Simultaneous developing/cleaning device

Details Simultaneous developing/cleaning device Simultaneous developing/cleaning device

2000-02-29

2001-11-06

Beatty, Robert (Department: 2852)

Electrophotography

Image formation

Combined or plural functions by single component

Reexamination Certificate

active

06314257

ABSTRACT:

FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a developing apparatus which develops an electrostatic latent image formed on an image bearing member such as an electrophotographic photosensitive member or an electrostatically recordable dielectric member, into a visible image with the use of developer (toner). It also relates to an image forming apparatus.
An electrophotographic method is a method for obtaining a copy. According to this method, in order to obtain a copy, an electrical latent image (electrostatic latent image) is formed on a photosensitive member through various image formation processes; the latent image is developed into a visible image with the use of toner; the visible image, or the toner image, is transferred onto a piece of transfer medium; and the transferred image is fixed to the piece of transfer medium with the use of heat and/or pressure.
With the current strong demand for a developing apparatus which is superior in resolution, clarity, and the like, it is imperative to develop a superior method for forming a thin layer of toner on the developer bearing member (developer conveying member) of a developing apparatus, and an apparatus for carrying out such a method. Thus, a number of methods have been proposed to answer such demand.
One of such methods, which has been developed recently, is a “nonmagnetic, single component, DC developing method”, according to which a latent image is developed with the use of a semiconductive development roller, or a development roller with a dielectric surface layer, as a developer bearing member. More specifically, a semiconductive development roller, or a development roller with a dielectric surface layer, which is coated with developer, is placed virtually in contact with the surface layer of a photosensitive member, with the interposition of developer between the peripheral surfaces of the development roller and photosensitive member.
FIG. 10
is a schematic sectional view of an example of a nonmagnetic, single component, DC developing apparatus, and depicts the general structure thereof.
A referential character
1
designates a photosensitive drum as an image bearing member. This photosensitive drum
1
is rotationally driven at a predetermined peripheral velocity in the clockwise direction indicated by an arrow mark A, and an electrostatic latent image is formed on the peripheral surface of the photosensitive drum
1
with the use of unillustrated means for carrying out image formation processes.
A referential character
4
designates a nonmagnetic, single component, DC developing apparatus. A referential character
4
a
designates a developing means housing portion, and referential characters
4
b
,
4
c
, and
4
d
designate a development roller as a developer bearing member, an elastic roller as a developer supplying member for supplying the development roller with developer, and an elastic blade as a developer layer regulating member, correspondingly, which all are housed in the developing means housing portion
4
a
. A referential character t stands for nonmagnetic toner as single component developer held in the developing means housing portion
4
a.
The development roller
4
b
is placed virtually in contact with the photosensitive drum
1
with the interposition of the developer between the two components, and is rotationally driven in the counterclockwise direction indicated by an arrow mark B. A referential character b stands for a development station, that is, the location in which the development roller
4
b
virtually makes contact with the photosensitive drum
1
, with the interposition of the developer between the two.
The elastic roller
4
c
is placed in contact with the development roller
4
b
, with the presence of a predetermined amount of contact pressure, and is rotationally driven in the counterclockwise direction indicated by an arrow mark D.
The elastic blade
4
d
is placed in contact with the development roller
4
b
, on the downstream side of the location in which the development roller
4
b
is placed in contact with the elastic roller
4
c
, in terms of the rotational direction of the development roller
4
b.
A referential character combination S
2
designates a development bias application electrical power source for applying DC voltage (bias) to the development roller
4
b.
The elastic roller
4
c
serves as a roller for supplying the development roller
4
b
with the toner t. After being supplied to the peripheral surface of the development roller
4
b
, the toner is conveyed further as the development roller
4
b
is rotated, and is triboelectrically charged, while being formed into a thin layer, in the contact area between the elastic blade
4
d
and development roller
4
b
. As the development roller
4
b
is further rotated, the thin layer of toner on the development roller
4
b
is conveyed to the development station b, in which the thin layer of toner is used to develop the electrostatic latent image on the photosensitive drum
1
. The toner which remains on the development roller
4
b
without being used for the development of the electrostatic latent image on the photosensitive drum
1
, in the development station b, is conveyed back into the development means housing portion
4
a
by the rotation of the development roller
4
b
, and is stripped away from the peripheral surface of the development roller
4
b
, in the contact area between the development roller
4
b
and elastic roller
4
c
. The portion of the development roller
4
b
, from which the residual toner has been stripped away, is provided with a fresh supply of toner t by the elastic roller
4
c.
This functional cycle, or operational, cycle is repeated.
However, the above described nonmagnetic, single component, DC developing method suffered from the following problems. That is, the repetition of the image forming process accelerated toner deterioration, which increased the amount of the toner, the polarity of which was opposite to the normal toner polarity. This toner with the wrong polarity transferred onto the areas of the photosensitive drum
1
correspondent to the background portions of the image (hereinafter, the effect created by this kind of toner will be referred to as “reversal fog”). Reversal fog does not easily transfer onto transfer medium, and therefore, its effect upon image quality is small. However, it increases the amount of wasteful toner consumption, reducing thereby the number of copies producible by a predetermined amount of toner initially held in the developing apparatus, and therefore, has a derogatory effect upon the effort to increase the length of the developing apparatus service life.
Referring to
FIG. 11
, in the case of a DC based contact development process, as long as the amount of the electrical charge held by the toner is within a proper range (−35 to −80 &mgr;C/g), control can be executed in such a manner that the height of the toner layer which forms a linear image, and the height of the toner layer which forms a solid image, become the same. The cause for the increase in the height of the linear image toner layer is thought to be that as development becomes possible on the downstream side (where there is a gap between the development roller and photosensitive drum) of the contact area between the development roller and photosensitive drum, the toner particles aggregate on the development roller
4
b
, as if broomed, increasing thereby the height of the linear image toner layer. However, as the amount of electrical charge held by the toner on the development roller
4
b
increases, the force with which the toner is held to the development roller also increases due to the reflective force. Therefore, it becomes possible to reproduce sharp lines and dots, that is, lines and dots which do not suffer from the effects of scattered toner particles. However, the decrease in the amount of electrical charge held by the toner on the development roller, which is caused by the toner deterioration, increases the height of the linear image toner l

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