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

Abstract

The purpose of the present invention is to provide a silver powder capable of imparting excellent volume resistivity and fine line printability to a conductive paste. 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 a laser diffraction method, 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.

Description

Silver powder, silver powder manufacturing method, silver powder manufacturing device, and resin-hardening conductive paste

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

[0002] BACKGROUND ART Conventionally, in order to form electrodes and wiring 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) solar cells have been attracting attention, and in HJT solar cells and the like, electrodes and conductor patterns are generally formed by baking and hardening a resin-curing conductive paste containing silver powder at a relatively low temperature of around 200°C in an air atmosphere.

[0004] For example, in Patent Document 1, the average particle diameter (D ＳＥＭ ) is 30 to 100 nm, and the tap density is 3.0 g / cm ３ The silver particles described above have been proposed, and it is described that the silver particles are used in resin-curing conductive pastes and the like.

[0005] Japanese Patent Application Laid-Open No. 2013-159805

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

[0007] In recent years, electrodes, conductor patterns, etc. have been increasingly thinned. Therefore, when forming electrodes, conductor patterns, etc. using a conductive paste containing silver powder, it is desirable that the conductive paste be excellent in fine line printability, i.e., be less likely to cause discontinuities even when printed with thinner lines than before, and less likely to cause breaks after firing.

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

[0009] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have completed the present invention described below.

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

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

[0012] [2] The silver powder according to [1], which has a shrinkage rate of 0.6% or more at 150°C in thermomechanical analysis.

[0013] [3] BET specific surface area is 0.90 m ２ / g or more 2.50m ２ The silver powder according to claim [1] or [2], wherein the silver content is 0.01g or less.

[0014] [4] The silver powder according to any one of [1] to [3], which is used in a resin-curing 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 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.

[0016] [6] A method for producing silver powder as described in [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 seconds or more and 10 seconds or less.

[0017] [7] A method for producing silver powder described in [5] or [6], in which 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.

[0018] [8] 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 pipe that forms a flow path for the silver-containing solution, a pH adjuster addition section connected to the pipe, and a complexing agent addition section, and having a nitric acid addition section and a reducing agent addition section connected to the pipe downstream of the complexing agent addition section.

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

[0020] According to the present invention, it is possible to provide a silver powder that can be made into a conductive paste and that can impart excellent volume resistivity and fine line printability even when fired at a low temperature, a method for manufacturing the silver powder, a silver powder manufacturing apparatus that can manufacture such silver powder, and a resin-cured conductive paste that has excellent volume resistivity and fine line printability even when fired at a low temperature.

[0021] 2A 。 FIG. 2B is a perspective view of the appearance of an example of a silver powder manufacturing apparatus. 2C is a cross-sectional view perpendicular to the flow path of the silver complex solution at the center position of a reducing agent supply pipe of a reducing agent addition member of the silver powder manufacturing apparatus. 2D is a cross-sectional view taken along line A-A in FIG. 2A in a horizontal direction relative to the flow path of the silver complex solution. 2E is a cross-sectional view taken along line B-B in FIG. 2A in a horizontal direction relative to the flow path of the silver complex solution. 2F is a graph showing the results of thermomechanical analysis of the silver powders obtained in Examples 1 to 8 and Comparative Examples 1 and 2. 2G is a graph showing an enlarged view of a portion of the graph in FIG. 3. 2G is a SEM photograph (20,000x) of the silver powder according to Example 1. 2G is a SEM photograph (20,000x) of the silver powder according to Example 2. 2G is a SEM photograph (20,000x) of the silver powder according to Example 3. 2G is a SEM photograph (20,000x) of the silver powder according to Example 4. 2G is a SEM photograph (20,000x) of the silver powder according to Example 5. 2G is a SEM photograph (20,000x) of the silver powder according to Example 6. 1 is an SEM photograph (20,000x magnification) of the silver powder according to Example 7. FIG. 2 is an SEM photograph (20,000x magnification) of the silver powder according to Example 8. FIG. 3 is an SEM photograph (20,000x magnification) of the silver powder according to Comparative Example 1. FIG. 4 is an SEM photograph (20,000x magnification) of the silver powder according to Comparative Example 2.

[0022] (Terminology and Measurement Methods) First, prior to describing the embodiments, the terminology and measurement methods used in this specification will be described.

[0023] <Shrinkage of Silver Powder> The shrinkage of the silver powder was measured as follows. First, 0.3 g of silver powder was weighed. Next, the silver powder was placed in a predetermined mold with a diameter of 5 mm and pressed for 1 minute using a press under a load of 50 kg to prepare a cylindrical measurement sample. This measurement sample was set in the sample holder of a thermomechanical analysis (TMA) device (Thermo plus EVO 2 series TMA8311). A measurement load of 98 mN was applied using the measurement probe, and the temperature was raised from room temperature (25°C ± 5°C) to 900°C at a heating rate of 10°C / min to perform thermomechanical analysis (TMA). The "shrinkage at 200°C in thermomechanical analysis" and the "shrinkage at 150°C in thermomechanical analysis" were calculated using the following equations (1) and (2), respectively. Shrinkage at 200°C in thermomechanical analysis (%) = (L ＲＴ -L ２００ ) / L ＲＴ × 100... (1) Shrinkage rate (%) at 150 ° C. in thermomechanical analysis = (LＲＴ -L １５０ ) / L ＲＴ × 100... (2) where L ＲＴ is the length (mm) of the cylindrical sample in the axial direction at room temperature (25°C ± 5°C), and L ２００ is the length (mm) of the cylindrical measurement sample in the axial direction at a temperature of 200 ° C., and 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 a BET single-point method using nitrogen adsorption using a Macsorb HM-model 1210 (manufactured by MOUNTECH). The BET specific surface area was measured with a sample weight of 3.0 g and N ２ A mixed gas of HCl / He (30 / 70) was used, the gas flow rate was 25 mL / min, and 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 (Micromeritics, Inc., device name: AccuPyc II 1340), the volume of the mass-measured silver powder was measured by the constant volume expansion method (the "gas pycnometer method" in the Japanese Pharmacopoeia), and the density was calculated. Note that the true density measurement includes the closed voids inside the silver particles that are not connected to the outside.

[0026] <BET diameter D ＢＥＴ > BET diameter D ＢＥＴ (Hereafter, simply "D ＢＥＴ ") (unit: μm) is the BET specific surface area (unit: m) measured by the BET single-point method. ２ / g) and true density (unit: g / cm ３ ) and was calculated using the following formula (3): ＢＥＴ =6 / (BET specific surface area x true density)...(3)

[0027] <Average primary particle diameter D ＳＥＭ >Average primary particle diameter D ＳＥＭ (Hereafter, simply "D ＳＥＭThe equivalent circle diameter (Heywood diameter) of 100 or more random silver particles in an SEM image of the silver powder was measured and the average value was calculated. ＳＥＭ can be determined, for example, by using an image taken at 10,000x magnification and using image shape measurement software such as Mac-View (manufactured by Mountec Co., Ltd.).

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

[0029] <D ＢＥＴ D against ５０ The ratio (D ５０ / D ＢＥＴ ) > In silver powder, individual particles are not completely separated, and multiple particles may be in an agglomerated state. When measuring particle size by laser diffraction, the particle size of agglomerated particles is measured. On the other hand, the BET single-point method measures the specific surface area by utilizing the amount of gas adsorbed to the particle, and the BET diameter converted from this specific surface area indicates the particle size (particle diameter) of the particle when the measured particle is assumed to be a perfect sphere. When there is little agglomeration and the particle is close to being monodispersed, the ratio (D ５０ / D ＢＥＴ) tends to be close to 1.

