Method for manufacturing copper powder

Abstract

To provide a production method capable of obtaining copper powder in which an average particle diameter is 250 nm or less at a reaction temperature of 230°C or lower, in a polyol method that reduces copper oxide powder in a polyol solvent to obtain copper powder.SOLUTION: A production method of copper powder is configured to heat a reaction liquid obtained by mixing and suspending copper oxide powder in a polyol solvent to obtain copper powder. The reaction liquid is mixed with a polar organic compound having a functional group capable of coordinating to copper ion in a molecule, with an HLB value of 3 to 12 obtained by a Griffin method and heated at a temperature of 230°C or lower.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a method for producing copper powder by reducing a copper compound in a polyol solvent. [Background technology]

[0002] Copper powder is also used as a material for conductive pastes to form internal and external electrodes of multilayer ceramic capacitors (MLCCs), which are electronic components, as well as electrodes for multilayer ceramic substrates. In recent years, with the miniaturization and increase in capacitance of multilayer ceramic capacitors, the internal electrodes have become thinner, and for this application, the copper powder used in the conductive paste (internal electrode paste) must be fine. In particular, metal nanoparticles with an average particle size of 250 nm or less have a lower firing temperature than ordinary submicron or larger particles, and are being considered for application in low-temperature firing pastes and other applications.

[0003] The most common method for producing copper powder is the so-called electrolytic method. However, the copper powder obtained by this method tends to form coarse aggregates. As a method for obtaining fine copper powder, for example, Patent Documents 1 and 2 disclose a method in which the raw material metal is evaporated by induction heating in a vacuum or in the presence of a small amount of gas, thereby obtaining it from the gas phase. However, these methods are costly due to the induction heating equipment and vacuum equipment, and because the metal fine particles are generated in the vacuum equipment, the amount of metal fine particles that can be obtained at one time is small, making them unsuitable for mass production.

[0004] To address the above problem, Patent Documents 3 and 4 disclose a method (polyol method) in which copper oxide powder (raw material) is reduced by heating in a polyol solvent. This method is highly productive and can produce copper powder in a concentrated system with a copper concentration of 0.n mol / liter or higher, with the polyol acting as a solvent, reducing agent, and dispersant. As a result, submicron-order copper powder can be obtained even in such a concentrated system. [Prior art documents]

Patent Document

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, it is known that the method (polyol method) described in Patent Document 3 above depends on the mass ratio of the raw material and the polyol solvent and the particle size of the copper powder obtained at the reaction temperature (heating temperature during the reduction reaction). When reducing the particle size of the copper powder obtained at the same mass ratio of the raw material and the polyol solvent, it was necessary to increase the reaction temperature. However, since the reaction temperature cannot be raised above the boiling point of the solvent, there were restrictions on the solvents that could be used depending on the desired particle size of the copper powder. Also, in this method, triethylene glycol (boiling point: 287°C) or tetraethylene glycol (boiling point: 327°C) was used as the polyol solvent, and a reaction temperature of 260°C or higher was required to obtain copper powder with an average particle size of 250 nm or less.

[0007] Also, when using the method described in Patent Document 4 above, copper powder with an average particle size of 100 nm or less can be obtained at a reaction temperature of 200°C or lower, but a silver salt must be added for nucleation, and polyvinylpyrrolidone must be added at 40% by mass or more with respect to copper as a dispersant.

[0008] The present invention has been made in view of such conventional circumstances, and in the polyol method of reducing copper oxide powder in a polyol solvent to obtain copper powder, an object is to provide a manufacturing method capable of obtaining copper powder with an average particle size of 250 nm or less at a reaction temperature of 230°C or lower. [Means for solving the problem]

[0009] The inventors of the present invention have conducted extensive research to solve the above problems and have found that by adding a polar organic compound to a polyol solvent that has a functional group capable of coordinating with copper ions within its molecule and an HLB value of 3 to 12 as determined by the Griffin method, the resulting copper powder becomes finer, thus completing the present invention. In other words, the present invention provides the following.

[0010] According to an aspect of the present invention, a method for producing copper powder is provided, which involves heating a reaction solution obtained by mixing copper oxide powder with a polyol solvent and suspending it, characterized in that a polar organic compound having a functional group capable of coordinating with copper ions in its molecule and having an HLB value of 3 or more and 12 or less determined by the Griffin method is added to the reaction solution, and the solution is heated at a temperature of 230°C or less.

