Flaky silver powder, method for producing the same, and conductive paste

Abstract

Provided is a flaky silver powder having a tap density of 0.8 to 1.9 g / mL, a cumulative 50% particle diameter (D 50 ) of 2 μm to 7 μm, as measured based on a laser diffraction scattering particle size distribution.

Description

TECHNICAL FIELD

[0001] The present application relates to a flaky silver powder and a method for producing the same, and a conductive paste. BACKGROUND

[0002] Conventionally, in order to form an electrode or a circuit of an electronic component or the like, a conductive paste in which silver powder is dispersed in an organic component is used. As the silver powder to be compounded in such a conductive paste, a silver powder having a flat shape (flaky silver powder) is sometimes used in order to make the contact area between the silver powders large.

[0003] As a method for producing a flaky silver powder, a method in which spherical silver powder is mechanically flattened is known. Alternatively, flaky silver particles can sometimes be partially obtained in a wet reduction method in which the crystal growth of silver particles is slow.

[0004] As a flaky silver powder obtained by mechanical flattening, a flaky silver powder having an average particle diameter D 50 of 10 μm to 13 μm, an aspect ratio ([average long diameter (μm)] / [average thickness (μm)]) of 6 to 15, a specific surface area of 1 m 2 / g or less, and a tap packing density of 2.4 g / cm 3 to 4.2 g / cm 3 (for example, Patent Document 1) is known so far.

[0005] Further, a metal powder having a tap density of 3.0 g / mL or more, an average particle diameter D 50 of 1 to 5 μm, and particles having an aspect ratio of 3 to 30 accounting for 80% or more in terms of number ratio, and an X value (=D 50 (μm) / BET specific surface area (m 2 / g)) of 0.5 or less (for example, Patent Document 2) is known.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT DOCUMENTS

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2007-254845

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2006-210214 SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] Previously, the tap density of flake silver powder was preferably greater than 2.0 g / mL. It has been recognized that by using flake silver powder with a high tap density, the filling rate of silver particles in the conductive paste can be increased, and the volume resistivity of the conductive film obtained by curing the conductive paste can be kept low.

[0012] However, in recent years, due to cost considerations, there has been a demand for flake silver powder with reduced silver content in conductive pastes and cured films. However, conductive pastes with reduced silver content have the problem of difficulty in maintaining good conductivity.

[0013] Furthermore, when fabricating electrodes and circuits using printing technology, there is a requirement for a conductive paste with excellent continuous printability that can maintain printability even after multiple printings, as well as flake silver powder for the conductive paste. However, conductive pastes have low volume resistivity, and in addition, it is difficult to obtain flake silver powder that can achieve excellent continuous printability when using conductive pastes.

[0014] The objective of this invention is to solve the aforementioned problems and achieve the following objective: Specifically, the objective of this invention is to provide a sheet-like silver powder that provides a conductive paste with excellent continuous printability and low volume resistivity.

[0015] Solution for solving the problem

[0016] This invention is based on the above-mentioned insights of the inventors, and the technical means for solving the above-mentioned problems is as follows. That is:

[0017] <1> A flake-like silver powder, characterized by a tap density of 0.8 g / mL to 1.9 g / mL, and a cumulative 50% particle size (D) determined based on laser diffraction scattering particle size distribution. 50 The size ranges from 2μm to 7μm.

[0018] <2> According to the above <1> The aforementioned flake-shaped silver powder, wherein the cumulative 90% particle size (D) determined based on laser diffraction scattering particle size distribution is... 90 ) and cumulative 10% particle size (D 10 The difference between the cumulative 50% particle size (D) and the cumulative 50% particle size (D) 50 The ratio of ) to [(D) 90 -D 10 ) / D 50 The value is below 1.35.

[0019] <3> According to the above <1> or <2> The flake-shaped silver powder has a tap density of 0.8 g / mL to 1.6 g / mL.

[0020] <4> A method for producing a flaky silver powder, characterized by comprising a flaking step of flaking a spherical silver powder by colliding a medium to obtain a flaky silver powder,

[0021] The flaking step is performed in such a manner that an average volume calculated from the following Formula 1 using an average primary particle diameter (D sem ) measured based on a scanning electron microscope using the spherical silver powder is set as VI, and an average volume calculated from the following Formula 2 using a cumulative average length (L) and a cumulative average thickness (T) of the flaky silver powder is set as V2, so that a ratio (V2 / V1) of the average volume V2 with respect to the average volume VI satisfies 1.0 to 1.5,

[0022] A tap density of the flaky silver powder is 0.8 g / mL to 1.9 g / mL.

[0023] V1 = 4 / 3 x π x (D sem / 2) 3 (Formula 1)

[0024] V2 = T x π x (L / 2) 2 (Formula 2)

[0025] <5> The method for producing a flaky silver powder according to the above <4>, wherein a cumulative 50% particle diameter (D 50 ) measured based on a laser diffraction scattering type particle size distribution of the spherical silver powder is 0.75 μm to 3 μm,

[0026] A cumulative 50% particle diameter (D 50 ) measured based on a laser diffraction scattering type particle size distribution of the flaky silver powder is 2 μm to 7 μm.

[0027] <6> An electrically conductive paste characterized by comprising the flaky silver powder according to any one of the above <1> to <3>,

[0028] A content of the flaky silver powder is 30 mass% to 80 mass%.

