Electrophotography – Image formation – Development
Reexamination Certificate
2000-02-17
2001-10-02
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Development
C399S152000, C399S159000
Reexamination Certificate
active
06298206
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic developing apparatus, such as a copier, a printer, or a facsimile apparatus, which renders an electrostatic latent image visible by using a toner in an electrophotographic process, and to an electrophotographic apparatus using the same.
2. Description of the Related Art
In a developing apparatus used in an electrophotographic image forming apparatus as an electrophotographic apparatus, toner particles reduced in size improve denseness of an image and reproducibility of extremely small dots, thereby enabling development with high image quality. However, it has been known that the toner particles reduced in size increase a surface area per unit volume, which increases the amount of frictional charging per unit volume or per unit weight, i.e., the specific charge of the toner and lowers developability.
For example, Japanese Unexamined Patent Publication JP-A 5-216274 (1993) discloses a contact development method using a one-component non-magnetic toner having a first surface region and a second surface region such that charging of a specified polarity occurs at the first surface region, while no charging occurs at the second surface region. The use of such a toner prevents an excess increase in the amount of charge even when a particle diameter is reduced. In the prior art technology, however, the composition of the toner is complicated.
When the specific charge of a toner is reduced to increase the amount of development, i.e., the amount of the toner adhering to an electrostatic latent image, an image force is lowered so that the ability to cause the toner to adhere to a toner holding member is reduced. For this reason, there has conventionally been required to coat a toner with a maximized mechanical force or by applying a supply bias voltage between a supply member and the toner holding member and thereby promote the supply of the toner by using such coating means. When a toner having a small particle diameter is coated continuously under mechanical pressure, the toner is more likely to be fixed to the toner holding member, which presents a problem. Normally, the amount of toner used for development corresponds to about two toner layers so that it is sufficient to coat and transport toner in a minimum required amount. If the coating means is used by performing mechanical coating or applying a bias voltage as described above, an excess amount of toner is coated so that a large amount of toner should be removed by using a regulating member. Mere lowering of the specific charge for an increased amount of development is undesirable and disadvantageous in terms of the supply and transportability of the toner.
In supplying toner, if the toner is highly charged one, namely, has a large amount of charge, the needed but minimum amount of the toner can be coated under low stress without the coating means mentioned above by performing mechanical coating or supplying a bias voltage. On the other hand, the amount of the toner consumed in a development region is reduced and the amount of the toner supplied to an electrostatic latent image is reduced, so that the density of image is lowered and the amount of development is thereby reduced. Thus, ease of supply and the amount of development are contradictory to each other.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an electrophotographic developing apparatus capable of providing improved development quality, wherein the amount of charge of toner can be increased during the transportation of the toner and decreased during development, and to an electrophotographic apparatus using the electrophotographic developing apparatus.
The invention provides an electrophotographic developing apparatus comprising:
a toner holding member for electrostatically attracting a toner to rotate and rendering, in a development region, an electrostatic latent image held on a surface of an electrostatic latent image holding member visible by using the toner;
toner supplying means for supplying the toner to the toner holding member; and
charge adjusting means disposed between the development region and the toner supplying means for decreasing amount of charge of the toner.
In accordance with the invention, the amount of charge of the toner is increased while the toner is supplied and transported by the toner supplying means so that the toner in a minimum required amount is supplied optimally to the surface of the toner holding member. This obviates the necessity to provide the coating means for coating the toner onto the toner holding member by using a mechanical coating force or a bias voltage, which has been described above in association with the prior art technology.
The charge adjusting means is interposed between the toner supplying means and the development region in which the toner holding member and the surface of the electrostatic latent image holding member for holding the electrostatic latent image are in contact with or spaced apart from each other to render the electrostatic latent image visible as a toner image. The arrangement reduces the amount of charge of the toner in the development region compared with the period during which the toner is transported. Accordingly, the specific charge of the toner can be reduced. Even when a toner having a small particle diameter is used, it becomes possible to increase the amount of the toner supplied to the electrostatic latent image in the development region, increase the amount of the toner consumed in the development region, prevent a reduction in image density, prevent a so-called fog at a non-image portion, and achieve an optimum image density.
In accordance with the invention, the toner is supplied and transported by the toner holding member toward the development region with a large amount of charge, while the amount of charge is reduced by the charge adjusting means in the development region to lower charge, whereby the amount of the toner supplied to the electrostatic latent image is increased and an optimum image density is achieved.
In the invention it is preferable that the charge adjusting means is a frictional charging member which has a same charging polarity as that of the toner to be charged, and is formed of a material more likely to be charged to have the polarity than the toner.
In accordance with the invention, the frictional charging member formed of a material charged as the charge adjusting means is used to absorb the charge of the toner. Such a structure is simple and capable of adjusting the amount of charge absorbed from the toner by selecting the material of the frictional charging member, thereby providing optimum development quality. The frictional charging member may be formed to cover a surface of a flat plate portion of, e.g., a conductive plate-like member having elasticity such as a plate spring such that the frictional member is elastically pressed against a surface of the toner holding member.
In accordance with the invention, since the frictional charging member is used as the charge adjusting means, it can be practiced easily because of its simple structure.
In the invention it is preferable that the charge adjusting means includes:
a conductive member to be brought into contact with a tone layer on the toner holding member; and
a voltage source connected to the conductive member, for supplying to the conductive member, such a potential as to decrease the charge of the toner.
In accordance with the invention, the conductive member implemented by a metal plate-like member composing the charge adjusting means is brought into contact with the toner layer on the surface of the toner holding member, the voltage source is connected to the conductive member, and a bias potential is set to, e.g., 0 V or to a value of the polarity opposite to the charging polarity of the toner, whereby the charge of the toner is decreased. Such a conductive member may also be a roller configured as a right cylinder and having at least a surface made of me
Azuma Nobuyuki
Iwamatsu Tadashi
Mutou Yoshinori
Nakajima Yoshinori
Toyoshima Tetsuro
Brase Sandra
Conlin David G.
Dike Bronstein, Roberts & Cushman IP Group, Edwards & Angell, LL
Sharp Kabushiki Kaisha
Tucker David A.
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