Method for producing copper powder and method for producing conductive paste

Abstract

A method for producing copper powder includes a step A of obtaining copper powder from a copper (I) compound, and a step B of treating the surface of the copper powder with a fatty acid salt. In the step A, a slurry A containing the copper (I) compound also contains a polyvinyl alcohol.

Description

Method for producing copper powder and method for producing conductive paste

[0001] The present invention relates to a method for producing copper powder and a method for producing a 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 method for producing copper powder that can improve the dispersibility of primary particles of copper powder and narrow the particle size distribution of copper powder.

[0006] That is, according to the present invention, there are provided the following methods for producing copper powder and conductive paste. 1. A method for producing copper powder, comprising: 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, wherein in Step A, slurry A containing the copper(I) compound contains polyvinyl alcohol. 2. The method for producing copper powder according to 1., wherein the copper powder is in a slurry state or a dry state. 3. The method for producing copper powder according to 1. or 2., wherein the copper(I) compound contains cuprous oxide. 4. The method for producing copper powder according to any of 1. to 3., wherein the content of the polyvinyl alcohol in slurry A is 0.01 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the copper(I) compound. 5. The method for producing copper powder according to any of 1. to 4., wherein the degree of saponification of the polyvinyl alcohol is 70 mol% or more and 100 mol% or less. 6. The method for producing copper powder according to any of 1. to 5., wherein the pH in the reaction vessel in Step A is 7 or less. 7. A method for producing copper powder according to any one of 1. to 6., wherein the temperature inside the reaction vessel in step A is 5°C or higher and 90°C or lower. 8. A method for producing copper powder according to any one of 1. to 7., wherein the copper powder is produced in step A by disproportionation of the copper(I) compound. 9. A method for producing copper powder according to any one of 1. to 8., wherein the slurry A contains sulfuric acid. 10. A method for producing copper powder according to any one of 1. to 9., further comprising step C of drying the copper powder. 11. A particle diameter D of the copper powder 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 of the copper powder calculated from the specific surface area s of the copper powder by the nitrogen adsorption method. ＢＥＴ and D obtained from ＢＥＴ / D ５０ 12. The method for producing copper powder according to any one of 1. to 10., 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 for the copper powder is 0.50 or less. 13. The method for producing copper powder according to 11., 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 for the copper powder is 0.50 or less. ５０14. The method for producing copper powder according to 11. or 12., wherein the D of the copper powder is 5.0 μm or less. ＢＥＴ 15. A method for producing a conductive paste, comprising the steps of obtaining copper powder by the method for producing copper powder according to any one of 1. to 14., and kneading the obtained copper powder with a resin and a solvent to obtain a conductive paste.

[0007] According to the present invention, it is possible to provide a method for producing copper powder that can improve the dispersibility of primary particles of copper powder and further narrow the particle size distribution of copper powder.

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

[0010] The method for producing copper powder of this embodiment 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, and in step A, the slurry A containing the copper(I) compound contains polyvinyl alcohol.

[0011] Although the mechanism by which the copper powder production method of this embodiment solves the above-mentioned problems is not clear, it is presumed that the presence of polyvinyl alcohol when copper powder is produced from a copper(I) compound adjusts the production speed of primary particles of the copper powder within an appropriate range, thereby improving the dispersibility of the primary particles of the copper powder and narrowing the particle size distribution of the copper powder.

[0012] In this embodiment, D ＢＥＴ / D ５０ is used as an index of the dispersibility of the primary particles of copper powder. ＢＥＴ / D ５０ The value of is close to 1, that is, D ＢＥＴ and D ５０ When the values ​​of D are close to each other, it is judged that the dispersibility of the primary particles of the copper powder is good. The inventors believe that this judgment is possible for the following reasons. First,ＢＥＴ The value of D is calculated from the specific surface area s of copper powder by nitrogen adsorption method and the density ρ, and represents the average diameter of the primary particles of copper powder. ５０ The value of D is the median diameter obtained by laser diffraction. ＢＥＴ and D ５０ When the values ​​are close to each other, it means that the median diameter obtained by laser diffraction is close to the primary particle diameter, and it can be determined that the formation of aggregates is suppressed, that is, the dispersibility of the primary particles is good.

