Electric lamp and discharge devices – Cathode ray tube – Screen
Reexamination Certificate
2000-05-08
2003-01-28
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Screen
C313S473000, C313S466000
Reexamination Certificate
active
06512327
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a solution for making a resin film, a method for manufacturing a screen of a CRT using the solution and a CRT manufactured by the method, and more particularly to a solution for making a resin film, by which an aluminum thin film having an improved effective plane of reflection can be formed.
DESCRIPTION OF THE PRIOR ART
A known CRT screen and method of making a CRT screen will now be described with reference to
FIGS. 1-3E
, which illustrate the prior art.
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 an inner sidewall of the panel
12
. A three color phosphor screen is formed on the inner surface of a display window or faceplate
18
of the panel
12
.
The electron gun
11
generates three elect-on beams
19
a
or
19
b
, said beams being directed along convergent paths through the shadow mask
16
to the screen
20
by means of several lenses of the gun 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
, which is formed on the inner surface of the faceplate
18
, 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
21
surrounding the phosphor elements R, G and B, as shown in FIG.
2
.
A thin film of aluminum
22
or electro-conductive layer, overlying the screen
20
in order to provide a means for applying the uniform potential applied through the anode button
15
to the screen
20
, increases the brightness of the phosphor screen, prevents ions from the phosphor screen and prevents the potential of the phosphor screen from decreasing. And also, a resin film
22
′ such as lacquer is applied to the phosphor screen
20
before forming the aluminum thin film
22
, so as to enhance the flatness and reflectivity of the aluminum thin film
22
. The resin film
22
′ must be burned to volatilize after the aluminum thin film
22
is formed, so as to improve the life of the tube.
In a photolithographic wet process, which is well known as a prior art process for forming the phosphor screen, a slurry of a photosensitive binder and phosphor particles is coated on the inner surface of the faceplate. It does not meet the higher resolution demands and requires a lot of complicated processing steps and a lot of manufacturing equipments with the use of a large quantity of clean water, thereby necessitating high cost in manufacturing the phosphor screen. In addition, it discharges a large quantity of effluent such as waste water, phosphor elements, 6th chrome sensitizer, etc.
To solve or alleviate the above problems, an improved process of electro-photographically manufacturing the screen utilizing dry-powdered phosphor particles is developed.
U.S. Pat. No. 4,921,767, issued to Datta at al. on May 1, 1990, discloses the improved method of electro-photographically manufacturing the phosphor screen assembly using dry-powdered phosphor particles through a series of steps represented in
FIGS. 3A
to
3
E, as is briefly explained in the following.
After the panel
12
is washed, an electro-conductive layer
32
is coated on the inner surface of the faceplate
18
of the panel
12
and the photo-conductive layer
34
is coated thereon, as shown in FIG.
3
A. Conventionally, the electro-conductive layer
32
is made from an inorganic conductive material such as tin oxide or indium oxide, or their mixture, and preferably, from a volatilizable organic conductive material such as a polyelectrolyte commercially known as polybrene (1,5-dimethyl-1,5-diaza-undecamethylene polymethobromide, hexadimethrine bromide), available from Aldrich Chemical Co.
The polybrene is applied to the inner surface of the faceplate
18
in an aqueous solution containing about 10 percent by weight of propanol and about 10 percent by weight of a water-soluble adhesion-promoting polymer (poly vinyl alcohol, polyacrylic acid, polyamide and the like), and the coated solution is dried to form the conductive layer
32
having a thickness from about 1 to 2 microns and a surface resistivity of less than about 10
8
&OHgr;/□ (ohms per square unit).
The photo-conductive layer
34
is formed by coating the conductive layer
32
with a photo-conductive solution comprising a volatilizable organic polymeric material, a suitable photo-conductive dye and a solvent. The polymeric material is an organic polymer such as polyvinyl carbazole, or an organic monomer such as n-ethyl carbazole, n-vinyl carbazole or tetraphenylbutatriene dissolved in a polymeric binder such as polymethylmethacrylate or polypropylene carbonate. The photo-conductive composition contains from about 0.1 to 0.4 percent by weight such dyes as crystal violet, chloridine blue, rhodamine EG and the like, which are sensitive to the visible rays, preferably rays having wavelength of from about 400 to 700 nm. The solvent for the photo-conductive composition is an organic material such as chlorobenzene or cyclopentanone and the like which will produce as little contamination as possible on the conductive layer
32
. The photo-conductive layer
32
is formed to have a thickness from about 2 to 6 microns.
FIG. 3B
schematically illustrates a charging step, wherein the photo-conductive layer
34
overlying the electro-conductive layer
32
is positively charged in a dark environment by a conventional positive corona discharger
36
. As shown, the charger or charging electrode of the discharger
36
is positively applied with direct current while the negative electrode of the discharger
36
is connected to the electro-conductive layer
32
and grounded. The charging electrode of the discharger
36
travels across the layer
34
and charges it with a positive voltage in the range from +200 to +700 volt.
FIG. 3C
schematically shows an exposure step, wherein the charged photo-conductive layer
34
is exposed through a shadow mask
16
by a xenon flash lamp
35
having a lens system
35
′ in the dark environment. In this step, the shadow mask
16
is installed on the panel
12
and the electro-conductive layer
32
is grounded. When the xenon flash lamp
35
is switched on to shed light on the charged photo-conductive layer
34
through the lens system
35
′ and the shadow mask
16
, portions of the photo-conductive layer
34
corresponding to apertures or slits
16
a of the shadow mask
16
are exposed to the light. Then, the positive charges of the exposed areas are discharged through the grounded conductive layer
32
and the charges of the unexposed areas remain in the photo-conductive layer
34
, thus establishing a latent charge image in a predetermined array structure, as shown in FIG.
3
C. In order to exactly attach light-absorptive materials, it is preferred that the xenon flash lamp
35
travels along three positions while coinciding with three different incident angles of the three electron beams.
FIG. 3D
schematically shows a developing step which utilizes a developing container
35
″ containing dry-powdered light-absorptive or phosphor particles and carrier beads for producing static electricity by coming into contact with the dry-powdered particles. Preferably, the carrier beads are so mixed as to charge the light-absorptive particles with negative electric charges and the phosphor powders with positive electric charges when they come into contact with the dry-powdered particles.
In this step, the panel
12
, from which the shadow mask
16
is removed, is put on the developing container
35
″ containing the dry-powde
Lee Hyo Sup
Shin Dong Ky
Yoon Sang Youl
Notaro & Michalos P.C.
Orion Electric Co. Ltd.
Patel Vip
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