Flake-like copper particles and conductive resin composition containing same

Abstract

Flake-like copper particles according to the present invention have an average number of crystal grains of 150 to 2,000 inclusive as measured by observing cross-sectional surfaces of the flake-like copper particles by an electron backscattered diffraction method. When viewed in plan, if the longest line segment crossing a particle is defined as the major axis and the perpendicular bisector of the major axis is defined as the minor axis, the number of crystal grains in the plan view is 4.5 per µm2 to 40.0 per µm2 inclusive with respect to the value (µm2) of the product of the major axis length and the minor axis length. It is preferable that the crystal grain size is 0.2 µm to 1.3 µm inclusive. In a plan view, it is preferable that the average size of the crystal grains that are positioned in the peripheral region of a particle is smaller than the average size of the crystal grains that are positioned in the central region of the particle.

Description

Flaky copper particles and a conductive resin composition containing the same

[0001] The present invention relates to flaky copper particles and a conductive resin composition containing the same.

[0002] For the purpose of achieving electrical conduction between conductors, conductive pastes, conductive adhesives, etc. containing metal powders are used. As the metal powder, for example, noble metals such as gold and silver, and base metals such as nickel and copper are used. Noble metals are less likely to be oxidized and have high conductivity, so they are suitable materials as conductive powders, but they are disadvantageous in terms of economy. Therefore, particles of copper or nickel are industrially used instead of gold or silver. In particular, flaky copper particles have a large specific surface area due to their shape and are easily contacted with each other, so it is easy to impart conductivity to the resin by adding them to the resin.

[0003] For example, the applicant has previously proposed silver-coated flaky copper particles in which the value of lightness L* with respect to the degree of dispersion, which is the ratio of the volume cumulative particle size D １０ to the volume cumulative particle size D ９０ is 13 or more and 25 or less, and the thickness is 0.1 μm or more and 0.3 μm or less. According to these silver-coated flaky copper particles, there is an advantage that the electrical resistance of the film formed from the conductive resin composition containing the same can be effectively reduced.

[0004] EP4205886A1

[0005] An object of the present invention is to provide copper particles having further improved conductivity than the above-described conventional technologies.

[0006] As a result of intensive studies to solve the above problems, the present inventors have surprisingly found that by controlling the production conditions of flaky copper particles, the crystallinity of the flaky copper particles changes and the conductivity is improved. The present invention has been made based on the above findings, and provides flaky copper particles, wherein the number of crystal grains measured by observing the cross section of the flaky copper particles by the electron backscatter diffraction method is 150 or more and 2000 or less on average.

[0007] Furthermore, the present invention relates to flake-shaped copper particles, wherein, in a plan view, the longest line segment crossing the particle is defined as the major axis, and the perpendicular bisector of the major axis is defined as the minor axis, and the number of crystal grains in a plan view is equal to the product of the major axis length and the minor axis length (μm). ２ ) 4.5 particles / μm ２ 40.0 pieces / μm or more ２ The following provides flake-shaped copper particles.

[0008] The present invention will be described below based on its preferred embodiments. The present invention relates to copper particles. Copper particles, when aggregated, constitute copper powder. Preferably, the copper particles are particles substantially composed of copper elements or copper-based alloy particles. The former particles are particles substantially composed of copper elements, with the remainder being unavoidable elements. In this case, it is desirable that the copper particles of the present invention consist only of copper elements, but the inclusion of trace amounts of unavoidable elements is acceptable. When unavoidable elements are included in the copper particles, it is preferable that the content is 0.01% by mass or less, in order to avoid impairing the inherent properties of the copper particles. Unavoidable elements include, for example, oxygen (O) and carbon (C) elements derived from oxygen and carbon dioxide in the atmosphere, and nitrogen (N) elements that may be mixed in during the manufacturing process of copper particles. The presence or absence of unavoidable elements and their content can be measured, for example, by ICP emission spectrometry. In the case of the latter particles, the content of copper elements in the particles is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0009] The copper particles of the present invention have a distinctive feature in their external shape. Specifically, the copper particles have a flake-like shape. In this specification, "flake-like" is synonymous with "flattened" and "flaky," meaning that the particles have a thin, plate-like shape with two opposing main surfaces. Flake-like copper particles are specified by the aspect ratio described later. The flake shape of the copper particles makes it easier for them to come into surface contact with each other, increasing the contact area. Therefore, when a conductive resin composition is manufactured by adding flake-shaped copper particles to a resin and an organic solvent, the contact area of ​​the copper particles in the conductive resin composition increases, and the conductive resin composition can be imparted with high conductivity. Furthermore, high conductivity can be imparted even when the amount of copper particles added is reduced, so that the conductive resin composition can be imparted with properties inherent to resins, such as flexibility and bending resistance. Flake-shaped copper particles can be suitably manufactured, for example, by the manufacturing method described later. In the following description, copper particles are also referred to as "flake-like copper particles." In this specification, the term "conductive resin composition" means, depending on the context, a composition containing a thermosetting resin before curing or a composition containing a thermosetting resin after curing.

[0010] The flake-shaped copper particles preferably have an aspect ratio within a predetermined range. The aspect ratio is defined as the ratio of the major axis length L to the minor axis length W (major axis length L / minor axis length W) when the longest line segment crossing the particle in a plan view is defined as the major axis, and the perpendicular bisector of the major axis that crosses the particle is defined as the minor axis. From the viewpoint of increasing the contact area between the copper particles and imparting high conductivity to the conductive resin composition, the aspect ratio of the flake-shaped copper particles is preferably 1.05 or higher, more preferably 1.10 or higher, and even more preferably 1.15 or higher. From the same viewpoint, the aspect ratio is preferably 4.00 or lower, more preferably 3.90 or lower, even more preferably 3.80 or lower, even more preferably 2.50 or lower, and particularly preferably 2.00 or lower.

[0011] The aspect ratio can be measured by the following method. Specifically, first, at least two fields of view are captured using a scanning electron microscope (hereinafter also referred to as "SEM") at a magnification that includes 50 or more flake-shaped copper particles to be measured. Next, 50 or more flake-shaped copper particles whose outlines can be confirmed are randomly selected from each image data, and the value of the major axis length L and the minor axis length W are measured for each of the selected flake-shaped copper particles. The average values ​​of the major axis length L and the minor axis length W are calculated, and the major axis length L / minor axis length W value is calculated from these average values. The value calculated in this way is referred to as the aspect ratio in this specification.

[0012] In flake-shaped copper particles, the average value of the long axis length L is preferably 8.0 μm or more, more preferably 9.0 μm or more, and even more preferably 10.0 μm or more, provided that the aspect ratio is within the above range. Furthermore, the average value of the long axis length L is preferably 20.0 μm or less, more preferably 19.0 μm or less, and even more preferably 18.0 μm or less, provided that the aspect ratio is within the above range. The average value of the short axis length W is preferably 3.0 μm or more, more preferably 3.5 μm or more, and even more preferably 4.0 μm or more, provided that the aspect ratio is within the above range. Furthermore, the average value of the short axis length W is preferably 12.0 μm or less, more preferably 11.5 μm or less, and even more preferably 11.0 μm or less, provided that the aspect ratio is within the above range.

[0013] The flake-shaped copper particles preferably have a thickness within a predetermined range. Specifically, from the viewpoint of increasing the contact area between copper particles and imparting high conductivity to the conductive resin composition, the thickness of the flake-shaped copper particles is preferably 0.05 μm or more, more preferably 0.07 μm or more, and even more preferably 0.10 μm or more. From a similar viewpoint, the thickness of the flake-shaped copper particles is preferably 0.40 μm or less, more preferably 0.35 μm or less, and even more preferably 0.30 μm or less.

[0014] The thickness of flake-shaped copper particles can be measured using the following method. Specifically, first, the flake-shaped copper particles to be measured are embedded in resin, and then cross-sectioned using a cross-section polisher. After that, images are taken at a desired magnification using an electron microscope, and the thickness is measured using image analysis particle size distribution measurement software (Mac-View, manufactured by Mountec Co., Ltd.).

[0015] In order to ensure that the aspect ratio of the flake-shaped copper particles, as well as the average values ​​of the major axis length L and minor axis length W, are within the aforementioned range, it is preferable to manufacture the flake-shaped copper particles using a manufacturing method described later.

[0016] The flake-shaped copper particles have no particular limitations on their shape in plan view, i.e., the shape of the plate surface, and can take shapes such as approximately circular, approximately oval, approximately elliptical, and irregular.

