EP0385205A1 - High-power radiation device - Google Patents

Abstract

In order to increase the yield in UV high-power cylindrical emitters, the inner dielectrics (3) are very small in comparison with the outer dielectric tube. As a result of the eccentric arrangement of the dielectrics and the outer electrodes (2) only on the surface adjacent to the inner dielectric (3), and the simultaneous design of the outer electrode (7) as a reflector, a preferred direction of the emitted radiation is achieved. <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 a first tubular and a second dielectric, which have first and second electrodes on its surfaces facing away from the discharge space with an AC power source connected to the first and second electrodes for feeding the discharge.

The invention relates to a state of the art, such as that derived from EP-A 054 111, US patent application 07/076 926 or EP patent application 88113393.3 from August 22, 1988 or US patent application 07 / 260,869 from October 21, 1988.

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 low-pressure mercury 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 their radiation over you distribute a larger wavelength range. The new excimer lasers have provided some new wavelengths for basic photochemical experiments. 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, up to the power supply, 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 case of omnidirectional radiators, on the other hand, a not inconsiderable proportion of the radiation due to the shadow effect of the inner electrode is not used.

Presentation of the invention

Based on 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 Shadow effect of the inner electrode (s) is reduced to a minimum.

To solve this problem in a high-power radiator of the type mentioned at the outset, it is provided according to the invention that a rod made of dielectric material is arranged within the first tubular dielectric, inside which an electrical conductor is inserted or embedded, which conductor forms the second electrode.

The outer diameter of the rod, which is preferably made of quartz glass, is preferably five to ten times smaller than the inner diameter of the outer tube.

In many cases, the radiation should preferably be coupled out in one direction, for example in order to irradiate a surface. The ideal discharge geometry for this purpose is a flat radiator mirrored on the back (for example according to EP-A-0254 111). The production of flat quartz cells is associated with great technical effort and correspondingly high costs. One can easily achieve a preferred direction of the radiation if the discharge is distributed unevenly in the discharge gap, which can be achieved most simply by an eccentric arrangement of the dielectric rod. It is thereby achieved that the electrical discharge takes place predominantly on the side on which the optical radiation is to be coupled out.

Instead of external electrodes applied over the entire circumference of the outer dielectric tube, partial vapor deposition or coating on the rear side is sufficient, the layer simultaneously serving as an electrode and reflector. Aluminum, which is provided with a suitable protective layer (anodized, MgF₂ coating), is a suitable material that is both easy to vaporize and has a high UV reflection.

You can easily combine several such eccentric emitters into blocks that are suitable for irradiating large areas. The (semi-cylindrical) recesses in the aluminum block also serve as a holder for the quartz discharge tubes, as an (earth) electrode and as a reflector. Any number of these discharge tubes can be connected in parallel by placing the internal electrodes on a common AC voltage source. For special applications you can combine tubes with different gas filling and therefore different (UV) wavelengths. The aluminum blocks described do not necessarily have to have flat surfaces. One can also imagine cylindrical arrangements in which the recesses for receiving the discharge tubes are either outside or inside.

At higher outputs it is possible to cool the aluminum blocks, e.g. by providing additional cooling channels. The individual gas discharge tubes can also be cooled if, for example, forms the inner electrode as a cooling channel.

When treating UV surfaces 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 the splitting of oxygen and thus to the un wanted 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 paints and inks. 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, it is provided according to the invention to provide means for purging the treatment room with an inert UV-transparent gas such as nitrogen or argon. In particular in configurations in which the first electrode is formed from a grooved metal block, such a flushing can be implemented without great technical effort, for example by means of 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 separate cooling channels can be dispensed with in some applications.

Brief description of the drawings

• Fig.1 Ein erstes Ausführungsbeispiel eines Zylinderstrah­lers mit konzentrischer Anordnung des inneren Di­elektrikumsstabes im Querschnitt;
• Fig.2 eine Abwandlung des Strahlers nach Fig.1 ,mit einer exzentrischen Anordnung des inneren Dielektrikums;
• Fig. 3 eine Ausführungsform eines Zylinderstrahlers mit konzentrischer Anordnung des inneren Dielektrikums und einer Aussenelektrode in Form einer Beschich­tung, die sich nur über einen Teil des Umfangs des äusseren Dielektrikumsrohres erstreckt, wobei die Beschichtung gleichzeitig als Reflektor dient;
• Fig.4 eine Ausführungsform eines Zylinderstrahlers analog Fig. 3 jedoch mit exzentrischer Anordnung des inne­ren Dielektrikums und einer Beschichtung, die sich nur über einen Teil des Umfanges des äusseren Di­elektrikumsrohres erstreckt, welche Beschichtung gleichzeitig als Aussenelektrode und als Reflektor dient;
• Fig.5 die Zusammenfassung mehrerer Strahler nach Fig.3 zu einem Flächenstrahler;
• Fig. 6 die Zusammenfassung mehrerer Strahler nach Fig.4 zu einem Flächenstrahler;
• Fig.7 eine Abwandlung von Fig. 5 in Gestalt eines aus ei­ner Vielzahl Strahlern gemäss Fig.3 zusammengesetz­ten grossflächigen Zylinderstrahlers.
• Fig. 8 eine Abwandlung von Fig. 6 in Gestalt eines aus ei­ner Vielzahl von Strahlern gemäss Fig.4 zusammen­gestzten grossflächigen Zylinderstrahlers;
• Fig. 9 eine Weiterbildung des Strahlers nach Fig.5 mit Mitteln zur Zufuhr eines Inertagases in den Behand­lungsraum;
• Fig.10 eine Weiterbildung des Strahlers nach Fig.6 mit Mitteln zur Zufuhr eines Inertgases in den Behand­lungsraum.

