EP0968521B1 - Flat spotlight with discharge separated by a dielectric layer and device for the electrodes into the leading discharge area - Google Patents

Description

Technical area

The invention relates to a flat radiator according to the preamble of claim 1.

By the term "flat radiator" herein is meant radiators having a planar geometry that emit light, i. visible electromagnetic radiation, or also ultraviolet (UV) and vacuum ultraviolet (VUV) radiation.

Such radiation sources are suitable, depending on the spectrum of the emitted radiation, for general and auxiliary lighting, such as home and office illumination or backlighting of displays, such as LCDs (L iquid C rystal D isplays), for the transport and signal lighting, for the UV radiation, eg sterilization or photolytic.

These are flat radiators, which are operated by dielectrically impeded discharge.

In this type of radiator, either the electrodes of one polarity or all the electrodes, ie both polarities, are separated from the discharge by means of a dielectric layer (unilaterally or two-sided dielectrically impeded discharge, see, for example, US Pat WO 94/23442 respectively. EP 0 363 832 ). Such electrodes are also referred to below as "dielectric electrodes".

The dielectric layer may be formed by the wall of the discharge vessel itself by the electrodes being arranged outside the discharge vessel, for instance on the outer wall. An advantage of this embodiment with external electrodes is that no gas-tight Stromdurchführunggen must be passed through the wall of the discharge vessel. However, the thickness of the dielectric layer - an important parameter that influences, inter alia, the ignition voltage and the burning voltage of the discharge - determined essentially by the requirements of the discharge vessel, in particular its mechanical strength. Since the height of the required supply voltage increases with the thickness of the dielectric layer, the following disadvantages arise among others. In the first place, the voltage supply provided for the operation of the flat radiator must be designed for the higher voltage requirement. This is usually associated with additional costs and larger external dimensions. In addition, higher safety precautions for contact protection are required.

On the other hand, the dielectric layer may also be realized in the form of an at least partial cladding or layer of at least one electrode arranged inside the discharge vessel. This has the advantage that the thickness of the dielectric layer can be optimized for the discharge properties. However, internal electrodes require gas-tight current feedthroughs. As a result, additional manufacturing steps are required, which usually makes the production more expensive.

Usually, elongate electrodes of different polarity (anodes and cathodes) are arranged alternately next to one another, as a result of which surface-like discharge configurations with relatively shallow discharge vessels can be realized. Likewise, the anodes and cathodes may be disposed on different sides of the inner wall of the discharge vessel, for example, such that each face an anode and cathode. In addition, the electrodes are connected in pairs to the two poles of a voltage source. A particularly efficient method for operating radiators with dielectric electrodes is in WO 94/23442 described.

State of the art

From the DE-OS 195 26 211 a flat radiator is known, with the help of a series of separate from each other by pause times active power pulses - ie according to the operating method of WO 94/23442 - is operated. In the exemplary embodiments, strip-shaped electrodes are arranged, inter alia, on the outer wall of the discharge vessel.

In the EP 0 363 832 Among other things, a UV high-power radiator with strip-shaped electrodes is disclosed, which are arranged inter alia on the inner wall of the discharge vessel. About current feedthroughs for connecting the inner electrodes to a voltage source, however, are not included.

Usually, the inner electrodes of discharge lamps and radiators are connected to a wire-shaped or foil-like current supply. A bushing connects the power supply in the interior of the discharge vessel with external power supply lines, which in turn serve to connect to an electrical supply source. To ensure the gas tightness, the implementation must be closely surrounded on the one hand by the material of the discharge vessel. On the other hand, the materials of implementation, usually a metal or a metal alloy, and discharge vessel, such as glass or ceramic, sometimes very different thermal expansion coefficients. In order to avoid excessive mechanical stresses and consequently stress ruptures and cracks in the leadthrough area, the bushings become thinner, among other things Wires realized. However, this technique is limited to low amperages or lamp powers because the thin wires would otherwise burn through like a fuse. This disadvantage is known to be remedied by using a thin film, such as a 10-20 microns thick molybdenum foil in the sealing area of the implementation.

Due to the many individual parts as well as handling and manufacturing steps, the mentioned techniques are not very suitable for the automated production of flat radiators with a large number of electrode strips.