[0030] <Ignition loss (Ig-loss) value> In this specification, the term "ignition loss (Ig-loss) value" refers to the amount of change in mass when heated from room temperature to 800°C, and specifically serves as an index of the amount of components other than silver contained in the silver powder, and indicates the amount of components remaining in the silver powder, such as processing agents and additives used in the silver powder manufacturing process. In this specification, the "ignition loss (Ig-loss) value" is determined by precisely weighing a silver powder sample (weighing value: w １ ) into a porcelain crucible, heated to 800°C, and held at 800°C for 30 minutes, sufficient time to reach a constant weight, after which it was cooled and reweighed (weight: w ２ ) and "Ignition loss (Ig-loss) value (mass%) = (w １ -w ２ ) / w １ × 100".

[0031] <Quantitative Analysis 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 method for quantitative analysis of fatty acids described in Japanese Patent No. 5622543. Specifically, the silver powder was first dissolved in nitric acid, and then an organic solvent (n-hexane) was mixed therewith to extract the entire amount of the surface treatment agent into the organic solvent phase. A predetermined amount of the organic solvent phase was then sampled, and the solvent was evaporated to dryness. The remaining solid (surface treatment agent that had solidified without evaporating) was measured for its carbon content using a carbon / sulfur analyzer, and the fatty acid content was calculated.

[0032] For example, if the surface treatment agent is specified as stearic acid and no carbon source other than stearic acid is contained in the silver powder, the method for measuring the stearic acid content is as described in the above publication.

[0033] In addition, in the present specification, for example, when the surface treatment agent for silver powder is benzotriazole, the content of benzotriazole was measured according to the quantitative analysis method for benzotriazole and benzotriazole salts described in Japanese Patent No. 5523153. Specifically, the silver powder was first washed with an aqueous hydrochloric acid solution, and the washing solution was quantitatively analyzed by absorptiometry.

[0034] The type of surface treatment agent can be identified by qualitative analysis by gas chromatography of the surface treatment agent vaporized by heating the silver powder.

[0035] <Crystallite diameter> The crystallite diameter Dx was measured using an X-ray diffractometer (SmartLab manufactured by Rigaku Corporation) according to the Scherrer formula (D ｈｋｌ = Kλ / β cos θ) where D ｈｋｌ means the size of the crystallite diameter (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 (rad) due to the size of the crystallite (expressed using the half-width), θ means the Bragg angle of the diffraction angle (rad) (the angle when the angle of incidence and the angle of reflection are equal, and the angle of the peak top is used), and K means the Scherrer constant (K = 0.94). Note that peak data of the Miller index (111) plane may also be used for the calculation.

[0036] (Silver Powder) The silver powder of the present invention has a volumetric D measured by laser diffraction method. ５０ is 0.1 μm or more and 1.0 μm or less, and D ＢＥＴ D against ５０ The ratio (D ５０ / D ＢＥＴ ) is 1.3 or less, and the shrinkage rate at 200°C in thermomechanical analysis is 1% or more. With the silver powder described above, excellent volume resistivity can be imparted to a conductive paste even when fired at a low temperature (150 to 200°C). The reason for this is that D ５０ / D ＢＥＴIt is presumed that this is because silver powder with a value of 1.3 or less and close to monodispersion has a shrinkage rate of a predetermined percentage or more at 200°C, and therefore in electrodes, conductor patterns, etc. obtained using a conductive paste containing this silver powder, the silver particles can form a good conductive network during firing, compared to silver powder with a low shrinkage rate at 200°C. In this specification, having low volume resistivity and low wire breakage rate even when fired at low temperatures (150 to 200°C) is also referred to as "having low-temperature firing properties." Furthermore, silver powders such as those described above can impart excellent fine-line printing properties to conductive pastes. The reason for this is that D ５０ It is presumed that this is because, by setting the particle size within a predetermined range, it is possible to effectively suppress the deterioration of fine line printing properties due to large particle size and the excessive increase in viscosity of the conductive paste containing the silver powder.

[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, low-temperature sintering properties can be improved. ５０ / D ＢＥＴ Since the shrinkage ratio is 1.3 or less, the shrinkage ratio does not exceed 5.0%, and the shrinkage ratio at 200° C. in thermomechanical analysis is, for example, preferably 5.0% or less, more preferably 3.0% or less.

[0038] The shrinkage percentage 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 percentage at 150°C in thermomechanical analysis is 0.6% or more, the low-temperature sintering property described above can be more effectively achieved. On the other hand, the shrinkage percentage 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. Furthermore, when it is important to obtain high conductivity in a conductive film obtained by firing a resin-curing conductive paste using the silver powder of the present invention at low temperature, the shrinkage percentage at 150°C in thermomechanical analysis of the present invention can be 1.05% or more and 1.5% or less, or even 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. ５０ / D ＢＥＴ If D is 1.3 or less, excellent dispersibility can be obtained, and therefore excellent fine line printing properties can be imparted. ５０ / D ＢＥＴ is often 1.0 or more, but may be less than 1.0 as in this embodiment. ５０ / D ＢＥＴ The value 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, and even more preferably 0.35 μm or more, and is 1.0 μm or less, preferably 0.9 μm or less, and more preferably 0.8 μm or less. ５０ In addition, when it is important to obtain a conductive film having high conductivity by firing the resin-curing conductive paste containing the silver powder of the present invention at a low temperature, the D of the silver powder of the present invention can be set to 100%. ５０ can be set to 0.1 μm or more and 0.5 μm or less, and further, can be set to 0.2 μm or more and 0.4 μm or less.

[0041] D １０ is preferably 0.05 μm or more, more preferably 0.10 μm or more, and is preferably 0.40 μm or less, more preferably 0.35 μm or less. １０ If 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, and even more preferably 0.6 μm or more, and is preferably 1.2 μm or less, more preferably 1.1 μm or less, and even more preferably 1.0 μm or less. ９０In addition, when it is important to obtain a conductive film having high conductivity by firing the resin-curing conductive paste containing the silver powder of the present invention at a low temperature, the D of the silver powder of the present invention can be set to 100%. ９０ can be set to 0.5 μm or more and 0.9 μm or less, and further, can be set to 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. ＢＥＴ is preferably 0.68 μm or less, more preferably 0.61 μm or less, and even more preferably 0.58 μm or less. ＢＥＴ If is within the above range, the fine line printability of the conductive paste can be improved.

[0044] The BET specific surface area is 0.90 m ２ / g or more, and 1.00m ２ / g or more, and more preferably 1.05m ２ / g or more, and more preferably 2.50m ２ / g or less, and ２ / g or less, and more preferably 2.00m ２ / g or less, and more preferably 1.80m ２ / g or less. 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 when fired at a low temperature. Also, it is easy to respond to high density, etc. On the other hand, ２ When it is important to obtain a conductive film having high conductivity by firing the resin-curing conductive paste containing the silver powder of the present invention at a low temperature, it is preferable to set the specific surface area of ​​the silver powder of the present invention to 1.35 m / g or less. ２ / g or more 2.50m２ / g or less, and further, 1.40m ２ / g or more 2.50m 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 It is preferable that the density is 9.8 g / cm or more. ３ More preferably, it is 9.9 g / cm or more. ３ More preferably, it is 10.49 g / cm or more. ３ Furthermore, when it is important to obtain high conductivity in a conductive film obtained by firing a resin-curing conductive paste using the silver powder of the present invention at a low temperature, the density of the silver powder of the present invention is preferably 9.7 g / cm or less. ３ 9.95g / cm or more ３ and further, 9.7 g / cm ３ More than 9.9g / cm ３ It can be as follows:

[0046] D ＳＥＭ is preferably 0.10 μm or more, more preferably 0.20 μm or more, even more preferably 0.25 μm or more, even more preferably 0.35 μm or more, and is preferably 1.00 μm or less, more preferably 0.90 μm or less, even more preferably 0.80 μm or less. ＳＥＭ In addition, when it is important to obtain a conductive film having high conductivity by firing the resin-curing conductive paste containing the silver powder of the present invention at a low temperature, the D of the silver powder of the present invention can be set to 100%. ＳＥＭ can be set to 0.10 μm or more and 0.4 μm or less, and further, can be set to 0.15 μm or more and 0.35 μm or less.

