Metal particles, method for producing metal particles, device for producing metal particles, and dispersion containing metal particles

Abstract

Provided are a method for efficiently producing metal particles, metal particles obtained by the production method, a production device for implementing the production method, and a dispersion containing metal particles obtained by the production method. The present invention relates to a method for producing metal particles, the method comprising a step for irradiating a reaction liquid with microwaves, the method comprising (i) a step for preparing a reaction liquid containing a metal particle precursor substance, an organic substance, and a solvent, and (ii) a step for irradiating the reaction liquid with microwaves while flowing the reaction liquid, and the relationship between the microwave absorption power E (unit: W / mL) and the pressure P (unit: MPa) with respect to the reaction liquid satisfies the following formula 1: E * P > = 20 (formula 1).

Description

Technical Field

[0001] This invention relates to metal particles, a method for manufacturing metal particles, an apparatus for manufacturing metal particles, and a dispersion containing metal particles. Background Technology

[0002] Metal nanoparticles, which sometimes have properties different from bulk materials, are being used and researched in various applications such as catalysts, ink materials, and electronic component components.

[0003] For example, Patent Document 1 discloses a method in which a raw material solution containing 50 mL of 1-decyl alcohol as a solvent and 5 mmol of carbonyl chromium powder as a raw material for chromium nanoparticles is irradiated with an ultrasonic wave at a frequency of 50 kHz and 150 W at 40 °C to thermally decompose the chromium nanoparticle raw material, thereby producing chromium nanoparticles with an average particle size of 5.6 nm.

[0004] Patent document 2 discloses a method for manufacturing metal microparticles, in which a reaction liquid containing a metal precursor substance is circulated in a flow tube, and electromagnetic waves are irradiated into the flow tube uniformly and concentratedly along the length of the flow tube, thereby uniformly heating the electromagnetic wave irradiation space in the flow tube along the flow direction to generate metal microparticles.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2015-129327

[0008] Patent Document 2: Japanese Patent Application Publication No. 2011-137226 Summary of the Invention

[0009] To use metal nanoparticles in the field of electronic assembly, it is desirable to reduce the particle size of the metal nanoparticles.

[0010] However, in order to manufacture metal nanoparticles with an average particle size in the nanometer range by irradiation with microwaves, high microwave intensity and high synthesis temperature are required to suppress nucleation deviations and grain growth.

[0011] Therefore, the objective of this invention is to provide a method for efficiently manufacturing metal particles, metal particles obtained by the manufacturing method, a manufacturing apparatus for carrying out the manufacturing method, and a dispersion containing the metal particles obtained by the manufacturing method.

[0012] The inventors conducted various studies on methods for solving the above-mentioned problems and found that in the method of producing metal particles by irradiating the reaction liquid with microwaves, by setting the microwave absorption power and the pressure applied to the reaction liquid to a certain level, the reaction time can be shortened, thereby producing metal particles with small particle size and low content of organic matter that may become impurities as a dispersant. The resulting metal particles have a low volume shrinkage rate, thus completing the present invention.

[0013] That is, the main idea of ​​this invention is as follows.

[0014] (1) A method for manufacturing metal particles, including the step of irradiating a reaction solution with microwaves, comprising:

[0015] (i) The step of preparing a reaction solution comprising a metal particle precursor, an organic compound as a dispersant, and a solvent.

[0016] (ii) The step of irradiating the above reaction solution with microwaves while the above reaction solution is flowing, and the relationship between the microwave absorption power E (unit: W / mL) and the pressure P (unit: MPa) of the above reaction solution satisfies the following Equation 1.

[0017] E×P≥20 (Equation 1).

[0018] (2) According to the method of (1), wherein, in step (i), the content of the organic matter in the reaction solution is 0.1% to 2% by weight relative to the total weight of the metal as the precursor of the metal particles.

[0019] (3) According to the method described in (1) or (2), wherein, in step (ii), the relationship between the microwave absorption power E (in W / mL) and the pressure P (in MPa) of the above reaction solution satisfies the following equation 2.

[0020] E×P≥30 (Equation 2).

[0021] (4) A type of metal particle, which is a metal particle containing organic matter.

[0022] The content of the organic matter relative to the total weight of the aforementioned metal particles is 0.1% to 2% by weight.

[0023] The median particle size (D50) measured by TEM was less than 20 nm.

[0024] (5) A metal particle dispersion comprising metal particles, an organic compound serving as a dispersant for the metal particles, and a solvent.

[0025] The content of the metal particles is 1% to 95% by weight relative to the total weight of the aforementioned metal particle dispersion.

[0026] The content of the organic matter relative to the total weight of the aforementioned metal particles is 0.1% to 2% by weight.

[0027] The median particle size (D50) of the aforementioned metal particles, as measured by TEM, is less than 20 nm.

[0028] (6) A manufacturing apparatus for metal nanoparticles, wherein the metal particles are generated by irradiating a reaction solution with microwaves, the manufacturing apparatus comprising:

[0029] The pump delivers the above reaction solution under pressure.

[0030] The irradiation device irradiates the reaction liquid, which is pumped by the aforementioned pump and flows within the reaction tube, along with the reaction tube itself, with the aforementioned microwaves.

[0031] A pressure regulating device adjusts the pressure of the reaction liquid within the reaction tube downstream of the reaction tube, and

[0032] A stirring device is used to stir the reaction liquid pumped by the pump between the pump and the reaction tube.

[0033] (7) The metal nanoparticle manufacturing apparatus according to (6), wherein the stirring device is configured in a position such that the stirring flow of the reaction liquid through the stirring device is continuous in the reaction tube between the pump and the reaction tube.

[0034] (8) The apparatus for manufacturing metal nanoparticles according to (6) or (7), wherein the stirring device has a straight pipe for the flow of the reaction liquid and a twisted blade fixed in the pipe and twisted about the axis of the pipe.

[0035] (9) The metal nanoparticle manufacturing apparatus according to (8), wherein the twisted blade is a blade in which twisted blade elements with different twisting directions around the axis are alternately arranged along the axial direction of the piping.

[0036] (10) The apparatus for manufacturing metal nanoparticles according to (8) or (9), wherein the twisted blade is made of a non-conductive material.

[0037] According to the present invention, a method for efficiently manufacturing metal particles is provided, metal particles obtained by the manufacturing method, a manufacturing apparatus for carrying out the manufacturing method, and a dispersion containing metal particles obtained by the manufacturing method are provided. Attached Figure Description

[0038] Figure 1This is a schematic diagram illustrating one embodiment of the manufacturing apparatus of the present invention.

[0039] Figure 2 This is a schematic diagram illustrating one embodiment of the stirring device in the manufacturing apparatus of the present invention.

[0040] Figure 3 These are TEM images of silver particles from Comparative Example 1 and Examples 1 and 4.

[0041] Figure 4 This is a graph showing the particle size distribution of the silver particles in Example 1.

[0042] Figure 5 It is a graph showing the relationship between the microwave absorption power E (W / mL) of the reaction solution and the pressure P (MPa) applied to the reaction solution (E×P) and D50.

[0043] Figure 6 This is a graph showing the relationship between the amount of organic matter and D50 in the examples and comparative examples.

