Copper powder and method for manufacturing the same

Abstract

A copper powder is provided that can be used to manufacture electrodes with high density and continuity without mixing. The copper powder of this invention has a tap density of 4.2 g / cm³ after 400 vibrations according to JIS Z2512:2012. 3 Above and 5.5g / cm 3 The tap density, measured after 100 vibrations according to JIS Z2512:2012, is 4.1 g / cm³. 3 Above and 5.5g / cm 3 The following is the standard deviation of the thickness of the aforementioned copper powder particles, SD (μm), and the average particle size, D. 50 The value of (μm) is greater than 0.08 and less than 0.26.

Description

Technical Field

[0001] This invention relates to copper powder and its manufacturing method. Background Technology

[0002] Copper is a highly conductive metal and a versatile material, making it widely used in industry as a conductive material. For example, copper powder, as an aggregate of copper particles, is widely used as a raw material for manufacturing external and internal electrodes of multilayer ceramic capacitors (MLCCs), as well as for wiring on various substrates and other electronic components.

[0003] For example, Patent Document 1 describes a flake-shaped copper powder, which is obtained by plastically deforming copper powder particles into flakes. The cumulative weight particle size D is determined based on a laser diffraction scattering particle size distribution method. 50 For particles smaller than 10 μm, the standard deviation SD / D of the particle size distribution determined using the laser diffraction scattering particle size distribution method. 50 The value is below 0.55, and the cumulative weight particle size D 90 / cumulative particle size D 10 The value is below 4.5. This document describes how flake copper powder can be used to control the viscosity of conductive pastes and impart appropriate thixotropic properties to them.

[0004] Patent document 2 describes a flake-shaped copper powder formed from flake-shaped copper particles with an average thickness D of 0.2 μm or more. The 50% diameter D of this flake-shaped copper powder is [not specified in the original text]. 50 The diameter is 1–30 μm, and the aspect ratio (D) is 1–30 μm. 50 The average thickness (D) is 5–70. This document states that this flake copper powder is suitable as a filler for conductive pastes.

[0005] Patent document 3 describes a flake-shaped copper powder formed from flake-shaped copper particles with an average thickness D of 0.2 μm or more, wherein 50% of the particle size distribution has a diameter D 50 The size is 1–30 μm, and it is composed of D. 50 / D defines the aspect ratio as 5–70, SD / (D) 90 / D 10 The value of ) is below 0.1. SD is the standard deviation of the thickness of 100 particles as measured by electron microscopy. 90 D represents 90% of the diameter in the particle size distribution. 10 This represents 10% of the particle size distribution. The literature describes how this flake-like copper powder can be used to obtain a conductive paste with excellent viscosity, printability, and conductivity.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2004-169155

[0009] Patent Document 2: Japanese Patent Application Publication No. 2005-200734

[0010] Patent Document 3: Japanese Patent Application Publication No. 2005-314755 Summary of the Invention

[0011] When copper powder is used as the external and internal electrodes of MLCCs and for wiring on various substrates, using the flake-shaped copper powder described in Patent Documents 1 to 3 can sometimes make it difficult to improve electrode density due to its particle shape. On the other hand, using spherical copper powder can sometimes make it difficult to ensure electrode continuity. Therefore, to compensate for each other's disadvantages, flake-shaped and spherical copper powder are often mixed together. However, using both flake-shaped and spherical copper powder together requires a mixing process, which is not necessarily advantageous from an industrial and economic point of view. A solution for manufacturing electrodes without the need for mixing is desired.

[0012] Therefore, the objective of this invention is to provide a copper powder that can be used to manufacture electrodes with high density and continuity without mixing, and a method thereof.

[0013] This invention provides a copper powder whose tap density is 4.2 g / cm³ after 400 vibrations according to JIS Z2512:2012. 3 Above and 5.5g / cm 3 the following,

[0014] The tap density after 100 vibrations according to JIS Z2512:2012 is 4.1 g / cm³. 3 Above and 5.5g / cm 3 the following,

[0015] Standard deviation of particle thickness SD (μm) / average particle size D 50 The value of (μm) is greater than 0.08 and less than 0.26.

[0016] In addition, the present invention provides a method for manufacturing copper powder, which includes the following steps:

[0017] In the process of preparing raw copper powder, the particle size distribution of the aforementioned raw copper powder has an SD value of 1.00 or higher and (D 90 -D 10 ) / D 50 The value is above 1.00, and it is composed of aggregates of spherical copper particles;

[0018] The process of preparing a slurry by mixing the aforementioned raw material copper powder with an organic solvent; and

[0019] The process of applying a flattening treatment based on a media grinding device to the aforementioned slurry to deform the aforementioned spherical copper particles into flat copper particles.

