Method for producing nickel nanoparticles, and method for producing conductive ink

Abstract

To provide a method for producing nickel nanoparticles that has a low environmental impact during production and that can produce nickel nanoparticles at low cost using a simple method, and to provide a method for producing conductive ink.SOLUTION: A method for producing nickel nanoparticles includes: an electrolyte generation step of dissolving a nickel compound in a conductive organic solvent to obtain a nickel electrolyte; and an electrolysis step of electrolyzing the nickel electrolyte to reduce to produce nickel nanoparticles on a cathode, wherein in the electrolysis step, an electric current is applied between an anode and a cathode and at least the cathode is irradiated with ultrasonic waves.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing nickel nanoparticles and a method for producing a conductive ink. [Background technology]

[0002] In recent years, as electronic devices have become smaller and thinner, the miniaturization of electronic components has led to a demand for miniaturization of the metal materials used. For example, nickel particles used in the electrode layers of multilayer ceramic capacitors and in forming wiring using conductive inks are so-called nickel nanoparticles with a particle size of 100 nm or less, which is on the nano order of size.

[0003] As a conventional method for producing nickel nanoparticles, for example, Patent Document 1 discloses a method in which a nickel complexation reaction liquid obtained by reacting a nickel salt with a reducing agent is heated to a predetermined temperature range while blowing nitrogen into the nickel complexation reaction liquid and stirring the liquid, thereby producing nickel nanoparticles.

[0004] Furthermore, Patent Document 2 discloses a method for producing metal nanoparticles containing nickel by dispersing powder of an inorganic compound, which is a metal source, in a solution and irradiating the solution with heat or cavitation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2022-156863 A [Patent Document 2] JP 2010-065265 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method for producing nickel nanoparticles as disclosed in Patent Document 1 has the problem that it has a large environmental impact and requires high costs for treating wastewater because it uses primary or secondary amines such as octylamine or trioctylamine as a reducing agent for reducing nickel salt.

[0007] In addition, in the method for producing metal nanoparticles as disclosed in Patent Document 2, the metal compounds that can be reduced to produce metal nanoparticles by simply irradiating heat or cavitation in a solvent are limited. In particular, there is no disclosure of nickel compounds at all.

[0008] The present invention has been made in consideration of this technical background, and aims to provide a method for producing nickel nanoparticles that has a small environmental impact during production and is capable of producing nickel nanoparticles at low cost in a simple manner, and a method for producing conductive ink. [Means for solving the problem]

[0009] In order to solve the above problems, the method for producing nickel nanoparticles and the method for producing conductive ink according to one embodiment of the present invention propose the following means.

[0010] (1) A method for producing nickel nanoparticles according to aspect 1 of the present invention includes an electrolyte generation step of dissolving a nickel compound in a conductive organic solvent to obtain a nickel electrolyte, and an electrolysis step of electrolyzing the nickel electrolyte to reduce and generate nickel nanoparticles at a cathode, the electrolysis step being characterized in that it is a step of applying a current between an anode and a cathode and irradiating ultrasonic waves toward at least the cathode.

[0011] (2) A second aspect of the present invention is characterized in that, in the method for producing nickel nanoparticles according to the first aspect, the conductive organic solvent contains ethylene glycol.

[0012] (3) Aspect 3 of the present invention is characterized in that, in the method for producing nickel nanoparticles of aspect 1 or 2, in the electrolysis process, at least one of the crystallite size and the particle size of the nickel nanoparticles generated at the cathode is controlled by adjusting the frequency or intensity of the ultrasonic waves.

[0013] (4) A fourth aspect of the present invention is the method for producing nickel nanoparticles according to any one of the first to third aspects, characterized in that the cathode is made of a metal containing nickel.

[0014] (5) A fifth aspect of the present invention is the method for producing nickel nanoparticles according to any one of the first to fourth aspects, characterized in that the nickel compound contains at least one of nickel chloride and nickel nitrate.