[0029] Effects of the Invention

[0030] According to the present invention, the above-described various problems of the past can be solved, the above-described object can be achieved, and a flaky silver powder capable of obtaining an electrically conductive paste having excellent continuous printability and a low volume resistivity is provided. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a scanning electron microscope photograph of the flaky silver powder of Example 1.

[0032] Figure 2 is a scanning electron microscope photograph of the flaky silver powder of Example 2.

[0033] Figure 3 is a scanning electron microscope photograph of the flaky silver powder of Example 3.

[0034] Figure 4 is a scanning electron microscope photograph of the silver powder of Comparative Example 1.

[0035] Figure 5 is a scanning electron microscope photograph of the silver powder of Comparative Example 2.

[0036] Figure 6 is a scanning electron microscope photograph of the silver powder of Comparative Example 3.

[0037] Figure 7 is a scanning electron microscope photograph of the flaky silver powder of Example 4.

[0038] Figure 8 is a scanning electron microscope photograph of the flaky silver powder of Example 5.

[0039] Figure 9 is a scanning electron microscope photograph of the flaky silver powder of Example 6. DETAILED DESCRIPTION

[0040] (Flaky Silver Powder)

[0041] The flaky silver powder of the present application has a tap density of 0.8 to 1.9 g / mL, and a cumulative 50% particle diameter (D50) of 2 μm to 7 μm as measured based on a laser diffraction scattering type particle size distribution. 50 ) for 2 μm to 7 μm.

[0042] The flaky shape includes a flat plate, a thin cuboid, a flaky shape, or a scale shape, and has an aspect ratio of 2 or more. On the other hand, the spherical shape means a shape close to a sphere, and has an aspect ratio of less than 2.

[0043] The silver particle aggregate having an aspect ratio of 2 or more on average is referred to as a flaky silver powder, and the flaky silver powder can contain silver particles having other shapes such as a spherical shape or a linear shape. On the other hand, the silver particle aggregate having an aspect ratio of less than 2 on average is referred to as a spherical silver powder.

[0044] The aspect ratio of the flaky silver powder is preferably 10 or more, more preferably 60 or more, and further preferably 70 or more. In addition, the aspect ratio is preferably 400 or less, more preferably 200 or less, and further preferably 150 or less. When the aspect ratio is less than 2, the contact area of the flaky silver powders with each other is sometimes insufficient, and the conductivity of the conductive film obtained by compounding the flaky silver powder in a conductive paste and forming a conductive film using the conductive paste cannot be sufficiently improved. When the aspect ratio is more than 400, it is sometimes difficult to produce the flaky silver powder.

[0045] The aspect ratio of the silver flake or the aspect ratio of the silver spherical powder can be calculated by (cumulative average long diameter L / cumulative average thickness T). Here, the "cumulative average long diameter L" and the "cumulative average thickness T" mean the cumulative average long diameter and the cumulative average thickness of 100 or more silver particles measured by a scanning electron microscope (SEM).

[0046] The aspect ratio of the silver flake or the aspect ratio of the silver spherical powder can be calculated by (cumulative average long diameter L / cumulative average thickness T). Here, the "cumulative average long diameter L" and the "cumulative average thickness T" mean the cumulative average long diameter and the cumulative average thickness of 100 or more silver particles measured by a scanning electron microscope (SEM).

[0047] Specifically, the aspect ratio can be measured in the following order.

[0048] (1) The silver powder, the epoxy resin, and the curing agent (name of the group: SpeciFix-20 Kit) were mixed (silver: resin = about 1:0.7, mass ratio).

[0049] (2) The mixture was poured into a mold and cured at room temperature.

[0050] (3) The cured sample was polished using an ion milling device (ArBlade5000 manufactured by Hitachi High-Tech Corporation) to produce a cross section.

[0051] (4) The cross section of the polished sample was observed with a SEM, and the short diameter (the shortest interval that can be held by parallel lines) of the cross section in the thickness direction of the silver particles was measured on the SEM as the thickness of the silver particles.

[0052] (Observation magnification 15000x, about 20 silver particles per 1 field of view, 100 to 150 or so were measured)

[0053] (5) The cumulative 50% thickness of the measured thickness data based on the number basis was taken as the cumulative average thickness (T).

[0054] (6) The silver powder was dispersed on a conductive tape on a SEM stage, and observed with a SEM, and the long diameter (the longest interval that can be held by parallel lines) of the silver particles in which the particle periphery could be confirmed was measured on the SEM.

[0055] (Observation magnification 2000x, about 10 particles per 1 field of view, 100 to 150 or so were measured)

[0056] (7) The cumulative 50% particle size of the measured length data based on the number basis was taken as the cumulative average long diameter (L).

[0057] (8) The cumulative average long diameter (L) / cumulative average thickness (T) was taken as the aspect ratio.

[0058] The cumulative average thickness of the flaky silver powder is preferably 41 nm to 100 nm, more preferably 42 nm to 70 nm, and further preferably 50 nm to 70 nm.

[0059] The cumulative average length diameter of the flaky silver powder is preferably 3 μm to 7 μm, and further preferably 5 μm to 7 μm.

