Manufacturing method of metal nanoparticle

Abstract

To provide means for manufacturing a metal nanoparticle having a fine particle diameter at a high yield.SOLUTION: A manufacturing method of a metal nanoparticle includes: a material preparation step of preparing a metallic material aqueous solution containing a metallic material less than 300 mM; a reaction tube preparation step of preparing a reaction tube having a microwave heating part having an inner wall charged positive by a corona charge treatment and formed with a material having positive electrification characteristics; and a metal nanoparticle formation step of forming a metal nanoparticle through circulating the metallic material aqueous solution to the microwave heating part of the reaction tube while irradiating, with microwave, the microwave heating part from an outside of the reaction tube.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Metal nanoparticles are metal particles such as silver, gold, or platinum with a particle size of several nanometers to several tens of nanometers. Metal nanoparticles are used as ink materials for patterning in printed electronics.

[0003] As an ink material for patterning in printed electronics, a material that can produce a dense sintered body with low resistance even when sintered at a low temperature is preferable. A liquid phase synthesis method is known as a method for producing such metal nanoparticles, in which a solution of metal ions is placed in a reaction vessel and heated and reduced by irradiating microwaves.

[0004] For example, Patent Document 1 discloses a method for producing a microwave-transparent reaction tube, a protective liquid introduction section for introducing a microwave-transparent protective liquid, which is incompatible with a microwave-absorbing reaction solution in which raw materials are dispersed or dissolved, into the reaction tube, into which the protective liquid is filled, and into which the reaction solution is introduced as droplets into the reaction tube filled with the protective liquid, and a microwave heating section for irradiating microwaves from outside the reaction tube into the reaction tube to heat the droplets flowing through the reaction tube, and the reaction solution introduction section has an inner diameter of the reaction tube that is D r The diameter of the droplet is D d Then, the following equation, D d ≦0.9D r The present invention also describes an apparatus for synthesizing chemical substances, which is characterized in that the droplets are introduced into the reaction tube so as to satisfy the relationship:

[0005] Patent Document 2 describes a method for producing metal microparticles, in which a reaction liquid containing a metal precursor is circulated through a flow tube placed in a microwave irradiation space, and microwaves are irradiated toward the flow tube in the microwave irradiation space from outside the flow tube, heating the reaction liquid in the flow tube by this microwave irradiation and synthesizing metal microparticles, characterized in that a device to which a frequency band of 2.4 to 2.5 GHz is assigned or which is the standard frequency band for the product is used as the microwave generating device, and the average inner diameter of the portion of the flow tube placed in the microwave irradiation field is narrower than 2.84 mm. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-47535 A [Patent Document 2] JP 2020-111831 A Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, there are known methods for producing metal nanoparticles by liquid phase synthesis. However, the conventional methods have a problem in that ions of the metal material aggregate on the inner wall of a reaction vessel such as a reaction tube used in the reaction, resulting in coarse metal particles.

[0008] Therefore, an object of the present invention is to provide a means for producing metal nanoparticles having a fine particle size in high yield. [Means for solving the problem]

[0009] The present inventors have investigated various means for solving the above problems. They have found that in a liquid phase synthesis method, by positively charging the inner wall of a reaction tube used in a reaction in advance by corona charging treatment, it is possible to substantially suppress the aggregation of ions of a metal material and obtain metal nanoparticles of a desired particle size in high yield. Based on the above findings, the present inventors have completed the present invention.

[0010] That is, the present invention includes the following aspects and embodiments. (Embodiment 1) A raw material preparation step of preparing an aqueous solution of a metal material containing less than 300 mM of the metal material; A reaction tube preparation step of preparing a reaction tube having a microwave heating part which is made of a material having a positive charging property and has an inner wall positively charged by a corona charging treatment; a metal nanoparticle forming step of circulating an aqueous solution of a metal material through the microwave heating part of the reaction tube while irradiating microwaves from outside the reaction tube toward the microwave heating part to form metal nanoparticles; A method for producing metal nanoparticles, comprising: (Embodiment 2) The method of embodiment 1, wherein the material having positive charging properties is quartz or nylon. (Embodiment 3) The method of embodiment 1 or 2, wherein the metallic material is a salt of silver, gold, platinum, copper, nickel, iron, cobalt, palladium or zinc, or a mixture thereof. (Embodiment 4) The method of embodiment 3, wherein the metallic material is silver nitrate and the metallic nanoparticles are silver nanoparticles. (Embodiment 5) The method according to any one of embodiments 1 to 4, wherein the metal material contained in the aqueous solution has a concentration in the range of 10 to 250 mM. Effect of the Invention

[0011] The present invention makes it possible to provide a means for producing metal nanoparticles having a fine particle size at a high yield. [Brief description of the drawings]

[0012] [Figure 1]1 shows a transmission electron microscope (TEM) image of the metal nanoparticles of Example 1. In the figure, the scale bar indicates 50 nm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Preferred embodiments of the present invention will now be described in detail.

