Silver powder and method for producing same

Abstract

A silver powder according to the present invention comprises a plurality of silver particles having a flake shape. When D50 (μm) is the volume cumulative particle size at 50 vol.% of the cumulative volume determined by a laser diffraction scattering type particle size distribution measuring method, and SSA (m2 / g) is the BET specific surface area, a value defined by D50 / SSA is 3.50-5.20. The crystallite size of the silver is preferably 40.0-45.0 nm. In a particle size distribution obtained by the laser diffraction scattering type particle size distribution measuring method, the ratio of silver particles having a particle size of greater than 18.50 μm is preferably 1.40 vol.% or less. The volume cumulative particle size D50 is preferably 3.80-7.40 μm. The BET specific surface area SSA is preferably from 0.70 m2 / g to 2.00 m2 / g.

Description

Silver powder and its manufacturing method

[0001] This invention relates to silver powder and a method for producing the same.

[0002] To improve electrical conductivity between conductors, the development of conductive pastes containing metal particles such as silver and copper is progressing. In particular, metal powders consisting of flake-shaped particles have a large specific surface area due to their shape, and the particles tend to come into contact with each other. Therefore, by adding them to a resin to prepare a conductive paste, it is easy to reduce the resistivity of the conductive paste.

[0003] For example, the present applicant previously used a laser diffraction scattering particle size distribution method to measure the average particle size D of a conductive film formed from a conductive paste, with the aim of reducing the resistivity of the conductive film. ５０ We proposed flake silver powder with a particle size of 10 μm to 13 μm and an aspect ratio of 6 to 15.

[0004] Japanese Patent Publication No. 2007-254845

[0005] According to the technology described in Patent Document 1, it is possible to reduce the resistivity of a conductive film. However, with the increasing performance of electronic devices in recent years, there is a growing demand for even higher performance conductors used to make these electronic devices electrically conductive. Therefore, the object of the present invention is to provide silver powder that can reduce the resistivity of a conductive film compared to conventional methods.

[0006] The present invention relates to a silver powder comprising a plurality of flake-shaped silver particles, wherein the cumulative volume particle size at a cumulative volume of 50% measured by laser diffraction scattering particle size distribution analysis is D ５０ Let (μm) be the specific surface area of ​​BET be SSA (m ２ When we set it to / g, D ５０ The above problem is solved by providing silver powder whose value defined by / SSA is between 3.50 and 5.20.

[0007] The present invention also provides a method for producing silver powder, which comprises subjecting a raw material powder composed of a plurality of silver particles having a non-flaky shape and a volume cumulative particle diameter at a cumulative volume of 50% by a laser diffraction scattering particle size distribution measurement method of 1.50 μm or more and 2.80 μm or less to a flattening process using a grinding medium having a diameter of 0.1 mm or less. The kinetic energy per particle of the grinding medium is 1.00×10 －８ kg·m ２ / s ２ or more and 1.00×10 －６ kg·m ２ / s ２ or less, and the stress number per unit time applied by the grinding medium to the raw material powder is 0.30 rpm / mm or more and 5.00 rpm / mm or less in the flattening process.

[0008] FIGS. 1(a) to 1(d) are schematic diagrams showing a method for measuring the aspect ratio of silver particles in the silver powder of the present invention.

[0009] The present invention will be described below based on its preferred embodiments. The silver powder of the present invention consists of a plurality of silver particles. The silver particles are preferably particles substantially composed of silver element, or silver-based alloy particles. The silver powder is preferably composed of aggregates of such particles. The former particles are particles substantially composed of silver element, with the remainder being unavoidable elements. In this case, it is desirable that the silver particles consist only of silver element, but the inclusion of trace amounts of unavoidable elements is acceptable. When unavoidable elements are included in the silver particles, it is preferable that their content be 1% by mass or less, as this makes it less likely that the inherent properties of the silver particles will be impaired and allows suitable properties to be imparted to the silver powder composed of the silver particles. Unavoidable elements include, for example, oxygen (O) and carbon (C) elements derived from oxygen and carbon dioxide in the atmosphere, and carbon (C) and nitrogen (N) elements that may be mixed in during the manufacturing process of the silver particles. The presence or absence of unavoidable elements and their content can be measured, for example, by gas analysis. In the case of the latter particles, the content of silver element in the particles is preferably 80% by mass or more, and more preferably 90% by mass or more. Elements that constitute silver-based alloys together with silver include, for example, copper (Cu) and nickel (Ni).

[0010] The silver powder of the present invention has a distinctive feature in the external shape of the silver particles that constitute it. Specifically, the silver particles preferably have a flake shape. In this specification, "flake shape" is synonymous with "flaky" and "flattened," meaning that the particles have a thin, plate-like shape. The flake shape of the silver particles is specified by the aspect ratio. Because the silver powder of the present invention consists of silver particles with a flake shape, the number of contact points between silver particles is reduced and surface contact is more likely to occur compared to the case where the silver powder consists of, for example, perfectly spherical silver particles. Therefore, when the silver powder of the present invention is added to a resin and an organic solvent to produce a conductive resin composition, the number of contact points between silver particles in the conductive resin composition is also reduced and surface contact is more likely to occur, and the resistivity of the conductive film formed from the conductive resin composition can be reduced compared to conventional methods. Furthermore, printability is improved, making it easier to obtain a conductive film from the conductive resin composition by printing. Flake-shaped silver particles can be suitably produced, for example, by the manufacturing method described later. In the following description, silver particles having a flake shape are also referred to as "flake-shaped silver particles." In this specification, when "conductive resin composition" refers to a composition containing a thermosetting resin, it means either a composition containing a thermosetting resin before curing or a composition containing a thermosetting resin after curing, depending on the context.

[0011] It is preferable that the aspect ratio of the flake-shaped silver particles is within a predetermined range. The aspect ratio is a value defined as the ratio of the major axis W1 to the minor axis W2 (major axis W1 / minor axis W2) when, in a cross-sectional view of the particle P, the major axis W1 is the longest side of the rectangle S with the smallest area among all rectangles S circumscribing the particle P (see Figure 1(d)), and the minor axis W2 is the shortest side of the rectangle S. The closer the aspect ratio is to 1, the closer the shape of the silver particle is to a perfect sphere, for example. In silver powder, it is preferable that the average aspect ratio of the silver particles (hereinafter also referred to as the "average aspect ratio") is 9.85 or higher, more preferably 9.90 or higher, and even more preferably 9.95 or higher. From a similar viewpoint, the silver particles are preferably 20.50 or less in average aspect ratio, more preferably 18.00 or less, and even more preferably 14.00 or less.

[0012] In the silver powder of the present invention, the average value of the major axis W1 is preferably 3.00 μm or more, more preferably 3.30 μm or more, and even more preferably 3.50 μm or more, provided that the average aspect ratio is within the above range. Furthermore, the average value of the major axis W1 is preferably 6.00 μm or less, more preferably 5.00 μm or less, and even more preferably 4.00 μm or less, provided that the average aspect ratio is within the above range. The average value of the minor axis W2 is preferably 0.30 μm or more, more preferably 0.33 μm or more, and even more preferably 0.35 μm or more, provided that the average aspect ratio is within the above range. Furthermore, the average value of the minor axis W2 is preferably 0.60 μm or less, more preferably 0.55 μm or less, and even more preferably 0.50 μm or less, provided that the average aspect ratio is within the above range.

