JP2023140370A - Nickel particle and use thereof - Google Patents

Abstract

To provide a technique that can optimally improve the dispersibility of conductive paste.SOLUTION: A nickel particle disclosed herein has nickel as the main constituent element. The surface of the nickel particle has an amine compound and a nitrile compound and/or an amide compound attached thereto. Based on GCMS analysis, when the total weight of the amine compound and the nitrile compound and/or the amide compound is 100 wt.%, the amine compound attached constitutes 40 wt.% or more.SELECTED DRAWING: None

Description

TECHNICAL FIELD This disclosure relates to nickel particles and their uses.

In recent years, there has been a demand for further miniaturization of electronic components (eg, multilayer ceramic capacitors: MLCCs). For example, when downsizing an MLCC, it is necessary to make the internal electrodes of the MLCC thinner, and the conductive paste used to form such internal electrodes has a small particle size (typically, an average particle size It is said that it is preferable to include conductive particles (with a diameter of about 150 nm or less). Patent Document 1 listed below discloses a technology regarding nickel particles that are suitably used in a conductive paste for forming internal electrodes of MLCC.

Patent No. 6799936

According to studies conducted by the present inventors, it has been found that in a conductive paste containing nickel particles having a small particle size as described above, the nickel particles in the conductive paste tend to aggregate together. Therefore, in a conductive paste having such a configuration, further improvement in the dispersibility of nickel particles is required.

The present disclosure has been made in view of such circumstances, and its main purpose is to provide a technique that can suitably improve the dispersibility of conductive paste.

In order to achieve this objective, the present disclosure provides nickel particles containing nickel as a main constituent element. An amine compound, a nitrile compound and/or an amide compound are attached to the surface of the nickel particles, and based on GCMS analysis, the amine compound, the nitrile compound and/or the amide compound are attached to the surface of the nickel particle. When the total weight of , is 100% by weight, the amine compound is attached in an amount of 40% by weight or more. Although details will be described later, the nickel particles having such a configuration can suitably improve the dispersibility of the conductive paste.

In a preferred embodiment of the nickel particles disclosed herein, the CuNi core-shell particles have a CV value of 0.2 or less. For example, CuNi core-shell particles having a CV value of 0.2 or less are preferable because the dispersibility of the conductive paste can be improved more suitably.

In a preferred embodiment of the nickel particles disclosed herein, the average particle diameter of the CuNi core-shell particles is 150 nm or less. As described above, particles having an average particle diameter of 150 nm or less are preferable because they can be suitably used, for example, to form internal electrodes of miniaturized MLCCs.

In one embodiment of the nickel particles disclosed herein, two or more types of amine compounds are attached to the surface of the nickel particles.

In another aspect, the present disclosure provides a powder material that includes any of the nickel particles disclosed herein. By using the powder material containing nickel particles disclosed herein, a conductive paste with excellent dispersibility can be obtained.

In another aspect, the present disclosure provides a conductive paste that includes any of the nickel particles disclosed herein and a medium in which the nickel particles are dispersed. The conductive paste containing nickel particles disclosed herein has excellent dispersibility and can therefore be preferably used.

FIG. 2 is a flow diagram showing the steps of a method for manufacturing nickel particles according to one embodiment.

Hereinafter, preferred embodiments of the present disclosure will be described. Note that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure can be understood as matters designed by those skilled in the art based on the prior art in the field. The present disclosure can be implemented based on the content disclosed in this specification and the common general knowledge in the field. Note that the following embodiments are not intended to limit the technology disclosed herein to such embodiments. Note that in this specification and claims, when a predetermined numerical range is expressed as A to B (A and B are arbitrary numerical values), it means greater than or equal to A and less than or equal to B. Therefore, cases in which the value exceeds A and are lower than B are included.

Furthermore, in this specification and claims, the term "nickel particles" refers to a group of many fine particles (ie, particles), unless specifically referring to a single particle. In Japanese, it is ambiguous whether it is singular or plural, so we define it as above to clarify the meaning of "nickel particle". Furthermore, in the present specification and claims, the term "conductive paste" may include a slurry-like composition and an ink-like composition.