[0017] The flake-shaped copper particles of the present invention are characterized by their crystallinity. As mentioned above, high conductivity is required for copper particles, and as a result of the inventors' research, it was unexpectedly found that even higher conductivity than that of the prior art can be obtained by setting the number of copper crystal grains within a predetermined range. Specifically, the number of crystal grains measured by observing the cross-section of the flake-shaped copper particles by electron beam backscatter diffraction (hereinafter also referred to as "EBSD") is preferably 150 or more on average, more preferably 250 or more, even more preferably 350 or more, even more preferably 500 or more, and particularly preferably 800 or more. Furthermore, the number of crystal grains is preferably 2000 or less on average, even more preferably 1900 or less, and even more preferably 1800 or less. By having the number of crystal grains in the flake-shaped copper particles within the above range, even higher conductivity can be imparted to the conductive resin composition than in the conventional method. In terms of measurement principles, the number of crystal grains is a value obtained by measuring the cross-section of the flake-shaped copper particles and the region from the cross-section to a depth of 50 nm. Therefore, the number of crystal grains referred to here is not the number of crystal grains contained in the entire flake-shaped copper particle. Flake-shaped copper particles having such a number of crystal grains can be suitably manufactured by the manufacturing method described later. The method for measuring the number of crystal grains will be explained in the examples described later.

[0018] The flaky copper particles of the present invention are also characterized in that, as another index related to crystallinity, the number of copper crystal grains in a plan view is within a predetermined range. Also by this, conductivity higher than that of the prior art can be obtained. By the way, since the plate surface of the flaky copper particles can take various shapes, it is complicated to obtain the area of the flaky copper particles in a plan view. Therefore, as the index, a value approximating the area in a plan view will be used for convenience. Specifically, in a plan view, when the longest line segment crossing the particle is defined as the major axis and the line segment that is the perpendicular bisector of the major axis and crosses the particle is defined as the minor axis, the number of crystal grains in a plan view is the value of the product of the major axis length and the minor axis length (μm ２ ) and is preferably 4.5 grains / μm ２ or more, more preferably 5.5 grains / μm ２ or more, still more preferably 6.5 grains / μm ２ or more, and even more preferably 8.0 grains / μm ２ or more. Also, the number of crystal grains in a plan view is preferably 40.0 grains / μm ２ or less with respect to the value of the product of the major axis length and the minor axis length (μm ), more preferably 30.0 grains / μm ２ or less, still more preferably 25.0 grains / μm ２ or less, even more preferably 15.0 grains / μm ２ or less, and even more preferably 15.0 grains / μm ２ or less. When the number of crystal grains in a plan view in the flaky copper particles is within the above range, higher conductivity than before can be imparted to the conductive resin composition. Due to the measurement principle, the number of the crystal grains is a value obtained by measuring the cross section of the flaky copper particles and the region up to a depth of 50 nm from the cross section. Therefore, the number of crystal grains referred to here is not the number of crystal grains contained in the entire flaky copper particles.The flaky copper particles having such a number of crystal grains in a plan view are preferably manufactured by the manufacturing method described later.The method for measuring the number of crystal grains in a plan view will be described in the examples described later.

[0019] The reason why high conductivity can be obtained when the number of crystal grains in flake-shaped copper particles is within the aforementioned range is not clear, but the inventors believe the following. However, they are not bound by this theory. As mentioned above, high conductivity can be obtained when copper particles have a flake shape, and the degree of flaking can be evaluated by the number of crystal grains in the flake-shaped copper particles. This is because, as the flattening (flaking) of copper particles progresses, the number of crystal grains in the copper particles is thought to increase compared to the copper particles before flattening, due to the reduction in the size of the crystal grains caused by the flattening. Therefore, in the present invention, when flattening copper particles, the number of crystal grains in the copper particles is controlled to obtain flake-shaped copper particles. By flattening in this way, the contact area between flake-shaped copper particles increases, so that the entire flake-shaped copper particle can be used for conductivity, and even higher conductivity can be obtained than in the conventional technology. In particular, if the surface of the flake-shaped copper particles becomes smoother, the contact area between the copper particles increases even further, so even higher conductivity can be obtained.

[0020] From the viewpoint of imparting high conductivity to the conductive resin composition, it is preferable that the flake-shaped copper particles have a copper crystal grain size within a predetermined range. Specifically, it is preferable that the crystal grain size is 0.2 μm or larger, more preferably 0.3 μm or larger, and even more preferably 0.4 μm or larger. Furthermore, it is preferable that the crystal grain size is 1.3 μm or smaller, more preferably 1.2 μm or smaller, and even more preferably 1.1 μm or smaller. The method for calculating the crystal grain size will be explained in the examples described later.

[0021] From the viewpoint of imparting high conductivity to the conductive resin composition, it is preferable that the crystallinity of the flake-shaped copper particles differs between the central and peripheral regions. Specifically, it is preferable that the crystallinity is relatively high in the central region of the particle and relatively low in the peripheral region. In other words, in a plan view, the average size D of the crystal grains located in the central region of the particle is preferable. １ Rather than the average size D of the crystal grains located in the peripheral region, ２A small value is preferable. In this specification, "central region" refers to a circular region centered on the concentration centroid of the flake-shaped copper particles, with a diameter equal to the length obtained by dividing the minimum Ferret diameter RF of the flake-shaped copper particles into four equal parts (RF / 4). "Peripheral region" refers to the region of the flake-shaped copper particles other than the central region. Furthermore, "concentration centroid position" as used herein refers to the position of the centroid calculated by adjusting the brightness of the crystal grains in the flake-shaped copper particles in order of decreasing crystal grain size, and then weighting them according to their brightness. "Minimum Ferret diameter" refers to the length of the shortest short side of any rectangle that circumscribing the flake-shaped copper particles. The concentration centroid position and the minimum Ferret diameter RF can be calculated using image analysis software (Dragonfly, manufactured by Comet Technologies Canada Inc.). Details of the calculation method will be explained in the examples described later.

[0022] In flake copper particles, the difference in crystallinity between the central and peripheral regions of the particle can also be defined by the magnitude of the value R, as defined by the following equation (1). Specifically, a smaller value R means that the crystallinity of the central region of the particle is relatively high and the crystallinity of the peripheral region is relatively low, while a larger value R means that the crystallinity of the central region of the particle is relatively low and the crystallinity of the peripheral region is relatively high. R = (N1 / S1) / (N2 / S2) (1) In equation (1), N1 is the number of crystal grains located in the central region in a plan view, S1 is the total area of ​​the crystal grains located in the central region in a plan view, N2 is the number of crystal grains located in the peripheral region in a plan view, and S2 is the total area of ​​the crystal grains located in the peripheral region in a plan view.

[0023] From the viewpoint of imparting high conductivity to the conductive resin composition, the value R is preferably 0.10 or higher, more preferably 0.12 or higher, and even more preferably 0.15 or higher. From the same viewpoint, the value R is preferably 0.80 or lower, more preferably 0.60 or lower, and even more preferably 0.50 or lower. Flake-shaped copper particles with a value R within the above range are suitably manufactured by the manufacturing method described later. Details of the method for measuring the value R will be explained in the examples described later.

[0024] Provided that the value R is within the above range, it is preferable that each of N1, S1, N2, and S2 in formula (1) is within a predetermined range. Specifically, from the viewpoint of imparting high conductivity to the conductive resin composition, it is preferable that the value N1 is 1 or more, more preferably 3 or more, and even more preferably 5 or more. From the same viewpoint, it is preferable that the value N1 is 70 or less, more preferably 60 or less, and even more preferably 50 or less. From the viewpoint of imparting high conductivity to the conductive resin composition, the value S1 is 5.00 μm. ２ Preferably, the size is 5.80 μm or larger. ２ It is even more preferable that the above is 6.50 μm. ２ It is even more preferable that the above is true. From a similar viewpoint, the value S1 is 25.00 μm ２ Preferably, the following, 23.00 μm ２ It is even more preferable that the following is the case: 20.00 μm ２ The following is even more preferable: From the viewpoint of imparting high conductivity to the conductive resin composition, the value N2 is preferably 10 or more, more preferably 25 or more, and even more preferably 40 or more. From the same viewpoint, the value N2 is preferably 350 or less, more preferably 300 or less, and even more preferably 250 or less. From the viewpoint of imparting high conductivity to the conductive resin composition, the value S2 is 3.00 μm. ２ Preferably, the size is 4.50 μm or larger. ２ It is even more preferable that the size be greater than or equal to 6.00 μm. ２It is even more preferable that the above is true. From a similar viewpoint, the value S2 is 25.00 μm ２ Preferably, the following is true: 24.50 μm ２ It is even more preferable that the following is the case: 24.00 μm ２ The following is even more preferable:

[0025] It is preferable that flake-shaped copper particles have a dissimilar metal other than copper arranged on at least a portion of their surface. This allows the properties of the dissimilar metal to be utilized, improving various performance characteristics such as conductivity. For example, if silver is used as the dissimilar metal, the exposure of copper particles can be suppressed, and the oxidation of copper can be inhibited, thereby imparting even higher conductivity to the conductive resin composition.