[0044] Figure 7 It is a graph showing the relationship between the amount of organic matter and the volume shrinkage rate at 120°C for 2 hours.

[0045] Figure 8 It is a schematic diagram illustrating the formation of the nucleus of a metal particle (silver particle as an example) to the growth of the particle when the prior art or E×P is less than 20.

[0046] Figure 9 This is a schematic diagram illustrating the formation of the nucleus of a metal particle (silver particle as an example) and the growth of the particle when E×P is 20 or more in this invention. Detailed Implementation

[0047] The preferred embodiments of the present invention will now be described in detail.

[0048] In this specification, the features of the invention are described with appropriate reference to the accompanying drawings. In the drawings, the dimensions and shapes of the parts are exaggerated for clarity and are not accurately depicted. Therefore, the scope of the invention is not limited to the dimensions and shapes of the parts shown in these drawings. It should be noted that the metal particles, the method for manufacturing the metal particles, the apparatus for manufacturing the metal particles, and the dispersion containing the metal particles of the present invention are not limited to the embodiments described below, and can be implemented in various forms with modifications and improvements that can be made by those skilled in the art without departing from the spirit of the invention. Furthermore, although the embodiments described in this specification are independent, two or more embodiments can be combined to form one embodiment of the present invention.

[0049] The use of “~” in this specification refers to a range of values, with the values ​​preceding and following it serving as lower and upper limits. Within the numerical ranges described in stages in this specification, the upper or lower limit of one range can be replaced by the upper or lower limit of another range described in stages. The upper or lower limit of the numerical ranges described in this specification can be replaced by the values ​​shown in the embodiments.

[0050] The present invention relates to a method for manufacturing metal particles, including a step of irradiating a reaction solution with microwaves, comprising (i) a step of preparing a reaction solution containing a metal particle precursor, an organic compound and a solvent, and (ii) a step of irradiating the reaction solution with microwaves while allowing it to flow.

[0051] (i) The step of preparing a reaction solution containing a metal particle precursor, an organic compound, and a solvent.

[0052] In step (i), a reaction solution containing a metal particle precursor, an organic compound, and a solvent is prepared.

[0053] In the method of this invention, the solvent used in the reaction solution is not limited as long as it is a polar solvent or ionic liquid capable of dissolving the metal particle precursor, the organic matter used as a dispersant, and the reducing agent, and further absorbing microwaves. Examples of solvents used in the reaction solution include low-boiling-point solvents with a boiling point below 300°C. There are no limitations on low-boiling-point solvents; examples include water, methanol, ethanol, polyol solvents such as ethylene glycol, ketone solvents such as acetone, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), other organic solvents, or mixtures of two or more of these. It should be noted that when using a mixture as a solvent, the ratio of each component in the mixture is not limited, as long as the ratio of each component is mixed under experimental conditions.

[0054] Using low-boiling-point polar solvents can improve the operability of the solvent and reduce the environmental impact.

[0055] There are no limitations on the metal particle precursor material as long as it dissolves in a solvent to generate metal ions, such as ions of noble metals, base metals, and alloys, such as ions of gold, silver, platinum, copper, nickel, iron, cobalt, or two or more of these metals. Examples of metal particle precursor materials include metal halides, such as fluorides, chlorides, bromides, iodides, metal sulfates, metal nitrates, metal phosphates, metal cyanides, and other inorganic salts of metals; metal carboxylates, metal sulfonates, and other organic salts of metals; and metal complexes containing metal complexes. Metal particle precursor materials can be prepared, for example, by dissolving materials containing metals or metal salts using acids such as nitric acid or bases such as ammonia. Inexpensive metal nitrates, such as nickel nitrate and silver nitrate, are preferred as metal particle precursor materials. Additionally, formates with reducing properties, such as nickel formate, can be used as metal particle precursor materials. Therefore, in one embodiment, when a salt consisting of metal ions and a reducing organic anion, such as formate ions, which are their counter anions, is used as a precursor material for metal particles, a reducing agent may not be required.

[0056] A homogeneous reaction solution can be prepared by dissolving the metal particle precursor in a solvent.

[0057] The concentration of metal ions in the reaction solution is not limited as long as it is below the saturation concentration. It is usually above 1 mmol / L (mM), above 10 mM in one embodiment, and usually below 600 mM, below 200 mM in one embodiment, for example, 1 mM to 600 mM, 10 mM to 200 mM in one embodiment, 20 mM to 180 mM in one embodiment, and 50 mM to 150 mM in one embodiment.

[0058] By maintaining the concentration of metal ions in the reaction solution within the aforementioned range, metal particles can be generated efficiently at high concentrations, significantly increasing the amount of metal particles that can be generated and recovered in a single step, while reducing the time, labor, and cost required for manufacturing the metal particles. Furthermore, the deviation of the obtained metal particles is reduced; in other words, the particle size distribution of the obtained metal particles is narrowed.

[0059] The reaction solution contains an organic compound as a dispersant. The dispersant is not limited, and examples include one or more dispersants selected from polyvinylpyrrolidone (PVP), dodecylamine (DDA), thiol polymers, polyvinyl alcohol (PVA), polyacrylic acid, polyacrylate, cyclodextrin, amino pectin, methylcellulose, polyethyleneimine cellulose, aliphatic amines, aliphatic carboxylic acids, and tannic acid. When the dispersant is a polymer, the molecular weight is not limited, but as a weight-average molecular weight (Mw), it is typically 1000 or more, in one embodiment 8000 or more, in another embodiment 10000 or more, and typically 50000 or less, in another embodiment 40000 or less, for example 1000 to 50000, in one embodiment 8000 to 50000, and in another embodiment 10000 to 40000. The amount of dispersant adsorbed onto the metal particles is not limited, but is typically 2% by weight or less relative to the total weight of the metal particles, and in one embodiment 1% by weight or less. The amount of dispersant is preferably small, so there is no lower limit. It is typically 0.1% by weight or more relative to the total weight of the metal particles, 0.2% by weight or more in one embodiment, 0.3% by weight or more in another embodiment, and 0.4% by weight or more in yet another embodiment.

[0060] Conventionally, in the manufacture of metal particles, the amount of organic matter required as a dispersant for particle size control during manufacturing is greater than the amount of organic matter required for dispersion. Furthermore, this organic matter cannot be removed and thus remains in the final metal nanoparticles. According to the method of the present invention, the amount of organic matter required for particle size control during manufacturing can be reduced, and metal particles with a reduced amount of organic matter, containing only the amount required for dispersion, can be manufactured.

[0061] Furthermore, the reaction solution may contain a reducing agent. A reducing agent is a material that can reduce metal ions to a metal with an oxidation number of 0 through a redox reaction.

[0062] The reducing agent is not limited. Examples of reducing agents include citric acid or citrate, such as trisodium citrate, disodium citrate, monosodium citrate, oxalic acid or oxalate, such as sodium oxalate, ascorbic acid or ascorbate, such as sodium ascorbate, formic acid or formate, such as sodium formate, DMF, and mixtures of two or more thereof. In one embodiment, DMF is used as the reducing agent for metal ions, particularly silver ions. Therefore, when DMF is used as the solvent of the reaction solution, since DMF can also function as a reducing agent, reducing agents other than DMF may not be used.

