JP6738460B1 - Method for producing copper powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper powder having high single crystallinity and a small particle size and its distribution, and a method for producing the copper powder. SOLUTION: The method for producing copper powder is to generate copper chloride gas by reaction of metallic copper and chlorine-containing gas, and to generate a plurality of copper particles by reaction of copper chloride gas and reducing gas. Reducing the chlorine content of the plurality of copper particles, and reducing the oxygen content of the plurality of copper particles. The removal of copper chloride may be performed by treating a plurality of copper particles with an aqueous solution of a base. The base can be selected from alkali metal hydroxides. [Selection diagram] Figure 1

Description

One of the embodiments of the present invention relates to a copper powder and a method for producing the copper powder.

Metal powder, which is an aggregate of fine metal particles, is used in various fields, and metal powder and conductive paste containing it are used for wiring and terminals of low temperature co-fired ceramics (LTCC) substrates, multilayer ceramic capacitors. It is widely used as a raw material for manufacturing various electronic components such as (MLCC) internal electrodes and external electrodes. In particular, copper powder has been widely used in the past because it is possible to make the internal electrodes of the MLCC thin and the external electrodes small due to the high conductivity of copper, and it is possible to greatly improve the frequency characteristics. It is expected as a material to replace nickel and silver powder.

A liquid phase method and a vapor phase method are mentioned as main methods for producing the metal powder. In the former case, metal compounds such as metal chlorides, nitrates, and sulfates are dissolved or dispersed in a solvent, and a reducing agent such as hydrazine is added to this to reduce the metal powder. On the other hand, in the latter, metal powder is manufactured by reducing the gas of a metal compound with a reducing gas such as hydrogen. The obtained metal powder may be subjected to a treatment for removing impurities existing on the surface or for preventing the surface from being oxidized. For example, Patent Documents 1 to 3 disclose that it is possible to reduce the cohesiveness and improve the purity of the copper powder by subjecting it to heat treatment, alkali treatment, anticorrosion treatment, etc., after the production of the copper powder. ..

JP-A-1-162701 JP-A-4-276001 JP 2004-211108 A

One of the embodiments of the present invention is to provide a copper powder and a method for producing the copper powder.

One of the embodiments according to the present invention is a method for producing a copper powder. This method is to produce copper chloride gas by the reaction of metallic copper and chlorine-containing gas, to produce a plurality of copper particles by the reaction of copper chloride gas and a reducing gas, chlorine content of the plurality of copper particles And reducing the oxygen content of the plurality of copper particles.

One of the embodiments according to the present invention is a copper powder containing a plurality of copper particles. Particle diameter D ₅₀ of when the accumulated frequency in the particle diameter histogram of the volume-based copper particles becomes 50% is at 100nm than 500nm or less, the ratio of the average crystallite diameter D of the copper particles to D ₅₀ (D / D ₅₀₎ Is 0.10 or more and 0.50 or less. The chlorine content of the copper powder is 1×10 ⁻⁴ mass% or more, or 5×10 ⁻⁴ mass% or more and 5×10 ⁻² mass% or less.

The flow for manufacturing copper powder concerning one of the embodiments of the present invention. 1 is a schematic cross-sectional view of an apparatus for producing copper powder according to one of the embodiments of the present invention. The scanning electron microscope image of the copper powder obtained in the Example. The scanning electron microscope image of the copper powder obtained in the Example. The transmission electron microscope image and oxygen mapping figure of the copper particle obtained in the Example. The transmission electron microscope image of the copper particle obtained in the Example. The scanning electron microscope image of the copper powder obtained in the Example. The optical microscope image of the coating film containing the copper powder obtained in the Example.

Hereinafter, each embodiment of the present invention will be described with reference to the drawings and the like. The present invention can be carried out in various modes without departing from the scope of the invention, and should not be construed as being limited to the description of the embodiments exemplified below. In order to make the description clearer, the drawings may schematically show the width, thickness, shape, etc. of each part as compared with the actual mode, but this is merely an example and limits the interpretation of the present disclosure. Not something to do.

Hereinafter, in expressing a mode in which another structure (second structure) is arranged above or below a certain structure (first structure), it is simply referred to as “upper” or “lower”. In this case, unless otherwise specified, the second structure is arranged immediately above or below so as to be in contact with the first structure, and when the second structure is arranged above or below a certain first structure. Both the case of arranging the second structure through the structure is included. The arrangement of the structures is mainly described based on the order of movement of the copper chloride gas, and includes a case where the structures referred to above and the structures referred to below are positioned horizontally, for example.

Copper Powder One of the embodiments of the present invention is a copper powder containing a plurality of copper particles (hereinafter, the copper powder according to the present embodiment is referred to as a copper powder CP). The particle size D ₅₀ when the cumulative frequency of the copper particles contained in the copper powder CP in the volume-based particle size histogram is 50% is relatively small, and specifically, 100 nm or more and 500 nm or less, 100 nm or more and 400 nm or less, or It is 100 nm or more and 300 nm or less. D ₅₀ is called the median diameter. The volume-based particle size of the powder is a particle size weighted by the volume of each particle contained in the powder. As represented by the following formula, the total volume of particles having a particle diameter di (i is a natural number from 1 to k, i≦k) is divided by the total volume of all particles contained in the powder to obtain the particle diameter. The frequency F of particles with di is obtained. The particle diameter when the frequency F is accumulated to be 50% is D ₅₀ .

Here, the particle diameter di is obtained as the diameter of the smallest circle that inscribes the image of each particle obtained when the powder is observed with a microscope such as an optical microscope or an electron microscope, or the long side of the smallest rectangle. Vi is a volume of particles having a particle diameter di, and is a volume of a sphere having a diameter of the above-mentioned smallest circle or a long side of the smallest rectangle as a diameter. ni is the number of particles having a particle diameter di. The particle diameter di can be determined, for example, by visually observing a plurality of (for example, 100 to 10000, typically 500) particles observed in an electron microscope image or using analysis software.

The copper powder CP has a small variation in particle size of copper particles and a narrow particle size distribution. Specifically, the span S represented by the following formula may be 0.5 or more and 1.5 or less, or 0.5 or more and 1.0 or less.

Here, D ₉₀ and D ₁₀ are the particle diameters when the cumulative frequencies of the particles contained in the powder in the volume-based particle diameter histogram are 90% and 10%, respectively, and are indexes representing the particle diameter distribution. ..

