Silver-coated copper powder, a conductive resin composition containing the same, and a method for manufacturing the same.

Abstract

The silver-coated copper powder of the present invention comprises a copper core particle and an aggregate of silver-coated copper particles having a silver coating layer disposed on at least a portion of the surface of the core particle. When the cross-section of the silver-coated copper particle is measured by electron beam backscattering diffraction, the number of copper crystal grains per silver-coated copper particle is set to N (pieces), the BET specific surface area is set to SSA (m² / g), and the volume cumulative particle size at 50% of the cumulative volume by laser diffraction scattering particle size distribution measurement is set to D50 (㎛), and the value defined as N / (SSA×D50) is 0.3 (pieces / {(m² / g)×(㎛)}) or more and 5.0 (pieces / {(m² / g)×(㎛)}) or less.

Description

Technology Field

[0001] The present invention relates to silver-coated copper powder, a conductive resin composition containing the same, and a method for manufacturing the same. Background Technology

[0002] Conductive pastes or conductive adhesives containing metal powder are used for the purpose of promoting electrical conduction between conductors. As metal powders, precious metals such as gold or silver and non-metals such as nickel or copper are used. Precious metals are suitable materials for conductive powders because they are resistant to oxidation and have high conductivity, but they pose economic challenges. Therefore, various attempts have been proposed to increase the electrical conductivity of conductive powders while reducing the use of precious metals by thinly coating gold or silver onto the surface of inexpensive metals such as nickel or copper.

[0003] For example, Patent Document 1 describes silver-coated copper particles that are formed by coating the surface of copper powder particles with a silver layer containing silver or a silver alloy and also exhibit a dendrite shape. It is described in the document that, due to the fact that the silver-coated copper particles exhibit a dendrite shape, the number of contact points between the particles increases, thereby obtaining conductivity. Prior art literature

[0004] US2018 / 0354033A1

[0005] When silver-coated copper particles described in Patent Document 1 are used as a resin composition, in order to obtain excellent conductivity, it was necessary to perform a press operation to increase the number of contact points between the particles exhibiting a dendrite shape. Therefore, when a press operation cannot be performed, it is not easy to obtain sufficient conductivity to be satisfactory for practical use.

[0006] Accordingly, the objective of the present invention is to provide silver-coated copper powder that makes it possible to obtain a conductive resin composition capable of increasing conductivity without performing press operations.

[0007] The present invention is a silver-coated copper powder comprising a copper core particle and an aggregate of silver-coated copper particles having a silver coating layer disposed on at least a portion of the surface of said core particle.

[0008] When the cross-section of the silver-coated copper particle is measured by electron backscattering diffraction, let N be the number of copper crystal grains per silver-coated copper particle, let SSA be the BET specific surface area, and let D be the volumetric cumulative particle diameter at 50% of the cumulative volume determined by the laser diffraction scattering particle size distribution method. 50 When set to (㎛), N / (SSA×D 50 The above problem was solved by providing silver-coated copper powder having a value defined as ) of 0.3 (pieces / {(㎡ / g)×(㎛)}) or more and 5.0 (pieces / {(㎡ / g)×(㎛)}) or less.

[0009] In addition, the present invention comprises a process of using an electrolyte containing a copper source and precipitating dendrite-shaped copper particles on a cathode by electrolytic reduction, and

[0010] A process of crushing the above copper particles to obtain core material particles, and

[0011] The present invention provides a method for manufacturing silver-coated copper powder, comprising the process of mixing the core material particles with an aqueous solution containing silver ions to reduce the silver ions and forming a silver coating layer on at least a portion of the surface of the core material particles. Brief explanation of the drawing

[0012] FIG. 1 (a) is a schematic diagram illustrating copper powder that serves as a raw material for the silver-coated copper powder of the present invention, and FIG. 1 (b) is a schematic diagram illustrating the process of manufacturing the silver-coated copper powder of the present invention from the copper powder of the raw material. Specific details for implementing the invention

[0013] The present invention will be described below based on its preferred embodiments. The silver-coated copper powder of the present invention is composed of an aggregate of silver-coated copper particles. The silver-coated copper particles have a copper core particle and a silver coating layer disposed on at least a portion of the surface of said core particle. In this specification, "copper core particle" includes particles substantially composed of copper elements and copper alloy particles.

[0014] In the case of the former particles, they are particles substantially composed of copper elements and also containing unavoidable elements in the remainder. In this case, the silver-coated copper powder of the present invention preferably consists only of silver and copper elements, but the inclusion of trace amounts of unavoidable elements is permitted. When unavoidable elements are included in the silver-coated copper powder, it is preferable that the content be 0.01 mass% or less, as this makes it difficult to impair the inherent properties of the silver-coated copper powder. Unavoidable elements include, for example, O (oxygen) elements and C (carbon) elements derived from oxygen and carbon dioxide in the atmosphere, and N (nitrogen) elements that may be incorporated during the manufacturing process of the silver-coated copper powder. The presence or absence of unavoidable elements and their content can be measured, for example, by ICP emission spectroscopy.

[0015] In the case of the latter particles, the content of copper element in the particles is preferably 80 mass% or more, and more preferably 90 mass% or more.

[0016] In the silver-coated copper powder of the present invention, it is preferable that the copper, which is the core material particle, has high crystallinity. As a result of the inventors' investigation, it has been determined that silver-coated copper powder with high copper crystallinity can impart high conductivity to a conductive resin composition when the powder is added to a resin and an organic solvent, etc., to prepare a conductive resin composition. In particular, the number of copper crystal grains per silver-coated copper particle, the BET specific surface area, and the particle size D 50 In the case of the relationship described below, it is desirable because it is possible to impart even higher conductivity to the conductive resin composition and also impart appropriate thixotropic properties to the conductive resin composition. In order to increase the crystallinity of the silver-coated copper powder, it is desirable to manufacture core material particles, for example, by the manufacturing method described below.

[0017] In this specification, when the term "conductive resin composition" is used, depending on the context, it means a composition comprising a thermosetting resin before curing or a composition comprising a thermosetting resin after curing.

[0018] First, the silver-coated copper powder of the present invention will be described.

[0019] In the silver-coated copper powder of the present invention, the shape of the copper core particles (hereinafter simply referred to as "core particles") may be spherical, flattened, polyhedral, spindle-shaped, or irregular. Among these, it is particularly desirable for the shape of the core particles to be anisotropic. In other words, it is desirable for the shape of the core particles to be non-spherical. It is desirable to use core particles having anisotropy so that high conductivity can be imparted to the conductive resin composition. From this perspective, it is desirable for the core particles to have shapes such as, for example, irregular shape, unidirectionally elongated rod shape, cigar shape, and spheroid shape. By manufacturing the core particles using the manufacturing method described below, the crystallinity of the silver-coated copper powder can be increased, and as a result, the core particles can be made to have anisotropy.

[0020] In this embodiment, since the thickness of the silver coating layer disposed on the surface of the core material particles is small, the shape of the silver-coated copper particles is substantially the same as the shape of the core material particles.

[0021] The degree of anisotropy of the core material particles can be evaluated by the aspect ratio of the silver-coated copper powder. The aspect ratio is calculated based on L / W, where L is defined as the longest cross-sectional length among the cross-sectional lengths of the target particles, and W is defined as the length of the perpendicular bisector of the cross-sectional length L that crosses the particle.