[0026] The dissimilar metal only needs to be present so as to cover at least a portion of the surface of the flake-shaped copper particles. Therefore, the dissimilar metal may be arranged over the entire surface of the flake-shaped copper particles, or it may be arranged over only a portion of the surface. Furthermore, the boundary between the flake-shaped copper particles and the dissimilar metal may be clear, or there may be a partially unclear area where the flake-shaped copper particles and the dissimilar metal can be distinguished. There are no particular limitations on the method of arranging the dissimilar metal on the surface of the flake-shaped copper particles. From the viewpoint of successfully arranging the dissimilar metal, it is preferable to use the displacement plating method described later or to use a reducing agent.

[0027] The amount of dissimilar metals can be evaluated by the chromaticity a* in the L*a*b* color space. Specifically, for example, from the viewpoint of imparting high conductivity to a conductive resin composition, the flake copper particles preferably have an a* value of 0.0 or higher in the L*a*b* color system, more preferably 1.0 or higher, even more preferably 2.0 or higher, even more preferably 3.0 or higher, and particularly preferably 5.0 or higher. On the other hand, for example, from the viewpoint of imparting appropriate viscosity to a conductive resin composition, the flake copper particles preferably have an a* value of 8.2 or lower in the L*a*b* color system, more preferably 8.0 or lower, and even more preferably 7.8 or lower. The method for measuring the a* value will be explained in the examples described later.

[0028] The flake-shaped copper particles preferably have a chromaticity b* in the L*a*b* color space within a predetermined range. Specifically, for example, from the viewpoint of imparting high conductivity to a conductive resin composition, the flake-shaped copper particles preferably have a b* value of 11.00 or higher in the L*a*b* color system, more preferably 11.10 or higher, and even more preferably 11.50 or higher. From a similar viewpoint, the flake-shaped copper particles preferably have a b* value of 16.00 or lower in the L*a*b* color system, more preferably 15.50 or lower, and even more preferably 15.00 or lower. The method for measuring the b* value will be explained in the examples described later.

[0029] The flake-shaped copper particles preferably have a lightness L* in the L*a*b* color space within a predetermined range. Specifically, for example, from the viewpoint of imparting high conductivity to the conductive resin composition, the flake-shaped copper particles preferably have an L* value of 72.00 or higher in the L*a*b* color system, more preferably 72.50 or higher, and even more preferably 73.00 or higher. From a similar viewpoint, the flake-shaped copper particles preferably have an L* value of 79.80 or lower in the L*a*b* color system, and more preferably 79.50 or lower. The method for measuring the L* value will be explained in the examples described later.

[0030] The arrangement of dissimilar metals can also be evaluated by the dissimilar metal content per unit BET specific surface area of ​​the flake-shaped copper particles. Specifically, for example, from the viewpoint of imparting high conductivity to a conductive resin composition, the flake-shaped copper particles have a dissimilar metal content of 1.2 mass% / (m²) per unit BET specific surface area. ２ Preferably, it is 1.6% by mass / (m) or more, and 1.6% by mass / (m ２ It is even more preferable that it be 1.8% by mass / (m) or more. ２ It is even more preferable that it be 4.5% by mass / (m) or more. ２ It is even more preferable that the amount of material per unit of BET specific surface area be 18.0% by mass / (m²). Furthermore, from the viewpoint of reducing the manufacturing cost of flake copper particles, the flake copper particles should have a dissimilar metal content of 18.0% by mass / (m²). ２Preferably, it should be less than or equal to 16.0% by mass / (m ２ It is even more preferable that it be less than or equal to 14.0% by mass / (m ２ It is even more preferable that it be less than or equal to 10.0% by mass / (m ２ It is even more preferable that the amount is less than or equal to ( / g). The method for measuring the dissimilar metal content per unit BET specific surface area will be explained in the examples described later.

[0031] The amount of dissimilar metals relative to the mass of the flake-shaped copper particles is preferably 3.0% by mass or more, more preferably 4.0% by mass or more, and even more preferably 5.0% by mass or more. Furthermore, from the viewpoint of reducing the manufacturing cost of the flake-shaped copper particles, the flake-shaped copper particles preferably contain 30.0% by mass or less of dissimilar metals, more preferably 25.0% by mass or less, even more preferably 20.0% by mass or less, and even more preferably 15.0% by mass or less. The method for measuring the dissimilar metal content in the flake-shaped copper particles will be explained in the examples described later.

[0032] In order to set the L*, a*, and b* values ​​in the L*a*b* color system within the aforementioned ranges, the dissimilar metal content per BET specific surface area within the aforementioned ranges, and the dissimilar metal content in flake-shaped copper particles within the aforementioned ranges, it is preferable to adjust the ion concentration of dissimilar metals in the solution in the manufacturing method described later.

[0033] The dissimilar metals are not particularly limited as long as they are different from the metal constituting the core material particles (i.e., copper), and examples include silver, nickel, zinc, niobium, molybdenum, tin, tungsten, iridium, platinum, gold, and bismuth. These dissimilar metals can be used individually or in combination of two or more. From the viewpoint of imparting even higher conductivity to the conductive resin composition, the dissimilar metals are preferably silver, nickel, platinum, or gold, and are particularly preferably silver.

[0034] From the viewpoint of obtaining a resin composition with high conductivity and improved coating properties, it is preferable that the BET specific surface area of ​​the flake-shaped copper particles is within a predetermined range. Specifically, regardless of whether or not dissimilar metals are arranged on the surface of the flake-shaped copper particles, the BET specific surface area of ​​the flake-shaped copper particles is 1.0 m². ２ It is preferable that the amount be 1.2 m or more. ２ It is even more preferable that the amount be 1.5 m or more. ２ It is even more preferable that the amount is greater than or equal to 10.0 m² / g. Also, from a similar viewpoint, the BET specific surface area of ​​the flake-shaped copper particles is 10.0 m². ２ It is preferable that the amount be less than or equal to 9.0 m ２ It is even more preferable that it be less than or equal to 8.0 m ２ It is even more preferable that it be less than or equal to 5.0 m ２ It is even more preferable that it be less than or equal to 3.0 m ２ It is particularly preferable that the amount be less than or equal to / g. The method for measuring the BET specific surface area will be explained in the examples described later.

[0035] It is preferable that the flake-shaped copper particles have a bulk density within a predetermined range, regardless of whether or not dissimilar metals are arranged on their surface. This allows the flake-shaped copper particles, when added to a thermosetting resin and organic solvent to produce a conductive resin composition, to have an appropriate thixotropic property and good coating properties. Specifically, from the viewpoint of suppressing an excessive increase in the thixotropic property of the conductive resin composition before curing and improving the coating properties of the conductive resin composition, the tap density of the flake-shaped copper particles is preferably 0.5 g / cm³. ３ Preferably, it is 0.6 g / cm³ or more. ３ It is even more preferable that the value be greater than or equal to 0.7 g / cm³. ３ It is even more preferable that the above conditions are met. Furthermore, from the viewpoint of suppressing a decrease in the thixotropic properties of the conductive resin composition before curing and improving the coatability of the conductive resin composition, the tap density of flake-shaped copper particles should be 4.0 g / cm³. ３ The following is also acceptable: 3.0 g / cm³ ３ The following may also be true: 2.0 g / cm³ ３The following may also apply. Flake-shaped copper particles having such tap density can be suitably produced by the manufacturing method described later. In this specification, "tap density" refers to a value measured in accordance with JIS Z2512.

[0036] The volume cumulative particle size D of the flake-shaped copper powder, which is composed of flake-shaped copper particles, at a cumulative volume of 50% by laser diffraction scattering particle size distribution measurement. ５０ (Hereafter simply referred to as "particle size D") ５０ It is also preferable that the particle size D of the flake copper powder is within a predetermined range. This improves the fluidity of the flake copper particles, so that when a conductive resin composition is manufactured by adding flake copper particles to a thermosetting resin and an organic solvent, the flake copper particles can spread throughout the conductive resin composition more easily. As a result, the contact area of ​​the flake copper particles throughout the conductive resin composition increases, and the conductive resin composition can be given high conductivity. From the viewpoint of making the above advantages even more pronounced, the particle size D of the flake copper powder is preferable regardless of whether or not dissimilar metals are arranged on the surface of the flake copper particles. ５０ The particle size D of the flake copper powder is preferably 7.0 μm or larger, more preferably 8.0 μm or larger, and even more preferably 9.0 μm or larger. From a similar viewpoint, the particle size D of the flake copper powder ５０ The particle size is preferably 30.0 μm or less, more preferably 25.0 μm or less, even more preferably 20.0 μm or less, and even more preferably 15.0 μm or less. ５０ The method for calculating this will be explained in the examples described later.

