Electrophotography – Image formation – Development
Reexamination Certificate
2001-12-14
2003-09-16
Tran, Hoan (Department: 2852)
Electrophotography
Image formation
Development
C399S239000
Reexamination Certificate
active
06621998
ABSTRACT:
This invention relates generally to electrostatic latent image development systems that operate using liquid developing material, and, more particularly, relates to a system for electrostatic development of a latent image, wherein the latent image is developed with use of a toner cake layer having a high solids content.
A typical electrostatographic printing process includes a development step whereby developing material including toner or marking particles is physically transported into the vicinity of a latent image bearing imaging member, with the toner or marking particles being caused to migrate via electrical attraction to the image areas of the latent image so as to selectively adhere to the imaging member in an image-wise configuration. Various methods of developing a latent image have been described in the art of electrophotographic printing and copying systems. Of particular interest with respect to contact electrostatic printing systems is the concept of forming a thin layer of liquid developing material on a first surface of a first member, wherein the layer has a high concentration of charged marking particles. The layer on the first member is brought into contact with an electrostatic latent image on a second surface of a second member, wherein development of the latent image occurs upon separation of the first and second surfaces, as a function of the electric field strength generated by the latent image. In this process, toner particle migration or electrophoresis is replaced by direct surface-to-surface transfer of a toner layer induced by image-wise fields.
Exemplary patents which may describe certain aspects of electrostatic and electrostatographic printing, as well as specific apparatus therefor, may be found in U.S. Pat. Nos. 4,504,138; 5,436,706; 5,596,396; 5,610,694; and 5,619,313, the disclosures of which are incorporated herein by reference.
It is desirable that the aforementioned layer of liquid developing material be provided in a very thin and very uniform layer that exhibits a high proportion of solids, that is, having a high solids content. Even more desirable is such a layer exhibiting the following advantageous characteristics: a selectable, uniform thickness, preferably in the range of 3-10 microns; a high solids content, preferably in the range of 15 to 35 percent solids; and an uniformly metered mass per unit area on the order of 0.1 mg per cm
2
.
The intuitive and conventional approach is to attempt the formation of such a layer by direct application of liquid developing material having a high solids content. However, due to the very complicated rheological behavior of a liquid developing material having the requisite high solids content, such direct application of a supply of such liquid developing material to a receiving member typically does not achieve a layer having the aforementioned desirable characteristics. For example, the resulting layer has been found to exhibit a variable thickness and a non-uniform mass per unit area, which renders the layer generally unsuitable for most electrostatic printing applications.
In accordance with one aspect of the present invention, there is provided an imaging system for effecting electrostatic printing of an image, wherein the imaging system includes at least one electrostatic printing engine operable in a novel fashion, wherein the electrostatic printing engine images and develops an electrostatic latent image representative of the image, and subsequently transfers the developed image to the copy substrate.
In accordance with another aspect of the present invention, a toner cake formation apparatus may be constructed and operated in accordance with the electrostatic printing process to which the present invention is directed, wherein a thin, uniform toner cake layer of high solids content is formed in a process nip between first and second movable members. The toner cake layer is generally characterized as having a high solids content (e.g., approximately 10-50 percent solids, and preferably in the range of approximately 15 to 35 percent solids, or greater), and exhibits the additional advantageous characteristics of a uniform thickness, in the range of 1-15 microns, and an uniformly metered mass per unit area in the range of 0.03-0.2 mg per cm
2
.
In accordance with another aspect of the present invention, an imaging system for effecting electrostatic printing of an output image may be constructed, wherein a first movable member is provided in the form of an imaging member having a latent electrostatic image on an image bearing surface, and the second movable member is provided in the form of a developed image receiving member. A toner cake layer of high solids content is formed in a process nip between the first and second movable members. A developed image is created as the toner cake layer exits the process nip, wherein portions of the toner cake layer separate in correspondence with the image and non-image regions of the latent image.
A preferred embodiment of the imaging system includes a supply of low solids content liquid developing material from which a low solids content liquid developing material applicator establishes a relatively uniform and constant aggregation of low solids content liquid developing material at the entrance of the process nip. The low solids content liquid developing material is a mixture of marking particles, such as toner particles, dispersed in a fluid carrier medium. This aggregation of low solids content liquid developing material is subject to compression in the process nip, such that the concentration of marking particles is increased in the process nip, and the concentration of carrier liquid is decreased in the process nip, thus causing formation of the desired toner cake layer.
In another aspect of the invention, a pre-development zone is established at the entrance of the process nip, wherein a controllable proportion of toner particles are believed to be preferentially capable of sustaining compression at the nip entrance so as to pass into the process nip. In contrast, a controllable proportion of the carrier fluid is believed to be preferentially restrained from entering the process nip. The increase in concentration of toner particles in the process nip thus yields a toner cake layer that is continuously formed therein.
In another aspect of the invention, the formation of the toner cake layer is accompanied by concurrent or near-concurrent development of the electrostatic latent image in a development zone situated in the process nip. The onset of formation of the toner cake layer is believed to occur during the forced migration of toner particles into the process nip. Complete formation of the toner cake layer is believed to occur concurrently or prior to the development of the latent image within the process nip, such that the developed image is completed upon separation of the toner cake layer into image and non-image portions at the process nip exit.
In accordance with another aspect of the present invention, an embodiment of a novel electrostatic printing engine may be constructed for imaging and development of a latent image, wherein the electrostatic printing engine includes an imaging member which is rotated so as to transport the surface thereof in a process direction for implementing steps for charging and formation of an electrostatic image corresponding to the desired latent image. A second movable member, in the form of a developed image receiving member, is provided in combination with an applicator of low solids content liquid developing material. The applicator establishes an aggregation of low solids content liquid developing material at the entrance of a process nip between the first and second movable members. Preferably, the aggregation is generally made up of toner particles immersed in a liquid carrier material and also typically including a charge director for providing a mechanism for producing an electrochemical reaction in the liquid developing material composition which generates the desired electrical charge on the toner
Liu Chu-heng
Zhao Weizhong
Tran Hoan
Xerox Corporation
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