JP2003253301A - Method for manufacturing metal powder for conductive paste, metal powder for conductive paste, conductive paste, and multilayer ceramic electronic part - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a metal powder for a conductive paste used for an internal electrode of a multilayer ceramic electronic part capable of improving the reliability of the multilayer ceramic electronic part. <P>SOLUTION: The method includes a washing process where the metal powder for the conductive paste is washed with water or an organic solvent. It also includes a pulverizing process where the metal powder in slurry 13 is pulverized by passing the slurry 13 containing the metal powder under washing through a clearance 14 between a stator 11 and a rotor 12 which makes the clearance 14 of ≥0.1 mm and ≤1.5 mm against the stator 11 and rotates at a circumferential velocity of ≥4 m/s. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a metal powder used as a conductive metal powder such as a paste for an internal electrode of a monolithic ceramic electronic component, in particular, a monolithic ceramic capacitor, and the electroconductivity obtained by the method. The present invention relates to a metal powder for paste, a conductive paste using the metal powder for conductive paste, and a laminated ceramic electronic component manufactured using the conductive paste.

[0002]

2. Description of the Related Art Conventionally, in a monolithic ceramic electronic component represented by a monolithic ceramic capacitor, a conductive paste is often used to form an internal electrode (internal conductor) thereof. In the method for manufacturing such a laminated ceramic electronic component, first, the conductive paste is formed into a thick film,
The internal electrode pattern is printed on a ceramic green sheet with a thickness of several tens of μm to several μm, and several to several hundreds of these green sheets are laminated on each other in the thickness direction, and then cut into a predetermined size and cut. The green chip thus obtained is fired at a temperature of from 800 ° C. to about 1500 ° C., and then a terminal electrode (external electrode) is formed by a method such as baking to obtain a laminated ceramic electronic component.

This conductive paste is composed of a metal powder serving as a conductive component, an organic vehicle composed of an organic solvent and an organic binder component, and in some cases, a ceramic powder substantially the same as the ceramic body used. Often composed of a binding control agent. Here, as the metal powder, at present, relatively inexpensive metal powder of nickel or copper is often used in place of the noble metal typified by palladium in accordance with the increase in capacity due to thin layers and multilayers of multilayer ceramic capacitors. It is like this.

In such a laminated ceramic electronic component, as described above, the ceramic green sheet is thinned,
As the number of layers increases, the metal powder contained in the conductive paste for internal electrodes is required to have a more uniform particle size and a small number of coarse particles.

The method for producing the metal powder is roughly classified into a gas phase method represented by Japanese Patent Application Laid-Open No. 4-45207, a method of reducing a metal salt vapor with a reducing gas,
JP-A-5-51610 and JP-A-2000-8712
The liquid phase method of reducing a metal salt with a reducing agent in water or an organic solvent, which is typified by Japanese Patent Publication No. 1), is roughly classified. More uniform particle size to accommodate
Those with few coarse particles have been produced.

Further, in order to improve the dispersibility of these metal powders, they may be crushed and crushed by a method as disclosed in JP-A-11-343501.

[0007]

However, in the conventional method for producing a metal powder for a conductive paste, as described in JP-A No. 11-343501, a metal powder that has been once washed and dried is used. It was crushed and crushed. Generally, it is said that the metal powder is agglomerated by two aggregating factors, that is, powder agglomeration that occurs in a solution during reaction or washing and powder agglomeration that occurs due to salt crosslinking during drying.

Therefore, in the process of crushing and crushing the metal powder that has been washed and dried, it is necessary to crush and crush the metal powder having the above two agglomeration factors.
In some cases, it was difficult to disperse even to a state close to monodispersion.

Here, the liquid phase method represented by JP-A-5-51610 and JP-A-2000-87121 is
Needless to say, since the metal powder is reacted and produced in water or an organic solvent, washing and drying steps are necessarily included. However, even in the gas phase method represented by JP-A-4-45207, JP-A-11- As shown in Japanese Patent No. 189813, the manufacturing method also includes washing and drying steps. Thus, in each of the above production methods, the metal powder having two aggregating factors, that is, powder agglomeration generated in the solution at the time of reaction or washing as described above and powder agglomeration generated by salt crosslinking during drying, is ground. , It is necessary to disintegrate.

When the crushing of the metal powder is insufficient, aggregate particles larger than the average particle size of the metal powder are present. If these agglomerated particles are not crushed or dispersed as they are and printed and formed as an internal electrode for a laminated ceramic capacitor, the thickness of the ceramic layer sandwiched between the internal electrodes after firing of the laminated ceramic capacitor is 5 μm or less. If it is thin, the aggregated particles may penetrate the ceramic layer and short-circuit between the internal electrodes facing each other with the ceramic layer interposed therebetween, which may cause a problem that the yield of the laminated ceramic capacitor is significantly reduced.

