addition section It is also preferable to have a surface treatment agent addition part in front of the reducing agent addition part and downstream of the complexing agent addition part. Hereinafter, with reference to the drawings, an example of a silver powder manufacturing apparatus that can be used in the manufacturing method of the present invention will be described.

[0084] FIG. 1 is an external perspective view of an example of a silver powder manufacturing apparatus. In FIG. 1, the silver powder manufacturing apparatus 1 includes a tube 2 through which a silver-containing solution flows, a pH adjuster supply tube 7 for supplying a pH adjuster, a complexing agent supply tube 6 located downstream of the pH adjuster supply tube 7 and for supplying a complexing agent, a surface treatment agent supply tube 5 located downstream of the complexing agent supply tube 6 and for supplying a surface treatment agent, and a reducing agent addition member 10 located downstream of the surface treatment agent supply tube 5 and for supplying a hydrazine-based reducing agent as a reducing agent. The reducing agent supply tubes 4a and 4b are eccentrically connected to the reducing agent addition member 10. The silver powder manufacturing apparatus 1 in FIG. 1 includes a surface treatment agent supply tube 5 between the complexing agent supply tube 6 and the reducing agent addition member 10, but the surface treatment agent supply tube 5 may be arranged downstream of the reducing agent addition member 10.

[0085] The pH adjuster addition section, the complexing agent addition section, and the surface treatment agent addition section may each be a Y-shaped pipe or a T-shaped pipe, or a structure may be adopted in which a second pipe is connected in the middle of the pipe forming the flow path of the silver-containing solution so that the flow path of the silver-containing solution and the flow path of the second pipe merge. Alternatively, the pH adjuster addition section, the complexing agent addition section, and the surface treatment agent addition section may each be a coaxial two-axis pipe.

[0086] If the reducing agent is added to the flow path from one direction, it takes time for the reducing agent to reach the side opposite to the addition point, and there is a possibility that the concentration of the reducing agent at the reducing agent addition position may vary. Therefore, even when a Y-shaped tube or a T-shaped tube is used to bring the silver complex solution and the reducing agent into contact and mix at the confluence, there is a possibility that the concentration may vary for the same reason. Further, when the reducing agent is added at the central position of the flow path by a coaxial double tube, the reducing agent is added in parallel with the flow of the silver complex solution, so it takes time for the silver complex solution and the reducing agent to mix, and in the coaxial double tube, the flow velocity at the center of the tube is relatively fast and the flow velocity near the wall surface is relatively slow, so the growth of particles is likely to be non-uniform.

[0087] The addition of the reducing agent is preferably performed in two or more directions with respect to the flow path, more preferably in four or more directions, and particularly preferably in all directions from the outer periphery of the flow path. The addition of the reducing agent can be performed from a plurality of directions with respect to the flow path depending on the number and shape of the orifices for oral communication.

[0088] Each of the plurality of directions preferably forms an angle of 75 degrees or more and 105 degrees or less with respect to the flow path. Adding the reducing agent to the flow path at a substantially perpendicular angle is advantageous in that the silver complex solution and the reducing agent are quickly mixed. The angle with respect to the flow path is more preferably 80 degrees or more and 100 degrees or less. "With respect to the flow path" can be rephrased as "with respect to the axial direction of the pipe through which the silver complex solution flows".

[0089] By using the silver powder manufacturing apparatus of the present invention, silver powder capable of imparting excellent low-temperature heatability and fine line printability to the conductive paste can be obtained.

[0090] FIG. 2A is a cross-sectional view perpendicular to the flow path of the silver complex solution at the central positions of the reducing agent supply pipes 4a and 4b of the reducing agent addition member 10 in FIG. 1. FIG. 2B is a cross-sectional view in the horizontal direction of the flow path of the silver complex solution and is a cross-sectional view taken along line A-A in FIG. 2A. FIG. 2C is a cross-sectional view in the horizontal direction of the flow path of the silver complex solution and is a cross-sectional view taken along line B-B in FIG. 2A.

[0091] In FIG. 2A, there is a gap 13 along the outer periphery of the pipe 2 that serves as the flow path of the silver complex solution, and the inside of the gap 13 is connected to the inside of the reducing agent supply pipes 4a and 4b. As shown in FIG. 2C, which is a cross-sectional view taken along line B-B in FIG. 2A, the downstream side of the flow path of the silver complex solution in the gap 13 leads to a slit portion 12 having an opening 11 facing radially outward along the inner periphery of the pipe 2. Then, as shown in FIG. 2B, which is a cross-sectional view taken along line A-A in FIG. 2A, when the reducing agent is poured into the gap 13 from inside the pipes of the reducing agent supply pipes 4a and 4b, the reducing agent reaches the slit portion 12 through the gap 13, and the reducing agent enters the pipe 2 from the opening 11 of the slit portion 12 substantially perpendicularly (for example, 75 degrees or more and 105 degrees or less) from the entire circumference of the pipe 2 and is added to the silver complex solution. Here, the angle at which the reducing agent enters the flow path of the silver complex solution is the angle at which the axial direction of the pipe 2 intersects the opening direction of the opening 11 through which the reducing agent enters the pipe 2. The opening direction can be regarded as the direction along the wall surface near the opening of the slit portion 12 as shown in FIG. 2B.

