JP7575419B2 - Nickel particles and their uses - Google Patents

Description

This disclosure relates to nickel particles and their uses.

In recent years, there has been a demand for further miniaturization of electronic components (e.g., multilayer ceramic capacitors: MLCCs). For example, to miniaturize MLCCs, it is necessary to thin the internal electrodes of the MLCCs, and it is considered preferable that the conductive paste used to form such internal electrodes contains conductive particles with small particle sizes (typically with an average particle size of about 150 nm or less). The following Patent Document 1 discloses technology related to nickel particles that are suitable for use in conductive pastes for forming internal electrodes of MLCCs.

Patent No. 6799936

However, according to the inventor's research, it was found that in a conductive paste containing nickel particles with a small particle size as described above, the nickel particles in the conductive paste tend to aggregate with each other. Therefore, there is a demand for further improvement in the dispersibility of the nickel particles in a conductive paste of this composition.

This disclosure has been made in light of these circumstances, and its main purpose is to provide a technology that can favorably improve the dispersibility of conductive pastes.

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 when the total weight of the amine compound, the nitrile compound and/or the amide compound is taken as 100% by weight based on GCMS analysis, 40% by weight or more of the amine compound is attached. Details will be described later, but nickel particles having such a configuration can favorably improve the dispersibility of a conductive paste.

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

In a preferred embodiment of the nickel particles disclosed herein, the CuNi core-shell particles have an average particle size of 150 nm or less. As described above, particles having an average particle size of 150 nm or less are preferred 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 containing any of the nickel particles disclosed herein. By using the powder material containing the nickel particles disclosed herein, a conductive paste with excellent dispersibility can be obtained.

In another aspect, the present disclosure provides a conductive paste containing any of the nickel particles disclosed herein and a medium for dispersing the nickel particles. The conductive paste containing the nickel particles disclosed herein has excellent dispersibility and can be preferably used.

FIG. 1 is a flow chart showing the steps of a method for producing nickel particles according to one embodiment.

The following describes preferred embodiments of the present disclosure. Matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. The following embodiments are not intended to limit the technology disclosed herein. In this specification and claims, when a certain numerical range is written as A to B (A and B are arbitrary numerical values), it means A or more and B or less. Therefore, it includes the case where it is greater than A and less than B.

Furthermore, in this specification and claims, "nickel particles" refers to a group of many fine particles (i.e., particles), except when referring to a single particle. In Japanese, it is unclear whether to use the singular or plural term, so the above definition is used to clarify the meaning of "nickel particles." In this specification and claims, "conductive paste" can be a concept that includes a slurry composition and an ink-like composition.

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

The reason why the above-mentioned configuration achieves the effects of the technology disclosed herein is thought to be the following, although this is not intended to be limiting: That is, for example, in the production of nickel particles, when nickel ions (Ni ²⁺ ) are reduced to metallic nickel (Ni), a nitrile compound can be produced from a portion of the amine compound added as a reducing agent by the reaction shown in the following formula (I) (R represents hydrogen or a hydrocarbon group).

In addition, an amide compound may be produced by reacting a part of the amine compound with the carboxylic acid attached to the nickel salt using the 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 a nickel particle, these compounds are said to play the role of a dispersant. On the other hand, according to the study by the present inventor, when nickel particles are synthesized by a conventional method, the amine compound is not attached to the surface of the nickel particles after synthesis (even if it is attached, it is not attached in sufficient amount), and it was found that mainly nitrile compounds and/or amide compounds are attached. And, when a conductive paste is prepared by performing a dispersion treatment in such a state, it was found that a large amount of aggregated particles is generated. Therefore, as a result of the intensive study by the present inventor, it was found that the amine compound can be suitably attached to the surface of the nickel particles by adding an amine compound to the nickel particles after synthesis and performing heating and stirring. Furthermore, according to the inventor's study, when the total weight of the amine compound and the nitrile compound and/or amide compound is taken as 100% by weight based on GCMS analysis, nickel particles having 40% by weight or more of the amine compound attached to the surface can suitably suppress the generation of aggregated particles even when a conductive paste is prepared by performing a dispersion treatment, 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 here should not be interpreted as being limited to the above mechanism. Each component will be explained below.

