Copper powder, flat copper powder, conductive paste, and method for producing flat copper powder

Abstract

Provided is copper powder in which the ratio (S / D50) of the specific surface area S (m2 / g) measured by the nitrogen adsorption BET method to the particle diameter D50 (μm) in the volume-based particle size distribution measured by the laser diffraction scattering method is 0.07 m2 / (g·μm) or greater. The particle diameter D50 of the copper powder is, for example, 0.1 μm to 10.0 μm (inclusive). The ratio (D50 / TA) of the particle diameter D50 (μm) to the average thickness TA (μm) of this copper powder, calculated by the method described below, is, for example, 20.0 or less. Method: The thicknesses of 100 arbitrary pieces of copper powder are measured from SEM images obtained by observing the copper powder with an electron microscope, and the average value of the thicknesses of the 100 pieces of copper powder is defined as the average thickness TA (μm) of the copper powder.

Description

Copper powder, flattened copper powder, conductive paste, and method for producing flattened copper powder

[0001] This invention relates to copper powder, flattened copper powder, conductive paste, and a method for producing flattened copper powder.

[0002] Traditionally, copper powder has been used as a raw material for conductive pastes used to form wiring on printed circuit boards. However, with the recent miniaturization of printed circuit boards and the resulting reduction in wiring thickness, there is a growing demand for copper powder suitable for conductive pastes that can accommodate such thinning.

[0003] Technology relating to copper powder is described, for example, in Patent Document 1. Patent Document 1 aims to provide flake copper powder that, when processed for copper paste and used in conductor formation, can stably lower the electrical resistance of the conductor and simultaneously achieve excellent filling properties for via holes, etc., and is a flake copper powder with a particle size of 10 μm or less, wherein the weight-cumulative particle size D of the flake copper powder is determined by laser diffraction scattering particle size distribution measurement. １０ , D ５０ , D ９０ SD / D is expressed using the standard deviation SD of the particle size distribution measured by the laser diffraction scattering particle size distribution measurement method. ５０ The value of is 0.5 or less, and D ９０ / D １０ The present invention describes a flake copper powder characterized in that the value represented by is 4.0 or less.

[0004] Japanese Patent Publication No. 2003-119501

[0005] One aspect of the present invention provides copper powder with improved packing properties. Another aspect of the present invention provides flattened copper powder with improved packing properties. Another aspect of the present invention provides a method for producing flattened copper powder with improved packing properties.

[0006] The inventors diligently conducted research to achieve the above objectives. As a result, specific surface area and particle size D ５０ By setting the ratio to a predetermined range, we discovered that copper powder with improved packing properties can be obtained, thus completing the present invention.

[0007] [1] Copper powder, wherein the ratio (S / D) of the specific surface area S (m² / g) by the nitrogen adsorption BET method to the particle diameter D (μm) in the volume-based particle size distribution by the laser diffraction scattering method of the copper powder is 0.07 m² / (g·μm) or more. ５０ (μm) to the specific surface area S (m² ２ / g) of the ratio (S / D ５０ ) is 0.07 m² ２ / (g·μm) or more, copper powder. [2] The copper powder according to [1], wherein the particle diameter D ５０ of the copper powder is 0.1 μm or more and 10.0 μm or less. [3] The ratio (D / T Ａ ) of the average thickness T (μm) of the copper powder by the following (method) to the particle diameter D (μm) is 20.0 or less, the copper powder according to [1] or [2]. (Method) From the SEM image obtained by observing the copper powder with an electron microscope, measure the thickness of any 100 copper powders respectively, and take the average value of the thickness of the 100 copper powders as the average thickness T (μm) of the copper powder. ５０ (μm) of the ratio (D ５０ / T Ａ ) is 20.0 or less, the copper powder according to [1] or [2]. (Method) From the SEM image obtained by observing the copper powder with an electron microscope, measure the thickness of any 100 copper powders respectively, and take the average value of the thickness of the 100 copper powders as the average thickness T (μm) of the copper powder. Ａ (μm) and set it as the average thickness T (μm) of the copper powder. [4] The average thickness T of the copper powder by the following (method) Ａ is 0.1 μm or more and 2.0 μm or less, the copper powder according to any one of [1] to [3]. (Method) From the SEM image obtained by observing the copper powder with an electron microscope, measure the thickness of any 100 copper powders respectively, and take the average value of the thickness of the 100 copper powders as the average thickness T (μm) of the copper powder. Ａ (μm) and set it as the average thickness T (μm) of the copper powder. [5] The specific surface area S of the copper powder by the nitrogen adsorption BET method is 0.10 m² / g or more and 3.0 m² / g or less, the copper powder according to any one of [1] to [4]. [6] The ratio (D / D) of the particle diameter D of the copper powder in the volume-based particle size distribution by the laser diffraction scattering method to the particle diameter D ２ / g or more and 3.0 m² ２ / g or less, the copper powder according to any one of [1] to [4]. [6] In the volume-based particle size distribution by the laser diffraction scattering method, the ratio (D / D) of the particle diameter D of the copper powder to the particle diameter D １０ is 5.0 or less, the copper powder according to any one of [1] to [5]. [7] The coefficient of variation (SD / D) obtained from the particle diameter D ９０ of the copper powder in the volume-based particle size distribution by the laser diffraction scattering method and the standard deviation SD ９０ / D １０ ) is 5.0 or less, the copper powder according to any one of [1] to [5]. [7] The coefficient of variation (SD / D) obtained from the particle diameter D ５０ and the standard deviation SD of the copper powder in the volume-based particle size distribution by the laser diffraction scattering method (SD / D ５０[1] to [6] Copper powder according to any one of [1] to [6], wherein the ratio is 0.60 or less. [8] Flat copper powder according to any one of [1] to [7]. [9] Conductive paste comprising copper powder according to any one of [1] to [8], resin, and solvent.

[10] Flat copper powder, wherein the average thickness T of the flat copper powder is determined by the following (method). Ａ The particle size D of the flattened copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution analysis. ５０ The ratio (D ５０ / T Ａ ) is 20.0 or less, and the particle size D of the flattened copper powder ５０ The particle size is 1.0 μm or more and 10.0 μm or less, and the particle size D in the volume-based particle size distribution of the flattened copper powder as measured by laser diffraction scattering particle size distribution measurement method. ５０ The standard deviation (SD) and the coefficient of variation (SD / D) obtained from it are... ５０ Flattened copper powder having a thickness of 0.30 or more and 0.60 or less. (Method) The thickness of 100 arbitrary flattened copper powders was measured from SEM images obtained by observing the flattened copper powder with an electron microscope, and the average value of the thicknesses of the 100 flattened copper powders was defined as the average thickness T of the flattened copper powder. Ａ (μm)

[11] The average thickness T of the flattened copper powder Ａ The flattened copper powder according to

[10] , wherein the particle size D is 0.1 μm or more and 2.0 μm or less.

[12] The particle size D of the flattened copper powder in the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution method. １０ Particle size D ９０ The ratio (D ９０ / D １０ The flattened copper powder according to

[10] or

[11] , wherein the ratio is 5.0 or less.

[13] The specific surface area S of the flattened copper powder obtained by nitrogen adsorption BET method is 0.10 m² ２ / g or more 3.0m ２ Flat copper powder according to any one of

[10] to

[12] , which is less than or equal to / g.

[14] The flat copper powder D ５０ / T ＡFlattened copper powder according to any one of

[10] to

[13] , wherein the ratio is greater than 3.4.

[15] A conductive paste comprising flattened copper powder according to any one of

[10] to

[14] , a resin, and a solvent.

[16] A method for producing flattened copper powder, comprising step A of flattening raw copper powder, wherein the particle size D of the flattened copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement method. ５０ The particle size fD of the flattened copper powder is calculated according to the following (method). ＢＥＴ The ratio (fD ＢＥＴ / D ５０ A method for producing flattened copper powder in which the particle size D of the raw copper powder is 0.70 or more and 1.50 or less. (Method) The particle size D of the raw copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement. ５０ The radius of the copper particles is measured and divided by 2. This value is taken as the radius r (μm) of the copper particles, assuming that the copper particles contained in the raw copper powder are spherical. The surface area of ​​the copper particles with radius r is S. １ (μm ２ ), the true density ρ of copper is 8.94 (g / cm³). ３ ) Specific surface area S per unit mass ＳＡ１ (m ２ The specific surface area S(m²) of the flattened copper powder is determined by the nitrogen adsorption BET method. ２ Measure the particle size fD of the flattened copper powder. Substitute each value into equation (1) below and solve the cubic equation for radius R, assuming that the flattened copper particles contained in the flattened copper powder are cylindrical. Of the solutions R obtained, double the largest positive value of R (2R) and use that value to determine the particle size fD of the flattened copper powder. ＢＥＴ Let (μm). 2πR ３ - S x S １ / S ＳＡ１ ×R + (8 / 3) ×πr ３ = 0 (1)

[17] Average thickness T of the flattened copper powder by the following (method) Ａ The particle size D of the raw copper powder ５０ The ratio (D ５０ / T ＡA method for producing flattened copper powder according to

[16] , wherein the ratio is 7.5 or less. (Method) The thickness of 100 arbitrary flattened copper powders is measured from SEM images obtained by observing the flattened copper powder with an electron microscope, and the average value of the thicknesses of the 100 flattened copper powders is defined as the average thickness T of the flattened copper powder. Ａ (μm)

[18] Particle size D of the raw copper powder in the volume-based particle size distribution by the laser diffraction scattering particle size distribution measurement method ５０ A method for producing flattened copper powder according to

[16] or

[17] , wherein the particle size is 0.1 μm or more and 10.0 μm or less.

[19] A method for producing flattened copper powder according to any one of

[16] to

[18] , wherein in step A, the raw copper powder is flattened using a bead mill.

[20] A method for producing flattened copper powder according to

[19] , wherein in step A, the bead diameter of the bead mill is 0.5 mm or less.

[21] A method for producing flattened copper powder according to

[19] or

[20] , wherein in step A, the bead filling amount of the bead mill is 50% or more.

[22] A method for producing flattened copper powder according to any one of

[19] to

[21] , wherein in step A, the peripheral speed of the bead mill is 5 m / s or more and 15 m / s or less.

[23] The particle size D in the volume-based particle size distribution of the flattened copper powder by laser diffraction scattering particle size distribution measurement. ５０ Specific surface area S (m²) of nitrogen adsorption by BET method relative to (μm) ２ The ratio (S / D) of / g ５０ ) is 0.07m ２ A method for producing flattened copper powder according to any one of

[16] to

[22] , wherein the particle size D in the volume-based particle size distribution of the flattened copper powder by laser diffraction scattering particle size distribution measurement method. ５０ A method for producing flattened copper powder according to any one of

[16] to

[23] , wherein the thickness is 0.1 μm or more and 10.0 μm or less.

[25] The average thickness T of the flattened copper powder according to the following (method) Ａ Particle size D in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution method. ５０ The ratio (D ５０ / T ＡA method for producing flattened copper powder according to any one of

[16] to

[24] , wherein the ratio is 20.0 or less. (Method) The thickness of 100 arbitrary flattened copper powders is measured from SEM images obtained by observing the flattened copper powder with an electron microscope, and the average value of the thicknesses of the 100 flattened copper powders is defined as the average thickness T of the flattened copper powder. Ａ (μm)

[26] The average thickness T of the flattened copper powder according to the following (method) Ａ A method for producing flattened copper powder according to any one of

[16] to

[25] , wherein the thickness is 0.1 μm or more and 2.0 μm or less. (Method) The thickness of 100 arbitrary flattened copper powders is measured from SEM images obtained by observing the flattened copper powder with an electron microscope, and the average value of the thicknesses of the 100 flattened copper powders is called the average thickness T of the flattened copper powder. Ａ (μm)

[27] The specific surface area S of the flattened copper powder obtained by nitrogen adsorption BET method is 0.10 m ２ / g or more 3.0m ２ A method for producing flattened copper powder according to any one of

[16] to

[26] , wherein the amount is less than or equal to / g.

[28] The particle size D of the flattened copper powder in the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution method. １０ Particle size D ９０ The ratio (D ９０ / D １０ A method for producing flattened copper powder according to any one of

[16] to

[27] , wherein the ratio of the flattened copper powder is 5.0 or less.

[29] The particle size D of the flattened copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement. ５０ The standard deviation (SD) and the coefficient of variation (SD / D) obtained from it are... ５０ A method for producing flattened copper powder according to any one of

[16] to

[28] , wherein the ratio is 0.60 or less.

[0008] According to one aspect of the present invention, copper powder with improved packing properties can be provided. According to one aspect of the present invention, flattened copper powder with improved packing properties can be provided. According to one aspect of the present invention, a manufacturing method for obtaining flattened copper powder with improved packing properties can be provided.

[0009] The present invention will be described below based on various embodiments. Note that when numerical ranges are described in steps, the upper and lower limits of each numerical range can be combined in any way.

[0010] <<First Embodiment>> <Copper Powder> The copper powder of the first embodiment has a particle diameter D in the volume-based particle size distribution measured by the laser diffraction and scattering method ５０ (μm), and the specific surface area S (m ２ / g) ratio (S / D ５０ ) is 0.07 m ２ / (g·μm) or more.

[0011] Although the mechanism by which the above problems are solved by the copper powder of the first embodiment is not clear, it is considered that when S / D ５０ is within the above numerical range, the dispersibility of the primary particles of the copper powder is improved, and further the particle size distribution of the copper powder becomes narrower. As a result, it is considered that the packing property of the particles is improved.

[0012] There are several advantages due to the improvement of the packing property of the particles. For example, when the copper powder with improved packing property is blended into the conductive paste, it is possible to mention the advantage that disconnection of the wiring obtained from the conductive paste is less likely to occur. The fact that the packing property is improved means that there are few voids between the particles, so even when the conductive paste is fired, the shrinkage is small and disconnection is less likely to occur.

[0013] The S / D ５０ of the copper powder of the first embodiment is 0.07 m ２ / (g·μm) or more, preferably 0.08 m ２ / (g·μm) or more, more preferably 0.09 m ２ / (g·μm) or more, and preferably 1.00 m ２ / (g·μm) or less, more preferably 0.75 m ２ / (g·μm) or less, still more preferably 0.50 m ２ / (g·μm) or less, still more preferably 0.40 m ２ / (g·μm) or less, still more preferably 0.30 m ２ / (g·μm) or less. Also, the S / D ５０ of the copper powder of the first embodiment is preferably 0.07 m ２ / (g·μm) or more and 1.00 m ２ / (g·μm) or less, more preferably 0.08 m ２ / (g・μm) or more 0.75m ２ / (g·μm) or less, more preferably 0.08 m ２ / (g・μm) or more 0.50m ２ / (g·μm) or less, more preferably 0.08 m ２ / (g・μm) or more 0.40m ２ / (g·μm) or less, more preferably 0.09 m ２ / (g・μm) or more 0.30m ２ It is less than or equal to / (g·μm).

[0014] The S / D ratio of copper powder ５０ By keeping the values ​​within the above range, copper powder with improved packing properties can be obtained.

[0015] The copper powder of the first embodiment can be obtained by appropriately selecting various conditions in step A, which is described later, for obtaining raw copper powder from a copper(I) compound, and various conditions in step B, which is flattening the raw copper powder. In particular, in step B, which is flattening the raw copper powder, the particle size D of the copper powder, as described later, ５０ Particle size fD of copper powder ＢＥＴ The ratio (fD ＢＥＴ / D ５０ ) and the average thickness T of the copper powder Ａ Particle size D of raw copper powder ５０ The ratio (D ５０ / T Ａ It is important to adjust the type of raw copper powder and the conditions for flattening the raw copper powder so that the result falls within a specific range. In the first embodiment, the copper powder before flattening is referred to as raw copper powder.

