JP2015158000A - Nickel powder production process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a nickel powder containing no coarse particles, and production process thereof, which is suitable for an internal electrode of thin layered multilayer ceramic capacitor; and specifically a process for producing a nickel powder in which the average particle size is 0.1 to 0.3 μm and in which the ratio of coarse particles having a particle length size of 1.0 μm or more is 5 ppm or less of the total number of particles.SOLUTION: The nickel powder production process is characterized in comprising: a first step for forming a water slurry in which the raw material nickel powder is at high dispersion state in water, and wet classification treating the water slurry to form a nickel slurry; a second step for drying the nickel slurry obtained from the first step to form a nickel powder, and heat the nickel powder under a reduction atmosphere; and a third step for dry classification treating the nickel powder obtained in the second step.

Description

  The present invention relates to a method for producing nickel powder that can be suitably used as an internal electrode of a multilayer ceramic capacitor (MLCC).

  Conventionally, nickel powder has been used as a material for a conductive paste for producing a thick film conductor. This thick film conductor is used for the formation of electric circuits, the electrodes of multilayer ceramic components such as multilayer ceramic capacitors and multilayer ceramic substrates, etc. Especially in multilayer ceramic capacitors, the increase in the number of layers is progressing due to the demand for smaller size and higher capacity. The amount of conductive paste used for that purpose has also increased significantly. For this reason, as the metal powder used for the conductive paste, the use of expensive noble metals is avoided, and inexpensive base metals such as nickel are mainly used.

This multilayer ceramic capacitor is manufactured, for example, by the following method.
First, a conductive paste obtained by kneading a nickel powder, a resin such as ethyl cellulose, and an organic solvent such as terpineol is screen-printed on a dielectric green sheet to produce an internal electrode. Next, dielectric green sheets are laminated and pressure bonded so that the printed internal electrodes are alternately overlapped. Thereafter, the laminate is cut into a predetermined size, subjected to a binder removal treatment for removing the resin such as ethyl cellulose used as an organic binder, and then fired at a high temperature to 1300 ° C. to obtain a ceramic body. Then, an external electrode is attached to this ceramic body to produce a multilayer ceramic capacitor.

  By the way, as described above, the base powder such as nickel is more prevalent than the precious metal in the metal powder in the conductive paste to be the internal electrode. Therefore, the nickel powder or the like is not oxidized in the binder removal treatment of the laminate. Thus, it is performed in an atmosphere in which the oxygen content is extremely small.

Further, in recent years, in a multilayer ceramic capacitor that is required to be downsized and increased in capacity, in order to achieve the downsizing and increase in capacity, both the internal electrode and the dielectric constituting the multilayer ceramic capacitor are reduced in thickness. It is being advanced. In particular, the particle diameter of nickel powder used for the internal electrode is mainly 0.5 μm or less.
The nickel powder used for the internal electrode is required to have various characteristics, and it is important that one of them does not contain coarse particles. The reason is that if coarse particles are included, the coarse particles protrude from the internal electrode layer, and contact with another internal electrode layer causes a short circuit.

In order to cope with this mixture of coarse particles, a method of suppressing the generation of coarse particles during the formation of nickel powder particles has been proposed (Patent Document 1). Moreover, after nickel powder particles are formed, a method of dispersing in water and removing coarse particles with a wet classifier (Patent Document 2) or a method of removing coarse particles with a dry classifier (Patent Document 3) has been proposed. ing.
However, in these methods, it is difficult to stably produce nickel powder that does not contain coarse particles, particularly in the region of fine particles having an average particle size of 0.3 μm or less that can be sufficiently expected to be thinned. There is a need for a production method for producing nickel powder that does not contain coarse particles.

JP 2007-138291 A JP 2004-292950 A Japanese Patent Laid-Open No. 11-253886

The present invention has been made in view of such problems, and it is an object of the present invention to provide a suitable nickel powder and a method for manufacturing the same in order to produce a thin-layered multilayer ceramic capacitor internal electrode. .
Specifically, it aims at providing the manufacturing method of nickel powder whose average particle diameter is 0.1-0.3 micrometer, and whose coarse particle whose particle | grain major axis is 1.0 micrometer or more is 5 ppm or less.