[0060] The tap density of the flaky silver powder is 0.8 g / mL to 1.9 g / mL, preferably 0.8 g / mL to 1.6 g / mL, and further preferably 1.0 g / mL to 1.6 g / mL.

[0061] When the tap density exceeds 1.9 g / mL and becomes large, although the reason is not yet determined, the viscosity of the conductive paste containing the flaky silver powder becomes low, and bleeding to the peripheral portion of the conductive paste occurs at the time of printing (also referred to as "bleeding"), and sometimes a short circuit occurs in the circuit composed of the conductive film obtained by curing the conductive paste, and the fine wiring cannot be sufficiently dealt with. When the tap density is less than 0.8 g / mL, it is difficult to maintain the good conductivity of the conductive paste containing the flaky silver powder.

[0062] When the tap density is 1.6 g / mL or less, the viscosity of the conductive paste containing the flaky silver powder can be sufficiently obtained, the fine wiring can be better dealt with, and the good conductivity of the conductive paste can be maintained.

[0063] As a method for measuring the tap density of the flaky silver powder, for example, a tap density measuring device (Shibata Science Co., Ltd., Pycnometer SS-DA-2) can be used, 15 g of a sample of the flaky silver powder is weighed and put into a 20 mL test tube, and is tapped 1000 times with a 20 mm drop, and is calculated from tap density = sample weight (15 g) / sample volume (mL) after tapping.

[0064] The cumulative 50 mass% particle diameter (D 50 ) of the flaky silver powder based on the laser diffraction scattering particle size distribution measurement method is 2 μm to 7 μm, preferably 3 μm to 7 μm, more preferably 5 μm to 7 μm, and further preferably 5.3 μm to 7 μm.

[0065] When the cumulative 50 mass% particle diameter (D 50 ) is less than 2 μm, flattening becomes insufficient, and sometimes the effect of lowering the volume resistance of the flaky silver powder cannot be obtained, and when it is more than 7 μm, clogging easily occurs at the time of printing, and sometimes the continuous printability is impaired.

[0066] The laser diffraction scattering particle size distribution determination can be performed, for example, using a laser diffraction / scattering particle size distribution determination device (Microtrac MT-3300EXII, manufactured by MicrotracBEL Corp.).

[0067] Specifically, 0.1g of silver powder can be added to 40mL of isopropanol (IPA) and dispersed for 2 minutes using an ultrasonic homogenizer (manufactured by Nippon Seiki Co., Ltd., US-150T; 19.5kHz, with a small piece tip diameter of 18mm). The particle size distribution can then be measured using a laser diffraction / scattering particle size distribution measuring device (manufactured by MicrotracBEL Corp., Microtrac MT-3300EXII).

[0068] [(D 90 -D 10 ) / D 50 ]

[0069] The cumulative 90% particle size (D) of the flake-like silver powder, as determined by laser diffraction scattering particle size distribution analysis, is... 90 The cumulative 10% particle size (D) of the flake silver powder, determined based on laser diffraction scattering particle size distribution, is... 10 The difference between the cumulative 50% particle size (D) of the flake silver powder and the particle size distribution determination method based on laser diffraction scattering is... 50 The ratio of ) to [(D) 90 -D 10 ) / D 50 The value is preferably 1.35 or less, more preferably 1.32 or less, and even more preferably 1.27 or less.

[0070] The ratio [(D)] 90 -D 10 ) / D 50 When the [value] is 1.35 or less, good flake silver powder can be obtained when the spherical silver powder is flaked, with fewer coarse flake silver powder particles that have increased in volume due to particle collision and fewer particles that have not undergone plastic deformation. Such flake silver powder is preferably manufactured by the flake silver powder manufacturing method of the present invention described later.

[0071] The loss on ignition (Ig-Loss) of the flake silver powder, also known as Ig-Loss, represents the change in weight when heated from room temperature to 800°C. Specifically, it represents the amount of the composition other than silver in the flake silver powder. As a component remaining in the flake silver powder, it serves as an indicator of the amount of residual components, such as surface treatment agents present in the spherical silver powder and lubricants added to the silver paste during flake formation.

[0072] The ignition loss of the flaky silver powder is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.05 to 5.0%, and more preferably 0.3 to 3.0%.

[0073] (Method for producing flaky silver powder)

[0074] The method for producing flaky silver powder of the present application is a method for producing the flaky silver powder of the present application, which comprises a flaking process, and further can comprise other processes as necessary.

[0075] (Flaking process)

[0076] The flaking process is a process for flaking a spherical silver powder by colliding a medium to obtain a flaky silver powder.

[0077] The flaking process is performed in such a manner that the average volume calculated from the following Formula 1 using the average primary particle diameter (D sem ) measured based on a scanning electron microscope using the spherical silver powder is set as VI, and the average volume calculated from the following Formula 2 using the cumulative average length (L) and the cumulative average thickness (T) of the flaky silver powder is set as V2, so that the ratio (V2 / V1) of the average volume V2 to the average volume VI satisfies 1.0 to 1.5.

[0078] V1 = 4 / 3 x π x (D sem / 2) 3 (Formula 1)

[0079] V2 = T x π x (L / 2) 2 (Formula 2)

[0080] In addition, the tap density of the flaky silver powder is 0.8 to 1.9 g / mL.

