JP2001200301A - Nickel powder and electrically conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide nickel powder having a narrow particle size distribution and excellent fillability in electrically conductive paste and particularly suitable for forming the thin and homogeneous internal electrode of a laminated ceramic capacitor without generating cracks and delamination and to provide an electrically conductive paste for a laminated ceramic capacitor. SOLUTION: In this nickel powder, the number of particles having a particle size of 1.2 times or more the average particle size by SEM observation is 5% or less of the number of all particles, the number of particles having a particle size of 0.8 times or less the average particle size is 5% or less of the number of all particles, and also, tap density is 2.5 g/cm3 or more, and the electrically conductive paste for a laminated ceramic capacitor contains the same nickel powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel powder and a conductive paste for a multilayer ceramic capacitor, and more particularly to a nickel powder and a conductive paste having a narrow particle size distribution and an excellent filling property in the conductive paste. The present invention relates to a nickel powder suitable for forming a thin and uniform internal electrode of a multilayer ceramic capacitor without using the same and a conductive paste for a multilayer ceramic capacitor containing the nickel powder.

[0002]

2. Description of the Related Art A multilayer ceramic capacitor is one in which a plurality of ceramic dielectric layers alternately stacked and an internal electrode layer are integrated. When such a multilayer ceramic capacitor is formed, the internal electrode material is used. A conductive paste is prepared by converting a metal fine powder into a paste, and printed on a ceramic dielectric green sheet using the conductive paste,
A plurality of ceramic dielectric green sheets and conductive paste layers are alternately layered, laminated by heating and pressing, and then fired at a high temperature in a reducing atmosphere to form a ceramic dielectric layer and internal electrode layers. Is generally integrated.

Conventionally, noble metals such as platinum, palladium, and silver-palladium have been used as the internal electrode material. However, in order to reduce costs, a technique using a base metal such as nickel instead of these noble metals has recently been used. Developed and evolving. However, when an internal electrode is formed using a paste containing nickel powder, problems such as cracks and delamination have occurred.

[0004] In recent years, electronic components manufactured using conductive paste, for example, multilayer ceramic capacitors and the like have been increasingly miniaturized, and with this, ceramic dielectric layers and internal electrode layers have become thinner and more multilayered. At present, the thickness of the dielectric layer is 2μ for multilayer components, especially multilayer ceramic capacitors.
m, the internal electrode thickness is 1.5 μm or less, and the number of laminated layers is 100 or more. In order to manufacture such a part, it is necessary to form a thin and uniform internal electrode without occurrence of cracks and delamination.

To obtain a thin internal electrode layer, it is considered appropriate to use metal fine powder having a small average particle size corresponding to the internal electrode layer. However, coarse particles are mixed even if the average particle size is within a predetermined range. When the internal electrode layer is formed using a conductive paste containing such metal fine powder, such coarse particles form projections on the internal electrode layer, and the projections break through the thin ceramic dielectric layer to form the internal electrode. May cause a short circuit between them. In order to prevent such a short circuit between the internal electrodes, it is necessary to use a metal fine powder having an average particle diameter considerably smaller than a metal fine powder having an average particle diameter suitable for obtaining a thin internal electrode layer.

For example, Japanese Patent Application Laid-Open No. H11-189801 discloses that the abundance ratio of coarse particles having an average particle size of 0.2 to 0.6 μm and having a particle size of 2.5 times or more the average particle size is disclosed. A nickel ultrafine powder of 0.1% or less based on the number is described, and in the fourth column, lines 21 to 24, “If the particle size of the coarse particles is limited to about 1.5 μm or more, for example, It is necessary to limit the average particle diameter of the nickel ultrafine powder to 0.6 μm. ”It is necessary to use a metal fine powder having a considerably small average particle diameter in order to obtain a thin internal electrode layer. .

In addition, in order to ensure the conductivity of the electrode stably, it is necessary to have a high filling property in a vehicle when producing a conductive paste even though it is a fine powder. However, the finer the powder, the more difficult it is for nickel powder containing such fine powder to fill in the conductive paste, and also the problem that the viscosity of the conductive paste increases. There is a problem that heat shrinkage and oxidation are accelerated.

[0008]

DISCLOSURE OF THE INVENTION The present invention has a narrow particle size distribution and an excellent filling property in a conductive paste.
An object of the present invention is to provide nickel powder suitable for forming a thin and uniform internal electrode of a multilayer ceramic capacitor without generation of cracks and delamination, and to provide a conductive paste for a multilayer ceramic capacitor.