Each of the copper particles contained in the copper powder CP has a single or a plurality of crystallites. The crystallite is a region that can be regarded as a metal single crystal in each metal particle, and can be determined by using the Scherrer method. Specifically, the parameters (wavelength λ of X-rays used, half-value width β of spread of diffracted X-rays, Bragg angle θ) obtained by X-ray analysis of metal powder, which is an aggregate of metal particles, are as follows. The crystallite size of the copper particles, that is, the average crystallite diameter D can be obtained by substituting into the Scherrer's equation shown. Here, K is a Scherrer constant.

The production by the vapor phase method is useful for achieving a larger crystallite size as compared with the production by the liquid phase method. Therefore, the copper powder CP has a large crystallite size with respect to the median diameter D ₅₀ . In addition, as described above, the plurality of copper particles contained in the copper powder CP have a small median diameter D ₅₀ . Therefore, the average crystallite diameter D (D/D ₅₀ ) with respect to the median diameter D ₅₀ is large, and for example, 0.10 or more and 0.50 or less, 0.12 or more and 0.50 or less, 0.20 or more and 0.50 or less, 0 It is 0.25 or more and 0.50 or less, or 0.30 or more and 0.50 or less.

The shape of the copper particles of the copper powder CP is close to a true sphere. More specifically, the average circularity AC of the copper powder CP, that is, the average circularity C of the copper particles is, for example, 0.83 or more and 0.95 or less, or 0.85 or more and 0.95 or less. The average circularity AC is one of the parameters representing the shape of each particle contained in the powder, and the image obtained by observing the powder with a microscope is analyzed to determine the circularity of a plurality of (for example, 500) particles. It is a value obtained by finding C and averaging it. The circularity C is represented by the following formula. Here, A is the perimeter of the projection surface of each particle in the microscope image, and B is the perimeter of a circle having an area equal to the area of this projection surface. Due to the high average circularity AC, the copper powder CP exhibits a high filling property.

As mentioned above, nickel powder and silver powder are typical metal powders, but the surface of copper is more easily oxidized than nickel and silver, and the surface of copper is oxidized by oxygen in the air. Easy to form oxides. Furthermore, this oxidation can proceed to the inside of the copper particles. Further, as will be described in detail later, copper chloride is likely to be formed on the surface by the reaction with hydrogen chloride produced as a by-product during the reduction of copper chloride.

However, the copper powder CP has a low impurity concentration and high copper purity. For example, the content of chlorine is 5×10 ^-2 mass% or less. The chlorine content of the copper powder CP is preferably as low as possible, and the lower limit thereof is not particularly limited, but may be, for example, 1×10 ⁻⁴ mass% or more, or 5×10 ⁻⁴ mass% or more. Similarly, the copper powder CP also has a low oxygen content. Since oxygen contained in the metal powder is ubiquitous on the surface of the metal particles, the surface area ratio increases in inverse proportion to the particle size, and the oxygen content in the whole metal powder increases. However, the copper powder CP has a low oxygen content despite the small D ₅₀ which is an index of the particle diameter, and the oxygen content (unit: mass%) in the copper powder CP is used as a parameter representing the oxygen content. The product of D ₅₀ (unit: mass%·μm) is, for example, 0.10 mass% or more and 0.40 mass% or less. Further, the thickness of the copper oxide layer formed on the surface of the copper particles is small, and the average thickness is 1 nm or more and 10 nm or less, or 1 nm or more and 5 nm or less. The chlorine and oxygen contents described above can be determined by a coulometric titration method and an inert gas melting-infrared analysis method, respectively. As for the thickness of the copper oxide layer, the thickness of the copper oxide is measured at a plurality of places (for example, four places) in a transmission electron microscope (TEM) image of individual copper particles or a scanning transmission electron microscope (STEM) image. Can be obtained as an average. The average thickness of the copper oxide layer of the copper powder CP described above is the average of the thicknesses of the copper oxide layer in the plurality of copper particles.

As described above, since the copper powder CP has a small D ₅₀ of the copper particles, it is possible to manufacture thinner electrodes and wirings by using the copper powder CP. Further, since copper has higher conductivity than nickel, which is one of the metals commonly used as metal powders, by using copper powder CP, even if electrodes or wirings are thinly formed, the electric resistance can be improved. The increase can be avoided. Therefore, an LTCC substrate having a low wiring resistance can be manufactured. On the other hand, when the copper powder CP is used for manufacturing the MLCC, the MLCC has a basic structure including a stack of a ceramic layer containing a dielectric material and an internal electrode containing a metal, and a pair of external electrodes connected to the internal electrode. Therefore, thinning of the internal electrodes and miniaturization of the external electrodes can be achieved without causing an increase in electrical resistance due to the high conductivity of copper, and it becomes possible to manufacture an MLCC having excellent frequency characteristics. ..

As described above, the copper powder CP has a small particle size distribution of copper particles. Therefore, when an electrode or wiring having excellent dispersibility in an organic solvent and having a small thickness is formed using a paste containing copper powder CP, a wiring having a small thickness variation and a uniform thickness is formed. Can be formed. Furthermore, unevenness is unlikely to occur on the electrodes or wirings, and electrodes or wirings having a flat surface can be formed. This prevents poor connection of electronic components and increase in connection resistance, and contributes to improvement of characteristics and reliability of electronic devices including electronic components.

As described above, since the copper powder CP has a large average crystallite diameter D with respect to the median diameter D ₅₀ , the sintering temperature is high. For example, when copper powder is used as a raw material for an internal electrode of MLCC, a dispersion liquid containing a dielectric material and a dispersion liquid containing a copper powder are alternately applied and then heated to sinter the copper powder and the dielectric material. .. Thereby, an MLCC in which dielectric thin films and copper thin films are alternately laminated is obtained. Generally, the sintering temperature of the dielectric is higher, so that the copper powder is sintered first during sintering. As a result, a gap is generated between the dielectric and the internal electrode during firing, and the gap may cause separation between the internal electrode and the dielectric film. However, since the copper powder CP has a high sintering temperature, peeling at the time of sintering can be suppressed. Therefore, it becomes possible to provide the MLCC with a high yield by using the copper powder CP.

As described above, the copper powder CP has a high copper purity and a small content of impurities that easily affect the sintering behavior and the characteristics of the film obtained by sintering. Therefore, generation of voids due to impurities during firing is effectively suppressed.

2. Manufacturing Method An example of a method of manufacturing the copper powder CP will be described using the flow shown in FIG. Here, a method for producing the copper powder CP using a so-called vapor phase method will be described.

