Apparatus for producing metal nanoparticles and method for producing metal nanoparticles

Abstract

To provide a production apparatus for efficiently producing metal nanoparticles and a production method therefor.SOLUTION: The present invention relates to an apparatus for producing metal nanoparticles and a method for producing the same, the apparatus comprising: a pump for pressure-feeding a reaction solution; a heating device for heating, together with a reaction tube, the reaction solution that is pressure-fed from the pump and flows through the reaction tube; a pressure control device for adjusting pressure of the reaction solution in the reaction tube at a downstream side of the reaction tube; a stirring device disposed between the pump and the reaction tube for stirring the reaction solution pressure-fed from the pump; and a gas introduction device disposed between the stirring device and the reaction tube for introducing an inert gas into the reaction solution stirred in the stirring device.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an apparatus for producing metal nanoparticles and a method for producing metal nanoparticles. [Background technology]

[0002] Metal nanoparticles, which may have properties different from those of bulk materials, are being used and investigated for a variety of applications, such as catalysts, ink materials, and electronic component materials.

[0003] For example, Patent Document 1 discloses a method for producing metal nanoparticles, which includes the steps of: circulating a reaction liquid containing a first liquid containing raw material salts of metal nanoparticles and / or a second liquid containing a reducing agent for the raw material salts and / or a liquid obtained by mixing the first liquid and the second liquid through a reaction tube, at least a portion of which is placed in a microwave irradiation field; irradiating microwaves from outside the reaction tube to at least a portion of the flowing liquid to heat the flowing liquid; and circulating at least one of the first liquid, the second liquid, and the reaction liquid through at least a portion of the reaction tube and / or flow tube and / or flow path to control a reduction reaction of the metal nanoparticles and synthesize the metal nanoparticles, wherein the method is characterized in that the first liquid and / or the second liquid and / or the reaction liquid are passed through a flow tube and / or flow path and / or reaction tube, mainly accompanied by an inert gas as an inhibitor of adhesion of metal precipitates to the inner wall of the reaction tube. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-197392 Summary of the Invention [Problem to be solved by the invention]

[0005] A method for producing metal nanoparticles by circulating a raw material solution (reaction liquid) through a tube (piping) and heating it using a microwave heating device has been investigated. However, according to the investigations of the present inventors, this method tends to result in a large amount of metal nanoparticles adhering to the inner wall of the piping, causing clogging and contamination of the piping, and a decrease in yield, i.e., a decrease in the recovery rate of metal nanoparticles.

[0006] To address this problem, Patent Document 1 circulates an inert gas as a metal deposit adhesion inhibitor. However, in the examples of Patent Document 1, a large amount of inert gas is used relative to the volume of the reaction solution. Because inert gas does not absorb microwaves, the amount of microwave absorption at the gas-liquid interface is small. As a result, the heating efficiency of the reaction solution decreases, raising concerns about a decline in productivity and an increase in costs.

[0007] Therefore, an object of the present invention is to provide a manufacturing apparatus for efficiently manufacturing metal nanoparticles, and a manufacturing method thereof. [Means for solving the problem]

[0008] As a result of examining various means for solving the above-mentioned problems, the inventors discovered that in a method for producing metal nanoparticles by irradiating a reaction solution with microwaves, by introducing an inert gas into the reaction solution at a certain flow rate and then irradiating the reaction solution with microwaves while applying pressure, adhesion of metal nanoparticles to the inner walls of the pipe can be suppressed and productivity of metal nanoparticles can be improved, thereby completing the present invention.

[0009] That is, the gist of the present invention is as follows. (1) An apparatus for producing metal nanoparticles, comprising: a pump for pressure-feeding a reaction liquid; a heating device for heating the reaction liquid pressure-fed from the pump and flowing through a reaction tube together with the reaction tube; a pressure adjusting device for adjusting the pressure of the reaction liquid in the reaction tube downstream of the reaction tube; a stirring device for stirring the reaction liquid pressure-fed from the pump between the pump and the reaction tube; and a gas introducing device for introducing an inert gas into the reaction liquid stirred in the stirring device between the stirring device and the reaction tube. (2) The apparatus for producing metal nanoparticles according to (1), wherein the gas introduction device has a flow rate control device for adjusting the flow rate of the inert gas to 5 × r (mL / min) or more with respect to the average inner diameter of the reaction tube, 2r (mm), and to 0.1v (mL / min) to 3.0v (mL / min) with respect to the flow rate v (mL / min) of the reaction solution. (3) The apparatus for producing metal nanoparticles according to (2), wherein the average inner diameter 2r is 2 mm to 10 mm. (4) The apparatus for producing metal nanoparticles according to any one of (1) to (3), wherein the heating device is a microwave irradiation device. (5) The apparatus for producing metal nanoparticles according to any one of (1) to (4), wherein the stirring device is disposed between the pump and the reaction tube at a position where the stirring flow of the reaction solution that has passed through the stirring device is maintained within the reaction tube. (6) The apparatus for producing metal nanoparticles according to any one of (1) to (5), wherein the stirring device has a straight pipe through which the reaction liquid flows and a twisted blade fixed within the pipe and twisted around the axis of the pipe. (7) The apparatus for producing metal nanoparticles according to (6), wherein the twisted blade is a blade in which twisted blade elements having different twist directions around the axis are arranged alternately along the axial direction of the pipe. (8) The apparatus for producing metal nanoparticles according to (6) or (7), wherein the twisted blade is made of a non-conductive material. (9) A method for producing metal nanoparticles, comprising the step of irradiating a reaction solution with microwaves, the method comprising the steps of: (i) preparing a reaction solution containing a metal nanoparticle precursor, an organic substance as a dispersant, and a solvent; and (ii) irradiating the reaction solution with microwaves while flowing it through a reaction tube, wherein an inert gas is introduced into the reaction solution before irradiating it with microwaves, the flow rate of the inert gas is 5 × r (mL / min) or more with respect to the average inner diameter of the reaction tube, 2r (mm), and is 0.1v (mL / min) to 3.0v (mL / min) with respect to the flow rate v (mL / min) of the reaction solution, and pressure is applied to the reaction solution when irradiating it with microwaves. (10) The method according to (9), wherein in step (ii), the average inner diameter 2r is 2 mm to 10 mm. (11) The method according to (9) or (10), wherein in step (ii), the flow rate v of the reaction solution is 70 mL / min to 300 mL / min. [Effects of the Invention]