[0009]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above object, and as a result, the ratio of coarse particles and fine particles in nickel powder has been made relatively small, and the tap density has been reduced. If the nickel powder is higher than the predetermined value, the internal electrode layer without protrusions can be formed on the surface without the need to make the nickel powder uselessly fine, and short-circuiting between the internal electrodes can be prevented, and the fine particles are small. In addition to suppressing oxidation, it was found that heat shrinkage could be suppressed, and that due to the high tap density, the filling of nickel powder in the conductive paste was high and a clean sintered film could be obtained. Completed the invention. Furthermore, in addition to the above characteristics, if the crystallite size in each particle is small, sintering is gentle and the sintering speed is not uneven, and as a result, a thin and uniform internal electrode without cracks or delamination is generated. Was found to be able to be formed.

That is, in the nickel powder of the present invention, the number of particles having a particle diameter 1.2 times or more the average particle diameter observed by SEM is 5% or less of the total number of particles, and the average particle diameter is 0.1% or less.
The number of particles having a particle diameter of 8 times or less is 5% or less of the total number of particles, and the tap density is 2.5 g / cm ³ or more. Further, the conductive paste for a multilayer ceramic capacitor of the present invention is characterized by containing nickel powder having the above characteristics.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the nickel powder of the present invention,
For convenience, the number of particles having a particle diameter of 1.2 times or more the average particle diameter by SEM observation of about 10,000 times is 5% of the total number of particles.
% Or less, preferably 4% or less, more preferably 3% or less, and the number of particles having a particle diameter of 0.8 times or less of the average particle diameter is 5% or less, preferably 4% or less of the total number of particles,
More preferably, it is important to be 3% or less. That is, since the ratio of coarse particles is relatively small and the particle size of each nickel particle in the nickel powder is considerably uniform, for example, in a multilayer ceramic capacitor obtained using a paste containing such nickel powder, nickel An internal electrode layer which is considerably thinner than the average particle diameter of the powder can be formed, and no projection is formed on the surface of the internal electrode layer, so that no short circuit occurs between the internal electrodes.
Further, since the ratio of the fine particles is relatively small, the problem that the viscosity of the conductive paste containing such nickel powder is increased does not occur, and heat shrinkage and oxidation are not promoted during firing. .

The nickel powder of the present invention has a tap density of 2.5 g / cm ³ or more, preferably 2.7 g / cm ^3.
/ Cm ³ or more, more preferably 3.0 g / cm ³ or more. That is, since the nickel powder has a high tap density, the filling property of the nickel powder in the conductive paste is high. For example, in the case of a multilayer ceramic capacitor obtained using the conductive paste containing such nickel powder, cleanness is high. A sintered film is obtained.

Further, in the nickel powder of the present invention, the average crystallite diameter in each particle is preferably less than 400 °, more preferably 300 ° or less. For example, in a multilayer ceramic capacitor obtained by using such a conductive paste containing nickel powder, a clean sintered film can be obtained. In addition, sintering progresses slowly due to the small crystallite diameter in each particle. That is,
In the case of particles having a large crystallite diameter in each particle, sintering occurs at once, but if the crystallite diameter in each particle is small,
During sintering, sintering between crystallites in the particles occurs first, and sintering between the particles gradually occurs, so that the sintering speed is not uneven, a clean film is formed, and cracks and delamination are hardly generated.

As described above, in the nickel powder of the present invention, the number of particles having a particle diameter 1.2 times or more the average particle diameter observed by SEM is 5% or less of the total number of particles, and the average particle diameter is 0%. The number of particles having a particle diameter of 0.8 times or less is 5% or less of the total number of particles, and the tap density is 2.5 g / cm.
³ or more, and the average crystallite size in each particle is 40
If the nickel powder is less than 0 °, for example, in a multilayer ceramic capacitor obtained by using a conductive paste containing such a nickel powder, the formation of protrusions on the surface of the internal electrode layer is prevented without occurrence of cracks and delamination. It is further sufficiently prevented that an extremely uniform, dense and thin internal electrode film can be formed.

In the nickel powder of the present invention, when a multilayer ceramic capacitor is manufactured using the above-mentioned conductive paste containing nickel powder, the SEM
The average particle size as observed is preferably from 0.1 to 1 μm, more preferably from 0.2 to 0.6 μm.

