Electrophotography – Image formation – Development
Patent
1996-12-13
1998-11-24
Beatty, Robert
Electrophotography
Image formation
Development
198630, G03G 1508
Patent
active
058420940
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for conveying magnetizable particles from a first position to a second position by means of a moving magnetic field produced by a converted electromotor and more particularly to a device for the electrostatographic development of a latent image.
2. Description of the Related Art
The art of electrostatic printing or copying involves the formation of an image by the steps of (i) applying on a dielectric an image-wise charge distribution, also called latent image, and (ii) developing the latent image, i.e. converting the latent image to a visible image by depositing selectively light-absorbing particles, called toner particles, on the latent image. The image made visible as a result of the deposition of toner particles on the latent image that was present on the dielectric is then transferred to a substrate and fixed on it to obtain the final print.
In electrophotographic printing or copying, a specific application of electrostatic printing or copying, the dielectric is a photoconductor and the image is formed by the steps of (i) uniformly charging a photoconductor, (ii) image-wise discharging the uniformly charged photoconductor for obtaining thereby a latent image, and (iii) developing the latent image, i.e. converting the latent image to a visible image by depositing selectively light-absorbing particles, called toner particles, on the latent image. The image made visible by the deposition of toner particles on the latent image that was present on the photoconductor is then transferred to a substrate and fixed on it for obtaining the final print.
In the application of toner development two processes are known, i.e. dry-powder development and liquid-dispersion development. The present invention relates to the dry-powder development. For further details on such dry-powder development reference is made to a.o. "IEEE Transactions on Electronic Devices", Vol. ED-19, No. 4, Apr. 1972, pp. 495-511.
According to the dry-powder process the toner particles are charged tribo-electrically as a result of their being mixed with carrier particles. A mixture comprising toner particles and carrier particles, possibly in admixture with further additives, is called developer.
Basically, xerographic copiers and printers 1 commonly use a developing system 2 with a magnetic brush 3 (see FIG. 1, which shows a schematic diagram of a magnetic-brush developing unit as known in the art) for transferring toner particles 4 from a supply 5 to a development zone 6 on an image carrier, e.g. a semiconductor photoconductive drum 7. On such a magnetic brush the developer particles commonly are provided as bristles on the surface of the outer sleeve. Said bristles are transferring toner to the development zone 6 on the photoconductive drum charged with a latent electrostatic image.
The amount of drawn particles 4 is controlled by a coating-thickness control means or doctor blade 13 before reaching the development zone 6. Part of the conveyed particles is picked up electrostatically by the photoconductor 7, whereas the remaining particles continue to move throughout the surface of the magnetic sleeve 8 and eventually return to the supply holder 5 after having passed a scraping means or cleaning blade 14. Optionally, a mixing system 15, such as a rotating paddle, may ensure an intimate mixing of toner and carrier particles. To prevent toner exhaustion a feed system or toner hopper 16 is provided. e.g. with a feed roller 17. Optionally, a bias voltage 18 may be applied to the developing system 2, e.g. to prevent fogging.
A variety of magnetic brushes is available, i.e. types with stationary magnetic core and revolving outer sleeve, types with revolving magnetic core and stationary outer sleeve, or types with revolving magnetic core and revolving outer sleeve. Developing systems with magnetic brushes are described a.o. in "HITACHI components for electrophotographic printing systems", pp. 5-11, published by HITACHI METALS INTERNATIONAL Ltd., Purchase,
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IBM Technical Disclosure Bulletin, vol. 26, No. 7A, Dec. 1983, pp. 3450-3451, G.E. Keefe et al. "Non-Mechanical Printing Toner Transport System"; cited in the application -- see whole document.
Bruyndonckx Jan
Vackier Leo
AGFA-GEVAERT
Beatty Robert
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