[0037] Particle size D of flake copper powder ５０ In order to achieve the above range, it is preferable to adjust the degree of flake formation of the pulverized particles or to control the shape of the pulverized particles before flake formation in the manufacturing method described later.

[0038] Next, a preferred method for producing the flake-shaped copper particles of the present invention will be described. The production method of the present invention includes the steps of obtaining copper particles as a base material and flaking the copper particles. Each of these steps will be described below.

[0039] Preferably, the copper particles used as the base material are dendrite-shaped copper particles manufactured by an electrolytic method (hereinafter, these copper particles will also be conveniently referred to as "dendrite-shaped copper particles"). Dendrite-shaped copper particles are obtained by using an electrolyte containing a copper source, immersing the anode and cathode in the electrolyte, and performing electrolysis by applying a DC voltage between the two electrodes. The dendrite-shaped copper particles reduced by electrolysis are deposited on the cathode. The deposited dendrite-shaped copper particles are recovered by scraping them off the cathode.

[0040] In this manufacturing method, particle size D ５０ It is preferable to obtain dendrite-shaped copper particles of 5.0 μm or larger, more preferably 5.5 μm or larger, even more preferably 6.0 μm or larger, and even more preferably 10.0 μm or larger. ５０ It is preferable to obtain dendritic copper particles with a particle size of 25.0 μm or less, more preferably 23.0 μm or less, and even more preferably 21.0 μm or less. ５０ As long as the particle size D is within the aforementioned range, by using the dendritic copper particles and performing the crushing and flakeping operations described later, flake-shaped copper particles with the number of crystal grains within the aforementioned range can be successfully produced. ５０ Dendrite-shaped copper particles having the properties of copper ions can be obtained by setting the current density during electrolysis within a predetermined range or by setting the concentration of copper ions in the electrolyte within a predetermined range.

[0041] Once dendritic copper particles are obtained, they are then crushed. This yields crushed particles for the flake-making process. By flake-making these crushed particles as described later, flake-shaped copper particles with a number of crystal grains within the aforementioned range can be obtained. The inventors have found that the crystallinity of the resulting flake-shaped copper particles changes significantly depending on the conditions for crushing the dendritic copper particles and the conditions for flake-making the crushed particles. Based on this finding, they have discovered that by crushing and flake-making dendritic copper particles under predetermined conditions, flake-shaped copper particles with a number of crystal grains within the aforementioned range can be obtained. Obtaining flake-shaped copper particles with a number of crystal grains within the aforementioned range is unique to using crushed dendritic copper particles as the raw material. If other copper particles, such as those obtained by atomization or wet reduction, are used as the raw material, it is not easy to achieve a number of crystal grains within the aforementioned range.

[0042] The pulverization of dendritic copper particles can be carried out using either a dry or wet method, as long as the desired pulverized particles are obtained. In either case, it is preferable to employ a pulverization method that cuts the dendritic copper particles, which have a main shaft and branches branching from the main shaft, and minimizes deformation of the pulverized particles resulting from the cutting, as this makes it easier to obtain flake-shaped copper particles with the desired shape. As such a pulverization method, it is advantageous to use a dry method that does not use a pulverization media. One example of such a pulverization method is to dry-pulverize dendritic copper particles using a rotating cutting blade (e.g., a stirring blade). In this pulverization method, the dendritic copper particles are cut by the rotating cutting blade to become pulverized particles. In this case, by appropriately controlling the rotation speed of the cutting blade, excessive external force on the pulverized particles is suppressed, and deformation of the pulverized particles is minimized. To pulverize dendritic copper particles with 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 cited. In this pulverization method, the dendritic copper particles collide with each other due to the jet stream, thereby cutting them and forming pulverized particles. In this case, by arranging multiple pulverization nozzles at positions that evenly divide the inner circumference of the pulverizer, and by using one or more pulverization nozzles as nozzles that supply dendritic copper particles, a concentrically swirling jet stream can be created inside the pulverizer. By controlling the swirling jet stream, the probability of dendritic copper particles colliding with the inner wall of the pulverizer can be reduced, and the dendritic copper particles can be made to collide with each other efficiently. As a result, excessive external force on the pulverized particles is suppressed, and deformation of the pulverized particles is suppressed as much as possible. To pulverize dendritic copper particles with a jet stream, for example, a jet stream type pulverizer can be used, but it is not limited to this. From the viewpoint of successfully producing flake-shaped copper particles with a number of crystal grains within the aforementioned range, it is preferable to use a dry pulverization method using a swirling jet stream.

[0043] When dry pulverizing dendritic copper particles with a rotating cutting blade, various conditions such as the number, shape, size, and rotation speed of the cutting blades, and when dry pulverizing dendritic copper particles with a jet stream, various conditions such as the pulverizing pressure and processing speed should be as described above, so as to cut the dendritic copper particles and cause as little deformation as possible to the pulverized particles resulting from the cutting.

[0044] Regardless of which method is adopted, the particle size D of the crushed particles ５０ It is preferable to pulverize the dendritic copper particles so that the grain size is in the range of 2.0 μm to 15.0 μm, from the viewpoint of successfully producing flake-shaped copper particles with a grain size within the aforementioned range by the flake-forming operation described later. It is also preferable to pulverize the dendritic copper particles so that the average value of the long axis length L of the pulverized particles is 2.0 μm to 15.0 μm, and the average value of the short axis length W is 1.0 μm to 7.5 μm.

[0045] Once the pulverized particles are obtained, they are then flaked. For flaking, a medium-agitated mill such as a bead mill, ball mill, or attritor can be used. Prior to flaking using a medium-agitated mill, the pulverized particles are dispersed in a liquid medium to prepare a dispersion. Examples of liquid mediums used to prepare the dispersion include water and organic solvents. A mixed solvent of water and an organic solvent can also be used. Examples of organic solvents include lower monoalcohols having 1 to 4 carbon atoms such as methanol and ethanol; lower polyhydric alcohols having 1 to 4 carbon atoms such as ethylene glycol; lower carboxylic acids having 1 to 4 carbon atoms; and lower amines having 1 to 4 carbon atoms. These organic solvents can be used individually or in combination of two or more. Of these liquid mediums, the use of an organic solvent is preferable because it improves the dispersibility of the pulverized particles in the dispersion and improves the stability of the quality when processed with a medium-agitated mill. In particular, the use of lower alcohols such as methanol is preferable because the medium volatilizes easily and does not easily remain on the desired flake-shaped copper particles.

[0046] From the viewpoint of productivity and the suppression of the generation of coarse particles, the concentration of pulverized particles in the dispersion is preferably 5.0% by mass or more, more preferably 10.0% by mass or more, and even more preferably 15.0% by mass or more, relative to the mass of the dispersion (total mass of pulverized particles and solvent). Similarly, from the viewpoint of productivity and the suppression of the generation of coarse particles, the concentration of pulverized particles in the dispersion is preferably 50.0% by mass or less, more preferably 45.0% by mass or less, even more preferably 40.0% by mass or less, and even more preferably 35.0% by mass or less.

[0047] To prepare a dispersion, simply mix the ground particles with a liquid medium. In some cases, a dispersion may be prepared using a stirring dispersion device. Examples of such devices include a fluid mill and the T.K. Filmix® manufactured by Primix Corporation.

[0048] In the manufacturing method of the present invention, it is preferable to include a first complexing agent in the dispersion. The action of the first complexing agent effectively suppresses the aggregation of pulverized particles during flake formation. Furthermore, oxides present on the surface of the pulverized particles are removed by the first complexing agent, and when dissimilar metals are placed on the surface of the flake-shaped copper particles, the dissimilar metals can be thinly and uniformly coated. From this viewpoint, the concentration of the first complexing agent in the dispersion is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, based on the mass of the dispersion (total mass of pulverized particles and solvent), provided that the concentration of pulverized particles in the dispersion is within the aforementioned range. Furthermore, from a similar viewpoint, the concentration of the first complexing agent contained in the dispersion is preferably 7.0% by mass or less, more preferably 6.0% by mass or less, even more preferably 5.0% by mass or less, even more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less, provided that the concentration of pulverized particles in the dispersion is within the aforementioned range.

[0049] The first complexing agent may be monodentate or multidentate, such as didentate, tridentate, and tetradentate. From the viewpoint of high coordination with copper, examples of the first complexing agent include citric acid, ascorbic acid, and ethylenediaminetetraacetate. These complexing agents can be used individually or in combination of two or more. Among these complexing agents, ethylenediaminetetraacetate is particularly preferred from the viewpoint of effectively suppressing aggregation of the base material in the process of flake-forming the pulverized particles and from the viewpoint of suppressing oxidation of the pulverized particles.