2-1. Generation of Copper Chloride Gas First, copper chloride gas is generated. One way to generate copper chloride gas is to heat copper chloride. In this method, solid copper chloride is melted at a high temperature to become a liquid, and then vaporized to become a gas. Therefore, it is difficult to control the production amount of copper chloride gas, and the supply amount of copper chloride gas in the subsequent reduction reaction tends to be unstable. As a result, it becomes difficult to control the median diameter D ₅₀ , which causes an increase in particle size distribution. Further, once the liquefied copper chloride remains in the apparatus (for example, the heating furnace), the heating furnace may be destroyed due to contraction during cooling, so that it is necessary to completely gasify the copper chloride.

Therefore, in the manufacturing method according to the present embodiment, copper chloride gas is generated by chlorination of metallic copper (that is, zero-valent copper). According to this method, not only can metallic copper, which is available at a lower cost than copper chloride, be used, but it is also possible to prevent damage to the device and to stabilize the supply amount of copper chloride gas. Specifically, copper chloride gas is generated by reacting metallic copper with chlorine at its melting point or lower (for example, 800° C. or higher and 1000° C. or lower). Hereinafter, the gas used for chlorination is referred to as a first chlorine-containing gas. The first chlorine-containing gas may contain substantially only chlorine, or may be a mixed gas of chlorine and an inert gas for dilution (hereinafter, diluent gas). By using a diluting gas, the amount of chlorine can be controlled easily and precisely.

2-2. Reduction of Copper Chloride Next, the generated copper chloride gas is treated with a reducing gas. As the reducing gas, for example, hydrogen, hydrazine, ammonia, methane or the like can be used. The reducing gas is used in a stoichiometric amount or more with respect to the copper chloride gas. For example, when the copper chloride gas consists of monovalent copper chloride and the reducing gas is hydrogen, the amount of the reducing gas introduced is It may be 50 mol% or more and 10000 mol% or less, 500 mol% or more and 10000 mol% or less, or 1000 mol% or more and 10000 mol% or less with respect to the copper chloride gas. By this treatment, copper chloride is reduced to copper, and the produced copper element grows into copper particles to give copper powder. Hereinafter, the powder obtained by the reduction reaction will be referred to as the primary powder.

As an optional step, chlorine may be added to the copper chloride gas before the reduction of the copper chloride gas. This is because the copper chloride gas and copper are in the equilibrium state shown below, so that part of the generated copper chloride returns to copper. When copper is deposited and liquefied by this equilibrium, the device for producing the copper powder CP is clogged, clogged, or broken. Further, if the concentration of the copper chloride gas decreases due to this equilibrium, the amount of the copper chloride gas provided for the reduction reaction changes. However, by adding chlorine to the copper chloride gas, this equilibrium shifts to the copper chloride side, and the occurrence of the above-mentioned problems can be suppressed. Hereinafter, the gas used to shift this equilibrium will be referred to as the second chlorine-containing gas. Like the first chlorine-containing gas, the second chlorine-containing gas may contain substantially only chlorine, or may contain diluent gas and chlorine. Since the chlorine added here does not significantly contribute to the chlorination of metallic copper, its volume may be smaller than the volume of chlorine contained in the first chlorine-containing gas. For example, the volume of chlorine contained in the second chlorine-containing gas is 0.001% or more and 20% or less, or 0.01% or more and 10% or less, or 0% of the volume of chlorine contained in the first chlorine-containing gas. It should be 1% or more and 2% or less.

When chlorine is added to the copper chloride gas, the temperature of the mixed gas of the copper chloride gas and the second chlorine-containing gas (second temperature) is higher than the temperature at which the copper chloride gas is generated (first temperature). Good. By setting the mixed gas temperature to a higher temperature, it is possible to more effectively suppress the reverse reaction that produces copper from the copper chloride gas. For example, copper chloride can be produced at a temperature selected in the range of 800° C. to 1000° C., and the temperature of the mixed gas can be selected in the range of 1000° C. to 1300° C. The difference between these temperatures may be, for example, 100° C. or higher and 400° C. or lower, 150° C. or higher and 350° C. or lower, or 200° C. or higher and 300° C. or lower. Thereby, the liquefaction of copper chloride in the manufacturing apparatus can be prevented more effectively.

When introducing the second chlorine-containing gas, it is possible to control the particle size of the copper powder CP by adjusting the amount of the diluent gas. Specifically, by reducing the total amount of chlorine contained in the first chlorine-containing gas and the second chlorine-containing gas with respect to the total amount of diluent gas contained in the first chlorine-containing gas and the second chlorine-containing gas. The median diameter D ₅₀ can be reduced, and conversely, the median diameter D ₅₀ can be increased. For example, by setting the volume ratio (Cl ₂ :diluting gas) to 5:95 or more and 40:60 or less, or 5:95 or more and 30:70 or less, or 10:90 or more and 25:75, high average circularity AC or median is obtained. A copper powder CP having a large average crystallite diameter D with respect to the diameter D ₅₀ can be obtained.

2-3. Reduction of chlorine content When copper chloride is reduced with a reducing agent such as hydrogen, hydrogen chloride is produced together with the metal primary powder. Hydrogen chloride is also generated when unreacted chlorine in the first chlorine-containing gas or chlorine in the second chlorine-containing gas reacts with the reducing gas. Therefore, the obtained copper primary powder may react with hydrogen chloride, resulting in the formation of copper chloride on the surface. This problem also occurs when other metals are used, but copper chloride has a low solubility of 0.0236 g/100 mL compared to the solubility of nickel chloride in water (54 g/100 mL). Then, a large amount of copper chloride may remain in the primary powder. This contributes to a decrease in the purity of the copper powder CP.

Thus, when the nickel powder refining method is directly applied to the production of copper powder, contamination of impurities such as copper chloride becomes a problem. Generally, the vapor phase method gives copper powder having a larger crystallite size than the liquid phase method, but if copper chloride remains, it becomes a factor that accelerates the deterioration of the metal in the MLCC which is the final product. As a method of reducing the chlorine content of copper particles, a method of heating the copper particles to a temperature higher than the boiling point of copper chloride is known. However, in this method, since it is necessary to heat the copper powder under reduced pressure, the cost is increased. Further, at high temperatures, the sintering of the copper powder may proceed, and the coupling particles and coarse particles are generated by the sintering. Therefore, a method of reducing the amount of chlorine while increasing the copper purity in the copper powder is desired.