[0022] Specifically, the method for calculating the aspect ratio first involves taking at least two fields of view with a scanning electron microscope (hereinafter also referred to as "SEM") at a magnification that includes at least 50 silver-coated copper particles to be measured. Next, at least 50 samples are randomly selected from each image data in which the outline of each silver-coated copper particle can be identified, and the values ​​of L and W are measured for each of the selected silver-coated copper particles. The average values ​​of L and W are each calculated, and the L / W value is calculated from the said average values. The value calculated in this manner is used as the aspect ratio in this specification.

[0023] In the case of silver-coated copper powder, from the perspective of imparting high conductivity to a conductive resin composition, it is preferable that the aspect ratio measured by the above method is 1.1 or higher, more preferable that it is 1.3 or higher, and even more preferable that it is 1.5 or higher. In the same regard, it is preferable that the aspect ratio measured by the above method is 4.5 or lower, more preferable that it is 4.3 or lower, and even more preferable that it is 4.1 or lower.

[0024] In the case of silver-coated copper powder, the average value of L is preferably 2.5 μm or more, more preferably 2.7 μm or more, and even more preferably 3.0 μm or more, provided that the aspect ratio is within the above range. Additionally, the average value of L is preferably 8.0 μm or less, more preferably 7.8 μm or less, and even more preferably 7.6 μm or less, provided that the aspect ratio is within the above range.

[0025] The average value of W is preferably 0.3 μm or more, more preferably 0.6 μm or more, and even more preferably 0.9 μm or more, provided that the aspect ratio is within the above range. Additionally, the average value of W is preferably 4.1 μm or less, more preferably 3.8 μm or less, and even more preferably 3.5 μm or less, provided that the aspect ratio is within the above range.

[0026] In order to make the aspect ratio and the average values ​​of L and W in the silver-coated copper powder within the above range, it is preferable to manufacture the silver-coated copper powder using, for example, the manufacturing method described below.

[0027] The silver coating layer of the present embodiment is composed of aggregates of fine silver particles. From the perspective of imparting high conductivity to the conductive resin composition, it is suitable for the silver coating layer having the above structure to be disposed on at least a portion of the surface of the core material particles. The boundary between the core material particles and the silver coating layer may be clear, and there may be some unclear portions within the range where the core material particles and the silver coating layer can be distinguished.

[0028] The method of placing a silver coating layer on the surface of the core material particles is not particularly limited. From the perspective of smoothly placing a silver coating layer on the surface of the core material particles, it is suitable to use the displacement plating method described later or to use a reducing agent.

[0029] The silver coating layer needs to be present to cover at least a portion of the surface of the core material particles. Accordingly, the silver coating layer may be disposed over the entire surface of the core material particles or may be disposed over a portion of the surface of the core material particles. The amount of the silver coating layer can be evaluated by the silver content per BET specific surface area in the silver-coated copper powder. Specifically, it is preferable that the silver content per BET specific surface area of ​​the silver-coated copper powder be 3.5 mass% / (m² / g) or higher, more preferable that it be 6.5 mass% / (m² / g) or higher, and even more preferable that it be 9.5 mass% / (m² / g) or higher. Furthermore, it is preferable that the silver content per BET specific surface area of ​​the silver-coated copper powder be 38.0 mass% / (m² / g) or lower, more preferable that it be 30.0 mass% / (m² / g) or lower, and even more preferable that it be 22.0 mass% / (m² / g) or lower. By having a silver content of 3.5 mass% / (m² / g) or more per BET specific surface area, when silver-coated copper particles come into contact with each other, silver also comes into contact with each other, thereby imparting high conductivity to the conductive resin composition. By having a silver content of 38.0 mass% / (m² / g) or less per BET specific surface area, highly conductive silver-coated copper powder can be obtained economically.

[0030] The method for measuring the silver content per BET specific surface area is explained in the examples described below.

[0031] It is preferable that the silver-coated copper powder of the present invention contains a predetermined amount of silver. Specifically, it is preferable that the silver-coated copper powder contains 3.0 mass% or more of silver, more preferable that it contains 4.0 mass% or more, even more preferable that it contains 5.0 mass% or more, and even more preferable that it contains 8.5 mass% or more. In addition, it is preferable that the silver-coated copper powder contains 30.0 mass% or less of silver, more preferable that it contains 25.0 mass% or less, even more preferable that it contains 20.0 mass% or less, and even more preferable that it contains 12.5 mass% or less. By including 3.0 mass% or more of silver in the silver-coated copper powder, when silver-coated copper particles come into contact with each other, it becomes easier for silver particles to come into contact with each other, thereby imparting high conductivity to the conductive resin composition. By including 30.0 mass% or less of silver element in the silver-coated copper powder, a silver-coated copper powder with high conductivity can be obtained economically.

[0032] The method for measuring the silver content in silver-coated copper powder is explained in the examples described below.

[0033] In order to set the silver content per BET specific surface area to the above range or the silver content in silver-coated copper powder to the above range, it is suitable to control the silver ion concentration in the aqueous solution or adjust the reaction time of the displacement plating method and the reduction method in the manufacturing method described below.

[0034] In the silver-coated copper powder of the present invention, the core material particles preferably have high copper crystallinity as described above. To explain the crystallinity in detail, it is preferable that when the cross-section of the silver-coated copper particles is measured by electron backscatter diffraction (hereinafter also referred to as "EBSD"), the number of copper crystal grains per silver-coated copper particle is 1.0 or more. Furthermore, when the cross-section of the silver-coated copper particles is measured by EBSD, it is preferable that the number of copper crystal grains per silver-coated copper particle is 7.0 or less, more preferable that it is 6.8 or less, and even more preferable that it is 6.6 or less. By having the number of copper crystal grains per silver-coated copper particle within the above range, even higher conductivity can be imparted to the conductive resin composition. The number of copper crystal grains per silver-coated copper particle is preferably as close to 1.0, but even if it is 2.0 or more, or 3.0 or more, the desired effect is sufficiently achieved.

[0035] Silver-coated copper powder having such a number of copper crystal grains is suitably produced by the manufacturing method described below.

[0036] A method for measuring the number of copper crystal grains per silver-coated copper particle is explained in the following examples.

[0037] In order to obtain a conductive resin composition with high conductivity and improved coating properties using the silver-coated copper powder of the present invention, it is preferable that the BET specific surface area of ​​the silver-coated copper powder be within a predetermined range. Specifically, it is preferable that the BET specific surface area of ​​the silver-coated copper powder be 0.40 m² / g or more, more preferable that it be 0.45 m² / g or more, and even more preferable that it be 0.50 m² / g or more. Furthermore, for the same reason, it is preferable that the BET specific surface area of ​​the silver-coated copper powder be 1.20 m² / g or less, more preferable that it be 1.10 m² / g or less, and even more preferable that it be 1.00 m² / g or less.