[0013] The average aspect ratio can be measured by the following method. Specifically, first, two or more fields of view are captured using a scanning electron microscope (hereinafter also referred to as "SEM") at a magnification that includes 20 or more cross-sections of the silver particles to be measured. Next, 60 or more silver particles whose outlines can be confirmed are randomly selected from each image data, and the value of the major axis W1, the minor axis W2, and the major axis W1 / minor axis W2 (aspect ratio) are calculated for each of the selected silver particles. The average value of each of these calculated values ​​is described herein. A detailed method for measuring the average aspect ratio will also be explained in the examples described later.

[0014] As described above, the silver powder of the present invention is preferably composed mainly of flake-shaped silver particles. In particular, from the viewpoint of reducing the number of contact points between silver particles in the silver powder and increasing the opportunity for surface contact, thereby reducing the resistivity of the conductive film compared to conventional methods, it is preferable that the degree of flake shape of the silver particles is relatively uniform. This is because, with a relatively uniform degree of flake shape, the silver particles in the silver powder can contact each other over a relatively large surface area, thereby reducing contact at relatively small points. The degree of uniformity of the flake shape is determined by the volume cumulative particle size at 50% of the cumulative volume, as measured by laser diffraction scattering particle size distribution analysis. ５０ (Hereafter simply referred to as "Particle Size D") ５０ It is also called ''. ) (μm), and the BET specific surface area is SSA (m ２ When we set it to / g, D ５０ It can be defined using the value defined in / SSA.

[0015] D ５０ The technical significance of the value defined by / SSA is as follows: When the degree of flake shape of the silver particles is large, that is, when the outer shape of silver particles of the same mass deviates from a perfect sphere and approaches a flake shape, the value of SSA tends to be large. As a result, even though the outer shape is different, D ５０ Even for silver particles with approximately the same SSA value, the greater the degree of flake shape, the greater the D due to the magnitude of the SSA value. ５０ The value of / SSA tends to decrease. Furthermore, if all of the small-particle silver particles in the particle size distribution of silver powder can be flakebed, then due to the magnitude of the SSA value, D５０ The value of / SSA tends to be small. On the other hand, when the degree of flake shape of the silver particles is small, that is, when the outer shape of silver particles of the same mass is close to a perfect sphere, the value of SSA tends to be small. As a result, although the outer shape is different, D ５０ Even for silver particles with approximately the same SSA value, the smaller the degree of flake shape, the smaller the SSA value, which is due to D ５０ The SSA value tends to be large. Furthermore, if not all of the small-particle silver particles in the particle size distribution of the silver powder can be flakebed, then due to the small SSA value, D ５０ The value of / SSA tends to increase. In this way, D ５０ / SSA is D ５０ Since it is a value that is not easily affected by the magnitude of the value, D ５０ The inventors believe that evaluating the uniformity of the flake shape using the / SSA value is advantageous from the standpoint of reducing the resistivity of the conductive film compared to conventional methods.

[0016] Specifically, in silver powder, from the perspective of reducing the number of contact points between silver particles and increasing the opportunities for surface contact, D ５０ The value defined by / SSA is preferably 3.50 or higher, more preferably 4.00 or higher, and even more preferably 4.60 or higher. Also, from a similar viewpoint, D ５０ The value defined by / SSA is preferably 5.20 or less, more preferably 5.10 or less, and even more preferably 5.00 or less. ５０ Silver powder having an SSA value is suitably produced by the manufacturing method described later.

[0017] The silver powder of the present invention preferably has a BET specific surface area SSA within a predetermined range. Specifically, from the viewpoint of reducing the number of contact points between silver particles in the silver powder and increasing the opportunity for surface contact, thereby reducing the resistivity of the conductive film compared to conventional methods, the BET specific surface area SSA of the silver powder is D ５０ Assuming the value of / SSA is within the above range, 0.70m ２ It is preferable that it be 0.73 m or more per g, and 0.73 m ２ It is even more preferable that it be 0.75 m or more per g, ２It is even more preferable that it be 1 / g or more. From a similar viewpoint, the BET specific surface area SSA of silver powder is D ５０ Assuming the value of / SSA is within the above range, 2.00m ２ It is preferable that the amount is less than or equal to 1.60 m ２ It is even more preferable that it be less than or equal to 1.00 m ２ It is even more preferable that the BET specific surface area SSA is less than or equal to / g. Silver powder having such a BET specific surface area SSA can be suitably produced by the manufacturing method described later. The method for measuring the BET specific surface area SSA will be explained in the examples described later.

[0018] The silver powder of the present invention has a particle size D ５０ It is preferable that the particle size D of the silver powder is within a predetermined range. Specifically, from the viewpoint of reducing the number of contact points between silver particles in the silver powder and increasing the opportunity for surface contact, thereby reducing the resistivity of the conductive film compared to conventional methods, the particle size D of the silver powder is preferable. ５０ D ５０ Provided that the value of / SSA is within the above range, it is preferably 3.80 μm or larger, more preferably 3.83 μm or larger, and even more preferably 3.85 μm or larger. From a similar viewpoint, the particle size D of the silver powder ５０ D ５０ Provided that the value of / SSA is within the above range, the particle size is preferably 7.40 μm or less, more preferably 6.60 μm or less, even more preferably 5.00 μm or less, and even more preferably 4.65 μm or less. ５０ The measurement method will be explained in the examples described later.

[0019] The silver powder of the present invention preferably has a low proportion of over-flattened coarse particles. Over-flattened coarse particles have a higher surface energy compared to fine particles due to their large specific surface area. If the surface energy is excessively high, the particles will aggregate. As a result, when a conductive film is formed using such particles, the film-forming ability decreases and a rough film is more likely to be formed, so excessive flake formation is undesirable. In contrast, the silver powder of the present invention has a low proportion of coarse particles, that is, the degree of flake formation is controlled, so when a conductive film is formed using this silver powder, the film-forming ability is improved. Furthermore, the conductive resin composition obtained using the silver powder of the present invention is less likely to have an excessive increase in viscosity, thus improving handling and printability. The inventors' research has revealed that a low proportion of coarse particles in silver powder can be defined by the proportion of silver particles having a particle size of 18.50 μm or more. Therefore, in order to reduce the number of contact points between silver particles in the silver powder and increase the opportunity for surface contact, thereby further reducing the resistivity of the conductive film compared to conventional methods, it is preferable that the proportion of silver particles having a particle size greater than 18.50 μm (hereinafter also simply referred to as "coarse particle proportion") in the particle size distribution obtained by the laser diffraction scattering particle size distribution measurement method be 1.40 volume% or less, more preferably 0.45 volume% or less, and even more preferably 0.40 volume% or less. From the viewpoint of making the above-mentioned effects even more pronounced, it is preferable that the coarse particle proportion be as small as possible, but it may also be 0.10 volume% or more. Silver powder having such a coarse particle proportion can be suitably manufactured by the manufacturing method described later. The method for measuring the coarse particle proportion will be explained in the examples described later.