Nickel particles are particles whose main constituent element is nickel. Here, in this specification and claims, "whose main constituent element is nickel" means that the component that is most abundant in the nickel particles on a mol% basis is nickel. When the amount of substance of all metal elements contained in the nickel particles is 100 mol%, the nickel particles are preferably particles that contain nickel in an amount of, for example, 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, or 95 mol% or more (or 100 mol%). The nickel particles may contain various metal elements (e.g., gold (Au), platinum (Pt), silver (Ag), palladium (Pd), copper (Cu)) and nonmetallic elements (e.g., hydrogen (H), carbon (C), nitrogen (N), oxygen (O), sulfur (S), phosphorus (P)) as unavoidable impurities. In addition, the nickel particles may be, for example, nickel alloys or core-shell particles in which the inside (core) is made of a metal other than nickel and the shell covering at least a part of the surface of the core is made of nickel. In the case of core-shell particles, examples of the metal other than nickel include copper (Cu), silver (Ag), gold (Au), platinum (Pt), and palladium (Pd). Core-shell particles are a typical example of the "nickel particles" referred to here. In addition, 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. The nickel particles may be used alone from the above-mentioned ones, or two or more types may be used in combination.

Here, when the nickel particles are core-shell particles, the shape of the core particles is not particularly limited as long as the effect of the technology disclosed herein is exhibited, and may be spherical or non-spherical. From the viewpoint of ease of handling, the core particles are preferably spherical. 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 with a transmission electron microscope (TEM). The thickness of the nickel shell can be calculated, for example, as the average value when the thickness of the nickel shell is measured at five random points. In addition, when the total weight of the nickel particles is 100% by weight, the weight ratio of the nickel shell can typically be approximately 0.5 to 95% by weight (for example, approximately 50 to 95% by weight). However, the weight ratio of the nickel shell is not limited to these.

In this specification and claims, "average particle size" can mean the particle size (hereinafter also referred to as "D50") that corresponds to 50% of the cumulative particle size from the smallest particle size in the number-based particle size distribution based on a field emission scanning electron microscope (FE-SEM). Such measurements can be performed using, for example, a commercially available device, the S-4700 manufactured by Hitachi High-Technologies Corporation.

The nickel particles disclosed herein have an amine compound, a nitrile compound and/or an amide compound attached to their surfaces. Based on GCMS analysis, the total weight of the amine compound, the nitrile compound and/or the amide compound is taken as 100% by weight, and the amine compound is attached at 40% by weight or more. The amounts of the amine compound, the nitrile compound and the amide compound attached to the surface of the nickel particles can be calculated using a calibration curve created based on the GCMS analysis. For details, please refer to the examples described below. As described above, the inventor has found that nickel particles having such a configuration can favorably improve the dispersibility of a conductive paste.

The type of the amine compound is not particularly limited as long as the effect of the technology disclosed herein is exerted. For example, the amine compound is preferably a monoamine compound that does not contain secondary or tertiary amino groups. 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; branched amine compounds such as 2-ethylhexylamine; cyclic amine compounds such as cyclopropylamine, cyclobutylamine, cyclopentylamine, cyclohexylamine, cycloheptylamine, and cyclooctylamine; and the like. 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. The nickel particles may have one or more of the above-mentioned amine compounds attached thereto. Alternatively, as long as the effect of the technology disclosed herein is exerted, in addition to the above-mentioned amine compounds, amine compounds other than the above-mentioned amine compounds may be attached thereto. 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. One example of a method for synthesizing nickel particles of this configuration is a method in which different amine compounds are used in steps S1 and S3, which will be described later. The amine compounds attached to the surface of the nickel particles can be identified, for example, by pyrolysis GCMS spectroscopy.

As described above, the nitrile compound may be generated from a part of the amine compound added as a reducing agent when nickel ions (Ni ²⁺ ) are reduced to metallic nickel. Examples of the nitrile compound include nitrile compounds generated from the amine compounds based on the above formula (I). The nickel particles may have one or more of the above-mentioned nitrile compounds attached thereto. Alternatively, in addition to the above-mentioned nitrile compounds, nitrile compounds other than the above-mentioned nitrile compounds may be attached thereto, as long as the effect of the technology disclosed herein is exhibited. The nitrile compounds attached to the surface of the nickel particles can be identified, for example, by pyrolysis GCMS spectrum.