Presentation of the invention

It is an object of the present invention to provide a flat radiator with strip-like inner electrodes according to the preamble of claim 1, the current feedthroughs such that the flat radiator - largely independent of the size and thus the number of electrodes - in relatively few manufacturing steps and therefore inexpensive to produce is.

This object is solved by the characterizing features of claim 1. Particularly advantageous embodiments can be found in the dependent claims.

The term "strip-like electrode" or shortening "electrode strip" is here and below an elongated, compared to its length very thin structure to be understood, which is able to act as an electrode can. The edges of this structure need not necessarily be parallel to each other. In particular, substructures should also be included along the longitudinal sides of the strips.

The invention proposes to further form the inner strip-like electrodes themselves as feedthroughs including external power supply lines.

For this purpose, the discharge vessel is composed of a bottom plate and a ceiling plate, which are soldered, e.g. Glass solder, - possibly, but not necessarily, via an additional frame - are interconnected.

A frame may be dispensed with if at least one of the two plates is e.g. Trough-shaped is such that a discharge space is enclosed by the bottom and top plate.

The electrode strips are each guided at one end through the solder through gas-tight to the outside. The strips themselves are gas-tightly applied directly to the bottom plate and / or ceiling plate - similar to tracks on an electrical circuit board -, e.g. by vapor deposition, screen printing followed by baking or similar techniques. The seal of the implementation and the other components takes over the solder.

In this way, the inner electrodes, the bushings and outer power supply lines are produced quasi simultaneously in a common manufacturing step as functionally different subregions of a respective single cathode-side or anode-side layer-like interconnect structure. Compared to the prior art, the number of handling and manufacturing steps is significantly reduced. Another advantage of the invention is that it allows the cost-effective production almost arbitrarily large flat radiator, since said manufacturing section can be practically always realized independently of the size of the radiator.

Outside the discharge vessel, in a first simple embodiment, the electrode strips may terminate after the feed-through region in a number of external power supply lines corresponding to the number of electrode strips. Each electrode strip is thus considered to be a conductor track-like structure, which in each case comprises the three following, functionally different partial regions: inner electrode region, leadthrough region and outer current supply region.

This embodiment takes into account the fact that the mutual connection of the power supply lines of the same polarity for connection to the two poles of a voltage source and within a suitable connected between flat radiator and power supply terminal device, such as a specially adapted plug-cable combination, can be done.

In a second embodiment, the electrode strips of the same polarity pass into a common bus-like external power supply. In operation, these two external power supply lines are each connected to one pole of a voltage source. The advantage over the first embodiment is that can be dispensed with a specially adapted connector cable combination.

In order to keep mechanical stresses low due to different thermal expansions and to ensure gas tightness even in continuous operation, the materials for glass solder and frame as well as floor and ceiling tile are coordinated. In addition, the thicknesses of the tracks (electrode, bushing, power supply) are chosen so thin that on the one hand, the thermal stresses remain low and on the other hand, the current strengths required during operation can be realized.

In this case, a sufficiently high current carrying capacity of the conductor tracks is of particular importance insofar as the high luminous intensities desired for such flat radiators ultimately result in high current intensities. In particular, in flat fluorescent lamps for the backlighting of liquid crystal displays (LCD) is due to the low transmission of such displays of typically 6%, a particularly high light intensity indispensable. This problem is further exacerbated in the preferred pulsed mode of operation of the discharge, since during the relatively short duration of repetitive active power injection, particularly high currents flow in the conductor tracks. Only in this way is it possible to couple sufficiently high mean effective powers and thereby achieve the desired high intensity of light over the course of time.

In order to ensure the aforementioned high current carrying capacity, relatively thick conductor tracks are used. Too low interconnect thicknesses entail the risk of cracking due to local overheating of the printed conductors. The heating of the conductor tracks by the ohmic portion of the conductor track current is higher, the lower the cross section of the conductor tracks. But the width of the tracks are limited, among other things, because with increasing width, the shading of the luminous surface of the flat radiator through the tracks also increases. Therefore, rather narrow, but as thick as possible strip conductors are sought in order to solve the problem of cracking due to heat generation by high current densities in the interconnects. Typical thicknesses for conductive silver strips are in the range of about 5 microns to about 50 microns, preferably in the range of about 5.5 microns to about 30 microns, more preferably in the range of about 6 microns to about 15 microns.

