EP0458140B1 - High power radiator - Google Patents

Abstract

In the case of UV high-power omnidirectional radiators, in order to be able to direct the radiation produced in only one preferred direction and in order to prevent shadowing by the inner dielectric tube (2), the outer electrodes (4) are arranged on only one part of the circumference of the outer dielectric tube (1). In this way, the object to be irradiated or the substance to be irradiated can thus be arranged directly in the radiation zone of the discharges (7). <IMAGE>

Description

Technical field

The invention relates to a high-power radiator, in particular for ultraviolet light, with a discharge space filled with filling gas emitting radiation under discharge conditions, the walls of which are formed by an outer and an inner tubular dielectric, each having an inner and an outer surface on the surfaces facing away from the discharge space outer electrode are provided, and with an alternating current source connected to these electrodes for supplying the discharge.

The invention relates to a state of the art, such as that disclosed in EP-A 0 254 111, US-A-5 013 959, EP-A-0 385 205 or EP-A-0 324 953 results.

Technological background and state of the art

The industrial use of photochemical processes depends heavily on the availability of suitable UV sources. The classic UV lamps deliver low to medium UV intensities at some discrete wavelengths, such as the mercury low-pressure lamps at 185 nm and especially at 254 nm. Really high UV powers can only be obtained from high-pressure lamps (Xe, Hg), which then but distribute their radiation over a larger wavelength range. The new excimer lasers have provided some new wavelengths for basic photochemical experiments, are currently for cost reasons for an industrial process probably only suitable in exceptional cases.

In the EP patent application mentioned at the beginning or in the conference paper "New UV and VUV excimer emitters" by U. Kogelschatz and B. Eliasson, distributed at the 10th lecture conference of the Society of German Chemists, Photochemistry Group, in Würzburg (FRG) 18. -20. November 1987, a new excimer radiator is described. This new type of emitter is based on the fact that excimer radiation can also be generated in silent electrical discharges, a type of discharge that is used on a large scale in ozone generation. In the current filaments of this discharge, which exist only for a short time (<1 microsecond), noble gas atoms are excited by electron impact, which react further to excited molecular complexes (excimers). These excimers only live for a few 100 nanoseconds and release their binding energy in the form of UV radiation when they decay.

The construction of such an excimer radiator largely corresponds to that of a conventional ozone generator, with the essential difference that at least one of the electrodes and / or dielectric layers delimiting the discharge space is transparent to the radiation generated.

The high-performance radiators mentioned are characterized by high efficiency, economical structure and enable the creation of large area radiators, with the restriction that large-area flat radiators require a rather large technical effort. In the known cylindrical emitters, however, a not inconsiderable portion of the radiation is not used due to the shadow effect of the inner electrode. In order to increase the yield in the case of cylinder emitters, the emitters in EP-A-0 385 205 mentioned at the outset the inner dielectric tubes are very small compared to the outer dielectric tubes. By eccentric arrangement of the inner dielectrics with a small diameter compared to the diameter of the outer dielectrics and outer electrodes only on the surface adjacent to the inner dielectric and simultaneous formation of the outer electrode as a reflector, a preferred direction of radiation is achieved.

Presentation of the invention

Starting from the prior art, the invention has for its object to provide a high-performance radiator, in particular for UV or VUV radiation, which is characterized in particular by high efficiency, is economical to manufacture, enables the construction of very large area radiators and in which the UV radiation can be specifically focused on a radiation angle that can be selected within wide limits and the inner electrode can no longer cast a shadow.

To achieve this object, it is provided according to the invention in a high-power radiator of the type mentioned at the outset that the outer electrode extends only over a fraction of the outer circumference of the outer dielectric tube, in such a way that discharges form only in a discharge segment which is essentially defined by the outer electrode.