As described above, the amide compound can be produced, for example, by the reaction of a carboxylic acid and an amine compound attached to a nickel salt using nickel particles as a catalyst. Examples of such amide compounds include amide compounds of the amine compound and a carboxylic acid (for example, formic acid or carboxylic acid) attached to the nickel salt. The nickel particles may have one or more of the above-mentioned amide compounds attached thereto. Alternatively, in addition to the above-mentioned amide compounds, amide compounds other than the above-mentioned amide compounds may be attached thereto, as long as the effects of the technology disclosed herein are exhibited. The amide compounds attached to the surface of the nickel particles can be identified, for example, by pyrolysis GCMS spectroscopy.

The nickel particles disclosed herein are characterized in that, based on GCMS analysis, when the total weight of the amine compound and the nitrile compound and/or amide compound is taken as 100% by weight, the amine compound is attached at 40% by weight or more. As described above, nickel particles having such a configuration can favorably improve the dispersibility of the conductive paste. Here, the amount of the amine compound attached is preferably 45% by weight or more, 50% by weight or more, 55% by weight or more, or more preferably 60% by weight or more. In addition, 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 exerted, but it is generally 90% by weight or less, and can be, for example, 80% by weight or less, 70% by weight or less, or 65% by weight or less.

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 can be approximately 0 to 50% by weight (e.g., approximately 20 to 45% by weight). The amount of the amide 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 can be approximately 0 to 20% by weight (e.g., approximately 5 to 15% by weight).

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 nickel particle surface can be increased by increasing the amount of the amine compound added and the heating time and heating temperature. In addition, the amount of the nitrile compound or amide compound attached to the nickel surface can be changed, for example, by adjusting the conditions of the reduction reaction shown in the above formula (I) (reaction time, reaction temperature, etc.). Typically, the amount of the nitrile compound or amide compound attached to the nickel particle surface can be increased by increasing the reaction time and reaction temperature of the reduction reaction shown in the above formula (I). However, it is not intended to be limited to these.

The average particle size 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 size of the nickel particles is generally 10 nm or more, and from the viewpoint of making it easier to control the aggregation of particles, 20 nm or more is preferable, 30 nm or more, and 40 nm or more is more preferable. On the other hand, the upper limit of the nickel particles is generally 200 nm or less, and from the viewpoint of use in forming internal electrodes of miniaturized MLCCs, for example, 150 nm or less is preferable, and 100 nm or less (for example, 60 nm or less or 50 nm or less) is more preferable.

The CV value of the nickel particles is not particularly limited as long as the effect of the technology disclosed herein is exhibited. Here, the CV value (coefficient of variation) means the ratio of the standard deviation σ to the average particle size of the nickel particles (standard deviation σ/average particle size), and it can be said that the smaller the CV value, the more uniform the particles. In addition, nickel particles with a small CV value (in other words, uniform particles) are preferable because they can effectively suppress the aggregation of particles. The CV value of the nickel particles is generally 0.5 or less, and from the viewpoint of effectively suppressing the aggregation of particles, 0.2 or less is preferable, 0.18 or less, and 0.15 or less is more preferable.

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) and hcp (hexagonal close-packed). From the viewpoint of stability, etc., it is preferable that at least a part of the crystal structure of the nickel particles is fcc, and more preferably the entirety is fcc. Note that such a crystal structure can be confirmed, for example, by peak analysis based on XRD (X-ray diffraction).

2. Nickel Particle Manufacturing Method Next, a preferred example of the nickel particle manufacturing method disclosed herein will be described. The nickel particle manufacturing method disclosed herein is characterized in that an amine compound is added to the synthesized nickel particles and heat-treated (see step S3). This makes it possible to suitably increase the amount of the amine compound attached to the nickel particle surface. The process before the amine compound is added later may be the same as the conventional process. In the following, a method for manufacturing copper-nickel core-shell particles (CuNi core-shell particles) consisting of a core particle made of copper and a nickel shell covering at least a part of the surface of the core particle will be described as nickel particles. In the following description, the manufacturing method of CuNi core-shell particles is not intended to be limited to the manufacturing method described below. Hereinafter, the description will be made with reference to FIG. 1 as appropriate.

Figure 1 is a general flow diagram showing the steps of a method for producing nickel particles (here, CuNi core-shell particles) according to one embodiment. As shown in Figure 1, the process includes producing nickel seed particles (step S1); producing nickel particles (step S2); adding an amine compound (step S3); and recovering the nickel particles (step S4). Each step will be described below.

