Electrophotography – Image formation – Development
Reexamination Certificate
2001-09-17
2003-02-11
Tran, Hoan (Department: 2852)
Electrophotography
Image formation
Development
C399S239000, C399S249000
Reexamination Certificate
active
06519435
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid electrophotographic printer and, more particularly, to an electrostatic transfer type liquid electrophotographic printer adopting a photoreceptor web as a photoreceptor medium.
2. Description of the Related Art
Electrophotographic printers such as laser printers output a desired image by forming a latent electrostatic image on a photoreceptor medium such as a photoreceptor drum or electroreceptor web, and developing the latent electrostatic image with a predetermined color toner. Electrophotographic printers are classified into a dry type or liquid type according to the toner used. For the liquid type printer, which uses an ink containing liquid carrier and solid toner in a predetermined ratio, it is easy to implement a color image with excellent print quality, compared with the dry type printer which uses solid toner. Electrophotographic printers are classified into a press transfer type and electrostatic transfer type according to the toner image transfer manner. To the press transfer type, after drying a toner image, the dried toner image is hot pressed by a transfer roller such that the image is transferred to a printer paper. The electrostatic transfer type printer transfers a toner image to a print paper by electric force.
FIG. 1
shows an example of a conventional electrostatic transfer type liquid electrophotographic printer, which adopts photoreceptor drums
10
a
,
10
b
,
10
c
and
10
d
as photoreceptor media. As shown in
FIG. 1
, this printer has a plurality of image forming units
1
a
,
1
b
,
1
c
and
1
d
for developing and transferring a predetermined color image to a print paper P. For a color printer, the four image forming units
1
a
,
1
b
,
1
c
and
1
d
for a color image development and transfer are arranged in a line in the direction of transferring the print paper P such that toner images are sequentially developed into four colors, yellow (Y), magenta (M), cyan (C), and black (K) to form a multi-color image. Reference numeral
2
denotes a feed belt
2
for feeding the print paper P.
The image forming units
1
a
,
1
b
,
1
c
and
1
d
include photoreceptor drums
10
a
,
10
b
,
10
c
and
10
d
on the surface of which a latent electrostatic image is to be formed, main chargers
20
a
,
20
b
,
20
c
and
20
d
being installed adjacent to the corresponding photoreceptor drums
10
a
,
10
b
,
10
c
and
10
d
to charge the surfaces of the photoreceptor drums
10
a
,
10
b
,
10
c
, and
10
d
to a predetermined potential, and laser scanning units (LSUs)
30
a
,
30
b
,
30
c
and
30
d
which scan light beams onto the surfaces of the respective photoreceptor drums
10
a
,
10
b
,
10
c
and
10
d
to form a latent electrostatic image thereon. Development units
50
a
,
50
b
,
50
c
and
50
d
which develop the latent electrostatic images into toner images with a predetermined color ink are installed below the respective photoreceptor drums
10
a
,
10
b
,
10
c
and
10
d
. Transfer chargers
70
a
,
70
b
,
70
c
and
70
d
which transfer the developed toner images formed on the respective photoreceptor drums
10
a
,
10
b
,
10
c
and
10
d
to a print paper P by electric force are spaced a predetermined distance apart from the surface of the corresponding facing photoreceptor drums
10
a
,
10
b
,
10
c
and
10
d.
The structure of the development units
50
a
,
50
b
,
50
c
and
50
d
will be described with reference to the development unit
50
a
for yellow (Y) toner image (referred to as Y-development unit
50
a
). Referring to
FIG. 2
, a developer roller
51
, a squeeze roller
52
and a setting roller
53
are installed in the Y-development unit
50
a
. An ink supply unit
57
for supplying an ink to the developer roller
51
is installed adjacent to the developer roller
51
. Scrapers
54
,
55
and
56
are attached to the lower portion of the developer roller
51
, the squeeze roller
52
and the setting roller
53
, respectively, to scrap off the ink adhering to the surface of the corresponding rollers.
Development of a Y-toner image by the Y-development unit
50
a
having the configuration above will be described in greater detail. First, as the surface of the photoreceptor drum
10
a
charged to a predetermined potential by a main discharger
20
a
is irradiated by a light beam from the LSU
30
a
, a latent electrostatic image corresponding to the yellow color is formed. The developer roller
51
of the Y-development unit
50
a
rotates counterclockwise while being separated by a predetermined distance from the photoreceptor drum
10
a
. As an ink is supplied to the rotating developer roller
51
from the ink supply unit
57
, the ink is carried to the gap between the photoreceptor drum
10
a
and the developer roller
51
by the rotation of the developer roller
51
. The toner particles of the ink adhere to the latent electrostatic image formed on the photoreceptor drum
10
a
, so that a toner image is formed. At this time, the surface of the developer roller
51
is charged to a predetermined development potential such that the toner selectively adheres to only the latent electrostatic image, not to a non-image region.
The squeeze roller
52
removes excess liquid carrier from the photoreceptor drum
10
a
while being separated by a predetermined distance from the photoreceptor drum
10
a
and rotating clockwise.
The setting roller
53
rotates counterclockwise while being separated by a predetermined distance from the photoreceptor drum
10
a
, and creates an electric field between the photoreceptor drum
10
a
and the setting roller
53
with application of a predetermined voltage. The binding force between toner particles becomes strengthened by the electric field produced between the setting roller
53
and the photoreceptor drum
10
a
. Adhesiveness of the toner image to the photoreceptor drum
10
a
also increases. As a result, although an excessive amount of liquid carrier remains on the surface of the photoreceptor drum
10
a
for a subsequent electrostatic transfer, the shape and location of the toner image can be kept intact.
Once the toner image is set by the setting roller
53
, the toner image is transferred to a print paper P by the electric field produced by the transfer charger
70
a
to which a potential is applied such that the transfer charger
70
a
is charged to the opposite polarity to the toner.
After a Y-toner image is transferred to the print paper P by the Y-image forming unit
1
a
, a magenta (M)-toner image is developed and transferred to the print paper P by the M-image forming unit
1
b.
As previously described, four toner images in Y, M, C and K are sequentially transferred to a predetermined area on the print paper P feed by a feed belt
2
in accordance with the print paper feed rate, so that a color image is printed on the print paper P. Because a large amount of liquid carrier remains on the resulting color image, a drying process is performed by a drying unit (not shown).
The conventional electrostatic transfer type liquid electrophotographic printer having the configuration described above has the following problems. First, since the conventional printer uses four photoreceptor drums as photoreceptor media, each for a particular color toner image, the multi-color toner images on the four photoreceptor drums must be sequentially transferred to a moving print paper with a predetermined time gap. The respective color toner images are separately transferred, and thus it is difficult to accurately transfer each of the color toner images in a particular area on the print paper in accordance with the print paper feed rate. In other words, an accurate registration control on the development and transfer processes performed by each image forming unit is difficult.
Second, four toner image transfer processes are carried out on a print paper feed by a feed belt, so that the print paper contacts the liquid carrier adhering to the surface of the photoreceptor drums four times. As a result, unnecessary co
Kyung Myung-ho
Park Mun-bae
Samsung Electronics Co,. Ltd.
Sughrue & Mion, PLLC
Tran Hoan
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