JP6608378B2 - Method for producing nickel particles - Google Patents

Description

  The present invention relates to a method for producing nickel particles that can be suitably used for applications such as a conductive paste for forming an internal electrode of a multilayer ceramic capacitor (MLCC).

  Since the metal fine particles have physical and chemical characteristics different from those of bulk metals, various materials such as electrode materials such as conductive pastes and transparent conductive films, high-density recording materials, catalyst materials, and ink-jet ink materials are used. It is used for industrial materials. In recent years, with the downsizing and thinning of electronic devices, fine metal particles have been made finer to about several tens to several hundreds of nanometers. For example, with the miniaturization of electronic devices, the multilayer ceramic capacitor (MLCC) electrodes have been increasingly made into thin film multilayers. As a result, it is considered that the material for the electrode layer is preferably nanoparticles having an average particle size as small as less than 150 nm, a uniform particle size, small variation, and excellent dispersibility as much as possible. It has been. Therefore, industrially, development of a technique for stably producing metal fine particles having a sharp particle size distribution is required.

  As a method for producing metal fine particles having a uniform particle shape and particle diameter and less secondary agglomeration, for example, in Patent Document 1, by adding a reducing agent to a solution of a metal salt, There has been proposed a multistage production method including a step of generating fine particles (nuclei) and a step of reducing and precipitating a metal from a solution of a metal salt in the presence of a reducing agent.

  Moreover, as a multistage production method of metal fine particles including a core and a shell of different metals, for example, in Patent Document 2, a step of heating a mixture containing nickel particles, a cobalt salt and a primary amine to obtain a complexing reaction solution; There has been proposed a method for producing nickel-cobalt nanoparticles comprising heating the complexing reaction solution to obtain a nickel-cobalt nanoparticle slurry.

JP-A-10-317022 International Publication WO2011 / 115214

  In the example of Patent Document 1, since the size of the ultrafine metal particles serving as a nucleus exceeds 100 nm and the average particle diameter of the finally produced metal fine particles is about 1 μm, aggregation is unlikely to occur. The allowable range for variation in particle size is also wide. For this reason, the technique of Patent Document 1 is not applicable to the production of fine metal particles which are required for current industrial materials, for example, the average particle diameter is smaller than 150 nm.

  An object of the present invention is to stably produce metal fine particles having an average particle size as small as, for example, less than 150 nm, a uniform particle size, and small variations.

The method for producing nickel particles of the present invention includes the following steps I to IV;
I) A step of forming seed particles by mixing and heating a metal salt containing at least nickel carboxylate and an aliphatic primary monoamine.
II) A step of preparing a nickel complex solution in which a nickel salt is dissolved in an organic amine by mixing and heating the nickel salt and an aliphatic primary monoamine,
III) A step of mixing the seed particles and the nickel complex solution to obtain a mixed solution,
IV) Step of forming nickel particles by heating and reducing nickel ions in the mixed solution, and depositing and growing nickel metal with the seed particles as nuclei,
It is characterized by providing.

  In the method for producing nickel particles of the present invention, the average particle diameter D1 of the seed particles may be in the range of 10 nm to 50 nm by observation with a scanning electron microscope, and the average particle diameter D2 of the nickel particles is 20 nm or more. It may be within a range of 150 nm or less, and 8 ≧ D2 / D1.

  In the method for producing nickel particles of the present invention, both the variation coefficient CV1 of the seed particle diameter and the variation coefficient CV2 of the nickel particle diameter may be 0.2 or less, and the ratio (CV1 / CV2). ) May be within the range of 0.7 to 1.3.

  In the method for producing nickel particles of the present invention, the aliphatic primary monoamine used in Step II may have a carbon number in the range of 6 or more and 20 or less.

  In the method for producing nickel particles of the present invention, the metal salt may contain nickel carboxylate and one or more metal salts selected from copper, silver, gold, platinum and palladium.

  In the method for producing nickel particles of the present invention, the heating in the step I and the step IV may be performed by a microwave.

  According to the present invention, by carrying out the above steps I to IV, nickel particles having a small average particle size of, for example, less than 150 nm, a sharp particle size distribution, and a small CV value are stably produced. can do. The nickel particles can be suitably used as an electronic material such as a conductive paste for forming an internal electrode of a multilayer ceramic capacitor (MLCC).

2 is a scanning electron micrograph of nickel particles (seed particles) produced in Example 1. FIG. 2 is a scanning electron micrograph of nickel particles produced in Example 1. FIG.

  The method for producing nickel particles according to the present embodiment includes steps I to IV.

[Step I]
In Step I, seed particles are formed by mixing and heating a metal salt containing at least nickel carboxylate and an aliphatic primary monoamine. The seed particles function as nuclei for the growth of nickel particles in Step IV.

<Metal salt containing nickel carboxylate>
As the nickel carboxylate used in Step I, for example, nickel formate, nickel acetate or the like having a relatively low dissociation temperature (decomposition temperature) in the reduction process is preferably used. The nickel carboxylate may be an anhydride or a hydrate. In addition, it is possible to use inorganic salts such as nickel chloride, nickel nitrate, nickel sulfate, nickel carbonate, nickel hydroxide instead of nickel carboxylate, but in the case of inorganic salts, dissociation (decomposition) is high temperature. In the reduction process, heating at a high temperature is necessary, which is not preferable. It is also possible to use nickel salts composed of organic ligands such as Ni (acac) ₂ (β-diketonato complex) and stearate ions, but using these nickel salts increases the cost of raw materials. It is not preferable.