[0020] The aforementioned flattening process is carried out while maintaining the water content in the slurry below 0.3% by mass under an inactive atmosphere. Attached Figure Description

[0021] Figure 1 This is a scanning electron microscope image of the copper powder obtained in Example 1.

[0022] Figure 2 This is a scanning electron microscope image of the copper powder obtained in Comparative Example 2. Detailed Implementation

[0023] The present invention will now be described based on its preferred embodiments.

[0024] This invention relates to copper powder primarily comprising flat copper particles. The copper powder and copper particles consist of copper and unavoidable impurities. One characteristic of the copper powder of this invention is its high density and high flowability. The high density and high flowability of the copper powder refer to the high particle density in the coating film of the paste prepared using the copper powder of this invention, and also to the high continuity of the coating film, i.e., the ability to form a coating film without discontinuity.

[0025] The degree of compactness can be evaluated by the tap density of the copper powder. The tap density of the copper powder of the present invention after 400 vibrations according to JIS Z2512:2012 (hereinafter also referred to as "400-vibration-density") is 4.2 g / cm³. 3 Above and 5.5g / cm 3 The preferred value is 4.3 g / cm³. 3 Above and 5.5g / cm 3 The preferred value is 4.3 g / cm³. 3 Above and 5.4 g / cm 3 The following describes how the density of copper powder increases by ensuring that its 400-times tap density is within the aforementioned range. To achieve this, flat copper particles can be manufactured, for example, according to the method described later.

[0026] The degree of fluidity can be evaluated according to JIS Z2512:2012 by the tap density after 100 vibrations (hereinafter also referred to as "100-vibration-density"). The 100-vibration-density of the copper powder of this invention is 4.1 g / cm³. 3 Above and 5.5g / cm 3The preferred value is 4.2 g / cm³. 3 Above and 5.4 g / cm 3 The preferred value is 4.2 g / cm³. 3 Above and 5.3g / cm 3 The following describes how, by achieving a tap density of 100 taps within the aforementioned range—that is, a tap density comparable to that of 400 taps—the fluidity of the copper powder is improved, resulting in increased density of the copper powder in the coating film when it is used to manufacture the coating. To achieve a tap density of 100 taps within the aforementioned range, copper particles with smooth and flat surfaces can be manufactured, for example, according to the method described later.

[0027] It should be noted that, depending on the type of copper powder, the density after 100 taps is the same as or smaller than the density after 400 taps.

[0028] Furthermore, for the copper powder of the present invention, the standard deviation SD (μm) of the thickness of the copper particles constituting the copper powder and the average particle size D 50 There is a specific relationship between (μm) and standard deviation SD(μm) / average particle size D. 50 The value of (μm) is 0.08 or more and 0.26 or less, preferably 0.09 or more and 0.25 or less, and more preferably 0.10 or more and 0.24 or less. This is achieved by setting the standard deviation SD(μm) / average particle size D... 50 Within the aforementioned range (μm), variations in the thickness of the copper particles constituting the copper powder relative to their particle size are suppressed. That is, the particle size and thickness of the copper particles become uniform, thus, when using copper powder formed from aggregates of such copper particles to form a coating film, the formation of gaps between copper particles is suppressed, resulting in a continuous presence of copper particles. Consequently, the continuity of copper particles in the coating film is increased.

[0029] The average particle size D of copper particles 50 The thickness of copper particles can be determined by laser diffraction scattering particle size distribution measurement. The standard deviation (SD) of the copper particle thickness can be determined by mixing copper powder, solvent and resin to form a resin composition, forming a coating film, drying the coating film, and measuring the thickness of copper particles in the cross section of the dried coating film using a scanning electron microscope.

[0030] From the viewpoint of making the various advantages of the copper powder of the present invention more significant, the average particle size D of the copper particles 50 Preferably, the micrometer is 2.0 μm or more and 5.0 μm or less, more preferably 2.5 μm or more and 4.8 μm or less, and even more preferably 3.0 μm or more and 4.5 μm or less.

