Method for producing silver powder, silver powder, and conductive paste

Abstract

The present invention provides a method for producing silver powder and the silver powder, which can prepare a conductive paste capable of obtaining a wiring pattern having a desired line width and height. This method for producing silver powder comprises: a crushing step for crushing aggregated silver powder by means of a jet mill (2); and a classification step for classifying the silver powder after the crushing step by means of a wind classifier (3), the water content of the aggregated silver powder being 2-20 wt%, in the crushing step, compressed air having a temperature of 80-180 DEG C is supplied to the jet mill (2) as supply air, and in the classification step, compressed air having a temperature of 80-180 DEG C is supplied to the jet mill (2) as supply air. The silver powder after the exhaust and crushing step of the jet mill (2) is supplied to the wind classifier (3), the exhaust temperature being 30 DEG C or higher, and the absolute volume humidity being 20 g / m < 3 > or higher.

Description

Technical Field

[0001] The present invention relates to a method for producing silver powder, silver powder and conductive paste. Background Art

[0002] Patent document 1 describes silver powder and a method for producing the silver powder. In the method for producing the silver powder, 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, and the filter cake is dried in an air flow drying device to obtain silver powder.

[0003] Patent Document 2 describes a method for producing silver particles. In the method for producing silver particles, alcohol is added to a slurry of silver particles having an average particle size of submicron order and stirred, followed by filtration, dehydration, drying, and crushing. In the method for producing silver particles, the drying treatment may be either hot air drying or vacuum drying. In the case of hot air drying, the filtrate is placed under hot air at 30 to 100°C.

[0004] Patent document 3 describes silver powder and a method for producing the same. In the method for producing the silver powder, a reducing agent is added to an aqueous reaction system containing silver ions to reduce and precipitate silver particles to obtain a silver-containing slurry, the silver-containing slurry is filtered, washed with water to obtain a filter cake, the filter cake is dehydrated at room temperature, crushed into powder at room temperature, and classified at room temperature to obtain the silver powder.

[0005] Prior art literature

[0006] Patent Literature

[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] Problem that the invention aims to solve

[0011] The wiring and contacts of the electronic parts manufactured by applying the conductive paste (hereinafter sometimes simply referred to as the paste) are obtained by applying the paste by printing or the like and then heating (typically by baking). The paste is required to obtain a wiring pattern with the desired line width and height when it is applied and baked. Generally, in electronic parts, in order to maximize the area other than the wiring part and to miniaturize the electronic parts, it is desirable to make the wiring thinner, and it is desirable to have a wiring pattern with a high wiring height so that the resistivity does not become too large even if the wiring is thinned.

[0012] In a conductive paste containing silver powder as a conductive material, in order to achieve the performance of the paste as described above, the surface properties (e.g., the shape of the surface) of the silver particles in the silver powder are sometimes controlled. For example, desired concavities and convexities are sometimes formed on the surface of the silver particles in the silver powder. However, in the existing method for manufacturing silver powder, it is sometimes impossible to obtain silver powder having the desired concavities and convexities on the surface of the silver particles. Therefore, it is sometimes impossible to provide a paste that can obtain a wiring pattern with a desired line width and height.

[0013] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing silver powder and the silver powder, wherein the silver powder can be used to prepare a conductive paste that can obtain a wiring pattern with a desired line width and height and a thin line width and a high height.

[0014] Solutions for solving problems

[0015] The method for producing silver powder, the silver powder, and the conductive paste containing the silver powder of the present invention in order to achieve the above-mentioned object are as follows.

[0016] <1> A method for producing silver powder, comprising:

[0017] A crushing process of crushing the aggregated silver powder using a jet mill; and,

[0018] A classification process of classifying the silver powder after the crushing process using a wind classifier,

[0019] The water content of the aggregated silver powder is greater than 2 wt % and less than 20 wt %,

[0020] In the crushing step, compressed air at a temperature of 80° C. or higher and 180° C. or lower is supplied as supply air to the air flow mill.

[0021] In the classification process, the exhaust gas of the air flow mill and the silver powder after the crushing process are supplied to the air classifier.

[0022] The exhaust temperature is above 30°C and the absolute volume humidity is 20g / m 3 above.

[0023] <2> According to the above <1> The method for manufacturing silver powder is characterized in that the air classifier and the air flow pulverizer are connected by a connecting pipe, and the exhaust gas of the air flow pulverizer and the silver powder after the crushing process are supplied from the air flow pulverizer to the air classifier by means of the connecting pipe.

[0024] <3> According to the above <1> or <2> The method for manufacturing silver powder further comprises a collecting step of collecting the silver powder after the classification step using a collector.

[0025] In the collecting step, the exhaust gas of the air classifier and the silver powder after the classification step are supplied to the collector.

[0026] <4> According to the above <1> ~ <3> The method for producing silver powder according to any one of the above aspects, wherein in the classification step, classification is performed while external air is sucked into the wind classifier.

[0027] <5> A silver powder, wherein the values ​​of the cumulative 10% particle size (μm), the cumulative 50% particle size (μm) and the cumulative 90% particle size (μm) accumulated from the smaller particle size side in a particle size distribution determined on a volume basis in a laser diffraction particle size distribution measurement are referred to as D10, D50 and D90, respectively,

[0028] The value obtained by subtracting the D10 from the D90 and dividing it by the D50 is less than 1.0,

[0029] The Sa×D50 value obtained by multiplying the arithmetic mean roughness Sa (nm) in the surface roughness measurement of the silver particle surface in the range of 500nm×500nm by the above D50 is 17000nm. 2 above.

[0030] <6> A silver powder, wherein the values ​​of the cumulative 10% particle size (μm), the cumulative 50% particle size (μm) and the cumulative 90% particle size (μm) accumulated from the smaller particle size side in a particle size distribution determined on a volume basis in a laser diffraction particle size distribution measurement are referred to as D10, D50 and D90, respectively,

[0031] The value obtained by subtracting the D10 from the D90 and dividing it by the D50 is less than 1.0,

[0032] There are closed pores in the silver particles.

[0033] The specific surface area (m 2 / g), with a true density of 9.7 g / cm 3 The BET particle size calculated using the following formula (1) and

[0034] In terms of the arithmetic mean roughness Sa (nm) in the surface roughness measurement of the silver particle surface in the range of 500nm×500nm,

[0035] The value of Sa×BET particle size obtained by multiplying the arithmetic mean roughness Sa by the BET particle size is 13000 nm. 2 above,

[0036] BET particle size = 6 / specific surface area / true density (1).

[0037] <7> According to the above <5> or <6> The silver powder, wherein the D50 is greater than or equal to 0.4 μm and less than or equal to 4.0 μm.

[0038] <8> A conductive paste comprising the above <5> ~ <7> The silver powder described in any one of the above.

[0039] Effects of the Invention

[0040] Provided is a method for producing silver powder, which can be used to prepare a conductive paste capable of obtaining a wiring pattern having a desired line width and height and having a fine line width and a high height, and the silver powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a flow chart of the equipment which realizes the manufacturing method of the silver powder of this embodiment.

[0042] Figure 2 This is a SEM image of the silver powder of Example 1.

[0043] Figure 3 This is a SEM image of the silver powder of Example 2.

[0044] Figure 4 This is a SEM image of the silver powder of Comparative Example 1.

[0045] Figure 5 This is a SEM image of the silver powder of Reference Example 1.