First, in step S1, nickel seed particles (hereinafter also simply referred to as "seed particles") are prepared. Here, the seed particles are those that can function as nuclei for nickel growth. Such seed particles can be synthesized, for example, by using nickel salt and copper salt as raw materials and performing wet reduction by heating in the presence of an amine compound. According to this method, due to the difference in standard potential between copper and nickel, copper particles that serve as nuclei are first generated, and then a nickel coating is formed on the surface of the copper particles, thereby obtaining the seed particles.

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

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

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 carboxylate include nickel formate and nickel acetate. The nickel carboxylate may be anhydride or hydrate. Examples of such hydrates include nickel formate dihydrate and nickel acetate tetrahydrate. As the nickel salt, for example, commercially available products can be used without any particular restrictions.

As the copper salt, a copper carboxylate having a relatively low decomposition temperature during reduction can be preferably used. Examples of such copper carboxylates include copper formate and copper acetate. Such copper carboxylates may be anhydrides or hydrates. An example of such a hydrate is copper acetate tetrahydrate. As the copper salt, for example, commercially available products can be used without any particular restrictions.

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 is performed by heating. This allows Ni shells to grow around the seed particles as nuclei. In this way, by growing Ni shells around the seed particles as nuclei, uniform nickel particles with a low CV value can be obtained, which is preferable.

Specifically, first, a predetermined amount of nickel salt (e.g., about 1 to 45 molar equivalents) is added to the seed particle slurry obtained in step S1, and the nickel-amine complex is synthesized by heating at a predetermined temperature (e.g., about 100 to 150°C) for a predetermined time (60 to 120 minutes). Nickel particles (nickel particle slurry) are then synthesized by heating in a nitrogen atmosphere at a predetermined temperature (e.g., about 150 to 200°C) for a predetermined time (30 to 60 minutes). Here, the nickel salt may be, for example, one as described in the nickel salt section of step S1.

Subsequently, in step S3, an amine compound is added, which makes it possible to suitably increase the amount of the amine compound attached to the surface of the nickel particles.
Specifically, the supernatant of the nickel particle slurry obtained in step S2 is removed, and the amine compound is added. Then, the mixture is heated in a nitrogen atmosphere at a predetermined temperature (e.g., about 50 to 150° C.) for a predetermined time (e.g., about 30 to 60 minutes) to obtain nickel particles (nickel particle slurry).

Subsequently, in step S4, the nickel particles are collected.
Specifically, first, the supernatant of the nickel particle slurry obtained in step S3 is removed. Then, a suitable washing solvent (e.g., isobornyl acetate, etc.) is added, and the mixture is dispersed using an ultrasonic cleaner or the like, after which the supernatant is removed. After repeating this operation multiple times (e.g., about 2 to 5 times), the mixture is dried in a dryer at a predetermined temperature (e.g., about 100 to 150° C.) for a predetermined time (e.g., about 30 to 60 minutes) to obtain nickel particles (powder).

In addition to the nickel particles disclosed herein, a binder (e.g., acrylic resin, epoxy resin, phenolic resin, amine resin, alkyd resin, cellulose resin such as ethyl cellulose), conductive material, other powder material (e.g., barium titanate), etc. can be added as necessary to obtain powder materials for various applications. For example, a powder material can be obtained by mixing and grinding nickel particles and the above-mentioned materials. Since such a powder material contains nickel particles as described above, the use of this powder material can favorably achieve both the dispersibility of the conductive paste and the reduction in the shrinkage rate of the conductive layer obtained after firing. The content of nickel particles in the powder material is not particularly limited, but it is preferably about 50 to 95% by weight (e.g., about 60 to 90% by weight) when the entire powder material is 100% by weight.

In addition, by dispersing the nickel particles disclosed herein in a suitable dispersion medium (medium) consisting of an aqueous or organic solvent, a dispersion (conductive paste) for various applications can be obtained. For example, by dispersing nickel particles in a specific organic solvent, and further adding components such as a binder (see those listed in the explanation of the powder material), a conductive material, other powder materials, a dispersant (e.g., a carboxylic acid-based dispersant), and a viscosity modifier as necessary, a composition prepared in a paste form (conductive paste) can be obtained. As described above, such a conductor paste contains nickel particles, and therefore can favorably achieve both excellent dispersibility and a reduced shrinkage rate of the conductive layer obtained after firing.

