Silver powder, method for producing silver powder, and conductive paste

Abstract

The purpose of the present invention is to provide: a silver powder capable of producing a conductive paste capable of obtaining a wiring pattern having a high ratio (aspect ratio) of height to line width; and a method for producing the silver powder. The silver powder of the present invention has closed voids in silver particles, and the value of Sa / BET diameter, which is obtained by dividing the arithmetic mean roughness Sa (nm) of the surface of the silver particles by the BET diameter calculated by BET diameter = 6 / (specific surface area * true density) using the values of the specific surface area (m2 / g) and true density measured by the BET1 point method, is 0.0070 or more. A method for producing silver powder according to the present invention comprises: a crushing step for crushing aggregated silver powder using an air-flow crusher; in the crushing step, compressed air having a temperature of 80-180 DEG C is supplied as supply air to the air-flow type crusher, and in the classification step, the compressed air having a temperature of 80-180 DEG C is supplied as supply air to the air-flow type crusher, the compressed air having a temperature of 80-180 DEG C is supplied as supply air to the air-flow type crusher, and in the classification step, the compressed air having a temperature of 80-180 DEG C is supplied as supply air to the air-flow type crusher. The exhaust temperature of the exhaust gas is 30 DEG C or higher and the volume absolute humidity is 20 g / m < 3 > or higher, and the silver powder after the crushing step is supplied to a wind classifier.

Description

Technical Field

[0001] This invention relates to silver powder, a method for manufacturing silver powder, and a conductive paste. Background Technology

[0002] Patent Document 1 describes silver powder and a method for manufacturing silver powder. In this method, a reducing agent is added to an aqueous reaction system containing silver ions to precipitate silver particles. The aqueous reaction system is then filtered to obtain a filter cake, which is dried using an airflow drying device to obtain silver powder.

[0003] Patent document 2 describes a method for manufacturing silver particles. In this method, alcohol is added to a slurry of silver particles with an average particle size of submicron, and the mixture is stirred. The particles are then filtered, dehydrated, dried, and crushed. In this method, the drying process can be either hot air drying or vacuum drying. In hot air drying, the filtered material is placed under hot air at 30-100°C.

[0004] Patent document 3 describes silver powder and its manufacturing method. In this method, a reducing agent is added to an aqueous reaction system containing silver ions to reduce and precipitate silver particles. The resulting silver-containing slurry is filtered, washed with water, and the resulting filter cake is dehydrated at room temperature, crushed at room temperature to form crushed powder, and graded at room temperature to obtain silver powder.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2008-1974

[0008] Patent Document 2: Japanese Patent Application Publication No. 2010-229481

[0009] Patent Document 3: Japanese Patent Application Publication No. 2016-216824 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] Wiring and / or contacts of electronic components manufactured by coating a conductive paste (hereinafter sometimes abbreviated as "paste") are obtained by applying the paste through printing or other methods and then heating it. During the application and heating of the paste, a wiring pattern with desired line width and height is desired. In electronic components, to maximize the area excluding the wiring portion and / or to miniaturize the electronic component, finer wiring lines and higher wiring heights are desired, such that even with thinner wiring, the resistivity does not become excessively high.

[0012] The object of the present invention is to provide silver powder capable of preparing conductive pastes that yield wiring patterns with a high height-to-width ratio (hereinafter, sometimes referred to as "aspect ratio"), a method for manufacturing silver powder, and conductive pastes comprising the silver powder.

[0013] Solution for solving the problem

[0014] The silver powder and method for manufacturing the silver powder of the present invention, and the conductive paste comprising the silver powder, for achieving the above-mentioned objectives are described below.

[0015] <1> A type of silver powder, which has closed pores within silver particles.

[0016] The arithmetic mean roughness Sa (nm) of the surface roughness measurement in the 500nm × 500nm range of the above-mentioned silver particles, divided by the BET diameter, has a value of Sa / BET diameter of 0.0070 or higher.

[0017] The BET diameter mentioned above uses the specific surface area (m²) determined by the BET1 point method. 2 The values ​​of / g) and true density are calculated by the following formula (1),

[0018] BET diameter = 6 / (specific surface area × true density) ... Equation (1).

[0019] <2> According to the above <1> The silver powder wherein the arithmetic mean roughness Sa is greater than 5 nm and less than 15 nm.

[0020] <3> According to the above <1> or <2> The silver powder, wherein,

[0021] In the volume-based particle size distribution determined by laser diffraction particle size distribution measurement, the cumulative 10% particle size (μm), cumulative 50% particle size (μm), and cumulative 90% particle size (μm) accumulated from the side with the smallest particle size are set as D10, D50, and D90, respectively.

[0022] The difference obtained by subtracting D10 from D90 and dividing it by D50 is less than 1.0.

[0023] <4> A method for manufacturing silver powder, comprising:

[0024] The crushing process involves using an airflow mill to crush the aggregated silver powder; and

[0025] In the grading process, an air classifier is used to classify the silver powder after the above crushing process.

[0026] The moisture content of the aforementioned aggregated silver powder is above 5.0 wt% and below 30.0 wt%.

[0027] In the above-mentioned crushing process, compressed air with a temperature of 80°C or higher and 180°C is supplied to the airflow pulverizer as feed air, and the concentration of silver powder in the airflow is 0.10 kg / m³. 3 Above and 0.50 kg / m 3 The above-mentioned aggregated silver powder is supplied in the following manner.

[0028] In the above-mentioned grading process, the exhaust gas from the airflow pulverizer and the silver powder from the crushing process are supplied to the air classifier.

[0029] The exhaust temperature is above 30℃ and the absolute humidity is 20g / m³. 3 above.

[0030] <5> According to the above <4> The method for manufacturing silver powder involves connecting the air classifier and the airflow pulverizer via a connecting pipe, through which the exhaust gas from the airflow pulverizer and the silver powder after the crushing process are supplied from the airflow pulverizer to the air classifier.

[0031] <6> According to the above <4> or <5> The method for manufacturing silver powder further includes:

[0032] The collection process involves using a collection machine to collect the silver powder remaining after the grading process described above.

[0033] In the above-mentioned collection process, the exhaust gas from the wind classifier and the silver powder after the classification process are supplied to the collection machine.

[0034] <7> According to the above <4> ~ <6> The method for manufacturing silver powder according to any one of the above-mentioned methods, wherein, in the above-mentioned grading process, grading is performed while the above-mentioned wind classifier draws in external air.

[0035] <8> A conductive paste comprising the above <1> ~ <3> The silver powder as described in any one of the following.

[0036] The effects of the invention

[0037] A method for manufacturing silver powder capable of preparing wiring patterns with a high height-to-width ratio (height-to-width ratio) can be provided, as well as the silver powder itself. Attached Figure Description

[0038] Figure 1 This is a flowchart of a complete set of equipment for implementing the silver powder manufacturing method of this embodiment.

[0039] Figure 2 This is an SEM image of the silver powder from Example 1.

[0040] Figure 3 This is an SEM image of the silver powder from Example 2.

[0041] Figure 4 This is an SEM image of the silver powder from Example 3.

[0042] Figure 5 This is an SEM image of the silver powder from Example 4.

[0043] Figure 6 This is a SEM image of the silver powder from Comparative Example 1.

[0044] Figure 7 This is a SEM image of the silver powder from Comparative Example 2.

[0045] Figure 8 This is a SEM image of the silver powder from Comparative Example 3.

[0046] Figure 9 This is a SEM image of the silver powder from Comparative Example 4.

[0047] Figure 10 It is a diagram showing the shape of the wiring pattern used for fine line evaluation. Detailed Implementation

[0048] The silver powder of the present invention will be described below.

[0049] The silver powder of the present invention has closed voids within the silver particles, and the arithmetic mean roughness Sa (nm) of the surface roughness measurement in a 500nm × 500nm range of the silver particle surface, divided by the BET diameter, has a Sa / BET diameter value of 0.0070 or higher. This BET diameter is determined using the specific surface area (m²) measured by the BET1-point method. 2 The values ​​of (g) and true density are calculated by the following formula (1).

[0050] BET diameter = 6 / (specific surface area × true density) ... Equation (1)

[0051] First, the silver particles constituting the silver powder of the present invention, by having closed voids within the silver particles, can reduce the firing temperature required to obtain wiring patterns. Because of the closed voids within the silver particles, the true density of the silver powder of the present invention is less than the density of silver (10.49 g / cm³). 3 ), at 9.0~10.0 g / cm³ 3 Within the range, for example, 9.7 g / cm³. 3 In this specification, true density refers to the value measured using a true density measuring device, such as the Micromeritics AccuPycII 1340. It can measure the density excluding voids on the particle surface leading to the outside, and can also measure the density including closed voids within the particle.

