Electrophotography – Image formation – Charging
Reexamination Certificate
2001-03-01
2003-03-25
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Charging
C399S130000, C399S150000, C399S176000
Reexamination Certificate
active
06539190
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an image forming apparatus such as a copying machine or a printer and a process cartridge detachably mountable thereto, and more particularly to a device for electrically charging an image bearing member using charging-promotion particles.
Referring first to
FIG. 6
, there is shown an example of a conventional image forming apparatus. The image forming apparatus of these examples is a cleanerless-type copying machine or a printer using an image-transfer-type electrophotographic process and a reverse development type process.
Designated by reference numeral
1
is an image bearing member in the form of a drum-type electrophotographic photosensitive member (photosensitive drum), which is rotated in the clockwise direction indicated by an arrow at a predetermined peripheral speed (process speed).
Designated by
2
is a charging roller (charging member) of a contact-type charging means, and is a solid or sponge roller of elastic electroconductive material. It is press-contacted to the photosensitive drum
1
with a predetermined pressure. Designated by a is a charging contact portion where the charging roller
2
is press-contacted to the photosensitive drum
1
(charging portion).
The outer surface of the charging roller
2
is coated with charging-promotion particles m, and therefore, in the charging contact portion a, there are charging-promotion particles m. The charging roller
2
is rotated in the clockwise direction indicated by the arrow, and in the charging contact portion a, the peripheral movement of the surface of the charging roller
2
is opposite from the moving direction of the surface of the photosensitive drum
1
, and therefore, the surface of the charging roller
2
and the surface of the photosensitive drum
1
are in sliding contact with each other with a peripheral speed difference with the charging-promotion particles m therebetween. The charging roller
2
is supplied with a predetermined charging bias voltage, DC-600V, for example, from a voltage source S
1
.
By doing so, the outer peripheral surface of the rotating photosensitive drum
1
is electrically charged uniformly to a potential substantially equal to be applied charging bias voltage applied to the charging roller
2
, through a direct injection charging process.
Subsequently, the surface of the photosensitive drum
1
having been uniformly charged is exposed to image light L at an exposed portion b by unshown image exposure means, by which the potential (light potential) at the light portion of the surface of the photosensitive drum
1
attenuates to provide a potential contrast between the light portion potential and the dark portion potential (dark potential). That is, the electrostatic latent image is formed on the surface of the photosensitive drum
1
, corresponding to the image exposure pattern.
Designated by
3
is a reverse-developing device using a developer T containing magnetic one component insulative toner (negative charged toner). Developer T is externally added with a predetermined amount of charging-promotion particles m. A thin layer of the developer T containing the charging-promotion particles m is formed on the surface of the rotatable developing sleeve
3
a
and is carried into a developing zone c where the developing sleeve
3
a
is closely opposed to the surface of the photosensitive drum
1
.
The developing sleeve
3
a
is supplied with a predetermined developing bias voltage from a voltage source S
2
.
By doing so, the electrostatic latent image on the surface of the rotatable photosensitive drum
1
is developed with the negative charged toner (reverse development) at the developing zone c, by deposition of the toner on the light portion of the surface of the photosensitive drum
1
. The charging-promotion particles m contained in the developer are supplied to and deposited on the surface of the photosensitive drum
1
.
Designated by
4
is a transfer roller as transfer means. It is contacted to the surface of the photosensitive drum
1
with a predetermined pressure, and is rotated such that it codirectionally moves with the surface of the photosensitive drum substantially at the same peripheral speed. Designated by d is a transfer nip where the transfer roller
4
is press-contacted to the photosensitive drum
1
. Into the transfer nip d, a transfer material P (recording material) is supplied at a predetermined timing from an unshown sheet feeder and is fed by the transfer nip d. The transfer roller
4
is supplied with a predetermined transfer bias voltage from a voltage source S
3
.
By doing so, the toner image is continuously transferred (electrostatic transfer) from the surface of the photosensitive drum
1
onto the surface of the transfer material P which is being fed by the transfer nip d
The transfer material P having passed through the transfer nip d is separated from the surface of the rotating photosensitive drum
1
and is introduced into an unshown fixing device, where the transferred toner image is subjected to a fixing process The transfer material is discharged to the outside of the machine as a print or copy.
In this example, the image forming apparatus is a cleanerless type in which there is not provided a cleaner (cleaning device) exclusively for removing a small amount of residual toner remaining on the surface of the photosensitive drum
1
. The untransferred toner, that is, the residual toner remaining on the surface of the photosensitive drum
1
after the image transfer operation, is carried again into the developing zone c by way of the charging contact portion a by the continuing rotation of the photosensitive drum
1
, and is removed by the developing device
3
(simultaneous development and cleaning).
Since the charging-promotion particles m contained in the developer T in the developing device and deposited onto the surface of the photosensitive drum
1
during the developing operation, are electroconductive, and also since the charge polarity thereof is opposite from that of the developer (toner), they are substantially not transferred onto the transfer material P at the transfer portion d, and most of the charging-promotion particles m are kept deposited on the surface of the photosensitive drum
1
. With the continuing rotation of the photosensitive drum
1
, they are carried thereon to the charging contact portion a and are supplied thereto to provide always new injection sites. Therefore, even if the toner is accumulated on the charging roller
2
, the deleterious result of improper charging can be avoided by supplying a large amount of the charging-promotion particles m.
A) Contact-type Charging Means Using the Charging-Promotion Particles m
A contact-type charging means using the charging-promotion particles m is disclosed in Japanese Laid-open Patent Application Hei 10-307454 and so on, and a structure with which the charging promotion particles are supplied to the contact portion between the charge member and the image bearing member from the developing means, is disclosed in Japanese Laid-open Patent Application Hei 10-307455 and so on. The contact-type charging means using the charging-promotion particles m is effective as a charging means for direct injection charging, uniformly to a predetermined voltage of a predetermined polarity, of the image bearing member (member to be charged) such as an electrophotographic photosensitive member, dielectric member for electrostatic recording or the like in electrophotographic image forming apparatuses or electrostatic recording image forming apparatuses.
The charging-promotion particles m are electroconductive fine particles for assisting the electric charging action, and it effects the direct injection charging by being present in the contact portion a between the charge member (charging roller
2
) and the image bearing member (photosensitive drum
1
). More particularly, the friction between the charging roller
2
and the photosensitive drum
1
at the charging contact portion a by the lubricating effect (frict
Kato Jun-ichi
Oba Hiroyuki
Satoh Hiroshi
Shimizu Yasushi
Yoshida Masahiro
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Pendegrass Joan
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