In order to prevent this, a method of classifying a metal powder typified by nickel to be used in advance to remove agglomerated particles and then forming a paste has been used. There may be a problem that the yield of the metal powder is significantly reduced.

In addition, these agglomerated particles may be dispersed and crushed during the paste processing step. However, if the agglomeration is particularly strong, it may not be sufficiently crushed by the dispersing force applied by a three-roll mill during the processing step. Alternatively, there may be a problem in that it is necessary to spend a long time in the dispersion process.

In view of the above problems, the present invention prevents or reduces agglomeration generated in the steps from washing of metal powder to drying, and eliminates the presence of uncrushed agglomerated particles in the conductive paste, or By reducing, it is possible to significantly improve the yield of multilayer ceramic electronic components typified by multilayer ceramic capacitors, a method for producing a metal powder for a conductive paste, a metal powder for a conductive paste obtained by the method, An object of the present invention is to provide a conductive paste using the same and a multilayer ceramic electronic component having the sintered body of the conductive paste as an internal electrode.

[0014]

In order to solve the above-mentioned problems, the method for producing a metal powder for a conductive paste of the present invention comprises:
In a method for producing a metal powder for a conductive paste, which comprises a washing step of at least one of water and an organic solvent for a metal powder for a conductive paste, a slurry containing the metal powder being washed, a stator, and the stator. And a peripheral speed of 4 m with a gap of 0.1 mm or more and 1.5 mm or less
It is characterized by including a step of crushing the metal powder by allowing the metal powder to pass through the gap between the rotor and the rotor rotating at a speed of / s or more.

In order to solve the above-mentioned problems, another method for producing a metal powder for a conductive paste according to the present invention is for a conductive paste, which comprises a step of washing the metal powder for a conductive paste with water or an organic solvent. In the method for producing a metal powder, after washing the metal powder, the metal powder is undried (before drying is completed) to form a slurry, and the slurry is 0.1 mm or more with respect to the stator and the stator.
It is characterized by including a step of crushing the metal powder by allowing it to pass through the above-mentioned gap between the rotor having a gap of 1.5 mm or less and rotating at a peripheral speed of 4 m / s or more.

In any case, the important thing is that
Rather than crushing the powder that has undergone the drying step by shearing force, there is a gap of 0.1 mm or more and 1.5 mm or less with respect to the undried metal powder during or after cleaning, and the peripheral speed is It is characterized by applying shear by a rotor rotating at a speed of 4 m / s or more. The peripheral speed indicates the linear speed of the outer diameter portion of the rotor.

That is, since the metal powder before drying has not undergone agglomeration due to salt cross-linking that occurs during drying, it is possible to loosen the agglomeration more easily and effectively than by crushing the metal powder after drying. It will be possible. Even in the case of agglomeration that cannot be crushed in the dispersion step after drying, it is possible to crush it by applying a shearing force before drying as in the present invention, and agglomerated particles in the conductive paste, that is, coarse particles. It is possible to prevent the occurrence of the above and improve the yield of the laminated ceramic electronic component represented by the laminated ceramic capacitor.

The crushing method in the present invention is 0.1 m
The shearing force is applied to the gap of m or more and 1.5 mm or less by the rotor rotating at the peripheral speed of 4 m / s or more because the dispersion machine using the dispersion media, for example, the ball mill or the sand mill, is caused by the collision of the media. There is a risk of deformation of metal powder, generation of contamination from media, and mixing, and a rotor (rotating body) that has a gap of 0.1 mm or more and 1.5 mm or less and rotates at a peripheral speed of 4 m / s or more. This is because the disperser of the type that applies a shearing force by means of () is easy to replace from the washing equipment by the normal propeller rotation.

Further, a disperser (crusher) of a type having a gap of 0.1 mm or more and 1.5 mm or less and applying a shearing force by a rotor rotating at a peripheral speed of 4 m / s or more.
Since it also has the effect of stirring the solution, it is possible to more effectively disintegrate the metal powder existing in water or the organic solvent by the shearing force.

An example of the above disperser will be described below with reference to FIG. As shown in FIG. 1, the disperser includes a bottomed cylindrical stator 11 and a rotor 12 that rotates coaxially with the stator 11. The stator 11 includes a cylindrical peripheral wall portion 11a, a bottom surface portion 11b, and a circular opening portion 11c coaxial with the bottom surface portion 11b.

The rotor 12 is provided coaxially with a bottomed cylindrical rotor body 12a having a truncated cone shape and a rotary shaft 12b for rotating the rotor body 11a. In the rotor body 11a, the ring-shaped tip surface 1
2c, a truncated cone-shaped outer peripheral surface 12d, and the outer peripheral surface 12
An inner peripheral surface 12e that is substantially parallel to d is formed.