[0052] Furthermore, the value of Sa / BET diameter, obtained by dividing the arithmetic mean roughness Sa (nm) of the surface roughness measurement in the 500nm × 500nm range of the silver particles constituting the silver powder by the BET diameter, is 0.0070 or more, preferably 0.009 or more, and preferably 0.015 or less. By setting this range, when the silver powder is pasted using the method of the embodiments described later to obtain a conductive paste with the same viscosity (approximately ±20 Pa·s at 1 rpm) regardless of the BET diameter, the aspect ratio of the wiring pattern obtained by firing the conductive paste using the method of the embodiments described later can be improved compared to the prior art. When the BET diameter is small (large specific surface area), the number of collisions between particles during the crushing process is high, making surface smoothing easier and tending to reduce the arithmetic mean roughness Sa. In the manufacturing method of the present invention, the smoothing and re-adhesion are different from those in the past, so silver powder with an uneven surface within the above range can be produced regardless of the BET diameter.

[0053] It should be noted that, for example, in the silver powder manufacturing method of the present invention described later, the silver powder supplied as raw material for the drying and crushing processes is silver powder containing moisture and agglomerated in a moist state (agglomerated silver powder). When using this agglomerated silver powder to manufacture silver powder with less agglomeration, for example, compressed air at a temperature of 80°C or higher and 180°C or lower is supplied as supply air to an airflow pulverizer for a crushing process (i.e., drying and crushing are performed simultaneously). Then, the silver powder is obtained by classification in a humid airflow, thereby setting the Sa / BET diameter value of the obtained silver powder to 0.0070 or higher. On the other hand, it is difficult to set the Sa / BET diameter value of silver powder obtained by drying the aforementioned agglomerated silver powder to a dry state and then crushing and classifying it. Therefore, generally, when using the same agglomerated silver powder as raw material, the silver powder that can be obtained by the silver powder manufacturing method of the present invention described later can set the Sa / BET diameter value to 0.0070 or higher, which can improve the height-to-width ratio (height-to-width ratio) of the wiring pattern obtained by gelatinization and firing.

[0054] The surface roughness of the silver particles constituting the silver powder over a 500 nm × 500 nm area can be measured using a scanning probe microscope (e.g., the SII NanoTechnology Nano Cute), and the arithmetic mean roughness Sa (nm) is the arithmetic mean roughness specified in ISO 25178. The arithmetic mean roughness Sa (nm) is preferably 5 nm or more, more preferably 7 nm or more, and more preferably 15 nm or less. The arithmetic mean roughness Sa (nm) of the silver powder that has been crushed and graded in a humid atmosphere in this invention is greater than that of the conventional case where crushing and grading are performed in a dry atmosphere.

[0055] The BET diameter (μm) of the silver powder is preferably 0.30 μm or more, more preferably 0.50 μm or more, preferably 3.00 μm or less, more preferably 1.50 μm or less, even more preferably 1.00 μm or less, and even more preferably 0.90 μm or less.

[0056] Specific surface area of ​​silver powder (m²) 2 The specific surface area ( / g) is the BET surface area determined by the BET method. For example, a BET surface area measuring apparatus (Macsorb HM-1210 manufactured by Mounttech Co., Ltd.) can be used. After degassing with a He-N2 mixed gas (30% nitrogen) flowing through the apparatus at 60°C for 10 minutes, the surface area is measured using the BET 1-point method. The specific surface area of ​​the silver powder, which has been crushed and graded in a humid atmosphere according to this invention, measured using the BET 1-point method, is larger than that obtained in conventional cases where the powder has been crushed and graded in a dry atmosphere; preferably, it is 0.3 m². 2 / g or more, preferably 0.55m 2 / g or more, further preferably 0.70m 2 / g or more, preferably 1.0m 2 / g or less. Furthermore, the preferred BET specific surface area is 1.00 m². 2 / g or less.

[0057] In the volume-based particle size distribution of the silver powder measured by laser diffraction, the cumulative 10% particle size (μm), 50% particle size (μm), and 90% particle size (μm) accumulated from the side with the smallest particle size are set as D10, D50, and D90, respectively. The value obtained by dividing the difference between D90 and D10 by D50 is preferably 1.0 or less, more preferably 0.85 or less, and even more preferably 0.75 or less. When this value exceeds 1.0, it is sometimes difficult to obtain the desired linewidth and height wiring pattern for wiring patterns obtained by gelatinizing and firing the silver powder.

[0058] Furthermore, it is preferable that the difference obtained by subtracting D10 from D90 and dividing it by D50 is 1.00 or less.

[0059] The D50 of the silver powder is preferably 0.4 μm or more, more preferably 0.8 μm or more, preferably 4.0 μm or less, more preferably 2.5 μm or less, even more preferably 1.6 μm or less, and even more preferably 1.35 μm or less. If the D50 of the silver powder exceeds 4.0 μm, it is sometimes difficult to obtain fine-width wiring patterns. When the D50 of the silver powder is less than 0.4 μm, the viscosity of the paste becomes too high during gelatinization, sometimes making it difficult to handle.

[0060] Furthermore, the D50 of the silver powder is preferably 0.40 μm or more, more preferably 0.80 μm or more, preferably 4.00 μm or less, more preferably 2.50 μm or less, and even more preferably 1.60 μm or less.

[0061] The D10 of the silver powder is preferably 0.1 μm or more, more preferably 0.3 μm or more, preferably 1.5 μm or less, more preferably 0.90 μm or less, and even more preferably 0.86 μm or less. If the D10 of the silver powder exceeds 1.5 μm, it is sometimes difficult to obtain fine-width wiring patterns. When the D10 of the silver powder is less than 0.1 μm, the viscosity of the paste becomes too high during gelatinization, sometimes making it difficult to handle.

[0062] Furthermore, the D10 of the silver powder is preferably 0.10 μm or more, more preferably 0.30 μm or more, and more preferably 1.50 μm or less.

[0063] The D90 of the silver powder is preferably 0.9 μm or more, more preferably 1.3 μm or more, preferably 8.0 μm or less, more preferably 5.0 μm or less, even more preferably 2.5 μm or less, and even more preferably 1.9 μm or less. If the D90 of the silver powder exceeds 8.0 μm, it is sometimes difficult to obtain fine-width wiring patterns. When the D90 of the silver powder is less than 0.9 μm, the viscosity of the paste becomes too high during gelatinization, sometimes making it difficult to handle.

[0064] Furthermore, the TAP (g / mL) of the silver powder of the present invention is the tap density. The tap density of the silver powder can be measured, for example, using a tap density measuring device (SS-DA-2, a bulk density measuring device manufactured by Shibayama Scientific Co., Ltd.). The TAP density is preferably 3.0 g / mL or more, more preferably 4.5 g / mL or more, even more preferably 4.8 g / mL or more, and preferably 6.5 g / mL or less. When the TAP density is less than 3.0 g / mL, the silver powder is in an aggregated state, and fine line printing is sometimes impossible during gelatinization. In addition, if the TAP density is 4.8 g / mL or more, the wiring pattern becomes dense, which is therefore preferred.

[0065] Furthermore, the loss on ignition (Ig-loss) (%) of the silver powder of the present invention is a value calculated based on the mass (w) of the heated silver powder using the following formula (2). The Ig-loss of the silver powder of the present invention represents the amount of dispersant, preferably 0.40% or more, more preferably 0.70% or more, even more preferably 0.80% or more, preferably 1.50% or less, and more preferably 1.10% or less. When the Ig-loss is less than 0.40%, the effect of sufficiently dispersing the silver powder may not be achieved. Additionally, when the Ig-loss is greater than 1.50%, impurities may remain in the electrode after the silver powder is sintered, causing a deterioration in resistance.

[0066] Loss on ignition (%) = (3-w) / 3×100…Equation (2)

[0067] Furthermore, the moisture content (%) of the silver powder indicates the moisture content of the silver powder obtained after the grading process. It is calculated by multiplying the weight of the dried sample by the weight of the undried sample by 100. The silver powder obtained after the grading process is dried, and its moisture content is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and even more preferably 0.01% by mass or less. If the silver powder is not dried and the moisture content exceeds 0.1% by mass, the silver powder may aggregate during storage and / or in the paste, leading to increased viscosity, and / or the aggregation of silver powder may produce coarse particles, causing printing plate blockage and line breakage.

[0068] Next, refer to the implementation Figure 1 The process flow of the complete set of equipment 100 for manufacturing silver powder according to this embodiment is shown, and the manufacturing method capable of manufacturing the silver powder of the present invention is described.

[0069] The method for manufacturing silver powder according to an embodiment of the present invention includes: a crushing step, in which aggregated silver powder is crushed using an air-jet mill; and a grading step, in which the silver powder after the crushing step is graded using an air classifier. Here, the moisture content of the aggregated silver powder is 5.0 wt% or more and 30.0 wt% or less. Furthermore, in the crushing step, compressed air at a temperature of 80°C or higher and 180°C is supplied to the air-jet mill as feed air, and the concentration of silver powder in the airflow is 0.10 kg / m³. 3 Above and 0.50 kg / m 3 The silver powder is supplied in the following manner. In the classification process, the exhaust gas from the air classifier and the silver powder after the crushing process are supplied to the air classifier. The exhaust gas temperature is above 30°C and the volumetric relative humidity is 20 g / m³. 3 above.