[0020] In the silver powder of the present invention, the particle size D is as follows: １０ and particle size D ９０ It is preferable that each of these be within a predetermined range. Particle size D １０ and particle size D ９０ According to this, the degree of the particle size distribution can be defined. In the silver powder of the present invention, it is preferable that the silver particles are in surface contact with each other, and the particle size D １０ and particle size D ９０By setting the range to a predetermined level, the opportunities for point contact between silver particles caused by an excessive spread of the particle size distribution towards the finer particles can be reduced, resulting in a lower resistivity of the conductive film compared to conventional methods. Furthermore, the increase in surface energy caused by an excessive spread of the particle size distribution towards the coarser particles can be suppressed, improving film formation properties and enhancing the handling and printability of the conductive resin composition. Therefore, from the viewpoint of causing surface contact between silver particles in silver powder and reducing the resistivity of the conductive film compared to conventional methods, the cumulative volume particle size D at 10% cumulative volume, as measured by laser diffraction scattering particle size distribution analysis, is set to a predetermined level. １０ (Hereafter simply referred to as "Particle Size D") １０ It is also called ". The particle size D of the silver powder is preferably 1.80 μm or larger, more preferably 1.90 μm or larger, and even more preferably 2.00 μm or larger. From a similar viewpoint, the particle size D of the silver powder １０ It is preferable that the particle size is 3.90 μm or less, more preferably 3.40 μm or less, and even more preferably 2.40 μm or less.

[0021] Furthermore, from the viewpoint of reducing the resistivity of the conductive film compared to conventional methods by causing silver particles to come into surface contact with each other in the silver powder, and from the viewpoint of suppressing the rise in surface energy and improving film formation properties, as well as improving the handling and printability of the conductive resin composition, the cumulative volume particle size D at 90% cumulative volume measured by laser diffraction scattering particle size distribution analysis is considered. ９０ (Hereafter simply referred to as "Particle Size D") ９０ It is also called ". The particle size D of the silver powder is preferably 6.40 μm or larger, more preferably 7.00 μm or larger, and even more preferably 7.40 μm or larger. From a similar viewpoint, the particle size D of the silver powder ９０ It is preferable that the particle size is 14.00 μm or less, more preferably 12.00 μm or less, even more preferably 10.00 μm or less, and even more preferably 8.50 μm or less.

[0022] Furthermore, the extent of the spread of the particle size distribution of the silver powder in this invention is (D ９０ -D １０ ) / D ５０It can also be defined by the value defined by . A small value means that the particle size distribution is not excessively spread toward the fine particle side and is not excessively spread toward the coarse particle side. Specifically, from the viewpoint of bringing silver particles into surface contact in silver powder and reducing the resistivity of the conductive film compared to conventional methods, as well as suppressing the rise in surface energy and improving film formation properties, and improving the handling and printability of the conductive resin composition, (D ９０ -D １０ ) / D ５０ The value of is preferably 1.60 or less, more preferably 1.50 or less, and even more preferably 1.45 or less. From the viewpoint of making the above-mentioned effects even more pronounced, (D ９０ -D １０ ) / D ５０ A smaller value is preferable, but a value of 0.90 or higher is also acceptable.

[0023] Particle size D as described above １０ and particle size D ９０ Silver powder having the following characteristics can be suitably produced by the manufacturing method described later. Particle size D １０ and particle size D ９０ The measurement method will be explained in the examples described later.

[0024] The silver powder of the present invention preferably has few voids between the silver particles, i.e., high packing properties. This allows for a reduction in the resistivity of the conductive film formed from a conductive resin composition when the silver powder of the present invention is added to a resin and an organic solvent to produce a conductive resin composition, compared to conventional methods. From the viewpoint of making this effect even more pronounced, the bulk density of the silver powder of the present invention is preferably within a predetermined range. Specifically, the tap density of the silver powder of the present invention is 2.00 g / cm³. ３ Preferably, it should be 2.40 g / cm³ or more. ３ It is even more preferable that the amount be greater than or equal to 4.50 g / cm³. ３ It is even more preferable that the above conditions are met. From a similar viewpoint, a tap density of silver powder of 6.00 g / cm³ is desirable. ３ Preferably, it is 5.70 g / cm³. ３ It is even more preferable that the following conditions be met: 5.60 g / cm³ ３The following is even more preferable. Silver powder having such tap density can be suitably manufactured by the manufacturing method described later. In this specification, "tap density" refers to a value measured in accordance with JIS Z2512. A detailed method for measuring tap density will be explained in the examples described later.

[0025] In the silver powder of the present invention, it is preferable that the crystallite size of the silver in the silver particles constituting it is within a predetermined range, from the viewpoint of achieving both a reduction in the resistivity of the conductive film and good sinterability. When the crystallite size of silver in the silver particles decreases, the number of crystallites in the silver particles increases, and consequently, the number of grain boundaries also increases. As the number of grain boundaries increases, the resistance at the grain boundaries increases, which raises the resistivity of the conductive film. Therefore, from the viewpoint of suppressing the increase in the resistivity of the conductive film caused by the increase in grain boundaries, it is preferable that the crystallite size of silver is 40.0 nm or more, more preferably 40.5 nm or more, and even more preferably 41.0 nm or more. Furthermore, from the viewpoint of improving sinterability by increasing the effect of melting point depression at the contact points between silver particles in the silver powder during heat treatment and allowing sintering to proceed at a lower temperature, it is preferable that the crystallite size of silver is 45.0 nm or less, more preferably 44.0 nm or less, and even more preferably 43.0 nm or less. Silver powder having such crystallite sizes can be suitably manufactured by the manufacturing method described later. Detailed methods for measuring crystallite size will be described in the examples below.

[0026] Next, a preferred method for producing the silver powder of the present invention will be described. The production method of the present invention includes a step of flattening the raw material powder.

[0027] First, the raw material powder is prepared. The raw material powder consists of multiple silver particles. The shape of the raw material powder can be spherical, polygonal, spindle-shaped, or irregular. Through the flattening process described later, D ５０ From the viewpoint of successfully obtaining silver powder with an SSA value within the above range, it is preferable to use raw material powder consisting of non-flake-shaped silver particles, and it is particularly preferable to use raw material powder consisting of spherical silver particles.

[0028] Using raw material powders whose physical properties fall within a predetermined range ensures that the physical properties of the manufactured product are within a certain range, for example, D ５０ This is preferable because it successfully yields silver powder in which the SSA value, coarse grain ratio, and silver crystallite size are within the above-mentioned range. Specifically, it is preferable to have a non-flake shape and a particle size D ５０ From the above viewpoint, it is preferable to use a raw material powder having a particle size of 1.50 μm or more, more preferably 1.80 μm or more, and even more preferably 1.90 μm or more. From a similar viewpoint, it is preferable to have a non-flake shape and a particle size D ５０ From the above viewpoint, it is preferable to use raw material powder having a particle size of 2.80 μm or less, more preferably 2.50 μm or less, and even more preferably 2.30 μm or less.