[0016] In the first embodiment, the specific surface area S of the copper powder obtained by the nitrogen adsorption BET method is preferably 0.10 m², from the viewpoint of further improving the packing performance of the copper powder. ２ / g or more, more preferably 0.15m ２ / g or more, more preferably 0.20m ２ / g or more, more preferably 0.23m ２ / g or more, more preferably 0.25m ２ It is 1 / g or more, and preferably 3.0 m ２ / g or less, more preferably 2.0m ２ / g or less, more preferably 1.5m２ / g or less, more preferably 1.0m ２ / g or less, more preferably 0.80m ２ It is less than or equal to / g. The specific surface area S of the copper powder of the first embodiment, obtained by the nitrogen adsorption BET method, is preferably 0.10 m² from the viewpoint of further improving the packing performance of the copper powder. ２ / g or more 3.0m ２ / g or less, more preferably 0.15m ２ / g or more 2.0m ２ / g or less, more preferably 0.20m ２ / g or more 1.5m ２ / g or less, more preferably 0.23m ２ / g or more 1.0m ２ / g or less, more preferably 0.25m ２ / g or more 0.80m ２ It is less than or equal to / g.

[0017] The particle size D of the copper powder in the first embodiment ５０ From the viewpoint of further improving the packing performance of the copper powder, the particle size D is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1.0 μm or more, even more preferably 1.5 μm or more, and preferably 10.0 μm or less, more preferably 9.0 μm or less, even more preferably 7.5 μm or less, and even more preferably 7.0 μm or less. The particle size D of the copper powder in the first embodiment ５０ From the viewpoint of further improving the packing performance of copper powder, the particle size is preferably 0.1 μm to 10.0 μm, more preferably 0.5 μm to 9.0 μm, even more preferably 1.0 μm to 7.5 μm, and even more preferably 1.5 μm to 7.0 μm.

[0018] The particle size D of the copper powder in the first embodiment ５０ The coefficient of variation (SD / D) obtained from the standard deviation SD is obtained from the coefficient of variation (SD / D ５０ From the viewpoint of further improving the packing performance of copper powder, the coefficient of the copper powder is preferably 0.60 or less, more preferably 0.59 or less, even more preferably 0.55 or less, even more preferably 0.50 or less, even more preferably 0.45 or less, and even more preferably 0.40 or less. SD / D ５０The lower limit of is not particularly limited, but for example, it may be 0.10 or more, 0.15 or more, 0.20 or more, or 0.30 or more. Also, the coefficient of variation (SD / D ５０ From the viewpoint of further improving the packing performance of copper powder, the coefficient of copper is preferably 0.10 to 0.60, more preferably 0.15 to 0.59, even more preferably 0.20 to 0.55, even more preferably 0.20 to 0.50, even more preferably 0.20 to 0.45, and even more preferably 0.30 to 0.40.

[0019] Particle size D in the volume-based particle size distribution of copper powder according to the first embodiment, measured by laser diffraction scattering particle size distribution analysis. １０ Particle size D ９０ The ratio (D ９０ / D １０ From the viewpoint of further improving the packing ability of the copper powder, the D is preferably 5.0 or less, more preferably 4.8 or less, even more preferably 4.6 or less, even more preferably 4.4 or less, and preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more, and even more preferably 2.5 or more. Also, the copper powder of the first embodiment, the D ９０ / D １０ From the viewpoint of further improving the packing performance of copper powder, the value is preferably 1.0 to 5.0, more preferably 1.5 to 4.8, even more preferably 2.0 to 4.6, and even more preferably 2.5 to 4.4.

[0020] The average thickness T of the copper powder of the first embodiment, determined by the following (method). Ａ From the viewpoint of further improving the packing performance of the copper powder, the thickness is preferably 0.1 μm or more, more preferably 0.15 μm or more, even more preferably 0.2 μm or more, and preferably 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 1.2 μm or less. The average thickness T of the copper powder of the first embodiment, according to the following (method) ＡFrom the viewpoint of further improving the packing performance of the copper powder, the thickness is preferably 0.1 μm or more and 2.0 μm or less, more preferably 0.15 μm or more and 1.5 μm or less, and even more preferably 0.2 μm or more and 1.2 μm or less. (Method) The thickness of 100 arbitrary copper powders is measured from the SEM image obtained by observing the copper powder with an electron microscope, and the average value of the thicknesses of the 100 copper powders is defined as the average thickness T of the copper powder. Ａ Let it be (μm).

[0021] The average thickness T of the copper powder in the first embodiment Ａ The particle size D in relation to (μm) ５０ Ratio of (μm) (D ５０ / T Ａ From the viewpoint of further improving the packing properties of the copper powder, the D is preferably 20.0 or less, more preferably 17.5 or less, even more preferably 15.0 or less, even more preferably 14.0 or less, and preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more, and even more preferably 3.0 or more. The D of the copper powder in the first embodiment ５０ / T Ａ From the viewpoint of further improving the packing performance of copper powder, the value is preferably 1.0 to 20.0, more preferably 1.5 to 17.5, even more preferably 2.0 to 15.0, and even more preferably 3.0 to 14.0.

[0022] In the first embodiment, the copper powder is preferably flattened copper powder, from the viewpoint of further improving the packing properties of the copper powder and improving the coatability and sintering density of the resulting conductive paste.

[0023] The copper powder of the first embodiment is not particularly limited in its applications, but because it has improved packing properties, it is suitably used in conductive pastes.

[0024] <Method for manufacturing copper powder> The method for manufacturing copper powder according to the first embodiment will be described below.

[0025] The method for producing copper powder according to the first embodiment is not particularly limited, but from the viewpoint of obtaining the copper powder according to the first embodiment more effectively, it is preferable to include a step A of obtaining raw material copper powder from a copper(I) compound and a step B of flattening the raw material copper powder. Furthermore, the method for producing copper powder according to the first embodiment may further include a step C of treating the surface of the copper powder with a fatty acid salt.

[0026] <Step A> Step A of the method for producing copper powder according to the first embodiment will be described below. Step A is a step in which raw material copper powder is obtained from a copper(I) compound. The specific method of Step A is not particularly limited, but from the viewpoint of further improving the dispersibility of the primary particles of copper powder and further narrowing the particle size distribution of copper powder, it is preferable to obtain raw material copper powder from a slurry A containing a copper(I) compound and polyvinyl alcohol.

[0027] The dispersion medium used in slurry A is not particularly limited, and commonly used dispersion mediums for slurry preparation, such as water or hydrophilic dispersion mediums, can be used. Furthermore, a mixture of multiple types of dispersion mediums may be used.

[0028] Examples of hydrophilic dispersion media include: alkanediols such as ethylene glycol and propylene glycol, polyhydric alcohols such as glycerin; sugar alcohols, lower alcohols such as ethanol, methanol, butanol, propanol, and isopropanol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene Examples include glycol ethers such as glycol mono-t-butyl ether, triethylene glycol monoethyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-iso-propyl ether, and tripropylene glycol monomethyl ether; and alkanolamines such as ethanolamine, diethanolamine, and triethanolamine.

[0029] The content of copper(I) compounds in slurry A is not particularly limited, and may be, for example, 1% by mass or more and 25% by mass or less.

[0030] The copper(I) compound is not particularly limited as long as it is a compound containing monovalent copper, and for example, it includes one or more selected from the group consisting of cuprous oxide, copper chloride, copper bromide, and copper iodide, and preferably contains cuprous oxide.

[0031] The content of polyvinyl alcohol in slurry A is not particularly limited, but from the viewpoint of further improving the dispersibility of primary copper powder particles and further narrowing the particle size distribution of copper powder, it is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of copper(I) compound, and may also be, for example, 5 parts by mass or less, 2 parts by mass or less, or 1 part by mass or less.

[0032] The degree of saponification of polyvinyl alcohol is not particularly limited, but from the viewpoint of further improving the dispersibility of the primary particles of copper powder and further narrowing the particle size distribution of copper powder, it is preferably 70 mol% or more, more preferably 75 mol% or more, even more preferably 80 mol% or more, and even more preferably 85 mol% or more, and may be, for example, 100 mol% or less, for example 95 mol% or less, and for example 90 mol% or less.

[0033] The viscosity of polyvinyl alcohol is not particularly limited, but from the viewpoint of further improving the dispersibility of primary copper particles and further narrowing the particle size distribution of copper powder, the viscosity of a 4% aqueous solution measured at 20°C using a Brookfield rotational viscometer in accordance with JIS K6726:1994 is, for example, 0.1 mPa·s or more, preferably 1 mPa·s or more, more preferably 4 mPa·s or more, and may be, for example, 100 mPa·s or less, for example, 50 mPa·s or less, and for example, 10 mPa·s or less.

[0034] The type of reaction used to produce the raw copper powder in step A is not particularly limited, but for example, the raw copper powder can be produced by disproportionating the copper(I) compound.

[0035] The raw material copper powder of the first embodiment is preferably obtained by a disproportionation reaction.

[0036] The components of slurry A are not particularly limited, but from the viewpoint of promoting the reaction in the reaction vessel, it preferably contains an acid, more preferably one or more selected from the group consisting of hydrochloric acid, nitric acid, and sulfuric acid, and even more preferably sulfuric acid. Here, during the disproportionation reaction of the copper(I) compound, the acid in slurry A may be in the form of a copper salt (copper hydrochloride, copper nitrate, copper sulfate, etc.). The particle size of the copper powder can be adjusted by adjusting the rate at which the acid is supplied into the reaction vessel. For example, lowering the acid supply rate tends to increase the particle size of the copper powder.

[0037] The pH in the reaction vessel in step A is not particularly limited, but for example it is 0.1 or higher, may be 0.5 or higher, may be 1 or higher, and from the viewpoint of further improving the dispersibility of the primary particles of copper powder and further narrowing the particle size distribution of copper powder, it is preferably 7 or lower, more preferably 6 or lower, even more preferably 5 or lower, and even more preferably 2.5 or lower. Here, the pH in the reaction vessel in step A is the pH of the slurry in the reaction vessel when step A is completed.

[0038] The temperature inside the reaction vessel in step A is not particularly limited, but may be, for example, 5°C or higher, for example, 10°C or higher, or 20°C or higher. From the viewpoint of further improving the dispersibility of the primary particles of copper powder and further narrowing the particle size distribution of copper powder, it is preferably 90°C or lower, more preferably 80°C or lower, even more preferably 70°C or lower, and may also be 60°C or lower, or 50°C or lower. Here, the temperature inside the reaction vessel in step A is the temperature of the slurry inside the reaction vessel. The particle size of the copper powder can be adjusted by adjusting the temperature inside the reaction vessel. For example, increasing the temperature inside the reaction vessel tends to increase the particle size of the copper powder.

[0039] <Step B> Step B of the copper powder manufacturing method of the first embodiment will now be described. Step B is a step of flattening the raw copper powder obtained in Step A. The equipment used for the flattening process in Step B is not particularly limited, but a bead mill is preferably used from the viewpoint of further improving the packing ability of the copper powder.

[0040] In step B, the bead diameter of the bead mill is preferably 0.5 mm or less, more preferably 0.4 mm or less, and even more preferably 0.3 mm or less. The lower limit of the bead diameter of the bead mill is not particularly limited, but for example it may be 0.1 mm or more, and may be 0.15 mm or more. Also in step B, the bead filling rate of the bead mill is preferably 50% or more, more preferably 60% or more, and even more preferably 65% ​​or more. The upper limit of the bead filling rate of the bead mill is not particularly limited, but for example it may be 98% or less, and may be 95% or less. Furthermore, in step B, the peripheral speed of the bead mill is preferably 5 m / s or more, more preferably 6 m / s or more, even more preferably 7 m / s or more, and preferably 15 m / s or less, more preferably 14 m / s or less, and even more preferably less than 14 m / s. In step B, the peripheral speed of the bead mill is preferably 5 m / s or more and 15 m / s or less, more preferably 6 m / s or more and 14 m / s or less, and even more preferably 7 m / s or more and less than 14 m / s. By setting the bead mill conditions within the above range, the shape of the copper powder particles after flattening can be controlled.

[0041] From the viewpoint of obtaining the copper powder of the first embodiment more effectively, the particle size D of the copper powder of the first embodiment in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement method ５０ The particle size fD of the copper powder in the first embodiment, calculated by the following (method), is as follows: ＢＥＴ The ratio (fD ＢＥＴ / D ５０ It is preferable to adjust the type of raw copper powder and the conditions of the flattening treatment of the raw copper powder so that the particle size D of the raw copper powder is preferably 0.70 or more and 1.50 or less, more preferably 0.75 or more and 1.40 or less, and even more preferably 0.80 or more and 1.30 or less. (Method) Particle size D of the raw copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement method ５０ The radius of the copper particles is measured and divided by 2. This value is taken as the radius r (μm) of the copper particles, assuming that the copper particles contained in the raw copper powder are spherical. The surface area of ​​the copper particles with radius r is S. １ (μm ２ ), the true density ρ of copper is 8.94 (g / cm³). ３) Specific surface area S per unit mass ＳＡ１ (m ２ The specific surface area S(m²) of the copper powder of the first embodiment is determined by the nitrogen adsorption BET method. ２ The particle size fD of the copper powder in the first embodiment is measured. Substitute each value into the following equation (1) and solve the cubic equation for radius R, assuming that the copper particles contained in the copper powder of the first embodiment are cylindrical. Of the solutions R obtained, the largest positive value of R is doubled (2R) to obtain the particle size fD of the copper powder of the first embodiment. ＢＥＴ Let (μm). 2πR ３ - S x S １ / S ＳＡ１ ×R + (8 / 3) ×πr ３ = 0 (1)

[0042] Furthermore, from the viewpoint of obtaining the copper powder of the first embodiment more effectively, the average thickness T of the copper powder of the first embodiment obtained by the following (method) is... Ａ The particle size D of the raw copper powder ５０ The ratio (D ５０ / T Ａ It is preferable to adjust the type of raw copper powder and the conditions of the flattening treatment of the raw copper powder so that the ratio is preferably 1.0 to 7.5, more preferably 1.5 to 7.4, and even more preferably 2.0 to 7.3. (Method) The thickness of 100 arbitrary copper powders is measured from the SEM image obtained by observing the copper powder with an electron microscope, and the average value of the thicknesses of the 100 copper powders is called the average thickness T of the copper powder. Ａ Let it be (μm).

[0043] <Step C> Step C of the copper powder manufacturing method of the first embodiment will now be described. In Step C, the surface of the copper powder is treated with a fatty acid salt. Step C includes, for example, a dispersion step of attaching fatty acids to the surface of the copper powder and dispersing the copper powder, and a film formation step of forming a fatty acid film on the surface of the copper powder.

[0044] The copper powder of the first embodiment preferably includes a fatty acid coating on its surface.

[0045] Examples of fatty acid salts include alkali metal salts of fatty acids having 8 to 20 carbon atoms. More specifically, fatty acid salts include straight-chain or branched fatty acids having 8 to 20 carbon atoms, such as straight-chain fatty acids like octanoic acid (8 carbon atoms), nonanoic acid (9 carbon atoms), decanoic acid (10 carbon atoms), dodecanoic acid (12 carbon atoms), tetradecanoic acid (14 carbon atoms), pentadecanoic acid (15 carbon atoms), hexadecanoic acid (palmitic acid) (16 carbon atoms), heptadecanoic acid (17 carbon atoms), octadecanoic acid (stearic acid) (18 carbon atoms), and eicosanoic acid (20 carbon atoms), as well as alkali metal salts of branched fatty acids such as oleic acid, linoleic acid, and linolenic acid (18 carbon atoms).

[0046] The amount of fatty acid salt added is preferably 0.05% by mass or more and 5% by mass or less, relative to the total amount of copper powder (in a dry state).

[0047] The pH in the reaction vessel during the dispersion process is not particularly limited, but from the viewpoint of facilitating the dissolution of fatty acid salts, it is preferably 9 or higher, more preferably 10 or higher, and for example, 11 or lower.