[0038] The silver-coated copper powder of the present invention has a volume cumulative particle size D at 50% volume cumulative volume measured by the laser diffraction scattering particle size distribution method. 50 (Hereafter simply, "Particle Size D 50 It is also desirable that [this is also referred to as ]) be within a predetermined range. As a result, since the fluidity of the silver-coated copper powder is improved, when a conductive resin composition is prepared by adding the silver-coated copper powder to a thermosetting resin and an organic solvent, the silver-coated copper powder becomes more easily spread throughout the entire conductive resin composition. Consequently, the conductivity of the cured body obtained by curing can be increased without performing a press operation during the curing of the resin. To further highlight this advantage, the silver-coated copper powder has a particle size D 50 It is preferable that the particle size be 1.0 μm or larger, more preferable that it be 2.0 μm or larger, and even more preferable that it be 3.0 μm or larger. In the same regard, silver-coated copper powder has a particle size D 50 It is preferable that this be 10.0㎛ or less, more preferable that it be 8.0㎛ or less, and even more preferable that it be 6.0㎛ or less.

[0039] Particle size D 50 The method for calculating is explained in the embodiments described below.

[0040] Particle size D of silver-coated copper powder 50 In order to keep it within the above range, it is suitable to adjust the degree of grinding of the dendrite-shaped copper particles in the manufacturing method described below, or to control the shape of the dendrite-shaped copper particles before grinding.

[0041] In the silver-coated copper powder of the present invention, the number of copper crystal grains per one of the aforementioned silver-coated copper particles, the BET specific surface area, and the particle size D 50It is desirable for this to exist in a predetermined relationship. By doing so, it is possible to impart even higher conductivity to the conductive resin composition, and furthermore, the coating properties of the conductive resin composition can be improved. Specifically, the number of copper crystal grains per silver-coated copper particle is set to N (pieces), the BET specific surface area is set to SSA (m² / g), and the particle size D 50 ul D 50 When set to (㎛), N / (SSA×D 50 It is preferable that the value defined as ) is 0.30 (pieces / {(㎡ / g)×(㎛)}) or higher, more preferable that it is 0.35 (pieces / {(㎡ / g)×(㎛)}) or higher, and even more preferable that it is 0.40 (pieces / {(㎡ / g)×(㎛)}) or higher. For the same reason, N / (SSA×D 50 It is preferable that the value defined as ) is 5.00 (pieces / {(㎡ / g)×(㎛)}) or less, more preferable that it is 4.00 (pieces / {(㎡ / g)×(㎛)}) or less, and even more preferable that it is 3.00 (pieces / {(㎡ / g)×(㎛)}) or less.

[0042] N / (SSA×D 50 The technical significance of the value defined as ) is as follows. In order to increase the conductivity of the conductive resin composition obtained using the silver-coated copper powder of the present invention and to improve its coating properties, it is preferable that SSA be within a predetermined range as described above. D 50 Regarding this as well, there exists a range of values ​​suitable for manufacturing a desired conductive resin composition. In this regard, SSA and D 50 It is desirable for the product of to be within a predetermined range from the perspective of increasing the conductivity of the conductive resin composition and improving its coating properties. Meanwhile, regarding N, it is also desirable for it to be within a predetermined range as described above from the perspective of increasing the conductivity of the conductive resin composition. In this regard, N is SSA and D 50The inventors believed that using the value divided by the product of as an index is advantageous for achieving a higher degree of compatibility between high conductivity and good coating properties.

[0043] It is preferable that the silver-coated copper powder of the present invention has a bulk density within a predetermined range. In other words, it is preferable that the silver-coated copper powder has few voids between the silver-coated copper particles constituting it, that is, has high packing efficiency. Accordingly, when the silver-coated copper powder is added to a thermosetting resin and an organic solvent to prepare a conductive resin composition, the thixotropic properties of the conductive resin composition can be made suitable and the coating properties of the conductive resin composition can be made good. To further highlight this advantage, it is preferable that the silver-coated copper powder has a tap density of 2.0 g / cm³ or more, more preferable that it is 2.2 g / cm³ or more, and even more preferable that it is 2.4 g / cm³ or more. In the same view, the silver-coated copper powder may have a tap density of 4.5 g / cm³ or less, 4.4 g / cm³ or less, or 4.3 g / cm³ or less. By having a tap density of 2.0 g / cm³ or higher, the excessive increase in thixotropic properties of the conductive resin composition before curing is suppressed, and the coating properties of the conductive resin composition are improved. Additionally, by having a tap density of 4.5 g / cm³ or lower, the decrease in thixotropic properties of the conductive resin composition before curing is suppressed, and the coating properties of the conductive resin composition are improved.

[0044] Silver-coated copper powder having such tap density is suitably produced by the manufacturing method described below.

[0045] In this specification, "tap density" refers to a value measured in accordance with JIS Z2512.

[0046] In the silver-coated copper powder of the present invention, it is preferable that the crystal grain size of copper in the silver-coated copper particles constituting the powder is within a predetermined range from the perspective of imparting high conductivity to a conductive resin composition. Specifically, it is preferable that the crystal grain size is 1.0 μm or larger, more preferable that it is 1.1 μm or larger, and even more preferable that it is 1.2 μm or larger. Furthermore, it is preferable that the crystal grain size of copper is 2.4 μm or smaller, more preferable that it is 2.3 μm or smaller, and even more preferable that it is 2.2 μm or smaller.

[0047] The method for calculating the grain size of copper is explained in the following examples.

[0048] In the silver-coated copper powder of the present invention, the aforementioned particle size D 50 It is also desirable that the crystal grain size of copper and the conductive resin composition have a predetermined relationship. By doing so, even higher conductivity can be imparted to the conductive resin composition. Specifically, the particle size D 50 Regarding (㎛), it is preferable that the value (㎛) of the copper grain size is 0.20 or higher, more preferable that it is 0.22 or higher, and even more preferable that it is 0.24 or higher. For the same reason, the grain size D 50 Regarding (㎛), it is preferable that the value of the copper grain size (㎛) is 0.50 or less, more preferable that it is 0.48 or less, and even more preferable that it is 0.46 or less.

[0049] Next, a suitable method for manufacturing the silver-coated copper powder of the present invention will be described.

[0050] Core particles, which are one of the raw materials for silver-coated copper powder, are suitably manufactured by crushing copper particles having a dendrite shape produced by an electrolytic method (hereinafter, these copper particles are also referred to as "dendrite-shaped copper particles" for convenience). In the process of manufacturing dendrite-shaped copper particles by an electrolytic method, an electrolyte containing a copper source is used, and an anode and a cathode are immersed in said electrolyte, and electrolysis is performed by applying a DC voltage between the anodes. The dendrite-shaped copper particles reduced by electrolysis are deposited on the cathode.

[0051] The cathode only needs to be composed of a conductive material that does not affect electrolysis. It is preferable that the cathode be composed of, for example, stainless steel or titanium. As for stainless steel, austenitic stainless steel is preferred, and SUS304L and SUS316 are particularly preferred.

[0052] On the other hand, it is desirable for the anode to be insoluble in electrolysis. The reason for this is as follows. For example, if copper is used as the anode, copper leaches into the electrolyte during electrolysis. The amount of copper deposited in the cathode is less than the amount of copper leached from the anode, due to the accompanying gas generation. As a result, the concentration of copper in the electrolyte increases over time, hindering the formation of dendrite-shaped copper particles. This problem becomes more pronounced as the electrolysis time increases.

