Electricity: electrical systems and devices – Electric charging of objects or materials – By charged gas irradiation
Patent
1980-07-16
1982-07-20
Moose, Jr., Harry E.
Electricity: electrical systems and devices
Electric charging of objects or materials
By charged gas irradiation
361230, H01T 1900
Patent
active
043409261
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
This invention concerns a device for electrostatic charging of sheet material eg paper typically for use in photocopiers and the like.
BACKGROUND TO THE INVENTION
Many photocopying processes involve the electrostatic charging of a sheet or roll of paper and the subsequent exposure of the charged surface to a light image of the document which is to be copied. The application of the electrostatic charge to the paper should be as uniform as possible to avoid differences in sensitivity over the surface of the paper.
Hitherto a charging device has typically comprised one or more lengths of wire which are stretched between insulating supports and are charged to a high potential from a high tension source and adjacent to which the paper is moved. Although a non-uniform pattern of charge would result from a static exposure of a sheet of paper to the charging device a relatively uniform charge can be produced over the surface of the paper by moving the paper relative to the charging device.
In addition a sufficient level of charge is obtained by using a charging device at a very much higher potential than in theory is necessary so as to ensure that the whole surface of the paper receives a charge which exceeds a minimum potential.
Known devices therefore require very high potential sources and appropriate traction means for moving the paper uniformly past the charging device and are not particularly suited to photocopying systems in which the power supply requirements are limited and/or in which the speed of movement of the paper past the charging device is not necessarily well controlled or uniform and in which the source of high tension does not necessarily produce a continuous charge but produces a series of pulses as in the case of a power supply incorporating a piezo-electric crystal which is squeezed so as to produce a high voltage across the crystal which can then be dissipated through the charging device onto the paper.
OBJECTS OF THE PRESENT INVENTION
With this in mind the present invention has as its object the production of a charging device which can be used to charge a paper more uniformly and more readily than hitherto particularly when using a non-uniform traction of paper past the charging device and/or a lower power and/or pulsed operation charge source.
THE INVENTION
According to the present invention a device for charging paper and like flexible material comprises a housing containing a cylindrical cavity at least the curved surface of which is conductive, an inlet and an outlet to allow the flexible medium to be introduced into and extend around the internal curved surface of the cylindrical cavity and to leave via the outlet, and an elongate conductor extending coaxially through the cavity and electrically insulated from said conductive surface and a source of electric potential with one terminal connected to the conductive surface and the other to the elongate conductor.
The housing may be of insulating material and the conductive surface may be a film or coating or sheet of conductive material such as metal.
Alternatively the housing may be of conductive material and may be mounted in an insulating manner with the elongate conductor stretched between insulating mountings at opposite ends of the housing.
The inlet and outlet may be separate slits in the housing or may be combined into a single slit into which the flexible medium is fed and from which the flexible medium leaves the housing.
The ends of the cavity may be adapted to receive and grip the incoming paper and may be rotatable relative to the remainder of the housing so as to provide a traction drive for the flexible material around the interior of the cavity.
A cylindrical guide may be located within the housing, the diameter of the guide being just less than the internal diameter of the housing, so as to leave a narrow gap around which the flexible medium will pass. The guide is preferably perforated or otherwise apertured to permit the passage of electric charge from the conductor to the medium.
It has
REFERENCES:
patent: 2000684 (1935-05-01), Allen et al.
"Corona Flat Cable Treatment"--Davies et al; IBM Technical Disclosure Bulletin, vol. 18, No. 7, 12/75.
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