[0081] [Spherical silver powder]

[0082] The spherical silver powder (also referred to as a raw powder) as a raw material of the flaking process is a silver powder having a shape close to a sphere, and a ratio of length to width of less than 2.

[0083] As the spherical silver powder, a commercially available product or a silver powder produced by a publicly known production method (for example, a wet reduction method) can be used. As the commercially available product, for example, AG-4-8F, AG-3-8W, AG-3-8FDI, AG-4-54F, AG-5-54F (all manufactured by Soe Giken Seisakusho Co., Ltd.), and the like can be used. The details of the wet reduction method are described in, for example, Japanese Patent Application Laid-Open No. 7-76710 and the like.

[0084] The cumulative 50% particle diameter (D50 ), preferably 0.75 μm to 3 μm, further preferably 1 μm to 2.5 μm.

[0085] The average primary particle diameter (D sem ) of the spherical silver powder can be calculated by measuring the circle equivalent diameter (Heywood diameter) of 50 or more arbitrary silver particles in an SEM-based image of the spherical silver powder, and calculating the average value, for example, using an image shape measuring software such as Mac-View (manufactured by MOUNTECH Co., Ltd.) for an image taken at 5000 times.

[0086] The average primary particle diameter (D sem ) of the spherical silver powder can be calculated by measuring the circle equivalent diameter (Heywood diameter) of 50 or more arbitrary silver particles in an SEM-based image of the spherical silver powder, and calculating the average value, for example, using an image shape measuring software such as Mac-View (manufactured by MOUNTECH Co., Ltd.) for an image taken at 5000 times.

[0087] The average primary particle diameter (D sem ) (μm) of the spherical silver powder can be used to calculate the average volume (V1) (μm 3 ) of the spherical silver powder using the following Equation 1.

[0088] V1 = 4 / 3 x π x (D sem / 2) 3 (Equation 1)

[0089] In addition, the cumulative average long diameter (L) (μm) and the cumulative average thickness (T) (μm) of the flaky silver powder can be used to calculate the average volume (V2) (μm 3 ) of the flaky silver powder using the following Equation 2.

[0090] V2 = T x π x (L / 2) 2 (Equation 2)

[0091] At this time, the ratio (V2 / V1) of the average volume V2 to the average volume V1 indicates the average volume change of the silver particles during the flaking process. Also, when the silver particles collide with the medium to be flaked, it approaches 1 as long as it is not integrated with other silver particles or becomes too thin to be torn into pieces.

[0092] The ratio (V2 / V1) is 1.0 to 1.5, further preferably 1.0 to 1.3.

[0093] The average volume V1 and the average volume V2 can be appropriately selected so as to satisfy the ratio (V2 / V1), but the average volume V1 is preferably 0.21 μm 3 to 3.8 μm 3 , further preferably 0.27 μm 3 to 2.6 μm3 The average volume V2 is preferably 0.32 μm 3 ~ 3.8 μm 3 Further preferably, the average volume V2 is 0.35 μm 3 ~ 2.7 μm 3 .

[0094] In the production method of the present application, by performing the flaking in such a manner that the ratio (V2 / V1) satisfies 1.0 to 1.5, a flaky silver powder having a tap density of 0.8 g / mL to 1.9 g / mL can be obtained. In the flaking step, it is difficult to control the flaking process performed in the device, but, for example, each silver particle is allowed to collide with each other once or so to cause plastic deformation from a spherical shape to a flaky shape, and it is preferable to adjust the flaking using the condition of the ratio (V2 / V1) to avoid causing more changes than the above changes.

[0095] The cumulative 50% particle diameter (D 50 ) of the flaky silver powder is preferably 2 μm to 7 μm, more preferably 3 μm to 7 μm, further preferably 5 μm to 7 μm, and particularly preferably 5.3 μm to 7 μm.

[0096] As the device for performing the flaking, there is no particular limitation, and it can be appropriately selected according to the purpose, and for example, a bead mill, a ball mill, an attritor, and the like can be exemplified as a media agitation pulverizer. Among them, a wet type media agitation pulverizer is preferably used.

[0097] In the wet type media agitation pulverizer, a slurry containing silver particles in a solvent is charged into a device containing media such as microbeads, and the silver particles are agitated together with the media, and the silver particles are plastically deformed.

[0098] Further, the productivity varies depending on the centrifugal force applied to the media and the silver particles at the time of the media collision, and by setting the centrifugal force in an appropriate range, the energy at the time of the media collision can be increased, and a flaky silver powder having a preferable aspect ratio can be produced with good productivity.

[0099] As the microbead (media), a microbead (media) having a diameter of 0.1 mm to 3 mm and a spherical shape is preferable. When the diameter of the microbead (media) is less than 0.1 mm, the efficiency of separation at the time of separating the flaky silver powder after the flaking treatment and the media is reduced due to clogging of the media or the like, and when it is more than 3 mm, the average particle diameter of the obtained flaky silver powder sometimes becomes too large.

[0100] As the material of the medium, there is no particular limitation as long as it can collide with the silver particles to cause plastic deformation of the silver particles, and it can be appropriately selected according to the purpose, and for example, ceramics such as zirconia and alumina; glass; metals such as titanium and stainless steel can be listed. Among them, in consideration of the decrease in reproducibility and the like due to abrasion of the medium, zirconia is preferable. Note that the element (Zr or Fe or the like) that mainly constitutes the medium can sometimes contain about 1 ppm to 10,000 ppm in the flaky silver powder due to the collision, and thus the medium can be selected according to the purpose.