[0092] The flow rate of the reducing agent flowing through the reducing agent supply pipes 4a and 4b and the size of the total area of the openings 11 can control the flow rate of the reducing agent when adding the reducing agent to the flow path of the silver complex solution. By controlling the flow rate of the reducing agent within the aforementioned range, the reaction between the silver complex and the reducing agent can be carried out promptly, thereby obtaining silver powder with a sharp width of particle size distribution.

[0093] The width of the opening 11 in the slit portion 12 in FIGS. 2B and 2C is referred to as the slit width. The slit width is preferably made narrower than the diameter of the reducing agent supply pipe in order to reduce the size of the total area of the opening 11. The addition of the reducing agent can be performed from a plurality of directions with respect to the flow path, and the shape of the gap 13 and the slit portion 12 that can form a slit width narrower than the diameter of the reducing agent supply pipe is not limited to the structure of FIGS. 2A to 2C, and various modifications are possible. Further, instead of providing the opening 11 of the slit portion 12 on the entire circumference of the tube 2, it is also possible to make a modification such as providing a plurality of through holes.

[0094] There may be one or more reducing agent supply pipes for flowing the reducing agent into the reducing agent addition member 10, and it is also preferable to have two or more. When there are two or more reducing agent supply pipes, the flow paths of the reducing agent leading from the reducing agent supply pipes to the opening 11 can be opposed or eccentric. In FIGS. 2A to 2C, the reducing agent supply pipes 4a and 4b are connected eccentrically to each other with respect to the center of the tube 2, and the flow paths of the reducing agent supply pipes 4a and 4b are connected to the slit portion 12 having the opening 11. When connecting a plurality of reducing agent supply pipes, if at least two reducing agent supply pipes are made eccentric to each other, the reducing agent can be made to flow into the opening 11 of the slit portion 12 while rotating the outer periphery of the flow path (tube 2) of the silver complex solution in one direction. When the reducing agent rotates around the outer periphery of the flow path of the silver complex solution, the flow rate of the reducing agent toward the opening 11 may be adjusted by changing the cross-sectional area of the flow path (gap 13 or slit portion 12) of the reducing agent.

[0095] (Resin-curing type conductive paste) The resin-curing type conductive paste of the present invention contains the silver powder of the present invention described above. Among the metal powders contained in the resin-curing type conductive paste, the proportion of the silver powder of the present invention in the total amount of the metal powders may be 20 to 100%. As the metal powder other than the silver powder of the present invention, it is also preferable to contain silver powder having a larger particle size (D 50 ) than the silver powder of the present invention. Since the resin-curing type conductive paste of the present invention contains the silver powder of the present invention, it is excellent in volume resistivity and fine line printability. The resin-curable conductive paste of the present invention usually contains the silver powder of the present invention, a resin, and a solvent. Further, the resin-curable conductive paste of the present invention may optionally further contain components other than the silver powder, the resin, and the solvent (hereinafter sometimes referred to as "other components").

[0096] The resin is not particularly limited, and examples thereof include epoxy resins, acrylic resins, polyester resins, polyimide resins, polyurethane resins, phenoxy resins, silicone resins, and ethyl cellulose. These may be used alone or in any combination of two or more in any ratio.

[0097] The solvent is not particularly limited, and examples thereof include alcohol solvents such as terpineol, butyl carbitol, texanol, ethylene glycol, diethylene glycol, and glycerin; ester solvents such as butyl carbitol acetate and ethyl acetate; and hydrocarbon solvents such as toluene, xylene, and cyclohexane. These may be used alone or in any combination of two or more in any ratio.

[0098] Examples of the other components include dispersants, surfactants, viscosity modifiers, slip agents, and the like.

[0099] The method for producing the resin-curable conductive paste is not particularly limited, and examples thereof include a method of mixing the silver powder, the organic binder, the solvent, and any other components of the present invention. The mixing method is not particularly limited, and for example, a planetary stirrer, ultrasonic dispersion, a disper, a three-roll mill, a ball mill, a bead mill, a twin-screw kneader, or the like can be used.

[0100] The resin-curable conductive paste of the present invention can be applied onto a substrate, for example, by printing such as screen printing, offset printing, or photolithography, or dipping, to form a coating film. The coating film may be formed into a predetermined pattern shape by photolithography or the like using a resist.

[0101] A conductive film can be formed by heating and curing the coating film. The heat curing may be performed in an air atmosphere or in a non-oxidizing atmosphere such as nitrogen.

[0102] Since the resin-curable conductive paste of the present invention is excellent in volume resistivity and fine line printability even when fired at a low temperature, it can be suitably used for the production of heterojunction (HJT) solar cells and the like in which electrodes and conductor patterns are formed by heating at a relatively low temperature.