[0053] As an insoluble anode, for example, DSE (registered trademark) (denora permelexase) can be used.

[0054] Water-soluble copper compounds are suitably used as copper sources. For example, copper salts are compounds formed in a manner where cations and anions neutralize charges. Examples of such copper salts include copper sulfate, copper chloride, copper acetate, copper carbonate, and copper nitrate. These copper compounds may be used individually or in combination of two or more. Among these copper salts, it is preferable to use copper sulfate.

[0055] In order to deposit dendrite-shaped copper particles having a dendrite shape by electrolysis, it is desirable to set the current density during electrolysis to a relatively high level. Specifically, it is desirable to set the current density during electrolysis to 300 A / m² or higher, more desirable to set it to 400 A / m² or higher, and even more desirable to set it to 500 A / m² or higher. For the same reason, it is desirable to set the current density during electrolysis to 2000 A / m² or lower, more desirable to set it to 1800 A / m² or lower, and even more desirable to set it to 1600 A / m² or lower.

[0056] In order to precipitate dendrite-shaped copper particles having a dendrite shape by electrolysis, in addition to making the current density during electrolysis relatively high, it is also desirable to make the concentration of copper ions in the electrolyte relatively low. Specifically, it is desirable to set the concentration of copper ions in the electrolyte to 0.02 mol / L or higher, more desirable to set it to 0.03 mol / L or higher, and even more desirable to set it to 0.04 mol / L or higher. For the same reason, it is desirable to set the concentration of copper ions in the electrolyte to 0.25 mol / L or lower, more desirable to set it to 0.20 mol / L or lower, even more desirable to set it to 0.18 mol / L or lower, and even more desirable to set it to 0.16 mol / L or lower.

[0057] It is desirable to set the pH of the electrolyte during electrolysis to a strongly acidic or weakly acidic range from the perspective of smoothly precipitating dendrite-shaped copper particles by electrolysis. Specifically, from the perspective of suppressing the generation of hydrogen gas rather than reducing copper ions and making it easier to obtain dendrite-shaped copper particles, it is desirable to maintain the pH of the electrolyte at -0.3 or higher during electrolysis, more desirable to maintain it at -0.2 or higher, and even more desirable to maintain it at -0.1 or higher. In the same regard, it is desirable to maintain the pH of the electrolyte at 3.0 or lower during electrolysis, more desirable to maintain it at 2.8 or lower, and even more desirable to maintain it at 2.6 or lower. For pH adjustment, inorganic acids such as sulfuric acid, for example, may be used. In addition, the supporting salt described below may also be used for pH adjustment.

[0058] For example, when sulfuric acid is used to adjust the pH, the concentration of sulfuric acid in the electrolyte is preferably set to 0.1 mol / L or higher, more preferably set to 0.2 mol / L or higher, and even more preferably set to 0.3 mol / L or higher from the perspective of providing sufficient conductivity to the electrolyte. In the same regard, the concentration of sulfuric acid in the electrolyte is preferably set to 2.0 mol / L or lower, more preferably set to 1.8 mol / L or lower, and even more preferably set to 1.6 mol / L or lower.

[0059] It is desirable to add a supporting salt to the electrolyte in order to smoothly obtain dendrite-shaped copper particles. Examples of supporting salts include neutral chlorides such as sodium chloride, potassium chloride, lithium chloride, rubigium chloride, and cesium chloride; alkali metal salts of perchloric acid such as lithium perchlorate and sodium perchlorate; ammonium salts such as ammonium chloride; and alkali metal salts of sulfuric acid such as sodium sulfate and potassium sulfate.

[0060] During electrolysis, it is desirable to heat the electrolyte and maintain it at a predetermined temperature, in order to promote the reduction of copper ions and smoothly obtain dendrite-shaped copper particles. In this regard, it is desirable to maintain the temperature of the electrolyte during electrolysis at 20°C or higher, more desirable to maintain it at 22°C or higher, and even more desirable to maintain it at 24°C or higher. In the same regard, it is desirable to maintain the temperature of the electrolyte during electrolysis at 60°C or lower, more desirable to maintain it at 55°C or lower, and even more desirable to maintain it at 50°C or lower.

[0061] By performing electrolysis for a predetermined time under the above conditions, dendrite-shaped copper particles are deposited on the cathode. The deposited dendrite-shaped copper particles are recovered by scraping them off from the cathode.

[0062] In the present manufacturing method, particle size D 50 It is desirable to obtain dendrite-shaped copper particles with a diameter of 5.0 μm or more, more preferably 5.5 μm or more, and even more preferably 6.0 μm or more. In addition, particle size D 50 It is desirable to obtain dendrite-shaped copper particles with a diameter of 25.0 μm or less, more preferably 23.0 μm or less, and even more preferably 21.0 μm or less. Particle diameter D of dendrite-shaped copper particles 50 By being within the above range, highly crystalline core material particles can be easily obtained by using the corresponding dendrite-shaped copper particles and performing the grinding operation described below. Such particle size D 50 Dendritic copper particles having the above can be obtained by setting the current density during electrolysis to the above range or by setting the concentration of copper ions in the electrolyte to the above range.

[0063] When dendrite-shaped copper particles are obtained, they are then crushed. By doing so, core material particles are obtained. In the obtained core material particles, the crystallinity of copper is improved. The inventors have found that the crystallinity of the obtained core material particles changes significantly depending on the conditions under which the dendrite-shaped copper particles are crushed, and based on such findings, they have discovered that copper particles with high crystallinity can be obtained by crushing the dendrite-shaped copper particles under predetermined conditions.

[0064] For grinding dendrite-shaped copper particles, either a dry method or a wet method may be employed as long as the desired silver-coated copper powder is obtained. Regardless of which method is employed, as shown in FIG. 1 (a) and FIG. 1 (b), it is preferable to employ a grinding method that cuts the dendrite-shaped copper particles (1) having a main shaft (2) and a branch portion (3) branching from the main shaft (2), and also minimizes deformation of the core material particles (4) generated by the cutting, in order to easily obtain silver-coated copper powder having the desired shape.

[0065] As such a grinding method, it is advantageous to use a dry method that does not use grinding media. As an example of such a grinding method, a method of grinding dendrite-shaped copper particles dryly using a rotating cutting blade (e.g., a stirring blade) can be cited. According to this grinding method, the dendrite-shaped copper particles (1) shown in FIG. 1 (a) are cut by the rotating cutting blade to become the core material particles (4) shown in FIG. 1 (b). In this case, by appropriately controlling the rotational speed of the cutting blade, the application of excessive external force to the core material particles (4) is suppressed, thereby minimizing deformation occurring in the core material particles (4). To grind dendrite-shaped copper particles using a rotating cutting blade, for example, a grinder of the stirring blade type can be used, but it is not limited to this.