[0070] In the complete set of equipment 100, silver powder containing moisture and agglomerated in a wet state, and silver powder with an uneven surface on the silver particles constituting the silver powder (hereinafter referred to as agglomerated silver powder) is supplied as raw material. This agglomerated silver powder can be manufactured, for example, by a wet reduction method. In the complete set of equipment 100, the agglomerated silver powder is crushed, dried, graded, and collected to produce silver powder suitable for preparing conductive pastes. The silver powder produced by the complete set of equipment 100 retains to some extent the surface shape of the silver particles in the agglomerated silver powder. According to the present invention, the silver powder produced by the complete set of equipment 100 can be smoother than the surface of the silver particles in the agglomerated silver powder, and has a desired unevenness on the surface of the silver particles.

[0071] Aggregated silver powder, as a raw material, can be manufactured using the following wet reduction method, as an example. The wet reduction method can be as follows: An alkali or complexing agent is added to an aqueous solution containing silver salts to generate a slurry containing silver oxide or an aqueous solution containing silver complex salts. Then, a reducing agent such as formalin is added to reduce and precipitate the silver powder. Alternatively, it can be manufactured by adding sodium hydroxide to the slurry containing silver oxide or the aqueous solution containing silver complex salts to adjust the pH. Hereinafter, these methods will be referred to as the wet reduction method. Additionally, silver particles are sometimes simply referred to as particles. It should be noted that silver powder refers to powdered silver, which is an aggregate of silver particles.

[0072] In the wet reduction method, it is preferable to prevent the aggregation of silver particles to obtain monodisperse silver powder. To obtain monodisperse silver powder, the wet reduction method may include treatment of adding a dispersant to the reduced silver paste, or treatment of adding a dispersant to an aqueous reaction system containing at least one of silver salt and silver oxide before the silver particles are reduced and precipitated. As a dispersant, one or more selected from fatty acids, fatty acid salts, surfactants, organic acids such as amino acids, organometallic compounds, chelating agents, and protective colloids can be used. To obtain dry silver powder from the above-mentioned silver paste, a solid-liquid separation process such as pressure filtration and a drying process are required. Even when the silver particles in the silver paste precipitated by the wet reduction method are monodisperse, the silver powder obtained immediately after the solid-liquid separation process such as pressure filtration, and / or the silver powder dried without breaking the filter cake after the solid-liquid separation process, may aggregate; this is referred to as aggregated silver powder in this specification.

[0073] The complete set of equipment 100 includes a feeder 1, an airflow pulverizer 2 (hereinafter referred to as pulverizer 2), an air classifier 3 (hereinafter referred to as classifier 3), a cyclone separator 4 as a collector, a dust collector 5, and a blower 6. Furthermore, the silver powder manufacturing method of this embodiment includes: a crushing step, in which the pulverizer 2 is used to crush the aggregated silver powder; and a grading step, in which the classifier 3 is used to grade the silver powder after the crushing step.

[0074] In the complete set of equipment 100, the pulverizer 2, classifier 3, cyclone separator 4, dust collector 5, and blower 6 are connected in series. The airflow passing through the pulverizer 2, classifier 3, cyclone separator 4, and dust collector 5 is drawn in by the blower 6. Silver powder is preferably conveyed via airflow between the pulverizer 2 and classifier 3, the classifier 3 and cyclone separator 4, and the cyclone separator 4 and dust collector 5.

[0075] The feeder 1 is a device that supplies aggregated silver powder to the pulverizer 2. The feeder 1 can be, for example, a screw feeder. Aggregated silver powder in a partially dried state, obtained through a solid-liquid separation process such as pressure filtration by wet reduction, is fed into the feeder 1. The moisture content of the aggregated silver powder is 5.0 wt% (mass %) or more, preferably 12.0 wt% or more, 30.0 wt% or less, preferably 20.0 wt% or less, and more preferably 15.0 wt% or less.

[0076] Crusher 2 is a device for crushing aggregated silver powder. In crusher 2, the aggregated silver powder is crushed by supplying aggregated silver powder and compressed air into its internal space. During the crushing process, compressed air at a temperature above 80°C and below 180°C is supplied to crusher 2 as feed air, resulting in a silver powder concentration of 0.10 kg / m³ in the airflow within crusher 2. 3 Above and 0.50 kg / m 3 The following is an example of setting the concentration of silver powder in the airflow of an air-jet mill to 0.10 kg / m³. 3 The above demonstrates that sufficient collisions between silver powder particles in the airflow can improve the dispersion efficiency of the silver powder. This is achieved by setting the concentration of silver powder in the airflow of the air-jet mill to 0.50 kg / m³. 3 The airflow imparts sufficient kinetic energy to the silver powder, thereby improving its dispersibility. When the moisture content of the aggregated silver powder is high, exceeding 12.0 wt%, to prevent clogging, it is preferable to set the silver powder concentration in the airflow of the air-jet mill to 0.30 kg / m³. 3 The concentration of silver powder in the airflow within the airflow pulverizer is obtained by dividing the supply speed of the agglomerated silver powder from feeder 1 by the total supply air volume (the sum of supply air A and supply air B). This concentration is controlled by adjusting the supply speed of the agglomerated silver powder and the total supply air volume. Depending on the capacity of the pulverizer 2, the supply speed of the agglomerated silver powder from feeder 1 can be set, for example, to between 0.50 kg / min and 2.00 kg / min, and the total supply air volume can be set, for example, to 1~20 m³ / min. 3 / min.

[0077] In the pulverizer 2, compressed air for breaking up the aggregated silver powder is supplied to the internal space via a nozzle that communicates with the internal space of the pulverizer 2. The nozzle is, for example, located at the bottom of the pulverizer 2, and configured to spray into the lower region of the internal space. The nozzle may also be located at multiple locations within the pulverizer 2. Figure 1 In the middle, the spray nozzles are set at the upper and lower parts of the crusher 2.

[0078] In the crushing process, the compressed air supplied to the injection nozzle of the crusher 2 (hereinafter referred to as supply air or crushing air) is heated by heater 22 in the supply air supply passage such that the temperature of the compressed air entering the crusher 2 is 80°C or higher and 180°C or lower. The temperature of the compressed air entering the crusher 2 is preferably set to 150°C or lower. Regarding the pressure of the compressed air supplied to the injection nozzle of the crusher 2, the supply pressure of the air pump 24 (at room temperature before heating) can be set to, for example, 0.1 MPa or higher, preferably 0.4 MPa or higher, preferably 0.8 MPa or lower, and preferably 0.6 MPa or lower.

[0079] In the pulverizer 2, the agglomerated silver powder is supplied to the internal space of the pulverizer 2 via a path different from that of the compressed air. During supply, any mechanism capable of delivering the agglomerated silver powder into the pulverizer 2 is acceptable; for example, a jet nozzle can be installed at the pulverizer supply port 21 to serve as the driving force for supplying the crushing air and agglomerated silver powder into the pulverizer. Alternatively, a venturi tube and / or a jet injector installed at the pulverizer supply port 21 can be used as a supply mechanism. The supply air used to supply the agglomerated silver powder to the pulverizer 2 can be heated to 80°C or higher and 180°C or lower via the heater 22 in the supply air supply passage. Regarding the supply air pressure, the supply pressure of the air pump 24 (at room temperature before heating) can be 0.1 MPa or higher and 0.8 MPa or lower.

[0080] Inside the pulverizer 2, the agglomerated silver powder is broken down by the shear force of the breaking air ejected from the nozzle, the collision of the agglomerated particles in the agglomerated silver powder accelerated by the breaking air, and the collision of the agglomerated particles accelerated by the breaking air with the wall of the pulverizer 2. It should be noted that, in this embodiment, the agglomerated particles in the agglomerated silver powder refer to the secondary particles formed by the aggregation of monodisperse silver particles as described in the wet reduction method above.

[0081] In the crushing process, through the aforementioned collisions, the surface roughness of the silver particles is reduced while they are being crushed, resulting in the generation of fine particles that are shaved off, and the surface of the silver particles is smoothed. In this embodiment, the atmosphere inside the pulverizer becomes a humid gas by evaporating the moisture in the silver powder with the high-temperature crushing air. The crushing and surface smoothing in the crushing process are carried out in the humid gas. Generally, particles tend to aggregate when there is moisture in the gas. Therefore, compared to crushing dry silver powder with dry air, crushing and surface smoothing are carried out in a state that is prone to agglomeration. As a result, it is expected that collisions between agglomerated particles and / or re-attachment of fine particles that are shaved off are also more likely to occur within the pulverizer. The silver particles obtained in this embodiment have a larger surface roughness compared to conventional silver particles that have undergone a crushing process in an atmosphere with low moisture content.

