Shadow mask for cathode ray tube

Details Shadow mask for cathode ray tube Shadow mask for cathode ray tube

2000-02-03

2002-08-13

Day, Michael D. (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Shadow mask, support or shield

C313S407000

Reexamination Certificate

active

06433467

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a shadow mask for a cathode ray tube (CRT) and, more particularly, to a shadow mask which has a sufficient degree of structural strength.
DESCRIPTION OF THE RELATED ART
Generally, CRTs are provided with a color selection shadow mask for ensuring the correct landing of electron beams on a phosphor screen.
FIG. 12
is a cross sectional view of a CRT with a shadow mask according to a prior art, and
FIG. 13
is a perspective view of the shadow mask shown in FIG.
12
.
As shown in
FIG. 12
, the CRT includes a faceplate panel
3
with an inner phosphor screen
1
, and a funnel
5
and a neck
7
sequentially connected to the panel
3
. An electron gun
9
is fitted within the neck
7
to emit R, G and B electron beams. A shadow mask
11
is mounted within the panel
3
while facing the phosphor screen
1
at a close distance. The shadow mask
11
is fixed to the panel
3
by interposing a mask frame
13
. The shadow mask
11
has a plurality of beam-guide apertures
11
a
that make it possible for each of the R, G and B electron beams to strike only its intended phosphor on the phosphor screen
1
.
As shown in
FIG. 13
, the shadow mask
11
is formed with a beam-guide portion
11
b
where the aforementioned apertures
11
a
are placed, a non-opening portion surrounding the beam-guide portion
11
b
, and a side wall
11
c
bent from the non-opening portion at an angle. The side wall
11
c
of the shadow mask
11
is welded to the mask frame
13
such that the beam-guide portion
11
b
faces the phosphor screen
1
at a close distance. The distance between the beam-guide portion
11
b
of the shadow mask
11
and the phosphor screen
1
is usually called the “Q value”.
In order to constantly maintain the Q value, the beam-guide portion
11
b
of the shadow mask
11
is curved with a curvature radius corresponding to that of the internal surface of the panel
3
where the phosphor screen
1
is formed. In this connection, as the panel
3
becomes flatter and flatter, the curvature radius of the effective screen portion
11
b
should be increased as much,.
When the curvature radius of the beam-guide portion
11
b
increases to a large extent, its mechanical strength is seriously deteriorated. Furthermore, considering that the shadow mask
11
is formed with an extremely thin metal plate where numerous apertures
11
a
are located, the beam-guide portion
11
b
of the shadow mask
11
exhibits extremely weak structural strength.
In the above structure, the beam-guide portion
11
b
of the shadow mask
11
is liable to suffer deformation even at minimum degrees of vibration or shock. In this case, the apertures
11
a
formed at the beam-guide portion
11
b
deviate from their proper positions so that the electron beams cannot strike correct phosphors on the phosphor screen
1
, and this deviation results in poor picture images.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a shadow mask for a CRT which has a sufficient degree of structural strength, and produces good picture images.
This and other objects may be achieved by a shadow mask for a CRT having a faceplate panel with an inner phosphor screen. The shadow mask includes a front surface and a side wall. The front surface is formed with a beam-guide portion having a plurality of apertures, and a non-opening portion surrounding the beam-guide portion. The side wall is bent from the non-opening portion at an angle, and fixed to the panel via a mask frame. The front surface of the shadow mask has a predetermined waved pattern in at least one direction.
The predetermined wave pattern of the front surface is structured to satisfy the following condition:
-
0.03
<
Δ
⁢
 
⁢
Q
Q
<
+
0.03
where Q indicates the average distance between the front surface and the phosphor screen, and &Dgr;Q indicates the difference between the actual distance of the aperture of the shadow mask to the phosphor screen and the average distance between the front surface and the phosphor screen.


REFERENCES:
patent: 4072876 (1978-02-01), Morrell
patent: 4280077 (1981-07-01), Villanyi
patent: 5384511 (1995-01-01), Fujimura

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