[0010] The present invention provides a manufacturing apparatus for efficiently manufacturing metal nanoparticles and a manufacturing method thereof. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram schematically illustrating a state in which an inert gas is introduced into a reaction liquid flowing through a reaction tube. [Figure 2] 1 is a diagram showing an outline of an embodiment of a manufacturing apparatus of the present invention. [Figure 3] FIG. 1 is a diagram schematically illustrating an embodiment of a stirring device in a manufacturing apparatus of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the present invention will now be described in detail. In this specification, the features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. The metal nanoparticle manufacturing apparatus and metal nanoparticle manufacturing method of the present invention are not limited to the following embodiments, and can be implemented in various forms incorporating modifications and improvements that can be made by those skilled in the art without departing from the spirit of the present invention. Furthermore, although each embodiment described in this specification is independent, two or more of each embodiment can also be combined to form one embodiment of the present invention.

[0013] The symbol "to" used herein means a range having the numerical values ​​before and after it as the upper and lower limits. In numerical ranges described in stages in this specification, the upper or lower limit described in one numerical range may be replaced with the upper or lower limit described in another stage. The upper or lower limit of a numerical range described herein may be replaced with a value shown in the examples.

[0014] First, the method for producing metal nanoparticles of the present invention will be described.

[0015] (i) preparing a reaction liquid containing a metal nanoparticle precursor, an organic substance as a dispersant, and a solvent; In the method of the present invention, the solvent used in the reaction solution is not limited as long as it is a polar solvent or ionic liquid that can dissolve materials such as metal nanoparticle precursors, organic dispersants, and reducing agents, and that can also absorb microwaves. Examples of solvents used in the reaction solution include low-boiling solvents with a boiling point of 300°C or less. Examples of low-boiling solvents include water, alcohols such as methanol and ethanol, polyhydric alcohol solvents such as ethylene glycol, ketone solvents such as acetone, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), other organic solvents, and mixtures of two or more of these low-boiling polar solvents. When a mixture is used as the solvent, the ratio of each component contained in the mixture is not limited, as long as the components are miscible under the experimental conditions.

[0016] By using a low boiling point polar solvent as the solvent, the handling of the solvent can be improved and the burden on the environment can be reduced.

[0017] The metal nanoparticle precursor may be any material that dissolves in a solvent to produce metal ions, such as ions of precious metals, base metals, and alloys, such as gold, silver, platinum, copper, nickel, iron, and cobalt, or ions of two or more of these metals. Examples of metal nanoparticle precursors include inorganic metal salts such as metal halides (e.g., fluorides, chlorides, bromides, and iodides), metal sulfates, metal nitrates, metal phosphates, and metal cyanides; organic metal salts such as metal carboxylates and metal sulfonates; and metal complexes, including metal complex salts. The metal nanoparticle precursor may be prepared, for example, by dissolving a material containing a metal or a metal salt in an acid such as nitric acid or a base such as aqueous ammonia. Preferred metal nanoparticle precursors include inexpensive metal nitrates (e.g., nickel nitrate and silver nitrate), metal chlorides (e.g., silver chloride), metal oxides (e.g., silver oxide), and metal carboxylates (e.g., silver carboxylate). Furthermore, a reducing formate, such as nickel formate, can be used as the metal nanoparticle precursor. Therefore, in one embodiment, when a salt composed of a metal ion and a reducing organic anion, such as a formate ion, is used as the metal nanoparticle precursor, a reducing agent may not be used.

[0018] A homogeneous reaction solution can be prepared by dissolving the metal nanoparticle precursor in a solvent.

[0019] The concentration of metal ions in the reaction solution is not limited as long as it is equal to or less than the saturated concentration, but is usually 0.05 mol / L (M) or more and usually 2.0 M or less, for example, 0.05 M to 2.0 M, and in one embodiment, 0.05 M to 1.0 M, in one embodiment, 0.05 M to 0.5 M, and in one embodiment, 0.05 M to 0.3 M.

[0020] By setting the metal ion concentration in the reaction solution within the above range, metal nanoparticles can be efficiently produced at a high concentration, the amount of metal nanoparticles that can be produced and recovered at one time can be significantly increased, and the time, labor, and cost required for producing metal nanoparticles can be reduced.Furthermore, the variation in the obtained metal nanoparticles can be reduced, in other words, the particle size distribution of the obtained metal nanoparticles can be narrowed.

[0021] The reaction liquid contains an organic substance as a dispersant. Examples of dispersants include, but are not limited to, one or more dispersants selected from polyvinylpyrrolidone (PVP), dodecylamine (DDA), thiol-based polymers, polyvinyl alcohol (PVA), polyacrylic acid, polyacrylates, cyclodextrin, aminopectin, methylcellulose, polyethyleneimine cellulose, aliphatic amines, aliphatic carboxylic acids, and tannic acid. When the dispersant is a polymer, the molecular weight of the dispersant is, but is not limited to, for example, a weight-average molecular weight (Mw) of typically 1,000 or more, in one embodiment 8,000 or more, and in one embodiment 10,000 or more, and typically 50,000 or less, in one embodiment 40,000 or less, for example 1,000 to 50,000, in one embodiment 8,000 to 50,000, and in one embodiment 10,000 to 40,000.