[0031] From the same perspective, the average thickness of the copper particles is preferably 0.20 μm or more and 2.00 μm or less, more preferably 0.30 μm or more and 1.80 μm or less, and even more preferably 0.40 μm or more and 1.70 μm or less. The average thickness of the copper particles can be determined by mixing copper powder, solvent, and resin to prepare a resin composition, forming a coating film, drying the coating film, and measuring the thickness of the copper particles observed in a cross-section of the resulting dried coating film. The measurement is performed using at least 300 copper particles. The cross-section is observed using a scanning electron microscope at 2000x magnification.

[0032] In this invention, the average value of the aspect ratio (hereinafter also referred to as "planar aspect ratio"), which is the value of the major diameter of the copper particle at the plate surface to the minor diameter of the particle, is preferably 1.25 or more and 3.00 or less, more preferably 1.27 or more and 2.50 or less, and even more preferably 1.30 or more and 2.00 or less. By constituting the copper powder of this invention with copper particles having the planar aspect ratio having the values ​​described above, when a coating film is formed from the copper powder containing these copper particles, the density and continuity of the copper powder in the coating film are further improved.

[0033] In this specification, "flat" refers to the shape of having a pair of plate surfaces that form the main surface of the particle and side surfaces that intersect with these plate surfaces. The plate surfaces and side surfaces can each be independently planar, curved, or concave-convex. The plate surfaces are preferably planar.

[0034] The average value of the aspect ratio (hereinafter also referred to as "side aspect ratio"), which is the value of the long side / short side of the thickness surface of the copper particles, is preferably 2.0 or more. By constructing the copper powder of the present invention from copper particles having such a side aspect ratio, when a coating film is formed from the copper powder containing these copper particles, the density and continuity of the copper powder in the coating film are further improved. The side aspect ratio can be measured using the same method as the method for measuring the standard deviation (SD) of the thickness of the copper particles described above.

[0035] It should be noted that, in this invention, "mainly comprising flat copper particles" means that the proportion of copper particles whose side aspect ratio meets the above range is, for example, 70% or more based on the number of particles.

[0036] When the copper powder of the present invention contains spherical particles, the proportion of spherical particles is preferably 30% or less, more preferably 28% or less, and even more preferably 25% or less, based on the number of particles.

[0037] In the copper powder of the present invention, the proportion of copper particles with an average aspect ratio of 1.25 or more is preferably 30% or more, more preferably 35% or more, and even more preferably 40% or more, and particularly preferably all copper particles are composed of copper particles with an average aspect ratio of 1.25 or more. Therefore, the effects of the copper powder of the present invention can be reliably achieved.

[0038] In this invention, the aspect ratio is determined by the following method: Copper powder is observed using a scanning electron microscope (SEM). For any 300 or more particles in the field of view, the aspect ratio is expressed as D / d, which is the ratio of the major axis D at the plate surface to the length of the minor axis d (the length of the particle cut by the perpendicular bisecting line of major axis D). The magnification of the SEM is selected based on the particle size of the copper particles. Generally, a magnification is chosen that allows for the observation of 300 to 600 particles in the field of view.

[0039] In the copper powder of the present invention, it is preferable to have a planar aspect ratio within a certain range, regardless of the particle size of the copper particles constituting the copper powder. For example, when the Heywood diameter of each copper particle is 2.0 μm or more and 6.5 μm or less, and the planar aspect ratio is 1.25 or more and 3.00 or less, it can become a copper powder with high density and high flowability. Therefore, it is preferable that the planar aspect ratio is particularly preferably 1.25 or more and 2.50 or less, and especially preferably 1.25 or more and 2.00 or less.

[0040] The copper powder of this invention may contain copper particles other than those with an average aspect ratio of 1.25 or higher. The shape of these copper particles is not particularly limited; any shape, whether round or non-round, can be used. Round copper particles are defined as having a roundness coefficient of 0.85 or higher when projected in two dimensions. Regarding the roundness coefficient, when taking a scanning electron microscope image of a single copper particle and setting the area of ​​the two-dimensional projection image of the copper particle as S and the perimeter as L, the coefficient is calculated using the formula 4πS / L. 2 Calculate the roundness coefficient of the copper particles. On the other hand, non-circular copper particles are defined as those with a roundness coefficient less than 0.85. Specific examples of non-circular shapes include polyhedral particles such as hexahedrons and octahedrons, spindle-shaped particles, and irregularly shaped particles.