1. Nickel Particles The nickel particles disclosed herein are nickel particles containing nickel (Ni) as a main constituent element. An amine compound, a nitrile compound and/or an amide compound are attached to the surface of such nickel particles. Based on GCMS analysis (gas chromatography mass spectrometry), when the total weight of the amine compound, nitrile compound and/or amide compound is 100% by weight, 40% by weight or more of the amine compound must be attached. It is characterized by

The reason why the above configuration achieves the effects of the technology disclosed herein is not particularly limited, but the following may be considered. That is, for example, in the production of nickel particles, when nickel ions (Ni ²⁺ ) are reduced to metallic nickel (Ni), the reaction shown in the following formula (I) (R represents hydrogen or a hydrocarbon group) is performed. A nitrile compound can be generated from a part of the amine compound added as a reducing agent.

Further, an amide compound can be generated by reacting the carboxylic acid attached to the nickel salt with a part of the amine compound using nickel particles as a catalyst. For example, when an amine compound, a nitrile compound, or an amide compound (especially an amine compound) is attached to the surface of nickel particles, these compounds are said to play a role as a dispersant. On the other hand, according to the inventor's study, when nickel particles are synthesized by the conventional method, no amine compound is attached to the surface of the synthesized nickel particles (even if there is, a sufficient amount is not attached). It was found that mainly nitrile compounds and/or amide compounds were attached. It has also been found that when a conductive paste is prepared by performing a dispersion treatment in such a state, a large amount of aggregated particles are generated. Therefore, as a result of intensive study by the present inventor, it was found that by adding an amine compound to the nickel particles after synthesis and performing heating and stirring, the amine compound can be suitably attached to the surface of the nickel particles. . Furthermore, according to the inventor's study, when the total weight of the amine compound, nitrile compound and/or amide compound is 100% by weight, based on GCMS analysis, 40% by weight or more of the amine compound adheres to the surface. The inventors have discovered that the generation of agglomerated particles can be suitably suppressed even when a conductive paste is prepared by performing a dispersion treatment using nickel particles, and the present disclosure has been completed. Note that the above explanation is the inventor's consideration based on experimental results, and the technology disclosed herein is not interpreted to be limited to the above mechanism. Each component will be explained below.

Nickel particles are particles containing nickel as a main constituent element. Here, in this specification and claims, "containing nickel as a main constituent element" means that among the components constituting the nickel particles, nickel is the component that is contained the most on a mol% basis. . Nickel particles are, for example, 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, when the amount of all metal elements contained in the nickel particles is 100 mol%. , or particles containing nickel in an amount of 95 mol % or more (may be 100 mol %). Nickel particles contain various metal elements (e.g., gold (Au), platinum (Pt), silver (Ag), palladium (Pd), copper (Cu)) and nonmetallic elements (e.g., hydrogen) as unavoidable impurities. (H), carbon (C), nitrogen (N), oxygen (O), sulfur (S), phosphorus (P)), etc. Further, as the nickel particles, for example, nickel alloys or core-shell particles whose interior (core) is made of a metal other than nickel and whose shell covering at least a part of the surface of the core is made of nickel may be used. can. In the case of core-shell particles, examples of metals other than nickel include copper (Cu), silver (Ag), gold (Au), platinum (Pt), palladium (Pd), and the like. Core-shell particles are a typical example of the "nickel particles" referred to herein. Examples of such nickel alloys include alloys of nickel and at least one metal selected from the group consisting of the metals listed above as metals other than nickel. In addition, the nickel particles may be used singly or in combination of two or more types from among those mentioned above.

Here, when the nickel particles are core-shell particles, the shape of the core particles is not particularly limited as long as the effects of the technology disclosed herein are exhibited, and may be spherical or non-spherical. There may be. In addition, from the viewpoint of ease of handling, it is preferable that the core particles have a spherical shape. Further, the average particle diameter of the core particles may be approximately 1 nm to 100 nm (for example, approximately 10 nm to 50 nm). The thickness of the nickel shell may be approximately 1 nm to 100 nm (for example, approximately 10 nm to 50 nm). The thickness of the nickel shell can be determined, for example, by observing the cross section of the core-shell particle using a transmission electron microscope (TEM). The thickness of the nickel shell can be calculated, for example, as the average value of five randomly measured thicknesses of the nickel shell. Further, when the total weight of the nickel particles is 100% by weight, the weight ratio occupied by the nickel shell can typically be about 0.5 to 95% by weight (for example, about 50 to 95% by weight). However, the weight proportion of the nickel shell is not limited to these.