  The inventor of the present invention has formed a thin ceramic film in which nickel powder forms a highly dispersed state in a water slurry, is subjected to wet classification from that state, then heated in a reducing atmosphere, and further subjected to dry classification. The present inventors have found that a suitable nickel powder for forming an internal electrode of a capacitor can be obtained, and the present invention has been completed.

  That is, the first aspect of the invention according to the present invention includes a first step of forming a water slurry in which the raw nickel powder is highly dispersed in water, and wet-classifying the water slurry to form a nickel slurry; After solid-liquid separation of the nickel slurry obtained in one step, the solid phase component is dried to form nickel powder, and the nickel powder obtained in the second step is heated in a reducing atmosphere. And a third step of performing a dry classification process.

  According to a second aspect of the present invention, there is provided a nickel powder manufacturing method characterized in that the raw material nickel powder in the first aspect is a nickel powder produced by a wet reduction method.

  The third invention of the present invention uses a wet reduction method in which the raw material nickel powder in the second invention crystallizes nickel powder from an aqueous nickel salt solution, a reducing agent, and an alkaline colloidal solution containing palladium and silver. A nickel powder production method, characterized in that the nickel powder is produced.

  According to a fourth invention of the present invention, the reducing atmosphere in the second step of the first to third inventions is an inert gas atmosphere containing 1 to 50% by volume of hydrogen. It is.

  According to a fifth aspect of the present invention, there is provided a nickel powder characterized in that the heating temperature in the step of heating the nickel powder in a reducing atmosphere in the second step of the first to fourth aspects is 150 to 350 ° C. It is a manufacturing method.

  In the sixth invention of the present invention, the number of coarse particles having a particle diameter of 1.0 μm or more of the nickel powder obtained through the third step in the first to fifth inventions is 5 ppm or less of the total number of particles. It is a manufacturing method of nickel powder characterized by being.

  7th invention of this invention is the manufacturing method of nickel powder characterized by the average particle diameter of the nickel powder obtained through the 3rd process in 6th invention being 0.1-0.3 micrometer. is there.

  The eighth invention of the present invention is the production of nickel powder characterized in that the oxygen content of the nickel powder obtained through the third step in the sixth or seventh invention is 1.5% by mass or less. Is the method.

According to the method for producing nickel powder according to the present invention, nickel particles having an average particle diameter of 0.1 to 0.3 μm and coarse particles having a particle major axis of 1.0 μm or more and a content of 5 ppm or less are produced. Is possible.
Therefore, if it is used for the internal electrode of a thin-film multilayer ceramic capacitor, the possibility of causing a short circuit of the internal electrode due to coarse particles can be reduced, the product yield of the capacitor can be improved, and a remarkable industrial effect can be achieved. It is what you play.

It is a manufacturing flowchart which shows the manufacturing method of this invention. It is a scanning electron micrograph (5000 times) of the nickel powder obtained by this invention.

  As shown in the manufacturing flow diagram of FIG. 1, the manufacturing method of the present invention includes a first step of performing wet classification after the raw nickel powder is made into a water slurry to be in a highly dispersed state, and wet classification of the water slurry. After the nickel slurry formed by the above method is dried, it is composed of a second step of performing a heat treatment in a reducing atmosphere and a third step of performing a dry classification treatment of the heated nickel powder.

  In addition, as a processing step for removing coarse particles other than the present invention, a highly dispersed water slurry using the obtained nickel powder is prepared, and once wet-classified, nickel powder is obtained by solid-liquid separation and drying. 1 method, a second method of obtaining a nickel powder by solid-liquid separation and drying after preparing a highly dispersed water slurry using the obtained nickel powder, once wet-classifying, then further wet-classifying multiple times and then solid-liquid separation and drying The third method to obtain nickel powder by dry-classifying the powder once, the fourth method to obtain nickel powder by dry-classifying the obtained nickel powder once, and then the nickel powder obtained by the first and second methods A fifth method for obtaining nickel powder by performing dry classification of the powder is conceivable.