[0047] The loss on ignition (Ig-loss) value is preferably 0.3% by mass or more, more preferably 0.35% by mass or more. It is also preferably 1.2% by mass or less, more preferably 1.1% by mass or less, and even more preferably 0.8% by mass or less. An ignition loss value of 0.3% by mass or more can suppress aggregation of silver powder particles and improve dispersibility. On the other hand, an ignition loss value of 1.2% by mass or less can prevent deterioration of resistance due to excess impurities. Furthermore, when it is important to obtain high conductivity in a conductive film obtained by firing a resin-type conductive paste using the silver powder of the present invention at a low temperature, the ignition loss value of the silver powder of the present invention can be 0.65% by mass or more and 1.2% by mass or less, or even 0.70% by mass or more and 1.2% by 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, even more preferably 32 nm or more, or may be 32 nm or more, and preferably 38 nm or less.

[0049] 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 later in the section "Method for producing silver powder."

[0050] 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 later in the section "Method for producing silver powder."

[0051] The silver powder of the present invention can be used in conductive pastes such as resin-curing conductive pastes and sintered conductive pastes without any particular limitations. However, the silver powder of the present invention has excellent volume resistivity and fine line printability even when fired at low temperatures when made into a conductive paste, and is therefore suitable for use in resin-curing conductive pastes.

[0052] (Method for Producing Silver Powder) The method for producing silver powder of the present invention (hereinafter sometimes 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 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, and adding a hydrazine-based reducing agent to the flow path at a reducing agent addition position downstream of the complexing agent addition position, thereby reducing and precipitating silver powder within the flow path. The above-described method can produce silver powder that can impart excellent volume resistivity and fine-line printability to a conductive paste even when fired at a low temperature. Furthermore, the production method of the present invention can produce the silver powder of the present invention described above. In the production method of the present invention, the silver-containing solution, pH adjuster, complexing agent, and hydrazine-based reducing agent are continuously supplied in this order and quantitatively mixed, thereby maintaining constant the rate of silver complex formation and the rate of reductive precipitation of silver powder, thereby enabling the desired silver powder to 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. Examples include aqueous solutions of silver nitrate, silver chloride, silver formate, silver oxalate, silver sulfate, etc., and from the viewpoint of availability, an aqueous silver nitrate solution is preferred.

[0054] From an economical viewpoint, the silver concentration of 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 of the silver-containing solution is preferably 0.5 mol / L or less, and 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 pipe, assuming that the pipe is filled with liquid. The elapsed time between specific positions is calculated by dividing the length between the positions by the flow rate. From the viewpoints of productivity and monodisperse particle formation, 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. From the viewpoints of aggregation suppression and monodisperse particle formation, the flow rate 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 manufacturing method of the present invention, a silver-containing solution is passed through a flow path, and a pH adjuster is added to the flow path at a pH adjuster addition position along the flow path, thereby adjusting the pH of the silver-containing solution. This effectively adjusts the particle size of the silver powder. Common alkaline or acidic pH adjusters, such as sodium hydroxide, potassium hydroxide, sodium carbonate, and nitric acid, can be used as the pH adjuster. The pH adjuster is usually added to the flow path in the form of an aqueous pH adjuster solution. The amount of pH adjuster added is adjusted appropriately to match the particle size of the silver powder to be manufactured.

[0057] In the production method of the present invention, a complexing agent is added to the flow channel at a complexing agent addition position downstream of the pH adjuster addition position, to form a silver complex. The complexing agent is usually added to the flow channel in the form of an aqueous complexing agent solution.

[0058] Examples of the complexing agent include ammonia, ammonium salts, citric acid, and acetic acid, with ammonia being 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 economical viewpoint, the concentration of aqueous ammonia is preferably 0.35 mol / L or more, more preferably 0.50 mol / L or more, and is preferably 16.2 mol / L or less, more preferably 15.1 mol / L or less, and even more preferably 10.0 mol / L or less.

[0060] The amount of ammonia added per mole of silver is preferably 2.10 moles or more, more preferably 2.20 moles or more, while the amount of ammonia added per mole of silver is preferably 10.00 moles or less, more preferably 8.00 moles or less.

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

[0062] When a complexing agent other than ammonia is used, the concentration, amount added and flow rate can be set in accordance with the above, taking into consideration the amount of complexing agent relative to the amount of silver required to form a complex.

[0063] In the manufacturing method of the present invention, a hydrazine-based reducing agent is added to the flow path at a reducing agent addition position downstream of the complexing agent addition position, thereby reducing and precipitating silver powder. The hydrazine-based reducing agent used in the present invention includes hydrazine, hydrazine hydrate, hydrazine carbonate, hydrazine sulfate, phenylhydrazine, etc., with hydrazine and hydrazine carbonate being preferred, and hydrazine being more preferred. The use of hydrazine allows for the stable production of silver powder with the desired particle size. Typically, the hydrazine-based reducing agent is added to the flow path in the form of an aqueous solution.

[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, even more preferably 0.10 mol / L or more, and preferably 3.3 mol / L or less, more preferably 2.0 mol / L or less, and even more preferably 1.0 mol / L or less. 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, even more preferably 0.10 mol / L or more, and preferably 3.3 mol / L or less, more preferably 2.0 mol / L or less, and even more preferably 1.0 mol / L or less.

[0065] The amount of hydrazine added per mole of silver is preferably 0.26 moles or more, more preferably 0.28 moles or more, so that unreacted silver is not substantially generated. On the other hand, the amount of hydrazine added per mole of silver is preferably 0.88 moles or less, more preferably 0.75 moles or less, and even more preferably 0.50 moles or less, so that an excessive amount of reducing agent is not added. Furthermore, the amount of hydrazine-based reducing agent added per mole of silver is preferably 0.26 moles or more, more preferably 0.28 moles or more, so that unreacted silver is not substantially generated. On the other hand, the amount of hydrazine-based reducing agent added per mole of silver is preferably 0.88 moles or less, more preferably 0.75 moles or less, and even more preferably 0.50 moles or less, so that an excessive amount of reducing agent is not added.

[0066] In the production method of the present invention, 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 from the viewpoint of productivity, and 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 from the viewpoint of suppressing aggregation and forming monodisperse particles.

[0067] The flow rate of the reducing agent when added to the flow path is preferably 0.5 times or more, more preferably 0.8 times or more, the flow rate of the silver complex solution immediately before the addition of the reducing agent, and is preferably 2.5 times or less, more preferably 2.0 times or less, and even more preferably 1.5 times or less, in order to prevent the liquid flow toward the piping wall from increasing and reducing the mixing efficiency.