[0048] In the dispersion process, it is preferable to add the fatty acid salt to the reaction vessel and then allow it to mature. The maturation time is preferably between 5 minutes and 60 minutes.

[0049] In the film formation process, the reaction vessel is neutralized with acid to form a fatty acid film on the surface of the copper powder. The type of acid is not particularly limited and may be a strong acid such as hydrochloric acid, sulfuric acid, or nitric acid, or a weak acid. However, from the following viewpoints, it is preferable to use a weak acid to neutralize the reaction vessel in the film formation process. By using a weak acid, the fatty acid film can be formed more uniformly, and the aggregation of the resulting copper fine particles can be suppressed. In addition, by using a weak acid, the fatty acid film increases the hydrophobicity of the resulting copper fine particles, which can speed up the settling rate of the copper fine particles in the washing process described later, thereby improving productivity. Furthermore, by using a weak acid, a fatty acid film can be formed uniformly on the copper powder, making it less likely for the copper fine particles to aggregate with each other, resulting in copper fine particles with fewer aggregated particles. The type of weak acid used for neutralization is not particularly limited and may include one or more selected from citric acid, ascorbic acid, and acetic acid.

[0050] In the film formation process, it is preferable to add acid to the reaction vessel and then allow it to mature. The maturation time is preferably between 5 minutes and 60 minutes.

[0051] <Other steps> The method for producing copper powder according to the first embodiment may include steps other than steps A to C described above.

[0052] The method for producing copper powder according to the first embodiment may further include a step of washing the copper powder. The washing method is not particularly limited and can be carried out, for example, by adding water and stirring.

[0053] The method for producing copper powder according to the first embodiment may further include a step of sorting copper powder and intermediates. Sorting of copper powder and intermediates can be done, for example, using a sieve, and by using a sieve of a specific size, materials within a specific particle size range can be sorted. This step may be performed at the slurry stage, or after drying to a powder state.

[0054] The method for producing copper powder according to the first embodiment may further include a step of drying the copper powder. The method for drying the copper powder is not particularly limited; for example, it can be dried by dewatering by centrifugal separation followed by heating and drying in a dryer or the like.

[0055] The method for producing copper powder according to the first embodiment may further include a step of crushing the copper powder or intermediate. The crushing of the copper powder or intermediate can be carried out using a known crusher. The type of crusher is not particularly limited, and any type such as a high-speed rotary mill, hammer mill, or atomizer can be used.

[0056] <Conductive Paste> The conductive paste of the first embodiment will be described below.

[0057] The conductive paste of the first embodiment includes, for example, the copper powder of the first embodiment, a resin, and a solvent.

[0058] Because the copper powder of the first embodiment has improved packing properties, it is possible to easily design a paste with high reproducibility and stability.

[0059] The resin used in the conductive paste of the first embodiment is not particularly limited, and any known raw material for conductive paste can be used as appropriate. For example, cellulosic resins such as ethylcellulose can be used, and they are added as an organic vehicle dissolved in an organic solvent such as terpineol. The amount of resin added should be kept to a level that does not hinder sinterability. For this reason, the amount of resin added is preferably 5% by mass or less of the total conductive paste, and more preferably 2% by mass or less.

[0060] The solvent used in the conductive paste of the first embodiment is not particularly limited, and known raw materials for conductive pastes can be used as appropriate. For example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, terpineol, and triethanolamine are preferred. Among these organic solvents, amines are preferred because they have reducing ability and have the effect of creating a locally reducing atmosphere on the paste surface during firing. Furthermore, using water as a solvent can reduce the amount of organic solvents that are harmful to the human body, thereby increasing the value of the copper paste. The amount of solvent is not particularly limited, but it should be adjusted as appropriate, taking into account the dispersibility and particle size distribution of the copper powder, so that the viscosity is suitable for conductive film formation methods such as screen printing and inkjet printing.

[0061] Although the first embodiment of the present invention has been described above, these are merely examples of the present invention, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and any modifications, improvements, etc., that can achieve the objectives of the present invention are included in the present invention.

[0062] <<Second Embodiment>> <Flat Copper Powder> The flat copper powder of the second embodiment has an average thickness T determined by the following (method). Ａ The particle size D of the flattened copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution analysis. ５０ The ratio (D ５０ / T Ａ ) is 20.0 or less, and the particle size D of the flattened copper powder ５０The particle size D of the flattened copper powder is 1.0 μm or more and 10.0 μm or less, and the particle size D of the volume-based particle size distribution of the flattened copper powder is measured by laser diffraction scattering particle size distribution measurement. ５０ The standard deviation (SD) and the coefficient of variation (SD / D) obtained from it are... ５０ ) is between 0.30 and 0.60. (Method) The thickness of 100 arbitrary flat copper powders was measured from SEM images obtained by observing the flat copper powder with an electron microscope, and the average value of the thicknesses of the 100 flat copper powders was used as the average thickness T of the flat copper powders. Ａ Let it be (μm).

[0063] The mechanism by which the flattened copper powder of the second embodiment solves the above-mentioned problems is not clear, but D ５０ / T Ａ , the particle size D ５０ and the SD / D ５０ Because the values ​​fall within the above range, the dispersibility of the primary particles of the flattened copper powder is improved, and the particle size distribution of the flattened copper powder is narrowed. This is expected to improve the particle packing efficiency.

[0064] There are several advantages to improved particle packing properties. For example, when flattened copper powder with improved packing properties is incorporated into a conductive paste, it becomes less likely for the wiring obtained from the conductive paste to break. Improved packing properties mean that there are fewer voids between particles, so even when the conductive paste is fired, shrinkage is small, and wire breakage is less likely to occur.

[0065] The average thickness T of the flattened copper powder in the second embodiment Ａ The particle size D in relation to (μm) ５０ Ratio of (μm) (D ５０ / T Ａ The D of the flattened copper powder in the second embodiment is 20.0 or less, and from the viewpoint of further improving the packing properties of the flattened copper powder, it is preferably 17.5 or less, more preferably 15.0 or less, even more preferably 14.0 or less, and preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more, even more preferably 3.0 or more, even more preferably more than 3.4, and even more preferably 3.5 or more. ５０ / T ＡFrom the viewpoint of further improving the packing performance of the flattened copper powder, the value is preferably 1.0 to 20.0, more preferably 1.5 to 17.5, even more preferably 2.0 to 15.0, even more preferably 3.0 to 14.0, even more preferably greater than 3.4 and 14.0 or less, and even more preferably 3.5 to 14.0.

[0066] The particle size D of the flattened copper powder in the second embodiment ５０ From the viewpoint of further improving the packing performance of the flattened copper powder, the particle size D is preferably 1.0 μm or more, more preferably 1.1 μm or more, even more preferably 1.3 μm or more, even more preferably 1.5 μm or more, and preferably 10.0 μm or less, more preferably 9.0 μm or less, even more preferably 8.0 μm or less, and even more preferably 7.5 μm or less. The particle size D of the flattened copper powder in the second embodiment ５０ The particle size is 1.0 μm or more and 10.0 μm or less, and from the viewpoint of further improving the packing properties of the flattened copper powder, it is preferably 1.1 μm or more and 9.0 μm or less, more preferably 1.3 μm or more and 8.0 μm or less, and even more preferably 1.5 μm or more and 7.5 μm or less.

[0067] The particle size D of the flattened copper powder in the second embodiment ５０ The coefficient of variation (SD / D) obtained from the standard deviation SD is obtained from the coefficient of variation (SD / D ５０ The ratio is 0.30 to 0.60, and from the viewpoint of further improving the packing performance of the flattened copper powder, it is preferably 0.59 or less, more preferably 0.55 or less, even more preferably 0.50 or less, even more preferably 0.45 or less, and even more preferably 0.40 or less. SD / D ５０ The lower limit of the coefficient of variation (SD / D) is 0.30 or higher, and may also be 0.31 or higher, 0.32 or higher, 0.33 or higher, 0.34 or higher, or 0.35 or higher. ５０ From the viewpoint of further improving the packing performance of the flattened copper powder, the coefficient is preferably 0.31 to 0.59, more preferably 0.32 to 0.55, even more preferably 0.33 to 0.50, even more preferably 0.34 to 0.45, and even more preferably 0.35 to 0.40.

[0068] The aforementioned D５０ / T Ａ , the particle size D ５０ and the SD / D ５０ By keeping the values ​​within the above range, flattened copper powder with improved packing properties can be obtained.

[0069] The flattened copper powder of the second embodiment can be obtained by appropriately selecting various conditions in step A, which is described later, for obtaining raw copper powder from a copper(I) compound, and various conditions in step B, which is flattening the raw copper powder. In particular, in step B, which is flattening the raw copper powder, the particle size D of the flattened copper powder, as described later, ５０ Particle size fD of flattened copper powder ＢＥＴ The ratio (fD ＢＥＴ / D ５０ ) and the average thickness T of the flattened copper powder Ａ Particle size D of raw copper powder ５０ The ratio (D ５０ / T Ａ It is important to adjust the type of raw copper powder and the conditions for flattening the raw copper powder so that the result falls within a specific range. In the second embodiment, the copper powder before flattening is referred to as raw copper powder.

[0070] The average thickness T of the flattened copper powder in the second embodiment Ａ From the viewpoint of further improving the packing properties of the flattened copper powder, the average thickness T is preferably 0.1 μm or more, more preferably 0.15 μm or more, even more preferably 0.2 μm or more, and preferably 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 1.2 μm or less. The average thickness T of the flattened copper powder of the second embodiment Ａ From the viewpoint of further improving the packing performance of the flattened copper powder, the particle size is preferably 0.1 μm or more and 2.0 μm or less, more preferably 0.15 μm or more and 1.5 μm or less, and even more preferably 0.2 μm or more and 1.2 μm or less.

[0071] Particle size D in the volume-based particle size distribution of the flattened copper powder of the second embodiment, measured by laser diffraction scattering particle size distribution analysis. １０ Particle size D ９０ The ratio (D ９０ / D １０From the viewpoint of further improving the packing properties of the flattened copper powder, the D is preferably 5.0 or less, more preferably 4.8 or less, even more preferably 4.6 or less, even more preferably 4.4 or less, and preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more, and even more preferably 2.5 or more. Also, the D of the flattened copper powder of the second embodiment ９０ / D １０ From the viewpoint of further improving the packing performance of the flattened copper powder, the value is preferably 1.0 to 5.0, more preferably 1.5 to 4.8, even more preferably 2.0 to 4.6, and even more preferably 2.5 to 4.4.

[0072] In the second embodiment, the specific surface area S of the flattened copper powder obtained by the nitrogen adsorption BET method is preferably 0.10 m², from the viewpoint of further improving the packing properties of the flattened copper powder. ２ / g or more, more preferably 0.15m ２ / g or more, more preferably 0.20m ２ / g or more, more preferably 0.23m ２ / g or more, more preferably 0.25m ２ It is 1 / g or more, and preferably 3.0 m ２ / g or less, more preferably 2.0m ２ / g or less, more preferably 1.5m ２ / g or less, more preferably 1.0m ２ / g or less, more preferably 0.80m ２ It is less than or equal to / g. The specific surface area S of the flattened copper powder of the second embodiment, obtained by the nitrogen adsorption BET method, is preferably 0.10 m² from the viewpoint of further improving the packing performance of the flattened copper powder. ２ / g or more 3.0m ２ / g or less, more preferably 0.15m ２ / g or more 2.0m ２ / g or less, more preferably 0.20m ２ / g or more 1.5m ２ / g or less, more preferably 0.23m ２ / g or more 1.0m ２ / g or less, more preferably 0.25m ２ / g or more 0.80m ２ It is less than or equal to / g.

[0073] The applications of the flattened copper powder of the second embodiment are not particularly limited, but because the flattened copper powder of the second embodiment has improved packing properties, it is suitably used in conductive pastes.

[0074] <Method for manufacturing flattened copper powder> The method for manufacturing flattened copper powder according to the second embodiment will be described below.

[0075] The method for producing the flattened copper powder of the second embodiment is not particularly limited, but from the viewpoint of obtaining the flattened copper powder of the second embodiment more effectively, it is preferable to include a step A of obtaining raw material copper powder from a copper(I) compound and a step B of flattening the raw material copper powder. Furthermore, the method for producing the flattened copper powder of the second embodiment may further include a step C of treating the surface of the flattened copper powder with a fatty acid salt.

[0076] <Step A> Step A of the method for producing flattened copper powder according to the second embodiment will be described below. Step A is a step in which raw material copper powder is obtained from a copper(I) compound. The specific method of Step A is not particularly limited, but from the viewpoint of further improving the dispersibility of the primary particles of the flattened copper powder and further narrowing the particle size distribution of the flattened copper powder, it is preferable to obtain the raw material copper powder from a slurry A containing a copper(I) compound and polyvinyl alcohol.

[0077] The dispersion medium used in slurry A is not particularly limited, and commonly used dispersion mediums for slurry preparation, such as water or hydrophilic dispersion mediums, can be used. Furthermore, a mixture of multiple types of dispersion mediums may be used.

[0078] Examples of hydrophilic dispersion media include: alkanediols such as ethylene glycol and propylene glycol, polyhydric alcohols such as glycerin; sugar alcohols, lower alcohols such as ethanol, methanol, butanol, propanol, and isopropanol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene Examples include glycol ethers such as glycol mono-t-butyl ether, triethylene glycol monoethyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-iso-propyl ether, and tripropylene glycol monomethyl ether; and alkanolamines such as ethanolamine, diethanolamine, and triethanolamine.

[0079] The content of copper(I) compounds in slurry A is not particularly limited, and may be, for example, 1% by mass or more and 25% by mass or less.

[0080] The copper(I) compound is not particularly limited as long as it is a compound containing monovalent copper, and for example, it includes one or more selected from the group consisting of cuprous oxide, copper chloride, copper bromide, and copper iodide, and preferably contains cuprous oxide.

[0081] The content of polyvinyl alcohol in slurry A is not particularly limited, but from the viewpoint of further improving the dispersibility of the primary particles of the flattened copper powder and further narrowing the particle size distribution of the flattened copper powder, it is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of copper(I) compound, and may also be, for example, 5 parts by mass or less, 2 parts by mass or less, or 1 part by mass or less.

[0082] The degree of saponification of polyvinyl alcohol is not particularly limited, but from the viewpoint of further improving the dispersibility of the primary particles of the flattened copper powder and further narrowing the particle size distribution of the flattened copper powder, it is preferably 70 mol% or more, more preferably 75 mol% or more, even more preferably 80 mol% or more, and even more preferably 85 mol% or more, and may be, for example, 100 mol% or less, for example 95 mol% or less, and for example 90 mol% or less.

[0083] The viscosity of polyvinyl alcohol is not particularly limited, but from the viewpoint of further improving the dispersibility of the primary particles of the flattened copper powder and further narrowing the particle size distribution of the flattened copper powder, the viscosity of a 4% aqueous solution measured at 20°C using a Brookfield type rotational viscometer in accordance with JIS K6726:1994 is, for example, 0.1 mPa·s or more, preferably 1 mPa·s or more, more preferably 4 mPa·s or more, and may be, for example, 100 mPa·s or less, for example, 50 mPa·s or less, and for example, 10 mPa·s or less.

[0084] The type of reaction used to produce the raw copper powder in step A is not particularly limited, but for example, the raw copper powder can be produced by disproportionating the copper(I) compound.

[0085] The raw material copper powder of the second embodiment is preferably obtained by a disproportionation reaction.

