Silver-coated copper powder, electroconductive resin composition containing same, and method for producing same

Abstract

This silver-coated copper powder is composed of aggregates of silver-coated copper particles each comprising a copper core particle and a silver coat layer disposed on at least some of the surface of the core particle. When the number of copper crystal grains per the silver-coated copper particle determined by examining cross sections of the silver-coated copper particles by an electron beam backscatter diffraction method is expressed by N (grains), the BET specific surface area is expressed by SSA (m2 / g), and the volume-cumulative particle diameter at 50% volume-cumulation determined by a laser diffraction / scattering particle size distribution examination is expressed by D50 (μm), then a value defined by N / (SSA×D50) is 0.3 (grains / {(m2 / g)×(μm)}) to 5.0 (grains / {(m2 / g)×(μm)\}) inclusive.

Description

Silver-coated copper powder, conductive resin composition containing the same, and method for producing the same

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

[0002] Conductive pastes and conductive adhesives containing metal powders are used to achieve electrical conduction between conductors. Examples of metal powders include precious metals such as gold and silver, and base metals such as nickel and copper. Precious metals are suitable for conductive powders because they are resistant to oxidation and have high conductivity, but they are economically disadvantageous. Therefore, various attempts have been proposed to reduce the use of precious metals while increasing the electrical conductivity of conductive powders by thinly coating the surface of inexpensive metals such as nickel and copper with gold or silver.

[0003] For example, Patent Document 1 describes silver-coated copper particles in which the surfaces of copper powder particles are coated with a silver layer containing silver or a silver alloy and which have a dendritic structure. The document also describes that the dendritic structure of the silver-coated copper particles increases the number of contact points between the particles, thereby providing electrical conductivity.

[0004] US2018 / 0354033A1

[0005] When the silver-coated copper particles described in Patent Document 1 are used in a resin composition, in order to obtain excellent conductivity, a pressing operation is required to increase the number of contact points between the dendritic particles. Therefore, if a pressing operation cannot be performed, it is difficult to obtain sufficient conductivity for practical use. Therefore, an object of the present invention is to provide a silver-coated copper powder that can obtain a conductive resin composition that can increase conductivity without performing a pressing operation.

[0006] The present invention provides a silver-coated copper powder comprising an aggregate of silver-coated copper particles having a copper core particle and a silver coating layer disposed on at least a portion of the surface of the core particle, wherein when a cross section of the silver-coated copper particle is measured by electron backscatter diffraction, the number of copper crystal grains per silver-coated copper particle is N (pieces), and the BET specific surface area is SSA (m ２ / g), and the volume cumulative particle size at 50% cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method is D ５０ (μm), N / (SSA×D ５０ ) is 0.3 (pieces / {(m ２ / g)×(μm)}) or more 5.0(pieces / {(m ２ The above-mentioned problems have been solved by providing a silver-coated copper powder having a particle size of 1 / 2000 (μm) × (μm) or less.

[0007] The present invention also provides a method for producing silver-coated copper powder, which comprises the steps of: precipitating dendritic copper particles on a cathode by electrolytic reduction using an electrolyte containing a copper source; pulverizing the copper particles to obtain core particles; and mixing an aqueous solution containing silver ions with the core particles to reduce the silver ions and form a silver coating layer on at least a portion of the surface of the core particles.

[0008] FIG. 1(a) is a schematic diagram showing the copper powder that is the raw material for the silver-coated copper powder of the present invention, and FIG. 1(b) is a schematic diagram showing the process for producing the silver-coated copper powder of the present invention from the raw copper powder.

[0009] The present invention will be described below based on 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 the core particle. In this specification, "copper core particles" includes particles composed essentially of elemental copper and copper-based alloy particles. In the former case, the particles are composed essentially of elemental copper, with the remainder containing unavoidable elements. In this case, the silver-coated copper powder of the present invention preferably consists only of elemental silver and elemental copper, but trace amounts of unavoidable elements are acceptable. If the silver-coated copper powder contains unavoidable elements, the content is preferably 0.01% by mass or less, since this prevents the inherent properties of the silver-coated copper powder from being impaired. Examples of unavoidable elements include oxygen (O) and carbon (C) derived from oxygen and carbon dioxide in the atmosphere, and nitrogen (N), which may be mixed in during the production process of the silver-coated copper powder. The presence and content of unavoidable elements can be measured, for example, by ICP atomic emission spectroscopy. In the latter case, the content of elemental copper in the particles is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0010] The silver-coated copper powder of the present invention preferably has high crystallinity of copper as a core particle. The inventors have found that when a silver-coated copper powder with high copper crystallinity is added to a resin and an organic solvent to produce a conductive resin composition, it can impart high conductivity to the conductive resin composition. In particular, the number of copper crystal grains per silver-coated copper particle, the BET specific surface area, and the particle diameter D ５０ When the relationship between the above and the conductive resin composition is as described below, it is possible to impart higher conductivity to the conductive resin composition and also to impart appropriate thixotropy to the conductive resin composition, which is preferable. In order to increase the crystallinity of the silver-coated copper powder, it is preferable to produce core particles by, for example, the production method described below. In this specification, the term "conductive resin composition" refers to a composition containing a thermosetting resin before curing or a composition containing a thermosetting resin after curing, depending on the context.

[0011] First, the silver-coated copper powder of the present invention will be described. 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, flat, polygonal, spindle-shaped, or irregular. Among these, it is preferable that the shape of the core particles is particularly anisotropic. In other words, it is preferable that the shape of the core particles is non-spherical. Using anisotropic core particles is preferable because it can impart high conductivity to the conductive resin composition. From this perspective, it is preferable that the core particles have shapes such as irregular shapes, rods elongated in one direction, cigar shapes, and spheroids. Producing core particles using the manufacturing method described below can increase the crystallinity of the silver-coated copper powder, resulting in core particles with anisotropy. In this embodiment, since the thickness of the silver coating layer arranged on the surface of the core particles is small, the shape of the silver-coated copper particles is substantially the same as the shape of the core particles.