[0082] Examples of pulverizers 2 include air jet mills (manufactured by Nisshin Engineering Co., Ltd.), SK JET-O-MILL (manufactured by SEISHIN CO.,LTD), super jet mills (manufactured by Nisshin Engineering Co., Ltd.) and / or spiral jet mills (manufactured by Hosokawa Micron Co., Ltd.), which continuously supply compressed air to the internal space and achieve crushing in the resulting swirling flow, and reverse jet mills (manufactured by Hosokawa Micron Co., Ltd.) and / or cross jet mills (manufactured by Kurimoto Iron Works Co., Ltd.) which have a built-in staged rotor and supply compressed air to the flow layer formed in the internal space to achieve crushing.

[0083] The following description illustrates the case where the pulverizer 2 is an airflow pulverizer. This airflow pulverizer continuously supplies crushing air into its internal space, and crushing is achieved in the resulting swirling flow. Aggregated silver powder is supplied into the internal space of the pulverizer 2 through a path different from that of the supplied air from the pulverizer supply port 21.

[0084] The silver powder from the pulverizer 2 and the crushing process is fed to the classifier 3 for classification. Furthermore, the exhaust temperature is adjusted to above 30°C, and the volumetric absolute humidity is adjusted to 20 g / m³. 3 The above. The absolute humidity per unit volume is also preferably set at 30 g / m³. 3 The above. Hereinafter, the volumetric absolute humidity will be referred to simply as absolute humidity. The temperature and absolute humidity of the exhaust gas from the pulverizer 2 can be determined, for example, by measuring the temperature and humidity (relative humidity) inside the connecting pipe 23 using a thermo-hygrometer 26.

[0085] The classifier 3 is an air classifier that performs a classification process (so-called classification) to further separate and remove coarse particles (coarse powder) or fine powder from the silver powder after the crushing process. The following explanation illustrates the further separation and removal of coarse powder by the classifier 3.

[0086] As the classifier 3, a classifier having a classifying mechanism can be illustrated, which classifies air by balancing the centrifugal force of the swirling flow generated by the supply or suction of airflow and the force of the airflow flowing in the opposite direction to the centrifugal force. Alternatively, a classifier having a classifying mechanism that performs classification by balancing the centrifugal force generated by a rotating rotor and the force of the airflow flowing in the opposite direction to the centrifugal force can be illustrated. Specific examples include a vortex air classifier (manufactured by Nisshin Engineering Co., Ltd.) that utilizes the centrifugal force of the swirling flow generated by the supply of high-speed airflow, and / or a turbine classifier (manufactured by Nisshin Engineering Co., Ltd.) that utilizes the centrifugal force of the swirling flow generated by a rotating rotor.

[0087] The following description illustrates a case where classifier 3 is an air classifier with a grading mechanism. This grading mechanism performs grading by balancing the centrifugal force of the swirling flow generated by the rotating rotor with the force of the airflow being drawn towards the exhaust port 39 of the airflow classifier when it overcomes the centrifugal force from the exhaust of the pulverizer 2 or an airflow different from the exhaust (e.g., outside air). Here, the exhaust of the pulverizer 2, along with the silver powder that has undergone the crushing process, is supplied to the classifier supply port 31. The aforementioned airflow different from the exhaust can be generated by gas drawn into the classifier 3 via a different path than the exhaust of the pulverizer 2. It should be noted that the absolute humidity of the outside air drawn into the classifier 3 can be less than 30 g / m³. 3 The absolute humidity can be less than 15 g / m³ 3 The absolute humidity can also be 12 g / m³. 3 The temperature of the external air drawn by the classifier 3 can be less than 50℃, less than 40℃, or less than 30℃, and the relative humidity can be less than 80%, less than 70%, less than 50%, or less than 40%.

[0088] Silver powder from the crushing process (silver powder crushed by pulverizer 2) and exhaust gas from pulverizer 2 are supplied to classifier 3. The classifier supply port 31 of classifier 3 can be connected to the pulverizer exhaust port 29 of pulverizer 2 via connecting pipe 23. Thus, all silver powder from the crushing process and all exhaust gas from pulverizer 2 are supplied to classifier 3 via connecting pipe 23 and classifier supply port 31. That is, air transport of silver powder from the crushing process based on the airflow of exhaust gas from pulverizer 2 is achieved in connecting pipe 23.

[0089] In the complete set of equipment 100, the exhaust temperature of the pulverizer 2 flowing in the connecting pipe 23 is made to be above 30°C and the absolute humidity is made to be 20 g / m³. 3The above methods are used for control. Therefore, a method for manufacturing silver powder can be realized, which simplifies the process by integrating the drying and crushing processes, and can prepare a conductive paste that yields wiring patterns with desired linewidths and heights.

[0090] In addition, the exhaust temperature of the pulverizer 2 flowing in the connecting pipe 23 is made to be above 30°C and the absolute humidity is made to be 20 g / m³. 3 The above method controls the flow, resulting in a humid gas supply to the classifier's inlet 31. However, as the classification process progresses, external air is mixed in, gradually reducing the moisture content of the gas transporting the silver powder. Classification is performed in conjunction with this change in the moisture content of the transporting gas. Normally, particles tend to aggregate when there is moisture in the gas; therefore, easily aggregated silver particles are easily excluded as coarse powder at the initial stage of classification. In other words, compared to classifying dry silver powder using dry air, screening of silver particles based on their ease of aggregation is possible.

[0091] The coarse powder in the silver powder after the crushing process of the classifier 3 is discharged from the coarse powder outlet 35. The substances in the silver powder after the crushing process of the classifier 3, excluding the coarse powder, are discharged from the classifier exhaust port 39 of the classifier 3 together with the exhaust of the classifier 3, and are supplied (sucked) to the cyclone separator 4 from the cyclone separator inlet 41 by air conveying.

[0092] In the cyclone separator 4, a collection process is performed to collect the silver powder supplied from the classifier 3 using a collection machine. At this time, fine particles are removed from the silver powder. In the cyclone separator 4, the silver powder is recovered to, for example, a recovery tank 49 at the bottom. The silver powder recovered by the cyclone separator 4 is the silver powder of this embodiment.

[0093] The aggregated silver powder is dried during the solid-gas contact process in the crushing process of the pulverizer 2, the classification process of the classifier 3, and the collection process of the cyclone separator 4, along with the crushing process. As a result, the silver powder recovered by the cyclone separator 4 is drier than the aggregated silver powder. In the complete set of equipment 100, the silver powder is dried in the pulverizer 2, the classifier 3, and the cyclone separator 4 by supplying compressed air heated to above 80°C and below 180°C into the internal space of the pulverizer 2. The silver powder recovered by the cyclone separator 4 is sufficiently dried to the point that no further final drying is required (for example, the moisture content of the silver powder is less than 0.1% by mass).

[0094] The exhaust gas from the cyclone separator 4 is drawn out by the blower 6 via the dust collector 5 and discharged to the outside of the complete set of equipment 100. In the dust collector 5, the exhaust gas from the cyclone separator 4 is filtered, and the fine silver powder that is not captured by the cyclone separator 4 is recovered.

[0095] The method for manufacturing silver powder according to this embodiment has been described above. The apparatus described above is illustrative, and various modifications and / or combinations of other apparatuses can be made within the scope of achieving the effects of the invention.

[0096] The conductive paste of the present invention contains at least the silver powder of the present invention, and may optionally contain an organic binder and a solvent.

[0097] Organic binders are not particularly limited, and examples include silicone resins, epoxy resins, acrylic resins, polyester resins, polyimide resins, polyurethane resins, phenoxy resins, and cellulose-based resins (ethyl cellulose, hydroxypropyl cellulose, etc.). They can be used alone or in combination of two or more in any ratio.

[0098] There are no particular limitations on the solvents. Examples include alcohol solvents such as terpineol, butylcarbitol, texanol, ethylene glycol, and diethylene glycol; ester solvents such as butylcarbitol acetate and ethyl acetate; hydrocarbon solvents such as toluene, xylene, and cyclohexane; and glycerol. They can be used alone or in combination of two or more in any ratio.

[0099] The silver powder content in the conductive paste can be set to 80% by mass or more, preferably 85% by mass or more, and can also be set to 95% by mass or less, preferably 90% by mass or less. Preferably, the silver powder of this invention accounts for more than half of the silver powder contained in the conductive paste.

[0100] The content of organic binder in the conductive paste can be set to 0.1% by mass or more, preferably 0.2% by mass or more, and can also be set to 0.4% by mass or less, preferably 0.3% by mass or less.

[0101] The solvent content in the conductive paste can be set to 6% by mass or more, preferably 7% by mass or more, and can also be set to 20% by mass or less, preferably 15% by mass or less.

