Structure of panel in flat-type CRT

Details Structure of panel in flat-type CRT Structure of panel in flat-type CRT

2001-09-12

2003-12-23

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Envelope

C313S461000, C220S00210A, C220S00230A

Reexamination Certificate

active

06667570

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a structure of panel in flat-type CRT (Cathode Ray Tube), and more particularly, to a structure of panel in flat-type CRT, which is capable of improving implosion-proof properties of a flat-type CRT by effectively reducing the advance of cracks caused by an external shock and scattering of fragments resulting from the shock.
2. Description of the Related Art
In general, as shown in
FIG. 1
, a flat-type CRT (Cathode Ray Tube) includes: a panel
1
; a shadow mask
3
fixed on a rear surface of the panel
1
such that a tension is applied to the shadow mask
3
and having a plurality of apertures of round or slot type for selecting colors of an electron beam
6
; a magnetic shield
7
fixed on the inside of the panel
1
to prevent the path of electron beam
6
from being changed by an earth magnetic field or a leakage magnetic field; a funnel
2
fixed on the panel
1
by a frit glass and having a neck part formed integrally at a rear portion; an electric gun (not shown) inserted and sealed in the neck part of the funnel
2
for emitting the electron beam
6
of three colors, i.e., R, G and B colors; and a deflection yoke
5
mounted to wrap the external circumference of the neck part for deflecting the electron beam
6
.
Meanwhile, because the inside of the flat-type CRT may be easily damaged due to an external shock (being in a high vacuum condition), the panel
1
is designed to withstand atmospheric pressure.
Moreover, the panel
1
is divided into a face part
1
a
and a skirt part
1
b
. The skirt part
1
b
has a safety band
8
mounted to disperse stress applied to the flat-type CRT due to the high vacuum condition and to secure the shock resistance capacity.
When the flat-type CRT is operated, the electron beam
6
of the electric gun mounted in the neck part of the funnel
2
strikes a luminescence surface
4
formed on an inner surface of the panel by anode voltage applied to the flat-type CRT. The electron beam
6
is deflected in all directions by the deflection yoke
5
before reaching the luminescence surface
4
, and then it reaches the luminescence surface
4
.
At this time, the neck part has magnets
9
of bipolarity, tetrapolarity and hexapolarity at a rear portion for correcting an advance orbit in order for the electron beam
6
to strike a prescribed fluorescence body, thereby preventing staining that affects color purity.
Referring to
FIG. 2
a
, a structure of the panel of the flat-type CRT will be described hereinafter in more detail.
In general, the panel of the flat-type CRT has an outer surface (in the form of a plane) and a curved inner surface having a prescribed curvature. As shown in
FIG. 2
a
, the panel
1
is the thinnest in a center face thickness (hereinafter, called as a CFT) and becomes gradually thicker toward the outer circumference.
The outer circumference of the panel
1
has a discontinuous part generated during a molding process of the panel. The discontinuous part is a mold match line (hereinafter, called as a MML) and is the same form which a belt is bound around the outer circumference of a panel thereof.
At this time, a size of a mold match height (hereinafter, called as a MMH), which is a height from the MML to a front surface of the panel
1
, is larger than that of the CFT of the panel
1
.
Particularly, an opposite angle portion thickness (OAPT) of the panel
1
is designed to be thick 160% or more, compared with the CFT.
A height from an end of the skirt part
1
b
of the panel
1
to a front surface of the face part
1
a
is designated as an overall height (hereinafter, called as an OAH).
A manufacturing process of the panel of the conventional flat-type CRT will be described as follows.
In general, as shown in
FIG. 2
a
, the outer circumference of the panel
1
has prescribed angles &thgr;
1
and &thgr;
2
formed toward the face part
1
a
and the skirt part
1
b
respectively centering around the MML. Thus, in consideration of a slip of the mold, if only one external mold is used, the molding cannot be performed.
Therefore, as shown in
FIG. 2
b
, one internal mold
10
and two external molds
11
a
and
11
b
are combined and used.
Here, the external molds are divided into an upper external mold
11
a
and a lower external mold
11
b.
Therefore, when the panel
1
is molded, the upper and lower external molds
11
a
and
11
b
are matched to form an external form of the panel
1
. After a glass material of a prescribed amount is inserted into the external molds
11
a
and
11
b
, the internal mold
10
(to form the inner surface of the panel
1
) is lowered to a position where a prescribed interval between the internal mold
10
and the external molds
11
a
and
11
b
is maintained. The internal mold
10
is raised up after a predetermined period of time is passed.
At this time, the panel
1
must be formed to have a thickness sufficient to endure a predetermined vacuum pressure after the CRT is finished. The interval between the external molds
11
a
and
11
b
and the internal mold
10
must be set to have different intervals according to the standard of the panel
1
.
That is, the CFT of the panel
1
is determined by the interval between the center of the external molds
11
a
and
11
b
and the center of the internal mold
10
.
Because the cathode ray tube manufactured by the above method is made of the glass material and the inside of the cathode ray tube is in a vacuum condition, there is a danger of accidents and scattering of the fragments if cracks or implosion occurs due to an external shock. The safety band
8
made of a metal material is attached to the skirt part
1
b
of the panel
1
to prevent such danger.
The reason that the safety band
8
is attached to the skirt part
1
b
of the panel
1
is that the greatest tension stress caused by the vacuum is at the skirt part
1
b
and the scattering of the glass fragments is generated in the skirt part
1
b
as well.
Therefore, the safety band
8
is contacted to the skirt part
1
b
of the panel
1
apply sufficient tension to the safety band
8
.
At this time, the tension of the safety band
8
must be adequate not only for the skirt part
1
b
but also for the face part
1
a
of the panel
1
.
Conventionally, the safety band
8
, which is bent to correspond with the outer angles of panel
1
of lower portion of MML &thgr;
1
and with the outer angles of panel
1
of upper portion of MML &thgr;
2
, is used to transfer the sufficient tension to the face part
1
a
of the panel
1
.
However, there is a problem in that the tension of the safety band
8
is not applied sufficiently to the face part
1
a
in spite of the bent structure of the safety band
8
.
That is, as shown in the drawing, based on the MML, because a circumference of the skirt part
1
b
located at the lower portion of the MML is larger than that of the face part
1
a
located at the upper portion of the MML, when the safety band
8
wound in a heat expansion state is contracted while cooled, stronger tension is applied to the skirt part
1
b
, which has the outer circumference larger than that of the face part
1
a
, compared to the face part
1
a.
In the conventional panel
1
, as described above, because the tension is not sufficiently applied to the face part
1
a
of the panel
1
, the crack generated by shock easily advances to the inside of the panel
1
as shown in
FIG. 4
, and thereby the crack may be generated throughout the face part
1
a
of the panel
1
.
That is, in the structure of the conventional panel
1
, the MML located at the lower portion of the CFT does not effectively prevent the advance of a crack toward the inside of the panel, and thereby there is a limitation in that the panel
1
has stable implosion-proof properties.
Furthermore, to use the safety band
8
of the bent structure, equipment for bending a straight band must be prepared, and thus additional expenses for preparing the equipment are required. Moreover, a recovery rate of the product is lowered in comparison wit

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