Examples

[0103] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples at all. Note that the BET specific surface area, true density, BET diameter D BET , average primary particle diameter D SEM , particle size distribution, loss on ignition (Ig-loss) value, quantification of surface treatment agent, crystallite diameter, and shrinkage rate of silver powder (200 °C and 150 °C) were measured or calculated by the methods described above.

[0104] (Example 1) Silver powder was produced using the silver powder production apparatus 1 shown in FIGS. 1 and 2A to 2C. A 0.160 mol / L silver nitrate aqueous solution was introduced into the pipe 2 (inner diameter 20 mm) at a liquid temperature of 50 °C at a flow rate of 23.35 L / min, and a 0.024 mol / L nitric acid aqueous solution was introduced from the pH adjuster supply pipe 7 (inner diameter 6 mm), which is a coaxial double pipe, at a flow rate of 2.13 L / min to adjust the pH. A 4.500 mol / L aqueous ammonia solution as a complexing agent was introduced from the complexing agent supply pipe 6 (inner diameter 6 mm), which is a coaxial double pipe, at a flow rate of 2.33 L / min to generate a silver ammine complex in the pipe 2. A surface treatment agent (0.10 mass% Cellosolve 920 (manufactured by Chukyo Yushi Co., Ltd., containing 15.5 wt% stearic acid)) was introduced from the surface treatment agent supply pipe 5 (inner diameter 6 mm) upstream of the reducing agent addition member 10 at a flow rate of 2.19 L / min. The amount of the silver nitrate aqueous solution is such that the silver concentration in the total liquid volume after adding the pH adjuster, complexing agent, reducing agent, and surface treatment agent is 0.115 mol / L. An aqueous hydrazine solution with a concentration of 0.50 mol / L as a reducing agent was introduced at a flow rate of 2.55 L / min from the entire circumference of the slit portion 12 (slit width: 0.44 mm, inner pipe diameter: 20.6 mm) of the reducing agent addition member 10 to precipitate silver powder. The flow velocity of the reducing agent entering from the slit portion with a slit width of 0.44 mm was 1.49 m / s, the flow velocity of the silver ammine complex immediately before the addition of the reducing agent at the inner pipe 2 with an inner diameter of 20.6 mm at the position where the reducing agent entered was 1.50 m / s, and the ratio of the flow velocity of the complex to the flow velocity of the reducing agent (complex flow velocity / reducing agent flow velocity) was 1.01. The operating time of the silver powder production apparatus (the time from the start to the stop of the introduction of the reducing agent into the silver ammine complex after the flow of the silver ammine complex into which the surface treatment agent was introduced became stable) was set to 616 seconds. The slurry generated before the flow of the silver ammine complex into which the surface treatment agent was introduced became stable was received in a separate container and not used in the processes after solid-liquid separation. In the above, it took 0.5 seconds from the flow path inlet of the silver nitrate aqueous solution to the nitric acid aqueous solution addition position, 0.5 seconds from the nitric acid aqueous solution addition position to the ammonia water addition position, 2.12 seconds (2.1 m) from the ammonia water addition position to the hydrazine aqueous solution addition position, 0.12 seconds from the surface treatment agent addition position to the hydrazine aqueous solution addition position, and the temperature of the silver ammine complex aqueous solution immediately before the hydrazine aqueous solution addition position was 47.2°C.

[0105] The silver powder-containing slurry was discharged from the pipe 2. The time from the hydrazine aqueous solution addition position to the discharge was about 2 seconds. The silver powder-containing slurry after the reduction reaction was stabilized was recovered, and the solid obtained by solid-liquid separation was washed with pure water to remove impurities in the solid. The end point of this washing can be judged by the electrical conductivity of the water after washing, and washing was performed until this electrical conductivity became 0.5 mS / m or less, and then dried to obtain 3.8 kg of silver powder.

[0106] The silver powder obtained above was charged into a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) at 120 g, and pulverized twice in 90 seconds to obtain the silver powder according to Example 1. Table 3 shows the measurement results and the like for the silver powder according to Example 1. Further, a graph of the thermomechanical analysis of the silver powder according to Example 1 is shown in FIG. 3, a graph obtained by enlarging a part (0°C to 250°C) of the graph in FIG. 3 is shown in FIG. 4, and an SEM photograph (20,000 times) is shown in FIG. 5.