[0046] Figure 6 The diagram shows the shape of an electrode pattern used for thin line evaluation.

[0047] Figure 7 This is a SEM image of the silver powder of Example 3.

[0048] Figure 8 This is a SEM image of the silver powder of Comparative Example 2. DETAILED DESCRIPTION

[0049] A method for producing silver powder according to an embodiment of the present invention will be described with reference to the drawings.

[0050] Figure 1 The flow of the apparatus 100 for realizing the method for producing silver powder according to the present embodiment is shown.

[0051] In the device 100, as a raw material, silver powder (hereinafter referred to as aggregated silver powder) is provided, which is silver powder that contains water and aggregates in a wet state, and has concavities and convexities on the surface of silver particles constituting the silver powder. The aggregated silver powder can be produced, for example, by a wet reduction method. In the device 100, the aggregated silver powder is crushed, dried, classified and captured to produce silver powder suitable for preparing a conductive paste. The silver powder produced in the device 100 retains the surface shape of the silver particles in the aggregated silver powder to a certain extent. According to the present invention, the silver powder produced in the device 100 can be smoother than the surface of the silver particles in the aggregated silver powder, while having desired concavities and convexities on the surface of the silver particles.

[0052] Aggregated silver powder as a raw material can be manufactured by the following wet reduction method as an example. The wet reduction method can be the following method: add an alkali or a complexing agent to an aqueous solution containing a silver salt, generate a slurry containing silver oxide or an aqueous solution containing a silver complex salt, and then add a reducing agent such as formalin to reduce and precipitate the silver powder. In addition, it can also be manufactured by the following method, which includes adding sodium hydroxide to a slurry containing silver oxide or an aqueous solution containing a silver complex salt to adjust the pH. Hereinafter, these methods are referred to as wet reduction methods. In addition, silver particles are sometimes referred to as particles. It should be noted that silver powder refers to silver powder, which is an aggregate of silver particles.

[0053] In the wet reduction method, it is preferred to prevent the silver particles from combining to obtain a monodisperse silver powder. In the wet reduction method, in order to obtain a monodisperse silver powder, a dispersant may be added to the silver paste reduced and precipitated, or a dispersant may be added to an aqueous reaction system containing at least one of a silver salt and silver oxide before the silver particles are reduced and precipitated. As a dispersant, any one or more of fatty acids, fatty acid salts, surfactants, organic acids such as amino acids, organic metals, chelate forming agents, and protective colloids may be selected and used. In order to obtain dry silver powder from the silver paste, a solid-liquid separation process such as filter pressing and a drying process are required. Even if the silver particles are monodispersed in the silver paste reduced and precipitated by the wet reduction method, after the silver paste is subjected to a solid-liquid separation process such as filter pressing and a drying process, the silver powder aggregates and is difficult to use as a conductive paste silver powder. It is generally believed that it is not ideal to mix coarse particles in the silver powder as a conductive paste silver powder. Therefore, as a method for obtaining silver powder for conductive paste from silver paste reduced and precipitated by a wet reduction method, a method of solid-liquid separation, drying, crushing, and classifying the silver paste to remove coarse particles is often used.

[0054] The apparatus 100 includes a feeder 1 , a jet mill 2 (hereinafter referred to as the mill 2 ), a wind classifier 3 (hereinafter referred to as the classifier 3 ), a cyclone separator 4 as a collector, a dust collector 5 , and a blower 6 .

[0055] In the device 100, the pulverizer 2, the classifier 3, the cyclone separator 4, the dust collector 5 and the blower 6 are sequentially connected in series, and the airflow passing through the pulverizer 2, the classifier 3, the cyclone separator 4 and the dust collector 5 is sucked into the blower 6. Preferably, the silver powder is transported by air between the pulverizer 2 and the classifier 3, the classifier 3 and the cyclone separator 4, and the cyclone separator 4 and the dust collector 5.

[0056] The feeder 1 is a device for feeding the aggregated silver powder to the pulverizer 2. For example, a screw feeder can be used as the feeder 1. The water content of the aggregated silver powder fed from the feeder 1 to the pulverizer 2 is set to be 2 wt% (mass %) or more and 20 wt% or less. The water content of the aggregated silver powder is preferably 8 wt% or more and 15 wt% or less, and more preferably 11 wt% or less.

[0057] The pulverizer 2 is a device for realizing a crushing process of crushing the aggregated silver powder. In the pulverizer 2, the aggregated silver powder and compressed air are supplied into the inner space of the pulverizer 2, thereby crushing the aggregated silver powder.

[0058] In the pulverizer 2, compressed air for breaking up the aggregated silver powder is supplied in a manner of being injected into the inner space via an injection nozzle connected to the inner space of the pulverizer 2. The injection nozzle is, for example, provided at the lower portion of the pulverizer 2 and configured in a manner of injecting toward the lower region of the inner space. The injection nozzle may be provided at a plurality of positions of the pulverizer 2. Figure 1 In the embodiment, the injection nozzles are arranged at the upper and lower parts of the pulverizer 2.

[0059] In the crushing process, the compressed air supplied to the injection nozzle of the pulverizer 2 (hereinafter, the compressed air supplied to the injection nozzle is referred to as supply air or crushing air) is heated by the heater 22 on the supply path of the supply air so that the temperature of the compressed air entering the pulverizer 2 is 80° C. or higher and 180° C. or lower. The temperature of the compressed air entering the pulverizer 2 is preferably set to 150° C. or lower. Regarding the pressure of the compressed air supplied to the injection nozzle of the pulverizer 2, the value of the supply pressure (at room temperature before heating) of the air pump 24 can be set to, for example, 0.1 MPa or higher and 0.8 MPa or lower, preferably 0.4 MPa or higher and 0.6 MPa or lower.

[0060] In the pulverizer 2, the aggregated silver powder is supplied to the internal space of the pulverizer 2 from a path different from the compressed air. When supplying, as long as there is a mechanism that can send the aggregated silver powder into the pulverizer 2, a jet nozzle can be set at the pulverizer supply port 21 to be used as a force for supplying crushing air and aggregated silver powder into the pulverizer. As other structures, supply mechanisms such as a venturi tube and an ejector set at the pulverizer supply port 21 can also be used. The supply air used when supplying the aggregated silver powder to the pulverizer 2 can be heated to a temperature of 80°C or more and 180°C or less by a heater 22 on the supply path of the supply air. For the pressure of the supply air, the supply pressure of the air pump 24 (at room temperature before heating) can be set to a value of 0.1MPa or more and 0.8MPa or less.

[0061] In the internal space of the pulverizer 2, the aggregated silver powder is crushed by the shear force of the crushing air ejected from the jet nozzle, the collision of aggregated particles in the aggregated silver powder accelerated by the crushing air, and the collision of aggregated particles accelerated by the crushing air with the wall surface in the tank of the pulverizer 2. It should be noted that in this embodiment, the aggregated particles in the aggregated silver powder refer to secondary particles formed by the aggregation of monodispersed silver particles described in the above-mentioned wet reduction method.