[0041] The crystallite size of copper in the copper particles constituting the copper powder is preferably 50 nm or more and 100 nm or less, more preferably 50 nm or more and 90 nm or less, and even more preferably 50 nm or more and 80 nm or less. By keeping the copper crystallite size within this range, when a coating is formed from the copper powder and the coating is calcined, the degree of shrinkage of the copper particles due to heat during coating can be controlled within a suitable range, thereby improving the dimensional stability of the electrode. To set the copper crystallite size within this range, for example, the degree of flattening of the spherical copper particles can be appropriately controlled in the preferred manufacturing method of the copper powder described later. This is because the copper crystallite size tends to decrease due to the application of external force.

[0042] To determine the crystallite size of copper, X-ray diffraction of copper powder was performed using an Ultima IV laser manufactured by Rigaku Corporation. The crystallite size was calculated by analyzing the diffraction peaks of the (111) plane of the copper obtained through this measurement using the Scherrer method.

[0043] <X-ray diffraction measurement conditions>

[0044] X-ray tube: CuKα wire

[0045] • Tube voltage: 40kV

[0046] Tube current: 50mA

[0047] • Determine the diffraction angle: 2θ = 20–100°

[0048] • Measurement step size: 0.01°

[0049] • Collection time: 3 seconds / step

[0050] • Light receiving slit width: 0.3mm

[0051] • Diverging longitudinal slit width limit: 10mm

[0052] • Detector: High-speed one-dimensional X-ray detector D / teX Ultra250

[0053] <Preparation Method of Samples for X-ray Diffraction>

[0054] The copper powder of the test object is laid on the test holder and smoothed using a glass plate in a way that the copper powder layer is 0.5 mm thick and smooth.

[0055] The X-ray diffraction pattern obtained under the above measurement conditions was analyzed using analytical software under the following conditions. Peak width correction was performed using the LaB6 value. Crystallite size was calculated using the full width at half maximum (FWHM) of the peak and the Scherer constant (0.94).

[0056] <Conditions for Data Analysis>

[0057] • Analysis software: Rigaku PDXL2

[0058] • Smoothing: Gaussian function, smoothing parameter = 10

[0059] Background subtraction: Fitting method

[0060] • Kα2 removal: intensity ratio 0.497

[0061] Peak Search: Second-order differential method

[0062] Curve fitting: FP method

[0063] • Crystallite size distribution type: Lorenz model

[0064] Scherrer constant: 0.9400

[0065] In this invention, the oxygen content in the copper powder is preferably as low as possible. Specifically, the oxygen content in the copper powder is preferably 0.50% by mass or less, more preferably 0.45% by mass or less, and even more preferably 0.40% by mass or less. By keeping the oxygen content in the copper powder below this value, the paste containing the copper powder of this invention exhibits good dispersion stability and can suppress aggregation and viscosity changes.

[0066] The oxygen content in copper powder can be achieved, for example, by setting the water content in the slurry for the flattening process in the copper powder manufacturing method described later to be below 3000 ppm and performing the flattening process in an inactive gas atmosphere.

[0067] In this invention, the carbon content in the copper powder is preferably as low as possible. Specifically, it is preferably 0.40% by mass or less, more preferably 0.30% by mass or less, and even more preferably 0.20% by mass or less. If the carbon content in the copper powder is too high, decomposition gases from carbon will be generated when the paste containing the copper powder is calcined, which may sometimes cause cracks and blistering in the sintered body.

[0068] To reduce the carbon content of the copper powder, for example, a raw material powder with a low carbon content can be used as the raw material for forming the copper powder of the present invention. Examples of such raw material powders include copper powder manufactured by atomization methods such as gas atomization and water atomization, and copper powder manufactured by plasma methods.

[0069] The carbon content in the copper powder of this invention can be determined using a carbon and sulfur analysis apparatus CS-844 manufactured by LECO, employing a combustion-infrared absorption method based on an oxygen flow. Specifically, a 0.5g sample is placed in a crucible, which is then placed in the apparatus for measurement.

[0070] The copper powder of the present invention can preferably be manufactured by the following method.

[0071] First, raw copper powder consisting of aggregates of spherical copper particles is prepared. From the viewpoint of easily obtaining copper powder with high density and flowability, copper powder with a wide particle size distribution is preferred as the raw copper powder. From this viewpoint, the raw copper powder used is (D... 90 -D 10 ) / D 50 Values ​​of 1.00 or higher, especially 1.05 or higher, and particularly 1.10 or higher, are advantageous. This raw material copper powder can be readily formed by atomization methods such as gas atomization and water atomization, or plasma methods. However, it is not limited to these methods; wet reduction methods can also be used, in which an aqueous solution of copper salt reacts with an alkaline reagent to precipitate copper hydroxide, which is then reduced to cuprous oxide in a liquid in a single step, and the resulting cuprous oxide is further reduced to metallic copper in a second step. (D) 90 -D 10 ) / D 50 The upper limit of the value is preferably around 2.00.