As a result, the outer peripheral surface 12d and the inner peripheral surface 12e each have a tapered shape in which the outer diameter and the inner diameter gradually increase from the bottom toward the tip surface 12c.

Further, the tip surface 12c is formed by the stator 11
It faces the inner bottom surface of the bottom surface portion 11b of the base 11 substantially in parallel. The clearance (gap) 14 between the tip surface 12c and the inner bottom surface can be adjusted by moving the rotor 12 along the rotation axis.

On the other hand, the inner diameter of the peripheral wall portion 11a of the stator 11 is set to be larger than the maximum outer diameter of the outer peripheral surface 12d of the rotor body 12a. Therefore, the rotor body 12a is rotatable within the stator 11. Further, the inner diameter of the opening 11c of the stator 11 is set to be smaller than the maximum outer diameter of the inner peripheral surface 12e of the rotor body 12a on the tip surface 12c side. As a result, the rotor body 12
The entire front end surface 12c of a is the bottom surface portion 11 of the stator 11.
It faces the inner bottom surface of b with the clearance 14.

In such a dispersing machine, when the rotor 12 rotates with respect to the stator 11, centrifugal force sucks the slurry 13 and discharges it from the upper opening of the stator 11 through the clearance 14 to the outside. Has become.

At this time, in the clearance 14, the slurry 13 is in a turbulent flow and the slurry 13 passing through
A large shearing force is generated against. In the clearance 14, the tip surface 12 of the rotor body 12a is
Since the peripheral speed increases in order from the inner diameter side of c to the outer diameter side, the shearing force also sequentially increases. By these things, it becomes possible with the above-mentioned disperser to crush the aggregated metal powder in the above-mentioned slurry 13.

The wetted portions of the stator 11 and the rotor 12 facing each other may have irregularities facing each other, or even if they do not exist, a sufficient shearing force can be expected.
More specifically, as equipment equipped with such a mechanism, T.K. K homomixer MARK II type and T.K. Examples include K homomic line flow type.

The effect of the present invention is not limited to the above-mentioned dispersion equipment, and any equipment having a similar shearing mechanism can be used. For example, it has a fixed body and a moving body (rotating body) adjusted to a clearance 14 of 0.1 mm or more and 1.5 mm or less, more preferably 0.1 mm or more and 1.0 mm or less with respect to the fixed body. Any equipment can be used as long as this moving body has a mechanism for moving (rotating) relative to the fixed body at a peripheral speed of 4 m / s or more.

The shearing force of these facilities is
Since the clearance 14 between the stator 11 and the rotor 12 depends on the clearance 14 between the rotor 12 and the rotor 12, the narrower the clearance 14 between the stator 11 and the rotor 12 and the higher the peripheral speed, the higher the shearing force. To do. Unless the clearance 14 is 1.5 mm or less, and more preferably 1.0 mm or less, a shearing force capable of crushing the agglomeration of the metal powder cannot be obtained.

In the present invention, the lower limit of the clearance 14 is specified as 0.1 mm, but this is not limited by the crushing force of the metal powder, and the stator 11
This is limited by the mechanical processing accuracy of the rotor 12 and if the clearance 14 of less than 0.1 mm can be achieved by improving the mechanical processing accuracy of the stator 11 and the rotor 12, this result will not be hindered.

Further, in the rotor 12, a peripheral speed of 4 m / s or more is required to break up the agglomeration of the metal powder. If the peripheral speed is slower than this, the agglomeration of the agglomerated particles will be incomplete, resulting in the production of agglomerated particles in the conductive paste, that is, coarse particles. This leads to a reduction in the yield of a typical multilayer ceramic electronic component.

In particular, in the case of the method for producing a metal powder for a conductive paste by the liquid phase method, the production reaction of the metal powder is often carried out under high alkali in order to enhance the reducing power of the reducing agent used. Therefore, the pH of the cleaning solution often shows a high alkali in the initial stage, and it is necessary to replace the cleaning solution a plurality of times in order to completely remove the ionic residues.

Here, as in the present invention, at the time of washing, 0.1
When the metal powder is crushed by applying a shearing force by the rotor 12 having a clearance 14 of not less than 1.5 mm and not more than 1.5 mm and rotating at a peripheral speed of 4 m / s or more, especially when the particle diameter of the metal powder is 0. When the particle size is as small as 0.5 μm or less, the sedimentation speed of the metal powder in the cleaning solution becomes remarkably slow, the separation from the cleaning liquid becomes impossible, and it may be difficult to replace the cleaning liquid or recover the metal powder.

Here, according to the Stokes sedimentation velocity equation,
It is widely known that finer particles have a slower sedimentation. Also in this case, the agglomerated metal powder rapidly settles as pseudo coarse particles, but since the agglomerated metal powder was crushed to the vicinity of the primary particle size by the method according to the present invention, the particle size was fine. Therefore, it is considered that the sedimentation was delayed.