[0086] The components of slurry A are not particularly limited, but from the viewpoint of promoting the reaction in the reaction vessel, it preferably contains an acid, more preferably one or more selected from the group consisting of hydrochloric acid, nitric acid, and sulfuric acid, and even more preferably sulfuric acid. Here, during the disproportionation reaction of the copper(I) compound, the acid in slurry A may be in the form of a copper salt (copper hydrochloride, copper nitrate, copper sulfate, etc.). The particle size of the raw copper powder can be adjusted by adjusting the rate at which the acid is supplied into the reaction vessel. For example, lowering the acid supply rate tends to increase the particle size of the raw copper powder.

[0087] The pH in the reaction vessel in step A is not particularly limited, but for example it is 0.1 or higher, may be 0.5 or higher, may be 1 or higher, and from the viewpoint of further improving the dispersibility of the primary particles of the flattened copper powder and further narrowing the particle size distribution of the flattened copper powder, it is preferably 7 or lower, more preferably 6 or lower, even more preferably 5 or lower, and even more preferably 2.5 or lower. Here, the pH in the reaction vessel in step A is the pH of the slurry in the reaction vessel when step A is completed.

[0088] The temperature inside the reaction vessel in step A is not particularly limited, but may be, for example, 5°C or higher, for example, 10°C or higher, or 20°C or higher. From the viewpoint of further improving the dispersibility of the primary particles of the flattened copper powder and further narrowing the particle size distribution of the flattened copper powder, it is preferably 90°C or lower, more preferably 80°C or lower, even more preferably 70°C or lower, and may also be 60°C or lower, or 50°C or lower. Here, the temperature inside the reaction vessel in step A is the temperature of the slurry inside the reaction vessel. The particle size of the raw copper powder can be adjusted by adjusting the temperature inside the reaction vessel. For example, increasing the temperature inside the reaction vessel tends to increase the particle size of the raw copper powder.

[0089] <Step B> Step B of the method for producing flattened copper powder according to the second embodiment will now be described. Step B is a step in which the raw copper powder obtained in Step A is flattened. The equipment used for the flattening process in Step B is not particularly limited, but a bead mill is preferably used from the viewpoint of further improving the packing properties of the flattened copper powder.

[0090] In step B, the bead diameter of the bead mill is preferably 0.5 mm or less, more preferably 0.4 mm or less, and even more preferably 0.3 mm or less. The lower limit of the bead diameter of the bead mill is not particularly limited, but for example it may be 0.1 mm or more, and may be 0.15 mm or more. Also in step B, the bead filling rate of the bead mill is preferably 50% or more, more preferably 60% or more, and even more preferably 65% ​​or more. The upper limit of the bead filling rate of the bead mill is not particularly limited, but for example it may be 98% or less, and may be 95% or less. Furthermore, in step A, the peripheral speed of the bead mill is preferably 5 m / s or more, more preferably 6 m / s or more, even more preferably 7 m / s or more, and preferably 15 m / s or less, more preferably 14 m / s or less, and even more preferably less than 14 m / s. In step B, the peripheral speed of the bead mill is preferably 5 m / s or more and 15 m / s or less, more preferably 6 m / s or more and 14 m / s or less, and even more preferably 7 m / s or more and less than 14 m / s. By setting the bead mill conditions within the above range, the shape of the flattened copper powder particles after the flattening treatment can be controlled.

[0091] From the viewpoint of more effectively obtaining the flattened copper powder of the second embodiment, the particle size D of the flattened copper powder of the second embodiment in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution analysis is... ５０ The particle size fD of the flattened copper powder of the second embodiment, calculated by the following (method), is as follows: ＢＥＴ The ratio (fD ＢＥＴ / D ５０ It is preferable to adjust the type of raw copper powder and the conditions of the flattening treatment of the raw copper powder so that the particle size D of the raw copper powder is preferably 0.70 or more and 1.50 or less, more preferably 0.75 or more and 1.40 or less, and even more preferably 0.80 or more and 1.30 or less. (Method) Particle size D of the raw copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement method ５０ The radius of the copper particles is measured and divided by 2. This value is taken as the radius r (μm) of the copper particles, assuming that the copper particles contained in the raw copper powder are spherical. The surface area of ​​the copper particles with radius r is S. １ (μm ２ ), the true density ρ of copper is 8.94 (g / cm³).３ ) Specific surface area S per unit mass ＳＡ１ (m ２ The specific surface area S(m²) of the flattened copper powder of the second embodiment is determined by the nitrogen adsorption BET method. ２ Measure the amount ( / g). Substitute each value into the following equation (1) and solve the cubic equation for radius R, assuming that the copper particles contained in the flattened copper powder of the second embodiment are cylindrical. Of the obtained solutions R, take twice the largest positive value of R (2R) and use that value to determine the particle size fD of the flattened copper powder of the second embodiment. ＢＥＴ Let (μm). 2πR ３ - S x S １ / S ＳＡ１ ×R + (8 / 3) ×πr ３ = 0 (1)

[0092] Furthermore, from the viewpoint of obtaining the flattened copper powder of the second embodiment more effectively, the average thickness T of the flattened copper powder of the second embodiment by the following (method) is described below. Ａ The particle size D of the raw copper powder ５０ The ratio (D ５０ / T Ａ It is preferable to adjust the type of raw copper powder and the conditions of the flattening treatment of the raw copper powder so that the ratio is preferably 1.0 to 7.5, more preferably 1.5 to 7.4, and even more preferably 2.0 to 7.3. (Method) The thickness of 100 arbitrary flattened copper powders is measured from the SEM image obtained by observing the flattened copper powder with an electron microscope, and the average value of the thicknesses of the 100 flattened copper powders is called the average thickness T of the flattened copper powder. Ａ Let it be (μm).

[0093] <Step C> Step C of the method for producing flattened copper powder according to the second embodiment will be described below. In Step C, the surface of the flattened copper powder is treated with a fatty acid salt. Step C includes, for example, a dispersion step in which fatty acids are attached to the surface of the flattened copper powder and the flattened copper powder is dispersed, and a film formation step in which a fatty acid film is formed on the surface of the flattened copper powder.

[0094] The flattened copper powder of the second embodiment preferably contains a fatty acid coating on its surface.

[0095] Examples of fatty acid salts include alkali metal salts of fatty acids having 8 to 20 carbon atoms. More specifically, fatty acid salts include straight-chain or branched fatty acids having 8 to 20 carbon atoms, such as straight-chain fatty acids like octanoic acid (8 carbon atoms), nonanoic acid (9 carbon atoms), decanoic acid (10 carbon atoms), dodecanoic acid (12 carbon atoms), tetradecanoic acid (14 carbon atoms), pentadecanoic acid (15 carbon atoms), hexadecanoic acid (palmitic acid) (16 carbon atoms), heptadecanoic acid (17 carbon atoms), octadecanoic acid (stearic acid) (18 carbon atoms), and eicosanoic acid (20 carbon atoms), as well as alkali metal salts of branched fatty acids such as oleic acid, linoleic acid, and linolenic acid (18 carbon atoms).

[0096] The amount of fatty acid salt added is preferably 0.05% by mass or more and 5% by mass or less, relative to the total amount of flattened copper powder (in a dry state).

[0097] The pH in the reaction vessel during the dispersion process is not particularly limited, but from the viewpoint of facilitating the dissolution of fatty acid salts, it is preferably 9 or higher, more preferably 10 or higher, and for example, 11 or lower.

[0098] In the dispersion process, it is preferable to add the fatty acid salt to the reaction vessel and then allow it to mature. The maturation time is preferably between 5 minutes and 60 minutes.

[0099] In the film formation process, the reaction vessel is neutralized with acid to form a fatty acid film on the surface of the flattened copper powder. The type of acid is not particularly limited and may be a strong acid such as hydrochloric acid, sulfuric acid, or nitric acid, or a weak acid. However, from the following viewpoints, it is preferable to use a weak acid to neutralize the reaction vessel in the film formation process. By using a weak acid, the fatty acid film can be formed more uniformly, and the aggregation of the resulting copper fine particles can be suppressed. In addition, by using a weak acid, the fatty acid film increases the hydrophobicity of the resulting copper fine particles, which can speed up the settling rate of the copper fine particles in the washing process described later, thereby improving productivity. Furthermore, by using a weak acid, a fatty acid film can be formed uniformly on the flattened copper powder, making it less likely for the copper fine particles to aggregate with each other, resulting in copper fine particles with fewer aggregated particles. The type of weak acid used for neutralization is not particularly limited and may include one or more selected from citric acid, ascorbic acid, and acetic acid.

[0100] In the film formation process, it is preferable to add acid to the reaction vessel and then allow it to mature. The maturation time is preferably between 5 minutes and 60 minutes.

[0101] <Other steps> The method for producing flattened copper powder according to the second embodiment may include steps other than steps A to C described above.

[0102] The method for producing flattened copper powder according to the second embodiment may further include a step of washing the flattened copper powder. The washing method is not particularly limited and can be carried out, for example, by adding water and stirring.

[0103] The method for producing flattened copper powder according to the second embodiment may further include a step of sorting the flattened copper powder and intermediates. Sorting the flattened copper powder and intermediates can be performed, for example, using a sieve, and by using a sieve of a specific size, materials within a specific particle size range can be sorted. This step may be performed at the slurry stage, or after drying to a powder state.

[0104] The method for producing flattened copper powder according to the second embodiment may further include a step of drying the flattened copper powder. The method for drying the flattened copper powder is not particularly limited; for example, it can be dried by dewatering by centrifugal separation followed by heating and drying in a dryer or the like.

[0105] The method for producing flattened copper powder according to the second embodiment may further include a step of crushing the flattened copper powder or intermediate. The crushing of the flattened copper powder or intermediate can be carried out using a known crusher. The type of crusher is not particularly limited, and any type such as a high-speed rotary mill, hammer mill, or atomizer can be used.

[0106] <Conductive Paste> The conductive paste of the second embodiment will be described below.

[0107] The conductive paste of the second embodiment includes, for example, the flattened copper powder of the second embodiment, a resin, and a solvent.

[0108] The flattened copper powder of the second embodiment has improved packing properties, making it easy to design pastes with high reproducibility and stability.

[0109] The resin used in the conductive paste of the second embodiment is not particularly limited, and any known raw material for conductive paste can be used as appropriate. For example, cellulosic resins such as ethylcellulose can be used, and they are added as an organic vehicle dissolved in an organic solvent such as terpineol. The amount of resin added should be kept to a level that does not hinder sinterability. For this reason, the amount of resin added is preferably 5% by mass or less of the total conductive paste, and more preferably 2% by mass or less.

[0110] The solvent used in the conductive paste of the second embodiment is not particularly limited, and known raw materials for conductive pastes can be used as appropriate. For example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, terpineol, and triethanolamine are preferred. Among these organic solvents, amines are preferred because they have reducing ability and have the effect of creating a locally reducing atmosphere on the paste surface during firing. Furthermore, using water as a solvent can reduce the amount of organic solvents that are harmful to the human body, thereby increasing the value of the copper paste. The amount of solvent is not particularly limited, but it should be adjusted as appropriate, taking into account the dispersibility and particle size distribution of the flattened copper powder, so that the viscosity is suitable for conductive film formation methods such as screen printing and inkjet printing.

[0111] Although a second embodiment of the present invention has been described above, these are merely examples of the present invention, and various other configurations can be adopted. Furthermore, the present invention is not limited to the second embodiment described above, and any modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention.

[0112] <<Third Embodiment>> <Method for Manufacturing Flattened Copper Powder> The third embodiment is a method for manufacturing flattened copper powder, comprising step A of flattening raw copper powder, and the particle size D of the raw copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement method. ５０ The particle size fD of the flattened copper powder is calculated according to the following (method). ＢＥＴ The ratio (fD ＢＥＴ / D ５０ ) is 0.70 or more and 1.50 or less. (Method) The particle size D of the raw copper powder in the volume-based particle size distribution by the laser diffraction scattering particle size distribution measurement method. ５０ The radius of the copper particles is measured and divided by 2. This value is taken as the radius r (μm) of the copper particles, assuming that the copper particles contained in the raw copper powder are spherical. The surface area of ​​the copper particles with radius r is S. １ (μm ２ ), the true density ρ of copper is 8.94 (g / cm³). ３) Specific surface area S per unit mass ＳＡ１ (m ２ The specific surface area S(m²) of the flattened copper powder is determined by the nitrogen adsorption BET method. ２ Measure the particle size fD of the flattened copper powder. Substitute each value into equation (1) below and solve the cubic equation for radius R, assuming that the flattened copper particles contained in the flattened copper powder are cylindrical. Of the solutions R obtained, double the largest positive value of R (2R) and use that value to determine the particle size fD of the flattened copper powder. ＢＥＴ Let (μm). 2πR ３ - S x S １ / S ＳＡ１ ×R + (8 / 3) ×πr ３ = 0 (1)

[0113] The mechanism by which the above-mentioned problems are solved by the method for producing flattened copper powder according to the third embodiment is not clear, fD ＢＥＴ / D ５０ Because the values ​​fall within the above range, the dispersibility of the primary particles in the resulting flattened copper powder is improved, and the particle size distribution of the resulting flattened copper powder is narrowed. This is expected to improve the particle packing efficiency.

[0114] There are several advantages to improved particle packing properties. For example, when copper powder with improved packing properties is incorporated into a conductive paste, it becomes less likely for the wiring obtained from the conductive paste to break. Improved packing properties mean that there are fewer voids between particles, so even when the conductive paste is fired, shrinkage is small, and wire breakage is less likely to occur.

[0115] The flattened copper powder obtained by the manufacturing method of the third embodiment, fD ＢＥＴ / D ５０ fD of the flattened copper powder obtained by the manufacturing method of the third embodiment ＢＥＴ / D ５０fD is 0.70 or more and 1.50 or less, preferably 0.75 or more and 1.40 or less, more preferably 0.80 or more and 1.30 or less. In the method for producing flattened copper powder, the fD ＢＥＴ / D ５０ By having the above numerical range, the packing properties of the resulting flattened copper powder can be improved. The fD of the flattened copper powder ＢＥＴ / D ５０ To achieve a specific range, this can be achieved by appropriately selecting various conditions and types of raw copper powder in step A, which involves flattening the raw copper powder, as described later.

[0116] The average thickness T of the flattened copper powder obtained by the manufacturing method of the third embodiment, according to the following (method). Ａ The particle size D of the raw copper powder ５０ The ratio (D ５０ / T Ａ ) is preferably 7.5 or less, more preferably 7.4 or less, even more preferably 7.3 or less, and preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more. Also, the D of the flattened copper powder obtained by the manufacturing method of the third embodiment ５０ / T Ａ The value is preferably 1.0 to 7.5, more preferably 1.5 to 7.4, and even more preferably 2.0 to 7.3. In the method for producing flattened copper powder, the D ５０ / T Ａ By having the above numerical range, the packing properties of the resulting flattened copper powder can be improved. The D of the flattened copper powder ５０ / T Ａ To achieve a specific range, this can be achieved by appropriately selecting various conditions and types of raw copper powder in step A, which involves flattening the raw copper powder, as described later.

[0117] The third embodiment of the method for producing flattened copper powder includes step A, which involves flattening the raw copper powder. The third embodiment of the method for producing flattened copper powder may further include step B, which involves obtaining the raw copper powder from a copper(I) compound before step A. The third embodiment of the method for producing flattened copper powder may further include step C, which involves treating the surface of the flattened copper powder with a fatty acid salt after step A.

[0118] [Step A] Step A of the method for producing flattened copper powder according to the third embodiment will be described below. Step A is a step of flattening the raw copper powder. From the viewpoint of further improving the packing properties of the obtained flattened copper powder, a bead mill is preferably used as the equipment for the flattening process in Step A.