[0011] Furthermore, the amount of polar organic compound added is preferably 0.25% to 10% by weight or less relative to the total amount of copper contained in the copper oxide powder. Also, the functional group that can coordinate with copper ions is preferably one or more selected from carboxyl group, hydroxyl group, amino group, aldehyde group, nitro group, thiol group, sulfo group, phosphoric acid group, cyanide group, chloro group, bromo group, and iodine group. The polar organic compound is preferably phthalic acid (HLB value: 10.8), 1,2-cyclohexanedicarboxylic acid (HLB value: 10.5), 4-cyclohexene-1,2-dicarboxylic acid (HLB value: 10.6), 1,1-cyclohexanediacetic acid (HLB value: 9.0), 2,2'-biphenyldicarboxylic acid (HLB value: 7.4), meso-2,3-diphenylsuccinic acid (HLB value: 6.7), (+)-camphoric acid (HLB value: 9.0), 1,1-cyclopentanediacetic acid (H It is preferable that the polyol solvent is one or more selected from the following: LB value: 9.7), 2,4-diethylglutaric acid (HLB value: 9.6), dipropylmalonic acid (HLB value: 9.6), cyclopentylmalonic acid (HLB value: 10.5), benzylmalonic acid (HLB value: 9.3), octanoic acid (HLB value: 6.2), decanoic acid (HLB value: 5.2), lauric acid (HLB value: 4.5), palmitic acid (HLB value: 3.5), and stearic acid (HLB value: 3.2), and salts thereof. Furthermore, it is preferable that the polyol solvent has a boiling point of 230°C or lower. Furthermore, the polyol solvent is preferably one or more selected from ethylene glycol (boiling point: 196°C), propylene glycol (boiling point: 188°C), 1,3-propanediol (boiling point: 214°C), 1,2-butanediol (boiling point: 194°C), 1,3-butanediol (boiling point: 207°C), 1,4-butanediol (boiling point: 228°C), 1,2-pentanediol (boiling point: 210°C), and 1,2-hexanediol (boiling point: 223°C). Furthermore, the copper oxide powder is preferably one or more selected from copper oxide and cuprous oxide. [Effects of the Invention]

[0012] According to the copper powder manufacturing method of this embodiment, in the polyol method for obtaining copper powder by reducing copper oxide powder in a polyol solvent, even when using a low-boiling-point polyol solvent with a boiling point of 250°C or less and setting the reaction temperature to 250°C or less, the copper powder obtained can have an average particle size of 250 nm or less by adding a polar organic compound (such as phthalic acid) that has a functional group capable of coordinating with copper ions in its molecule and has an HLB value of 3 or more and 12 or less as determined by the Griffin method. [Modes for carrying out the invention]

[0013] The following describes in detail specific embodiments of the present invention (hereinafter referred to as "this embodiment"). It should be noted that the present invention is not limited to the following embodiments, and various modifications are possible without altering the essence of the invention. Furthermore, in this specification, the notation "X~Y" (where X and Y are arbitrary numerical values) means "X or greater and Y or less".

[0014] In the polyol method, copper oxide powder is suspended in a polyol solvent and heated. The polyol solvent acts as a reducing agent, and the reduction to copper powder proceeds. When copper oxide (CuO) is used as the copper oxide powder, reduction occurs from copper oxide (CuO) to copper (Cu) via cuprous oxide (Cu2O). When cuprous oxide (Cu2O) is used as the copper oxide, cuprous oxide (Cu2O) is reduced to copper (Cu). In both cases, copper powder (sometimes referred to as "polyol copper powder") is ultimately obtained. The obtained copper powder is washed with pure water, filtered, and then washed again and dried as needed. Specifically, one example of washing is to allow the copper powder obtained by reduction (polyol copper powder) to settle and decantate, then supply pure water and wash with stirring. One example of filtration is to dehydrate by centrifugal separation.

[0015] The method for producing copper powder according to this embodiment will be described in detail.

[0016] The copper powder manufacturing method according to this embodiment is a method for manufacturing copper powder comprising a reduction step to obtain copper powder by reducing copper oxide powder (raw material) in a polyol solvent, wherein in the reduction step, a polar organic compound having a functional group capable of coordinating with copper ions in its molecule and an HLB value of 3 or more and 12 or less determined by the Griffin method is added to a polyol solvent in which copper oxide powder is suspended (hereinafter, the liquid in which this polyol solvent and copper oxide powder are mixed and suspended may be referred to as the reaction solution), and the obtained copper powder is finely milled by heating and reducing at a temperature of 230°C or less.

[0017] The HLB value (Hydrophilic-Lipophilic Balance value) obtained by the Griffin method described above is an indicator representing the balance between hydrophobicity and hydrophilicity, and can be calculated using equation (1). HLB value = 20 × (formula weight of hydrophilic functional group contained in polar organic compound) / (formula weight of polar organic compound) ... (1)

[0018] The HLB value represents the degree of hydrophilicity on a scale of 0 to 20. A lower HLB value indicates higher hydrophobicity (lipophilicity), while a higher HLB value indicates higher hydrophilicity.