[0068] In the production method of the present invention, since a hydrazine-based reducing agent is added to the site where the silver complex has been 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 calculated by dividing the distance from the complexing agent addition position to the reducing agent addition position by the flow rate of the silver complex solution immediately before the addition of the reducing agent) is preferably 0.1 seconds or more, more preferably 0.5 seconds or more. On the other hand, since a longer elapsed time after the formation of the complex may increase the stability of the silver complex and make it difficult for the reduction reaction to proceed, in order to ensure the freshness of the silver complex when the reducing agent is added, the elapsed time is preferably 10.0 seconds or less, more preferably 5.0 seconds or less.

[0069] In the manufacturing 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 downstream of the reducing agent addition position. Addition of a surface treatment agent is advantageous in that it suppresses aggregation of the reduced and precipitated silver powder. The addition is preferably carried out between the complexing agent addition position and the reducing agent addition position.

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

[0071] (1) Fatty Acids 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 ricinoleic acid.

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

[0073] (3) Surfactants Examples of 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 betaine, and nonionic surfactants such as polyoxyethylene alkyl ethers and polyoxyethylene fatty acid esters.

[0074] Examples of organic metals include acetylacetone tributoxyzirconium, magnesium citrate, diethyl zinc, dibutyl tin oxide, dimethyl zinc, tetra-n-butoxyzirconium, triethyl indium, triethyl gallium, trimethyl indium, trimethyl gallium, monobutyl tin oxide, tetraisocyanate silane, tetramethyl silane, tetramethoxy silane, monomethyl triisocyanate silane, silane coupling agents, titanate-based coupling agents, and aluminum-based coupling agents.

[0075] (5) Chelate-forming agents 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-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, and 1,2,5-thiadiazole. Examples thereof include diazole, 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, and the like, salts of these chelating agents, and polycarboxylic acids such as dicarboxylic acids such as succinic acid, malonic acid, glutaric acid, and adipic acid.

[0076] (6) Protective Colloids Examples of protective colloids include peptides, gelatin, albumin, gum arabic, prothalbic acid, risalbic acid, glue, and the like.

[0077] As the surface treatment agent, (1) fatty acids are preferred, and stearic acid is particularly preferred, from the viewpoint of ease of modifying the silver particle surface. (1) Fatty acids are preferably in the form of emulsions, such as stearic acid emulsions.

[0078] In the production method of the present invention, 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, from the viewpoint of the reactivity of the reduction reaction. On the other hand, the temperature of the solution flowing through the flow path is preferably 65° C. or lower, more preferably 60° C. or lower, from the viewpoint of operability.

[0079] In the production method of the present invention, a mixer may be used to apply spiral rotation in the axial direction of the flow channel to mix the liquids.

[0080] In the manufacturing method of the present invention, the liquid containing the reduced and precipitated silver powder (hereinafter also referred to as "silver powder-containing liquid") is discharged outside the flow path and then recovered to obtain the silver powder. The silver powder-containing liquid is usually obtained in the form of a slurry or dispersion.

[0081] The time from the addition of the reducing agent to the release of the silver powder-containing liquid outside the flow path is preferably 1 second or more, more preferably 2 seconds or more, in order to anticipate the completion of the reduction reaction, while the time from the addition of the reducing agent to the release of the silver powder-containing liquid outside the flow path is preferably 10 seconds or less, more preferably 5 seconds or less, in order to prevent the silver powder-containing liquid from settling in the piping.

[0082] The silver powder-containing liquid discharged from the flow channel is filtered and washed with water to obtain a lumpy cake containing silver powder and water and having almost no fluidity. The silver powder of the present invention is obtained by drying this cake in a dryer such as a forced-circulation atmospheric dryer, vacuum dryer, or flash dryer. The drying process can be accelerated by replacing the water in the cake with a lower alcohol or the like. The cake can then be subjected to dry crushing, surface smoothing, and other treatments. Dry crushing can be performed using, for example, a sample mill, blender, coffee mill, or multipurpose mixer. Surface smoothing can be performed by mechanically colliding particles with each other using a high-speed agitator. Subsequently, a classification process can be performed to remove silver powder aggregates larger than a predetermined particle size. Furthermore, the cake can be dried, crushed, and classified using an integrated device capable of drying, crushing, and classification (e.g., Dry Meister or Micron Dryer, manufactured by Hosokawa Micron Corporation).

[0083] (Silver Powder Manufacturing Apparatus) The silver powder manufacturing apparatus of the present invention is 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, and has a pipe that forms a flow path for the silver-containing solution, a pH adjuster addition section connected to the pipe, a complexing agent addition section, and a reducing agent addition section that is connected to the pipe downstream of the nitric acid addition section and the complexing agent addition section. It is also preferable to have a surface treatment agent addition section downstream of the nitric acid addition section and the complexing agent addition section and before the reducing agent addition section. Below, 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] Figure 1 is an external perspective view of an example of a silver powder manufacturing apparatus. In Figure 1, the silver powder manufacturing apparatus 1 includes a pipe 2 for flowing a silver-containing solution, a pH adjuster supply pipe 7 for supplying a pH adjuster, a complexing agent supply pipe 6 located downstream of the pH adjuster supply pipe 7 and supplying a complexing agent, a surface treatment agent supply pipe 5 located downstream of the complexing agent supply pipe 6 and supplying a surface treatment agent, and a reducing agent adding member 10 located downstream of the surface treatment agent supply pipe 5 and supplying a hydrazine-based reducing agent as a reducing agent. Reducing agent supply pipes 4a and 4b are eccentrically connected to the reducing agent adding member 10. The silver powder manufacturing apparatus 1 in Figure 1 includes the surface treatment agent supply pipe 5 between the complexing agent supply pipe 6 and the reducing agent adding member 10, but the surface treatment agent supply pipe 5 may also be located downstream of the reducing agent adding member 10.

[0085] The pH adjuster addition section, complexing agent addition section, and surface treatment agent addition section may each be a Y-shaped or T-shaped conduit, or may have a structure in which a second conduit is connected to the middle of a conduit forming the silver-containing solution conduit, and the conduit for the silver-containing solution and the conduit for the second conduit join together. Alternatively, the pH adjuster addition section, complexing agent addition section, and surface treatment agent addition section may each be a coaxial biaxial conduit.

[0086] When the reducing agent is added from one direction to the flow path, it takes time for the reducing agent to reach the opposite side of the addition point, which can lead to variations in the concentration of the reducing agent at the adding point. Therefore, when a Y-shaped pipe or a T-shaped pipe is used to bring the silver complex solution and the reducing agent into contact with each other at the confluence and mix them, variations in concentration can occur for the same reason. Furthermore, when the reducing agent is added at the center of the flow path using a coaxial double pipe, the reducing agent is added parallel to the flow of the silver complex solution, which requires time for the silver complex solution and the reducing agent to mix. Furthermore, in a coaxial double pipe, the flow velocity at the center of the pipe is relatively fast and the flow velocity near the wall is relatively slow, which can lead to uneven particle growth.

[0087] The reducing agent is preferably added in two or more directions relative to the flow path, more preferably in four or more directions, and particularly preferably from all directions around the circumference of the flow path. Depending on the number and shape of the openings, the reducing agent can be added to the flow path from multiple directions.

[0088] Each of the multiple 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 approximately perpendicularly 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 tube through which the silver complex solution flows."

[0089] By using the silver powder manufacturing apparatus of the present invention, silver powder can be obtained that can impart excellent low-temperature heating properties and fine-line printing properties to conductive paste.