[0119] In step A, the bead diameter of the bead mill is preferably 0.5 mm or less, more preferably 0.4 mm or less, and even more preferably 0.3 mm or less. The lower limit of the bead diameter of the bead mill is not particularly limited, but for example it may be 0.1 mm or more, and may be 0.15 mm or more. Also in step A, the bead filling rate of the bead mill is preferably 50% or more, more preferably 60% or more, and even more preferably 65% ​​or more. The upper limit of the bead filling rate of the bead mill is not particularly limited, but for example it may be 98% or less, and may be 95% or less. Furthermore, in step A, the peripheral speed of the bead mill is preferably 5 m / s or more, more preferably 6 m / s or more, even more preferably 7 m / s or more, and preferably 15 m / s or less, more preferably 14 m / s or less, and even more preferably less than 14 m / s. In step A, the peripheral speed of the bead mill is preferably 5 m / s or more and 15 m / s or less, more preferably 6 m / s or more and 14 m / s or less, and even more preferably 7 m / s or more and less than 14 m / s. By setting the bead mill conditions within the above range, the shape of the flattened copper powder particles after the flattening treatment can be controlled.

[0120] Furthermore, in process A, the particle size D in the volume-based particle size distribution of the raw copper powder measured by laser diffraction scattering particle size distribution measurement method. ５０ Preferably, the particle size is 0.1 μm to 10.0 μm, more preferably 0.5 μm to 9.0 μm, even more preferably 1.0 μm to 7.0 μm, and even more preferably 1.5 μm to 5.0 μm.

[0121] [Step B] Step B of the method for producing flattened copper powder according to the third embodiment will be described below. Step B is a step in which raw material copper powder is obtained from a copper(I) compound. The specific method of Step B is not particularly limited, but from the viewpoint of further improving the dispersibility of the primary particles of the flattened copper powder and further narrowing the particle size distribution of the flattened copper powder, it is preferable to obtain the raw material copper powder from a slurry A containing a copper(I) compound and polyvinyl alcohol.

[0122] The dispersion medium used in slurry A is not particularly limited, and commonly used dispersion mediums for slurry preparation, such as water or hydrophilic dispersion mediums, can be used. Furthermore, a mixture of multiple types of dispersion mediums may be used.

[0123] Examples of hydrophilic dispersion media include: alkanediols such as ethylene glycol and propylene glycol, polyhydric alcohols such as glycerin; sugar alcohols, lower alcohols such as ethanol, methanol, butanol, propanol, and isopropanol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene Examples include glycol ethers such as glycol mono-t-butyl ether, triethylene glycol monoethyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-iso-propyl ether, and tripropylene glycol monomethyl ether; and alkanolamines such as ethanolamine, diethanolamine, and triethanolamine.

[0124] The content of copper(I) compounds in slurry A is not particularly limited, and may be, for example, 1% by mass or more and 25% by mass or less.

[0125] The copper(I) compound is not particularly limited as long as it is a compound containing monovalent copper, and for example, it includes one or more selected from the group consisting of cuprous oxide, copper chloride, copper bromide, and copper iodide, and preferably contains cuprous oxide.

[0126] The content of polyvinyl alcohol in slurry A is not particularly limited, but from the viewpoint of further improving the dispersibility of the primary particles of the flattened copper powder and further narrowing the particle size distribution of the flattened copper powder, it is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of copper(I) compound, and may also be, for example, 5 parts by mass or less, 2 parts by mass or less, or 1 part by mass or less.

[0127] The degree of saponification of polyvinyl alcohol is not particularly limited, but from the viewpoint of further improving the dispersibility of the primary particles of the flattened copper powder and further narrowing the particle size distribution of the flattened copper powder, it is preferably 70 mol% or more, more preferably 75 mol% or more, even more preferably 80 mol% or more, and even more preferably 85 mol% or more, and may be, for example, 100 mol% or less, for example 95 mol% or less, and for example 90 mol% or less.

[0128] The viscosity of polyvinyl alcohol is not particularly limited, but from the viewpoint of further improving the dispersibility of the primary particles of the flattened copper powder and further narrowing the particle size distribution of the flattened copper powder, the viscosity of a 4% aqueous solution measured at 20°C using a Brookfield type rotational viscometer in accordance with JIS K6726:1994 is, for example, 0.1 mPa·s or more, preferably 1 mPa·s or more, more preferably 4 mPa·s or more, and may be, for example, 100 mPa·s or less, for example, 50 mPa·s or less, and for example, 10 mPa·s or less.

[0129] The type of reaction used to generate the raw copper powder in step B is not particularly limited, but for example, the raw copper powder can be generated by disproportionating the copper(I) compound.

[0130] The raw material copper powder of the third embodiment is preferably obtained by a disproportionation reaction.

[0131] The components of slurry A are not particularly limited, but from the viewpoint of promoting the reaction in the reaction vessel, it preferably contains an acid, more preferably one or more selected from the group consisting of hydrochloric acid, nitric acid, and sulfuric acid, and even more preferably sulfuric acid. Here, during the disproportionation reaction of the copper(I) compound, the acid in slurry A may be in the form of a copper salt (copper hydrochloride, copper nitrate, copper sulfate, etc.). The particle size of the raw copper powder can be adjusted by adjusting the rate at which the acid is supplied into the reaction vessel. For example, lowering the acid supply rate tends to increase the particle size of the raw copper powder.

[0132] The pH in the reaction vessel in step B is not particularly limited, but for example it is 0.1 or higher, may be 0.5 or higher, may be 1 or higher, and from the viewpoint of further improving the dispersibility of the primary particles of the flattened copper powder and further narrowing the particle size distribution of the flattened copper powder, it is preferably 7 or lower, more preferably 6 or lower, even more preferably 5 or lower, and even more preferably 2.5 or lower. Here, the pH in the reaction vessel in step B is the pH of the slurry in the reaction vessel when step B is completed.

[0133] The temperature inside the reaction vessel in step B is not particularly limited, but may be, for example, 5°C or higher, for example, 10°C or higher, or 20°C or higher. From the viewpoint of further improving the dispersibility of the primary particles of the flattened copper powder and further narrowing the particle size distribution of the flattened copper powder, it is preferably 90°C or lower, more preferably 80°C or lower, even more preferably 70°C or lower, and may also be 60°C or lower, or 50°C or lower. Here, the temperature inside the reaction vessel in step B is the temperature of the slurry inside the reaction vessel. The particle size of the raw copper powder can be adjusted by adjusting the temperature inside the reaction vessel. For example, increasing the temperature inside the reaction vessel tends to increase the particle size of the raw copper powder.

[0134] [Step C] Step C of the method for producing flattened copper powder according to the third embodiment will be described below. In Step C, the surface of the flattened copper powder is treated with a fatty acid salt. Step C includes, for example, a dispersion step in which fatty acids are attached to the surface of the flattened copper powder and the flattened copper powder is dispersed, and a film formation step in which a fatty acid film is formed on the surface of the flattened copper powder.

[0135] The flattened copper powder obtained by the manufacturing method of the third embodiment preferably contains a fatty acid coating on its surface.

[0136] Examples of fatty acid salts include alkali metal salts of fatty acids having 8 to 20 carbon atoms. More specifically, fatty acid salts include straight-chain or branched fatty acids having 8 to 20 carbon atoms, such as straight-chain fatty acids like octanoic acid (8 carbon atoms), nonanoic acid (9 carbon atoms), decanoic acid (10 carbon atoms), dodecanoic acid (12 carbon atoms), tetradecanoic acid (14 carbon atoms), pentadecanoic acid (15 carbon atoms), hexadecanoic acid (palmitic acid) (16 carbon atoms), heptadecanoic acid (17 carbon atoms), octadecanoic acid (stearic acid) (18 carbon atoms), and eicosanoic acid (20 carbon atoms), as well as alkali metal salts of branched fatty acids such as oleic acid, linoleic acid, and linolenic acid (18 carbon atoms).

[0137] The amount of fatty acid salt added is preferably 0.05% by mass or more and 5% by mass or less, relative to the total amount of flattened copper powder (in a dry state).

[0138] The pH in the reaction vessel during the dispersion process is not particularly limited, but from the viewpoint of facilitating the dissolution of fatty acid salts, it is preferably 9 or higher, more preferably 10 or higher, and for example, 11 or lower.

[0139] In the dispersion process, it is preferable to add the fatty acid salt to the reaction vessel and then allow it to mature. The maturation time is preferably between 5 minutes and 60 minutes.

[0140] In the film formation process, the reaction vessel is neutralized with acid to form a fatty acid film on the surface of the flattened copper powder. The type of acid is not particularly limited and may be a strong acid such as hydrochloric acid, sulfuric acid, or nitric acid, or a weak acid. However, from the following viewpoints, it is preferable to use a weak acid to neutralize the reaction vessel in the film formation process. By using a weak acid, the fatty acid film can be formed more uniformly, and the aggregation of the resulting copper fine particles can be suppressed. In addition, by using a weak acid, the fatty acid film increases the hydrophobicity of the resulting copper fine particles, which can speed up the settling rate of the copper fine particles in the washing process described later, thereby improving productivity. Furthermore, by using a weak acid, a fatty acid film can be formed uniformly on the flattened copper powder, making it less likely for the copper fine particles to aggregate with each other, resulting in copper fine particles with fewer aggregated particles. The type of weak acid used for neutralization is not particularly limited and may include one or more selected from citric acid, ascorbic acid, and acetic acid.

[0141] In the film formation process, it is preferable to add acid to the reaction vessel and then allow it to mature. The maturation time is preferably between 5 minutes and 60 minutes.

[0142] [Other steps] The method for producing flattened copper powder according to the third embodiment may include steps other than steps A to C described above.

[0143] The third embodiment of the method for producing flattened copper powder may further include a step of washing the flattened copper powder. The washing method is not particularly limited and can be carried out, for example, by adding water and stirring.

[0144] The third embodiment of the method for producing flattened copper powder may further include a step of sorting the flattened copper powder and intermediates. Sorting the flattened copper powder and intermediates can be done, for example, using a sieve, and by using a sieve of a specific size, materials within a specific particle size range can be sorted. This step may be performed at the slurry stage, or after drying to a powder state.

[0145] The method for producing flattened copper powder according to the third embodiment may further include a step of drying the flattened copper powder. The method for drying the flattened copper powder is not particularly limited; for example, it can be dried by dewatering by centrifugal separation followed by heating and drying in a dryer or the like.

[0146] The third embodiment of the method for producing flattened copper powder may further include a step of crushing the flattened copper powder or intermediate. The crushing of the flattened copper powder or intermediate can be carried out using a known crusher. The type of crusher is not particularly limited, and any type such as a high-speed rotary mill, hammer mill, or atomizer can be used.

[0147] <Flattened Copper Powder> The flattened copper powder obtained by the method for producing flattened copper powder of the third embodiment will be described below.

[0148] The particle size D in the volume-based particle size distribution of the flattened copper powder obtained by the method for producing flattened copper powder of the third embodiment, as measured by laser diffraction scattering particle size distribution analysis. ５０ Specific surface area S (m²) of nitrogen by BET method relative to (μm) ２ The ratio (S / D) of / g ５０ ) is preferably 0.07 m ２ / (g·μm) or more, more preferably 0.08 m ２ / (g·μm) or more, more preferably 0.09 m ２ The density is greater than or equal to (g·μm), and preferably 1.00 m ２ / (g·μm) or less, more preferably 0.75 m ２ / (g·μm) or less, more preferably 0.50 m ２ / (g·μm) or less, more preferably 0.40 m ２ / (g·μm) or less, more preferably 0.30 m ２ / (g・μm) or less. Also, the S / D of the flattened copper powder obtained by the method for producing flattened copper powder of the third embodiment. ５０ Preferably 0.07 m ２ / (g・μm) or more 1.00m ２ / (g·μm) or less, more preferably 0.08 m ２ / (g・μm) or more 0.75m ２ / (g·μm) or less, more preferably 0.08 m２ / (g・μm) or more 0.50m ２ / (g·μm) or less, more preferably 0.08 m ２ / (g・μm) or more 0.40m ２ / (g·μm) or less, more preferably 0.09 m ２ / (g・μm) or more 0.30m ２ The S / D ratio of the obtained flattened copper powder is less than or equal to / (g・μm). ５０ By keeping the values ​​within the above range, flattened copper powder with improved packing properties can be obtained.

[0149] From the viewpoint of further improving the packing properties of the flattened copper powder, the specific surface area S of the flattened copper powder obtained by the method of the third embodiment, as determined by the nitrogen adsorption BET method, is preferably 0.10 m². ２ / g or more, more preferably 0.15m ２ / g or more, more preferably 0.20m ２ / g or more, more preferably 0.23m ２ / g or more, more preferably 0.25m ２ It is 1 / g or more, and preferably 3.0 m ２ / g or less, more preferably 2.0m ２ / g or less, more preferably 1.5m ２ / g or less, more preferably 1.0m ２ / g or less, more preferably 0.80m ２ It is less than or equal to / g. The specific surface area S of the flattened copper powder obtained by the method for producing flattened copper powder of the third embodiment, as determined by nitrogen adsorption BET, is preferably 0.10 m² from the viewpoint of further improving the packing properties of the flattened copper powder. ２ / g or more 3.0m ２ / g or less, more preferably 0.15m ２ / g or more 2.0m ２ / g or less, more preferably 0.20m ２ / g or more 1.5m ２ / g or less, more preferably 0.23m ２ / g or more 1.0m ２ / g or less, more preferably 0.25m ２ / g or more 0.80m ２ It is less than or equal to / g.

[0150] The average thickness T of the flattened copper powder obtained by the method for producing flattened copper powder of the third embodiment, according to the following (method). Ａ Particle size D in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution method. ５０ The ratio (D ５０ / T Ａ From the viewpoint of further improving the packing properties of the flattened copper powder, the D is preferably 20.0 or less, more preferably 17.5 or less, even more preferably 15.0 or less, even more preferably 14.0 or less, and preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more, and even more preferably 3.0 or more. The D of the flattened copper powder obtained by the method for producing flattened copper powder of the third embodiment ５０ / T Ａ From the viewpoint of further improving the packing properties of the flattened copper powder, the value is preferably 1.0 to 20.0, more preferably 1.5 to 17.5, even more preferably 2.0 to 15.0, and even more preferably 3.0 to 14.0. (Method) The thickness of 100 arbitrary flattened copper powders is measured from SEM images obtained by observing the flattened copper powder with an electron microscope, and the average value of the thicknesses of the 100 flattened copper powders is the average thickness T of the flattened copper powder. Ａ Let it be (μm).

[0151] The particle size D of the flattened copper powder obtained by the method for producing flattened copper powder according to the third embodiment ５０ From the viewpoint of further improving the packing properties of the flattened copper powder, the particle size D is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1.0 μm or more, even more preferably 1.5 μm or more, and preferably 10.0 μm or less, more preferably 9.0 μm or less, even more preferably 7.5 μm or less, and even more preferably 7.0 μm or less. The particle size D of the flattened copper powder obtained by the method for producing flattened copper powder of the third embodiment. ５０ From the viewpoint of further improving the packing performance of the flattened copper powder, the particle size is preferably 0.1 μm to 10.0 μm, more preferably 0.5 μm to 9.0 μm, even more preferably 1.0 μm to 7.5 μm, and even more preferably 1.5 μm to 7.0 μm.

[0152] The average thickness T of the flattened copper powder obtained by the method for producing flattened copper powder of the third embodiment. Ａ From the viewpoint of further improving the packing properties of the flattened copper powder, the average thickness T is preferably 0.1 μm or more, more preferably 0.15 μm or more, even more preferably 0.2 μm or more, and preferably 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 1.2 μm or less. The average thickness T of the flattened copper powder obtained by the method for producing flattened copper powder of the third embodiment. Ａ From the viewpoint of further improving the packing performance of the flattened copper powder, the particle size is preferably 0.1 μm or more and 2.0 μm or less, more preferably 0.15 μm or more and 1.5 μm or less, and even more preferably 0.2 μm or more and 1.2 μm or less.