[0063] The amount of reducing agent is not limited as long as it is sufficient to reduce the metal ions to a metal with an oxidation state of 0 through a redox reaction. It is typically 1.0 equivalent or more relative to the metal ions, 4.0 equivalent or more in one embodiment, and typically 20 equivalents or less, 15 equivalents or less in one embodiment. For example, it is 1.0 to 20 equivalents, and 4.0 to 15 equivalents in one embodiment. It should be noted that when the reducing agent for the metal ions contains one or more functional groups such as carboxyl, hydroxyl, or ether groups that can interact with the metal, it can also function as a dispersant. When the reducing agent also functions as a dispersant, the dispersant described above may not be included in the reaction solution. Furthermore, the amount of reducing agent for the metal ions may exceed the amount required to reduce the metal ions to a metal with an oxidation state of 0 through a redox reaction.

[0064] The reaction solution may consist of the metal particle precursors described above, solvents, dispersants, and, depending on the circumstances, reducing agents. In addition to these materials, it may further contain additives commonly used in conventional methods for producing metal particles by microwave irradiation, such as chelating agents, ethylenediaminetetraacetic acid (EDTA), and / or its salts. The amount of additives is not limited, but is typically 10% by weight or less relative to the total weight of the reaction solution, and in one embodiment, 3% by weight or less. No additives may be added, therefore, there is no lower limit for the amount of additives.

[0065] The pH of the reaction solution is not limited, but is usually between pH 3 and pH 12.

[0066] In this invention, there are no limitations on the order of addition, temperature, mixing method, or mixing time of the materials in the preparation of the reaction solution; the materials are mixed to prepare a homogeneous reaction solution. In this invention, the reaction begins after the homogeneous reaction solution is prepared.

[0067] (ii) The step of irradiating the above reaction solution with microwaves while it is flowing.

[0068] In step (ii), the reaction solution prepared in step (i) is irradiated with microwaves while flowing.

[0069] In step (ii), the microwave absorption power E (in W / mL) and pressure P (in MPa) of the reaction solution are adjusted to satisfy the following relationship: Equation 1.

[0070] E×P≥20 (Equation 1).

[0071] In one embodiment, the microwave absorption power E (in W / mL) and pressure P (in MPa) of the reaction solution are adjusted to satisfy the following relationship: Equation 2.

[0072] E×P≥30 (Equation 2).

[0073] In one embodiment, the microwave absorption power E (in W / mL) and pressure P (in MPa) of the reaction solution are adjusted to satisfy the following relationship, Equation 3.

[0074] E×P≥35 (Equation 3).

[0075] Here, the microwave absorption power E of the reaction liquid is calculated by dividing the intensity (W) of the microwaves absorbed by the reaction liquid (i.e., the output minus the reflected power reflected from the reaction liquid) by the volume (mL) of the reaction liquid irradiated with that output. The pressure P is the pressure (MPa) applied to the reaction liquid, measured at the outlet of the reaction liquid after microwave irradiation. It should be noted that the reflected power can be measured using a power monitor in the microwave irradiation device.

[0076] In this invention, by adjusting the microwave absorption power E (unit: W / mL) and pressure P (unit: MPa) of the reaction solution in a manner that satisfies Equations 1 to 3, the formation of metal particle nuclei occurs simultaneously and uniformly, and the growth of the formed nuclei also occurs simultaneously and uniformly. As a result, metal particles with small particle sizes can be obtained.

[0077] There are no restrictions on the method of flow of the reaction liquid, as long as it flows in any direction. The reaction liquid can flow at a certain speed in, for example, a reaction tube, a straight tube, or a spiral tube.

[0078] In one embodiment, when the reaction tube is a straight tube, the size and shape are not limited as long as the irradiated microwaves uniformly irradiate the entire reaction tube. In one embodiment, the inner diameter of the tube is typically 1 mm or more, in another embodiment it is 2 mm or more, in another embodiment it is 4 mm or more, and typically 20 mm or less, in another embodiment it is 10 mm or less, for example 1 mm to 20 mm, in another embodiment it is 2 mm to 10 mm, and in another embodiment it is 4 mm to 10 mm. In one embodiment, when the cavity is a cuboid with a length of 100 mm, a reaction tube with an inner diameter of 1 mm to 6 mm, an outer diameter of 3 mm to 8 mm (wall thickness: 1 mm), and a length of 100 mm is used as the reaction tube.

[0079] There is no limitation on the pressure P of the reaction liquid as long as it satisfies the above equations 1 to 3. It is usually above 0.10 MPa and usually below 1.0 MPa, for example, 0.10 MPa to 1.0 MPa.

[0080] As long as the pressure P of the reaction liquid satisfies the above equations 1 to 3, there is no limit to the flow rate of the reaction liquid. It is usually above 1 m / min and usually below 100 m / min, for example, 1 m / min to 100 m / min.

[0081] By setting the flow rate of the reaction liquid within the aforementioned range, a specified pressure can be applied to the reaction liquid, and the reaction liquid can be allowed to circulate, thus forming small metal particles even when the amount of organic matter used as a dispersant is small.

[0082] The microwave absorption power (E) of the reaction solution is not limited as long as it satisfies Equations 1 to 3 above. It is usually above 20 W / mL and usually below 500 W / mL relative to the volume of the reaction solution, for example, 20 W / mL to 500 W / mL.

[0083] By adjusting the output of the microwave irradiation source to the above range, the sufficient reducing power generated by the microwaves can form small metal particles with low organic content.

[0084] During the irradiation of the reaction solution with microwaves, the irradiated reaction solution is preferably stirred.

[0085] By stirring the reaction solution, the homogeneity of the reaction solution can be maintained, which is based on the localized changes in the concentration and viscosity of the reaction solution that may occur due to the reaction. This suppresses the segregation of metal particles and allows the segregated metal particles to be redissolved.

[0086] Other conditions for the microwaves used in the method of the present invention are not limited. In the method of the present invention, as described above, the reaction is carried out by irradiating microwaves with a microwave synthesis apparatus in a manner satisfying Formulas 1 to 3 above while the reaction solution is being irradiated with microwaves. When the reaction solution is irradiated with microwaves, the polar solvent contained in the reaction solution absorbs the microwaves and converts them into heat energy, thereby generating heat. Therefore, in the microwave-irradiated reaction solution, a uniform and rapid temperature rise occurs in the irradiated portion, and as this temperature rises, a uniform and rapid reaction occurs.

[0087] Microwaves are preferably used to uniformly irradiate the object in which the reaction occurs, i.e., the part in the reaction solution where the reaction takes place.

[0088] In microwave synthesis apparatuses, the material of the microwave-irradiated portion within the container holding the reaction liquid is not limited as long as it can uniformly irradiate the reaction liquid. In cases where microwaves are irradiated onto the reaction liquid from outside the reactor, the material of the microwave-irradiated portion can be a microwave-transmitting (i.e., non-absorbing) material, such as ceramics, glass, quartz, Teflon (registered trademark, PTFE, etc.), or silicone, which are non-conductive materials with low relative permittivity ε and dielectric loss angle tanδ. It should be noted that the material of the non-microwave-irradiated portion within the container holding the reaction liquid, in addition to the aforementioned materials, can be metals such as aluminum or stainless steel. Furthermore, the casing of the container housing the microwave irradiation source and the microwave-irradiating reaction tube is not limited as long as it is made of a leak-proof and non-absorbing material; examples include non-magnetic metal plates, such as aluminum plates.