The conductive paste for a multilayer ceramic capacitor of the present invention contains the above-mentioned nickel powder of the present invention. The conductive paste for a multilayer ceramic capacitor of the present invention comprises the above-mentioned nickel powder having excellent characteristics. By containing it, it is particularly suitable for forming a thin and uniform internal electrode.

Next, a preferred method for producing the nickel powder of the present invention will be described. The nickel powder of the present invention is obtained by subjecting a nickel hydroxide-containing slurry produced by adding a nickel salt aqueous solution containing a nickel complex to an alkali metal hydroxide aqueous solution to a hydrazine-based reduction under a temperature condition of 55 ° C. or more. And reducing the nickel hydroxide to nickel by contact with an agent and subjecting the resulting nickel powder to a pulverizing treatment and air classification to remove coarse and fine particles.

The aqueous nickel salt solution containing such a nickel complex is prepared by dissolving a nickel salt and a compound for forming a nickel complex, preferably a water-soluble compound having a carboxyl group and / or an amino group, in water in an arbitrary order. Let me
It can be obtained by dissolving a water-soluble compound having a carboxyl group and / or an amino group in an aqueous nickel salt solution, or dissolving a nickel salt in an aqueous solution of a water-soluble compound having a carboxyl group and / or an amino group. In short, an aqueous solution containing a nickel salt and a water-soluble compound having a carboxyl group and / or an amino group may be generated. However, when a water-soluble compound having a carboxyl group and / or an amino group is dissolved in an aqueous nickel salt solution, formation of a nickel complex is easy, and the nickel complex-containing aqueous nickel salt solution thus obtained is used. This is preferable because the obtained nickel has a uniform particle size and the filling property in the conductive paste is improved.

Specific examples of the water-soluble compound having a carboxyl group and / or an amino group include ethylenediaminetetraacetic acid, acetic acid, oxalic acid, malonic acid, salicylic acid, thioglycolic acid, glycine, ethylenediamine, alanine, citric acid, and the like. Glutamic acid, lactic acid, malic acid, tartaric acid, triethanolamine and the like can be mentioned.

The amount of the water-soluble compound having a carboxyl group and / or an amino group added to form a nickel complex in a nickel salt aqueous solution is 0.005 to 0 in molar ratio with respect to nickel in the nickel salt aqueous solution. .5, more preferably 0.01 to 0.1. Such an addition amount is preferable because the particle size distribution of the nickel powder can be further narrowed and the cost is well balanced.

Nickel salts that can be used in the above preferred production method include nickel sulfate, nickel nitrate,
Nickel halides such as nickel chloride and the like can be mentioned. As the alkali metal hydroxide, sodium hydroxide and potassium hydroxide can be mentioned. As the hydrazine-based reducing agent, hydrazine, hydrazine hydrate, hydrazine sulfate and the like can be mentioned. Hydrazine carbonate, hydrazine hydrochloride and the like.

The concentration of the aqueous nickel salt solution used in the production of the nickel hydroxide-containing slurry is preferably 10 to 150 g / L as a nickel ion concentration.
More preferably, it is 50 to 150 g / L. By using the nickel salt aqueous solution having such a concentration, a narrow particle size distribution characteristic of the nickel powder of the present invention is achieved, and a favorable result is also obtained in terms of production efficiency.

The concentration of the aqueous alkali metal hydroxide solution used in the production of the nickel hydroxide-containing slurry is 20 to
It is preferably 300 g / L, and 60 to 250 g / L.
L is more preferred. The relative amounts of the aqueous nickel salt solution and the aqueous alkali metal hydroxide solution are such that the alkali metal hydroxide in the aqueous alkali metal hydroxide solution is 1.1 to 2 equivalents to the nickel salt in the aqueous nickel salt solution. Is more preferable, and more preferably 1.3 to 1.8 equivalents. It is preferable to use such relative amounts because the state of nickel hydroxide generation is stabilized and the cost is well balanced.

In the above preferred production method, it is important that the nickel hydroxide-containing slurry is brought into contact with a hydrazine-based reducing agent at a temperature of 55 ° C. or higher to reduce the nickel hydroxide. The temperature during this reduction is 55 ° C
If it is less than 1, it is difficult to obtain a nickel powder having a uniform particle diameter, and the mixture is formed by mixing a coarser nickel powder. In addition, the mixing ratio of alkali metal, which is an impurity, increases. Therefore, in the above preferred production method, the reaction temperature at the time of reducing the nickel hydroxide is 55 ° C. or higher, preferably 60 ° C. or higher.