Further, this phenomenon remarkably occurs when the amount of ionic residues in the solution decreases. Therefore, as a countermeasure against this, it is preferable to add a step of separating the cleaning solution and the metal powder by centrifugation by gravitational acceleration of 100 G or more. By giving a gravitational acceleration of 100 G or more to the metal powder, the precipitation of the metal powder is accelerated, and the separation and recovery of the metal powder are facilitated. In the case of a metal powder having an average particle size of about 0.5 μm, sedimentation of the metal powder within a practical time due to gravitational acceleration of about 100 G,
Although it is possible to collect the powder, a gravitational acceleration of 1000 G or more may be required in the case of powder having an average particle size of 0.1 μm or less.

The metal powder of the present invention is a metal powder containing at least one of nickel and copper as a main component. This is because, as described above, relatively inexpensive metal powders of nickel and copper have come to be used more and more with the thin layers and multilayers of recent multilayer ceramic capacitors.
Other common metal powders used in conductive thick film pastes,
For example, it does not prevent the same effect on palladium powder and silver powder.

These metal powders have an average particle size of 1.0 μm.
It is characterized in that the metal powder having an average particle size of 1.0 μm or less has a stronger tendency to cause aggregation, and the effect of the present invention becomes more prominent. The same effect can be expected for metal powders exceeding 1.0 μm. In the present invention, the average particle size refers to a numerical value obtained by measuring the length of a metal powder photographed by an electron microscope.

The present invention is also directed to the metal powder prepared by the above-mentioned method, and a conductive paste for a multilayer ceramic electronic component such as a multilayer ceramic capacitor using the metal powder.

By the way, as described above, there are two aggregating factors as a cause of the agglomeration of metal powders: powder agglomeration occurring in the solution during reaction or washing, and powder agglomeration occurring due to salt crosslinking during drying. I explained that. As in the present invention, crushing the agglomerated particles before drying the metal powder enables more effective crushing than performing the dispersion treatment on the dried metal powder.

However, when the metal powder once crushed in the wet or after the cleaning is directly subjected to the drying step, reaggregation due to salt crosslinking during the drying occurs.

Even when re-aggregation occurs due to salt crosslinking during drying, according to the present invention, it is referred to as powder agglomeration occurring in a solution during reaction or washing, and powder agglomeration occurring due to salt crosslinking during drying. Since one of the two aggregating factors has already been removed, the agglomeration can be more easily disintegrated as compared with the method for producing a metal powder that does not use the method of the present invention, and the effect of the present invention is not denied.

However, in order to completely remove the cause of aggregation of the metal powder, it is necessary to remove the powder aggregation factor generated by salt crosslinking during drying. Therefore, in a more effective embodiment of the present invention, in a method for producing a metal powder including a washing step with water or an organic solvent, a circumferential speed of a gap of 0.1 mm or more and 1.5 mm or less is set in a water or organic solvent. It is a method for producing a conductive paste in which a metal powder crushed by a shearing force by a rotor rotating at a speed of 4 m / s or more is used as a conductive component for a conductive paste without being completely dried.

Since the metal powder crushed in the moisture by the method according to the present invention is used as the metal powder for the conductive paste without being completely dried, that is, in the undried state (before completion of drying), It is possible to prevent the occurrence of aggregation due to salt crosslinking.

As a method for converting the crushed metal powder into a conductive material for a conductive thick film paste without completely drying it, a solvent having a high boiling point is added at the time of powder drying described in JP-A-12-48644. A method, or a method of crushing in a solvent of a conductive thick film paste, for example, terpineol or the like, or a method of substituting with a solvent for a conductive paste after crushing to use the conductive paste material as it is, crushed As a method of using the metal powder of No. 1 as a conductive material for a conductive paste without completely drying the solid powder, a solid component, a diluting solvent, a dispersant, and an organic resin described in JP 2001-67951 A. A method for producing a conductive paste using components and a main solvent, wherein the boiling point of the diluent solvent is 100 ° C. or more lower than the boiling point of the main solvent, and the diluent solvent is A first dispersion step that is compatible with the organic resin component and the main solvent, and first disperses a first mill base obtained by mixing the solid component, the diluent solvent, and the dispersant to obtain a first slurry; Then, a second dispersion step of dispersing a second mill base obtained by mixing the organic resin component and the main solvent in the first slurry to obtain a second slurry, and then from the second slurry A step of removing the diluent solvent, in a method for producing a conductive paste, characterized by comprising crushing in the diluent solvent, or replacing the diluent solvent after crushing the conductive paste material as it is There is a method of doing. Whichever method is used, the metal powder is not completely dried, and therefore aggregation due to salt crosslinking can be prevented.

