Bias shield and method of developing a latent charge image

Details Bias shield and method of developing a latent charge image Bias shield and method of developing a latent charge image

1999-06-14

2001-10-09

Rodee, Christopher (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Producing cathode-ray tube or element thereof

C430S103000, C427S469000, C427S476000, C396S546000, C118S622000

Reexamination Certificate

active

06300021

ABSTRACT:

The invention relates to an apparatus and method of developing a latent charge image on a photoreceptor which is disposed on an interior surface of a faceplate of a cathode-ray tube (CRT), and, more particularly, to an apparatus having a bias shield, and a method of operating a developing apparatus with the bias shield.
BACKGROUND OF THE INVENTION
U.S. patent application, Ser. No. 09/131,022, filed on Aug. 7, 1998 now U.S. Pat No. 6,007,952, and entitled, APPARATUS AND METHOD OF DEVELOPING A LATENT CHARGE IMAGE, by D. P. Ciampa et al., describes an apparatus for developing an electrostatic latent charge image on a photoreceptor that is disposed on an interior surface of a faceplate panel of a cathode-ray tube (CRT). The developing apparatus includes a developer tank having a back electrode and two pairs of panel skirt sidewall shields. The back electrode has a potential applied thereto that establishes an electrostatic drift field between the back electrode and the photoreceptor on the faceplate panel. Triboelectrically charged phosphor materials are introduced into the developer tank and directed toward the photoreceptor on the faceplate panel by the electrostatic drift field shown schematically in FIG.
1
. The panel skirt sidewall shields are disposed around the peripheral sidewall of the faceplate panel to prevent the triboelectrically charged phosphor materials from reaching the sidewall of the faceplate panel. The panel skirt sidewall shields are formed of a suitable insulative material, such as ultra high molecular weight (UHMW) polyethylene. As shown in
FIG. 2
, to prevent the accumulation of phosphor particles on the shields, the shields are primed with positive charges that cancel the normal component of the electric field at the shields, so that the shields will not attract and accumulate the positively charged phosphor particles. While priming with positive charges reduces the accumulation of phosphor particles, it does not provide a means for controlling the amount of phosphor material deposition at the edge of the photoreceptor or of ensuring that the weight of the phosphor materials deposited in the peripheral areas of the photoreceptor is the same as that deposited in the central portion thereof A need therefore exists for a developing apparatus having means to provide uniform phosphor deposition while preventing an accumulation of phosphor materials on the shields.
SUMMARY OF THE INVENTION
In accordance with the present invention, an apparatus and method are disclosed for developing an electrostatic latent charge image which is formed on a photoreceptor that is disposed on an interior surface of a faceplate panel of a CRT. The apparatus comprises a developer tank having a sidewall closed at one end by a bottom portion and at the other end by a panel support having an opening therethrough to provide access to the panel. A back electrode is disposed within the developer tank and spaced from, but substantially parallel to, the interior surface of the faceplate panel. The back electrode has a first potential applied thereto to establish an electrostatic drift field between the back electrode and the photoreceptor that is grounded. Triboelectrically-charged, dry-powdered, light emitting phosphor materials, having a charge of the same polarity as the first potential applied to the back electrode, are introduced into the developer tank, between the back electrode and the faceplate panel. The triboelectrically charged phosphor materials are directed toward the photoreceptor on the faceplate panel by the applied electrostatic drift field. A bias shield is disposed around a peripheral sidewall of the faceplate panel. The bias shield comprises two pairs of insulative members having oppositely disposed major surfaces with at least one conductive strip provided on one of the major surfaces thereof. A suitable potential is provided to the conductive strip to create a surface electric field that directs the triboelectrically charged phosphor materials uniformly towards the photoreceptor and prevents the accumu on of phosphor materials on the bias shield.


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PCT Search Report; Sep. 28, 2000.

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