[0062] In the crushing process, the above-mentioned collision reduces the unevenness on the surface of the silver particles while crushing, generates scraped fine particles, and the surface of the silver particles becomes smooth. In the present embodiment, the moisture in the aggregated silver powder evaporates due to the high-temperature crushing air, and thus the atmosphere in the pulverizer becomes a humid gas. The crushing and surface smoothing in the crushing process are carried out in a humid gas. Generally speaking, when there is moisture in the gas, the particles are more likely to aggregate. Therefore, compared with the case of crushing the silver powder in a dry state with dry air, the crushing and surface smoothing are carried out in a state where aggregation is likely to occur. As a result, it is predicted that the collision between the aggregated particles in the crusher and the re-attachment of the scraped fine particles will also become easy to occur. The silver particles obtained in the present embodiment have larger unevenness on the surface of the silver particles compared with the existing silver particles that undergo a crushing process in an atmosphere with a low water content.

[0063] Examples of the pulverizer 2 include: an air jet mill (manufactured by Nissin Engineering Co., Ltd.) and a Sk Jet-O-Mill (manufactured by SEISHINENTERPRISE Co., Ltd.) that continuously supply compressed air to the internal space and achieve crushing in the swirling flow thus generated; a super jet mill (manufactured by Nissin Engineering Co., Ltd.); a spiral jet mill (manufactured by Hosokawa Micron Co., Ltd.); a reverse jet mill (manufactured by Hosokawa Micron Co., Ltd.) that has a built-in classifying rotor and achieves crushing by supplying compressed air to a fluidized bed formed in the internal space; and a transverse jet mill (manufactured by Kurimoto Iron Works Co., Ltd.).

[0064] The following is an explanation of the case where the pulverizer 2 is a pulverizer that continuously supplies crushing air to the internal space and achieves crushing in the swirling flow generated thereby, and an air flow pulverizer that supplies aggregated silver powder to the internal space of the pulverizer 2 from the pulverizer supply port 21 through a path different from the supply air.

[0065] The aggregated silver powder and the supplied air were adjusted so that the exhaust temperature of the pulverizer 2 was 30°C or higher and the absolute volume humidity was 20 g / m 3 The above ratio is supplied to the pulverizer 2. The volume absolute humidity is also preferably set to 30 g / m 3 Hereinafter, the volume absolute humidity is referred to as simply absolute humidity. The temperature and absolute humidity of the exhaust gas of the pulverizer 2 can be obtained by measuring the temperature and humidity (relative humidity) in the connecting pipe 23 using a thermohygrometer 26, for example.

[0066] The classifier 3 is a wind classifier for implementing a classification process, wherein the classification process further separates and removes coarse particles (coarse powder) or fine powder (so-called classification) from the silver powder after the crushing process. The following description will be made by taking the case where the classifier 3 further separates and removes coarse powder as an example.

[0067] As the classifier 3, a classifier having a classifying mechanism is listed, which performs classification by utilizing the balance between the centrifugal force generated by the swirling flow generated by the supply or suction of the airflow and the force of the airflow flowing in the direction opposite to the centrifugal force. In addition, a classifier having a classifying mechanism is listed, which performs classification by utilizing the balance between the centrifugal force generated by the rotating rotor and the force of the airflow flowing in the direction opposite to the centrifugal force. Specific examples include: a fine airflow classifier (manufactured by Nissin Engineering Co., Ltd.), which performs classification by utilizing the centrifugal force generated by the swirling flow generated by the supply of high-speed airflow; and a turbine classifier (manufactured by Nissin Engineering Co., Ltd.) that utilizes the centrifugal force generated by the swirling flow generated by the rotating rotor.

[0068] In the following, the classifier 3 is described by taking the case of a wind classifier having the following grading mechanism as an example, wherein the grading mechanism performs classification by utilizing the balance between the centrifugal force generated by the swirling flow generated by the rotating rotor and the force of the airflow when the exhaust gas of the pulverizer 2 or an airflow different from the exhaust gas (such as external air) overcomes the centrifugal force and is attracted and flows to the exhaust port 39 of the airflow classifier. Here, the exhaust gas of the pulverizer 2 is supplied to the classifier supply port 31 together with the crushed silver powder, and the other airflow can be generated by the gas sucked into the classifier 3 through a path different from the exhaust gas of the pulverizer 2. It should be noted that the absolute humidity of the external air sucked into the classifier 3 is preferably less than 15 g / m 3 The absolute humidity is preferably 12 g / m 3The temperature of the outside air sucked into the classifier 3 may be set to be lower than 30° C. and the relative humidity may be lower than 50%, and the relative humidity may be set to be lower than 40%.

[0069] The silver powder after the crushing process (silver powder crushed in the pulverizer 2) and the exhaust gas of the pulverizer 2 are supplied to the classifier 3. The classifier supply port 31 of the classifier 3 can be connected to the pulverizer exhaust port 29 of the pulverizer 2 by the connecting pipe 23. Thus, all the silver powder after the crushing process and all the exhaust gas of the pulverizer 2 are supplied to the classifier 3 via the connecting pipe 23 and the classifier supply port 31. That is, in the connecting pipe 23, the air transportation of the silver powder after the crushing process is realized by the airflow of the exhaust gas of the pulverizer 2.

[0070] In the apparatus 100, the exhaust gas of the pulverizer 2 flowing through the connecting pipe 23 is controlled to have a temperature of 30° C. or higher and an absolute humidity of 20 g / m 3 As described above, it is possible to simplify the process by integrating the drying process and the crushing process, and realize a method for producing a silver powder that can prepare a conductive paste capable of obtaining a wiring pattern having a desired line width and height.

[0071] The exhaust gas of the pulverizer 2 flowing through the connecting pipe 23 is controlled to have a temperature of 30° C. or higher and an absolute humidity of 20 g / m 3 As described above, although the gas at the classifier supply port 31 is humid, as the classification process proceeds, the water content of the gas conveying the silver powder gradually decreases due to the mixing of external gas. Classification is performed with the change of the water content of the conveying gas. Generally speaking, when there is water in the gas, particles are more likely to aggregate, so silver particles that are easy to aggregate are easily eliminated as coarse powder at the initial stage of classification. That is, compared with the case of using dry air to classify the silver powder in a dry state, the silver particles can be screened according to the ease of aggregation.

[0072] Among the silver powder after the crushing process supplied to the classifier 3, the coarse powder is discharged from the coarse powder discharge port 35. The silver powder other than the coarse powder among the silver powder after the crushing process supplied to the classifier 3 is discharged from the classifier exhaust port 39 of the classifier 3 together with the exhaust gas of the classifier 3, and is supplied (sucked) to the cyclone separator 4 from the cyclone separator inlet 41 by air transportation.

[0073] In the cyclone separator 4, a collecting process is performed in which the silver powder supplied from the classifier 3 is collected by the collector. At this time, fine particles are removed from the silver powder. In the cyclone separator 4, for example, the silver powder is recovered in a recovery tank 49 at the bottom. The silver powder recovered by the cyclone separator 4 is the silver powder of this embodiment.

[0074] The aggregated silver powder is dried while being crushed by solid-gas contact during the crushing in the pulverizer 2, the classification in the classifier 3, and the capture in the cyclone separator 4. As a result, the silver powder recovered by the cyclone separator 4 is drier than the aggregated silver powder. In the device 100, compressed air heated to 80° C. or higher and 180° C. or lower is supplied to the internal space of the pulverizer 2, thereby drying the silver powder in the pulverizer 2, the classifier 3, and the cyclone separator 4, and the silver powder recovered by the cyclone separator 4 is fully dried to a degree that does not require further fine drying (for example, the water content of the silver powder is 0.1% by mass or less).

