Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
1999-05-19
2001-01-30
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S113000
Reexamination Certificate
active
06181061
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. 4
is a cross-sectional view schematically showing a conventional flat image display device. As shown in
FIG. 4
, the conventional image display device comprises a front glass case
21
having a phosphor screen
22
on an inner surface thereof and a rear case
23
. The front glass case
21
and the rear case
23
are hermetically sealed by frit glass at a sealing portion
25
. Within an airtight chamber
24
are provided a cathode board
26
having cathodes facing the phosphor screen
22
for emitting electrons and a collector electrode
27
for collecting electrons emitted from the cathodes. As shown in
FIG. 4
, the electrode board
26
is supported by a plurality of support columns
28
fixed to the inner surface of the rear case
23
to face the phosphor screen
22
.
FIG. 5
is an enlarged cross sectional view schematically showing a broken line part
30
of FIG.
4
. In
FIG. 5
, a reference numeral
31
denotes a cathode (for instance, a conical cathode) for emitting electrons. A plurality of cathodes are orderly arranged in matrix form so that the cathodes correspond to the phosphor dots composing the phosphor surface
22
. In
FIG. 5
, a reference numeral
32
denotes a cathode electrode for applying a voltage to the cathodes
41
, a reference numeral
33
denotes an insulating layer, and a reference numeral
34
denotes a gate electrode. Although the cathodes
31
in
FIG. 5
are field emission type, they may be replaced with thermionic emission type cathodes.
In the above-described image display device, the electrons are emitted from the desired cathodes
31
when a predetermined negative voltage is applied to the cathode electrode
32
and a predetermined positive voltage is applied to the gate electrode
34
. The emitted electrons are converged by electrostatic lens effect of the penetrating hole
27
a
formed in the collector electrode
27
, and impinge on a metal back layer (not shown) provided on the phosphor surface
22
and to which a high voltage (e.g., +10kV) is applied. As a result, the phosphor dots of the phosphor screen
32
emit light to form an image. At this time, a considerable amount of heat is generated due to the electron emission in case of the field emission type or current flowing wiring an resistance in case of thermionic emission type.
However, in the above-described conventional image display device, since a high vacuum is maintained in the picture tube, there is no heat dissipation such as convection. Therefore, considerable heat is accumulated in the cathode board
6
to make it high temperature. The thermal expansion of the cathode board
6
makes the problems that a relationship between the electron emission points in the cathode
31
and pixels of the phosphor surface
22
is changed. 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 case of too excessive thermal expansion of the cathode board
6
, it may be broken.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image display device having high thermal radiation from the cathode board.
According to the present invention, an image display device comprises a front case provided with a phosphor screen on an inner surface thereof; a rear case fixed to the front case so that the front case and the rear case are hermetically sealed to form an airtight chamber therebetween; a cathode board including a cathode which is disposed within the airtight chamber and faces the phosphor screen; and a black surface treatment film disposed on at least one of a surface of the cathode board on a side of the rear case and an inner surface of the rear case.
REFERENCES:
patent: 5497046 (1996-03-01), Van Gorkom et al.
patent: 5910705 (1999-06-01), Cathey et al.
patent: 5-205668 (1993-08-01), None
Mitsubishi Denki & Kabushiki Kaisha
Patel Ashok
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