Copper powder and conductive paste

Abstract

In the copper powder according to the present invention: the ratio DBET / 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 DBET 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

[0001] The present invention relates to copper powder and conductive paste.

[0002] 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, the miniaturization of printed wiring boards has led to thinner wiring, and there is a demand for copper powder suitable for conductive pastes that can accommodate thinner wiring.

[0003] Patent Document 1 describes a copper powder made of copper particles coated with collagen peptide, in which the average particle diameter D is determined from the circle-equivalent diameter of the primary particles obtained from an SEM image. ＳＥＭ Patent Document 1 also discloses a copper powder having a particle size of 0.1 to 1.0 μm and a carbon content of 0.10 to 0.50 mass % in the powder. Patent Document 1 also describes that the invention described in Patent Document 1 makes it possible to provide copper powder of a relatively fine size having an average primary particle size of 1 μm or less, at which sintering occurs at a high temperature.

[0004] JP 2016-191112 A

[0005] The present invention provides a copper powder with improved packing properties.

[0006] That is, according to the present invention, there are provided the following copper powder and conductive paste: 1. A particle diameter D at which the cumulative frequency is 50% in a volume-based cumulative frequency distribution curve measured using a laser diffraction / scattering particle size distribution analyzer. ５０ and the particle diameter D calculated from the specific surface area s by the nitrogen adsorption method. ＢＥＴ and D obtained from ＢＥＴ / D ５０ 1. The copper powder of claim 1, wherein the coefficient of variation (SD / MV) obtained from the volume average diameter MV and the standard deviation SD of the particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is 0.50 or less. ５０ 3. The copper powder according to 1., wherein the average particle size is 5.0 μm or less. ＢＥＴThe copper powder according to 1. or 2., having a particle size of 0.1 μm or more and 5.0 μm or less. 4. The copper powder according to any one of 1. to 3., having a residual chlorine content of 50 ppm or less as determined by chemical analysis. 5. The copper powder according to any one of 1. to 4., obtained by a disproportionation reaction. 6. The copper powder according to any one of 1. to 5., having 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.

[0007] According to the present invention, it is possible to provide copper powder with improved packing properties.

[0008] The present invention will be described below based on the embodiments. When numerical ranges are described in stages, the upper and lower limits of each numerical range can be combined in any way.

[0009] (1) Copper Powder The copper powder of this embodiment will be described below.

[0010] The copper powder of this embodiment has a particle diameter D at a cumulative frequency of 50% in a volume-based cumulative frequency distribution curve measured using a laser diffraction scattering particle size distribution analyzer. ５０ and the particle diameter D calculated from the specific surface area s by the nitrogen adsorption method. ＢＥＴ and D obtained from ＢＥＴ / D ５０ is 0.70 or more and 1.20 or less, and the coefficient of variation (SD / MV) obtained from the volume average diameter MV and the standard deviation SD of the particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is 0.50 or less.

[0011] The mechanism by which the copper powder of this embodiment solves the above-mentioned problems is not clear, but ＢＥＴ / D ５０ It is believed that the dispersion of primary particles of the copper powder is improved and the particle size distribution of the copper powder is narrowed by ensuring that the SD / MV ratio is within a certain range, thereby improving the packing of the particles.

[0012] There are several advantages to improving the packing of particles, but one such advantage is that when copper powder with improved packing is blended into a conductive paste, the wiring obtained from the conductive paste is less likely to break. Improved packing means fewer voids between particles, so even when the conductive paste is fired, shrinkage is small and breaks are less likely to occur.

[0013] From the viewpoint of further improving the packing property, the above D of the copper powder of this embodiment ＢＥＴ / D ５０ is preferably 0.70 or more, more preferably 0.75 or more, even more preferably 0.78 or more, and even more preferably 0.80 or more, and is preferably 1.20 or less, more preferably 1.10 or less, and even more preferably 1.00 or less. ＢＥＴ / D ５０ 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 even more preferably 0.80 or more and 1.00 or less.