  The metal salt used in Step I may contain, for example, one or more metal salts selected from copper, silver, gold, platinum and palladium in addition to nickel carboxylate. As these metal salts, for example, carboxylates such as copper formate and palladium acetate, nitrates such as silver nitrate, and chlorides such as chloroauric acid and chloroplatinic acid are preferably used. The metal salt may be an anhydride or a hydrate. Among the metal salts, it is preferable to use a copper salt, and it is most preferable to use copper formate having a relatively low decomposition temperature. In Step I, by adding a metal salt other than nickel carboxylate, the formation of seed particles can be promoted, and the particle diameter of the seed particles can be easily controlled.

  In Step I, when a metal salt other than nickel carboxylate is used, the blending ratio with the metal salt is preferably as follows, for example. When copper salt is used as the metal salt, the ratio of nickel carboxylate to copper salt is determined from the viewpoint of oxidation stability of nickel and copper alloy seed particles produced in step I and nickel particles produced in step IV. The ratio of the copper element to the element is preferably in the range of 3 wt% to 50 wt%. When a metal salt other than copper salt is used, the ratio of nickel carboxylate to metal salt is, for example, from the viewpoint of product defects such as short circuit due to migration by different metals other than nickel, such as silver, and decrease in capacitance. The ratio of the metal element other than the copper salt to the nickel element is preferably in the range of 0.01 wt% to 2 wt%.

<Aliphatic primary monoamine>
The aliphatic primary monoamine is not particularly limited as long as it can form a complex with nickel ions, and can be solid or liquid at room temperature. Here, room temperature means 20 ° C. ± 15 ° C. The aliphatic primary monoamine that is liquid at room temperature also functions as an organic solvent for forming the nickel complex. In addition, even if it is an aliphatic primary monoamine solid at normal temperature, there is no particular problem as long as it is liquid by heating or can be dissolved using an organic solvent. In Step I, secondary amines have great steric hindrance, which may hinder the good formation of nickel complexes, and tertiary amines do not have the ability to reduce nickel ions, so none can be used. Also, diamines are not preferred because of the high stability of complexes formed with nickel ions, among metal ions, and the reduction temperature is high, so that the reactivity is very low and the resulting nickel particles are easily distorted.

  The aliphatic primary monoamine can control the particle size of the seed particles produced by adjusting the length of its carbon chain, for example. From the viewpoint of controlling the particle size of the seed particles, the aliphatic primary monoamine is preferably selected from those having about 6 to 20 carbon atoms. The larger the carbon number, the smaller the particle size of the seed particles obtained. Examples of such amines include octylamine, trioctylamine, dioctylamine, hexadecylamine, dodecylamine, tetradecylamine, stearylamine, oleylamine, myristylamine, and laurylamine.

Since the aliphatic primary monoamine functions as a surface modifier during the production of seed particles, secondary aggregation can be suppressed even after the removal of the aliphatic primary monoamine. In addition, the aliphatic primary monoamine is also preferable from the viewpoint of ease of processing operation in the washing step of separating the solid component of the seed particles generated after the reduction reaction from the solvent or the unreacted aliphatic primary monoamine. Furthermore, the aliphatic primary monoamine is preferably one having a boiling point higher than the reduction temperature from the viewpoint of ease of reaction control when the nickel complex is reduced to obtain seed particles. That is, the aliphatic primary monoamine has a boiling point of preferably 180 ° C. or higher, more preferably 200 ° C. or higher. The aliphatic primary monoamine preferably has 9 or more carbon atoms. Here, for example, the boiling point of C ₉ H ₂₁ N (nonylamine), which is an aliphatic primary monoamine having 9 carbon atoms, is 201 ° C.

  The aliphatic primary monoamine is liquid at room temperature from the viewpoint of ease of processing operation in the washing step of separating the solid component of the seed particles produced after the reduction reaction and the solvent or the unreacted aliphatic primary monoamine. Is preferred. Furthermore, the aliphatic primary monoamine is preferably one having a boiling point higher than the reduction temperature from the viewpoint of easy control of reaction when reducing the nickel complex to obtain seed particles. The amount of the aliphatic primary monoamine is preferably 2 mol or more, more preferably 2.2 mol or more with respect to 1 mol of the metal ion. When the amount of the aliphatic primary monoamine is less than 2 mol, it is difficult to control the particle diameter of the obtained nickel particles, and the particle diameter is likely to vary. The upper limit of the amount of the aliphatic primary monoamine is not particularly limited. For example, from the viewpoint of productivity, the amount is preferably 20 mol or less, more preferably 4 mol or less with respect to 1 mol of the metal ion. That is, the amount of the aliphatic primary monoamine is preferably in the range of 2 to 20 mol, more preferably in the range of 2 to 4 mol, and most preferably in the range of 2.2 to 4 mol with respect to 1 mol of the metal ion.