[0101] As the addition amount at the time of flaking of the microbeads (medium), there is no particular limitation, and it can be appropriately selected according to the purpose, but it is preferably 30% to 95% by volume with respect to the volume of the device. When the addition amount is 30% by volume or less, the number of the microbeads (medium) that collide sometimes decreases, and thus the processing time becomes long and the processing cost becomes high. When the addition amount is more than 95% by volume, the microbeads (medium) sometimes excessively fill in the device, and thus the operation of the device becomes difficult.

[0102] The processing time of the flaking is not particularly limited, and it can be appropriately selected according to the purpose, but it is preferably 10 minutes to 50 hours. When the processing time is less than 10 minutes, it sometimes becomes difficult to obtain flaky silver powder of a sufficiently long aspect ratio, and when it is more than 50 hours, there is no effect, and it is not economical. Note that, for the flaking, not all of the silver powder that is put in is flaked, and it is also possible to mix silver powder that is not flaked after the flaking.

[0103] <Other Process>

[0104] As the other process, for example, a spherical silver powder production process, a cleaning process, a drying process, and the like can be listed.

[0105] (Electrically Conductive Paste)

[0106] The electrically conductive paste of the present application is an electrically conductive paste containing the flaky silver powder of the present application, and for example, a resin curing type electrically conductive paste and the like can be listed.

[0107] The content of the flaky silver powder is 30% to 80% by mass with respect to the total amount of the electrically conductive paste, and it is preferably 40% to 70% by mass.

[0108] As the viscosity of the electrically conductive paste, there is no particular limitation, and it can be appropriately selected according to the purpose, but it is preferably 200 Pa-s to 900 Pa-s, more preferably 200 Pa-s to 600 Pa-s, and further preferably 300 Pa-s to 500 Pa-s at a paste temperature of 25°C and a rotation speed of 1 rpm.

[0109] When the viscosity of the conductive paste is less than 200 Pa-s, "bleeding" sometimes occurs at the time of printing, and when it is more than 900 Pa-s, uneven printing sometimes occurs.

[0110] The viscosity of the conductive paste can be measured, for example, using an E-type viscometer (manufactured by Brookfield Engineering Labs., Inc., model number: DV-III+) under the conditions of a cone-plate CP-52, a paste temperature of 25°C, and a rotational speed of 1 rpm.

[0111] The method for producing the conductive paste is not particularly limited, and can be appropriately selected from among publicly known methods according to the purpose, for example, the conductive paste can be produced by mixing the flaky silver powder with a resin.

[0112] The resin is not particularly limited, and can be appropriately selected according to the purpose, for example, an epoxy resin, an acrylic resin, a polyester resin, a polyimide resin, a polyurethane resin, a phenoxy resin, a silicone resin, or a mixture thereof, or the like can be mentioned.

[0113] The content of the flaky silver powder in the conductive paste is also not particularly limited, and can be appropriately selected according to the purpose. Note that the flaky silver powder of the present application can also be mixed with other silver powders.

[0114] The conductive paste of the present application contains the flaky silver powder of the present application, and thus has excellent conductivity, and is suitable for use in a current collecting electrode of a solar cell unit, an external electrode of a chip-type electronic component, an electrode or a wire for RFID, electromagnetic wave shielding, a thin film switch, electroluminescence, or the like, or is suitable for use in a conductive adhesive for adhesion of a vibrator, adhesion between solar cell units, or the like.

[0115] Example

[0116] Hereinafter, examples of the present application will be described, but the present application is not limited to these examples.

[0117] (Example 1)

[0118] <Production of flaky silver powder>

[0119] A spherical silver powder (AG-4-8F, manufactured by Soe Giken Co., Ltd.) was used as a silver powder (raw powder) for flaky formation. The D 50 was 1.95 μm, and the average primary particle diameter D sem was 1.38 μm.

[0120] - sheeting process -

[0121] To 2.49 kg of spherical silver powder, 74.6 g (an amount of 3.0 mass% relative to the silver powder) of oleic acid as a lubricant was added, 5.80 kg of a mixed solution (Neoethanol P-7, manufactured by DKS Co., Ltd.) in which ethanol was the main component as a solvent was mixed, and the mixture was stirred with a blender to obtain a total of 8.36 kg of silver slurry (silver slurry ratio: silver powder concentration of 29.8 mass%).

[0122] The obtained silver slurry was put into a bead mill device LMZ2 (manufactured by Ashizawa Finetech Ltd., volume 1.65 L, outer diameter of stirring blade 11.6 cm), and plastic deformation of the spherical silver powder in the silver slurry was performed by mixing and stirring under the following conditions to obtain sheet silver particles.

[0123] • Medium: partially stabilized zirconia (PSZ) beads with a diameter of 0.8 mm (TORAY CERAM beads AGB-K-0.8, manufactured by Toray Industries, Inc.)