[0066] Alternatively, as an example of the aforementioned grinding method, a method of dry grinding dendrite-shaped copper particles by means of a swirling jet stream may be cited. According to this grinding method, the dendrite-shaped copper particles (1) shown in FIG. 1 (a) collide with each other by means of the jet stream and are cut to become core material particles (4) shown in FIG. 1 (b). In this case, a plurality of grinding nozzles are arranged at positions that divide the inner circumference of the grinder evenly, and one or more grinding nozzles are used as nozzles to supply dendrite-shaped copper particles (1), thereby creating a jet stream that swirls concentrically within the grinder. By controlling the swirling jet stream, the probability of the dendrite-shaped copper particles (1) colliding with the inner wall of the grinder is reduced, and the dendrite-shaped copper particles (1) can be efficiently made to collide with each other. As a result, excessive external force is suppressed from being applied to the core material particles (4), and deformation occurring in the core material particles (4) is suppressed to the maximum extent. In order to crush dendrite-shaped copper particles by a jet stream, for example, a jet stream type crusher may be used, but it is not limited to this.

[0067] The grinding method can be appropriately selected according to the application of the silver-coated copper powder. For example, when obtaining silver-coated copper powder with a relatively high tap density, that is, silver-coated copper powder with a relatively high BET specific surface area, it is preferable to use a dry grinding method by means of a swirling jet stream. Alternatively, for example, when obtaining silver-coated copper powder with a relatively low tap density, that is, silver-coated copper powder with a relatively low BET specific surface area, it is preferable to use a dry grinding method by means of a rotating cutting blade to grind dendrite-shaped copper particles.

[0068] Various conditions such as the number, shape, size, and rotational speed of the cutting blades when dry-grinding dendrite-shaped copper particles by a rotating cutting blade, and various conditions such as the grinding pressure and processing speed when dry-grinding dendrite-shaped copper particles by a jet stream, are such that they cut the dendrite-shaped copper particles (1) as described above and minimize deformation of the core material particles (4) generated by the cutting.

[0069] Regardless of which method is adopted, the particle size D of the core material particles after grinding 50 It is desirable to grind the dendrite-shaped copper particles so that the range is 1.0㎛ or more and 10.0㎛ or less, from the perspective of obtaining core material particles with high crystallinity. In addition, it is also desirable to grind the dendrite-shaped copper particles so that the average L value of the core material particles after grinding is 2.5㎛ or more and 8.0㎛ or less, and the average W value is 0.3㎛ or more and 4.1㎛ or less.

[0070] Once core material particles are obtained, surface treatment may be performed on the core material particles as needed. In the present embodiment, for example, a treatment may be performed to attach a nitrogen-containing surface treatment agent, such as benzotriazole, to the surface of the core material particles. By doing so, the conductivity of the conductive resin composition can be increased even if the silver content in the silver-coated copper powder is relatively low.

[0071] Next, a silver coating layer is formed on at least a portion of the surface of the core material particles. As a method of application, a displacement plating method utilizing a substitution reaction between copper and silver due to differences in ionization tendencies, or a reduction method using a reducing agent, may be used. When forming a silver coating layer on the surface of the core material particles, both the displacement plating method and the reduction method may be used, or either one may be used. When both the displacement plating method and the reduction method are used, the displacement plating method and the reduction method may be used in this order or in the reverse order. In particular, using the displacement plating method is preferable because it allows for a relatively uniform coating of the silver coating layer on the surface of the core material particles and also prevents the silver particles forming the silver coating layer from aggregating.

[0072] In either the displacement plating method or the reduction method, a chelating agent may be used in the dispersion to form a relatively uniform silver coating layer. As for the chelating agent, it is desirable to use a chelating agent with a high degree of attachment constant with respect to copper ions, etc., so that copper ions, etc., which are byproducts of the substitution reaction between copper and silver ions, are not reprecipitated. In particular, since the core material particles that serve as the core of the silver-coated copper powder have copper as their main component, it is desirable to select the chelating agent while paying attention to the degree of attachment constant with copper. Specifically, as the chelating agent, a chelating agent selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid, diethylenetriamine, triethylenediamine, and salts thereof may be used.

[0073] First, the case of using the displacement plating method will be explained. In the case of the displacement plating method, an aqueous solution containing silver ions and core material particles are prepared and mixed. By doing so, the copper and silver of the core material particles in the aqueous solution undergo a displacement reaction, and silver is precipitated on the surface of the core material particles, thereby forming a silver coating layer, and silver-coated copper powder can be obtained.

[0074] As a silver ion source, commonly used silver salts can be used. Specifically, silver salts such as silver nitrate, silver oxide, silver sulfate, silver acetate, and silver carbonate can be used, but are not limited to these.

[0075] In the case of a displacement plating method, it is desirable that the concentration of an aqueous solution containing silver ions be within a predetermined range in order to smoothly form a silver coating layer on the surface of the core material particles. Specifically, it is desirable to set the concentration of silver ions in the aqueous solution to 0.010 mol / L or higher, and more desirable to set it to 0.040 mol / L or higher. In the same regard, it is desirable to set the concentration of silver ions in the aqueous solution to 10.0 mol / L or lower, and more desirable to set it to 2.0 mol / L or lower.

[0076] In the case of the displacement plating method, from the perspective of smoothly forming a silver coating layer on the surface of the core material particles, it is desirable that the pH of the aqueous solution containing silver ions be within a predetermined range. Specifically, the pH of the aqueous solution is preferably 4.0 or higher, more preferably 4.5 or higher, and even more preferably 5.0 or higher. In the same regard, the pH of the aqueous solution is preferably 12.0 or lower, more preferably 11.5 or lower, and even more preferably 11.0 or lower. The pH of the aqueous solution can be adjusted by adding a basic substance, for example, sodium hydroxide. The pH of the aqueous solution is the value at the temperature at which the said aqueous solution and the core material particles are mixed.

[0077] In addition, if the silver coating layer is placed while the core material particles are in contact with each other, it is undesirable because multiple silver-coated copper particles form a mass bonded with silver interposed. Therefore, in order to prevent sedimentation until the formation of the silver coating layer by the silver displacement plating reaction is completed, it is preferable to perform the process while stirring the core material particles with an aqueous solution containing silver ions. While it is common to use stirring blades, known methods may also be applied.

[0078] In the case of displacement plating, the reaction time varies depending on the temperature, but for example, it is between 10 minutes and 120 minutes.

[0079] Next, the case of using the reduction method is described. In the case of the reduction method, an aqueous solution containing silver ions, core material particles, and a silver reducing agent are prepared and mixed. By doing so, silver in the aqueous solution is reduced, and silver-coated copper powder is obtained in which a silver coating layer is formed on at least a portion of the surface of the core material particles.

[0080] Examples of reducing agents for silver include lithium aluminum hydride, sodium amalgam, sulfates, sulfites, hydrazine, zinc amalgam, diisobutylaluminum hydride, sodium borohydride, and oxalic acid.

[0081] As a silver ion source, the same as that described in the displacement plating method can be used.

[0082] In the case of the reduction method, from the perspective of smoothly forming a silver coating layer on the surface of the core material particles, it is desirable that the concentration of the aqueous solution containing silver ions be within a predetermined range. Specifically, it is desirable to set the concentration of silver ions in the aqueous solution to 0.01 mol / L or higher, and more desirable to set it to 0.04 mol / L or higher. In the same regard, it is desirable to set the concentration of silver ions in the aqueous solution to 10 mol / L or lower, and more desirable to set it to 2.0 mol / L or lower.