Here, as one of the more preferred embodiments of the present invention, crushing is carried out in a diluting solvent at the time of preparing the conductive paste described in the third of the above-mentioned methods, or after crushing, a diluting solvent is used. A method of substituting the conductive paste material as it is will be described.

As the diluting solvent described in JP 2001-67951 A, a solvent having a boiling point lower than the boiling point of the main solvent by 100 ° C. or more is appropriately used. For example, in the case of a conductive paste using terpineol as the main solvent and ethyl cellulose as the organic resin component, acetone as the diluting solvent,
A ketone solvent such as dimethyl ketone and an alcohol solvent such as methanol and ethanol are preferable.

For example, after synthesizing a metal powder by a liquid phase method, first washing with water, and then substituting ethanol with water, for example, JP-A-2001-6795.
It can be used as it is as a conductive component in the conductive paste manufacturing method described in JP-A-1.

Since this diluent solvent is removed from the conductive paste in the step of removing the diluent solvent, it is possible to use it without drying the metal powder. Here, in water or an organic solvent, which is a feature of the present invention,
The crushing step based on the shearing force by the rotor 12 having a clearance 14 of 0.1 mm or more and 1.5 mm or less and rotating at a peripheral speed of 4 m / s or more may be performed during washing with water or during replacement with ethanol. The same effect can be expected in either case.

The present invention is a conductive material according to the present invention, which is preferably used for forming an internal electrode of a laminated ceramic electronic component in which the thickness of the ceramic layer sandwiched between the internal electrodes after firing is 5 μm or less. The present invention is also directed to a paste, and further to a laminated ceramic electronic component using the conductive paste according to the present invention.

Here, the reason why the thickness of the ceramic layer sandwiched between the internal electrodes after fabrication is set to 5 μm or less is that the reduction of the occurrence rate of short-circuit defects is remarkably reduced due to the removal of aggregates due to the effect of the present invention. Therefore, the same effect can be expected even when the thickness of the ceramic layer exceeds 5 μm.

A laminated ceramic capacitor as such a laminated ceramic electronic component will be described below with reference to FIG. As shown in FIG. 2, the monolithic ceramic capacitor includes ceramic layers 2a laminated on each other.
Ceramic body 2 having a substantially rectangular parallelepiped shape and each ceramic layer 2
It has an internal electrode (internal conductor) 3 provided between a and an external electrode 4. Further, it is preferable that the Ni plating film 5 and the Sn plating film 6 are laminated in this order on the external electrode 4.

The ceramic body 2 has ceramic layers 2a formed by laminating and firing a plurality of ceramic green sheets containing a dielectric material, for example, BaTiO ₃ as a main component.

The internal electrodes 3 are formed by simultaneously firing the internal electrode conductive paste formed on a predetermined number of ceramic green sheets together with the ceramic green sheets, and each edge is formed on one end surface of the ceramic layer 2a. It is formed so as to be exposed. The internal electrode 3 is N
Since the conductive paste for internal electrodes containing i as the main component was used, Ni was the main component.

Therefore, the internal electrodes 3 and 3 are alternately exposed on any one end surface (side portion) of the ceramic layer 2a, and face each other with a space between the ceramic layers 2a. In Fig. 2, it is arranged so that an electrostatic capacity is formed and a function as a capacitor can be exhibited.

The external electrodes 4 are a pair of thick-film electrodes formed by applying conductive paste, which will be described later, to both end faces of the ceramic body 2, respectively, and then drying and firing the paste. It is formed so as to be electrically and mechanically connected to each exposed internal electrode 3.

It is desirable that the external electrodes 4 and 4 as described above are arranged so as to face each other and be substantially parallel to each other, since the insulation between them can be easily ensured. That is, it is preferable that the external electrodes 4 and 4 are formed on both end surfaces of the ceramic body 2 that face each other substantially in parallel. In this case, the exposed surfaces of the internal electrodes 3 and 3 are the both end surfaces.

The shape and material of the ceramic body 2, the formation position and the number of the internal electrodes 3, the material of the plating films 5 and 6, the number of layers, etc. in the monolithic ceramic electronic component of the present invention are the same as those in one embodiment described above. Is not particularly limited to the monolithic ceramic capacitor.

The material of the ceramic body 2 in the monolithic ceramic capacitor of the present invention is not limited to the above-mentioned embodiment, and may be, for example, PbTiO ₃ or PbZrO.
_It may be made of other dielectric material such as ₃ . Further, the number of internal electrodes in the monolithic ceramic capacitor of the present invention is not limited to that in the above embodiment.

The shearing force by the rotor 12 having a clearance 14 of 0.1 mm or more and 1.5 mm or less and rotating at a peripheral speed of 4 m / s or more in water or an organic solvent, which is a feature of the present invention. During the crushing step by adding a dispersion aid, for example, saturated fatty acid, unsaturated fatty acid, nonionic polymer dispersant, cationic polymer dispersant, anionic polymer dispersant, etc., to further disperse and crush It can be easily inferred from the various published patent documents and the like up to now.