In this specification and claims, "average particle diameter" refers to the particle size distribution based on number based on a field emission scanning electron microscope (FE-SEM), from the small particle size side to an integrated value of 50%. It can also mean the corresponding particle size (hereinafter also referred to as "D50"). Such measurements can be carried out using, for example, a commercially available device, S-4700 manufactured by Hitachi High-Technologies Corporation.

An amine compound, a nitrile compound and/or an amide compound are attached to the surface of the nickel particles disclosed herein. Based on GCMS analysis, when the total weight of the amine compound, nitrile compound and/or amide compound is 100% by weight, 40% by weight or more of the amine compound is attached. The amount of the amine compound, nitrile compound, and amide compound attached to the surface of the nickel particles can be calculated using a calibration curve created based on GCMS analysis. For details, please refer to the Examples below. As described above, the present inventors have found that the dispersibility of the conductive paste can be suitably improved by using nickel particles having such a configuration.

The type of the amine compound is not particularly limited as long as the effects of the technology disclosed herein are exhibited. The amine compound is preferably a monoamine compound that does not contain a secondary or tertiary amino group, for example. Examples of such amine compounds include linear amine compounds such as n-propylamine, n-butylamine, n-pentylamine, n-hexylamine, n-heptylamine, n-octylamine, n-dodecylamine, stearylamine, and oleylamine. Amine compounds with a branched structure such as 2-ethylhexylamine; amine compounds with a cyclic structure such as cyclopropylamine, cyclobutylamine, cyclopentylamine, cyclohexylamine, cycloheptylamine, and cyclooctylamine; and the like. Further, the number of carbon atoms in the amine compound is preferably 6 or more, more preferably 7 or more, and more preferably 8 or more. Note that one type of the above-mentioned amine compound may be attached to the nickel particles, or two or more types of amine compounds may be attached to the nickel particles. Alternatively, in addition to the above-mentioned amine compounds, amine compounds other than the above-mentioned amine compounds may be attached as long as the effects of the technology disclosed herein are exhibited. In one embodiment of the nickel particles disclosed herein, two or more types of amine compounds are attached to the surface of the nickel particles. An example of a method for synthesizing nickel particles having such a configuration is a method using different amine compounds in steps S1 and S3, which will be described later. The amine compound attached to the surface of the nickel particles can be identified, for example, by pyrolysis GCMS spectroscopy.

As mentioned above, nitrile compounds can be generated, for example, from a portion of the amine compound added as a reducing agent when nickel ions (Ni ²⁺ ) are reduced to metallic nickel. Examples of such nitrile compounds include nitrile compounds produced from the above amine compound based on the above formula (I). Note that one type of the above-mentioned nitrile compound may be attached to the nickel particles, or two or more types of nitrile compounds may be attached to the nickel particles. Alternatively, in addition to the above-mentioned nitrile compounds, a nitrile compound other than the above-mentioned nitrile compounds may be attached as long as the effects of the technology disclosed herein are exhibited. The nitrile compound attached to the surface of the nickel particles can be identified, for example, by pyrolysis GCMS spectroscopy.

As described above, the amide compound can be produced, for example, by reacting a carboxylic acid attached to a nickel salt with an amine compound using nickel particles as a catalyst. Examples of such amide compounds include amide compounds of the above amine compound and a carboxylic acid (eg, formic acid or carboxylic acid) attached to a nickel salt. Note that one type of the above-mentioned amide compound may be attached to the nickel particles, or two or more types of amide compounds may be attached to the nickel particles. Alternatively, in addition to the above-mentioned amide compound, an amide compound other than the above-mentioned amide compound may be attached as long as the effect of the technology disclosed herein is exhibited. The amide compound attached to the surface of the nickel particles can be identified, for example, by pyrolysis GCMS spectroscopy.

