Photocopying – Contact printing – Light boxes
Patent
1994-08-02
1996-07-02
Brase, Sandra L.
Photocopying
Contact printing
Light boxes
118659, G03G 1510
Patent
active
055328059
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates generally to methods and apparatus for printing of images and more particularly to a method for direct printing of images without plates or the formation of an electrostatic latent image.
BACKGROUND OF THE INVENTION
Imaging apparatus, such as laser printers, typically comprise complex electrophotographic apparatus which are utilized to form an initial electrostatic latent image of the image which is to be printed. The electrostatic latent image is then developed by means of a liquid or powder toner, and the developed image is transferred either directly or indirectly to a final substrate.
U.S. Pat. No. 4,014,693 to Clark describes a method for forming a colored liquid deposit in image configuration on a surface without forming an initial electrostatic latent image. The method utilizes liquids which are electroviscous, i.e. whose viscosity changes as a function of the application of an electric field across them. In the Clark patent, images are deposited on a substrate by selectively applying specific voltages across such electroviscous liquids, such that at one voltage the liquid jells while at another voltage the liquid flows.
U.S. Pat. No. 4,504,138 describes a method of developing a latent imaging which includes applying a thin viscous layer of toner particles onto the circumferential surface of a rotating roller and bringing the layer so formed to a rotating photoconductive drum having a latent electrostatic image formed thereon. Transfer of portions of the toner layer then occurs as a function of the various voltages on the image and background portions of the latent image.
U.S. Pat. No. 3,623,122 describes a system in which a moving probe or a series of stationary probes are arranged to form a liquid toner image on a substrate. The liquid developer used in the apparatus has a solids concentration of 0.5% and apparently prints using electrophoretic deposition of toner particles on the substrate.
SUMMARY OF THE INVENTION
The present invention provides a new and improved method for printing images directly on a substrate without need for the prior formation of an electrostatic latent image, and without need for using electroviscous fluids. Because of the simplicity and economy of the method of the present invention, it is possible to design and construct imaging apparatus which is relatively uncomplicated, thus making them simpler and cheaper to manufacture and operate.
In general, the present invention is based on the discovery that a thin layer of highly viscous charged liquid toner concentrate can be made to "stick" to a surface in the presence of an electric field. Thus, if in a imaging region, a thin layer of such concentrate is placed between a moving surface, such as a roller and a fixed member, such as a blade, then the application of an electric field in one direction will cause the toner concentrate to be drawn toward the moving member and to leave the region with the moving member. An electric field in the opposite direction will cause the concentrate to be drawn to the fixed member which then acts as a brake for stopping the concentrate from leaving the region. If selective electric fields are set up over the region, then an image is formed.
There is therefore provided in accordance with a preferred embodiment of the present invention a method for forming images on a member including the steps of: comprising charged toner particles and carrier liquid and preferably having a high cohesiveness and viscosity to a space between a first, moving member and a second, stationary member closely spaced therefrom; and and transverse to the direction of motion of the moving member across selected segments of the layer of liquid toner, whereby certain segments of the layer adhere to the moving member in image configuration thereon for a first value of the electric field and other segments of the layer adhere to the stationary member for a second value of the electric field.
Preferably the method includes the step of transferring the image from t
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Brase Sandra L.
Indigo N.V.
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