Electrophotography – Control of electrophotography process – Control of developing
Patent
1996-04-04
1998-04-07
Pendegrass, Joan H.
Electrophotography
Control of electrophotography process
Control of developing
399240, G03G 1510
Patent
active
057376662
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to development control in electrostatographic imaging and, more particularly, to liquid toner development control.
BACKGROUND OF THE INVENTION
Generally, there are two types of development systems employed by electrostatographic imaging apparatus, namely, powder toner development systems and liquid toner development systems. Although powder toner is more conventional, liquid toner is often preferred for its higher intrinsic resolution. Considerable efforts have been made in the past to design more efficient and more convenient liquid toner development systems.
Liquid toner systems are sensitive to physical changes in the toner, such as changes in temperature, charge level, viscosity and liquid concentration, most of which are not relevant in powder toner systems. It is appreciated that these toner changes may affect the development level, thereby resulting in inconsistent imaging. Therefore, control of the liquid toner properties is generally considered to be crucial for maintaining a constant level of developed mass per unit area (DMA) on a photoreceptor of the imaging apparatus.
One current approach to maintaining image quality measures the optical density, volume and conductivity of the liquid toner used in the process. Based on these measurements, toner concentrate, carrier liquid or charge director, respectively are added to the liquid toner. Such an approach is described in U.S. Pat. No. 4,860,924, the disclosure of which is incorporated herein by reference.
It is appreciated that construction and maintenance of a closed loop development system as described above is both complex and expensive. Therefore, liquid toner development systems have never been embodied in low-cost disposable cartridges, as normally is the case in powder toner systems.
In U.S. Pat. No. 4,341,461, the bias voltage of a development roller in a powder development system is adjusted in accordance with a measurement of toner density on a developed patch on a photoreceptor. The toner density is measured by an infrared densitometer which apparently measures the optical density of the layer of toner developed on the photoreceptor.
U.S. Pat. No. 4,678,317 describes a liquid toner system in which a sensor electrode is used to sense the potential of a charged photoreceptor and to adjust a development electrode voltage to compensate for variations in the sensed potential.
WO 93/01531, the disclosure of which is incorporated herein by reference, describes a direct-transfer liquid toner development system. A layer of concentrated liquid toner coating a toning roller is brought into virtual contact with a photoreceptor, and portions of substantially even thickness are transferred from the toning roller onto attractive portions of the photoreceptor. Either the full thickness of the portions is transferred, in a binary mode of operation or, in a quasi-binary mode of operation, a partial yet even thickness is transferred. The voltage between the toning roller and the photoreceptor determines the thickness of the layer which is transferred. In the binary mode, the DMA on the photoreceptor is substantially equal to the DMA on the toning roller and, in the quasi-binary mode, the photoreceptor DMA is dependent in a well defined manner upon the toning roller DMA. For quasi-binary transfer the photoreceptor DMA is generally more uniform than the toning roller DMA.
The direct-transfer system described above normally employs a toner applicator and a squeegee associated with the toning roller.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved liquid toning system. In accordance with a preferred embodiment of the present invention, consistent toning of latent electrostatic images is maintained throughout numerous toning cycles without adding liquid toner or liquid toner components to the system and/or adjusting the material composition of the liquid toner, i.e. the ratio between toner particles and carrier liquid.
In general, liquid toner including charged
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International Search Report and Annex.
Chatow Ehud
Lavon Amiran
Lior Ishaiau
Indigo N.V.
Pendegrass Joan H.
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