The nickel powder obtained by reducing the above nickel hydroxide by contacting with an aqueous solution of hydrazine at 55 ° C. or higher, preferably 60 ° C. or higher, is SEM
When the particle size is measured by observation, the particle size is uniform, and the total amount of impurities derived from the reaction raw materials is extremely small.

In producing the nickel powder of the present invention, it is important that after the reduction reaction is carried out as described above, the obtained nickel powder is subjected to a granulation treatment. The reason is that the nickel powder obtained by the wet reaction as it is has a strong agglomeration of the nickel powder, shows the same disadvantage as the case of containing coarse particles described in the conventional technology, and has a low tap density and a low tap density in the conductive paste. This is because, since the filling property cannot be improved, a problem when such a nickel powder is used for a conductive paste, for example, cannot be suppressed.

The pulverizing method is not particularly limited, but a high-speed rotary collision-pulverizing treatment in which nickel powder is collided with a rotating part rotating at a high speed and pulverized, and the nickel powder is agitated together with beads or the like and pulverized. Media stirring type pulverization process, high water pressure type pulverization process in which a slurry of nickel particles is crushed by colliding from two directions at high water pressure, and jet abutment process.

As a device for performing such a pulverizing treatment, a high-speed moving body collision type air flow type pulverizer, an impact type pulverizer,
Examples thereof include a cage mill, a medium stirring mill, an axial flow mill, and a jet abutment device. Specifically, Super Hybrid Mill (made by Ishikawajima-Harima Heavy Industries), Jet Mill (made by Ebara Corporation), Super Mass Colloider (made by Masuyuki Sangyo),
Bead mill (manufactured by Irie Shokai), Ultimizer (manufactured by Sugino Machine), NC mill (manufactured by Ishii Grinding Machine Works), disintegrator (manufactured by Otsuka Teikoku), ACM Pulverizer (manufactured by Hosokawa Micron), turbo mill (manufactured by Matsubo),
Supermicron (manufactured by Hosokawa Micron), Micros (manufactured by Nara Machinery), New Cosmomizer (manufactured by Nara Machinery), Fine Victor Mill (manufactured by Hosokawa Micron),
Ecoplex (manufactured by Hosokawa Micron), CF mill (manufactured by Ube Industries), hybridizer (manufactured by Nara Machinery), pin mill (manufactured by Alpinay), pressure homogenizer (manufactured by Nippon Seiki Seisakusho), harel homogenizer (manufactured by Kokusan Seiko), mechano fusion system ( Hosokawa Micron) and a sand mill (Yodocasting).

In the production of the nickel powder of the present invention, it is also important to remove coarse and fine particles by air classification before and after the pulverization. The reason is that
If air classification is performed before the pulverizing treatment, strongly agglomerated particles and giant particles can be removed in advance, and if the air classification is performed after the pulverizing treatment, strongly agglomerated particles and the like that cannot be completely processed by the pulverization treatment can be removed. This is because fine particles including the maximum coarse particles can be removed. The time of this removal treatment can be appropriately selected according to the quality of the nickel powder to be produced, and of course, it may be carried out both before and after the pulverization treatment.

Regarding this removal treatment, it is inappropriate to use a sieving machine or the like in view of the prevention of oxidation of the nickel powder surface and the workability, and the most appropriate means is an air classifier. An air separator, a Spedd classifier, an Acucut, a turbo classifier, etc., which are force classifiers, are suitable.

Next, a preferred method for producing the conductive paste for a multilayer ceramic capacitor of the present invention will be described. The conductive paste for a multilayer ceramic capacitor of the present invention is composed of the above-described nickel powder, resin, solvent and the like of the present invention. Specifically, as a resin, a cellulose derivative such as ethyl cellulose, an acrylic resin, a polyvinyl butyral resin, a vinyl-based non-curable resin such as polyvinyl alcohol, and a thermosetting resin such as epoxy and acrylic, which is preferably used in combination with a peroxide. Can be used. In addition, terpineol, tetralin, butyl carbitol, carbitol acetate and the like can be used alone or in combination as a solvent. Further, a glass frit may be added to this paste as needed. The conductive paste for a multilayer ceramic capacitor of the present invention can be obtained by mixing and stirring the above raw materials using a mixing machine such as a ball mill or a three-roll mill.