[0089] Microwaves are generated from a microwave irradiation source (a microwave oscillator (magnetron)), which can be either a single-mode system or a multi-mode system.

[0090] The frequency of the microwaves generated from the microwave irradiation source can be appropriately varied and is not limited. The microwave frequency is typically above 1 GHz, above 2 GHz in one embodiment, and typically below 10 GHz, for example, 1 GHz to 10 GHz. In this invention, the frequency of an industrial microwave power supply, i.e., 2.45 GHz, is preferably used as the microwave frequency.

[0091] The microwaves are preferably uniform during the irradiation period, and the irradiation conditions described above are preferably constant during the irradiation period.

[0092] In this invention, the temperature of the reaction solution heated by microwave irradiation is the reaction temperature. This reaction temperature can be appropriately varied depending on the reaction conditions (type of solvent, reaction pressure, etc.) and is not limited, but is generally 25°C or higher, and in one embodiment, it is 80°C or higher. There is no upper limit to the reaction temperature, but it is generally lower than the boiling point of the solvent. For example, when the solvent is water, the reaction temperature is generally in the range of 25°C or higher and lower than 100°C under atmospheric pressure, and in one embodiment, it is 80°C to 90°C. It should be noted that in this invention, because pressure is applied to the reaction solution, 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 can 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.

[0093] By setting the reaction temperature above 25°C, a reduction reaction from metal ions to metal particles occurs. By setting the reaction temperature below the boiling point of the solvent, it is possible to prevent the particle size disorder of the metal particles generated, i.e., the expansion of the particle size distribution, which may be caused by the non-uniformity of the reaction field due to the boiling of the reaction liquid, and thus prepare metal particles with small and uniform particle size.

[0094] The irradiation time of the microwave onto the reaction liquid is the time taken until the temperature of the reaction liquid reaches the reaction temperature. It can be appropriately varied according to the reaction conditions (microwave conditions, type of metal, type of solvent, reaction pressure, amount of reaction liquid, reaction temperature, etc.), and there is no limit.

[0095] By irradiating the reaction solution with microwaves under the above conditions to raise the temperature of the reaction solution to the reaction temperature, metal particle nuclei are generated in the reaction solution.

[0096] In the method of the present invention, the reaction solution is circulated, and microwave irradiation of the reaction solution is usually continued until the reaction is complete.

[0097] In the method of the present invention, by applying pressure to the reaction liquid, the reaction can be carried out at a high temperature. Therefore, the total reaction time can be significantly reduced compared to the case without pressure. In one embodiment, the ratio of the reaction time in the method of the present invention to the reaction time in the method without pressure (reaction time under pressure / reaction time under atmospheric pressure) is generally 1.1 or more, in one embodiment 1.5 or more, in one embodiment 2.0 or more, and generally 10 or less, in one embodiment 8.0 or less, in one embodiment 6.0 or less, for example 1.1 to 10, in one embodiment 1.5 to 8.0, in one embodiment 2.0 to 6.0, for example 5.0. Therefore, by using the method of the present invention to produce metal particles, the time can be significantly reduced.

[0098] The completion of the reaction can be determined by observing whether the absorbance of the metal particle precursor material or the metal particles in the reaction solution stops changing. For example, when using silver particle precursor material as the metal particle precursor material, the change in absorbance of the reaction solution in the range of 280 nm to 780 nm is observed, and the time point at which the absorbance no longer changes is taken as the time point of reaction completion.

[0099] In the method of the present invention, after the reaction is completed, the microwave irradiation of the reaction liquid can be stopped, and the reaction liquid can be kept warm using a heat preservation device, such as a heater or a cooler.

[0100] The temperature at which the reaction liquid is kept warm using the heat-preserving device is not limited, but is generally below the reaction temperature. The lower limit of the heat-preserving temperature is not limited, but is generally above 25°C, and in one embodiment above 80°C. For example, when the solvent is water, the heat-preserving temperature is generally in the range of 25°C to 100°C under atmospheric pressure, and in one embodiment is 80°C to 90°C.

[0101] By switching from microwave irradiation of the reaction solution to a heat preservation device, even if the temperature of the reaction solution is lower than the target heat preservation temperature during the switching process, the heat preservation device can be used to adjust it to an appropriate heat preservation temperature.

[0102] There are no limitations on the heat preservation device used for keeping the reaction liquid warm, as long as it can maintain the temperature of the reaction liquid at the desired temperature; conventional heat preservation devices can be used. Examples of heat preservation devices include heaters, heating jackets, immersion heaters, water baths, oil baths, and coolers.

[0103] There is no limit to the heat preservation time of the reaction liquid using the heat preservation device, but it is usually more than 1 minute and usually less than 15 minutes.

[0104] By using a heat preservation device to keep the reaction solution warm, the growth of the nuclei of the metal particles in the generated reaction solution can be promoted, and the metal particles can be further homogenized (aged).

[0105] The dispersion containing the metal particles obtained by the present invention can be separated and purified (e.g., salting out, centrifugation) as needed by methods known in the art to obtain the target metal particles or a dispersion containing the metal particles.

[0106] The present invention also relates to an apparatus for manufacturing metal particles for efficiently carrying out the method of the present invention.

[0107] The following uses Figure 1 and 2 The manufacturing apparatus 1 for generating metal particles will be described. For example... Figure 1 As shown, manufacturing apparatus 1 is a manufacturing apparatus that generates metal particles by irradiating the reaction liquid L with microwave M.

[0108] The manufacturing apparatus 1 includes a receiving tank 10 for receiving the reaction liquid L and a pump 20 for drawing and pressurizing the reaction liquid L from the receiving tank 10. It should be noted that the reaction liquid L flows along path 5 from the receiving tank 10 to the reaction apparatus 40. A slurry-like suspension containing metal particles generated by passing the reaction liquid L through the reaction apparatus 40 flows continuously from the reaction apparatus 40 to the pressure regulating device 60, and this slurry also flows along path 5. In this embodiment, for convenience, all fluids flowing along path 5 will be referred to as (before and after the reaction) the reaction liquid L.

[0109] The manufacturing apparatus 1 includes a stirring device 30 and a reaction device 40, which will be described later. The reaction device 40 includes a housing 41 for housing a reaction tube 43 through which the reaction liquid L is flowed by the stirring device 30, and an irradiation device 42 for irradiating the reaction tube 43 inside the housing 41 with microwaves M.

[0110] Therefore, the irradiation device 42 can be used to irradiate the reaction liquid L, which is pumped by the pump 20 and flows in the reaction tube 43, together with the reaction tube 43, with microwave M. The material of the reaction tube 43 can be the same as the material of the container for holding the reaction liquid described in the method of the present invention, or it can be made of a ceramic material made of silicon oxide such as glass or quartz, or a resin material such as PTFE. The piping outside the path 5 forming the reaction tube 43 can also be made of these piping, or, since the piping outside the path 5 forming the reaction tube 43 is not irradiated with microwave M, it can be made of metal, such as stainless steel or aluminum. In addition, the reaction tube 43 can be a straight tube or, for example, a spiral-shaped pipe. Therefore, compared with a straight tube, the irradiation efficiency of microwave M can be improved.