<Organic solvent>
Although the aliphatic primary monoamine can proceed as an organic solvent, in order to proceed the reaction in a homogeneous solution more efficiently, an organic solvent different from the aliphatic primary monoamine is used in Step I. You may add newly. The organic solvent that can be used is not particularly limited as long as it does not inhibit complex formation between an aliphatic primary monoamine and a metal ion such as nickel ion. For example, an ether-based organic solvent having 4 to 30 carbon atoms, A saturated or unsaturated hydrocarbon-based organic solvent having 7 to 30 carbon atoms, an alcohol-based organic solvent having 8 to 18 carbon atoms, or the like can be used. Moreover, from the viewpoint of enabling use even under heating conditions by microwave irradiation, it is preferable to select an organic solvent having a boiling point of 170 ° C. or higher, more preferably in the range of 200 to 300 ° C. It is better to choose one. Specific examples of such an organic solvent include tetraethylene glycol, n-octyl ether, polyalphaolefin having a carbon number in the range of 20 to 40, and the like.

<Heat reduction>
In Step I, the heating method for forming seed particles is not particularly limited, and for example, heating by a heat medium such as an oil bath or heating by microwave irradiation may be used. Heating is preferred. Heating by microwave irradiation enables uniform heating and energy can be directly applied to metal ions, so that rapid heating can be performed. As a result, the entire reaction solution can be made uniform at a desired temperature, and reduction of metal ions, formation of nuclei, and growth occur simultaneously in the entire solution. As a result, monodisperse seed particles having a narrow particle size distribution can be shortened. It can be manufactured easily in time. The use wavelength of the microwave is not particularly limited and is, for example, 2.45 GHz.

  The heating temperature for forming the seed particles is preferably 170 ° C. or higher, more preferably 180 ° C. or higher, from the viewpoint of suppressing variation in the shape of the seed particles to be obtained. The upper limit of the heating temperature is not particularly limited, but is preferably set to 270 ° C. or less, for example, from the viewpoint of efficiently performing the treatment.

  In Step I, the slurry of seed particles obtained by heating is coated with an aliphatic primary monoamine by, for example, static separation, removing the supernatant, washing with an appropriate solvent, and drying. Seed particles are obtained.

<Seed particles>
The average particle diameter D1 of the seed particles obtained in the step I by observation with a scanning electron microscope is, for example, preferably 50 nm or less, and more preferably in the range of 10 nm to 50 nm. When the average particle diameter D1 of the seed particles is less than 10 nm, the handling property is lowered and the particles are easily aggregated. When used as a nucleating agent, it is difficult to stably produce nickel particles having a sharp particle diameter distribution. Become. On the other hand, when the average particle diameter D1 of the seed particles exceeds 50 nm, the dispersion of the particle diameter at the seed particle stage becomes large, and when used as a nucleating agent, nickel particles having a sharp particle diameter distribution are stable. Manufacturing becomes difficult.

  Further, the nickel particles obtained in Step I have a particle diameter variation coefficient (CV1) of preferably 0.2 or less, and more preferably 0.15 or less. When the CV value exceeds 0.2, the variation in the particle diameter of the nickel particles obtained in the later step IV may increase.

[Step II]
In Step II, a nickel salt solution and an aliphatic primary monoamine are mixed and heated to prepare a nickel complex solution in which the nickel salt is dissolved in an organic amine.

<Nickel salt>
In step II, the kind of nickel salt is not particularly limited, and for example, nickel hydroxide, nickel chloride, nickel nitrate, nickel sulfate, nickel carbonate, nickel carboxylate, Ni (acac) ₂ (β-diketonato complex), nickel stearate Among them, nickel chloride or nickel carboxylate is preferable, and it is advantageous to use nickel carboxylate having a relatively low dissociation temperature (decomposition temperature) in the reduction process. The nickel carboxylate may be used alone or in combination with other nickel salts. Moreover, the same thing as the process I can be used for nickel carboxylate.

<Aliphatic primary monoamine>
In Step II, the same aliphatic primary monoamine as in Step I can be used.

<Nickel complex solution>
The nickel concentration in the nickel complex solution is preferably in the range of 2 to 13% by weight, for example, and more preferably in the range of 6 to 12% by weight. In the manufacturing method of the present embodiment, a multi-step reaction that distinguishes Step I for forming seed particles and Step IV for growing nickel particles from the seed particles, and compared with a one-step synthesis method, The concentration of nickel can be increased and productivity can be improved. In the one-step synthesis method, when the nickel concentration exceeds 10% by weight, the reactivity is lowered and the particle size is difficult to control.

  A divalent nickel ion is known as a ligand-substituted active species, and the ligand of the complex to be formed may easily change in complex formation by ligand exchange depending on temperature and concentration. For example, in the step of obtaining a reaction liquid by heating a mixture of nickel carboxylate and aliphatic primary monoamine, considering steric hindrance such as the carbon chain length of the amine used, for example, the carboxylate ion is bidentate or monodentate. There is a possibility of coordination at any of the positions. Furthermore, when the amine concentration is excessively large, there is a possibility that a carboxylate ion is present in the outer sphere. In order to obtain a uniform solution at the intended reaction temperature (reduction temperature), at least one of the ligands must be coordinated with an aliphatic primary monoamine. In order to take this state, it is necessary that the aliphatic primary monoamine is excessively present in the reaction solution, and it is preferable that at least 2 mol per 1 mol of nickel ions is present, and 2.2 mol or more exist. More preferably. The upper limit of the amount of the aliphatic primary monoamine is not particularly limited. For example, from the viewpoint of productivity, the amount is preferably 20 mol or less, more preferably 4 mol or less with respect to 1 mol of nickel ions. That is, the amount of the aliphatic primary monoamine is preferably in the range of 2 to 20 mol, more preferably in the range of 2 to 4 mol, and most preferably in the range of 2.2 to 4 mol with respect to 1 mol of nickel ions.