[0090] Fig. 2A is a cross-sectional view perpendicular to the flow path of the silver complex solution at the center 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 horizontal to the flow path of the silver complex solution, taken along line A-A in Fig. 2A. Fig. 2C is a cross-sectional view horizontal to the flow path of the silver complex solution, taken along line B-B in Fig. 2A.

[0091] In FIG. 2A , a gap 13 is formed along the outer periphery of tube 2, which serves as a flow path for the silver complex solution, and gap 13 is connected to the interior of reducing agent supply tubes 4a and 4b. As shown in FIG. 2C , a cross-sectional view taken along line B-B of FIG. 2A , the downstream side of the flow path for the silver complex solution at gap 13 is connected to a slit portion 12 having an opening 11 facing radially outward along the inner periphery of tube 2. As shown in FIG. 2B , a cross-sectional view taken along line A-A of FIG. 2A , when a reducing agent is poured into gap 13 from the interior of reducing agent supply tubes 4a and 4b, the reducing agent reaches slit portion 12 through gap 13. The reducing agent then enters tube 2 from opening 11 of slit portion 12, approximately perpendicular (e.g., at an angle of 75 degrees or greater and 105 degrees or less) from the entire circumference of tube 2, and is added to the silver complex solution. Here, the angle at which the reducing agent enters the flow path for the silver complex solution is the angle between the axial direction of tube 2 and the opening direction of opening 11 through which the reducing agent enters tube 2. The opening direction can be considered to be 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 when it is added to the flow path of the silver complex solution can be controlled by adjusting the flow rate of the reducing agent flowing through the reducing agent supply pipes 4a and 4b and the total area of ​​the openings 11. By controlling the flow rate of the reducing agent within the above-mentioned range, the reaction between the silver complex and the reducing agent can be carried out quickly, thereby producing silver powder with a narrow particle size distribution.

[0093] The width of the opening 11 of the slit portion 12 in Figures 2B and 2C is referred to as the slit width. The slit width is preferably narrower than the diameter of the reducing agent supply pipe in order to reduce the total area of ​​the opening 11. The shapes of the gap 13 and slit portion 12 that allow the addition of the reducing agent to the flow path from multiple directions and that can form a slit width narrower than the diameter of the reducing agent supply pipe are not limited to the structures shown in Figures 2A to 2C and can be modified in various ways. Furthermore, modifications are also possible, such as providing the opening 11 of the slit portion 12 as multiple through-holes rather than providing it around the entire circumference of the pipe 2.

[0094] The number of reducing agent supply pipes that feed the reducing agent into the reducing agent addition member 10 may be one or more, and two or more are also preferred. When two or more reducing agent supply pipes are used, the reducing agent flow paths connecting the reducing agent supply pipes to the opening 11 may be arranged opposite to each other or eccentrically. 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 pipe 2, and the flow paths of the reducing agent supply pipes 4a and 4b are connected to a slit portion 12 having the opening 11. When connecting multiple reducing agent supply pipes, if at least two reducing agent supply pipes are eccentric to each other, the reducing agent can flow into the opening 11 of the slit portion 12 while rotating the outer periphery of the silver complex solution flow path (pipe 2) in one direction. As the reducing agent rotates around the outer periphery of the silver complex solution flow path, the flow rate of the reducing agent toward the opening 11 may be adjusted by changing the cross-sectional area of ​​the reducing agent flow path (gap 13 or slit portion 12).

[0095] (Resin-curable conductive paste) The resin-curable conductive paste of the present invention contains the silver powder of the present invention described above. The proportion of the silver powder of the present invention in the total amount of metal powder contained in the resin-curable conductive paste may be 20 to 100%. The metal powder other than the silver powder of the present invention may have a particle size (D ５０ It is also preferable that the resin-curable conductive paste of the present invention contains a silver powder having a large surface area. The resin-curable conductive paste of the present invention is excellent in volume resistivity and fine line printability because it contains the silver powder of the present invention. The resin-curable conductive paste of the present invention usually contains the silver powder of the present invention, a resin, and a solvent. The resin-curable conductive paste of the present invention may further contain, as desired, components other than the silver powder, resin, and solvent (hereinafter, these may be referred to as "other components").

[0096] The resin is not particularly limited and may be, for example, an epoxy resin, an acrylic resin, a polyester resin, a polyimide resin, a polyurethane resin, a phenoxy resin, a silicone resin, or ethyl cellulose. These may be used alone or in any combination of two or more kinds in any ratio.

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

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

[0099] The method for producing the resin-curing conductive paste is not particularly limited, and examples thereof include a method of mixing the silver powder of the present invention, an organic binder, a solvent, and any other components. The mixing method is also not particularly limited, and examples thereof include a planetary mixer, ultrasonic dispersion, a disperser, a three-roll mill, a ball mill, a bead mill, a twin-axis kneader, etc.

[0100] The resin-curing conductive paste of the present invention can be applied to a substrate to form a coating film by, for example, screen printing, offset printing, photolithography, or other printing methods, dipping, etc. The coating film may be formed into a predetermined pattern by photolithography using a resist, etc.

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

[0102] The resin-curing conductive paste of the present invention has excellent volume resistivity and fine line printability even when fired at low temperatures, and therefore can be suitably used in the manufacture of heterojunction (HJT) solar cells and the like in which electrodes and conductor patterns are formed by heating at relatively low temperatures.

[0103] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples. ＢＥＴ , average primary particle diameter D ＳＥＭThe particle size distribution, ignition loss (Ig-loss) value, quantitative amount of the surface treatment agent, crystallite diameter, and shrinkage rate (200°C and 150°C) of the silver powder were measured or calculated by the methods described above.

[0104] Example 1 Silver powder was produced using silver powder production apparatus 1 shown in Figure 1 and Figures 2A to 2C. A 0.160 mol / L aqueous silver nitrate solution was introduced into pipe 2 (inner diameter 20 mm) at a flow rate of 23.35 L / min at a liquid temperature of 50°C, and a 0.024 mol / L aqueous nitric acid solution was introduced into coaxial double-pipe pH adjuster supply pipe 7 (inner diameter 6 mm) at a flow rate of 2.13 L / min to adjust the pH. 4.500 mol / L aqueous ammonia as a complexing agent was introduced into pipe 2 at a flow rate of 2.33 L / min through coaxial double-pipe complexing agent supply pipe 6 (inner diameter 6 mm), and a silver ammine complex was produced in pipe 2. A surface treatment agent (0.10 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 from a surface treatment agent supply pipe 5 (inner diameter 6 mm) upstream of the reducing agent adding member 10. The amount of the silver nitrate aqueous solution was such that the silver concentration in the total liquid volume after adding the pH adjuster, complexing agent, reducing agent, and surface treatment agent would be 0.115 mol / L. A 0.50 mol / L aqueous hydrazine solution 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, tube inner diameter 20.6 mm) of the reducing agent addition member 10, and silver powder was precipitated. The flow rate of the reducing agent entering through the 0.44 mm slit portion was 1.49 m / sec, and the flow rate of the silver ammine complex immediately before the addition of the reducing agent at the 20.6 mm inner diameter tube 2 where the reducing agent entered was 1.50 m / sec. The ratio of the complex flow rate to the reducing agent flow rate (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 introduction of the reducing agent to the silver ammine complex after the flow of the silver ammine complex into which the surface treatment agent had been introduced stabilized) was 616 seconds. The slurry generated before the flow of the silver ammine complex into which the surface treatment agent had been introduced stabilized was received in a separate container and was not subjected to solid-liquid separation or subsequent processes. 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 water addition position, 2.12 seconds (2.1 m) from the ammonia water addition position to the hydrazine aqueous solution addition position, and 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 tube 2. The time from the addition of the aqueous hydrazine solution to the discharge was approximately 2 seconds. After the reduction reaction stabilized, the silver powder-containing slurry was recovered, and the solid matter obtained by solid-liquid separation was washed with pure water to remove impurities. The end point of this washing could be determined by the electrical conductivity of the water after washing. The washing was continued until the electrical conductivity reached 0.5 mS / m or less, and then dried to obtain 3.8 kg of silver powder.

