Single pass, multicolor contact electrostatic printing system

Details Single pass, multicolor contact electrostatic printing system Single pass, multicolor contact electrostatic printing system

1999-11-26

2001-09-11

Beatty, Robert (Department: 2852)

Electrophotography

Image formation

Development

C055S299000, C055S299000

Reexamination Certificate

active

06289191

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 multicolor imaging system that employs contact electrostatic development of a series of latent images, wherein the latent images are representative of respective component images that are combinable to form a composite color image.
BACKGROUND OF THE INVENTION
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 of toner or marking particles 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 the present invention is the concept of forming a thin layer of liquid developing material on a first surface, wherein the layer has a high concentration of charged marking particles. The layer is brought into contact with an electrostatic latent image on another surface, 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.
Landa et al., in U.S. Pat. No. 5,436,706, disclose a multicolor system wherein a plurality of developer rollers are said to be provided, one for each color, which are sequentially engaged with a photoconductive surface to develop sequentially produced latent images.
Domoto et al., in U.S. Pat. No. 5,619,313, disclose a multicolor embodiment of a liquid electrophotographic simultaneous development and transfer apparatus that includes a continuous transfer belt. Four latent imaging units are positioned about the periphery of the transfer belt. Each latent imaging unit are said to be substantially identical to one another, except for the color of the liquid developer material employed therein.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, there is provided an imaging system for effecting single pass, multicolor printing of a color image, wherein the imaging system includes a plurality of contact electrostatic printing engines operable in serial fashion upon a copy substrate, wherein each contact electrostatic printing engine images and develops a respective electrostatic latent image representative of a component image of the color image, and subsequently transfers the developed component image to the copy substrate as the copy substrate proceeds in a single pass through the imaging system.
In accordance with another aspect of the present invention, the imaging system employs a plurality of contact electrostatic printing engines for imaging and development of a series of latent images, wherein the latent images are representative of respective component images that are combinable to form a composite color image. Each 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 a liquid developing material layer applicator is provided in combination with a liquid developing material supply apparatus. After the material layer is formed on the surface of the liquid developing material layer applicator, the material layer is brought into pressure contact with the latent image bearing surface of imaging member by transporting the material layer through a process nip formed by the operative engagement of the layer applicator and the imaging member. A development step then occurs, producing a developed image made up of selectively separated portions of the material layer on the surface of the material layer applicator, while leaving background image byproduct on the surface of the imaging member. Transfer of the developed image from the surface of the material layer applicator may then be accomplished. Accordingly, high-temperature and pressure transfer and/or transfix apparatus may be advantageously employed for carrying out the transfer step, which heretofore would be more difficult to achieve at the photoconductive surface of the imaging member.
In accordance with another aspect of the present invention, a first embodiment of a contact electrostatic printing engine operable in the imaging system provides a process nip formed by operative engagement of first and second movable members for positioning a thin layer of liquid developing material in pressure contact with the electrostatic latent which generates imagewise electric fields across the layer of liquid developing material in the process nip. The process nip is defined by a nip entrance and a nip exit, wherein the process nip and the nip entrance are operative to apply compressive stress forces on the layer of liquid developing material thereat, and the nip exit is operative to apply tensile stress forces to the layer of liquid developing material, causing imagewise separation of the layer of liquid developing material corresponding to the electrostatic latent image. The layer of liquid developing material is defined by a yield stress threshold in a range sufficient to allow the layer of liquid developing material to behave substantially as a solid at the nip entrance and in the nip, while allowing the layer of liquid developing material along the image-background boundary to behave substantially as a liquid at the nip exit.
In accordance with another aspect of the present invention, a second embodiment of a contact electrostatic printing engine operable in the imaging system includes an imaging member for receiving an electrostatic latent image. The imaging member includes a surface capable of supporting a layer of marking material which may be in the form of toner particles. An imagewise exposure device is also provided for generating the electrostatic latent image on the imaging member, wherein the electrostatic latent image includes image areas defined by a first charge voltage and non-image areas defined by a second charge voltage distinguishable from the first charge voltage. A marking material supply apparatus is also provided for depositing marking material on the surface of the imaging member to form a layer of marking material thereon adjacent the electrostatic latent image on the imaging member. In addition, a charge source is provided for selectively delivering charges to the layer in an image-wise manner responsive to the electrostatic latent image on the imaging member to form a secondary latent image in the marking material layer having image and non-image areas corresponding to the electrostatic latent image on said imaging member. A separator member is also provided for selectively separating portions of the layer of marking material in accordance with the secondary latent image in the layer of marking material to create a developed image corresponding to the secondary electrostatic latent image formed on said imaging member.
In accordance with another aspect of the present invention, a third embodiment of a contact elect

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