Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2000-03-17
2001-08-14
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Photoconductive member
C347S055000, C347S134000, C347S241000, C399S152000
Reexamination Certificate
active
06275673
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photosensitive unit, a light source, and an image forming apparatus for use in a copying machine, a printer and a facsimile.
2. Description of the Related Art
Known, as a conventional image forming process, is an electrophotography. A representative example is a Carlson process or xerography. According to xerography, a resinous powder forms on an electrically charged plate an image, and this image is transferred and thermally fixed onto a paper. This image recording technique requires six processes, which include charging, exposing, developing, transferring, fixing, and cleaning. Each of such processes requires its own unit, resulting in a bulky machine.
U.S. Pat. No. 5,815,774 (=JP-A 9-204092) issued to Funayama et al. discloses a simplified process alternative to the Carlson process. This simplified process uses a porous photosensitive unit (PPU). The PPU includes a transparent substrate, a transparent conductive layer formed over the substrate, and a photoconductive layer formed over the transparent conductive layer. The PPU also includes a porous insulating layer formed over the photoconductive layer. The porous insulating layer has a screen or an upper electrode formed over the surface thereof. Conductive color particles that are charged to one polarity are attracted to the PPU to fill holes of the porous insulating layer. Subsequently, when a light corresponding to an image is irradiated to the photoconductive layer of the PPU, the color particles within an area exposed to the light are charged to the opposite polarity. These color particles are transferred to a recording medium, forming the image thereon.
Referring to
FIG. 13
, a description is made on the image recording technique disclosed in the above-mentioned U.S. Pat. No. 5,815,774.
FIG. 13
illustrates the principle of the image recording technique.
The image recording technique requires processes, which include color particles filling, exposing and transferring, and fixing. Hereinafter, a description is made on the exposing and transferring process.
In
FIG. 13
, the reference numeral
11
generally designates holes of a porous insulating layer
4
of a PPU
10
, namely, first, second and third holes
11
a,
11
b,
and
11
c.
As illustrated, the minute holes
11
a,
11
b,
and
11
c
are filled with conductive color particles that have been fed thereto during color particles filling process.
A light source illuminates in a pattern corresponding to data to be printed. Light
9
from the light source passes through a transparent substrate
1
and a transparent conductive layer
2
to reach a photoconductive layer
3
, exposing a region
7
, called “exposed region, ” of the photoconductive layer
3
in the pattern corresponding to the data to be printed. Electric charges are induced within the exposed region
7
, only. An upper electrode
5
above the porous insulating layer
4
is held at a predetermined negative potential for attracting positive electric charges
8
induced by the light irradiation. Thus, among the electric charges inducted by the light irradiation, positive electric charges move toward the surface of the photoconductive layer
3
for injection into the negatively charged color particles
6
that are received in the holes
11
. The negatively charged color particles
6
are neutralized and then positively charged. The transparent conductive layer
2
is held at a predetermined positive potential to neutralize the negatively charged particles that have been induced due to the light irradiation. As a result, an electric repulsion force is generated between the positively charged color particles
6
and the transparent conductive layer
2
, causing the color particles
6
to fly out of the holes
11
. The color particles
6
that have flown are attached by adhesion to a recording medium to form an image of the data to be printed. This image is fixed during the subsequent fixing process.
According to the image recording technique, color particles filling process, exposing and transferring process, and fixing process complete an image recording. Making it possible to construct a compact machine. Since a light source as used in ordinary electrophotography may be used, the conventional technology is advantageous in cost.
SUMMARY OF THE INVENTION
The Applicants have made studies from various aspects to improve the above-mentioned conventional technology. These studies have revealed a problem as follows. According to the conventional image recording technology, transferring the color particles out of one hole of the PPU forms the minimum dot. This means that the resolution of the image formed on the recording medium may be increased to a level as high as the resolution determined by the holes of the PPU. However, the actual resolution of the image is still lower than this level.
The Applicants have made further study to clarify what causes the above-mentioned problem.
FIG. 14
is a schematic view illustrating the phenomena occurring in an actual machine employing the above-mentioned image recording technique. Referring to
FIG. 14
, a description is made on what causes the reduction in resolution.
Here, attention should be paid on the case where color particles
6
are to be transferred from the hole
11
a
of the PPU
10
. If the diameter of the exposed region
7
is greater than the diameter of the hole
11
a,
electric charges are induced within a region, namely, an insulating concave portion
12
, right below the portion of the porous insulating layer
4
which is not formed with the holes
11
. If the exposed region
7
extends to regions right below the adjacent holes
11
b
and
11
c,
electric charges are induced also within the regions right below the holes
11
b
and
11
c.
All of the electric charges
8
move toward the surface of the photoconductive layer
3
as indicated by arrows in FIG.
14
. In the process, the electric charges
8
induced within the regions right below the adjacent holes
11
b
and
11
c
are injected into the color particles
6
located within the holes
11
b
and
11
c,
causing the color particles
6
to fly out of the holes
11
b
and
11
c.
The electric charges
8
induced within the regions right below the exposed convex portions
12
move along the surface of the photoconductive layer
3
toward the regions below the adjacent holes
11
b
and
11
c
and injected into the color particles
6
therein. This causes a flight of the color particles
6
out of the holes
11
b
and
11
c.
Scattering of light within the transparent substrate
1
exposes regions that are not desired to be exposed, increasing the probability that color particles may fly out of holes
11
other than the desired hole
11
a.
The preceding description clearly explains that an undesired flight of color particles out of the holes
11
b
and
11
b
other than the hole
11
a
causes a reduction in resolution.
Accordingly, an object of the present invention is to provide a photosensitive unit, a source of light and an image recording apparatus, which can realize the minimum dot.
According to one aspect of the present invention, there is provided a porous photosensitive unit, comprising:
a substrate;
a conductive layer formed on a surface of said substrate;
a photoconductive layer formed on a surface of said conductive layer;
a porous insulating layer formed on a surface of said photoconductive layer, said porous insulating layer having a plurality of holes for holding conductive color particles, said plurality of holes including a first hole and the adjacent second and third holes,
said plurality of holes exposing a plurality of surface portions of the surface of said photoconductive layer, respectively, so that said first, second and third holes exposing first, second and third surface portions of said plurality of surface portions, respectively;
an electrode formed on a surface of said porous insulating layer except where said plurality of holes are formed; and
restrainer means whereby an optical
Funayama Yasuhiro
Hori Takeshi
Uezono Tsutomu
Yoshii Tomoyuki
Chen Sophia S.
NEC Corporation
Scully Scott Murphy & Presser
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