GB2261320A

GB2261320A - Light emitting panel

Info

Publication number: GB2261320A
Application number: GB9221372A
Authority: GB
Inventors: Neil Anthony Fox
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1991-11-05
Filing date: 1992-10-12
Publication date: 1993-05-12
Also published as: GB9221372D0

Abstract

A light-emitting panel has two glass plates (1 and 2) heat sealed around their edge to enclose two electrodes. The panel is evacuated through a port (20) which projects at right angles from the rear face of the lower plate (2) towards one edge. The port comprises a metal flange that supports a glass pipe (22) which is heat sealed after evacuation. <IMAGE>

Description

RADIATION-EMITTING PANELS AND THEIR MANUFACTURE This invention relates to radiation-emitting panels and their manufacture.

In many applications, it is desired to be able to produce even illumination over a large area, such as when back lighting instruments. Preferably, the illumination is of high intensity with a low power and heat dissipation whilst being compact and of light weight.

It can be important, such as in aircraft instrument applications, to have a back light with a minimum frame or margin so that even illumination is produced right up to the edge of the display, and so that the display area can be as large as possible for a given size of housing.

Fluorescent lighting, in which light is generated by photo-ionisation of a phosphor layer in a gas-discharge tube, is ideally suited to this, as far as the level of illumination and power dissipation is concerned. Where even illumination is required over a large area, however, it is necessary either to use several fluorescent tubes in parallel with one another or to use a tube that is bent, in an attempt to produce an even distribution of light. In WO 87/04562 there is described a display in which an arrangement of parallel tubes is reproduced in a flat panel by means of walls that divide the panel into separate discharge paths, each having their own electrode. A bent tube arrangement is similarly reproduced by walls defining a circuitous path between two electrodes.It is usually also necessary to use some form of diffuser in front of such arrangements to produce a more even illumination. This does still not produce illumination which is distributed sufficiently evenly for some applications because of the presence of the walls.

WO 87/04562 also describes a flat panel fluorescent device formed by two glass plates coated with phosphor on their facing surfaces. The plates are spaced from one another and sealed around their edges, the space between the plates being evacuated to a low pressure. Electrodes extend along opposite edges inside the space between the plates, so that discharge can be produced between them. The problem with this construction is that, because of the reduced pressure within the device, the plates must be relatively thick to be able to withstand the pressure differential across them. This leads to a device which is relatively heavy and bulky.

Proposals for supporting the opposite plates of the panel by internal structures have been described in J58-46568, GB 2217905, EP 0283014, WO 90/09676, GB 2247563, GB 2247977 and GB 2244855. The technique for manufacturing these panels involves sealing the edges of the plates together and then evacuating the space between the plates by pumping through an exhaust port in the form of a:glass pipe that projects from the edge of the panel in the plane of the panel. The glass pipe is then melted with a gas flame to seal it and the interior of the panel.

There are several problems with this technique and with panels made by the technique.

Because the pump pipe projects from the panel in the region of the seal between the plates, the heat used to melt and seal the pipe can damage the seal between the plates. It is convenient to mount the panel flat in a horizontal jig during assembly with the pipe also extending horizontally. When heat is applied to seal the pipe, it melts and bends down under the influence of gravity, leading to an unpredictable seal and shape. If the pipe moves under gravity this may cause it to move out of the gas flame and prevent an effective seal. This can be a particular problem with some kinds of glasses which become plastic on the initial application of heat but, once they have cooled and set, they remain crystalline in form even when heat is subsequently applied.With these forms of glass; therefore, a satisfactory seal must be achieved on the first attempt since otherwise the entire panel may have to be scrapped.

Panels made by evacuating through a pipe extending from the edge of the panel have disadvantages in that the pipe, after sealing, still forms a projection from the edge of the panel which increases its total width or height. In display applications where there is a limit on the maximum size of the display casing, this can lead to a reduction in the visible display area or a reduction in the evenness of illumination of the display. The remnants of the pump pipe projecting from the edge of the panel are also vulnerable to damage.