[0029] Regarding the BET specific surface area (SSA) of the raw material powder, from the perspective mentioned above, it is 0.20 m². ２ It is preferable to use raw material powder of 0.25 m or more, and more preferably 0.25 m ２ It is 1 / g or more, and more preferably 0.28 m ２ It is 1 / g or more. From a similar perspective, 0.40m ２ It is preferable to use raw material powder of 0.38 m or less, and more preferably 0.38 m ２ It is less than or equal to / g, and more preferably 0.35m ２ It is less than / g.

[0030] Raw material powder D ５０ Regarding the SSA value, from the above viewpoint, it is preferable to use raw material powder with a value of 2.5 or higher, more preferably 5.0 or higher, even more preferably 5.5 or higher, and even more preferably 6.0 or higher. From a similar viewpoint, it is preferable to use raw material powder with a value of 8.0 or lower, more preferably 7.0 or lower, even more preferably 6.5 or lower, and even more preferably 6.3 or lower.

[0031] Particle size D of raw material powder １０Regarding this, from the above viewpoints, it is preferable to use raw material powder with a particle size of 0.80 μm or more, more preferably 0.90 μm or more, and even more preferably 1.00 μm or more. From the same viewpoints, it is preferable to use raw material powder with a particle size of 1.80 μm or less, more preferably 1.40 μm or less, and even more preferably 1.30 μm or less. Also, for the particle size D of the raw material powder ９０ Regarding this, from the above viewpoints, it is preferable to use raw material powder with a particle size of 2.80 μm or more, more preferably 2.90 μm or more, and even more preferably 3.00 μm or more. From the same viewpoints, it is preferable to use raw material powder with a particle size of 3.90 μm or less, more preferably 3.80 μm or less, and even more preferably 3.60 μm or less.

[0032] For the value of (D ９０ - D １０ ) / D ５０ from the above viewpoints, it is preferable to use raw material powder with a value of 1.30 or less, more preferably 1.20 or less, and even more preferably 1.10 or less. From the viewpoint of making the above effects more remarkable, the smaller the value of (D ９０ - D １０ ) / D ５０ is, the more preferable it is, but it may also be 0.90 or more.

[0033] Also, it is preferable that the volume average particle size D ＳＥＭ５０ (μm) of the raw material powder is within a predetermined range. Specifically, from the above viewpoints, it is preferable to use raw material powder with D ＳＥＭ５０ being 1.30 μm or more, more preferably 1.50 μm or more, and even more preferably 1.80 μm or more. From the same viewpoints, it is preferable to use raw material powder with a particle size of 3.00 μm or less, more preferably 2.80 μm or less, and even more preferably 2.50 μm or less.

[0034] Also, it is preferable that the raw material powder has a value defined by D ５０ / D ＳＥＭ５０ within a predetermined range. The value of D ５０ / D ＳＥＭ５０ is a value indicating the degree of aggregation of primary particles (i.e., silver particles constituting the raw material powder). D ５０ / D ＳＥＭ５０The larger the value of D, the greater the degree of aggregation of primary particles. ５０ / D ＳＥＭ５０ Ideally, the closer the value is to 1, the smaller the degree of primary particle aggregation can be considered to be. Therefore, from the above viewpoint, D ５０ / D ＳＥＭ５０ It is preferable to use raw material powder with a value of 1.50 or less, more preferably 1.30 or less, and even more preferably 1.10 or less. From the viewpoint of making the above-mentioned effects even more pronounced, D ５０ / D ＳＥＭ５０ The smaller the value, the more preferable it is, especially if it is close to 1, but it may also be 0.90 or greater.

[0035] Volume-average particle size D ＳＥＭ５０ This is the average value of the cumulative 50% particle size (Heywood diameter: equivalent to a circle diameter) in the volume distribution, measured by selecting more than 150 particles with clear outlines from images captured by SEM using image analysis software (MAC-VIEW ver. 5, manufactured by Mountec Co., Ltd.), and treating each particle as a sphere.

[0036] Raw material powders possessing such physical properties can be easily obtained, for example, by atomization methods such as wet reduction, gas atomization, and water atomization, as well as by plasma methods. ５０ From the viewpoint of successfully obtaining silver powder in which the SSA value, coarse grain ratio, and silver crystallite size are within the above-mentioned range, it is preferable to use raw material powder obtained by the wet reduction method.

[0037] Once the raw material powder is prepared, the workpiece containing the raw material powder is prepared. The workpiece consists of a slurry containing the raw material powder and a liquid medium. Examples of the liquid medium include water and organic solvents. A mixed solvent of water and an organic solvent can also be used. Examples of organic solvents include aliphatic alcohols having 1 to 22 carbon atoms. These organic solvents can be used individually or in combination of two or more. Of these liquid mediums, the use of an organic solvent is preferable because it increases the dispersibility of the raw material powder in the workpiece and improves the stability of the quality when subjected to the flattening process. Furthermore, it is preferable from the viewpoint of high solubility of the lubricant described later and successful plastic deformation of the raw material powder. It is preferable to use a monohydric alkyl alcohol having 1 to 4 carbon atoms because the medium volatilizes easily and does not easily remain on the target silver powder. Examples of such alcohols include methanol, ethanol, n-propanol, sec-propanol, n-butanol, sec-butanol, and tert-butanol.

[0038] It is preferable to include additives such as lubricants in the material to be processed. Lubricants have the property of improving the dispersibility of raw material powders, suppressing aggregation between particles, reducing friction between particles, and making them slippery. As lubricants, it is preferable to use fatty acid salts, for example. Fatty acids may be saturated fatty acids or unsaturated fatty acids. In either case, the number of carbon atoms in the fatty acid is preferably 4 to 20, and more preferably 5 to 19. Examples of such fatty acids include saturated fatty acids such as caproic acid, caprylic acid, and stearic acid, and unsaturated fatty acids such as oleic acid. As lubricants, it is particularly preferable to use group 1 metal salts or group 2 metal salts of these fatty acids. Examples of group 1 metal salts or group 2 metal salts of fatty acids include sodium caproate, sodium caprylate, potassium stearate, sodium stearate, potassium oleate, magnesium oleate, and calcium oleate. These additives can be used individually or in combination of two or more. From the viewpoint of effectively plastically deforming raw material powders that have a non-flake shape, it is preferable to use a lubricant, and it is particularly preferable to use sodium stearate.

[0039] To prepare the material to be processed, it is sufficient to simply mix the raw material powder, the liquid medium, and preferably the additive. In some cases, the dispersibility of the raw material powder may be improved using a stirring and dispersion device. Examples of such devices include a fluid mill and the T.K. Filmix® manufactured by Primix Corporation.

