Electrophotography – Cleaning of imaging surface – Including lubricant
Reexamination Certificate
2001-07-30
2003-08-26
Grainger, Quana M. (Department: 2852)
Electrophotography
Cleaning of imaging surface
Including lubricant
Reexamination Certificate
active
06611671
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image forming apparatus, and particularly to an image forming apparatus in which the surface of an image bearing member is adapted to be cleaned by a cleaning blade.
2. Related Background Art
In some image forming apparatuses according to the prior art, a toner residual on the surface of an image bearing member after a toner image formed on the surface of the image bearing member has been transferred to a transferring material is adapted to be removed by a cleaning blade.
FIG. 5
of the accompanying drawings schematically shows the construction of the image forming portion of such an image forming apparatus according to the prior art, and in
FIG. 5
, the reference numeral
1
designates an image bearing member. This image bearing member
1
is adapted to be rotatively driven in the direction of arrow a by driving means, not shown.
Also, around this image bearing member
1
, there are disposed a primary contact electrifying roller
2
which is electrifying means (electrifying member) for electrifying the surface of the image bearing member
1
to uniform potential, a developing apparatus
5
which is developing means for causing a toner to adhere to an electrostatic latent image formed on the surface of the image bearing member
1
and forming a toner image thereon, a cleaning apparatus
8
for removing any toner residual on the surface of the image bearing member
1
, etc.
In
FIG. 5
, the reference numeral
11
denotes a process cartridge compactly containing the image bearing member
1
, the primary contact electrifying roller
2
, the developing apparatus
5
, the cleaning apparatus
8
, etc. in a housing
9
and making them into a cartridge, and this process cartridge
11
is detachably mounted with resect to the image forming apparatus. Also, the reference numeral
10
designates a transfer electrifying roller which is a transferring member for transferring the toner image on the surface of the image bearing member onto a transferring material P, and this transfer electrifying roller
10
is adapted to contact with the image bearing member
1
when the process cartridge
11
is mounted.
In the thus constructed image forming apparatus, exposure light L from exposing means, not shown, is applied to the image bearing member
1
having had its surface electrified by the primary contact electrifying roller
2
to thereby form an electrostatic latent image on the surface of the image bearing member
1
, whereafter this electrostatic latent image is developed by the developing apparatus
5
to thereby form a toner image on the image bearing member.
Thereafter, the toner image is transferred onto the transferring material P passing through the nip between the transfer electrifying roller
10
and the image bearing member
1
, by the transfer electrifying roller
10
. The transferring material P onto which the toner image has thus been transferred is thereafter conveyed to a fixing apparatus, not shown, and is heated and pressurized in this fixing apparatus, whereby the toner image is fixed.
Now, the developing apparatus
5
, as shown in
FIG. 5
, is provided with a developing sleeve
3
rotated in the direction of arrow b for carrying the toner, not shown, and an elastic blade
4
for regulating the thickness of a toner coat on the developing sleeve
3
. Also, the cleaning apparatus
8
is provided with a cleaning blade
6
(hereinafter referred to as the blade) supported by a supporting member
13
to scrape off any untransferred toner from the image bearing member
1
, a dip sheet
7
for collecting the scraped-off untransferred toner, and a cleaner container
8
a
for containing the scraped-off toner therein.
Further, as shown in
FIG. 6
of the accompanying drawings, cleaning end portion seals
14
which are seal members formed of an elastic material such as foamed polyurethane are provided on the opposite end portions of the blade
6
on the cleaner container with the gaps thereof with respect to the blade
6
made infinitely small so as not to leak the scraped-off toner from the cleaner container
8
a
. That is, the area which can collect the toner in the cleaning apparatus
8
is an opening portion (toner collecting opening) surrounded by the blade
6
, the dip sheet
7
and the blade end portion seals
14
which is indicated by a halftone portion.
As the blade
6
of this cleaning apparatus
8
, urethane rubber is often used usually from the viewpoint of durability, but urethane rubber is high in degree of adhesion and bad in slidability and therefore, a lubricant such as silicon resin fine particles or fluorine particles is applied to the edge portion of the blade (the fore end portion of the blade) which is the portion of contact with the image bearing member
1
to thereby obtain lubricity.
Now, in the prior-art image forming apparatus provided with such a blade
6
, the lubricant may come off the blade
6
in some cases, and when the lubricant thus comes off, the friction between the blade
6
and the image bearing member
1
becomes great.
When the friction becomes great as described above, the blade
6
comes to receive a force in the direction of arrow F indicated in
FIG. 5
because it abuts against the surface of the image bearing member
1
in a counter direction, whereby the blade edge is reversed in the direction of arrow F and turn-up of the blade
6
occurs. That is, the blade
6
obtaining lubricity by having a lubricant applied thereto will instantly cause turn-up thereof particularly under high temperature and high humidity if the lubricant comes off.
Description will now be made of the cause for the coming-off of this lubricant.
If the material of the blade
6
is urethane rubber, when the electrification polarity of the blade
6
frictionally sliding with respect to the image bearing member
1
is measured, the blade
6
is electrified to the plus polarity. On the other hand, silicon resin fine particles or fluorine particles which are the lubricant are electrification-serially minus, but the lubricant present in the form of fine particles is often minus by triboelectrification as a matter of course, and because of triboelectrification, there are also present fine particles electrified to plus. Consequently, the plus-electrified blade
6
retains the minus-electrified lubricant thereon, but conversely electrically repels the plus-electrified fine particles, whereby the lubricant tries to come off the blade
6
.
On the other hand, for example, in a reversal developing system, when a toner electrified to minus is used, the primary contact electrifying roller
2
effects minus electrification and the transfer electrifying roller
10
effects plus electrification.
That is, in the reversal developing system, the toner is used for development in a portion lowered in electrification potential by being exposed and therefore, design is made such that in the opposite end portions which are not desired to be toner-developed, the primary electrification area width is secured widely and minus electrification is effected so that the toner may not be used for development. Accordingly, as shown in
FIG. 7
of the accompanying drawings, the primary contact electrifying roller
2
is greater in length than the transfer electrifying roller
10
.
Here, paying attention to the electrification potential of the surface of the image bearing member, the hatched portions of the surface of the usually minus-electrified image bearing member (organic photosensitive drum) which are shown in
FIG. 7
are always minus-electrified by the primary contact electrifying roller
2
. In contrast, the surface potential does not become uniform in that range of the surface of the image bearing member which is electrified by the transfer electrifying roller
10
, but is electrified substantially plus after that range has passed the transfer electrifying roller
10
.
In the lengthwise range which is thus electrified by the transfer electrifying roller
10
, the surface of the image bearing member is plus-electri
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