Electrophotography – Control of electrophotography process – Having temperature or humidity detection
Reexamination Certificate
1999-08-25
2003-03-04
Grainger, Quana M. (Department: 2852)
Electrophotography
Control of electrophotography process
Having temperature or humidity detection
C399S045000, C399S066000
Reexamination Certificate
active
06529693
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic process or an electrostatic recording process and in particular to an image forming apparatus in which an amount of toner formed on an image bearing member is controlled.
2. Related Background Art
FIG. 22
shows a color image forming apparatus of the electrophoto graphic process. The image forming process will be outlined. First, on a photosensitive drum
101
, a toner image based on image information is formed. Then, the toner image on the photosensitive drum
101
is transferred to a transfer material adsorbed on a transfer drum
108
. This transfer step is repeated by the times needed to form a desired image on the transfer material. Thereafter, the transfer material is separated from the transfer drum
108
and the toner image is fixed on the transfer material by a fixing device
107
and discharged from the apparatus outward.
Besides, as alternative example,
FIG. 23
shows a color image forming apparatus.
This image forming apparatus comprises a charging roller
202
, an unshown exposure device, a developing device
204
having developing units
204
a
,
204
b
,
204
c
and
204
d
, a cleaner
207
a
of the photosensitive drum
201
and an intermediate transfer drum
205
provided around the photosensitive drum
201
, a cleaner
207
b
and a transfer roller
208
provided around the intermediate transfer drum
205
and a fixing unit
209
disposed a little apart from the intermediate transfer drum
205
. Connected to the intermediate transfer drum
205
and the transfer roller
208
is a high-voltage power supply
210
a.
In forming a color image, first a photosensitive drum
201
is rotationally driven at a predetermined peripheral speed in the direction of the arrowhead, the surface of the photosensitive drum
201
is primarily charged by the charging roller
202
, a laser beam
203
is scanning exposed by the unshown exposure device and a first color electrostatic latent image is formed on the photosensitive drum
201
and developed by the developing device
204
.
The developing device
204
is equipped with a first, a second, a third and a fourth developing units
204
a
,
204
b
,
204
c
and
204
d
connectable and disconnectable from the photosensitive drum
201
, in which a yellow toner, a magenta toner, a cyan toner and a black toner, for example, are contained respectively. The first latent image is developed by the first developing unit
204
a
and visualized as yellow toner image.
By applying a voltage of the polarity opposite to the charged polarity of the toner from the high-voltage power supply
210
a
to the intermediate transfer drum
205
in a first transfer position
206
a
where the intermediate transfer drum
205
and the photosensitive drum
201
contact with each other, the obtained yellow toner image is electrostatically transferred to the surface of the intermediate transfer drum
205
(primary transfer). The photosensitive drum
201
after the completion of primary transfer is subjected to the next color image forming after the removal of the toner remaining on the surface with the cleaner
207
a.
Similarly, after the primary charging of the photosensitive drum
201
by the charging roller
202
, exposure with a laser beam
203
is made to form a second color electrostatic latent image and the latent image is developed by the second developing unit
204
b
to form a magenta toner image on the surface of the photosensitive drum
201
. This magenta toner image is superposed and transferred over the yellow toner image on the intermediate transfer drum
205
.
The above step is also repeated similarly concerning cyan and black color images, while the cyan and black toner images respectively obtained by the development of the third developing unit
204
c
and the fourth developing unit
204
d
are subsequently superposed over and transferred to the surface of the intermediate transfer drum
205
. Thereby, a color image with four color toner images of yellow, magenta, cyan and black stacked is formed on the surface of the intermediate transfer drum
205
.
Thereafter, the transfer roller
208
disconnected is brought into contact with the surface of the intermediate transfer drum
205
and a voltage of the polarity opposite the charged polarity of the toner is applied from the high-voltage power supply
210
a
to the transfer roller
208
, so that at a second transfer position
206
b
, the four color toner image on the intermediate transfer drum
205
is collectively htransferred to the surface of a transfer material P to be conveyed at a predetermined timing to the second transfer position
206
b
where the intermediate transfer drum
205
and the transfer roller
208
contact each other (secondary transfer).
The transfer material P onto which the four color toner image is transferred is conveyed from the intermediate transfer drum
205
to the fixing unit
209
, subjected to fixation with a heat roller or the like to make a permanent,image of full color, then discharged from the image forming apparatus outward. The intermediate transfer drum
205
after the completion of the secondary transfer is made ready for the next image forming, a certain amount of toner remaining on the surface is removed by the cleaner
207
b
to be set into action on the intermediate transfer drum
205
at a predetermined timing.
Besides, both of the image forming apparatuses mentioned above are so arranged as capable of forming images on both faces of a transfer material.
Especially in an image forming apparatus as shown in
FIG. 22
, however, since a transfer of superposing a toner image onto the transfer material is repeated, a so-called counter-transfer may occur in which the toner image transferred already is much apt to be transferred again to the photosensitive drum at the next transfer step.
In the case of forming a blue image, for example, first, a solid magenta image (image of maximum density set in the image forming apparatus) is formed on the transfer material, then a solid cyan image is multiply transferred on the solid magenta image and at a later transfer step, e.g., a transfer step of yellow or black, there takes place a situation that no toner to be transferred is present on the photosensitive drum. Under this situation, when a toner image on the transfer material comes near or contacts the surface of the photosensitive drum, a phenomenon may occur in which part of toner image (here, mainly cyan toner image) on the transfer material is very apt to be counter-transferred onto the photosensitive drum.
In this case, at the portion of cyan toner counter-transferred to the photosensitive drum, the density of the cyan toner image lowers and the color of magenta forming the image under the layer of the cyan toner image appears, thus resulting in a significant deterioration of image quality. Furthermore, this phenomenon is also a factor for making the stability of a multiple transfer difficult because of being dependent on a change in the toner charge amount or in the resistance value of a transfer material accompanying a change in temperature and humidity.
Besides, in recent years, since the particle diameter of toner has become smaller with a higher image quality, the toner charge amount per particle decreases but the total amount of charges tends to increase. Thus, the amount of transfer electric current or the transfer voltage required for the transfer of a solid image has increased. This rise in transfer electric current or transfer voltage is found to also adversely affect the above phenomenon of counter-transfer.
Besides, if the water content of a transfer material is small on occasions, an image fault (poor transfer) like marks of an abnormal discharge occurs during the progress of transfer.
Besides, in an image forming apparatus using an intermediate transfer member as shown in
FIG. 23
, a great amount of toner for four colors stacked on the intermediate transfer drum
205
ought to be transferred to the transfer ma
Bessho Yuji
Inoue Masahiro
Omata Haruhiko
Tomizawa Takeshi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Grainger Quana M.
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