[0040] From the viewpoint of successfully plastically deforming the raw material powder, the concentration of raw material powder in the material to be processed is preferably 25.0% by mass or more, more preferably 27.0% by mass or more, and even more preferably 29.0% by mass or more. From the same viewpoint, the concentration of raw material powder in the material to be processed is preferably 35.0% by mass or less, more preferably 33.0% by mass or less, and even more preferably 31.0% by mass or less.

[0041] When the workpiece contains a lubricant, the lubricant content in the workpiece is preferably 0.10% by mass or more, more preferably 0.50% by mass or more, and even more preferably 0.90% by mass or more, relative to the silver particle content in the raw material powder, from the viewpoint of effectively plastically deforming the raw material powder having a non-flake shape. From the viewpoint of suppressing sintering defects caused by residual lubricant, the lubricant content in the workpiece is preferably 2.00% by mass or less, more preferably 1.50% by mass or less, and even more preferably 1.10% by mass or less, relative to the silver particle content in the raw material powder.

[0042] Once the material to be processed is ready, the raw material powder consisting of silver particles in the material is subjected to a flattening process to plastically deform the silver particles into flakes. Flattening of the raw material powder can be carried out using a grinding media, such as a bead mill, ball mill, or attritor. The material of the grinding media is generally zirconia and alumina. D ５０ From the viewpoint of successfully obtaining silver powder in which the SSA value, coarse grain ratio, and silver crystallite size are within the above range, the particle size D of the silver powder after flattening is important. ５０ It is preferable that the plastic deformation occurs so that the value is greater than or equal to the above value. Particle size D of silver powder ５０ By flattening the silver powder so that it does not become excessively small, the BET specific surface area SSA value of the silver powder can also be prevented from becoming excessively small, and as a result, the D of the silver powder ５０ This is because the value of / SSA can be effectively brought within the above range. Furthermore, the silver powder D ５０ By setting the value of / SSA within the above range, the silver crystallite size can also be set within the above range. The reason for this is D ５０ The value of / SSA indicates the degree of uniformity of the flake shape, D ５０ The value of / SSA allows us to evaluate whether the flattening process is excessive or insufficient. ５０ The inventors speculate that by setting the value of / SSA within the above range, it is possible to avoid situations where the crystallite size, which changes as flattening progresses, becomes excessively small or cannot be made small enough. However, the inventors are not bound by this theory. Particle size D of silver powder after flattening５０ This can be controlled by adjusting various flattening conditions, such as the diameter of the grinding media, the packing ratio of the grinding media to the volume of the crushing section of the media stirring mill, the amount of kinetic energy per particle of the grinding media, the stress number per unit time, and the grinding time.

[0043] Specifically, it is preferable to use a grinding media with a relatively small diameter. By using such a grinding media, the particle size D of the raw material powder can be reduced. ５０ Silver particles of various particle sizes can be flattened without depending on the particle size D of the flattened silver powder. ５０ This makes it easier to achieve the above-mentioned value or higher. From the viewpoint of making this effect even more pronounced, it is preferable to use spherical crushed media with a diameter of 0.25 mm or less, more preferably 0.20 mm or less, and even more preferably 0.15 mm or less. From the viewpoint of making the above-mentioned effect even more pronounced, the smaller the diameter of the crushed media, the better, but it may be 0.015 mm or more.

[0044] Furthermore, when the diameter of the grinding media (mm) is M, the particle size D of the raw material powder is... ５０ It is preferable to set the diameter M of the grinding media such that the value defined by / (1000 × M) falls within a predetermined range. Specifically, from the viewpoint of effectively flattening the raw material powder, the particle size D of the raw material powder ５０ It is preferable to set the diameter M such that / (1000 × M) is 0.010 or more, more preferably 0.015 or more, and even more preferably 0.018 or more. From a similar viewpoint, the particle size D of the raw material powder ５０ It is preferable to set the diameter M such that / (1000 × M) is 0.050 or less, more preferably 0.030 or less, and even more preferably 0.025 or less.

[0045] Regarding the packing ratio of the grinding media to the volume of the crushing section of the media stirring mill, the goal is to effectively flatten the silver particles and the particle size D of the silver powder after flattening. ５０ From the viewpoint of making it easier to set the above value or higher, it is preferable to set it to 60 volume% or more, more preferably 70 volume% or more, and even more preferably 75 volume% or more. Also, the particle size D of the silver powder ５０The particles are flattened to prevent them from becoming excessively small, and the particle size D of the silver powder after flattening is ５０ From the viewpoint of making it easier to achieve the above-mentioned value or higher, it is preferable to set the packing rate of the pulverized media to the volume of the crushing section of the media stirring mill to 90 volume% or less, more preferably to 85 volume% or less, and even more preferably to 83 volume% or less. In this specification, "packing rate" refers to the ratio of the apparent volume (L) of the pulverized media to the volume (L) of the crushing section of the media stirring mill.

[0046] From the viewpoint of successfully plastically deforming the raw material powder, it is preferable to control the amount of energy applied to the raw material powder in the flattening process so that it is within a predetermined range. The amount of energy applied to the raw material powder can be defined by the kinetic energy per particle of the grinding media. Specifically, the silver particles are flattened effectively, and the particle size D of the silver powder after flattening is controlled. ５０ From the perspective of making it easier to achieve a value greater than the above, the kinetic energy per particle of the crushed media should be 1.00 × 10 －８ kg・m ２ / s ２ It is preferable to subject the flattening process to the above, and more preferably to 5.00 × 10 －８ kg・m ２ / s ２ That's all. Also, the particle size D of the silver powder ５０ The particles are flattened to prevent them from becoming excessively small, and the particle size D of the silver powder after flattening is ５０ From the perspective of making it easier to achieve a value greater than the above, the kinetic energy per particle of the crushed media should be 1.00 × 10 －６ kg・m ２ / s ２ It is preferable to subject the flattening process to the following, and more preferably to 5.00 × 10 －７ kg・m ２ / s ２ The following applies. In this specification, "kinetic energy per particle of grinding media" is the value defined by the following equation (1). Since the speed of the grinding media can be considered to be the same as the peripheral speed of the media stirring mill device, the speed of the grinding media is defined in equation (1) by this peripheral speed. 0.5 × Mass per particle of grinding media (kg) × Peripheral speed of the media stirring mill device (m / s)２ ... (1)

[0047] The amount of energy imparted to the raw material powder can also be determined by the stress number per unit time that the grinding media imparts to the raw material powder. Specifically, the amount of silver particles is effectively flattened, and the particle size D of the flattened silver powder is determined. ５０ From the viewpoint of making it easier to achieve the above-mentioned value or higher, it is preferable to subject the flattening process to such a stress rate per unit time that the grinding media imparts to the raw material powder is 0.30 rpm / mm or more, more preferably 0.50 rpm / mm or more, and even more preferably 1.0 rpm / mm or more. Also, the particle size D of the silver powder ５０ The particles are flattened to prevent them from becoming excessively small, and the particle size D of the silver powder after flattening is ５０ From the viewpoint of making it easier to achieve a value greater than the above-mentioned value, it is preferable to subject the flattening process to such a stress number per unit time as 5.00 rpm / mm or less, more preferably 4.00 rpm / mm or less, and even more preferably 3.00 rpm / mm or less. In this specification, "stress number per unit time that the grinding media imparts to the raw material powder" is the value defined by the following formula (2): Rotational speed of the media stirring mill (rpm) × {particle size D of the raw material powder} ５０ (mm) / Diameter of the crushed media (mm) ２ ... (2)