[0014] Particle diameter D of the copper powder of this embodiment ＢＥＴ can be calculated by the following formula (1): ＢＥＴ = 6 / (ρ·s) (1) In formula (1), ρ is the density of copper powder (8.96 g / cm ３ ) and s is the specific surface area of ​​the copper powder as determined by the nitrogen adsorption method.

[0015] From the viewpoint of further improving the packing 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. Also, from the viewpoint of further improving the packing property, the 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.

[0016] From the viewpoint of improving handling properties and dispersibility, the copper powder of this embodiment has a D ５０ 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. ５０ 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.

[0017] From the viewpoint of improving handling properties and dispersibility, the copper powder of this embodiment has a D ＢＥＴ is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1.0 μm or more, and is preferably 5.0 μm or less, and more preferably 4.5 μm or less. ＢＥＴ 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.

[0018] The amount of residual chlorine in the copper powder of this embodiment, as determined by chemical analysis, 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, thereby preventing problems caused by residual chlorine, such as corrosion.

[0019] The use of the copper powder of this embodiment is not particularly limited, but since 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.

[0020] [Method for Producing Copper Powder] Hereinafter, a method for producing copper powder according to this embodiment will be described.

[0021] The method for producing copper powder of 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 comprises 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.

[0022] <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 for Step A is not particularly limited, but from the viewpoint of further improving the dispersibility of primary particles of the copper powder and further narrowing the particle size distribution of the copper powder, it is preferable to obtain copper powder from a slurry A containing a copper(I) compound and polyvinyl alcohol.

[0023] The dispersion medium used in the slurry A is not particularly limited, and may be any dispersion medium commonly used in preparing slurries, such as water or a hydrophilic dispersion medium. A mixture of several types of dispersion medium may also be used.

[0024] Examples of hydrophilic dispersion media include 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, and diethylene glycol monomethyl ether. 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.

[0025] 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.

[0026] The copper(I) compound is not particularly limited as long as it is a compound containing monovalent copper, and includes, for example, one or more compounds selected from the group consisting of cuprous oxide, copper chloride, copper bromide, and copper iodide, and preferably includes cuprous oxide.

[0027] 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, 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, 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. 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 content of the polyvinyl alcohol in Slurry A is preferably 0.01 parts by mass or more and 5 parts by mass or less, more preferably 0.05 parts by mass or more and 2 parts by mass or less, and even more preferably 0.1 parts by mass or more and 1 part by mass or less, relative to 100 parts by mass of the copper(I) compound.

[0028] The degree of saponification of polyvinyl alcohol is not particularly limited, but from the viewpoint of further improving the dispersibility of 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 still 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 primary particles of copper powder and further narrowing the particle size distribution of copper powder, the degree of saponification of 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 still more preferably 85 mol% or more and 90 mol% or less.

[0029] The viscosity of the polyvinyl alcohol is not particularly limited. However, 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 of the polyvinyl alcohol 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, for example, 0.1 mPa s or more and 100 mPa s or less, preferably 1 mPa s or more and 50 mPa s or less, and more preferably 4 mPa s or more and 10 mPa s 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.

[0030] The type of reaction for producing the copper powder in step A is not particularly limited, but for example, the copper powder can be produced by subjecting the copper(I) compound to a disproportionation reaction.

[0031] The copper powder of this embodiment is preferably obtained by a disproportionation reaction.

[0032] The components contained in the 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 the slurry A may be converted into 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, decreasing the acid supply rate tends to increase the particle size of the copper powder.

[0033] 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. 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 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. 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.

[0034] The temperature in the reaction vessel 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. 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 temperature is preferably 90°C or lower, more preferably 80°C or lower, 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. 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 temperature in the reaction vessel 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. Here, the temperature in the reaction vessel in step A refers to the temperature of the slurry in the reaction vessel. The particle size of the copper powder can be adjusted by adjusting the temperature in the reaction vessel. For example, increasing the temperature in the reaction vessel tends to increase the particle size of the copper powder.

