WO2024224522A1 - Method for producing copper particles - Google Patents

Abstract

The present application provides a method for producing copper particles having an average particle diameter within the range of 1 nm to 1,000 nm, the method being characterized by comprising a step of mixing at least a first fluid and a second fluid to precipitate copper particles, wherein one of the first fluid and the second fluid is a copper raw material solution containing a raw material of the copper particles, the other of the first fluid and the second fluid is a reducing agent solution containing at least one kind of reducing agent, the copper raw material solution contains monovalent copper ions and/or divalent copper ions, and the oxidation-reduction potential of the copper raw material solution is set so that the average particle diameter is achieved. According to this production method, copper particles having a controlled average particle diameter can be supplied easily and stably by using a method suitable for large-scale production without requiring a complex chemical reaction or a heat treatment.

Description

Manufacturing method of copper particles

The present invention relates to a method for producing copper particles. More specifically, the present invention relates to a method for producing copper particles whose average particle size is controlled within the range of 1 nm to 1000 nm, and a method for controlling the average particle size of copper particles within the range of 1 nm to 1000 nm.

In recent years, conductive pastes with dispersed metal particles have been used as materials for forming wiring and electrodes on the substrates of electronic devices. Silver, which has high conductivity, is the most commonly used metal particle, but it is expensive and has migration issues. For this reason, there has been much consideration of using copper, but the problem is that the copper particles are prone to oxidation because the surface area relative to the mass increases when the particles are atomized.

For wiring and electrodes, metal particles of various particle sizes are required depending on the electronic device and the formation method for which they are intended. Furthermore, when applying metal particles using screen printing, inkjet printing, dispensers, etc., if there is a distribution in the particle sizes of the metal particles used, not only can clogging occur, but wettability with the substrate can deteriorate, resulting in defects during printing, so a uniform particle size is required.

Patent Document 1 describes a method for producing copper microparticles by adding a reducing agent to a solvent containing copper oxide as the raw material, a complexing agent, and a protective agent. Impurity ions are removed by subjecting the gelatin used as the protective agent to an enhanced desalting process, and the enhanced desalting gelatin controls the particle shape and prevents particle aggregation, but the desalting process requires several passes using an ion exchange membrane, making the process complicated and increasing production costs.

Patent Document 2 describes a method for producing copper powder that is granular in shape and has a particle size of 0.1 μm to 3.0 μm. After mixing with a dispersant solution, a reducing agent solution is added at a temperature range of 50°C to 90°C to produce particles with high oxidation resistance. It also states that if the average particle size is less than 0.1 μm, the particles tend to aggregate and are difficult to form into a paste.

Patent Document 3 describes a method for synthesizing copper nanoparticles in an aqueous solution and producing copper nanoparticles that form low wiring resistance. It states that by using ascorbic acid as a reducing agent and antioxidant, the OH group of ascorbic acid adheres to the surface of the copper particles, suppressing the oxidation of copper. It states that a reducing agent other than ascorbic acid may be used in combination, but a follow-up test showed that when hydrazine monohydrate was used as the reducing agent and ascorbic acid was used as the antioxidant, an oxide layer was confirmed on the surface of the generated copper particles when the amount of hydrazine monohydrate added was 10% by weight or more relative to the ascorbic acid, and the antioxidant effect of copper particles was confirmed only when copper ions were reduced with ascorbic acid. When ascorbic acid is used as a reducing agent, its reducing power is lower than that of hydrazine monohydrate, and it is difficult to produce copper particles with a small particle size of, for example, 50 nm or less.

JP 2012-241213 A JP 2017-137530 A JP 2017-71816 A

In response to recent demand, there is a demand to precisely control the average particle size of copper particles and to obtain them easily and stably, but as described above, it has been difficult to satisfy these demands using conventional techniques.
In view of the above circumstances, the object of the present invention is to provide a manufacturing method that can easily and stably produce copper particles with a controlled average particle size using a method suitable for mass production without requiring complex chemical reactions or heat treatment.

As a result of intensive research conducted by the inventors to solve the above problems, they discovered that the average particle size can be controlled by adjusting the oxidation-reduction potential of a copper raw material solution containing copper particle raw materials, and that copper particles with a controlled average particle size can be continuously and stably obtained, thus completing the present invention.