[0032]

The present invention will be specifically described below based on examples and comparative examples. Example 1 Nickel sulfate hexahydrate 44.8 kg (grade 22.2% by mass) and citric acid monohydrate 1.8 kg were purified with 80 L of pure water.
The aqueous solution obtained by dissolving in
The solution was slowly dropped into 100 L of a g / L aqueous solution while maintaining the solution temperature at 60 ° C. to precipitate nickel hydroxide. While maintaining the liquid temperature at 60 ° C., 30 kg of hydrazine monohydrate was added to the suspension over 30 minutes to reduce nickel hydroxide to nickel. The obtained nickel powder was washed with pure water until the pH of the washing solution became 9 or less, filtered, and dried. Thereafter, the mixture was charged into a pulperizer AP-1SH type (manufactured by Hosokawa Micron) equipped with a knife-type hammer and subjected to a granulation treatment at a rotation speed of 2500 rpm. This pulverized nickel powder is treated with an SF sharp cut separator KSC-02 type (manufactured by Kurimoto Steel Works), which is an air separator, at a rotor rotation speed of 6000 rpm and an air amount of 7.2 m ³ / min. Was removed to obtain a nickel powder.

This nickel powder was observed with a 10,000-fold SEM, and the particle diameters of 1500 particles were measured in a total of five randomly selected visual fields. The average particle diameter determined from the measured value was 0.51 μm, and 0.61 μm (0.
The number of particles having a particle diameter exceeding 51 × 1.2 = 0.612) is 30 (2.0% of the total number of measured particles),
The number of particles having a particle diameter smaller than 0.41 μm (0.51 × 0.8 = 0.408) was 40 (2.7% of the total number of measured particles). The tap density of this nickel powder was 3.23 g / cm ³ , and the average crystallite size in each particle was 195 °.

Also, 100 parts by mass of the above nickel powder is
A binder consisting of 8 parts by mass of ethylcellulose, 100 parts by mass of terpineol and 12 parts by mass of butyl carbitol was added, mixed, and kneaded with a roll mill to prepare a conductive paste. 38 prepared conductive paste
Using a 0-mesh Tetron screen mask, a polyimide (PI) film (UPIREX manufactured by Ube Industries:
(Printed pattern is 4cm ×
4 cm). After the printed PI film was leveled at room temperature for 15 minutes, it was preliminarily dried for 30 minutes in a hot air circulation type constant temperature dryer set at 60 ° C. Further, it was transferred to a hot air circulation type constant temperature dryer set at 120 ° C., and was subjected to main curing for 60 minutes. After taking out from the dryer and allowing to cool to room temperature, the film densities at 20 points randomly selected were measured. Its average film density is 4.71 g / cm ³ and its standard deviation is 0.08 g
/ Cm ³ .

Further, the above-mentioned conductive paste was pressure-bonded so that the dielectric layer thickness was 2 μm, the internal electrode layer thickness was 1.5 μm, and the number of layers was 350. 2.0mm ×
It was cut to a size of 1.25 mm, dried, and subjected to a binder removal treatment. After that, it is baked in a hydrogen-nitrogen mixed gas at 1200 ° C. and is 2.0 mm × 1.25 mm × 1.25 mm
Was obtained. 200 pieces were taken out at random from the obtained multilayer ceramic capacitor and inspected for cracks, delaminations and the like. As a result, the number of defective products was 2, and the defective rate was 1%. The above measurement results, calculated values, and observation results are summarized in Table 1. In Table 1, “Ratio of ≧ 1.2d”
Is the ratio of the number of particles having a particle diameter of 1.2 times or more of the average particle diameter to the total number of particles, and “the ratio of ≦ 0.8d”
It is a ratio of the number of particles having a particle diameter of 0.8 times or less of the average particle diameter to the total number of particles.

Example 2 An aqueous solution obtained by dissolving 44.8 kg of nickel sulfate hexahydrate (grade: 22.2% by mass) and 0.65 kg of glycine in 80 L of pure water was treated with a sodium hydroxide concentration of 200 g / L. The solution was slowly dropped into 100 L of the aqueous solution while maintaining the solution temperature at 60 ° C. to precipitate nickel hydroxide. While maintaining the liquid temperature at 60 ° C., 42 kg of hydrazine monohydrate was added to this suspension over 20 minutes to reduce nickel hydroxide to nickel. The obtained nickel powder was washed with pure water until the pH of the washing solution became 9 or less, filtered, and dried. Thereafter, the particles were subjected to a pulverization treatment at a rotation speed of 4000 rpm for 5 minutes using a hybridizer NHS-3 (Nara Machinery). This pulverized nickel powder is used as an air separator SF sharp cut separator KSC-
Rotor speed 600 using Type 02 (manufactured by Kurimoto Steel Works)
The mixture was treated at 0 rpm with an air amount of 7.2 m ³ / min to remove coarse particles to obtain nickel powder.