[0083] In the case of the reduction method, from the perspective of smoothly forming a silver coating layer on the surface of the core material particles, it is desirable that the pH of the aqueous solution containing silver ions be within a predetermined range. Specifically, the pH of the aqueous solution is preferably 6.0 or higher, more preferably 6.5 or higher, and even more preferably 7.0 or higher. In the same regard, the pH of the aqueous solution is preferably 12.0 or lower, more preferably 11.7 or lower, and even more preferably 11.5 or lower. The pH of the aqueous solution can be adjusted by adding a basic substance, for example, sodium hydroxide. The pH of the aqueous solution is the value at the temperature at which the aqueous solution and the core material particles are mixed.

[0084] Similar to the displacement plating method, in the reduction method as well, if a silver coating layer is placed while the core material particles are in contact with each other, it is undesirable because multiple silver-coated copper particles form a lump bonded with silver interposed therein. Therefore, in order to prevent sedimentation until the formation of the silver coating layer by the silver reduction reaction is completed, it is preferable to perform the process while stirring an aqueous solution containing silver ions, core material particles, and a silver reducing agent. While it is common to use a stirring blade, known methods may also be applied.

[0085] In the case of the reduction method, the reaction time varies depending on the temperature, but for example, it is between 5 minutes and 60 minutes.

[0086] Next, in either the displacement plating method or the reduction method, silver-coated copper particles are separated and removed from the aqueous solution by solid-liquid separation methods such as vacuum dehydration, filter press, centrifugation, and ultrafiltration, and then washed with a solvent, etc.

[0087] After cleaning, surface treatment may be performed as necessary for the convenience of handling the powder. There are no particular restrictions on the surface treatment agent, and it can be appropriately selected according to the purpose; examples include fatty acids, fatty acid salts, surfactants, organometallic compounds, chelating agents, polymer dispersants, etc.

[0088] After washing, silver-coated copper particles can be separated into solid and liquid phases and dried to produce silver-coated copper powder.

[0089] The silver-coated copper powder of the present invention obtained in this manner is suitable for use in applications where it is mixed with a non-conductive material to impart conductivity to the said non-conductive material. For example, a conductive resin composition can be obtained by kneading the silver-coated copper powder of the present invention with a thermosetting resin. By curing this conductive resin composition, for example, a conductive film or a conductive sheet can be obtained. The cured body possesses high conductivity even without press operation during curing. Examples of such thermosetting resins include phenolic resin, epoxy resin, polyurethane resin, melamine resin, unsaturated polyester resin, urea resin, and acrylic resin. One type of these thermosetting resin may be used alone or two or more types may be used. These thermosetting resins can be appropriately selected according to the specific application of the cured body.

[0090] In addition, the conductive resin composition may include, in addition to the silver-coated copper powder and thermosetting resin of the present invention, a curing agent of the thermosetting resin and an organic solvent, etc.

[0091] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments.

[0092] With respect to the above embodiments, silver-coated copper powder, a conductive resin composition containing the same, and a method for manufacturing the same are also disclosed below.

[0093] [1] Silver-coated copper powder comprising a copper core particle and an aggregate of silver-coated copper particles having a silver coating layer disposed on at least a portion of the surface of the core particle, and

[0094] When the cross-section of the silver-coated copper particle is measured by electron backscattering diffraction, let N be the number of copper crystal grains per silver-coated copper particle, let SSA be the BET specific surface area, and let D be the volumetric cumulative particle diameter at 50% of the cumulative volume determined by the laser diffraction scattering particle size distribution method. 50 When set to (㎛), N / (SSA×D 50 Silver-coated copper powder having a value defined as ) of 0.3 (pieces / {(㎡ / g)×(㎛)}) or more and 5.0 (pieces / {(㎡ / g)×(㎛)}) or less.

[0095] [2] Silver-coated copper powder described in [1], wherein the number of copper crystal grains per silver-coated copper particle is 1.0 or more and 7.0 or less.

[0096] [3] Silver-coated copper powder as described in [1] or [2], having a tap density of 2.0 g / cm³ or more and 4.5 g / cm³ or less.

[0097] [4] Volume cumulative particle size D at 50% volume cumulative volume by laser diffraction scattering particle size distribution measurement method 50 Silver-coated copper powder described in any one of [1] to [3], wherein the value of the copper crystal grain size (㎛) relative to (㎛) is 0.20 or more and 0.50 or less.

[0098] [5] Silver-coated copper powder as described in any one of [1] to [4], having a BET specific surface area of ​​0.40 m² / g or more and 1.20 m² / g or less.

[0099] [6] Silver-coated copper powder as described in any one of [1] to [5], having a copper crystal grain size of 1.0㎛ or more and 2.4㎛ or less.

[0100] [7] A conductive resin composition comprising a thermosetting resin and silver-coated copper powder as described in any one of [1] to [6].

[0101] [8] A process of using an electrolyte containing a copper source and precipitating dendrite-shaped copper particles on the cathode by electrolytic reduction, and

[0102] A process of crushing the above copper particles to obtain core material particles, and

[0103] A method for manufacturing silver-coated copper powder, comprising the process of mixing the core material particles with an aqueous solution containing silver ions to reduce the silver ions and forming a silver coating layer on at least a portion of the surface of the core material particles.

[0104] [9] A manufacturing method described in [8], wherein silver is deposited on the surface of the core material particles by displacement plating to form the silver coating layer.

[0105] Examples

[0106] The present invention will be explained in more detail below by way of examples. However, the scope of the present invention is not limited to these examples. Unless specifically stated otherwise, “%” means “mass%”.

[0107] [Example 1]

[0108] (1) Preparation of dendrite-shaped copper particles

[0109] In an electrolytic cell measuring 2.5m × 1.1m × 1.5m (approx. 4㎥), nine SUS cathodes and insoluble anodes (DSE (manufactured by Denora Permelexa), each measuring 1.0m × 1.0m), were suspended with a distance of 5cm between electrodes. A copper sulfate solution was circulated as the electrolyte at a rate of 30L / min, and the anodes and cathodes were immersed in this electrolyte. Electrolysis was performed by passing a direct current through the solution, causing dendrite-shaped copper particles to precipitate on the surface of the cathode. The precipitated dendrite-shaped copper particles were scraped off and recovered. Particle size D of the dendrite-shaped copper particles50 It was 6.2㎛.

[0110] At this time, the copper concentration of the circulating electrolyte was set to 10 g / L, the sulfuric acid (H2SO4) concentration to 100 g / L, and the chlorine concentration to 5 mg / L. Additionally, the current density was adjusted to 800 A / m², and electrolysis was performed for 30 minutes while maintaining the electrolyte temperature at 30°C. The pH of the aqueous solution was 1.

[0111] During electrolysis, the copper ion concentration of the electrolyte between the electrodes was always kept lower than the copper ion concentration of the electrolyte at the bottom of the electrolytic cell.

[0112] (2) Grinding of dendrite-shaped copper particles

[0113] Dendrite-shaped copper particles were dry-ground for 10 minutes using a stirred-blade type grinder to obtain core material particles. Particle size D of the core material particles 50 It was 3.5㎛.