[0022] The concentration of the dispersant in the reaction solution is not limited, but is usually 3000 mmol / L (mM) or less, and in one embodiment, 1000 mM or less. Since a smaller amount of dispersant in the reaction solution is preferable, the lower limit is not limited, but is usually 0.1 mM or more.

[0023] Conventionally, when producing metal nanoparticles, the amount of organic substance used as a dispersant to control particle size during production was greater than the amount of organic substance required for dispersion. Furthermore, because the organic substance could not be removed, it remained in the final metal nanoparticles. According to the method of the present invention, the amount of organic substance required for particle size control during production can be reduced, making it possible to produce metal nanoparticles with a reduced amount of organic substance, which contain only the amount of organic substance required for dispersion.

[0024] The reaction solution may further contain a reducing agent, which is a material capable of reducing metal ions to a metal with an oxidation number of 0 through an oxidation-reduction reaction.

[0025] The reducing agent is not limited. Examples of the reducing agent include sodium borohydride (NaBH), hydrazine, polyol, citric acid or citrates such as trisodium citrate, disodium citrate, and monosodium citrate, oxalic acid or oxalate salts such as sodium oxalate, ascorbic acid or ascorbate salts such as sodium ascorbate, formic acid or formate salts such as sodium formate, DMF, and mixtures of two or more thereof. In one embodiment, the reducing agent for metal ions, particularly silver ions, is DMF. Therefore, when DMF is used as the solvent for the reaction solution, DMF can also function as a reducing agent, so it is not necessary to use a reducing agent other than DMF.

[0026] The amount of reducing agent is not limited as long as it can reduce metal ions to a metal whose oxidation state is 0 through a redox reaction. The amount is typically 1.0 equivalent or more, and in one embodiment, 4.0 equivalents or more, and typically 20 equivalents or less, and in one embodiment, 15 equivalents or less, for example, 1.0 to 20 equivalents, and in one embodiment, 4.0 to 15 equivalents, relative to the metal ions. Note that a reducing agent for metal ions may also function as a dispersant if it contains one or more functional groups capable of interacting with metals, such as a carboxyl group, a hydroxyl group, or an ether group. When the reducing agent also functions as a dispersant, the reaction solution need not contain the dispersant described above. Furthermore, the amount of reducing agent for metal ions may be greater than the amount required to reduce metal ions to a metal whose oxidation state is 0 through a redox reaction.

[0027] The reaction solution may further contain a base. The base functions as a pH adjuster, and examples thereof include 2-amino-1-butanol, sodium hydroxide, magnesium hydroxide, potassium hydroxide, and calcium hydroxide. The base may be a mixture of two or more types. The base may be used as a basic solution containing a base dissolved in a solvent such as water or alcohol. When the reaction solution contains a base, it is possible to promote the reduction reaction and increase the reaction rate, thereby enabling metal particles to be produced efficiently at a high concentration, significantly increasing the amount of metal particles that can be produced and recovered at one time, and reducing the time, effort, and cost required for producing metal particles.

[0028] When the reaction solution further contains a base, the concentration of the base in the reaction solution is not limited as long as it is not more than the saturated concentration, but is usually 1 mmol / L (mM) or more, and in one embodiment, 50 mM or more and usually 250 mM or less. The concentration of the base in the reaction solution is, for example, 1 mM to 250 mM, and in one embodiment, 50 mM to 250 mM.

[0029] The pH of the reaction solution is not limited, but is usually pH5 to pH14.

[0030] The reaction solution may be composed of the metal nanoparticle precursor, solvent, dispersant, and optionally a reducing agent and base described above. In addition to these materials, the reaction solution may further contain additives that are commonly used in conventional methods for producing metal nanoparticles by microwave irradiation, such as chelating agents, such as ethylenediaminetetraacetic acid (EDTA) and / or salts thereof. The amount of additive is not limited. The amount of additive is typically 10% by weight or less, and in one embodiment, 3% by weight or less, based on the total weight of the reaction solution. Because additives are not required, there is no lower limit for the amount of additive. However, when the reaction solution further contains an additive, the amount of additive is typically 0.1% by weight or more based on the total weight of the reaction solution.

[0031] In the present invention, the order of addition of each material, the addition temperature, the mixing method, the mixing time, etc. in preparing the reaction solution are not limited, and the materials are mixed so as to prepare a homogeneous reaction solution. Note that the reaction solution may be prepared containing all materials, or, as in the Examples described below, two solutions, for example, Solution A and Solution B, may be prepared and supplied to the reaction system so that the two solutions are mixed to form a homogeneous reaction solution at the stage of supplying them to the reaction tube, for example, immediately before the reaction, i.e., immediately before microwave irradiation.

[0032] In one embodiment, a solution (Liquid A) in which a metal nanoparticle precursor is dissolved in water and a solution (Liquid B) in which a basic solution containing a dispersant and a base is dissolved in DMF may be prepared and supplied to the reaction system. In one embodiment, Liquid A contains a metal nanoparticle precursor. In one embodiment, Liquid B contains a dispersant and a base. The volume ratio of Liquid B to Liquid A (B / A) is not limited, but is typically 0.5 to 10, and in one embodiment, 1 to 5. The concentrations of each component, i.e., the metal nanoparticle precursor in Liquid A and the dispersant and base in Liquid B, are preferably adjusted to fall within the concentration ranges described above in the reaction solution prepared by combining Liquid A and Liquid B. Liquid A is preferably supplied to the reaction system at a flow rate of 20 mL / min to 100 mL / min, depending on the inner diameter of the reaction tube. Liquid B is preferably supplied to the reaction system at a flow rate of 50 mL / min to 200 mL / min, depending on the inner diameter of the reaction tube.