[0107] (Example 2) An aqueous silver nitrate solution of 0.153 mol / L was introduced into tube 2 (inner diameter 20 mm) at a liquid temperature of 50°C at a flow rate of 23.35 L / min, and an aqueous nitric acid solution of 0.008 mol / L was introduced from the pH adjuster supply tube 7 (inner diameter 6 mm), which is a coaxial double tube, at a flow rate of 3.15 L / min to adjust the pH. An aqueous ammonia solution of 4.919 mol / L was introduced from the complexing agent supply tube 6 (inner diameter 6 mm), which is a coaxial double tube, at a flow rate of 2.33 L / min to form a silver ammine complex in tube 2. From the surface treatment agent supply tube 5 (inner diameter 6 mm) upstream of the reducing agent addition member 10, a surface treatment agent (0.10 mass% cellosolve 920 (manufactured by Chukyo Yushi Co., Ltd., containing 15.5 wt% stearic acid)) was introduced at a flow rate of 2.19 L / min. The amount of the aqueous silver nitrate solution is such that the silver concentration in the total liquid volume after adding the pH adjuster, complexing agent, reducing agent, and surface treatment agent is 0.106 mol / L. An aqueous hydrazine solution of 0.478 mol / L was introduced at a flow rate of 2.55 L / min from the entire circumference of the slit portion (slit width 0.44 mm, inner tube diameter 20.6 mm) of the reducing agent addition member 10 to precipitate silver powder. The flow rate of the reducing agent entering from the slit portion with a slit width of 0.44 mm is 1.49 m / s, and the flow rate of the silver ammine complex immediately before the addition of the reducing agent at the inner tube diameter of 20.6 mm of tube 2 where the reducing agent enters is 1.55 m / s (calculated from the sum of the flow rates of the aqueous silver nitrate solution, aqueous nitric acid solution, and aqueous ammonia solution), and the ratio of the flow rate of the complex to the flow rate of the reducing agent (complex flow rate / reducing agent flow rate) is 1.04. The operating time of the silver powder manufacturing apparatus (the time from the start to the stop of the introduction of the reducing agent into the silver ammine complex after the flow of the silver ammine complex into which the surface treatment agent was introduced became stable) was set to 115 seconds. Note that the slurry generated before the flow of the silver ammine complex into which the surface treatment agent was introduced became stable was received in a separate container and not used in the steps after solid-liquid separation. In the above, from the flow path inlet of the silver nitrate aqueous solution to the nitric acid aqueous solution addition position is 0.5 seconds, from the nitric acid aqueous solution addition position to the ammonia aqueous solution addition position is 0.48 seconds, from the ammonia aqueous solution addition position to the hydrazine aqueous solution addition position is 2.05 seconds (2.1 m), from the surface treatment agent addition position to the hydrazine aqueous solution addition position is 0.12 seconds, and the temperature of the silver ammine complex solution immediately before the hydrazine aqueous solution addition position was 46.6°C.

[0108] The silver powder-containing slurry was discharged from pipe 2. The time from the hydrazine aqueous solution addition position to the discharge was about 2 seconds. After the reduction reaction was stabilized, the silver powder-containing slurry was recovered, solid-liquid separated, and the obtained solid was washed with pure water to remove impurities in the solid. The end point of this washing can be judged by the electrical conductivity of the water after washing. Washing was carried out until this electrical conductivity became 0.5 mS / m or less, and 0.55 kg of dried silver powder was obtained.

[0109] In addition, the silver powder obtained in Example 2 was subjected to the same pulverization treatment as in Example 1. The measurement results and the like for the silver powder according to Example 2 are shown in Table 3. Also, graphs of the thermomechanical analysis of the silver powder according to Example 2 are shown in FIGS. 3 and 4. The SEM photograph (20,000 times) is shown in FIG. 6.

[0110] (Example 3) A 0.160 mol / L silver nitrate aqueous solution was introduced into pipe 2 (inner diameter 20 mm) at a liquid temperature of 50°C at a flow rate of 23.35 L / min, and a 0.024 mol / L nitric acid aqueous solution was introduced from the pH adjuster supply pipe 7 (inner diameter 6 mm), which is a coaxial double pipe, at a flow rate of 2.13 L / min to adjust the pH. A 4.436 mol / L ammonia aqueous solution from the complexing agent supply pipe 6 (inner diameter 6 mm), which is a coaxial double pipe, was introduced at a flow rate of 2.33 L / min to form a silver ammine complex in pipe 2. From the surface treatment agent supply pipe 5 (inner diameter 6 mm) upstream of the reducing agent addition member 10, a surface treatment agent (0.10 mass% cellosolve 920 (manufactured by Chukyo Yushi Co., Ltd., containing 15.5 wt% stearic acid)) was introduced at a flow rate of 2.19 L / min. The amount of the silver nitrate aqueous solution is such that the silver concentration in the total liquid volume after adding the pH adjuster, complexing agent, reducing agent, and surface treatment agent becomes 0.115 mol / L. An aqueous hydrazine solution of 0.50 mol / L was introduced at a flow rate of 2.55 L / min from the entire circumference of the slit portion (slit width: 0.44 mm, inner tube diameter: 20.6 mm) of the reducing agent addition member 10 to deposit silver powder. The flow velocity of the reducing agent entering from the slit portion with a slit width of 0.44 mm was 1.49 m / s, and the flow velocity of the silver ammine complex immediately before the addition of the reducing agent at the inner diameter of 20.6 mm of the tube 2 where the reducing agent entered was 1.50 m / s (calculated from the sum of the flow rates of the silver nitrate aqueous solution, nitric acid aqueous solution, and ammonia aqueous solution). The ratio of the flow velocity of the complex to the flow velocity of the reducing agent (complex flow velocity / reducing agent flow velocity) was 1.01. The operating time of the silver powder manufacturing apparatus (the time from the start to the stop of the introduction of the reducing agent into the silver ammine complex after the flow of the silver ammine complex introduced with the surface treatment agent became stable) was set to 617 seconds. The slurry generated before the flow of the silver ammine complex introduced with the surface treatment agent became stable was received in a separate container and not used in the steps after solid-liquid separation. In the above, it took 0.5 seconds from the inlet of the silver nitrate aqueous solution flow path to the nitric acid aqueous solution addition position, 0.5 seconds from the nitric acid aqueous solution addition position to the ammonia aqueous solution addition position, 2.12 seconds (2.1 m) from the ammonia aqueous solution addition position to the hydrazine aqueous solution addition position, 0.12 seconds from the surface treatment agent addition position to the hydrazine aqueous solution addition position, and the temperature of the silver ammine complex solution immediately before the hydrazine aqueous solution addition position was 47.4°C.