[0072] D 10 D 50 and D 90 These are the cumulative particle sizes at 10%, 50%, and 90% of the cumulative volume, obtained using the laser diffraction scattering particle size distribution method.

[0073] For raw copper powder, from the viewpoint of easily obtaining copper powder with high density and flowability, a particle size distribution SD value of 1.00 or higher is preferred. From this viewpoint, for raw copper powder, a particle size distribution SD value of 1.10 or higher is further preferred, and more preferably 1.15 or higher. The upper limit of the particle size distribution SD value is preferably around 3.00.

[0074] Next, the raw copper powder is mixed with an organic solvent to prepare a slurry. As the organic solvent, an aliphatic alcohol with 1 or more and 22 or fewer carbon atoms is preferred, and a saturated aliphatic monohydric alcohol with 1 or more and 10 or fewer carbon atoms is more preferred. Monoalkyl alcohols with 1 or more and 4 or fewer carbon atoms are particularly preferred. Examples of such alcohols include methanol, ethanol, n-propanol, sec-propanol, n-butanol, sec-butanol, and tert-butanol. One alcohol may be used alone, or two or more may be used in combination.

[0075] Regarding the mixing ratio of raw copper powder and organic solvent, relative to the total mass of the two, it is preferable that the raw copper powder is mixed at 10% by mass or more and 90% by mass or less, and particularly preferably at 30% by mass or more and 70% by mass or less. This allows for the smoothing process described below.

[0076] It is advantageous to keep the water content in the slurry below 0.3% by mass. This allows the oxygen content in the copper powder to be controlled to below 0.5% by mass, resulting in good dispersion stability of the copper powder, suppressing aggregation and viscosity changes, and thus easily obtaining copper powder with the properties described above. When the water content in the slurry is too high, the surface of the flat copper particles becomes rough due to oxidation by moisture, and the smoothness of this surface is easily compromised. This is because tiny particles of copper oxides such as cuprous oxide are generated on the surface of the copper particles. Flat copper particles with an uneven surface tend to have reduced flowability.

[0077] Next, the aforementioned slurry is subjected to a flattening process using a media milling apparatus, which deforms the spherical copper particles into flat copper particles. A bead mill, ball mill, or vibratory mill can be used as the media milling apparatus. If other conditions in this flattening process remain constant, a longer processing time will result in flat copper particles with a large aspect ratio; typically, a flattening processing time of about 30 minutes to 4 hours is sufficient.

[0078] The flattening process is carried out while maintaining the water content in the slurry below 3000 ppm under an inactive atmosphere such as nitrogen or argon. This allows the oxygen content in the copper powder to be controlled below 0.5% by mass, resulting in good dispersion stability, suppressing aggregation and hardness changes, and thus obtaining copper powder with the aforementioned properties.

[0079] The media used in ball mills and vibratory mills can be ceramics, glass, metals, etc. While not limited to a specific material, ceramics with strength that will not become a source of impurities due to damage or wear during the grinding process are preferred. From a strength / cost perspective, zirconium oxide is more preferably used. The diameter of the media used is preferably 0.03 mm or more and 5 mm or less, more preferably 0.05 mm or more and 2.5 mm or less.

[0080] Furthermore, in the flattening process, it is preferable not to use lubricants such as fatty acids. When lubricants are used, small-diameter copper particles are difficult to crush, making it difficult to obtain copper powder with a flat shape and the aforementioned characteristics. However, the use of lubricants is not completely excluded; lubricants may be included in the raw copper powder at a proportion of 0.1% by mass or more and 1.0% by mass or less, as needed.

[0081] Examples of lubricants include oleic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, etc.

[0082] Copper powder can have a surface treatment agent attached to its surface. By attaching the surface treatment agent to the surface of the copper powder, excessive aggregation of the copper powder particles can be inhibited.

[0083] There are no particular limitations on the surface treatment agent; fatty acids, aliphatic amines, silane coupling agents, titanate coupling agents, aluminate coupling agents, etc., can be used. By using these surface treatment agents, they can interact with the surface of the particles, thereby improving the compatibility with the organic solvents contained in the paste, improving the flowability of the paste, and preventing oxidation of the particle surface.