[0102] Conductive pastes can contain glass frit, dispersants, surfactants, viscosity modifiers, lubricants, etc., as any of their components. The conductive pastes used in the manufacture of solar cell electrodes preferably contain glass frit, such as Pb-Te-Bi and Pb-Si-B based glass frits.

[0103] The method for manufacturing the conductive paste is not particularly limited, but examples include mixing the spherical silver powder of the present invention, an organic binder, a solvent, and any other components as appropriate. The mixing method is not particularly limited, and for example, a rotary mixer, ultrasonic disperser, disperser, three-roll mill, ball mill, bead mill, biaxial kneader, etc., can be used.

[0104] The conductive paste of the present invention can be applied to a substrate by means of printing, dipping, or other methods, such as screen printing, offset printing, or photolithography, to form a coating film. Alternatively, the coating film can be formed into a predetermined pattern shape using photolithography or other methods that utilize a photoresist.

[0105] The coating can be fired to form a conductive film. Firing can be carried out in an atmospheric atmosphere or in a non-oxidizing atmosphere such as nitrogen. The firing temperature of the coating can be set to 600°C or higher, preferably 690°C or higher, and can be set to 800°C or lower, preferably 740°C or lower. The firing time can be set to 20 seconds or higher, preferably 40 seconds or higher, and can be set to 1 hour or less, preferably 2 minutes or less.

[0106] Example

[0107] Hereinafter, the method for manufacturing silver powder according to this embodiment and examples of silver powder manufactured in this method will be described.

[0108] (Example 1)

[0109] The powder in Example 1 was manufactured as follows.

[0110] In a 5L beaker, while stirring 3.3L of a silver nitrate aqueous solution containing 50.8g of silver at 332rpm, 153.0g of a 28.0% by mass ammonia aqueous solution was added to generate a silver ammonia complex aqueous solution. Then, the resulting silver ammonia complex solution was heated to 26.5℃, and 339.1g of 25.9% by mass formalin was added in a single batch as a reducing agent to obtain a silver-containing slurry. It should be noted that to ensure the silver in the slurry reaches the specified particle size, 19.9g of 20% by mass sodium hydroxide aqueous solution was added before the addition of the reducing agent, and the amount added was adjusted to match the particle size.

[0111] Then, 13.238 g of an aqueous emulsion containing 0.382% by mass stearic acid relative to the silver in the slurry was added, and stirring was continued for 3 minutes after the reduction was completed to obtain a slurry of silver particles. The silver slurry was filtered, washed with pure water until the conductivity of the filtrate reached 0.5 mS / m, and then filtered by vacuum to obtain silver powder (aggregated silver powder). The cross-section of the silver particles (raw material particles) of the obtained silver powder was observed using a scanning electron microscope, and the results showed that they had closed pores inside. The moisture content (loss on drying) of the aggregated silver powder was 12.8 wt%. The above process was repeated to prepare 4000 g of aggregated silver powder.

[0112] Subsequently, the aggregated silver powder was fed into the pulverizer 2 at a feed rate of 1 kg / min in the aforementioned complete set of equipment 100 for crushing and drying. The silver powder, along with moist hot air, was then conveyed to the classifier 3 for classification. The silver powder collected in the cyclone separator 4 was further sieved using a 40 μm mesh sieve. The silver powder passing through this sieve was used as the silver powder of Example 1. The cross-sectional area of ​​the silver powder of Example 1 was observed using a scanning electron microscope, revealing closed voids within the particles. Furthermore, the true density was measured using a true density measuring device (Micromeritics AccuPycII 1340), yielding a result of 9.7 g / cm³. 3 .

[0113] Table 1 shows the operating conditions of the complete equipment 100 used to manufacture the silver powder of Example 1. Examples 2-4 and Comparative Examples 1-4, which will be described later, are also shown. Here, supply air B is air supplied to the injection nozzle at the bottom of the pulverizer, and supply air A is air supplied to the injection nozzle at the top of the pulverizer.

[0114] [Table 1]

[0115]

[0116] Table 1 shows the ambient temperature (°C), relative humidity (%), and absolute humidity (g / m³) around the equipment 100 during manufacturing in the "Environment" section. 3 ( ) refers to the temperature and relative humidity of the outside air drawn in by the classifier 3, which will be described later.

[0117] Additionally, Table 1 shows the moisture content (wt%) of the aforementioned aggregated silver powder under the item "Moisture content of aggregated silver powder".

[0118] In addition, Table 1 shows the supply rate (kg / min) of the aggregated silver powder supplied from the feeder 1 to the crusher 2 under the "Feeder" item. Furthermore, the total air volume (m³) supplied to the crusher 2 is shown under the "Crusher" item as the crushing condition in the crusher 2. 3 / min), the supply air quantity supplied to each injection nozzle (m³ / min), and the supply air quantity supplied to each injection nozzle. 3 / min) and its pressure (MPa), temperature (°C), silver powder concentration (kg / m 3It should be noted that the total air volume here refers to the total amount of supply air supplied to the nozzles located at the top and bottom of the pulverizer. It should also be noted that the total air volume and the supply air volume supplied to each nozzle are values ​​before heating, measured by the flow meter 27 installed in the supply path, and represent values ​​at 1 atmosphere and 0°C (standard conversion value). In Table 1, the value in the pulverizer temperature column is the outlet temperature of the heater 22, representing the temperature of the supply air after heating and before being supplied to the pulverizer.

[0119] In the following description, the case where the temperature of supply air A and supply air B is set to 80°C or higher is considered as the case where drying treatment is performed in the complete equipment 100. In Example 1, as shown in Table 1, the temperature of supply air A and supply air B is set to 160°C, and therefore drying treatment is performed in the complete equipment 100. Then, crushing and grading are performed in a humid airflow.

[0120] Additionally, Table 1 shows the temperature (°C), relative humidity (%), and absolute humidity (g / m³) of the exhaust gas from the pulverizer 2 under the "Pulverizer Exhaust" item. 3 ).

[0121] Additionally, in Table 1, as a condition for classifier 3, the intake air volume (m³) of external air drawn into classifier 3 separately from the exhaust of pulverizer 2 is shown in the "classifier" item. 3 / min). It should be noted that the intake air volume represents the standard flow rate.

[0122] Additionally, in Table 1, the exhaust air volume (m³) of blower 6 is shown in the "Blower" item. 3 The set value is ( / min). It should be noted that the exhaust air volume represents the standard flow rate.

[0123] Here, the intake air volume of the external air drawn by the classifier 3 in Table 1 is not a measured value, but a calculated value obtained by subtracting the total air volume supplied to the pulverizer 2 from the exhaust air volume of the blower 6.

[0124] (Example 2)

[0125] The silver powder in Example 2 was prepared as follows.

[0126] In a 5L beaker, while stirring a 3.4L aqueous solution containing 53.7g of silver at 332rpm, 113.2g of a 28.0% by mass ammonia solution was added to form an aqueous solution of silver ammonia complex. The silver ammonia complex solution was heated to 26.5℃, and then 251.4g of 25.9% by mass formalin was added in a single batch as a reducing agent. It should be noted that, to achieve the specified particle size, 12.9g of 20% by mass sodium hydroxide aqueous solution was added before the addition of the reducing agent, and the amount added was adjusted to match the particle size.

[0127] Then, 7.970 g of an aqueous emulsion containing 0.230% by mass stearic acid relative to silver was added, and stirring was continued for 3 minutes after the reduction was completed to obtain a slurry of silver particles. The silver slurry was filtered, washed with pure water until the conductivity of the filtrate reached 0.5 mS / m, and then vacuum filtered to obtain silver powder (aggregated silver powder). The cross-section of the silver particles (raw material particles) of the obtained silver powder was observed using a scanning electron microscope, and the results showed that they had closed pores inside. The moisture content (loss on drying) of the aggregated silver powder was 17.0 wt%. The above process was repeated to prepare 4000 g of aggregated silver powder.

[0128] Subsequently, the aggregated silver powder was fed into the pulverizer 2 at a feed rate of 1 kg / min in the aforementioned complete set of equipment 100 for crushing and drying. The silver powder, along with moist hot air, was then conveyed to the classifier 3 for classification. The silver powder collected in the cyclone separator 4 was further sieved using a 40 μm mesh sieve. The silver powder passing through this sieve was used as the silver powder of Example 2. The cross-section of the silver powder particles in Example 2 was observed using a scanning electron microscope, revealing closed voids within. The true density was measured using a true density measuring device, yielding a result of 9.7 g / cm³. 3 .

[0129] Table 1 shows the operating conditions of the equipment 100 used to manufacture the silver powder of Example 2. In Example 2, as shown in Table 1, the temperatures of supply air A and supply air B are set to 135°C, and therefore a drying process is performed in the equipment 100. Then, crushing and grading are carried out in a humid airflow.

[0130] (Example 3)

[0131] The silver powder in Example 3 was prepared as follows.