[1] A method for producing copper particles having an average particle size in the range of 1 nm to 1000 nm, comprising:
The method includes a step of mixing at least a first fluid and a second fluid to precipitate copper particles,
one of the first fluid and the second fluid is a copper raw material solution containing a raw material of copper particles;
the other of the first fluid and the second fluid is a reducing agent solution containing at least one reducing agent;
the copper source solution contains at least monovalent copper ions and/or divalent copper ions,
a potential difference between an oxidation-reduction potential of the copper raw material solution and an oxidation-reduction potential of the reducing agent solution is set so as to obtain the average particle diameter.

[2] The production method according to [1], wherein an oxidation-reduction potential of the copper source solution is set by adjusting a molar concentration ratio ([Cu ⁺ ]/([Cu ⁺ ]+[Cu ²⁺ ])) of monovalent copper ions to total copper ions in the copper source solution.
[3] a ligand coordinated to a copper ion in the copper source solution is at least one selected from water, a hydroxide ion, ammonia, a halide ion, an amino acid, a phosphine, a carboxylic acid, a thiol, a cyanide ion, a thiocyanide ion, a nitrile, an amine, and ethylenediaminetetraacetic acid;
The method according to claim 1 or 2, wherein the redox potential of the copper raw material solution is set by selecting the ligand.

[4] The reducing agent is at least one selected from the group consisting of ascorbates, ferrous sulfate, sulfites, hydroxylamine, formic acid, hydroquinone, reducing sugars, aldehydes, tetrahydroborates, hydrazine, and hydrazine compounds;
The manufacturing method according to any one of [1] to [3], wherein the redox potential of the reducing agent solution is set by selecting the reducing agent.
[5] The manufacturing method according to any one of [1] to [4], wherein the mixed liquid obtained by mixing the first fluid and the second fluid contains oxidized ascorbic acid.
[6] The method according to any one of [1] to [5], wherein the oxide layer on the surface of the copper particles is 4 nm or less.

[7] Continuously introducing at least two fluids to be treated, including the copper raw material solution and the reducing agent solution, between processing surfaces that are disposed opposite to each other and rotate relatively and are capable of approaching and separating from each other;
mixing the at least two fluids to be treated between processing surfaces disposed opposite to each other and rotating relatively to each other so as to be able to approach and separate from each other, thereby precipitating copper particles;
The method according to any one of [1] to [6], wherein a mixed fluid containing the precipitated copper particles is discharged from between the processing surfaces to continuously produce copper particles.
[8] One of the copper raw material solution and the reducing agent solution passes between the processing surfaces while forming a thin film fluid;
the other of the copper raw material solution and the reducing agent solution is introduced into the space between the processing surfaces through another introduction path independent of the flow path introduced into the space between the processing surfaces, and from an opening formed in at least one of the processing surfaces;
The method according to [7], wherein the copper source solution and the reducing agent solution are mixed between the processing surfaces.

[9] A method for controlling the average particle size of copper particles to within a range of 1 nm to 1000 nm, comprising:
The method includes a step of mixing at least a first fluid and a second fluid to precipitate copper particles,
one of the first fluid and the second fluid is a copper raw material solution containing a raw material of copper particles;
the other of the first fluid and the second fluid is a reducing agent solution containing at least one reducing agent;
the copper source solution contains at least monovalent copper ions and/or divalent copper ions,
A control method comprising changing a potential difference between an oxidation-reduction potential of the copper raw material solution and an oxidation-reduction potential of the reducing agent solution.

The manufacturing method of the present invention does not require complex chemical reactions or heat treatments, and is suitable for mass production, allowing for the easy and stable production of copper particles with a controlled average particle size.

1 is a schematic cross-sectional view of a fluid treatment arrangement according to an embodiment of the present invention. 2 is a schematic plan view of a first processing surface of the fluid treatment device shown in FIG. 1. 1 is a TEM photograph of copper particles obtained in Example 1 of the present invention. 1 is a TEM photograph of copper particles obtained in Example 9 of the present invention.

An example of an embodiment of the present invention will be described below.
1. Method for producing copper particles The method for producing copper particles of the present invention is a method for producing copper particles having an average particle diameter in the range of 1 nm to 1000 nm,
The method includes a step of mixing at least a first fluid and a second fluid to precipitate copper particles,
one of the first fluid and the second fluid is a copper raw material solution containing a raw material of copper particles;
the other of the first fluid and the second fluid is a reducing agent solution containing at least one reducing agent;
the copper source solution contains at least monovalent copper ions and/or divalent copper ions,
The production method is characterized in that a potential difference between an oxidation-reduction potential of the copper raw material solution and an oxidation-reduction potential of the reducing agent solution is set so as to obtain the average particle diameter.