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

• 1 shows a first embodiment of a cylinder radiator with a concentric arrangement of the inner dielectric rod in cross section;
• 2 shows a modification of the radiator according to FIG. 1, with an eccentric arrangement of the inner dielectric;
• 3 shows an embodiment of a cylinder radiator with a concentric arrangement of the inner dielectric and an outer electrode in the form of a coating which extends only over part of the circumference of the outer dielectric tube, the coating simultaneously serving as a reflector.
• 4 shows an embodiment of a cylinder emitter analogous to FIG. 3, but with an eccentric arrangement of the inner dielectric and a coating which extends only over part of the circumference of the outer dielectric tube, which coating serves simultaneously as an outer electrode and as a reflector;
• 5 shows the combination of several radiators according to FIG. 3 to form a surface radiator;
• 6 shows the combination of several radiators according to FIG. 4 to form a surface radiator;
• 7 shows a modification of FIG. 5 in the form of a large-area cylinder radiator composed of a plurality of radiators according to FIG.
• 8 shows a modification of FIG. 6 in the form of a large-area cylinder radiator composed of a plurality of radiators according to FIG. 4;
• 9 shows a development of the radiator according to FIG. 5 with means for supplying an inert gas into the treatment room;
• 10 shows a development of the radiator according to FIG. 6 with means for supplying an inert gas into the treatment room.

Ways of Carrying Out the Invention

1, a 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 is provided with an outer electrode 2 in the form of a wire mesh. A second quartz tube 3 is arranged concentrically in the quartz tube 1 and has a substantially smaller outside diameter than the inside diameter of the quartz tube 1, typically 3 to 5 mm outside diameter.
A wire 4 is inserted into the inner quartz tube 3. This forms the inner electrode of the radiator, the wire mesh 2 the outer electrode of the radiator.
The outer quartz tube 1 is closed at both ends. The space between the two tubes 1 and 3, the discharge space 5, is filled with a gas / gas mixture which emits radiation under discharge conditions. The two electrodes 2, 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. Typically, it supplies 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 filling 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: Filling gas radiation helium 60-100 nm neon 80 - 90 nm argon 107 - 165 nm Argon + fluorine 180-200 nm Argon + chlorine 165-190 nm Argon + krypton + chlorine 165-190, 200-240 nm xenon 160-190 nm nitrogen 337 - 415 nm krypton 124, 140-160 nm Krypton + fluorine 240 - 255 nm Krypton + chlorine 200-240 nm mercury 185, 254, 320-370, 390-420 nm selenium 196, 204, 206 nm deuterium 150-250 nm Xenon + fluorine 340 - 360 nm, 400 - 550 nm Xenon + chlorine 300-320 nm

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;
- An inert 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 2, 4, a large number of discharge channels (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 quartz tubes 3 with inserted wire, quartz rods into which a metal wire is melted can also be used. Metal rods covered with a dielectric also lead to success.

Instead of a wire mesh 2, a perforated metal foil or a UV-transparent, electrically conductive covering can also be used.

If you want to achieve a preferred direction of radiation with simple means, the discharge is distributed unevenly in the discharge space. The easiest way to do this is by eccentrically arranging the inner dielectric tube 3 in the outer tube 1, as is illustrated in FIG. 2, for example.

In Figure 2, the inner quartz tube 3 is arranged outside the center near the inner wall of the tube 1. In the borderline case, the pipe 3 can even rest against the pipe 1 and be glued there linearly or selectively to the inner wall.

The eccentric arrangement of the inner quartz tube and thus the inner electrode 4 has no decisive influence on the quality of the discharge. When the peak voltage is set just a small area ignites in the immediate vicinity of the quartz tube 3. By increasing the voltage, one can gradually increase the discharge zone until the entire discharge space 5 is filled with luminous plasma.

Instead of an electrode 2 (FIG. 2) applied to the entire outer circumference of the outer dielectric tube 1 (FIG. 2) is sufficient also a partial coating of the outer surface of the tube 1, as illustrated in Figure 3. The coating 7, which extends over approximately half the outer circumference of the tube 1, is simultaneously the outer electrode and the reflector. According to FIG. 2, an eccentric arrangement of the inner quartz tube 3 is also possible here, the coating 7 only extending symmetrically over the outer wall section facing the inner quartz tube 3. This layer 7 is simultaneously the outer electrode and the reflector. Aluminum is particularly suitable as a material that is both easy to vaporize and has a high UV reflection.