  Although the complexing reaction can proceed even at room temperature, it is preferable to perform heating at a temperature of 100 ° C. or higher in order to perform the reaction reliably and more efficiently. This heating is particularly advantageous when a nickel carboxylate hydrate such as nickel acetate tetrahydrate is used as the nickel carboxylate. The heating temperature is preferably a temperature exceeding 100 ° C., more preferably a temperature of 105 ° C. or more, so that the ligand substitution reaction between the coordinated water coordinated with nickel carboxylate and the aliphatic primary monoamine is performed. It is done efficiently. In addition, water molecules as complex ligands can be dissociated, and the water can be discharged out of the system, so that complexes can be formed efficiently. For example, nickel acetate tetrahydrate has a complex structure in which two coordinated water, two acetate ions that are bidentate ligands, and two water molecules exist in the outer sphere at room temperature. In order to efficiently form a complex by ligand substitution of these two coordinated water and aliphatic primary monoamine, the water molecule as the complex ligand can be dissociated by heating at a temperature higher than 100 ° C. preferable. The heating temperature is preferably 175 ° C. or lower from the viewpoint of reliably separating from the subsequent reduction process and completing the complex formation reaction. If the heating temperature in step II is too high, the formation of nickel complex and the reduction reaction to nickel (zero-valent) proceed simultaneously, and nickel nuclei are newly generated, resulting in nickel with a narrow particle size distribution. There is a possibility that generation of particles may be difficult. Accordingly, the heating temperature in Step II is preferably in the range of 105 ° C. to 175 ° C., more preferably in the range of 125 to 160 ° C.

  The heating time can be appropriately determined according to the heating temperature and the content of each raw material, but is preferably 15 minutes or longer from the viewpoint of reliably completing the complex formation reaction. Although there is no upper limit on the heating time, heating for a long time is useless from the viewpoint of saving energy consumption and process time. The heating method is not particularly limited, and for example, heating by a heat medium such as an oil bath or heating by microwave irradiation may be used, but heating by microwave irradiation is preferable. Heating by microwave irradiation enables uniform heating in the mixed solution, and energy can be directly applied to nickel ions, so that rapid heating can be performed. The use wavelength of the microwave is not particularly limited and is, for example, 2.45 GHz.

  A complex formation reaction between nickel carboxylate and an aliphatic primary monoamine can be confirmed by a change in the color of the solution when a solution obtained by mixing nickel carboxylate and an aliphatic primary monoamine is heated. In addition, this complex formation reaction is carried out by measuring the absorption maximum wavelength of the absorption spectrum observed in the wavelength region of 300 nm to 750 nm using, for example, an ultraviolet / visible absorption spectrum measuring apparatus, and measuring the maximum absorption wavelength of the raw material (for example, nickel acetate). It can be confirmed by observing the shift of the complexing reaction solution with respect to tetrahydrate.

[Step III]
This step is a step in which the seed particles obtained in Step I and the nickel complex solution obtained in Step II are mixed to obtain a mixed solution.

In Step III, seed particles or a slurry containing seed particles may be added to the nickel complex solution, or a nickel complex solution may be added to the slurry containing seed particles. The nickel complex mixed in step III is not used for the formation of new nuclei, but is used for the growth from seed particles to nickel particles in the next step IV. That is, as long as the concentration of the nickel complex in the mixed solution does not exceed the critical concentration for nucleation, the nickel complex is used only for particle growth. Therefore, the amount of the nickel complex for obtaining nickel particles having the target particle size in Step IV can be calculated based on the particle size of the seed particles. In this step, the nickel concentration in the nickel complex in the mixed solution can be calculated by, for example, the following formula (1). For example, in the case where nickel particles having an average particle diameter in the range of 20 to 150 nm are obtained using seed particles having an average particle diameter in the range of 10 to 50 nm and a coefficient of variation of the particle diameter of 0.2 or less, mixing is performed. The nickel concentration in the nickel complex in the liquid is preferably in the range of 4 to 13% by weight, for example, and more preferably in the range of 6 to 12% by weight.
D2 = D1 (1 + Y / X) ^1/3 (1)
[Wherein, in Formula (1), D2 is the average particle size (unit; nm) of the nickel particles, D1 is the average particle size (unit: nm) of the seed particles, and Y is the nickel complex in the mixed solution] Is the amount of nickel in the unit (g), and X is the amount of nickel in the seed particles (unit: g). ]

[Step IV]
In the step IV, nickel ions in the mixed liquid obtained in the step III are heated and reduced, and nickel particles are formed by depositing and growing nickel metal with the seed particles as nuclei.

<Heat reduction>
The heating method in Step IV is not particularly limited, and for example, heating by a heat medium such as an oil bath or heating by microwave irradiation may be used, but heating by microwave irradiation is preferable. Heating of the nickel complex by microwave irradiation enables uniform heating of the nickel complex and energy can be directly applied to the nickel complex, so that rapid heating can be performed. As a result, the entire reaction solution can be made uniform at a desired temperature, and the reduction and growth of the nickel complex (or nickel ions) can occur simultaneously in the entire solution, resulting in monodisperse nickel particles having a narrow particle size distribution. It can be easily manufactured in a short time. The use wavelength of the microwave is not particularly limited and is, for example, 2.45 GHz.