The nickel particles disclosed herein have at least 40% by weight of the amine compound attached when the total weight of the amine compound, nitrile compound, and/or amide compound is 100% by weight, based on GCMS analysis. It is characterized by As described above, the nickel particles having such a configuration can suitably improve the dispersibility of the conductive paste. Here, the amount of the amine compound attached is more preferably, for example, 45% by weight or more, 50% by weight or more, 55% by weight or more, or 60% by weight or more. Further, the upper limit of the amount of the amine compound attached is not particularly limited as long as the effect of the technology disclosed herein is exhibited, but it is generally 90% by weight or less, for example, 80% by weight or less, 70% by weight or less, 65% by weight or less. It can be less than % by weight.

Further, the amount of the nitrile compound attached to the surface of the nickel particles is not particularly limited as long as the effects of the technology disclosed herein are exhibited, and is approximately 0 to 50% by weight (for example, approximately 20 to 45% by weight). can do. The amount of the amide compound attached to the surface of the nickel particles is not particularly limited as long as the effect of the technology disclosed herein is exhibited, and is generally about 0 to 20% by weight (for example, about 5 to 15% by weight). can do.

The amount of the amine compound, nitrile compound, and amide compound attached to the nickel surface can be easily changed, for example, by the following method. The amount of the amine compound attached to the nickel surface can be changed, for example, by adjusting the amount of the amine compound added to the nickel particles after synthesis and the conditions of the heat treatment (heating time, heating temperature, etc.). Typically, the amount of the amine compound attached to the surface of the nickel particles can be increased by increasing the amount of the amine compound added and the heating time and temperature. Further, the amount of the nitrile compound or amide compound deposited on the nickel surface can be changed, for example, by adjusting the conditions (reaction time, reaction temperature, etc.) of the reduction reaction shown in the above formula (I). Typically, by increasing the reaction time and reaction temperature of the reduction reaction shown in formula (I) above, the amount of the nitrile compound or amide compound attached to the surface of the nickel particles can be increased. However, it is not intended to be limited to these.

The average particle diameter of the nickel particles is not particularly limited as long as the effects of the technology disclosed herein are exhibited. The lower limit of the average particle diameter of the nickel particles is approximately 10 nm or more, preferably 20 nm or more, more preferably 30 nm or more, and more preferably 40 nm or more, from the viewpoint of easily controlling aggregation of particles. On the other hand, the upper limit of the nickel particles is approximately 200 nm or less, and from the viewpoint of use, for example, in forming internal electrodes of a miniaturized MLCC, the upper limit is preferably 150 nm or less, and more preferably 100 nm or less (for example, 60 nm or less or 50 nm or less).

The CV value of the nickel particles is not particularly limited as long as the effects of the technology disclosed herein are exhibited. Here, the CV value (coefficient of variation) means the ratio of the standard deviation σ to the average particle diameter of the nickel particles (standard deviation σ/average particle diameter), and the smaller the CV value, the more uniform the particles are. I can do it. Further, nickel particles having a small CV value (in other words, the particles are uniform) are considered preferable because agglomeration of the particles can be suitably suppressed. The CV value of the nickel particles is approximately 0.5 or less, preferably 0.2 or less, more preferably 0.18 or less, and more preferably 0.15 or less from the viewpoint of suitably suppressing aggregation of particles.

The crystal structure of the nickel particles is not particularly limited as long as the effects of the technology disclosed herein are exhibited. Here, examples of the crystal structure of the nickel particles include fcc (face-centered cubic structure) and hcp (hexagonal close-packed structure). From the viewpoint of stability and the like, the crystal structure of the nickel particles is preferably at least partially FCC, and more preferably entirely FCC. Note that such a crystal structure can be confirmed, for example, by peak analysis based on XRD (X-ray diffraction).