[0153] The particle size D in the volume-based particle size distribution of the flattened copper powder obtained by the method for producing flattened copper powder of the third embodiment, as measured by laser diffraction scattering particle size distribution analysis. １０ Particle size D ９０ The ratio (D ９０ / D １０ From the viewpoint of further improving the packing properties of the flattened copper powder, the D is preferably 5.0 or less, more preferably 4.8 or less, even more preferably 4.6 or less, even more preferably 4.4 or less, and preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more, and even more preferably 2.5 or more. Furthermore, the flattened copper powder obtained by the method for producing flattened copper powder of the third embodiment, the D ９０ / D １０ From the viewpoint of further improving the packing performance of the flattened copper powder, the value is preferably 1.0 to 5.0, more preferably 1.5 to 4.8, even more preferably 2.0 to 4.6, and even more preferably 2.5 to 4.4.

[0154] The particle size D of the flattened copper powder obtained by the method for producing flattened copper powder according to the third embodiment ５０ The coefficient of variation (SD / D) obtained from the standard deviation SD is obtained from the coefficient of variation (SD / D ５０From the viewpoint of further improving the packing performance of the flattened copper powder, the value is preferably 0.60 or less, more preferably 0.59 or less, even more preferably 0.55 or less, even more preferably 0.50 or less, even more preferably 0.45 or less, and even more preferably 0.40 or less. SD / D ５０ The lower limit of is not particularly limited, but for example, it may be 0.10 or more, 0.15 or more, 0.20 or more, or 0.30 or more. Also, the coefficient of variation (SD / D ５０ From the viewpoint of further improving the packing performance of the flattened copper powder, the value is preferably 0.10 to 0.60, more preferably 0.15 to 0.59, even more preferably 0.20 to 0.55, even more preferably 0.20 to 0.50, even more preferably 0.20 to 0.45, and even more preferably 0.30 to 0.40.

[0155] The use of the flattened copper powder obtained by the method for producing flattened copper powder of the third embodiment is not particularly limited, but the flattened copper powder of the third embodiment is suitable for use in conductive pastes because it has improved packing properties.

[0156] Although embodiments of the present invention have been described above, these are merely examples of embodiments of the present invention, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention.

[0157] The first embodiment of the present invention will be described in more detail below with reference to examples, but the first embodiment of the present invention is not limited to the following examples unless it exceeds the spirit of the invention.

[0158] <<Examples 1A to 5A and Comparative Examples 1A to 2A>> The first embodiment of the present invention will be described in detail below with reference to Examples 1A to 5A and Comparative Examples 1A to 2A. However, the first embodiment is not limited in any way to the description in these examples.

[0159] [Measurement using a laser diffraction scattering particle size distribution analyzer] Using a laser diffraction scattering particle size distribution analyzer (Microtrac-Bell, model: MT3300EX II), the particle size D of copper powder when the cumulative frequency is 10% in the volume-based cumulative frequency distribution curve was measured. １０ And, the particle size D of copper powder and raw copper powder when the cumulative frequency is 50% in the volume-based cumulative frequency distribution curve. ５０ And, the particle size D of copper powder when the cumulative frequency is 90% in the volume-based cumulative frequency distribution curve. ９０ The standard deviation (SD) of the particle size distribution was obtained. For the measurement sample, a tank (capacity 200 ml) in the sample circulation chamber of a laser diffraction scattering particle size distribution analyzer was filled with a dispersion medium (ethanol). The required amount (approximately 0.02 to 0.10 g) of dry raw copper powder or copper powder obtained by the method described below was added to the tank while observing the optimal concentration range displayed on the analyzer. Then, the instrument was irradiated with ultrasound at an output of 40 W for 3 minutes. From the obtained results, the coefficient of variation for the particle size D of the copper powder was obtained. ５０ The ratio of the standard deviation SD to (SD / D) ５０ ) and the particle size D of the copper powder １０ The particle size D of copper powder relative to ９０ The ratio (D ９０ / D １０ The result was calculated. The results are shown in Table 2A.

[0160] [Measurement of Specific Surface Area of ​​Copper Powder by Nitrogen Adsorption BET Method] The specific surface area S of copper powder was determined by the nitrogen adsorption BET method using a specific surface area measuring device (Shimadzu Corporation, model name: FlowSorb III). As a pretreatment, a mixed gas (N) was used. ２ Degassing was performed for 1 hour under conditions of 30% saturates and 70% helium at a temperature of 110°C. The results are shown in Table 2.

[0161] [Particle size fD of copper powder] ＢＥＴ [Method of calculation] The particle size D of the raw copper powder ５０ The value obtained by dividing the measured value by 2 is taken as the radius r (μm) of the copper particles, assuming that the copper particles contained in the raw copper powder are spherical, and the surface area of ​​the copper particles of radius r is S. １ (μm ２ ) and the true density ρ of copper is 8.94 (g / cm³). ３) Specific surface area S per unit mass ＳＡ１ (m ２ The specific surface area S(m²) of the copper powder obtained in the examples and comparative examples was calculated and substituted into the following formula (1). ２ Substitute ( / g) into the following formula (1), solve the cubic equation for radius R assuming that the copper particles contained in the copper powder obtained in the examples and comparative examples are cylindrical, and take twice the largest positive value of R obtained as the particle size fD of the copper powder obtained in the examples and comparative examples. ＢＥＴ (μm) was used for the calculation. Furthermore, fD ＢＥＴ (μm) / D ５０ The (copper powder) was calculated as follows: 2πR ３ - S x S １ / S ＳＡ１ ×R + (8 / 3) ×πr ３ = 0 (1)

[0162] [Average thickness T of copper powder particles contained in copper powder] Ａ [Measurement] The thickness of 100 arbitrary copper powder particles was measured from SEM images obtained by observing copper powder particles with an electron microscope. The average thickness of the 100 copper powder particles was calculated, and the average thickness T of the copper powder was determined. Ａ (μm) was used. Furthermore, the average thickness T Ａ Particle size D of copper powder ５０ The ratio and average thickness T Ａ Particle size D of raw copper powder ５０ The ratio was calculated. The particles to be measured were selected based on visual inspection of the electron microscope's field of view, where the thickness direction of the particles was judged to be approximately parallel to the observation surface. The results are shown in Table 2A.

[0163] [Measurement of Tap Density] As an indicator of packing performance, the tap density of copper powder was measured after 3000 taps in accordance with the metal powder-tap density measurement method specified in JIS Z2512:2012. The results are shown in Table 2A.

[0164] [Example 1A] <Step 1: Step to obtain raw copper powder from copper(I) compound> Cuprous oxide (manufactured by Furukawa Chemicals, product name: cuprous oxide) and deionized water were mixed in a reaction vessel so that the cuprous oxide content in the slurry (hereinafter referred to as slurry concentration) was 12.5% ​​by mass, and the resulting slurry was heated to 30-50°C. Then, when the cuprous oxide content in the slurry was 100 parts by mass, 0.2 parts by mass of polyvinyl alcohol was added to the slurry and stirred for 15 minutes. While stirring in the reaction vessel, a 20% sulfuric acid aqueous solution was continuously added to the slurry so that the amount of sulfuric acid was 1.1 times (molar ratio) of the cuprous oxide in the slurry. Next, the slurry containing the obtained raw copper powder was washed with deionized water until the resistivity was 1000 Ω·cm.

[0165] <Process 2: Flattening Process> The slurry obtained in Process 1 was flattened using a bead mill (manufactured by Ashizawa Finetech Co., Ltd.). The grinding chamber of the bead mill was filled with 0.2 mm diameter beads to a packing rate of 85%, and the bead mill was started at a peripheral speed of 8 m / s and a circulating slurry flow rate of 30 L / min. At the start of operation, the total liquid volume in the slurry storage tank was 765 kg, and the slurry concentration was 23 mass%. After operating the bead mill for 150 minutes, 391 kg of slurry was withdrawn from the slurry storage tank of the bead mill.

[0166] <Step 3: Sorting Process> Next, the extracted slurry was passed through a sieve with a mesh size of 25 μm.

[0167] <Step 4: Surface Treatment Step> The slurry containing copper powder obtained in Step 3 was adjusted to a copper concentration of 100 g / L and stirred. Next, sodium carbonate was added to the reaction vessel so that the pH was 10.0 to 10.5. Next, sodium stearate was added to the reaction vessel at a concentration of 0.2% by mass relative to the copper powder, the temperature in the reaction vessel was raised to 60°C, and the mixture was stirred for 15 minutes. Next, a neutralizing agent (ascorbic acid) was added to the reaction vessel so that the pH was 7.5, and the mixture was stirred for 15 minutes. Next, a 20% sulfuric acid aqueous solution was added to the reaction vessel so that the pH was 7.0, and the mixture was stirred for 15 minutes.

[0168] <Step 5: Washing Process> Next, the slurry in the reaction vessel was washed with deionized water until the resistivity reached 10,000 Ω·cm.

[0169] <Step 6: Drying and Crushing Process> Next, the precipitate was filtered off the washed slurry, the filtered precipitate was dried, and then crushed in a pulverizer to obtain dry copper powder.

[0170] [Example 2A] After extracting the slurry in step 2 of Example 1A, deionized water was poured into the slurry storage tank of the bead mill, and the copper powder adhering to the inner wall was mixed with the slurry remaining in the slurry storage tank. Then, the operation of the bead mill was restarted under the same conditions as in Example 1A, and the operation was performed for 190 minutes (a total of 340 minutes including the operation time before restarting) to obtain the slurry. The slurry concentration in the slurry storage tank at the time of restarting the bead mill operation was 20% by mass. Steps 3 to 6 were performed on the obtained slurry in the same manner as in Example 1A to obtain dry copper powder.

[0171] [Example 3A] <Step 1: Step to obtain raw copper powder from copper(I) compound> Cuprous oxide (manufactured by Furukawa Chemicals, product name: cuprous oxide) and deionized water were mixed in a reaction vessel so that the cuprous oxide content in the slurry (hereinafter referred to as slurry concentration) was 12.5% ​​by mass, and the resulting slurry was heated to 50-70°C. Then, when the cuprous oxide content in the slurry was 100 parts by mass, 0.2 parts by mass of polyvinyl alcohol was added to the slurry and stirred for 15 minutes. While stirring in the reaction vessel, a 20% sulfuric acid aqueous solution was continuously added to the slurry so that the amount of sulfuric acid was 1.25 times (molar ratio) of the cuprous oxide in the slurry. Next, the slurry containing the obtained raw copper powder was washed with deionized water until the resistivity was 1000 Ω·cm. <Step 2: Flattening Process> The bead mill was operated in the same manner as in Step 2 of Example 1A, and after 120 minutes of operation, 125 kg of slurry was withdrawn from the slurry storage tank of the bead mill. At the start of operation of the bead mill, the total amount of slurry in the slurry storage tank was 345 kg, and the slurry concentration was 20% by mass. Steps 3 to 6 were carried out in the same manner as in Example 1A, except that the amount of sodium stearate added to the reaction layer in Step 4 of Example 1A was changed to 0.1% by mass relative to the copper powder, to obtain dry copper powder from the obtained slurry.

[0172] [Example 4A] After extracting the slurry in step 2 of Example 3A, deionized water was poured into the slurry storage tank of the bead mill, and the copper powder adhering to the inner wall was mixed with the slurry remaining in the slurry storage tank. Then, the operation of the bead mill was restarted under the same conditions as in Example 1A, and the operation was performed for 135 minutes (a total of 255 minutes including the operation time before restarting) to obtain the slurry. The slurry concentration in the slurry storage tank at the time of restarting the bead mill operation was 15% by mass. Steps 3 to 6 were performed on the obtained slurry in the same manner as in Example 3A to obtain dry copper powder.

[0173] [Example 5A] <Step 1: Step to obtain raw copper powder from copper(I) compound> A slurry containing raw copper powder was prepared in the same manner as in Example 3A. <Step 2: Flattening process> As shown in Table 1A, the bead mill was operated under the same conditions as in Example 1A, except that the bead filling rate, bead quantity, and peripheral speed were changed. After 15 minutes of operation, 4 kg of slurry was withdrawn from the slurry storage tank of the bead mill. At the start of operation of the bead mill, the total amount of slurry in the slurry storage tank was 67 kg, and the slurry concentration was 30% by mass. Steps 3 to 6 were performed on the obtained slurry in the same manner as in Example 3A to obtain dry copper powder.

[0174] [Comparative Example 1A] <Step 1: Step to obtain raw copper powder from copper(I) compound> A slurry containing raw copper powder was prepared in the same manner as in Example 3A. <Step 2: Flattening treatment> After operating the bead mill for 120 minutes under the conditions described in Table 1A, 4 kg of slurry was withdrawn from the slurry storage tank of the bead mill. At the start of operation of the bead mill, the total amount of slurry in the slurry storage tank was 67 kg, and the slurry concentration was 30% by mass. Steps 3 to 6 were performed on the obtained slurry in the same manner as in Example 3A to obtain dry copper powder.

[0175] [Comparative Example 2A] After extracting the slurry in step 2 of Comparative Example 1A, deionized water was poured into the slurry storage tank of the bead mill, and the copper powder adhering to the inner wall was mixed with the slurry remaining in the slurry storage tank. Then, the operation of the bead mill was restarted under the same conditions as in Comparative Example 1A, and it was operated for 20 minutes (a total of 140 minutes including the operating time before restarting) to obtain slurry. Steps 3 to 6 were performed on the obtained slurry in the same manner as in Example 3A to obtain dry copper powder.

[0176]

[0177] The slurry concentration and total liquid volume in Table 1A represent the values ​​at the start of bead mill operation in the flattening process, and the amount of copper powder is obtained by multiplying the total liquid volume by the slurry concentration.

[0178]

[0179] Specific surface area S / D in Table 2A ５０ (Copper powder) is the particle size D in the volume-based particle size distribution of copper powder measured by laser diffraction scattering particle size distribution analysis. ５０ This refers to the ratio of the specific surface area S of copper powder obtained by nitrogen adsorption BET method to (μm).

[0180] The copper powders of Examples 1A to 5A showed improved tap density compared to the copper powders of Comparative Examples 1A and 2A. This indicates that the copper powder of the first embodiment has improved packing properties. Because the copper powder of the first embodiment has improved packing properties, it is considered suitable for use in conductive pastes.

[0181] The second embodiment of the present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0182] <<Examples 1B to 5B and Comparative Examples 1B to 2B>> The second embodiment of the present invention will be described in detail below with reference to Examples 1B to 5B and Comparative Examples 1B to 2B. However, the second embodiment is not limited in any way to the description in these examples.

[0183] [Measurement using a laser diffraction scattering particle size distribution analyzer] Using a laser diffraction scattering particle size distribution analyzer (Microtrac-Bell, model: MT3300EX II), the particle size D of flattened copper powder when the cumulative frequency is 10% in the volume-based cumulative frequency distribution curve was measured. １０ And, the particle size D of the flattened copper powder and raw copper powder when the cumulative frequency is 50% in the volume-based cumulative frequency distribution curve. ５０ And, the particle size D of flattened copper powder when the cumulative frequency is 90% in the volume-based cumulative frequency distribution curve. ９０ The standard deviation (SD) of the particle size distribution was obtained. For the measurement sample, a tank (capacity 200 ml) in the sample circulation chamber of a laser diffraction scattering particle size distribution analyzer was filled with a dispersion medium (ethanol). The required amount (approximately 0.02 to 0.10 g) of the dry raw copper powder or flattened copper powder obtained by the method described below was added to the tank while observing the optimal concentration range displayed on the analyzer. Then, the instrument was irradiated with ultrasound at an output of 40 W for 3 minutes. From the obtained results, the coefficient of variation was the particle size D of the flattened copper powder. ５０The ratio of the standard deviation SD to (SD / D) ５０ ) and the particle size D of the flattened copper powder １０ The particle size D of the flattened copper powder relative to ９０ The ratio (D ９０ / D １０ The result was calculated. The results are shown in Table 2B.