[0132] In a 5L beaker, while stirring a 3.8L aqueous solution of silver nitrate containing 50.8g of silver at 332rpm, 153.0g of a 28.0% by mass ammonia solution was added to generate an aqueous solution of silver ammonia complex. Then, the resulting silver ammonia complex solution was heated to 20.0℃, and 339.1g of 25.9% by mass formalin was added in a single batch as a reducing agent to obtain a silver-containing slurry. It should be noted that, to ensure the silver in the slurry reaches the specified particle size, 14.61g of a 20% by mass sodium hydroxide aqueous solution was added before adding the reducing agent, and the amount added was adjusted to match the particle size.

[0133] Then, 18.577 g of an aqueous emulsion containing 0.566% by mass stearic acid relative to the silver in the slurry was added, and stirring was continued for 3 minutes after the reduction was completed to obtain a slurry of silver particles. The silver slurry was filtered, washed with pure water until the conductivity of the filtrate reached 0.5 mS / m, and then vacuum filtered to obtain silver powder (aggregated silver powder). The cross-section of the silver particles (raw material particles) of the obtained silver powder was observed using a scanning electron microscope, and the results showed that they had closed pores inside. The moisture content (loss on drying) of the aggregated silver powder was 12.6 wt%. The above process was repeated to prepare 4000 g of aggregated silver powder.

[0134] Subsequently, the aggregated silver powder was fed into the pulverizer 2 at a feed rate of 1 kg / min in the aforementioned complete set of equipment 100 for crushing and drying. The silver powder, along with moist hot air, was then conveyed to the classifier 3 for classification. The silver powder collected in the cyclone separator 4 was further sieved using a 40 μm mesh sieve. The silver powder passing through this sieve was used as the silver powder of Example 3. The cross-sectional area of ​​the silver powder of Example 3 was observed using a scanning electron microscope, revealing closed voids within the particles. Furthermore, the true density was measured using a true density measuring device (Micromeritics AccuPycII 1340), yielding a result of 9.7 g / cm³. 3 .

[0135] Table 1 shows the operating conditions of the complete equipment 100 used to manufacture the silver powder of Example 3. In Example 3, as shown in Table 1, the temperatures of supply air A and supply air B are set to 127°C, and therefore a drying process is performed in the complete equipment 100. Then, crushing and grading are carried out in a humid airflow.

[0136] (Example 4)

[0137] The silver powder in Example 4 was prepared as follows.

[0138] In a 5L beaker, while stirring 3.8L of a silver nitrate aqueous solution containing 50.8g of silver at 332rpm, 153.0g of a 28.0% by mass ammonia aqueous solution was added to generate a silver ammonia complex aqueous solution. Then, the resulting silver ammonia complex solution was heated to 20.0℃, and 339.1g of 25.9% by mass formalin was added in a single batch as a reducing agent to obtain a silver-containing slurry. It should be noted that to ensure the silver in the slurry reaches the specified particle size, 9.14g of 20% by mass sodium hydroxide aqueous solution was added before adding the reducing agent, and the amount added was adjusted to match the particle size.

[0139] Then, 11.300 g of an aqueous emulsion containing 0.344% by mass stearic acid relative to the silver in the slurry was added, and stirring was continued for 3 minutes after the reduction was completed to obtain a slurry of silver particles. The silver slurry was filtered, washed with pure water until the conductivity of the filtrate reached 0.5 mS / m, and then vacuum filtered to obtain silver powder (aggregated silver powder). The cross-section of the silver particles (raw material particles) of the obtained silver powder was observed using a scanning electron microscope, and the results showed that they had closed pores inside. The moisture content (loss on drying) of the aggregated silver powder was 12.2 wt%. The above process was repeated to prepare 4000 g of aggregated silver powder.

[0140] Subsequently, the aggregated silver powder was fed into the pulverizer 2 at a feed rate of 1 kg / min in the aforementioned complete set of equipment 100 for crushing and drying. The silver powder, along with hot, moist air, was then conveyed to the classifier 3 for classification. The silver powder collected in the cyclone separator 4 was further sieved using a 40 μm mesh sieve. The silver powder passing through this sieve was used as the silver powder of Example 4. The cross-sectional area of ​​the silver powder of Example 4 was observed using a scanning electron microscope, revealing closed voids within the particles. Furthermore, the true density was measured using a true density measuring device (Micromeritics AccuPycII 1340), yielding a result of 9.7 g / cm³. 3 .

[0141] Table 1 shows the operating conditions of the equipment 100 used to manufacture the silver powder of Example 4. In Example 4, as shown in Table 1, the temperatures of supply air A and supply air B are set to 120°C, and therefore a drying process is performed in the equipment 100. Then, crushing and grading are carried out in a humid airflow.

[0142] (Comparative Example 1)

[0143] The silver powder of Comparative Example 1 differs from that of the above-described embodiments in that it is manufactured without the drying process in the complete equipment 100. That is, for the silver powder of Comparative Example 1, unlike Example 1, the aggregated silver powder manufactured in the same manner as in Example 1 is dried using a vacuum rotary dryer, stirred using a Henschel mixer, and the coarsely crushed and dried silver powder (moisture content: 0.01 wt%) is supplied to the complete equipment 100 in the same manner as in Example 1. Compared to Example 1, the operating conditions of the complete equipment 100 are changed, and the silver powder that has been crushed and collected by the cyclone separator 4 is used as the silver powder of Comparative Example 1. Table 1 shows the operating conditions of the complete equipment 100 when manufacturing the silver powder of Comparative Example 1. In Comparative Example 1, as shown in Table 1, the temperatures of supply air A and supply air B are set to 16°C, therefore, as described above, the drying process in the complete equipment 100 is not performed. Furthermore, the absolute humidity of the exhaust air from the pulverizer supplied to the classifier is lower, and the crushing and classification in a humid airflow as in the embodiments is not performed.

[0144] (Comparative Example 2)

[0145] The silver powder of Comparative Example 2 differs from that of the above-described embodiments in that it is manufactured without the drying process in the complete set of equipment 100. That is, for the silver powder of Comparative Example 2, unlike Example 2, the aggregated silver powder manufactured in the same manner as in Example 2 is dried using a vacuum rotary dryer, stirred using a Henschel mixer, and the coarsely crushed and dried silver powder (moisture content: 0.01 wt%) is supplied to the complete set of equipment 100 in the same manner as in Example 2. Compared to Example 2, the operating conditions of the complete set of equipment 100 are changed, and the silver powder that has been crushed and collected by the cyclone separator 4 is used as the silver powder of Comparative Example 2. Table 1 shows the operating conditions of the complete set of equipment 100 when manufacturing the silver powder of Comparative Example 2. In Comparative Example 2, as shown in Table 1, the temperatures of supply air A and supply air B are set to 16°C, therefore, as described above, the drying process in the complete set of equipment 100 is not performed. Furthermore, the absolute humidity of the exhaust air from the pulverizer supplied to the classifier is lower, and the crushing and classification in a humid airflow as in the embodiments is not performed.

[0146] (Comparative Example 3)

[0147] The silver powder of Comparative Example 3 differs from that of the above-described embodiments in that it is manufactured without the drying process in the complete set of equipment 100. That is, for the silver powder of Comparative Example 3, unlike Example 3, the aggregated silver powder manufactured in the same manner as in Example 3 is dried using a vacuum rotary dryer, stirred using a Henschel mixer, and the coarsely crushed and dried silver powder (moisture content: 0.01 wt%) is supplied to the complete set of equipment 100 in the same manner as in Example 3. Compared to Example 3, the operating conditions of the complete set of equipment 100 are changed, and the silver powder that has been crushed and collected by the cyclone separator 4 is used as the silver powder of Comparative Example 3. Table 1 shows the operating conditions of the complete set of equipment 100 when manufacturing the silver powder of Comparative Example 3. In Comparative Example 3, as shown in Table 1, the temperatures of supply air A and supply air B are set to 25°C, therefore, as described above, the drying process in the complete set of equipment 100 is not performed. Furthermore, the absolute humidity of the exhaust air from the pulverizer supplied to the classifier is lower, and the crushing and classification in a humid airflow as in the embodiments is not performed.

[0148] (Comparative Example 4)

[0149] The silver powder of Comparative Example 4 differs from that of the above-described embodiments in that it is manufactured without the drying process in the complete equipment 100. That is, unlike Example 4, the aggregated silver powder manufactured in the same manner as in Example 4 is dried using a vacuum rotary dryer, stirred using a Henschel mixer, and the coarsely crushed and dried silver powder (moisture content: 0.01 wt%) is supplied to the complete equipment 100 in the same manner as in Example 4. Compared to Example 4, the operating conditions of the complete equipment 100 are changed, and the silver powder that has been crushed and collected by the cyclone separator 4 is used as the silver powder of Comparative Example 4. Table 1 shows the operating conditions of the complete equipment 100 when manufacturing the silver powder of Comparative Example 3. In Comparative Example 4, as shown in Table 1, the temperatures of supply air A and supply air B are set to 25°C, therefore, as described above, the drying process in the complete equipment 100 is not performed. Furthermore, the absolute humidity of the exhaust air from the pulverizer supplied to the classifier is lower, and the crushing and classification in a humid airflow as in the embodiments is not performed.