2. Method for Manufacturing Nickel Particles Next, a preferred example of the method for manufacturing nickel particles disclosed herein will be described. The method for producing nickel particles disclosed herein is characterized by adding an amine compound to the synthesized nickel particles and performing a heat treatment (see step S3). Thereby, the amount of the amine compound attached to the surface of the nickel particles can be suitably increased. The steps up to the post-addition of the amine compound may be the same as conventional ones. In addition, below, as nickel particles, a method for producing copper-nickel core-shell particles (CuNi core-shell particles) consisting of a core particle composed of copper and a nickel shell covering at least a part of the surface of the core particle will be explained. do. Note that the following explanation is not intended to limit the manufacturing method of CuNi core-shell particles to the following manufacturing method. This will be explained below with reference to FIG. 1 as appropriate.

FIG. 1 is a rough flowchart showing the steps of a method for manufacturing nickel particles (here, CuNi core-shell particles) according to an embodiment. As shown in FIG. 1, the process includes production of nickel seed particles (step S1); production of nickel particles (step S2); addition of an amine compound (step S3); and collection of nickel particles (step S4). Each step will be explained below.

First, in step S1, nickel seed particles (hereinafter also simply referred to as "seed particles") are produced. Here, the seed particles are particles that can function as nuclei for the growth of nickel. Such seed particles can be synthesized, for example, by using nickel salts and copper salts as raw materials and subjecting them to wet reduction by heating in the presence of an amine compound. According to this method, seed particles can be obtained by first producing core copper particles due to the difference in standard potential between copper and nickel, and then forming a nickel coating on the surface of the copper particles.

Specifically, first, a predetermined amount (e.g., about 0.005 to 0.1 molar equivalent) of a nickel salt is added to an amine compound, and the mixture is heated at a predetermined temperature (e.g., about 100 to 150°C) for a predetermined time (e.g., 60 A nickel-amine complex is synthesized by heating (about 120 minutes). Subsequently, a predetermined amount (e.g., about 0.0005 to 0.01 molar equivalent) of a copper salt is added to the nickel-amine complex, and the mixture is heated at a predetermined temperature (e.g., about 50 to 100°C) for a predetermined time (e.g., 30 to 100°C). A copper-amine complex is synthesized by heating (for about 60 minutes). Thereafter, seed particles (seed particle slurry) can be synthesized by heating at a predetermined temperature (for example, about 150 to 200° C.) for a predetermined time (for example, about 10 to 30 minutes) in a nitrogen atmosphere.

As the amine compound, for example, the amine compound described above can be used. As these amine compounds, for example, commercially available ones can be used without particular restriction.

Examples of the nickel salt include nickel carboxylate, nickel chloride, nickel carbonate, nickel nitrate, and nickel hydroxide. Among these, nickel carboxylate, which has a relatively low decomposition temperature during reduction, can be preferably used. Examples of such nickel carboxylates include nickel formate and nickel acetate. Nickel carboxylate may be anhydrous or hydrated. Examples of such hydrates include nickel formate dihydrate and nickel acetate tetrahydrate. As the nickel salt, for example, commercially available ones can be used without particular restriction.

As the copper salt, copper carboxylate, which has a relatively low decomposition temperature during reduction, can be preferably used. Examples of such copper carboxylates include copper formate and copper acetate. Such copper carboxylate may be anhydrous or hydrated. Such hydrates include copper acetate tetrahydrate. As the copper salt, for example, commercially available ones can be used without particular restriction.

Next, in step S2, nickel particles are produced. In step S2, nickel salt is added to the seed particle slurry obtained in step S1, and wet reduction by heating is performed. This allows the Ni shell to grow using the seed particles as nuclei. By growing the Ni shell using the seed particles as nuclei in this way, uniform nickel particles with a low CV value can be obtained, which is preferable.

Specifically, first, a predetermined amount (e.g., about 1 to 45 molar equivalents) of nickel salt is added to the seed particle slurry obtained in step S1, and the mixture is heated at a predetermined temperature (e.g., about 100 to 150°C). A nickel-amine complex is synthesized by heating for a period of time (approximately 60 to 120 minutes). Thereafter, nickel particles (nickel particle slurry) are synthesized by heating in a nitrogen atmosphere at a predetermined temperature (for example, about 150 to 200° C.) for a predetermined time (30 to 60 minutes). Here, as the nickel salt, for example, those described in the column of nickel salt in step S1 can be used.