In this way, the radiation can be coupled out in a defined direction, which is particularly advantageous when irradiating flat or curved surfaces, since the electrical discharges can only form on the surface facing the material to be irradiated. As the outer electrodes, in addition to those already in the relevant Wire networks or wire meshes described in the literature also serve electrically conductive, UV-transparent coatings, for example made of conductive lacquer or thin metal films.
It is also possible to design the outer electrode in liquid form by only partially immersing the outer tube in a transparent electrolyte, preferably water. This arrangement is particularly suitable for irradiating temperature-sensitive substances (for example gluing LCD cells, irradiating thin foils) because water very effectively blocks any infrared radiation from the discharge.
The electrolyte can be circulated via a thermostat and thus kept at a constant low temperature. A suitable filtering effect can additionally be achieved by suitable selection of the electrolyte. In addition, the angular range of the ignited segment can be changed via the immersion depth of the outer tube in the electrolyte.

The inner electrode is preferably of classic design, i.e. consists of a metal coating applied to the inner surface of the inner dielectric tube, e.g. Aluminum vapor deposition. In this way, the inner electrode also acts as a reflector for the UV radiation. If cooling is desired, a flow of coolant (gas or liquid) can be passed through the inner tube.

You can easily combine several such emitters into blocks that are suitable for irradiating large areas. For this purpose, the outer tubes are advantageously arranged in groove-shaped semi-cylindrical recesses in a support body made of an electrically insulating, but good heat-conducting material. Such materials are available on a ceramic basis, for example aluminum nitride (AlN) or beryllium oxide (BeO) as well as on a plastic basis (casting compounds for transformers and electrical circuits). With less extreme requirements more common materials such as aluminum oxide (Al₂O₃), glass ceramics or heat-resistant plastics such as polytetrafluoroethylene are also suitable. At higher capacities, it is possible to cool the supporting body and thus the outer pipes, for example by providing cooling channels running in the longitudinal direction of the pipe in the supporting body.
The reflectivity of the semi-cylindrical recesses in the supporting body can be improved by a metallic mirror coating, for example an aluminum layer with a protective layer of magnesium fluoride (MgF₂). However, it can also prove to be advantageous to apply a diffusely reflecting layer such as is used in radiometry in what is known as an Ulbricht sphere. In this case, one would use a layer of magnesium oxide (MgO) or barium sulfate (BaSO₄).

When treating surfaces with UV and curing UV inks and varnishes, it is advantageous in certain cases not to work in air. There are at least two reasons why UV treatment in the absence of air is indicated. The first reason is when the radiation is so short-wave that it is absorbed by air and thus weakened (wavelengths <190 nm). This radiation leads to oxygen splitting and thus to undesired ozone formation. The second reason is when the intended photochemical effect of UV radiation is hindered by the presence of oxygen (oxygen inhibition). This occurs, for example, in the photo crosslinking (UV polymerization, UV drying) of lacquers and paints. These processes are known per se and are described, for example, in the book "UVand EB Curing Formulation for Printing Ink, Coatings and Paints", published in 1988 by SITA-Technology, 203 Gardiner House, Broomhill Road, London SW18, pages 89-91. In these cases, provision is made to provide means for purging the treatment room with an inert UV-transparent gas such as nitrogen or argon. Especially in configurations in which the first tubes are arranged in a support body provided with grooves, such a flushing can be implemented without great technical effort, for example by additional channels fed by an inert gas source and open to the discharge space. The inert gas passed through said channels can also be used to cool the radiator, so that in some applications there is no need for separate cooling channels.

Brief description of the drawings

Fig.1

Ein erstes Ausführungsbeispiel eines Zylinderstrahlers mit konzentrischer Anordnung des inneren Dielektrikumsrohres im Querschnitt mit verschiedenen Elektrodenanordnungen auf dem äusseren Dielektrikumsrohr;

Fig.2

einen UV-Strahler mit einer Aussenelektrode in flüssiger Form;

Fig. 3

eine Ausführungsform einer Bestrahlungseinrichtung mit drei nebeneinanderliegenden Zylinderstrahlern gemäss Fig.1c, welche auf einem Tragkörper aus Isoliermaterial angeordnet sind;

Fig.4

eine Ausführungsform einer Bestrahlungseinrichtung analog Fig. 3, jedoch mit einer die gesamte freie Oberfläche der äusseren Dielektrikumsrohre überdeckenden Aussenelektrode.