[0106] The silver powder obtained above was milled in a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) in an amount of 120 g, twice for 90 seconds to obtain the silver powder of Example 1. The measurement results for the silver powder of Example 1 are shown in Table 3. A graph of the thermomechanical analysis of the silver powder of Example 1 is shown in FIG. 3, a graph in which a portion of the graph of FIG. 3 (0°C to 250°C) is enlarged is shown in FIG. 4, and an SEM photograph (20,000x magnification) is shown in FIG. 5.

[0107] Example 2 A 0.153 mol / L aqueous silver nitrate solution was introduced into tube 2 (inner diameter 20 mm) at a flow rate of 23.35 L / min at a liquid temperature of 50°C. A 0.008 mol / L aqueous nitric acid solution was introduced into coaxial double tube pH adjuster supply tube 7 (inner diameter 6 mm) at a flow rate of 3.15 L / min to adjust the pH. A 4.919 mol / L aqueous ammonia solution was introduced into coaxial double tube complexing agent supply tube 6 (inner diameter 6 mm) at a flow rate of 2.33 L / min to generate a silver ammine complex in tube 2. A surface treatment agent (0.10% by mass Cellosol 920 (manufactured by Chukyo Yushi Co., Ltd., containing 15.5 wt % of stearic acid) was introduced at a flow rate of 2.19 L / min from a surface treatment agent supply pipe 5 (inner diameter 6 mm) upstream of the reducing agent adding member 10. The amount of the aqueous silver nitrate solution was such that the silver concentration in the total amount of the solution after adding the pH adjuster, complexing agent, reducing agent, and surface treatment agent would be 0.106 mol / L. Silver powder was precipitated by introducing a 0.478 mol / L aqueous hydrazine solution at a flow rate of 2.55 L / min from the entire circumference of the slit portion (slit width: 0.44 mm, tube inner diameter: 20.6 mm) of the reducing agent addition member 10. The flow rate of the reducing agent entering through the 0.44 mm slit portion was 1.49 m / sec, and the flow rate of the silver ammine complex just before the addition of the reducing agent at the 20.6 mm inner diameter tube 2 where the reducing agent entered was 1.55 m / sec (calculated from the combined flow rates of the silver nitrate aqueous solution, nitric acid aqueous solution, and ammonia aqueous solution). 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 1.04. 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 had been introduced stabilized) was 115 seconds. The slurry produced before the flow of the silver ammine complex into which the surface treatment agent had been introduced stabilized was collected in a separate container and not subjected to subsequent steps after solid-liquid separation. In the above, it took 0.5 seconds from the silver nitrate aqueous solution flow path inlet to the nitric acid aqueous solution addition position, 0.48 seconds from the nitric acid aqueous solution addition position to the ammonia aqueous solution addition position, 2.05 seconds (2.1 m) from the ammonia aqueous solution addition position to the hydrazine aqueous solution addition position, and 0.12 seconds from the surface treatment agent addition position to the hydrazine aqueous solution addition position. The temperature of the silver ammine complex solution just before the hydrazine aqueous solution addition position was 46.6°C.

[0108] The silver powder-containing slurry was discharged from tube 2. The time from the addition of the aqueous hydrazine solution to the discharge was approximately 2 seconds. After the reduction reaction had stabilized, the silver powder-containing slurry was recovered, and the solid obtained by solid-liquid separation was washed with pure water to remove impurities. The end point of this washing could be determined by the electrical conductivity of the water after washing. Washing was continued until the electrical conductivity reached 0.5 mS / m or less, yielding 0.55 kg of dried silver powder.

[0109] The silver powder obtained in Example 2 was subjected to the same pulverization treatment as in Example 1. Table 3 shows the measurement results for the silver powder in Example 2. Graphs of the thermomechanical analysis of the silver powder in Example 2 are shown in Figures 3 and 4. An SEM photograph (20,000x magnification) is shown in Figure 6.

[0110] Example 3 A 0.160 mol / L aqueous silver nitrate solution was introduced into tube 2 (inner diameter 20 mm) at a flow rate of 23.35 L / min at a liquid temperature of 50°C. A 0.024 mol / L aqueous nitric acid solution was introduced into coaxial double tube pH adjuster supply tube 7 (inner diameter 6 mm) at a flow rate of 2.13 L / min to adjust the pH. A 4.436 mol / L aqueous ammonia solution was introduced into tube 2 at a flow rate of 2.33 L / min from coaxial double tube complexing agent supply tube 6 (inner diameter 6 mm). A silver ammine complex was produced in tube 2. A surface treatment agent (0.10 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 from a surface treatment agent supply pipe 5 (inner diameter 6 mm) upstream of the reducing agent adding member 10. The amount of the silver nitrate aqueous solution was such that the silver concentration in the total liquid volume after adding the pH adjuster, complexing agent, reducing agent, and surface treatment agent would be 0.115 mol / L. A 0.50 mol / L aqueous hydrazine solution was introduced at a flow rate of 2.55 L / min around the entire periphery of the slit portion (slit width 0.44 mm, tube inner diameter 20.6 mm) of the reducing agent addition member 10, and silver powder was precipitated. The flow rate of the reducing agent entering through the 0.44 mm slit portion was 1.49 m / sec, and the flow rate of the silver ammine complex just before the addition of the reducing agent at the 20.6 mm inner diameter tube 2 where the reducing agent entered was 1.50 m / sec (calculated from the combined flow rates of the silver nitrate aqueous solution, nitric acid aqueous solution, and ammonia aqueous solution). 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 introduction of the reducing agent into the silver ammine complex after the flow of the silver ammine complex into which the surface treatment agent had been introduced stabilized) was 617 seconds. The slurry produced before the flow of the silver ammine complex containing the surface treatment agent stabilized was received in a separate container and was not subjected to solid-liquid separation or subsequent steps. In the above process, it took 0.5 seconds from the 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 aqueous solution addition position, 2.12 seconds (2.1 m) from the ammonia aqueous solution addition position to the hydrazine aqueous solution addition position, and 0.12 seconds from the surface treatment agent addition position to the hydrazine aqueous solution addition position. 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 tube 2. The time from the addition of the aqueous hydrazine solution to the discharge was approximately 2 seconds. After the reduction reaction stabilized, the silver powder-containing slurry was recovered, and the solid matter obtained by solid-liquid separation was washed with pure water to remove impurities. The end point of this washing could be determined by the electrical conductivity of the water after washing. Washing was continued until the electrical conductivity reached 0.5 mS / m or less, yielding 3.6 kg of dried silver powder.

[0112] The silver powder obtained in Example 3 was subjected to the same pulverization treatment as in Example 1. Table 3 shows the measurement results for the silver powder according to Example 3. Graphs of the thermomechanical analysis of the silver powder according to Example 3 are shown in Figures 3 and 4. An SEM photograph (20,000x magnification) is shown in Figure 7.

