Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
2002-03-08
2004-09-28
Ngo, Hung V. (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C348S819000, C348S820000, C313S313000, C313S479000
Reexamination Certificate
active
06797876
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a panel grounding electrode and a display device, and more particularly, to a grounding electrode for providing electrical connection between a conductive coat and a grounding member such as a reinforcing band or a frame, the conductive coat having a low-reflection antistatic function or an unwanted radiation electric field leakage preventing function and being formed on a surface of a display area of a panel which constitutes an image display device such as a color cathode ray tube or a liquid crystal display panel, as well as to a display device which has an antistatic function or an unwanted radiation electric field leakage preventing function using such a grounding electrode.
There are image display devices such as various kinds of cathode ray tubes including color cathode ray tubes and flat panel displays including liquid crystal panels and cold cathode panels. Such an image display device has a conductive coat coated on at least the surface of its display area which constitutes its screen, for the purpose of preventing electrical-shock accidents or attraction of dust to its surface from being caused by static electricity which occurs on its display surface, or for the purpose of preventing an unwanted radiation electric field from leaking to the outside.
This conducive coat ordinarily has a low-reflection layer on its outermost surface and is also called a low-reflection antistatic film. The conductive coat prevents reflection of external light on the panel, and is electrically connected to grounding members of the device so that static electricity occurring due to the operation of the device is not accumulated in the conductive coat.
For example, a color cathode ray tube includes a vacuum envelope (glass bulb) which is made of a panel having phosphors, a neck which houses an electron gun, and a funnel which connects the panel and the neck, and provides image display by causing electron beams to scan the phosphor film applied to the inner surface of the panel. In the color cathode ray tube, a high-voltage anode voltage is applied to the phosphor film. For this reason, static electricity is induced on the surface of the panel and is accumulated at a high potential, and this static electricity gives adverse influences such as giving an electric shock to a user and attracting surrounding dust to degrade the quality of display images. In addition, there is a likelihood that the low-reflection antistatic film may be destroyed by a high-voltage electric field (unwanted radiation electric field) radiated during the operation of the display device or by discharge accompanying the on/off operation of its power source.
For this reason, the conductive coat is coated onto the surface of the panel, and is electrically connected to a reinforcing band which is a grounding member held at ground potential, by using a conductive member such as metal tape or conductive rubber.
Similarly, in a flat panel display such as a liquid crystal panel, a conductive coat coated on its panel is electrically connected to a frame positioned at the periphery of its display area, by using a conductive member similar to the aforementioned one.
The manner of conductive connection between the panel and the grounding member will be described below with reference to a color cathode ray tube by way of example.
FIG. 7
is a schematic view of the front of a panel portion of a color cathode ray tube, aiding in explaining the essential construction of the color cathode ray tube whose panel has a surface coated with a conductive coat, while
FIG. 8
is a schematic side view of the entire color cathode ray tube.
In
FIGS. 7 and 8
, reference numeral
1
denotes a panel which forms a screen serving as a display area, and the panel
1
has a surface coated with an antireflection film as well as a conductive coat
2
for preventing static charging and for preventing an unwanted radiation electrical field. Reference numeral
60
denotes a grounding tape (metal tape) made of a metal foil which serves as a grounding electrode. Reference numeral
4
denotes a reinforcing band for preventing implosion, which is tightly wrapped around the vicinity of a portion in which the panel
1
and a funnel are sealed together. Reference numeral
10
denotes a mounting support (lug or bracket) which is provided at each required position on the reinforcing band
4
. Reference numeral
11
denotes a neck which houses an electron gun. Reference numeral
12
denotes a funnel portion which connects the panel
1
and the neck
11
.
The surface of the panel
1
is coated with the conductive coat
2
made of a transparent conductive material, and the grounding tape (metal tape)
60
is stuck to both the conductive coat
2
and the reinforcing band
4
so that the conductive coat
2
is electrically connected and grounded to the reinforcing band
4
(for example, Japanese Patent Laid-Open No. 174945/1992).
The conductive coat
2
has a surface resistance of approximately 10-100 k&OHgr;/□ so that unwanted radiation electric fields leaking from the panel
1
can be reduced. For this reason, in the related art, in the case where the grounding tape
60
made of a metal foil is used as a grounding electrode, a discharge phenomenon occurs at the interface between the conductive coat
2
and the grounding tape
60
and the destruction of the conductive coat gradually proceeds, so that the reliability of electrical conduction is impaired.
Accordingly, to inhibit the destruction of the conductive coat, the conductive coat and the reinforcing band are connected together by a silicone resin which contains a conductive filler, instead of by the metal-foil grounding tape (Japanese Patent Laid-Open No. 83434/1990), or the conductive coat is subjected to ultrasonic soldering and the obtained solder portion and the reinforcing band are connected together by a conductive material such as metallic wire (Japanese Patent Laid-Open No. 286229/1989).
SUMMARY OF THE INVENTION
As described above, the construction in which the metal-foil grounding tape is used to provide connection between the conductive coat and the reinforcing band can realize a high work efficiency during its manufacturing process. However, in the case where the conductive coat has a multi-layer structure in which its outermost layer is an insulator, its electrical conduction becomes unstable. In the case of a conductive coat having a surface resistance of 100 k&OHgr;/□ or less, the destruction of the conductive coat due to discharge occurs.
In the case where the silicone resin (conductive silicone) which contains a conductive filler is used to connect the conductive coat and the reinforcing band, the destruction of the conductive coat due to discharge can be inhibited so that electrical conduction can be effectively ensured. However, the conductive silicone has the problems that its curing time after application is long and its handling until curing is not easy, and that its adhesion to the conductive coat after curing is good but the conductive silicone is difficult to remove during a recycle process and is inferior in work efficiency.
Furthermore, in the case of silicone having a high resistivity, in an antistatic film which includes a conductive coat having a surface resistance of several hundred &OHgr;/□ and is provided with a low-reflection function, it is impossible to fully utilize the low-resistance characteristic of the conductive coat, so that it is impossible to reduce leakage unwanted radiation electric fields which are minute alternating potentials.
Even in the method of subjecting the conductive coat to ultrasonic soldering and connecting the obtained solder portion and the reinforcing band together by a conductive material such as metal-foil grounding tape, if the surface resistance of the conductive coat is several hundred &OHgr;/□, the destruction of the conductive coat due to discharge occurs, and the conductive silicone is difficult to remove even during a recycle process.
Incidentally, the ab
Matsudate Noriharu
Nakagawa Atsuo
Milbank Tweed Hadley & McCloy LLP
Ngo Hung V.
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