[0184] [Measurement of Specific Surface Area of ​​Flattened Copper Powder by Nitrogen Adsorption BET Method] The specific surface area S of flattened copper powder was determined by the nitrogen adsorption BET method using a specific surface area measuring device (Shimadzu Corporation, model name: FlowSorb III). The results are shown in Table 2B.

[0185] [Particle size fD of flattened copper powder] ＢＥＴ [Method of calculation] The particle size D of the raw copper powder ５０ The value obtained by dividing the measured value by 2 is taken as the radius r (μm) of the copper particles, assuming that the copper particles contained in the raw copper powder are spherical, and the surface area of ​​the copper particles of radius r is S. １ (μm ２ ) and the true density ρ of copper is 8.94 (g / cm³). ３ ) Specific surface area S per unit mass ＳＡ１ (m ２ The specific surface area S(m²) of the flattened copper powder obtained in the examples and comparative examples was calculated and substituted into the following formula (1). ２ Substitute ( / g) into the following formula (1), solve the cubic equation for radius R assuming that the copper particles contained in the flattened copper powder obtained in the examples and comparative examples are cylindrical, and take twice the largest positive value of R obtained as the particle size fD of the flattened copper powder obtained in the examples and comparative examples. ＢＥＴ (μm) was used for the calculation. Furthermore, fD ＢＥＴ (μm) / D ５０ The (flattened copper powder) was calculated as follows: 2πR ３ - S x S １ / S ＳＡ１ ×R + (8 / 3) ×πr ３ = 0 (1)

[0186] [Average thickness T of flattened copper powder particles contained in flattened copper powder] Ａ[Measurement] The thickness of 100 arbitrary flattened copper powder particles was measured from SEM images obtained by observing the copper powder particles contained in the flattened copper powder with an electron microscope. The average thickness of the 100 flattened copper powder particles was calculated, and the average thickness T of the flattened copper powder was determined. Ａ (μm) was used. Furthermore, the average thickness T Ａ Particle size D of flattened copper powder ５０ The ratio and average thickness T Ａ Particle size D of raw copper powder ５０ The ratio was calculated. The results are shown in Table 2B.

[0187] [Measurement of Tap Density] As an indicator of packing performance, the tap density of flattened copper powder was measured after 3000 taps in accordance with the metal powder-tap density measurement method specified in JIS Z2512:2012. The results are shown in Table 2B.

[0188] [Example 1B] <Step 1: Step to obtain raw copper powder from copper(I) compound> Cuprous oxide (manufactured by Furukawa Chemicals, product name: cuprous oxide) and deionized water were mixed in a reaction vessel so that the cuprous oxide content in the slurry (hereinafter referred to as slurry concentration) was 12.5% ​​by mass, and the resulting slurry was heated to 30-50°C. Then, when the cuprous oxide content in the slurry was 100 parts by mass, 0.2 parts by mass of polyvinyl alcohol was added to the slurry and stirred for 15 minutes. While stirring in the reaction vessel, a 20% sulfuric acid aqueous solution was continuously added to the slurry so that the amount of sulfuric acid was 1.1 times (molar ratio) of the cuprous oxide in the slurry. Next, the slurry containing the obtained raw copper powder was washed with deionized water until the resistivity was 1000 Ω·cm.

[0189] <Process 2: Flattening Process> The slurry obtained in Process 1 was flattened using a bead mill (manufactured by Ashizawa Finetech Co., Ltd.). The grinding chamber of the bead mill was filled with 0.2 mm diameter beads to a packing rate of 85%, and the bead mill was started at a peripheral speed of 8 m / s and a circulating slurry flow rate of 30 L / min. At the start of operation, the total liquid volume in the slurry storage tank was 765 kg, and the slurry concentration was 23 mass%. After operating the bead mill for 150 minutes, 391 kg of slurry was withdrawn from the slurry storage tank of the bead mill.

[0190] <Step 3: Sorting Process> Next, the extracted slurry was passed through a sieve with a mesh size of 25 μm.

[0191] <Step 4: Surface Treatment Step> The slurry containing copper powder obtained in Step 3 was adjusted to a copper concentration of 100 g / L and stirred. Next, sodium carbonate was added to the reaction vessel so that the pH was 10.0 to 10.5. Next, sodium stearate was added to the reaction vessel at a concentration of 0.2% by mass relative to the copper powder, the temperature in the reaction vessel was raised to 60°C, and the mixture was stirred for 15 minutes. Next, a neutralizing agent (ascorbic acid) was added to the reaction vessel so that the pH was 7.5, and the mixture was stirred for 15 minutes. Next, a 20% sulfuric acid aqueous solution was added to the reaction vessel so that the pH was 7.0, and the mixture was stirred for 15 minutes.

[0192] <Step 5: Washing Process> Next, the slurry in the reaction vessel was washed with deionized water until the resistivity reached 10,000 Ω·cm.

[0193] <Step 6: Drying and Crushing Process> Next, the precipitate was filtered off the washed slurry, the filtered precipitate was dried, and then crushed in a pulverizer to obtain dry flattened copper powder.

[0194] [Example 2B] After extracting the slurry in step 2 of Example 1B, deionized water was poured into the slurry storage tank of the bead mill, and the copper powder adhering to the inner wall was mixed with the slurry remaining in the slurry storage tank. Then, the operation of the bead mill was restarted under the same conditions as in Example 1B, and the operation was performed for 190 minutes (a total of 340 minutes including the operation time before restarting) to obtain slurry. The slurry concentration in the slurry storage tank at the time of restarting the bead mill operation was 20% by mass. Steps 3 to 6 were performed on the obtained slurry in the same manner as in Example 1B to obtain flattened copper powder in a dry state.

[0195] [Example 3B] <Step 1: Step to obtain raw copper powder from copper(I) compound> Cuprous oxide (manufactured by Furukawa Chemicals, product name: cuprous oxide) and deionized water were mixed in a reaction vessel so that the cuprous oxide content in the slurry (hereinafter referred to as slurry concentration) was 12.5% ​​by mass, and the resulting slurry was heated to 50-70°C. Then, when the cuprous oxide content in the slurry was 100 parts by mass, 0.2 parts by mass of polyvinyl alcohol was added to the slurry and stirred for 15 minutes. While stirring in the reaction vessel, a 20% sulfuric acid aqueous solution was continuously added to the slurry so that the amount of sulfuric acid was 1.25 times (molar ratio) of the cuprous oxide in the slurry. Next, the slurry containing the obtained raw copper powder was washed with deionized water until the resistivity was 1000 Ω·cm. <Step 2: Flattening Process> The bead mill was operated in the same manner as in Step 2 of Example 1B, and after 120 minutes of operation, 125 kg of slurry was withdrawn from the slurry storage tank of the bead mill. At the start of operation of the bead mill, the total amount of slurry in the slurry storage tank was 345 kg, and the slurry concentration was 20% by mass. Steps 3 to 6 were carried out in the same manner as in Example 1B, except that the amount of sodium stearate added to the reaction layer in Step 4 of Example 1B was changed to 0.1% by mass relative to the copper powder, to obtain flattened copper powder in a dry state.

[0196] [Example 4B] After extracting the slurry in step 2 of Example 3B, deionized water was poured into the slurry storage tank of the bead mill, and the copper powder adhering to the inner wall was mixed with the slurry remaining in the slurry storage tank. Then, the operation of the bead mill was restarted under the same conditions as in Example 1B, and the operation was performed for 135 minutes (a total of 255 minutes including the operation time before restarting) to obtain slurry. The slurry concentration in the tank at the time of restarting the bead mill operation was 15% by mass. Steps 3 to 6 were performed on the obtained slurry in the same manner as in Example 3B to obtain flattened copper powder in a dry state.

[0197] [Example 5B] <Step 1: Step to obtain raw copper powder from copper(I) compound> A slurry containing raw copper powder was prepared in the same manner as in Example 3B. <Step 2: Flattening process> As shown in Table 1B, the bead mill was operated under the same conditions as in Example 1B, except that the bead filling rate, bead quantity, and peripheral speed were changed. After 15 minutes of operation, 4 kg of slurry was withdrawn from the slurry storage tank of the bead mill. At the start of operation of the bead mill, the total amount of slurry in the slurry storage tank was 67 kg, and the slurry concentration was 30% by mass. Steps 3 to 6 were performed on the obtained slurry in the same manner as in Example 3B to obtain flattened copper powder in a dry state.

[0198] [Comparative Example 1B] <Step 1: Step to obtain raw copper powder from copper(I) compound> A slurry containing raw copper powder was prepared in the same manner as in Example 3B. <Step 2: Flattening treatment> After operating the bead mill for 120 minutes under the conditions described in Table 1B, 4 kg of slurry was withdrawn from the slurry storage tank of the bead mill. At the start of operation of the bead mill, the total amount of slurry in the slurry storage tank was 67 kg, and the slurry concentration was 30% by mass. Steps 3 to 6 were performed on the obtained slurry in the same manner as in Example 3B to obtain flattened copper powder in a dry state.

[0199] [Comparative Example 2B] After extracting the slurry in step 2 of Comparative Example 1B, deionized water was poured into the slurry storage tank of the bead mill, and the copper powder adhering to the inner wall was mixed with the slurry remaining in the slurry storage tank. Then, the operation of the bead mill was restarted under the same conditions as in Comparative Example 1B, and it was operated for 20 minutes (a total of 140 minutes including the operating time before restarting) to obtain slurry. Steps 3 to 6 were performed on the obtained slurry in the same manner as in Example 3B to obtain flattened copper powder in a dry state.

[0200]

[0201] The slurry concentration and total liquid volume in Table 1B represent the values ​​at the start of the bead mill operation during the flattening process, and the amount of copper powder is obtained by multiplying the total liquid volume by the slurry concentration.

[0202]

[0203] Specific surface area S / D in Table 2B ５０ (Flat copper powder) is the particle size D in the volume-based particle size distribution of flat copper powder measured by laser diffraction scattering particle size distribution analysis. ５０ This refers to the ratio of the specific surface area S of flattened copper powder obtained by nitrogen adsorption BET method to (μm).

[0204] The flattened copper powders of Examples 1B to 5B showed improved tap density compared to the flattened copper powders of Comparative Examples 1B and 2B. From this, it can be understood that the flattened copper powder of the second embodiment has improved packing properties. Because the flattened copper powder of the second embodiment has improved packing properties, it is considered suitable for use in conductive pastes. <<Examples 1C to 5C and Comparative Examples 1C to 2C>> The third embodiment of the present invention will be described in detail below with reference to Examples 1C to 5C and Comparative Examples 1C to 2C. However, the third embodiment is not limited in any way to the descriptions in these examples.

[0205] [Measurement using a laser diffraction scattering particle size distribution analyzer] Using a laser diffraction scattering particle size distribution analyzer (Microtrac-Bell, model: MT3300EX II), the particle size D of flattened copper powder when the cumulative frequency is 10% in the volume-based cumulative frequency distribution curve was measured. １０ And, the particle size D of the flattened copper powder and raw copper powder when the cumulative frequency is 50% in the volume-based cumulative frequency distribution curve. ５０ And, the particle size D of flattened copper powder when the cumulative frequency is 90% in the volume-based cumulative frequency distribution curve. ９０ The standard deviation (SD) of the particle size distribution was obtained. For the measurement sample, a tank (capacity 200 ml) in the sample circulation chamber of a laser diffraction scattering particle size distribution analyzer was filled with a dispersion medium (ethanol). The required amount (approximately 0.02 to 0.10 g) of the dry raw copper powder or flattened copper powder obtained by the method described below was added to the tank while observing the optimal concentration range displayed on the analyzer. Then, the instrument was irradiated with ultrasound at an output of 40 W for 3 minutes. From the obtained results, the coefficient of variation was the particle size D of the flattened copper powder. ５０ The ratio of the standard deviation SD to (SD / D) ５０ ) and the particle size D of the flattened copper powder １０ The particle size D of the flattened copper powder relative to ９０ The ratio (D９０ / D １０ The result was calculated. The results are shown in Table 2C.

[0206] [Measurement of Specific Surface Area of ​​Flattened Copper Powder by Nitrogen Adsorption BET Method] The specific surface area S of flattened copper powder was determined by the nitrogen adsorption BET method using a specific surface area measuring device (Shimadzu Corporation, model name: FlowSorb III). The results are shown in Table 2C.

[0207] [Particle size fD of flattened copper powder] ＢＥＴ [Method of calculation] The particle size D of the raw copper powder ５０ The value obtained by dividing the measured value by 2 is taken as the radius r (μm) of the copper particles, assuming that the copper particles contained in the raw copper powder are spherical, and the surface area of ​​the copper particles of radius r is S. １ (μm ２ ) and the true density ρ of copper is 8.94 (g / cm³). ３ ) Specific surface area S per unit mass ＳＡ１ (m ２ The specific surface area S(m²) of the flattened copper powder obtained in the examples and comparative examples was calculated and substituted into the following formula (1). ２ Substitute ( / g) into the following formula (1), solve the cubic equation for radius R assuming that the copper particles contained in the flattened copper powder obtained in the examples and comparative examples are cylindrical, and take twice the largest positive value of R obtained as the particle size fD of the flattened copper powder obtained in the examples and comparative examples. ＢＥＴ (μm) was used for the calculation. Furthermore, fD ＢＥＴ (μm) / D ５０ The (flattened copper powder) was calculated as follows: 2πR ３ - S x S １ / S ＳＡ１ ×R + (8 / 3) ×πr ３ = 0 (1)

[0208] [Average thickness T of flattened copper powder particles contained in flattened copper powder] Ａ [Measurement] The thickness of 100 arbitrary flattened copper powder particles was measured from SEM images obtained by observing the copper powder particles contained in the flattened copper powder with an electron microscope. The average thickness of the 100 flattened copper powder particles was calculated, and the average thickness T of the flattened copper powder was determined. Ａ (μm) was used. Furthermore, the average thickness T Ａ Particle size D of flattened copper powder５０ The ratio and average thickness T Ａ Particle size D of raw copper powder ５０ The ratio was calculated. The results are shown in Table 2C.

[0209] [Measurement of Tap Density] As an indicator of packing performance, the tap density of flattened copper powder was measured after 3000 taps in accordance with the metal powder-tap density measurement method specified in JIS Z2512:2012. The results are shown in Table 2C.

[0210] [Example 1C] <Step 1: Step to obtain raw copper powder from copper(I) compound> Cuprous oxide (manufactured by Furukawa Chemicals, product name: cuprous oxide) and deionized water were mixed in a reaction vessel so that the cuprous oxide content in the slurry (hereinafter referred to as slurry concentration) was 12.5% ​​by mass, and the resulting slurry was heated to 30-50°C. Then, when the cuprous oxide content in the slurry was 100 parts by mass, 0.2 parts by mass of polyvinyl alcohol was added to the slurry and stirred for 15 minutes. While stirring in the reaction vessel, a 20% sulfuric acid aqueous solution was continuously added to the slurry so that the amount of sulfuric acid was 1.1 times (molar ratio) of the cuprous oxide in the slurry. Next, the slurry containing the obtained raw copper powder was washed with deionized water until the resistivity was 1000 Ω·cm.

[0211] <Process 2: Flattening Process> The slurry obtained in Process 1 was flattened using a bead mill (manufactured by Ashizawa Finetech Co., Ltd.). The grinding chamber of the bead mill was filled with 0.2 mm diameter beads to a packing rate of 85%, and the bead mill was started at a peripheral speed of 8 m / s and a circulating slurry flow rate of 30 L / min. At the start of operation, the total liquid volume in the slurry storage tank was 765 kg, and the slurry concentration was 23 mass%. After operating the bead mill for 150 minutes, 391 kg of slurry was withdrawn from the slurry storage tank of the bead mill.