Demnach ist die Dehnungsgrenze umso geringer, je größer die Schichtdicke ist. Außerdem wächst mit zunehmender Schichtdicke die Wahrscheinlichkeit von Diskontinuitäten innerhalb der Schicht dramatisch. Diese Diskontinuitäten führen zu lokal erhöhten Zugspannungen innerhalb der Schicht. Daraus folgt schließlich die Gefahr der Ablösung der Schicht vom Trägermaterial.However, such thick traces on relatively broad flat substrate materials, such as those used in flat radiators, cracking expected by material stresses, for example, resulting from the bending loads during evacuation during the manufacturing process. The reason for the growing risk of cracking is the dependence of the strain limit ε of a layer on the thickness d thereof $\mathrm{\epsilon }\mathrm{<figure-callout\; id="1"\; label="\alpha "\; filenames="imgf0001.png"\; state="\{\{state\}\}">\alpha </figure-callout>}\mathrm{1}\mathrm{/}\sqrt{\mathrm{d}}\mathrm{,}$

Thus, the larger the layer thickness, the lower the strain limit. In addition, as the layer thickness increases, the probability of discontinuities within the layer increases dramatically. These discontinuities lead to locally increased tensile stresses within the layer. This ultimately leads to the risk of detachment of the layer from the carrier material.

Surprisingly, it has been shown that nevertheless flat radiator can be made gas-tight with such thick conductor tracks and that, moreover, the life can be quite a few thousand hours.

Possibly also contribute specifically targeted at a suitable distance from each other between floor and ceiling plate arranged supporting points, for example in the form of glass balls, which give the flat radiator sufficient bending stability, without causing unacceptable strong shading.

According to the current state of knowledge, inter alia, the two parameters P ₁ = d _{St E1} and P ₂ = d _St / d _{P1 are} considered to be relevant for the life of the flat radiator, where d _{St is} the distance of the support points to each other or to the limiting Sidewall, d _E1 denote the thickness of the electrode tracks and d _P1 the smaller of the two thicknesses of bottom plate or top plate. Typical values for P ₁ are in the range from 50 mm .mu.m to 680 mm .mu.m, preferably in the range from 100 mm .mu.m to 500 mm .mu.m, particularly preferably from 200 mm .mu.m to 400 mm .mu.m. typical Values for P ₂ are in the range of 8 to 20, preferably in the range of 9 to 18, particularly preferably in the range of 10 to 15.

Good experiences were made, for example, with 10 μm thick printed silver layers and between each 2.5 mm thick bottom and top plate at a mutual distance of about 34 mm glass beads fitted glass beads. From these values result P ₁ = 340 mm μm and P ₂ = 13.6.

In addition, protection for an irradiation system is claimed, which consists of the aforementioned new flat radiator and a pulse voltage source.

Description of the drawings

Fig. 1a

ein erstes Ausführungsbeispiel eines Flachstrahlers in teilweise durchbrochener Draufsicht,

Fig. 1b

einen Querschnitt durch den Flachstrahler aus Figur 1a entlang der Linie AA.

Fig. 2a

ein zweites Ausführungsbeispiel eines Flachstrahlers in teilweise durchbrochener Draufsicht,

Fig. 2b

einen Querschnitt durch den Flachstrahler aus Figur 2a entlang der Linie AA,

Fig. 2c

eine ausschnittsweise Darstellung eines Querschnitts durch den Flachstrahler aus Figur 2b entlang der Linie BB.

In the following the invention with reference to two embodiments will be explained in more detail. Show it:

Fig. 1a

a first embodiment of a flat radiator in a partially broken plan view,

Fig. 1b

a cross section through the flat radiator FIG. 1a along the line AA.

Fig. 2a

A second embodiment of a flat radiator in a partially broken plan view,

Fig. 2b

a cross section through the flat radiator FIG. 2a along the line AA,

Fig. 2c

a partial view of a cross section through the flat radiator FIG. 2b along the line BB.

The FIGS. 1a and 1b schematically show a flat radiator 1 in plan view and a sectional view along the line AA. The flat radiator 1 consists of a discharge vessel 2, strip-shaped cathodes 3 and dielectrically impeded, strip-shaped anodes 4.