[0084] In this manufacturing method, from the viewpoint of efficient flattening of spherical copper particles, it is preferable to perform the flattening process while circulating a slurry containing raw copper powder and an organic solvent. Specifically, it is preferable to connect the circulation tank to the media grinding apparatus via outgoing and returning piping, allowing the slurry to circulate between the circulation tank and the media grinding apparatus. In this case, it is preferable to maintain the water content in the slurry below 0.3% by mass in the circulation tank, the media grinding apparatus, and each piping, to ensure that no lubricant is present, and to use an inactive atmosphere.

[0085] When the aforementioned copper powder is applied to an electrode, a copper paste containing the copper powder is prepared. The copper paste can be prepared simply by mixing the copper powder of the present invention with a binder, solvent, and glass frit. This allows for the preparation of a high-temperature sintering type copper paste. Alternatively, a resin-curing type copper paste can be prepared by mixing the copper powder of the present invention with a binder and solvent, and then with a curing agent as needed.

[0086] Examples of adhesives include, but are not limited to, liquid epoxy resins, acrylic resins, phenolic resins, and unsaturated polyester resins. Examples of solvents include terpineol, ethyl carbitol, carbitol acetate, butyl cellosolve, and butyl carbitol acetate. Examples of curing agents include 2-ethyl-4-methylimidazole. Examples of curing accelerators include tertiary amines, tertiary amine salts, imidazoles, phosphine derivatives, and phosphonium salts.

[0087] It should be noted that this application also includes the following technical solutions.

[0088] <1> A copper powder, whose tap density is 4.2 g / cm³ after 400 vibrations according to JIS Z2512:2012. 3 Above and 5.5g / cm 3 the following,

[0089] The tap density after 100 vibrations according to JIS Z2512:2012 is 4.1 g / cm³. 3 Above and 5.5g / cm 3 the following,

[0090] Standard deviation of particle thickness SD (μm) / average particle size D 50 The value of (μm) is greater than 0.08 and less than 0.26.

[0091] <2> The copper powder according to <1> has an average aspect ratio of 1.25 or more and 3.00 or less, wherein the aspect ratio is the value of the long diameter of the particle / the short diameter of the particle.

[0092] <3> The copper powder according to <2> contains more than 30% of the aforementioned particles with an aspect ratio of 1.25 or more, based on the number of particles.

[0093] <4> The copper powder according to any one of <1> to <3> has an oxygen content of 0.5% by mass or less.

[0094] <5> The copper powder according to any one of <1> to <4> has an average particle size D 50 It is above 2.0μm and below 5.0μm.

[0095] <6> The copper powder according to any one of <1> to <5>, wherein the crystallite size of the copper powder is 50 nm or more and 80 nm or less.

[0096] <7> The copper powder according to any one of <1> to <6> has a carbon content of 0.40% by mass or less.

[0097] <8> A method for manufacturing copper powder, comprising the following steps:

[0098] The process of preparing raw copper powder, the aforementioned raw copper powder (D) 90 -D 10 ) / D 50 The value is 1.00 or higher and it is composed of aggregates of spherical copper particles;

[0099] The process of preparing a slurry by mixing the aforementioned raw material copper powder with an organic solvent; and

[0100] The process of applying a flattening treatment based on a media grinding device to the aforementioned slurry to deform the aforementioned spherical copper particles into flat copper particles.

[0101] The aforementioned flattening process is carried out while maintaining the water content in the slurry below 0.30% by mass under an inactive atmosphere.

[0102] <9> The manufacturing method described in <8> involves manufacturing the aforementioned raw material copper powder using an atomization method.

[0103] <10> The manufacturing method according to <8> or <9>, wherein the aforementioned raw material copper powder with a particle size distribution SD value of 1.00 or higher is prepared.

[0104] <11> The manufacturing method according to any one of <8> to <10>, wherein the aforementioned flattening process is performed in the absence of a lubricant.

[0105] Example

[0106] The present invention will now be described in more detail through embodiments. However, the scope of the present invention is not limited to the corresponding embodiments.

