Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
2000-11-06
2003-05-20
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C313S461000, C220S00210A
Reexamination Certificate
active
06566802
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display panel for a cathode ray tube, and more particularly to a display panel for a cathode ray tube which has a panel structure approximate to a completely-flat panel structure in accordance with a correction of radiuses of curvature at inner and outer surfaces thereof while being capable of reducing a breakage thereof resulting from an in-furnace thermal impact in accordance with an optional variation in the compressive stress distribution exhibited therein.
2. Description of the Related Art
Referring to
FIG. 1
, an example of a typical cathode ray tube is illustrated. As shown in
FIG. 1
, the cathode ray tube includes a panel
10
mounted to a front portion of the cathode ray tube and made of a glass material, a shadow mask
12
arranged in rear of the panel
10
and adapted to allow electron beams to be accurately projected onto desired portions of a fluorescent film formed on an inner surface of the panel
10
, and a frame
14
for supporting the shadow mask
12
. The frame
14
is mounted to the panel
10
by means of stud pins
16
fixed to the panel
10
and springs
18
mounted to the frame
14
. The springs
18
are coupled to the stud pins
16
, respectively, thereby coupling the frame
14
to the panel
10
. The cathode ray tube also includes a funnel
20
coupled to a rear end of the panel
10
at a front end thereof and adapted to maintain the interior of the cathode ray tube in a vacuum state, a cylindrical neck
22
connected to a rear end of the funnel
20
and made of a glass material, and an electron gun (not shown) fitted in the neck
22
and adapted to emit an electron beam. The cathode ray tube further includes an inner shield
26
mounted to a peripheral end of the frame
14
and adapted to shield an external magnetic field, a deflection yoke
28
mounted around the rear end of the funnel
20
and adapted to deflect the electron beam emitted from the electron gun, and a band
30
fitted around jointed portions of the panel
10
and funnel
20
.
FIG. 2
a
illustrates the case in which the panel
10
has a panel structure for general screens. In this case, the panel structure of the panel
10
has a certain curvature at an outer surface thereof.
FIG. 2
a
illustrates the case in which the panel
10
has a flat panel structure. In the case of
FIG. 2
b,
the outer surface of the panel
10
is flat.
In either case, the panel
10
has, at the inner surface thereof, a face part
10
a
provided with a fluorescent film consisting of red, green, and blue dot trios of a fluorescent material to form an effective region for displaying an image, a central part
10
b
arranged at a central coordinate portion of the face part
10
a,
and a skirt part
10
c
arranged around the face part
10
a.
The skirt part
10
c
includes corner parts
10
d
and a seal edge part
10
e
coupled to the funnel
20
.
In the general panel structure of
FIG. 2
a,
an image displayed onto the screen is viewed in a convex state because of curved inner and outer surfaces of the panel. Furthermore, this panel structure also involves a diffused reflection of external light resulting in an increased fatigue of viewers.
The flat panel structure of
FIG. 2
b
can eliminate the problems involved in the panel structure of
FIG. 2
a
in that it is flat, thereby avoiding a phenomenon that an image displayed onto the screen is viewed in a convex state, and that it reduces the fatigue of viewers. However, this flat panel structure involves a thermal breakage of the panel resulting from an insurance of structural strength for the shadow mask.
To this end, in order to improve the surface strength of the panel
10
having the flat panel structure, a proposal has been made, in which a compressive stress layer is formed at the surface of the panel to avoid a thermal breakage of the panel due to heat generated during the manufacture of the cathode ray tube.
Meanwhile, a method has also been proposed, in which a high stress is temporarily generated at the panel
10
. An example of such a method is a method for cooling the panel
10
to an annealing point or less. In accordance with this method, a thermal distribution is exhibited in the panel not only in a thickness direction, but also in a plane direction perpendicular to the thickness direction, due to a thermal distribution resulting from a three-dimensional structure of the panel and a cooling of the panel by air.
In particular, the cooling of the panel
10
at the corner parts
10
d
in accordance with a general cooling process tends to be carried out at a slow rate, as compared to the cooling of the panel
10
at the central part
10
b,
due to an influence of the three-dimensional structure of the panel
10
.
In accordance with this process, a higher temperature gradient and a high stress are exhibited in the thickness direction at a higher cooling rate of the panel
10
. Under this condition, the stress exhibited at the corner parts
10
d
of the panel
10
is less than that exhibited at the central part
10
b.
Accordingly, the panel
10
, which is physically reinforced, exhibits a stress distribution in which the reinforced stress exhibited around each corner part
10
d
is lower than that exhibited at the central part
10
b,
and the reinforce stress exhibited at the inner surface of the face part
10
a
is lower than that exhibited at the outer surface of the face part
10
a.
Due to such a stress distribution, the panel
10
exhibits a degraded effect of preventing a thermal breakage from occurring during the manufacture of the cathode ray tube.
The conventional panel has a certain curvature at inner and outer surfaces thereof so that they have a desired structural strength, as shown in FIG.
2
. By virtue of such a curvature, the panel also has, at each panel corner part
10
d
thereof, a thickness corresponding to 130% or less of the thickness of the central part
10
b.
As a result, the panel involve a greatly reduced in-furnace thermal breakage. In the case of a panel having a radius of curvature corresponding to 50,000 mm or more at the outer surface thereof while having a certain radius of curvature at the inner surface thereof, which is so called a “flat panel”, as shown in
FIG. 2
b,
however, the thickness of each panel corner part
10
d
should be 170% or more of the thickness of the central part
10
b
in order to maximize the structural strength of the shadow mask
12
. Due to such an abrupt increase in thickness, the panel
10
has a very undesirable structure in association with a breakage thereof, even though it makes it possible to maintain a desired strength of the shadow mask
12
.
In order to solve this problem, it is necessary to considerably compress the surface of the panel
10
. However, the in-furnace thermal breakage problem cannot be completely solved only using this method.
This is because an abrupt increase in thermal stress, which may result in an insolvable in-furnace thermal breakage is exhibited when the thickness difference, that is, the wedge rate, between the central part
10
b
and corner part
10
d
of the panel
10
is 230% or more. In the manufacture of a cathode ray tube, such a high thermal stress results in an in-furnace thermal breakage of the cathode ray tube. In order to minimize such a phenomenon, it is necessary to make a huge investment in order to achieve an improvement in furnace temperature. A great reduction in productivity is also involved, which results in a great increase in manufacturing costs.
The most effective method for preventing an in-furnace thermal breakage is to minimize the stress difference among the central part
10
b,
face part
10
a,
corner parts
10
d,
and seal edge part
10
e
of the panel
10
.
Korean Patent Laid-open Publication No. 98-71757 discloses a technique in which compressive stresses are optionally provided at desired portions of a panel, respectively, so that the panel can be designed to have a reduced thickness while ensuring a security against explosions, in order to
Fleshner & Kim LLP
LG Electronics Inc.
Patel Ashok
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