[0012] The degree of anisotropy of the core 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 the longest transverse length of the target particle and W is the length across the particle of the perpendicular bisector of the transverse length L. Specifically, the aspect ratio is calculated by first photographing two or more fields of view using a scanning electron microscope (hereinafter also referred to as "SEM") at a magnification sufficient to include 50 or more silver-coated copper particles to be measured. Next, 50 or more silver-coated copper particles whose outlines can be confirmed are randomly selected from each image data, and the L and W values ​​are measured for each of the selected silver-coated copper particles. The average L and W values ​​are calculated, and the L / W value is calculated from the average values. The value calculated in this manner is referred to as the aspect ratio in this specification. In the silver-coated copper powder, from the viewpoint of imparting high conductivity to the conductive resin composition, the aspect ratio measured by the above method is preferably 1.1 or more, more preferably 1.3 or more, and even more preferably 1.5 or more. From the same viewpoint, the aspect ratio measured by the above method is preferably 4.5 or less, more preferably 4.3 or less, and even more preferably 4.1 or less.

[0013] In the 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-mentioned range. Furthermore, 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-mentioned range. 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-mentioned range. Furthermore, 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-mentioned range.

[0014] In order to set the aspect ratio and the average values ​​of L and W in the silver-coated copper powder within the above ranges, it is preferable to produce the silver-coated copper powder by, for example, the production method described below.

[0015] The silver coating layer of this embodiment is composed of an aggregate of minute silver particles. From the viewpoint of imparting high conductivity to the conductive resin composition, it is preferable that the silver coating layer having the above structure is disposed on at least a portion of the surface of the core particle. The boundary between the core particle and the silver coating layer may be clear, or there may be an unclear portion within the range where the core particle and the silver coating layer can be distinguished.

[0016] The method for disposing the silver coating layer on the surface of the core particle is not particularly limited. From the viewpoint of successfully disposing the silver coating layer on the surface of the core particle, it is preferable to use the displacement plating method described below or the use of a reducing agent.

[0017] The silver coating layer may be present so as to cover at least a portion of the surface of the core particle. Therefore, the silver coating layer may be disposed on the entire surface of the core particle, or may be disposed on only a portion of the surface of the core particle. The amount of the silver coating layer disposed can be evaluated by the silver content per BET specific surface area of ​​the silver-coated copper powder. Specifically, the silver-coated copper powder has a silver content per BET specific surface area of ​​3.5 mass% / (m ２ / g) or more, and 6.5 mass% / (m ２ / g) or more, and more preferably 9.5 mass% / (m ２ / g) or more. In addition, the silver-coated copper powder has a silver content per BET specific surface area of ​​38.0 mass% / (m ２ / g) or less, and 30.0 mass% / (m ２ / g) or less, and more preferably 22.0 mass% / (m ２ It is more preferable that the silver content per BET specific surface area is 3.5 mass% / (m ２ When the silver-coated copper particles come into contact with each other, the silver particles also come into contact with each other easily, and high conductivity can be imparted to the conductive resin composition. ２ / g) or less, a highly conductive silver-coated copper powder can be economically obtained. The method for measuring the silver content per BET specific surface area will be explained in the examples below.

[0018] The silver-coated copper powder of the present invention preferably contains a predetermined amount of silver. Specifically, the silver-coated copper powder preferably contains 3.0% by mass or more of silver, more preferably 4.0% by mass or more, even more preferably 5.0% by mass or more, and even more preferably 8.5% by mass or more. Furthermore, the silver-coated copper powder preferably contains 30.0% by mass or less of silver, more preferably 25.0% by mass or less, even more preferably 20.0% by mass or less, and even more preferably 12.5% ​​by mass or less. When the silver-coated copper powder contains 3.0% by mass or more of silver, when silver-coated copper particles come into contact with each other, the silver particles also easily come into contact with each other, thereby imparting high conductivity to the conductive resin composition. When the silver-coated copper powder contains 30.0% by mass or less of elemental silver, highly conductive silver-coated copper powder can be obtained economically. The method for measuring the silver content in the silver-coated copper powder will be explained in the Examples below.

[0019] In order to set the silver content per BET specific surface area within the above range or the silver content in the silver-coated copper powder within the above range, it is preferable to adjust the silver ion concentration in the aqueous solution in the production method described below or to adjust the reaction times of the displacement plating method and the reduction method.

[0020] As described above, the core particles in the silver-coated copper powder of the present invention preferably have high copper crystallinity. Specifically, when the cross section of the silver-coated copper particle is measured by electron backscatter diffraction (hereinafter also referred to as "EBSD"), the number of copper crystal grains per silver-coated copper particle is preferably 1.0 or more. Furthermore, when the cross section of the silver-coated copper particle is measured by EBSD, the number of copper crystal grains per silver-coated copper particle is preferably 7.0 or less, more preferably 6.8 or less, and even more preferably 6.6 or less. Having the number of copper crystal grains per silver-coated copper particle within the above range can impart even higher conductivity to the conductive resin composition. The number of copper crystal grains per silver-coated copper particle is preferably as close to 1.0 as possible, but the desired effect can be fully achieved even if the number is 2.0 or more, or even 3.0 or more. Silver-coated copper powder having such a number of copper crystal grains is suitably produced by the production method described below. The method for measuring the number of copper crystal grains per silver-coated copper particle will be explained in the examples below.

[0021] In order to obtain a conductive resin composition having high conductivity and improved coatability 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 is within a predetermined range. Specifically, the BET specific surface area of ​​the silver-coated copper powder is 0.40 m ２ / g or more, and 0.45m ２ / g or more, and more preferably 0.50m ２ For the same reason, it is more preferable that the BET specific surface area of ​​the silver-coated copper powder is 1.20 m / g or more. ２ / g or less, and ２ / g or less, and more preferably 1.00m ２ It is more preferable that the SiO2 content is 1 / g or less.

[0022] The silver-coated copper powder of the present invention has a volume cumulative particle size D at 50% cumulative volume by a laser diffraction / scattering particle size distribution measurement method. ５０ (Hereinafter, simply referred to as "particle size D ５０"). It is also preferable that the particle diameter D of the silver-coated copper powder is within a predetermined range. This improves the fluidity of the silver-coated copper powder, and when the silver-coated copper powder is added to a thermosetting resin and an organic solvent to produce a conductive resin composition, the silver-coated copper powder is more likely to spread throughout the conductive resin composition. As a result, the conductivity of the cured product obtained by curing can be improved even without performing a pressing operation when curing the resin. From the viewpoint of making this advantage even more pronounced, the silver-coated copper powder has a particle diameter D ５０ From the same viewpoint, the particle diameter D of the silver-coated copper powder is preferably 1.0 μm or more, more preferably 2.0 μm or more, and even more preferably 3.0 μm or more. ５０ is preferably 10.0 μm or less, more preferably 8.0 μm or less, and even more preferably 6.0 μm or less. ５０ The calculation method will be explained in the examples below.