[0015] (6) A sixth aspect of the present invention is the method for producing nickel nanoparticles according to any one of the first to fifth aspects, characterized in that in the electrolysis step, the temperature of the nickel electrolyte is maintained at 25°C or higher and 65°C or lower.

[0016] (7) A method for producing a conductive ink according to aspect 7 of the present invention includes an electrolyte generation step of dissolving a nickel compound in a conductive organic solvent to obtain a nickel electrolyte, an electrolysis step of electrolyzing the nickel electrolyte to reduce and generate nickel nanoparticles at a cathode, and a dispersion step of adding a dispersion solvent and a binder to the nickel nanoparticles and stirring them to obtain a conductive ink, wherein the electrolysis step is characterized by applying a current between an anode and a cathode and irradiating ultrasonic waves toward at least the cathode. Effect of the Invention

[0017] According to the present invention, it is possible to provide a method for producing nickel nanoparticles that has a small environmental impact during production and is capable of producing nickel nanoparticles in a simple manner at low cost, and a method for producing conductive ink. [Brief description of the drawings]

[0018] [Figure 1] 1 is a flowchart showing a step-by-step method for producing nickel nanoparticles and a method for producing a conductive ink according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing an example of an electrolysis device used in the electrolysis step of the nickel nanoparticle production method of the present embodiment. [Diagram 3] FIG. 2 is a schematic diagram showing an example of electrolysis of a nickel electrolyte in Verification Example 1. [Figure 4] 1 is a photograph showing the state of a precipitate after electrolysis and the state of a cathode and an anode in Verification Example 1. [Diagram 5] 1 is an electron microscope photograph of nickel nanoparticles in Verification Example 2. [Figure 6] 1 is a graph showing peaks of nickel nanoparticles in Verification Example 2 by X-ray diffraction (XRD). [Figure 7] 13 is a schematic diagram showing a manufacturing example of a conductive ink in Verification Example 3. FIG. [Figure 8] 13 is a graph showing the measurement results of the resistance value of the conductive ink in Verification Example 3. [Figure 9] 13 is a graph showing the results of weight gain obtained by TG and calculated weight gain in Verification Example 4. [Figure 10] FIG. 13 is a schematic diagram showing the creation procedure of Verification Example 5. [Figure 11] 13 is a photograph showing the state of the solution before and after the reduction reaction of a conventional example (H2O) and an example of the present invention (EG) in Verification Example 5. [Figure 12] 11 is an electron microscope photograph showing nickel particles of a conventional example (H2O) and an example of the present invention (EG) in Verification Example 5. [Figure 13] 1 is a graph showing peaks of X-ray diffraction (XRD) in Verification Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may show characteristic parts in an enlarged scale for the sake of convenience in order to make the characteristics easier to understand, and the dimensional ratios of each component may not necessarily be the same as in reality. In addition, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited to them, and may be appropriately modified and implemented within a range that does not change the effects of the present invention.

[0020] In the following description, nickel nanoparticles are metal particles containing nickel with a crystallite diameter of 1 nm to 100 nm. The shape of the particles is not particularly limited, and may be any shape, such as spherical, flaky, cubic, or irregular.

[0021] [Method of manufacturing nickel nanoparticles] Fig. 1 is a flow chart showing a step-by-step method for producing nickel nanoparticles and a method for producing conductive ink according to an embodiment of the present invention, and Fig. 2 is a schematic diagram showing an example of an electrolysis device used in the electrolysis step of the method for producing nickel nanoparticles according to the present embodiment. When nickel nanoparticles are produced by the nickel nanoparticle production method of the present embodiment, first, a nickel compound is dissolved in a conductive organic solvent to form a nickel electrolyte (electrolytic solution production step S1).

[0022] The conductive organic solvent for dissolving the nickel compound may be any liquid that can dissolve the nickel compound, has electrical conductivity, and does not react with the metallic nickel produced by reduction. Specific examples of such conductive organic solvents include ethylene glycol, a deep eutectic solvent containing choline chloride and ethylene glycol, and an organic solvent containing polyaniline.

