Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2001-04-11
2003-09-30
O'Shea, Sandra (Department: 2875)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S402000, C313S408000
Reexamination Certificate
active
06628058
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is relates to a flat CRT (Cathode Ray Tube), in particular to a flat tension mask type CRT which improves structures of a shadow mask and a panel.
2. Description of the Prior Art
In general, a cathode ray tube is for reproducing a received electric signal into a video signal, it is used for a video displaying apparatus such as a television, a monitor etc., and it is divided into a curved surface type and a flat type.
Between the above-mentioned CRT, the flat CRT which is superior than the curved CRT in the image distortion and outer light reflexibility aspects will now be described.
As depicted in
FIG. 1
, a general flat CRT
1
comprises a panel
13
, a funnel
14
, and an electron gun
17
.
The panel
13
comprises a fluorescent screen
11
constructed with red, green, blue stripes or dots shape fluorescent material, and a safety glass
12
adhered to the front surface by a resin as a hardening adhesion for preventing damage of the panel
13
due to durability lowering caused by the flat surface of the panel
13
.
In addition, a shadow mask
18
is fixedly formed on a rail
15
adhered to the back of the fluorescent screen
11
of the panel
13
by welding.
And, the funnel
14
as a vacuum bulb is fixedly formed on the rear of the panel
13
, the electron gun
17
for scanning an electron beam
16
is placed in a neck unit
14
a
of the funnel
14
, and a deflection yoke
21
for deflecting the electron beam
16
is installed on the outer circumference of the neck unit
14
a.
Particularly, as depicted in
FIG. 2
, the shadow mask
18
is fabricated as a very thin film having a thickness of about 25 &mgr;m in order to improve a transmittance of the electron beam
16
, and a plurality of through holes
19
are formed with a certain interval.
The plurality of through holes
19
are formed by an etching process in fabrication of the shadow mask
18
, as depicted in
FIG. 3
, an outlet size L
0
of the through hole
19
on the front surface is bigger than an inlet size L
1
of the through hole
19
on the inner surface.
Meanwhile, a vertical direction width between the through holes
19
on the shadow mask
18
is called as a bridge width W.
A video reproducing process of the above-described flat CRT will now be described.
As depicted in
FIG. 1
, the received electric signal is controlled, accelerated, collimated by a voltage applied to each electrode, and its orbit is adjusted to a horizontal direction or a vertical direction by a magnetic field of the deflection yoke
21
.
After that, as depicted in
FIG. 3
, the deflected electron beam
16
radiates the fluorescent material of the fluorescent screen
11
coated on the back of the panel
13
by passing through the through hole
19
of the shadow mask
18
, accordingly a picture is reproduced.
However, in the above-mentioned shadow mask
18
used for the conventional flat CRT, a rolling process is additionally required in order to fabricate the shadow mask
18
as a very thin film having a thickness of about 25 &mgr;m, deformation of the mask largely occurs in the etching process for forming the through hole
19
, an error such as a fracture etc. occurs in fabrication process of the flat CRT (Cathode Ray Tube), accordingly fabrication of the shadow mask is not easy, error rate in fabrication is high, handling is difficult, and the price is high.
In addition, in the conventional flat CRT, when the shadow mask
19
is fixed to the rail
15
, a rip etc. can occur due to a shear stress, because the heat quantity of the shadow mask
18
is small, a doming can occur due to collision of the electron beam and the electron beam can not land accurately on the fluorescent material, accordingly luminance and color vividness of the picture quality can lower.
Because of the above-mentioned problems, as depicted in
FIG. 4
, when the thickness t of the shadow mask
18
increases from (a) to (b), a size L
1
′ of the through hole on the inner surface can be fabricated as same with the size L
1
which is the size when the shadow mask
18
has a thickness t of 25 &mgr;m in fabrication of a through hole
19
′ of a shadow mask
18
′ with the etching process.
However, in the shadow mask
18
′, because of a problem from the fabrication technology point of view, a size L
0
′ of the through hole
19
′ on the front surface has to be a little smaller than the size L
0
when the shadow mask
18
has a thickness t of 25 &mgr;m.
Accordingly, in the shadow mask
18
′ having the increased thickness t′, the inner surface
19
a
′ from the inlet to the outlet of the through hole
19
′ is formed gently, and the bridge width W′ between the through holes
19
′ increases.
In order to improve the durability of the shadow mask
18
, when the thickness t increases, because the outlet size L
0
′ of the through hole
19
′ decreases due to a difficult point of the fabrication process of the through hole
19
′, the transmittance of the electron beam decreases.
It can be described as below table 1.
TABLE 1
Shadow Mask
Thickness (t)
Bridge Width (W)
Luminance of CRT (FL)
25 &mgr;m
0.027 mm
About 31.5 FL
50 &mgr;m
0.035 mm
About 30.4 FL
80 &mgr;m
0.038~0.040 mm
About 29.9 FL
As described in table 1, when the shadow mask
18
′ has a thickness of not less than 50 &mgr;m, because the outlet size L
0
′ of the through hole
19
′ decreases, the bridge width W′ increases. Herein, the electron beam transmittance of the shadow mask
18
′ decreases not less than 10%.
After all, when the thickness t increases in order to improve the durability of the shadow mask
18
, the electron beam transmittance decreases, the ratio of the electron beam
16
for radiating the red, green, blue fluorescent material of the fluorescent screen
11
decreases, accordingly the luminance as the brightness of the CRT lowers.
SUMMARY OF THE INVENTION
In order to solve above-mentioned problems, the object of the present invention is to provide a flat CRT (Cathode Ray Tube) which is capable of making fabrication and handling of a shadow mask easier by designing a panel so as to get an appropriate luminance while increasing a thickness of the shadow mask, and improving a picture quality by heightening the final luminance of the CRT.
In order to achieve the object of the present invention, the flat tension mask type CRT in accordance with the present invention comprises a flat panel fixed to the front of a funnel, and a shadow mask fixed inside of the funnel with a certain distance from the panel, herein the shadow mask has a thickness of 50 &mgr;m~80 &mgr;m, and the panel has a transmittance of 47%~50%.
The flat tension mask type CRT has a luminance of not less than 31 FL, and the panel has a thickness of 13 mm~14.5 mm.
REFERENCES:
patent: 4565946 (1986-01-01), Barrett et al.
patent: 5532545 (1996-07-01), Okamoto et al.
patent: 5818156 (1998-10-01), Misono
patent: 6107729 (2000-08-01), Banno
patent: 6139996 (2000-10-01), Choi et al.
patent: 6246163 (2001-06-01), Matsudate et al.
patent: 6411025 (2002-06-01), Bae
Fleshner & Kim LLP
Krishnan Sumati
LG Electronics Inc.
O'Shea Sandra
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