[0023] Particle size D of silver-coated copper powder ５０ In order to make the particle diameter fall within the above range, it is preferable to adjust the degree of pulverization of the dendritic copper particles in the production method described below, or to control the shape of the dendritic copper particles before pulverization.

[0024] In the silver-coated copper powder of the present invention, the number of copper crystal grains per silver-coated copper particle, the BET specific surface area, and the particle diameter D ５０ It is preferable that the above relationship be satisfied. This not only makes it possible to impart higher conductivity to the conductive resin composition, but also makes it possible to improve the coatability of the conductive resin composition. Specifically, the number of copper crystal grains per silver-coated copper particle is N (pieces), and the BET specific surface area is SSA (m ２ / g), and the particle size D ５０ D ５０ (μm), N / (SSA×D ５０ ) is 0.30 (pieces / {(m ２ / g)×(μm)}) or more, and ２ / g)×(μm)}) or more, and ２For the same reason, it is more preferable that N / (SSA×D)×(μm)) or more. ５０ ) is 5.00 (pieces / {(m ２ / g)×(μm)}) or less, and ２ / g)×(μm)}) or less, and more preferably 3.00 (pieces / {(m ２ / g × (μm)) or less is more preferable.

[0025] N / (SSA x D ５０ The technical meaning of the value defined by D is as follows. In order to improve the coating property while increasing the conductivity of the conductive resin composition obtained using the silver-coated copper powder of the present invention, it is preferable that the SSA is within a predetermined range, as described above. ５０ Regarding SSA and D, there is a suitable range of values ​​from the viewpoint of producing a desired conductive resin composition. ５０ It is preferable that the product of SSA and D is within a predetermined range from the viewpoint of increasing the conductivity of the conductive resin composition and improving the coatability. On the other hand, as described above, it is also preferable that N is within a predetermined range from the viewpoint of increasing the conductivity of the conductive resin composition. From this viewpoint, N is set to the product of SSA and D ５０ The present inventors have considered that using the value obtained by dividing by the product of and as an index is advantageous in achieving both high conductivity and good coatability at a higher level.

[0026] The silver-coated copper powder of the present invention preferably has a bulk density within a predetermined range. In other words, the silver-coated copper powder preferably has few voids between the silver-coated copper particles that make it up, i.e., has high packing properties. As a result, when the silver-coated copper powder is added to a thermosetting resin and an organic solvent to produce a conductive resin composition, the silver-coated copper powder can provide the conductive resin composition with appropriate thixotropy and good coatability. From the viewpoint of making this advantage even more pronounced, the silver-coated copper powder preferably has a tap density of 2.0 g / cm. ３ It is preferable that the density is 2.2 g / cm or more. ３ More preferably, it is 2.4 g / cm or more. ３From the same viewpoint, it is more preferable that the silver-coated copper powder has a tap density of 4.5 g / cm or more. ３ or less, 4.4 g / cm ３ or less, 4.3 g / cm ３ The tap density may be 2.0 g / cm or less. ３ By setting the tap density to 4.5 g / cm or more, an excessive increase in the thixotropy of the conductive resin composition before curing is suppressed, and the coatability of the conductive resin composition is improved. ３ By ensuring that the tap density is not more than 100%, the thixotropy of the conductive resin composition before curing is prevented from decreasing, and the coatability of the conductive resin composition is improved. Silver-coated copper powder having such a tap density is preferably produced by the production method described below. In this specification, the "tap density" refers to a value measured in accordance with JIS Z2512.

[0027] In the silver-coated copper powder of the present invention, it is preferable that the copper crystal grain size in the silver-coated copper particles constituting the powder be within a predetermined range, from the viewpoint of imparting high conductivity to the conductive resin composition. Specifically, the crystal grain size is preferably 1.0 μm or more, more preferably 1.1 μm or more, and even more preferably 1.2 μm or more. Furthermore, the copper crystal grain size is preferably 2.4 μm or less, more preferably 2.3 μm or less, and even more preferably 2.2 μm or less. A method for calculating the copper crystal grain size will be explained in the Examples below.

[0028] In the silver-coated copper powder of the present invention, the particle diameter D ５０ It is also preferable that the particle diameter D and the crystal grain size of the copper have a predetermined relationship. This makes it possible to impart higher conductivity to the conductive resin composition. Specifically, ５０ The value (μm) of the copper crystal grain size relative to the particle size (μm) is preferably 0.20 or more, more preferably 0.22 or more, and even more preferably 0.24 or more. ５０The value (μm) of the copper crystal grain size relative to the value (μm) is preferably 0.50 or less, more preferably 0.48 or less, and even more preferably 0.46 or less.

[0029] Next, a preferred method for producing the silver-coated copper powder of the present invention will be described. Core particles, one of the raw materials for the silver-coated copper powder, are preferably produced by pulverizing copper particles having a dendritic shape produced by electrolysis (hereinafter, these copper particles will also be referred to as "dendritic copper particles" for convenience). In the process of producing dendritic copper particles by electrolysis, an electrolyte containing a copper source is used, an anode and a cathode are immersed in the electrolyte, and a DC voltage is applied between the two electrodes to perform electrolysis. Dendritic copper particles reduced by electrolysis are deposited on the cathode. The cathode may be made of any conductive material that does not affect the electrolysis. The cathode is preferably made of, for example, stainless steel or titanium. Austenitic stainless steel is preferred as the stainless steel, with SUS304L and SUS316 being particularly preferred. On the other hand, the anode is preferably insoluble in electrolysis. The reason for this is as follows: When copper is used as the anode, copper dissolves into the electrolyte during electrolysis. The amount of copper electrodeposited at the cathode is less than the amount of copper dissolved at the anode due to gas generation. As a result, the copper concentration in the electrolyte increases over time, hindering the formation of dendritic copper particles. This problem becomes more pronounced as the electrolysis time increases. As an insoluble anode, for example, DSE (registered trademark) (manufactured by De Nora Permelec) can be used.

[0030] As the copper source, a water-soluble copper compound is preferably used. For example, there is a copper salt, which is a compound formed by neutralizing the charge of a cation and an anion. Examples of such copper salts include copper sulfate, copper chloride, copper acetate, copper carbonate, and copper nitrate. These copper compounds can be used alone or in combination. Of these copper salts, copper sulfate is preferably used.