[0050] In the process of flake-forming the pulverized particles, the dispersion and the pulverizing media are placed in a media stirring mill and mixed and stirred. Various types of media stirring mills can be used. From the viewpoint of successfully producing flake-shaped copper particles with a number of crystal grains within the aforementioned range, it is preferable to use a device that can apply relatively large stress to the pulverized particles in the dispersion. Such a device is, for example, a media stirring mill with a relatively wide gap between the rotor and the screen. Conventionally, when a device with a narrow gap between the rotor and the screen was used, stress was applied not only to the pulverized particles but also to the screen, and it was not possible to apply large enough stress to the pulverized particles. Specifically, the goal is to cause the pulverized particles to collide with each other by applying stress to them, thereby promoting flake formation. However, when the gap between the rotor and the screen is narrow, the pulverized particles collide with the screen, which hinders collisions between the pulverized particles. The inventors were the first to discover that in a device with a relatively wide gap between the rotor and the screen, stress is more easily applied to the pulverized particles than to the screen, resulting in smaller copper grain sizes compared to before processing with the device, and effectively producing flake-shaped copper particles with a grain count within the aforementioned range. Alternatively, as an example of the aforementioned device, a device without a screen can be cited. This device also effectively applies stress to the pulverized particles, so it is possible to effectively produce flake-shaped copper particles with a grain count within the aforementioned range. In either case, the diameter of the pulverizing media is preferably 0.05 mm or more and 1.00 mm or less. The material of the pulverizing media is generally zirconia and alumina. The operating time, rotation speed, and number of passes of the media stirring mill device should be adjusted as appropriate to obtain the desired flake-shaped copper particles.

[0051] Regardless of which method is adopted, the particle size D of the flake-shaped copper particles ５０From the viewpoint of successfully producing flake-shaped copper particles with a number of crystal grains within the aforementioned range, it is preferable to flake the pulverized particles so that the grain size is in the range of 7.0 μm to 30.0 μm. It is also preferable to flake the pulverized particles so that the average value of the long axis length L of the flake-shaped copper particles is 8.0 μm to 20.0 μm, and the average value of the short axis length W is 3.0 μm to 12.0 μm.

[0052] In this way, flake-shaped copper particles of the present invention are obtained. Flake-shaped copper particles can be obtained by washing and drying the solid components obtained by solid-liquid separation of the dispersion. Alternatively, before solid-liquid separation of the dispersion, a dissimilar metal may be placed on at least a portion of the surface of the flake-shaped copper particles as needed. In the step of placing the dissimilar metal, the copper particles deformed into a flake shape are treated with an aqueous solution containing ions of the dissimilar metal and a second complexing agent. This treatment can be carried out by either treatment 1 or treatment 2 below. Alternatively, treatment 2 may be performed after treatment 1. [Treatment 1] If the dissimilar metal is an element with a lower ionization tendency than copper, the ions of the dissimilar metal and the flake-shaped copper particles are brought into contact in water to perform displacement plating and precipitate the dissimilar metal on the surface of the flake-shaped copper particles. Precursor particles are obtained by this precipitation. [Process 2] The flake-shaped copper particles or the precursor particles obtained in Process 1 are brought into contact with ions of a different metal and a reducing agent for the ions of the different metal in water to further precipitate the different metal on the surface of the precursor particles.

[0053] The dissimilar metal ions used in processes 1 and 2 can be generated from dissimilar metal compounds that serve as dissimilar metal sources. Examples of such compounds include water-soluble silver compounds such as silver nitrate, water-soluble nickel compounds, water-soluble zinc compounds, water-soluble niobium compounds, water-soluble molybdenum compounds, water-soluble tin compounds, water-soluble tungsten compounds, water-soluble iridium compounds, water-soluble platinum compounds, water-soluble gold compounds, and water-soluble bismuth compounds. From the viewpoint of preserving a desirable amount of dissimilar metal on the surface of flake-shaped copper particles, the ion concentration of the dissimilar metal in water is preferably set to 0.01 mol / L or higher, and more preferably to 0.04 mol / L or higher. Similarly, from the same viewpoint, the ion concentration of the dissimilar metal in water is preferably set to 10 mol / L or lower, and more preferably to 2.0 mol / L or lower.

[0054] In process 1, from the viewpoint of preserving a desirable amount of dissimilar metals on the surface of the flake-shaped copper particles, the amount of flake-shaped copper particles in the water is preferably 1 g / L or more, and more preferably 50 g / L or more. Also, from the same viewpoint, the amount of flake-shaped copper particles in the water is preferably 1000 g / L or less, and more preferably 500 g / L or less.

[0055] In process 1, there are no particular restrictions on the order in which flake copper particles and ions of dissimilar metals are added. For example, flake copper particles and ions of dissimilar metals can be added to water simultaneously. From the viewpoint of ease of controlling silver deposition by displacement plating, it is preferable to prepare a solution by pre-dispersing flake copper particles in water, and then add a compound of dissimilar metals that will serve as a source of dissimilar metals to this solution. In this case, the solution may be at room temperature, or in a temperature range of 0°C to 80°C.

[0056] Prior to adding the compound of dissimilar metals, it is preferable to add a second complexing agent to the solution to control the reduction of the dissimilar metals. Examples of the second complexing agent include ethylenediaminetetraacetate, triethylenediamine, iminodiacetic acid and its salts, citric acid and its salts, and tartaric acid and its salts.

[0057] The first complexing agent described above and the second complexing agent may be of the same type or different types, but from the viewpoint of matching the stability constants of the complex, it is preferable that the first complexing agent and the second complexing agent are of the same type. In particular, from the viewpoint of effectively suppressing the aggregation of copper particles in the flake formation process and from the viewpoint of thinly and uniformly coating the dissimilar metals in the process of arranging the dissimilar metals, it is preferable that both the first complexing agent and the second complexing agent are ethylenediaminetetraacetate salts.

[0058] In process 1, it is preferable to add the dissimilar metal compound in aqueous solution. This aqueous solution can be added all at once to the solution, or it can be added continuously or discontinuously over a predetermined time. From the viewpoint of easily controlling the displacement plating reaction, it is preferable to add the aqueous solution of the dissimilar metal compound to the dispersion over a predetermined time.

[0059] In process 1, it is preferable to irradiate the solution with ultrasound before or simultaneously with the addition of the compound of dissimilar metals. Irradiation with ultrasound promotes the dispersion of flake-shaped copper particles in the solution, making it easier for the flake-shaped copper particles to be uniformly coated by the dissimilar metals. While any irradiation with ultrasound has a certain effect, the frequency is preferably 200 kHz or less, and more preferably 45 kHz or less. A lower frequency limit of 10 kHz is sufficient.

[0060] In process 1, a dissimilar metal is deposited on the surface of the flake-shaped copper particles by the displacement plating described above, thereby obtaining precursor particles. From the viewpoint of forming a thin and uniform coating of dissimilar metals, the amount of dissimilar metal deposited in the precursor particles is preferably 0.1% by mass or more of the dissimilar metal content in the final flake-shaped copper particles on which the dissimilar metal is arranged on the surface, and more preferably 1% by mass or more. Also, from a similar viewpoint, the amount of dissimilar metal deposited in the precursor particles is preferably 50% by mass or less of the dissimilar metal content in the flake-shaped copper particles on which the dissimilar metal is arranged on the surface, and more preferably 10% by mass or less.

[0061] Next, we will describe process 2. In process 2, ions of a different metal and a reducing agent of a different metal are added to a solution containing flake-shaped copper particles or precursor particles obtained in process 1. In this case, the precursor particles obtained in process 1 may be separated into solid and liquid phases and then dispersed in water to form a solution, or the solution of precursor particles obtained in process 1 may be used directly in process 2. In the latter case, the ions of the different metal added in process 1 may or may not remain in the solution.

[0062] In process 2, the ions of the dissimilar metals added are generated from a compound of the dissimilar metals, as in process 1. It is preferable to add the compound of the dissimilar metals to the solution in aqueous solution form. The concentration of the dissimilar metal ions in the solution is preferably 0.01 mol / L or more and 10 mol / L or less, and more preferably 0.1 mol / L or more and 2.0 mol / L or less. It is preferable to add a solution containing dissimilar metal ions at a concentration within this range in an amount of 0.1 parts by mass or more and 55 parts by mass, particularly 1 part by mass or more and 25 parts by mass, per 100 parts by mass of precursor particles in the solution containing precursor particles at a concentration of 1 g / L or more and 1000 g / L or less, particularly 50 g / L or more and 500 g / L or less, since this allows for the formation of a thin and uniform coating of the dissimilar metals.