[0019] In the case of the above polar organic compounds, the HLB value determined by the Griffin method is preferably 3 to 12, and more preferably 3 to 11. Although the details of the mechanism are not clear, if the HLB value is too large or too small beyond the above range, the desired fineness of the copper powder cannot be sufficiently obtained. For example, in the case of phthalic acid (1,2-benzenedicarboxylic acid) as a polar organic compound, there are two carboxyl groups that can coordinate to copper ions, and when phthalic acid is applied to the HLB value calculation formula by the Griffin method (Formula (1): HLB value = 20 × (formula weight of hydrophilic functional group contained in the polar organic compound) / (formula weight of polar organic compound)), the HLB value is 10.8.

[0020] Examples of functional groups capable of coordinating with copper ions include one or more selected from the group consisting of carboxyl groups, hydroxyl groups, amino groups, aldehyde groups, nitro groups, thiol groups, sulfo groups, phosphoric acid groups, cyanide groups, chloro groups, bromo groups, and iodine groups, with carboxyl groups being particularly preferred. Furthermore, the number of functional groups capable of coordinating with copper ions constituting the polar organic compound should be one or more, but it is particularly preferable to have one or two functional groups capable of coordinating with copper ions.

[0021] Specific examples of polar organic compounds to be added to polyol solvents are shown in (Chemical Formula 1) to (Chemical Formula 17) below, but include phthalic acid (HLB value: 10.8), 1,2-cyclohexanedicarboxylic acid (HLB value: 10.5), 4-cyclohexene-1,2-dicarboxylic acid (HLB value: 10.6), 1,1-cyclohexanediacetic acid (HLB value: 9.0), 2,2'-biphenyldicarboxylic acid (HLB value: 7.4), meso-2,3-diphenylsuccinic acid (HLB value: 6.7), (+)-camphoric acid (HLB value: 9.0), 1,1-cyclopentanediacetic acid (HLB value: 9.7), 2,4-diethylglutaric acid (HLB value: 9.6), dipropylmalonic acid (HLB value: 9.6), and cyclopentylmalonic acid (HLB value: 10.5). Preferably, one or more selected from the group consisting of ), benzylmalonic acid (HLB value: 9.3), octanoic acid (HLB value: 6.2), decanoic acid (HLB value: 5.2), lauric acid (HLB value: 4.5), palmitic acid (HLB value: 3.5), and stearic acid (HLB value: 3.2) is selected, and more preferably, one or more selected from the group consisting of phthalic acid, 1,2-cyclohexanedicarboxylic acid, 4-cyclohexen-1,2-dicarboxylic acid, 1,1-cyclohexanediacetic acid, 2,2'-biphenyldicarboxylic acid, meso-2,3-diphenylsuccinic acid, (+)-camphoric acid, 1,1-cyclopentanediacetic acid, 2,4-diethylglutaric acid, dipropylmalonic acid, cyclopentylmalonic acid, and benzylmalonic acid is selected. Furthermore, if the polar organic compound is soluble in polyol, its salt (alkali metal salt (Na, K), etc.) may be used, such as disodium phthalate (HLB value: 8.6). Note that the polar organic compound only needs to exhibit the above properties in the polyol solvent; for example, an anhydrous form may be added to the polyol solvent.

[0022] [ka] [ka] [ka] [ka] [ka] [ka] [ka] [ka] [ka] [ka] [ka] [ka] [ka] [ka] [ka] [ka] [ka]

[0023] In the reduction reaction (reduction step), copper oxide powder is heated and reduced in a polyol solvent to which the above-mentioned polar organic compound is added to obtain the copper powder according to this embodiment. The reduction reaction is started by adding the polar organic compound to the reaction solution before heating. However, the polar organic compound may be added to the reaction solution later while it is being heated.

[0024] Furthermore, when using polar organic compounds that do not become neutral (pH around 6.5-7.5) when dissolved in water, it is preferable to add an alkali or acid as a neutralizing agent to neutralize the polar organic compounds added to the reaction solution. When using an alkali as a neutralizing agent, alkali metal hydroxides are preferred, specifically sodium hydroxide or potassium hydroxide can be used. When using an acid as a neutralizing agent, inorganic acids are preferred, specifically sulfuric acid or hydrochloric acid can be used. The neutralizing agent may be added to the reaction solution as an aqueous solution beforehand.

[0025] As the amount of polar organic compound in the reaction solution increases, the particle size of the resulting copper powder also becomes finer. This allows for control over the particle size of the resulting copper powder. The amount of polar organic compound in the reaction solution (the amount of polar organic compound added to the polyol solvent) is set according to conditions such as the particle size of the copper powder obtained after the reduction reaction. The amount of polar organic compound in the reaction solution can be determined by preliminary experiments. The amount of polar organic compound in the reaction solution is preferably 0.25% to 10% by mass, and more preferably 0.25% to 5% by mass, relative to the total amount of copper contained in the raw material copper oxide. Since the effect of adding polar organic compound decreases with increasing amount, adding more than 10% by mass of polar organic compound relative to the total amount of copper contained in the raw material copper oxide is not economical because it increases production costs. Furthermore, regarding the lower limit of the amount of polar organic compound to add, if the amount is less than 0.25% by mass relative to the total amount of copper contained in the raw material copper oxide, the average particle size of the copper powder may exceed 250 nm, so this can be used as the lower limit.