[0031] In order to deposit dendritic copper particles having a dendritic shape by electrolysis, it is preferable to make the current density during electrolysis relatively high. Specifically, the current density during electrolysis is set to 300 A / m ２ It is preferable to set it to 400 A / m or more. ２ It is more preferable to set it to 500 A / m or more. ２ For the same reason, it is more preferable to set the current density during electrolysis to 2000 A / m or more. ２ It is preferable to set it to 1800 A / m or less. ２ It is more preferable to set it to 1600 A / m or less. ２ It is more preferable to set it as follows:

[0032] In order to deposit dendritic copper particles having a dendritic shape by electrolysis, it is preferable to set the current density during electrolysis relatively high and also to set the copper ion concentration in the electrolyte relatively low. Specifically, the copper ion concentration in the electrolyte is preferably set to 0.02 mol / L or more, more preferably 0.03 mol / L or more, and even more preferably 0.04 mol / L or more. For the same reason, the copper ion concentration in the electrolyte is preferably set to 0.25 mol / L or less, more preferably 0.20 mol / L or less, even more preferably 0.18 mol / L or less, and even more preferably 0.16 mol / L or less.

[0033] The pH of the electrolyte during electrolysis is preferably set in the strong acidic range or the weak acidic range from the viewpoint of successfully precipitating dendritic copper particles by electrolysis. Specifically, from the viewpoint of suppressing the generation of hydrogen gas rather than the reduction of copper ions and facilitating the production of dendritic copper particles, the pH of the electrolyte during electrolysis is preferably maintained at −0.3 or higher, more preferably at −0.2 or higher, and even more preferably at −0.1 or higher. From the same viewpoint, the pH of the electrolyte during electrolysis is preferably maintained at 3.0 or lower, more preferably at 2.8 or lower, and even more preferably at 2.6 or lower. A mineral acid such as sulfuric acid can be used to adjust the pH. Furthermore, the supporting salt described below can also be used to adjust the pH.

[0034] When sulfuric acid is used to adjust the pH, the concentration of sulfuric acid in the electrolytic solution is preferably set to 0.1 mol / L or more, more preferably 0.2 mol / L or more, and even more preferably 0.3 mol / L or more, from the viewpoint of imparting sufficient conductivity to the electrolytic solution. From the same viewpoint, the concentration of sulfuric acid in the electrolytic solution is preferably set to 2.0 mol / L or less, more preferably 1.8 mol / L or less, and even more preferably 1.6 mol / L or less.

[0035] From the viewpoint of successfully obtaining dendritic copper particles, it is preferable to add a supporting salt to the electrolyte, such as neutral chlorides such as sodium chloride, potassium chloride, lithium chloride, rubidium 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 sulfate such as sodium sulfate and potassium sulfate.

[0036] It is preferable to heat the electrolyte solution during electrolysis to maintain the electrolyte solution at a predetermined temperature, from the viewpoint of promoting the reduction of copper ions and successfully obtaining dendritic copper particles. From this viewpoint, the temperature of the electrolyte solution during electrolysis is preferably maintained at 20° C. or higher, more preferably at 22° C. or higher, and even more preferably at 24° C. or higher. From the same viewpoint, the temperature of the electrolyte solution during electrolysis is preferably maintained at 60° C. or lower, more preferably at 55° C. or lower, and even more preferably at 50° C. or lower.

[0037] By carrying out electrolysis under the above conditions for a predetermined time, dendritic copper particles are deposited on the cathode, and the deposited dendritic copper particles are collected by scraping them off the cathode.

[0038] In this manufacturing method, particle size D ５０ It is preferable to obtain dendritic copper particles having a particle diameter D of 5.0 μm or more, more preferably 5.5 μm or more, and even more preferably 6.0 μm or more. ５０ It is preferable to obtain dendritic copper particles having a particle size D of 25.0 μm or less, more preferably 23.0 μm or less, and even more preferably 21.0 μm or less. ５０ When the particle diameter D is within the above range, core particles having high crystallinity can be easily obtained by using the dendritic copper particles and performing the grinding operation described below. ５０ Dendritic copper particles having the above formula can be obtained by setting the current density during electrolysis within the above range and by setting the copper ion concentration in the electrolyte within the above range.

[0039] Once the dendritic copper particles are obtained, they are then pulverized to obtain core particles. The obtained core particles have improved copper crystallinity. The inventors have found that the crystallinity of the obtained core particles varies significantly depending on the conditions under which the dendritic copper particles are pulverized. Based on this finding, they have discovered that copper particles with high crystallinity can be obtained by pulverizing the dendritic copper particles under specified conditions.

[0040] The pulverization of dendritic copper particles may be carried out by either a dry method or a wet method, as long as the desired silver-coated copper powder can be obtained. Regardless of the method used, it is preferable to employ a pulverization method that cuts dendritic copper particles 1, each having a main axis 2 and branches 3 branching from the main axis 2, as shown in FIGS. 1( a) and 1(b), and minimizes deformation of the core particles 4 produced by the cutting, since this method facilitates obtaining silver-coated copper powder having the desired shape. As such a pulverization method, a dry method that does not use a pulverization medium is advantageous. One example of such a pulverization method is a method in which dendritic copper particles are dry-pulverized using a rotating cutting blade (e.g., a stirring blade). According to this pulverization method, the dendritic copper particles 1 shown in FIG. 1( a) are cut by the rotating cutting blade to form the core particles 4 shown in FIG. 1( b). In this case, by appropriately controlling the rotation speed of the cutting blade, excessive external force is prevented from being applied to the core particles 4, and deformation of the core particles 4 is minimized. To pulverize dendritic copper particles using a rotating cutting blade, for example, a stirring blade-type pulverizer can be used, but is not limited to this. Alternatively, as an example of the aforementioned pulverization method, a method of dry pulverizing dendritic copper particles using a swirling jet stream can be mentioned. According to this pulverization method, dendritic copper particles 1 shown in FIG. 1( a) collide with each other due to the jet stream, thereby cutting them into core particles 4 shown in FIG. 1( b). In this case, by arranging multiple pulverization nozzles at equally spaced positions around the inner circumference of the pulverizer and using one or more pulverization nozzles as nozzles for supplying dendritic copper particles 1, a concentrically swirling jet stream can be created within the pulverizer. Controlling the swirling jet stream reduces the probability of dendritic copper particles 1 colliding with the inner wall of the pulverizer, allowing dendritic copper particles 1 to efficiently collide with each other. As a result, excessive external force is prevented from being applied to the core particles 4, minimizing deformation of the core particles 4. In order to pulverize the dendritic copper particles by a jet stream, for example, a jet stream type pulverizer can be used, but the present invention is not limited to this.The pulverization method can be appropriately selected from the above-mentioned methods depending on the application of the silver-coated copper powder. For example, when obtaining silver-coated copper powder with a relatively high tap density, i.e., a relatively high BET specific surface area, it is preferable to use a method of dry pulverization using a swirling jet stream. Alternatively, when obtaining silver-coated copper powder with a relatively low tap density, i.e., a relatively low BET specific surface area, it is preferable to use a method of dry pulverizing dendritic copper particles using a rotating cutting blade.

