Electrophotography – Image formation – Development
Reexamination Certificate
2001-07-26
2003-09-16
Beatty, Robert (Department: 2852)
Electrophotography
Image formation
Development
C399S284000
Reexamination Certificate
active
06622000
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developing apparatus used for an image forming apparatus such as a copying machine, a printer or the like, and, more specifically, to a developing apparatus and image forming apparatus in which electric charges generated by gas electrolytic dissociation are used for charging a developer.
2. Description of the Background Art
A structure of a developing apparatus used for a conventional image forming apparatus in accordance with electrophotography will be described with reference to FIG.
10
.
FIG. 10
shows a schematic structure of a developing apparatus applied to mono component developing method using a mono component developer consisting of toner only, in a conventional electrophotographic image forming apparatus.
Opposing to a photoreceptor drum
1
as an image carrier, a developing apparatus
4
for visualizing a latent electrostatic image formed on a surface of photoreceptor drum
1
is arranged. Developing apparatus
4
generally has a rotatable developing roller
41
provided opposing to a developer tank
40
, and especially to an opening thereof, which tank contains a toner
10
which is an insulative developer. Developing roller
41
is arranged such that a portion thereof is exposed through the opening of developer tank
40
to be in contact, for example, with photoreceptor drum
1
. This contact area serves as the developing area.
Mono component toner
10
is supplied by a supply roller
42
and absorbed by the surface of developing roller
41
. In order to regulate the amount of toner absorbed by developing roller
41
, a regulating member
43
is provided, in pressure-contact with the surface of developing roller
41
. The toner absorbed by developing roller
41
has its amount regulated to a constant value, as it passes through the pressure-contact portion of regulating member
43
. As it passes through the pressure-contact portion of regulating member
43
, toner
10
absorbed by developing roller
41
is charged, by the friction with the regulating member
43
.
Thereafter, toner
10
is conveyed to the developing area opposing to photoreceptor drum
1
, while it is carried on the surface of developing roller
41
. Toner
10
is then selectively adhered to photoreceptor drum
1
and developed, corresponding to the latent electrostatic image formed on the surface of photoreceptor drum
1
.
After development, toner
10
that has not been used for development is conveyed to developer tank
40
. In developer tank
40
, a supply roller
42
is provided, in pressure-contact with developing roller
41
, in order to remove and recover the toner
10
which was not used for development, from the surface of developing roller
41
. Toner
10
that was not used for development and carried on the surface of developing roller
41
is scraped off by supply roller
42
. Further, by supply roller
42
, toner
10
is newly supplied to the surface of developing roller
41
.
In order to ensure satisfactory development, generally, a developing bias voltage is supplied to developing roller
41
. The developing bias voltage is set to such a voltage value that ensures adhesion of toner
10
on the latent electrostatic image at the time of development while toner
10
is not adhered to portions other than the latent electrostatic image on photoreceptor drum
1
.
In order to apply a prescribed amount of electric charges of a prescribed polarity to the toner
10
absorbed by developing roller
41
, a regulating voltage is supplied from regulating member
43
. Therefore, as toner
10
passes through the pressure-contact portion of regulating member
43
, the amount of the toner is made constant, the toner is friction-charged, and the toner thus charged by a prescribed amount with a prescribed polarity is conveyed to the developing area.
As described above, the mono-component toner as the developer is absorbed by the developing roller and conveyed to the developing area, and the toner is adhered to the latent electrostatic image on the photoreceptor drum, whereby an image is formed.
In the developing apparatus
4
to which the method of friction charging described above is applied, the charge amount of the toner charged by the regulating member
43
does not obtain to a sufficiently saturated state, and therefore, charge amount varies among toner particles. Further, there arc uncharged toner particles resulting from mis-contact with the regulating member
43
, as well as toner particles charged to a polarity opposite to the desired polarity (hereinafter referred to as reverse-charged toner) that are inevitable in friction charging.
As a result, the developer comes to have wide distribution of charge amount, degrading stability of development. Particularly, it follows that the reverse-charged toner develops a portion which is inherently a non-image portion, and hence quality of the image is degraded. Further, an average value of charge amount significantly differs dependent on the material of the regulating member, toner material, toner particle diameter and the environment of use.
Therefore, in order to attain a desired average value of the charge amount and a desired charge polarity, it has been necessary to arrange delicately the materials to be added to the toner. Methods for improving such a problem include a developing apparatus disclosed in Japanese Patent Laying-Open No. 10-63096 (hereinafter referred to as a first prior art example) and a developing apparatus disclosed in Japanese Patent Laying-Open No. 10-148999, in which among electric charges generated by discharge, those having a desired polarity are extracted from an electric charge generating apparatus and applied to the toner (hereinafter, this method will be referred to as electric charge supplying method).
The developing apparatus disclosed in the first prior art example will be described with reference to FIG.
11
.
FIG. 11
is a schematic diagram representing a structure of the developing apparatus disclosed in the first prior art example. A developing apparatus
80
is provided at a position opposing to a photoreceptor drum
91
as an image carrier. In a housing
90
of developing apparatus
80
, there are a developer carrier
92
opposing to and close to photoreceptor drum
91
and conveying toner adhered on its surface, a layer forming member
93
regulating the toner on developer carrier
92
to form a toner layer, a stirring supply member
94
stirring the toner and supplying the toner to developer carrier
92
, an electric charge supplying member
95
arrange opposing to developer carrier
92
and generating discharge at the opposing position, and a charge control member
96
arranged between electric charge supplying member
95
and developer carrier
92
to limit an electrolytic dissociation area of discharge generated therebetween.
Developer carrier
92
mentioned above is rotatably supported, and to which a DC voltage of about −200V and having the same polarity as the toner is applied. Thus, an electric field is formed between developer carrier
92
and photoreceptor drum
91
, and the toner is transferred onto the latent image on photoreceptor drum
91
. By the above-described method, the average value of the charge amount can be controlled in a relatively simple manner, and the distribution of the charge amount can be made sharper to some extent. Further, in the developing apparatus
80
, discharge is generated in a small space formed by developer carrier
92
having a surface rubber layer with volume resistivity of 10
6
&OHgr;·cm and layer forming member
93
formed of silicone rubber having volume resistivity of about 10
4
to 10
10
&OHgr;·cm. At this time, the charge amount in the toner layer on developer carrier
92
is reduced by the electric charges of both polarities generated, and thereafter, the toner layer is charged to a desired charge amount, by electric charge supplying member
95
. Consequently, variation in the charge amount between the toner once charged by the electric charge supplying member
95
Furukawa Kazuhiko
Hirakawa Hiroyuki
Nishio Shigeru
Beatty Robert
Conlin David C.
Edwards & Angell LLP
Sharp Kabushiki Kaisha
Tucker David A.
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