The dispersion medium used in the conductive paste may be any one that can disperse this type of conductive powder material well, and any one that has been used in the preparation of conventionally known conductive pastes may be used without any particular restriction. Examples of organic solvents include one or more combinations of high-boiling organic solvents such as mineral spirits (particularly aliphatic hydrocarbons), ethylene glycol, diethylene glycol derivatives, toluene, xylene, butyl carbitol (BC), isobornyl acetate, and terpineol. Here, the content of nickel particles in the conductive paste is not particularly limited, but is preferably about 30 to 70% by weight (e.g., about 40 to 60% by weight) when the entire conductive paste is taken as 100% by weight. The content of the dispersion medium in the conductive paste is not particularly limited, but is preferably about 30 to 70% by weight (e.g., about 40 to 60% by weight) when the entire conductive paste is taken as 100% by weight. The viscosity of the conductive paste is not particularly limited, but is preferably about 10 to 100 mPa·s (e.g., about 20 to 50 mPa·s). The viscosity can be measured, for example, by a commercially available viscometer.

The above-mentioned technology can be used in the electronic materials field, for example, to make it possible to miniaturize electronic components and thin electrodes.

Below, we will explain test examples related to the nickel particles disclosed herein, but we do not intend to limit this disclosure to such test examples. In the following, we will explain the case where CuNi core-shell particles are used as an example of nickel particles.

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

(Synthesis of nickel seed particle slurry)
A nickel formate-oleylamine complex was synthesized by adding 1.7 g of nickel formate dihydrate (a product of Fujifilm Wako Pure Chemical Industries, Ltd.; the same applies below) to 319.2 g of oleylamine (a product of Fujifilm Wako Pure Chemical Industries, Ltd.) and heating at 120° C. for 120 minutes. Next, 0.23 g of copper formate tetrahydrate (a product of Fujifilm Wako Pure Chemical Industries, Ltd.; the same applies below) was added to the nickel formate-oleylamine complex and heating at 60° C. for 30 minutes to synthesize a copper formate-oleylamine complex. Thereafter, a nickel seed particle slurry was synthesized by heating at 190° C. for 10 minutes under 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 Fujifilm Wako Pure Chemical Industries, Ltd., the same applies below) was added, and the mixture was heated at 135° C. for 120 minutes to synthesize a nickel acetate-oleylamine complex. Thereafter, the mixture was heated at 200° C. for 30 minutes in a nitrogen atmosphere to synthesize a nickel particle slurry.

Synthesis of nickel particle slurry according to Example 1 The supernatant of the nickel particle slurry synthesized above was removed. 200 mL of oleylamine was added to the slurry, and the mixture was heated and stirred at 100° C. for 30 minutes to synthesize the nickel particle slurry according to Example 1.

Synthesis of nickel particle slurry according to Example 2 The supernatant liquid of the nickel particle slurry synthesized above was removed. 100 mL of oleylamine was added to the slurry, and the mixture was heated and stirred at 100° C. for 30 minutes to synthesize a nickel particle slurry according to Example 2.

Synthesis of nickel particle slurry according to Example 3 The supernatant of the nickel particle slurry synthesized above was removed. 200 mL of oleylamine was added to the slurry, and the mixture was heated and stirred at 50° C. for 60 minutes to synthesize a nickel particle slurry according to Example 3.

Synthesis of nickel particle slurry according to Example 4 The supernatant of the nickel particle slurry synthesized above was removed. 200 mL of 2-ethylhexylamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the slurry, and the mixture was heated and stirred at 100° C. for 30 minutes to synthesize the nickel particle slurry according to Example 4.

Synthesis of nickel particle slurry according to Example 5 The supernatant of the nickel particle slurry synthesized above was removed. 100 mL of oleylamine was added to the slurry, and the mixture was heated and stirred at 50° C. for 60 minutes to synthesize the nickel particle slurry according to Example 1.

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

The supernatant liquid of the nickel particle slurry for each example synthesized above was removed. Isobornyl acetate was then added, dispersed using an ultrasonic cleaner, and the supernatant liquid was removed. This process was repeated three times, and then the mixture was dried in a dryer at 120°C for 60 minutes to obtain a powder material made of nickel particles for each example.