Therefore, in one of the embodiments of the present invention, with respect to the copper primary powder obtained after the reduction, copper chloride is removed, or the chlorine content is reduced (hereinafter, copper chloride is removed and the chlorine content is reduced. It is generally described as a reduction in chlorine content). The chlorine content can be reduced by treating the primary powder with a cleaning liquid, and examples of the cleaning liquid include an aqueous solution or suspension of a base. Hereinafter, the solutions and suspensions that can be used to reduce the chlorine content are collectively referred to as the cleaning liquid or the first cleaning liquid. Examples of the base include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The cleaning liquid may contain two kinds of hydroxides. The base concentration of the cleaning liquid may be 0.1 mol/L or higher, or 0.5 mol/L or higher, and may be 1.5 mol/L or lower, or 1.2 mol/L or lower. In this concentration range, the chlorine content can be sufficiently reduced without increasing the viscosity of the cleaning liquid, as shown in the examples.

As shown in the examples, by using a cleaning liquid containing a base, it is possible to reduce the chlorine content even when the concentration of the base in the cleaning liquid is low, and it is also possible to prevent alkali metal ions from remaining. Compared with the treatment using, for example, ammonia water, this simultaneously produces advantages such as no bad odor and easy post-treatment neutralization treatment. In addition, this treatment can be achieved by simply mixing and stirring the primary powder and the cleaning liquid, and it requires no special additional operation other than cleaning with water as a post-treatment after reducing the chlorine content. It is advantageous. Further, by applying this treatment to the primary powder obtained by using the vapor phase method, copper powder having high purity and a large average crystallite size and a high average circularity as shown in the examples. You can get the body.

2-4. Reduction of oxygen content Although copper has a lower ionization tendency than nickel, the oxidation of copper is more likely to proceed not only to the surface but also to the inside as compared with the oxidation of nickel. As the oxidation progresses, a copper oxide layer is formed on the surface and unevenness occurs. This not only lowers the average circularity of the copper powder CP, but also causes copper oxide to be mixed into wirings and electrodes obtained by using the copper powder CP and lowers the flatness. As a result, in electronic parts. It causes an increase in electrical resistance and poor contact. In addition, since the shrinkage rate at the time of sintering increases, peeling of the wiring and electrodes is likely to occur.

Therefore, in the present embodiment, after the chlorine content is reduced, the copper oxide is removed or the oxygen content is reduced (hereinafter, the removal of copper oxide and the reduction of the oxygen content are collectively referred to as the reduction of the oxygen content). .. To reduce the oxygen content, treat the primary powder after reducing the chlorine content with a solution or suspension containing ascorbic acid, hydrazine, citric acid, etc., and then wash with water. Then filter and dry. Hereinafter, the solutions and suspensions that can be used to reduce the oxygen content are collectively referred to as the cleaning liquid or the second cleaning liquid. Examples of the solvent in the cleaning liquid include water, alcohols such as ethanol and isopropyl alcohol, ketones such as acetone and methyl ethyl ketone, and mixed solvents thereof. When ascorbic acid is used, the concentration of ascorbic acid in the cleaning liquid may be 5% by mass or more or 10% by mass or more, and 25% by mass or less or 20% by mass or less. By this operation, the copper oxide can be removed, and the irregularities on the surface due to the generation of the copper oxide are alleviated, and the copper powder CP having a high average circularity and a high filling property can be obtained.

2-5. Anticorrosion Treatment After the treatment of copper oxide, the anticorrosion treatment may be further performed on the copper powder CP. This is because, depending on the storage environment of the copper powder CP, the surface of the copper particles may be oxidized again to generate copper oxide, and accordingly, irregularities may be formed on the surface to reduce the average circularity. Unlike nickel particles, when the surface of copper particles is oxidized, copper oxide tends to grow toward the inside of the copper particles, so it is effective to suppress oxidation on the surface of the copper particles.

Anticorrosion treatment is exemplified by nitrogen-containing heteroaromatic compounds such as benzotriazole and its derivatives, triazole and its derivatives, thiazole and its derivatives, benzothiazole and its derivatives, imidazole and its derivatives, and benzimidazole and its derivatives. It can be performed by treating the copper powder CP with a solution or suspension containing the material. Hereinafter, solutions and suspensions that can be used to suppress the oxidation of the surfaces of copper particles are generally referred to as treatment liquids. The material contained in the treatment liquid is not limited to the above compounds, and may be selected from compounds that react with copper to passivate or form a complex, for example. Examples of the solvent in the treatment liquid include water, alcohols such as ethanol and isopropyl alcohol, ketones such as acetone and methyl ethyl ketone, amides such as N,N-dimethylacetamide and N,N-dimethylformamide, and aromas such as toluene and xylene. Examples thereof include group compounds. Of these, water, which is inexpensive and has low toxicity, is suitable. After treating the copper powder CP with the treatment liquid, it may be further washed with water or alcohol and dried. By performing this rustproofing treatment, it is possible to prevent the surface from being oxidized even if the copper powder CP is stored in the air for a long period of time. This also means an improvement in the handleability of the copper powder in an environment containing oxygen, for example, in the atmospheric environment. That is, the chemical stability of the copper powder CP is improved by this treatment operation, and its quality can be maintained for a long period of time. Therefore, the embodiment of the present invention is also useful as a quality control method for copper powder.

2-6. Other Steps As an optional step, the obtained copper powder CP may be dried and further subjected to steps such as classification, crushing and sieving.

The classification may be dry classification or wet classification. In the dry classification, any method such as air flow classification, gravity field classification, inertial force field classification, centrifugal force field classification, etc. can be adopted. Similarly in wet classification, methods such as gravity field classification and centrifugal force field classification can be adopted.

For example, the classification can be carried out by low temperature air flow classification using a lower alcohol having a carbon number of 1 to 3 such as methanol, ethanol, n-propanol or isopropanol, or an alcohol having a vapor pressure at 20° C. of 18.7 hPa or more. In this case, first, alcohol is sprayed on the copper powder CP, or the copper powder CP is treated with alcohol vapor. At this time, it is preferable that 40% or more and 1000% or less of the saturated adsorption amount is adsorbed on the copper powder CP. After that, the classification temperature is maintained at a temperature of 0° C. or higher and 35° C. or lower, and the classification is performed under the condition that the classification pressure is 0.2 MPa or higher and 0.8 MPa or lower, or 0.3 MPa or higher and 0.6 MPa or lower.