In the drawing, embodiments of the invention are shown schematically; in it shows

Fig. 1

A first embodiment of a cylinder radiator with a concentric arrangement of the inner dielectric tube in cross section with different electrode arrangements on the outer dielectric tube;

Fig. 2

a UV lamp with an outer electrode in liquid form;

Fig. 3

an embodiment of an irradiation device with three adjacent cylinder emitters according to Fig.1c, which are arranged on a support body made of insulating material;

Fig. 4

an embodiment of an irradiation device analogous to FIG. 3, but with an outer electrode covering the entire free surface of the outer dielectric tubes.

Ways of Carrying Out the Invention

1a to 1c, an inner quartz tube 2 is arranged coaxially in an outer quartz tube 1 with a wall thickness of approximately 0.5 to 1.5 mm and an outer diameter of approximately 20 to 30 mm. The inner surface of the inner quartz tube 2 is provided with an inner electrode 3, which is produced for example by coating with aluminum. An outer electrode 4 in the form of a narrow strip of wire mesh extends only over a small part of the circumference of the outer quartz tube 1. The quartz tubes 1 and 2 are closed at both ends. The space between the two tubes 1 and 2, the discharge space 5, is filled with a gas / gas mixture which emits radiation under discharge conditions. The two electrodes 3, 4 are connected to the two poles of an alternating current source 6. The AC power source basically corresponds to those used to feed ozone generators. It typically delivers an adjustable AC voltage in the order of magnitude of several 100 volts to 20,000 volts at frequencies in the range of technical alternating current up to a few 1000 kHz - depending on the electrode geometry, pressure in the discharge space and composition of the filler gas.

The fill gas is e.g. Mercury, noble gas, noble gas-metal vapor mixture, noble gas-halogen mixture, optionally using an additional further noble gas, preferably Ar, He, Ne, as a buffer gas.

Depending on the desired spectral composition of the radiation, a substance / substance mixture according to the following table can be used:

• Ein Edelgas (Ar, He, Kr, Ne, Xe) oder Hg mit einem Gas bzw. Dampf aus F₂, J₂, Br₂, Cl₂ oder eine Verbindung die in der Entladung ein oder mehrere Atome F, J, Br oder Cl abspaltet;
• ein Edelgas (Ar, He, Kr, Ne, Xe) oder Hg mit O₂ oder einer Verbindung, die in der Entladung ein oder mehrere 0-Atome abspaltet;
• ein Edelgas (Ar, He, Kr, Ne, Xe) mit Hg.

In addition, a whole series of other filling gases are possible:

• A noble gas (Ar, He, Kr, Ne, Xe) or Hg with a gas or vapor from F₂, J₂, Br₂, Cl₂ or a compound that splits off one or more atoms F, J, Br or Cl in the discharge;
• a noble gas (Ar, He, Kr, Ne, Xe) or Hg with O₂ or a compound that splits off one or more 0 atoms in the discharge;
• an inert gas (Ar, He, Kr, Ne, Xe) with Hg.

In the silent discharge that forms, the electron energy distribution can be optimally adjusted by the thickness of the dielectrics and their properties, pressure and / or temperature in the discharge space.

When an alternating voltage is applied between the electrodes 3 and 4, a plurality of discharge channels 7 (partial discharges) form in the discharge space 5. These interact with the atoms / molecules of the filling gas, which ultimately leads to UV or VUV radiation.

Instead of a narrow wire mesh as the outer electrode 4, two narrow outer electrodes 4a and 4b (FIG. 1b) spaced apart from one another or a wider wire mesh that extends approximately over a sixth of the tube circumference (FIG. 1c) can also be used. Instead of a wire mesh, a perforated metal foil or a UV-transparent, electrically conductive covering can also be used.
In addition to the fixed outer electrodes mentioned above, a transparent electrolyte can also be used. In the embodiment according to FIG. 2, three dielectric tubes 1 with internal dielectric tubes 2 provided with internal electrodes 3 dip into a quartz vessel 8 filled with water 4 '. The size of the ignited segment can be varied via the immersion depth t. By selecting the appropriate electrolyte, an additional optical filter effect can be achieved: for example, water very effectively blocks any infrared radiation from the discharge. This is particularly important when irradiating very temperature-sensitive substances.