[0114] (3) is the formation of a coat layer

[0115] 25 kg of the obtained core material particles were added to 25 L of pure water maintained at 50°C and stirred thoroughly. Separately, 2.3 kg of silver nitrate was added to 2.5 L of pure water to prepare a silver nitrate solution. These solutions were mixed and reacted for 1 hour to obtain a slurry of silver-coated copper powder by the displacement plating method. The pH of the slurry was 7.5.

[0116] Next, the slurry of silver-coated copper powder was filtered by vacuum filtration. After filtration, the powder was washed using a solution of 600g of EDTA-2Na (ethylenediamine tetraacetic acid 2Na salt) dissolved in 6L of pure water, and the residual EDTA was subsequently washed with 3L of pure water. Afterward, the powder was dried at 90°C for 3 hours to obtain the desired silver-coated copper powder.

[0117] [Example 2]

[0118] In Example 1, dendrite-shaped copper particles were obtained by changing the copper concentration of the electrolyte to 11 g / L, the chlorine concentration to 10 mg / L, and the current density to 600 A / m². Additionally, when grinding the dendrite-shaped copper particles, a jet stream type grinder was used instead of a stirring blade type grinder. Except for this, the desired silver-coated copper powder was obtained in the same manner as in Example 1.

[0119] [Example 3]

[0120] In Example 2, dendrite-shaped copper particles were obtained by changing the copper concentration of the electrolyte to 12 g / L, the chlorine concentration to 9 mg / L, and the current density to 580 A / m². Except for this, the desired silver-coated copper powder was obtained in the same manner as in Example 2.

[0121] [Example 4]

[0122] In Example 2, the copper concentration of the electrolyte was changed to 13 g / L, the chlorine concentration to 8 mg / L, and the current density to 570 A / m² to obtain dendrite-shaped copper particles. Except for this, the silver-coated copper powder of the desired product was obtained in the same manner as in Example 2.

[0123] [Comparative Example 1]

[0124] In Example 2, the obtained dendrite-shaped copper particles were not ground, and a silver coating layer was formed on the surface of the dendrite-shaped copper particles by a displacement plating method to obtain the desired silver-coated copper powder.

[0125] [Comparative Example 2]

[0126] In Example 1, the obtained dendrite-shaped copper particles were not ground, and a silver coating layer was formed on the surface of the dendrite-shaped copper particles by a displacement plating method to obtain the desired silver-coated copper powder.

[0127] [Comparative Example 3]

[0128] Spherical copper particles with a copper content of 99% were obtained by the water atomization method. Copper powder consisting of copper particles was classified using a classification facility to obtain spherical copper particles. Particle size D of the spherical copper particles 50 The silver was 5.1 μm. In addition, without grinding the obtained spherical copper particles, a silver coating layer was formed on the surface of the spherical copper particles by a displacement plating method, and the desired silver-coated copper powder was obtained.

[0129] [Comparative Example 4]

[0130] The spherical copper particles obtained in Comparative Example 3 were classified under conditions different from those of the said Comparative Example, and spherical copper particles were obtained. Particle size D of the spherical copper particles 50 The silver was 2.1 μm. In addition, without grinding the obtained spherical copper particles, a silver coating layer was formed on the surface of the spherical copper particles by a displacement plating method, and the desired silver-coated copper powder was obtained.

[0131] 〔evaluation〕

[0132] In the silver-coated copper powder obtained in the examples and comparative examples, the tap density was calculated according to the method described below.

[0133] In the silver-coated copper powder obtained in the examples and comparative examples, according to the method described below, the number of copper crystal grains per silver-coated copper particle, the copper crystal grain size, the BET specific surface area, and the particle size D 50 The silver content per BET specific surface area and the silver content in silver-coated copper powder were calculated.

[0134] In the silver-coated copper powder obtained in the examples and comparative examples, the resistivity of the conductive resin composition was measured according to the method described below.

[0135] Their results are shown in Table 1.

[0136] [Tap Density]

[0137] Tap density was measured using a tapping machine (model: KRS-406, manufactured by Kuramochi Kagaku Kikai Seisakusho Co., Ltd.). Specifically, 120 g of silver-coated copper powder was placed in a graduated cylinder with a capacity of 150 cm³. The tap stroke was set to 4 cm and the number of taps was set to 400 to measure.

[0138] [Number of copper grains per silver-coated copper particle]

[0139] The number of copper grains per silver-coated copper grain was measured by the following method. For the measurement, a scanning electron microscope (SUPRA 55VP, Carl Zeiss Co., Ltd.) equipped with an EBSD evaluation device (OIM Data Collection Ver. 7.2.0, manufactured by TSL Solutions Co., Ltd.) and an attached EBSD analysis device were used.

[0140] First, silver-coated copper powder was embedded in a room-temperature curing epoxy resin to obtain a resin block. The resin block was cut with a single-edged razor blade, and a carbon coating was applied to the obtained cut surface. Subsequently, a sample was prepared by using a cross-section polisher (IB-19510CP or IB-19520CCP, both manufactured by Nippon Denshi Co., Ltd.) to precisely smooth the cross-section of the resin block. Based on the EBSD method, the number of copper crystal grains was measured for the cross-section (the surface where the core material of the silver-coated copper particle is exposed) of each silver-coated copper particle in the sample. From the image of the cross-section of the particle, 10 silver-coated copper particles with a longest transverse length of 1 μm or more were randomly selected, and measurements were taken on the silver-coated copper particles to obtain the average value of the copper crystal grains. This average value was taken as the number of copper crystal grains per silver-coated copper particle.

[0141] When measuring the number of grains, the WD value was set to 15±1 mm, and with "Background Subtraction," "Normalize Intensity Histgram," and "Dynamic Background Subtraction" checked in "Image Processing," "Cu" was selected in "Phase" within "Capture Pattern" of the EBSD evaluation device at the observation site, and the WD value was adjusted under conditions where the "Fit" value of "Solutions" was within 1.5 and the "CI" value was higher than 0.1.

[0142] [Copper Grain Size]

[0143] The grain size of copper was measured by the following method. For the measurement, data from the sample cross-section obtained from the measurement of the number of copper grains per silver-coated copper particle described above was used.

[0144] Specifically, for the examples and comparative examples, a photograph of a sample cross-section taken from "Capture SEM" in "Scan" was measured in "Start Scan". Using this measurement data, the grain size (average area) was calculated by selecting "All data" from the "Grain Size Quick Chart" in the analysis menu of the EBSD analysis program (OIM Analysis Ver. 7.3.1, manufactured by TSL Solutions, Inc.). This grain size (average) was taken as the average grain size in the silver-coated copper powder of the present invention.

[0145] In measuring the grain size of copper, an orientation difference of 5° or greater was considered a grain boundary. However, since the crystal structure of copper is face-centered, twin grain boundaries were taken into account; the orientation difference at any grain boundary was expressed in terms of a rotation axis and a rotation angle, and the rotation axis <111> It is indicated as such, and in the case where the rotation angle is 60±1°, and the rotation axis is <110> It was indicated as such, and when the rotation angle was 38.94±1°, it was not considered a grain boundary. The conditions of the scanning electron microscope during observation were set as follows: acceleration voltage: 15 kV, aperture diameter: 60 µm, High Current mode, and sample angle: 70°. The observation magnification, measurement area, and step size may be appropriately changed depending on the size of the grain.

