WO2025070075A1 - Copper powder and conductive paste - Google Patents

Abstract

In the copper powder according to the present invention: the ratio D_BET/D₅₀ obtained from the particle diameter D₅₀ when the cumulative frequency in a cumulative frequency distribution curve based on volume measured using a laser diffraction/scattering type particle size distribution measurement device is 50%, and the particle diameter D_BET calculated from a specific surface area s by a nitrogen adsorption method, is 0.70-1.20; and the coefficient of variation (SD/MV) obtained from the volume average diameter MV and a standard deviation SD of a particle size distribution measured by a laser diffraction/scattering type particle size distribution measurement method is 0.50 or less.

Description

Copper Powder and Conductive Paste

The present invention relates to copper powder and conductive paste.

　Conventionally, copper powder has been used as a raw material for conductive pastes used to form wiring on printed wiring boards. However, in recent years, as printed wiring boards have become smaller, the wiring has become thinner, and there is a demand for copper powder for conductive pastes that can accommodate thinner wiring.

Patent Document 1 discloses a copper powder consisting of copper particles coated with a collagen peptide, in which the average particle diameter D _SEM , which is the circle-equivalent diameter of primary particles determined from an SEM image, is 0.1 to 1.0 μm, and the carbon content in the powder is 0.10 to 0.50 mass %.
Furthermore, Patent Document 1 describes that the invention described in Patent Document 1 makes it possible to provide copper powder of relatively fine size, with an average primary particle diameter of 1 μm or less, at which sintering occurs at a high temperature.

JP 2016-191112 A

The present invention provides copper powder with improved packing properties.

That is, according to the present invention, there are provided the copper powder and conductive paste described below.
1. D BET /D 50 calculated from a particle diameter D ₅₀ at a cumulative frequency of 50% in a volume-based cumulative frequency distribution curve measured using a laser diffraction scattering type particle size distribution measurement device and a particle diameter D _BET calculated from a specific surface area _s by a nitrogen adsorption method is 0.70 or more and _1.20 or less;
A copper powder having a coefficient of variation (SD/MV) obtained from the volume average diameter MV and the standard deviation SD of a particle size distribution measured by a laser diffraction/scattering particle size distribution measurement method of 0.50 or less.
2. The copper powder according to 1., wherein the _D50 is 5.0 μm or less.
3. The copper powder according to 1. or 2., wherein the D _BET is 0.1 μm or more and 5.0 μm or less.
4. The copper powder according to any one of 1. to 3., wherein the amount of residual chlorine determined by chemical analysis is 50 ppm or less.
5. The copper powder according to any one of 1. to 4., which is obtained by a disproportionation reaction.
6. The copper powder according to any one of 1. to 5., which comprises a fatty acid coating on the surface.
7. A conductive paste comprising the copper powder according to any one of 1. to 6., a resin, and a solvent.

The present invention makes it possible to provide copper powder with improved packing properties.

Hereinafter, the present invention will be described based on an embodiment.
In addition, when a numerical range is described in stages, the upper and lower limits of each numerical range can be combined in any manner.

(1) Copper Powder Hereinafter, the copper powder of the present embodiment will be described.

The copper powder of this embodiment has a D BET /D 50 ratio of 0.70 or more and 1.20 or less, calculated from a particle diameter D ₅₀ at a cumulative frequency of 50% in a volume-based cumulative frequency distribution curve measured using a laser diffraction scattering type particle size distribution measurement device and a particle _diameter D _BET calculated from a specific surface area s by a nitrogen adsorption method, and has a coefficient of variation ( _SD /MV) of 0.50 or less, calculated from a volume average diameter MV and a standard deviation SD of the particle size distribution measured by a laser diffraction scattering type particle size distribution measurement method.

Although the mechanism by which the copper powder of this embodiment solves the above problems is unclear, it is believed that the D _BET /D ₅₀ and the coefficient of variation (SD/MV) are each in a certain numerical range, thereby improving the dispersibility of the primary particles of the copper powder and narrowing the particle size distribution of the copper powder, which is believed to improve the particle packing.

There are several advantages to improving the particle packing, one of which is that when copper powder with improved packing is mixed into a conductive paste, the wiring obtained from the conductive paste is less likely to break. Improved packing means that there are fewer voids between the particles, so even when the conductive paste is fired, there is less shrinkage and breaks are less likely to occur.