Further, the present invention can be applied not only to the powder manufacturing method by the liquid phase method but also to the powder manufacturing method by the gas phase method including the washing step, and further, not only at the time of synthesizing the metal powder, but also at the sintering. It can also be applied in a cleaning step in a coating method of an inorganic material or an organic material for controlling speed and dispersibility.

[0061]

Example 1 Hereinafter, a preferred example 1 relating to a method for producing a metal powder for a conductive paste according to the present invention.
Will be described.

First, according to the method described in JP-A-5-51610, which is a known method for producing nickel powder,
Nickel powder of 0.5 μm was prepared according to the method described in JP-A-2000-8712.
According to the method described in Japanese Patent Laid-Open No. 1, a 0.1 μm nickel powder was produced. Separate each powder from the reaction stock solution,
The cleaning process was performed under the conditions shown in Table 1.

[0063]

[Table 1]

In Table 1 above, * indicates outside the scope of the present invention.

In any of the cleaning methods, in the preliminary evaluation, the pH of the cleaning liquid was 8 when the number of times of cleaning exceeded 4 times.
Since it converged on the table, the number of washings was set to 4 times. By the way, the pH of the first washing liquid is 1 for all particle sizes.
3 was shown. The cleaning liquid is water, the container is a 10 liter beaker, the liquid amount is 5 liters, and the metal powder amount is 20 liters.
It was set to 0 g.

Samples 1 and 7 for comparison, samples 6 for comparison,
In No. 12, washing with a three-blade propeller with a diameter of 50 mm for 10 minutes at a rotation speed of 200 rpm was added,
After 10 minutes of settling, washing was performed by a method of exchanging the supernatant.

Samples 2, 3, 4, 5, 8, 9, 10, 1
1, T.K. manufactured by Tokushu Kika Kogyo Co., Ltd. The clearance (gap) 14 was adjusted to 0.5 mm using a K homomixer MARK II type (corresponding product in FIG. 1), and cleaning and crushing treatments were performed at the peripheral speed shown in Table 1.

In each of Samples 6 and 12, after washing with a propeller was added as described above, T. The clearance 14 was adjusted to 0.5 mm using a K homomixer MARKII type, and the crushing treatment was also performed at the peripheral speed shown in Table 1. In addition, the number of times of the crushing process at that time was made into 2 times.

Samples 2, 3, 4, 5 and Samples 8, 9, 1
At 0 and 11, when the pH of the cleaning solution fell below 10, it was difficult to separate and collect the metal powder by settling. Therefore, for 0.5 μm metal powder, centrifugation by 100 G gravity acceleration was performed at 0.1 μm. With respect to the metal powder of (3), centrifugal separation was performed for 3 minutes at a gravitational acceleration of 1000 G to separate the metal powder from the cleaning liquid.

It should be noted that 1 for 0.5 μm metal powder.
When centrifugation was not performed by the gravitational acceleration of 00G, it took a maximum of 5 hours to settle and separate the metal powder. In a powder manufacturing and manufacturing facility equipped with a settling tank that can be left for a long time to settle, it is possible that production can be performed without centrifugation. Therefore, centrifugation was performed on all the samples 2-6 and 8-12.

1000 for 0.1 μm metal powder
In the case where the centrifugal separation due to the gravitational acceleration of G was not performed, the metal powder was not completely settled even when the cleaning liquid was left standing overnight for a fast peripheral speed of 15 m / s or more.

The undried nickel powder washed by the above method was put into a 5 liter beaker and 3 liters of ethanol was added. For each of Samples 1 and 7 for comparison, stirring was performed by a three-bladed propeller having a diameter of 50 mm at a rotation speed of 200 rpm for 10 minutes, and then 10
After stationary precipitation for minutes, replacement with ethanol was performed by a method of exchanging the supernatant. For each of the samples 2-6 and 8-12, T. K homomixer MARK type II was used to replace the ethanol solution. The replacement with the ethanol solution was performed three times, and the samples 2-6 and 8-12 were subjected to powder separation by centrifugation each time.

Next, the nickel powder was recovered from ethanol and left in an oven at 100 ° C. for 3 hours to dry the nickel powder. To 50 parts by weight of these nickel powders, 0.5 part by weight of stearic acid and 10 parts by weight of an ethylcellulose-based binder as a dispersant were added to terpineol 90.
A conductive paste containing nickel powder was prepared by adding 49.5 parts by weight of an organic vehicle prepared by dissolving it in parts by weight and performing a dispersion mixing process with a three-roll mill under the same conditions. The conditions for the three-roll mill were that the roll gap was about 15 μm and the number of rolls was two.