[0026] In the copper powder production method according to this embodiment, when copper oxide powder is reduced using a polyol solvent to which a polar organic compound having a functional group capable of coordinating with copper ions in its molecule and an HLB value of 3 to 12 as determined by the Griffin method is added, significantly finer copper powder can be obtained compared to when no polar organic compound is added. Although the mechanism by which copper powder becomes finer when copper oxide powder is reduced using a polyol solvent to which a polar organic compound is added has not been fully elucidated, it is thought that during the reduction reaction process in the polyol solvent, the polar organic compound having a ligand for copper adsorbs onto the surface of the initial copper nuclei that are generated, forming an organic film incorporating the polar organic compound, which has different properties from the organic film derived from the polyol solvent formed by normal polyol reduction, and thus acts to suppress copper grain growth. In this case, polar organic compounds with an HLB value of more than 12 as determined by the Griffin method have extremely high hydrophilicity, so they are more energetically stable when solvated in a hydrophilic solvent such as ethylene glycol than when adsorbed onto the surface of the initial copper nuclei that are generated, so adsorption to the surface of the initial copper nuclei is less likely to occur, and the effect of suppressing copper grain growth is poor. On the other hand, polar organic compounds with an HLB value of less than 3, as determined by the Griffin method, have an extremely high ratio of hydrocarbons to hydrophilic functional groups. As a result, the carbon content of the copper powder obtained by adsorption of the polar organic compounds onto the surface is high, and even if the powder is fine, it is considered unsuitable for low-temperature sintering applications.

[0027] The copper oxide powder used as a raw material in the reduction process can be one or more selected from copper oxide (CuO) and cuprous oxide (Cu2O). Alternatively, the copper oxide powder may be pre-ground before being subjected to the reduction reaction.

[0028] The polyol solvent used as the solvent in the reduction step is a polyhydric alcohol that has a reducing effect on copper oxide powder and preferably has 2 to 6 OH groups. However, in the copper powder production method according to this embodiment, it is preferable to use a polyol solvent with a boiling point of 230°C or lower, more preferably a polyol solvent with a boiling point of 210°C or lower, and even more preferably a polyol solvent with a boiling point of 200°C or lower. Specifically, one or more selected from ethylene glycol (1,2-ethanediol, boiling point: 196°C), propylene glycol (1,2-propanediol, boiling point: 188°C), 1,3-propanediol (boiling point: 214°C), 1,2-butanediol (boiling point: 194°C), 1,3-butanediol (boiling point: 207°C), 1,4-butanediol (boiling point: 228°C), 1,2-pentanediol (boiling point: 210°C), and 1,2-hexanediol (boiling point: 223°C) are preferred. Particularly preferred are one or more selected from ethylene glycol and propylene glycol.

[0029] The reaction temperature (heating temperature of the reaction solution in which the polyol solvent and copper oxide powder are mixed and suspended) is preferably -50°C or higher relative to the boiling point of the polyol solvent and ±0°C or lower relative to the boiling point of the polyol solvent, and more preferably -40°C or higher relative to the boiling point of the polyol solvent and -5°C or lower relative to the boiling point of the polyol solvent. In other words, the reaction temperature (heating temperature of the reaction solution) is 230°C or lower. If the above reaction temperature is lower than -50°C relative to the boiling point of the polyol solvent, the reduction reaction may not proceed sufficiently, and copper oxide powder (raw material) may remain, resulting in a high oxygen content in the resulting copper powder (polyol copper powder), and the reaction time will be significantly extended, worsening productivity. Furthermore, if the above heating temperature is higher than the boiling point of the polyol, the decrease (consumption) due to decomposition and volatilization of the polyol will be significant, and there is a risk that sufficient reduction will not be possible.

[0030] The copper powder obtained by the copper powder manufacturing method of this embodiment has an organic coating containing a polar organic compound formed on its surface. The organic coating consists of a polyol or a polyol-derived product (such as a hydrocarbon) produced by a reduction reaction, and a polar organic compound, and even fine copper powder has excellent oxidation resistance in an oxidizing atmosphere such as air.

[0031] The average particle size of the copper powder obtained by the copper powder manufacturing method according to this embodiment is preferably 250 nm or less. The copper powder (polyol copper powder) obtained by the manufacturing method described above can be controlled to be below the above average particle size by using a polar organic compound during the reduction reaction. Because it is a fine copper powder, it can be used in electronic components such as electrodes for multilayer ceramic capacitors. There is no particular lower limit to the average particle size of the copper powder obtained by the copper powder manufacturing method according to this embodiment, but in the manufacturing method described above, the lower limit is about 20 nm. Note that the average particle size of the copper powder in this embodiment is the value measured by the method described in the example.