[0124] • Medium amount: 5.19 kg (filling rate: 85 vol%)

[0125] • Bead mill operating conditions: circumferential velocity 14 m / s (rotation speed 2305 rpm, 344 G), 2.5 hours of treatment

[0126] In addition, for this mixing and stirring, mixing and stirring was performed by connecting the tank containing the obtained silver slurry and the bead mill device via a pump to perform a circulation operation, whereby the silver slurry that had been transported from the tank to the bead mill device was returned to the tank from the outlet of the bead mill device, and the amount of silver slurry transported during the operation of the bead mill was set to 4 L / minute.

[0127] After that, the beads and the slurry were separated by the partition of the bead mill device to obtain a slurry containing sheet silver powder. Furthermore, the slurry was filtered using a filter to obtain a wet cake of sheet silver powder. After that, the wet cake was dried using a vacuum drier at 50°C for 10 hours. Furthermore, after being broken up for 1 minute using a blender, sieving was performed using a vibrating sieve with an opening size of 40 μm to obtain the sheet silver powder of Example 1.

[0128] A 5000-fold scanning electron microscope photograph of the sheet silver powder obtained in Example 1 is shown in Figure 1 .

[0129] (Example 2)

[0130] In Example 1, the bead diameter was set to 0.5 mm (TORAY CERAM beads AGB-K-0.5, manufactured by Toray Industries, Inc.), the treatment time was set to 3 hours, and otherwise, the flaky silver powder of Example 2 was obtained in the same manner as in Example 1.

[0131] A 5000-fold scanning electron microscope photograph of the flaky silver powder obtained in Example 2 is shown in Figure 2 .

[0132] (Example 3)

[0133] In Example 1, the bead diameter was set to 1.0 mm (TORAY CERAM beads AGB-K-1.0, manufactured by Toray Industries, Inc.), the treatment time was set to 2 hours, and otherwise, the flaky silver powder of Example 3 was obtained in the same manner as in Example 1.

[0134] A 5000-fold scanning electron microscope photograph of the flaky silver powder obtained in Example 3 is shown in Figure 3 .

[0135] (Comparative Example 1)

[0136] <Manufacture of flaky silver powder>

[0137] To 644 g of the spherical silver powder described in Example 1, 12.9 g (2.0 mass% relative to the silver powder) of oleic acid was added, 966 g of Neoethanol P-7 was mixed, and the mixture was stirred with a blender to obtain a total of 1622.9 g of silver slurry (silver slurry ratio: silver powder concentration of 39.7 mass%).

[0138] The obtained silver slurry and the medium beads were put into a grinder (manufactured by NIPPON COKE & ENGINEERING CO., LTD., MA-1SE-X), and the silver particles in the silver slurry were plastically deformed by mixing and stirring under the following conditions to obtain flaky silver particles.

[0139] • Medium: SUS304 beads, 1.6 mm in diameter

[0140] • Medium amount: 16.62 kg (filling rate: 65 vol%)

[0141] • Grinding machine operating conditions: rotation speed 360 rpm, 6 hours of treatment

[0142] Further, the slurry was filtered using a filter to obtain a wet cake of flaky silver powder. Thereafter, the vacuum drier was used for drying at 70°C for 10 hours. Further, the blender was used for 1 minute of crushing, and a vibrating sieve with an opening size of 40 μm was used for sieving to obtain the flaky silver powder of Comparative Example 1.

[0143] A 5000-fold scanning electron microscope photograph of the flaky silver powder obtained in Comparative Example 1 is shown in Figure 4 .

[0144] (Comparative Example 2)

[0145] A spherical silver powder (AG-3-8W, manufactured by Soe Giken Co., Ltd.) was used as the silver powder (raw powder) for flaking. The D 50 of the spherical silver powder AG-3-8W was 1.91 μm, and the average primary particle diameter D sem was 0.85 μm, which was measured by averaging the circular equivalent diameters (Heywood diameters) of 50 or more arbitrary silver particles in an image based on a scanning electron microscope (SEM).

[0146] In Comparative Example 1, the spherical silver powder was changed from AG-4-8F to AG-3-8W, 1250 g of the spherical silver powder, 18.8 g of oleic acid, and 966 g of Neoethanol P-7 were mixed, and the mixture was stirred with a blender to obtain a total of 2234.8 g of a silver slurry, the mass of the medium was set to 10.5 kg (filling rate 42 vol%), and otherwise, the flaky silver powder of Comparative Example 2 was obtained in the same manner as in Comparative Example 1.

[0147] A 5000-fold scanning electron microscope photograph of the flaky silver powder obtained in Comparative Example 2 is shown in Figure 5 .

[0148] (Comparative Example 3)

[0149] In Comparative Example 3, the treatment time for flaking was set to 1 hour, and otherwise, the flaky silver powder of Comparative Example 3 was obtained in the same manner as in Example 2.

[0150] A 5000-fold scanning electron microscope photograph of the flaky silver powder obtained in Comparative Example 3 is shown in Figure 6 .

[0151] (Example 4)

[0152] In the flaking process of Example 1, the amount of the spherical silver powder was changed to 3.75 kg, the amount of oleic acid as the lubricant was changed to 112.5 g (an amount of 3.0 mass% relative to the silver powder), the amount of a mixed solution (Neoethanol P-7, manufactured by Otsu Chemical Co., Ltd.) in which ethanol was used as the main component as the solvent was mixed to 5.62 kg, and the mixture was stirred with a blender to obtain a total of 9.48 kg of a silver slurry (silver slurry ratio: silver powder concentration 39.6 mass%), the treatment time of the bead mill operating conditions was set to 4 hours, and otherwise, the flaky silver powder of Example 4 was obtained in the same manner as in Example 1.