[0048] Regarding the grinding time of the raw material powder, the goal is to effectively flatten the silver particles and the particle size D of the silver powder after flattening. ５０ From the viewpoint of making it easier to achieve the above-mentioned value or higher, it is preferable to set it to 15 minutes or more, more preferably 18 minutes or more, and even more preferably 20 minutes or more. Also, the particle size D of the silver powder ５０ The particles are flattened to prevent them from becoming excessively small, and the particle size D of the silver powder after flattening is ５０ From the viewpoint of making it easier to achieve the above-mentioned value or higher, it is preferable to set the grinding time of the raw material powder to 100 minutes or less, more preferably 95 minutes or less, and even more preferably 50 minutes or less.

[0049] Flattening of raw material powder can be performed by a media stirring mill device, and from the viewpoint of easily adjusting the various flattening conditions described above, it is preferable to perform the flattening using a device employing a predetermined operating method. As operating methods for media stirring mill devices, generally, circulating type, material-passing type (so-called pass type), and material-multiple-passing type are known. Generally, it is known that the material-passing type and material-multiple-passing type allow for easier and relatively uniform control of the particle size of the processed material after flattening compared to the circulating type. In the manufacturing method of the present invention, by controlling various conditions such as the diameter of the grinding media, the kinetic energy per particle of the grinding media, and the stress number per unit time that the grinding media imparts to the raw material powder, it is possible to easily and relatively uniformly control the particle size of the processed material even in a circulating type. Furthermore, media stirring mill devices are broadly classified into vertical and horizontal types depending on the orientation of the grinding chamber, but horizontal devices cannot utilize the weight of the grinding media, so a large amount of energy is required for the plastic deformation of the raw material powder. In contrast, vertical devices can effectively utilize the weight of the grinding media, and therefore require less energy for the plastic deformation of the raw material powder compared to horizontal devices. Consequently, the particle size D of the silver powder after flattening... ５０ Plastically deform the material so that it is greater than or equal to the above value, D ５０ From the viewpoint of successfully obtaining silver powder in which the SSA value, coarse grain ratio, and silver crystallite size are within the above-mentioned range, it is preferable to use a vertical apparatus. As such an apparatus, for example, the Ultra Apex Mill, a bead mill manufactured by Hiroshima Metal & Machinery Co., Ltd., can be used.

[0050] In the flattening process, D ５０ From the viewpoint of successfully obtaining silver powder in which the SSA value, coarse particle ratio, and silver crystallite size are within the above range, it is preferable to control the physical properties of the raw material powder and the diameter of the grinding media to a predetermined relationship. In particular, the particle size D of the raw material powder is ５０ The size is 1.50 μm or more and 2.80 μm or less, (D ９０ -D １０ ) / D ５０ The value of is 0.90 or more and 1.30 or less, and D ５０ / D ＳＥＭ５０Using a value of 0.90 or more and 1.50 or less, the particle size D of the raw material powder is used. ５０ It is preferable to use a grinding media such that / (1000 × M) is between 0.010 and 0.050.

[0051] After the raw material powder is subjected to a flattening process, solid-liquid separation is performed using solid-liquid separation methods such as vacuum dehydration, filter pressing, centrifugal separation, and ultrafiltration to separate and remove the silver powder from the processed material. Subsequently, the silver powder is washed with a solvent and dried.

[0052] In this way, the silver powder of the present invention is obtained. A metal can be placed on the surface of the silver powder, to the extent that the effects of the present invention are not impaired. This allows for the utilization of various properties of the metal. There are no particular restrictions on the type of metal.

[0053] The silver powder of the present invention can be used in the form of a conductive resin composition by mixing it with a resin (polymer material). The conductive resin composition comprises at least the silver powder and resin of the present invention. Examples of resins include thermosetting resins and thermoplastic resins. Examples of thermosetting resins include epoxy resins, phenolic resins, urea resins, melamine resins, and silicone resins. These thermosetting resins can be used individually or in combination of two or more. Examples of thermoplastic resins include various polyolefin resins such as polyethylene, polypropylene, polymethylpentene, and copolymers thereof; various polyamide resins such as polyamide 6, polyamide 66, polyamide 12, polyamide 11, metaxylylene adipamide (mXD6), hexamethylene terephthalamide (6T), and copolymers thereof; polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene-2,6-naphthalate (PEN), polymethylene terephthalate (PMT), polypropylene terephthalate (PPT), polyethylene-p-oxybenzoate (PEOB), and poly-1,4-cyclohexyl terephthalate. Xylene dimethylene terephthalate (PCT) and various polyester resins obtained by copolymerizing diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, or dicarboxylic acid components such as adipic acid, sebatic acid, phthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid; and other examples include acrylic resins, methacrylic resins, ethyl cellulose, carboxyethyl cellulose, polyacetal (POM) resins, polyphenylene sulfide (PPS) resins, polycarbonate resins, polyvinyl chloride (PVC), and chlorine-containing resins such as polyvinylidene chloride (PVdC). These thermoplastic resins can be used individually or in combination of two or more. Among these resins, epoxy resin is preferred as the thermosetting resin. Acrylic resin, ethyl cellulose, or carboxyethyl cellulose is preferred as the thermoplastic resin.

[0054] The conductive resin composition may contain, in addition to the silver powder and resin of the present invention, at least one of an organic solvent, a dispersant, glass frit, and other metal powders. The organic solvent can be any of the same types that have been used in the art of conductive resin compositions containing metal powders, without any particular limitations. Examples of such organic solvents include monohydric alcohols such as terpineol and dihydroterpineol; polyhydric alcohols; polyhydric alcohol alkyl ethers such as ethyl carbitol and butyl carbitol; polyhydric alcohol aryl ethers; polyethers such as polyethylene glycol and polypropylene glycol; esters such as carbitol acetate, butyl cellosolve acetate, and butyl carbitol acetate; nitrogen-containing heterocyclic compounds; amides; amines, and saturated hydrocarbons. These organic solvents can be used individually or in combination of two or more. From the viewpoint of easily dispersing silver powder due to its surface activity such as wetting, permeability, and dispersibility, from the viewpoint of being able to volatilize at relatively low temperatures, from the viewpoint of having appropriate viscosity, and from the viewpoint of being easily soluble in other organic solvents and easily dissolving various resins, it is preferable to use a monohydric alcohol as the organic solvent. From the viewpoint of making such effects even more pronounced, it is more preferable to use terpineol or dihydroterpineol among monohydric alcohols, and more preferable to use terpineol. Separately from the above viewpoint, from the viewpoint of having a high reducing effect, it is preferable to use polyethers such as polyethylene glycol and polypropylene glycol. From a similar viewpoint, when polyethylene glycol is used as the organic solvent, its number average molecular weight is preferably 120 or more and 400 or less, and more preferably 180 or more and 400 or less. Examples of dispersants include nonionic surfactants that do not contain sodium, calcium, phosphorus, sulfur, and chlorine. Examples of glass frits include borosilicate glass, barium borosilicate glass, and zinc borosilicate glass. These can be used individually or in combination of two or more. Examples of other metal powders include copper powder and silver-coated copper powder. These can be used individually or in combination of two or more.