[0032] The carbon content of the copper powder, which corresponds to the organic coating, is preferably 0.05% to 0.5% by mass. By keeping the carbon content within this range, excellent oxidation resistance is achieved even when fired in an oxidizing atmosphere such as air. Although oxidation resistance is not impaired even if the carbon content of the copper powder exceeds 0.5% by mass, the amount of gases such as carbon dioxide generated during firing may increase.

[0033] As described above, the copper powder manufacturing method of this embodiment is a method for obtaining copper powder by heating and reducing copper oxide powder in a polyol solvent, characterized in that a polar organic compound having a functional group capable of coordinating with copper ions in its molecule and an HLB value of 3 to 12 determined by the Griffin method is added to a reaction solution obtained by mixing copper oxide powder with a polyol solvent and suspending it, and the mixture is heated to 230°C or below. In the copper powder manufacturing method of this embodiment, the other components are arbitrary. According to the copper powder manufacturing method of this embodiment, even when using a low-boiling point polyol solvent with a boiling point of 230°C or below and setting the reaction temperature to 230°C or below in the polyol method for obtaining copper powder by reducing copper oxide powder in a polyol solvent, the average particle size of the obtained copper powder can be made 250 nm or below by adding the polar organic compound. [Examples]

[0034] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The method for measuring the physical properties is as follows.

[0035] (1) Average particle size and particle size distribution The average particle size of the obtained copper powder (polyol copper powder) was determined as the number-average particle size obtained from image analysis of 200 or more particles observed with a scanning electron microscope (SEM). Regarding the particle size distribution, similar to the average particle size, the distribution of particle sizes was determined from image analysis of 200 or more particles observed with a scanning electron microscope (SEM), and whether it was monodisperse was evaluated. (2) Analysis of the copper powder surface The surface of the obtained copper powder was qualitatively analyzed for composition using a Fourier transform infrared spectrophotometer (FT / IR-6600, powder diffuse reflectance method, manufactured by JASCO Corporation). If a hydrocarbon film derived from polyols is present, it will be 2800 cm². -1 ~3000cm -1An absorption peak appeared, and the presence or absence of this absorption peak was used to confirm the presence or absence of a hydrocarbon coating. To determine the presence or absence of other organic components on the copper powder surface, the copper powder was immersed in tetrahydrofuran to extract organic matter from the surface. If necessary, the extract was pretreated, and qualitative analysis of organic components was performed by combining data obtained from nuclear magnetic resonance spectroscopy (NMR, AVANCE400, Bruker Biospin), gel permeation chromatography (GPC, ACQUITY UPLC H-class, Waters), and FT-IR data.

[0036] (Example 1) 27 g of cuprous oxide (Cu2O) powder (Chemet, product code: Ultrafine) was placed in a 200 ml separable flask. 100 g of ethylene glycol (EG, boiling point: 197°C, molecular weight: 62) was added, followed by 0.63 g of phthalic acid (2.62% by mass (1 mol%) relative to the total amount of copper in the cuprous oxide; HLB value determined by the Griffin method = 10.8) and 1.21 ml of 25% by mass sodium hydroxide aqueous solution for neutralization. The mixture was then mixed to form a homogeneous slurry. This slurry was heated to 190°C and maintained at that temperature for 45 minutes with stirring to carry out the reduction reaction. After cooling the reaction solution, the resulting polyol copper powder was centrifuged, washed, and dried. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 190 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 Absorption peaks attributed to hydrocarbons were detected. Furthermore, based on the combined results of other analyses, phthalates were identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0037] (Example 2) Instead of phthalic acid, 0.79 g of disodium phthalate (3.31 mass% (1 mol%) based on the total amount of copper in copper oxide, HLB value determined by the Griffin method = 8.6) was added, and the same procedure as in Example 1 was carried out except that a 25 mass / volume% aqueous sodium hydroxide solution was not added, to obtain polyol copper powder. When the particle size distribution of the obtained polyol copper powder was measured, it was found to be monodisperse particles with an average particle size of 190 nm. Also, when Fourier transform infrared spectroscopic measurement of the polyol copper powder was carried out, an absorption peak attributed to hydrocarbons at 2800 cm -1 ~3000 cm -1 was detected. Furthermore, as a result of comprehensively considering the other analysis results obtained, it was identified that phthalic acid was present on the surface of the copper powder. The production conditions and the measurement results are shown in Table 1.

[0038] (Example 3) The same procedure as in Example 2 was carried out except that 0.60 g of disodium phthalate (2.48 mass% (0.75 mol%) based on the total amount of copper in copper oxide) was added, to obtain polyol copper powder. When the particle size distribution of the obtained polyol copper powder was measured, it was found to be monodisperse particles with an average particle size of 220 nm. Also, when Fourier transform infrared spectroscopic measurement of the polyol copper powder was carried out, an absorption peak attributed to hydrocarbons at 2800 cm -1 ~3000 cm -1 was detected. Furthermore, as a result of comprehensively considering the other analysis results obtained, it was identified that phthalic acid was present on the surface of the copper powder. The production conditions and the measurement results are shown in Table 1.

