Picture display device with emission-reducing means

Emission-reducing shield for a display, including two glass plates. A conducting layer is present on one of the glass plates. The layer is a continuous layer so that there is no Moire effect. The shield may also have an anti-static coating and an anti-reflection coating.

BACKGROUND OF THE INVENTION 
The invention relates to a picture display device provided with 
emission-reducing means which comprise two substantially parallel glass 
plates enclosing a thermoplastic material and an electrically conducting 
material. 
The invention also relates to a shield with emission-reducing means which 
is suitable for use in a picture display device, which means comprise two 
substantially parallel glass plates enclosing a thermoplastic material and 
an electrically conducting material. 
A device of this type is known from U.S. Pat. No. 4,381,421. This patent 
describes an electromagnetic shield for an electronic apparatus such as, 
for example a picture display device. The shield has two glass plates 
enclosing a metal gauze embedded in polyvinyl butyral (PVB). This gauze 
projects on the sides and is used for suspending the shield. Due to the 
presence of the metal gauze, the shield protects the internal part of an 
electronic apparatus from electromagnetic fields. This is necessary to 
ensure that neighboring apparatuses are not disturbed. 
The known picture display device has a considerable drawback. The 
electromagnetic shield present in this device exhibits the Moire effect. 
This produces troublesome patterns in the picture. Moreover, the gauze 
used is relatively expensive. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the invention to provide a picture display device 
comprising emission-reducing means which do not exhibit any Moire effect 
and are preferably inexpensive. 
According to the invention, the electrically conducting material is 
transparent. No Moire effect occurs when a transparent material is used. 
Hitherto, non-transparent means, necessarily in a gauze shape, have been 
used. This non-transparent gauze exhibits the Moire effect. 
The transparent electrically conducting material preferably comprises a 
layer which is vapor-deposited on one of the glass plates. An advantage 
thereof is that these emission-reducing means for the picture display 
device can easily be made and are therefore relatively inexpensive. If 
desired, the layer may also be provided on both plates. 
In accordance with a further embodiment, the vapor-deposited layer is a 
continuous layer. A layer of this type is easier to provide. 
In accordance with a preferred embodiment of the invention, the 
vapor-deposited continuous layer includes a metal. It has surprisingly 
been found that such a layer also shields infrared radiation. This 
embodiment is particularly suitable for use in a plasma display. In 
operation, this type of display produces strong electromagnetic fields and 
emits much infrared radiation, which has very detrimental effects on 
persons in the neighborhood of the display. 
Preferably, polyvinyl butyral (PVB) is present between the glass plates. 
The glass plates may be secured together with this material by means of 
heating and vacuum suction. The use of such a layer is an additional 
advantage when the electrically conducting material is a vapor-deposited 
layer. Such layers are generally very thin and the PVB protects the vapor 
deposited layer against damage. If the layer is not to be exposed to 
oxygen, the PVB also provides a satisfactory protection against this 
oxygen. 
The conducting material preferably comprises silver and tin oxide. This 
material has satisfactory electrically conducting properties and is 
readily available. 
If, in addition to a part with conducting material between the glass 
plates, the emission-reducing means also comprise another conducting part 
and if this part must be connected in a conducting manner to the 
conducting material between the glass plates (for example, for forming a 
Faraday cage), then this connection is preferably formed by means of a 
metal strip. This strip is partly present between the glass plates where 
it makes contact with the conducting layer. The projecting part is 
connected to the rest of the emission-reducing means. 
The emission-reducing means includes a shield which comprises two 
substantially parallel glass plates enclosing a thermoplastic material and 
an electrically conducting material, the electrically conducting material 
being transparent. The advantage of accommodating the transparent 
emission-reducing means in a separate shield is that it is usable for 
general purposes. A standard shield may be produced, which shield may 
subsequently be built into the cabinets of various types of picture 
display devices. 
These and other aspects of the invention are apparent from and will be 
elucidated with reference to the embodiments described hereinafter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a diagrammatic longitudinal section of a picture display device 
with a cathode ray tube, provided with emission-reducing means. This 
picture display device comprises a cathode ray tube (11) and an 
emission-reducing shield (1) in a cabinet (3). The cabinet (3) may 
comprise a conducting layer which, together with the conducting layer in 
the emission-reducing shield, constitutes the emission-reducing means. 
These two layers may be interconnected in a conducting manner by a metal 
strip (12) and constitute a closed space, also called Faraday cage. For 
the sake of clarity, all components which are not relevant in this case 
have been omitted. 
FIG. 2 is a diagrammatic longitudinal section of a plasma display provided 
with emission-reducing means. This display comprises a plasma display 
panel (2) and an emission-reducing shield (1) accommodated in a cabinet 
(3). The cabinet (3) may comprise a conducting coating which, together 
with a conducting coating in the emission-reducing shield, constitutes the 
emission-reducing means. These two layers may be interconnected in a 
conducting manner and constitute a closed space, also called a Faraday 
cage. For the sake of clarity, all components which are not relevant in 
this case have been omitted. 
FIG. 3 shows a part of a diagrammatic cross-section of an embodiment of 
emission-reducing shield according to the invention. A thermoplastic layer 
(7) of PVB is present between two glass plates (4, 5). A conducting layer 
(6) is vapor- deposited on one of the glass plates (4). The glass plates 
may have a thickness of, for example 2.8 mm and 1.2 mm, respectively. The 
PVB layer may have a thickness of 0.76 mm. The vapor-deposited layer has a 
much smaller thickness. 
FIG. 4 shows a glass plate (5) with an anti-reflection coating (8) and an 
anti-static coating (9). The panel in question had the following 
properties: 
surface area of 997.times.597 mm 
thickness of 3-4 mm 
(chemically) cured glass or security glass 
metal layer with a resistance per square of approximately 
3.OMEGA./.quadrature. 
grounded by metal contact all round 
infrared radiation (800-1000 nm) of less than 10% 
screening at the edge by rim of paint on the glass 
reflection of approximately 2.5% 
visual transmission of approximately 70-75% 
heat resistance up to 80.degree. C. 
The embodiments may of course have alternative dimensions. By varying the 
composition, other properties may also be obtained. 
FIG. 5 is a diagrammatic longitudinal section of a picture display device 
with a separate shield. A picture display panel (2) is accommodated in a 
cabinet (3). An emission-reducing shield (1) in a frame (10) is placed in 
front of the cabinet. For the sake of clarity, all components which are 
not relevant in this case have been omitted. 
In summary, the invention relates to an emission-reducing shield for a 
display, comprising two glass plates. A conducting layer is present on one 
of the glass plates. The layer is transparent so that there is no Moire 
effect. The shield may also have an anti-static coating and an 
anti-reflection coating.