Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2002-12-12
2004-12-07
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S402000
Reexamination Certificate
active
06828716
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a shadow mask for a color cathode ray tube, and more particularly to a shadow mask for a color cathode ray tube having a modified shape and arrangement of slits, and embossments of a skirt portion of the shadow mask.
2. Description of the Related Art
As a main element for realizing pictures in a picture display apparatus such as a television receiver or a computer monitor, a color cathode ray tube (CRT) is a device for realizing color pictures by emitting light from fluorescent substance in a fluorescent screen including R, G and B fluorescent substance patterned in an inner side of a panel, which is a front body of the CRT, by means of electron beam controlled by picture signals.
FIG. 1
is a partial sectional view showing a structure of a general color CRT.
Referring to
FIG. 1
, the color CRT generally comprises a panel
1
having a roughly rectangular shape and arranged in the front of the color CRT and a funnel
2
having a roughly conical shape and arranged in the rear of the panel
1
.
In addition, in an inner space formed by the panel
1
and the funnel
2
, the color CRT further includes a fluorescent screen
4
for emitting light, an electron gun
12
provided within a neck
13
of the funnel
2
for projecting electron beam
6
for emitting light from the fluorescent screen
4
, a shadow mask
3
for selecting color so that light is emitted from the fluorescent screen
4
, a frame assembly
7
for supporting the shadow mask
3
by applying tension to it, a spring
8
for coupling the frame assembly
7
to the panel
1
, an inner shield
9
welded and fixed to the frame assembly
7
for shielding an external earth magnetic field, and a reinforcement band
11
for provided at a circumference of a side portion of the panel
1
for preventing an external impact.
In addition, outside the neck
13
of the funnel
2
is provided a deflection yoke
5
for deflecting the electron beam
6
projected from the electron gun
12
in various directions, i.e., up, down, left and right and 2, 4 and 6-pole magnets for correcting a traveling locus of the projected electron beam
6
so that the projected electron beam
6
is precisely hit on prescribed fluorescent substance for the purpose of preventing the badness of color purity.
Now, as a main element in connection with the present invention, the shadow mask
3
will be in detail explained.
FIG. 2
is a front sectional view of the shadow mask
3
.
Referring to
FIG. 2
, the shadow mask
3
made of thin metal film having a thickness of about 0.1 to 0.12 mm is a portion positioned opposite the fluorescent screen
4
. The shadow mask
3
is completed by punching a circle plate with a plurality of electron beam through holes
110
formed by an etching process into a prescribed shape, pressing the punched plate into a curve shape such that it has same curve as a screen of the panel
1
, and forming a skirt portion
130
to be welded to the frame assembly
7
by bending four sides of the curve shape by 90 degree.
Herein, the steps of pressing and bending are continuously performed in a single process.
Therefore, the shadow mask
3
includes a porous portion
100
having a curved shape, a nonporous portion
120
connected adjacent to the porous portion
100
and having a curved shape, and the skirt portion
130
bent backward from a periphery of the nonporous portion
120
.
In the shadow mask
3
formed as above, the so-called “spring back” due to a property of material is generated in the skirt portion
130
. Accordingly, the skirt portion is bent in a spaced direction from an outside direction. That is, when a specific time elapses after pressing the skirt portion
130
by use of a presser, the skirt portion
130
becomes wider at an initial position with a specific interval. Under such a condition, when the skirt portion
130
is fixed to the frame assembly
7
, a deformation due to the bend of the skirt portion
130
is generated in a part of the porous portion having the curved shape (hereinafter referred to as “a curved portion”) of the shadow mask
3
. In this way, as the skirt portion
130
becomes more widened, a support force for supporting the curved portion become more weakened, which results in decrease of a strength of the curved portion of the shadow mask
3
. In addition, due to a close pressing to the shadow mask
3
by an amount of the widened of the skirt portion, a repulsive force is applied to the curved portion, which results in a variation of a curvature of the curved portion.
As a solution for the above problems, Korean patent application No. 10-1998-0008030 (published on Nov. 25, 1998, with publication No. 1998-0080110) is disclosed, which will be explained below.
FIG. 3
is a side sectional view of long and short sides of a shadow mask in the published patent application.
Referring to
FIG. 3
, a skirt portion (
130
in
FIG. 2
) of the shadow mask has a plurality of pairs of embossments
200
and
300
and slit
210
and
310
having a prescribed shape and formed alternately in parallel, with one of the plurality of pairs of embossments positioned at both sides on the basis of central lines of the long and short sides.
By absorbing surplus material remaining after performing the steps of pressing and bending the shadow mask, the slits
210
and
310
and the embossments
200
and
300
formed in the skirt portion
130
are intended to substantially reduce a tendency of returning to an initial shape of the skirt portion
130
, reduce a curl generated in the skirt portion
130
, and minimize the occurrence of curl into a comparatively small region over the whole periphery of the skirt portion.
As shown in
FIG. 3
, however, the slits
210
and
310
and the embossments
200
and
300
in the skirt portion
130
of the conventional shadow mask
3
are configured to be positioned erectly and alternately in parallel with a specific interval. Thus, since the erected slits
210
and
310
and the embossments
200
and
300
undertake all amount of curl of the skirt portion
130
generated in a crossing direction upon forming the shadow mask
3
, they do not have a strength sufficient to absorb a compression force applied upon forming the shadow mask, which results in excessive creases in the slits
210
and
310
and the embossments
200
and
300
and a deformation of contour of the curved shape of the shadow mask
3
.
Typically, after a CRT is manufactured using a conventional shadow mask
3
as shown in
FIG. 1
, the CRT is subject to various kinds of reliability tests including, particularly, a falling test as a strength test. The falling test is a test for checking whether the shadow mask is deformed when the CRT is fallen from a specific height.
If an impact on the fallen CRT is weak in the falling test, the shadow mask
3
returns immediately to its original state though it is slightly deformed. In contrast, if the impact is strong, the shadow mask
3
cannot return to the original state due to a deformation such as a distortion of a portion of its surface caused while it is largely vibrated up and down.
The above problem involves with various causes, particularly, a structure of the shadow mask
3
. In other words, the slits
210
and
310
and the embossments
200
and
300
in the skirt portion
130
of the shadow mask
3
cannot endure the impact in the falling test due to failure of a proper dispersion of load, which results in a serious deformation of the shadow mask.
When such a plastic deformation is generated in the shadow mask, the electron beam
6
emitted from the electron gun
12
can collide with the shadow mask since it cannot properly pass through the electron beam through holes of the shadow mask
3
, which results in a deterioration of the shadow mask. In addition, the electron beam
6
cannot properly hit the fluorescent substance on the fluorescent screen
4
of the panel
1
, which results in a badness of the picture on the screen and hence a deterioration of productivity.
In addition, for an aco
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