(Preparation of copper particle raw material and copper raw material solution)
The raw material of the copper particles used in the production method of the present invention is not particularly limited as long as it can supply monovalent copper ions or divalent copper ions in the solution, and examples of the raw material include copper simple substance, oxide, hydroxide, salt, etc. These raw materials of the copper particles may be used alone or in combination.

Examples of raw materials for copper particles that supply monovalent copper ions include copper(I) chloride, copper(I) sulfide, and copper(I) oxide.
Examples of raw materials for copper particles that supply divalent copper ions include copper(II) oxide, copper(II) chloride, copper(II) sulfate, copper(II) nitrate, copper(II) acetate, copper(II) citrate, copper(II) hydroxide, copper(II) carbonate, and copper(II) sulfide.

A copper raw material solution can also be prepared by adding an oxidizing agent or reducing agent to monovalent copper ions and/or divalent copper ions to oxidize or reduce the copper ions. That is, by adding a required amount of oxidizing agent to a solution in which monovalent copper ions have been dissolved, some of the monovalent copper ions can be oxidized and converted to divalent copper ions. By adding a required amount of reducing agent to a solution in which divalent copper ions have been dissolved, some of the divalent copper ions can be reduced and converted to monovalent copper ions.

The ligand that coordinates with the copper ions in the copper raw material solution can be at least one selected from the group consisting of water, hydroxide ions, ammonia, halide ions, amino acids, phosphines, carboxylic acids, thiols, cyanide ions, thiocyanide ions, nitriles, amines, ethylenediaminetetraacetic acid, and the like. In order to coordinate the ligand, a raw material containing the ligand can be added to the copper raw material solution. For example, when coordinating chloride ions, the raw material containing the ligand can be a substance containing chloride ions, such as hydrochloric acid or a salt with chloride ions as the anion. The redox potential of the copper raw material solution can be changed by changing the type and concentration of the ligand.

In the manufacturing method of the present invention, at least the copper particle raw material and the ligand raw material are mixed in a solvent to dissolve or molecularly disperse them, thereby preparing a copper raw material solution.

(Preparation of reducing agent and reducing agent solution)
Examples of the reducing agent used in the production method of the present invention include ascorbic acid salts, ferrous sulfate, sulfite salts, hydroxylamine, formic acid, hydroquinone, reducing sugar, aldehyde, tetrahydroboric acid salts (sodium borohydride, potassium borohydride, etc.), hydrazine, hydrazine compounds, etc., and ascorbic acid salts, hydrazine, and hydrazine compounds are preferred. These may be used alone or in combination. In the present invention, at least the reducing agent can be mixed in a solvent to dissolve or molecularly disperse the reducing agent solution. Since most reducing agents undergo reduction reactions well under alkaline conditions, a basic substance can be mixed in the reducing agent solution. Examples of the basic substance include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, metal alkoxides, quaternary ammoniums such as tetramethylammonium hydroxide, ammonia, amines, etc.

(solvent)
The solvent is not particularly limited as long as it can dissolve or molecularly disperse the raw material of the copper particles and the reducing agent, and examples thereof include water, organic solvents, and mixed solvents thereof. Examples of water include tap water, ion-exchanged water, pure water, ultrapure water, RO water, and the like. Examples of organic solvents include alcohol solvents such as ethanol, ethylene glycol, and glycerin, ketone solvents such as acetone and 2-butanone, ether solvents such as diethyl ether and tetrahydrofuran, aromatic solvents such as toluene and xylene, amine solvents such as triethylamine and ethylenediamine, amide solvents such as N,N-dimethylformamide, aliphatic hydrocarbon solvents such as hexane and liquid paraffin, nitrile solvents such as acetonitrile, sulfoxide solvents such as dimethyl sulfoxide, halogen-based solvents such as dichloromethane, ester solvents such as ethyl acetate and ethylene glycol monoethyl ether acetate, carboxylic acid solvents such as acetic acid and propionic acid, aprotic polar solvents such as carbon disulfide and N-methyl-2-pyrrolidone, ionic liquids, sulfonic acid compounds, and the like. Each of the solvents may be used alone, or a plurality of solvents may be used in combination. From the viewpoint of the solubility of the copper particle raw material and the reducing agent, it is preferable to prepare the copper raw material solution and the reducing agent solution using an alcohol solvent or a mixed solvent of water and an alcohol solvent.