[0111] In one embodiment, when the reaction tube 43 is a straight tube, its size and shape are not limited as long as the irradiated microwave M uniformly irradiates the entire reaction tube 43. For example, the inner diameter of the tube is usually 1 mm or more, in one embodiment it is 2 mm or more, in another embodiment it is 4 mm or more, and usually 20 mm or less, in another embodiment it is 10 mm or less, for example 1 mm to 20 mm, and in another embodiment it is 2 mm to 10 mm. For example, when the cavity is a cuboid with a length of 100 mm, the reaction tube 43 is preferably a reaction tube with an inner diameter of 1 mm to 6 mm, an outer diameter of 3 mm to 8 mm (wall thickness: 1 mm), and a length of 100 mm. It should be noted that the size and shape of the reaction device 40 are also not limited.

[0112] The manufacturing apparatus 1 includes a heat preservation device 50 and a pressure regulating device 60 sequentially downstream of the reaction apparatus 40. The heat preservation device 50 is optional and may not be included. The reaction liquid L (specifically, a slurry-like suspension containing metal particles) flowing in path 5 is heated in the reaction apparatus 40. Therefore, the heat preservation device 50 is a device that maintains the reaction liquid L at the heat preservation temperature in the method of the present invention, i.e., the reaction temperature, to a predetermined temperature below that reaction temperature. Specifically, the reaction liquid L flowing in path 5 is heated or cooled using the heat preservation device, and the reaction liquid L maintained at the predetermined temperature is discharged to the pressure regulating device 60. In addition to the heater described above, a cooler may also be used as the heat preservation device 50.

[0113] The pressure regulating device 60 adjusts the pressure of the reaction liquid L in the reaction tube 43 downstream of the reaction apparatus (reaction tube 43) 40, or in one embodiment, the pressure of the reaction liquid L in the path 5 from the pump 20 to the pressure regulating device 60. Specifically, the pressure regulating device 60 adjusts the pressure of the reaction liquid L in the path 5 by limiting the discharge rate of the reaction liquid L through it. Thus, the pressure of the reaction liquid L in the reaction tube 43 can be increased to above atmospheric pressure within a range not exceeding the discharge pressure of the pump 20. The reaction liquid L pressurized by the pressure regulating device 60 is recovered to the recovery tank 70.

[0114] Thus, the reaction liquid L sent by pump 20 is pressurized into the reaction tube 43. The pressure of the pressurized reaction liquid L is adjusted to a pressurized state by pressure adjusting device 60. By irradiating the pressurized reaction liquid L with microwave M by irradiation device 42, the boiling point of the reaction liquid L can be increased compared with atmospheric pressure, thereby increasing the generation rate of metal particles.

[0115] However, if metal particles are generated in the reaction solution L, the concentration and viscosity of the reaction solution L may sometimes change locally, and the reaction solution L may pulsate slightly. As a result, the uniformity of microwave irradiation of the reaction solution L may be impaired, and metal particles in the reaction solution L may segregate. From this perspective, the manufacturing apparatus 1 is equipped with a stirring device 30 between the pump 20 and the reaction tube 43 of the reaction apparatus 40 to stir the reaction solution L pumped by the pump 20.

[0116] As long as the segregation of metal particles in the reaction solution L can be suppressed, the configuration, structure, and placement of the stirring device 30 are not particularly limited. In this embodiment, an example of the stirring device 30 is a [device name missing]. Figure 2 It has the same structure as the static mixer shown.

[0117] The stirring device 30 has a straight pipe 31 for the flow of reaction liquid L and a twisted blade 32 fixed inside the pipe 31 and twisted around the axis CL of the pipe 31. With the twisted blade 32 arranged in the pipe 31, a flow path 33 (path 5) for the flow of reaction liquid L is formed inside the pipe 31.

[0118] The twisted blade 32 can be twisted spirally in the same direction around the axis CL, but in this embodiment, it has the structure shown below. Specifically, the twisted blade 32 is a blade in which twisted blade elements 32a and 32b with different twisting directions around the axis are alternately arranged along the axial direction of the pipe 31.

[0119] Specifically, the twisted blade elements 32a and 32b are the shapes of twisted flat plates. The twisted blade element 32a is twisted in the opposite direction to the twisting direction of the twisted blade element 32a. These twisted blade elements 32a and 32b are alternately connected along the axial direction of the piping 31.

[0120] Therefore, the reaction liquid L passing through the twisted blades 32 easily generates a stable stirred flow along the axial direction of the piping 31, thus easily reducing the segregation of metal particles in the reaction tube 43, and further facilitating the redissolution of the segregated metal particles. It is particularly preferable that the twisted blades are blades with alternating twisted blade elements 32a and 32b arranged along the axial direction of the piping 31, each with a different twisting direction around the axis. This creates flows of reaction liquids La and Lb that are stirred in different directions, and easily forms a stirred flow around the axis, thus further easily reducing the segregation of metal particles in the reaction tube 43, and further facilitating the redissolution of the segregated metal particles.

[0121] The material of the twisted blade 32 is not limited. When the twisted blade 32 is positioned immediately before the reaction apparatus 40, it is made of a non-conductive material that does not absorb or reflect microwaves. For example, the material exemplified in the reaction tube 43 is preferred; other examples include ceramic materials made of silicon dioxide such as glass or quartz, or resin materials such as PTFE. Furthermore, the piping 31 is also preferably made of the same material. Thus, by making the twisted blade 32 a non-conductive material, microwaves M can be prevented from reaching the twisted blade from the reaction tube 43 via the reaction liquid L. Therefore, microwaves M can be efficiently irradiated into the reaction liquid within the reaction tube 43.

[0122] However, the stirring device 30 is preferably positioned closer to the reaction device 40 in the path 5 between the pump 20 and the reaction device 40. More specifically, the stirring device 30 is preferably positioned where the stirring flow of the reaction liquid L passing through the stirring device 30 is continuous within the reaction tube 43. For example, it could be near the inlet where the reaction liquid L flows into the reaction device 40, but it is not particularly limited to this position as long as the stirring flow is continuous.

[0123] Thus, the stirring flow of the reaction liquid L through the stirring device 30 continues within the reaction tube 43, thereby suppressing local changes in the concentration and viscosity of the reaction liquid L during metal particle generation. Consequently, within the reaction tube 43, it is possible to prevent the reaction liquid L from becoming non-uniform, suppress the segregation of metal particles in the reaction liquid L, and further facilitate the redissolution of the segregated metal particles.

[0124] Therefore, by using the metal particle manufacturing apparatus 1 of the present invention, changes in the volume, viscosity, and other physical properties of the reaction liquid L before and after pressure application are not caused, nor is there a decrease in the absorption rate (uniformity) of the irradiated microwaves based on these changes in physical properties. Furthermore, segregation of metal particles can be prevented, and the segregated metal particles can be re-dissolved, thus efficiently implementing the metal particle manufacturing method of the present invention.