  In the first, second, and fifth methods that undergo high-dispersion water slurry treatment, the surface of the nickel powder is high-pressure ground in water when forming a highly-dispersed water slurry, so that the majority of the surface is a hydroxide. In many cases, the surface of the nickel powder becomes hydroxide-dominated even after drying. Therefore, when using this powder and petroleum-based solvent as an internal electrode paste, the petroleum-based solvent and nickel powder used do not fit well, and only the powder re-aggregates and the powder and solvent are easily separated. In many cases, a preferable internal electrode paste cannot be obtained.

  In the third method in which the obtained nickel powder is once dry-classified to obtain nickel powder, coarse particles are often not removed to a sufficient level, and the reliability of coarse particle removal is low.

  In the fourth method in which the obtained nickel powder is once subjected to dry classification and further subjected to dry classification a plurality of times to obtain nickel powder, it is possible to improve the reliability of removing coarse particles by repeatedly performing dry classification. However, there is a problem that the adhesion and accumulation of the dry classifier occur and the production by continuous processing becomes difficult.

  From the above, it is difficult to obtain a suitable nickel powder for MLCC in the classification treatment steps such as the first to fifth methods considered other than the present invention, and the method for obtaining the nickel powder required in terms of production and characteristics is as follows. The method for producing nickel powder according to the present invention is suitable.

<Manufacturing method of nickel powder>
Hereinafter, the present invention will be described in detail.
In the present invention, nickel powder obtained by various methods such as a wet reduction method, a gas phase method such as a CVD method or a plasma method, or a spray pyrolysis method can be used as a raw material nickel powder. Since it is made into a slurry, it is suitable to apply to the nickel powder obtained by the wet reduction method which can be easily made into a water slurry. The nickel powder obtained by the wet reduction method will be described below as a specific example of the raw material nickel powder, but is not limited to this.

[Raw material nickel powder]
The step of obtaining the nickel powder by the wet reduction method may use a known method, and the nickel powder is crystallized by adding a reducing agent, an aqueous nickel salt solution and, if necessary, a complexing agent or a dispersing agent.
In the present invention, in order to obtain raw material nickel powder having an average particle diameter of 0.1 to 0.3 μm, it is desirable to further add an alkaline colloidal solution containing palladium and silver described in Japanese Patent No. 4957172. .

[First step]
The first step is a step of performing wet classification after using the nickel powder obtained by the above method as a raw material nickel powder, making the raw material nickel powder into a water slurry to a highly dispersed state.
The nickel powder (raw material nickel powder) obtained by the wet reduction method and the reaction solution are solid-liquid separated by a known method, pure water is added to the solid phase component, and the nickel powder is highly dispersed in pure water. A method of forming a water slurry and classifying it with a wet classifier is desirable.
In the case of nickel powder obtained by a method other than the wet reduction method, pure water may be added directly and highly dispersed in pure water to form a water slurry. In addition, washing may be added to remove the impurity component before forming the water slurry.

  As a high dispersion method, a wet counter jet mill, a wet pulverizer that grinds the surface of the powder particles in the slurry by rotating a stirring blade having the same diameter as the inner wall of the stirring vessel at high speed, for example, an optimizer (Sugino) Machine Co., Ltd.) and TK Philmix (made by Special Machine Industry Co., Ltd.). As another means, an apparatus that accelerates slurry pressurized by a pump through a narrowed flow path and collides with a diamond hard plate, for example, a microfluidizer (Mizuho Industrial Co., Ltd.) Company) and Nanomizer (manufactured by Yoshida Machinery Co., Ltd.) can be used.

Here, the reason why wet classification is performed first will be described.
In order to ensure the coarse particle removal level of the product, it is desirable that classification processing is performed in the final process. Therefore, the final process is dry classification or wet classification.
In the case of wet classification, the above-described problems are likely to occur when the finished nickel powder surface becomes a hydroxide to form a paste. Therefore, the final process is dry classification.

  As already mentioned, it is impractical to repeat the dry classification only once or a plurality of times in order to ensure the reliability of removing coarse particles. Therefore, in order to ensure the reliability of removing coarse particles by repeating the classification, classification is performed by another method before the dry classification of the final treatment, and the classification method is preferably wet classification. .