Additives such as oxidizing agents or reducing agents for changing the valence of copper ions in the copper raw material solution, acidic or basic substances or their salts for adjusting the pH or ion concentration, surface protective agents for preventing particle aggregation, surfactants, dispersants, etc. can be added to the solvent as needed. Examples of acidic substances include inorganic acids such as aqua regia, hydrochloric acid, nitric acid, fuming nitric acid, sulfuric acid, and fuming sulfuric acid, and organic acids such as formic acid, acetic acid, chloroacetic acid, dichloroacetic acid, oxalic acid, trifluoroacetic acid, and trichloroacetic acid. Surface protective agents, surfactants, and dispersants can be various commonly used commercial products, products, or newly synthesized products. Examples include dispersants such as anionic surfactants, cationic surfactants, nonionic surfactants, and various polymers. These may be used alone or in combination of two or more. Surface protective agents, surfactants, and dispersants may be contained in either the copper raw material solution or the reducing agent solution, or both.

(Preparation Apparatus)
In the production method of the present invention, the apparatus for preparing the copper raw material solution or the reducing agent solution is preferably an apparatus that realizes homogeneous mixing by applying a shear force to the fluid, such as an apparatus that rotates stirrers of various shapes such as rod-shaped, plate-shaped, propeller-shaped, etc. in a tank, an apparatus equipped with a screen that rotates relative to the stirrers, etc. As a preferred example of a rotary disperser, the stirrer disclosed in Japanese Patent No. 5147091 can be used.

The rotary dispersing machine may be of a batch type or a continuous type. In the case of a continuous type device, the supply and discharge of fluid to the stirring tank may be performed continuously, or a continuous mixer may be used without using a stirring tank, and the stirring energy can be appropriately controlled using a known stirrer or stirring means. The stirring energy is described in detail in JP 4-114725 by the applicant of the present application. The stirring method in the present invention is not particularly limited, but can be performed using various shear type, friction type, high pressure jet type, ultrasonic type stirrers, dissolvers, emulsifiers, dispersers, homogenizers, etc. Examples include continuous emulsifiers such as Ultra Turrax (IKA), Polytron (Kinematica), TK Homomixer (Primix), Ebara Milder (Ebara Corporation), TK Homomic Lineflow (Primix), Colloid Mill (Kobe Steel Pantech), Thrasher (Nippon Coke Industrial Co., Ltd.), Trigonal Wet Fine Mill (Mitsui Miike Chemical Engineering Co., Ltd.), Cavitron (Eurotech), and Fine Flow Mill (Pacific Ocean Machinery Co., Ltd.), and batch or continuous dual-use emulsifiers such as Clearmix (M Technique), Clearmix Dissolver (M Technique), and Filmix (Primix). In particular, it is desirable to prepare the copper raw material solution or copper precipitation solution using a stirrer equipped with rotating stirring blades, particularly the above-mentioned Clearmix (M Technique) and Clearmix Dissolver (M Technique).

(Manufacturing method: equipment)
In the manufacturing method of the present invention, the copper raw material solution and the reducing agent solution can be mixed by a known method such as a batch type in a beaker or tank, a tubular reactor, or a continuous type in which a reaction is performed in a microreactor. Among them, it is preferable to use a fluid treatment device that can contact and mix at least two types of fluids to be treated between at least two processing surfaces, at least one of which rotates relative to the other, as described in JP 2011-189348 A shown in Figs. 1 and 2, specifically, a device similar to the forced thin film microreactor ULREA manufactured by M Technique Co., Ltd. Note that, although the number of types of fluids to be treated and the number of flow paths used in the fluid treatment device are two in the example of Fig. 1, they may be three or more. In addition, the shape, size, and number of the introduction openings provided in each processing part are not particularly limited and may be appropriately changed. For example, as shown in Fig. 1, the shape of the opening d20 may be a concentric annular shape surrounding the central opening of the processing surface 2, which is a ring-shaped disk, and the annular opening may be continuous or discontinuous. An introduction opening may be provided immediately before the first and second processing surfaces 1 and 2 or further upstream.