[0125] This invention also relates to metal particles containing organic matter, which can be obtained by the method or manufacturing apparatus of this invention, having a small particle size and a low content of organic matter. Here, "organic matter" refers to a non-volatile compound attached to the metal particles in order to uniformly disperse the metal particles in a solvent or solvent medium, and is distinguished from organic compounds used as solvents or solvents.

[0126] In one embodiment, the metal particles are metal nanoparticles. Here, "metal nanoparticles" refers to metal particles with a particle size typically ranging from 1 nm to 100 nm. Therefore, in the case where the metal particles of the present invention are metal nanoparticles, the metal particles of the present invention are metal particles comprising a main part and an auxiliary part, with a Heywood diameter of 1 nm to 100 nm.

[0127] In one embodiment, the metal particles are spherical. Here, when observing metal particles using a transmission electron microscope (TEM), "spherical" includes not only true spheres, but also approximately spherical, ellipsoidal, polygonal with approximately the same sides, etc.

[0128] The median particle size (D50) of the metal particles of the present invention, as measured by TEM, is 20 nm or less, and in one embodiment, it is 10 nm or less. This D50 is preferably small, therefore the lower limit is not limited, and it is typically 1.0 nm or more.

[0129] Here, the method for determining the D50 of metal particles using TEM is as follows.

[0130] First, TEM images of the metal particles are captured. Next, 500 arbitrary metal particles are selected from the TEM images. Then, for each selected metal particle, the diameter is measured when the projected surface area of ​​the metal particle is converted to the area of ​​a circle. These are then plotted as particle sizes, with particle size (nm) on the x-axis and cumulative number (%) on the y-axis. Finally, the particle size at which the cumulative number of particles reaches 50% can be calculated from this plot as D50.

[0131] In addition, the metal particles of the present invention have a narrow particle size distribution.

[0132] The organic matter, particularly the dispersant, contained in the metal particles (powder formed from the metal particles) of the present invention is 2% by weight or less relative to the total weight of the metal particles, 1% by weight or less in one embodiment, and 0.8% by weight or less in another embodiment. The content of this organic matter is preferably low, therefore the lower limit is not limited, but it is generally 0.1% by weight or more relative to the total weight of the metal particles, 0.2% by weight or more in one embodiment, 0.3% by weight or more in another embodiment, and 0.4% by weight or more in another embodiment.

[0133] Here, the method for determining the content of organic matter contained in metal particles is as follows.

[0134] First, purified water, such as ion-exchanged water, is added to the metal particles or a dispersion containing the metal particles. The mixture is then purified using a solid-liquid separator such as centrifuge until the conductivity of the slurry is below tens of μS / cm. Conductivity can be measured using a handheld universal separator. This step is performed to remove impurities and water-soluble byproducts that may be present in the metal particles or the dispersion containing them. It should be noted that organic matter adsorbed onto the metal particles from organic matter added during manufacturing for dispersant purposes is not removed in this step. Next, the purified metal particles are dispersed in a low-boiling-point solvent (alcohol-based, such as methanol or ethanol) to prepare a slurry containing the metal particles. This slurry is then coated onto a glass surface to form a film. The formed film is then dried in an oven at 80°C for approximately 1 hour, peeled off from the glass, and collected as a sample for organic matter content determination. Finally, the collected organic matter content determination sample is powdered, and the C content (wt%) of the organic matter is determined using a CS meter (combustion method).

[0135] The metal particles of the present invention are metal particles with low organic content and small particle size, which have excellent low-temperature sintering properties. As a result, the sintered body formed by the metal particles has low volume resistivity and small volume shrinkage during sintering.

[0136] Specifically, the metal particles of the present invention have a low organic content and a small median particle size. During sintering, the metal particles of the present invention exhibit a low volume shrinkage rate, typically less than 60% of the volume relative to the volume of the metal particles before sintering under pressure, less than 50% in one embodiment, and less than 15% in another embodiment. It should be noted that the volume shrinkage rate resulting from the sintering of the metal particles of the present invention is preferably small, therefore a lower limit value is not limited.

[0137] Furthermore, the metal particles of the present invention contain the minimum amount of organic matter required as a dispersant to disperse the metal particles in the solvent, thus enabling them to be sufficiently dispersed in the solvent even without further addition of a dispersant. This is because in the metal particles of the present invention, the dispersant adheres to the metal particles immediately after their formation, thereby uniformly adhering to the metal particles. Even if they are temporarily in a quasi-dry or dry state, they can resume their function as a dispersant upon addition to the solvent. Therefore, the metal particles of the present invention are redispersible metal particles. It should be noted that when the metal particles do not contain any dispersant, if they are temporarily in a quasi-dry or dry state, the cohesive force of the nano-sized metal particles is particularly large, making redispersibility difficult. In addition, when mixing metal particles and a dispersant that do not contain any dispersant, if they are temporarily in a quasi-dry or dry state, uniform mixing is difficult due to the large cohesive force of the metal particles.

[0138] The present invention also relates to a dispersion comprising the metal particles of the present invention described above, an organic compound as a dispersant for the metal particles, and a solvent for dispersing the metal particles and the organic compound.

[0139] In the dispersion of the present invention, the content of metal particles is not limited. This is because the metal particles contained in the dispersion of the present invention contain the minimum amount of dispersant required for the metal particles to be dispersed in the solvent. For example, relative to the total weight of the dispersion, the content of metal particles is generally 1% by weight or more, in one embodiment 5% by weight or more, in one embodiment 10% by weight or more, in one embodiment 20% by weight or more, in one embodiment 50% by weight or more, in one embodiment 70% by weight or more, and generally 95% by weight or less, in one embodiment 90% by weight or less, in one embodiment 85% by weight or less, in one embodiment 80% by weight or less, for example 1% to 95% by weight, in one embodiment 5% to 90% by weight, and in one embodiment 50% to 80% by weight.

[0140] By increasing the metal particle content of the dispersion of the present invention, the cost of solvent, the time and labor costs spent on solvent evaporation after dispersion coating, as well as storage and transportation costs, can be reduced, thereby reducing the environmental impact.

[0141] In the dispersion of the present invention, the content of organic matter serving as a dispersant for the metal particles is 2% by weight or less relative to the total weight of the metal particles, 1% by weight or less in one embodiment, and 0.8% by weight or less in another embodiment. The content of this organic matter is preferably low, therefore the lower limit is not limited, but is typically 0.1% by weight or more relative to the total weight of the metal particles, 0.2% by weight or more in one embodiment, 0.3% by weight or more in another embodiment, and 0.4% by weight or more in another embodiment.

[0142] In the dispersion of the present invention, by using a small amount of dispersant, the sintered body formed from the dispersion can have low volume resistivity and low volume shrinkage.

[0143] The solvent contained in the dispersion of the present invention can be any solvent known in the art, without limitation. For example, it can be selected from solvents that are liquid at 20°C, water, alcohols, aldehydes, carboxylic acids, ethers, esters, amines, monosaccharides, polysaccharides, straight-chain hydrocarbons, fatty acids, aromatics, etc., and two or more of the above solvents can also be used in combination.