＜Evaluation test＞

(1) Characteristic properties of nickel particles The nickel particles in the 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 50,000-fold field of view, 200 nickel particles were randomly extracted, and their projected areas were determined. The diameter of a circle having the same area (Heywood diameter) was measured. The cumulative 50% particle diameter (D50) in the number-based particle size distribution was calculated as the average particle diameter (nm). The coefficient of variation (CV) of the average particle diameter was also calculated. Here, the CV value means the ratio of the standard deviation σ to the average particle diameter of the 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 matter on nickel particle surface 0.6 mL of methanol was added to 500 mg of nickel particles according to each of the above synthesized examples, and ultrasonic irradiation was performed for 1 hour using an ultrasonic cleaner. The supernatant liquid after collecting the particles with a magnet was used as an extract, and was measured using a GCMS device (GCMS-QP-2010Ultra manufactured by Shimadzu Corporation) to analyze the organic matter attached to the surface of the nickel particles. Specifically, the organic matter attached to the surface of the nickel particles was identified, and the amount of attachment (wt%) of the amine compound, nitrile compound, and amide compound was calculated when the total weight of the organic matter was 100 wt%. The amount of attachment was calculated using a calibration curve based on the peak area and sample concentration of GCMS. The measurement results are shown in the corresponding columns of Table 1.

Although not shown in Table 1, it was confirmed that oleylamine, oleylnitrile, and an amide compound of oleylamine and acetic acid (or formic acid) were attached to the surface of the nickel particles in Examples 1 to 3, 5, and 6. It was also confirmed that oleylamine, 2-ethylhexylamine, oleylnitrile, 2-ethylhexylnitrile, an amide compound of oleylamine and acetic acid (or formic acid), and an amide compound of 2-ethylhexylamine and acetic acid (or formic acid) were attached to the surface of the nickel particles in Example 4.

(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 were mixed and dispersed with a three-roll mill to prepare a conductive paste. The amounts of each raw material were 45% by weight of nickel particles, 4.5% by weight of barium titanate, 2% by weight of ethyl cellulose resin, 2% by weight of carboxylic acid dispersant, and the remainder was isobornyl acetate, assuming that the entire conductive paste was 100% by weight. Here, the viscosity of the conductive paste was about 20 to 50 mPa·s at 25°C-100 rpm (measured with a Brookfield DV type viscometer).

(3) Evaluation of Dispersibility The conductive paste obtained above was applied to a substrate with a film thickness of 2 μm and dried at 120° C. for 5 minutes. Next, the coating film was observed in a total of three fields of view using an optical microscope (Eclipse LV150 manufactured by Nikon Solutions Corporation), and the presence or absence of aggregated particles was confirmed from the obtained observation images. Here, such aggregated particles are observed as white lumps in optical microscope observation. Dispersibility was evaluated as “○” when the number of aggregated particles per field was 10 or less, and dispersibility was evaluated as “×” when the number of aggregated particles per field was more than 10. The evaluation results are shown in the corresponding columns in Table 1.

As shown in Table 1, nickel particles having nickel as the main constituent element, an amine compound, a nitrile compound and/or an amide compound attached to the surface of the nickel particles, and based on GCMS analysis, when the total weight of the amine compound, the nitrile compound and/or the amide compound is taken as 100 wt%, the conductive paste containing nickel particles (nickel powder) according to Examples 1 to 5 was confirmed to have 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 amine compound attached is outside the above range, does not have excellent dispersibility.

Specific examples of the present disclosure have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples given above.

Claims (6)

Nickel particles containing nickel as a main component,
an amine compound and a nitrile compound and/or an amide compound are attached to the surface of the nickel particles;
Here, when the total weight of the amine compound and the nitrile compound and/or the amide compound is taken as 100% by weight, the amine compound adheres to the nickel particles in an amount of 40% by weight or more and 65% by weight or less based on GCMS analysis. The nickel particles according to claim 1, wherein the CV value of the nickel particles is 0.2 or less. The nickel particles according to claim 1 or 2, wherein the average particle size of the nickel particles is 150 nm or less. The nickel particles 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 particles. A powder material containing nickel particles according to any one of claims 1 to 4. The nickel particles according to any one of claims 1 to 4,
A medium for dispersing the nickel particles;
A conductive paste comprising:

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