FIG. 5 illustrates the manner in which a multiplicity of concentric radiators according to FIG. 3 can be combined to form a surface radiator. 6 shows a corresponding arrangement with eccentrically arranged inner quartz tubes 3 according to FIG. For this purpose, an aluminum body 8 is provided with a plurality of parallel grooves 9 with a circular cross section, which are spaced apart from one another by more than one outer tube diameter. The grooves 9 are adapted to the outer quartz tubes 1 and treated by polishing or the like so that they reflect well. Additional bores 10, which run in the direction of the tubes 1, serve to cool the radiators.

The AC source 6 leads with one pole to the aluminum body 8, the inner electrodes 4 of the radiators are connected in parallel and connected to the other pole of the source 6.

Analogously to the coatings 7 in FIGS. 3 and 4, in the case of FIGS. 5 and 6, the groove walls serve both as an outer electrode and as reflectors.

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

The aluminum bodies 8 do not necessarily have to have flat surfaces. E.g. 7 and 8 illustrate a variant with a hollow cylindrical aluminum body 8a with axially parallel grooves 9 regularly distributed over its inner circumference, in each of which a radiator element according to FIGS. 3 and 4 is inserted.

The radiator according to Fig. 9 basically corresponds to that according to Fig. 5. with additional channels 11 running in the longitudinal direction of the metal block 8. These channels are connected to the treatment room 12 via a multiplicity of bores or slots 13 in the metal block 8, specifically via the comparatively narrow gap between the outer ones, which is caused by inevitable manufacturing tolerances of the quartz tubes 1 Quartz tubes 1 and the grooves 9 in the metal block 8 in connection. The channels 11 are connected to an inert gas source, not shown, e.g. Nitrogen or argon source connected. The pressurized inert gas reaches the treatment room 12 from the channels 11 in the manner described. This treatment room is delimited on the one hand by legs 14 on the metal block 8 and by the substrate 15 to be irradiated. It fills with inert gas in a short time. Depending on the size of the gap 16 between the substrate 15 and the ends of the legs 14, a certain amount of leakage gas escapes, but this is replenished by the inert gas source. In this way, the interactions described at the outset between the UV radiation generated in the discharge spaces 5 and the atmospheric oxygen are reliably avoided.

A further possibility of supplying inert gas to the treatment room 12 is illustrated in FIG. The emitter largely corresponds to that according to Fig. 6. In addition, however, between adjacent quartz tubes 5 in the longitudinal direction Metal blocks 8 extending channels 11 are provided, which are connected directly to the treatment room 12 via bores or slots 13. Otherwise the structure and mode of operation correspond to those according to Fig. 9.

It goes without saying that the cylinder emitters according to FIGS. 7 and 8 can also be provided with means for supplying inert gas to the treatment room (there the inside of the tube 8a) without leaving the scope of the invention.

Claims (10)

1. High-power radiator, in particular for ultraviolet light, with a discharge space (5) filled with filling gas emitting radiation under discharge conditions, the walls of which are formed by a first tubular (1) and a second dielectric (3), which on its discharge space (5) surfaces facing away from the first (2, 7) and second electrodes (4), with an alternating current source (6) connected to the first and second electrodes for supplying the discharge, characterized in that a rod is located within the first tubular dielectric (1) (3) made of dielectric material, in the interior of which an electrical conductor (4) is inserted or embedded, which conductor forms the second electrode. 2. High-power radiator according to claim 1, characterized in that the outer diameter of the rod (3) is five to ten times smaller than the inner diameter of the first tubular dielectric (1). 3. High-power radiator according to claim 1 or 2, characterized in that the rod (3) made of dielectric material is arranged eccentrically in the first tubular dielectric (1). 4. High-power radiator according to claim 3, characterized in that the first electrode (7) covers the outer wall of the first dielectric (1) only in the section which is assigned to the second dielectric (3) and is designed as a reflector. 5. High-power radiator according to claim 4, characterized in that the first electrode and the reflector are formed as material recesses, preferably grooves (9), in a metal body (8). 6. High-power radiator according to claim 5, characterized in that in the metal body (8) cooling bores (10) are provided which do not cut the material recesses (9). 7. High-power radiator according to claim 5, characterized in that the cross section of the material recesses (9) is adapted to the outer diameter of the first dielectric (1) and the recess walls are designed as UV reflectors. 8. High-power radiator according to one of claims 5 to 7, characterized in that means (11, 13) for supplying inert gas into the space (12) are provided outside the first tubular dielectric (1). 9. High-power radiator according to claim 8, characterized in that channels (11) are provided in the metal body (8, 8a) which are directly or indirectly connected to the treatment room (12), through which channels (11) an inert gas, preferably nitrogen or argon, can be supplied. 10. High-power radiator according to claim 9, characterized in that the channels (11) are each arranged between adjacent dielectric tubes (1) and are connected to the treatment room (12) via bores or slots (13).

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