Electrophotography – Image formation – Development
Reexamination Certificate
2002-01-17
2004-08-17
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Development
Reexamination Certificate
active
06778800
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a squeezing device of a wet printer and a developing unit employing the same, and more particularly to a squeezing device of a wet printer and a developing unit, capable of stabilizing image forming conditions for a photosensitive medium. The present application is based on Korean Patent Application No. 2001-8777, which is incorporated herein by reference.
2. Description of the Related Art
FIG. 1
is a view for schematically showing a general wet printer.
As shown in
FIG. 1
, a wet printer is equipped with a photosensitive belt
1
, light scanning units
4
, a transfer unit
7
, and a plurality of developing units
10
.
The light scanning units
4
each scan light to the photosensitive belt
1
charged with a certain potential to correspond to image information. The developing units
10
are provided for the respective colors, supply ink to the photosensitive belt
1
, and develop an electrostatic latent image that is formed on the photosensitive belt
1
by the light scanning units
4
. The transfer unit
7
transfers a toner image formed on the photosensitive belt
1
to supplied sheets of paper.
The developing units
10
include a container
16
for reserving ink mixed with liquid carrier element and toner in a predetermined ratio, developing rollers
12
, ink suppliers
17
for supplying ink of certain colors reserved in the containers
16
between the photosensitive belt
1
and the developing rollers
12
, setup rollers
13
, and squeezing rollers
14
.
The developing rollers are each installed to form a nip which is a minute gap from the photosensitive belt
1
, and biased with a certain potential to fix supplied ink on an electrostatic latent image region of the photosensitive belt
1
by an electric force. The setup rollers
13
are installed to form a minute gap from the photosensitive belt
1
in order to separate ink oversupplied to the photosensitive belt
1
from the photosensitive belt
1
by the surface tension.
The squeezing rollers
14
separate the liquid carrier element not participating in the formation of an image from the photosensitive belt
1
and collect the separated liquid carrier element into a collecting reservoir
11
.
A reference numeral
15
indicates backup rollers each of which restrains the looseness of the photosensitive belt
1
and supports the squeezing roller
14
to stably contact the photosensitive belt
1
.
As shown in
FIG. 2
, between the squeezing rollers
14
and the photosensitive belt
1
are defined squeeze nips that are contact regions for the squeezing roller
14
and the photosensitive belt
1
. Substantially, these squeeze nips may be minute gaps between the squeezing rollers
14
and the photosensitive belt
1
which are positioned side by side at a certain distance from each other.
The squeezing rollers
14
include a core
14
a
of a conductive material and a contact layer
14
b
of a rubber material surrounding the outer circumference of the core
14
a
. Further, the squeezing rollers
14
can apply a bias potential to the core
14
a
in order to build a condition in which another electrostatic latent image of another color is to be formed on the photosensitive belt
1
.
Ink developed on the photosensitive belt
1
has conductivity, but the liquid carrier included in the ink is a dielectric substance preventing electricity from flowing. However, if an electric field stronger than a critical potential is applied to the squeeze nips, a townsend discharge occurs so that electric currents flow in the carrier. Accordingly, in order to charge the photosensitive belt
1
, a bias voltage over the critical potential should be applied to the core
14
a
of the squeezing roller
14
, which could enable currents to flow from the squeezing rollers
14
to the photosensitive belt
1
.
The charging performance of the squeezing rollers
14
varies with a critical potential related to the townsend discharge occurrence, a time constant to be determined by characteristics of the squeezing rollers
14
and the photosensitive belt
1
, and a charging time.
Meanwhile, in a conventional developing unit
10
, since the squeezing rollers
14
are supported by one cylindrical backup roller
15
and contacted with the photosensitive belt
1
, the width of the squeeze nip formed between the photosensitive belt
1
and the squeezing roller
14
is short. The shortness of the squeeze nip means that time required to charge the photosensitive belt
1
by the squeezing rollers
14
is short. Accordingly, in the conventional developing unit
10
, since the charging time for the photosensitive belt
1
is so short that the photosensitive belt
1
is not charged with an even potential in order for an electrostatic latent image to be formed for different colors, there exists a problem in that a printing quality is deteriorated.
Further, in the conventional developing unit
10
, since a resistance of the contact layer
14
b
of each of the squeezing rollers
14
varies with changing temperature, a critical potential for the townsend discharge occurrence varies. Accordingly, since a charging potential of the photosensitive belt
1
varies with temperature, there exists a problem in that an optimum image formation condition changes.
SUMMARY OF THE INVENTION
The present invention has been devised to solve the above problems of the related art, and accordingly, it is an object of the present invention to provide a squeezing device and a developing unit employing the same, capable of securing charging time sufficiently.
Another object of the present invention is to provide a squeezing device that is stable with temperature changes and a developing unit employing the same.
The above object is accomplished by a squeezing device of a wet printer for separating a liquid carrier element not used for forming an image from ink supplied to a photosensitive belt in accordance with the present invention, including a squeezing roller mounted to be contacted with the photosensitive belt, a bias applying unit for biasing the squeezing roller at a certain potential, and a plurality of backup rollers mounted side by side to be opposite to the squeezing roller across the photosensitive belt, which is placed between the plurality of backup rollers and the squeezing roller.
The squeezing roller includes a core to which a bias potential is applied to charge the photosensitive belt by the bias applying unit, and a contact layer surrounding an outer circumference of the core, and preferably further includes a heater mounted in the core for heating the contact layer.
The above object is also accomplished by a developing unit of a wet printer for developing an electrostatic latent image by supplying ink to a photosensitive belt in accordance with the present invention, including an ink supplying unit for supplying ink to the photosensitive belt, a squeezing roller mounted in contact with the photosensitive belt for separating liquid carrier element, which is not used for forming an image, from the ink supplied to the photosensitive belt, a bias applying unit for biasing the squeezing roller at a certain potential, and a heater for heating the squeezing roller.
Another object is accomplished by a squeezing device having a squeezing roller mounted to be contacted with the photosensitive belt, a bias applying unit for biasing the squeezing roller at a certain potential, and a heater for heating a surface of the squeezing roller at a certain temperature.
Another object of the present invention is also accomplished by a developing unit of a wet printer for developing an electrostatic latent image by supplying ink to the photosensitive belt in accordance with the present invention, including an ink supplying unit for supplying ink to the photosensitive belt, a squeezing roller mounted in contact with the photosensitive belt for separating liquid carrier element, which is not used for forming an image, from the ink supplied to the photosensitive belt, a bias applying unit for biasing the squeezing rolle
Baek Chung-guk
Shim Woo-jung
Brase Sandra
Samsung Electronics Company, Ltd.
Sughrue & Mion, PLLC
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