[0033] In one embodiment, the flow rate of the reaction solution introduced into the reaction tube is typically 70 mL / min or more, for example, 70 mL / min to 300 mL / min, and in one embodiment, 120 mL / min to 180 mL / min. Within this range, the reaction solution flowing in the reaction tube can be efficiently irradiated with microwaves. Note that when solution A and solution B are supplied to the reaction system as the reaction solution, the flow rate of the reaction solution is the sum of the flow rates of solution A and solution B.

[0034] By setting the flow rate of the reaction liquid within the above range, in step (ii) described below, the reaction liquid can be circulated while applying a predetermined pressure to the reaction liquid, and small metal nanoparticles can be formed even with a small amount of organic matter as a dispersant.

[0035] (ii) A step of irradiating the reaction solution with microwaves while the reaction solution is flowing through the reaction tube. In step (ii), an inert gas is introduced into the reaction solution before, for example, immediately before, microwave irradiation. The inert gas may include, but is not limited to, nitrogen gas, argon gas, etc.

[0036] The flow rate of the inert gas is 5×r (mL / min) or more where 2r (mm) is the average inner diameter of the reaction tube irradiated with microwaves, and 0.1v (mL / min) to 3.0v (mL / min) where v (mL / min) is the flow rate of the reaction solution.

[0037] Here, the reaction tube is the part of the pipe through which the reaction solution flows where the reaction takes place, and is usually the part of the pipe that is irradiated with microwaves.

[0038] When the reaction tube is a straight tube, the dimensions and shape are not limited as long as the microwave irradiation is uniform throughout the reaction tube. In one embodiment, the average inner diameter 2r (2 × r) of the reaction tube is usually 2 mm or more, in one embodiment, 4 mm or more, and usually 10 mm or less, in one embodiment, 8 mm or less, for example, 2 mm to 10 mm, and in one embodiment, 4 mm to 10 mm. In one embodiment, when the cavity is a rectangular parallelepiped with a length of 100 mm, the reaction tube used has an average inner diameter 2r of 1 mm to 6 mm, an average outer diameter of 3 mm to 8 mm (wall thickness: 1 mm), and a length of 100 mm.

[0039] The material of the reaction tube is not limited as long as it can uniformly irradiate the reaction solution with microwaves. Examples of the material of the reaction tube include materials that transmit microwaves, i.e., materials that do not absorb microwaves, such as ceramic materials, for example, ceramic materials made of silicon oxide such as glass and quartz, and non-conductive materials with small relative dielectric constant ε and dielectric loss angle tanδ, such as resins.

[0040] In one embodiment, the material of the reaction tube is a resin, and the loss coefficient (ε r tanδ) is usually 0.1×10 -3 In one embodiment, 0.3 × 10 -3 or more, usually 1.0 × 10 -3 In one embodiment, less than 0.9×10 -3 is less than.

[0041] The loss factor refers to the loss factor at the wavelength of the irradiated microwave, and the relative dielectric constant (ε r ) and the dielectric loss tangent (tan δ).

[0042] When the loss coefficient is within the above range, the rate at which microwaves are absorbed by the reaction tube is low, and microwaves can be used efficiently to heat the reaction liquid.

[0043] Examples of the resin include PFA (perfluoroalkoxy fluororesin), PTFE (polytetrafluoroethylene), and FEP (tetrafluoroethylene-hexafluoropropylene copolymer).

[0044] The arithmetic mean roughness Ra of the inner wall of the reaction tube is usually 0.01 μm or more, and in one embodiment 0.02 μm or more, and is usually less than 0.1 μm, and in one embodiment less than 0.08 μm.

[0045] The maximum height roughness Rz of the inner wall of the reaction tube is usually 0.1 μm or more, and in one embodiment 0.2 μm or more, and usually less than 1.0 μm, and in one embodiment less than 0.8 μm, and in one embodiment less than 0.5 μm.

[0046] By using a reaction tube having an inner wall with Ra and Rz within the above ranges, it is possible to prevent the produced metal nanoparticles from adhering to the pipe.

[0047] The flow rate v of the reaction liquid is as explained in step (i), and means the flow rate of the reaction liquid introduced into the reaction tube before the inert gas is introduced.

[0048] The flow rate of the inert gas is not limited as long as it is within the range determined by the average inner diameter 2r of the reaction tube and the flow rate v of the reaction solution described above, but is usually 10 mL / min to 420 mL / min, and in one embodiment, 14 mL / min to 360 mL / min.

[0049] Figure 1 shows a schematic diagram of an inert gas being introduced into the reaction liquid flowing through a reaction tube. By setting the flow rate of the inert gas within the range described above, reaction liquid segments and inert gas segments are alternately formed in the reaction tube, as shown in Figure 1, resulting in the formation of turbulent flow within the reaction liquid for each reaction liquid segment. This turbulent flow efficiently stirs the reaction liquid within the reaction liquid segments, and therefore a stirring effect can be obtained even near the inner wall of the reaction tube, where the flow rate of the reaction liquid can be nearly zero without the introduction of inert gas, and this can suppress the retention, precipitation, and / or adhesion of metal nanoparticles to the inner wall of the reaction tube.

[0050] In step (ii), a pressure P is applied to the reaction liquid. By applying the pressure P, the flow rate can be easily adjusted. In one embodiment, the pressure P is usually 0.1 MPa to 1.0 MPa, and in another embodiment, 0.1 MPa to 0.5 MPa. The pressure P is the pressure measured at the outlet of the reaction liquid after microwave irradiation.

[0051] In step (ii), microwaves are generated from a microwave irradiation source (microwave oscillator (magnetron)), and the microwave irradiation source can be either a single-mode system or a multi-mode system.