The crushing process may be performed using, for example, a jet mill. The sieving process is performed by vibrating a sieve having a desired mesh size and passing the copper powder CP through the sieve. By performing classification, crushing, and sieving, the particle size distribution of the copper powder CP can be made smaller, that is, the span S can be made larger.

The copper powder CP is manufactured through the above steps. As described above, in the manufacturing method of the present embodiment, the chlorine powder reduction treatment and the oxygen content reduction treatment are performed on the primary powder obtained by reducing copper chloride. As a result, a copper powder containing copper particles having high average circularity and high single crystallinity and having a small median diameter D ₅₀ and a small particle diameter distribution can be obtained. Rust prevention treatment may be further performed on the obtained copper powder CP. As a result, it is possible to provide a copper powder with a small change in characteristics even after long-term storage.

3. Manufacturing Apparatus FIG. 2 shows an example of an apparatus for manufacturing the copper powder CP, which is suitable for carrying out the manufacturing method described above. Here, a manufacturing apparatus applicable when using the second chlorine-containing gas will be described.

3-1. Overall Configuration The production apparatus 100 shown in FIG. 2 includes a copper chloride production apparatus 110, a heating apparatus 140, and a reduction apparatus 160 as main configurations. The copper chloride generation device 110 and the heating device 140 are connected to each other, and the reduction device 160 and the heating device 140 are also connected to each other. Although not shown, the manufacturing apparatus 100 may further include a separating device connected to the reducing device 160, a collecting device such as a bag filter connected to the reducing device 160 or the separating device.

In the example shown in FIG. 2, the heating device 140 is located below the copper chloride production device 110, but the heating device 140 and the copper chloride production device 110 may be arranged horizontally. Further, the reducing device 160 may be provided below the copper chloride producing device 110 or the heating device 140, or may be arranged horizontally with respect to the copper chloride producing device 110 or the heating device 140.

3-2. Copper Chloride Generator The copper chloride generator 110 has one of the functions of producing copper chloride by the reaction of metallic copper and chlorine contained in the first chlorine-containing gas. The copper chloride production device 110 has a chlorination furnace 112 as a main component, and is provided so as to surround the chlorination furnace 112, and includes a first heater 114 for heating the chlorination furnace 112. As a material used for the chlorination furnace 112, quartz, ceramics or the like can be used.

The chlorination furnace 112 has an inlet 116 for charging metallic copper into the chlorination furnace 112, and for supplying a first gas introduction pipe 118 for supplying a first chlorine-containing gas and a second chlorine-containing gas. The second gas introduction pipe 122 is connected to the chlorination furnace 112. Although not shown, the plurality of first gas introduction pipes 118 or the plurality of second gas introduction pipes 122 may be connected to the chlorination furnace 112. A chlorine gas supply source and an inert gas supply source (not shown) are connected to the first gas introduction pipe 118 and the second gas introduction pipe 122. Although the first gas introduction pipe 118 is connected to the inlet 116 in FIG. 2, the first gas introduction pipe 118 may be connected between the inlet 116 and the second gas introduction pipe 122. Alternatively, the first chlorine-containing gas may be introduced into the chlorination furnace 112 by using the inlet 116 without providing the first gas introduction pipe 118.

The supply amounts of the first chlorine-containing gas and the second chlorine-containing gas can be adjusted by using valves 120 and 124 provided in the first gas introduction pipe 118 and the second gas introduction pipe 122, respectively. By configuring the first chlorine-containing gas and the second chlorine-containing gas to contain chlorine and an inert gas, the introduction amount of chlorine can be easily and precisely controlled. In the example shown in FIG. 2, the second gas introducing pipe 122 is surrounded by the first heater 114, but the second gas introducing pipe 122 is not surrounded by the first heater 114, and the first heater 114 is not surrounded. It may be exposed from.

The chlorination furnace 112 is heated to a first temperature by the first heater 114, and the metallic copper placed in the chlorination furnace 112 is converted into chlorine in the first chlorine-containing gas supplied from the first gas introduction pipe 118. Reacts with to give copper chloride. There is no restriction on the shape of the metal copper used, and for example, pellet-shaped, wire-shaped, or plate-shaped metal can be used. FIG. 2 shows an example in which copper pellets 130 are used.

Most of the obtained copper chloride exists as a gas in the chlorination furnace 112, but a part thereof may also exist as a liquid. Therefore, in order to efficiently vaporize copper chloride existing as a liquid, a vaporization auxiliary material 132 may be arranged in the chlorination furnace 112, and metallic copper may be arranged thereon (see FIG. 2). The vaporization auxiliary material 132 is, for example, a metal or semi-metal oxide such as quartz, alumina, or zirconia, a ceramic, a nitride such as boron nitride, or particles or pellets containing graphite, thereby vaporizing liquid copper chloride. A large heating area for heating is provided. The vaporization auxiliary material 132 is preferably arranged such that the upper surface of the layer formed by the vaporization auxiliary material 132 is higher than the position where the second gas introduction pipe 122 is connected to the chlorination furnace 112. With this configuration, chlorine in the second chlorine-containing gas introduced from the second gas introduction pipe 122 is suppressed from being directly consumed by the chlorination of metallic copper, and the second chlorine-containing gas is changed to copper chloride gas. It can be mixed effectively.

Although not shown, a separator for separating the vaporization auxiliary material 132 and the metallic copper may be arranged between the vaporization auxiliary material 132 and the metallic copper. The separator is provided with at least one opening so that the first chlorine-containing gas introduced into the chlorination furnace 112 and the generated copper chloride gas can pass through the separator.

As described above, when producing the copper powder CP, the second chlorine-containing gas for shifting the equilibrium between copper and copper chloride is used. It is preferable that this second chlorine-containing gas is efficiently mixed with the gas of copper chloride generated in the chlorination furnace 112. Therefore, the second gas introduction pipe 122 is preferably connected to the chlorination furnace 112 at a position closer to the heating device 140 (more specifically, the heating furnace 142 described later) than the first gas introduction pipe 118. The obtained mixed gas is introduced into the heating device 140 from the outlet 126 provided at or near the bottom of the chlorination furnace 112.

3-3. Heating Device The heating device 140 has a tubular heating furnace 142 and a second heater 144 for heating the heating furnace 142 as a basic configuration, and the copper chloride gas generated in the chlorination furnace 112 and the second chlorine are generated. It has one of the functions of mixing the contained gas and heating the mixed gas. The inner diameter of the heating furnace 142 is smaller than the inner diameter of the chlorination furnace 112, and as shown in FIG. 2, the heating furnace 142 can have a bent or folded structure. Specifically, the tubular heating furnace 142 has a plurality of extending directions, and the heating furnace 142 may have one or a plurality of points (bending points) at which the extending direction changes. With the heating furnace 142 having such a shape, the mixed gas can be heated more efficiently without increasing the occupied area.