[0063] In process 2, the reducing agent to be added should have a reducing power sufficient to simultaneously carry out displacement plating and reduction plating of dissimilar metals. By using such a reducing agent, a thin and uniform coating of dissimilar metals can be successfully formed. If a reducing agent with strong reducing power is used, the reduction plating will proceed unilaterally, making it difficult to form a coating of dissimilar metals with the desired structure. On the other hand, if a reducing agent with weak reducing power is used, the reduction plating of the dissimilar metal ions will not proceed easily, and as a result, it will also be difficult to form a coating of dissimilar metals with the desired structure. From the above viewpoint, it is preferable to use an organic reducing agent that exhibits acidity when dissolved in water. Specifically, these include formic acid, oxalic acid, L-ascorbic acid, erythorbic acid, and formaldehyde. These organic reducing agents can be used individually or in combination of two or more. Among these organic reducing agents, it is preferable to use L-ascorbic acid. In this context, "acidic" means that an aqueous solution prepared by dissolving 0.1 moles of an organic reducing agent in 1000 g of water exhibits a pH of 1 to 6 at 25°C.

[0064] From the viewpoint of facilitating simultaneous displacement plating and reduction plating of dissimilar metals, the amount of reducing agent added is preferably 0.5 equivalents or more relative to the ions of the dissimilar metals in the solution to which it is added, and more preferably 1.0 equivalent or more. Similarly, from the same viewpoint, the amount of reducing agent added is preferably 5.0 equivalents or less relative to the ions of the dissimilar metals in the solution to which it is added, and more preferably 2.0 equivalents or less.

[0065] There are no particular restrictions on the order in which the reducing agent and dissimilar metal ions are added to the solution containing precursor particles. From the viewpoint of controlling the reduction of dissimilar metal ions and forming a thin and uniform coating of dissimilar metals, it is preferable to add the reducing agent to the solution first, followed by the addition of dissimilar metal ions. The dissimilar metal compound that serves as the dissimilar metal source can be added to the solution all at once, or it can be added continuously or discontinuously over a predetermined time. From the viewpoint of easily controlling the reduction of dissimilar metal ions, it is preferable to add the dissimilar metal compound to the solution in aqueous solution form over a predetermined time.

[0066] In process 2, when disparate plating and reduction plating of dissimilar metals are carried out simultaneously, the dispersion may be left at room temperature, or it may be heated to a temperature range of 0°C to 80°C.

[0067] In process 2, as in process 1, it is preferable to irradiate the solution with ultrasound before or simultaneously with the addition of the reducing agent. Ultrasound irradiation promotes the dispersion of precursor particles in the solution, making it easier for the precursor particles to be uniformly coated with dissimilar metals. While any irradiation with ultrasound will have a certain effect, a frequency of 200 kHz or less is particularly preferable, and 45 kHz or less is more preferable. A lower frequency limit of 10 kHz is sufficient.

[0068] Once dissimilar metals are arranged on the surface of the flake-shaped copper particles in this manner, the flake-shaped copper particles are separated and removed from the solution by solid-liquid separation methods such as vacuum dehydration, filter pressing, centrifugation, and ultrafiltration, and then washed with a solvent or the like. After washing, surface treatment may be applied as needed for convenience in handling the particles. 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, and polymer dispersants. After washing, the particles can be subjected to solid-liquid separation and dried to produce the desired flake-shaped copper particles.

[0069] The flake-shaped copper particles of the present invention obtained in this manner are suitably used in applications where they are 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 flake-shaped copper particles of the present invention into a thermosetting resin. By curing this conductive resin composition, a conductive film or a conductive sheet can be obtained, for example. 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 individually or in combination of two or more. These thermosetting resins should be appropriately selected according to the specific application of the cured product. In addition to the flake-shaped copper particles and thermosetting resin of the present invention, the conductive resin composition may also contain a curing agent for the thermosetting resin and an organic solvent.

[0070] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments.

[0071] Further relating to the above embodiments, flake-shaped copper particles and conductive resin compositions containing them are disclosed. [1] Flake-shaped copper particles wherein the number of crystal grains measured by observing the cross-section of the flake-shaped copper particles by electron beam backscatter diffraction is 150 or more and 2000 or less on average. [2] Flake-shaped copper particles wherein, in a plan view, when the longest line segment crossing the particle is defined as the major axis and the perpendicular bisector to the major axis is defined as the minor axis, the number of crystal grains in a plan view is the product of the length of the major axis and the length of the minor axis (μm ２ ) 4.5 particles / μm ２ 40.0 pieces / μm or more ２The following are flake-shaped copper particles: [3] Flake-shaped copper particles according to [1] or [2], wherein the crystal grain size is 0.2 μm or more and 1.3 μm or less. [4] Flake-shaped copper particles according to any one of [1] to [3], wherein, in a plan view, the average size of the crystal grains located in the peripheral region is smaller than the average size of the crystal grains located in the central region of the particle. [5] Flake-shaped copper particles according to [4], wherein the value R defined by the following formula (1) is 0.10 or more and 0.80 or less. R = (N1 / S1) / (N2 / S2) (1) In equation (1), N1 is the number of crystal grains located in the central region in a plan view, S1 is the total area of ​​the crystal grains located in the central region in a plan view, N2 is the number of crystal grains located in the peripheral region in a plan view, S2 is the total area of ​​the crystal grains located in the peripheral region in a plan view, the central region is a circular region centered on the concentration centroid of the flake-shaped copper particles and having a diameter equal to the length obtained by dividing the minimum Ferret diameter of the flake-shaped copper particles into four equal parts, and the peripheral region is the region of the flake-shaped copper particles other than the central region. [6] Flake-shaped copper particles according to any one of [1] to [5], wherein a dissimilar metal other than copper is arranged on the surface.

[0072] [7] The flake-shaped copper particles according to [6], wherein the dissimilar metal is silver. [8] The flake-shaped copper particles according to [7], wherein the a* value in the L*a*b* color system is 0.0 or more and 8.2 or less. [9] The flake-shaped copper particles according to any one of [1] to [8], wherein the aspect ratio defined by the long axis length / short axis length is 1.05 or more and 4.00 or less.

[10] The flake-shaped copper particles according to [9], wherein the long axis length is 8.0 μm or more and 20.0 μm or less, and the short axis length is 3.0 μm or more and 12.0 μm or less.

[11] The flake-shaped copper particles according to any one of [1] to

[10] , wherein the thickness is 0.05 μm or more and 0.40 μm or less.

[12] The BET specific surface area is 1.0 m ２ / g or more 10.0m ２ Flake-shaped copper particles according to any one of [1] to

[11] , having a concentration of less than or equal to / g.

[13] A conductive resin composition comprising a resin and flake-shaped copper particles according to any one of [1] to

[12] .

[0073] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0074] [Example 1] (1) Production of dendritic copper particles Size: 2.5m x 1.1m x 1.5m (approximately 4m ３ Nine SUS cathodes and insoluble anodes (DSE® (manufactured by Denora Permelec Co., Ltd.), each measuring 1.0 m x 1.0 m) were suspended in an electrolytic cell with a distance of 5 cm between electrodes. Copper sulfate solution was circulated at 30 L / min as the electrolyte, immersing the anodes and cathodes in the electrolyte. A direct current was then passed through them to perform electrolysis, depositing dendritic copper particles on the cathode surface. The deposited dendritic copper particles were scraped off and collected. Particle size D of the dendritic copper particles ５０ The size was 16.2 μm. At this time, the copper concentration of the circulating electrolyte was set to 10 g / L, and sulfuric acid (H ２ SO ４ The concentration was set to 100 g / L, the chlorine concentration to 5 mg / L, and the current density to 800 A / m². ２ The electrolyte temperature was adjusted to 30°C and electrolysis was performed 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 kept lower than the copper ion concentration in the electrolyte at the bottom of the electrolytic cell.

[0075] (2) Grinding of dendrite copper particles The dendrite copper particles were ground dry for 10 minutes using a jet-stream type grinder to obtain ground particles. Particle size D of the ground particles ５０ The particle size D was 4.9 μm. ５０ Table 1 also shows the average values ​​of the long axis length L and short axis length W of the crushed particles.

[0076] (3) A methanol solution of the pulverized particles was prepared by mixing 3 kg of flaked pulverized particles, 9 kg of methanol, and 0.1 kg of disodium ethylenediaminetetraacetate (hereinafter also referred to as "EDTA2Na"). 12.1 kg of this solution was placed in an Ultra Apex Mill UAM, a bead mill manufactured by Hiroshima Metal & Machinery Co., Ltd., which does not use a screen, and 5.0 kg of zirconia beads with a diameter of 0.20 mm were added. The bead mill was operated for 125 minutes to flake the pulverized particles. After that, the solution and beads were separated by filtration, and the solution was allowed to stand to settle the flake copper particles. The supernatant was removed and the flake copper particles were collected by filtration. The flake copper particles were then washed with water, and subsequently washed twice with methanol.