[0153] A 5000-fold scanning electron microscope photograph of the flaky silver powder obtained in Example 5 is shown in Figure 7 .

[0154] (Example 5)

[0155] Spherical silver powder (AG-4-54F, manufactured by Sohando Electronics Co., Ltd.) was used as the silver powder (raw powder) for flaking. The D 50 of the spherical silver powder AG-4-54F was 1.81 μm, and the average primary particle diameter D sem was 1.26 μm, which was measured by determining the circular equivalent diameters (Heywood diameters) of 50 or more arbitrary silver particles in an image based on a scanning electron microscope (SEM).

[0156] In the flaking step, the bead diameter was set to 1.0 mm (TORAYCERAM beads AGB-K-1.0, manufactured by Toray Industries, Inc.), the mass of the beads was set to 5.50 kg (filling rate: 90 vol%), the silver slurry delivery amount during the operation of the bead mill was set to 6 L / min, and the processing time was set to 2.5 hours, and otherwise, the flaky silver powder of Example 5 was obtained in the same manner as in Example 1.

[0157] A 5000-fold scanning electron microscope photograph of the flaky silver powder obtained in Example 5 is shown in Figure 8 .

[0158] (Example 6)

[0159] Spherical silver powder (AG-3-8FDI, manufactured by Sohando Electronics Co., Ltd.) was used as the silver powder (raw powder) for flaking. The D 50 of the spherical silver powder AG-3-8FDI was 1.61 μm, and the average primary particle diameter D sem was 1.17 μm, which was measured by determining the circular equivalent diameters (Heywood diameters) of 50 or more arbitrary silver particles in an image based on a scanning electron microscope (SEM).

[0160] In the flaking step, the mass of the beads was set to 5.50 kg (filling rate: 90 vol%), the silver slurry delivery amount during the operation of the bead mill was set to 5 L / min, and the processing time was set to 4 hours, and otherwise, the flaky silver powder of Example 6 was obtained in the same manner as in Example 1.

[0161] A 5000-fold scanning electron microscope photograph of the flaky silver powder obtained in Example 6 is shown in Figure 9 .

[0162] Next, the particle size distribution, aspect ratio, average volume, and tap density of the flaky silver powder of Examples 1 to 6 and Comparative Examples 1 to 3 were measured as follows. The results are shown in Table 1.

[0163] <Particle size distribution measurement method>

[0164] The cumulative 10% particle diameter (D10), cumulative 50% particle diameter (D50), and cumulative 90% particle diameter (D90) of each of the produced flaky silver powders were measured on a volume basis by the following method. 10 50 90

[0165] After 0.1 g of silver powder was added to 40 mL of isopropyl alcohol (IPA) and dispersed for 2 minutes by an ultrasonic homogenizer (device name: US-150T, manufactured by Japan Precision Machine Mfg. Co., Ltd.; 19.5 kHz, small piece front end diameter 18 mm), measurement was performed by a laser diffraction / scattering particle size distribution measuring device (Microtrac BEL Corp., Microtrac MT-3300EXII).

[0166] <Aspect ratio and average volume measurement method>

[0167] The aspect ratio of each of the produced flaky silver powders was calculated from (cumulative average long diameter L / cumulative average thickness T). The average volume of each of the produced flaky silver powders was calculated from (cumulative average thickness T x π x (cumulative average long diameter L / 2) 2 ). Here, the "cumulative average long diameter L" and the "cumulative average thickness T" indicate the cumulative average long diameter and the cumulative average thickness of 100 or more particles of the flaky silver powder measured by a scanning electron microscope.

[0168] <Tap density measurement method>

[0169] The tap density of each of the produced flaky silver powders was measured using a tap density measuring device (Shibata Science Co., Ltd., Pycnometer SS-DA-2), 15 g of silver powder was weighed and placed in a 20 mL test tube, and was tapped 1000 times with a 20 mm drop, and was calculated from the following formula.

[0170] Tap density = sample weight (15 g) / sample volume after tapping (mL)

[0171] <Silver powder loss on ignition>

[0172] The loss on ignition (Ig-Loss) of the silver powder was calculated as follows: 2 g of a silver powder sample was weighed (w1) and placed in a magnetic crucible, and was strongly heated at 800°C for 30 minutes until a constant weight was reached, and was cooled, and was weighed (w2), and was calculated from the following formula.

[0173] ​​​Burning loss (%) = [(w1 - w2) / w1] x 100

[0174] <Manufacture of conductive paste>

[0175] Each of the silver flake powders of Examples 1 to 6 and Comparative Examples 1 to 3, 55.8 mass%, an epoxy resin (EP-4901E, manufactured by ADEKA Corporation), 37.2 mass%, a curing agent (AJICURE MY-24, manufactured by Ajinomoto Fine-Techno Co., Inc.), 3.7 mass%, and a solvent (ethyl 2-(2-butoxyethoxy)acetate, manufactured by FUJIFILM and Otsuka Pharmaceutical Co., Ltd.), 3.3 mass% were mixed, and kneaded for 1 minute using a propellerless planetary centrifugal mixing defoaming device (manufactured by EME, Inc., VMX-N360), thereby manufacturing each of the conductive pastes of Examples 1 to 6 and Comparative Examples 1 to 3.