When part of the copper chloride is produced as a liquid in the chlorination furnace 112, liquid copper chloride is likely to accumulate in the lower portion of the chlorination furnace 112. Therefore, the heating furnace 142 and the chlorination furnace 112 are connected to each other, and the second gas introduction pipe 122 and the chlorination furnace 112 are connected to each other through the discharge port 126 of the chlorination furnace 112 (or the tip of the heating furnace 142 on the chlorination furnace 112 side). However, it is preferable to perform so as to be higher than the position where the second gas introduction pipe 122 is connected to the chlorination furnace 112. This can prevent liquid copper chloride from directly entering the heating furnace 142.

The second heater 144 is arranged so as to surround the heating furnace 142. The second heater 144 is controlled independently of the first heater 114. Therefore, the chlorination furnace 112 and the heating furnace 142 can be heated at different temperatures. As described above, the first heater 114 and the second heater 144 are controlled so that the temperature of the heating furnace 142 (that is, the second temperature) becomes higher than the temperature of the chlorination furnace 112 (that is, the first temperature). The temperature difference is preferably 100° C. or higher and 400° C. or lower, 150° C. or higher and 350° C. or lower, or 200° C. or higher and 300° C. or lower. By controlling the first heater 114 and the second heater 144 in this way, even when liquid-state copper chloride moves from the chlorination furnace 112 to the heating furnace 142, the copper chloride is quickly vaporized in the heating furnace 142. Can be made.

The first chlorine-containing gas mainly contributes to the chlorination of metallic copper, and at the same time gives a positive pressure to the chlorination furnace 112. Therefore, the copper chloride gas generated in the chlorination furnace 112 is guided to the heating furnace 142 by this positive pressure. On the other hand, although the second chlorine-containing gas may partially contribute to the chlorination of metallic copper, most of the chlorination is caused by the reaction between metallic copper and chlorine contained in the first chlorine-containing gas. It is mixed with copper gas and introduced into the heating furnace 142. Therefore, the mixed gas of copper chloride gas and chlorine is heated in the heating furnace 142, the equilibrium between the copper chloride gas and copper is shifted to the copper side, and metallic copper is deposited in the heating furnace 142. Liquefaction is prevented. This not only prevents the heating furnace 142 from being clogged, destroyed, and the process efficiency from decreasing, but also prevents the supply amount of the copper chloride gas from decreasing and becoming unstable due to equilibrium, and prevents the copper chloride gas from flowing into the reducing furnace 162. It contributes to stabilizing the supply. In other words, the second chlorine-containing gas is not only a physical means for providing a positive pressure for introducing the copper chloride gas produced in the chlorination furnace 112 into the reduction furnace 162, but also the equilibrium between copper and copper chloride. To the copper chloride side to function as a chemical means to prevent copper precipitation and liquefaction.

3-4. Reducing Device The reducing device 160 basically includes a reducing furnace 162 and a third heater 164 surrounding the reducing furnace 162. The reducing furnace 162 is connected to the heating furnace 142 and also to the third gas introducing pipe 166, and the third gas introducing pipe 166 is connected to a reducing gas supply source (not shown). A reducing gas such as hydrogen, hydrazine, ammonia, or methane is supplied from the reducing gas supply source, and the supply amount thereof is adjusted using the valve 168. At the time of reduction, the reducing gas may be supplied to the reducing furnace 162 alone, or the reducing gas may be supplied together with an inert gas such as nitrogen or argon.

The reduction furnace 162 provides a space where the copper chloride gas and the reducing gas come into contact with each other. The copper chloride gas supplied from the heating furnace 142 contacts and reacts with the reducing gas supplied through the third gas introduction pipe 166 in the reduction furnace 162, and is reduced to copper element. The copper element grows into copper particles to form copper powder (hereinafter, primary powder), and the primary powder is transported from the discharge pipe 170 to a cooling device, a separation device, a recovery device, etc. not shown. Although detailed description is omitted, the separation device has a function of purifying the primary powder by removing a copper agglomerate and a sintered product that are by-produced in the reduction furnace 162. The recovery device is provided to isolate the copper powder CP obtained after purification from other gases (hydrogen chloride produced as a by-product, nitrogen gas used for cooling, etc.).

3-5. Other Configurations As shown in FIG. 2, a heater (fourth heater) 180 for heating the mixed gas may be provided between the heating device 140 and the reducing device 160. By providing the fourth heater 180, the temperature decrease of the copper chloride gas before being introduced into the reduction furnace 162 is prevented.

Hereinafter, an example of manufacturing the copper powder CP will be described. Here, a copper primary powder is produced using the production apparatus 100 including the copper chloride production apparatus 110 shown in FIG. 2, and the chlorine content and the oxygen content of the obtained primary powder are reduced, and An example in which anticorrosion treatment is performed will be described.

1. Preparation of Primary Powder A vaporization auxiliary material 132 made of quartz was placed in the chlorination furnace 112, and pellets of metallic copper were put thereon. The chlorination furnace 112 and the heating furnace 142 are heated to 900° C. and 1150° C., respectively, and a chlorine-containing gas containing chlorine and nitrogen is introduced from the first gas introduction pipe 118 and the second gas introduction pipe 122 under the conditions shown in Table 1. did.

The reducing furnace 162 was heated to 1150° C., and hydrogen was introduced into the reducing furnace 162 at 4600 mol% and nitrogen at 24600 mol% with respect to the copper chloride gas. The copper particles generated in the reduction furnace 162 were cooled using nitrogen gas to obtain a copper primary powder.

2. Reduction of chlorine content The obtained primary powder was subjected to a chlorine content reduction treatment using various cleaning liquids. Specifically, about 300 mL of hydrochloric acid, aqueous ammonia, or sodium hydroxide aqueous solution was added as a cleaning liquid to 30 g of the primary powder, and the mixture was stirred at room temperature for 10 minutes. After completion of stirring, the supernatant was removed, and then the primary powder was washed with water until pH 7 and dried. The chlorine content of the dried primary powder was measured by the silver nitrate titration method. The sodium content of the primary powder treated with the aqueous sodium hydroxide solution was also measured by the atomic absorption method. The results are shown in Table 2.

