FR2588693A1 - PLASMA PANEL - Google Patents

Abstract

PLASMA PANEL CONTAINING IN PARTICULAR A LAYER OF COLOR 4 ENAMEL COVERING THE REAR V3 ELECTRODES OF THE PANEL. SUCH A PANEL ALLOWS A BETTER CONTRAST.

Description

I 2588693

PLASMA PANEL

  The present invention relates to a plasma panel. It more particularly relates to the structure of a plasma panel and in particular the layers of enamel covering the faces

internal panel.

  Plasma panels are devices for displaying alphanumeric or graphic data. This display is therefore made in two dimensions and is obtained by combinations of zones

  or points on a surface made bright by appropriate commands

  prayed. A plasma panel is formed by a network of elementary cells, arranged in crossed lines and columns, so as to constitute a matrix screen controlled by two crossed networks of electrodes. The cells are filled with an ionized gas and are selectively addressable. Applying tension

  sufficient at the terminals of an elementary cell makes the gas lumi-

  nescent and produces one of the luminous points which was discussed previously. Plasma panels of the alternative type are those whose

structure is the simplest.

  In one embodiment, a plasma panel is constructed

  formed by two plates of insulating material, at least one being

  transparent so as to allow the observation of light points.

  These plates are located in parallel planes and carry on their internal faces two arrays of electrodes, which face each other and are orthogonal. They are positioned and sealed together to enclose a sheet of gas mixture at a pressure

  determined. The electrode networks are metallic and are iso-

  gas lines by dielectric layers. These are often made from enamel 15 to 30 micrometers thick covered with a thin layer, about one micrometer thick

  or less, evaporated magnesia. The enamel thus deposited is trans-

  parent. Plasma panels emit an orange-red light, the intensity of which always remains relatively modest. The luminance is average: at best a few tens of candela per square meter. Under these conditions, the contrast between the lit zones and the extinct zones may, if the ambient lighting exceeds a few hundred lux, become so low as to interfere with the readability of these panels. Various solutions are known to try to improve this

contrast.

  The simplest consists of depositing on the rear face of the panel, not visible to an observer, a layer of black paint or resin. This eliminates the stray light reflected behind the panel, without affecting the amount of useful light

issued.

  We can also provide for the addition on the front of the

  panel of an anti-reflective filter which allows to reduce noticeable-

  the ambient light reflected by the panel, without reducing

excessively useful light.

  One can also consider reducing the reflection by the metal electrodes. For example, aluminum or chromium electrodes are, from this point of view, less reflective than gold electrodes. It is a basic technological choice, including

  consequences go far beyond simply improving con-

traste.

  Another solution was also considered based on the notion

  color contrast, regardless of the light intensities

  neuses. We know in particular that red contrasts well with green, and that it is therefore a priori favorable to place, behind the panel, a green background, or even an electroluminescent background of

green color.

  The aforementioned solutions make it possible to obtain plasma panels that can be read even under illuminations greater than a thousand lux. However, they have the drawback of complicating the production of the panels, by adding additional operations such as painting, coating of resin, installation of the filter or the electroluminescent plate. The invention aims to improve the contrast of a panel to

  plasma while keeping the procedure simple.

  This is why the invention relates to a plasma panel comprising a first and a second plate of insulating material arranged in parallel planes and enclosing a layer of an ionized gas, the first plate bearing on its face in contact with the ionized gas. at least a first electrode, the second plate also carrying on its face in contact with the ionized gas at least a second electrode disposed opposite the first electrode, each of the two electrodes being covered with a layer of a dielectric material; the second plate and the

  layer of dielectric material covering this second electro

  at least the trode being transparent, characterized in that at least the dielectric material covering the first electrode is a

colored enamel.

  The different objects and characteristics of the invention appear

  will appear in the description which follows made by way of example in

  referring to the appended figures which represent: - figure 1, an exploded view of an example of plasma panel according to the known art - figure 2, a sectional view of the panel of figure I; - Figure 3, a sectional view of an exemplary embodiment of the plasma panel according to the invention; Figure 4, an exploded view of an exemplary embodiment of a plasma panel according to the invention; Figure 5, a sectional view of the plasma panel of Figure 4;

4 2588693

  - Figure 6, a sectional view of an alternative embodiment of

  plasma panel according to the invention.