[0077] (4) Arrangement of dissimilar metals 100 g of flake-shaped copper particles were added to 500 mL of pure water heated to 40°C to form a solution. While stirring this solution, 4.3 g of EDTA2Na was added and dissolved. Further, 48 mL of a 0.44 mol / L silver nitrate aqueous solution was continuously added to this solution for 6 minutes to perform displacement plating, depositing silver on the surface of the flake-shaped copper particles to obtain precursor particles. During this time, the solution was irradiated with ultrasound (100 W, 28 kHz). Next, L-ascorbic acid as a reducing agent was added to the solution and dissolved. Furthermore, 192 mL of a 0.44 mol / L silver nitrate aqueous solution was continuously added to the solution for 24 minutes. This allowed reduction plating and displacement plating to proceed simultaneously, further depositing silver on the surface of the precursor particles to obtain the desired flake-shaped copper particles. Ultrasound irradiation was continued during this time.

[0078] [Example 2] In Example 1, when flakeming the pulverized particles, the Star Mill® LMZ bead mill manufactured by Ashizawa Finetech Co., Ltd. was used instead of the Ultra Apex Mill UAM. The Star Mill® LMZ was pre-adjusted to increase the distance between the screen and the rotor. 4.85 kg of zirconia beads with a diameter of 0.2 mm were placed in the mill and the bead mill was operated for 180 minutes. Except for this, the desired flake-shaped copper particles were obtained in the same manner as in Example 1. Note that the particle size D of the pulverized particles ５０The average values ​​of the major axis length L and minor axis length W are shown in Table 1.

[0079] [Comparative Example 1] In Example 2, when flakeming the pulverized particles, the amount of EDTA2Na added was 1.0 kg, and the spacing between the screen and rotor in the Star Mill (registered trademark) LMZ was pre-adjusted to the normal setting. Other than this, the desired flake-shaped copper particles were obtained in the same manner as in Example 1. Note that the particle size D of the pulverized particles was... ５０ The average values ​​of the major axis length L and minor axis length W are shown in Table 1.

[0080] [Evaluation] For the flake-shaped copper particles obtained in the examples and comparative examples, the average values ​​of the major axis length L and minor axis length W, the aspect ratio, and the thickness were calculated according to the method described above. For the flake-shaped copper particles obtained in the examples and comparative examples, the average value of the number of copper crystal grains, the number of copper crystal grains in a plan view, the copper crystal grain size, L* value, a* value and b* value, BET specific surface area, tap density, and particle size D were calculated according to the method described below. ５０ The content of dissimilar metals and the content of dissimilar metals per unit BET specific surface area were measured. Furthermore, the value R was calculated according to the method described below. The resistivity of the conductive resin composition was measured for the flake-shaped copper particles obtained in the examples and comparative examples according to the method described below. These results are shown in Table 2.

[0081] [Average number of copper crystal grains] The average number of copper crystal grains was measured using the following method. For the measurement, an FE gun type scanning electron microscope (SUPRA 55VP, manufactured by Carl Zeiss Co., Ltd.) equipped with an EBSD evaluation device (OIM Data Collection Ver. 7.2.0, manufactured by TSL Solutions Co., Ltd.) and its attached EBSD analyzer were used. First, conductive carbon paste was applied to a metal foil, flake copper particles were sprinkled on it, and after drying, excess powder was shaken off to fix the particles in place. Using a cross-section polisher (IB-19510CP or IB-19520CCP, both manufactured by JEOL Ltd.), ion milling in accordance with the planar milling method was performed on the metal foil sprinkled with flake copper particles to prepare a sample in which silver and other phases other than the copper phase arranged on the surface of the flake copper particles were removed. Subsequently, following the EBSD method, the number of copper crystal grains was measured on the exposed main surface of each flake-shaped copper particle in the sample. Ten particles that were flatly fixed to the metal foil and conductive carbon paste were extracted from the SEM image, and the number of copper crystal grains was measured for these flake-shaped copper particles to determine the average value. This average value was taken as the average number of copper crystal grains.

[0082] The WD value used to measure the number of crystal grains was set to 15 ± 1 mm. With "Background Subtraction," "Normalize Intensity Histogram," and "Dynamic Background Subtraction" checked in "Image Processing," an EBSD pattern was collected from an arbitrary point at the observation site using "Capture Pattern" of the EBSD evaluation device. After selecting "Cu" from "Phase," the WD value was adjusted under the conditions that the "Fit" value in "Solutions" was within 1.5 and the "CI" value was greater than 0.1.

[0083] [Number of copper crystal grains in plan view] Samples were prepared in the same manner as for the "average number of copper crystal grains," and the number of copper crystal grains was measured according to the EBSD method. Specifically, 10 particles that were flatly fixed to the metal foil and conductive carbon paste were extracted from the SEM image, and the number of copper crystal grains per particle, the length of the longest line segment crossing the particle (the major axis), and the length of the line segment crossing the particle (the perpendicular bisector of the major axis) were measured. The product of the major axis length and the minor axis length (μm) ２ The number of crystal grains (individual grains) for each of the following was calculated, and the average value of 10 values ​​was obtained. This value was taken as the number of copper crystal grains in a plan view. The measurement conditions were the same as those for the "average number of copper crystal grains".

[0084] [Copper Crystal Grain Size] The copper crystal grain size was measured using the following method. For the measurement, data from the sample cross-section obtained by measuring the average number of copper crystal grains as 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) (Grain Size (Average Area)) using "All data" from "Grain Size Quick Chart" in the 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 copper crystal grains in the flake-shaped copper particles of the present invention.

[0085] In measuring the size of copper crystal grains, a grain boundary was considered to be a difference in orientation of 5° or more. However, since copper has a face-centered cubic crystal structure, twin grain boundaries were considered, and the orientation difference at a given grain boundary was expressed in terms of the axis of rotation and the angle of rotation. When the axis of rotation was represented by <111> and the angle of rotation was 60±1°, and when the axis of rotation was represented by <110> and the angle of rotation was 38.94±1°, these were not considered grain boundaries. The scanning electron microscope conditions during observation were: acceleration voltage: 15kV, aperture diameter: 60μm, High Current mode, and sample angle: 70°. The observation magnification, measurement area, and step size may be changed as appropriate depending on the size of the crystal grains.

[0086] <Filtering> When measuring the cross-section of flake-shaped copper particles using the prepared sample as described above, not only copper crystal grains but also silver crystal grains, which are a different metal, are detected. Therefore, filtering was performed under the following conditions to allow observation of only 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" analysis menu of the EBSD analysis program, and then the copper crystal grain boundaries were detected. The filtering conditions (conditions (1) to (4) above) for each sample in the examples and comparative examples are shown in Table 3 below. Specifically, (1) "CI" was set to "0.05", and the target particles in the EBSD image and SEM image were confirmed during processing (1). In this case, for samples in which silver crystal grains were still observed in the EBSD and SEM images, the "CI" value was kept at "0.05". On the other hand, for samples in which no silver crystal grains were observed (i.e., samples that had been excessively filtered), the "CI" value was changed to "0.03". In addition, during processing (2), the contrast of the SEM image was checked along with the EBSD image, and the value was set to "2" in order to remove only crystal grains other than those of the copper phase. In addition, after processing (1) and processing (2), if crystal grains other than those of the copper phase were present, the contrast of the SEM image was checked along with the EBSD image, and (3) the "IQ" value was set to >4.0 × 10 ６" to ">5.0 x 10 ６ Set within the range of ". In addition, if crystal grains other than the copper phase are present after processing (1), processing (2), and processing (3), check the contrast of the SEM image along with the EBSD image, and set (4) "Grain Aspect ratio" to "0.6" and perform the processing. Note that "-" in Table 3 indicates that the copper crystal grains could be sufficiently observed and subsequent filtering was not necessary, so the filtering was not performed.