  The heating temperature in the step IV is preferably 170 ° C. or higher, more preferably 180 ° C. or higher, from the viewpoint of suppressing variation in the shape of the obtained nickel particles. On the other hand, if the heating temperature in step IV is too low, the reduction reaction rate from the nickel complex to nickel (zero valence) tends to be slow, and the growth of metallic nickel covering the seed particles tends to be slow. The upper limit of the heating temperature is not particularly limited, but is preferably set to 270 ° C. or less, for example, from the viewpoint of efficiently performing the treatment. Moreover, when it exceeds 270 degreeC, since carbonization reaction will advance and it will become easy to produce | generate nickel carbide, it is not preferable.

  In step IV, the slurry of nickel particles obtained by wet heat reduction is, for example, statically separated, the supernatant liquid is removed, washed with an appropriate solvent, and dried to obtain aliphatic 1 Nickel particles coated with quaternary monoamine are obtained.

  Part of Step III and Step IV can be repeated a plurality of times. That is, after performing Step IV, a nickel complex solution may be further added, and Step IV may be performed again. Also in this case, the nickel complex added later is not used for the formation of new nuclei, but is used for the growth from seed particles to nickel particles. In other words, even when part of Step III and Step IV are repeated, the concentration of the nickel complex will not exceed the critical concentration for nucleation unless the rate of addition of the nickel complex into the mixture exceeds the rate consumed for particle growth. The added nickel complex is only used for particle growth because it does not exceed. Therefore, the amount of the nickel complex for obtaining the target particle size can be calculated based on the particle size of the seed particles.

<Nickel particles>
The nickel particles obtained in step IV are various shapes such as spherical, pseudospherical, oblong, cubic, truncated tetrahedral, dihedral pyramid, octahedral, icosahedral, icosahedral, etc. However, from the viewpoint of improving the packing density when nickel particles are used for an electrode of an electronic component, for example, a spherical shape or a pseudospherical shape is preferable, and a spherical shape is more preferable. Here, the shape of the nickel particles can be confirmed by observing with a scanning electron microscope (SEM), for example.

  The average particle diameter D2 of the nickel particles obtained in step IV, as observed by a scanning electron microscope, is preferably 150 nm or less, and more preferably 100 nm or less. More specifically, the average particle diameter of the nickel particles is preferably in the range of 20 to 150 nm, more preferably in the range of 20 to 100 nm. The relationship between the average particle diameter D1 of the seed particles obtained in step I and the average particle diameter D2 of the nickel particles obtained in step IV is, for example, 8 ≧ D2 / D1 from the viewpoint of keeping the particle size distribution of the nickel particles sharp. It is preferable that On the other hand, when 8 <D2 / D1, the particle size distribution of the nickel particles becomes broad, and aggregated particles are gradually generated, which may result in poor dispersibility.

  Further, the nickel particles obtained in Step IV have a particle diameter variation coefficient (CV2) of preferably 0.2 or less, and more preferably 0.15 or less. When the CV value exceeds 0.2, for example, when used as a conductive paste material for an internal electrode of MLCC, irregularities occur on the surface of the electrode layer, making it difficult to make the electrode layer thinner and multilayered. In some cases, the electrical characteristics may be deteriorated. Here, the relationship between the variation coefficient CV1 of the seed particle diameter and the variation coefficient CV2 of the nickel particle diameter is such that the ratio (CV1 / CV2) is within a range of 0.7 to 1.3. preferable. When CV1 / CV2 is less than 0.7, seed particles are aggregated, or nickel particles become coarse due to non-uniform or local heating. Variation in growth rate may increase.

<Action>
In the nickel particle manufacturing method of the present embodiment, the reason why it is possible to control the particle diameter with high accuracy compared to the conventional one-step synthesis method is not clear, but it is reasonable to consider it as follows. Is possible. In the conventional one-step synthesis method, that is, the method of performing nucleation to nickel particle growth in a single pot, the environmental factors of the reaction system (for example, the concentration of the reaction solution, stirring conditions, moisture, and the natural rate affecting the reaction rate) The presence of trace amounts of impurities and trace metals derived from raw materials greatly affects the growth of nickel particles, making it difficult to control the particle size. On the other hand, in the method for producing nickel particles according to the present embodiment, since the seed particles to be generated have a small particle size in the step I where the influence of environmental factors of the reaction system is likely to occur, the variation in the particle size is suppressed accordingly. Can do. In Step IV where nickel particles are grown, seed particles have a greater influence on nickel particle growth than environmental factors in the reaction system. It is thought that it can be controlled with high accuracy.

  As described above, by carrying out Steps I to IV, nickel particles having a small average particle size of, for example, less than 150 nm, a sharp particle size distribution, and a small CV value can be stably produced. Can do. The nickel particles can be suitably used as an electronic material such as a conductive paste for forming an internal electrode of a multilayer ceramic capacitor (MLCC).

  EXAMPLES Next, although an Example and a comparative example are given and this invention is further demonstrated, this invention is not limited to the Example demonstrated below. In the following examples, various measurements and evaluations are as follows unless otherwise specified.

[Measurement of average particle size]
Take a photograph of the sample with an SEM (scanning electron microscope), extract 200 samples randomly from it, determine the area for each particle size, and use the particle size as a number reference when converted to a true sphere. The average particle size of the primary particles was used. The CV value (coefficient of variation) was calculated by (standard deviation) / (average particle diameter). In addition, it shows that a particle diameter is so uniform that a CV value is small.