As shown in Table 2, when the cleaning liquid was not used (Experiment 6), that is, when the treatment for reducing the chlorine content was not performed, the chlorine content in the primary powder was 0.70 mass %. On the other hand, it was found that the chlorine content was lowered in any case by using the cleaning liquid shown in Table 1 (Experiments 1 to 5). However, with an acidic cleaning solution, the chlorine content of the copper powder after the treatment was still high (Experiment 1), and when ammonia water was used, a highly concentrated cleaning solution was necessary to obtain a sufficient effect ( Experiments 2 and 3). On the other hand, when an aqueous solution of sodium hydroxide was used, it was found that the chlorine content was sufficiently reduced even if the concentration was significantly lowered (Experiments 4 and 5). In addition, it was confirmed that almost no sodium ions remained in the treated primary powder.

From the above, it was found that the chlorine content can be effectively reduced by treating the primary powder with a cleaning liquid containing an alkali metal hydroxide such as sodium hydroxide.

3. Reduction of oxygen content After the chlorine content reduction treatment, the oxygen content reduction treatment was performed. Specifically, 6 g of ascorbic acid was added to the primary powder of a sample (Experiment 5 in Table 2, hereinafter referred to as Sample A) subjected to a chlorine content reduction treatment using a 1 mol/L sodium hydroxide aqueous solution. Was added (about 300 mL), and the resulting mixture was stirred at room temperature for 30 minutes. After completion of stirring, the mixture was filtered, the furnace product was washed with water (about 500 mL) four times, and dried to obtain a copper powder CP.

Oxygen content reduction by aqueous ascorbic acid solution Scanning electron microscope (SEM: JEOL Ltd., JSM-7800F, and so on) images of sample A before treatment and sample after this treatment (hereinafter referred to as sample B) (Magnification: 200,000 times) are shown in FIGS. 3A and 3B, respectively. As shown in FIG. 3A, in Sample A, irregularities were observed on the surface, and the average circularity AC was 0.82. This result suggests that a layer of copper oxide has formed on the surface. This is probably because the surface exposed by the treatment for reducing the chlorine content has high activity and was oxidized by oxygen in the cleaning liquid used for the treatment for reducing the chlorine content or oxygen in the air. To be

On the other hand, it was confirmed that in sample B treated with the ascorbic acid aqueous solution, this unevenness was alleviated (FIG. 3(B)), and the average circularity AC increased to 0.86. As a result of measuring the oxygen contents of Sample A and Sample B, they were 1.19% by mass and 0.43% by mass, respectively. The median diameters D ₅₀ of sample A and sample B are 0.263 μm and 0.251 μm, respectively, and the products of oxygen content and D ₅₀ of sample A and sample B are 0.31% by mass·μm and 0.11 mass, respectively. %·Μm. From this, it was found that by treating with an ascorbic acid aqueous solution as the cleaning liquid, the copper powder CP having a reduced average oxygen content and a high average circularity AC can be obtained.

4. Rust prevention treatment Rust prevention treatment was performed as follows. An aqueous solution (about 300 mL) containing 0.33% by mass of benzotriazole was added as a treatment liquid to the copper powder CP obtained by the above-mentioned oxygen content reduction treatment, and the obtained mixture was stirred for 30 minutes. did. After completion of stirring, the mixture was allowed to stand, the supernatant was removed, and the mixture was dried.

After the oxygen content reduction treatment, a sample (hereinafter referred to as sample C) left in the atmosphere for about 1 week without the rust prevention treatment, and after the oxygen content reduction treatment, the rust prevention treatment was continuously performed. Then, SEM images (magnification: 200,000 times) of a sample (hereinafter, referred to as sample D) that was left to stand in the atmosphere for about 1 week are shown in FIGS. 4A and 4B, respectively. As shown in FIG. 4(A), sample C had a morphology similar to that of FIG. 3(A), and its average circularity was 0.80. From this, it can be seen that even when the treatment for reducing the oxygen content is performed, the copper particles are oxidized again due to the high activity of copper, and copper oxide is generated on the surface. In fact, the oxygen content of sample C, median diameter D ₅₀ , and the product of oxygen content and median diameter D ₅₀ are 1.67 mass%, 0.334 μm, and 0.56 mass% μm, respectively, and the oxygen content of sample B is The content (0.43% by mass), the median diameter D ₅₀ (0.251 μm), and the product of the oxygen content and the median diameter D ₅₀ (0.11% by mass/μm) are increased. On the other hand, in Sample D, even though almost the same time has passed after the oxygen content reduction treatment, almost no unevenness was observed on the surface, and the oxygen content, median diameter D ₅₀ , and oxygen content were The products of median diameter D ₅₀ were 0.67% by mass, 0.438 μm and 0.29% by mass, respectively, and the average circularity AC was 0.92 (FIG. 3(B)). This indicates that this rustproofing treatment suppresses the oxidation of the copper particle surface.

Scanning transmission electron microscope (STEM: manufactured by JEOL Ltd., accelerating voltage: 200 kV) images (magnification: 800,000 times) of Samples C and D are shown in FIGS. 5(A) and 5(B), respectively. In each of these figures, the left side is a STEM image and the right side is a mapping diagram of oxygen element detected by the energy dispersive X-ray spectroscopic analyzer provided in the STEM.

In the TEM image on the left side of FIG. 5(A), the central portion observed as black is a region existing as metallic copper, and the gray region surrounding it is a region where many elements having a smaller number of atoms are distributed. Is. From this, it can be said that the copper oxide layer is formed on the surface of the sample C. On the other hand, in the TEM image of FIG. 5B, there is almost no grayed portion, and it can be seen that the copper oxide layer does not exist or is very thin. This is also supported by the mapping diagrams of oxygen atoms in FIGS. 5A and 5B. In the mapping diagrams of FIGS. 5(A) and 5(B), white points are regions where oxygen element is detected. From the comparison of these diagrams, in the sample C, the relatively thick copper oxide on the surface of the copper particles is shown. It can be concluded that a layer is formed, whereas in sample D a layer of copper oxide is present but its thickness is very small.

6A and 6B are enlarged views of a region surrounded by a square in the left side of FIGS. 5A and 5B, respectively. From FIG. 6A, the maximum thickness of the copper oxide layer in this region was 16.0 nm. On the other hand, from FIG. 6B, the thickness of the copper oxide layer in this region was about 1.8 nm. Moreover, as a result of measuring the thickness of the copper oxide at four locations in the STEM image of the copper particles, the average thickness of the copper oxide was 2.0 nm. On the other hand, when the same measurement was performed on the above-mentioned sample C (a sample which was subjected to the chlorine content reduction treatment and the oxygen content reduction treatment but not subjected to the rust prevention treatment), the thickness of the copper oxide was It was 16.1 nm.