The discharge vessel 2 consists of a bottom plate 5, a ceiling plate 6 and a frame 7, all of which have a rectangular base. Base plate 5 and ceiling plate 6 are gas-tightly connected by means of glass solder 8 with the frame such that the interior 9 of the discharge vessel 2 is formed cuboid. The wall thickness of the floor and ceiling slab consisting of glass is approx. 2.5 mm in each case. The frame is made of a glass tube with a diameter of about 5 mm. Between floor and ceiling slab precision glass spheres with a diameter of 5 mm are fitted equidistantly as supporting points at a mutual distance of about 34 mm by means of glass solder (not shown for the sake of clarity). The bottom plate 5 is larger than the ceiling plate 6 such that the discharge vessel 2 has a circumferential freestanding edge.

The cathodes 3 and anodes 4 are arranged alternately and parallel to each other at a mutual distance of about 6 mm on the inner wall of the bottom plate 5. The cathodes 3 and anodes 4 are extended at opposite ends and guided on both sides to the outside as cathode-side 10 or anode-side 11 feedthroughs from the interior 9 of the discharge vessel 2 on the bottom plate 5. On the edge of the base plate 5 go through the bushings 10, 11 in each case in the cathode side 12 and the anode side 13 external power supply lines. The external power supply lines serve as external contacts for the connection to preferably an electrical pulse voltage source (not shown), optionally by means of suitable plug connections (not shown).

On the inner wall of the ceiling plate 6, a layer 16 of a phosphor mixture is applied, which converts the predominantly short-wave radiation of the discharge into visible white light. It is a three-band phosphor with the blue component BAM (BaMgA1 ₁₀ O ₁₇ : Eu ²⁺ ), the green component LAP (LaPO ₄ : [Tb ³⁺ , Ce ³⁺ ]) and the red component YOB ([Y, Gd] BO ₃ : Eu ³⁺ ). The layer thickness is about 27 microns. In a preferred variant (not shown), in addition to the inner wall of the ceiling slab, the inner wall of the floor slab, including the electrodes and of the frame, is additionally coated with a phosphor mixture. Furthermore, a light-reflecting layer of TiO ₂ and Al ₂ O _{3 is} applied directly on the inner wall of the bottom plate. The layer thicknesses are about 15 microns and 7 microns. This variant is therefore not shown because the view of the electrode strips would be obscured by the phosphor layer.

The breakthrough in the ceiling plate 6 is for illustrative purposes only and gives a view of a portion of the anodes 4 and 3 cathodes free. In the interior 9 of the discharge vessel 2, the anodes 4 are completely covered with a glass layer 17 (see also FIG FIG. 1b , which shows a section of the flat radiator 1 along an anode 4), whose thickness is about 250 microns. The electrodes 3, 4, feedthroughs 10, 11 and external power supply lines 12, 13 are realized as functionally different sections of a cathode-side and an anode-side continuous layer structure made of silver, which are jointly applied by means of screen printing technology and subsequent baking. The layer thickness is about 10 microns.

The in the Figures 2a-2c Flat radiator 1 'shown schematically in plan view and as a section along the lines AA and BB differs from the flat radiator 1 (FIG. FIGS. 1a and 1b ) only in the design of the external power supply 12; 13. The feedthroughs 10, 11 of each electrode strip 3, 4 are initially continued on the edge of the bottom plate 5 and open into a cathode-side 12 or anode-side 13 bus-like conductor track. These interconnects 12, 13 finally terminate in two adjacent sections 14, 15. The two sections 14, 15 serve as external contacts for connection to an electrical voltage source (not shown).

In Figure 2c is just one opposite FIG. 2b enlarged section along the line BB shown so that the conditions are better visible.

In a further variant (not shown), the cathode strips are applied to the inner wall of the ceiling plate. Each cathode strip is associated with an anode strip pair such that viewed in cross-section each of the imaginary connection of cathodes and corresponding anodes results in the form of an inverted "V". Cathode and anode strips are guided on the same side of the fluorescent lamp by means of feedthroughs to the outside and go on the corresponding edge of the ceiling or floor plate in the cathode-side or anode-side power supply over. Both the anode strips and the cathode strips are completely covered with a dielectric layer which extends over the entire inner wall of the bottom and the top plate such that the dielectric layer additionally serves as a glass solder for the gas-tight connection. On the dielectric layer of the bottom plate, a respective light-reflecting layer of TiO ₂ and Al ₂ O _{3 is} applied. As a last layer follows and also on the dielectric layer of the ceiling plate, a phosphor layer of a BAM, LAP, YOB mixture.

