Reversible or irreversible production of an image

Details Reversible or irreversible production of an image Reversible or irreversible production of an image

1992-03-13

1994-05-17

Bowers, Jr., Charles L.

Radiation imagery chemistry: process, composition, or product th

Erasable imaging

430 20, 430 51, 430945, 430 97, 430124, 430126, 430 42, 355211, 365108, 359 43, 359 45, G03G 5024, G03G 512, G03G 15056

Patent

active

053127030

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a novel process for the reversible or irreversible production of an image by imagewise exposure of a recording layer to energy in the presence or absence of an electrical and/or magnetic field, resulting in a pattern of surface charges on the surface of the recording layer corresponding to the imagewise exposure to energy.
Processes of this type in which patterns of surface charges can be produced in a variety of ways utilizing various physical mechanisms are known. Specific examples are xerography or electrophotography, in which a photoconductive recording layer is provided with a positive or negative electrical charge, for example by means of a high-tension corona discharge, and the electrically charged recording layer is then exposed imagewise to actinic light. The exposure causes the photoconductive recording layer to become electroconducting in its exposed areas, and the previously produced electrostatic charge in these areas can thus dissipate via an electroconductive substrate. A latent electrostatic image is thus produced on the photoconductive recording layer and can be developed using suitable liquid or solid toners to give a visible image. This toner image can then be transferred in a conventional manner from the recording layer to another surface, resulting in a photocopy. Alternatively, the toner image can be fixed on the photoconductive recording layer, for example by heating, and the exposed and therefore toner-free areas of the photoconductive recording layer can then be washed out using suitable liquid developer solvents. The resultant relief layer can then be used, for example, for printing. The physical process on which this imagewise information-recording technique is based is also known in the scientific literature as the Carlson process. In summary, xerography involves the formation of the pattern of surface charges by the production and imagewise removal of free charge carriers.
As is known, xerography has disadvantages. For example, generation of the high-voltage corona discharge for charging the surface of the photoconductive recording layer requires direct voltages of the order of from 6 kV to 10 kV, which causes problems from a safety and, due to the formation of ozone, toxicological point of view. In addition, since the pattern of surface charges is formed from free electrical charges, the success of the process is impaired by the presence of water. This means that excessive atmospheric moisture causes premature dissipation of the surface charges, even in the dark, or prevents sufficient charging of the surface of the photoconductive recording layer. Moreover, it is not possible in xerography to produce more than one copy from a single exposure.
A modified xerographic process which overcomes these disadvantages to a certain extent is disclosed in DE-A-15 22 688. In this process, the pattern of surface charges is produced by exposing the entire surface of a suitable photoconductive recording layer to light in the presence of an electrical field having a field strength of from 1000 V/cm to 15,000 V/cm, producing a uniform internal electrical polarization in the recording layer. The pattern of surface charges is then formed by local destruction or modification of the internal polarization. Unlike xerography, the pattern of surface charges is thus in the narrower sense a residual electrical polarization image comprising either positively or negatively electrically charged areas and uncharged areas or comprising positively and negatively electrically charged areas. This residual electrical polarization image can be toned in a conventional manner using liquid or solid toners, it being possible to simultaneously tone the residual electrical polarization image composed of negatively and positively electrically charged areas using two toners of opposite electrical charge and different color.
Even this known process still has numerous disadvantages. For example, the photoconductive recording layer used is a relatively thick (15 to 55 .mu.m) inhomogeneous l

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Research Disclosure 31660, Aug. 1990, "Rewritable Xeroprinting Master".

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