(Average particle size)
The average particle size of the copper particles produced by the production method of the present invention can be controlled by setting the redox potential of the copper raw material solution. In addition, the redox potential of the copper raw material solution can be changed by changing the molar concentration ratio of monovalent copper ions to the total copper ions in the copper raw material solution ([Cu ⁺ ]/([Cu ⁺ ]+[Cu ²⁺ ])) or by selecting a ligand that coordinates to the copper ions in the copper raw material solution. One of the reasons for the change in the average particle size is thought to be due to the free energy and reaction rate of each copper ion. The relationship between the potential difference E of the redox potential in the reaction and the difference ΔG of the standard free energy of formation is expressed by the following formula. Here, E is calculated as a value relative to the standard hydrogen electrode.
ΔG = -nFE
n: number of electrons involved in the reaction F: Faraday constant

As shown in the above formula, the free energy of each copper ion is correlated with the redox potential. However, the free energy in the actual reaction system changes not only depending on the valence of the ion, but also depending on the ligand, the concentration in the solution, and other coexisting compounds. When the copper raw material solution and the reducing agent solution are mixed, the driving force of the reduction reaction increases as the potential difference between the redox potential of the copper raw material solution and the redox potential of the reducing agent solution increases, so the reaction rate increases, and a large number of crystal nuclei of copper particles are generated, which reduces the copper raw material concentration near the crystal nuclei and produces a small amount of copper particles. When the literature value of the redox potential is used, in the presence of chloride ions, the potential difference between Cu ²⁺ /Cu ⁺ is +0.56 V at the standard hydrogen electrode potential, and the potential difference between Cu ⁺ /Cu is +0.12 V, and the particle size is smaller when copper particles are produced from a Cu(II) solution.

On the other hand, since copper ions in a solution are partially coordinated with solvent molecules due to solvation, it may be difficult to obtain all the redox potentials of the prepared copper raw material solution from literature values. If there is no literature data, it can be calculated from the standard free energy of formation of each ion. According to this idea, for example, in the case of a Cu ammine complex coordinated with ammonia molecules, the redox potentials obtained from the standard free energy of formation of Cu(NH ₃ ) ₄ ²⁺ ions and Cu(NH ₃ ) ²⁺ ions are -0.028 V and -0.100 V, respectively, and it was expected that the copper particles from the Cu(II) ammine complex would be smaller because the redox potential of the Cu(NH ₃ ) ₄ ²⁺ ion is more noble, but the particle sizes obtained in the examples implemented this time were 185.3 nm and 59.6 nm, respectively, which is the opposite of the prediction. One of the reasons for this is that the standard free energy of formation in the literature is a value in an aqueous solution, and the embodiment uses a mixed solvent of ethylene glycol and water, so the coordination state of the copper ions is different from that in the case of water alone. Accordingly, it is considered that the standard free energy of formation in pure water has changed to the standard free energy of formation in ethylene glycol and pure water, and it is presumed that the oxidation-reduction potential is different from that in an aqueous solution. In the embodiment, the potential of the ORP meter reflecting the oxidation-reduction potential of the copper raw material solution is more noble than that of the Cu(I) ammine complex, and it is predicted that the driving force of the reduction reaction to copper particles is greater when the Cu(I) ammine complex is used than when the Cu(II) ammine complex is used, and the experimental results actually support this. For this reason, it is considered that the potential of the ORP meter reflecting the oxidation-reduction potential of the copper raw material solution replaces the oxidation-reduction potential of the copper raw material solution being used, and in the present invention, the particle size control of copper can also be performed based on the potential of the copper raw material solution measured by the ORP meter.

The reference electrode for the ORP meter is an Ag/AgCl (KCl saturated) electrode, and this electrode potential is +0.199 V nobler than the standard hydrogen electrode that is often used in the literature, so conversion is necessary when comparing with literature values.

(pH Adjustment)
In the production method of the present invention, the pH during the reaction can be adjusted by controlling the concentrations of the copper particle raw material, basic substance, acidic substance, etc. contained in the copper raw material solution and the reducing agent solution, and the introduction flow rates of the copper raw material solution and the reducing agent solution. Since the reduction reaction of most reducing agents proceeds well under alkaline conditions, the pH during the reaction is preferably 7 to 14, more preferably 8 to 13.

(Reducing Agent)
In order to set the potential difference between the oxidation-reduction potential of the copper raw material solution and the oxidation-reduction potential of the reducing agent solution, the oxidation-reduction potential of the reducing agent solution can also be changed by selecting a reducing agent.
The molar concentration ratio ([e ^- ]/([Cu ⁺ ]+2×[Cu 2+ ])) of the electron donating amount of the reducing agent in the reducing agent solution to the amount of electrons required to reduce the copper ions in the copper raw material solution to metallic ^copper is preferably 1 or more and 100 or less, and more preferably 1.5 or more and 50 or less. If it is 1 or less, oxides will be mixed in, and if it is 100 or more, the amount of raw material used will increase, which is not preferable as it increases the production cost. Increasing [e ^- ]/([Cu ⁺ ]+2×[Cu ²⁺ ]) increases the reaction rate and reduces the particle diameter, and decreasing [e ^- ]/([Cu ⁺ ]+2×[Cu ²⁺ ]) increases the particle diameter.