[0144] The boiling point of the solvent is not particularly limited, but is generally above 100°C, above 130°C in one embodiment, above 150°C in another embodiment, and generally below 300°C, below 250°C in one embodiment, and below 200°C in another embodiment, for example, 100°C to 300°C, 130°C to 250°C in one embodiment, and 150°C to 200°C in another embodiment. If the boiling point of the solvent is above 100°C, for example, when the dispersion is used as ink paste, the evaporation of the solvent at room temperature can be suppressed, thereby ensuring the viscosity stability and coatability of the ink paste. Furthermore, if the boiling point of the solvent is below 300°C, in bonding processes involving calcination, especially non-pressurized calcination, the solvent's non-evaporation and residue in the metal sintered body at the temperature at which the semiconductor element is connected to the support member can be suppressed, resulting in better preservation of the properties of the metal sintered body.

[0145] As a solvent, it is preferable to select a solvent suitable for dispersing silver particles from the above-mentioned solvents. Specifically, from the perspective of improving the thermal conductivity, electrical conductivity, and adhesive strength of the metal sintered body, solvents having an alcohol structure, ether structure, or ester structure are preferred. Examples of solvents included in the dispersion of the present invention include butyl cellosolve, carbitol, butyl acetate cellosolve, carbitol acetate, ethylene glycol diethyl ether, dipropylene glycol methyl ether acetate, dipropylene glycol mono-n-butyl ether, dipropylene glycol mono-n-methyl ether, terpineol, ethylene glycol, isobornylcyclohexanol, glyceryl tributyrate, etc. Ethylene glycol is preferred as a solvent included in the dispersion of the present invention.

[0146] When the dispersion of the present invention is used as ink paste, the amount of solvent contained in the ink paste can vary depending on the content of metal particles contained in the dispersion, etc., and is generally 5% by weight or more, and generally 99% by weight or less, relative to the total weight of the ink paste, and in one embodiment is 90% by weight or less.

[0147] By adjusting the amount of solvent to the range described above, the viscosity of the ink paste can be adjusted to the appropriate viscosity range described later. In this way, the volume shrinkage that accompanies solvent evaporation during the sintering of the ink paste can be suppressed, and the density of the formed silver sintered body can be improved.

[0148] The dispersion of the present invention may further include components other than the metal particles and solvent of the present invention, to a extent that does not impair the effects of the present invention. Examples of components that can be added besides the metal particles and solvent of the present invention include those known in the art, without limitation, such as carboxylic acids with a boiling point of 400°C or less at atmospheric pressure and solid at 20°C, such as stearic acid, lauric acid, docosanoic acid, sebacic acid, 1,16-octadecanoic acid, etc.; metal particles other than the metal particles of the present invention; anti-settling agents for the metal particles in the dispersion; fluxes for promoting the sintering of the metal particles; etc. The amount of components that can be added besides the metal particles and solvent of the present invention, relative to the total weight of the dispersion, is generally 0% by weight or more, and generally 10% by weight or less, in one embodiment 1% by weight or less, for example 0% to 10% by weight, in another embodiment 0% to 1% by weight.

[0149] When the dispersion of the present invention is used as an ink paste, the viscosity of the ink paste, when measured using a cone-plate viscometer, is typically 10 mPa·s or higher, and typically 10,000 Pa·s or lower. This viscosity can be appropriately adjusted, as described above, by the aspect ratio and amount of the plate-shaped silver particles, the type and amount of the polymer used as a dispersant, and the type and amount of the solvent.

[0150] By adjusting the viscosity of the ink paste to the above range, the coatability of the ink paste can be improved, and bleeding after the ink paste is applied can be prevented.

[0151] The metal particles or dispersions manufactured by this invention can be used not only as materials for catalysts, electronic components, and inks, but also as conductive wiring materials in the field of electronic assembly, thereby reducing the number of steps in ink production, such as in wiring substrates.

[0152] Example

[0153] The following describes several embodiments of the present invention, but it is not intended to limit the present invention to the solutions shown in these embodiments.

[0154] 1. Synthesis of metal particles

[0155] use Figure 1 and 2 The manufacturing apparatus 1 for generating metal particles, as shown, and the reaction solutions shown in Table 1 or 2, are used to manufacture silver or nickel particles according to the conditions shown in Table 3. In Table 1, the weight-average molecular weight of PVP is 40,000. In Table 3, E is the absorbed power (W / mL) of the reaction solution irradiated by the irradiation device 42 irradiating microwave M, and P is the pressure (MPa) applied to the reaction solution as measured in the pressure adjusting device 60. It should be noted that the cavity of the irradiation device 42 irradiating microwave M in the manufacturing apparatus 1 is a cuboid with a length of 100 mm, and the following reaction tube is used as the reaction tube.

[0156] Composition of the reaction tube

[0157] • Inner diameter of the tube: 1mm~6mm

[0158] • Outer diameter of the tube: 3mm~8mm (wall thickness: 1mm)

[0159] • Tube length: 100mm

[0160] [Table 1]

[0161]

[0162] [Table 2]

[0163]

[0164] [Table 3]

[0165]

[0166] In this experiment, the total reaction time in the examples was approximately one-fifth of the total reaction time when the reaction was carried out without pressure. This is because the boiling point of the reaction liquid under pressure is higher than that under atmospheric pressure, thus allowing for a further increase in the temperature of the reaction liquid during the reaction.

[0167] 2. Evaluation Results

[0168] (Evaluation using transmission electron microscopy (TEM))

[0169] TEM images were taken of the dispersions obtained in Examples 1-5 and Comparative Examples 1-5. Figure 3 TEM images of silver particles in Comparative Example 1, as well as Examples 1 and 4, are shown.

[0170] Then, the particle size distribution was determined from the obtained TEM image. The particle size distribution was performed as follows: First, 500 arbitrary silver or nickel particles were selected from the TEM image. Next, the diameter of each selected silver or nickel particle was measured when the projected surface area of ​​the silver or nickel particle was converted into the area of ​​a circle. Then, these were used as particle diameters, and a graph was created with particle diameter (nm) as the x-axis and cumulative number (%) as the y-axis. Figure 4 The particle size distribution of silver particles in Example 1, as an example, is shown. Finally, the particle size at which the cumulative number of particles reaches 50% is determined from this graph as D50. Table 4 and Figure 5 The results are shown.

[0171] [Table 4]

[0172]

[0173] From Table 4 and Figure 5 The results show that if the value (E×P) obtained by multiplying the microwave absorption power E (W / mL) of the reaction solution and the pressure P (MPa) applied to the reaction solution is greater than 20, the D50 of the obtained metal particles becomes smaller, especially below 15 nm.

[0174] Next, the organic matter content of Examples 1, 3, and 4, as well as Comparative Examples 3 and 5, was determined, and the relationship with D50 was measured. It should be noted that the organic matter content was determined as follows.

[0175] First, purified water, such as ion-exchanged water, is added to the dispersion containing the examples or comparative examples. The mixture is then purified using a solid-liquid separator such as centrifuge until the conductivity of the slurry is below tens of μS / cm. The conductivity is measured using a handheld, general-purpose separator. This step is performed to remove impurities and water-soluble byproducts contained in the dispersion. Next, the purified particles are dispersed in a low-boiling-point solvent (alcohol-based, such as methanol or ethanol) to prepare a slurry containing metal particles. This slurry is then coated onto a glass surface to form a film. The formed film is then dried in an oven at 80°C for approximately 1 hour, peeled off from the glass, and collected as a sample for organic matter content determination. Finally, the collected organic matter content determination sample is powdered, and the C content (wt%) of the organic matter is determined using a CS meter (combustion method). Figure 6 The results are shown.