Subsequently, in step S3, an amine compound is added. Thereby, the amount of the amine compound attached to the surface of the nickel particles can be suitably increased.
Specifically, the supernatant liquid of the nickel particle slurry obtained in step S2 is removed, and the above-mentioned amine compound is added. Thereafter, nickel particles (nickel particle slurry) can be obtained by heating in a nitrogen atmosphere at a predetermined temperature (for example, about 50 to 150° C.) for a predetermined time (for example, about 30 to 60 minutes).

Subsequently, in step S4, nickel particles are recovered.
Specifically, first, the supernatant liquid of the nickel particle slurry obtained in step S3 is removed. Subsequently, a suitable cleaning solvent (for example, isobornyl acetate, etc.) is added and dispersed using an ultrasonic cleaner or the like, and then the supernatant liquid is removed. After repeating this operation multiple times (for example, about 2 to 5 times), the nickel particles ( powder) can be obtained.

In addition to the nickel particles disclosed herein, if necessary, a binder (for example, an acrylic resin, an epoxy resin, a phenol resin, an amine resin, an alkyd resin, a cellulose resin such as ethyl cellulose), By adding a conductive material, another powder material (for example, barium titanate), etc., powder materials for various uses can be obtained. For example, a powder material can be obtained by mixing and pulverizing nickel particles and the materials described above. As described above, this powder material contains nickel particles, so by using this powder material, it is possible to improve the dispersibility of the conductive paste and reduce the shrinkage rate of the conductive layer obtained after firing. Both can be suitably achieved. The content of nickel particles in the powder material is not particularly limited, but is approximately 50 to 95% by weight (for example, about 60 to 90% by weight) when the entire powder material is 100% by weight. It is preferable.

Further, by dispersing the nickel particles disclosed herein in a dispersion medium (medium) consisting of an appropriate aqueous solvent or organic solvent, dispersions (conductive pastes) for various uses can be obtained. For example, nickel particles are dispersed in a predetermined organic solvent, and if necessary, binders (see those listed in the description of powder materials), conductive materials, other powder materials, dispersants (for example, carboxylic acid dispersion), etc. A composition prepared in the form of a paste (conductive paste) can be obtained by adding components such as a conductive agent) and a viscosity modifier. Since such a conductive paste contains nickel particles as described above, it is possible to suitably achieve both excellent dispersibility and a reduction in the shrinkage rate of the conductive layer obtained after firing.

The dispersion medium used in the conductive paste may be any dispersion medium as long as it can disperse this type of conductive powder material well, and any dispersion medium used in the preparation of conventionally known conductive pastes may be used without particular limitation. can be used. Examples of organic solvents include petroleum hydrocarbons (especially aliphatic hydrocarbons) such as mineral spirits, ethylene glycol and diethylene glycol derivatives, toluene, xylene, butyl carbitol (BC), isobornyl acetate, terpineol, and other high-carbon solvents. One kind or a combination of two or more kinds of boiling point organic solvents can be used. Here, the content of nickel particles in the conductive paste is not particularly limited, but when the entire conductive paste is taken as 100% by weight, it is approximately 30 to 70% by weight (for example, approximately 40 to 60% by weight). It is preferable that there be. Further, the content of the dispersion medium in the conductive paste is not particularly limited, but is approximately 30 to 70% by weight (for example, approximately 40 to 60% by weight) when the entire conductive paste is 100% by weight. It is preferable. The viscosity of such a conductive paste is not particularly limited, but it is preferably about 10 to 100 mPa·s (for example, about 20 to 50 mPa·s). Such viscosity can be measured, for example, with a commercially available viscometer.

The above-described technology can be used, for example, in the field of electronic materials to make electronic components smaller and electrodes thinner.

Test examples regarding the nickel particles disclosed herein will be described below, but the present disclosure is not intended to be limited to such test examples. In addition, below, the case where CuNi core-shell particles are used as an example of nickel particles will be explained.

<Synthesis of nickel particles>
First, the synthesis of nickel particles according to Examples 1 to 6 will be explained.