[0113] Example 4 A 0.160 mol / L aqueous silver nitrate solution was introduced into tube 2 (inner diameter 20 mm) at a flow rate of 27.24 L / min at a liquid temperature of 50°C. A 0.024 mol / L aqueous nitric acid solution was introduced into coaxial double tube pH adjuster supply tube 7 (inner diameter 6 mm) at a flow rate of 2.49 L / min to adjust the pH. A 4.436 mol / L aqueous ammonia solution was introduced into coaxial double tube complexing agent supply tube 6 (inner diameter 6 mm) at a flow rate of 2.72 L / min to generate a silver ammine complex in tube 2. A surface treatment agent (0.10 mass % Cellosol 920 (manufactured by Chukyo Yushi Co., Ltd., containing 15.5 wt % stearic acid) was introduced at a flow rate of 2.55 L / min from a surface treatment agent supply pipe 5 (inner diameter 6 mm) upstream of the reducing agent adding member 10. The amount of the silver nitrate aqueous solution was such that the silver concentration in the total liquid volume after adding the pH adjuster, complexing agent, reducing agent, and surface treatment agent would be 0.115 mol / L. A 0.50 mol / L hydrazine aqueous solution was introduced at a flow rate of 2.97 L / min around the entire circumference of the slit portion (slit width 0.44 mm, tube inner diameter 20.6 mm) of the reducing agent addition member 10, and silver powder was precipitated. The flow rate of the reducing agent entering through the 0.44 mm slit portion was 1.74 m / sec, and the flow rate of the silver ammine complex just before the addition of the reducing agent at the 20.6 mm inner diameter tube 2 where the reducing agent entered was 1.75 m / sec. The ratio of the complex flow rate to the reducing agent flow rate (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 introduction of the reducing agent to the silver ammine complex after the flow of the silver ammine complex into which the surface treatment agent had been introduced stabilized) was 568 seconds. The slurry generated before the flow of the silver ammine complex into which the surface treatment agent had been introduced stabilized was received in a separate container and was not subjected to solid-liquid separation or subsequent processes. In the above, it took 0.43 seconds from the inlet of the silver nitrate aqueous solution flow path 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, and 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 of the hydrazine aqueous solution to the discharge was approximately 1.7 seconds. After the reduction reaction had stabilized, the silver powder-containing slurry was recovered, and the solid obtained by solid-liquid separation was washed with pure water to remove impurities. The end point of this washing could be determined by the electrical conductivity of the water after washing. Washing was continued until the electrical conductivity reached 0.5 mS / m or less, yielding 3.2 kg of dried silver powder.

[0115] The silver powder obtained in Example 4 was subjected to the same pulverization treatment as in Example 1. Table 3 shows the measurement results for the silver powder according to Example 4. Graphs of the thermomechanical analysis of the silver powder according to Example 4 are shown in Figures 3 and 4. An SEM photograph (20,000x magnification) is shown in Figure 8.

[0116] Example 5 A 0.070 mol / L aqueous silver nitrate solution was introduced into tube 2 (inner diameter 20 mm) at a flow rate of 23.35 L / min at a liquid temperature of 50°C. A 0.016 mol / L aqueous sodium carbonate solution was introduced into tube 2 (inner diameter 20 mm) at a flow rate of 2.13 L / min through coaxial double tube pH adjuster supply tube 7 (inner diameter 6 mm) to adjust the pH. 3.773 mol / L aqueous ammonia as a complexing agent was introduced into tube 2 (inner diameter 6 mm) at a flow rate of 2.33 L / min as a complexing agent. A silver ammine complex was generated in tube 2. 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 from a surface treatment agent supply pipe 5 (inner diameter 6 mm) upstream of the reducing agent addition member 10. The amount of the aqueous silver nitrate solution was such that the silver concentration in the total liquid volume after adding the pH adjuster, complexing agent, reducing agent, and surface treatment agent would be 0.050 mol / L. A 0.240 mol / L aqueous solution of hydrazine carbonate 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, tube inner diameter 20.6 mm) of the reducing agent addition member 10, and silver powder was precipitated. The flow rate of the reducing agent entering through the slit portion with a slit width of 0.44 mm was 1.49 m / sec. The flow rate of the silver ammine complex just before the addition of the reducing agent at the tube 2 with an inner diameter of 20.6 mm where the reducing agent entered was 1.50 m / sec. 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 introduction of the reducing agent to the silver ammine complex after the flow of the silver ammine complex into which the surface treatment agent had been introduced stabilized) was 83 seconds. The slurry generated before the flow of the silver ammine complex into which the surface treatment agent had been introduced stabilized was received in a separate container and was not subjected to solid-liquid separation or subsequent processes. In the above, it took 0.5 seconds from the inlet of the silver nitrate aqueous solution flow path to the position where the aqueous sodium carbonate solution was added, 0.5 seconds from the position where the aqueous sodium carbonate solution was added to the position where the aqueous ammonia solution was added, 2.12 seconds (2.1 m) from the position where the aqueous ammonia solution was added to the position where the aqueous hydrazine carbonate solution was added, and 0.12 seconds from the position where the surface treatment agent was added to the position where the aqueous hydrazine carbonate solution was added. The temperature of the aqueous silver ammine complex solution immediately before the position where the aqueous hydrazine carbonate solution was added was 46.5°C.

[0117] The silver powder-containing slurry was discharged from tube 2. The time from the addition of the aqueous hydrazine carbonate solution to the discharge was approximately 2 seconds. After the reduction reaction stabilized, the silver powder-containing slurry was recovered, and the solid matter obtained by solid-liquid separation was washed with pure water to remove impurities. The end point of this washing could be determined by the electrical conductivity of the water after washing. The washing was continued until the electrical conductivity reached 0.5 mS / m or less, and then dried to obtain 0.24 kg of silver powder.

[0118] The silver powder obtained in Example 5 was subjected to the same pulverization treatment as in Example 1. Table 3 shows the measurement results for the silver powder according to Example 5. Graphs of the thermomechanical analysis of the silver powder according to Example 5 are shown in Figures 3 and 4. An SEM photograph (20,000x magnification) is shown in Figure 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 used as a complexing agent was 3.144 mol / L and the operating time was 85 seconds. The obtained silver powder weighed 0.25 kg. The silver powder obtained in Example 6 was subjected to the same pulverization treatment as in Example 1. Measurement results for the silver powder according to Example 6 are shown in Table 3. Graphs of thermomechanical analysis of the silver powder according to Example 6 are shown in Figures 3 and 4. An SEM photograph (20,000x magnification) is shown in Figure 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 used as a complexing agent was 3.041 mol / L and the operating time was 84 seconds. The obtained silver powder weighed 0.25 kg. The silver powder obtained in Example 7 was subjected to the same pulverization treatment as in Example 1. Measurement results for the silver powder according to Example 7 are shown in Table 3. Graphs of thermomechanical analysis of the silver powder according to Example 7 are shown in Figures 3 and 4. An SEM photograph (20,000x magnification) is shown in Figure 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 used as a complexing agent was 2.728 mol / L and the operating time was 84 seconds. The obtained silver powder weighed 0.25 kg. The silver powder obtained in Example 8 was subjected to the same pulverization treatment as in Example 1. Measurement results for the silver powder according to Example 8 are shown in Table 3. Graphs of thermomechanical analysis of the silver powder according to Example 8 are shown in Figures 3 and 4. An SEM photograph (20,000x magnification) is shown in Figure 12.