Example 1
<Step I: Preparation of first nickel particles>
Add 2.45 g of copper formate tetrahydrate and 21.9 g of nickel formate dihydrate to 331 g of oleylamine, and dissolve copper formate and nickel formate in oleylamine by heating at 120 ° C for 20 minutes under nitrogen flow. did.

  The solution was irradiated with microwaves and heated to 190 ° C. to prepare 347 g of nickel particle slurry (1-A). 10 g of the resulting nickel particle slurry (1-A) was collected, the supernatant was removed, washed twice with toluene and methanol, respectively, and then washed with a vacuum dryer maintained at 60 ° C. Nickel particles (1-B) were prepared by drying for a period of time.

  An SEM photograph of the nickel particles (1-B) is shown in FIG. Referring to FIG. 1, the average particle diameter of nickel particles (1-B) was 17 nm, and the CV value was 0.13.

<Step II: Preparation of nickel complex solution>
A nickel complex solution was prepared by adding 2611 g of nickel acetate tetrahydrate to 6949 g of oleylamine and heating at 140 ° C. for 4 hours under a nitrogen flow.

<Steps III to IV: Preparation of liquid mixture and preparation of nickel particles>
To the above nickel complex solution, 337 g of nickel particle slurry (1-A) is added, and after stirring, heated to 225 ° C. by microwave irradiation and maintained at that temperature for 15 minutes. C) was prepared. The obtained nickel particle slurry (1-C) was allowed to stand and separated, the supernatant was removed, washed twice with toluene and methanol, and then dried in a vacuum dryer maintained at 60 ° C. for 6 hours. Thus, nickel particles (1-D) were prepared.

  An SEM photograph of the nickel particles (1-D) is shown in FIG. Referring to FIG. 2, the nickel particles (1-D) had an average particle diameter of 80 nm and a CV value of 0.13.

(Example 2)
<Step I: Preparation of first nickel particles>
Copper formate and nickel formate were dissolved in oleylamine in the same manner as in Example 1 except that the amount of copper formate tetrahydrate used in Example 1 was changed to 0.61 g.

  In the same manner as in Example 1, 343 g of nickel particle slurry (2-A) was obtained, washed with toluene and methanol, and dried to prepare nickel particles (2-B). From the result of the SEM photograph, the average particle diameter of the nickel particles (2-B) was 45 nm, and the CV value was 0.12.

<Step II: Preparation of nickel complex solution>
A nickel complex solution was prepared in the same manner as in Example 1 by adding 882 g of nickel acetate tetrahydrate to 1977 g of dodecylamine.

<Steps III to IV: Preparation of liquid mixture and preparation of nickel particles>
333 g of nickel particle slurry (2-A) is added to the above nickel complex solution, and nickel particle slurry (2-C) is obtained in the same manner as in Example 1, washed with toluene and methanol, and then dried. Nickel particles (2-D) were thus prepared. From the result of the SEM photograph, the average particle diameter of the nickel particles (2-D) was 141 nm, and the CV value was 0.14.

(Example 3)
<Step I: Preparation of first nickel particles>
In place of 331 g of oleylamine in Example 1, 314 g of dodecylamine was used, and the amounts of copper formate tetrahydrate and nickel formate dihydrate were changed to 0.49 g and 43.8 g, respectively. Except for this, copper formate and nickel formate were dissolved in dodecylamine in the same manner as in Example 1.

  In the same manner as in Example 1, 342 g of nickel particle slurry (3-A) was obtained, washed with toluene and methanol, and dried to prepare nickel particles (3-B). From the result of the SEM photograph, the average particle diameter of the nickel particles (3-B) was 20 nm, and the CV value was 0.11.

<Step II: Preparation of nickel complex solution>
A nickel complex solution was prepared in the same manner as in Example 1 by adding 1797 g of nickel acetate tetrahydrate to 4028 g of dodecylamine.

<Steps III to IV: Preparation of liquid mixture and preparation of nickel particles>
To the above nickel complex solution, 332 g of nickel particle slurry (3-A) was added to obtain nickel particle slurry (3-C) in the same manner as in Example 1, washed with toluene and methanol, and then dried. Thus, nickel particles (3-D) were prepared. From the result of the SEM photograph, the average particle diameter of the nickel particles (3-D) was 63 nm, and the CV value was 0.10.

Example 4
<Step I: Preparation of first nickel particles>
297 g of octylamine was used instead of 331 g of oleylamine in Example 1, and the amounts of copper formate tetrahydrate and nickel formate dihydrate were changed to 0.98 g and 65.7 g, respectively. Except for the above, copper formate and nickel formate were dissolved in octylamine in the same manner as in Example 1.

  The above solution was irradiated with microwaves and heated to 170 ° C., and the temperature was maintained for 5 minutes to prepare 347 g of nickel particle slurry (4-A). The obtained nickel particle slurry (4-A) was treated in the same manner as in Example 1 to prepare nickel particles (4-B). From the result of the SEM photograph, the average particle diameter of the nickel particles (4-B) was 15 nm, and the CV value was 0.12.

<Step II: Preparation of nickel complex solution>
A nickel complex solution was prepared by adding 636 g of nickel acetate tetrahydrate to 1050 g of octylamine and heating at 120 ° C. for 4 hours under a nitrogen flow.