From the viewpoint of further improving the filling property, the D _BET /D ₅₀ of the copper powder of this embodiment is preferably 0.70 or more, more preferably 0.75 or more, even more preferably 0.78 or more, even more preferably 0.80 or more, and is preferably 1.20 or less, more preferably 1.10 or less, even more preferably 1.00 or less.
From the viewpoint of further improving the filling property, the D _BET /D ₅₀ of the copper powder of this embodiment is preferably 0.70 or more and 1.20 or less, more preferably 0.75 or more and 1.20 or less, even more preferably 0.78 or more and 1.10 or less, and still more preferably 0.80 or more and 1.00 or less.

The particle diameter D _BET of the copper powder of this embodiment can be calculated by the following formula (1).
D _BET =6/(ρ・s) (1)
In formula (1), ρ is the density of the copper powder (8.96 g/cm ³ ), and s is the specific surface area of the copper powder measured by the nitrogen adsorption method.

From the viewpoint of further improving the filling property, the coefficient of variation (SD/MV) of the copper powder of this embodiment is, for example, 0.01 or more, and preferably 0.50 or less, more preferably 0.45 or less, even more preferably 0.40 or less, and even more preferably 0.35 or less.
From the viewpoint of further improving the filling property, the above-mentioned coefficient of variation (SD/MV) of the copper powder of this embodiment is preferably 0.01 or more and 0.50 or less, more preferably 0.01 or more and 0.45 or less, even more preferably 0.01 or more and 0.40 or less, and even more preferably 0.01 or more and 0.35 or less.

From the viewpoint of improving handleability and dispersibility, the _D50 of the copper powder of this embodiment is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1.0 μm or more, and even more preferably 1.4 μm or more, and is preferably 5.0 μm or less, more preferably 4.7 μm or less, even more preferably 4.5 μm or less, and even more preferably 4.3 μm or less.
From the viewpoint of improving handleability and dispersibility, the _D50 of the copper powder of this embodiment is preferably 0.1 μm or more and 5.0 μm or less, more preferably 0.5 μm or more and 4.7 μm or less, even more preferably 1.0 μm or more and 4.5 μm or less, and even more preferably 1.4 μm or more and 4.3 μm or less.

From the viewpoint of improving handleability and dispersibility, the D _BET of the copper powder of this embodiment is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1.0 μm or more, and is preferably 5.0 μm or less, more preferably 4.5 μm or less.
From the viewpoint of improving handleability and dispersibility, the D _BET of the copper powder of this embodiment is preferably 0.1 μm or more and 5.0 μm or less, more preferably 0.5 μm or more and 5.0 μm or less, and even more preferably 1.0 μm or more and 4.5 μm or less.

The amount of residual chlorine quantified by the chemical analysis method of the copper powder of this embodiment is preferably 50 ppm or less, more preferably 10 ppm or less, even more preferably 1 ppm or less, even more preferably 0.1 ppm or less, and even more preferably 0.01 ppm or less. This prevents problems caused by residual chlorine, such as corrosion.

The uses of the copper powder of this embodiment are not particularly limited, but because the copper powder of this embodiment has improved dispersibility and a narrow particle size distribution, it is suitable for use as a raw material for conductive pastes.

[Method of manufacturing copper powder]
The method for producing copper powder according to this embodiment will be described below.

The method for producing copper powder in this embodiment is not particularly limited, but from the viewpoint of further improving the dispersibility of the primary particles of the copper powder and further narrowing the particle size distribution of the copper powder, it is preferable that the method includes step A of obtaining copper powder from a copper(I) compound and step B of treating the surface of the copper powder with a fatty acid salt.

<Step A>
Step A of the method for producing copper powder according to this embodiment will be described below.
Step A is a step of obtaining copper powder 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 copper powder and further narrowing the particle size distribution of the copper powder, it is preferable to obtain the copper powder from a slurry A containing a copper(I) compound and polyvinyl alcohol.

The dispersion medium used in slurry A is not particularly limited, and any dispersion medium commonly used in slurry preparation, such as water or a hydrophilic dispersion medium, can be used. In addition, a mixture of multiple types of dispersion medium can be used.

Hydrophilic dispersion media include, for example, polyhydric alcohols such as alkanediols such as ethylene glycol and propylene glycol, and glycerin; lower alcohols such as sugar alcohols, 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 glycol Examples of the glycol ethers include ethylene 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.