[0212] <Step 3: Sorting Process> Next, the extracted slurry was passed through a sieve with a mesh size of 25 μm.

[0213] <Process 4: Surface Treatment Process> The slurry containing the copper powder obtained in Process 3 was adjusted to a copper concentration of 100 g / L and stirred. Next, sodium carbonate was added so that the pH in the reaction tank became 10.0 to 10.5. Then, 0.2% by mass of sodium stearate was added to the copper powder in the reaction tank, the temperature in the reaction tank was raised to 60 °C, and it was stirred for 15 minutes. Next, a neutralizing agent (ascorbic acid) was added so that the pH in the reaction tank became 7.5, and it was stirred for 15 minutes. Then, a 20% sulfuric acid aqueous solution was added so that the pH in the reaction tank became 7.0, and it was stirred for 15 minutes.

[0214] <Process 5: Washing Process> Next, the slurry in the reaction tank was washed with ion-exchanged water until the resistivity reached 10000 Ω·cm.

[0215] <Process 6: Drying and Crushing Process> Next, the precipitate was filtered off from the washed slurry, the filtered precipitate was dried, and further crushed by a crusher to obtain flat copper powder in a dry state.

[0216] [Example 2C] After extracting the slurry in Step 2 of Example 1C, ion-exchanged water was poured into the slurry storage tank of the bead mill to mix the copper powder adhering to the inner wall and the slurry remaining in the slurry storage tank. Then, the operation of the bead mill was restarted under the same conditions as in Example 1C and operated for 190 minutes (a total of 340 minutes including the operation time before the restart of the operation) to obtain a slurry. The slurry concentration in the slurry storage tank at the time of restarting the bead mill operation was 20% by mass. For the obtained slurry, Steps 3 to 6 were performed in the same manner as in Example 1C to obtain flat copper powder in a dry state.

[0217] [Example 3C] <Step 1: Step of obtaining raw copper powder from copper (I) compound> The copper oxide (manufactured by Furukawa Chemicals Co., Ltd., product name: copper oxide) and ion-exchanged water were mixed in a reaction tank so that the content of copper oxide in the slurry (hereinafter referred to as slurry concentration) became 12.5% by mass, and the obtained slurry was heated to 50 to 70 °C. Then, when the content of copper oxide in the slurry was 100 parts by mass, 0.2 parts by mass of polyvinyl alcohol was added to the slurry and stirred for 15 minutes. While stirring the inside of the reaction tank, a 20% sulfuric acid aqueous solution was continuously added to the slurry so that the amount of sulfuric acid became 1.25 times (molar ratio) that of copper oxide in the slurry. Next, using ion-exchanged water, the slurry containing the obtained raw copper powder was washed until the resistivity became 1000 Ω·cm. <Step 2: Flattening treatment step> The bead mill was operated in the same manner as in Step 2 of Example 1C. When it was operated for 120 minutes, 125 kg of slurry was withdrawn from the slurry storage tank of the bead mill. The total amount of the slurry in the slurry storage tank at the start of the bead mill operation was 345 kg, and the slurry concentration was 20% by mass. Steps 3 to 6 were performed in the same manner as in Example 1C except that the amount of sodium stearate added into the reaction layer in Step 4 of Example 1C was changed to 0.1% by mass with respect to the copper powder, and flattened copper powder in a dry state was obtained.

[0218] [Example 4C] After the slurry was withdrawn in Step 2 of Example 3C, ion-exchanged water was poured into the slurry storage tank of the bead mill to mix the copper powder adhering to the inner wall and the slurry remaining in the slurry storage tank. Then, the operation of the bead mill was restarted under the same conditions as in Example 1C and operated for 135 minutes (a total of 255 minutes in combination with the operation time before the restart of the operation) to obtain a slurry. The slurry concentration in the slurry storage tank at the restart of the bead mill operation was 15% by mass. Steps 3 to 6 were performed in the same manner as in Example 3C, and flattened copper powder in a dry state was obtained.

[0219] [Example 5C] <Step 1: Step to obtain raw copper powder from copper(I) compound> A slurry containing raw copper powder was prepared in the same manner as in Example 3C. <Step 2: Flattening process> As shown in Table 1C, the bead mill was operated under the same conditions as in Example 1C, except that the bead filling rate, bead quantity, and peripheral speed were changed. After 15 minutes of operation, 4 kg of slurry was withdrawn from the slurry storage tank of the bead mill. At the start of operation of the bead mill, the total amount of slurry in the slurry storage tank was 67 kg, and the slurry concentration was 30% by mass. Steps 3 to 6 were performed on the obtained slurry in the same manner as in Example 3C to obtain flattened copper powder in a dry state.

[0220] [Comparative Example 1C] <Step 1: Step to obtain raw copper powder from copper(I) compound> A slurry containing raw copper powder was prepared in the same manner as in Example 3C. <Step 2: Flattening treatment> After operating the bead mill for 120 minutes under the conditions described in Table 1C, 4 kg of slurry was withdrawn from the slurry storage tank of the bead mill. At the start of operation of the bead mill, the total amount of slurry in the slurry storage tank was 67 kg, and the slurry concentration was 30% by mass. Steps 3 to 6 were performed on the obtained slurry in the same manner as in Example 3C to obtain flattened copper powder in a dry state.

[0221] [Comparative Example 2C] After the slurry was extracted in step 2 of Comparative Example 1C, deionized water was poured into the slurry storage tank of the bead mill, and the copper powder adhering to the inner wall was mixed with the slurry remaining in the slurry storage tank. Then, the operation of the bead mill was restarted under the same conditions as in Comparative Example 1C, and it was operated for 20 minutes (a total of 140 minutes including the operating time before restarting) to obtain slurry. Steps 3 to 6 were performed on the obtained slurry in the same manner as in Example 3C to obtain flattened copper powder in a dry state.

[0222]

[0223] The slurry concentration and total liquid volume in Table 1C represent the values ​​at the start of the bead mill operation during the flattening process, and the amount of copper powder is obtained by multiplying the total liquid volume by the slurry concentration.

[0224]

[0225] Specific surface area S / D in Table 2C ５０ (Flat copper powder) is the particle size D in the volume-based particle size distribution of flat copper powder measured by laser diffraction scattering particle size distribution analysis. ５０ This refers to the ratio of the specific surface area S of flattened copper powder obtained by nitrogen adsorption BET method to (μm).

[0226] The flattened copper powder obtained by the manufacturing methods of Examples 1C to 5C showed improved tap density compared to the flattened copper powder obtained by the manufacturing methods of Comparative Examples 1C and 2C. From this, it can be understood that the flattened copper powder of the third embodiment has improved packing properties. Since the flattened copper powder obtained by the manufacturing method of the third embodiment has improved packing properties, it is considered suitable for use in conductive pastes.

[0227] This application claims priority based on Japanese Patent Applications No. 2025-018215, No. 2025-018216, and No. 2025-018217, filed on 6 February 2025, and incorporates all of their disclosures herein.

Claims

1. Copper powder, wherein the particle size D in the volume-based particle size distribution of the copper powder as measured by laser diffraction scattering particle size distribution analysis. ５０ Specific surface area S (m²) of nitrogen adsorption by BET method relative to (μm) ２ The ratio (S / D) of / g ５０ ) is 0.07m ２ Copper powder with a particle size of / (g·μm) or larger.

2. The particle size D of the copper powder ５０ The copper powder according to claim 1, wherein the particle size is 0.1 μm or more and 10.0 μm or less.

3. The average thickness T of the copper powder by the following (method) Ａ The particle size D ５０ (μm) ratio (D ５０ / T Ａ ) is 20.0 or less, and the copper powder according to claim 1 or 2. (Method) The thickness of any 100 copper powders is measured respectively from the SEM image obtained by observing the copper powder with an electron microscope, and the average value of the thicknesses of the 100 copper powders is taken as the average thickness T Ａ (μm).

4. The average thickness T of the copper powder according to the following (method) Ａ The copper powder according to any one of claims 1 to 3, wherein the thickness is 0.1 μm or more and 2.0 μm or less. (Method) The thickness of 100 arbitrary copper powders is measured from SEM images obtained by observing the copper powder with an electron microscope, and the average value of the thicknesses of the 100 copper powders is called the average thickness T of the copper powder. Ａ Let it be (μm).

5. The specific surface area S of the copper powder obtained by the nitrogen adsorption BET method is 0.10 m². ２ / g or more 3.0m ２ The copper powder according to any one of claims 1 to 4, wherein the amount is less than or equal to / g.

6. The particle size D of the copper powder in the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution method. １０ Particle size D ９０ The ratio (D ９０ / D １０ The copper powder according to any one of claims 1 to 5, wherein the coefficient of the copper is 5.0 or less.

7. The particle size D of the copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution analysis. ５０ The standard deviation (SD) and the coefficient of variation (SD / D) obtained from it are... ５０ The copper powder according to any one of claims 1 to 6, wherein the coefficient of the copper is 0.60 or less.

8. The copper powder according to any one of claims 1 to 7, which is a flattened copper powder.

9. A conductive paste comprising copper powder according to any one of claims 1 to 8, a resin, and a solvent.

10. Flattened copper powder, wherein the average thickness T of the flattened copper powder is determined by the following (method). Ａ The particle size D of the flattened copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution analysis. ５０ The ratio (D ５０ / T Ａ ) is 20.0 or less, and the particle size D of the flattened copper powder ５０ The particle size is 1.0 μm or more and 10.0 μm or less, and the particle size D in the volume-based particle size distribution of the flattened copper powder as measured by laser diffraction scattering particle size distribution measurement method. ５０ The standard deviation (SD) and the coefficient of variation (SD / D) obtained from it are... ５０ Flattened copper powder having a thickness of 0.30 or more and 0.60 or less. (Method) The thickness of 100 arbitrary flattened copper powders was measured from SEM images obtained by observing the flattened copper powder with an electron microscope, and the average value of the thicknesses of the 100 flattened copper powders was defined as the average thickness T of the flattened copper powder. Ａ Let it be (μm).

11. The average thickness T of the flattened copper powder. Ａ The flattened copper powder according to claim 10, wherein the particle size is 0.1 μm or more and 2.0 μm or less.

12. Particle size D of the flattened copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement method. １０ Particle size D ９０ The ratio (D ９０ / D １０ The flattened copper powder according to claim 10 or 11, wherein the coefficient of the product is 5.0 or less.

13. The specific surface area S of the flattened copper powder obtained by the nitrogen adsorption BET method is 0.10 m². ２ / g or more 3.0m ２ Flattened copper powder according to any one of claims 10 to 12, wherein the amount is less than or equal to / g.

14. The flattened copper powder D ５０ / T Ａ The flattened copper powder according to any one of claims 10 to 13, wherein the amount exceeds 3.

4.

15. A conductive paste comprising flattened copper powder according to any one of claims 10 to 14, a resin, and a solvent.

16. A method for producing flattened copper powder, comprising step A of flattening raw copper powder, wherein the particle size D of the flattened copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement method. ５０ The particle size fD of the flattened copper powder is calculated according to the following (method). ＢＥＴ The ratio (fD ＢＥＴ / D ５０ A method for producing flattened copper powder in which the particle size D of the raw copper powder is 0.70 or more and 1.50 or less. (Method) The particle size D of the raw copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement. ５０ The radius of the copper particles is measured and divided by 2. This value is taken as the radius r (μm) of the copper particles, assuming that the copper particles contained in the raw copper powder are spherical. The surface area of ​​the copper particles with radius r is S. １ (μm ２ ), the true density ρ of copper is 8.94 (g / cm³). ３ ) Specific surface area S per unit mass ＳＡ１ (m ２ The specific surface area S(m²) of the flattened copper powder is determined by the nitrogen adsorption BET method. ２ Measure the particle size fD of the flattened copper powder. Substitute each value into equation (1) below and solve the cubic equation for radius R, assuming that the flattened copper particles contained in the flattened copper powder are cylindrical. Of the solutions R obtained, double the largest positive value of R (2R) and use that value to determine the particle size fD of the flattened copper powder. ＢＥＴ Let (μm). 2πR ３ - S x S １ / S ＳＡ１ ×R + (8 / 3) ×πr ３ = 0 (1) 17. Average thickness T of the flattened copper powder by the following (method) Ａ The particle size D of the raw copper powder ５０ The ratio (D ５０ / T Ａ A method for producing flattened copper powder according to claim 16, wherein the ratio is 7.5 or less. (Method) The thickness of 100 arbitrary flattened copper powders is measured from SEM images obtained by observing the flattened copper powder with an electron microscope, and the average value of the thicknesses of the 100 flattened copper powders is defined as the average thickness T of the flattened copper powder. Ａ Let it be (μm).

18. Particle size D of the raw copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement method. ５０ A method for producing flattened copper powder according to claim 16 or 17, wherein the particle size is 0.1 μm or more and 10.0 μm or less.

19. A method for producing flattened copper powder according to any one of claims 16 to 18, wherein in step A, the raw copper powder is flattened using a bead mill.

20. The method for producing flattened copper powder according to claim 19, wherein in step A, the diameter of the beads of the bead mill is 0.5 mm or less.

21. The method for producing flattened copper powder according to claim 19 or 20, wherein in step A, the amount of beads filling the bead mill is 50% or more.

22. A method for producing flattened copper powder according to any one of claims 19 to 21, wherein in step A, the peripheral speed of the bead mill is 5 m / s or more and 15 m / s or less.

23. Particle size D in the volume-based particle size distribution of the flattened copper powder as measured by laser diffraction scattering particle size distribution analysis. ５０ Specific surface area S (m²) of nitrogen adsorption by BET method relative to (μm) ２ The ratio (S / D) of / g ５０ ) is 0.07m ２ A method for producing flattened copper powder according to any one of claims 16 to 22, wherein the particle size is 1 / (g·μm) or larger.

24. Particle size D in the volume-based particle size distribution of the flattened copper powder as measured by laser diffraction scattering particle size distribution analysis. ５０ A method for producing flattened copper powder according to any one of claims 16 to 23, wherein the particle size is 0.1 μm or more and 10.0 μm or less.

25. The average thickness T of the flattened copper powder determined by the following (method). Ａ Particle size D in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution method. ５０ The ratio (D ５０ / T Ａ A method for producing flattened copper powder according to any one of claims 16 to 24, wherein the ratio of the flattened copper powder to the 20.0 is 20.0 or less. (Method) The thickness of any 100 flattened copper powders is measured from SEM images obtained by observing the flattened copper powder with an electron microscope, and the average value of the thicknesses of the 100 flattened copper powders is defined as the average thickness T of the flattened copper powder. Ａ Let it be (μm).

26. The average thickness T of the flattened copper powder obtained by the following (method) Ａ A method for producing flattened copper powder according to any one of claims 16 to 25, wherein the thickness is 0.1 μm or more and 2.0 μm or less. (Method) The thickness of any 100 flattened copper powders is measured from SEM images obtained by observing the flattened copper powder with an electron microscope, and the average value of the thicknesses of the 100 flattened copper powders is called the average thickness T of the flattened copper powder. Ａ Let it be (μm).

27. The specific surface area S of the flattened copper powder obtained by the nitrogen adsorption BET method is 0.10 m². ２ / g or more 3.0m ２ A method for producing flattened copper powder according to any one of claims 16 to 26, wherein the amount is less than or equal to / g.

28. Particle size D of the flattened copper powder in the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement method. １０ Particle size D ９０ The ratio (D ９０ / D １０ A method for producing flattened copper powder according to any one of claims 16 to 27, wherein the ratio is 5.0 or less.

29. Particle size D in the volume-based particle size distribution of the flattened copper powder as measured by laser diffraction scattering particle size distribution analysis. ５０ The standard deviation (SD) and the coefficient of variation (SD / D) obtained from it are... ５０ A method for producing flattened copper powder according to any one of claims 16 to 28, wherein the ratio is 0.60 or less.

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