Various characteristics of this nickel powder were measured in the same manner as in Example 1. Further, a conductive paste was prepared in the same manner as in Example 1, and the film density as an internal electrode was measured in the same manner as in Example 1. Further, the multilayer ceramic capacitor manufactured using the conductive paste in the same manner as in the first embodiment was inspected for cracks, delaminations and the like in the same manner as in the first embodiment. The measurement results, calculated values and observation results are as shown in Table 1.

Example 3 Nickel sulfate hexahydrate 44.8 kg (grade 22.2% by mass) and citric acid monohydrate 1.8 kg were mixed with 80 L of pure water.
The aqueous solution obtained by dissolving in
The solution was slowly dropped into 100 g of a g / L aqueous solution while maintaining the solution temperature at 70 ° C., to precipitate nickel hydroxide. While maintaining the liquid temperature at 70 ° C., 42 kg of hydrazine monohydrate was added to the suspension over 30 minutes to reduce nickel hydroxide to nickel. The obtained nickel powder was washed with pure water until the pH of the washing solution became 9 or less, filtered, and dried. After that, Evarator Rard Jet PM100, a jet mill (manufactured by Ebara Corporation)
6000 rpm, air amount 7.2 using
The treatment was performed at m ³ / min, and coarse particles were removed to obtain nickel powder.

Various characteristics of this nickel powder were measured in the same manner as in Example 1. Further, a conductive paste was prepared in the same manner as in Example 1, and the film density as an internal electrode was measured in the same manner as in Example 1. Further, the multilayer ceramic capacitor manufactured using the conductive paste in the same manner as in the first embodiment was inspected for cracks, delaminations and the like in the same manner as in the first embodiment. The measurement results, calculated values and observation results are as shown in Table 1.

Comparative Example 1 An aqueous solution obtained by dissolving 44.8 kg of nickel sulfate hexahydrate (grade: 22.2% by mass) in 80 L of pure water was added to 100 L of an aqueous solution having a sodium hydroxide concentration of 200 g / L. 5
While maintaining the temperature at 0 ° C., the solution was slowly dropped to precipitate nickel hydroxide. While maintaining the liquid temperature at 50 ° C. to this suspension, 42 kg of hydrazine monohydrate was added over 20 minutes to reduce nickel hydroxide to nickel, and the obtained nickel powder was washed with pure water. Was washed until the pH of the solution became 9 or less, filtered and dried. Thereafter, the mixture was charged into a pulperizer AP-1SH type (manufactured by Hosokawa Micron) equipped with a knife-type hammer, and was subjected to pulverization at a rotation speed of 2500 rpm to obtain a kernel powder.

Various characteristics of this nickel powder were measured in the same manner as in Example 1. Further, a conductive paste was prepared in the same manner as in Example 1, and the film density as an internal electrode was measured in the same manner as in Example 1. Further, the multilayer ceramic capacitor manufactured using the conductive paste in the same manner as in the first embodiment was inspected for cracks, delaminations and the like in the same manner as in the first embodiment. The measurement results, calculated values and observation results are as shown in Table 1.

Comparative Example 2 Nickel sulfate hexahydrate 44.8 kg (grade 22.2% by mass) and citric acid monohydrate 1.8 kg were mixed with 80 L of pure water.
The aqueous solution obtained by dissolving in
The solution was slowly dropped into 100 L of a g / L aqueous solution while maintaining the solution temperature at 60 ° C. to precipitate nickel hydroxide. While maintaining the liquid temperature at 60 ° C., 30 kg of hydrazine monohydrate was added to the suspension over 30 minutes to reduce nickel hydroxide to nickel. The obtained nickel powder was washed with pure water until the pH of the washing solution became 9 or less, filtered, and dried. Thereafter, the mixture was charged into a pulperizer AP-1SH type (manufactured by Hosokawa Micron) equipped with a knife-type hammer, and was subjected to granulation at a rotation speed of 2500 rpm to obtain nickel powder.