(Synthesis of nickel seed particle slurry)
Add 1.7 g of nickel formate dihydrate (Fuji Film Wako Pure Chemical Industries, Ltd. product, hereinafter the same) to 319.2 g of oleylamine (Fuji Film Wako Pure Chemical Industries, Ltd. product), and heat at 120° C. for 120 minutes. By this method, a nickel formate-oleylamine complex was synthesized. Next, 0.23 g of copper formate tetrahydrate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., hereinafter the same) was added to the nickel formate-oleylamine complex, and the formic acid was heated at 60°C for 30 minutes. A copper-oleylamine complex was synthesized. Thereafter, a nickel seed particle slurry was synthesized by heating at 190° C. for 10 minutes in a nitrogen atmosphere.

(Synthesis of nickel particle slurry)
To the nickel seed particle slurry synthesized above, 114.0 g of nickel acetate tetrahydrate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., hereinafter the same) was added, and by heating at 135°C for 120 minutes, nickel acetate-tetrahydrate was added. An oleylamine complex was synthesized. Thereafter, a nickel particle slurry was synthesized by heating at 200° C. for 30 minutes in a nitrogen atmosphere.

- Synthesis of nickel particle slurry according to Example 1 The supernatant liquid of the nickel particle slurry synthesized above was removed. A nickel particle slurry according to Example 1 was synthesized by adding 200 mL of oleylamine to the slurry and heating and stirring at 100° C. for 30 minutes.

- Synthesis of nickel particle slurry according to Example 2 The supernatant liquid of the nickel particle slurry synthesized above was removed. A nickel particle slurry according to Example 2 was synthesized by adding 100 mL of oleylamine to the slurry and heating and stirring at 100° C. for 30 minutes.

- Synthesis of nickel particle slurry according to Example 3 The supernatant liquid of the nickel particle slurry synthesized above was removed. A nickel particle slurry according to Example 3 was synthesized by adding 200 mL of oleylamine to the slurry and heating and stirring at 50° C. for 60 minutes.

- Synthesis of nickel particle slurry according to Example 4 The supernatant liquid of the nickel particle slurry synthesized above was removed. A nickel particle slurry according to Example 4 was synthesized by adding 200 mL of 2-ethylhexylamine (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) to the slurry and heating and stirring at 100° C. for 30 minutes.

- Synthesis of nickel particle slurry according to Example 5 The supernatant liquid of the nickel particle slurry synthesized above was removed. A nickel particle slurry according to Example 1 was synthesized by adding 100 mL of oleylamine to the slurry and heating and stirring at 50° C. for 60 minutes.

- Synthesis of nickel particle slurry according to Example 6 The supernatant liquid of the nickel particle slurry synthesized above was removed. This slurry was designated as the nickel particle slurry according to Example 5.

The supernatant liquid of the nickel particle slurry according to each of the above synthesized examples was removed. After adding isobornyl acetate and dispersing it with an ultrasonic cleaner, the supernatant liquid was removed. After repeating this operation three times, the material was dried in a dryer at 120° C. for 60 minutes to obtain a powder material consisting of nickel particles according to each example.

<Evaluation test>

(1) Characteristics of Nickel Particles Nickel particles in the above powder material were observed using a field emission scanning electron microscope (FE-SEM: S-4700 manufactured by Hitachi High-Technologies Corporation). Specifically, five images were extracted from a 50,000x field of view, 200 nickel particles were randomly extracted, and their projected areas were determined. The diameter (Heywood diameter) of a circle having the same area as this was measured. Then, the cumulative 50% particle diameter (D50) in the number-based particle size distribution was calculated as the average particle diameter (nm). In addition, the coefficient of variation (CV) of the average particle diameter was calculated. Here, the CV value means the ratio of the standard deviation σ to the average particle diameter of nickel particles (standard deviation σ/average particle diameter). The average particle diameter of the nickel particles in each example was about 50 nm, and the CV value was about 0.15.