<Steps III to IV: Preparation of liquid mixture and preparation of nickel particles>
To the above nickel complex solution, 337 g of nickel particle slurry (4-A) was added, and after stirring, heated to 170 ° C. by irradiation with microwaves, and the temperature was maintained for 60 minutes to maintain the nickel particle slurry (4- C) was prepared. The obtained nickel particle slurry (4-C) was treated in the same manner as in Example 1 to prepare nickel particles (4-D). From the result of the SEM photograph, the average particle diameter of the nickel particles (4-D) was 30 nm, and the CV value was 0.13.

(Example 5)
<Step I: Preparation of first nickel particles>
Nickel formate was dissolved in oleylamine in the same manner as in Example 1 except that the copper formate tetrahydrate in Example 1 was not used.

  To the above oleylamine solution, 0.11 g of silver nitrate was added to prepare a solution, which was then irradiated with microwaves and heated to 190 ° C. to prepare 345 g of nickel particle slurry (5-A). The obtained nickel particle slurry (5-A) was treated in the same manner as in Example 1 to prepare nickel particles (5-B). From the result of the SEM photograph, the average particle diameter of the nickel particles (5-B) was 30 nm, and the CV value was 0.14.

<Step II: Preparation of nickel complex solution>
A nickel complex solution was prepared by adding 1526 g of nickel acetate tetrahydrate to 1918 g of octylamine and heating at 120 ° C. for 4 hours under a nitrogen flow.

<Steps III to IV: Preparation of liquid mixture and preparation of nickel particles>
To the above nickel complex solution, 335 g of nickel particle slurry (5-A) is added, stirred, heated to 170 ° C. by microwave irradiation, and maintained at that temperature for 60 minutes, thereby maintaining the nickel particle slurry (5- C) was prepared. The obtained nickel particle slurry (5-C) was treated in the same manner as in Example 1 to prepare nickel particles (5-D). From the result of the SEM photograph, the average particle diameter of the nickel particles (5-D) was 112 nm, and the CV value was 0.15.

(Example 6)
<Step I: Preparation of first nickel particles>
Palladium acetate and nickel formate were dissolved in oleylamine in the same manner as in Example 1 except that 0.036 g of palladium acetate was used instead of 2.45 g of copper formate tetrahydrate in Example 1.

  In the same manner as in Example 1, 344 g of nickel particle slurry (6-A) was obtained, and nickel particles (6-B) were prepared. From the result of the SEM photograph, the average particle diameter of the nickel particles (6-B) was 45 nm, and the CV value was 0.13.

<Step II: Preparation of nickel complex solution>
A nickel complex solution was prepared by adding 543 g of nickel acetate tetrahydrate to 1216 g of oleylamine and heating at 140 ° C. for 4 hours under a nitrogen flow.

<Steps III to IV: Preparation of liquid mixture and preparation of nickel particles>
334 g of nickel particle slurry (6-A) was added to the above nickel complex solution, and nickel particle slurry (6-C) was prepared in the same manner as in Example 1. The obtained nickel particle slurry (6-C) was treated in the same manner as in Example 1 to prepare nickel particles (6-D). From the result of the SEM photograph, the average particle diameter of the nickel particles (6-D) was 120 nm, and the CV value was 0.13.

(Example 7)
<Step I: Preparation of first nickel particles>
29.7 g of nickel acetate tetrahydrate was added to 330 g of oleylamine, and nickel acetate was dissolved in oleylamine by heating at 120 ° C. for 20 minutes under a nitrogen flow.

  0.06 g of silver nitrate was added to the oleylamine solution to prepare a solution, which was then irradiated with microwaves and heated to 190 ° C. to prepare 346 g of nickel particle slurry (7-A). The obtained nickel particle slurry (7-A) was treated in the same manner as in Example 1 to prepare nickel particles (7-B). From the results of the SEM photograph, the average particle diameter of the nickel particles (7-B) was 19 nm, and the CV value was 0.11.

<Step II: Preparation of nickel complex solution>
A nickel complex solution was prepared by adding 2670 g of nickel acetate tetrahydrate to 5092 g of dodecylamine and heating at 140 ° C. for 4 hours under a nitrogen flow.

<Steps III to IV: Preparation of liquid mixture and preparation of nickel particles>
336 g of nickel particle slurry (7-A) was added to the nickel complex solution, and a nickel particle slurry (7-C) was prepared in the same manner as in Example 1. The obtained nickel particle slurry (7-C) was treated in the same manner as in Example 1 to prepare nickel particles (7-D). From the result of the SEM photograph, the average particle diameter of the nickel particles (7-D) was 85 nm, and the CV value was 0.11.

(Example 8)
<Step I: Preparation of first nickel particles>
59.3 g of nickel acetate tetrahydrate was added to 307 g of dodecylamine, and nickel acetate was dissolved in dodecylamine by heating at 120 ° C. for 20 minutes under a nitrogen flow.

  To the above dodecylamine solution, 0.24 g of chloroplatinic acid hexahydrate was added to prepare a solution, which was then heated to 190 ° C. by irradiation with microwaves, and 348 g of nickel particle slurry (8-A). Was prepared. The obtained nickel particle slurry (8-A) was treated in the same manner as in Example 1 to prepare nickel particles (8-B). From the result of the SEM photograph, the average particle diameter of the nickel particles (8-B) was 31 nm, and the CV value was 0.14.

<Step II: Preparation of nickel complex solution>
A nickel complex solution was prepared by adding 1653 g of nickel acetate tetrahydrate to 2730 g of octylamine and heating at 120 ° C. for 4 hours under a nitrogen flow.

<Steps III to IV: Preparation of liquid mixture and preparation of nickel particles>
To the above nickel complex solution, 338 g of the nickel particle slurry (8-A) is added, and after stirring, heated to 170 ° C. by microwave irradiation and maintained at that temperature for 60 minutes. C) was prepared. The obtained nickel particle slurry (8-C) was treated in the same manner as in Example 1 to prepare nickel particles (8-D). From the result of the SEM photograph, the average particle diameter of the nickel particles (8-D) was 92 nm, and the CV value was 0.15.

Example 9
<Step I: Preparation of first nickel particles>
In the same manner as in Example 8, nickel acetate was dissolved in dodecylamine.

  To the above dodecylamine solution, 0.29 g of chloroauric acid tetrahydrate was added to prepare a solution, which was then heated to 190 ° C. by irradiation with microwaves, and 348 g of nickel particle slurry (9-A). Was prepared. The obtained nickel particle slurry (9-A) was treated in the same manner as in Example 8 to prepare nickel particles (9-B). From the result of the SEM photograph, the average particle diameter of the nickel particles (9-B) was 16 nm, and the CV value was 0.12.

<Step II: Preparation of nickel complex solution>
In the same manner as in Example 8, a nickel complex solution was prepared.

<Steps III to IV: Preparation of liquid mixture and preparation of nickel particles>
To the above nickel complex solution, 338 g of the nickel particle slurry (9-A) was added, and in the same manner as in Example 8, a nickel particle slurry (9-C) was prepared. The obtained nickel particle slurry (9-C) was treated in the same manner as in Example 8 to prepare nickel particles (9-D). From the result of the SEM photograph, the average particle diameter of the nickel particles (9-D) was 41 nm, and the CV value was 0.13.

(Example 10)
<Step I: Preparation of first nickel particles>
To 287 g of octylamine were added 0.29 g of palladium acetate and 89.1 g of nickel acetate tetrahydrate, and the mixture was heated at 120 ° C. for 20 minutes under a nitrogen flow to dissolve palladium acetate and nickel acetate in octylamine.

  The solution was irradiated with microwaves and heated to 170 ° C., and the temperature was maintained for 5 minutes to prepare 347 g of nickel particle slurry (10-A). The obtained nickel particle slurry (10-A) was treated in the same manner as in Example 1 to prepare nickel particles (10-B). From the result of the SEM photograph, the average particle diameter of the nickel particles (10-B) was 19 nm, and the CV value was 0.16.

<Step II: Preparation of nickel complex solution>
A nickel complex solution was prepared by adding 954 g of nickel acetate tetrahydrate to 1819 g of octylamine and heating at 120 ° C. for 4 hours under a nitrogen flow.

<Steps III to IV: Preparation of liquid mixture and preparation of nickel particles>
To the above nickel complex solution, 337 g of nickel particle slurry (10-A) is added, and after stirring, heated to 170 ° C. by microwave irradiation, and the temperature is maintained for 60 minutes to maintain the nickel particle slurry (10−A). C) was prepared. The obtained nickel particle slurry (10-C) was treated in the same manner as in Example 1 to prepare nickel particles (10-D). From the result of the SEM photograph, the average particle diameter of the nickel particles (10-D) was 77 nm, and the CV value was 0.14.

  The results of Examples 1 to 10 are summarized in Table 1.

  As mentioned above, although embodiment of this invention was described in detail for the purpose of illustration, this invention is not restrict | limited to the said embodiment.

  This international application claims the priority based on the Japan patent application 2014-199998 for which it applied on September 30, 2014, and uses all the content of the said application here.

Claims (6)

A method for producing nickel particles, comprising the following steps I to IV:
I) A step of forming seed particles by mixing and heating a metal salt containing at least nickel carboxylate and an aliphatic primary monoamine.
II) A step of preparing a nickel complex solution in which a nickel salt is dissolved in an organic amine by mixing and heating the nickel salt and an aliphatic primary monoamine,
III) A step of mixing the seed particles and the nickel complex solution to obtain a mixed solution,
IV) Step of forming nickel particles by heating and reducing nickel ions in the mixed solution, and depositing and growing nickel metal with the seed particles as nuclei,
A method for producing nickel particles, comprising:   According to the observation with a scanning electron microscope, the average particle diameter D1 of the seed particles is in the range of 10 nm to 50 nm, the average particle diameter D2 of the nickel particles is in the range of 20 nm to 150 nm, and 8 ≧ D2 The method for producing nickel particles according to claim 1, which is / D1.   Both the variation coefficient CV1 of the particle size of the seed particles and the variation coefficient CV2 of the particle size of the nickel particles are 0.2 or less, and the ratio (CV1 / CV2) is within the range of 0.7 to 1.3. The method for producing nickel particles according to claim 1 or 2.   The method for producing nickel particles according to any one of claims 1 to 3, wherein the aliphatic primary monoamine used in Step II has a carbon number in the range of 6 to 20.   The nickel particles according to any one of claims 1 to 4, wherein the metal salt includes nickel carboxylate and a salt of one or more metals selected from copper, silver, gold, platinum, and palladium. Method. The method for producing nickel particles according to any one of claims 1 to 5, wherein the heating in the step I and the step IV is performed by microwaves.