[0023] In this embodiment, ethylene glycol (HO-CH-CH-OH) was used as the conductive organic solvent. Ethylene glycol dissolves and ionizes inorganic nickel salt, and its conductivity is 1.07×10 -4 (S / m:25℃).

[0024] The nickel compound dissolved in the conductive organic solvent may be either an inorganic nickel compound or an organic nickel compound, but an inorganic nickel compound is preferred in terms of cost and solubility. Examples of the inorganic nickel compound include nickel chloride, nickel nitrate, and nickel sulfate. In this embodiment, nickel chloride (NiCl2) is used as the nickel compound. The solubility of nickel chloride in ethylene glycol is 2.36 (g / 100 ml).

[0025] Next, a direct current is applied between the cathode (negative electrode) 11 and the anode (positive electrode) 12 using an electrolysis device 10 to electrolyze the nickel electrolyte Q obtained in the electrolyte generation step S1, and nickel is reduced and generated at the cathode 11 (electrolysis step S2). In this electrolysis step S2, an ultrasonic generator 13 is used to irradiate ultrasonic waves toward the cathode 11 while applying a current. As a result, the nickel metal reduced and precipitated at the cathode 11 becomes nickel nanoparticles having a crystallite size on the nanometer order.

[0026] The ultrasonic generator 13 used in the electrolysis process S2 includes a container 14 for containing nickel electrolyte Q, a cathode 11 and an anode 12 immersed in the nickel electrolyte Q and arranged at a predetermined distance from each other, a power source 15 for applying a direct current between the cathode 11 and the anode 12, and the ultrasonic generator 13 for irradiating ultrasonic waves toward the cathode 11.

[0027] The container 14 may be made of a material that is not corroded by the nickel electrolyte Q and is capable of transmitting ultrasonic waves, such as glass or resin. In this embodiment, a glass container is used as the container 14 that is capable of transmitting ultrasonic waves.

[0028] The ultrasonic generator 13 may be capable of emitting ultrasonic waves U having a frequency of, for example, about 20 kHz to 300 MHz. In this embodiment, an ultrasonic generator 13 capable of emitting ultrasonic waves U having a frequency of 28 kHz is used. Note that, although this ultrasonic generator 13 is disposed outside the container 14 in this embodiment, it may be disposed inside the container 14 so as to be immersed in the nickel electrolyte Q as long as it has a waterproof function.

[0029] A conductive material, such as a metal plate, can be used for the cathode 11 and the anode 12. The metals used for the cathode 11 and the anode 12 may be the same or different, and various metals such as nickel, copper, aluminum, silver, and platinum can be used.

[0030] In order to prevent the metal materials constituting the cathode 11 and anode 12 from peeling off and mixing as impurities into the nickel nanoparticles electrolytically deposited, it is preferable that at least the cathode 11 is made of nickel (nickel electrode). Furthermore, if both the cathode 11 and the anode 12 are made of nickel (nickel electrode), it is possible to prevent the elution of impurity metals other than nickel into the nickel electrolyte Q, which is more preferable.

[0031] In the electrolysis step S2 performed using the electrolysis device 10 configured as described above, the temperature of the nickel electrolyte Q may be set to, for example, 25° C. or higher and 65° C. If the temperature of the nickel electrolyte Q is lower than 25° C., there is a concern that the rate of production of nickel nanoparticles may decrease. Also, if the temperature of the nickel electrolyte Q exceeds 65° C., there is a concern that the crystallite size and particle size of the generated nickel nanoparticles may become too large.

[0032] Then, a direct current is applied between the cathode 11 and the anode 12 from the power source 15. The applied direct current may have a voltage value of about 27.0V to 30.0V and a current value of about 0.05A to 0.2A.

