Electrophotography – Image formation – Transfer
Reexamination Certificate
2001-06-18
2003-01-28
Tran, Hoan (Department: 2852)
Electrophotography
Image formation
Transfer
Reexamination Certificate
active
06512912
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an image forming apparatus with a transfer device which transfers the toner images formed on the image bearer to transfer media, and preferably relates to an image forming apparatus in which toner images are transferred to transfer media under the presence of electric field, such as a copier, laser beam printer and other image recording apparatus using an electrophotographic process including liquid development process.
(2) Description of the Prior Art
FIGS. 1A and 1B
show a conventional electrophotographic image forming apparatus such as a copier, laser printer or the like. In
FIG. 1A
, the image forming apparatus includes: a photosensitive member
101
as an image bearer; a charger
102
for charging photosensitive member
101
; an exposure unit
103
for forming a latent image by light exposure; a developing unit
104
for performing development with toner; a transfer device
105
for transferring the toner image to a transfer medium
108
; a fixing device (not shown) for fixing the toner image on transfer medium
108
; an erasing device
106
for erasing charge on the photosensitive member; and a cleaning unit
107
for removing the leftover toner from the photosensitive member. This apparatus further includes power supplies
109
,
110
and
111
for applying voltages to charger
102
, developing unit
104
and transfer device
105
, respectively.
In recent years, various contact type transfer devices have been developed in order to provide an ozoneless, low-cost, compact and energy saving configuration for transfer device
105
for transferring the toner image on photosensitive member
101
to transfer medium
108
, as shown in FIG.
1
B.
This contact type transfer device
105
has a roller configuration made of a metal core
105
-
1
of aluminum, iron or the like, which is covered with an electrically conductive tubular elastomeric element
105
-
2
or an electrically insulative tubular elastomeric element
105
-
2
(polyurethane, EPDM, silicone rubber, NBR, etc.) in which a conductor (ionic conductors, carbon black, metal oxides, metal powders, graphite, etc.) is dispersed. This roller (to be referred to hereinbelow as transfer roller) is set in abutment with the photosensitive member
101
surface and a bias voltage of +(−)500 V to +(−)3000 V is applied to metal core
105
-
1
, so as to cause the toner on photosensitive member
101
to transfer to transfer medium
108
.
Other than the above problem, ozone generation due to a Paschen discharge from transfer device
105
should be mentioned. Contact type transfer device
105
has a roller configuration made of a metal core
105
-
1
of iron, aluminum or the like, which is covered with an elastomer(silicone rubber, polyurethane rubber, EPDM, NBR, etc.)
105
-
2
in which a conductor (such as ionic conductors, carbon black, metal oxides, metal powders, graphite, etc. as a conductive filler) is dispersed. A voltage is applied to the metal core when this roller is set in abutment with the photosensitive member
101
surface with transfer medium
108
in between so that the voltage can be applied to the undersurface of transfer medium
108
. The volume resistivity of the elastomer used in this configuration is 10
6
to 10
10
&OHgr;•cm.
However, since the conventional transfer device
105
performs a transfer operation by applying a bias voltage to transfer roller core
105
-
1
, high-voltage power supply
111
is needed, which leads to increase in the cost of the apparatus, increase in apparatus size for installing the power source, increase in consumption of power and increase in the number of consumable parts, results in inconsistency with regard to energy saving and ecologically-oriented development, which have become increasingly important for manufactures.
It is true that the above conventional contact transfer device
105
thus configured generates ozone in an amount of only about {fraction (1/50)} as much as that from a corona-discharge type, but it still releases ozone.
The inventors hereof have earnestly studied the mechanism of ozone generation from the contact type transfer device. As a result, it was found that Paschen discharge will occur at the micro gap Ep (the gap distance of about 10 to 100 &mgr;m) near the nip N on the entrance side with respect to the rotational direction of the photosensitive member, generating ozone. It has been known that the thus generated ozone corrodes the photosensitive member and other elements, degrading the image quality.
SUMMARY OF THE INVENTION
The present invention has been achieved in order to solve the above problems, it is therefore an object of the present invention to provide an image forming apparatus capable of transferring images from the photosensitive member to transfer media without applying a bias voltage to the transfer device and generating even a small amount of ozone.
The present invention for attaining the above object is configured as follows:
In accordance with the first aspect of the present invention, an image forming apparatus including a transfer device for transferring toner images from an image bearer to a transfer medium comprising:
a ferroelectric subjected to a dipole orienting treatment, and
the transfer device being arranged opposing to the image bearer and having a layer containing the ferroelectric at least as part,
wherein the toner images are transferred to the transfer medium by electric field formed by the dipoles thus oriented.
In accordance with the second aspect of the present invention, the image forming apparatus having the above first aspect is characterized in that the transfer device is set floating without any voltage applied thereto.
In accordance with the third aspect of the present invention, the image forming apparatus having the above first or second aspect is characterized in that the transfer device is constructed such that the ferroelectric layer is formed on an electrically conductive support.
In accordance with the fourth aspect of the present invention, the image forming apparatus having the above third aspect is characterized in that the electrically conductive support is grounded.
In accordance with the fifth aspect of the present invention, the image forming apparatus having any one of the above first through fourth aspects is characterized in that the polarity of the ferroelectric layer is set positive when the toner on the image bearer is charged negative and the polarity of the ferroelectric layer is set negative when the toner on the image bearer is charged positive.
In accordance with the sixth aspect of the present invention, the image forming apparatus having any one of the above first through fourth aspects is characterized in that a potential difference is given between the surface potential of the ferroelectric and that of the toner portion on the image bearer.
In accordance with the seventh aspect of the present invention, the image forming apparatus having any one of the above first through fourth aspects is characterized in that the ferroelectric layer is formed with a film thickness of 8 &mgr;m or greater.
In accordance with the eighth aspect of the present invention, the image forming apparatus having any one of the above first through fourth aspects is characterized in that the ferroelectric at least includes an organic material as part thereof.
In accordance with the ninth aspect of the present invention, the image forming apparatus having any one of the above first through fourth aspects is characterized in that the ferroelectric at least includes an inorganic material as part thereof.
In accordance with the tenth aspect of the present invention, the image forming apparatus having any one of the above first through fourth aspects is characterized in that the inorganic material is a ceramics sintered compact composed of at least three components.
In accordance with the eleventh aspect of the present invention, the image forming apparatus having any one of the above first through fourth
Doshoda Hiroshi
Kamei Yukikazu
Oikawa Tomohiro
Onishi Hideki
Wakahara Shiro
Conlin David C.
Dike, Bronstein, Roberts & Cushman IP
Sharp Kabushiki Kaisha
Tran Hoan
Tucker David A.
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