[0035] <Step B> Step B of the copper powder manufacturing method of this embodiment will now be described. In Step B, the surface of the copper powder is treated with a fatty acid salt. Step B may include, for example, a dispersion step of adhering a fatty acid salt to the surface of the copper powder and dispersing the copper powder, and a coating step of forming a fatty acid coating on the surface of the copper powder.

[0036] The copper powder of this embodiment preferably includes a fatty acid coating on the surface.

[0037] 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 straight-chain or branched fatty acids having 8 to 20 carbon atoms, such as straight-chain 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.

[0038] 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 (in a dry state).

[0039] 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. Furthermore, from the viewpoint of facilitating dissolution of the fatty acid salt, 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.

[0040] In the dispersion step, it is preferable to add the fatty acid salt to the reaction vessel and then allow it to age for a period of 5 to 60 minutes.

[0041] In the coating process, the reaction vessel is neutralized with an acid, and a fatty acid coating is formed 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. From the following perspectives, it is preferable to use a weak acid as the acid used to neutralize the reaction vessel in the coating process. Using a weak acid allows for more uniform formation of the fatty acid coating, thereby suppressing aggregation of the resulting copper microparticles. Furthermore, using a weak acid increases the hydrophobicity of the resulting copper microparticles through the fatty acid coating, which can increase the settling rate of the copper microparticles in the washing process described below, thereby improving productivity. Furthermore, using a weak acid allows for the formation of a uniform fatty acid coating on the copper powder, making it difficult for the copper microparticles to aggregate, resulting in copper microparticles with fewer aggregated particles. The type of weak acid used for neutralization is not particularly limited, and examples include one or more selected from citric acid, ascorbic acid, and acetic acid.

[0042] In the film-forming step, it is preferable to add an acid to the reaction vessel and then allow the mixture to age for a period of 5 to 60 minutes.

[0043] <Other Steps> The method for producing copper powder of this embodiment may include steps other than steps A and B described above.

[0044] The method for producing copper powder according to the present 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.

[0045] 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 can be performed using, for example, a sieve. By using a sieve of a specific size, it is possible to select copper powder or intermediates having particle sizes within a specific range. This step may be performed at the stage of a slurry, or after drying to form a powder.

[0046] The method for producing copper powder according to the present 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 may be dried, for example, by dehydrating the powder by centrifugation and then drying the powder by heating in a dryer or the like.

[0047] The method for producing copper powder according to the present embodiment may further include a step of crushing the copper powder or the intermediate. The copper powder or the intermediate can be crushed using a known crusher. The type of crusher is not particularly limited, and any type such as a high-speed rotary mill, a hammer mill, or an atomizer can be used.

[0048] (2) Conductive Paste The conductive paste of this embodiment will now be described.

[0049] The conductive paste of this embodiment contains the above-mentioned copper powder, a resin, and a solvent.

[0050] The copper powder of this embodiment has improved dispersibility and a narrow particle size distribution, making it easy to design a paste with high reproducibility and stability.

[0051] 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. Examples include cellulose-based resins, such as ethyl cellulose, 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. Therefore, 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.

[0052] 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, or amine is preferably used. Among these organic solvents, amine is preferred because it has reducing ability and thus has the effect of creating a localized reducing atmosphere on the paste surface during firing. Furthermore, using water as the solvent can reduce the amount of organic solvents used, which are harmful to the human body, thereby increasing the usefulness of the copper paste. The amount of solvent is not particularly limited, but can be adjusted appropriately taking into account the dispersibility and particle size distribution of the copper powder so as to achieve a viscosity suitable for conductive film formation methods such as screen printing and inkjet printing.

[0053] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0054] 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 depart from the gist of the invention.

[0055] [Measurement by Laser Diffraction Scattering Particle Size Distribution Analyzer] A laser diffraction scattering particle size distribution analyzer (manufactured by Microtrac Bell, model name: MT3300EX II) was used to measure the particle diameter D of the copper powder at a cumulative frequency of 50% in a volume-based cumulative frequency distribution curve. ５０ The standard deviation SD of the particle size distribution and the volume mean diameter MV were obtained. The measurement sample was a dispersion prepared by dispersing dry copper powder obtained by the following method in water or an alcohol solvent such as ethanol. The results are shown in Table 1.