[0176] Depend on Figure 6 It is known that even if the amount of organic matter in the metal particles is reduced, a small D50 can still be maintained in the metal particles manufactured by the method of the present invention.

[0177] Next, the volume shrinkage rate during sintering at 120°C for 2 hours was measured for Examples 1, 3, and 4, and Comparative Examples 3 and 5, for which the organic matter content was determined. The volume shrinkage rate was measured as follows.

[0178] (1) First, a solid-liquid separator such as centrifuge is used to recover the metal particles purified by ion-exchange water to filter paper, and ethanol is added for vacuum filtration to replace the solvent.

[0179] (2) Next, the filter cake layer remaining in the filter paper after solvent replacement is recovered, and solvents such as butyl carbitol, butyl acetate, and terpineol are added in such a way that the concentration of metal particles is 80% by weight. The mixture is crushed and mixed using a rotation-revolution mixer to prepare a paste containing metal particles.

[0180] (3) The obtained paste is coated onto a glass slide using a metal mask with a thickness of 100μm, a width of 15mm, and a length of 15mm (100μm×15mm×15mm).

[0181] (4) Calcination at 120°C for 2 hours using a constant temperature bath.

[0182] (5) After calcination, use a micrometer to measure the film thickness at 5 specified points, and take the average value as the film thickness.

[0183] (6) Calculate the volume of the paste before calcination and the volume of the sintered body after calcination from the dimensions and thickness of the metal mask and the dimensions and thickness after calcination. Calculate the volume shrinkage rate using the following formula.

[0184] {(Volume of paste before calcination - Volume of sintered body after calcination) / (Volume of paste before calcination)} × 100.

[0185] Figure 7 The results are shown. Figure 7 It can be seen that the amount of organic matter in the metal particles decreases, and the volume shrinkage rate also decreases.

[0186] Furthermore, in order to confirm the redispersibility of the silver and nickel particles manufactured and purified in the embodiments of the present invention, the quasi-dry or dry silver and nickel particles manufactured and purified in the embodiments were redispersed in various solvents, such as aqueous solvents, nonpolar solvents, etc. As a result, it was confirmed that the metal particles of the embodiments can be redispersed in various solvents.

[0187] Figure 8 and 9 The state of metal particle generation based on the results of the above comparative examples and embodiments is schematically shown.

[0188] Figure 8 This schematically illustrates the process from nucleus formation to particle growth of a metallic particle (silver particle, for example) when the prior art or E×P is less than 20. Figure 8As shown, when the microwave absorption power is weak and no pressure is applied, the reaction temperature decreases, and nucleus formation becomes uneven, resulting in variations in nucleus size. Consequently, the reaction solution contains nuclei of different sizes, with smaller, later-formed nuclei attaching to larger, earlier-formed nuclei, causing the particles to grow larger.

[0189] Figure 9 This schematically illustrates the process from nucleus formation to particle growth of a metal particle (e.g., a silver particle) when the E×P of the present invention is 20 or higher. Figure 9 As shown, under conditions of strong microwave absorption power and applied pressure, the reaction temperature increases, and nuclei are generated uniformly without causing deviations in nuclei size. As a result, with uniformly sized nuclei present, nuclei of similar size adhere to each other and grow, resulting in smaller particles. Furthermore, the dispersant required to disperse the metal particles in the reaction solution can also adhere uniformly to the uniformly formed particles, requiring only a minimal amount. Moreover, by reacting under a high-temperature atmosphere, the reaction time can be significantly reduced to, for example, one-fifth. Additionally, the method for forming metal particles according to the present invention is characterized by applying a certain level of microwave absorption power and pressure to the reaction solution, raising the reaction temperature, and inducing a one-time reduction of metal ions based on microwave heating. Therefore, the type of metal particles produced by the method of the present invention can be any metal whose metal ions are reduced by microwave heating; examples include not only the aforementioned metal particles, namely silver and nickel particles, but also particles such as gold, platinum, copper, iron, and cobalt.

[0190] All publications, patents and patent applications referenced in this specification are incorporated herein by reference directly.

Claims

1. A method for manufacturing metal particles, including the step of irradiating a reaction solution with microwaves, comprising: (i) The step of preparing a reaction solution containing a metal particle precursor, an organic compound as a dispersant, and a solvent; as well as (ii) The step of irradiating the reaction solution with microwaves while the reaction solution is flowing, and the relationship between the microwave absorption power E and the pressure P of the reaction solution satisfies the following Equation 1, wherein the unit of absorption power E is W / mL and the unit of pressure P is MPa. E×P≥20 (Equation 1).

2. The method according to claim 1, wherein, In step (i), the content of the organic matter in the reaction solution is 0.1% to 2% by weight relative to the total weight of the metal as the precursor of the metal particles.

3. The method according to claim 1 or 2, wherein, In step (ii), the relationship between the microwave absorption power E and the pressure P of the reaction solution satisfies the following equation 2, where the unit of absorption power E is W / mL and the unit of pressure P is MPa. E×P≥30 (Equation 2).

4. A type of metal particle, which is a metal particle containing organic matter. The content of the organic matter is 0.1% to 2% by weight relative to the total weight of the metal particles. The median particle size, D50, measured by TEM, is below 20 nm.

5. A metal particle dispersion comprising metal particles, an organic compound as a dispersant for the metal particles, and a solvent. The content of the metal particles is 1% to 95% by weight relative to the total weight of the metal particle dispersion. The content of the organic matter is 0.1% to 2% by weight relative to the total weight of the metal particles. The median particle size, D50, of the metal particles measured by TEM is less than 20 nm.

6. An apparatus for manufacturing metal nanoparticles, wherein the metal particles are generated by irradiating a reaction solution with microwaves, the apparatus comprising: Pump, pressurizes and delivers the reaction solution. The irradiation device irradiates the reaction liquid, which is pumped by the pump and flows in the reaction tube, along with the reaction tube itself, with microwaves. A pressure regulating device adjusts the pressure of the reaction liquid within the reaction tube downstream of the reaction tube, and A stirring device is used to stir the reaction liquid pumped by the pump between the pump and the reaction tube.

7. The apparatus for manufacturing metal nanoparticles according to claim 6, wherein, The stirring device is positioned such that the stirring flow of the reaction liquid through the stirring device is continuous within the reaction tube, between the pump and the reaction tube.

8. The apparatus for manufacturing metal nanoparticles according to claim 6 or 7, wherein, The stirring device has a straight pipe for the flow of the reaction liquid and twisted blades fixed inside the pipe and twisted about the axis of the pipe.

9. The apparatus for manufacturing metal nanoparticles according to claim 8, wherein, The twisted blade is a blade in which twisted blade elements with different twisting directions around the axis are alternately arranged along the axial direction of the pipe.

10. The apparatus for manufacturing metal nanoparticles according to claim 8 or 9, wherein, The twisted blades are made of a non-conductive material.

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