(2) Analysis of organic substances on the surface of nickel particles 0.6 mL of methanol was added to 500 mg of nickel particles according to each example synthesized above, and ultrasonic irradiation was performed for 1 hour using an ultrasonic cleaner. Then, the supernatant liquid after collecting the particles with a magnet was used as an extraction liquid, and it was measured with a GCMS device (GCMS-QP-2010Ultra manufactured by Shimadzu Corporation) to analyze the organic substances attached to the surface of the nickel particles. Ta. Specifically, identification of organic substances attached to the surface of nickel particles and calculation of the amount (wt%) of amine compounds, nitrile compounds, and amide compounds attached when the total weight of the organic substances is 100% by weight. I did this. The amount of adhesion was calculated using a calibration curve based on the peak area of GCMS and sample concentration. The measurement results are shown in the relevant column of Table 1.

Although not listed in Table 1, oleylamine, oleylonitrile, and an amide compound of oleylamine and acetic acid (or formic acid) were attached to the surface of the nickel particles according to Examples 1 to 3, 5, and 6. It was confirmed that Further, on the surface of the nickel particles according to Example 4, oleylamine, 2-ethylhexylamine, oleylonitrile, 2-ethylhexylonitrile, an amide compound of oleylamine and acetic acid (or formic acid), 2-ethylhexylamine and acetic acid ( It was confirmed that an amide compound with (or formic acid) was attached.

(Preparation of conductive paste)
The nickel particles (powder material) obtained above, commercially available barium titanate powder, ethyl cellulose resin, carboxylic acid dispersant, and isobornyl acetate are mixed and dispersed with three rolls to create a conductive material. A paste was prepared. In addition, when the entire conductive paste is 100% by weight, the blending amounts of each raw material are 45% by weight of nickel particles, 4.5% by weight of barium titanate, 2% by weight of ethyl cellulose resin, and the carboxylic acid dispersant. 2% by weight, and the remainder was isobornyl acetate. Here, the viscosity of the conductive paste was about 20 to 50 mPa·s at 25° C. and 100 rpm (measured with a Brookfield DV type viscometer).

(3) Evaluation of dispersibility The conductive paste obtained above was coated on a substrate to a film thickness of 2 μm and dried at 120° C. for 5 minutes. Next, the coating film was observed using an optical microscope (ECLIPSE LV150 manufactured by Nikon Solutions Co., Ltd.) for a total of three fields of view, and the presence or absence of aggregated particles was confirmed from the obtained observation images. Here, such aggregated particles are observed as white lumps when observed under an optical microscope. When the number of aggregated particles per field of view was 10 or less, the dispersibility was rated "○", and when the number of aggregated particles per field of view was more than 10, the dispersibility was rated "x". The evaluation results are shown in the relevant column of Table 1.

As shown in Table 1, nickel particles have nickel as a main constituent element, and an amine compound, a nitrile compound, and/or an amide compound are attached to the surface of the nickel particles, and they are suitable for GCMS analysis. When the total weight of the amine compound, the nitrile compound and/or the amide compound is 100% by weight, the amine compound is attached in an amount of 40% by weight or more on the nickel particles according to Examples 1 to 5 ( It was confirmed that the conductive paste containing nickel powder) has excellent dispersibility. On the other hand, it was confirmed that the conductive paste containing nickel particles according to Example 6, in which the amount of the amine compound attached was outside the above range, did not have excellent dispersibility.

Although specific examples of the present disclosure have been described above in detail, these are merely examples and do not limit the scope of the claims. The techniques described in the claims include various modifications and changes to the specific examples illustrated above.

Claims (6)

Nickel particles whose main constituent element is nickel,
An amine compound, a nitrile compound and/or an amide compound are attached to the surface of the nickel particle,
Here, based on GCMS analysis, when the total weight of the amine compound, the nitrile compound and/or the amide compound is 100% by weight, 40% by weight or more of the amine compound is attached to the nickel particles. . The nickel particles according to claim 1, wherein the nickel particles have a CV value of 0.2 or less. The nickel particles according to claim 1 or 2, wherein the nickel particles have an average particle diameter of 150 nm or less. The nickel particle according to any one of claims 1 to 3, wherein two or more types of amine compounds are attached to the surface of the nickel particle. A powder material comprising nickel particles according to any one of claims 1 to 4. Nickel particles according to any one of claims 1 to 4,
a medium for dispersing the nickel particles;
conductive paste.

Images