[0041] As described above, the various conditions, such as the number, shape, size, and rotation speed of the cutting blades when dendritic copper particles are dry-pulverized using a rotating cutting blade, and the various conditions, such as the crushing pressure and processing speed when dendritic copper particles are dry-pulverized using a jet stream, should be such that the dendritic copper particles 1 are cut while causing as little deformation as possible to the core particles 4 produced by the cutting.

[0042] Regardless of which method is used, the particle size D of the core material particles after pulverization ５０ From the viewpoint of obtaining highly crystalline core particles, it is preferable to pulverize the dendritic copper particles so that the average value of L of the pulverized core particles is in the range of 2.5 μm to 8.0 μm and the average value of W is in the range of 0.3 μm to 4.1 μm.

[0043] Once the core particles are obtained, they may be subjected to a surface treatment, if necessary. In this embodiment, for example, a nitrogen-containing surface treatment agent such as benzotriazole may be applied to the surface of the core particles. This can increase the conductivity of the conductive resin composition even if the silver content in the silver-coated copper powder is relatively low.

[0044] Next, a silver coating layer is formed on at least a portion of the surface of the core particle. Examples of methods for disposing the silver coating include displacement plating, which utilizes a displacement reaction between copper and silver due to differences in ionization tendency, and reduction, which uses a reducing agent. When forming a silver coating layer on the surface of the core particle, both displacement plating and reduction may be used, or either one may be used. When both displacement plating and reduction are used, the displacement plating and reduction may be used in this order, or in the reverse order. In particular, displacement plating is preferred because it allows the silver coating layer to be coated relatively uniformly on the surface of the core particle and also prevents the silver particles forming the silver coating layer from agglomerating.

[0045] In both the displacement plating method and the reduction method, a chelating agent may be used in the dispersion to form a relatively uniform silver coating layer. As the chelating agent, it is preferable to use a chelating agent with a high complex stability constant with respect to copper ions, etc., so that copper ions, etc., which are by-products of the substitution reaction between copper and silver ions, do not reprecipitate. In particular, since the core particles that form the core of the silver-coated copper powder are primarily composed of copper, it is preferable to select a chelating agent taking into consideration the complex stability constant with copper. Specifically, the chelating agent may be selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid, diethylenetriamine, triethylenediamine, and salts thereof.

[0046] First, the case of using the displacement plating method will be described. In the displacement plating method, an aqueous solution containing silver ions and core particles are prepared and mixed. As a result, a displacement reaction occurs between the copper and silver of the core particles in the aqueous solution, and silver is deposited on the surfaces of the core particles, thereby obtaining a silver-coated copper powder having a silver coating layer formed thereon.

[0047] As the silver ion source, any commonly used silver salt can be used, including, but not limited to, silver nitrate, silver oxide, silver sulfate, silver acetate, and silver carbonate.

[0048] In the case of the displacement plating method, from the viewpoint of successfully forming a silver coating layer on the surface of the core particle, it is preferable that the concentration of the aqueous solution containing silver ions is within a predetermined range. Specifically, it is preferable that the concentration of silver ions in the aqueous solution is set to 0.010 mol / L or more, and more preferably 0.040 mol / L or more. From the same viewpoint, it is preferable that the concentration of silver ions in the aqueous solution is set to 10.0 mol / L or less, and more preferably 2.0 mol / L or less.

[0049] In the case of the displacement plating method, from the viewpoint of successfully forming a silver coating layer on the surface of the core material particles, it is preferable that the pH of the aqueous solution containing silver ions is 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. From the same viewpoint, 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 such as sodium hydroxide. The pH of the aqueous solution is the value at the temperature when the aqueous solution and the core material particles are mixed.

[0050] It is not preferable to arrange the silver coating layer in a state where the core particles are in contact with each other, because this would result in the formation of a mass of silver-coated copper particles bonded together via silver. Therefore, it is preferable to stir the aqueous solution containing silver ions and the core particles while plating to prevent settling until the formation of the silver coating layer by the silver displacement plating reaction is complete. Although a stirring blade is generally used, any known method can be applied.

[0051] In the case of displacement plating, the reaction time varies depending on the temperature, but is, for example, 10 minutes or more and 120 minutes or less.

[0052] Next, the case of using the reduction method will be described. In the reduction method, an aqueous solution containing silver ions, core particles, and a silver reducing agent are prepared and mixed. This reduces the silver in the aqueous solution, resulting in a silver-coated copper powder in which a silver coating layer is formed on at least a portion of the surface of the core particles.

[0053] Examples of the reducing agent for silver include lithium aluminum hydroxide, sodium amalgam, sodium borohydride, sulfates, sulfites, hydrazine, zinc amalgam, diisobutylaluminum hydride, sodium amalgam, sodium borohydride, and oxalic acid. The same silver ion sources as those described in the displacement plating method can be used.

[0054] In the case of the reduction method, from the viewpoint of successfully forming a silver coating layer on the surface of the core particle, it is preferable that the concentration of the aqueous solution containing silver ions is within a predetermined range. Specifically, it is preferable that the concentration of silver ions in the aqueous solution is set to 0.01 mol / L or more, and more preferably 0.04 mol / L or more. From the same viewpoint, it is preferable that the concentration of silver ions in the aqueous solution is set to 10 mol / L or less, and more preferably 2.0 mol / L or less.

[0055] In the case of the reduction method, from the viewpoint of successfully forming a silver coating layer on the surface of the core material particles, it is preferable that the pH of the aqueous solution containing silver ions is 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. From the same viewpoint, 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 such as sodium hydroxide. The pH of the aqueous solution is the value at the temperature when the aqueous solution and the core material particles are mixed.