[0014] One aspect of the present invention relates to a method for producing metal nanoparticles.

[0015] In each aspect of the present invention, the metal nanoparticles generally refer to fine particles of metals including precious metals or base metals, or alloys thereof. The metal constituting the metal nanoparticles is preferably silver, gold, platinum, copper, nickel, iron, cobalt, palladium, zinc, or the like, or an alloy thereof, more preferably silver or an alloy containing silver, and even more preferably silver. The metal nanoparticles may have a coating of an organic compound on the surface of the metal particles. In this case, examples of the organic compound forming the coating include 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. The coating may be formed by the organic compounds listed above alone, or may be formed by a mixture of two or more organic compounds.

[0016] The particle size of the metal nanoparticles obtained by the method of this embodiment is usually 50 nm or less, preferably 40 nm or less, and more preferably 30 nm or less. For example, in the particle size distribution measurement of the metal nanoparticles obtained by the method of this embodiment, the D90 value of the metal nanoparticles is usually in the range of 5 to 50 nm, preferably in the range of 5 to 40 nm, and more preferably in the range of 5 to 30 nm. By the method of this embodiment, metal nanoparticles having a finer particle size can be obtained compared to metal nanoparticles obtained by the method of the prior art.

[0017] In each embodiment of the present invention, the D90 value of the metal nanoparticles can be determined based on the particle size distribution of the metal nanoparticles measured using a particle size distribution measuring device, for example. The particle size of the metal nanoparticles can be expressed as the D90 value of silver nanoparticles, or can be determined by measuring the particle sizes of multiple metal nanoparticles by TEM and calculating the average value of the measured values.

[0018] The method of this embodiment includes a raw material preparation step, a reaction tube preparation step, and a metal nanoparticle formation step. Each step will be described in detail below.

[0019] [1: Raw material preparation process] The process includes providing an aqueous solution of a metallic material that includes a metallic material.

[0020] The metal material prepared in this step is not limited as long as the metal salt can dissolve in the solvent and generate metal ions in the aqueous solution. The metal material is, for example, a salt of the metal exemplified above or a mixture thereof, and is preferably a metal salt such as an inorganic salt of the metal exemplified above, such as hydrochloride, sulfate, nitrate, or phosphate, an organic salt of the metal exemplified above, such as carboxylate or sulfonate, or a mixture thereof, and more preferably silver nitrate. The metal salt may be prepared, for example, by dissolving a material containing the metal exemplified above or a salt thereof with an acid such as nitric acid or aqueous ammonia.

[0021] The aqueous solution of the metallic material prepared in this step usually contains less than 300 mM of the metallic material. The concentration of the metal salt contained in the aqueous solution of the metallic material is preferably in the range of more than 10 mM and less than 300 mM, more preferably in the range of 10 to 250 mM, and even more preferably in the range of 50 to 200 mM. If the concentration of the metal salt exceeds the upper limit, the resulting metallic particles may become coarse. If the concentration of the metal salt is less than the lower limit, the yield of the resulting metallic particles may decrease. Therefore, by carrying out the method of this embodiment using an aqueous solution of the metallic material containing the metal salt at a concentration in the above range, metallic nanoparticles having a fine particle size can be obtained in high yield.

[0022] The aqueous solution of the metal material prepared in this step may contain a protective agent, if desired. The protective agent is preferably selected from the organic compounds exemplified above as the organic compounds that form a coating on the surface of the metal nanoparticles. When the aqueous solution of the metal salt contains a protective agent, the concentration of the protective agent contained in the aqueous solution of the metal salt is preferably in the range of 50 to 3,000 mmol / L, preferably in the range of 50 to 2,500 mmol / L, more preferably in the range of 200 to 2,000 mmol / L, and even more preferably in the range of 250 to 2,000 mmol / L. By using the metal salt exemplified above and, if desired, a protective agent, metal nanoparticles having a fine particle size can be obtained in high yield.