[0055] A conductive film of silver powder can be formed by applying the above-described conductive resin composition onto a substrate to form a coating film, and then sintering it. The conductive film is suitably used, for example, for die bonding of electronic devices, circuit formation on printed circuit boards, electrodes for solar cells, and ensuring electrical conductivity for external electrodes of multilayer ceramic capacitors. Examples of printed circuit boards include those made of glass epoxy resin, flexible printed circuit boards made of polyimide, etc., depending on the type of electronic circuit in which silver powder is used.

[0056] The content of silver powder and organic solvent in the conductive resin composition can be appropriately set according to the specific application and application method of the conductive resin composition, but the silver powder content is preferably 5% by mass or more and 95% by mass or less, and more preferably 50% by mass or more and 90% by mass or less.

[0057] The conductive resin composition can be applied by methods such as inkjet printing, dispenser printing, microdispenser printing, gravure printing, screen printing, dip coating, spin coating, spray coating, bar coating, and roll coating.

[0058] The sintering temperature of the coating film should be above the sintering start temperature of the silver powder, for example, 100°C to 350°C. Sintering can be carried out, for example, under an oxidizing atmosphere or a non-oxidizing atmosphere. An example of an oxidizing atmosphere is an atmospheric atmosphere. Examples of non-oxidizing atmospheres are reducing atmospheres such as hydrogen and carbon monoxide, weakly reducing atmospheres such as a hydrogen-nitrogen mixed atmosphere, and inert atmospheres such as argon, neon, helium and nitrogen. In any atmosphere, the sintering time is preferably 0.1 hours to 5 hours, and more preferably 0.2 hours to 3 hours, provided that the temperature is within the above-mentioned temperature range.

[0059] The conductive film obtained in this way has a lower resistivity than conventional films because it is obtained by sintering the silver powder of the present invention.

[0060] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments.

[0061] Further disclosure relating to the above embodiments is provided for silver powder and a method for producing the same. [1] Silver powder comprising a plurality of silver particles having a flake shape, wherein the cumulative volume particle size at 50% of the cumulative volume, as measured by laser diffraction scattering particle size distribution analysis, is D ５０ Let (μm) be the specific surface area of ​​BET be SSA (m ２ When we set it to / g, D ５０ [1] Silver powder having a value defined by / SSA of 3.50 or more and 5.20 or less. [2] Silver powder according to [1], wherein the crystallite size of silver is 40.0 nm or more and 45.0 nm or less. [3] Silver powder according to [1] or [2], wherein the proportion of silver particles having a particle size greater than 18.50 μm in the particle size distribution obtained by the laser diffraction scattering particle size distribution measurement method is 1.40 volume% or less. [4] The volume cumulative particle size D ５０ Silver powder according to any one of [1] to [3], wherein the particle size is 3.80 μm or more and 7.40 μm or less. [5] The BET specific surface area SSA is 0.70 m ２ / g or more 2.00m ２ Silver powder as described in any one of [1] to [4], which is less than or equal to / g.

[0062] [6] Tap density is 2.00 g / cm³ ３ 6.00g / cm or more ３ The silver powder described in any one of the following [1] to [5]. [7] A method for producing silver powder comprising subjecting a raw material powder consisting of multiple silver particles having a non-flake shape and a cumulative volume particle size of 1.50 μm or more and 2.80 μm or less at a cumulative volume of 50% measured by laser diffraction scattering particle size distribution measurement to a flattening step using a grinding media with a diameter of 0.25 mm or less, wherein the kinetic energy per particle of the grinding media is 1.00 × 10 －８ kg・m ２ / s ２ The above 1.00 x 10 －６ kg・m ２ / s ２A method for producing silver powder, comprising subjecting the material to a flattening step so that the number of stresses per unit time that the grinding media imparts to the raw material powder is 0.30 rpm / mm or more and 5.00 rpm / mm or less. [8] Using the raw material powder consisting of spherical silver particles, and determining the cumulative volume particle size of the raw material powder at a cumulative volume of 50% by the laser diffraction scattering particle size distribution method, D ５０ (μm) is defined as the BET specific surface area of ​​the raw material powder, and SSA (m ２ When we set it to / g, D ５０ The manufacturing method described in [7], wherein the value defined by / SSA is 3.00 or more and 8.00 or less.

[0063] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0064] [Example 1] As the raw material powder, SL02, which is wet-processed silver particles manufactured by Mitsui Mining & Smelting Co., Ltd., was prepared. Details of the wet-processed silver particles are shown in Table 1 below. 514 g of wet-processed silver particles, 1200 g of methanol, and 5.14 g of sodium stearate were mixed to prepare a slurry to be processed. Next, the raw material powder was flattened using a zirconia grinding media with an Ultra Apex Mill (UAM-015-1199, effective crushing volume 0.17 L), a bead mill manufactured by Hiroshima Metal & Machinery Co., Ltd. Details of the flattening conditions are shown in Table 1 below. After that, the silver powder was subjected to solid-liquid separation, washed, and dried to obtain the desired silver powder.

[0065] [Examples 2 to 4] In Example 1, the grinding time was changed to the conditions shown in Table 1. Otherwise, the target silver powder was obtained in the same manner as in Example 1.

[0066] [Comparative Examples 1 and 2] In Example 1, instead of the Ultraapex mill, a Dyno Mill (MULTI LAB, effective crushing volume 0.56 L), a bead mill manufactured by Willy e Bakkofen, was used to flatten the raw material powder. Details of the flattening conditions are shown in Table 1 below. Except for these, the target silver powder was obtained in the same manner as in Example 1.

[0067] [Evaluation] The average aspect ratio, particle size and coarseness ratio, BET specific surface area (SSA), tap density, and silver crystallite size of the silver powder obtained in the examples and comparative examples were measured according to the method described below. Furthermore, the resistivity of the conductive film was measured for the silver powder obtained in the examples and comparative examples according to the method described below. These results are shown in Table 2.

[0068] [Average Aspect Ratio] A small amount of hardener, which is epoxy resin dissolved in a small amount of silver powder obtained in the examples and comparative examples, was added to a small amount of silver powder. This was thoroughly mixed with a spatula to obtain a paste. This was heated in a vacuum atmosphere at 120°C for 15 minutes to obtain a sample. An observation sample was obtained by polishing the surface of the sample. Using a JEOL cross-section polisher (SM-09010), the observation sample obtained under conditions of 5kV and 40-50mA was cross-sectionally processed, Pt was deposited on the polished surface, and a particle cross-sectional image was obtained using a JEOL scanning electron microscope (JSM-7100F). Using image analysis particle size distribution measurement software (Mac-Viewer ver. 5) from Mountec Co., Ltd., more than 60 silver particles in the obtained particle cross-sectional image were measured to obtain the aspect ratio. The average value of the obtained aspect ratios was taken as the average aspect ratio.

