Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
1999-04-12
2001-06-26
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S493000, C313S495000, C313S496000
Reexamination Certificate
active
06252349
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a flat image display device in which electrons emitted from a plurality of cathodes disposed on a cathode board impinge on a phosphor screen coated on an inner surface of a front glass case to display an image.
FIG. 12
is a cross-sectional view schematically showing a conventional flat image display device. As shown in
FIG. 12
, the conventional image display device comprises a front glass case
31
having a phosphor screen
32
on an inner surface thereof and a rear case
33
. The front glass case
31
and the rear case
33
are hermetically sealed by frit glass at a sealing portion
35
. Within an airtight chamber
34
are provided a cathode board
36
having cathodes facing the phosphor screen
32
for emitting electrons and a collector electrode
37
for collecting electrons emitted from the cathodes. As shown in
FIG. 12
, the cathode board
36
is supported by a plurality of support columns
38
fixed to the inner surface of the rear case
33
to face the phosphor screen
32
.
FIG. 13
is an enlarged cross sectional view schematically showing a broken line part
40
of FIG.
12
. In
FIG. 13
, a reference numeral
41
denotes a cathode (for instance, a conical cathode) for emitting electrons. A plurality of cathodes are orderly arranged in matrix form and corresponds to phosphor dots composing the phosphor surface
32
. In
FIG. 13
, a reference numeral
42
denotes a cathode electrode for applying a voltage to the cathodes
41
, a reference numeral
43
denotes an insulating layer, and a reference numeral
44
denotes a gate electrode.
In the above-described image display device, the electrons are emitted from the desired cathodes
41
when a predetermined negative voltage is applied to the cathode electrode
42
and a predetermined positive voltage is applied to the gate electrode
44
. The emitted electrons are converged by electrostatic lens effect of the penetrating hole
37
a
formed in the collector electrode
37
, and impinge on a metal back layer (not shown) provided on the phosphor surface
32
and to which a high voltage (e.g., +10 kV) is applied. As a result, the phosphor dots of the phosphor screen
32
emit light to form an image.
However, in the above-described conventional image display device, since the cathode board
36
is supported by the support columns
38
fixed to the rear case
33
, a deformation or inward warp of the rear case
33
occurring after ejection of gas from the airtight chamber
34
causes a deformation or warp of the cathode board
36
toward the phosphor screen
32
. As a result, a positional relationship between the cathodes
41
of the cathode board
36
and the phosphor dots of the phosphor screen
32
is changed, so the electrons emitted from the cathode electrodes
41
cannot impinge on the adequate phosphor dots, making it impossible to form an image of high quality.
Further, in the above-described conventional image display device, wiring of the lead lines
39
for applying the drive voltage to the cathodes
41
of the cathode board
36
is performed so that the lead lines
39
extend from the cathode board
36
through the sealing portion
35
to outside the case, while maintaining the insulating performance between the respective lead lines. This makes assembling the image display device very difficult.
Furthermore, in the above-described conventional image display device, since the outer and inner surfaces of the face portion
31
a
of the frond glass case
31
are flat, the face portion must be made thick in order to resist external atmospheric pressure. This, however, has caused a problem that an image is perceived as being floated near the edges of the face portion
31
a
and a displayed image is perceived concavely.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image display device that can prevent image deterioration due to a deformation of the rear case and that can be made by simplified process.
It is another object of the present invention to provide an image display device that can display an image which is perceived as being flat.
According to the present invention, an image display device comprises: a front case having with a phosphor screen on an inner surface thereof; a rear case facing the front case; a sealing portion with which the front case and the rear case are hermetically sealed so that an airtight chamber is formed between the inner surface of the front case and an inner surface of the rear case; and a cathode board including a cathode which is disposed within the airtight chamber and faces the phosphor screen, and a wiring pattern for applying a voltage to the cathode; wherein the cathode board is held between the front case and the rear case by the sealing portion so that the cathode board is not in contact with the inner surface of the front case and the inner surface of the rear case.
Further, the face portion of the front case may include a substantially flat outer surface facing a viewer and the inner surface on which the phosphor screen is coated; and the inner surface of the face portion may be concavely curved with a radius of curvature R
x
in a horizontal direction parallel to a side of the face portion. In this arrangement, the following conditions (1), (2) and (3) are satisfied:
R
x
≤
(
W
2
)
2
+
Δ
t
2
2
*
Δ
t
(
1
)
Δ
t
=
t
*
[
1
-
cos
2
θ
2
n
1
-
1
n
1
*
sin
2
θ
2
]
(
2
)
θ
2
=
tan
-
1
(
W
2
*
L
)
(
3
)
where W denotes a horizontal width of an effective picture area in the face portion, L denotes an optimum viewing distance, n
1
denotes a refractive index of the face portion, and t denotes a thickness of the face portion at a center thereof.
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patent: 5532545 (1996-07-01), Okamoto et al.
patent: 5536995 (1996-07-01), Sugawara et al.
patent: 6133686 (2000-10-01), Inoue et al.
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patent: 10214564 (1998-08-01), None
Inoue Akira
Iwasaki Yasuo
Mitsubishi Denki & Kabushiki Kaisha
Patel Vip
Quarterman Kevin
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