[0056] As with the displacement plating method, the reduction method is also undesirable in that if the silver coating layer is arranged in a state where the core particles are in contact with each other, multiple silver-coated copper particles will form clumps bonded together via silver, which is undesirable. Therefore, in order to prevent settling until the formation of the silver coating layer by the silver reduction reaction is completed, it is preferable to carry out the process while stirring the aqueous solution containing silver ions, the core particles, and the silver reducing agent. Although a stirring blade is generally used, known techniques can also be applied.

[0057] In the case of the reduction method, the reaction time varies depending on the temperature, but is, for example, 5 minutes or more and 60 minutes or less.

[0058] Next, in either the displacement plating method or the reduction method, the silver-coated copper particles are separated and removed from the aqueous solution by a solid-liquid separation method such as vacuum dehydration, filter press, centrifugation, or ultrafiltration, and then washed with a solvent or the like.

[0059] After washing, the powder may be subjected to a surface treatment as needed for ease of handling. The surface treatment agent is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include fatty acids, fatty acid salts, surfactants, organometallic compounds, chelating agents, and polymer dispersants. After washing, the silver-coated copper particles are subjected to solid-liquid separation and dried to produce silver-coated copper powder.

[0060] The silver-coated copper powder of the present invention obtained in this manner is suitable for use in applications in which it is mixed with a non-conductive substance to impart conductivity to the non-conductive substance. For example, a conductive resin composition can be obtained by kneading the silver-coated copper powder of the present invention into a thermosetting resin. Curing this conductive resin composition can produce, for example, a conductive film or sheet. The cured product has high conductivity even without a pressing operation during curing. Examples of such thermosetting resins include phenolic resins, epoxy resins, polyurethane resins, melamine resins, unsaturated polyester resins, urea resins, and acrylic resins. These thermosetting resins can be used alone or in combination. These thermosetting resins can be appropriately selected depending on the specific application of the cured product. In addition to the silver-coated copper powder of the present invention and the thermosetting resin, the conductive resin composition may also contain a curing agent for the thermosetting resin, an organic solvent, and the like.

[0061] Although the present invention has been described above based on the preferred embodiments, the present invention is not limited to the above embodiments.

[0062] In relation to the above-mentioned embodiment, the following further discloses a silver-coated copper powder, a conductive resin composition containing the same, and a method for producing the same. [1] A silver-coated copper powder comprising an aggregate of silver-coated copper particles each having a copper core particle and a silver coating layer disposed on at least a portion of the surface of the core particle, wherein, when a cross section of the silver-coated copper particle is measured by electron backscatter diffraction, the number of copper crystal grains per silver-coated copper particle is N (pieces), and the BET specific surface area is SSA (m ２ / g), and the volume cumulative particle size at 50% cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method is D ５０ (μm), N / (SSA×D ５０ ) is 0.3 (pieces / {(m ２ / g)×(μm)}) or more 5.0(pieces / {(m ２ / g) × (μm)}) or less.

[0063] [2] The silver-coated copper powder according to [1], wherein the number of copper crystal grains per silver-coated copper particle is 1.0 or more and 7.0 or less. [3] A silver-coated copper powder having a tap density of 2.0 g / cm ３ 4.5g / cm or more ３ [4] The silver-coated copper powder according to [1] or [2], which is: [4] a volume cumulative particle size D at 50% cumulative volume by a laser diffraction / scattering particle size distribution measurement method; ５０ [5] The silver-coated copper powder according to any one of [1] to [3], wherein the value (μm) of the copper crystal grain size relative to the BET specific surface area (μm) is 0.20 or more and 0.50 or less. ２ / g or more 1.20m ２ [6] The silver-coated copper powder according to any one of [1] to [5], wherein the copper crystal grain size is 1.0 μm or more and 2.4 μm or less.

[0064] [7] A conductive resin composition comprising a thermosetting resin and the silver-coated copper powder according to any one of [1] to [6]. [8] A method for producing silver-coated copper powder, comprising the steps of: precipitating dendritic copper particles on a cathode by electrolytic reduction using an electrolyte containing a copper source; pulverizing the copper particles to obtain core particles; and mixing an aqueous solution containing silver ions with the core particles to reduce the silver ions, thereby forming a silver coating layer on at least a portion of the surface of the core particles. [9] The method according to [8], wherein the silver coating layer is formed by precipitating silver on the surface of the core particles by displacement plating.

[0065] 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 such examples. Unless otherwise specified, "%" means "% by mass."

[0066] [Example 1] (1) Production of dendritic copper particles Dimensions: 2.5 m x 1.1 m x 1.5 m (approximately 4 m ３ In an electrolytic cell (1.0 m x 1.0 m), nine SUS cathodes and nine insoluble anodes (DSE (manufactured by De Nora Permelec)) each measuring 1.0 m x 1.0 m were suspended so that the distance between the electrodes was 5 cm, and a copper sulfate solution serving as an electrolyte was circulated at 30 L / min. The anode and cathode were immersed in the electrolyte, and a direct current was passed through them to perform electrolysis, causing dendritic copper particles to precipitate on the surface of the cathode. The precipitated dendritic copper particles were scraped off and collected. The particle size D of the dendritic copper particles ５０ At this time, the copper concentration of the circulating electrolyte was 10 g / L, sulfuric acid (H ２ SO ４ ) concentration is 100 g / L, chlorine concentration is 5 mg / L, and current density is 800 A / m ２ The temperature of the electrolyte was maintained at 30° C. and electrolysis was carried out for 30 minutes. The pH of the aqueous solution was 1. During electrolysis, the copper ion concentration in the electrolyte between the electrodes was always maintained lower than the copper ion concentration in the electrolyte at the bottom of the electrolytic cell.

[0067] (2) Pulverization of Dendritic Copper Particles The dendritic copper particles were pulverized in a dry state for 10 minutes using a stirring blade pulverizer to obtain core particles.５０ was 3.5 μm.

[0068] (3) Formation of Silver Coating Layer 25 kg of the obtained core particles were added to 25 L of pure water kept at 50°C and stirred thoroughly. Separately, a silver nitrate solution was prepared by adding 2.3 kg of silver nitrate to 2.5 L of pure water. These solutions were mixed and reacted for 1 hour, and a silver-coated copper powder slurry was obtained by displacement plating. The pH of the slurry was 7.5. Next, the silver-coated copper powder slurry was filtered by vacuum filtration. After filtration, it was washed with a solution prepared by dissolving 600 g of EDTA-2Na (ethylenediaminetetraacetic acid disodium salt) in 6 L of pure water, and then the remaining EDTA was washed off with 3 L of pure water. The resulting mixture was then dried at 90°C for 3 hours to obtain the desired silver-coated copper powder.