[0052] The microwave output is usually 100 W to 2000 W. The microwave wavelength is usually 0.915 to 2.45 GHz, for example, 0.915 GHz or 2.45 GHz.

[0053] The incident microwave power is usually 200W to 1800W, and the average incident microwave power is usually 200W to 1700W.

[0054] The reflected microwave power is usually 50W to 1300W, and the average reflected microwave power is usually 100W to 900W.

[0055] The microwave absorption power (E) of the reaction solution is usually 20 W / mL or more and usually 500 W / mL or less, for example, 20 W / mL to 500 W / mL, relative to the volume of the reaction solution.

[0056] Here, the microwave absorption power E of the reaction solution is calculated by dividing the microwave intensity (W) absorbed by the reaction solution, i.e., the value obtained by subtracting the reflected power irradiated and reflected from the reaction solution from the output of the microwave irradiation source (output - reflected power), by the volume (mL) of the reaction solution irradiated with that output. The reflected power can be measured using a power monitor in the microwave irradiation device.

[0057] In the present invention, by adjusting the pressure and the output of the microwave irradiation source, etc., within the above ranges, the formation of metal nanoparticle nuclei and their growth occur simultaneously and uniformly due to the sufficient reduction properties of the microwaves, and metal nanoparticles with a low organic content and small particle size can be formed.

[0058] The microwaves are preferably uniform during irradiation, and the microwave irradiation conditions are preferably constant during microwave irradiation.

[0059] The method of flowing the reaction solution is not limited as long as the reaction solution flows in any direction. For example, the reaction solution can be flowed at a constant speed in a reaction tube, such as a straight tube or a spiral tube.

[0060] While the reaction solution is being irradiated with microwaves, the reaction solution being irradiated with microwaves is stirred with an inert gas.

[0061] By stirring the reaction solution during the reaction, the uniformity of the reaction solution can be maintained in response to non-uniformity of the reaction solution due to local changes in the concentration and viscosity of the reaction solution that may occur during the reaction, segregation of metal nanoparticles can be suppressed, and segregated metal nanoparticles can be re-dissolved.

[0062] Other microwave conditions in the method of the present invention are not limited. In the method of the present invention, as described above, a reaction solution is irradiated with microwaves using a microwave synthesis device while flowing, and the reaction proceeds. When the reaction solution is irradiated with microwaves, the polar solvent contained in the reaction solution absorbs the microwaves and converts them into thermal energy, thereby generating heat. Therefore, in the reaction solution irradiated with microwaves, a uniform and rapid temperature rise occurs in the irradiated portion, and a uniform and rapid reaction occurs in accordance with this temperature rise.

[0063] It is preferable that the microwaves be uniformly irradiated onto the target of reaction, that is, the part of the reaction solution where the reaction occurs.

[0064] In the production method of the present invention, the material of the portion not irradiated with microwaves may be, in addition to the above-mentioned materials, metals such as aluminum, stainless steel, etc. Furthermore, the housing for accommodating the microwave irradiation source and the reaction tube irradiated with microwaves is not limited as long as it is a material that does not leak or absorb microwaves, and examples thereof include non-magnetic metal plates such as aluminum plates.

[0065] In the present invention, the temperature of the reaction solution elevated by microwave irradiation is the reaction temperature. This reaction temperature can be appropriately varied depending on the reaction conditions (e.g., the type of solvent, the pressure during the reaction, etc.). It is not limited, but is usually 25°C or higher, and in one embodiment, 80°C or higher. The upper limit of the reaction temperature is not limited, but is usually lower than the boiling point of the solvent. For example, when the solvent is water, the reaction temperature is usually in the range of 25°C or higher but lower than 100°C, and in one embodiment, 80°C to 90°C, at atmospheric pressure. Since pressure is applied to the reaction solution in the present invention, the reaction temperature can be higher than the boiling point of the solvent under atmospheric pressure. The boiling point of the solvent under the applied pressure may vary depending on the pressure. Therefore, in one embodiment, the reaction temperature is higher than the boiling point of the solvent under atmospheric pressure and lower than the boiling point of the solvent under the applied pressure. When the reaction tube is made of a resin, the upper limit of the reaction temperature is lower than the glass transition temperature of the resin. According to the study by the present inventors, it was found that when the reaction solution is heated to the glass transition temperature of the resin or higher, the reaction tube is softened, and metal nanoparticles are likely to adhere to the reaction tube. Therefore, the upper limit of the reaction temperature is usually the glass transition temperature (Tg) of the resin - 5°C or less, and in one embodiment, Tg - 10°C or less.

[0066] By setting the reaction temperature at 25°C or higher, a reduction reaction from metal ions to metal nanoparticles occurs, and by setting the reaction temperature below the boiling point of the solvent, it is possible to prevent the particle size of the resulting metal nanoparticles from becoming uneven due to the non-uniformity of the reaction field that can occur when the reaction solution boils, i.e., to prevent the broadening of the particle size distribution, and it is possible to prepare metal nanoparticles with small and uniform particle sizes.

[0067] The irradiation time of microwaves to the reaction solution is the time required for the temperature of the reaction solution to reach the reaction temperature, and is not limited and may be appropriately changed depending on the reaction conditions (microwave conditions, type of metal, type of solvent, pressure during the reaction, amount of reaction solution, reaction temperature, etc.).

[0068] The reaction solution is irradiated with microwaves under the above conditions to raise the temperature of the reaction solution to the reaction temperature, thereby generating nuclei of metal nanoparticles in the reaction solution.

[0069] In the method of the present invention, the reaction solution is circulated, and microwave irradiation of the reaction solution is generally continued until the reaction is completed.