[0039] (Example 4) The same procedure as in Example 2 was carried out except that 0.40 g of disodium phthalate (1.65 mass% (0.5 mol%) based on the total amount of copper in copper oxide) was added, to obtain polyol copper powder. When the particle size distribution of the obtained polyol copper powder was measured, it was found to be monodisperse particles with an average particle size of 240 nm. Also, when Fourier transform infrared spectroscopic measurement of the polyol copper powder was carried out, an absorption peak attributed to hydrocarbons at 2800 cm -1 ~3000 cm -1Absorption peaks attributed to hydrocarbons were detected. Furthermore, based on the combined results of other analyses, phthalates were identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0040] (Example 5) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.65 g of cis-1,2-cyclohexanedicarboxylic acid (2.71% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 10.5) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 150 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, 1,2-cyclohexanedicarboxylic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0041] (Example 6) Polyol copper powder was obtained by the same procedure as in Example 5, except that 0.33 g of cis-1,2-cyclohexanedicarboxylic acid (1.36% by mass (0.5 mol%) relative to the total amount of copper in cuprous oxide) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 170 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, 1,2-cyclohexanedicarboxylic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0042] (Example 7) Polyol copper powder was obtained by the same procedure as in Example 5, except that 0.16 g of cis-1,2-cyclohexanedicarboxylic acid (0.68% by mass (0.25 mol%) relative to the total amount of copper in cuprous oxide) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 230 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, 1,2-cyclohexanedicarboxylic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0043] (Example 8) Polyol copper powder was obtained by the same procedure as in Example 5, except that 0.07 g of cis-1,2-cyclohexanedicarboxylic acid (0.27% by mass (0.1 mol%) relative to the total amount of copper in cuprous oxide) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 250 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, 1,2-cyclohexanedicarboxylic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0044] (Example 9) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.64 g of cis-4-cyclohexene-1,2-dicarboxylic acid (2.68% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 10.6) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 220 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, 4-cyclohexene-1,2-dicarboxylic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0045] (Example 10) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.76 g of 1,1-cyclohexanediacetic acid (3.15% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 9.0) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 90 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm². -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses performed, 1,1-cyclohexanediacetic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0046] (Example 11) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.91 g of 2,2'-biphenyldicarboxylic acid (3.81% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 7.4) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 90 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm². -1 ~3000cm -1An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses performed, 2,2'-biphenyldicarboxylic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0047] (Example 12) Polyol copper powder was obtained by the same procedure as in Example 1, except that 1.02 g of meso-2,3-diphenylsuccinic acid (4.26% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 6.7) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 90 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm². -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, meso-2,3-diphenylsuccinic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0048] (Example 13) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.76 g of (+)-camphoric acid (3.15% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 9.0) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 80 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm². -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, camphoric acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0049] (Example 14) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.70 g of 1,1-cyclopentanediacetic acid (2.93% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 9.7) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 160 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, 1,1-cyclopentanediacetic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0050] (Example 15) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.71 g of 2,4-diethylglutaric acid (2.96% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 9.6) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 80 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm². -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, 2,4-diethylglutaric acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0051] (Example 16) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.71 g of dipropylmalonic acid (2.96% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 9.6) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 190 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, dipropylmalonic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0052] (Example 17) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.65 g of cyclopentylmalonic acid (2.71% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 10.5) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 220 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, cyclopentylmalonic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0053] (Example 18) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.73 g of benzylmalonic acid (3.06% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 9.3) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 180 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, benzylmalonic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0054] (Example 19) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.54 g of octanoic acid (2.27% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 6.2) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 180 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, octanoic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0055] (Example 20) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.65 g of decanoic acid (2.71% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 5.2) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 150 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, decanoic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0056] (Example 21) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.76 g of lauric acid (3.15% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 4.5) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 80 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm². -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, lauric acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0057] (Example 22) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.97 g of palmitic acid (4.04% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 3.5) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 100 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm². -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, palmitic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0058] (Example 23) Polyol copper powder was obtained by the same procedure as in Example 1, except that 1.07 g of stearic acid (4.48% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 3.2) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 70 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm-1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, stearic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0059] (Example 24) Polyol copper powder was obtained by following the same procedure as in Example 5, except that 100g of propylene glycol (abbreviated as PG, boiling point: 188°C, molecular weight 76) was used instead of ethylene glycol, and the slurry heating temperature was set to 185°C. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 60 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm². -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, 1,2-cyclohexanedicarboxylic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0060] (Example 25) Polyol copper powder was obtained by following the same procedure as in Example 10, except that 100g of propylene glycol (abbreviated as PG, boiling point: 188°C, molecular weight 76) was used instead of ethylene glycol, and the slurry heating temperature was set to 185°C. Particle size distribution measurements of the obtained polyol copper powder revealed that it consisted of monodisperse particles with an average particle size of 40 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses performed, 1,1-cyclohexanediacetic acid was identified as being present on the copper powder surface. The manufacturing conditions and measurement results are shown in Table 1.