(Anti-oxidation)
The presence of oxidized ascorbic acid in the solution obtained after mixing the copper raw material solution and the reducing agent solution can prevent oxidation of the obtained copper particles. Oxidized ascorbic acid is generated by the oxidation of ascorbic acid when copper ions are reduced by using ascorbic acids as a reducing agent, and when other reducing agents are used and oxidized ascorbic acid is not generated, oxidized ascorbic acid can be added to the copper raw material solution and/or the reducing agent solution in advance to make it present in the system. FT-IR confirmed that oxidized ascorbic acid such as dehydroascorbic acid is bonded to copper on the surface of the particles obtained under the above conditions, and oxidation hardly progresses even when stored under air, allowing stable storage.

(Cleaning of particles)
The copper particles produced by the production method of the present invention can be washed as necessary. There is no particular limitation on the washing method, and various known methods such as decantation, centrifugation, and filtration can be used. As the washing solvent, a solvent capable of dissolving the inorganic salt, which is a by-product, can be used, and examples thereof include alcohols such as methanol, pure water, and ion-exchanged water. From the viewpoint of preventing oxidation of the copper particles, alcohols are preferred, and deoxygenated alcohols are more preferred.

In the manufacturing method of the present invention, it is preferable that at least one selected from the group consisting of the temperature of the first fluid, the temperature of the second fluid, and the temperature of the mixed fluid obtained by mixing the first fluid and the second fluid is 100°C or higher. This at least one temperature is more preferably 110 to 250°C, and even more preferably 120 to 200°C. By raising the temperature to 100°C or higher, the crystallinity of the copper particles increases, and the higher the temperature, the higher the reaction rate, so the particle size tends to become smaller.

The manufacturing method of the present invention makes it possible to manufacture copper particles with a controlled particle size in a simple and stable manner, in a manner suitable for mass production.

2. Method for controlling the average particle size of copper particles The method for controlling the average particle size of copper particles of the present invention is a method for controlling the average particle size of copper particles to within a range of 1 nm to 1000 nm,
The method includes a step of mixing at least a first fluid and a second fluid to precipitate copper particles,
one of the first fluid and the second fluid is a copper raw material solution containing a raw material of copper particles;
the other of the first fluid and the second fluid is a reducing agent solution containing at least one reducing agent;
the copper source solution contains at least monovalent copper ions and/or divalent copper ions,
The control method is characterized by changing the oxidation-reduction potential of the copper raw material solution.
The average particle size of the copper particles can be controlled by referring to the description of the above-mentioned method for producing copper particles.

The present invention will be described below using examples, but the present invention is not limited to these examples. In the following examples and comparative examples, liquid A refers to the first treated fluid introduced from the first introduction part d1 of the device shown in Figure 1, and liquid B refers to the second treated fluid introduced from the second introduction part d2 of the device.

Example 1
A copper source solution and a reducing agent solution were each prepared using a Clearmix (product name: CLM-0.8S, manufactured by M Technique), which is a high-speed rotary dispersion and emulsification device.
Specifically, argon was flowed into the solvent in advance to perform bubbling for 1 hour, and the solvent was deoxidized. Based on the formulation of the copper raw material solution shown in Example 1 of Table 1, the copper particle raw material, the solvent, and the additive were mixed, and the mixture was homogeneously mixed by stirring for 30 minutes at a rotor speed of 20,000 rpm using Clearmix at an argon atmosphere and a preparation temperature of 50 ° C., and the copper particle raw material and the additive were dissolved in the solvent to prepare a copper raw material solution. In addition, based on the formulation of the reducing agent solution shown in Example 1 of Table 1, the reducing agent, the basic substance, and the solvent were mixed, and the mixture was homogeneously mixed by stirring for 30 minutes at a rotor speed of 15,000 rpm using Clearmix at an argon atmosphere and a preparation temperature of 45 ° C., to prepare a reducing agent solution.