[0069] Example 2 Dendritic 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 in Example 1. Furthermore, when pulverizing the dendritic copper particles, a jet stream pulverizer was used instead of the stirring blade pulverizer. Other than this, the target silver-coated copper powder was obtained in the same manner as in Example 1.

[0070] [Example 3] Dendritic copper particles were obtained in Example 2 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. Other than these, the same procedure as in Example 2 was carried out to obtain the target silver-coated copper powder.

[0071] [Example 4] Dendrite-shaped copper particles were obtained in Example 2 by changing the copper concentration of the electrolyte to 13 g / L, the chlorine concentration to 8 mg / L, and the current density to 570 A. Except for these changes, the same procedure as in Example 2 was carried out to obtain the target silver-coated copper powder.

[0072] Comparative Example 1 The dendritic copper particles obtained in Example 2 were not pulverized, but instead a silver coating layer was formed on the surface of the dendritic copper particles by displacement plating to obtain the desired silver-coated copper powder.

[0073] Comparative Example 2 The dendritic copper particles obtained in Example 1 were not pulverized, but instead a silver coating layer was formed on the surface of the dendritic copper particles by displacement plating to obtain the desired silver-coated copper powder.

[0074] Comparative Example 3: Spherical copper particles with a copper content of 99% were obtained by water atomization. The copper powder was classified using a classification device to obtain spherical copper particles. Particle size D of the spherical copper particles ５０ Furthermore, without pulverizing the obtained spherical copper particles, a silver coating layer was formed on the surface of the spherical copper particles by displacement plating to obtain the desired silver-coated copper powder.

[0075] [Comparative Example 4] The spherical copper particles obtained in Comparative Example 3 were classified under conditions different from those in Comparative Example 3 to obtain spherical copper particles. ５０ Furthermore, without pulverizing the obtained spherical copper particles, a silver coating layer was formed on the surface of the spherical copper particles by displacement plating to obtain the desired silver-coated copper powder.

[0076] [Evaluation] For the silver-coated copper powders obtained in the Examples and Comparative Examples, the tap density was calculated according to the method described below. For the silver-coated copper powders obtained in the Examples and Comparative Examples, the number of copper crystal grains per silver-coated copper particle, the copper crystal grain size, the BET specific surface area, the particle diameter D ５０ The silver content per BET specific surface area and the silver content in the silver-coated copper powder were calculated. The specific resistance of the conductive resin composition of the silver-coated copper powder obtained in the examples and comparative examples was measured according to the method described below. The results are shown in Table 1.

[0077] [Tap Density] The tap density was measured using a tapping machine (model: KSR-406, manufactured by Kuramochi Scientific Machinery Manufacturing Co., Ltd.). ３ 120 g of silver-coated copper powder was placed in a measuring cylinder. The tap stroke was set to 4 cm, and the number of tappings was set to 400 times for measurement.

[0078] [Number of Copper Crystal Grains per Silver-Coated Copper Particle] The number of copper crystal grains per silver-coated copper particle was measured by the following method. For the measurement, a center gun-type scanning electron microscope (SUPRA 55VP, manufactured by Carl Zeiss K.K.) equipped with an EBSD evaluation device (OIM Data Collection Ver. 7.2.0, manufactured by TSL Solutions Co., Ltd.) was used, along with an attached EBSD analyzer. First, the 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, and the resulting cut cross section was carbon-coated. Then, a cross-section polisher (IB-19510CP or IB-19520CCP, both manufactured by JEOL Ltd.) was used to precisely smooth the cross section of the resin block to prepare a sample. According to the EBSD method, the number of copper crystal grains was measured on the cross section of each silver-coated copper particle in the sample (the surface where the core particle of the silver-coated copper particle was exposed). From the image of the cross section of the particle, 10 silver-coated copper particles having the longest transverse length of 1 μm or more were randomly selected, and the silver-coated copper particles were measured to determine the average number of copper crystal grains. This average value was taken as the number of copper crystal grains per silver-coated copper particle.

[0079] The WD value when measuring the number of crystal grains was 15±1 mm, and with "Background Subtraction," "Normalize Intensity Histogram," and "Dynamic Background Subtraction" checked in "Image Processing," "Cu" was selected from "Phase" in "Capture Pattern" of the EBSD evaluation device at the observation point, and the WD value was adjusted under the conditions that the "Fit" value in "Solutions" was within 1.5 and the "CI" value was higher than 0.1.

[0080] [Copper Crystal Grain Size] The copper crystal grain size was measured by the following method. For the measurement, data on the sample cross section obtained by measuring the number of copper crystal grains per silver-coated copper particle described above was used. Specifically, for the Examples and Comparative Examples, photographs of the sample cross section taken with "Capture SEM" in "Scan" were measured with "Start Scan." This measurement data was used to determine the crystal grain size (average area) using "All data" in the "Grain Size Quick Chart" analysis menu of the EBSD analysis program (OIM Analysis Ver. 7.3.1, manufactured by TSL Solutions Co., Ltd.). This crystal grain size (average) was taken as the average size of the crystal grains in the silver-coated copper powder of the present invention.

[0081] In measuring the size of copper crystal grains, a misorientation of 5° or more was considered a grain boundary. However, since the crystal structure of copper is a face-centered cubic structure, twin grain boundaries were taken into consideration, and the misorientation at a certain grain boundary was expressed by the rotation axis and rotation angle. When the rotation axis was represented by <111> and the rotation angle was 60±1°, or when the rotation axis was represented by <110> and the rotation angle was 38.94±1°, it was not considered a grain boundary. The conditions of the scanning electron microscope during observation were an acceleration voltage of 15 kV, an aperture diameter of 60 μm, a high current mode, and a sample angle of 70°. The observation magnification, measurement area, and step size may be changed as appropriate depending on the size of the crystal grains.