[0061] (Comparative Example 1) 27 g of cuprous oxide (Cu2O) powder (Chemet, product code: Ultrafine) was placed in a 200 ml separable flask, 100 g of ethylene glycol was added, and the polyol solvent was heated to 190°C. The mixture was kept at this temperature for 60 minutes with stirring to carry out the reduction reaction. After cooling the reaction mixture, the resulting polyol copper powder was centrifuged, washed, and dried. Particle size distribution measurements of the obtained polyol copper powder revealed that it was monodisperse with an average particle size of 1790 nm, but the particles were coarse. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 Although absorption peaks attributable to hydrocarbons were detected, no other organic substances other than those derived from the polyol solvent were identified, even after considering all other analytical results. The manufacturing conditions and measurement results are shown in Table 1.

[0062] (Comparative Example 2) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.34 g of oxalic acid (1.42% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 20.0) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it was monodisperse but coarse, with an average particle size of 870 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 Absorption peaks attributed to hydrocarbons were detected. Furthermore, based on the combined results of other analyses, oxalic acid was identified as being present on the copper powder surface, but sufficient particle refinement was not achieved. The manufacturing conditions and measurement results are shown in Table 1.

[0063] (Comparative Example 3) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.45 g of succinic acid (1.86% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 15.2) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it was monodisperse but coarse, with an average particle size of 920 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm². -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, succinic acid was identified as being present on the copper powder surface, but a sufficient fine-grit effect was not achieved. The manufacturing conditions and measurement results are shown in Table 1.

[0064] (Comparative Example 4) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.50 g of glutaric acid (2.08% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 13.6) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it was monodisperse with an average particle size of 760 nm, but consisted of coarse particles. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, glutaric acid was identified as being present on the copper powder surface, but a sufficient fine-grit effect was not achieved. The manufacturing conditions and measurement results are shown in Table 1.

[0065] (Comparative Example 5) Polyol copper powder was obtained by the same procedure as in Example 1, except that 0.54 g of 1,1-cyclobutanedicarboxylic acid (2.27% by mass (1 mol%) relative to the total amount of copper in cuprous oxide, HLB value determined by the Griffin method = 12.5) was added instead of phthalic acid. Particle size distribution measurements of the obtained polyol copper powder revealed that it was monodisperse but coarse, with an average particle size of 290 nm. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm². -1 ~3000cm -1An absorption peak attributed to hydrocarbons was detected. Furthermore, based on the combined results of other analyses, 1,1-cyclobutanedicarboxylic acid was identified as being present on the copper powder surface, but a sufficient fine-grit effect was not obtained. The manufacturing conditions and measurement results are shown in Table 1.

[0066] (Comparative Example 6) Polyol copper powder was obtained by following the same procedure as in Comparative Example 1, except that 100 g of propylene glycol was used instead of ethylene glycol and the slurry heating temperature was set to 185°C. Particle size distribution measurements of the obtained polyol copper powder revealed that it was monodisperse with an average particle size of 1560 nm, but consisted of coarse particles. Furthermore, Fourier transform infrared spectroscopy measurements of the polyol copper powder showed a particle size of 2800 cm⁻¹. -1 ~3000cm -1 Although absorption peaks attributable to hydrocarbons were detected, no other organic substances other than those derived from the polyol solvent were identified, even after considering all other analytical results. The manufacturing conditions and measurement results are shown in Table 1.

[0067] [Table 1]

[0068] (Evaluation results) Comparing Examples 1-23 and Comparative Examples 1-5, and Examples 24 and 25 and Comparative Example 6, which all used the same polyol solvent with a boiling point of 230°C or lower, it is shown that the particle size of the resulting polyol copper powder was significantly reduced when the Examples were heated and reduced by adding a polar organic compound (one of phthalic acid, disodium phthalate, cis-1,2-cyclohexanedicarboxylic acid, cis-4-cyclohexene-1,2-dicarboxylic acid, 1,1-cyclohexanediacetic acid, 2,2'-biphenyldicarboxylic acid, meso-2,3-diphenylsuccinic acid, (+)-camphoric acid, 1,1-cyclopentanediacetic acid, 2,4-diethylglutaric acid, dipropylmalonic acid, cyclopentylmalonic acid, benzylmalonic acid, octanoic acid, decanoic acid, lauric acid, palmitic acid, and stearic acid) to the polyol solvent, which has a functional group capable of coordinating with copper ions in its molecule and an HLB value of 3 or more and 12 or less as determined by the Griffin method. Furthermore, the obtained polyol copper powder was shown to have an organic coating containing polar organic compounds on its surface. On the other hand, in Comparative Examples 2 to 5, in which polar organic compounds (oxalic acid, succinic acid, glutaric acid, 1,1-cyclobutanedicarboxylic acid) that have functional groups capable of coordinating with copper ions in their molecules but whose HLB value, as determined by the Griffin method, exceeds 12 were added to the polyol solvent, the average particle size of the obtained polyol copper powder exceeded 250 nm, and the degree of reduction in particle size of the obtained polyol copper powder was limited.