[0107] [Example 1]

[0108] The copper powder used as raw material is MA-CO3K, a copper powder produced by the atomization process and manufactured by Mitsui Metals & Minerals Co., Ltd. The average particle size of this raw material powder is D. 50 It is 3.08 μm in size and contains 100 ppm of carbon. Additionally, (D 90 -D 10 ) / D 50 The value is 1.13, and the SD value of the particle size distribution is 1.27.

[0109] 100 kg of methanol and 100 kg of raw copper powder were mixed to form a slurry, which was then fed into a StirMill (registered trademark) LMZ10 mill manufactured by Ashizawa Fine Technology Co., Ltd., which was used as a media dispersion mill. Zirconia beads with a diameter of 0.1 mm were filled into the mill.

[0110] The mill was run at a circumferential speed of 12 m / s for 300 minutes to flatten the raw copper powder through plastic deformation. Oleic acid (0.1 kg) was added to the treated slurry and stirred for 30 minutes to perform surface treatment. The resulting copper slurry was then subjected to solid-liquid separation, and the obtained copper powder was dried and recovered.

[0111] During bead milling, the water content in the slurry is maintained below 3000 ppm, and a nitrogen atmosphere is maintained inside the mill. Additionally, no lubricant is present in the slurry during bead milling. The slurry circulates between the circulation tank and the mill.

[0112] The SEM image of the copper powder obtained in this embodiment is shown below. Figure 1 .

[0113] [Example 2]

[0114] In Example 1, the average particle size D of the raw material copper powder was used. 50 3.30μm, (D 90 -D 10 ) / D 50 The raw copper powder had a value of 1.22 and a particle size distribution SD value of 1.47. Otherwise, copper powder was obtained in the same manner as in Example 1.

[0115] [Example 3]

[0116] In Example 1, the average particle size D of the raw material copper powder was used. 50 2.90μm, (D90 -D 10 ) / D 50 The raw copper powder with a particle size distribution SD value of 1.16 and a particle size distribution SD value of 1.10 was used, and the mill running time was set to 240 minutes. Otherwise, copper powder was obtained in the same manner as in Example 1.

[0117] [Example 4]

[0118] In Example 1, the average particle size D of the raw material copper powder was used. 50 2.60μm, (D 90 -D 10 ) / D 50 Copper powder with a particle size distribution (SD) of 1.44 and a particle size distribution (SD) of 1.45 was subjected to a flattening process by dissolving 250g of oleic acid in a slurry during a mill run of 660 minutes. The resulting copper powder was then subjected to solid-liquid separation, dried, and recovered. No oleic acid was added after the flattening process. Otherwise, copper powder was obtained in the same manner as in Example 1.

[0119] [Example 5]

[0120] In Example 1, the average particle size D of the raw material copper powder was used. 50 3.19μm, (D 90 -D 10 ) / D 50 The raw copper powder with a particle size distribution (SD) of 1.07 and a particle size distribution of 1.10 was subjected to a flattening process by milling for 300 minutes. 0.1 kg of oleylamine was dissolved in the treated slurry for surface treatment. The resulting copper powder was then subjected to solid-liquid separation, dried, and recovered. Otherwise, copper powder was obtained in the same manner as in Example 1.

[0121] [Comparative Example 1]

[0122] In Example 4, the atmosphere in the slurry was atmospheric, the moisture content was not maintained below 3000 ppm, and the mill running time was set to 300 minutes. Otherwise, copper powder was obtained in the same manner as in Example 4.

[0123] [Comparative Example 2]

[0124] In Example 1, the average particle size D of the raw material copper powder was used. 50 3.10μm, (D 90 -D 10 ) / D 50The raw copper powder with a particle size distribution SD value of 1.20 and a particle size distribution SD value of 1.37 was used. The atmosphere in the slurry was atmospheric, and the moisture content was not maintained below 3000 ppm. Otherwise, copper powder was obtained in the same manner as in Example 1. SEM images of the copper powder obtained in this comparative example are shown below. Figure 2 Because the moisture content was not controlled, surface irregularities originating from oxidation could be identified.

[0125] 〔evaluate〕

[0126] For the copper powder obtained in the examples and comparative examples, the tap density after 400 taps and the tap density after 100 taps were determined using the above method. Additionally, the standard deviation of the thickness (SD / D) was determined using the above method. 50 The following parameters were considered: planar aspect ratio, lateral aspect ratio, crystallite size, oxygen content, and carbon content. Furthermore, the coating density and continuity were evaluated using the following methods. These results are shown in Table 1. It should be noted that although not shown in the table, the copper powder obtained in the examples contained more than 70% copper particles with a lateral aspect ratio of 2.0 or higher, based on the number of particles.

