Electrophotography – Image formation – Development
Patent
1996-04-12
1998-05-12
Smith, Matthew S.
Electrophotography
Image formation
Development
347 55, 347103, 399239, 399246, 430117, G03G 1510
Patent
active
057521425
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of and an apparatus for developing electrostatic images and particularly, to the development of such images by means of generated finite marking entities which are based on water and hence are environmentally friendly.
BACKGROUND ART
In the process of xerography, as disclosed in Carlson U.S. Pat. No. 2,297,691, issued Oct. 6, 1942, a xerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter by conventional projection techniques. This exposure discharges the plate areas in accordance with the radiation intensity that reaches them, and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is usually effected with an electrostatically charged, finely-divided material such as an electroscopic powder that is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. The developed electrostatic image is usually transferred to a support surface to which it is fixed by any suitable means. Where the electrostatic plate comprises a consumable material the developed image may be fixed directly.
Alternatively, the recording member may be a dielectric, as disclosed in Beaudet et al, U.S. Pat. No. 4,413,049 issued Nov. 1, 1983, where the dielectric recording member comprises sealed porous anodised aluminium. The recording member is charged with an electrostatic image, as so described in Fotland et al, U.S. Pat. No. 4,267,556 issued May 12, 1981, by a glow discharge electron source. Development of the so formed latent image is again effected with an electrostatically charged, finely-divided material such as an electroscopic powder that is brought into surface contact with the dielectric surface and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. The developed latent image is usually transferred to a support surface to which it is fixed by any suitable means. Where the dielectric recording member comprises a consumable material the developed image may be fixed directly. Various development systems are known in the art including cascade, powder cloud, liquid, magnetic, brush and the like, each of which employ electroscopic marking particles that are preferentially charged to a polarity. The charged particles are presented to the latent image to develop it. One common drawback of many of said development systems is dust generation which further requires the necessity to contain such dust.
In U.S. Pat. No. 2,690,394 to Carlson issued 28 Sept., 1954 there is described a system of electrostatic imaging which utilises an atomiser to produce a spray of droplets of a solvent. The droplets of solvent are charged by an electrode and then are drawn by means of a suction pump over a recording surface including an electrostatic image. Droplets of solvent are attracted by the oppositely charged image and deposit on the recording surface. The solvent is then transferred from the recording member to a sheet of paper and the paper then passes over a dye coated roller so that some of the dye is dissolved onto the paper to produce an image. Solvents proposed include high boiling point alcohols, cellosolve, toluene, cyclohexanol acetate and alcohol-water mixtures. It is also suggested that mixtures of solvent with an ink or dye can be atomised and also that the solvent can contain suspended pigments and binders. There is no disclosure, however, of a liquid system where the liquid is composed primarily of water.
It has been disclosed in Heine-Geldern et al, U.S. Pat. No. 3,795,443, issued Mar. 5, 1974, that some liquids not always characterised as being electrically resistive when generated into a fine mist in the vicinity of an electrostatic charge pattern will deposit selectively onto an electrostatic image. By chemically colouring the liquid, as b
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Lima-Marques Luis
Staples Phillip Eric
Smith Matthew S.
Watermark Imaging Ltd.
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