Electrophotography – Image formation – Development
Reexamination Certificate
2000-09-22
2002-03-19
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Development
C399S286000
Reexamination Certificate
active
06360068
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electrophotographic image formation process and an apparatus for this process. More particularly, this invention relates to a color image formation process that restricts the thickness of a developer layer on a developing roller by the use of a toner layer thickness-limiting blade having a specific structure and visualizes an electrostatic latent image formed on an image support by the use of a nonmagnetic one-component developer, for example, and to an apparatus for this process. The present invention relates further to an image formation apparatus employing an electrophotographic process that uses a specific developer support and a developer feeding member in combination with a specific one-component developer.
2. Description of the Related Art
Electrophotographic image formation apparatuses such as laser printers have gained a wide application for output terminal devices of computers, facsimiles, copying machines, and so forth, with the progress of office automation. An image formation apparatus of this kind includes generally a charging device for electrically and uniformly charging a photosensitive drum as an image support, an exposing device for forming an electrostatic image on the photosensitive drum by the irradiation of light, a developing device for developing the electrostatic image on the photosensitive drum and making it visible by using a developer (toner), an image transferring device for transferring the toner image formed on the photosensitive drum by development to a recording medium such as a recording sheet, and an image fixing device for fusing the toner image so transferred to the recording medium and fixing the image to the medium.
The developing device generally comprises a developing roll so disposed as to oppose, and to come into contact with, the photosensitive drum, a toner container for storing the toner, a toner supplementing device for feeding the toner to the developing roll and a toner layer thickness-limiting blade for controlling the thickness of the toner supplied onto the developing roll. As the toner is allowed to adhere electrically and uniformly from the toner layer on the developing roll to the electrostatic latent image on the photosensitive drum, development, that is, visualization, of the electrostatic latent image, can be conducted. To use again the used photosensitive drum after the toner image is transferred, a de-charging device for removing the charge from the surface of the photosensitive drum and a cleaning device for scraping off the residual toner is disposed round the photosensitive drum.
The developing device used for the image formation apparatus described above includes a device of the type designed to use a one-component developer comprising only the toner and a device of the type designed to use a two-component developer comprising the combination of the toner and a carrier. Since the one-component type developing device does not use a carrier, it need not take into consideration degradation of the carrier, mixing of the carrier with the toner and the mixing ratio, in particular. Therefore, the one-component type developing device has the advantages that the apparatus can be made compact in size and its production cost can be lowered. Furthermore, when the developer used is nonmagnetic, this developing device can form a high-quality color image because the toner has high transparency.
When a one-component developing device is used, a process step for charging compulsively the developer, imparting the charge to the developing roller and causing the toner to adhere to the developing roller is necessary unlike the two-component developing device, that uses the developer comprising the mixture of the carrier and the toner and lets it adhere to the magnet roller, because the one-component developer used does not have a carrier. Therefore, the one-component developer uses a toner having a relatively high volume resistivity. When a toner having a volume resistivity of 10
10
&OHgr;cm to 10
13
&OHgr;cm, or more, is used, a compulsive charging operation to a predetermined polarity is necessary. Therefore, a triboelectrical or frictional charging member for imparting triboelectrical charge to the toner is also provided to the developing device.
A blade for uniformly limiting the toner adhering to the developing roller to a predetermined thickness and a charging member used for imparting exclusively triboelectrical charge to the toner, for example, have been used as the triboelectrical charging member. Among them, the blade for limiting the toner to a predetermined thickness and at the same time, charging the toner, has the simplest structure and can reduce the cost. As will be understood from the following explanation, the toner layer thickness-limiting blade used inside the developing device in the embodiments of the present invention includes a blade that has the function of exclusively limiting the toner layer thickness, a blade having the exclusive function of frictional charging, and a blade having both of these functions.
FIGS. 1
to
5
schematically depict the developing devices equipped with the conventional toner layer thickness-limiting blades (partial views).
In the developing device shown in
FIG. 1
, a blade
50
made of a resin or a metal having a relatively high hardness and a thickness of 2 to 4 mm is fitted into a blade guide
51
in such a fashion as to be capable of moving in and out due to a coil spring
52
. The blade
50
is brought into pressure contact with a developing roller
2
, rotating in a direction indicated by an arrow B, at a constant pressure. The developing roller
2
can rotate while keeping contact with an image support (typically, a photosensitive drum)
1
that is so disposed as to oppose the developing roller
2
and to be capable of rotating in a direction indicated by an arrow A.
The developing device shown in
FIG. 2
uses a blade
50
produced by shaping the distal end portion of a leaf spring into an L shape. In this device, one of the ends of the blade
50
is fixed to a blade holder
51
made of a material having high rigidity, and an L-shaped edge as the other end of the blade
50
is brought into pressure contact at a constant pressure with the developing roller
2
by its own flexibility.
In the developing device shown in
FIG. 3
, a blade
50
made of a flexible material such as a rubber is bonded to, and extended from, one of the ends of the blade holder
51
, and the distal end portion of the blade
50
is brought into pressure contact with the developing roller
2
.
The developing device shown in
FIG. 4
uses a blade
50
formed by shaping the distal end portion of a leaf spring into a U-shaped. In this device, one of the ends of the blade
50
is fixed to a blade holder
51
made of a material having high rigidity, and a U-shaped surface as the other end of the blade
50
is brought into pressure contact with the developing roller
2
at a predetermined pressure by its own flexibility.
In the developing device shown in
FIG. 5
, one of the ends of a blade
50
comprising a leaf spring is fixed to a blade holder
51
. The distal end of the blade is subjected to rounded edge machining to impart roundness (not shown). The edge portion having this roundness is brought into pressure contact with the developing roller
2
at a constant pressure.
However, the toner layer thickness-limiting blades used in the developing devices shown in
FIGS. 1
to
5
involve respective problems to be solved. The toner layer thickness-limiting blade shown in
FIG. 1
, for example, involves the problems of distortion of the developing roller resulting from creep, the occurrence of horizontal stripes resulting from this distortion and the occurrence of “fog” resulting from non-uniformity of the toner layer thickness. The blade shown in
FIG. 2
involves the problem of deterioration of the toner resulting from fine cracks at the L-shaped edge. The blade shown in
FIG. 3
involves the problem of the drop of the fri
Hamazoe Kazuhiko
Katagiri Yoshimichi
Kinoshita Masakazu
Kuramoto Shin-ichi
Nakamura Masae
Armstrong Westerman & Hattori, LLP
Chen Sophia S.
Fujitsu Limited
Tran Hoan
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