[0023] The aqueous solution of the metal material prepared in this step usually contains a reducing agent. The reducing agent may be included in the aqueous solution of the metal material, or may be prepared as an aqueous solution separate from the aqueous solution of the metal material. The reducing agent is preferably N,N-dimethylformamide (DMF), citric acid, a citrate salt (e.g., trisodium citrate, disodium citrate, or monosodium citrate), oxalic acid, an oxalate salt (e.g., sodium oxalate), ascorbic acid, an ascorbate salt (e.g., sodium ascorbate), formic acid or a formate salt (e.g., sodium formate), or a mixture thereof, and more preferably DMF. The concentration of the reducing agent is preferably in the range of 1,000 to 10,000 mmol / L, more preferably in the range of 2,000 to 10,000 mmol / L, more preferably in the range of 5,000 to 10,000 mmol / L, and even more preferably in the range of 8,000 to 10,000 mmol / L. By using the reducing agents exemplified above, metal salts can be efficiently reduced to obtain metal nanoparticles having fine particle sizes in high yields.

[0024] The aqueous solution of the metal material prepared in this step preferably contains a base in addition to the reducing agent exemplified above. The base can improve the reaction rate of the reduction reaction of the metal salt and the reducing agent in the metal nanoparticle formation step described below. The base is preferably an alkali metal hydroxide or an alkaline earth metal hydroxide, or a mixture thereof, more preferably potassium hydroxide, sodium hydroxide, lithium hydroxide, calcium hydroxide, magnesium hydroxide, or beryllium hydroxide, or a mixture thereof, even more preferably potassium hydroxide or sodium hydroxide, and particularly preferably potassium hydroxide. By carrying out the method of this embodiment using an aqueous solution of the reducing agent containing the base exemplified above, the reaction rate of the reduction reaction of the metal salt and the reducing agent can be improved, and metal nanoparticles having a fine particle size can be obtained in high yield.

[0025] In this step, the aqueous solution of the metal material may be prepared by self-preparation of an aqueous solution having the characteristics described above, or may be prepared by purchasing a pre-prepared aqueous solution.

[0026] [2: Reactor tube preparation process] This step involves preparing a reaction tube for use in the method of this embodiment.

[0027] The reaction tube prepared in this step has at least a microwave heating part. The microwave heating part may be the whole reaction tube or a part of the reaction tube. In the microwave heating part, the aqueous solution of the metal material flowing inside can be heated by irradiating microwaves from the outside.

[0028] The reaction tube prepared in this step, particularly the microwave heating part thereof, is formed of a material having a positive charging characteristic. The material having a positive charge resistance characteristic is preferably quartz or nylon, or a mixture thereof, more preferably quartz or nylon, and even more preferably quartz. The above-exemplified materials have a characteristic of being easily positively charged by the corona charging treatment described below. In addition, the above-exemplified materials have a characteristic of being easily permeable to microwaves. Therefore, by carrying out the method of this embodiment using a reaction tube formed of the above-exemplified material, it is possible to substantially suppress the aggregation of ions of the metal material, and efficiently proceed with the reduction reaction of the ions of the metal material, thereby obtaining metal nanoparticles having a fine particle size in high yield.

[0029] The microwave heating section of the reaction tube prepared in this process has an inner wall positively charged by a corona charging treatment. The corona charging treatment is preferably performed using an ion irradiation method. The positive charge charged by the corona charging treatment is held on the inner wall for a certain period of time. Therefore, in this process, it is not necessary to perform the corona charging treatment every time.

[0030] [3: Metal nanoparticle formation process] This process involves irradiating microwaves from outside the reaction tube toward the microwave heating section while flowing an aqueous solution of a metal material through the microwave heating section of the reaction tube to form metal nanoparticles.

[0031] In this step, microwave irradiation may be performed using a microwave irradiation device commonly used in the art. The microwave frequency is preferably in the range of 2 to 3 GHz. The microwave irradiation intensity is preferably in the range of 100 to 2,000 W / mL.

[0032] In this process, a microwave irradiation device is used to irradiate microwaves from the outside of the reaction tube toward the microwave heating section, while an aqueous solution of a metal material is circulated through the microwave heating section of the reaction tube. As a result, the aqueous solution of the metal material circulating through the microwave heating section is heated, and the reduction reaction of the ions of the metal material proceeds to form metal nanoparticles. At this time, the inner wall of the microwave heating section is positively charged by corona charging treatment. Therefore, the aggregation of the ions of the metal material is substantially suppressed. Therefore, by carrying out this process, the aggregation of the ions of the metal material is substantially suppressed, and the reduction reaction of the ions of the metal material is efficiently promoted, so that metal nanoparticles having a fine particle size can be obtained in high yield.

[0033] In this process, the flow rate of the aqueous solution of the metallic material is preferably in the range of 5 to 300 mL / min. If the flow rate of the aqueous solution of the metallic material exceeds the upper limit, the reduction reaction of the ions of the metallic material may not proceed sufficiently. If the flow rate of the aqueous solution of the metallic material is below the lower limit, the ions of the metallic material may aggregate, resulting in coarse metallic particles. Therefore, by carrying out this process under the above conditions, metallic nanoparticles having a fine particle size can be obtained in high yield.