[0146] <Filter Processing>

[0147] In addition, when the cross-section of silver-coated copper powder is measured by EBSD using the sample adjusted as described above, not only the copper grains but also the silver grains are detected. Therefore, by performing filter treatment under the following conditions, only the copper grains can be observed.

[0148] Specifically, before measuring the grain size, filter processing was performed using (1) "CI", (2) "Minimum Grain Size", (3) "IQ" and (4) "Grain Aspect ratio" from the "Formula" of the analysis menu of the EBSD analysis program, and then the grain boundaries of copper were detected.

[0149] The conditions for filter treatment in each sample of the examples and comparative examples (conditions of (1) to (4) above) are shown in Table 2 below. Specifically, (1) "CI" was set to "0.05" and target particles were identified in the EBSD image and SEM image during treatment (1). At this time, for samples in which silver crystal grains were still observed in the EBSD image and SEM image, "CI" was kept at "0.05". On the other hand, for samples in which silver crystal grains were not observed (i.e., samples in which filter treatment was performed excessively), "CI" was changed to "0.03". In addition, during treatment (2), the contrast in the SEM image along with the EBSD image was checked, and treatment was performed with a value of "5" for the purpose of removing only crystal grains other than copper. In addition to this, after treatment (1) and treatment (2), if crystal grains other than copper are present, the contrast of the SEM image is checked together with the EBSD image, and (3) "IQ" is ">4.0×10 6 」 to 「>5.0×10 6 The range was set to ”. Additionally, after treatment (1), treatment (2) and treatment (3), if there were grains other than copper, the contrast of the SEM image along with the EBSD image was checked, and (4) the “Grain Aspect ratio” was set to “0.6” and treatment was performed.

[0150] In addition, “-” in Table 2 indicates that the copper crystal grains could be sufficiently observed and subsequent filter treatment was not required, so the filter treatment was not performed.

[0151] [BET Specific Surface Area]

[0152] Measurements were taken using the BET 1-point method with a Monosorb manufactured by Yuasa Ionics Co., Ltd.

[0153] [Particle size D 50 〕

[0154] Using an automatic sample feeder for a laser diffraction particle size distribution measuring device ("Microtrac SDC" manufactured by Microtrac Bell Co., Ltd.), silver-coated copper powder was introduced into a solvent mixed with 0.1% hexametaphosphoric acid, and after irradiating with 40W ultrasound for 90 seconds at a flow rate of 40%, the particle size distribution was measured using the "MT3000II" laser diffraction particle size distribution measuring instrument manufactured by Microtrac Bell Co., Ltd., and from the obtained volume-based particle size distribution chart, the particle size D 50 Measured.

[0155] Particle size D 50 When measuring, the water-soluble solvent is passed through a 60㎛ filter, the "solvent refractive index" is set to 1.33, the particle permeability condition to "transmittance," the measurement range to 0.243㎛ or more and 704.0㎛ or less, the measurement time to 30 seconds, and the average value of two measurements is the particle size D 50 did as.

[0156] [Silver content in silver-coated copper powder]

[0157] 1 g of silver-coated copper powder obtained in the examples and comparative examples was completely dissolved in a 1:1 nitric acid solution. Then, the silver content (%) was calculated by titrating with sodium chloride.

[0158] [Silver content per BET specific surface area]

[0159] From the silver content measured by the above-described method and the BET specific surface area value measured by the above-described method, the silver content per BET specific surface area was calculated.

[0160] [Resistivity of conductive resin composition]

[0161] A conductive resin composition was prepared using the silver-coated copper powder obtained in the examples and comparative examples. Specifically, a conductive resin composition consisting of a paste was prepared by mixing silver-coated copper powder, an epoxy resin, 2-methylimidazole, and dimethylacetamide. Each composition was prepared such that the amount of silver-coated copper powder in the conductive resin composition was 90 mass%. The mass ratio of the epoxy resin, dimethylacetamide, and 2-methylimidazole in each conductive resin composition was set to 49:40:1.

[0162] Next, the paste was applied onto a glass plate. A bar coater with a width of 200 mm was used for the application. The gap was set to 100 μm. The formed film was cured by drying it in an atmospheric hot air dryer at 110°C for 60 minutes, and a conductive film with a thickness of 80 μm was obtained. The resistance value of the conductive film was measured using a resistivity meter (Mitsubishi Kagaku MCP-T600) by the four-probe method.

[0163]

[0164]

[0165] As is evident from the results shown in Table 1, the silver-coated copper powder obtained in the example has a lower resistivity of the conductive resin composition compared to the silver-coated copper powder obtained in the comparative example. Industrial applicability

[0166] According to the present invention, it is possible to provide a silver-coated copper powder and a method for manufacturing the same, which can obtain a conductive resin composition capable of increasing conductivity without performing press operations. In addition, according to the present invention, it is possible to provide a conductive resin composition capable of increasing conductivity without performing press operations.

Claims

Claim 1 A silver-coated copper powder comprising a copper core particle and an aggregate of silver-coated copper particles having a silver coating layer disposed on at least a portion of the surface of said core particle, wherein when the cross-section of said silver-coated copper particle is measured by electron backscattering diffraction, the number of copper crystal grains per said silver-coated copper particle is N (pieces), the BET specific surface area is SSA (m² / g), and the volume cumulative particle diameter at 50% of the cumulative volume measured by laser diffraction scattering particle size distribution is D 50 When set to (㎛), N / (SSA×D 50 Silver-coated copper powder having a value defined as ) of 0.3 (pieces / {(㎡ / g)×(㎛)}) or more and 5.0 (pieces / {(㎡ / g)×(㎛)}) or less. Claim 2 Silver-coated copper powder according to claim 1, wherein the number of copper crystal grains per silver-coated copper particle is 1.0 or more and 7.0 or less. Claim 3 Silver-coated copper powder according to claim 1 or 2, having a tap density of 2.0 g / cm³ or more and 4.5 g / cm³ or less. Claim 4 In claim 1 or 2, the volume cumulative particle size D at a cumulative volume of 50% by the laser diffraction scattering particle size distribution measurement method 50 Silver-coated copper powder having a copper grain size value (㎛) of 0.20 or more and 0.50 or less relative to (㎛). Claim 5 Silver-coated copper powder according to claim 1 or 2, having a BET specific surface area of ​​0.40 m² / g or more and 1.20 m² / g or less. Claim 6 Silver-coated copper powder according to claim 1 or 2, wherein the copper crystal grain size is 1.0㎛ or more and 2.4㎛ or less. Claim 7 A conductive resin composition comprising a thermosetting resin and silver-coated copper powder as described in claim 1 or 2. Claim 8 A method for manufacturing silver-coated copper powder, comprising: a process of using an electrolyte containing a copper source and precipitating dendrite-shaped copper particles on a cathode by electrolytic reduction; a process of crushing the copper particles to obtain core material particles; and a process of mixing the core material particles with an aqueous solution containing silver ions to reduce the silver ions and forming a silver coating layer on at least a portion of the surface of the core material particles. Claim 9 A manufacturing method according to claim 8, wherein silver is deposited on the surface of the core material particles by displacement plating to form the silver coating layer.

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