[0013] In this embodiment, the coefficient of variation (SD / MV) is used as an index of the particle size distribution of the copper powder. Specifically, a small coefficient of variation is determined to indicate a narrow particle size distribution of the copper powder.

[0014] [Step A] Step A of the copper powder production method of this embodiment will be described below. Step A is a step of obtaining copper powder from a copper(I) compound. Specifically, copper powder is obtained from a slurry A containing a copper(I) compound and polyvinyl alcohol.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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 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 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] [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.

[0027] 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.

[0028] 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).

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] [Other Steps] The method for producing copper powder of this embodiment may include steps other than steps A and B described above.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The method for producing copper powder according to the present embodiment may further include a step of crushing the copper powder or the intermediate. Crushing of the copper powder or the intermediate can be performed 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.

[0038] [Copper Powder] Hereinafter, the copper powder obtained by the copper powder production method of the present embodiment will be described.

[0039] The state of the copper powder obtained by the method for producing copper powder of this embodiment is not particularly limited, and the copper powder may be in a slurry state in which the copper powder is dispersed in a dispersion medium such as water, or may be in a dry state.

[0040] The particle diameter D at which the cumulative frequency is 50% in the volume-based cumulative frequency distribution curve of the copper powder obtained by the copper powder manufacturing method of this embodiment measured using a laser diffraction scattering particle size distribution analyzer. ５０ and the particle diameter D of the copper powder calculated from the specific surface area s of the copper powder obtained by the copper powder manufacturing method of this embodiment, measured by a nitrogen adsorption method. ＢＥＴ and D obtained from 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. As described above, in this embodiment, D ＢＥＴ / D ５０ is used as an index of the dispersibility of the primary particles of copper powder. ＢＥＴ / D ５０ When D is close to 1, it is judged that the dispersibility of the primary particles of the copper powder is good. ＢＥＴ / D ５０If the value of is within the above range, it can be determined that the dispersibility of the primary particles of the copper powder is good.

[0041] The particle diameter D of the copper powder obtained by the copper powder manufacturing method 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.

[0042] The coefficient of variation (SD / MV) obtained from the volume mean diameter MV and standard deviation SD of the particle size distribution of the copper powder obtained by the copper powder production method of this embodiment, measured by a laser diffraction / scattering particle size distribution measurement method, 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. Furthermore, the coefficient of variation (SD / MV) of the copper powder obtained by the copper powder production method 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. As described above, in this embodiment, the coefficient of variation is used as an index of the particle size distribution of the copper powder. Specifically, a small coefficient of variation is determined to indicate a narrow particle size distribution of the copper powder. Therefore, a coefficient of variation of the above-mentioned value or less indicates that the particle size distribution of the copper powder is narrow.

[0043] D of the copper powder obtained by the copper powder manufacturing method of this embodiment 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. ５０is 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.

[0044] D of the copper powder obtained by the copper powder manufacturing method of this embodiment 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.

[0045] The amount of residual chlorine quantified by chemical analysis of the copper powder obtained by the copper powder manufacturing method 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.

[0046] The uses of the copper powder obtained by the copper powder manufacturing method of this embodiment are not particularly limited, but the copper powder obtained by the copper powder manufacturing method of this embodiment has improved dispersibility and a narrow particle size distribution, and is therefore suitable for use as a raw material for conductive pastes.

[0047] (2) Method for Producing Conductive Paste Hereinafter, a method for producing the conductive paste of this embodiment will be described.

[0048] The method for producing a conductive paste of this embodiment includes a step of obtaining copper powder by the above-mentioned copper powder production method, and a step of obtaining a conductive paste by kneading the obtained copper powder, a resin, and a solvent.

[0049] The copper powder obtained by the copper powder manufacturing method of this embodiment has improved dispersibility and a narrow particle size distribution, making it easy to design a paste with high reproducibility and stability.

[0050] The resin used in the method for producing a conductive paste according to this embodiment is not particularly limited, and any known resin may be used as a raw material for conductive pastes. For example, a cellulose-based resin, such as ethyl cellulose, may be 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 sinterability. Therefore, the amount of resin added is preferably 5% by mass or less, and more preferably 2% by mass or less, of the total conductive paste.

