Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
2001-05-14
2003-02-25
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C399S281000, C399S285000
Reexamination Certificate
active
06526238
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developing device for developing a latent image on a latent image carrier with a thin developer layer formed on a developer carrier by a layer forming member under application of an AC-superimposed bias voltage to the developer carrier, the AC-superimposed bias voltage being formed by superimposing an alternating current on a DC bias voltage.
2. Discussion of Related Art
Conventionally, developing devices are arranged to apply a DC bias voltage to a developer carrier to form a thin layer of a developer on the developer carrier by a layer forming member and to allow the developer to move and adhere to an image area on a latent image carrier. In one type of conventional developing devices, an alternating current is superimposed on the DC bias voltage in order to vibrate the developer and to thereby facilitate the movement of the developer from the developer carrier to the image area on the latent image carrier (for example, see Japanese Patent Application Post-Exam Publication No. Sho 58-32375). This type of developing devices adopts the non-contact jumping development in which a gap is provided between the developer carrier and the latent image carrier, and the developer is caused to fly from the developer carrier to the image area on the latent image carrier. The amplitude (V
max
−V
min
) of the alternating current is, as shown in
FIG. 1
, set to a value exceeding the width between the non-image area potential V
0
and image area potential V
on
of the latent image carrier. The reason for this is that the threshold value of the bias voltage sufficient to allow the developer to adhere to the image area on the latent image carrier is higher than the electric potential at the non-image area, and conversely, the threshold value of the bias voltage sufficient to separate the developer adhering to the non-image area is lower than the electric potential at the image area on the latent image carrier.
Meanwhile, a developing device has been proposed in which an AC-superimposed bias voltage is applied to a developing member provided in opposing relation to a latent image retaining member, and a constant-voltage bias is applied to a developer conveying member for conveying a developer to the developing member, thereby forming an electric potential gradient between the two members to supply the developer (for example, see Japanese Patent Application Post-Exam Publication No. Hei 3-21906). There has also been proposed another type of developing device in which a constant-voltage bias is applied to a developer carrier provided in opposing relation to a latent image carrier, and a constant-current bias is applied to a toner supply member placed in contact with the developer carrier, thereby allowing a constant electric current to flow to the toner supply member from the developer carrier (for example, see Japanese Patent Application Unexamined Publication (KOKAI) Nos. Hei 9-106172 and Hei 10-104936).
The conventional developing devices suffer, however, from some problems as stated below. The developer adhering to the non-image area on the latent image carrier cannot sufficiently be separated. Accordingly, the developer is likely to adhere to the non-image area, causing fogging. Further, blur may occur in a halftone image owing to disconnection, thickening or scattering of thin lines of the image. This causes image quality degradation. In color image formation, in particular, if there occurs such fogging or blur due to disconnection, thickening or scattering of thin lines of the image, it becomes impossible to provide satisfactory colors in halftone because a color image is outputted in the form of a combination of various color materials superimposed on one another. To minimize these problems, high-precision control is required for the gap between the developer carrier and the latent image carrier.
Further, in a case where an AC-superimposed bias voltage is applied as a developing bias voltage, if the bias applied to the toner supply member is subjected to constant-voltage control, the electric potential cannot follow the alternating current of the developing bias voltage but acts as a constant potential at all times. Accordingly, the bias may become an inverted electric potential that acts in a direction in which the developer separates from the developer carrier toward the toner supply member. Alternatively, it may become impossible to provide the desired potential difference even if the bias does not act in the separating direction. Therefore, stable supply of toner cannot be ensured. As a result, undesired brush marks occur on the developer carrier, and toner deterioration occurs with time. In addition, the resistance between the developer carrier and the toner supply member changes with time, causing a delay in the supply of toner. This makes it impossible to obtain favorable images. If the supply voltage is increased, the required toner supply can be ensured, but the amount of toner conveyed becomes excessively large. Consequently, image defects such as stripes due to positive charge occur in the developed image. Further, fogging occurs in the developed image.
In contact development type developing devices, an electrically charged one-component developer is conveyed from a developer carrier to a latent image carrier placed in contact with the developer carrier to develop an electrostatic latent image on the latent image carrier with the one-component developer. In this case, a metal roller made of aluminum or iron-base material is used as the developer carrier. In particular, an aluminum roller is frequently used because it is easy to form by machining and less costly.
Incidentally, the developer carrier used in the developing device is demanded to have the functions of {circle around (1)} conveying the developer, {circle around (2)} electrically charging the developer, and {circle around (3)} preventing discharge of the developing bias voltage.
To improve the developer conveying performance and the developer chargeability, a carrier roll (i.e. developer carrier) has heretofore been proposed in Japanese Patent Application Post-Exam Publication No. Hei 6-46331 in which the surface of a metal roller is sandblasted to form a dimpled surface, which is then subjected to metal plating treatment, e.g. nickel plating. With the carrier roll disclosed in the post-exam publication, the dimpled surface formed on the carrier roll allows the developer conveying capability to be enhanced mechanically. Thus, the developer conveying performance is improved. Moreover, the dimpled surface allows an increase in the area of contact with the developer and hence permits an improvement in the developer chargeability. Further, the wear resistance of the dimpled surface of the metal roller is improved by subjecting the dimpled surface to metal plating treatment.
To prevent discharge of the developing bias voltage, a developer carrier having a resistivity set to a predetermined value has heretofore been proposed. For example, Japanese Patent Application Post-Exam Publication No. Hei 2-26226 proposes a non-magnetic one-component toner carrier (i.e. developer carrier) comprising a cylindrical rigid member formed of a resin material with an electrically conductive powder dispersed therein and having a resistivity in the range of 10
4
to 10
12
&OHgr;cm. The inner surface of the cylindrical rigid member is formed with an electrically conductive film or coated with an electrically conductive paint having a resistivity of not more than 10
7
&OHgr;cm. Japanese Gazette Containing the Patent No. 2705090 proposes a non-magnetic one-component toner carrier (i.e. developer carrier) having a semiconductive layer with a thickness of 100 to 1000 micrometers formed on the surface thereof by using a ceramic material, e.g. alumina, with a resistivity of 10
4
to 10
12
&OHgr;cm. With the non-magnetic one-component toner carriers disclosed in these official gazettes, because at least the surface thereof has a predetermined resistivit
Kin Hidenori
Koga Yoshiro
Okamura Takehiko
Takagi Fumio
LandOfFree
Developing device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Developing device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Developing device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3145827