Electrophotography – Image formation – Transfer
Reexamination Certificate
1999-10-15
2001-01-23
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S299000, C399S390000
Reexamination Certificate
active
06178307
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copier, a printer, a facsimile apparatus or the like, which transfers an image on an image bearing member onto a recording material carried on a recording-material carrying member.
2. Description of the Related Art
Image forming apparatuses have been produced in which image formation is performed by conveying a recording material, such as paper or the like, in a state of being attracted on an endless belt (a recording-material carrying member), and transferring a visual image formed on an image bearing member onto the recording material at a transfer portion.
An example of such image forming apparatuses will be briefly described with reference to FIG.
7
.
In
FIG. 7
, within a main body of an image forming apparatus
100
, a photosensitive drum
105
is disposed at a central portion. A pre-exposure lamp
101
, a photosensitive drum charger
102
, an exposure apparatus
103
, a developing unit
104
, a transfer charger
107
and a cleaner
108
are provided around an outer circumference of the photosensitive drum
105
.
A recording-material carrying member (hereinafter termed a “transfer belt”)
106
is provided near the photosensitive drum
105
. A toner image formed on the photosensitive drum
105
is transferred onto a recording material P carried and conveyed on the transfer belt
106
.
The toner image on the recording material P is fixed by a fixing unit
109
by means of heat and pressure, and the recording material P having the toner image transferred thereto is discharged to the outside of the apparatus as a recorded image.
In the exposure apparatus
103
, a laser beam emitted from a light source (not shown) provided at an upper portion of the main body of the apparatus is converted into a scanning beam by a rotating polygonal mirror. The scanning beam is reflected by a reflecting mirror and is condensed onto the generatrix of the photosensitive drum
105
by an f&thgr; lens to expose the photosensitive drum
105
. Thus, a latent image corresponding to an image signal is formed on the photosensitive drum
105
.
A predetermined amount of toner is filled in the developing unit
104
from a toner supply device (not shown). The latent image on the photosensitive drum
105
is developed by the toner, to provide a visualized toner image.
The recording material P is supplied from a recording-material cassette (not shown) or a manual-insertion sheet feeding tray
117
to the transfer belt
106
via a plurality of conveying rollers and a pair of registration rollers
113
, and is further fed to a transfer portion facing the photosensitive drum
105
by being conveyed by the transfer belt
106
.
The transfer belt
106
is made of a material obtained by dispersing a conductive filler, such as carbon black or the like, in a sheet of a dielectric resin, such as a polycarbonate resin, a polyethylene terephthalate (PET) resin, a polyvinylidene fluoride resin, a polyurethane resin, a polyamide resin, a polyimide resin or the like, in order to reduce the volume resistivity of the insulating resin to about 10
7
-10
11
&OHgr;·cm, and has an endless shape by superposing and bonding both end portions of the sheet, or the shape of a seamless belt.
When the transfer belt
106
is rotated by a driving roller
111
in conjunction with an idler roller
112
and reaches a constant speed, the recording material P is fed from the pair of registration rollers
113
to the transfer belt
106
, and is conveyed to the transfer portion. At the same time, an image write signal is generated, and image formation is performed on the photosensitive drum
105
at a certain timing based on the signal.
By providing an electric field or electric charges from the transfer charger
107
at the transfer portion below the photosensitive drum
105
, the toner image formed on the photosensitive drum
105
is transferred onto the recording material P. When the recording material P is fed from the pair of registration rollers
113
onto the transfer belt
106
, the recording material P is immediately grasped by an attracting charger
114
and a roller
115
facing it, together with the transfer belt
106
. By being supplied with an electric field of electric charges from the attraction charger
114
, the recording material P is electrostatically held and conveyed on the transfer belt
106
.
A noncontact-type charger utilizing corona discharge, or a contact-type charger using a charging member, such as a charging roller, a charging brush or a charging blade, is used as the transfer charger
107
. Noncontact-type chargers have problems such as, generation of ozone, weakness against variations in the temperature and humidity of atmospheric air because charging is performed via air, resulting in, for example, unstable image formation. On the other hand, contact-type chargers have advantages, such as no generation of ozone, strength against variations in the temperature and humidity of atmospheric air, and the like.
Charges on the recording material P having the toner image transferred thereto are removed by a separation charger
116
at a downstream portion in the conveying direction of the transfer belt
106
. The electrostatic attracting force of the recording material P is thereby attenuated, so that the recording material P is separated from an end portion of the transfer belt
106
.
Particularly, since in a low-humidity environment, the recording material P is dried and has a high electrical resistivity, the electrostatic attracting force with the transfer belt
106
is large. Hence, the effect of the separation charger
116
is large. Usually, the separation charger
116
removes charges from the recording material P in a state in which the toner image is unfixed. Accordingly, a noncontact-type charger is used as the separation charger
116
.
An AC voltage of about Vp−p=10 kV, and a frequency of 500 Hz is used as the output of the separation charger
116
. In order to prevent failures in the obtained image, such as dispersion of toner particles, and the like, a positive or negative DC component of about +100 &mgr;A is, in some cases, superposed on the AC output.
The separated recording material P is conveyed to the fixing unit
109
. The fixing unit
109
includes a fixing roller, a pressing roller, a heat-resistant cleaning member for cleaning these rollers, heaters disposed within the respective rollers, a coating roller for coating a release oil, such as a dimethylsilicone oil or the like, on the fixing roller, a reservoir for the oil, and a thermistor for controlling the fixing temperature by detecting the surface temperature of the pressing roller.
The toner image formed on the recording material P is fixed to provide a copy image, and the recording material P having the fixed toner image is discharged onto a discharged-sheet tray.
Toner particles remaining on the photosensitive drum
105
after the image transfer are cleaned and removed by the cleaner
108
, and the photosensitive drum
105
is used for the subsequent latent-image formation.
Toner particles and other foreign matter remaining on the transfer belt
106
and accumulated charges after separating the recording material P are cleaned by being passed between a conductive fur brush
110
and a grounded driving roller
111
facing it. An idler roller
112
provides tension on the transfer belt
106
. A conductive web (nonwoven fabric) may be used instead of the conductive fur brush.
The above-described image forming apparatus uses a pair of rollers, i.e., the attraction charger
114
and the roller
115
facing it, as electrostatic attraction means for the recording material P. However, as in the case of the transfer charging means, a noncontact-type charger utilizing corona discharge, or a contact-type charger using a charging member, such as a charging roller, a charging brush or a charging blade, may, of course, also be used as the electrostatic attraction means.
However, when a contact-type charger is used,
Canon Kabushiki Kaisha
Chen Sophia S.
Fitzpatrick ,Cella, Harper & Scinto
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