The content of the copper (I) compound in the slurry A is not particularly limited, and is, for example, 1% by mass or more and 25% by mass or less.

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

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

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 copper powder and further narrowing the particle size distribution of the 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, or for example, 90 mol% or less.
Furthermore, from the viewpoint of further improving the dispersibility of the primary particles of the copper powder and further narrowing the particle size distribution of the copper powder, the degree of saponification of the polyvinyl alcohol is preferably 70 mol% or more and 100 mol% or less, more preferably 75 mol% or more and 100 mol% or less, even more preferably 80 mol% or more and 95 mol% or less, and even more preferably 85 mol% or more and 90 mol% or less.

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

The type of reaction that produces the copper powder in step A is not particularly limited, but for example, the copper powder can be produced by disproportionating the copper(I) compound.

The copper powder of this embodiment is preferably obtained by a disproportionation reaction.

The components contained in 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 contains one or more selected from the group consisting of hydrochloric acid, nitric acid, and sulfuric acid, and even more preferably contains sulfuric acid. Here, the acid in slurry A may be in the form of a copper salt (copper hydrochloride, copper nitrate, copper sulfate, etc.) during the disproportionation reaction of the copper (I) compound. The particle size of the copper powder can be adjusted by adjusting the rate at which the acid is supplied to the reaction vessel. For example, the particle size of the copper powder tends to increase when the acid supply rate is reduced.

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

The temperature in the reaction tank in step A is not particularly limited, but may be, for example, 5°C or higher, or may be, for example, 10°C or higher, and from the viewpoint of further improving the dispersibility of the primary particles of the copper powder and further narrowing the particle size distribution of the copper powder, it is preferably 90°C or lower, more preferably 80°C or lower, and even more preferably 70°C or lower, and may be 60°C or lower, 50°C or lower, 40°C or lower, 30°C or lower, 20°C or lower, or 15°C or lower.
The temperature in the reaction tank in step A of this embodiment is preferably 5° C. or higher and 90° C. or lower, more preferably 5° C. or higher and 80° C. or lower, from the viewpoint of further improving the dispersibility of the primary particles of the copper powder and further narrowing the particle size distribution of the copper powder.
Here, the temperature in the reaction tank in step A is the temperature of the slurry in the reaction tank. The particle size of the copper powder can be adjusted by adjusting the temperature in the reaction tank. For example, when the temperature in the reaction tank is increased, the particle size of the copper powder tends to increase.

<Step B>
Step B of the method for producing copper powder according to this embodiment will now be described.
In step B, the surface of the copper powder is treated with a fatty acid salt. Step B includes, for example, a dispersing step of attaching a fatty acid salt to the surface of the copper powder and dispersing the copper powder, and a coating step of forming a coating of a fatty acid on the surface of the copper powder.

The copper powder of this embodiment preferably includes a fatty acid coating on the surface.

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

The amount of fatty acid salt added is preferably 0.05% by mass or more and 5% by mass or less based on the total amount of copper powder (dry state).

The pH in the reaction tank in the dispersion step is not particularly limited, but from the viewpoint of facilitating dissolution of the fatty acid salt, it is preferably 9 or more, more preferably 10 or more, and is, for example, 11 or less.
The pH in the reaction tank in the dispersion step of this embodiment is preferably 9 or more and 11 or less, more preferably 10 or more and 11 or less, from the viewpoint of facilitating dissolution of the fatty acid salt.

In the dispersion process, it is preferable to add the fatty acid salt to the reaction tank and then allow it to age. The aging time is preferably 5 minutes or more and 60 minutes or less.

In the coating process, the inside of the reaction vessel is neutralized with an acid, and a fatty acid coating is formed on the surface of the copper powder using the fatty acid. The type of acid is not particularly limited, and may be a strong acid such as hydrochloric acid, sulfuric acid, or nitric acid, or may be a weak acid.
From the following viewpoint, it is preferable to use a weak acid as the acid for neutralizing the inside of the reaction vessel in the coating formation step.
By using a weak acid, a fatty acid coating can be formed more uniformly, and aggregation of the obtained copper microparticles can be suppressed. In addition, by using a weak acid, the fatty acid coating can increase the hydrophobicity of the obtained copper microparticles, and the settling rate of the copper microparticles can be increased in the washing step described below, thereby improving productivity. In addition, by using a weak acid, a fatty acid coating can be formed uniformly on the copper powder, making it difficult for the copper microparticles to aggregate with each other, and copper microparticles with fewer aggregated particles can be obtained.
The type of weak acid used for neutralization is not particularly limited, and examples thereof include one or more acids selected from citric acid, ascorbic acid, and acetic acid.

