Compositions – Electrically conductive or emissive compositions – Free metal containing
Reexamination Certificate
2000-01-27
2001-03-27
Jenkins, Daniel J. (Department: 1742)
Compositions
Electrically conductive or emissive compositions
Free metal containing
C252S513000, C252S514000, C148S513000, C148SDIG001
Reexamination Certificate
active
06207081
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing an electrically conductive composition, and to an electrically conductive composition obtained thereby. More particularly, the invention relates to a process for producing an electrically conductive composition, which process is characterized by its treatment method for an electrically conductive powder contained in the conductive composition, and to an electrically conductive composition obtained thereby.
BACKGROUND ART
One of the conductive compositions of interest in the present invention is an electrically conductive coating material. Such an electrically conductive coating material is used for forming an electrode of an electronic element such as a monolithic ceramic capacitor. The electrically conductive coating material employed for such use contains an electrically conductive component comprising a powder of metal such as silver, copper, nickel, or palladium, which component is dispersed in a vehicle containing a solvent, a binder, and other components.
In the above-mentioned conductive coating material, the metal powder must be contained in a sufficiently dispersed state, and when the composition is applied onto an object to form a coating film, the resultant coating film must have a smooth surface with the metal being highly packed. If the metal powder is poorly dispersed, when an internal electrode of a monolithic ceramic capacitor, for example, is formed by use of the conductive coating material, the target capacitance decreases and values thereof are dispersed, and the equivalent series resistance increases disadvantageously.
When a metal powder assumes the form of a micropowder, such a powder typically forms aggregates. Therefore, in order to produce an electrically conductive coating material, the metal powder must be disintegrated to thereby be sufficiently dispersed in a vehicle.
In order to attain the above-mentioned requirements, an electrically conductive coating material is typically produced through the steps of kneading a metal powder and a vehicle containing a solvent, a binder, and other components by use of a kneader or a mixer and dispersing the metal powder in the vehicle by use of a three-roll mill or the like.
However, when the metal powder has a particle size of submicron order or smaller or the metal powder aggregates tightly, disintegrating the aggregated metal powder to a sufficient level through the above-described method so as to thoroughly disperse the powder in a vehicle is difficult. Therefore, in an electronic element having electrodes formed by use of such an electrically conductive composition, satisfactory characteristics are difficult to obtain.
In an alternative method, an electrically conductive coating material is produced through dispersing a metal powder in a vehicle by use of a mill employing a medium, such as a ball mill or a sand mill, instead of a three-roll mill or a like apparatus.
However, when the metal powder is dispersed through the above-described method, the metal powder collides with the medium to form an oblate spherical powder. When an electrically conductive coating material containing such an oblate spherical powder is used for forming an internal electrode of an element such as a monolithic ceramic capacitor, the oblate spherical powder serves as an unfavorable material in the coating film, to thereby adversely affect the reliability of the element; for example, the oblate spherical powder causes interlayer short circuits.
As described above, in a conventional process, disintegrating a metal powder to primary particles or nearly primary particles and sufficiently dispersing the powder in a vehicle has been difficult. Thus, an electronic element having an electrode formed by use of an electrically conductive coating material or an electrically conductive composition does not possess sufficient electric characteristics.
In view of the foregoing, the present invention provides a process for producing an electrically conductive composition which can solve the above-described problems, as well as an electrically conductive composition obtained through the process.
DISCLOSURE OF THE INVENTION
In order to solve the above-described problems, the process for producing an electrically conductive composition according to the present invention is characterized by comprising a first step of providing a slurry containing an electrically conductive powder and a second step of disintegrating and dispersing the conductive powder by either causing collision of the powder or applying a shear force to the powder, or both, the slurry being in a pressurized state.
In order to carry out the above-described second step, there is typically employed a first method in which two flows of slurry are cause to collide with each other from at least two directions; or a second method in which a single flow of slurry is caused to hit a wall; or a third method in which slurry is caused to flow at a high rate in a narrow conduit.
When the first method is employed, slurry is preferably split into a plurality of flow paths and subsequently unified again, collision among flows of slurry being carried out at the time of intermingling.
In the present invention, a powder formed of at least one metal selected from among silver, copper, nickel, and palladium is advantageously used as an electrically conductive powder.
Preferably, the electrically conductive powder employed in the present invention has an average particle size of 1 &mgr;m or less as determined under an electron microscope.
In the second step, the slurry is preferably pressurized at 300 kg/cm
2
or more.
An additive which enhances dispersibility of the conductive powder may optionally be incorporated into the slurry before the second step.
A binder which imparts viscosity to the slurry may optionally be incorporated before the second step.
Alternatively, the binder which imparts viscosity to the slurry may be incorporated after the second step.
The electrically conductive powder disintegrated and dispersed in the second step may optionally be collected, and a vehicle may be added to the thus-collected powder to thereby produce a coating material such as an electrically conductive coating material.
The present invention is also directed to an electrically conductive composition produced through any one of the above-described production processes.
When any of the above-described processes for producing an electrically conductive composition according to the present invention is used, since a slurry containing an electrically conductive powder is pressurized and the pressure causes collision of the conductive powder to thereby disintegrate and disperse the powder, the conductive powder can be disintegrated into primary particles or near-primary particles and sufficiently dispersed in the slurry without formation of a powder of oblate spherical particles.
Therefore, when an electrically conductive composition such as an electrically conductive coating material containing the thus-treated conductive powder is used for forming an electrode of an electronic element, the non-defective ratio of finished products and reliability of the electronic element can be enhanced. As a result, product yield is increased.
When the process for producing an electrically conductive composition according to the present invention employs a step in which two slurry flows are caused to collide with each other from at least two directions, a slurry is caused to hit a collision wall, or a shear force is applied to a slurry, an apparatus having a comparatively simple structure can be employed to obtain a dispersion of an electrically conductive powder easily and efficiently.
Particularly, when the former step in which two slurry flows are caused to collide with each other from at least two directions is employed, an electrically conductive powder can be easily dispersed through a simple manner according to which slurry is distributed in a plurality of flow paths and unified again.
The effect of the present invention is most remarkable when the con
Ogura Taketsugu
Sasaki Tsutomu
Jenkins Daniel J.
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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