[0111] The silver powder-containing slurry was discharged from the tube 2. The time from the hydrazine aqueous solution addition position to the discharge was about 2 seconds. The silver powder-containing slurry after the reduction reaction was stabilized was recovered, and the solid obtained by solid-liquid separation was washed with pure water to remove impurities in the solid. The end point of this washing can be determined by the electrical conductivity of the water after washing. Washing was performed until the electrical conductivity became 0.5 mS / m or less, and 3.6 kg of dried silver powder was obtained.

[0112] Note that the silver powder obtained in Example 3 was subjected to the same pulverization treatment as in Example 1. Table 3 shows the measurement results and the like for the silver powder according to Example 3. Also, graphs of the thermomechanical analysis of the silver powder according to Example 3 are shown in FIGS. 3 and 4. An SEM photograph (20,000 times) is shown in FIG. 7.

[0113] (Example 4) An aqueous silver nitrate solution of 0.160 mol / L was introduced into tube 2 (inner diameter 20 mm) at a liquid temperature of 50°C at a flow rate of 27.24 L / min. An aqueous nitric acid solution of 0.024 mol / L was introduced from the pH adjuster supply tube 7 (inner diameter 6 mm), which is a coaxial double tube, at a flow rate of 2.49 L / min to adjust the pH. An aqueous ammonia solution of 4.436 mol / L was introduced from the complexing agent supply tube 6 (inner diameter 6 mm), which is a coaxial double tube, at a flow rate of 2.72 L / min to form a silver ammine complex in tube 2. From the surface treatment agent supply tube 5 (inner diameter 6 mm) upstream of the reducing agent addition member 10, a surface treatment agent (0.10 mass% cellosolve 920 (manufactured by Chukyo Yushi Co., Ltd., containing 15.5 wt% stearic acid)) was introduced at a flow rate of 2.55 L / min. The amount of the aqueous silver nitrate solution was an amount such that the silver concentration in the total liquid volume after adding the pH adjuster, complexing agent, reducing agent, and surface treatment agent was 0.115 mol / L. An aqueous hydrazine solution of 0.50 mol / L was introduced from the entire circumference of the slit portion (slit width 0.44 mm, inner tube diameter 20.6 mm) of the reducing agent addition member 10 at a flow rate of 2.97 L / min to deposit silver powder. The flow rate of the reducing agent entering from the slit portion with a slit width of 0.44 mm was 1.74 m / s, the flow rate of the silver ammine complex immediately before the addition of the reducing agent at the inner diameter of tube 2 of 20.6 mm at the position where the reducing agent enters was 1.75 m / s, and the ratio of the flow rate of the complex to the flow rate of the reducing agent (complex flow rate / reducing agent flow rate) was 1.01. The operating time of the silver powder production apparatus (the time from the start to the stop of the introduction of the reducing agent into the silver ammine complex after the flow of the silver ammine complex into which the surface treatment agent was introduced became stable) was set to 568 seconds. The slurry generated before the flow of the silver ammine complex into which the surface treatment agent was introduced became stable was received in a separate container and not used in the steps after solid-liquid separation. In the above, it took 0.43 seconds from the flow path inlet of the aqueous silver nitrate solution to the nitric acid aqueous solution addition position, 0.43 seconds from the nitric acid aqueous solution addition position to the ammonia aqueous solution addition position, 1.82 seconds (2.1 m) from the ammonia aqueous solution addition position to the hydrazine aqueous solution addition position, 0.10 seconds from the surface treatment agent addition position to the hydrazine aqueous solution addition position, and the temperature of the silver ammine complex solution immediately before the hydrazine aqueous solution addition position was 47.3°C.

[0114] The silver powder-containing slurry was discharged from tube 2. The time from the addition position of the aqueous hydrazine solution to the discharge was about 1.7 seconds. After the reduction reaction was stabilized, the silver powder-containing slurry was recovered, solid-liquid separated, and the obtained solid was washed with pure water to remove impurities in the solid. The end point of this washing can be determined by the electrical conductivity of the water after washing, and washing was performed until this electrical conductivity became 0.5 mS / m or less, and 3.2 kg of dried silver powder was obtained.