Next, the prepared copper raw material solution and the reducing agent solution were mixed in the fluid treatment device shown in FIG. 1 under the treatment conditions shown in Table 1. Specifically, the copper raw material solution was introduced between the treatment surfaces as the first fluid to be treated (liquid A) from the first inlet d1 of the fluid treatment device shown in FIG. 1, and while the treatment unit 10 was operated at a rotation speed of 2000 rpm, the reducing agent solution was introduced between the treatment surfaces 1 and 2 as the second fluid to be treated (liquid B) from the second inlet d2 of the fluid treatment device shown in FIG. 1, and mixed in the thin film fluid. Copper particles were precipitated between the treatment surfaces 1 and 2, and a discharge liquid containing the copper particles was discharged from between the treatment surfaces 1 and 2 of the fluid treatment device. The discharge liquid containing the copper particles was collected in a beaker b via a vessel v.

The introduction temperatures (liquid delivery temperatures) of liquid A and liquid B were measured using a thermometer installed in the sealed introduction path (first introduction part d1 and second introduction part d2) that leads between the processing surfaces 1 and 2. The introduction temperature of liquid A shown in Table 1 is the actual temperature of liquid A in the first introduction part d1, and the introduction temperature of liquid B is the actual temperature of liquid B in the second introduction part d2.

A HORIBA pH meter, model D-51, was used for pH measurements. A DKK-TOA ORP meter, model RM-30P, was used for ORP measurements. Before introducing the first and second treated fluids into the fluid treatment device, the pH of the treated fluids and the temperature at the time of pH measurement were measured. In addition, since it is difficult to measure the pH and ORP of the mixed fluid immediately after mixing the copper raw material solution and the reducing agent solution, the copper particle dispersion discharged from the device and collected in beaker b was measured at room temperature.

A dry powder and a wet cake sample were prepared from the discharged liquid containing the copper particles collected in beaker b. The preparation method was performed according to a known method, specifically, the discharged liquid containing the copper particles was collected by centrifugation, the copper particles were allowed to settle and the supernatant liquid was removed, and then the copper particles were washed by repeating washing and settling twice with methanol deoxygenated by argon flow, and a part of the finally obtained wet cake of copper particles was dried to make a dry powder. The other was used as a wet cake sample.

(Preparation of sample for TEM observation)
A part of the wet cake sample of the copper particles after the washing treatment obtained in Example 1 was dispersed in methanol. The obtained dispersion was dropped onto a grid with a supporting film and dried to prepare a sample for TEM observation.

(Transmission Electron Microscope)
A transmission electron microscope, JEM-2100 (manufactured by JEOL) was used for the transmission electron microscope (TEM) observation. The observation conditions were an acceleration voltage of 200 kV and an observation magnification of 10,000 to 500,000 times. The average particle size (D) is the average value of the primary particle size, and is the average value of the results of measuring the particle sizes of 100 particles by TEM observation. In addition, the thickness of the oxide layer on the particle surface was measured under the condition of an observation magnification of 500,000 times.

(X-ray diffraction measurement)
For the X-ray diffraction (XRD) measurement, an EMPYREAN powder X-ray diffraction measuring device (manufactured by Malvern Panalytical) was used. The measurement conditions were: measurement range: 10 to 100 [°2Theta] Cu anticathode, tube voltage: 45 kV, tube current: 40 mA, and scanning speed: 0.3°/min.

(Examples 2 to 13)
In Examples 2 to 13, similarly to Example 1, the copper source solution and the reducing agent solution were mixed in accordance with the respective formulations and treatment conditions shown in Table 1, and particles were precipitated between the treatment surfaces 1 and 2. Dry powder and wet cake samples were prepared from the discharged liquid containing copper particles that was discharged from the fluid treatment device and recovered in a beaker b via a vessel v, and TEM observation and XRD measurement were performed in the same manner as in Example 1.

The measurement results for Examples 1 to 13 are shown in Tables 1 and 2. TEM photographs of the copper particles obtained in Examples 1 and 9 are shown in Figures 3 and 4.

As shown in Tables 1 and 2 and Figures 3 and 4, by changing the molar ratio of monovalent copper ions to the total copper ions in the raw material in the copper raw material solution and the ligands, it was possible to change the redox potential of the copper raw material solution and control the average particle size.

(Comparative Example 1)
In Comparative Example 1, except that sodium ascorbate was omitted from the reducing agent solution, the copper raw material solution and the reducing agent solution were mixed in the same manner as in Example 1 under the respective formulations and treatment conditions shown in Table 6, and particles were precipitated between the treatment surfaces 1 and 2. A dry powder and a wet cake sample were prepared from the discharged liquid containing copper particles that was discharged from the fluid treatment device and recovered in a beaker b via a vessel v, and TEM observation and XRD measurement were performed in the same manner as in Example 1.