[0075] The exhaust gas of the cyclone separator 4 is sucked into the blower 6 via the dust collector 5 and discharged to the outside of the system of the equipment 100. In the dust collector 5, the exhaust gas of the cyclone separator 4 is filtered, and the fine silver powder not collected by the cyclone separator 4 is recovered.

[0076] The method for producing the silver powder of the present embodiment is performed as follows.

[0077] The silver powder of the present invention is described below.

[0078] In the silver powder of the present invention, the values ​​of the cumulative 10% particle size (μm), the cumulative 50% particle size (μm) and the cumulative 90% particle size (μm) accumulated from the small particle size side in the particle size distribution obtained on a volume basis in the laser diffraction particle size distribution measurement are set as D10, D50 and D90, respectively, and the value obtained by subtracting the difference obtained by subtracting the D10 from the D90 and dividing it by the D50 is preferably 1.0 or less. When this value exceeds 1.0, for the wiring pattern obtained by pasting and baking the silver powder, it is sometimes impossible to obtain a wiring pattern with the desired line width and height. It should be noted that the difference obtained by subtracting the D10 from the D90 can be set to 0.1μm or more, 4.0μm.

[0079] The silver particles constituting the silver powder preferably have closed pores in the silver particles, thereby lowering the firing temperature for obtaining a wiring pattern.

[0080] The arithmetic mean roughness Sa (nm) in the surface roughness measurement of 500nm×500nm range of the silver particle surface constituting the silver powder is preferably 9nm or more, more preferably 10nm or more. When Sa is less than 9nm, for the wiring pattern obtained by forming the silver powder into a paste and baking it, it is sometimes impossible to obtain a wiring pattern with a desired line width and height. When Sa is too large, the viscosity of the paste may become too high, and Sa can be set to 40nm or less.

[0081] The specific surface area (m 2 / g), with a true density of 9.7 g / cm 3The BET particle size calculated by the following formula (1) and the arithmetic mean roughness Sa (nm) in the surface roughness measurement of the silver particles constituting the silver powder in the range of 500 nm × 500 nm, the value of Sa × BET particle size obtained by multiplying the arithmetic mean roughness Sa by the BET particle size is preferably 13000 nm. 2 More preferably, 14000nm 2 By setting it as this range, regardless of the size of the BET particle size, the line width in the wiring pattern obtained by forming the silver powder into a paste and baking it can be made narrower than the line width in the conventional art.

[0082] BET particle size = 6 / specific surface area / true density (1)

[0083] In the silver powder, the value of Sa×D50 obtained by multiplying the Sa by the D50 is preferably 17000 nm. 2 More preferably 18500nm 2 By setting it as this range, regardless of the size of D50, the line width in the wiring pattern obtained by forming the silver powder into a paste and baking it can be made narrower than the line width in the conventional technology.

[0084] The D50 of the silver powder is preferably 0.4 μm or more and 4.0 μm or less, more preferably 1.0 μm or more and 3.0 μm or less, and further preferably 1.0 μm or more and 2.5 μm or less. When the D50 of the silver powder exceeds 4.0 μm, it is sometimes difficult to obtain a wiring pattern with a narrow width. When the D50 of the silver powder is less than 0.4 μm, the viscosity of the paste becomes too high when the paste is formed, and sometimes it becomes difficult to handle. For the same reason, the D90 is preferably 0.45 μm or more and 7.0 μm or less, and the D10 is preferably 0.1 μm or more and 3.8 μm or less.

[0085] The BET particle size of the silver powder is preferably 0.3 μm or more and 3.5 μm or less, more preferably 0.8 μm or more and 3.0 μm or less, and further preferably 0.8 μm or more and 2.5 μm or less. When the BET particle size of the silver powder exceeds 3.5 μm, it is sometimes difficult to obtain a wiring pattern with a narrow width. When the BET particle size of the silver powder is less than 0.3 μm, the viscosity of the paste becomes too high when forming a paste, which sometimes makes it difficult to handle.

[0086] The value calculated by formula (2) as the ratio of the BET particle size of the silver powder to the D50 is preferably 1.8 or less, more preferably 1.6 or less, and further preferably 1.5 or less. When the value exceeds 1.8, the degree of aggregation of the silver particles in the silver powder becomes stronger, and it is sometimes difficult to obtain a wiring pattern with a desired line width and height, especially a wiring pattern with a narrow width.

[0087] D50 / BET particle size formula (2)

[0088] The water content of the silver powder is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and further preferably 0.01% by mass or less. When the water content of the silver powder exceeds 0.1% by mass, the silver powder may aggregate in the paste, thereby increasing the viscosity, or the silver powder may aggregate and clog the printing plate, resulting in a short circuit.

[0089] 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.

[0090] There is no particular limitation on the organic binder, and examples thereof include silicone resins, epoxy resins, acrylic resins, polyester resins, polyimide resins, polyurethane resins, phenoxy resins, cellulose resins (ethyl cellulose, hydroxypropyl cellulose, etc.), etc. These may be used alone or in combination of two or more in any ratio.

[0091] The solvent is not particularly limited, and examples thereof include: alcohol solvents such as terpineol, butyl carbitol, ester-12, ethylene glycol, and diethylene glycol; ester solvents such as butyl carbitol acetate and ethyl acetate; hydrocarbon solvents such as toluene, xylene, and cyclohexane; glycerol, etc. These may be used alone or in combination of two or more in any ratio.

[0092] The content of the silver powder of the present invention in the conductive paste can be 80% by mass or more, preferably 85% by mass or more, and can be 95% by mass or less, preferably 90% by mass or less.

[0093] The content of the organic binder in the conductive paste can be 0.1% by mass or more, preferably 0.2% by mass or more, and can be 0.4% by mass or less, preferably 0.3% by mass or less.

[0094] The content of the solvent in the conductive paste can be 6% by mass or more, preferably 7% by mass or more, and can be 20% by mass or less, preferably 15% by mass or less.

[0095] The conductive paste may contain, as optional components, glass frit, dispersant, surfactant, viscosity modifier, lubricant, etc. The conductive paste used in the manufacture of the electrode of the solar cell preferably contains glass frit, for example, glass frits such as Pb-Te-Bi system and Pb-Si-B system can be mentioned.

[0096] There is no particular limitation on the method for producing the conductive paste, and examples thereof include a method of mixing the spherical silver powder of the present invention, an organic binder, a solvent, and optional components as required. The mixing method is not particularly limited, and for example, a self-revolving stirrer, ultrasonic dispersion, disperser, three-roll mill, ball mill, bead mill, twin-screw kneader, etc. can be used.

[0097] The conductive paste of the present invention can be applied on a substrate to form a coating film by printing such as screen printing, offset printing, photolithography, etc., or by dipping, etc. The coating film can also be formed into a predetermined pattern shape by photolithography using a resist.

[0098] The coating film can be baked to form a conductive film. The baking can be carried out in an air atmosphere or in a non-oxidizing atmosphere such as nitrogen. The baking temperature of the coating film can be set to 600° C. to 800° C., preferably 690° C. to 740° C. The baking time can be set to 20 seconds to 1 hour, preferably 40 seconds to 2 minutes.

[0099] Hereinafter, the method for producing the silver powder according to the present embodiment and examples of the silver powder produced by the method will be described.

[0100] (Example 1)

[0101] The silver powder of Example 1 was produced in the following manner.