The coarse particles in the produced conductive paste were measured using a ground meter having a maximum measured coarse particle diameter of 25 μm. The results are also shown in Table 1. Note that it was difficult to accurately measure coarse particles of 5 μm or less by the measurement with a ground meter, so that all samples showing a coarse particle value of 5 μm or less are indicated as 5 μm or less.

Sample 1, which has a clearance 14 of 0.1 mm or more and 1.5 mm or less and is not washed or disintegrated based on the shearing force of the rotor 12 rotating at a peripheral speed of 4 m / s or more, Regarding No. 7, the size of coarse particles in the conductive paste reached around 20 μm regardless of the particle size of the nickel powder used. In particular, the average particle size is 0.1μ
25 μm for Sample 7 using m nickel powder
It contained coarse particles that were larger than

This means that the finer the particle size of the nickel powder, the greater the cohesive force and the more difficult the crushing becomes. In any case, in Samples 1 and 7, the aggregation of the metal powder was strong, and the aggregation was not crushed under the dispersion conditions in the present three-roll mill, and these aggregates appeared as coarse particles in the conductive paste.

When a conductive paste containing coarse particles with a size of about 20 μm is used as an internal electrode of a laminated ceramic electronic component having a ceramic layer thickness of 5 μm or less, the granules penetrate the ceramic layer as an insulator. It can be easily imagined that it causes a short circuit defect.

T. Regarding Samples 2-5 and 8-11 which were sheared by K homomixer MARK II type, the size of coarse particles was smaller than that of Comparative Samples 1 and 7 having the same powder particle size. I know that

Samples 2 and 8 having a peripheral speed of 2 m / s have coarse particles of 15 μm and 20 μm, respectively, but samples 3 and 9 having a peripheral speed of 4 m / s each have 7 μm.
m and 11 μm, which are almost halved, and it can be seen that the crushing effect of aggregates is improved by setting the peripheral speed to 4 m / s or more. When the peripheral speed was 15 m / s or more, the crushing of the metal powder proceeded to a coarse particle size of 5 μm or less in all the samples. From this, it can be judged that the intended effect of the present invention is exhibited by setting the peripheral speed to 4 m / s or more.

Further, after the cleaning treatment is once performed with a propeller, T. For each of Samples 6 and 12 to which shearing force was applied by K homomixer MARKII type, the metal powder was crushed to a coarse particle size of 5 μm or less, and the washed nickel powder was crushed. However, it can be seen that the same effect can be expected.

(Embodiment 2) A preferred embodiment 2 of the conductive paste and the laminated ceramic capacitor using the same according to the present invention will be described below.

Dried nickel powder 11-1 and undried slurry nickel powder 11-2 using ethanol as a solvent were prepared under the conditions shown in Sample 11 of Example 1 above.

Next, a conductive paste was produced by using each of the above nickel powders according to the method described in JP 2001-67951 A. That is, to 200 g of nickel powder, 2 g of stearic acid as a dispersant,
400 ml of ethanol as a diluting solvent was mixed to obtain a first mill base, which was compounded with a cobblestone (2 mm diameter) in a resin pot having a volume of 1 liter.

In the case of the nickel powder 11-2, it was weighed and added as an ethanol slurry according to the weight ratio of nickel powder contained in the slurry. Regarding ethanol as a diluting solvent, the ethanol in the ethanol slurry containing nickel powder was added to prepare 400 ml.

The prepared resin pot is rotated at a constant rotation speed for 12 hours to carry out a pot mill dispersion treatment.
A slurry was obtained.

Next, 198 g of an organic vehicle having the same composition as in Example 1 was added to the above resin pot, and the mixture was further rotated at a constant rotation speed for 12 hours to carry out a pot mill dispersion treatment.
A second slurry was obtained. Next, the second slurry is evacuated to 7
The diluted solvent was removed by heating to 0 ° C., and the solvent was distilled off under reduced pressure to obtain a conductive paste. The coarse particle value in the obtained conductive paste was measured using a ground meter having a maximum measured coarse particle diameter of 25 μm, and all showed good values of 5 μm or less.

Similarly, sample 7 described in the above Example 1 was used.
Under the conditions shown in, a nickel powder 7-1 as a comparative example was prepared and a conductive paste was obtained in the same manner.

Next, these conductive pastes were mixed with BaT.
A reduction-resistant ceramic green sheet containing iO ₃ as a main component was printed, laminated and fired to obtain a laminated ceramic sintered body having an internal electrode containing nickel as a main component. Then, a conductive paste for external electrodes was applied and baked to obtain a laminated ceramic capacitor.

The number of samples was 100 each, the thickness of the ceramic layer after firing was 3 μm, and the number of internal electrode layers was 100. The insulation resistance of the obtained monolithic ceramic capacitor was measured by an IR meter to calculate the short circuit defect rate. The results are shown in Table 2.