[0176] Next, for each of the obtained conductive pastes, the viscosity was measured as follows. The results are shown in Table 1.

[0177] <Viscosity measurement of conductive paste>

[0178] The viscosity of each of the obtained conductive pastes was measured using an E-type viscometer (manufactured by Brookfield Engineering Labs., Inc., DV-III+) under conditions of a cone rotor CP-52, a paste temperature of 25°C, and a rotation speed of 1 rpm.

[0179] <Formation of conductive film>

[0180] Each of the obtained conductive pastes was printed into a circuit having a width of 500 μm and a length of 37.5 mm on an alumina substrate using a screen printer (manufactured by Micro-tech Co., Ltd., MT-320T). Two circuits were continuously printed, and the number of continuous printing was set to 2.

[0181] The obtained circuits were subjected to heat treatment at 200°C for 30 minutes using an atmospheric circulation type drying machine, thereby forming each of the conductive films.

[0182] For each of the obtained conductive films, the average thickness and the average line width of the conductive film, the volume resistivity, and the continuous printability of the conductive film were evaluated as follows. The results are shown in Table 3.

[0183] <Measurement of average thickness and average line width of conductive film>

[0184] For each of the obtained conductive films, the height difference between the portion of the alumina substrate on which the conductive film was not printed and the portion of the alumina substrate on which the conductive film was printed was measured by using a surface roughness meter (Tokyo Denshoku Co., Ltd., SURFCOM 480B-12), thereby measuring the average thickness of the conductive film. In addition, the line width of the conductive film (average value of 2 times) was measured by a digital microscope. The results are shown in Table 3.

[0185] <Volume resistivity of conductive film>

[0186] Using a digital multimeter (manufactured by ADVANTEST Corporation, R6551), the resistance value at the position of the length (interval) of the conductive film was measured. From the size of the conductive film (average thickness, average line width, length), the volume of the conductive film was calculated, and from the volume and the measured resistance value, the volume resistivity (average value of 2 times) was calculated. The results are shown in Table 3. If the volume resistivity is 1.0E-03 Ω·cm or less, the practicality is excellent.

[0187] <Evaluation of continuous printability of conductive film>

[0188] In 2 times of continuous printing, for the 1st and 2nd times, respectively, the measurement of the average thickness, the average line width, and the volume resistivity of the conductive film was performed, and the case where the conductive film in the 2nd time had a broken line or a large increase in resistance value was determined to be poor in continuous printability (x). The results are shown in Table 3.

[0189] [Table 1]

[0190]

[0191] [Table 2]

[0192]

[0193] [Table 3]

[0194]

Claims

1. A flaky silver powder, characterized by, tap density is 0.8 g / mL to 1.9 g / mL, cumulative 50% particle size D50 determined based on laser diffraction scattering particle size distribution 50 is 2 μm to 7 μm, Cumulative 90% particle diameter D 90 with the difference of the cumulative 10% particle diameter D 10 with respect to the cumulative 50% particle diameter D 50 (D 90 -D 10 ) / D 50 is 1.35 or less.

2. The flake-shaped silver powder according to claim 1, wherein The tap density is 0.8 g / mL to 1.6 g / mL.

3. A method for producing a flaky silver powder, characterized by, including a sheeting process for sheeting the spherical silver powder by colliding the medium to obtain a sheet silver powder, The flake-forming process is performed in such a manner that the average primary particle diameter D sem The average volume calculated from the following Formula 1 is set as V1, the average volume calculated from the cumulative average length L and the cumulative average thickness T of the flake-shaped silver powder using the following Formula 2 is set as V2, and the ratio V2 / V1 of the average volume V2 with respect to the average volume V1 is made to satisfy 1.0 to 1.5, The cumulative 50% particle diameter D50 of the spherical silver powder determined based on a laser diffraction scattering particle size distribution 50 is 1 to 3 μm, The cumulative 90% particle size D90of the flaky silver powder determined based on laser diffraction scattering particle size distribution 90 The difference between the cumulative 10% particle size D10 10 and the cumulative 50% particle size D50 50 The ratio (D 90 -D 10 ) / D 50 is 1.35 or less, The tap density of the sheet silver powder is 0.8 g / mL to 1.9 g / mL, V1 = 4 / 3 x π x (D sem / 2) 3 (Formula 1) V2 = T x π x (L / 2) 2 (Formula 2).

4. The method of producing a flaky silver powder according to claim 3, wherein The cumulative 50% particle size D50 determined by laser diffraction scattering particle size distribution of the flaky silver powder 50 is 2 μm to 7 μm.

5. An electrically conductive paste characterized by comprising The sheet silver powder according to claim 1 or 2, The content of the sheet silver powder is 30 mass% to 80 mass%. The tap density is 0.8 g / mL to 1.6 g / mL. including a sheeting process for sheeting the spherical silver powder by colliding the medium to obtain a sheet silver powder, The tap density of the sheet silver powder is 0.8 g / mL to 1.9 g / mL, The sheet silver powder according to claim 1 or 2, The content of the sheet silver powder is 30 mass% to 80 mass%.

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