It is an object of the present invention to provide a radiation-emitting panel and a method of manufacture of such a panel that can be used to reduce these problems.

According to one aspect of the present invention there is provided a radiation-emitting panel including two plates enclosing a gas-discharge volume, electrodes arranged to effect a discharge within the volume, the plates being sealed together around their edge and at least one of the plates being transparent to radiation emitted by the discharge, and a sealable exhaust port by which gas in the panel can be evacuated during manufacture, the port being provided in a face of one of the plates and projecting at right angles to the plane of the panel.

In this way, the exhaust port can be spaced from the edge of the plates so that sealing the port by heat does not damage the edge seal of the plates. The port furthermore does not add to the dimensions of the panel across the plane of the panel.

The exhaust port preferably includes a glass pipe and may include a metal flange secured to the face of one of the plates, the glass pipe being secured to the flange. The exhaust port is preferably located towards one edge of the panel. The panel may include a plurality of support pillars extending between the two plates internally of the panel.

According to another aspect of the present invention there is provided a method of manufacture of a radiation-emitting panel including the steps of providing an upper transparent plate and a lower plate having a sealable exhaust port projecting at right angles from the lower face of the plate, sealing the lower face of the upper plate around its edge with the upper face of the lower plate, evacuating the space between the two plates through the exhaust port and subsequently sealing the exhaust port.

The exhaust port may include a glass pipe and the pipe be sealed by application of heat to melt the glass. The upper plate may be sealed to the lower plate by application of heat.

A light-emitting panel and its manufacture, in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view from above of the panel; Figure 2 is a sectional elevation view of the panel to a larger scale, along the line II - II of Figure 1 including an associated display and electronic circuit boards; and Figures 3 to 5 illustrate steps in the manufacture of the panel.

With reference to Figures 1 and 2, the light-emitting panel comprises upper and lower rectangular glass plates 1 and 2 which are both transparent to light. The upper surface 3 of the lower plate 2 is sealed to the lower surface 4 of the upper plate 1 around the edge 5 of the panel. The outer face 6 and 7 of both plates 1 and 2 is flat and plane, the lower face 7 of the lower plate being coated by a sputtered aluminium layer 8 which provides a reflective surface.

The lower, inner surface 4 of the upper plate 1 is flat, whereas the upper, inner surface 3 of the lower plate 2 is interrupted by an array of pillars 10. The pillars are square in section, being about lmm wide, and have vertical sides about lmm high. The pillars 10 are arranged in orthogonal rows and columns which extend parallel to the edges of the panel. Between adjacent rows and columns of pillars 10 there are channels that extend parallel to the rows and columns and which each have a floor 11 of V-shape in section.

The lower plate 2 has an exhaust port 20 through it located midway along its length towards the upper edge of the panel. The port 20 takes the form of a drilled hole 21 through the thickness of the plate 2 and a short glass pump pipe 22 aligned with the hole 21 which is sealed to the outer face 7 of the plate to extend at right angles from it. The pipe 22 is sealed with the hole 21 by means of an annular metal flange 23, such as of Nilo 48, which is sealed to the plate 2 by a ring 24 of glass. The pipe 22 extends within the neck of the flange 23 and is sealed closed near to the flange.

The space inside the panel between the pillars 10 contains a mixture of argon gas and mercury vapour or other gases at low pressure. The exposed surfaces inside the panel, that is, the flat lower surface 4 of the upper plate 1, the vertical surfaces of the pillars 10 and the floor 11 of the channels in the upper surface 3 of the lower plate 2, are coated with one or more layers 30 of phosphor which emit the desired radiation spectrum when caused to fluoresce by a gas-discharge. Discharge within the panel is effected by applying a high voltage between two electrodes 31 and 32 which extend into the panel through its edge and extend along the left and right sides of the panel. Light emitted from the phosphor layer 30 travels into the gas space between the plates 1 and 2 and into the glass itself underlying the phosphor.Light passes into the upper plate 1 either directly or indirectly, via the pillars 10, such as after reflection from the reflecting layer 8. In this way, even illumination is produced across the upper face 6 of the panel apart from a short region close to each electrode.