[0102] Aggregated silver powder supplied to the apparatus 100 was produced as follows. 27.74 kg of a 26 wt % ammonia solution was added to 2955 kg of a silver nitrate aqueous solution containing 47.5 kg of silver as a silver ion aqueous solution, and the liquid temperature was set to 28.3° C. Furthermore, 154.6 kg of a 37 wt % formalin aqueous solution was added as a reducing agent and stirred thoroughly to obtain a slurry containing silver powder.

[0103] Furthermore, 5.0 kg of liquid containing pure water and 0.54 kg of stearic acid emulsion was added to the obtained slurry to obtain a silver slurry. The silver slurry was filtered, washed with water, and then filtered under pressure to obtain silver powder (aggregated silver powder). The particle cross-section of the silver particles (raw material particles) of the obtained silver powder was observed with a scanning electron microscope, and it was found that there were closed pores inside. The water content (loss on drying) of the aggregated silver powder was 10.02 wt%.

[0104] Furthermore, the aggregated silver powder was crushed and dried in the above-mentioned apparatus 100, and the silver powder captured by the cyclone separator 4 was further sieved with a sieve having an aperture of 40 μm, and the silver powder passing through the sieve was used as the silver powder of Example 1. When the particle cross-section of the silver powder of Examples 1 and 2 was observed with a scanning electron microscope, it was found that the silver powder had closed pores inside.

[0105] Table 1 shows the operating conditions of the apparatus 100 when the silver powder of Example 1 is manufactured. Also shown are Example 2, Example 3, Comparative Example 1, Comparative Example 2, and Reference Example 1 described later. Here, the supply air B is the air supplied to the injection nozzle at the bottom of the pulverizer, and the supply air A is the air supplied to the injection nozzle at the top of the pulverizer.

[0106] [Table 1]

[0107]

[0108] In Table 1, the item "Environment" shows the temperature (°C) and relative humidity (%) of the atmosphere around the equipment 100 during manufacturing, and is the temperature and relative humidity of the outside air sucked into the classifier 3 described later.

[0109] In Table 1, the item "Agglomerated silver powder water content" shows the water content (wt %) of the above-mentioned aggregated silver powder.

[0110] In Table 1, the item "Supply machine" shows the supply speed (kg / min) when the aggregated silver powder is supplied from the supply machine 1 to the pulverizer 2. In addition, the item "Pulverizer" shows the total air volume (m2) of the supply air supplied to the pulverizer 2 as the crushing condition in the pulverizer 2. 3 / min), the supply amount of supply air supplied to each injection nozzle (m 3 / min) and its pressure (MPa) and temperature (°C). It should be noted that, here, the total air volume refers to the total amount of supply air supplied to the upper and lower injection nozzles in the grinder. It should be noted that the total air volume and the supply amount of supply air supplied to each injection nozzle are values ​​before heating, and are values ​​measured by the flow meter 27 arranged in the supply path, indicating the value at 1 atmosphere and 0°C (standard conversion value). In Table 1, the value in the grinder temperature column is the outlet temperature of the heater 22, indicating the temperature of the supply air after heating and before being supplied to the grinder.

[0111] 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 to be a case where a drying process is performed in the device 100. In Example 1, as shown in Table 1, the temperature of supply air A and supply air B is set to 120°C, so the drying process is performed in the device 100.

[0112] In Table 1, the item "Pulverizer exhaust gas" shows the temperature (°C) of the exhaust gas of the pulverizer 2, the relative humidity (%) of the exhaust gas, and the absolute humidity (g / m 3 ).

[0113] In Table 1, the item "Classifier" shows the air volume (m2) of the outside air sucked into the classifier 3, which is different from the exhaust gas of the pulverizer 2, as the condition of the classifier 3. 3 / min). It should be noted that the suction air volume represents the standard flow rate.

[0114] In Table 1, the exhaust air volume in the item "blower" indicates the exhaust air volume (m 3 It should be noted that the exhaust air volume represents the standard flow rate.

[0115] Here, the air volume of the outside air sucked into the classifier 3 in Table 1 is not an actually 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 .

[0116] (Example 2)

[0117] As for the silver powder of Example 2, the aggregated silver powder (water content: 10.02 wt%) produced in the same manner as in Example 1 was supplied to the apparatus 100, and the operating conditions of the apparatus 100 were changed compared with those of Example 1 to perform crushing and drying, and the silver powder collected by the cyclone separator 4 in the same manner as in Example 1 was sieved with a sieve having an aperture of 40 μm, and the silver powder that passed through the sieve was used as the silver powder of Example 2. Table 1 shows the operating conditions of the apparatus 100 when producing the silver powder of Example 2. In Example 2, the temperatures of the supply air A and the supply air B were set to 130° C. as shown in Table 1, and thus the drying process was performed in the apparatus 100.

[0118] (Comparative Example 1)

[0119] Unlike the above-mentioned embodiment, the silver powder of Comparative Example 1 was produced without performing a drying process in the apparatus 100. That is, for the silver powder of Comparative Example 1, the aggregated silver powder produced in the same manner as in Example 1 was subjected to a drying process using a vacuum rotary dryer in a manner different from that of Example 1, and then roughly crushed by stirring using a Henschel type mixer, and the roughly crushed, aggregated silver powder (water content: 0.01 wt%) was supplied to the apparatus 100 in the same manner as in Example 1, and the silver powder was crushed by changing the operating conditions of the apparatus 100 compared to Example 1, and the silver powder collected by the cyclone separator 4 was used as the silver powder of Comparative Example 1. Table 1 shows the operating conditions of the apparatus 100 when producing the silver powder of Comparative Example 1. In Comparative Example 1, the temperatures of the supply air A and the supply air B were set to 16° C. as shown in Table 1, and therefore, no drying process was performed in the apparatus 100 as described above. In addition, the absolute humidity of the air as the exhaust gas of the pulverizer supplied to the classifier was reduced.

[0120] (Reference Example 1)

[0121] The silver powder of Reference Example 1 is different from Example 1 in that it is silver powder that has been processed twice in the apparatus 100. That is, the aggregated silver powder (water content: 10.40 wt%) produced in the same manner as in Example 1 is supplied to the apparatus 100, and the operating conditions of the apparatus 100 are changed compared with those in Example 1 to perform crushing and drying (first time), the silver powder (water content: 0.01 wt%) collected by the cyclone separator 4 in the same manner as in Example 1 is supplied to the apparatus 100 again (second time), and the silver powder collected by the cyclone separator 4 again is sieved with a sieve having an aperture of 40 μm, and the silver powder that passes through the sieve is used as the silver powder of Reference Example 1.

[0122] Table 1 shows the operating conditions of the device 100 when manufacturing the silver powder of Reference Example 1. It should be noted that in Table 1, the water content of the silver powder supplied to the device 100 for the second time (the silver powder captured by the cyclone separator 4 in the first treatment) is recorded in the item of "moisture content of aggregated silver powder". In Table 1, "Reference Example 1 (1st time)" shows the operating conditions of the first treatment in the device 100. In addition, "Reference Example 1 (2nd time)" shows the operating conditions of the second treatment in the device 100. In Reference Example 1, the drying treatment in the device 100 was performed in the first treatment (the temperature of the supply air A and the supply air B was 110°C), and the drying treatment in the device 100 was not performed in the second treatment (the temperature of the supply air A and the supply air B was 13°C).

