Electrophotography – Image formation – Development
Reexamination Certificate
2001-09-17
2003-11-18
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Development
C399S249000
Reexamination Certificate
active
06650856
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid electrophotographic printer, and more particularly, to a liquid electrophotographic printer having a development system that includes three rollers.
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 photoreceptor web, developing the latent electrostatic image with a predetermined color toner, and transferring the toner image to a print paper. Electrophotographic printers are classified into a dry type or liquid type according to the toner used. The liquid type printer uses an ink containing a volatile liquid carrier and toner particles in a predetermined ratio to implement a color image with excellent print quality. The dry type printer uses toner in a powder form.
FIG. 1
shows a conventional liquid electrophotographic printer, which uses a photoreceptor web
10
as a photoreceptor medium. The photoreceptor web
10
circulates around a continuous path by being supported by three rollers
11
,
12
and
13
, and a main charger
20
is provided adjacent to the photoreceptor web
10
to uniformly charge the photoreceptor web
10
to a predetermined potential. Laser scanning units (LSUs)
30
a
,
30
b
,
30
c
and
30
d
for emitting light beams onto the charged photoreceptor web
10
to form a latent electrostatic image, and development units
40
a
,
40
b
,
40
c
and
40
d
for developing the latent electrostatic image as a toner image with a predetermined color ink are provided below the photoreceptor web
10
. The conventional liquid electrophotographic printer includes a drying unit
50
for drying the developed image, a transfer unit
60
for printing the dried image on a print paper P, and an eraser
70
for removing the remaining latent electrostatic image from the surface of the photoreceptor web
10
. For a color printer, the four development units
40
a
,
40
b
,
40
c
, and
40
d
for sequentially developing four color toner images of yellow (Y), cyan (C), magenta (M), and black (K), respectively, to implement a multi-color image are provided. The four LSUs
30
a
,
30
b
,
30
c
, and
30
d
are provided corresponding to the number of the development units.
The drying unit
50
includes a drying roller
51
which rotates in contact with the photoreceptor web
10
and absorbs the liquid carrier from the surface of the photoreceptor web
10
, and a heat roller
52
for evaporating the liquid carrier absorbed by the surface of the drying roller
51
by heating.
The transfer unit
60
includes a transfer roller
61
which rotates in contact with the photoreceptor web
10
and transfers the toner image formed on the surface of the photoreceptor web
10
to the print paper P, and a fusing roller
63
for hot pressing the print paper against the transfer roller
61
. Reference numerals
62
and
64
are cleaning rollers for cleaning the transfer roller
61
and the fusing roller
63
, respectively.
The four development units
40
a
,
40
b
,
40
c
, and
40
d
are arranged below the photoreceptor web
10
in series in a circulation direction of the photoreceptor web
10
. In a lower portion of the development units
40
a
,
40
b
,
40
c
and
40
d
, ink reservoirs
80
a
,
80
b
,
80
c
and
80
d
which contain Y, C, M, and K inks, are provided, respectively. In the inks contained in the ink reservoirs
80
a
,
80
b
,
80
c
and
80
d
, toner particles are mixed with a pure liquid carrier in a concentration amount of 2.5-3% solution by weight.
The structure of the development units
40
a
,
40
b
,
40
c
, and
40
d
will be described with reference to the development unit
40
a
for developing a yellow (Y) toner image, referred to herein as a Y-development unit. Referring to
FIG. 2
, a developer roller
41
, a squeeze roller
43
and a topping corona
45
are installed in the upper portion of the Y-development unit
40
a
. An ink supply nozzle
49
for supplying an ink to the gap between the photoreceptor web
10
and the developer roller
41
is installed adjacent to the developer roller
41
. A cleaning roller
47
is installed underneath the developer roller
41
. A cleaning blade
48
is affixed to the lower portion of the squeeze roller
43
. The developer roller
41
serves to make the ink adhere to a latent electrostatic image region of the photoreceptor web
10
. The squeeze roller
43
squeezes the liquid carrier out of the ink adhering to the photoreceptor web
10
. The topping corona
45
recharges the photoreceptor web
10
to a predetermined potential for development of another color image. The cleaning roller
47
and blade
48
are used for removing the excessive ink or liquid carrier remaining on the surface of the developer roller
41
and the squeeze roller
43
, respectively.
A development system of the conventional liquid electrophotographic printer having the configuration described above will now be described in greater detail.
The photoreceptor web
10
is charged to a potential of about 650 volts by the main charger
20
. The Y-LSU
30
a
emits a beam onto the charged surface of the photoreceptor web
10
to form a latent electrostatic image of Y color. The Y-LSU
30
a
selectively erases the surface potential of the photoreceptor web
10
to form a latent electrostatic image, so that the potential of an image region in which a latent electrostatic image is formed drops to about 100 volts or less.
The latent electrostatic image is developed into a Y-image by the Y-development unit
40
a
. In particular, the surface of the developer roller
41
is charged to a potential V
D
of about 500 volts, and the developer roller
41
rotates in a circulation direction of the photoreceptor web
10
with a development gap G of 100-200 &mgr;m from the photoreceptor web
10
. When a Y-ink is supplied into the gap between the photoreceptor web
10
and the developer roller
41
by the ink supply nozzle
49
, a nip N having about 6-mm width is formed between the photoreceptor web
10
and the developer roller
41
. The toner particles contained in the ink are generally charged to a positive potential. Thus, toner particles selectively adhere to an image region B having a potential relatively lower than that in a non-image region A in which no latent electrostatic image is formed, so that a high-concentration toner image is developed.
During this development process, excess ink adhering to the surface of the rotating developer roller
41
is removed by the cleaning roller
47
. The squeeze roller
43
squeezes the liquid carrier out of the developed toner image region by compression, so that a toner image having a concentration of about 50% is formed in the image region B of the photoreceptor web
10
passed through the squeeze roller
43
. The liquid carrier squeezed by the squeeze roller
43
is also removed from the surface of the squeeze roller
43
by the cleaning blade
48
. The ink and liquid carrier removed by the cleaning roller
47
and blade
48
is recovered into the ink reservoir
80
a.
After the Y-image is developed, the photoreceptor web
10
is charged again to a predetermined potential by the topping corona
45
for development of a next color image, i.e., a C-image. The C-LSU
30
b
emits a light beam onto the surface of the photoreceptor web
10
to form a latent electrostatic image of C color. The latent electrostatic image is developed into a C-toner image by the C-development unit
40
b.
As described above, the images of four colors are sequentially developed in the order of Y, C, M, and K, so that a full color image is formed. The developed color image is dried in the drying unit
50
to the extent of appropriately performing a subsequent transfer process, and in turn transferred to the print paper P in the transfer unit
60
.
However, the conventional liquid electrophotographic printer which operates with the configuration, as described above, has the following problems.
First, two layers are
Ahn Hyeong-jin
Byun Seung-young
Han Cheol-young
Kyung Myung-ho
Park Woo-yong
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