In the coating formation process, it is preferable to add acid to the reaction tank and then age the mixture. The ageing time is preferably 5 minutes or more and 60 minutes or less.

<Other processes>
The method for producing copper powder according to the present embodiment may include steps other than steps A and B described above.

The method for producing copper powder according to this embodiment may further include a step of washing the copper powder. The washing method is not particularly limited, and can be performed, for example, by adding water and stirring.

The method for producing copper powder according to this embodiment may further include a step of selecting the copper powder or intermediate. The selection of the copper powder or intermediate may be performed, for example, using a sieve, and by using a sieve of a specific size, it is possible to select those with particle sizes in a specific range. This step may be performed at the slurry stage, or after drying to produce a powder state.

The method for producing copper powder according to this embodiment may further include step C of drying the copper powder. The method for drying the copper powder is not particularly limited, and the copper powder can be dried, for example, by dehydrating the powder by centrifugation, followed by heating and drying in a dryer or the like.

The method for producing copper powder according to this embodiment may further include a step of crushing the copper powder or the intermediate. The copper powder or the intermediate can be crushed by a known crusher. There are no particular limitations on the type of crusher, and any type can be used, such as a high-speed rotary mill, a hammer mill, or an atomizer.

(2) Conductive Paste The conductive paste of this embodiment will now be described.

The conductive paste of this embodiment contains the above-mentioned copper powder, a resin, and a solvent.

The copper powder of this embodiment has improved dispersibility and a narrow particle size distribution, making it easy to design a paste that is highly reproducible and stable.

The resin used in the conductive paste of this embodiment is not particularly limited, and any known raw material for conductive pastes can be used as appropriate. For example, cellulose-based resins such as ethyl cellulose can be used, which are added as an organic vehicle dissolved in an organic solvent such as terpineol. The amount of resin added must be kept to a level that does not inhibit sintering. For this reason, the amount of resin added is preferably 5% by mass or less of the entire conductive paste, and more preferably 2% by mass or less.

The solvent used in the conductive paste of this embodiment is not particularly limited, and any known raw material for conductive pastes can be used as appropriate. For example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, terpineol, triethanol, and amines are preferably used. Among these organic solvents, amines are preferred because they have reducing ability and have the effect of locally creating a reducing atmosphere on the paste surface during firing. In addition, when water is used as the solvent, the amount of organic solvents that are harmful to the human body can be reduced, thereby increasing the utility value of the copper paste. The amount of solvent is not particularly limited, but may be appropriately adjusted in consideration of the dispersibility and particle size distribution of the copper powder so as to obtain a viscosity suitable for a conductive film formation method such as screen printing or inkjet printing.

Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than those described above can also be adopted.
Furthermore, the present invention is not limited to the above-described embodiment, and modifications and improvements within the scope of the present invention that can achieve the object of the present invention are included in the present invention.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention.

[Measurement using a laser diffraction/scattering particle size distribution analyzer]
A laser diffraction scattering type particle size distribution analyzer (Microtrac Bell, model name: MT3300EX II) was used to obtain the particle diameter _D50 of the copper powder when the cumulative frequency was 50% in the volume-based cumulative frequency distribution curve, the standard deviation SD of the particle size distribution, and the volume average diameter MV. The measurement sample was a dispersion in which dry copper powder obtained by the method described below was dispersed in water or an alcohol solvent such as ethanol. The results are shown in Table 1.

[Measurement by nitrogen adsorption method]
The specific surface area s of the copper powder was measured by nitrogen adsorption using a specific surface area measuring device (Shimadzu Corporation, model name: FlowSorb III). The particle diameter D _BET of the copper powder was calculated from the specific surface area s of the copper powder by the following formula (1). The results are shown in Table 1.
D _BET =6/(ρ・s) (1)
In formula (1), ρ is the density of the copper powder (8.96 g/cm ³ ), and s is the specific surface area of the copper powder measured by the nitrogen adsorption method.

As an index of filling ability, the tap density of the copper powder was measured in accordance with the metal powder tap density measurement method specified in JIS Z2512:2012. The results are shown in Table 1.