[0123] Next, aggregated silver powder different from the aggregated silver powder used in Examples 1 and 2, Comparative Example 1, and Reference Example 1 was used, and the operating conditions of the apparatus 100 were also changed to confirm the obtained silver powder.

[0124] (Example 3)

[0125] The silver powder of Example 3 was produced as follows.

[0126] First, the aggregated silver powder to be supplied to the apparatus 100 was produced as follows. 35.52 kg of a 26 wt % ammonia solution was added to 2630 kg of a silver nitrate aqueous solution containing 38.9 kg of silver as a silver ion aqueous solution, and the liquid temperature was set to 32.0° C. Furthermore, 171.2 kg of a 37 wt % formalin aqueous solution was added as a reducing agent and stirred thoroughly to obtain a slurry containing silver powder.

[0127] Furthermore, 4.05 kg of stearic acid emulsion was added to the obtained slurry to obtain a silver slurry. The silver slurry was filtered, washed with water, and then filtered under pressure to obtain silver powder (aggregated silver powder). The particle cross-section of the silver particles (raw material particles) of the obtained silver powder was observed using a scanning electron microscope, and it was found that there were closed pores inside. The water content (loss on drying) of the aggregated silver powder was 7.83 wt%.

[0128] Furthermore, the aggregated silver powder was crushed and dried in the above-mentioned apparatus 100, and the silver powder captured by the cyclone separator 4 was further sieved with a sieve having an aperture of 40 μm, and the silver powder passing through the sieve was used as the silver powder of Example 3. The particle cross section of the silver powder of Example 3 was observed with a scanning electron microscope, and it was found that the silver powder had closed pores inside.

[0129] Table 1 shows the operating conditions of the apparatus 100 when the silver powder of Example 3 was produced. In Example 3, the temperature of the supply air A and the supply air B was set to 150° C. as shown in Table 1, and thus the drying process was performed in the apparatus 100 .

[0130] (Comparative Example 2)

[0131] As in Comparative Example 1, the silver powder of Comparative Example 2 was produced without performing the drying treatment in the apparatus 100. That is, for the silver powder of Comparative Example 2, the aggregated silver powder produced in the same manner as in Example 3 was dried by a vacuum rotary dryer in a manner different from that in Example 3, and then roughly crushed by stirring with a Henschel type mixer, and the roughly crushed and aggregated silver powder (water content: 0.01 wt%) was supplied to the apparatus 100 in the same manner as in Example 3, and the silver powder was crushed by changing the operating conditions of the apparatus 100 compared with that in Example 3, and the silver powder collected by the cyclone separator 4 was used as the silver powder of Comparative Example 2. Table 1 shows the operating conditions of the apparatus 100 when producing the silver powder of Comparative Example 2. In Comparative Example 2, the temperatures of the supply air A and the supply air B were set to 14° C. as shown in Table 1, and therefore, the drying treatment in the apparatus 100 was not performed as described above. In addition, the absolute humidity of the air as the exhaust gas of the pulverizer supplied to the classifier was reduced.

[0132] Evaluation values ​​of the silver powders of Examples, Comparative Examples, and Reference Examples are shown in Tables 2 and 3. The evaluation values ​​shown in Tables 2 and 3 are described below.

[0133] [Table 2]

[0134]

[0135] [Table 3]

[0136]

[0137] In Table 2, “SSA” (m 2 / g) is the specific surface area of ​​the silver powder. The specific surface area of ​​the silver powder adopts the BET specific surface area obtained by the BET method. A BET specific surface area measuring device (Macsorb HM-model1210 manufactured by MOUNTECH Co., Ltd.) was used, and a He-N2 mixed gas (nitrogen 30%) was circulated in the measuring device at 60°C for 10 minutes and degassed, and then the BET specific surface area was measured by the BET one-point method.

[0138] In Table 2, “BET particle size” (μm) is based on the BET specific surface area (m 2 / g) and the true density of the silver powder (in this embodiment, 9.7 g / cm is used as the true density) 3 ) and use the following formula (1) to calculate the specific surface area particle size.

[0139] BET particle size (μm) = 6 / specific surface area / true density formula (1)

[0140] In Table 2, "D10" (μm), "D50" (μm) and "D90" (μm) refer to the particle size distribution of the silver powder obtained on a volume basis in the laser diffraction particle size distribution measurement, and represent the values ​​of the cumulative 10% particle size (μm), the cumulative 50% particle size (μm) and the cumulative 90% particle size (μm) accumulated from the small particle size side. It should be noted that the cumulative 50% particle size on a volume basis refers to the median particle size. Below, the values ​​of the cumulative 10% particle size (μm), the cumulative 50% particle size (μm) and the cumulative 90% particle size (μm) are recorded as D10, D50 and D90, respectively.

[0141] As the particle size distribution of the silver powder, the particle size distribution measured by a laser diffraction / scattering particle size distribution measuring device (Microtrac MT-3300EXII manufactured by Microtrac BEL Co., Ltd.) was used.

[0142] The particle size distribution using the above-mentioned laser diffraction / scattering particle size distribution measuring device is measured in the following manner. First, 0.1 g of silver powder is added to 40 mL of isopropyl alcohol (IPA) and dispersed. During dispersion, an ultrasonic homogenizer (manufactured by Nippon Seiki Co., Ltd., device name: US-150T; 19.5 kHz, front end diameter 20 mm) is used. The dispersion time is set to 2 minutes. Then, the dispersed sample is provided to the above-mentioned laser diffraction / scattering particle size distribution measuring device, and the particle size distribution is calculated using the accompanying analysis software.

[0143] In Table 2, "(D90-D10) / D50" indicates the value obtained by subtracting D10 from D90 and dividing the difference by D50. This value indicates the degree of spread of the particle size distribution (the width of the particle size distribution). The larger the value, the wider the particle size distribution, and the smaller the value, the narrower the particle size distribution. Hereinafter, "(D90-D10) / D50" may be referred to as the width value.

[0144] The "silver powder moisture content" in Table 2 is the moisture content of the silver powder obtained through the classification process. In Table 1, the "aggregate silver powder moisture content" (%) and the "silver powder moisture content" (%) in Table 2 were calculated as follows. The value was calculated as follows: 10 g of aggregated silver powder or silver powder was weighed as a sample and placed in a weighing bottle, dried at 90°C without covering for 3 hours, left to cool for more than 40 minutes, and the value obtained by dividing the weight reduction of the sample by the weight of the sample before drying (10 g) was multiplied by 100.

[0145] In Table 2, the "loss on ignition" (%) is a value obtained as follows. First, 3 g of silver powder is weighed and placed in a magnetic crucible and heated to 800°C. Then, it is heated at 800°C for 30 minutes to fully heat until a constant weight is reached. Then, the silver powder is cooled and weighed to obtain the mass (w) after heating. The loss on ignition (%) is a value obtained based on the mass (w) using the following formula (2).

[0146] Loss on ignition (%) = (3-w) / 3×100 Formula (2)

[0147] In Table 2, "TAP" (g / mL) is the tap density of the silver powder. The tap density of the silver powder is the value obtained using a tap density measuring device (volumetric specific gravity measuring device SS-DA-2 manufactured by Shibayama Scientific Co., Ltd.). The tap density is measured as follows. Weigh 30 g of the silver powder sample, put it into a 20 mL test tube, and tap it 1000 times with a drop of 20 mm. Then, calculate the sample volume (cm 3 ). Tap density (g / cm 3 ) is based on the sample volume after tapping (cm 3 ) and use the following formula (3) to find the value.