Various characteristics of this nickel powder were measured in the same manner as in Example 1. Further, a conductive paste was prepared in the same manner as in Example 1, and the film density as an internal electrode was measured in the same manner as in Example 1. Further, the multilayer ceramic capacitor manufactured using the conductive paste in the same manner as in the first embodiment was inspected for cracks, delaminations and the like in the same manner as in the first embodiment. The measurement results, calculated values and observation results are as shown in Table 1.

Comparative Example 3 22.0 kg of sufficiently dried anhydrous nickel chloride having a sulfur content of 500 ppm was allowed to stand in a quartz container, and the carrier was controlled while keeping the temperature in the container at 900 ° C. It was heated and evaporated in an air flow of 10 L / min of argon gas for use. A hydrogen gas for reduction was passed through the vaporized nickel chloride gas at 3.5 L / min, and the reduction temperature was controlled at 1000 ° C. to obtain nickel powder. The obtained nickel powder is washed with pure water until the pH of the washing solution becomes 9 or less, filtered, and dried, and then the pulperizer AP- equipped with a knife-type hammer is used.
1SH type (made by Hosokawa Micron) and rotating speed 2
The granulation was performed at 500 rpm. This pulverized nickel powder is treated with an SF sharp cut separator KSC-02 type (manufactured by Kurimoto Steel Works), which is an air separator, at a rotor rotation speed of 6000 rpm and an air amount of 7.2 m ³ / min. Was removed to obtain a nickel powder.

Various characteristics of this nickel powder were measured in the same manner as in Example 1. In Comparative Example 3, since the particles were produced by a dry method, the average crystallite diameter in each particle was large. Further, a conductive paste was prepared in the same manner as in Example 1, and the film density as an internal electrode was measured in the same manner as in Example 1. Further, the multilayer ceramic capacitor manufactured using the conductive paste in the same manner as in the first embodiment was inspected for cracks, delaminations and the like in the same manner as in the first embodiment. The measurement results, calculated values and observation results are as shown in Table 1.

[0046]

[Table 1]

As is clear from the data in Table 1,
The nickel powder of the present invention in Examples 1 to 3 has few coarse particles having a specific particle size or more and fine particles having a specific particle size or less, and has a narrow particle size distribution and a high tap density. It was also excellent. Further, the film formed using the conductive paste containing nickel powder has a high film density and is uniform, and the defect rate of the multilayer ceramic capacitor manufactured using the conductive paste containing such nickel powder is high. Was also low.

On the other hand, the nickel powder of Comparative Example 1 contains many coarse particles and fine particles, has a low filling property in the conductive paste, and uses a conductive paste containing such nickel powder. The defective rate of the multilayer ceramic capacitor manufactured by the above method was also high. Since the nickel powder of Comparative Example 2 had a low tap density, the filling property in the conductive paste was low, and the defective rate of the multilayer ceramic capacitor manufactured using the conductive paste containing such nickel powder was also high.
Furthermore, since the nickel powder of Comparative Example 3 is a dry powder, it has many fine particles and a large average crystallite diameter, and the film density of a film formed by using a conductive paste containing such nickel powder varies. Further, the defective rate of the multilayer ceramic capacitor manufactured using the conductive paste containing such nickel powder was also high.

[0049]

The nickel powder of the present invention has a narrow particle size distribution and an excellent filling property in a conductive paste, and the conductive paste containing the nickel powder can be used for various applications. Even when used to form the internal electrode, without unnecessarily reducing the particle size of the nickel fine powder, without generation of cracks and delamination, and furthermore, the formation of protrusions on the surface of the internal electrode layer is more sufficiently prevented, It is possible to form a very uniform, dense and thin internal electrode film. Further, the conductive paste for a multilayer ceramic capacitor of the present invention is particularly suitable for forming a thin and uniform internal electrode by using the nickel powder having the above-mentioned excellent characteristics.

Claims (3)

[Claims] 1. The number of particles having a particle diameter of 1.2 times or more of the average particle diameter by SEM observation is 5% or less of the total number of particles, and has a particle diameter of 0.8 times or less of the average particle diameter. Nickel powder wherein the number of particles is 5% or less of the total number of particles and the tap density is 2.5 g / cm ³ or more. 2. The nickel powder according to claim 1, wherein the average crystallite size in each particle is less than 400 °. 3. A conductive paste for a multilayer ceramic capacitor comprising the nickel powder according to claim 1 or 2.