Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
2003-06-12
2004-12-14
Ngo, Hoang (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
Reexamination Certificate
active
06832059
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image formation apparatus which forms images by transferring a toner image formed on an image carrying member onto a transfer medium.
2. Description of the Related Art
Hitherto, there have been proposed image formation apparatuses such as electrostatic photocopiers and printers and the like which form images based on image information converted into digital signals, and some arrangements of such image formation apparatuses comprise an image carrying member upon which an electrostatic latent image is formed, a developing device for developing the electrostatic image formed on the image carrying member using a developing agent so as to form a developing agent image, and a transfer device for transferring the developing agent image formed on the image carrying member onto a transfer medium.
FIG. 7
is a schematic diagram illustrating the interior configuration of such a conventional image formation apparatus, wherein reference numeral
101
denotes a photosensitive drum, which comprises a photosensitive member formed of amorphous silicon or the like on the surface thereof, and which serves as an image-carrying member for forming an electrostatic latent image,
102
denotes a primary charger for charging the surface of the photosensitive drum
101
,
104
denotes a developing device which applies voltage between a developing sleeve
104
a
and the photosensitive drum
101
to develop the electrostatic latent image with toner serving as a developing agent, thereby forming a toner image which is the developing agent image formed on the photosensitive drum
101
, and
110
denotes a pre-transfer charger for making uniform a charge of the toner image formed on the photosensitive drum
101
,
108
denotes a transfer belt for holding and transporting a transfer medium P in contact with the photosensitive drum
101
,
113
denotes a transfer blade which applies a current from the back side of the transfer belt
108
so as to transfer the toner image formed on the photosensitive drum
101
onto the transfer medium P,
105
denotes a separating charge for separating the transfer medium P from the transfer belt
108
,
111
denotes a cleaning device which removes toner residually adhering to the photosensitive drum
101
instead of being transferred onto the transfer medium P (untransferred residual toner), using a cleaning blade
111
a
,
106
denotes a fixing device for fixing the image formed on the transfer medium P thereupon, and
112
denotes a semiconductor layer for casting a laser beam
123
modulated by image signals, wherein the laser beam
123
cast from the semiconductor laser
112
is reflected by a rotating polygonal mirror
114
and then passes through an imaging lens
116
and reflected by a reflecting mirror
115
, so as to perform raster scanning on the surface of the photosensitive drum
101
.
With such an image formation apparatus configuration, a toner image is first formed applying the image-creating processes of charging, exposing, and developing on the photosensitive drum
101
, followed by transferring of the toner image onto the transfer medium P, and subsequently fixing the toner image so as to obtain an article with an image formed thereupon.
The cleaning blade
111
a
cleans the surface of the photosensitive member by rubbing the surface thereof, and the residual toner and any external additives on the surface of the photosensitive drum
101
following the transfer processes play an important role in increasing the lubricity between the cleaning blade
111
a
and the photosensitive member, polishing the photosensitive member, and suitably grinding the photosensitive member.
The effects thereof are great in the event of using an external additive effective in increasing lubricity such as titanium oxide or alumina fine powder, or using an external additive effective in increasing polishability such as strontium titanate powder, ceric oxide powder, calcium titanate powder, and so forth, for example.
That is to say, these external additives are effective in increasing the lubricity on the surface of the photosensitive member, polishing the photosensitive member, and suitably grinding the photosensitive member. Also, these external additives serve to prevent deterioration of image quality due to substances generated by discharge of the chargers
102
and
110
, or components in the toner, adhering to the surface of the photosensitive member, and to prevent deterioration of the slidability of the cleaning blade due to an increase in the friction coefficient on the surface of the photosensitive member.
However, some of these external additives have weak adhesion as to the toner, and some have a polarity which is inverse to a friction charging polarity of the toner, so in the event that the developing device
104
is operated at any time other than when forming an image, this results in the external additives scattering off of the toner on the developing agent holding member (developing sleeve), and even in the event that an electrical field is formed between the developing agent holding member and the photosensitive member so that the toner does not adhere to the photosensitive member, the external additives charged with the inverse polarity may depart from the toner and adhere to the photosensitive member. Accordingly, operating the developing device at times other than when forming images causes the amount of external additives within the developing agent to decrease.
In the event that the amount of external additives within the developing agent in the developing device decreases, the amount of external additives adhering to the photosensitive member along with the toner also decreases, so the amount of external additives sent to the cleaning device
111
as untransferred residue decreases.
In the event that the amount of external additives sent to the cleaning device
111
decreases thus, the lubricity with the surface of the photosensitive member decreases, and the effects of polishing and suitably grinding the photosensitive member decrease, leading to deterioration of image quality due to substances generated by a discharge from the chargers, or components in the toner, adhering to the surface of the photosensitive member.
Also, the friction coefficient on the surface of the photosensitive member rises due to the adhering substances, leading to poor slidability of the cleaning blade
111
a
, which further leads to chattering of the cleaning blade
111
a
or eversion thereof. Such problems occur particularly readily with photosensitive drums which are not readily ground, such as a-Si drums, since the substances adhering to the drums are not readily removed.
Such problems also occur in the event that the time in which the developing device operates during non-image-formation periods is long, for example, and the time of the developing device operating during non-image-formation periods becomes long in cases such as forming continuous images with a transfer medium having a great basis weight, such as heavy paper or the like.
The reasons for these problems are as follows: in the event of carrying out the fixing process consecutively on a transfer medium having a great basis weight, the fixing speed generally must be slowed since defective fixing readily occurs due to the temperature of the fixing device dropping, which in turn leads to more spacing between the transfer mediums (hereafter also referred to as “sheet spacing”). This slowdown is to prevent a subsequent transfer medium from colliding with a transfer medium undergoing fixing in the event that the fixing speed is slower but the image formation speed is not changed, which could lead to faulty transportation and improper images. Or, in the event that both the image formation speed and the fixing speed are made to be slower, the amount of time elapsed is longer even in the event that the sheet spacing is the same as before the change in speed. Due to such reasons, the sheet spacing time becomes greater, and consequently
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