[0148] Tap density (g / cm 3 ) = 30 (g) / sample volume after tapping (cm 3 ) Formula (3)

[0149] In Table 2, "Sa" (nm) is the arithmetic mean roughness specified in ISO25178 in the surface roughness measurement of the silver particle surface. In addition, in Table 3, "Sz", "Sp", "Sv" and "Sq" are also the maximum height, maximum peak height, maximum valley depth and root mean square height specified in ISO25178. These values ​​are obtained based on the shape image obtained by the scanning probe microscope (SPM). Specifically, SPM (Nano Cute) manufactured by SII NanoTechnology Inc. is used, and SI-DF40P2 manufactured by Hitachi High-Tech Fielding is used as the cantilever. The tapping mode (DFM) is selected as the measurement mode. In detail, the Q curve is first measured and the cantilever is adjusted. At this time, it is confirmed that the resonant frequency is in the range of 200Hz to 500Hz, and the Q value is in the range of 100 to 1000. The target vibration amplitude of the cantilever is set to 1V. Next, the shape image and error signal image of the silver particles with a field of view range of 5μm are obtained using SPM. At this time, the amplitude attenuation rate is automatically set to the range of -0.1 to -0.2. In addition, the scanning frequency is set to a range of 0.6 Hz to 1 Hz. The feedback control parameters are set automatically. The number of pixels when acquiring the shape image is set to 256×256. Then, the range of roughness to be analyzed is specified in the shape image, and on this basis, three tilt corrections and flattening processes are performed to remove the components originating from the curved surfaces of the particles, thereby automatically calculating the arithmetic mean roughness Sa and the values ​​of Sz, Sp, Sv, and Sq of the particle surface specified in ISO25178. At this time, no cutoff processing is performed. The analysis range is set to a square range with a side of 500 nm (hereinafter referred to as a 500nm×500nm range). During the analysis, 10 particles are randomly selected for analysis, and their average value is calculated.

[0150] In Table 2, "Sa×D50" (nm 2 ) is the value obtained by multiplying Sa by D50.

[0151] In Table 2, “Sa×BET particle size” (nm 2 ) is a value obtained by multiplying Sa by the BET particle size.

[0152] Figures 2 to 5 as well as Figure 7 , Figure 8The SEM images (20,000 times) of the silver powders of Example 1, Example 2, Comparative Example 1, Reference Example 1, and Example 3 and Comparative Example 2 are shown respectively. It can be seen from the SEM images of Examples 1 to 3 that the silver particles have concavities and convexities on their surfaces. For the concavities and convexities on the silver particle surfaces observed in the SEM images of Examples 1 to 3, it is speculated that the concavities and convexities on the silver particle surfaces generated by the wet reaction are not sufficiently removed in the crushing process and the classification process, and more remain on the silver particle surfaces constituting the silver powder of the present invention, resulting in larger concavities and convexities on the silver particle surfaces. The concavities and convexities on the silver particle surfaces observed in the SEM images of Comparative Example 1, Reference Example 1, and Comparative Example 2 are smaller than those in the examples. It is speculated that the water content of the atmosphere enveloping the silver particles in the crushing process and the classification process is small, so the concavities and convexities on the silver particle surfaces are not sufficiently removed in the crushing process and the classification process, resulting in smaller concavities and convexities on the silver particle surfaces than in the examples. The degree of concavities and convexities on the silver particle surfaces of the examples, comparative examples, and reference examples is reflected in their Sa values.

[0153] Next, conductive pastes were prepared using the silver powders of Examples, Comparative Examples, and Reference Examples, and thin line evaluation (EL) was further performed.

[0154] Conductive pastes were prepared as follows using the silver powders of Examples 1 to 3, Comparative Examples 1 and 2, and Reference Example 1. Conductive pastes were obtained by subjecting the materials shown in Table 4 having the composition ratios shown in Table 4 to the following treatments. After stirring and mixing at 1400 rpm for 30 seconds using a propeller-free self-revolving stirring and degassing device (AR310 manufactured by THINKY Co., Ltd.), a three-roll mill (80S manufactured by EXAKT Co., Ltd.) was used to pass through the roll gap from 100 μm to 20 μm and knead.

[0155] [Table 4]

[0156]

[0157] * Pb-Te-Bi series

[0158] ** NAMLON206T manufactured by Kusunoki Chemicals Co., Ltd.

[0159] *** Shin-Etsu Chemical Co., Ltd. KF96-100

[0160] The viscosity of the paste was measured using a viscometer 5XHBDV-IIIUC manufactured by Brookfield. The measurement conditions were as follows: the cone shaft was CP-52. The paste temperature was set to 25°C. The rotation speed and measurement time were set to 1 rpm (shear rate 2 sec -1 )5 minutes and 5rpm (shear rate 10sec -1 ) for 1 minute.

[0161] Fine line evaluation was performed by forming a conductive pattern. The conductive pattern was formed as follows. First, a screen printer (Microtech, MT-320TV) was used to form a solid pattern of 154 mm on the back of a silicon substrate (100 Ω / □) for solar cells using an aluminum paste (Rutech, 28D22G-2). Next, the paste was filtered through a 500-mesh sieve and then sieved according to the method. Figure 6 The pattern shown is printed (coated) on the surface of the substrate with electrodes (finger electrodes) with a design line width of 14 to 26 μm (screen opening width) and electrodes (bus electrodes) with a design line width of 1 mm at a squeegee speed of 350 mm / sec. The printed paste is dried with hot air at 200°C for 10 minutes, and then fired in a high-speed firing furnace IR furnace (Japan Insulator Co., Ltd., high-speed firing test 4-chamber furnace) at a peak temperature of 750°C and an in-and-out time of 41 seconds to obtain a conductive pattern.

[0162] The line width and height of the electrical pattern were measured using a laser microscope (KEYENCE VKX-1000). Figure 6 The electrodes printed with a designed line width of 24μm were measured. The images were taken with a 20x objective lens (the electrode length in each field of view was about 500μm), and 601 cross-sectional shapes were measured at intervals of 0.687μm in each field of view (equivalent to an electrode length of about 400μm), and their average cross-sectional shape was calculated. For the average cross-sectional shape, the height of the substrate was used as the baseline, the distance rising from the baseline was measured as the line width, and the height difference between the highest point and the baseline was measured as the height, to obtain the line width and height in each field of view. Among the 10 electrodes with a designed line width of 24μm, the 4th, 6th, and 8th electrodes from the left were photographed at two positions, 5cm and 10cm away from the upper end of the electrode, respectively. The average value of the line width and height of the 6 fields of view was calculated.

[0163] Table 5 shows the height and line width of the electrode in the thin line evaluation using the silver powder paste of the example, comparative example and reference example. In addition, the viscosity of the silver powder paste of the example, comparative example and reference example is shown.

[0164] [Table 5]

[0165]

[0166] As shown in Table 5, in Comparative Example 1, Reference Example 1, Examples 1 and 2 manufactured based on the same aggregated silver powder, the paste using the silver powder in Examples 1 and 2 achieved a line width of the conductive pattern closer to the designed line width in the fine line evaluation, and had good characteristics, compared with Comparative Example 1 and Reference Example 1. In addition, the paste using the silver powder of Examples 1 and 2 achieved a line width of the conductive pattern closer to the designed line width, and at the same time, the aspect ratio obtained by dividing the height by the line width was large, so it had good characteristics. It can also be seen that in Comparative Example 2 and Example 3 manufactured based on the same aggregated silver powder, the paste using the silver powder of Example 3 also achieved a line width of the conductive pattern closer to the designed line width, and had a large aspect ratio, compared with Comparative Example 2, so it had good characteristics.