[0051] The solvent used in the conductive paste manufacturing method 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.

[0052] 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.

[0053] 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.

[0054] [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.

[0055] [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.

[0056] 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.

[0057] [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.

[0058] 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.

[0059] Comparative Example 1 Dry copper powder was obtained under the same conditions as in Example 1, except that polyvinyl alcohol was not used.

[0060] [Comparative Example 2] 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.

[0061] Comparative Example 3 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.

[0062]

[0063] According to the manufacturing method of the example, D ＢＥＴ / D ５０ became close to 1. As mentioned above, D ＢＥＴ / D ５０ When the coefficient of variation is close to 1, it can be determined that the dispersibility of the primary particles of the copper powder is good. Therefore, it can be seen that the dispersibility of the primary particles of the copper powder is good according to the manufacturing method of this embodiment. Furthermore, according to the manufacturing methods of the examples, the coefficient of variation was 0.50 or less in all examples, which can be said to have reduced coefficient of variation. As mentioned above, when the coefficient of variation is small, it can be determined that the particle size distribution of the copper powder is narrow. Therefore, it can be seen that the particle size distribution of the copper powder is narrow according to the manufacturing method of this embodiment. From the above, it can be seen that the manufacturing method of this embodiment can improve the dispersibility of the primary particles of the copper powder and further narrow the particle size distribution of the copper powder.

[0064] This application claims priority based on Japanese Patent Application No. 2023-168782, filed September 28, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A method for producing copper powder, comprising: 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, wherein in step A, slurry A containing the copper (I) compound contains polyvinyl alcohol.

2. The method for producing copper powder according to claim 1, wherein the copper powder is in a slurry state or a dry state.

3. The method for producing copper powder according to claim 1 or 2, wherein the copper (I) compound comprises cuprous oxide.

4. A method for producing copper powder described in any one of claims 1 to 3, wherein the content of the polyvinyl alcohol in the slurry A is 0.01 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the copper (I) compound.

5. A method for producing copper powder according to any one of claims 1 to 4, wherein the degree of saponification of the polyvinyl alcohol is 70 mol % or more and 100 mol % or less.

6. A method for producing copper powder according to any one of claims 1 to 5, wherein the pH in the reaction tank in step A is 7 or less.

7. A method for producing copper powder according to any one of claims 1 to 6, wherein the temperature inside the reaction tank in step A is 5°C or higher and 90°C or lower.

8. A method for producing copper powder according to any one of claims 1 to 7, wherein in step A, the copper powder is produced by disproportionation reaction of the copper (I) compound.

9. A method for producing copper powder according to any one of claims 1 to 8, wherein the slurry A contains sulfuric acid.

10. A method for producing copper powder according to any one of claims 1 to 9, further comprising a step C of drying the copper powder.

11. The particle diameter D of the copper powder when the cumulative frequency is 50% in a volume-based cumulative frequency distribution curve measured using a laser diffraction scattering type particle size distribution measuring device ５０ and the particle diameter D of the copper powder calculated from the specific surface area s of the copper powder by the nitrogen adsorption method. ＢＥＴ And D obtained from ＢＥＴ / D ５０ The method for producing copper powder according to any one of claims 1 to 10, wherein the ratio is 0.70 or more and 1.20 or less.

12. A method for producing copper powder as described in claim 11, wherein the coefficient of variation (SD / MV) obtained from the volume average diameter MV and standard deviation SD of the particle size distribution measured by a laser diffraction scattering particle size distribution measurement method for the copper powder is 0.50 or less.

13. D of the copper powder ５０ The method for producing copper powder according to claim 11 or 12, wherein the average particle size is 5.0 μm or less.

14. D of the copper powder ＢＥＴ The method for producing copper powder according to any one of claims 11 to 13, wherein the average particle size is 0.1 μm or more and 5.0 μm or less.

15. A method for producing a conductive paste, comprising the steps of obtaining copper powder by the method for producing copper powder according to any one of claims 1 to 14, and obtaining a conductive paste by kneading the obtained copper powder with a resin and a solvent.

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