[0069] [Particle size D ５０ , particle size D １０ , particle size D ９０ , and coarse particle ratio] A dispersion liquid made by adding a dispersant (DISPERBYK, manufactured by BYK) and silver powder to a solvent (IPA) was irradiated with a 110W bath-type ultrasonic wave for 3 minutes, and the particle size distribution was measured using a Microtrac-Bell Co., Ltd. laser diffraction particle size distribution analyzer "MT3300EX II", and the particle size D was obtained from the volume-based particle size distribution chart. ５０ , particle size D １０ , particle size D ９０ The following was measured. Furthermore, the proportion of particles larger than 18.50 μm was defined as the coarse particle proportion from the volume-based particle size distribution chart. Particle size D ５０ , particle size D １０ , particle size D ９０ Furthermore, when measuring the proportion of coarse particles, the flow velocity was set to 70%, the solvent refractive index to 1.36, and the particle permeability condition to "reflection."

[0070] [BET Specific Surface Area] Measured using a single-point method with a macsorb manufactured by Mountec Co., Ltd. The amount of powder to be measured was 4.0 g, and the pre-degassing conditions were 75°C for 10 minutes.

[0071] [Tap Density] Tap density was measured using a tapping machine (model: TPM-3A, Tsutsui Rikagakukikai Co., Ltd.). Specifically, a volume of 150 cm³ was used. ３ 50g of silver powder was placed in the graduated cylinder. The tap stroke was set to 4cm and the number of taps to 1000, and measurements were taken.

[0072] [Silver Crystallite Size] The crystallite size of the silver powder obtained in the examples and comparative examples was calculated by analyzing the diffraction peaks originating from silver, obtained by X-ray diffraction measurement, using the FP method. The conditions were as follows: Instrument Name: Ultima IV: Manufactured by Rigaku Corporation <Instrument Configuration> Wavelength / Target: Cu Wavelength Type: Kα1 Kα1: 1.5405929 (Å) Kα2: 1.544414 (Å) Kα12 Intensity Ratio: 0.497 Horizontal Polarization Ratio: 0.500 Diffraction Device / Goniometer: Ultima IV <Measurement Conditions> Optical System Attributes: Focusing Method CBO Selection Slit: BB Entrance Slit: 2 / 3 deg Longitudinal Limiting Slit: 10.0 mm Receiving Slit 1: 8.0 mm Receiving Slit 2: Open Detector: D / teX Ultra Scan Axis: 2θ / θ Scan Mode: CONTINUOUS Scan Range: 20.0000 to 80.0000 deg • Step size: 0.0200 deg • Scan speed / measurement time: 20.0000 deg / min • Tube voltage: 40 kV • Tube current: 40 mA <Preparation of X-ray diffraction sample> The silver powder obtained in the examples and comparative examples, which were to be measured, was spread in the measurement holder, and the layer of silver powder was smoothed using a glass plate so that the thickness of the layer was 0.5 mm and the measurement surface was smooth. The X-ray diffraction pattern obtained under the above measurement conditions was analyzed using analysis software under the following conditions. The crystallite size was calculated using the FP method. <Measurement data analysis conditions> • Analysis software: Rigaku PDXL2 • Analysis method: FP method

[0073] [Resistivity] 1.50 g of silver powder was mixed with 0.50 g of terpineol, which is ethylcellulose dissolved in silver powder. These were mixed at 1000 rpm for 3 minutes using a rotation-orbit mixer manufactured by Thinky Co., Ltd. to prepare conductive resin compositions with a silver powder content of 75%. The mass ratio of ethylcellulose to terpineol in each conductive resin composition was 5:95. Next, the paste was coated onto an alumina substrate. A screen printing machine (ST325 / 28, φ20 mm pattern) manufactured by Mitani Micronics Kyushu Co., Ltd. was used for coating. The formed coating film was dried in an air-hot air drying oven at 300°C for 60 minutes to obtain a conductive film. The resistivity (μΩ・cm) of the conductive film was measured using a resistivity meter (Mitsubishi Chemical Analytec, Loresta-GP MCP-T610) by the four-probe method.

[0074]

[0075]

[0076] As is clear from the results shown in Table 2, the silver powder obtained in the example has a lower resistivity than the silver powder obtained in the comparative example.

[0077] The present invention provides silver powder and a method for manufacturing the same that can reduce the resistivity of a conductive film compared to conventional methods.

Claims

1. A silver powder consisting of multiple silver particles having a flake shape, wherein the cumulative volume particle size at a cumulative volume of 50% is determined by laser diffraction scattering particle size distribution measurement method. ５０ Let (μm) be the specific surface area of ​​BET be SSA (m ２ When we set it to / g, D ５０ Silver powder whose value, as defined by / SSA, is between 3.50 and 5.

20.

2. The silver powder according to claim 1, wherein the silver crystallite size is 40.0 nm or more and 45.0 nm or less.

3. The silver powder according to claim 1 or 2, wherein, in the particle size distribution obtained by the laser diffraction scattering particle size distribution measurement method, the proportion of silver particles having a particle size greater than 18.50 μm is 1.40 volume% or less.

4. The volume cumulative particle size D ５０ The silver powder according to claim 1 or 2, wherein the particle size is 3.80 μm or more and 7.40 μm or less.

5. The BET specific surface area SSA is 0.70 m². ２ / g or more 2.00m ２ The silver powder according to claim 1 or 2, wherein the amount is less than or equal to / g.

6. Tap density is 2.00 g / cm³ ３ 6.00g / cm or more ３ The silver powder according to claim 1 or 2, which is as follows:

7. A method for producing silver powder, comprising subjecting a raw material powder composed of a plurality of silver particles having a non-flaky shape and a volume-cumulative particle diameter at a cumulative volume of 50% by a laser diffraction scattering particle size distribution measurement method of 1.50 μm or more and 2.80 μm or less to a flattening step using a grinding medium having a diameter of 0.25 mm or less, wherein the kinetic energy per particle of the grinding medium is 1.00×10 －８ kg·m ２ / s ２ or more and 1.00×10 －６ kg·m ２ / s ２ or less, and subjecting the flattening step so that the stress number per unit time applied by the grinding medium to the raw material powder is 0.30 rpm / mm or more and 5.00 rpm / mm or less.

8. Using the raw material powder consisting of spherical silver particles, and determining the cumulative volume particle size of the raw material powder at a cumulative volume of 50% by the laser diffraction scattering particle size distribution method, D ５０ (μm) is defined as the BET specific surface area of ​​the raw material powder, and SSA (m ２ When we set it to / g, D ５０ The manufacturing method according to claim 7, wherein the value defined by / SSA is 3.00 or more and 8.00 or less.

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