Radiation imagery chemistry: process – composition – or product th – Producing cathode-ray tube or element thereof
Reexamination Certificate
1999-08-31
2001-04-10
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Producing cathode-ray tube or element thereof
C252S301360
Reexamination Certificate
active
06214501
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for coating phosphor particles, phosphor particles therethrough and dry electrophotographic screening process using them for a CRT, more particularly to a method for coating phosphor particles easily and uniformly with high-molecular polymers in order to improve chargeability thereof and to improve developing characteristics thereof onto a photoconductive film, phosphor particles therethrough and dry electrophotographic screening process using them for a CRT.
BACKGROUND OF THE INVENTION
Referring to
FIG. 1
, a color CRT
10
generally comprises an evacuated glass envelope consisting of a panel
12
, a funnel
13
sealed to the panel
12
and a tubular neck
14
connected by the funnel
13
, an electron gun
11
centrally mounted within the neck
14
and a shadow mask
16
removably mounted to a sidewall of the panel
12
.
A three color phosphor screen
20
is formed on the inner surface of a display window or faceplate
18
of the panel
12
. The electron gun
11
generates three electron beams
19
a
or
19
b
. Said beams are directed along convergent paths through the shadow mask
16
to the screen
20
by means of several lenses of the gun
11
and a high positive voltage applied through an anode button
15
and being deflected by a deflection yoke
17
so as to scan over the screen
20
through apertures or slits
16
a
formed in the shadow mask
16
.
In the color CRT
10
, the phosphor screen
20
formed on the inner surface of faceplate
18
, as shown in
FIG. 2
, comprises an array of three phosphor elements R, G and B of three different emission colors arranged in a cyclic order of a predetermined structure of multiple-stripe or multiple-dot shape and a matrix of light-absorptive material surrounding the phosphor elements R, G and B. And a thin conductive film of aluminum
22
overlies the screen
20
in order to provide a means for applying the uniform potential applied through the anode button
15
to the screen
20
, increasing the brightness of the phosphor screen
20
, preventing ions from damaging the phosphor screen
20
and preventing from decreasing the potential of the phosphor screen
20
. And also, a resin film
22
′ such as lacquer film may be applied between the aluminum thin film
22
and the phosphor screen
20
to enhance the flatness and reflectivity of the aluminum thin film
22
. The resin or lacquer film
22
′ is to be ignited and volatilized off after that the aluminum thin film
22
have formed onto it.
In a photolithographic wet process, which is well known as a prior art process for forming the phosphor screen
20
, a slurry including phosphor particles such as phosphorus components for emission colors or light-absorptive materials is coated on the inner surface of the faceplate
18
. It does not, however, meet the higher resolution demands. Moreover, it requires a lot of complicated processing steps and a lot of manufacturing equipments, thereby necessitating a high cost in manufacturing the phosphor screen
20
. Also, it discharges a large quantity of effluent such as waste water, phosphor elements, 6th chrome sensitizer, etc., with the use of a large quantity of clean water.
Recently, to solve or alleviate the above problems of said photolithographic wet process, electrophotographic screening process is developed. In wet electrophotographic screening process, however, the above-mentioned problems remains unsolved. What solves or alleviates mostly the above-mentioned problems is the dry electrophotographic screening process.
U.S. Pat. No. 4,921,767, issued to Datta at al. on May 1, 1990, describes one method of electrophotographically manufacturing the phosphor screen assembly using dry-powdered phosphor particles. This invention, however, has some problems such that it requires dark environment during all the steps since the photoconductive layer is sensitive to the visual light, and that its energy consumption is so large because its fixing step comprises infrared radiation for fixing the deposited particles to the photoconductive layer.
The above problem is solved by forming the photoconductive layer with a solution sensitive to the ultraviolet radiation, which is suggested in other inventions assigned to the assignees of the present invention.
For such an example, our Korean patent application Serial No. 95-10420 filed in Apr. 29, 1995 and assigned to the assignees of the present invention describes “Method of manufacturing a screen of a CRT”, as is briefly explained in the following.
FIGS. 3A through 3E
schematically show various steps in the above-described manufacturing method.
FIG. 3A
represents a coating step that forms an electrically conductive layer
132
is formed on the inner surface of the faceplate
18
and overlies an photoconductive layer
134
on the conductive layer
132
.
The conductive layer
132
, for example, can be formed by conventionally applying a volatilizable organic conductive material consisting of about 1 to 50 weight % of a polyelectrolyte commercially known as Catfloc-c, available from Calgon Co., Pittsburgh, Pa., to the inner surface of the faceplate
18
in an aqueous solution containing about 1 to 50 weight % of 10% poly vinyl alcohol and drying the solution. Said conductive layer
132
serving as an electrode for the overlying photoconductive layer
134
. The photoconductive layer
134
is formed by conventionally applying to the conductive layer
132
, a novel photoconductive solution containing ultraviolet-sensitive material and by drying it.
An example of the ultraviolet-sensitive material can consist of 0.01 to 1 weight % of bis-1,4-dimethyl phenyl(-1,4-diphenyl(butatriene)) or 2 to 5 weight % of tetraphenyl ethylene as a donor, 0.01 to 1 weight % of at least one compound from the group including trinitro-fluorenon (TNF) and ethylanthraquinone (EAQ) as an accepter, 1 to 30 weight % of polystyrene (PS) as a polymeric binder, and balance with solvent such as toluene or xylene. The photoconductive solution is prepared by dissolving 0.01 to 1% by weight of the ultraviolet-sensitive material and 1 to 30% by weight of polystyrene as a polymeric binder in a suitable solvent such as toluene or xylene. The useful compounds as a polymeric binder also may comprise, addition to polystyrene, polyalphamethylstyrene (P&agr;MS) polymethylmethacrylate (PMMA) and polystyrene-oxalzoline copolymer (PS-OX), et cetera.
FIG. 3B
schematically illustrates a charging step, in which the photoconductive layer
134
is charged to a positive potential of less than 1 Volt, preferably above 700 volts by a corona discharger
3
b
. The charging step does not require a dark environment since the photoconductive layer
134
is sensitive to ultraviolet rays below about 450 nm of wave length.
FIG. 3C
schematically shows an exposing step. The shadow mask
16
is inserted in the panel
12
and the positively charged photoconductive layer
134
is selectively exposed through an ultraviolet-transmissive lens system
140
and apertures or slits
16
a
of the shadow mask
16
to the ultraviolet rays from a ultraviolet lamp
138
with each predetermined incident angle with respect t
6
each aperture or slit
16
a
. The charges of the exposed areas are discharged through the grounded conductive layer
132
and the charges of the unexposed areas remain in the photoconductive layer
134
, thus establishing a latent charge image in a predetermined array structure. This exposing step also does not require a dark environment since the ultraviolet rays are used. Three exposures with three different incident angles of the three electron beams, respectively are required for forming a light-absorptive matrix.
FIG. 3D
diagrammatically illustrates the outline of a developing step. In conventional developing step of the process such as U.S. Pat. No. 4,921,767, the charging of the dry-powdered particles such as phosphor particles or light-absorptive material is executed by a triboelectrical charging method in which surface-treated carrier beads and phosphor particles, or the
McPherson John A.
Notaro & Michalos P.C.
Orion Electric Co. Ltd.
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