Table 3 summarizes the average circularity AC of samples A to D described above. In Table 3, as a comparative example, the circularity of a sample (hereinafter, referred to as sample E) obtained by performing the rust prevention treatment without performing the oxygen content reduction treatment after performing the chlorine content reduction treatment Are also shown. From Table 3, it can be seen that the low average circularity AC of Sample A is greatly improved by the oxygen content reduction treatment (Sample B), and this large average circularity AC is maintained by the anticorrosion treatment (Sample D). On the other hand, the average circularity of sample E, which was not subjected to the oxygen content reduction treatment, was as low as 0.82. It is considered that this is because although the rust-prevention treatment prevented the oxidation of the surface of the copper particles, the low average circularity of Sample A after the treatment for reducing the chlorine content was maintained as it was.

From the above, after performing the oxygen content reduction treatment, by using a treatment liquid containing a nitrogen-containing heteroaromatic compound exemplified by benzotriazole, it is possible to contain high-purity copper particles for a long period of time. It was found that the copper powder CP can be manufactured.

5. Characteristic Evaluation FIG. 7 shows an SEM image (magnification: 15000 times) of Sample D imaged using a scanning electron microscope (SEM: manufactured by Hitachi High-Technologies Corporation, SU5000). As understood from FIG. 7, it was confirmed that each particle of the copper powder CP of this example has a shape close to a true sphere. Approximately 500 copper particles existing in one visual field of the SEM image at a magnification of 15,000 were analyzed using image analysis software (Macview 4.0 manufactured by Mountech Co., Ltd.), and as a result, the average circularity AC of the copper particles was 0. It was 90. Further, the particle size and its distribution were also small, D ₉₀ , D ₁₀ and D ₅₀ were 0.431 μm, 0.212 μm and 0.297 μm, respectively, and the span S was 0.739.

The copper powder CP after the rust prevention treatment was subjected to X-ray crystallography using an X-ray diffractometer (Spectres Co., Ltd., X'Pert Pro). Specifically, using a CuKα ray generated under the conditions of an acceleration voltage of 45 kV and a discharge current of 40 mA, the half widths of the diffraction peaks of the (111) plane, (200) plane, and (220) plane of the copper crystal were obtained, The crystallite diameter D was calculated by the formula As a result, the crystallite diameter D of the copper powder CP was 92.3 nm, and the crystallite diameter D (D/D ₅₀ ) with respect to the median diameter D ₅₀ was 0.31.

As a comparative example, a wet method using copper chloride and hydrazine was applied to produce a copper powder, and its evaluation was conducted. The median diameter D ₅₀ was 352 nm (0.352 μm), and the span S was 0.596, D. /D ₅₀ was 0.09 and the average circularity AC was 0.86.

Table 4 summarizes the characteristics of the sample D of the example and the copper powder of the comparative example. As is clear from this table, the copper powder according to the embodiment of the present invention has a shape closer to a true sphere and a higher single crystallinity than the comparative example. Further, the copper powder of Example 1 has a good span S even though the median diameter D ₅₀ which is an index of the particle diameter is small.

It was confirmed from the following experiments that the high average circularity of the copper powder CP also contributes to its high dispersibility. Specifically, 2 parts by weight of the copper powder CP after the oxygen content reduction treatment and 1 part by weight of terpineol as an organic solvent are mixed and coated on a glass substrate to form a coating film (hereinafter, coating film B). Was produced. The coating was performed by dropping a mixture of copper powder CP and a dispersant on a glass substrate and spreading the mixture on the substrate using an applicator. As a comparative example, the same experiment was performed using the primary powder before the oxygen content reduction treatment, and a coating film (hereinafter, coating film A) was produced.

Images (magnification: 200 times) of optical films (VHX-6000, manufactured by Keyence Corp.) of the coating films A and B are shown in FIGS. 8A and 8B, respectively. As shown in FIG. 8(A), spots were observed on the coating film A, and it was confirmed that the surface was uneven and uneven. On the other hand, such unevenness was not observed in the coating film B, and it was found that the coating film B had a highly uniform surface.

As described above, it was found that by applying the embodiment of the present invention, a copper powder having high purity and single crystallinity, a small particle size and its distribution, and chemically stable can be provided.

The embodiments described above as the embodiments of the present invention can be implemented in appropriate combination as long as they do not conflict with each other. Further, based on each embodiment, those having a person skilled in the art appropriately adding, deleting or changing the design, or those having added, omitted or changed the conditions of the process also have the gist of the present invention. As long as they are included in the scope of the present invention.

Even if other action and effect different from the action and effect brought about by the aspects of the respective embodiments described above are obvious from the description of the present specification or can be easily predicted by those skilled in the art, naturally, It is understood to be brought about by the invention.

100: manufacturing apparatus, 110: copper chloride production apparatus, 112: chlorination furnace, 114: first heater, 116: inlet, 118: first gas introduction pipe, 120: valve, 122: second gas introduction pipe, 124: valve, 126: discharge port, 130: pellet, 132: vaporization auxiliary material, 140: heating device, 142: heating furnace, 144: second heater, 160: reduction device, 162: reduction furnace, 164: third Heater, 166: third gas introduction pipe, 168: valve, 170: discharge pipe, 180: fourth heater

Claims (3)

Generating copper chloride gas by reacting metallic copper with a chlorine-containing gas,
Generating a plurality of copper particles by the reaction of the copper chloride gas and a reducing gas,
By treating the plurality of copper particles with a cleaning solution containing an alkali metal hydroxide , reducing the chlorine content of the plurality of copper particles, and the plurality of copper particles, ascorbic acid, hydrazine, or quenching. Reducing the oxygen content of the plurality of copper particles by treating with a cleaning liquid containing an acid , and
A method for producing a copper powder, comprising treating the plurality of copper particles obtained by reducing the oxygen content with a treatment liquid containing a nitrogen-containing heteroaromatic compound . The method of claim 1, wherein the cleaning solution comprises ascorbic acid. The nitrogen-containing heteroaromatic compound is at least one selected from benzotriazole and its derivative, triazole and its derivative, thiazole and its derivative, benzothiazole and its derivative, imidazole and its derivative, and benzimidazole and its derivative. The method of claim 1 , wherein: