JP6494338B2 - 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. In connection with this, it is considered that the material of the electrode layer is preferably nanoparticles having an average particle size of 300 nm or less, a uniform particle size, a small variation thereof, and an excellent dispersibility as much as possible. ing. 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. Therefore, the technique of Patent Document 1 is not applicable to the production of small metal fine particles required for current industrial materials, for example, an average particle diameter of 300 nm or less.

  An object of the present invention is to stably produce metal fine particles having an average particle size of, for example, 300 nm or less, a uniform particle size, and a small variation.

The method for producing nickel particles of the present invention includes the following steps I to III;
I) a step of preparing seed particles having an average particle diameter D1 by observation with a scanning electron microscope within a range of 10 nm to 30 nm and a particle diameter variation coefficient CV1 of 0.12 or less,
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) Mixing the seed particles and the nickel complex solution to obtain a mixed solution, heating and reducing nickel ions in the mixed solution, and depositing and growing nickel metal using the seed particles as nuclei to form nickel particles Forming step,
Is included. Then, in the method for producing nickel particles of the present invention, in the step III, the nickel complex in the mixed solution is converted into metal elements in terms of the metal element weight with respect to the metal element weight of the seed particles or the nickel particles grown from the seed particles. Maintain below 200 times.

  In the method for producing nickel particles according to the present invention, the average particle diameter D2 of the nickel particles observed with a scanning electron microscope may be in the range of 100 nm or more and 300 nm or less, and the coefficient of variation CV2 of the particle diameter is 0.12. It may be the following.

  In the method for producing nickel particles of the present invention, the average particle diameter D1 may be in the range of 10 nm or more and 20 nm or less, and the average particle diameter D2 of the nickel particles observed by a scanning electron microscope is in the range of 100 nm or more and 200 nm or less. And when the particle size variation coefficient CV2 is 0.12 or less, in the step III, the nickel complex solution or the separately prepared nickel complex solution is further divided into a plurality of times. It may be additionally supplied to the liquid mixture stepwise or continuously.

  In the method for producing nickel particles of the present invention, the concentration of the nickel complex in the nickel complex solution additionally supplied stepwise or continuously in the step III or the nickel complex solution separately prepared is 3 in terms of nickel element. It may be in the range of ˜12% by weight.

  In the method for producing nickel particles of the present invention, the seed particles may be formed by mixing and heating a metal salt containing at least nickel carboxylate and an aliphatic primary monoamine.

  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 III may be performed by microwaves.

  According to the present invention, by carrying out the above steps I to III, nickel particles having an average particle size of, for example, 300 nm or less, a sharp particle size distribution, and a small CV value can be stably produced. it can. 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 an SEM photograph of nickel particles (seed particles) produced in Example 1. 2 is an SEM photograph of nickel particles produced in Example 1. 4 is a SEM photograph of nickel particles (seed particles) produced in Example 4. 4 is a SEM photograph of nickel particles produced in Example 4. 4 is a SEM photograph of nickel particles (seed particles) produced in Example 8. 4 is a SEM photograph of nickel particles produced in Example 8. 4 is a SEM photograph of nickel particles produced in Comparative Example 2.

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

[Step I]
In Step I, seed particles having an average particle diameter D1 by scanning electron microscope observation in the range of 10 nm to 30 nm and a particle diameter variation coefficient CV1 of 0.12 or less are prepared.

<Seed particles>
The seed particles function as nuclei for the growth of nickel particles in Step III. The average particle diameter D1 of the seed particles by observation with a scanning electron microscope is, for example, in the range of 10 nm to 30 nm, and preferably in the range of 10 nm to 20 nm. When the average particle diameter D1 of the seed particles is less than 10 nm, the handling properties are lowered and the particles are easily aggregated. When used as a core material, 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 30 nm, the dispersion of the particle diameter at the seed particle stage becomes large, and when used as a core material, nickel particles having a sharp particle diameter distribution are stable. Manufacturing becomes difficult. The average particle diameter of the seed particles is obtained by taking a photograph of the sample with an SEM (scanning electron microscope), randomly extracting 200 particles from it, obtaining the area of each particle, and converting to a true sphere. The particle size can be determined based on the number of particles.

  The seed particles have a particle diameter variation coefficient (CV1) of 0.12 or less, preferably 0.10 or less. When the CV value exceeds 0.12, variation in the particle diameter of the nickel particles obtained in the later step III may increase. In the method for producing nickel particles according to the present embodiment, the CV value of the nickel particles obtained in step III can be maintained substantially equal to the CV value of the seed particles, and therefore the CV value of the seed particles is preferably as small as possible.

  The seed particles are preferably formed by mixing and heating a metal salt containing at least nickel carboxylate and an aliphatic primary monoamine. For example, it is preferable to produce from a raw material containing a nickel salt and a copper salt by wet reduction by heating in the presence of an organic amine. In this case, due to the difference in the standard electrode potential between copper and nickel, first, copper particles are formed, and then a nickel coating is formed on the surface of the copper particles, whereby seed particles are obtained.

<Metal salt containing nickel carboxylate>
For example, nickel formate or nickel acetate having a relatively low dissociation temperature (decomposition temperature) in the reduction process is preferably used as the nickel carboxylate used for producing the seed particles. 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 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 for the production of the seed particles may contain, for example, one or more metal salts selected from copper, silver, gold, platinum and palladium in addition to the 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. By blending 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 the production of seed particles, 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 based on the nickel and copper alloy seed particles and the oxidation stability of nickel particles produced in step III. The element ratio 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 reduction 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. Since secondary amines have great steric hindrance, there is a risk that good formation of nickel complexes may be hindered, and tertiary amines cannot be used because they do not have the ability to reduce nickel ions. 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 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 reducing the nickel complex 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 1 mol or more, more preferably 2 mol or more, relative to 1 mol of the metal ion. When the amount of the aliphatic primary monoamine is less than 1 mol, it is difficult to control the particle diameter of the obtained nickel particles, and the particle diameters tend 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 1 to 20 mol, more preferably in the range of 2 to 20 mol, and most preferably in the range of 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 different from the aliphatic primary monoamine is used in the production of seed particles. A solvent may be newly added. 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>
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, but heating by microwave irradiation is preferable. 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 the step I, seed particles obtained by heating are separated by standing, for example, after removing the supernatant, washed with an appropriate solvent, and dried to obtain seed particles.

[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. In this case, the “seed particles” in step I may be replaced with “nickel particles”.

<Aliphatic primary monoamine>
In Step II, the same aliphatic primary monoamine as in Step I can be used. In this case, the “seed particles” in step I may be replaced with “nickel particles”.

<Nickel complex solution>
The initial nickel concentration in the nickel complex solution is, for example, preferably in the range of 3 to 12% by weight, and more preferably in the range of 5 to 10% by weight. In the manufacturing method of the present embodiment, a multi-stage reaction that distinguishes Step I for forming seed particles and Step III for growing nickel particles from the seed particles makes it possible to produce a solution in a nickel complex solution as compared with a one-step synthesis method. The concentration of the initial nickel can be increased, and productivity can be improved.

  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, 4 mol or more is desirable. 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. This is carried out efficiently, so that the water molecule as the complex ligand can be dissociated, and further, the water can be discharged out of the system, so that the complex 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]
In this step, the seed particles obtained in step I and the nickel complex solution obtained in step II are mixed to obtain a mixed solution, and nickel ions in the mixed solution are heated and reduced, and the seed particles are used as a nucleus to form a metal. In this step, nickel particles are formed by depositing and growing nickel.

  In Step III, when preparing the mixed solution, the seed particles or the slurry containing the seed particles may be added to the nickel complex solution, or the nickel complex solution may be added to the slurry containing the seed particles. The nickel complex in the mixed solution is not used for the formation of new nuclei, but is used for the growth from seed particles to nickel particles. In Step III, nickel ions in the mixed solution are heated and reduced, and nickel particles are formed by depositing and growing metallic nickel using seed particles as nuclei. Here, in Step III, the nickel complex in the mixed solution is maintained at 200 times or less with respect to the weight of the metal element of the seed particles or nickel particles grown from the seed particles in terms of metal elements. That is, in Step III, the nickel complex in the mixed solution is maintained at a concentration that does not reach supersaturation (below the concentration at which metallic nickel nuclei are formed). When the nickel complex in the mixed solution exceeds 200 times the weight of the metal element of the seed particles or the nickel particles grown from the seed particles, the nickel complex becomes larger than the number of nickel particles. Instead of being used, it is used for the generation of new seed particles. As a result, coarse particles are likely to be generated, and the CV value tends to deteriorate. In addition, when the concentration exceeds 200 times, the variation in the concentration of the seed particles and the nickel complex existing therearound increases, so that new nickel nuclei are generated in the portion where the concentration of the seed particles is low, and this rapidly occurs. It is considered that it grows and remarkably large particles (coarse particles) are easily generated.

<Additional supply of nickel complex>
In Step III, the nickel complex solution may be additionally supplied to the mixed solution stepwise or continuously in a plurality of times while maintaining the nickel complex in the mixed solution below the nucleation concentration. The additional supply of the nickel complex can be performed in parallel with the heat reduction. Even when the nickel complex solution is additionally supplied, the nickel complex in the mixed solution is 200 times or less, preferably 150 times the weight of the metal element of the seed particles or the nickel particles grown from the seed particles in terms of metal elements. Maintain below. As long as the rate of additional supply of nickel complex into the mixture does not exceed the rate consumed for particle growth, the concentration of nickel complex will not exceed the critical concentration for nucleation. Used only for growth. Therefore, the supply amount of the nickel complex for obtaining the target particle size can be calculated based on the particle size of the seed particles.

  The additional supply of the nickel complex solution is effective when the nickel particles to be produced are relatively small. For example, when the average particle diameter D2 of the nickel particles obtained in step III is in the range of 100 nm to 200 nm and the coefficient of variation CV2 of the particle diameter is 0.12 or less, the nickel complex solution is additionally supplied. Is preferably carried out stepwise or continuously in a plurality of times. In this case, as the seed particles obtained in step I, it is preferable to use those having an average particle diameter D1 in the range of 10 nm to 20 nm.

(In case of additional supply in stages divided into multiple times)
In Step III, when the additional supply of the nickel complex solution to the mixed solution is performed stepwise in multiple steps, in the first additional supply, the nickel complex in the mixed solution after the supply is converted into a seed in terms of metal element. It is set so as to be 200 times or less, preferably 150 times or less, based on the weight of the metal element of the particles. Next, in the second additional supply, the nickel complex in the mixed solution after supply is 200 times based on the metal element weight of the nickel particles during the growth in the mixed solution after the first supply in terms of metal element. Hereinafter, it is preferably set to 150 times or less. Further, in the third additional supply, the nickel complex in the mixed liquid after the additional supply is 200 based on the metal element weight of the nickel particles during the growth in the mixed liquid after the second additional supply in terms of metal element. It is set to be less than double, preferably 150 times or less. As described above, in the N-th additional supply, nickel particles in the middle of growth in the mixed liquid after the N-1th additional supply (where N-1 = 0 means the mixed liquid prepared first in Step III). It is preferable to sequentially supply additional nickel complexes sequentially so that the metal element weight is 200 times or less based on the weight of the metal element.

  In addition, when the additional supply of the nickel complex solution is performed stepwise by dividing into a plurality of times, for example, the total amount of the nickel complex solution finally additionally supplied is 1. It is preferable to supply at intervals of 5 to 20 minutes, divided into 2 to 5 times so that the volume is about 2 to 1.5 times. Here, due to the influence of the temperature of the nickel complex to be additionally supplied, the temperature of the mixed solution tends to decrease immediately after the additional supply, but the temperature of the mixed solution can be immediately increased by microwave irradiation. Since it can be accelerated, the supply interval may be 5 to 20 minutes. On the other hand, when the additional supply of the nickel complex solution is continuously performed, the carbonization reaction of the nickel particles easily proceeds over a long period of time, which is not preferable.

(In case of continuous supply)
When the additional supply of the nickel complex solution is continuously performed, the nickel complex in the mixed solution at the start of the additional supply is set to be 200 times or less based on the metal element weight of the seed particles in terms of metal element. It is preferable to do. Further, during continuous supply, the nickel complex in the mixed solution is always set to be 200 times or less based on the metal element weight of the nickel particles during the growth in the mixed solution in terms of metal element. In this case, the “metal element weight of the nickel particles during the growth in the mixed solution” may be obtained, for example, experimentally in advance or calculated.

  In addition, when the additional supply of the nickel complex solution is continuously performed, for example, the total amount of the nickel complex solution to be additionally supplied finally is about 2 to 5 times the total volume of the initial mixed liquid. It is preferable to supply over 0.5-2.0 hours so that it may become.

  Moreover, when performing additional supply of a nickel complex solution, it is preferable to make the density | concentration of the nickel complex in a nickel complex solution into the range of 3-12 weight% in conversion of nickel element. If the concentration of the nickel complex is less than the above lower limit, the growth rate of the seed particles becomes slow. In order to increase the growth rate of nickel particles and increase the production efficiency, the concentration of the nickel complex to be additionally supplied is preferably as high as possible. However, if the upper limit is exceeded, the viscosity of the nickel complex increases, resulting in poor workability. There is a tendency for a uniform reaction to occur.

  In addition, as the nickel complex solution to be additionally supplied, one prepared in Step II may be used, or a nickel complex solution prepared separately may be used. When using the nickel complex solution prepared separately, this nickel complex solution can be manufactured according to the process II. In this case, the concentration of the nickel complex in the nickel complex solution separately prepared, and the kind of nickel salt or aliphatic primary monoamine used as a raw material may be different from those in step II.

<Heat reduction>
The heating method in step III 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. In heating the nickel complex by microwave irradiation, the nickel complex can be heated uniformly 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 step III is preferably 170 ° C. or higher, more preferably 180 ° C. or higher, from the viewpoint of suppressing variation in the shape of the nickel particles obtained. On the other hand, if the heating temperature in Step III 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 III, the nickel particle slurry obtained by wet-type heat reduction is, for example, statically separated, and after removing the supernatant, it is washed with an appropriate solvent and dried to obtain nickel particles. It is done.

<Nickel particles>
The nickel particles obtained in step III are various shapes such as spherical, pseudo-spherical, 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 of the nickel particles is obtained by taking a photograph of the sample with an SEM (scanning electron microscope), extracting 200 particles randomly from it, obtaining the area of each particle, and converting it to a true sphere. The particle size can be determined based on the number of particles.

  The average particle diameter D2 of the nickel particles obtained in step III as observed by a scanning electron microscope is preferably in the range of 100 nm to 300 nm, and more preferably in the range of 100 nm to 200 nm.

  The nickel particles obtained in Step III are, for example, grown particles having an average particle size D2 in the range of 100 nm to 300 nm, and the particle size variation coefficient (CV2) is, for example, 0.12 or less, preferably 0.10. It has extremely high uniformity as follows. Therefore, when the nickel particles obtained by the method of the present embodiment are used as, for example, a conductive paste material for an internal electrode of MLCC, the surface of the electrode layer can be smoothed, and the electrode layer is thin. And multilayering are facilitated, and electrical characteristics can be improved.

<Action>
In the nickel particle manufacturing method of the present embodiment, it is possible to control the particle diameter with higher accuracy than in the conventional one-step synthesis method. In the conventional one-step synthesis method, that is, a method in which nucleation to nickel particle growth is performed in one pot, nickel particle growth and nucleation occur simultaneously in parallel, so that the particle size is difficult to control and the CV value is increased. There was a trend. On the other hand, in the method for producing nickel particles of the present embodiment, seed particles are used, and in step III, the nickel complex in the mixed solution is maintained at a concentration that does not reach supersaturation. As a result, new nucleation can be suppressed, so that nickel particles can be grown while maintaining a CV value comparable to the CV value of the seed particles (for example, CV = 0.1). Can be kept low. Therefore, it is considered that the particle diameter of the finally produced nickel particles can be controlled with high accuracy.

  As described above, by performing Steps I to III, nickel particles having an average particle size of 300 nm or less, a sharp particle size distribution, and a small CV value can be stably produced. 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 when converted to a true sphere as the number standard 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.

[Evaluation of surface roughness of conductive paste]
Two pieces of slide glass S1112 (76 mm × 26 mm × t1.1 mm) manufactured by Matsunami Glass Industry Co., Ltd. were wiped off with absorbent cotton moistened with acetone and dried. 0.05 g of conductive paste is weighed in the center of one slide glass, sandwiched between the other slide glass, and then printed while being pressed to the extent that it does not protrude from the side, and the slide glass is slid in the parallel direction. As a result, a smooth coating surface was obtained. After the coating film was dried at 60 ° C. for 3 hours, the arithmetic average roughness Ra was measured with a fine shape measuring apparatus [Kosaka Laboratory ET-200].

[Thermomechanical analysis (TMA), thermogravimetric analysis (TGA), 5% heat shrinkage temperature]
A sample is put into a 5Φ × 2 mm cylindrical molding machine, and a molded body obtained by press molding is prepared. Under an atmosphere of nitrogen gas (containing 3% hydrogen gas), thermomechanical analysis (TMA) and thermogravimetric analysis ( TGA). Moreover, the temperature of 5% heat shrinkage measured by a thermomechanical analyzer (TMA) was taken as 5% heat shrinkage temperature.

[Example 1]
<Step I: Preparation of seed particles>
80 g of copper formate tetrahydrate and 350 g of nickel formate dihydrate were added to 6000 g of oleylamine, and copper formate and nickel formate were dissolved in oleylamine by heating at 120 ° C. for 60 minutes under a nitrogen flow.

  The solution was irradiated with microwaves and heated to 190 ° C. to prepare 6130 g of nickel particle slurry (1-A). 100 g of the obtained 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 15 nm, and the CV value was 0.09.

<Step II: Preparation of nickel complex solution>
A nickel complex solution was prepared by adding 20.6 kg of nickel acetate tetrahydrate to 50.0 kg of oleylamine and heating at 140 ° C. for 4 hours under a nitrogen flow.

<Step III: Preparation of mixed solution and preparation of nickel particles>
2.82 kg of the above nickel complex solution was taken, 100 g of nickel particle slurry (1-A) was added thereto, and after stirring, heated to 225 ° C. by irradiation with microwaves, while maintaining the temperature, Furthermore, a nickel particle slurry (1-C) was prepared by adding 2.60 kg of the nickel complex solution in three portions every 10 minutes. 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 average particle diameter of nickel particles (1-D) was 108 nm, and the CV value was 0.12.

<Preparation of conductive paste>
After 10 g of the nickel particle slurry (1-C) was left and separated and the supernatant was removed, a polyester polymer dispersant (manufactured by Nippon Lubrizol Co., Ltd., trade name: Solsperse 13240, secondary amino group and tertiary amino group) Mixture of polyester-based graft copolymer contained, polar: low, insoluble in water, amine value: 37 mg KOH / g, acid value: 7 mg KOH / g) was added and shaken for 10 minutes, and 4 times with toluene After washing, it was replaced twice with terpineol (TP) and concentrated with a magnet to prepare a nickel particle slurry (1-E).

  0.15 g of cellulosic binder (Nisshin Kasei Co., Ltd., trade name: E3625) was added to the resulting slurry (1-E), and a rotating / revolving mixer (Shinky Co., trade name: Neritaro AR-100) ) To prepare a conductive paste (1-F). As a result of measuring the surface roughness of the obtained conductive paste (1-F), the arithmetic average roughness Ra was 12 nm.

  Moreover, the 5% heat shrink temperature of the obtained nickel particles (1-D) was 310 ° C.

[Example 2]
<Step I: Preparation of seed particles>
After preparing 6125 g of nickel particle slurry (2-A) in the same manner as in Example 1 except that instead of 80 g of copper formate tetrahydrate in Example 1, 60 g of copper formate tetrahydrate was used. Nickel particles (2-B) were prepared.

  From the SEM photograph of nickel particles (2-B), the average particle size of nickel particles (2-B) was 18 nm, and the CV value was 0.09.

<Step II: Preparation of nickel complex solution>
In the same manner as in Example 1, a nickel complex solution was prepared.

<Step III: Preparation of mixed solution and preparation of nickel particles>
2.70 kg of the above nickel complex solution was taken, 100 g of nickel particle slurry (2-A) was added thereto, and after stirring, heated to 225 ° C. by irradiation with microwaves, while maintaining the temperature, Furthermore, a nickel particle slurry (2-C) was prepared by adding 2.70 kg of the nickel complex solution in three portions every 10 minutes. In the same manner as in Example 1, the obtained nickel particle slurry (2-C) was allowed to stand and separated, and after removing the supernatant, washed and dried to prepare nickel particles (2-D).

  From the SEM photograph of nickel particles (2-D), the average particle diameter of nickel particles (2-D) was 132 nm, and the CV value was 0.12.

<Preparation of conductive paste>
In the same manner as in Example 1, after preparing the nickel particle slurry (2-E), a conductive paste (2-F) was prepared. As a result of measuring the surface roughness of the obtained conductive paste (2-F), the arithmetic average roughness Ra was 11 nm.

  Moreover, the 5% heat shrink temperature of the obtained nickel particles (2-D) was 325 ° C.

[Example 3]
<Step I: Preparation of seed particles>
In the same manner as in Example 2, after preparing the nickel particle slurry (3-A), nickel particles (3-B) were prepared.

<Step II: Preparation of nickel complex solution>
In the same manner as in Example 1, a nickel complex solution was prepared.

<Step III: Preparation of mixed solution and preparation of nickel particles>
2.70 kg of the above nickel complex solution was taken, 100 g of nickel particle slurry (3-A) was added thereto, and after stirring, heated to 225 ° C. by irradiation with microwaves, while maintaining the temperature, Furthermore, nickel particle slurry (3-C) was prepared by adding 13.5 kg of the nickel complex solution continuously with a pump for 20 minutes. In the same manner as in Example 1, the obtained nickel particle slurry (3-C) was allowed to stand and separated, and after removing the supernatant, washed and dried to prepare nickel particles (3-D).

  From the SEM photograph of nickel particles (3-D), the average particle diameter of nickel particles (3-D) was 149 nm, and the CV value was 0.09.

<Preparation of conductive paste>
In the same manner as in Example 1, after preparing the nickel particle slurry (3-E), a conductive paste (3-F) was prepared. As a result of measuring the surface roughness of the obtained conductive paste (3-F), the arithmetic average roughness Ra was 16 nm.

  Further, the 5% heat shrink temperature of the obtained nickel particles (3-D) was 345 ° C.

[Example 4]
<Step I: Preparation of seed particles>
After preparing 6120 g of nickel particle slurry (4-A) in the same manner as in Example 1, except that 40 g of copper formate tetrahydrate was used instead of 80 g of copper formate tetrahydrate in Example 1. Nickel particles (4-B) were prepared.

  An SEM photograph of the nickel particles (4-B) is shown in FIG. Referring to FIG. 3, the nickel particles (4-B) had an average particle diameter of 22 nm and a CV value of 0.10.

<Step II: Preparation of nickel complex solution>
In the same manner as in Example 1, a nickel complex solution was prepared.

<Step III: Preparation of mixed solution and preparation of nickel particles>
3.35 kg of the above nickel complex solution was taken, 100 g of nickel particle slurry (4-A) was added thereto, and after stirring, heated to 225 ° C. by irradiation with microwaves, while maintaining the temperature, Furthermore, nickel particle slurry (4-C) was prepared by adding 3.35 kg of the nickel complex solution in two portions every 10 minutes. In the same manner as in Example 1, the obtained nickel particle slurry (4-C) was allowed to stand and separated, and after removing the supernatant, washed and dried to prepare nickel particles (4-D).

  An SEM photograph of the nickel particles (4-D) is shown in FIG. Referring to FIG. 4, the nickel particles (4-D) had an average particle size of 158 nm and a CV value of 0.09.

<Preparation of conductive paste>
In the same manner as in Example 1, after preparing a nickel particle slurry (4-E), a conductive paste (4-F) was prepared. As a result of measuring the surface roughness of the obtained conductive paste (4-F), the arithmetic average roughness Ra was 13 nm.

  Further, the 5% heat shrink temperature of the obtained nickel particles (4-D) was 347 ° C.

[Example 5]
<Step I: Preparation of seed particles>
After preparing 6110 g of nickel particle slurry (5-A) in the same manner as in Example 1, except that 20 g of copper formate tetrahydrate was used instead of 80 g of copper formate tetrahydrate in Example 1. Nickel particles (5-B) were prepared.

  From the SEM photograph of the nickel particles (5-B), the average particle diameter of the nickel particles (5-B) was 27 nm, and the CV value was 0.11.

<Step II: Preparation of nickel complex solution>
In the same manner as in Example 1, a nickel complex solution was prepared.

<Step III: Preparation of mixed solution and preparation of nickel particles>
3.20 kg of the above nickel complex solution is taken, 100 g of nickel particle slurry (5-A) is added thereto, and after stirring, the mixture is heated to 225 ° C. by irradiation with microwaves to thereby prepare nickel particle slurry (5- C) was prepared. In the same manner as in Example 1, the obtained nickel particle slurry (5-C) was allowed to stand and separated, and after removing the supernatant, washed and dried to prepare nickel particles (5-D).

  From the SEM photograph of nickel particles (5-D), the average particle size of nickel particles (5-D) was 135 nm and the CV value was 0.10.

<Preparation of conductive paste>
In the same manner as in Example 1, after preparing the nickel particle slurry (5-E), a conductive paste (5-F) was prepared. As a result of measuring the surface roughness of the obtained conductive paste (5-F), the arithmetic average roughness Ra was 16 nm.

  Further, the 5% heat shrink temperature of the obtained nickel particles (5-D) was 330 ° C.

[Example 6]
<Step I: Preparation of seed particles>
In the same manner as in Example 5, after preparing the nickel particle slurry (6-A), nickel particles (6-B) were prepared.

<Step II: Preparation of nickel complex solution>
In the same manner as in Example 1, a nickel complex solution was prepared.

<Step III: Preparation of mixed solution and preparation of nickel particles>
3.20 kg of the above nickel complex solution was taken, 100 g of nickel particle slurry (6-A) was added thereto, and after stirring, heated to 225 ° C. by irradiation with microwaves, while maintaining the temperature, Further, 9.60 kg of the nickel complex solution was continuously added by a pump for 25 minutes to prepare a nickel particle slurry (6-C). In the same manner as in Example 1, the obtained nickel particle slurry (6-C) was allowed to stand and separated, and after removing the supernatant, washed and dried to prepare nickel particles (6-D).

  From the SEM photograph of nickel particles (6-D), the average particle size of nickel particles (6-D) was 214 nm and the CV value was 0.12.

<Preparation of conductive paste>
In the same manner as in Example 1, after preparing the nickel particle slurry (6-E), a conductive paste (6-F) was prepared. As a result of measuring the surface roughness of the obtained conductive paste (6-F), the arithmetic average roughness Ra was 16 nm.

  Further, the 5% heat shrink temperature of the obtained nickel particles (6-D) was 371 ° C.

[Example 7]
<Step I: Preparation of seed particles>
In the same manner as in Example 6, after preparing the nickel particle slurry (7-A), nickel particles (7-B) were prepared.

<Step II: Preparation of nickel complex solution>
In the same manner as in Example 1, a nickel complex solution was prepared.

<Step III: Preparation of mixed solution and preparation of nickel particles>
3.20 kg of the above nickel complex solution was taken, 100 g of nickel particle slurry (7-A) was added thereto, and after stirring, heated to 225 ° C. by irradiation with microwaves, while maintaining the temperature, Further, after 10 minutes, 3.20 kg of the nickel complex solution was added to prepare a nickel particle slurry (7-C). In the same manner as in Example 1, the obtained nickel particle slurry (7-C) was allowed to stand and separated, and after removing the supernatant, washed and dried to prepare nickel particles (7-D).

  From the SEM photograph of the nickel particles (7-D), the average particle diameter of the nickel particles (7-D) was 170 nm, and the CV value was 0.09.

<Preparation of conductive paste>
In the same manner as in Example 1, after preparing the nickel particle slurry (7-E), a conductive paste (7-F) was prepared. As a result of measuring the surface roughness of the obtained conductive paste (7-F), the arithmetic average roughness Ra was 16 nm.

  Further, the 5% heat shrink temperature of the obtained nickel particles (7-D) was 365 ° C.

[Example 8]
<Step I: Preparation of seed particles>
After preparing 6100 g of nickel particle slurry (8-A) in the same manner as in Example 1, except that 15 g of copper formate tetrahydrate was used instead of 80 g of copper formate tetrahydrate in Example 1. Nickel particles (8-B) were prepared.

  An SEM photograph of the nickel particles (8-B) is shown in FIG. Referring to FIG. 5, the nickel particles (8-B) had an average particle size of 29 nm and a CV value of 0.10.

<Step II: Preparation of nickel complex solution>
In the same manner as in Example 1, a nickel complex solution was prepared.

<Step III: Preparation of mixed solution and preparation of nickel particles>
7.90 kg of the above nickel complex solution was taken, 500 g of nickel particle slurry (8-A) was added thereto, and after stirring, the mixture was heated to 225 ° C. by irradiation with microwaves to obtain a nickel particle slurry (8- C) was prepared. In the same manner as in Example 1, the obtained nickel particle slurry (8-C) was allowed to stand and separated, and after removing the supernatant, washed and dried to prepare nickel particles (8-D).

  An SEM photograph of the nickel particles (8-D) is shown in FIG. Referring to FIG. 6, the average particle diameter of nickel particles (8-D) was 114 nm, and the CV value was 0.07.

<Preparation of conductive paste>
In the same manner as in Example 1, after preparing a nickel particle slurry (8-E), a conductive paste (8-F) was prepared. As a result of measuring the surface roughness of the obtained conductive paste (8-F), the arithmetic average roughness Ra was 12 nm.

  Further, the 5% heat shrink temperature of the obtained nickel particles (8-D) was 328 ° C.

[Comparative Example 1]
<Step I: Preparation of seed particles>
After preparing a nickel particle slurry (9-A) in the same manner as in Example 2, nickel particles (9-B) were prepared.

<Step II: Preparation of nickel complex solution>
In the same manner as in Example 1, a nickel complex solution was prepared.

<Step III: Preparation of mixed solution and preparation of nickel particles>
10.8 kg of the above-mentioned nickel complex solution is taken, 100 g of nickel particle slurry (9-A) is added thereto, and after stirring, the mixture is heated to 225 ° C. by irradiating with microwaves. C) was prepared. In the same manner as in Example 1, the obtained nickel particle slurry (9-C) was allowed to stand and separated, and after removing the supernatant, washed and dried to prepare nickel particles (9-D).

  From the SEM photograph of nickel particles (9-D), the average particle diameter of nickel particles (9-D) was 126 nm, and the CV value was 0.19.

<Preparation of conductive paste>
In the same manner as in Example 1, after preparing a nickel particle slurry (9-E), a conductive paste (9-F) was prepared. As a result of measuring the surface roughness of the obtained conductive paste (9-F), the arithmetic average roughness Ra was 38 nm.

  Further, the 5% heat shrink temperature of the obtained nickel particles (9-D) was 315 ° C.

[Comparative Example 2]
<Step I: Preparation of seed particles>
After preparing a nickel particle slurry (10-A) in the same manner as in Example 4, nickel particles (10-B) were prepared.

<Step II: Preparation of nickel complex solution>
In the same manner as in Example 1, a nickel complex solution was prepared.

<Step III: Preparation of mixed solution and preparation of nickel particles>
10.1 kg of the above nickel complex solution is taken, and 100 g of nickel particle slurry (10-A) is added thereto, and after stirring, the mixture is heated to 225 ° C. by irradiation with microwaves to thereby obtain a nickel particle slurry (10− C) was prepared. In the same manner as in Example 1, the obtained nickel particle slurry (10-C) was allowed to stand and separated, and after removing the supernatant, washed and dried to prepare nickel particles (10-D).

  An SEM photograph of the nickel particles (10-D) is shown in FIG. Referring to FIG. 7, the nickel particles (10-D) had an average particle diameter of 155 nm and a CV value of 0.18.

<Preparation of conductive paste>
In the same manner as in Example 1, after preparing a nickel particle slurry (10-E), a conductive paste (10-F) was prepared. As a result of measuring the surface roughness of the obtained conductive paste (10-F), the arithmetic average roughness Ra was 42 nm.

  Moreover, the 5% heat shrink temperature of the obtained nickel particles (10-D) was 352 ° C.

[Comparative Example 3]
<Step I: Preparation of seed particles>
After preparing a nickel particle slurry (11-A) in the same manner as in Example 5, nickel particles (11-B) were prepared.

<Step II: Preparation of nickel complex solution>
In the same manner as in Example 1, a nickel complex solution was prepared.

<Step III: Preparation of mixed solution and preparation of nickel particles>
6.4 kg of the nickel complex solution was taken, 100 g of nickel particle slurry (11-A) was added thereto, and after stirring, the mixture was heated to 225 ° C. by irradiating with microwaves. C) was prepared. In the same manner as in Example 1, the obtained nickel particle slurry (11-C) was allowed to stand and separated, and after removal of the supernatant, washed and dried to prepare nickel particles (11-D).

  From the SEM photograph of nickel particles (11-D), the average particle size of nickel particles (11-D) was 162 nm and the CV value was 0.24.

<Preparation of conductive paste>
In the same manner as in Example 1, after preparing a nickel particle slurry (11-E), a conductive paste (11-F) was prepared. As a result of measuring the surface roughness of the obtained conductive paste (11-F), the arithmetic average roughness Ra was 52 nm.

  Further, the 5% heat shrink temperature of the obtained nickel particles (11-D) was 348 ° C.

  Table 1 summarizes the results of Examples 1 to 8 and Comparative Examples 1 to 3.

  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.

Claims (6)

A method for producing nickel particles, comprising the following steps I to III:
I) a metal salt having an average particle diameter D1 by observation with a scanning electron microscope within a range of 10 nm or more and 30 nm or less, a coefficient of variation CV1 of the particle diameter of 0.12 or less, and at least nickel carboxylate; A step of preparing seed particles formed by mixing and heating 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) Mixing the seed particles and the nickel complex solution to obtain a mixed solution, heating and reducing nickel ions in the mixed solution, and depositing and growing nickel metal using the seed particles as nuclei to form nickel particles Forming step,
Including
In the step III, the nickel complex in the mixed solution is maintained at 200 times or less with respect to the metal element weight of the seed particles or nickel particles grown from the seed particles in terms of metal elements Particle production method.   The nickel particle production according to claim 1, wherein an average particle diameter D2 of the nickel particles observed by a scanning electron microscope is in a range of 100 nm to 300 nm and a coefficient of variation CV2 of the particle diameter is 0.12 or less. Method.   The average particle diameter D1 is in the range of 10 nm to 20 nm, the average particle diameter D2 of the nickel particles by scanning electron microscope observation is in the range of 100 nm to 200 nm, and the coefficient of variation CV2 of the particle diameter is In the case of 0.12 or less, in the step III, the nickel complex solution or the separately prepared nickel complex solution is additionally supplied to the mixed solution stepwise or continuously in a plurality of times. Item 2. A method for producing nickel particles according to Item 1.   In the step III, the concentration of the nickel complex in the nickel complex solution additionally supplied stepwise or continuously or in a separately prepared nickel complex solution is in the range of 3 to 12% by weight in terms of nickel element. Item 4. The method for producing nickel particles according to Item 3. The method for producing nickel particles according to claim 1 , wherein the metal salt includes nickel carboxylate and a salt of at least one metal selected from copper, silver, gold, platinum and palladium. The method for producing nickel particles according to any one of claims 1 to 5 , wherein the heating in the step III is performed by microwaves.