  Referring to Figures 1 and 2, we will first describe an embodiment of a plasma panel known in the art. This plasma panel is constituted by two glass plates 1 and 2 arranged in parallel planes. The plate I carries on its internal face 10 a network of vertical parallel electrodes VI, V2, V3. The plate 2 carries on its internal face 20, a network of horizontal electrodes HI, H2, H3, etc ... orthogonal to the electrodes VI, V2, V3. The electrodes, in gold or aluminum, can be produced by screen printing or photoengraving. They are distributed on each face 10 and 20 with a step of a few hundred micrometers. There are generally several hundred electrodes per network

of electrodes.

  The plates 1 and 2 are positioned and sealed together by means of a seal 3. The assembly of the two plates 1 and 2 and of the seal 3 defines a volume filled with a gaseous mixture at a determined pressure. The electrode networks are separated from the gas mixture by

  layers of dielectric material 4 and 5 from 20 to 25 micro-

  meters, for example, depending on the quality of the dielectric.

  The layers of dielectric material 4 and 5 are covered with a thin layer of a material, such as magnesia having the

  property of being a good emitter of secondary electrons (for

maintain the discharges).

  Putting under sufficient voltage a vertical electrode of the first plate 1, V1 for example, and a horizontal electrode of the second plate 2, H3 for example, determines the ionization of the gas located at the crossing point, called cell, two electrodes V1 and H3. An observer looking at the plate 2 in the direction indicated by the arrow F, as shown in FIG. 1, therefore sees a light point due to the ionization of the gas and

  this through plate 2 and layer 5.

  As described above, it is necessary to guard against parasitic reflections from plate 1 and

  vertical electrodes such as V1 of this plate.

  For this, the invention provides for covering the plate 1 and the vertical electrodes VI, V2, V3, etc. with a colored enamel 4 as shown in FIG. 3, the enamel 5 covering the face 20 of the

  plate 2 and the electrodes such as H3 being a transparent enamel.

  This is possible for example by adding to the usual enamel a

  pigment which, after baking, gives the enamel the desired color.

  Such enamels exist commercially. Their implementation (deposit and firing conditions) is similar to that of conventional transparent enamels, as well as their characteristics

physico-chemical and electrical.

  The invention thus makes it possible to improve the contrast due to the fact that the vertical electrodes such as VI of the plate 1 are hidden, the amount of ambient light that they would have been

  likely to reflect thus being diminished.

  By choosing for example a black enamel one will be able to note a reduction in the reflection of the stray light in a

proportion of 50 to 60%.

  This is how measurement results with black enamel made it possible to establish the following table:

Type Email Reflection Coeffi-

  Electro-panel cient of. Contrast

or trans-

parent 8.6% 0.24 black 3.5% 0.44

aluminum trans-

  parent 3.4% 0.64 black 1.8% 0.77 i In this table, the contrast coefficient is determined by the formula:

LON - LOFF

LON + LOFF

  in which: - LON = luminance of the lit points; - LOFF = luminance of the extinct points; These luminances being measured under an illumination which here is

of 1000 lux.

  It will be noted that in this table, the contrast coefficient was measured for an ambient lighting of 1000 lux, and in

  typical panel supply conditions.

  The contrast of the lit cells is thus notably improved. Furthermore, the screen of the invention allows a simple realization without additional step thus eliminating the need for

  color, by painting for example, the face 10 of the plate 1.