  For the wet classification, an apparatus using a cyclone system or a centrifugal system, for example, a hydrocyclone (manufactured by Nippon Chemical Machinery Co., Ltd.), LCSS (manufactured by CMS Co., Ltd.), nano cut / micro cut (manufactured by Krettek) or the like is used. be able to.

[Second step]
The second step is a step of heating the obtained nickel powder in a reducing atmosphere after solid-liquid separation of the nickel slurry after classification and drying of the solid phase component.
The role of the second step is to remove excess hydroxide on the surface of the nickel powder formed from the formation of the highly dispersed water slurry to the wet classification.

The drying after the wet classification may be performed using a known method, and the heating conditions of the nickel powder obtained after the drying in a reducing atmosphere are as follows: the amount of hydrogen gas in which the hydrogen concentration is 1 to 50% by volume as the reducing atmosphere to be used It is desirable to use a mixed gas consisting of an inert gas and supply it to the heating furnace.
When the hydrogen gas concentration is less than 1% by volume, the removal of hydroxide and the like on the surface of the nickel powder does not proceed sufficiently, and the effect does not appear clearly. On the other hand, even if the hydrogen gas concentration is higher than 50% by volume, the effect is not changed.
The inert gas is not particularly limited, and nitrogen gas, argon gas, or the like can be used.

Furthermore, the heating temperature is desirably 150 to 350 ° C. When the heating temperature is less than 150 ° C., the removal of hydroxide and the like on the surface of the nickel powder does not proceed sufficiently, and the effect does not appear clearly. When the heating temperature is higher than 350 ° C., coarse particles are generated due to necking and sintering of nickel powders, which is not desirable.
The furnace used for heating is not particularly limited as long as it can be used in a reducing atmosphere, and a batch furnace, a roller hearth furnace, a pusher furnace, or the like can be used.

[Third step]
In the third step, the nickel powder obtained by heating in the reducing atmosphere in the second step is subjected to dry classification.
Since the nickel powder that has undergone the second step forms a dry powder of weak agglomerates, the addition of dry classification reduces the coarse particles in the nickel powder and has a certain level of dispersibility. .

  It is also possible to use wet classification instead of dry classification, but the nickel powder is made into a water slurry again, and the manufacturing cost increases from the point that drying or heating in a reducing atmosphere is required after wet classification. It is not preferable. In dry classification, devices such as microspin (manufactured by Nippon Pneumatic Industry Co., Ltd.), counter jet mill AFG (manufactured by Hosokawa Micron Co., Ltd.) and the like can be used.

<Characteristics of nickel powder according to the present invention>
[Number of coarse particles]
The nickel powder according to the present invention is characterized in that the number of coarse particles having a particle size of 1.0 μm or more is 5 ppm or less of the total number of particles. If the number of coarse particles exceeds 5 ppm, the coarse particles protrude from the internal electrode layer when used for the internal electrode of the thin-layered multilayer ceramic capacitor, and contact with another internal electrode layer to cause a short circuit. Product yield tends to deteriorate. The particle diameter is a diameter measured from a scanning electron microscope (SEM) image.

[Average particle size]
Further, the nickel powder preferably has an average particle size of 0.1 to 0.3 μm.
Nickel powder with an average particle size of less than 0.1 μm is liable to generate coarse particles due to necking or sintering between particles during heat treatment. On the other hand, in the region where the average particle diameter exceeds 0.3 μm, the film thickness of the electrode using nickel powder also increases, so that it is not necessary to reduce the coarse particles to the level obtained by this method. For this reason, the application of this method is not desirable because unnecessary process processing is performed, resulting in high costs and excessive quality.

[Oxygen content]
The oxygen content of the nickel powder is preferably 1.5% by mass or less. When the oxygen content exceeds 1.5% by mass, the volumetric shrinkage of the nickel powder increases during firing of the multilayer ceramic capacitor in a reducing atmosphere, and the continuity of the electrode cannot be maintained, and the gas due to oxide reduction This is because generation of cracks and delamination in the capacitor causes a decrease in the capacitance of the capacitor.

  Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to these examples. The nickel powder was evaluated as follows.

[Average particle size]
A scanning electron microscope (SEM, JSM-5510, manufactured by JEOL Ltd.) was used to obtain a photograph of an SEM image (field of view: vertical 9.6 μm × horizontal 12.8 μm) at a magnification of 10,000. This SEM image is measured using image analysis software (Mac-View, manufactured by Mountec Co., Ltd.) to measure the area and number of particles in which the entire shape of the particle shape can be seen, and from these, the diameter of each particle is obtained and averaged. Calculated.

[Number of coarse particles]
Using a scanning electron microscope, 100 views of a SEM image (field of view: length 19.2 μm × width 25.6 μm) at a magnification of 5000 times are obtained. This 100-field SEM image is measured using the image analysis software to measure the area and number of particles that can be seen in their entire shape, and the diameter of each particle is obtained from them. Were counted as coarse particles.

[Oxygen content of nickel powder]
The oxygen content of nickel powder was measured with an analyzer (manufactured by LECO, TC436AR).

The step of obtaining nickel powder by the wet reduction method is as follows.
An alkaline hydrazine solution was mixed with an alkaline colloidal solution composed of palladium, a small amount of silver and gelatin to prepare an alkaline colloidal solution for reducing nickel.
The content of palladium, silver, and gelatin in the prepared alkaline colloidal solution was palladium: 50 mass ppm, silver: 0.5 mass ppm, gelatin: 500 with respect to the total mass of nickel in the nickel salt aqueous solution as the starting solution. The mass was ppm. The contents of palladium and silver in the solution were analyzed by ICP emission spectroscopic analysis.

The production of the alkaline colloid solution for reducing the nickel was specifically performed as follows.
First, after a predetermined amount of gelatin was dissolved in 300 L of pure water, hydrazine was mixed so that the concentration of hydrazine was 0.02 g / L to prepare a solution containing gelatin and hydrazine.
Next, a 10 L mixed solution of pure water, a predetermined amount of palladium salt and silver salt was prepared, and dropped into the previously prepared solution containing gelatin and hydrazine to obtain a colloidal solution.

  A sodium hydroxide aqueous solution is added to this colloidal solution to adjust the pH to 10 or more, and hydrazine is further added until the nickel weight: hydrazine weight becomes 1: 3.75, so that the composite composed of palladium and a small amount of silver is added. An alkaline hydrazine solution mixed with colloidal particles was prepared and used as an alkaline colloid solution for reducing nickel. At this time, pure water was further added so that the total solution amount was 400 L.

  And 25 L of nickel chloride aqueous solution whose nickel concentration is 100 g / L was dripped at this alkaline colloid solution as nickel salt aqueous solution, nickel was reduced, and raw material nickel powder was obtained.

The process of making the obtained raw material nickel powder highly dispersed in water as a water slurry and performing wet classification is as follows.
The obtained nickel powder was separated from the solution after the wet reduction reaction, 6 L pure water was added to the nickel powder cake, and suspended with a blade stirring type stirrer. Next, the process of opposing collision at 2000 atmospheric pressure by an optimizer (manufactured by Sugino Machine Co., Ltd.), the obtained water slurry is allowed to stand, and the supernatant liquid is removed by decantation is repeated 10 times to obtain a nickel powder dispersed water slurry. It was.

  Next, the operating pressure of hydrocyclone (NHC-1 type (manufactured by Nippon Chemical Machinery Co., Ltd.)) was adjusted to 1.2 MPa, the treatment volume was 200 L / hr with pure fluid, and nickel powder dispersed water slurry Processed. Thereafter, solid-liquid separation and vacuum drying were performed to obtain nickel powder.

  In the step of heating the dried nickel powder in a reducing atmosphere, the obtained nickel powder is treated in a hydrogen-nitrogen mixed gas atmosphere having a hydrogen concentration of 1.4% by volume at a heating temperature of 200 ° C. and a heating time of 60 minutes. went.

  In the step of dry classification of the obtained nickel powder, in microspin (MP-250 manufactured by Nippon Pneumatic Industry Co., Ltd.), the dispersion pressure is 0.6 MPa, the supply nozzle is 6 mm, the amount of nickel powder supplied is 0.5 kg / hr. Was processed.

