Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
1999-10-06
2002-04-23
Tucker, Philip (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S423100, C399S279000, C399S308000
Reexamination Certificate
active
06376087
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates a developing agent carrier for carrying and conveying a developing agent used to develop an electrostatic latent image formed on an image carrier by using an electrophotographic scheme or electrostatic recording process, and a developing unit and image forming apparatus which include such developing agent carriers.
2. Related Background Art
In a conventional image forming apparatus, such as a copying machine or printer, the surface of a drum-like electrophotographic photosensitive member, i.e., a photosensitive drum, is uniformly charged, and an electrostatic latent image is formed on the surface by performing exposure in accordance with an image signal. This electrostatic latent image is developed into a toner image by a developing unit, and the toner image is transferred onto a recording medium. The image is then fixed to obtain a permanent image. As such an apparatus, an image forming apparatus having a developing unit for developing an electrostatic latent image on an image carrier by using an insulating, nonmagnetic, single-component toner is known.
FIG. 4
shows a developing device used in a conventional image forming apparatus.
A developing unit
4
has a developing agent vessel
15
open at a position to oppose a photosensitive drum
1
. A developing roller
11
as a developing agent carrier is partly exposed outside the developing agent vessel and supported in the developing agent vessel
15
to be rotatable in the direction indicated by an arrow Y.
The developing agent vessel
15
contains a nonmagnetic single-component developing agent (to be simply referred to as toner hereinafter) as an insulating developing agent. An agitating member
13
agitates this toner and conveys it to an area where the developing roller
11
is in contact with a toner feed roller
12
as a means for feeding the toner to the developing roller
11
.
The toner comes into contact with the developing roller
11
and is fed onto the developing roller
11
by the reflection force generated when the toner is fictionally charged in the slidable contact area between the developing roller
11
and the toner feed roller
12
that rotates in the direction indicated by an arrow Z, i.e., a direction opposite the rotational direction Y of the developing roller
11
. The thickness of the toner fed onto the developing roller
11
by the toner feed roller
12
is controlled by a developing blade
14
as a means for controlling the thickness and charge amount of toner upon rotation of the developing roller
11
in the direction indicated by the arrow Y. This toner is applied to the surface of the developing roller
11
and carried/conveyed on the developing roller
11
to reach the developing area where the photosensitive drum
1
rotating in the direction indicated by an arrow X is in contact with the developing roller
11
, i.e., a developing nip N.
A developing bias is applied from a power supply (not shown) to the developing roller
11
. The toner is electrostatically attracted to the electrostatic latent image on the photosensitive drum
1
to form a toner image. The toner that does not contribute to the development of the electrostatic latent image and is left on the surface of the developing roller
11
reaches the developing agent vessel
15
upon rotation of the developing roller
11
. This toner is scraped off from the surface of the developing roller
11
and recovered into the developing agent vessel
15
.
The developing roller
11
that comes into contact with the rigid photosensitive drum
1
as an image carrier to perform development is preferably a roller having an body. In the deveoloping unit
4
including the developing roller
11
having an elastic member, a metal developing blade
14
is suitably used as the developing blade
14
to charge nonmagnetic single-component toner.
The above conventional image forming apparatus includes the developing unit using an insulating nonmagnetic single-component developing agent as a developing agent. The toner is fed from the toner feed roller
12
to the developing roller
11
by the reflection force generated when the toner is rub/charged in the slidable contact area between the toner feed roller
12
and the developing roller
11
. Therefore, the toner itself is nonmagnetic, and hence this developing device is advantageous in forming a color image. In a developing unit using a magnetic single-component developing agent as a developing agent, as is known, a member that generate a magnetic field, i.e., a magnet, is disposed in the developing roller
11
to apply a magnetic force so as to feed and convey the toner. However, the arrangement of this image forming apparatus is basically the same as that of the above apparatus.
In the conventional image forming apparatus, which is designed to develop an electrostatic latent image on the photosensitive drum
1
by bringing the developing roller
11
having the elastic member into contact with the photosensitive drum
1
, i.e., include a contact developing step, the surface of the developing roller
11
vibrates owing to the friction between the developing roller
11
and the photosensitive drum
1
in the developing nip N (developing area) where the developing roller
11
comes into contact with the photosensitive drum
1
. As a result, in developing operation, the toner image on the photosensitive drum
1
is scattered in the developing nip N.
If the surface of the developing roller
11
is greatly distorted when the developing roller
11
comes into slidable contact with the photosensitive drum
1
, the vibrations of the surface of the developing roller
11
are accelerated, and the developing roller
11
itself vibrates. As a result, the developing nip N varies in width. In the worst case, the developing roller
11
itself greatly vibrates, the developing roller
11
and photosensitive drum
1
are set in a noncontact state periodically. As a consequence, a non-development area periodically appears on the developing roller
11
in the developing unit to which a DC developing bias voltage is applied, resulting in pitch irregularity on the image formed a recording medium.
The following is the reason why a distorting force and vibration are generated on the surface of the developing roller
11
when the developing roller
11
comes into slidable contact with the photosensitive drum
1
in this manner. Conventionally, the developing roller
11
is an elastic roller having an elastic member including a solid layer made of silicone rubber, EPDM, or urethane rubber or sponge layer, and the dynamic friction coefficient of the surface of the developing roller
11
is generally set to about 0.2 to 1.5. As the coefficient of dynamic friction of the developing roller
11
increases, the frictional force between the developing roller
11
and the photosensitive drum
1
increases. As a result, the surface of the developing roller
11
vibrates. The vibration of the surface of the developing roller
11
becomes noticeable as the hardness of the developing roller
11
decreases. As a consequence, the toner is scattered on an output image on a recording medium.
Assume that a solid layer or sponge layer having a low hardness is used as an elastic layer, the dynamic friction coefficient of the developing roller
11
exceeds 0.2, and the hardness measured by an Asker C durometer is about 40 or less. In this case, in particular, the developing nip N between the developing roller
11
and the photosensitive drum
1
increases to increase the contact force on the surface of the developing roller
11
with respect to the surface of the photosensitive drum
1
. As a result, the frictional force between the developing roller
11
and the photosensitive drum
1
increases. If, therefore, the dynamic friction coefficient of the surface of the developing roller
11
is large, the distortion of the surface of the developing roller
11
is large.
The “dynamic friction coefficient”used in this specification is defined as the value measured by the fol
Ozeki Yukihiro
Sakaizawa Katsuhiro
Canon Kabushiki Kaisha
Feely Michael J
Tucker Philip
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