[0034] As described in detail above, by the method of this aspect, metal nanoparticles having a fine particle size can be produced as compared with the metal nanoparticles obtained by the method of the prior art. The metal nanoparticles obtained by the method of this aspect can be a dense sintered body that can have a low resistance value even at low-temperature firing. Therefore, by obtaining the metal nanoparticles having the above characteristics by the method of this aspect, an ink material applicable to wiring formation in a resin-based printed electronics material and a bonding material having low heat resistance can be provided.

Example

[0035] Hereinafter, the present invention will be described more specifically using examples. However, the technical scope of the present invention is not limited to these examples.

[0036] <I: Production of Metal Particles> [I-1: Raw Material Preparation Step] Silver nitrate was used as a metal source, polyvinylpyrrolidone (PVP) was used as a protective agent, N,N-dimethylformamide (DMF) was used as a reducing agent, potassium hydroxide was used as a base, and water was used as a solvent. An aqueous solution of a silver salt containing silver nitrate at a predetermined final concentration and PVP at a final concentration of 600 mmol / L, and an aqueous solution of a reducing agent containing potassium hydroxide at a final concentration of 120 mmol / L and DMF at a final concentration of 8,000 mmol / L were prepared.

[0037] [I-2: Reaction Tube Preparation Step] A reaction tube formed of a predetermined piping material and having a microwave heating section (outer diameter: 6 mm, inner diameter: 4 mm) was prepared. The inner wall of the microwave heating section of the reaction tube was positively charged by corona charging treatment (treatment conditions: output 20 kV, 2 mA) using an ion irradiation method. As a reaction tube for a comparative example, a reaction tube having a microwave heating section with an inner wall negatively charged without corona charging treatment was prepared.

[0038] [I-3: Metal Nanoparticle Formation Step] An aqueous solution of a silver salt and an aqueous solution of a reducing agent obtained in the raw material preparation step were mixed and passed through a reaction tube at a flow rate of 150 mL / min. At this time, microwaves were irradiated from the outside of the reaction tube toward the microwave heating section (frequency: 2.45 GHz, irradiation intensity: 1,700 W / mL). Thereby, silver particles were formed.

[0039] <II: Analysis of Metal Particles> The obtained silver particles were observed with a transmission electron microscope (TEM). Also, using a particle size distribution measuring device, the particle size distribution of the obtained silver particles was measured. The TEM image of the silver particles of Example 1 is shown in FIG. 1. In the figure, the scale bar indicates 50 nm.

[0040] The production conditions of the examples and comparative examples, and the particle size distributions of the obtained silver particles of the examples and comparative examples are shown in Table 1.

[0041]

Table 1

[0042] As shown in FIG. 1, the silver particles of Example 1 were fine particles having a homogeneous shape. As a result of the particle size distribution measurement, it was confirmed that the silver particles of Examples 1 to 4 had D90 values in the range of 10.4 to 26.8 nm. On the other hand, it was confirmed that the silver particles of Comparative Examples 1 to 3 had D90 values in the range of 85.1 to 90.5 nm. From these results, it became clear that the silver particles of the present invention are nanoparticles having a fine particle size.

[0043] Note that the present invention is not limited to the above-described examples, and various modifications are included. For example, the above-described examples have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Also, for a part of the configuration of each example, addition, deletion, and / or substitution of other configurations are possible.

Claims

1. a raw material preparation step of preparing an aqueous solution of a metallic material containing less than 300 mM of the metallic material; A reaction tube preparation step of preparing a reaction tube having a microwave heating part which is made of a material having a positive charging property and has an inner wall positively charged by a corona charging treatment; a metal nanoparticle forming step of circulating an aqueous solution of a metal material through the microwave heating part of the reaction tube while irradiating microwaves from outside the reaction tube toward the microwave heating part to form metal nanoparticles; A method for producing metal nanoparticles, comprising:

2. 2. The method according to claim 1, wherein the material having positive charging properties forming the reaction tube is quartz or nylon.

3. 2. The method of claim 1, wherein the metallic material is a salt of silver, gold, platinum, copper, nickel, iron, cobalt, palladium or zinc, or mixtures thereof.

4. The method of claim 3 , wherein the metallic material is silver nitrate and the metallic nanoparticles are silver nanoparticles.

5. The method of claim 1 , wherein the metal material is present in the aqueous solution at a concentration in the range of 10 to 250 mM.

Images