[0115] Note that the silver powder obtained in Example 4 was subjected to the same pulverization treatment as in Example 1. The measurement results and the like for the silver powder according to Example 4 are shown in Table 3. Also, graphs of the thermomechanical analysis of the silver powder according to Example 4 are shown in FIGS. 3 and 4. An SEM photograph (20,000 times magnification) is shown in FIG. 8.

[0116] (Example 5) A 0.070 mol / L silver nitrate aqueous solution was introduced into tube 2 (inner diameter 20 mm) at a liquid temperature of 50°C at a flow rate of 23.35 L / min, and a 0.016 mol / L sodium carbonate aqueous solution was introduced from the pH adjuster supply tube 7 (inner diameter 6 mm), which is a coaxial double tube, at a flow rate of 2.13 L / min to adjust the pH. 3.773 mol / L aqueous ammonia as a complexing agent was introduced from the complexing agent supply tube 6 (inner diameter 6 mm), which is a coaxial double tube, at a flow rate of 2.33 L / min to form a silver ammine complex in tube 2. From the surface treatment agent supply tube 5 (inner diameter 6 mm) upstream of the reducing agent addition member 10, a surface treatment agent having a stearic acid concentration of 0.08 mass% (Cellosol 920 (manufactured by Chukyo Yushi Co., Ltd., containing 15.5 wt% stearic acid)) was introduced at a flow rate of 2.19 L / min. The amount of the silver nitrate aqueous solution is an amount such that the silver concentration in the total liquid volume after adding the pH adjuster, complexing agent, reducing agent, and surface treatment agent becomes 0.050 mol / L. An aqueous solution of carbohydrazide with a concentration of 0.240 mol / L as a reducing agent was introduced at a flow rate of 2.55 L / min from the entire circumference of the slit portion 12 (slit width: 0.44 mm, inner pipe diameter: 20.6 mm) of the reducing agent addition member 10 to deposit silver powder. The flow velocity of the reducing agent entering from the slit portion with a slit width of 0.44 mm was 1.49 m / s, and the flow velocity of the silver ammine complex immediately before the addition of the reducing agent at the inner pipe 2 with an inner diameter of 20.6 mm at the position where the reducing agent entered was 1.50 m / s. The ratio of the flow velocity of the complex to the flow velocity of the reducing agent (complex flow velocity / reducing agent flow velocity) was 1.01. The operating time of the silver powder production apparatus (the time from the start to the stop of the introduction of the reducing agent into the silver ammine complex after the flow of the silver ammine complex into which the surface treatment agent was introduced became stable) was set to 83 seconds. The slurry generated before the flow of the silver ammine complex into which the surface treatment agent was introduced became stable was received in a separate container and not used in the processes after solid-liquid separation. In the above, it took 0.5 seconds from the flow path inlet of the silver nitrate aqueous solution to the sodium carbonate aqueous solution addition position, 0.5 seconds from the sodium carbonate aqueous solution addition position to the ammonia water addition position, 2.12 seconds (2.1 m) from the ammonia water addition position to the carbohydrazide aqueous solution addition position, 0.12 seconds from the surface treatment agent addition position to the carbohydrazide aqueous solution addition position, and the temperature of the silver ammine complex aqueous solution immediately before the carbohydrazide aqueous solution addition position was 46.5°C.

[0117] The silver powder-containing slurry was discharged from the pipe 2. The time from the carbohydrazide aqueous solution addition position to the discharge was about 2 seconds. The silver powder-containing slurry after the reduction reaction was stabilized was recovered, and the solid obtained by solid-liquid separation was washed with pure water to remove impurities in the solid. The end point of this washing can be determined by the electrical conductivity of the water after washing. Washing was performed until the electrical conductivity became 0.5 mS / m or less, and then dried to obtain 0.24 kg of silver powder.

[0118] Note that the silver powder obtained in Example 5 was subjected to the same pulverization treatment as in Example 1. The measurement results and the like of the silver powder according to Example 5 are shown in Table 3. Also, graphs of the thermomechanical analysis of the silver powder according to Example 5 are shown in FIGS. 3 and 4. An SEM photograph (20,000 times) is shown in FIG. 9.

[0119] (Example 6) Silver powder according to Example 6 was obtained in the same manner as in Example 5, except that the concentration of aqueous ammonia as a complexing agent was 3.144 mol / L and the operation time was 85 seconds. The obtained silver powder was 0.25 kg. Note that the silver powder obtained in Example 6 was subjected to the same pulverization treatment as in Example 1. Table 3 shows the measurement results and the like for the silver powder according to Example 6. Also, graphs of the thermomechanical analysis of the silver powder according to Example 6 are shown in FIGS. 3 and 4. An SEM photograph (20,000 times) is shown in FIG. 10.

[0120] (Example 7) Silver powder according to Example 7 was obtained in the same manner as in Example 5, except that the concentration of aqueous ammonia as a complexing agent was 3.041 mol / L and the operation time was 84 seconds. The obtained silver powder was 0.25 kg. Note that the silver powder obtained in Example 7 was subjected to the same pulverization treatment as in Example 1. Table 3 shows the measurement results and the like for the silver powder according to Example 7. Also, graphs of the thermomechanical analysis of the silver powder according to Example 7 are shown in FIGS. 3 and 4. An SEM photograph (20,000 times) is shown in FIG. 11.