[0070] In the method of the present invention, the reaction can be carried out at a high temperature by applying pressure to the reaction solution. Therefore, the total reaction time required for the reaction can be significantly shortened compared to when pressure is not applied. In one embodiment, the ratio of the reaction time in the method of the present invention to the reaction time in a method without applying pressure (reaction time under applied pressure / reaction time under atmospheric pressure) is typically 1.1 or more, in one embodiment 2.0 or more and typically 10 or less, in one embodiment 6.0 or less, for example 1.5 to 8.0, for example 5.0. Therefore, by producing metal nanoparticles using the method of the present invention, a significant time reduction is possible.

[0071] The completion of the reaction can be determined by observing that the absorbance or the like derived from the metal nanoparticle precursor or metal nanoparticles in the reaction solution no longer changes. For example, when a silver nanoparticle precursor is used as the metal nanoparticle precursor, the change in the absorbance of the reaction solution at 280 nm to 780 nm is observed, and the time when the absorbance no longer changes is regarded as the time when the reaction is completed.

[0072] In the method of the present invention, after the reaction is completed, the irradiation of the reaction solution with microwaves may be stopped, and the reaction solution may be kept warm using a heat-retaining device such as a heater or a cooler.

[0073] The temperature at which the reaction solution is kept warm by the warming device is not limited, but is usually the reaction temperature or lower. The lower limit of the temperature is not limited, but is usually 25°C or higher, and in one embodiment, 80°C or higher. For example, when the solvent is water, the temperature at which the reaction solution is kept warm is usually in the range of 25°C or higher to lower than 100°C, and in one embodiment, 80°C to 90°C, at atmospheric pressure.

[0074] Even if the temperature of the reaction liquid falls below the desired temperature upon switching from microwave irradiation to the heat-retaining device, the temperature can be adjusted to an appropriate temperature by the heat-retaining device.

[0075] The heat-retaining device used to keep the reaction solution warm is not limited as long as it can maintain the temperature of the reaction solution at the warming temperature, and any conventional heat-retaining device can be used. Examples of the heat-retaining device include heaters such as mantle heaters, immersion heaters, water baths, oil baths, and coolers.

[0076] The time for keeping the reaction solution warm in the warming device is not limited, but is usually 1 minute or more and usually 15 minutes or less.

[0077] By keeping the reaction solution warm using a heat retaining device, the growth of nuclei of the metal nanoparticles produced in the reaction solution can be promoted, and the metal nanoparticles can be made more uniform (aged).

[0078] Table 1 summarizes the synthesis conditions other than the introduction of the inert gas in one embodiment of the present invention. [Table 1]

[0079] The dispersion containing metal nanoparticles obtained by the present invention can be subjected to separation and purification (e.g., salting out or centrifugation) by methods known in the art, as needed, to obtain the desired metal nanoparticles or a dispersion containing metal nanoparticles. The metal nanoparticles in the dispersion can be used as low-temperature sintered metal nanoparticles for printed electronics.

[0080] The present invention also relates to an apparatus for producing metal nanoparticles for efficiently carrying out the method of the present invention.

[0081] A manufacturing apparatus 1 for producing metal nanoparticles will be described below with reference to FIGS. 2 and 3. As shown in FIG. 2, the manufacturing apparatus 1 is a manufacturing apparatus for producing metal nanoparticles by irradiating a reaction solution L with microwaves M. The method for producing metal nanoparticles of the present invention can be easily implemented by using the metal nanoparticle manufacturing apparatus of the present invention. Note that FIG. 2 illustrates an embodiment in which two liquids, liquid A and liquid B, are prepared and supplied to the reaction system so as to form a homogeneous reaction solution when supplied to the reaction tube. However, a reaction solution containing all materials may be prepared in advance. In this case, only one storage tank and one pump are required, and the reaction solution is stored in the storage tank. Furthermore, although FIG. 2 illustrates an irradiation device (microwave irradiation device) 42 that irradiates microwaves M as a heating device for the reaction solution, another heating device, such as a heater, may be used as the irradiation device 42.

[0082] The production apparatus 1 includes a storage tank 10 that stores liquid A L0, a pump 20 that sucks liquid A L0 from the storage tank 10 and pumps it out, a storage tank 11 that stores liquid B L1, and a pump 21 that sucks liquid B L1 from the storage tank 11 and pumps it out. Liquid A L0 sucked from the storage tank 10 and liquid B L1 sucked from the storage tank 11 join together, and the resulting reaction liquid L, a mixture of the two liquids, flows through a path 5 to a reactor 40. A slurry-like suspension containing metal nanoparticles, generated by the reaction liquid L passing through the reactor 40, flows continuously from the reactor 40 to a pressure regulator 60, and this slurry also flows through the path 5. For convenience, in the present invention, all fluids flowing through the path 5 are referred to as the reaction liquid L (before and after the reaction). The average inner diameters of the pipes that form the path 5 are typically the same.

[0083] The production apparatus 1 includes a stirrer 30, a reaction device 40, and a gas introduction device 80 and a check valve 90 between the stirrer 30 and the reaction device 40. The reaction device 40 includes a housing 41 that houses a reaction tube 43 through which a reaction liquid L flows via the stirrer 30, and an irradiation device (microwave irradiation device) 42 that irradiates the reaction tube 43 in the housing 41 with microwaves M.