[0127] [Coating density]

[0128] 2.5 g of terpineol containing 10% by mass of ethyl cellulose was added to 10 g of copper powder obtained in the examples and comparative examples. The mixture was stirred at 2000 rpm for 1 minute using a self-rotating mixer, followed by degassing at 2200 rpm for 30 seconds to obtain a paste. This paste was applied to a glass substrate with a width of 10 mm and a length of 20 mm. The substrate was heated at 120°C under a nitrogen atmosphere to obtain a dried coating. The coating thickness was measured to determine the coating volume. Furthermore, the coating weight was determined from the pre-measured substrate weight, and the coating density (g / cm³) was calculated from the coating weight / coating volume. 3 .

[0129] [Coating Continuity]

[0130] 10g of terpineol containing 10% by mass of ethyl cellulose was added to 10g of copper powder obtained in the examples and comparative examples. The mixture was stirred at 2000 rpm for 1 minute using a self-rotating mixer, followed by degassing at 2200 rpm for 30 seconds to obtain a paste. This paste was coated onto a PET film with a thickness of approximately 20 μm and heated at 120°C under a nitrogen atmosphere to obtain a dried coating. The coating was then bent at a 90° angle. The bending was repeated three times. After bending, the bent portions were observed using an optical microscope. Cases where the PET film serving as the substrate remained intact and the copper powder continuity was maintained were evaluated as 0, while cases where the copper powder continuity was lost and the PET film was exposed were evaluated as ×.

[0131] [Table 1]

[0132]

[0133] As can be clearly seen from the results shown in Table 1, the copper powder obtained in each example exhibits superior density and continuity compared to the copper powder in the comparative example. Furthermore, it is evident that Examples 1-3 and 5, which did not use lubricant during the flattening process in the manufacture of the copper powder, showed improved coating density compared to Example 4, which used lubricant.

[0134] In addition, by Figure 1 and Figure 2 The comparison clearly shows that the surface of the copper particles constituting the copper powder obtained in Example 1 is smooth, while the surface of the copper particles constituting the copper powder obtained in Comparative Example 2 is rough. The inventors' analysis revealed that the roughness is caused by cuprous oxide, resulting from the oxidation of copper.

[0135] Industrial availability

[0136] According to the present invention, a copper powder that can be used to manufacture electrodes with high density and continuity without mixing is provided, and a method for manufacturing the same.

Claims

1. A copper powder, wherein the tap density is 4.2 g / cm³ after 400 vibrations according to JIS Z2512:2012. 3 Above and 5.5g / cm 3 the following, The tap density after 100 vibrations according to JIS Z2512:2012 is 4.1 g / cm³. 3 Above and 5.5g / cm 3 the following, Standard deviation of particle thickness SD (μm) / average particle size D 50 The value of (μm) is above 0.08 and below 0.

26. The carbon content of the copper powder is less than 0.30% by mass.

2. The copper powder according to claim 1, wherein the average aspect ratio is 1.25 or more and 3.00 or less, wherein the aspect ratio is the value of the long diameter of the particle / the short diameter of the particle.

3. The copper powder according to claim 2, wherein, The number of particles contains more than 30% of the particles with an aspect ratio of 1.25 or more.

4. The copper powder according to claim 1, wherein the oxygen content is less than 0.5% by mass.

5. The copper powder according to claim 1, wherein the average particle size D 50 It is above 2.0μm and below 5.0μm.

6. The copper powder according to claim 1, wherein, The crystallite size of copper is greater than 50 nm and less than 80 nm.

7. A method for manufacturing copper powder, comprising the following steps: The process of preparing raw copper powder, wherein the raw copper powder (D) 90 -D 10 ) / D 50 The value is 1.00 or higher and it is composed of aggregates of spherical copper particles; The process of preparing a slurry by mixing the raw copper powder with an organic solvent; and The process of applying a flattening treatment based on a media grinding device to the slurry to deform the spherical copper particles into flat copper particles. in, The flattening process is carried out in an inactive atmosphere while maintaining the water content in the slurry below 0.30% by mass, and the flattening process is carried out in the absence of lubricant.

8. The manufacturing method according to claim 7, wherein, The raw material copper powder is manufactured using an atomization method.

9. The manufacturing method according to claim 7 or 8, wherein, Prepare the raw material copper powder with a particle size distribution SD value of 1.00 or higher.

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