[0121] (Example 8) Silver powder according to Example 8 was obtained in the same manner as in Example 5, except that the concentration of aqueous ammonia as a complexing agent was 2.728 mol / L and the operation time was 84 seconds. The obtained silver powder was 0.25 kg. Note that the silver powder obtained in Example 8 was subjected to the same pulverization treatment as in Example 1. Table 3 shows the measurement results and the like for the silver powder according to Example 8. Also, graphs of the thermomechanical analysis of the silver powder according to Example 8 are shown in FIGS. 3 and 4. An SEM photograph (20,000 times) is shown in FIG. 12.

[0122] (Comparative Example 1) To 3233.4 g of an aqueous silver nitrate solution containing 40.99 g (0.38 mol) of silver, 124.65 g of industrial aqueous ammonia with a concentration of 28 mass% (corresponding to 5.4 molar equivalents of ammonia per 1 mol of silver) was added to obtain an aqueous silver ammine complex solution. To this aqueous solution of silver ammine complex, 2.28 g of an aqueous sodium hydroxide solution with a concentration of 20% by mass was added. After adjusting the liquid temperature to 25°C, 111.17 g of an aqueous hydrazine solution with a concentration of 7.3% by mass was added while stirring to obtain a slurry containing silver particles. Further, 12.69 g of a 1.55% by mass stearic acid emulsion was added to the obtained slurry containing silver particles and stirred. Then, the stirring was stopped to allow the silver particles to settle, and the liquid in which the silver particles had precipitated was filtered. The filter cake was washed with water until the electrical conductivity of the liquid after passing water was 0.5 mS / m or less, and then vacuum dried at 73°C.

[0123] The silver powder obtained by repeating the above silver powder production three times was charged with 120 g of silver powder using a sample mill (manufactured by Kyoritsu Riko Co., Ltd., SK-M10) and crushed twice in 90 seconds to obtain the silver powder according to Comparative Example 1.

[0124] The measurement results and the like for the silver powder according to Comparative Example 1 are shown in Table 3. Also, the graphs of the thermomechanical analysis of the silver powder according to Comparative Example 1 are shown in FIGS. 3 and 4. The SEM photograph (20,000 times) is shown in FIG. 13.

[0125] (Comparative Example 2) To 3374.7 g of an aqueous silver nitrate solution containing 45.32 g (0.42 mol) of silver, 3.3 g of a 60% by mass nitric acid aqueous solution was added, and further, 76.5 g of an industrial ammonia water with a concentration of 28% by mass (corresponding to 3 molar equivalents of ammonia per 1 mol of silver) was added to obtain an aqueous solution of silver ammine complex. The liquid temperature of this aqueous solution of silver ammine complex was adjusted to 35°C. Then, while stirring, 20.57 g of a 1.1% by mass aqueous sodium benzotriazole solution (0.5% by mass of sodium benzotriazole was added to silver) was added as azoles to obtain a first liquid. Then, as a reducing agent, 142.7 g of an aqueous hydrazine hydrate solution with a concentration of 5.6% by mass was added to the first liquid to obtain a slurry containing silver fine particles as a second liquid. Further, 17.54 g of a 1.55% by mass stearic acid emulsion was added to the second liquid and stirred. Then, the stirring was stopped to allow the silver particles to settle, and the liquid in which the silver particles had precipitated was filtered. The filter cake was washed with water until the electrical conductivity of the liquid after passing water was 0.5 mS / m or less, and then vacuum dried at 73°C.

[0126] The silver powder obtained by repeating the above silver powder production three times was charged with 120 g of silver powder using a sample mill (manufactured by Kyoritsu Riko Co., Ltd., SK-M10) and crushed twice in 90 seconds to obtain the silver powder according to Comparative Example 2.

[0127] Table 3 shows the measurement results and the like for the silver powder according to Comparative Example 2. In addition, graphs of the thermomechanical analysis of the silver powder according to Comparative Example 1 are shown in FIGS. 3 and 4. An SEM photograph (20,000 times) is shown in FIG. 14.

[0128] Tables 1 and 2 show the production conditions in Examples 1 to 8 and Comparative Examples 1 and 2.

[0129]

Table 1

[0130]

Table 2

[0131]