FIG. 2 shows an SEM image (5000 times magnification) of the nickel powder obtained. The average particle size of the obtained sample was 0.18 μm.
Three lots of these series of samples were prepared, and the number of coarse particles and the average particle size were evaluated in all three lots. The results are shown in Table 1.

(Comparative Example 1)
A nickel powder was produced under the same conditions as in Example 1, except that the first step of making the raw nickel powder obtained by the wet reduction method in Example 1 highly dispersed in water and performing wet classification was omitted.
That is, nickel powder was produced, solid-liquid separated and vacuum dried, then subjected to a reduction treatment in a hydrogen-containing gas atmosphere, and then subjected to a dry classification treatment to produce nickel powder.
Three lots of these series of samples were prepared, and the coarse particle number and average particle size were evaluated in all three lots. The results are shown in Table 1.

(Comparative Example 2)
A nickel powder was produced under the same conditions as in Example 1 except that the third step of dry-classifying the nickel powder by the wet reduction method in Example 1 was omitted.
That is, nickel powder was produced, made into a highly dispersed state in water, wet-classified, solid-liquid separated, and vacuum-dried, and then heat-treated in a hydrogen-containing gas atmosphere.
Three lots of these series of samples were prepared, and the number of coarse particles and the average particle size were evaluated in all three lots. The results are shown in Table 1.

(Comparative Example 3)
The same conditions as in Example 1 except that the first step of wet-classifying the nickel powder obtained by the wet reduction method in Example 1 into a highly dispersed state in water and the third step of dry-classifying the nickel powder were omitted. Nickel powder was prepared.
That is, the nickel powder produced, solid-liquid separated and vacuum dried was heat-treated in a hydrogen-containing gas atmosphere.
Three lots of these series of samples were prepared, and the number of coarse particles and the average particle size were evaluated in all three lots. The results are shown in Table 1.

From Table 1, it can be seen that in Example 1 processed in this order from the first step to the third step, nickel powder having coarse particles of 1.0 μm or more and 5 ppm or less was obtained. On the other hand, it can be seen that in Comparative Examples 1 to 3 in which either or both of the first step and the third step are omitted, the amount of coarse particles of 1.0 μm or more exceeds 5 ppm.
In Example 1, wet classification was performed to increase the oxygen content. However, since reduction heating was performed thereafter, it was suppressed to a practical level of 1.5 mass% or less.

Claims (8)

Forming a water slurry in which the raw material nickel powder is highly dispersed in water, and subjecting the water slurry to wet classification to form a nickel slurry; and
A second step of drying the solid phase component after solid-liquid separation of the nickel slurry obtained in the first step to form a nickel powder, and heating the nickel powder in a reducing atmosphere;
And a third step of dry-classifying the nickel powder obtained in the second step.   The method for producing nickel powder according to claim 1, wherein the raw material nickel powder is nickel powder produced by a wet reduction method.   The raw material nickel powder is a nickel powder produced by a wet reduction method in which nickel powder is crystallized from an aqueous nickel salt solution, a reducing agent, and an alkaline colloidal solution containing palladium and silver. The manufacturing method of the nickel powder of Claim 2.   The method for producing nickel powder according to any one of claims 1 to 3, wherein the reducing atmosphere in the second step is an inert gas atmosphere containing 1 to 50% by volume of hydrogen.   The method for producing nickel powder according to any one of claims 1 to 4, wherein the heating temperature in the step of heating the nickel powder in a reducing atmosphere in the second step is 150 to 350 ° C. .   The number of coarse particles having a particle diameter of 1.0 μm or more in the nickel powder obtained through the third step is 5 ppm or less of the total number of particles. The manufacturing method of the nickel powder as described in 2.   The nickel powder production method according to claim 6, wherein an average particle diameter of the nickel powder obtained through the third step is 0.1 to 0.3 μm.   The method for producing nickel powder according to claim 6 or 7, wherein the oxygen content of the nickel powder obtained through the third step is 1.5 mass% or less.