[Example 1]
<Step A>
A reaction tank was charged with 5,600 g of ion-exchanged water, 1.6 g of polyvinyl alcohol (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name: GOHSENOL GL-05, degree of saponification: 86.5 to 89.0 mol%, viscosity (4% aqueous solution, 20° C.) 4.8 to 5.8 mPa·s), and 800 g of cuprous oxide (manufactured by Furukawa Chemicals Corporation, product name: cuprous oxide), and the mixture was stirred.
Next, the temperature inside the reaction vessel was brought to 30 to 50°C, and a 20% aqueous sulfuric acid solution (total of 3015 g) was continuously added to the reaction vessel while stirring the inside of the reaction vessel, followed by stirring for 15 minutes to obtain a slurry containing copper powder. The pH of the slurry in the reaction vessel was 1.8.
<Cleaning step (1)>
Next, the obtained slurry containing copper powder was washed with ion-exchanged water until the resistance value reached 1000 Ω·cm.
<Sorting process>
The washed slurry was then screened using a sieve with 25 μm openings.
<Step B>
The resulting slurry containing copper powder was adjusted to a copper concentration of 100 g/L and stirred.
Then, sodium carbonate was added to the reaction vessel so that the pH value in the reaction vessel was 10.0 to 10.5.
Next, sodium stearate was added to the reaction vessel in an amount of 0.2% by mass based on the copper powder, the reaction vessel was heated 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 in the reaction vessel was adjusted to 7.5, and the mixture was stirred for 15 minutes.
Next, a 20% aqueous sulfuric acid solution was added to the reaction vessel so that the pH in the reaction vessel became 7.0, and the mixture was stirred for 15 minutes.
<Cleaning step (2)>
Next, the slurry in the reaction vessel was washed with ion-exchanged water until the resistance value reached 10,000 Ω·cm.
<Drying and crushing process>
Next, the precipitate was filtered off from the washed slurry, and the filtered off precipitate was dried and further crushed in a crusher to obtain a dry copper powder.

[Example 2]
Dry copper powder was obtained under the same conditions as in Example 1, except that in step A, the temperature in the reaction vessel was increased and the average addition time per gram of the 20% aqueous sulfuric acid solution was shortened.

[Example 3]
In step A, dry copper powder was obtained under the same conditions as in Example 2, except that the temperature inside the reaction vessel was increased.

[Comparative Example 1]
Dry copper powder was obtained under the same conditions as in Example 1, except that in step A, 8.0 g of polyvinylpyrrolidone was used instead of polyvinyl alcohol, and the average addition time per gram of the 20% aqueous sulfuric acid solution was shortened.

[Comparative Example 2]
Dry copper powder was obtained under the same conditions as in Example 1, except that in step A, 8.0 g of a polycarboxylic acid resin (manufactured by Nippon Shokubai Co., Ltd., product name: PM-103) was used instead of polyvinyl alcohol, and the average addition time per gram of the 20% aqueous sulfuric acid solution was shortened.

The copper powder of the example had a higher tap density than the copper powder of the comparative example, which shows that the copper powder of the present embodiment has improved packing properties.
The copper powder of this embodiment has improved packing properties and is therefore considered suitable for use in conductive pastes.

This application claims priority based on Japanese Patent Application No. 2023-168783, filed on September 28, 2023, the entire disclosure of which is incorporated herein by reference.

Claims (7)

D BET /D 50 calculated from a particle diameter D ₅₀ at which the cumulative frequency is 50% in a volume-based cumulative frequency distribution curve measured using a laser _diffraction /scattering type particle size distribution measurement device and a particle diameter D _BET calculated from a specific surface area _s by a nitrogen adsorption method is 0.70 or more and 1.20 or less,
A copper powder having a coefficient of variation (SD/MV) obtained from the volume average diameter MV and the standard deviation SD of a particle size distribution measured by a laser diffraction/scattering particle size distribution measurement method of 0.50 or less. The copper powder according to claim 1 , wherein the D ₅₀ is 5.0 μm or less. The copper powder according to claim 1 or 2, wherein the D _BET is 0.1 μm or more and 5.0 μm or less. Copper powder according to any one of claims 1 to 3, in which the amount of residual chlorine determined by chemical analysis is 50 ppm or less. 　Copper powder according to any one of claims 1 to 4, obtained by a disproportionation reaction. The copper powder according to any one of claims 1 to 5, which has a fatty acid coating on its surface. A conductive paste comprising the copper powder according to any one of claims 1 to 6, a resin, and a solvent.