[0084] As a result, the reaction liquid L flowing through the reaction tube 43, obtained by joining the liquid A L0 pressure-fed from the pump 20 and the liquid B L1 pressure-fed from the pump 21, can be introduced with an inert gas by the gas introduction device 80 and the check valve 90, and then irradiated with microwaves M together with the reaction tube 43 using the irradiation device 42. The material of the reaction tube 43 may be the same as the material of the container containing the reaction liquid described in the method of the present invention. The piping other than the path 5 forming the reaction tube 43 may also be composed of these piping. Alternatively, the piping other than the path 5 forming the reaction tube 43 may be composed of metal, such as stainless steel or aluminum, since it is not irradiated with microwaves M. The reaction tube 43 may be a straight pipe, or may be a spiral pipe, for example. This can improve the irradiation efficiency of microwaves M compared to a straight pipe. Furthermore, as described above, the gas introduction device 80 and the check valve 90 have a flow rate adjusting device for adjusting the flow rate of the inert gas to 5×r (mL / min) or more with respect to the average inner diameter 2r (mm) of the reaction tube irradiated with microwaves, and to 0.1v (mL / min) to 3.0v (mL / min) with respect to the flow rate v (mL / min) of the reaction solution. Note that the average inner diameter of the pipe in which the gas introduction device 80 and the check valve 90 are installed is usually the same as the average inner diameter of the reaction tube.

[0085] In one embodiment, when the reaction tube 43 is a straight tube, the size and shape are not limited as long as the microwave M is uniformly applied to the entire reaction tube 43. For example, the inner diameter of the tube is as described above. The size and shape of the reaction apparatus 40 are also not limited.

[0086] The production apparatus 1 is equipped with a heat retention device 50 and a pressure adjustment device 60, in that order, downstream of the reaction device 40. The heat retention device 50 is an optional device and does not necessarily have to be installed. Since the post-reaction reaction liquid L (specifically, a slurry-like suspension containing metal nanoparticles) flowing through the path 5 is heated in the reaction device 40, the heat retention device 50 is a device that maintains the reaction liquid L at the heat retention temperature in the method of the present invention described above, i.e., at a predetermined temperature between the reaction temperature and the reaction temperature which is lower than the reaction temperature. Specifically, the reaction liquid L flowing through the path 5 is heated or cooled using the heat retention device, and the reaction liquid L maintained at the predetermined temperature is released to the pressure adjustment device 60. In addition to the heater described above, a cooler can also be used as the heat retention device 50.

[0087] The pressure regulator 60 is located downstream of the reaction apparatus (reaction tube 43) 40 and regulates the pressure of the reaction liquid L in the reaction tube 43, in one embodiment, the pressure of the reaction liquid L in a path 5 extending from the pumps 20 and 21 to the pressure regulator 60. Specifically, the pressure regulator 60 regulates the pressure of the reaction liquid L in the path 5 by throttling down the discharge rate of the reaction liquid L passing through it. This allows the pressure of the reaction liquid L in the reaction tube 43 to be increased to atmospheric pressure or higher without exceeding the discharge pressure of the pumps 20 and 21. The reaction liquid L pumped by the pressure regulator 60 is recovered in a recovery tank 70. The inert gas that has circulated to the recovery tank 70 can be reused by returning it to the gas introducing device 80.

[0088] In this way, the liquid A L0 pumped by the pump 20 and the liquid B L1 pumped by the pump 21 join together and are pumped into the reaction tube 43 as the reaction liquid L. The pressure of the pumped reaction liquid L is adjusted by the pressure adjusting device 60 while the reaction liquid L is pressurized. By irradiating the pressurized reaction liquid L with microwaves M using the irradiation device 42, the boiling point of the reaction liquid L can be raised compared to that under atmospheric pressure, and therefore the rate of production of metal nanoparticles can be increased.

[0089] Incidentally, when metal nanoparticles are generated in the reaction liquid L, the concentration and viscosity of the reaction liquid L may change locally, causing the reaction liquid L to pulsate slightly. This may impair the uniformity of microwave irradiation of the reaction liquid L, and may cause the metal nanoparticles in the reaction liquid L to segregate. For this reason, the production apparatus 1 is provided with an agitator 30 between the pumps 20 and 21 and the reaction tube 43 of the reaction device 40, which agitates the reaction liquid L pumped from the pumps 20 and 21.

[0090] There are no particular limitations on the device configuration, structure, or location of the agitator 30, as long as it can suppress segregation of metal nanoparticles in the reaction solution L. In the present invention, the agitator 30 has, as an example, a structure equivalent to that of the static mixer shown in FIG.

[0091] The stirring device 30 has a straight pipe 31 through which the reaction liquid L flows, and a twisted blade 32 fixed within the pipe 31 and twisted around the axis CL of the pipe 31. With the twisted blade 32 disposed in the pipe 31, a flow path 33 (path 5) through which the reaction liquid L flows is formed within the pipe 31.

[0092] The twist vane 32 may be twisted spirally around the same axis CL, but in the present invention, it has the following structure: Specifically, the twist vane 32 is a vane in which twist vane elements 32a and 32b, which have different twist directions around the axis, are alternately arranged along the axial direction of the pipe 31.

[0093] Specifically, the twist blade element 32a and the twist blade element 32b have a shape obtained by twisting a flat plate material. The twist blade element 32a is twisted in the opposite twist direction to the twist direction of the twist blade element 32a. Such twist blade elements 32a and twist blade elements 32b are alternately connected along the axial direction of the piping 31.

[0094] As a result, a stable agitated flow is easily generated in the reaction solution L that has passed through the twisted blade 32 along the axial direction of the pipe 31, which makes it easy to reduce segregation of metal nanoparticles in the reaction tube 43 and further makes it easy to re-dissolve the segregated metal nanoparticles. In particular, it is preferable that the twisted blade is a blade in which twisted blade elements 32a, 32b having different twist directions around the axis are alternately arranged along the axial direction of the pipe 31. As a result, flows of the reaction solutions La, Lb that are agitated in different directions are formed and a stirring flow is easily formed around the axis, which makes it easy to further reduce segregation of metal nanoparticles in the reaction tube 43 and further makes it easy to re-dissolve the segregated metal nanoparticles.