[0122] Comparative Example 1: 124.65 g of 28% by mass industrial ammonia water (corresponding to 5.4 molar equivalents of ammonia per mole of silver) was added to 3,233.4 g of a silver nitrate aqueous solution containing 40.99 g (0.38 mol) of silver to obtain a silver ammine complex aqueous solution. 2.28 g of a 20% by mass sodium hydroxide aqueous solution was added to this silver ammine complex aqueous solution, and the liquid temperature was adjusted to 25°C. 111.17 g of a 7.3% by mass hydrazine aqueous solution was then added with stirring to obtain a silver particle-containing slurry. Furthermore, 12.69 g of a 1.55% by mass stearic acid emulsion was added to the obtained silver particle-containing slurry and stirred. Stirring was then stopped to allow the silver particles to settle, and the liquid containing the precipitated silver particles was filtered, washed with water until the electrical conductivity of the liquid after passing through the 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 milled twice for 90 seconds using a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) in an amount of 120 g, to obtain the silver powder according to Comparative Example 1.

[0124] The measurement results for the silver powder according to Comparative Example 1 are shown in Table 3. Graphs of the thermomechanical analysis of the silver powder according to Comparative Example 1 are shown in Figures 3 and 4. An SEM photograph (20,000x magnification) is shown in Figure 13.

[0125] Comparative Example 2: 3.3 g of 60% by weight nitric acid aqueous solution was added to 3,374.7 g of a silver nitrate aqueous solution containing 45.32 g (0.42 mol) of silver. 76.5 g of 28% by weight industrial ammonia water (corresponding to 3 molar equivalents of ammonia per mole of silver) was then added to obtain a silver ammine complex aqueous solution. The liquid temperature of this silver ammine complex aqueous solution was adjusted to 35°C. Subsequently, while stirring, 20.57 g of a 1.1% by weight aqueous solution of benzotriazole sodium was added as an azole (0.5% by weight of benzotriazole sodium added relative to silver) to obtain a first solution. Subsequently, 142.7 g of a 5.6% by weight aqueous solution of hydrazine was added as a reducing agent to the first solution to obtain a slurry containing silver fine particles as a second solution. Furthermore, 17.54 g of a 1.55% by weight stearic acid emulsion was added to the second solution and stirred. Thereafter, stirring was stopped to allow the silver particles to settle, and the liquid in which the silver particles had precipitated was filtered, washed with water until the electrical conductivity of the liquid after passing the water was 0.5 mS / m or less, and then dried in a vacuum at 73°C.

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

[0127] The measurement results for the silver powder according to Comparative Example 2 are shown in Table 3. Graphs of the thermomechanical analysis of the silver powder according to Comparative Example 1 are shown in Figures 3 and 4. An SEM photograph (20,000x magnification) is shown in Figure 14.

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

[0129]

[0130]

[0131]

[0132] (Paste Evaluation) <Disconnection Rate and Volume Resistivity> First, resin-curing conductive pastes were prepared using the silver powders obtained in Examples 1, 5, and 7 and Comparative Examples 1 and 2. Specifically, the silver powders to be evaluated and AG-5-54F (D) manufactured by DOWA Electronics, which was used as a filler together with the silver powder to be evaluated, were used.５０ : :. ２ g、\P\:!.｢cm ３) were mixed in a mass ratio of 5:5 to obtain a mixed silver powder. 91.92 parts by mass of the mixed silver powder, 3.87 parts by mass of a first epoxy resin (EP4901E manufactured by ADEKA), 0.97 parts by mass of a second epoxy resin (JER1009 manufactured by Mitsubishi Chemical Corporation), 0.24 parts by mass of a curing agent (boron trifluoride monoethylamine complex manufactured by Wako Pure Chemical Industries, Ltd.), and 3.00 parts by mass of a solvent (BCA: butyl carbitol acetate) were separated and charged into a propellerless rotary and revolutionary stirring and degassing apparatus (VMX-N360 manufactured by EME Corporation) and mixed at 1200 rpm for 30 seconds. After that, the mixture was kneaded by passing it through a three-roll mill (80S manufactured by EXAKT Co., Ltd.) with a roll gap of 100 μm to 20 μm, to obtain a resin-curing conductive paste before viscosity adjustment. Furthermore, the required amount of BCA was added to the resin-curing conductive paste before viscosity adjustment to obtain a viscosity-adjusted conductive paste with a viscosity of 300 Pa·s. The viscosity of the resin-curing conductive paste was adjusted by gradually adding BCA to the resin-curing conductive paste before viscosity adjustment and measuring the viscosity. Using the obtained resin-curing conductive paste, 10 lines each with line widths (design widths) of 15 μm, 17 μm, 19 μm, and 21 μm were prepared using a screen printing plate (#480 mesh) and evaluated. The squeegee speed during printing was 350 mm / sec, and printing was performed twice. The conductive film was then 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 line-shaped conductive film (wiring). The wire breakage rate and volume resistivity of the obtained conductive film were measured. Measurement terminals were attached to both ends of the conductive film, and the line resistance (Ω) was measured using a digital multimeter (manufactured by ADC Corporation). The line resistance value was the average value of 20 line patterns (10 lines printed twice) (excluding those considered to be broken, as described below). The breakage rate was the percentage of broken lines among all 20 line patterns, assuming that a very high measured value of 100 kΩ or more was considered to be a break when measuring the line resistance. In addition, the shape of the wiring in the line width direction was measured at 10 locations (5 locations printed twice) using a laser microscope (Keyence Corporation, VK-X1000), and the average 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 was calculated using the following formula (4): Volume resistivity [Ω·cm] = Line resistance [Ω] × Cross-sectional area [cm. ２ ]÷line length [cm] (4) The volume resistivity (Ω·cm) was calculated for line widths (design widths) of 15 μm and 19 μm. Note that the line length (design length) in measuring the line resistance was 150 mm.

[0133]

[0134] As is clear from Table 4, the cumulative 50% diameter D ５０ is 0.1 μm or more and 1.0 μm or less, and D ＢＥＴ D against ５０ The silver powder according to this example, in which the ratio of 1.3 or less and the shrinkage rate at 200°C in thermomechanical analysis is 1% or more, exhibits low volume resistivity and low rate of breakage in the thin wires when fired at a low temperature of 200°C, and therefore can impart excellent volume resistivity and thin wire printability to the conductive paste.

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

[0136] REFERENCE SIGNS LIST 1 Silver powder manufacturing device 2 Pipe 4a Reducing agent supply pipe 4b Reducing agent supply pipe 5 Surface treatment agent supply pipe 6 Complexing agent supply pipe 7 pH adjuster supply pipe 10 Reducing agent addition member 11 Opening 12 Slit portion 13 Gap

Claims

1. Cumulative 50% diameter D based on volume measured by laser diffraction method ５０ is 0.1 μm or more and 1.0 μm or less, and the BET diameter D ＢＥＴ The above D ５０ and a shrinkage rate at 200°C in thermomechanical analysis of 1% or more.

2. The silver powder according to claim 1, which has a shrinkage rate of 0.6% or more at 150°C in thermomechanical analysis.

3. BET specific surface area is 0.90m ２ / g or more 2.50m ２ The silver powder according to claim 1, wherein the silver content is 0.01 to 0.15 wt %.

4. The silver powder according to any one of claims 1 to 3, which is used in a resin-curing type conductive paste.

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 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.

6. A method for producing silver powder as described in claim 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 seconds or more and 10 seconds or less.

7. A method for producing silver powder as described in claim 5, 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.

8. 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 nitric acid addition section and the complexing agent addition section.

9. A resin-curing conductive paste containing the silver powder according to any one of claims 1 to 3.

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