[0033] Then, a direct current is applied between the cathode 11 and the anode 12, and ultrasonic waves U having a frequency of, for example, 28 kHz are irradiated from an ultrasonic generator 13 toward the cathode 11. By irradiating the ultrasonic waves U in this manner, the nickel deposited on the cathode 11 becomes nickel nanoparticles that are miniaturized to nano-order size without adhering to the surface of the cathode 11 in the form of a film, and are dispersed in the nickel electrolyte Q and deposited on the bottom of the container 14.

[0034] Ultrasonic waves U, which convert the nickel deposited on the cathode 11 into nanoparticles, may be continuously irradiated while a direct current is applied between the cathode 11 and the anode 12, or may be irradiated intermittently in a pulsed manner. When ultrasonic waves U are irradiated intermittently, the crystallite size and particle size of the nickel nanoparticles generated can be controlled by controlling the irradiation interval. For example, the longer the irradiation interval of ultrasonic waves U, the larger the crystallite size and particle size of the nickel nanoparticles generated can be. In addition, the crystallite size and particle size of the nickel nanoparticles generated can be increased by adjusting the output intensity of the irradiated ultrasonic waves U.

[0035] As described above, according to the method for producing nickel nanoparticles of this embodiment, when electrolyzing a nickel electrolyte solution in which a nickel compound is dissolved in a conductive organic solvent, ultrasonic waves are applied to the cathode 11 on which nickel is precipitated, and the precipitated nickel does not adhere to the surface of the cathode 11 in the form of a film, but becomes fine nickel nanoparticles, which peel off from the cathode 11, disperse in the nickel electrolyte solution Q, and accumulate on the bottom of the container 14. This makes it possible to easily obtain nickel nanoparticles having an average crystallite size of, for example, 1 nm or more and 100 nm or less.

[0036] Furthermore, nickel nanoparticles with even higher purity can be obtained by adsorbing the nickel nanoparticles obtained in the electrolysis step S2 using, for example, a neodymium magnet and separating out the unadsorbed particles.

[0037] Furthermore, the nickel nanoparticle manufacturing method of this embodiment has a smaller environmental impact than a method of chemically reducing nickel nanoparticles by using a reducing agent that has a large environmental impact to reduce nickel from a nickel electrolyte, and the cost required for treating the waste liquid is also small, making it possible to manufacture nickel nanoparticles in a simple manner at low cost.

[0038] [Conductive ink manufacturing method] Next, a method for producing a conductive ink according to an embodiment of the present invention will be described. When producing a conductive ink according to this embodiment, nickel nanoparticles obtained by the above-mentioned method for producing nickel nanoparticles are used.

[0039] A dispersion solvent and a binder are added to the nickel nanoparticles and stirred to form a conductive ink (dispersion step S3).

[0040] Examples of the dispersion solvent that can be used to disperse the nickel nanoparticles include cyclohexanone, acetone, etc. In this embodiment, a mixed solvent of cyclohexanone and acetone is used as the dispersion solvent.

[0041] The binder may be cellulose acetate, epoxy, ethyl cellulose, polyvinyl acetal, etc. In this embodiment, cellulose acetate is used as the binder.

[0042] In the dispersion step S3, the nickel nanoparticles, the dispersion solvent, and the binder may be mixed using a stirring device such as a ball mill, etc. In this way, the conductive ink can be obtained by the conductive ink manufacturing method of the present embodiment.

[0043] The conductive ink thus obtained can form a thin and narrow fine circuit pattern by patterning on a circuit board, since the crystallite size and particle size of the nickel nanoparticles, which are the conductors, are small. The formation of a circuit pattern using such a conductive ink can be achieved, for example, by applying the conductive ink to a substrate in a predetermined circuit pattern, and then heating and drying the ink at 90°C to 100°C for about 30 minutes to 1 hour.