[0167] From the results of the above-described thin line evaluation, it can be evaluated that the silver powder of the example is a silver powder that can prepare a paste capable of obtaining a wiring pattern having a desired line width and height.

[0168] It can be seen from Table 2 that, as in the embodiment, comparative example and reference example, when the operating conditions of the device 100 are changed as shown in Table 1 for the same aggregated silver powder, the silver powder of the embodiment has larger surface irregularities than the silver powder of the comparative example or the reference example, and the Sa value becomes larger.

[0169] In addition, as shown in Table 2, compared with Comparative Example 1, in Examples 1 and 2, the temperature of the exhaust gas of the pulverizer 2 flowing through the connecting pipe 23 is controlled to be above 30°C, and the absolute humidity is controlled to be 20 g / m 3 As described above, based on the improvement of the classification performance of the classifier, (D90-D10) / D50 in Example 1 is smaller than that in Comparative Example 1. In Example 3, which is an aggregated silver powder different from the aggregated silver powder prepared in Example 1, (D90-D10) / D50 in Example 3 is also smaller than that in Comparative Example 2.

[0170] Thus, in order to prepare a paste capable of obtaining a wiring pattern having a desired line width and height, it is necessary to use silver powder having appropriate irregularities on the surface of the silver particles. Figure 2 to Figure 5 It can also be clearly seen in the SEM images of the silver powders of the examples, comparative examples and reference examples shown. Figure 2 , Figure 3 , Figure 7 ), moderate irregularities can be observed on the surface of the spherical silver particles. Figure 4 , Figure 5 , Figure 8) Compared with the silver powder of the embodiment, the surface of the silver particles has less unevenness and the surface of the silver particles is smooth as a whole. It can be seen that according to the manufacturing method of this embodiment, silver particles suitable for preparing a paste that suppresses the smoothness of the surface of the silver particles and thereby can obtain a wiring pattern with a desired line width and height can be obtained.

[0171] From the operating conditions of the apparatus 100 shown in Table 1, the method for producing silver powder capable of preparing a paste capable of obtaining a wiring pattern having a desired line width and height is not a method for producing silver powder aggregated in advance by drying and then performing treatment other than drying in the apparatus 100 as in the comparative example or the reference example, but a method for producing silver powder by crushing, classifying, and drying the aggregated silver powder in the apparatus 100 as in the embodiment. It is also considered that when the aggregated silver powder is dried in the apparatus 100 to obtain the dried silver powder, it is necessary to supply compressed air having a temperature of 80° C. or higher and 180° C. or lower to the crusher 2 in the crushing process, and it is necessary to supply the exhaust gas of the crusher 2 to the classifier 3, and the temperature of the exhaust gas is 30° C. or higher and the relative humidity is 30%.

[0172] As described above, it is possible to provide a method for producing a silver powder and the silver powder capable of preparing a conductive paste capable of obtaining a wiring pattern having a desired line width and height.

[0173] It should be noted that, as long as there is no contradiction, the structures disclosed in the above-mentioned embodiments (including other embodiments, the same below) can be combined with the structures disclosed in other embodiments, and the embodiments disclosed in this specification are exemplary, and the embodiments of the present invention are not limited to this, and can be appropriately modified within the scope without departing from the purpose of the present invention.

[0174] Industrial Applicability

[0175] The present invention can be used for a method for producing silver powder and the silver powder.

[0176] Description of Reference Numerals

[0177] 1: Supply machine

[0178] 100: Equipment

[0179] 2: Pulverizer (air flow pulverizer)

[0180] 21: Crusher supply port

[0181] 22: Heater

[0182] 23: Connecting pipe

[0183] 24: Air pump

[0184] 26: Thermohygrometer

[0185] 27: Flow meter

[0186] 29: Exhaust port of crusher

[0187] 3: Classifier (wind classifier)

[0188] 31: Classifier supply port

[0189] 35: Coarse powder discharge outlet

[0190] 39: Classifier exhaust port

[0191] 4: Cyclone separator

[0192] 41: Cyclone separator inlet

[0193] 49: Recovery tank

[0194] 5: Dust collector

[0195] 6: Blower

Claims

1. A method for producing silver powder, comprising: include: A crushing process of crushing the aggregated silver powder using a jet mill; and, A classification process of classifying the silver powder after the crushing process using a wind classifier, The water content of the aggregated silver powder is greater than 2 wt % and less than 20 wt %, In the crushing step, compressed air at a temperature of 80° C. or higher and 180° C. or lower is supplied as supply air to the air flow mill. In the classification process, the exhaust gas of the air flow mill and the silver powder after the crushing process are supplied to the air classifier. The exhaust temperature is above 30°C and the absolute volume humidity is 20g / m 3 above.

2. The method for producing silver powder according to claim 1, in, The air classifier and the air flow pulverizer are connected via a connecting pipe, and exhaust gas of the air flow pulverizer and the silver powder after the crushing step are supplied from the air flow pulverizer to the air classifier via the connecting pipe.

3. The method for producing silver powder according to claim 1 or 2, further comprising a collecting step of collecting the silver powder after the classification step using a collector, In the collecting step, the exhaust gas of the air classifier and the silver powder after the classification step are supplied to the collector.

4. The method for producing silver powder according to claim 1 or 2, in, In the classification step, classification is performed while external air is sucked into the wind classifier.

5. A silver powder, in, The values ​​of the cumulative 10% particle size (μm), the cumulative 50% particle size (μm), and the cumulative 90% particle size (μm) accumulated from the small particle size side in the particle size distribution determined on a volume basis in the laser diffraction particle size distribution measurement are denoted as D10, D50, and D90, respectively. The value obtained by subtracting the D10 from the D90 and dividing it by the D50 is less than 1.0, The Sa×D50 value obtained by multiplying the arithmetic mean roughness Sa (nm) in the surface roughness measurement of the silver particle surface in the range of 500nm×500nm by the above D50 is 17000nm. 2 above.

6. A silver powder, in, The values ​​of the cumulative 10% particle size (μm), the cumulative 50% particle size (μm), and the cumulative 90% particle size (μm) accumulated from the small particle size side in the particle size distribution determined on a volume basis in the laser diffraction particle size distribution measurement are denoted as D10, D50, and D90, respectively. The value obtained by subtracting the D10 from the D90 and dividing it by the D50 is less than 1.0, There are closed pores in the silver particles. The specific surface area (m 2 / g), with a true density of 9.7 g / cm 3 The BET particle size calculated using the following formula (1) and In terms of the arithmetic mean roughness Sa (nm) in the surface roughness measurement of the silver particle surface in the range of 500nm×500nm, The value of Sa×BET particle size obtained by multiplying the arithmetic mean roughness Sa by the BET particle size is 13000 nm. 2 above, BET particle size = 6 / specific surface area / true density (1).

7. The silver powder according to claim 5 or 6, in, The D50 is greater than or equal to 0.4 μm and less than or equal to 4.0 μm.

8. A conductive paste comprising the silver powder according to claim 5 or 6.

Images