Photocopying – Projection printing and copying cameras – Combined with or convertible to a contact printer
Patent
1986-08-13
1988-04-26
Moses, R. L.
Photocopying
Projection printing and copying cameras
Combined with or convertible to a contact printer
355 4, 118645, 118659, G03G 1510, G03G 1501
Patent
active
047408162
DESCRIPTION:
BRIEF SUMMARY
SUBJECT OF INVENTION
This invention relates to a method of and means for developing electro-photographic images and in particular it relates to a machine of the type in which a photo-conductive surface is charged, exposed to an image, and then developed by a system of liquid development.
PRIOR ART
It is customary in electro-photography to have a surface on which is a layer of a photo-sensitive material which is energized by first charging the surface and then exposing the surface to produce an image and to then develop the image with particles which are attracted to the surface according to the charge pattern.
The particles which are attracted to the latent electro-static image can be suspended in air or applied with a magnetic brush to form the final image by fixing to the paper and constitutes what is referred to as the dry system of development, or they can be suspended in an insulating liquid, such particles being controlled with fixing agents so that on drying the image is fixed, this being referred to generally as the liquid system which this invention uses.
The problem associated with the liquid system of development as exemplified in the office copying machines are mainly due to the fact that the electro-photographic papers is immersed entirely in the hydro-carbon insulating liquid in which the developer particles are suspended, thus requiring considerable energy to dry the copy after development.
OBJECTS OF THE INVENTION
One of the objects of the present invention is to overcome this problem, this being achieved by developing latent electro-static images using liquid toners applied only to the electro-photographic surface on which the latent electro-static image resides. To achieve this the electro-photographic paper is subjected on one side to the developer and is then passed between pressure means, such as a pair of rollers, one of the rollers being formed by smooth conductive material such as polished metal while the other roller, which is urged against the first roller, is coated with a non-solvent aborbent but resilient material so as to squeeze the excess liquid developer from the surface of the sheet.
The progressive pressure means act not only to remove the excess hydro-carbon liquid required for development but also applies a bias to bring about "fill in" of the solid areas of the latent electro-static image.
Another problem associated with liquid office copying machines arises from the fact that the paper base on which the electrophotographic sensitising layer is coated is treated, sometime prior to coating with the electro-photographic material with a conductive substrate, and this conductive substrate material "bleeds up" into the electrophotographic layer so that on close examination of the image developed by a liquid developer system, myriads of white spots are revealed throughout the coating which degrades the image and thus destroys the resolving power of the photoconductor. Another object is to avoid this problem, and this is achieved according to this invention by using a paper which is not provided with such a conductive layer, such a paper having been disclosed in U.S. Pat. No. 4,134,762. When this paper is used with this development and charging system the defects in the final image of prior art systems are eliminated.
A preferred embodiment of the principle established above of using a metal roller acting as a bias and which is urged against a resilient non-solvent absorbent covered roller so as to squeeze the excess liquid developer from the surface of the sheet of electrophotographic paper can be constructed in a machine so that the charging means, the exposure means and the development means are all situated in the same plane thus eliminating the problem of turning the exposed electrophotographic membrane through 180.degree. to bring to the development rollers.
By using a system of small individual belts suitable for handling a large drawing or transparency the electrophotographic paper can be fed into the machine by various means either as individual sheets or from
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Brock Alan J.
Clements Alwin S.
Horrocks Brian J.
Jauncey Peter
Cameronics Technology Corp. Ltd.
Moses R. L.
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