  Another advantage of the invention lies in the fact that the presence of a colored enamel makes it possible to improve the readability by the use of color contrasts. The choice of dye is then important and a green dye will in many cases allow a better reading. Depending on the type of application, ergonomic and aesthetic advantages may result from the choice of dye. It is also possible, according to the invention, to provide for the enamel layer 4, an opalescent enamel which reduces the reflections of light on the vertical electrodes V1, V2, V3 while allowing light to be diffused. Such opalescent enamel can constitute a projection screen on which to project an image such as a card or the like, with the advantage of not introducing parallax. The projection can be done directly on the plasma panel in reflection, from the front of the panel, or in transmission from the rear of the panel. In certain application cases, it will also be advantageous to provide for the enamel layer 4 several zones each covered with an enamel of a particular color, which will make it possible to

  display various display areas on a display device

  chage for viewing specific information. According to an exemplary embodiment of a plasma panel, the deposits of enamel layers 4 and 5 are produced so as to obtain smooth surfaces. A panel is thus obtained as represented by the exploded view of FIG. 4 and the sectional view of FIG. 5 in which we find the layer of colored enamel 4 and the layer

transparent enamel 5.

  Finally, according to a variant of the invention, provision is also made to color the enamel layer 5 deposited on the face 20 of the plate 2

  and on the horizontal electrodes HI, H2, H3, etc ...

  In particular, in certain applications, it may be useful

  to hide parts of the panel from an observer

  looking at plate 2 of the panel in direction F. More particularly

  Lier, it is known to provide in the panel discharges called "conditioning" to create ionization and

  facilitate the lighting of cells (crossing points between elect

  vertical and horizontal trodes). These condition discharges-

  They operate continuously and take place in areas of the panel where no useful information should be displayed. These zones will advantageously be provided at the periphery of the plasma panel. However, the permanent lighting of the cells in these areas

  conditioning discomfort the observer for reading the information

  displayed on the panel. A mask or a frame is therefore generally provided on the outside of the panel between

  the observer and the panel. However, a parallax due to the thick-

  plate 2 sister may exist and an observer may be

  nevertheless hampered by the light emitted by the condition zones-

  ment. According to the invention, provision is made to color the enamel layer 5 in the zones 7 corresponding to the conditioning zones, as shown in FIG. 6. In this way the enamel layer 7 provides masking having the advantage of '' be free from any parallax effect because the enamel is in direct contact with the conditioning discharge areas. The pigment incorporated in the enamel 5 will preferably color the enamel in black.

Claims (10)

  1. Plasma panel comprising first and second plates (1 and 2) of insulating material arranged in parallel planes and enclosing a layer of an ionized gas (6), the first plate (1) bearing on its face (10 ) in contact with the ionized gas (6) at least a first electrode (VI), the second plate (2) also bearing on its face (20) in contact with the ionized gas (6) at least a second electrode (H3) arranged opposite the first electrode (V1), each of the two electrodes being covered with a layer of dielectric material (4, 5), the second plate (2) and the layer of dielectric material (5 )   covering this second electrode (H3) at least being trans-   related, characterized in that at least the dielectric material (4)   covering the first electrode (VI) is a colored enamel.   2. Plasma panel according to claim 1, characterized in that the colored enamel (4) covers the first electrode (VI) as well as the face (10) of the first plate (1) which carries this electrode (VI). 3. Plasma panel according to claim 1, characterized in   that the colored enamel (4) is opaque to visible light.   4. Plasma panel according to claim 1, characterized in   that the colored enamel (4) is black.   5. Plasma panel according to claim 1, characterized in   that the colored enamel (4) is green.   6. Plasma panel according to claim 1, characterized in   that the enamel (4) is colored in opalescent white.   7. Plasma panel according to claim 1, characterized in that the face (10) of the first plate (1) has different   areas each covered by an enamel of a particular color.   8. Plasma panel according to claim 1, characterized in that the face (20) of the second plate (1) has different   areas each covered by an enamel of a particular color.   9. Plasma panel according to claim 8, characterized in that said different zones are covered by an enamel   opaque emitted by the ionized gas (6).   10. Plasma panel according to claim 8, comprising at least one conditioning zone (7), characterized in that the face (20) of the second plate (2) comprises, according to said conditioning zone (7), a layer of enamel (5) opaque to light emitted by the ionized gas (6).