[0056] [Measurement by Nitrogen Adsorption Method] The specific surface area s of the copper powder was determined by nitrogen adsorption using a specific surface area measuring device (Shimadzu Corporation, model name: FlowSorb III). From the specific surface area s of the copper powder, the particle diameter D of the copper powder was calculated using the following formula (1): ＢＥＴ The results are shown in Table 1. ＢＥＴ = 6 / (ρ·s) (1) In formula (1), ρ is the density of copper powder (8.96 g / cm ３ ) and s is the specific surface area of ​​the copper powder as determined by the nitrogen adsorption method.

[0057] As an index of packing property, 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.

[0058] Example 1 <Step A> 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) were added to a reaction vessel and stirred. Next, the temperature inside the reaction vessel was brought to 30 to 50°C, and a 20% aqueous sulfuric acid solution (3,015 g in total) was continuously added to the reaction vessel while stirring the reaction vessel. The mixture was then stirred for 15 minutes to obtain a slurry containing copper powder. The pH of the slurry in the reaction vessel was 1.8. <Washing Step (1)> Next, the obtained slurry containing copper powder was washed with ion-exchanged water until the resistance value reached 1,000 Ω·cm. <Sorting Step> The washed slurry was then sorted using a sieve with 25 μm mesh. <Step B> The resulting copper powder-containing slurry was adjusted to a copper concentration of 100 g / L and stirred. Sodium carbonate was then added to the reaction vessel to adjust the pH to 10.0 to 10.5. Sodium stearate was then added to the reaction vessel in an amount of 0.2% by mass relative to the copper powder, and the reaction vessel was heated to 60°C and stirred for 15 minutes. A neutralizer (ascorbic acid) was then added to the reaction vessel to adjust the pH to 7.5, followed by stirring for 15 minutes. A 20% aqueous sulfuric acid solution was then added to the reaction vessel to adjust the pH to 7.0, followed by stirring for 15 minutes. <Washing Step (2)> The slurry in the reaction vessel was then washed with ion-exchanged water until the resistance reached 10,000 Ω·cm. <Drying and Crushing Step> Next, the precipitate was filtered off from the washed slurry, dried, and crushed in a crusher to obtain a dry copper powder.

[0059] [Example 2] Dry copper powder was obtained under the same conditions as in Example 1, except that in step A, the temperature inside the reaction vessel was increased and the average addition time per gram of the 20% aqueous sulfuric acid solution was shortened.

[0060] Example 3 Dry copper powder was obtained under the same conditions as in Example 2, except that in step A, the temperature inside the reaction vessel was increased.

[0061] [Comparative Example 1] Dry copper powder was obtained under the same conditions as in Example 1, except that 8.0 g of polyvinylpyrrolidone was used instead of polyvinyl alcohol in step A and the average addition time per gram of the 20% aqueous sulfuric acid solution was shortened.

[0062] 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.

[0063]

[0064] The copper powders of the Examples had higher tap densities than the copper powders of the Comparative Examples. This indicates that the copper powder of the present embodiment has improved packing properties. Because the copper powder of the present embodiment has improved packing properties, it is believed to be suitable for use in conductive pastes.

[0065] This application claims priority based on Japanese Patent Application No. 2023-168783, filed September 28, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. The particle diameter D 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 analyzer ５０ and the particle diameter D calculated from the specific surface area s by the nitrogen adsorption method. ＢＥＴ And D obtained from ＢＥＴ / D ５０ and 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 is 0.50 or less.

2. The above D ５０ The copper powder according to claim 1, wherein the average particle size is 5.0 μm or less.

3. The above D ＢＥＴ The copper powder according to claim 1 or 2, wherein the average particle size is 0.1 μm or more and 5.0 μm or less.

4. The copper powder according to any one of claims 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 claims 1 to 4, which is obtained by a disproportionation reaction.

6. The copper powder according to any one of claims 1 to 5, which has a fatty acid coating on its surface.

7. A conductive paste comprising the copper powder according to any one of claims 1 to 6, a resin, and a solvent.

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