Electrophotography – Image formation – Development
Reexamination Certificate
2002-03-21
2004-05-11
Tran, Hoan (Department: 2852)
Electrophotography
Image formation
Development
C399S239000, C399S240000
Reexamination Certificate
active
06735408
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image formation apparatus such as copying machines, facsimiles and printers, liquid development image formation apparatus, liquid development image formation apparatus which uses the liquid development image formation apparatus, and wet-type image formation apparatus which develops a latent image formed on a latent image support by a liquid developer supported on the developer support.
BACKGROUND OF THE INVENTION
Conventionally in this type of image formation apparatus, there is known a method for forming a developing nip by making a developer support which supports a thin film of a liquid developer on the surface thereof abut against a latent image support, and developing the latent image formed on this latent image support using the liquid developer. For example, in Japanese Patent Application No. 11-38447, the present applicant has proposed an image formation for forming a nip section by making a developer support having an elastic layer abut against a latent image support.
In this image formation method, a thin film of a liquid developer is formed on a developer support, and a toner in the thin film is electrostatically transferred to an image section in the latent image on the latent image support which forms the nip section, to thereby effect development. On the other hand, the toner is not allowed to adhere on the ground section (on the background section) on the latent image support which passes through the nip section.
FIGS. 2A and 2B
are schematic diagrams which show the condition of the developer
60
at the developing nip.
FIG. 2A
shows the developing nip between an image section on a photosensitive drum
1
and a developing roller, and
FIG. 2B
shows the developing nip between the background section on the photosensitive drum and the developing roller. Prior to entering into the developing nip, the toner density in the developer layer is substantially uniform, but when the toner enters into the developing nip, the toner starts to migrate in the developer layer, and as the toner proceeds in the developing nip, the toner density in the developer layer has a gradient. As shown in
FIG. 2A
, in the image section, the density of the toner
60
a
in the developer becomes such that it becomes relatively high on the photosensitive drum
1
side and relatively low on the developing roller side. Also as shown in
FIG. 2B
, in the background section, the gradient of the toner density becomes opposite to that in the image section. Therefore, in the developing nip, it is necessary to secure the developing time (the time for the thin layer of the liquid developer to pass via the nip) so that the toner can electrically migrate sufficiently. By securing sufficient developing time, sufficient development is performed, and high image density contrast (high image density, low ground density), high resolution and excellent uniformity in contact print can be obtained.
The developing time relies on the width of the developing nip (the size of surface migration on the photosensitive drum and the developing roller at the developing nip, and hereinafter referred to as “width of the developing nip”), and the process linear velocity which is the peripheral speed of the latent image support and the developer support. Normally, by setting the width of the developing nip to at least a value obtained by multiplying the process linear velocity by the developing time constant, such developing time can be secured. This developing time constant is a time required for the developed amount to saturate, and is a value obtained by dividing the process linear velocity by a minimum width of the developing nip required for the saturation of the developed amount. For example, if the process linear velocity is 300 mm/sec, and the developing time constant is 10 msec, the width of the developing nip becomes 3 mm.
When the width of the developing nip is too small compared to a predetermined size, sufficient development cannot be performed at the developing nip, and the density of the toner image becomes low. On the other hand, when the width of the developing nip is too large compared to the predetermined size, sufficient density of the toner image can be obtained, but the toner may adhere on the ground section of the latent image support, to thereby cause a phenomenon referred to as fogging (also referred to as greasing). Therefore, the width of the developing nip is set to an optimum value, taking the process linear velocity and the developing time constant into consideration in the designing step.
In Japanese Patent Application No. 11-38447, the applicant of this invention has proposed an image formation method for forming a nip section by making a developer support which has an elastic layer abut against a latent image support. In this image formation method, a thin layer of a liquid developer is formed on the developer support, so that the carrier liquid in the thin layer and the toner are electrostatically transferred to an image section in the latent image on the latent image support which forms the nip section, to thereby effect development. On the other hand, the toner is not allowed to adhere on the ground section (on the background section) on the latent image support which passes through the nip section, and only the carrier liquid is slightly transferred thereto.
Even if the toner adheres on the ground section, it is possible to shift the toner towards the developer support to thereby remove it, while passing through the nip section.
In order to prevent residual toner, there is also a technique which prevents adhesion of the toner onto the background section by forming a sufficient electric field between the background section on the latent image support and the developer support (hereinafter referred to as a background section developing electric field). In the method of preventing the toner from adhering on the background section by this background section developing electric field, the larger the background section developing electric field, the larger the effect of prevention of the toner adhesion onto the background section.
The present applicant has also proposed a method of removing the residual toner remaining in the background section after development by a removal member, in Japanese Patent Application No. 2000-42582. Specifically, an electric field (hereinafter referred to as removal electric field) is formed between the background section and the removal member, to attract the floating residual toner towards the removal member to thereby remove the residual toner from the surface of the latent image support. By this proposal, image fogging due to the residual toner is prevented.
In liquid developing apparatus of an electrostatic latent image which develops an image by a toner, as a method of supplying a liquid developer to the latent image face on an image support, there have been used a method for providing unevenness on the surface of the developing roller which is developer support, and holding a liquid developer in the recess to supply it to the image support, a method for using a sponge roller as the developer support, and supplying the liquid developer absorbed by the sponge roller to the image support by pressing the sponge roller against the image support, a method for supplying the liquid developer to the image support directly, without using the developer support, by soaking the image support in a developer tank which stores a liquid developer.
However, the nip width determined at the time of designing may not be formed as designed in the designing step after completion of the apparatus assembly, due to the influence of the production accuracy and assembly accuracy of the parts. By improving the production accuracy and assembly accuracy of the parts, the width of the developing nip can be formed within the allowable range in the design, but it may cause an increase in the production cost or the structure may become complicated.
If it is tried to increase the image formation speed by using the image formation meth
Kurotori Tsuneo
Nakano Tohru
Sasaki Tsutomu
Takeda Yusuke
Takeuchi Noriyasu
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
Tran Hoan
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