[0095] The material of the twisted blade 32 is not limited. When the twisted blade 32 is placed immediately before the reaction apparatus 40, it is made of a non-conductive material that does not absorb or reflect microwaves. For example, the materials exemplified for the reaction tube 43 are preferred, and examples of such materials include ceramic materials made of silicon oxide such as glass and quartz, and resin materials such as PTFE. It is also preferred that the piping 31 is made of a similar material. By using a non-conductive material for the twisted blade 32 in this way, it is possible to prevent microwaves M from reaching the twisted blade from the reaction tube 43 via the reaction liquid L. This allows microwaves M to be efficiently irradiated onto the reaction liquid in the reaction tube 43.

[0096] Incidentally, the agitator 30 is preferably disposed at a position closer to the reactor 40 in the path 5 between the pump 20 and the pump 21 and the reactor 40. More specifically, the agitator 30 is preferably disposed at a position where the agitated flow of the reaction liquid L that has passed through the agitator 30 is maintained in the reaction tube 43. For example, the agitator 30 may be disposed near the inlet into which the reaction liquid L flows into the reactor 40, and is not particularly limited to this position as long as the agitated flow is maintained.

[0097] In this way, the agitated flow of the reaction liquid L that has passed through the agitator 30 is maintained in the reaction tube 43, so that it is possible to prevent local changes in the concentration and viscosity of the reaction liquid L during the production of metal nanoparticles. This prevents the reaction liquid L from becoming non-uniform in the reaction tube 43, prevents the metal nanoparticles in the reaction liquid L from segregating, and further allows the segregated metal nanoparticles to be redissolved.

[0098] Therefore, the metal nanoparticle manufacturing apparatus 1 of the present invention can efficiently carry out the metal nanoparticle manufacturing method of the present invention without causing changes in the physical properties such as the volume and viscosity of the reaction liquid L before and after pressure application, or a decrease in the absorption rate (uniformity) of the irradiated microwaves due to such changes in physical properties, and further, can prevent segregation of the metal nanoparticles and re-dissolve segregated metal nanoparticles. [Example]

[0099] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to those shown in these examples.

[0100] 1. Synthesis of Metal Nanoparticles Silver nanoparticles were produced using the production apparatus 1 for producing metal nanoparticles shown in Figures 2 and 3 and the following solutions A and B, according to the conditions shown in Tables 1 and 2. Resin piping was used for the piping including the reaction tube. Solution A: 76 g of silver nitrate was added to 1000 mL of water and dissolved by stirring. Solution B: 200 g of PVP and 113 mL of 3 mol / L 2-amino-1-butanol were dissolved in DMF to prepare a 1500 mL solution, which was then further dissolved by stirring.

[0101] [Table 2]

[0102] [Table 3]

[0103] The recovery rate is calculated using the following formula: 100 - 100 x (weight of Ag attached to the pipe / weight of Ag reacted) (%) (In the formula, the weight of Ag adhering to the piping is determined by running nitric acid through the piping after synthesis, eluting the Ag, and measuring the ICP amount, and the weight of reacted Ag is determined from the yield.) It was calculated by:

[0104] From Table 3, the following was found. First, in the example, the recovery rate was 98%, and no adhesion to the piping was observed. On the other hand, as shown in Comparative Example 1, it was found that if an inert gas was not introduced, silver nanoparticles would adhere to the inner wall of the reaction tube, reducing the recovery rate. Furthermore, as shown in Comparative Examples 2 and 3, it was found that when the flow rate of the inert gas was high, the maximum amount of microwave absorption by the reaction liquid fluid decreased, making it impossible to generate and grow nanoparticles sufficiently, resulting in a reduced recovery rate.

[0105] Furthermore, as shown in Comparative Example 4, when the flow rate of the inert gas is slow relative to the average inner diameter of the pipe, 2r, it was found that silver nanoparticles adhere near the inner wall of the reaction tube, resulting in a decrease in recovery rate.

Claims

1. a pump for pressure-feeding the reaction solution; a heating device that heats the reaction liquid that is pressure-fed from the pump and flows through the reaction tube together with the reaction tube; a pressure adjusting device downstream of the reaction tube that adjusts the pressure of the reaction solution in the reaction tube; a stirring device that is disposed between the pump and the reaction tube and stirs the reaction liquid pressure-fed from the pump; a gas introducing device disposed between the stirring device and the reaction tube, which introduces an inert gas into the reaction liquid stirred by the stirring device; An apparatus for producing metal nanoparticles, comprising:

2. 2. The apparatus for producing metal nanoparticles according to claim 1, wherein the gas introduction device has a flow rate control device for adjusting the flow rate of the inert gas to 5 × r (mL / min) or more with respect to an average inner diameter of the reaction tube, 2r (mm), and to 0.1 v (mL / min) to 3.0 v (mL / min) with respect to a flow rate v (mL / min) of the reaction solution.

3. 3. The apparatus for producing metal nanoparticles according to claim 2, wherein the average inner diameter 2r is 2 mm to 10 mm.

4. 4. The apparatus for producing metal nanoparticles according to claim 1, wherein the heating device is a microwave irradiation device.

5. A method for producing metal nanoparticles, comprising a step of irradiating a reaction solution with microwaves, (i) preparing a reaction liquid containing a metal nanoparticle precursor, an organic substance as a dispersant, and a solvent; (ii) irradiating the reaction solution with microwaves while flowing the reaction solution through a reaction tube, an inert gas is introduced into the reaction solution before the microwave irradiation; a flow rate of the inert gas is 5×r (mL / min) or more where 2r (mm) is the average inner diameter of the reaction tube, and is 0.1v (mL / min) to 3.0v (mL / min) where v (mL / min) is the flow rate of the reaction solution; applying pressure to the reaction solution when irradiating the reaction solution with microwaves; The method comprising:

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