[0150] (Example for reference)

[0151] When the feed rate of the aggregated silver powder in Examples 1 and 2 to the pulverizer was increased to 1.5 kg / min, blockage occurred in the pulverizer, causing it to stop operating.

[0152] Table 2 shows the evaluation values ​​of the silver powder of the Examples and Comparative Examples, and the evaluation values ​​of the aspect ratio in the wiring patterns obtained by pasteurizing and firing the silver powder of the Examples and Comparative Examples (described later). The evaluation values ​​shown in Table 2 will be explained below.

[0153] [Table 2]

[0154]

[0155] In Table 2, “Specific Surface Area (SSA)” (m²) 2 The specific surface area of ​​the silver powder is given by (g). The specific surface area of ​​the silver powder is determined using the BET specific surface area method. The BET specific surface area is measured using a BET specific surface area measuring device (Macsorb HM-1210 manufactured by Mounttech Co., Ltd.). After degassing in the measuring device by flowing a He-N2 mixed gas (30% nitrogen) at 60°C for 10 minutes, the BET 1-point method is used.

[0156] In Table 2, "BET diameter" (μm) is based on the BET specific surface area (m²) of the silver powder. 2 The specific surface area diameter is obtained by calculating the true density of the silver powder (g) and the specific surface area diameter using the following formula (1).

[0157] BET diameter (μm) = 6 / (specific surface area × true density) ... Equation (1)

[0158] It should be noted that in the above formula (1), the true density measurement result of 9.7 g / cm³ is used. 3 .

[0159] In Table 2, “D10” (μm), “D50” (μm), and “D90” (μm) represent the particle size distribution of silver powder determined on a volume basis using laser diffraction particle size distribution measurement. These values ​​indicate the cumulative 10% (μm), 50% (μm), and 90% (μm) particle size distributions accumulated from the smaller particle size side. It should be noted that the cumulative 50% particle size on a volume basis refers to the median particle size. Hereinafter, the values ​​for the cumulative 10% (μm), 50% (μm), and 90% (μm) particle sizes will be recorded as D10, D50, and D90, respectively.

[0160] Specifically, the particle size distribution of the silver powder was measured using a laser diffraction and scattering particle size distribution measuring device (Microtrac BEL Co., Ltd., Microtrac MT-3300 EXII) that performs laser diffraction-based particle size distribution measurement. The particle size distribution measurement in the laser diffraction and scattering particle size distribution measuring device was performed as follows: First, 0.1 g of silver powder was added to 40 mL of isopropanol (IPA) for dispersion. Dispersion was performed using an ultrasonic homogenizer (Nippon Seiki Co., Ltd., device name: US-150T; 19.5 kHz, probe diameter 20 mm). The dispersion time was set to 2 minutes. Then, the dispersed sample was fed into the aforementioned laser diffraction and scattering particle size distribution measuring device, and the particle size distribution was determined using the accompanying analytical software.

[0161] In Table 2, "(D90-D10) / D50" represents the value obtained by subtracting D10 from D90 and dividing that difference by D50. This value indicates the extent of particle size distribution (the width of the particle size distribution); a larger value indicates a wider particle size distribution, and a smaller value indicates a narrower particle size distribution. Hereinafter, "(D90-D10) / D50" will sometimes be referred to as the width value.

[0162] The "Moisture Content of Silver Powder" in Table 2 refers to the moisture content of the silver powder obtained after the grading process. The "Moisture Content of Aggregated Silver Powder" (%) in Table 1 and the "Moisture Content of Silver Powder" (%) in Table 2 are calculated as follows: Take 10g of aggregated silver powder or silver powder as a sample into a weighing bottle, dry it at 90℃ for 3 hours without a cap, divide the weight reduction of the sample after natural cooling for at least 40 minutes by the weight of the sample before drying (10g), and multiply the result by 100.

[0163] In Table 2, the "loss on ignition" (%) is calculated as follows. First, 3g of silver powder is weighed and placed in a magnetic crucible, which is then heated to 800°C. Then, to achieve a constant weight, the powder is heated at 800°C for 30 minutes. The silver powder is then cooled, weighed, and the mass (w) after heating is determined. The loss on ignition (%) is calculated based on this mass (w) using the following formula (2).

[0164] Loss on ignition (%) = (3-w) / 3×100…Equation (2)

[0165] In Table 2, "TAP" (g / mL) represents the tap density of the silver powder. The tap density of the silver powder was determined using a tap density measuring device (SS-DA-2, manufactured by Shibayama Scientific Corporation). The tap density was determined as follows: 30g of silver powder sample was weighed and placed in a 20mL test tube, and the sample was tapped 1000 times with a drop height of 20mm. Then, the volume of the sample after tapping (cm³) was calculated. 3 Tap density (g / cm³) 3 ) is based on the volume of the sample after compaction (cm³) 3 The value is obtained by the following formula (3).

[0166] Tap density (g / cm³) 3 ) = 30(g) / Volume of the compacted sample (cm³) 3 ...Equation (3)

[0167] In Table 2, “Sa” (nm) represents the arithmetic mean roughness as specified in ISO 25178 for the determination of surface roughness of silver particles. The arithmetic mean roughness Sa is calculated based on the shape image obtained using a scanning probe microscope (SPM). Specifically, an SPM (Nano Cute) manufactured by SII NanoTechnology Co., Ltd. was used, and a cantilever manufactured by Hitachi High-Tech Fielding Co., Ltd. SI-DF40P2 was used. The tapped mode (DFM) was selected as the measurement mode. In detail, firstly, Q-curve measurements were performed, and the cantilever was adjusted. At this time, the resonant frequency range of 200Hz to 500Hz and the Q value range of 100 to 1000 were confirmed. The target vibration amplitude of the cantilever was set to 1V. Next, shape images and error signal images of silver particles with a field of view of 5μm were obtained using the SPM. At this time, the amplitude attenuation rate was automatically set in the range of -0.1 to -0.2. In addition, the scanning frequency was set in the range of 0.6Hz to 1Hz. The feedback control parameters were set to automatic. The pixel count for obtaining the shape image is set to 256×256. Then, based on the range of roughness to be resolved specified in the shape image, three tilt corrections and flattening processes are performed to remove components originating from the curved surfaces of the particles, thereby automatically calculating the arithmetic mean roughness Sa of the particle surface as specified in ISO 25178. No cutoff processing is performed at this time. The resolution range is set to a square range with a side length of 500 nm (referred to as "500 nm × 500 nm range" in this specification). During resolution, 10 particles are randomly selected for resolution, and their average value is calculated. The Sa / BET diameter value is calculated from the arithmetic mean roughness Sa and the aforementioned BET diameter values.

[0168] A conductive paste was prepared from the obtained silver powder. To determine the aspect ratio of the wiring pattern of the conductive paste, the conductive paste was prepared using the silver powders of Examples 1-4 and Comparative Examples 1-4 as follows. Specifically, the conductive paste was obtained by treating the substances with the composition ratios shown in Table 3 as follows: After mixing using a propellerless rotary stirring degassing device (THINKY AR310, Ltd.) at 1400 rpm for 30 seconds, the mixture was kneaded using a three-roll mill (EXAKT 80S, Ltd.) with the roller gap decreasing from 100 μm to 20 μm.

[0169] [Table 3]

[0170]

[0171] The viscosity of the paste was measured using a Brookfield 5XHBDV-IIIUC viscometer. The measurement conditions were as follows: a CP-52 conical rotor was used; the paste temperature was set to 25°C; and the rotation speed and measurement time were set to 1 rpm (shear rate 2 seconds).-1 ) for the next 5 minutes and 5 rpm (shearing speed 10 sec -1 ) for the next 1 minute.

[0172] The thin line evaluation is to form a wiring pattern for evaluation. The formation of the wiring pattern is carried out as follows. First, on a silicon substrate for solar cells (100 Ω / sq), using a screen printing machine (manufactured by Microtec, MT-320TV), an aluminum paste (Rutech 28D22G-2) is used to form a solid pattern of 154 mm□ on the back surface of the substrate. Then, after filtering the above paste with 500 mesh, on the surface side of the substrate, in the Figure 10 pattern shown, electrodes (finger electrodes) with a designed line width (screen opening width) of 14 - 26 μm and electrodes (bus bar electrodes) with a designed line width of 1 mm are printed (coated) at a squeegee speed of 350 mm / sec. After the printed paste is dried by hot air at 200 °C for 10 minutes, a high-speed firing furnace IR furnace (manufactured by NGK INSULATORS, LTD., high-speed firing test 4-chamber furnace) is used for firing at a peak temperature of 750 °C and an in-and-out time of 41 seconds to obtain a wiring pattern.