[0087] [Number of crystal grains located in the "central region" and "peripheral region" of the particle, and the total area of ​​the crystal grains, value R] For the measurement, the sample cross-section data obtained from the measurement of the average number of copper crystal grains as described above was used. First, the sample cross-section data was read using the EBSD analysis program (OIM Analysis Ver. 7.3.1, manufactured by TSL Solutions Co., Ltd.), and after opening an arbitrary Map, the copper crystal grains were processed in grayscale to convert their color by setting "Grayscale" to "Grain Size" and "Color" to "none" in "Map Properties". At this time, the items that can be edited in "Edit" of "Grayscale" were not changed. Filtering was also performed in the same way as "<Filtering>" in "Copper Crystal Grain Size". Next, the pixel size of the image to be captured was calculated. The "SummaryView" was opened from the "Data Set" of the data read by the EBSD analysis program described above, and the "X" and "Y" values ​​displayed in "Dimensions" were read. The "Width" and "Height" values ​​displayed when the aforementioned grayscale processed "Map" was copied were read. Then, the pixel size was calculated by dividing the "X" value in "Dimensions" by "Width" and the "Y" value in "Dimensions" by "Height". Next, the grayscale processed crystal grain mapping image was loaded into image analysis software (Dragonfly, manufactured by Comet Technologies Canada Inc.), and the pixel size calculated using the method described above was entered into "Image Spacing". At this time, the value of Z was set to 1. Subsequently, the loaded image was processed using "New Gray Level Multi-ROI" from "Data Properties and Setting Panel" to create "ROI: A," which assigned grayscale as its class. This image was then processed using "Refine Region of Interest / Remove Empty Labels" and "Split Non-Connected Labels," and the LUT was adjusted to create "ROI: B," which separated individual crystal grains.Next, the diameter and center position were calculated, and the central and peripheral regions were determined. Specifically, the "New ROI" process was first applied to "ROI: B," and then "ROI: C" was created by combining them using the "Create Multi-ROI from ROI" process. "Weighted Center of Mass X" and "Weighted Center of Mass Y" were calculated from "ROI: C" using "Compute Measurement," and the coordinates indicated by these "X" and "Y" values ​​were used as the density centroid position. In addition, the minimum Ferret diameter RF was calculated from "2D Min Ferret" in "Compute Measurement" for "ROI: C." The diameter was defined as the length obtained by dividing the Ferret diameter RF into four equal parts (RF / 4). Next, a central region was created. A "Cylinder" was created from the "Tool Panel," with the concentration centroid as the center and the length obtained by dividing the Ferret diameter into four equal parts (RF / 4) as the diameter. "ROI:D" was created by applying the "Add ROI" process to this. "ROI:B" and "ROI:D" were selected, and the central region was cut out by applying the "Keep Intersected" process. The number of crystal grains located in the central region was defined as N1, and the total area of ​​the crystal grains located in the central region was defined as S1. Furthermore, the peripheral region was cut out by applying the "Remove Intersected" process. The number of crystal grains located in the peripheral region was defined as N2, and the total area of ​​the crystal grains located in the peripheral region was defined as S2. Then, the value R was calculated based on the aforementioned equation (1).

[0088] [L* value, a* value, and b* value] The L* value, a* value, and b* value were measured using a colorimeter (CR-400) manufactured by Konica Minolta, Inc., which uses the diffuse illumination vertical light receiving method described in JIS Z 8722 (conforms to geometric condition c / including specular reflection).

[0089] [BET specific surface area] Measured using the BET single-point method with a monosorb manufactured by Yuasa Ionics Co., Ltd.

[0090] [Tap Density] Tap density was measured using a tapping machine (model: KSR-406, manufactured by Kuramochi Kagaku Kikai Seisakusho Co., Ltd.). Specifically, a volume of 150 cm³ was used. ３120g of flake-shaped copper particles were placed in a graduated cylinder. The tap stroke was set to 4cm and the number of taps to 400 for measurement.

[0091] [Particle size D ５０ Using an automated sample feeder for laser diffraction particle size distribution analyzers (Microtrac SDC, manufactured by Microtrac-Bell Corporation), flake copper particles were placed in a solvent mixture of 20% ethanol and 0.1% hexametaphosphoric acid. After irradiating with 40W ultrasound at a flow rate of 40% for 90 seconds, the particle size distribution was measured using the Microtrac-Bell Corporation laser diffraction particle size distribution analyzer "MT3000II," and the particle size D was determined from the obtained volume-based particle size distribution chart. ５０ The particle size D was measured. ５０ When measuring the particle size D, the water-soluble solvent was passed through a 60 μm filter, the "solvent refractive index" was set to 1.33, the particle permeability condition to "permeation", the measurement range to 0.243 μm to 704.0 μm, and the measurement time to 30 seconds. The average of two measurements was taken. ５０ That's what I decided.

[0092] [Dissimilar metal content in flake copper particles] One g of flake copper particles obtained in the examples and comparative examples was completely dissolved in a 1:1 nitric acid solution. The silver content (%) was then calculated by titration with sodium chloride.

[0093] [Dissimilar metal content per BET specific surface area] The silver content per BET specific surface area was calculated from the dissimilar metal content measured by the method described above and the BET specific surface area measured by the method described above.

[0094] [Resistivity of Conductive Resin Compositions] Conductive resin compositions were prepared using flake copper particles obtained in the examples and comparative examples. Specifically, a conductive resin composition consisting of a paste was prepared by mixing flake copper particles, epoxy resin, 2-methylimidazole, and dimethylacetamide. Each conductive resin composition was prepared so that the amount of flake copper particles was 90% by mass. The mass ratio of epoxy resin, dimethylacetamide, and 2-methylimidazole in each conductive resin composition was 49:40:1. Next, the paste was coated onto a glass plate. A bar coater with a width of 200 mm was used for coating. The gap was set to 100 μm. The formed coating film was dried and cured in an air-heated hot air drying oven at 110°C for 60 minutes to obtain a conductive film with a thickness of 80 μm. The resistance value of the conductive film was measured using a resistivity meter (Mitsubishi Chemical MCP-T600) by the four-probe method.

[0095]

[0096]

[0097]

[0098] As is clear from the results shown in Table 2, the flake-shaped copper particles obtained in the example have a lower resistivity in the conductive resin composition compared to the flake-shaped copper particles obtained in the comparative example.

[0099] According to the present invention, flake-shaped copper particles with even greater conductivity than those of the prior art are provided.

Claims

1. Flake-shaped copper particles, wherein the number of crystal grains measured by observing the cross-section of the flake-shaped copper particles using electron beam backscatter diffraction is 150 or more and 2000 or less on average.

2. In the case of flake-shaped copper particles, when the longest line segment crossing the particle in a plan view is defined as the major axis and the perpendicular bisector of the major axis is defined as the minor axis, the number of crystal grains in a plan view is equal to the product of the major axis length and the minor axis length (μm). ２ ) 4.5 particles / μm ２ 40.0 pieces / μm or more ２ The following are flake-shaped copper particles.

3. Flake-like copper particles according to claim 1 or 2, wherein the crystal grain size is 0.2 μm or more and 1.3 μm or less.

4. The flake-shaped copper particles according to claim 1 or 2, wherein, in a plan view, the average size of the crystal grains located in the peripheral region is smaller than the average size of the crystal grains located in the central region of the particles.

5. The flake-shaped copper particles according to claim 4, wherein the value R defined by the following formula (1) is 0.10 or more and 0.80 or less. R = (N1 / S1) / (N2 / S2) (1) In formula (1), N1 is the number of crystal grains located in the central region in a plan view, S1 is the total area of ​​the crystal grains located in the central region in a plan view, N2 is the number of crystal grains located in the peripheral region in a plan view, S2 is the total area of ​​the crystal grains located in the peripheral region in a plan view, the central region is a circular region centered on the concentration centroid of the flake-shaped copper particles and having a diameter equal to the length obtained by dividing the minimum Ferret diameter of the flake-shaped copper particles into four equal parts, and the peripheral region is the region of the flake-shaped copper particles other than the central region.

6. Flake-like copper particles according to claim 1 or 2, wherein a dissimilar metal other than copper is arranged on the surface.

7. The flake-shaped copper particles according to claim 6, wherein the dissimilar metal is silver.

8. The flake-shaped copper particles according to claim 7, wherein the a* value in the L*a*b* color system is 0.0 or more and 8.2 or less.

9. Flake-shaped copper particles according to claim 1 or 2, wherein the aspect ratio defined by the long axis length / short axis length is 1.05 or more and 4.00 or less.

10. Flake-shaped copper particles according to claim 9, wherein the average value of the major axis length is 8.0 μm or more and 20.0 μm or less, and the average value of the minor axis length is 3.0 μm or more and 12.0 μm or less.

11. Flake-shaped copper particles according to claim 1 or 2, wherein the thickness is 0.05 μm or more and 0.40 μm or less.

12. BET specific surface area is 1.0 m² ２ / g or more 10.0m ２ Flake-shaped copper particles according to claim 1 or 2, wherein the amount is less than or equal to / g.

13. A conductive resin composition comprising a resin and flake-shaped copper particles as described in claim 1 or 2.

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