[0044] Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention. EXAMPLES

[0045] Below, verification examples of the present invention will be described, but the present invention is not limited to the configurations shown in these verification examples. (Verification example 1) Nickel nanoparticles (samples) were actually produced by electrolysis of nickel electrolyte solution, in which nickel chloride hexahydrate (special grade, manufactured by Kanto Chemical Co., Ltd.) was dissolved in ethylene glycol (99.5% purity, manufactured by Wako Pure Chemical Industries, Ltd.), and ultrasonic irradiation, using an electrolysis apparatus with the configuration shown in the schematic diagram of Figure 3. Pure nickel plates were used as the cathode and anode, and electrolysis was performed with the temperature of the nickel electrolyte set to 25°C, 45°C, and 65°C, respectively. Ultrasound was irradiated toward the cathode continuously during electrolysis, with a frequency of 28 kHz.

[0046] The appearance of the precipitate after electrolysis at each solution temperature, as well as the appearance of the cathode and anode, are photographed in Figure 4. According to the results shown in Figure 4, at each solution temperature, a black precipitate containing nickel nanoparticles was formed at the bottom of the nickel electrolyte after electrolysis.

[0047] In addition, after electrolysis, the surface of the anode was observed to dissolve, and the nickel that constituted the anode was dissolved into the nickel electrolyte. 2+ In addition, black deposits were found on the surface of the cathode after electrolysis, suggesting the generation of nickel nanoparticles.

[0048] (Verification example 2) FIG. 5 shows electron microscope images of nickel nanoparticles obtained in Verification Example 1 when the nickel electrolyte temperature was 25° C., 45° C., and 65° C., and FIG. 6 shows a peak graph obtained by X-ray diffraction (XRD).

[0049] According to the results shown in Figure 5, it was confirmed that flaky nickel nanoparticles were produced at all liquid temperatures. Also, according to Figure 6, it was confirmed that nickel peaks were observed for the nickel nanoparticles obtained at each liquid temperature, indicating nano-sized crystallite diameters. Therefore, it was confirmed that the precipitates were nickel nanoparticles.

[0050] (Verification example 3) As shown in the schematic diagram of Fig. 7, conductive inks were prepared using nickel nanoparticles (electrolysis method) of the present invention and nickel particles (chemical reduction method) of the comparative example. The nickel nanoparticles used in the present invention were those produced at a liquid temperature of 25°C in Verification Example 1. Nickel powder with a purity of 99.0 mass% (special grade, manufactured by Kanto Chemical Co., Ltd.) was used as the nickel particles of the comparative example.

[0051] The resistance value of each of the conductive inks obtained was then measured. The resistivity was measured using a resistance meter (MCP-T370, manufactured by Nitto Seiko Analytic Co., Ltd.). The resistance values ​​of each conductive ink thus obtained are shown in the graph of FIG. According to the measurement results shown in FIG. 8, the resistance value of the conductive ink using the nickel nanoparticles (prepared Ni particles) of the present invention is 0.85 (Ω / cm 2), and the resistance value of the conductive ink using nickel particles (commercially available Ni particles) in the comparative example (0.79 (Ω / cm 2 )) and it was confirmed that it can be used as a conductive ink.

[0052] (Verification example 4) The purity of nickel was calculated based on the following formula (1) for the nickel nanoparticles (electrolysis method) of the present invention prepared in Verification Example 1 (25°C), the nickel powder obtained by reducing nickel salt with hydrazine (hydrazine reduction), and commercially available nickel powder. Amount of Ni calculated from ICP (g) / Amount of Ni powder added × 100 (%) (1) The results are shown in Table 1.

[0053] [Table 1]

[0054] According to the results shown in Table 1, the commercially available particles and the prepared particles (electrolysis) were almost identical, whereas the prepared particles (hydrazine reduction) had a lower purity. This suggests that the purity of the prepared particles (hydrazine reduction) is reduced due to the hydrazine used during reduction, whereas the prepared particles (electrolysis) use only electrical energy to perform the reduction.