[0173] The line width and height of the wiring pattern are measured using a laser microscope (KEYENCE Corporation VKX-1000) for the Figure 10 electrodes printed with a designed line width of 24 μm in the designed line width. Photographs are taken with an objective lens magnification of 20 times (the electrode length per field of view is approximately 500 μm). In one field of view, the cross-sectional shapes (equivalent to an electrode length of approximately 400 μm) are measured at intervals of 0.687 μm for 601 sheets, and their average cross-sectional shape is calculated. Regarding the average cross-sectional shape, with the height of the substrate as the baseline, the distance from the upper edge (rise) away from the baseline is taken as the line width, and the height difference between the highest point and the baseline is taken as the height for measurement, obtaining the line width and height in one field of view. For the 3rd, 6th, and 8th electrodes from the left among the 10 electrodes with a designed line width of 24 μm, photographs are taken at 2 locations, 5 cm and 10 cm from the upper end of the electrode, for a total of 6 locations, and the average of the line width and height for the 6 fields of view is calculated. The "aspect ratio" in Table 2 is calculated from this result.

[0174] Figures 2 to 9SEM images (20,000x magnification) of the silver powders of Examples 1-4 and Comparative Examples 1-4 are shown below. In the SEM images of the Examples, it is evident that unevenness exists on the surface of the silver particles. Regarding the unevenness observed on the surface of the silver particles in the SEM images of the Examples, it is presumed that the unevenness on the surface of the silver particles generated by the wet reaction was not sufficiently removed during the crushing and grading processes, resulting in a relatively large residue on the surface of the silver particles constituting the silver powder of the present invention, thus making the surface unevenness of the silver particles larger. The unevenness on the surface of the silver particles observed in the SEM images of Comparative Examples 1-4 is smaller than that of Examples 1-4. It is presumed that this is because, due to the low moisture content of the atmosphere surrounding the silver particles in the crushing and grading processes, the unevenness on the surface of the silver particles was sufficiently removed during the crushing and grading processes, resulting in a smaller unevenness on the surface of the silver particles compared to the Examples. The degree of unevenness on the surface of the silver particles in the Examples and Comparative Examples is reflected in their Sa values.

[0175] As shown in Table 2, it can be seen that among the wiring patterns obtained by pasteurizing and firing the silver powder from Comparative Examples 1 and 1, 2 and 2, 3 and 3, and 4 and 4, which were made based on the same aggregated silver powder, the height-to-width ratio (height-to-width ratio) of the examples was larger in any comparison, thus exhibiting preferred characteristics. It should be noted that since the viscosity of the paste also affects the height-to-width ratio, pastes with similar viscosity (approximately ±20 Pa·s at 1 rpm) were compared with each other.

[0176] Based on the results of the fine line evaluation above, the silver powder of the embodiment can be evaluated as a silver powder capable of preparing a paste that can achieve wiring patterns with desired line width and height.

[0177] Furthermore, as shown in Table 2, compared to Comparative Examples 1-4, in Examples 1-4, the exhaust gas from the pulverizer 2 flowing in the connecting pipe 23 was controlled to have a temperature of 30°C or higher and an absolute humidity of 20 g / m³. 3 The grading performance of the grading machine is improved, and the (D90-D10) / D50 ratio in Examples 1-4 is smaller compared to Comparative Examples 1-4.

[0178] Therefore, in order to prepare a paste that yields wiring patterns with the desired linewidth and height, silver powder with a moderately uneven surface on the silver particles is required. This is from Figures 2 to 9The SEM images of the silver powders in the illustrated embodiments and comparative examples also clearly show that the silver powders of the embodiments exhibit moderate unevenness on the surface of their spherical silver particles. In contrast, the silver powders of the comparative examples have less unevenness on the surface of their silver particles compared to the silver powders of the embodiments, and the surface of the silver particles is generally smooth. Thus, according to the manufacturing method of this embodiment, silver particles suitable for preparing a paste that suppresses the smoothing of the silver particle surface to obtain wiring patterns with desired linewidth and height can be obtained.

[0179] From the operating conditions of the complete set of equipment 100 shown in Table 1, it can be seen that the method for manufacturing silver powder capable of producing a paste with a desired line width and height wiring pattern is not, as in the comparative example, where the aggregated silver powder is pre-dried and then subjected to processing other than drying in the complete set of equipment 100. Instead, as in the embodiment, the method involves crushing, classifying, and drying the aggregated silver powder in the complete set of equipment 100 to obtain silver powder. Then, when drying the aggregated silver powder in the complete set of equipment 100 to obtain dry silver powder, in the crushing process, compressed air at a temperature of 80°C or higher and 180°C or lower needs to be supplied to the crusher 2. Furthermore, the exhaust from the crusher 2 is supplied to the classifier 3, and it is assumed that the exhaust temperature needs to be 30°C or higher and the relative humidity 30%.

[0180] As described above, a method for manufacturing silver powder capable of preparing a conductive paste that yields wiring patterns with desired line widths and heights, and the silver powder itself, can be provided.

[0181] It should be noted that the configurations disclosed in the above embodiments (including other embodiments, the same below) can be combined with the configurations disclosed in other embodiments as long as they do not create contradictions. In addition, the embodiments disclosed in this specification are illustrative, and the embodiments of the present invention are not limited thereto, and can be appropriately modified within the scope of the purpose of the present invention.

[0182] Industrial availability

[0183] This invention is applicable to silver powder, methods for manufacturing silver powder, and conductive pastes.

[0184] Explanation of reference numerals in the attached figures

[0185] 1: Supply machine

[0186] 100: Complete sets of equipment

[0187] 2: Crusher (Airflow Crusher)

[0188] 21: Crusher feed port

[0189] 22: Heater

[0190] 23: Connecting pipe

[0191] 24: Air pump

[0192] 26: Thermometer and hygrometer

[0193] 27: Flow meter

[0194] 29: Crusher exhaust port

[0195] 3: Classifier (Wind Classifier)

[0196] 31: Grading machine supply port

[0197] 35: Coarse powder discharge outlet

[0198] 39: Classifier exhaust port

[0199] 4: Cyclone Separator

[0200] 41: Cyclone separator inlet

[0201] 49: Recycling bins

[0202] 5: Dust collector

[0203] 6: Blower

Claims

1. A silver powder having closed voids within silver particles, The arithmetic mean roughness Sa (nm) of the surface roughness measurement in the 500nm × 500nm range of the silver particle, divided by the BET diameter, has a value of Sa / BET diameter of 0.0070 or higher. The BET diameter is defined using the specific surface area (m²) measured by the BET1 point method. 2 The values ​​of / g) and true density are calculated by the following formula (1), BET diameter = 6 / (specific surface area × true density) ... Equation (1).

2. The silver powder according to claim 1, wherein, The arithmetic mean roughness Sa is greater than 5 nm and less than 15 nm.

3. The silver powder according to claim 1, wherein, In the volume-based particle size distribution determined by laser diffraction particle size distribution measurement, the cumulative 10% particle size (μm), cumulative 50% particle size (μm), and cumulative 90% particle size (μm) accumulated from the side with the smallest particle size are set as D10, D50, and D90, respectively. The difference obtained by subtracting D10 from D90 and dividing it by D50 yields a value of 1.0 or less.

4. A method for manufacturing silver powder, comprising: The crushing process involves using an airflow pulverizer to crush the aggregated silver powder. as well as In the grading process, an air classifier is used to classify the silver powder after the crushing process. The moisture content of the aggregated silver powder is above 5.0 wt% and below 30.0 wt%. In the crushing process, compressed air with a temperature between 80°C and 180°C is supplied to the airflow pulverizer as feed air, and the concentration of silver powder in the airflow is 0.10 kg / m³. 3 Above and 0.50 kg / m 3 The aggregated silver powder is supplied in the following manner. In the grading process, the exhaust gas from the airflow pulverizer and the silver powder from the crushing process are supplied to the air classifier. The exhaust temperature is above 30℃ and the volumetric absolute humidity is 20g / m³. 3 above.

5. The method for manufacturing silver powder according to claim 4, wherein, The wind classifier is connected to the airflow pulverizer via a connecting pipe, through which the exhaust gas from the airflow pulverizer and the silver powder after the crushing process are supplied from the airflow pulverizer to the wind classifier.

6. The method for manufacturing silver powder according to claim 4, further comprising: The collection process involves using a collection machine to collect the silver powder remaining after the grading process. In the collection process, the exhaust gas from the wind classifier and the silver powder from the classification process are supplied to the collection machine.

7. The method for manufacturing silver powder according to any one of claims 4 to 6, wherein, In the grading process, the wind classifier draws in outside air while performing grading.

8. A conductive paste comprising the silver powder as described in claims 1 to 3.

Images