The invention is not limited by the specified embodiments. In addition, features of different embodiments can also be combined.

Claims (15)

1. Flat lamp (1) with an at least partially transparent, closed discharge vessel (2) which is filled with a gas fill and is made from an electrically nonconductive material and with strip-like electrodes (3, 4), which are arranged on the inner wall of the discharge vessel (2), at least the anodes (4) each being covered by a dielectric layer (17), characterized in that

   • the discharge vessel (2) has at least a bottom plate (5) and a top plate (6), the bottom plate (5) and the top plate (6) being connected to one another in a gas-tight manner by means of solder (8), possibly also via an additional frame (7) arranged between the top plate and the bottom plate,

   • the strip-like inner electrodes (3, 4) additionally merge into leadthroughs (10, 11), and the latter in turn merge into external power supply lines (12; 13) in such a way that the electrodes (3, 4), the leadthroughs (10, 11) and the external power supply lines (12; 13) are in the form of in each case functionally different subregions of conductor-track-like structures (3, 10, 12; 4, 11, 13),

   the leadthroughs (10, 11) being guided to the outside so as to be covered in a gas-tight manner by the solder (8), and the external power supply lines (12, 13) connected directly thereto being used for connecting an electrical supply source.
2. Flat lamp according to Claim 1, characterized in that the dielectric layers additionally act as solder for the gas-tight leadthroughs.
3. Flat lamp according to Claim 1 or 2, characterized in that the external power supply lines (12; 13) are arranged on the outer wall of the discharge vessel.
4. Flat lamp according to one of Claims 1 to 3, characterized in that the cathode-side and anode-side structures each consist of a metal layer, the layer thickness being in the range of between 5 µm and 50 µm, preferably in the range of 5.5 µm to 30 µm, particularly preferably in the range of 6 µm to 15 µm.
5. Flat lamp according to Claim 4, characterized in that the layer thickness is approximately 10 µm.
6. Flat lamp according to one of Claims 1 to 5, characterized in that spacers are arranged between the bottom plate and the top plate.
7. Flat lamp according to Claim 6, characterized in that the spacers are formed by glass beads.
8. Flat lamp according to Claim 6 or 7, characterized in that the parameter P₁=d_St · d_E1 is in the range of 50 mm µm to 680 mm µm, preferably in the range of 100 mm µm to 500 mm µm, particularly preferably in the range of 200 mm µm to 400 mm µm, d_St denoting the distance between the supporting points or between the supporting points and the delimiting side wall, and d_E1 denoting the thickness of the electrode tracks.
9. Flat lamp according to one of Claims 6 to 8, characterized in that the parameter P₂=d_St/d_P1 is in the range of 8 to 20, preferably in the range of 9 to 18, particularly preferably in the range of 10 to 15, d_St denoting the distance between the supporting points or between the supporting points and the delimiting side, and d_P1 denoting the smaller of the two thicknesses of the bottom plate or cover plate.
10. Flat lamp according to Claim 1, characterized in that the coefficient of thermal expansion of the solder (8) is matched to the coefficients of thermal expansion of the materials of the bottom plate (5) and of the top plate (6) and possibly of the frame (7).
11. Flat lamp according to Claim 1, characterized in that at least part of the inner wall of the discharge vessel has a layer of phosphor or phosphor mixture.
12. Flat lamp according to Claim 11, characterized in that a light-reflecting layer is applied to part of the inner wall of the discharge vessel, in particular to the inner wall of the bottom plate, between the inner wall and the phosphor layer.
13. Flat lamp according to one or more of the preceding claims, the external power supply lines being designed such that the leadthroughs (10; 11) of the cathodes (3) and anodes (4) open out into a cathode-side or anode-side bus-like conductor track (12, 14; 13, 15).
14. Flat lamp according to Claim 13, the two bus-like power supply lines (12, 14; 13, 15) being arranged on the outer wall of the discharge vessel.
15. Irradiation system with a flat lamp and an electrical pulsed voltage source, which is suitable for supplying voltage pulses which are separated from one another by intervals during operation, characterized in that the flat lamp has features of one or more of Claims 1 to 8, the pulsed voltage source being electrically conductively connected to the external power supply lines of the flat lamp.

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