Locating the exhaust port 20 on the underside of the panel, ensures that there is no additional protrusion from the edge of the panel. This enables the effective area of the panel to be as large as possible so that, when used to illuminate a display, such as that shown marked 40 in Figure 2, the display may also be as large as possible. Because the gas port projects at right angles to the plane of the panel, it is not exposed to damage during assembly and maintenance to the same extent as previous panels having ports that project to the side. The exhaust port 20 can be further protected by circuit boards 50 which are commonly mounted below the display and backlight. The circuit boards 50 may each have an aperture 51 within which the gas port 20 is received.

The panel may be manufactured in the manner shown in Figures 3 to 5. Initially, the upper and lower plates 1 and 2 are brought together face-to-face, with the exhaust port 20 open. The two plates 1 and 2 are held together in a jig 50 which is inverted so that plate 2 is located above plate 1, with the plates horizontal and the exhaust port 20 extending vertically upwards. The jig 50 and assembly are placed in an oven 51 which is heated to cause the glass of the two plates 1 and 2 to flow into one another so that a seal is produced around the edge of the plates.

The assembly is then removed from the oven 51, the pump pipe 22 is connected to a vacuum pump 60 and the panel is evacuted to low pressure, as shown in Figure 4. The gas discharge mixture can then be admitted to the panel from a suitable supply 61.

The final step in manufacture is shown in Figure 5, in which a gas jet 70 is used to melt the pump pipe 22 and seal off the exhaust port. Heating of the pipe 22 in this way causes it to soften and flow. Because the pump pipe 22 is oriented vertically, any flow of material will be along the length of the pipe.

It can be seen that, because the exhaust port projects away from the edge of the panel, it is possible to heat seal it without damaging the seal of the edge of the panel. The vertical orientation of the pump pipe ensures that, as it melts, it flows in a predictable manner, producing a reliable seal.

Claims

1. A radiation-emitting panel including two plates enclosing a gas-discharge volume, electrodes arranged to effect a discharge within the volume, the plates being sealed together around their edge and at least one ofthe plates being transparent to radiation emitted by the discharge, and a sealable exhaust port by which gas in the panel can be evacuated during manufacture, wherein the port is provided in a face of one of the plates and projects at right angles to the plane of the panel,

2. A radiation-emitting panel according to Claim 1, wherein the exhaust port includes a glass pipe.

3. A radiation-emitting panel according to Claim 2, wherein the exhaust port includes a metal flange, wherein the flange is secured to the face of one of the plates, and wherein the glass pipe is secured to the flange.

4. A radiation-emitting panel according to any one ofthe preceding claims, wherein the exhaust port is located towards one edge ofthe panel.

5. A radiation-emitting panel according to any one ofthe preceding claims, wherein the panel includes a plurality of support pillars extending between the two plates internally of the panel.

6. A radiation-emitting panel substantially as hereinbefore described with reference to Figures 1 and 2 ofthe accompanying drawings.

7. A method of manufacture of a radiation-emitting panel including the steps of providing an upper transparent plate and a lower plate having a sealable exhaust port projecting at right angles from the lower face of the plate, sealing the lower face of the upper plate around its edge with the upper face of the lower plate, evacuating the space between the two plates through the exhaust port and subsequently sealing the exhaust port.

8. A method according to Claim 7, wherein the exhaust port includes a glass pipe, and wherein the port is sealed by application of heat to melt the glass.

9. A method according to Claim 7 or 8, wherein the upper plate is sealed to the lower plate by application of heat.

10. A method of manufacture of a radiation-emitting panel substantially as hereinbefore described with reference to Figures 3 to 5 of the accompanying drawings.

11. A radiation-emitting panel made by a method according to any one of Claims 7 to 10.

12. Any novel feature or combination of features as hereinbefore described.