[0055] FIG. 9 is a graph showing the weight gain (%) obtained by TG and the calculated weight gain (%) for the three types of nickel particles described above. According to these results, the weight gain of the produced particles (electrolysis) obtained by TG almost coincided with the calculated weight gain, suggesting high nickel purity.

[0056] (Verification example 5) FIG. 10 is a schematic diagram showing the creation procedure of Verification Example 5. A comparison was made between nickel powder obtained by electrolyzing nickel salt using water as a solvent as in the conventional method (conventional example) and nickel powder obtained by electrolyzing nickel salt using ethylene glycol as a solvent (example of the present invention). FIG. 11 shows the state of the solutions before and after the reduction reaction of the above-mentioned conventional example (H2O) and the example of the present invention (EG).

[0057] According to these results, in the conventional example (H2O), nickel generated by oxidation is oxidized by water, becoming oxide (NiO) and remaining in suspension as black fine particles. On the other hand, in the present invention example (EG), nickel is not oxidized and precipitates as nickel nanoparticles. It was confirmed that by using ethylene glycol as the solvent, the generated nickel is generated without being oxidized.

[0058] FIG. 12 shows an electron microscope photograph of the nickel particles of the conventional example (H2O) and the example of the present invention (EG) in Verification Example 5, and FIG. 13 shows a peak graph by X-ray diffraction (XRD).

[0059] According to the results shown in Fig. 13, the example of the present invention (EG) showed no peaks other than those specific to Ni, and was confirmed to be nickel particles of high purity. On the other hand, the nickel particles of the conventional example (H2O) showed a low peak specific to Ni and a peak indicating nickel hydroxide, suggesting that the purity of nickel had decreased due to the generation of impurities caused by electrolysis using water as a solvent. [Industrial Applicability]

[0060] According to the method for producing nickel nanoparticles and the method for producing conductive ink of the present invention, nickel nanoparticles and conductive ink using the same can be produced efficiently at low cost using a simple device without using a reducing agent, which is costly for wastewater treatment. Therefore, the method has industrial applicability. [Explanation of symbols]

[0061] 10...Electrolysis device 11...Cathode 12...Anode 13...Ultrasonic generator 14...Container 15...Power supply

Claims

1. an electrolyte solution producing step of dissolving a nickel compound in a conductive organic solvent to obtain a nickel electrolyte solution; An electrolysis step of electrolyzing the nickel electrolyte to reduce and generate nickel nanoparticles at a cathode, The method for producing nickel nanoparticles, wherein the electrolysis step is a step of applying a current between an anode and a cathode and irradiating ultrasonic waves toward at least the cathode.

2. The method for producing nickel nanoparticles according to claim 1 , wherein the conductive organic solvent includes ethylene glycol.

3. The method for producing nickel nanoparticles according to claim 1 or 2, characterized in that in the electrolysis process, at least one of the crystallite size or particle size of the nickel nanoparticles generated at the cathode is controlled by adjusting the frequency or intensity of the ultrasonic waves.

4. The method for producing nickel nanoparticles according to claim 1 or 2, characterized in that the cathode is made of a metal containing nickel.

5. The method for producing nickel nanoparticles according to claim 1 or 2, characterized in that the nickel compound contains at least one of nickel chloride and nickel nitrate.

6. The method for producing nickel nanoparticles according to claim 1 or 2, characterized in that in the electrolysis step, the temperature of the nickel electrolyte is kept at 25°C or higher and 65°C or lower.

7. an electrolyte solution producing step of dissolving a nickel compound in a conductive organic solvent to obtain a nickel electrolyte solution; an electrolysis step of electrolyzing the nickel electrolyte to reduce and generate nickel nanoparticles at a cathode; A dispersion process of adding a dispersion solvent and a binder to the nickel nanoparticles and stirring the mixture to obtain a conductive ink, A method for producing a conductive ink, wherein the electrolysis step is a step of applying a current between an anode and a cathode and irradiating ultrasonic waves toward at least the cathode.

Images