[0082] <Filtering> Note that when the cross section of the silver-coated copper powder prepared as described above is measured by EBSD, not only copper crystal grains but also silver crystal grains are detected. Therefore, filtering was performed under the following conditions to observe only the copper crystal grains. Specifically, before measuring the crystal grain size, filtering was performed using (1) "CI," (2) "Minimum Grain Size," (3) "IQ," and (4) "Grain Aspect Ratio" from the "Formula" section of the analysis menu of the EBSD analysis program, and then copper crystal grain boundaries were detected. The filtering conditions (conditions (1) to (4) above) for each sample of the Examples and Comparative Examples are shown in Table 2 below. Specifically, (1) "CI" was set to "0.05," and target particles were confirmed in the EBSD image and SEM image during process (1). At this time, for samples in which silver crystal grains were still observed in the EBSD and SEM images, the "CI" was left at "0.05". On the other hand, for samples in which silver crystal grains were not observed (i.e., samples in which excessive filtering had been performed), the "CI" was changed to "0.03". In addition, during the process (2), the contrast of the SEM image was checked together with the EBSD image, and the process was carried out with the aim of removing only crystal grains other than the copper phase, with the value set to "5". In addition, after the processes (1) and (2), if crystal grains other than the copper phase were present, the contrast of the SEM image together with the EBSD image was checked, and (3) the "IQ" was changed to ">4.0 × 10 ６ " to ">5.0 x 10 ６ " range. In addition, after the processes (1), (2), and (3), if crystal grains other than the copper phase were present, the contrast of the SEM image was checked together with the EBSD image, and (4) the process was carried out with the "Grain Aspect Ratio" set to "0.6." Note that "-" in Table 2 indicates that the copper crystal grains could be sufficiently observed and subsequent filter treatment was not required, and therefore the filter treatment was not carried out.

[0083] [BET Specific Surface Area] Measurement was carried out by the BET single-point method using a Monosorb manufactured by Yuasa Ionics Co., Ltd.

[0084] [Particle size D５０ Using an automatic sample feeder for a laser diffraction particle size distribution analyzer (Microtrac SDC manufactured by Microtrac Bell Co., Ltd.), the silver-coated copper powder was placed in a solvent prepared by mixing 0.1% hexametaphosphoric acid with a 20% ethanol solvent, and the mixture was irradiated with 40W ultrasonic waves for 90 seconds at a flow rate of 40%, after which the particle size distribution was measured using a laser diffraction particle size distribution analyzer "MT3000II" manufactured by Microtrac Bell Co., Ltd., and the particle size D was determined from the obtained volume-based particle size distribution chart. ５０ The particle size D ５０ The water-soluble solvent used for measuring the particle diameter D was passed through a 60 μm filter, the "solvent refractive index" was set to 1.33, the particle permeability condition was set to "permeation", the measurement range was set to 0.243 μm or more and 704.0 μm or less, and the measurement time was set to 30 seconds. The average value of two measurements was taken as the particle diameter D ５０ It was decided.

[0085] [Silver Content in Silver-Coated Copper Powder] 1 g of the silver-coated copper powder obtained in each of the Examples and Comparative Examples was completely dissolved in a 1:1 nitric acid solution, and then titrated with sodium chloride to calculate the silver content (%).

[0086] [Silver Content per BET Specific Surface Area] The silver content per BET specific surface area was calculated from the silver content measured by the above-mentioned method and the value of the BET specific surface area measured by the above-mentioned method.

[0087] [Specific Resistivity of Conductive Resin Composition] Conductive resin compositions were prepared using the silver-coated copper powder obtained in the examples and comparative examples. Specifically, conductive resin compositions consisting of pastes were prepared by mixing the silver-coated copper powder, epoxy resin, 2-methylimidazole, and dimethylacetamide. Each conductive resin composition was prepared so that the blending amount of silver-coated copper powder in the conductive resin composition was 90% by mass. The mass ratio of epoxy resin, dimethylacetamide, and 2-methylimidazole in each conductive resin composition was 49:40:1. The paste was then applied to a glass plate. A bar coater with a width of 200 mm was used for application. The gap was set to 100 μm. The formed coating film was dried and cured in an atmospheric hot air drying oven at 110°C for 60 minutes to obtain an 80 μm-thick conductive film. The resistance value of the conductive film was measured using a four-probe method using a resistivity meter (Mitsubishi Chemical MCP-T600).

[0088]

[0089]

[0090] As is clear from the results shown in Table 1, the silver-coated copper powders obtained in the examples have a lower resistivity of the conductive resin composition than the silver-coated copper powders obtained in the comparative examples.

[0091] According to the present invention, it is possible to provide a silver-coated copper powder that can be used to obtain a conductive resin composition that can increase conductivity without performing a pressing operation, and a method for producing the same. Also, according to the present invention, it is possible to provide a conductive resin composition that can increase conductivity without performing a pressing operation.

Claims

1. A silver-coated copper powder consisting of an aggregate of silver-coated copper particles having a copper core particle and a silver coating layer disposed on at least a portion of the surface of the core particle, wherein, when the cross section of the silver-coated copper particle is measured by electron backscatter diffraction, the number of copper crystal grains per silver-coated copper particle is N (pieces), and the BET specific surface area is SSA (m ２ / g), and the volume cumulative particle size at 50% cumulative volume measured by a laser diffraction scattering particle size distribution measurement method is D ５０ (μm), N / (SSA×D ５０ The value defined by is 0.3 (pieces / {(m ２ / g)×(μm)}) or more 5.0(pieces / {(m ２ / g × (μm)) or less.

2. The 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.

3. Tap density is 2.0 g / cm ３ 4.5g / cm or more ３ The silver-coated copper powder according to claim 1 or 2, wherein:

4. Volume cumulative particle size D at 50% cumulative volume measured by laser diffraction scattering particle size distribution measurement method ５０ 3. The silver-coated copper powder according to claim 1, wherein the value (μm) of the copper crystal grain size relative to the copper content (μm) is 0.20 or more and 0.50 or less.

5. BET specific surface area is 0.40m ２ / g or more 1.20m ２ The silver-coated copper powder according to claim 1 or 2, wherein the silver-coated copper powder has a molecular weight of 1000 or less.

6. The silver-coated copper powder according to claim 1 or 2, wherein the copper crystal grain size is 1.0 μm or more and 2.4 μm or less.

7. A conductive resin composition comprising a thermosetting resin and the silver-coated copper powder according to claim 1 or 2.

8. A method for producing silver-coated copper powder, comprising the steps of: using an electrolyte containing a copper source to precipitate dendritic copper particles on a cathode by electrolytic reduction; pulverizing the copper particles to obtain core particles; and mixing an aqueous solution containing silver ions with the core particles to reduce the silver ions and form a silver coating layer on at least a portion of the surface of the core particles.

9. The method according to claim 8, wherein the silver coating layer is formed by depositing silver on the surface of the core particles by displacement plating.

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