[0069] Furthermore, the results from Examples 2 to 4 and 5 to 8, which use different amounts of polar organic compounds (disodium phthalate and cis-1,2-cyclohexanedicarboxylic acid) (as a percentage of the total amount of copper in the raw copper oxide, by mass), show that as the amount of disodium phthalate and cis-1,2-cyclohexanedicarboxylic acid (polar organic compounds) increases, the average particle size of the resulting polyol copper powder decreases, resulting in finer particle size. In other words, it is possible to control the particle size by adjusting the amount of polar organic compounds added.

[0070] From the examples and comparative examples, it has been confirmed that the copper powder production method according to this embodiment, in a polyol method for obtaining copper powder by heating and reducing copper oxide powder in a polyol solvent, can produce copper powder with an average particle size of 250 nm or less, even when using a low-boiling-point polyol solvent with a boiling point of 230°C or less and a reaction temperature of 230°C or less, by adding a polar organic compound to the polyol solvent that has a functional group capable of coordinating with copper ions in its molecule and has an HLB value of 3 or more and 12 or less determined by the Griffin method.

[0071] Furthermore, the technical scope of the present invention is not limited to the embodiments described above. One or more of the requirements described above may be omitted. Also, the requirements described above may be combined as appropriate. In addition, to the extent permitted by law, all disclosures of the documents cited above shall be incorporated as part of the description herein.

Claims

1. A method for producing copper powder, comprising heating a reaction solution obtained by mixing copper oxide powder with a polyol solvent and suspending it, The reaction solution is heated to a temperature of -50°C or higher and 230°C or lower relative to the boiling point of the polyol solvent, The aforementioned additive is a polar organic compound having a functional group capable of coordinating with copper ions within its molecule, and having an HLB value of 3 or more and 12 or less as determined by the Griffin method. A method for producing copper powder characterized by the following:

2. The amount of the polar organic compound added is 0.25% by mass to 10% by weight or less relative to the total amount of copper contained in the copper oxide powder. The method for producing copper powder according to feature 1.

3. The functional group that can coordinate with the copper ion is one or more selected from carboxyl group, hydroxyl group, amino group, aldehyde group, nitro group, thiol group, sulfo group, phosphate group, cyanide group, chloro group, bromo group, and iodine group. A method for producing copper powder according to claim 1 or 2.

4. The aforementioned polar organic compounds are phthalic acid (HLB value: 10.8), 1,2-cyclohexanedicarboxylic acid (HLB value: 10.5), 4-cyclohexene-1,2-dicarboxylic acid (HLB value: 10.6), 1,1-cyclohexanediacetic acid (HLB value: 9.0), 2,2'-biphenyldicarboxylic acid (HLB value: 7.4), meso-2,3-diphenylsuccinic acid (HLB value: 6.7), (+)-camphoric acid (HLB value: 9.0), and 1,1-cyclopentanediacetic acid. One or more selected from acids (HLB value: 9.7), 2,4-diethylglutaric acid (HLB value: 9.6), dipropylmalonic acid (HLB value: 9.6), cyclopentylmalonic acid (HLB value: 10.5), benzylmalonic acid (HLB value: 9.3), octanoic acid (HLB value: 6.2), decanoic acid (HLB value: 5.2), lauric acid (HLB value: 4.5), palmitic acid (HLB value: 3.5), and stearic acid (HLB value: 3.2), and salts thereof. The method for producing copper powder according to feature 3.

5. The method for producing copper powder according to any one of claims 1 to 4, characterized in that the polyol solvent has a boiling point of 230°C or lower.

6. The polyol solvent is one or more selected from ethylene glycol (boiling point: 196°C), propylene glycol (boiling point: 188°C), 1,3-propanediol (boiling point: 214°C), 1,2-butanediol (boiling point: 194°C), 1,3-butanediol (boiling point: 207°C), 1,4-butanediol (boiling point: 228°C), 1,2-pentanediol (boiling point: 210°C), and 1,2-hexanediol (boiling point: 223°C). The method for producing copper powder according to feature 5.

7. The copper oxide powder is one or more selected from copper oxide and cuprous oxide. A method for producing copper powder according to any one of claims 1 to 6.

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