FIG. 3 illustrates the manner in which a plurality of cylinder radiators according to FIG. 1c can be combined to form a surface radiator. A support body 9 from a For this purpose, electrically insulating material, but with good thermal conductivity, for example on a ceramic basis, is provided with parallel grooves 10 with a semicircular cross section, which are spaced apart by more than one outer tube diameter. The grooves 10 are adapted to the outer quartz tubes 1 and by coating with a UV-reflecting material, for example aluminum, which is provided with a protective layer of MgF₂. Additional bores 11, which run in the direction of the tubes 1, serve to cool the individual radiators.

For special applications, single emitters can be combined with different gas fillings and thus different (UV) wavelengths.

The support body 9 does not necessarily have to be plate-shaped. It can also have a hollow cylindrical cross section with axially parallel grooves distributed regularly over its inner circumference, into each of which a radiator element according to FIGS. 1a to 1c is inserted, analogously to FIG. 7 or FIG. 8 of the aforementioned EP-A-0 385 205.

The radiation device according to FIG. 4 basically corresponds to that according to FIG. 3. with additional channels 12 running in the longitudinal direction of the support body 9. These channels are connected to the outer space 13 via a multiplicity of bores or slots 14 in the support body 9. The channels 12 are connected to an inert gas source, not shown, for example nitrogen or argon source. The pressurized inert gas reaches the treatment room 13 from the channels 12 in the manner described. In addition, FIG. 4 shows a particularly simple and economical embodiment for the outer electrode. This outer electrode is common to all emitters. It consists of a continuous wire mesh or wire mesh 15 with in Pipe longitudinal direction extending semicircular bulges that nestle against the outer quartz tubes 1.

Claims (10)

1. A high power radiating device, in particular for ultraviolet light, with a discharge chamber (5) filled with filling gas emitting radiation under discharge conditions, the walls of which are formed by a first (1) and a second tubular dielectric (2), which is provided in each case on the surfaces facing away from the discharge chamber (5) with an outer (4) and an inner electrode (3), and with an alternating current source (6) connected to these electrodes to supply the discharge, characterised in that the outer electrode (4;4a;4b;4′;15) only extends over a fraction of the circumference of the first dielectric tube (1), such that discharges (7) only form in a discharge segment substantially defined by the outer electrode (4).
2. A high-power radiating device according to Claim 1, characterised in that the outer electrode(s) extend in strip form in the longitudinal direction of the tube.
3. A high-power radiating device according to Claim 1, characterised in that the outer electrode is formed by an electrolyte (4′), into which the outer dielectric tube(s) immerse at the most partially.
4. A high-power radiating device according to Claim 3, characterised in that the size of the effective radiating segment is able to be adjusted by the immersion depth (t) of the outer dielectric tube (1) in electrolyte (4′).
5. A high-power radiating device according to Claim 4, characterised in that the outer tubes (1) are arranged partially in material recesses (10) in a carrier body (9) of insulating material with good thermal conductivity.
6. A high-power radiating device according to Claim 5, characterised in that cooling bores (11) are provided in the support body (9), which do not intersect the material recesses (10).
7. A high-power radiating device according to Claim 5, characterised in that the cross-section of the material recesses (10) are matched to the external diameter of the outer tubes (1) and the recess walls are constructed as UV reflectors.
8. A high-power radiating device according to one of Claims 5 to 7, characterised in that means (11,14) are provided for the supply of inert gas into the chamber (13) outside the outer tubes (1).
9. A high-power radiating device according to Claim 8, characterised in that channels (12) are provided in the support body, which are connected directly or indirectly with said chamber (13), through which channels (12) an inert gas, preferably nitrogen or argon, is able to be fed.
10. A high-power radiating device according to Claim 9, characterised in that the channels (12) are arranged in each case between adjacent dielectric tubes (1) and communicate with said chamber via bores or slits (14).

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