Classifying – separating – and assorting solids – Fluid suspension – Gaseous
Reexamination Certificate
2001-02-26
2003-05-27
Nguyen, Tuan N. (Department: 3653)
Classifying, separating, and assorting solids
Fluid suspension
Gaseous
C209S143000, C209S148000, C209S710000
Reexamination Certificate
active
06568536
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a classifier and a method for preparing a toner. More specifically, the present invention relates to a classifier for classifying particles to obtain toner particles with a desired particle diameter in the process of preparing a dry toner, which toner is used to develop latent electrostatic images into visible toner images, particularly in the fields of electrophotography, electrostatic recording, and electrostatic printing.
2. Discussion of Background
A conventional classifier for separating a solid powder material with a particle size in the order of micron into fine particles and coarse particles is composed of a cylindrical dispersion chamber and a classification chamber. A conical member is disposed between the dispersion chamber and the classification chamber. The solid material is fed into the dispersion chamber through a feed inlet formed at an outer upper end portion of the dispersion chamber. The solid material undergoes a dispersion operation in a stream of cyclonic air introduced into the dispersion chamber, and is then introduced into the classification chamber where the solid material is subjected to centrifugal classification, so that the solid material is separated into fine particles and coarse particles, which are then respectively discharged from a fine particle discharge outlet and from a coarse particle discharge outlet.
FIG. 6
is a schematic cross sectional view of a conventional classifier, showing the structure thereof.
The classifier shown in
FIG. 6
is composed of a feed pipe
1
for feeding a solid material and a stream of transport air serving as primary transport air stream for transporting the solid material into a dispersion chamber
3
; an exhaust pipe
2
for discharging ultrafine particles together with air; the dispersion chamber
3
; an air flow-in inlet
4
through which air serving as secondary transport air is to be fed into the dispersion chamber
3
is caused to flow in; a fine particle discharge outlet
5
from which fine particles are discharged together with air; a coarse particle discharge outlet
6
from which coarse particles are discharged together with air; a conical member/disposed at a lower portion of the dispersion chamber
3
for increasing the cyclonic flow of the solid material within the dispersion chamber
3
; a classification plate
8
disposed under the conical member
7
; and a classification chamber
9
formed so as to be enclosed with the conical member
7
and the classification plate
8
. The above-mentioned conventional classifier is provided in its entirely in a substantially cylindrical housing.
The operation of the conventional classifier shown in
FIG. 6
will now be explained.
To begin with, air is introduced into the dispersion chamber
3
and the classification chamber
9
from the feed pipe
1
and from the air flow-in inlet
4
, and at the same time, the introduced air is discharged from the dispersion chamber
3
and from the classification chamber
9
through the fine particle discharge outlet
5
and the coarse particle discharge outlet
6
, whereby a cyclonic air stream is formed within both the dispersion chamber
3
and the classification chamber
9
.
With the formation of the cyclonic air stream within the dispersion chamber
3
and the classification chamber
9
, a solid material is introduced into the dispersion chamber
3
together with air through the feed pipe
1
. In the dispersion chamber
3
, the solid material is rotated and caused to fall down while being subjected to centrifugal force by the cyclonic air stream. In the course of the falling down of the centrifuged solid material, ultra-fine particles of the solid material with an extremely small particle size are led toward a central portion of the dispersion chamber
3
and discharged outside through the exhaust pipe
2
which is connected to a suction device such as a suction fan (not shown).
The solid material, while rotating and falling in the dispersion chamber
3
, is led into the classification chamber
9
through a ring-shaped slit A. In the classification chamber
9
, the solid material again undergoes centrifugation. In the course of the centrifugation, coarse particles of the solid material are moved away from the central portion of the classification chamber
9
by centrifugal force, and are caused to pass through a ring-shaped slit B which is formed between the classification plate
8
and the inner wall of the classification chamber
9
, and are finally discharged outside from the coarse particle discharge outlet
6
, for example, with the aid of a suction fan (not shown).
On the other hand, fine particles of the solid material are attracted to the central portion of the classification chamber
9
by centripetal force, and are then discharged outside through the fine particle discharge outlet
5
which is connected to a suction device such as a suction fan (not shown).
For use in such a conventional classifier as mentioned above, there is proposed a method of preventing an aggregate from mixing with the solid material which is led into the classification chamber, for instance, in Japanese Laid-Open Patent Application 10-43692. In the Japanese Laid-open Patent Application, there is disclosed a classifier comprising a rotor for producing the cyclonic air stream, which rotor is disposed at an upper portion of the dispersion chamber, thereby preventing the particles of the solid material from aggregating in the dispersion chamber and improving the yield of the product.
The above-mentioned conventional classifier is capable of preventing the aggregation of the particles of the solid material by the provision of the rotor for producing the cyclonic air stream. However, it is not always easy to provide such a rotor.
Furthermore, the conventional classifier has two major problems to be tackled.
One problem is that there must be improved the dispersing performance for the solid material introduced into the dispersion chamber. It will be ideal that the particles of the solid material individually smoothly pass through the dispersion chamber and are then subjected to centrifugal classification in the classification chamber. However, there is a case where the particles interact to form aggregates while the particles descend in the dispersion chamber, and continually stay or reside, whirling, even in an upper portion of the classification chamber. This will bring about a significant reduction in the classification accuracy.
The other problem is that there must be improved the classification accuracy of the classification chamber.
Ideally, the solid particles led into the classification chamber from the dispersion chamber would be classified, for example, in such a manner that the solid particles with a desired particle diameter or more are all collected as coarse particles and the solid particles with a particle diameter less than the desired particle diameter are all collected as fine particles. However, in the conventional classifier, there occurs a problem that part of the particles having the particle diameters larger than the desired particle diameter are collected as the fine particles, while part of the particles having particle diameters smaller than the desired particle diameter are collected as the coarse particles. Therefore, a classifier capable of classifying the particles with a minimum classification inaccuracy and a sharp particle size distribution is in demand.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a classifier which is capable of solving the above-mentioned problems in the conventional classifier, improving the particle dispersion performance of the dispersion chamber by structural modification of the classifier, which can be carried out without difficulty, and also improving the classification accuracy in the classification chamber, thereby separating particles with particle diameters within a desired range, with high efficiency.
A second object of the present invention is t
Morii Kazuyoshi
Saitoh Yoshihiro
Sugisawa Eisuke
Tanaka Tetsuya
Nguyen Tuan N.
Ricoh & Company, Ltd.
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