Electrophotography – Image formation – Development
Reexamination Certificate
2000-03-13
2001-07-03
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Development
C399S130000, C399S133000, C430S117200
Reexamination Certificate
active
06256468
ABSTRACT:
FIELD OF THE INVENTION
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 toner.
BACKGROUND OF THE INVENTION
Various methods of developing a latent image have been described in the art of electrophotographic printing and copying systems. A typical electrostatographic printing process includes a development step whereby a quantity of developing material is physically transported into the vicinity of a latent image bearing imaging member, with the marking material (described herein as toner) in the developing material are caused to migrate via, e.g., electrical attraction, to the image areas of the latent image so as to selectively adhere to the imaging member in an image-wise configuration.
Of particular interest with respect to the present invention 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 toner. 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.
For the purposes of the present description, the concept of latent image development via direct surface-to-surface transfer of a toner layer via image-wise fields will be identified generally as contact electrostatic printing (CEP). Exemplary patents which may describe certain general aspects of contact electrostatic 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.
It is desirable that the aforementioned layer of liquid developing material be provided in a very thin and 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 accurately 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 contact electrostatic printing applications.
SUMMARY OF THE INVENTION
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 contact electrostatic printing engine operable in a novel fashion upon a copy substrate, wherein each contact 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 delivery apparatus may be constructed and operated in accordance with the contact electrostatic printing process to which the present invention is directed, wherein a toner cake layer of high solids content is created. The toner cake layer may, after delivery to a suitable receiving member, be brought into pressure contact with the surface of a latent image bearing imaging member such that a developed image is created by separating and selectively transferring portions of the toner cake layer in correspondence with the image and non-image regions of the latent image. 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 accurately metered mass per unit area on the order of 0.1 mg per cm
2
.
The toner cake delivery apparatus of the present invention includes a supply of low solids content liquid developing material 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 particles. A low solids content liquid developing material applicator provides a relatively uniform layer of low solids content liquid developing material onto a carrier fluid separation (CFS) surface on a coating member. The layer of low solids content liquid developing material applied to the CFS surface is subject to a rapid migration of at least a portion of the carrier fluid into the coating member and away from the exterior of the CFS surface. As a result, a reduction of the ratio of carrier fluid to toner solids in the outermost portions of the liquid developing material layer results in the formation of the desired toner cake layer. The toner cake layer is then available for transfer to the surface of a receiving member for subsequent use in development of an electrostatic latent image.
In accordance with another aspect of the present invention, a first embodiment of a novel contact electrostatic printing engine may be constructed for imaging and development of a latent image, wherein the contact electrostatic printing engine includes a photosensitive imaging member which is rotated so as to transport the surface thereof in a process direction for implementing steps for charging and imagewise exposure of a light image corresponding to the desired component image. A second movable member in the form of an applicator is provided in combination with a toner cake delivery apparatus, the latter including a supply of low solids content liquid developing material. The toner cake layer delivery apparatus includes a third movable member in the form of the coating member, the supply of low solids content liquid developing material, and a low solids content liquid developing material applicator. After the toner cake layer is formed on the surface of the coating member and transferred to the applicator, the toner cake layer may be brought into pressure contact with the latent image bearing surface of the imaging member by transporting the toner cake layer through a process nip formed by the operative engagement of the applicator and the imaging member. A development step then occurs, producing a developed image made up of selectively separated portions of the toner cake layer on the surface of the applicator, while leaving background image byproduct on the surface of the imaging member. Transfer of the developed image from the surface of the applicator may then be accomplished. Accordingly, apparatus for high-temperature and pressure transfer and/or transfixing may be advantageously employed for carrying out an image transfer step, which would be more difficult to achieve at the photoconductive surface of the imaging member.
In accordance with another aspect of the present invention, the contact electrostatic printing engine provides a process nip formed by operative engagement o
Chen Sophia S.
Dudley Mark Z.
Xerox Corporation
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