The measurement results for Comparative Example 1 are shown in Table 2. In the comparative example, the thickness of the oxide layer on the particle surface was 5.6 nm. In addition, XRD measurement confirmed the copper diffraction pattern and the cuprous oxide diffraction pattern, confirming that the particles were partially oxidized.

As can be seen from the examples and comparative examples, the manufacturing method of the present invention makes it possible to easily produce copper particles with a controlled average particle size.

The manufacturing method of the present invention does not require complex chemical reactions or heat treatments, and is suitable for mass production, allowing for the easy and stable production of copper particles with a controlled average particle size.

1 First processing surface 2 Second processing surface 10 First processing member 11 First holder 20 Second processing member 21 Second holder d1 First introduction part d2 Second introduction part d20 Opening

Claims (9)

A method for producing copper particles having an average particle size in the range of 1 nm to 1000 nm,
The method includes a step of mixing at least a first fluid and a second fluid to precipitate copper particles,
one of the first fluid and the second fluid is a copper raw material solution containing a raw material of copper particles;
the other of the first fluid and the second fluid is a reducing agent solution containing at least one reducing agent;
the copper source solution contains at least monovalent copper ions and/or divalent copper ions,
a potential difference between an oxidation-reduction potential of the copper raw material solution and an oxidation-reduction potential of the reducing agent solution is set so as to obtain the average particle diameter. 2. The method according to claim 1, wherein the redox potential of the copper source solution is set by adjusting a molar concentration ratio ([Cu ⁺ ]/([Cu ⁺ ]+[Cu ²⁺ ])) of monovalent copper ions to total copper ions in the copper source solution. a ligand coordinated to the copper ion in the copper source solution is at least one selected from water, hydroxide ions, ammonia, halide ions, amino acids, phosphines, carboxylic acids, thiols, cyanide ions, thiocyanide ions, nitriles, amines, and ethylenediaminetetraacetic acid;
The method according to claim 1 or 2, wherein the redox potential of the copper raw material solution is set by selecting the ligand. the reducing agent is at least one selected from ascorbate salts, ferrous sulfate, sulfite salts, hydroxylamine, formic acid, hydroquinone, reducing sugars, aldehydes, tetrahydroboric acids, hydrazine, and hydrazine compounds;
The method according to any one of claims 1 to 3, wherein the oxidation-reduction potential of the reducing agent solution is set by selecting the reducing agent. The manufacturing method according to any one of claims 1 to 4, wherein the mixed liquid obtained by mixing the first fluid and the second fluid contains oxidized ascorbic acid. The manufacturing method according to any one of claims 1 to 5, wherein the oxide layer on the surface of the copper particles is 4 nm or less. Continuously introducing at least two fluids to be treated, including the copper raw material solution and the reducing agent solution, between processing surfaces disposed opposite to each other and rotating relatively so as to be capable of approaching and separating from each other;
mixing the at least two fluids to be treated between processing surfaces disposed opposite to each other and rotating relatively to each other so as to be able to approach and separate from each other, thereby precipitating copper particles;
The method according to any one of claims 1 to 6, wherein the mixed fluid containing the precipitated copper particles is discharged from between the processing surfaces to continuously produce copper particles. one of the copper source solution and the reducing agent solution passes between the processing surfaces while forming a thin film fluid;
the other of the copper raw material solution and the reducing agent solution is introduced into the space between the processing surfaces through another introduction path independent of the flow path introduced into the space between the processing surfaces, and from an opening formed in at least one of the processing surfaces;
The method of claim 7 , wherein the copper source solution and the reducing agent solution are mixed between the processing surfaces. A method for controlling the average particle size of copper particles to within a range of 1 nm to 1000 nm, comprising the steps of:
The method includes a step of mixing at least a first fluid and a second fluid to precipitate copper particles,
one of the first fluid and the second fluid is a copper raw material solution containing a raw material of copper particles;
the other of the first fluid and the second fluid is a reducing agent solution containing at least one reducing agent;
the copper source solution contains at least monovalent copper ions and/or divalent copper ions,
A control method comprising changing a potential difference between an oxidation-reduction potential of the copper raw material solution and an oxidation-reduction potential of the reducing agent solution.