[0090]

[Table 2]

The mark * in Table 2 above is outside the scope of the present invention.

Sample 7-1 having a clearance 14 of 0.1 mm or more and 1.5 mm or less and not washed or disintegrated by the shearing force of the rotor 12 rotating at a peripheral speed of 4 m / s or more. The short-circuit failure rate reached 100%. This is an easily guessable result, considering that the conductive paste used for the sample 7-1 for comparison contains coarse particles having a size of more than 25 μm.

Sample 11-1 prepared by crushing nickel powder having the same particle size as sample 7-1 at a peripheral speed of 20 m / s and then drying it into paste 11-1 was the same as the multilayer ceramic capacitor of the same design. The short-circuit defect rate was 41%, which was improved to less than half.

Further, the nickel powder crushed at a peripheral speed of 20 m / s was pasted into a sample 11-
In No. 2, it can be seen that the short-circuit defect rate is 12%, which is a significant improvement. This is because the metal powder was made into a paste without being dried, so that the occurrence of agglomeration due to salt crosslinking during drying was suppressed, and the nickel powder was more easily dispersed in the paste.

In the laminated ceramic capacitors using the sintered bodies of the conductive pastes of the present invention of Samples 11-1 and 11-2 as internal electrodes, 41% and 41%, respectively.
Although a short-circuit defect of 12% and a double digit occurs, this is only a result of the trial manufacturing conditions of this time, and if a yield improving method for another known monolithic ceramic capacitor is added to the contents of the present invention. Needless to say, the short-circuit defect rate is further reduced.

Further, in the present embodiment, an example in which nickel powder is used as the metal powder has been shown, but the same effect can be expected by using other metal powder such as copper powder.

Further, the peripheral speed in this embodiment is 20 m.
Although / s is set as the upper limit, this is because the practical maximum peripheral speed of the equipment used is 20 m / s, and the same effect is not denied at peripheral speeds exceeding 20 m / s.

[0098]

EFFECTS OF THE INVENTION By using the method for producing a metal powder for a conductive paste and the conductive paste according to the present invention, it is possible to prevent or reduce agglomeration that occurs during the steps from washing to drying of the metal powder. By eliminating or reducing the presence of agglomerated particles that have not been crushed in the paste, the generation of coarse particles in the conductive paste is suppressed, and the yield of multilayer ceramic electronic components typified by multilayer ceramic capacitors is greatly improved. There is an effect that it becomes possible.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a disperser used in the method for producing a metal powder for conductive paste of the present invention.

FIG. 2 is a schematic sectional view of a monolithic ceramic capacitor of the present invention.

[Explanation of symbols]

2 Ceramic body 2a Ceramic layer 3 internal electrodes 4 external electrodes 5 Ni plating 6 Sn plating 11 Stator 12 rotor 13 slurry 14 Clearance

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4K018 BA02 BA04 BB04 BC08 BC13                       BD04                 5E001 AB03 AC09                 5G301 DA10 DA42 DD01

Claims (8)

[Claims] 1. A method of producing a metal powder for a conductive paste, comprising a step of washing the metal powder for a conductive paste with water or an organic solvent, wherein a slurry containing the metal powder being washed is used as a stator.
A step of crushing the metal powder by passing the stator through a gap having a gap of 0.1 mm or more and 1.5 mm or less and rotating with a rotor rotating at a peripheral speed of 4 m / s or more; A method for producing a metal powder for a conductive paste, comprising: 2. A method for producing a metal powder for a conductive paste, comprising a step of washing the metal powder for a conductive paste with water or an organic solvent, wherein the metal powder is undried after washing the metal powder. Slurry, and the slurry is passed through the gap between the stator and a rotor that has a gap of 0.1 mm or more and 1.5 mm or less with respect to the stator and rotates at a peripheral speed of 4 m / s or more. The method for producing a metal powder for a conductive paste, comprising the step of crushing the metal powder. 3. A slurry containing crushed metal powder is centrifuged by gravity acceleration of 100 G or more,
The method for producing a metal powder for a conductive paste according to claim 1 or 2, further comprising a step of separating the metal powder. 4. The method for producing a metal powder for conductive paste according to claim 1, wherein the metal powder is made of at least one of nickel and copper. 5. The method for producing a metal powder for a conductive paste according to claim 1, wherein the metal powder has an average particle size of 1.0 μm or less. 6. A metal powder for a conductive paste, which is obtained by the method for producing a metal powder for a conductive paste according to any one of claims 1 to 5. 7. A conductive paste comprising an organic vehicle and the metal powder for a conductive paste according to claim 6. 8. A laminated ceramic electronic component comprising a plurality of ceramic layers and a sintered body of the conductive paste according to claim 7, which is formed between the ceramic layers.