Table 3

[0132] (Paste evaluation) <Disconnection rate and volume resistivity> First, resin-cured conductive pastes were prepared using the silver powders obtained in Examples 1, 5, 7 and Comparative Examples 1, 2. Specifically, the silver powder to be evaluated and DOWA Electronics AG-5-54F (D 50 : 2.9 μm, BET: 0.21 m 2 / g, TAP: 6.1 g / cm 3They were mixed so that the mass ratio was 5:5 to obtain mixed silver powder. Then, 91.92 parts by mass of the mixed silver powder, 3.87 parts by mass of the first epoxy resin (EP4901E manufactured by ADEKA), 0.97 parts by mass of the second epoxy resin (JER1009 manufactured by Mitsubishi Chemical), 0.24 parts by mass of a curing agent (boron trifluoride monoethylamine complex manufactured by Wako Pure Chemical Industries), and 3.00 parts by mass of a solvent (BCA: butyl carbitol acetate) were weighed out, and these were put into a propellerless self-revolving stirring and degassing device (VMX-N360 manufactured by EME Co., Ltd.), stirred and mixed at 1200 rpm for 30 seconds, and then the mixture was kneaded using three rolls (80S manufactured by EXAKT) by passing through a roll gap from 100 μm to 20 μm to obtain a resin-curing type conductive paste before viscosity adjustment. Further, a necessary amount of BCA was added to the resin-curing type conductive paste before viscosity adjustment to obtain a conductive paste after viscosity adjustment whose viscosity was adjusted to 300 Pa·s. The viscosity adjustment of the resin-curing type conductive paste was carried out by sequentially measuring the viscosity while adding BCA little by little to the resin-curing type conductive paste before viscosity adjustment. Using the obtained resin-curing type conductive paste, 10 lines each with line widths (designed widths) of 15 μm, 17 μm, 19 μm, and 21 μm were produced using a screen printing plate (#480 mesh) as evaluation targets. The squeegee speed during printing was 350 mm / second, and printing was performed twice. Next, it was dried at 150 °C for 10 minutes using an air circulation dryer, and further cured by heating at 200 °C for 30 minutes to form a linear conductive film (wiring). The obtained conductive film was measured for disconnection rate and volume resistivity. Measurement terminals were applied to both ends of the conductive film, and the line resistance (Ω) was measured using a digital multimeter (manufactured by ADC Co., Ltd.). The value of the line resistance is the average value of 20 line patterns (printed twice × 10 lines) (excluding those regarded as disconnection described later). The disconnection rate is the ratio of the number of lines with disconnection observed among all 20 line patterns when a measurement value of 100 kΩ or more, which is extremely high, is regarded as disconnection during line resistance measurement. Also, the shape in the line width direction of the wiring was measured at 10 locations (printed twice × 5 locations) using a laser microscope (VK-X1000 manufactured by Keyence Corporation), and the average value of the cross-sectional area of the wiring was calculated. From the measured value of the line resistance and the above cross-sectional area, the volume resistivity represented by the following formula (4) was calculated. Volume resistivity [Ω·cm] = line resistance [Ω] × cross-sectional area [cm 2 ÷ line length [cm] ··· (4) The volume resistivity (Ω·cm) of line widths (designed widths) of 15 μm and 19 μm was calculated. In the measurement of the line resistance, the line length (designed length) was 150 mm.

[0133]

Table 4

[0134] As is clear from Table 4, for the silver powder according to this example, the cumulative 50% diameter D 50 by the laser diffraction method is 0.1 μm or more and 1.0 μm or less, the ratio of D BET to D 50 is 1.3 or less, and the shrinkage rate at 200°C in the thermomechanical analysis is 1% or more. When fired at a low temperature of 200°C, the volume resistivity and disconnection rate in the fine line are low, indicating that it is possible to impart excellent volume resistivity and fine line printability to the conductive paste.

Industrial Applicability

[0135] According to the present invention, it is possible to provide silver powder that can impart excellent volume resistivity and fine line printability even when fired at a low temperature when made into a conductive paste, a method for producing silver powder, a silver powder production apparatus capable of producing such silver powder, and a resin-cured conductive paste having excellent volume resistivity and fine line printability even when fired at a low temperature.

Explanation of Symbols

[0136] 1 Silver powder production apparatus 2 Tube 4a Reducing agent supply tube 4b Reducing agent supply tube 5 Surface treatment agent supply tube 6 Complexing agent supply tube 7 pH adjuster supply tube 10 Reducing agent addition member 11 Opening 12 Slit portion 13 Gap

Claims

1. A method for producing silver powder, comprising: flowing a silver-containing solution through a flow path; adding a pH adjuster to the flow path at a pH adjuster addition position midway through the flow path; adding a complexing agent to the flow path at a complexing agent addition position downstream of the pH adjuster addition position; adding a hydrazine-based reducing agent to the flow path at a reducing agent addition position downstream of the complexing agent addition position; and reducing and precipitating silver powder within the flow path.

2. The method for producing silver powder according to claim 1 , wherein the time required for the silver-containing solution to flow from the complexing agent addition position to the reducing agent addition position is 0.1 seconds or more and 10 seconds or less.

3. The method for producing silver powder according to claim 1 , wherein a surface treatment agent is added to the flow path between the complexing agent addition position and the reducing agent addition position, or downstream of the reducing agent addition position.

4. A silver powder manufacturing apparatus that reduces and precipitates silver powder by adding a pH adjuster, a complexing agent, and a hydrazine-based reducing agent as a reducing agent to a silver-containing solution, the silver powder manufacturing apparatus having a tube that forms a flow path for the silver-containing solution, a pH adjuster addition section connected to the tube, and a complexing agent addition section, and a reducing agent addition section connected to the tube downstream of the pH adjuster addition section and the complexing agent addition section.

Images