Charge emitting print head for image forming systems

Details Charge emitting print head for image forming systems Charge emitting print head for image forming systems

2001-05-29

2003-01-07

Pendegrass, Joan (Department: 2852)

Incremental printing of symbolic information

Electric marking apparatus or processes

Electrostatic

Reexamination Certificate

active

06504557

ABSTRACT:

TECHNICAL FIELD
The present invention relates generally to image forming systems, and specifically relates to charged particle emitting print heads utilized in electron beam imaging printing.
BACKGROUND OF THE INVENTION
In an image forming system, such as ionography, or electron beam imaging (EBI), a latent electrostatic image is formed on an imaging dielectric surface by directing beams of charged particles onto the surface. The latent electrostatic image thus formed may then be developed by applying toner particles to the imaging surface that are attracted to those areas of the imaging surface where the electrostatic latent image resides. The toner particles on the imaging surface are then transferred to a receiving member (such as paper) before the imaging surface is cleaned in preparation for a new imaging cycle.
The source of the beams of charged particles in the image forming system is a print head. Referring to
FIG. 1A
, a typical print head
10
includes three layers that have electrodes. A first layer includes a plurality of RF-line electrodes
16
separated from a second layer of finger electrodes
12
by a dielectric layer
14
. A third layer is a screen electrode
18
isolated from the finger electrodes by a spacer layer
20
. The surface of both the RF-line electrodes
16
and the finger electrodes
12
can be smoothed by a smoothing dielectric
11
. In thin film structures, the smoothing dielectric is usually SOG (spin on glass). The finger electrodes
12
have finger openings
13
, typically circular, which are generally aligned with the apertures
22
in the screen electrode
18
, as shown in FIG.
1
A. The RF line electrodes
16
intersect the finger electrodes
12
where the finger openings
13
are located. If a high voltage is applied to the finger electrodes
12
and the RF-line electrodes
16
, an electrical breakdown of air inside the finger openings
13
occurs.
Referring to
FIG. 1B
, a cross-section of a single charge production site of the print head
10
is shown. The electrical breakdown causes formation of gaseous plasma full of charged ions and electrons. While the polarity of particles used for imaging is determined by the polarity of the screen electrode
18
potential with respect to a grounded imaging member
24
, on/off switching of charge emission from the print head
10
is regulated by a potential difference between the screen electrode
18
and the finger electrodes
12
.
The dielectric layer
14
is typically formed from stoichiometric compounds, such as silicon oxide, silicon nitride, silicon oxy-nitride, aluminum oxide, titanium oxide, boron nitride, etc., or their combination. Electrical conductivity of such materials is very low, about 10
−14
S/cm or less at room temperature.
A disadvantage of conventional print heads, and especially print heads designed for high density printing, is that the dielectric layer is subject to degradation. In particular, with repeated printing cycles, the plasma generated in the finger openings
13
degrades the dielectric layer.
Referring to
FIG. 2
, evidence of the dielectric degradation is shown. Underneath the finger electrode with a circular opening, there can be seen a dielectric layer, which in this particular case is aluminum oxide. The dielectric layer has been subjected to electrical discharges for a time equivalent to printing about 150,000 pages. Significant erosion of the dielectric material can be seen in the amount of dielectric by-products formed in the area around the opening. Such deterioration leads to charge generation reduction and therefore to print quality degradation. Ultimately, such degradation can lead to a full dielectric breakdown of the print head.
SUMMARY OF THE INVENTION
For the aforementioned reasons, there exists in the art a need for an electron beam imaging print head less susceptible to degradation arising from plasma generation.
The present invention provides a print head for an image forming system that is resistant to erosion. The print head comprises RF-line and finger electrodes separated by an isolating structure containing a dielectric and a semiconductor or resistive material. For example, the isolating structure may include a dielectric coated with a layer of semiconducting material. Typically, the semiconductor utilized in the present invention has a conductivity between about 10
−6
and about 10
−3
S/cm. The semiconductor can be made of a solid solution of a gas in a metal or semiconductor, where the gas includes a hydrogen gas, a nitrogen gas, an oxygen gas, and a halogen gas, or their mixtures. The semiconductor may also include solid solutions of non-metals in a metal, where the nonmetals include boron and/or carbon.


REFERENCES:
patent: 4426654 (1984-01-01), Tarumi et al.
patent: 6377289 (2002-04-01), Philebrown et al.
patent: 9-123516 (1997-05-01), None

Affiliated with

Also associated with

Rating

Charge emitting print head for image forming systems does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Charge emitting print head for image forming systems, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Charge emitting print head for image forming systems will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3001858