Electrophotography – Cleaning of imaging surface – Blade
Reexamination Certificate
2000-09-29
2002-04-30
Chapman, Mark (Department: 1753)
Electrophotography
Cleaning of imaging surface
Blade
C399S071000, C399S116000, C399S159000, C430S110100, C430S125320
Reexamination Certificate
active
06381437
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an image formation method using electrophotography. More particularly, the present invention relates to an image formation method using electrophotography, capable of ensuring excellent printing properties and cleanability over a long period of time in a printing apparatus such as a printer.
BACKGROUND ART
An image formation method using electrophotography is in wide use in the printing apparatus such as a printer and a facsimile, and consists basically of the following four steps (1) to (4):
(1) a step of uniformly charging a photosensitive body in darkness;
(2) a step of exposing the charged photosensitive body to light to form a desired electrostatic latent image thereon;
(3) a step of forming a toner image by a developer (toner) corresponding to the electrostatic latent image; and
(4) a step of transferring the toner image on the photosensitive body to transfer paper and fixing it thereat to form an image.
Therefore, in order to carry out such an image formation method using electrophotography, as shown in
FIG. 1
, members such as a photosensitive drum
11
, a charging device
13
, an image signal exposing device
15
, a developing device
17
, a transfer roll
19
, a cleaning blade
21
and a full area exposing device
23
are provided in the interior of a printing apparatus such as a printer.
Thus, to form an image in the printing apparatus, the charging device
13
is used to uniformly charge the rotating photosensitive drum
11
in darkness, after which the image signal exposing device
15
is used to expose the charged photosensitive drum
13
to light to thereby form a desired electrostatic latent image. Then, in such a manner as to correspond to the thus formed electrostatic latent image, the developer is supplied from the developing device
17
to form a toner image, which toner image in turn is transferred to the transfer paper and fixed thereat to form an image while removing untransferred developer by use of the cleaning blade
21
.
Here, known as an example of the conventional photosensitive drum is a photosensitive drum using amorphous silicon as a photosensitive layer. Use of a transfer paper longitudinal feeding apparatus having such a photosensitive drum ensures formation of images with a stabilized printing density even in the case where by way of example 10,000 sheets or more have been printed at a printing speed of 6 sheets (A4 size transfer paper)/min.
However, the photosensitive drum using amorphous silicon as the photosensitive layer suffered from a drawback that it was generally difficult to manufacture it in a stabilized manner, with its high manufacturing costs.
An organic photoconductor (hereinafter “OPC”) photosensitive drum has thus been proposed which consists of an electrically conductive base and an OPC photosensitive layer formed on top of the surface thereof.
Then, the OPC photosensitive drum is characterized by the provision of a photosensitive layer made of a photosensitive material (OPC material) dispersed or carried in a binder resin, the photosensitive layer typically having the initial thickness within a range of 15 to 20 mm. Such an OPC photosensitive drum as shown in
FIGS. 2 and 3
includes a single or a plurality of photosensitive layer(s)
27
disposed on top of the electrically conductive base
25
. In case the photosensitive layer
27
comprises a plurality of layers, it consists typically of a charge generation layer
31
formed on the electrically conductive base
25
and of a charge transfer layer
33
further formed thereon. Then, such an OPC photosensitive drum has an advantage that it is generally easy to manufacture it, with the result that its manufacturing costs are low.
However, the conventional OPC photosensitive drum posed a problem that the photosensitive layer was easy to wear, making it substantially difficult to form images with stabilized printing density for a long period of time, for example, over 100,000 sheets at a printing speed of 6 sheets/ min using the A4 size transfer paper longitudinal feeding apparatus.
Another problem was found that in the case of using the OPC photosensitive drum the cleanability of the OPC photosensitive drum was liable to lower in a short period of time. It was therefore disadvantageously difficult to remove untransferred developer in the form of toner filming phenomena by use of the cleaning blade.
For this reason, when the OPC photosensitive drum was used as the photosensitive drum, the replacement of the OPC photosensitive drum in a short period of time was hitherto inevitable. Accordingly, such a frequent replacement of the OPC photosensitive drum led to a rise in the print costs and maintenance costs, and further went against a trend toward savings of resources with the aim of global environmental protection.
In recent years, a so-called process cartridge is also employed which has been formed by integrating the photosensitive drum, the charging device, the developing device, the cleaning blade, etc., into a single unit. In this case, replacement of the OPC photosensitive drum will need the replacement and discard of other constituent elements as well, resulting further increased economical disadvantages.
Thus, as a result of wholehearted consideration, the inventors of the present invention have found out that by forming on the electrically conductive base an OPC photosensitive layer having a relatively large thickness and by limiting to a value within a certain range the amount X of reduction in the thickness of the photosensitive layer in a relatively short period of time (by way of example, a period of time corresponding to when 10,000 sheets have been printed at a printing speed of 6 sheets/ min using the A4 size transfer paper longitudinal feeding apparatus, which may hereinafter be referred to as 10,000 sheets corresponding time) in the OPC photosensitive drum, it is possible to maintain the charging retention function in the photosensitive drum over a longer period of time (by way of example, a period of time corresponding to when 100,000 sheets have been printed at a printing speed of 6 sheets/ min using the A4 size transfer paper longitudinal feeding apparatus, which may hereinafter be referred to as 100,000 sheets corresponding time), with the result that the surface potential necessary for the image formation can be secured over a longer period of time.
DISCLOSURE OF THE INVENTION
It is therefore the object of the present invention to provide an image formation method using electrophotography, capable of ensuring excellent printing properties and cleanability over a long period of time even in case the OPC photosensitive drums having the photosensitive layers with variously different diameters have been used.
According to an aspect of the present invention, there is provided an image formation method using electrophotography, comprising the steps of supplying a developer by a developing device onto a photosensitive drum in rotation to form a toner image thereon, transferring the formed toner image onto a transfer paper to form an image on the transfer paper, and removing untransferred developer by use of a cleaning blade, wherein
an OPC photosensitive drum is used for the photosensitive drum and includes a photosensitive layer being formed on an electrically conductive base and having an initial thickness which is a value within a range of 20 to 50 &mgr;m and wherein
the amount X of reduction in the thickness of the photosensitive layer in the OPC photosensitive drum satisfies the following expression (1)
0.5 &mgr;m<30
X/R<
1.5 &mgr;m (1)
X: by way of example, the amount (&mgr;m) of reduction in the thickness of photosensitive layer when 10,000 sheets have been printed at printing speed of 6 sheets/min using A4 size transfer paper longitudinal feeding apparatus; and
R: diameter (mm) of OPC photosensitive drum.
In this manner, by forming on the electrically conductive base an OPC photosensitive layer having a relatively large thickness and by limiting to a value within a certain range the amount X
Kamiyama Yuji
Moriguchi Motoki
Mukataka Hisashi
Ozawa Yoshio
Sato Yojiro
Angotti Donna
Chapman Mark
Kyocera Corporation
Lutzker Joel
Schulte Roth & Zabel
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