EP0517929B1 - Irradiation device with a high power radiator - Google Patents

Description

Technical field

The invention relates to an irradiation device with a high-power radiator, in particular for ultraviolet light, which has a discharge space filled with filling gas emitting radiation under discharge conditions, the walls of which are formed by a first dielectric, the first dielectric having first metallic electrodes on its surface facing away from the discharge space is provided, and has second electrodes, and with an alternating current source connected to the first and second electrodes for feeding the discharge, the high-power radiator being immersed in a coolant bath, in such a way that the coolant is at least partially washed around the first dielectric and at least the first electrodes , and that at least one wall of the coolant bath and the coolant itself are permeable to the radiation generated.

Technological background and state of the art

From DE-A-38 42 993 an irradiation device with a high-power radiator is known, whereby a discharge space filled with filling gas emitting radiation under discharge conditions is specified, the walls of which are formed by a dielectric which has first metallic and second ones on its surfaces facing away from the discharge space Electrodes are provided; an AC power source connected to the first and second electrodes is provided for feeding the discharge, the radiator being immersed in a coolant bath in such a way that the dielectric and at least the first electrodes from Coolant is washed around, and that at least one wall of the coolant bath and the coolant itself are permeable to the radiation generated.

The industrial use of photochemical processes depends heavily on the availability of suitable UV sources. The classic UV lamps provide low to medium UV intensities at some discrete wavelengths, e.g. the mercury low-pressure lamps at 185 nm and especially at 254 nm. Really high UV power can only be obtained from high-pressure lamps (Xe, Hg), which then distribute their radiation over 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 EP-A-254 111 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) 18th-20th November 1987, a new excimer radiator is described. This new type of radiator is based on the fact that excimer radiation can also be generated in silent electrical discharges, a type of discharge which is used on a large scale in ozone generation. In the current filaments of this discharge, which are only present 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 classic 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. At least one of these electrodes may only shade the radiation generated a little. Another requirement for the radiator is that it emits as little heat as possible, even at high power densities. This is particularly important for applications in the graphics industry, where printing inks often have to be cured on a heat-sensitive surface.

Brief description of the invention

Starting from the prior art, the object of the invention is to create an irradiation device with a radiator, in particular for UV or VUV radiation, the electrodes of which shield the radiation as little as possible and the radiator can be optimally cooled.

To solve this problem, the invention provides that the walls of the discharge space are further formed by a second dielectric, which is provided on its surface facing away from the discharge space with the second electrodes that the walls of the coolant bath with the exception of the radiation-permeable wall with a UV radiation reflecting layer are provided or in the case of walls made of aluminum or an aluminum alloy they are polished and that the first metallic electrode is designed in the form of a grid or a network.

• Die Erfindung ermöglicht den Aufbau eines absolut kalten Strahlers, was insbesondere im Zusammenhang mit der Aushärtung von Druckfarben auf hitzeempfindlichen Untergrund wichtig ist.
• Die Außenelektroden können von einfacher Konstruktion sein - es genügen einige wenige in Strahlerlängsrichtung verlaufende Metallstreifen oder Metalldrähte, die nicht notwenig auf dem äußeren Dielektrikum aufliegen müssen. Auf diese Weise können die Dielektrika leicht ausgewechselt werden.
• Das Kühlmittel, bevorzugt Wasser, verhindert Außenentladungen zwischen Außenelektroden und Außenwand des Strahlers. Dies verhindert die Ozonbildung.
• Weil sich keine Außenentladungen mehr ausbilden können, wird auch Metallabscheidung durch Sputtern verhindert, d.h. die UV-Durchlässigkeit wird auch nach längerer Betriebszeit nicht beeinträchtigt.
• Falls die jeweilige Anwendung einen Betrieb nur mit einem allseitig abgeschlossenen Kühlmittelbad erlaubt und die UV-Strahlung dieses nur durch ein Fenster verlassen kann, ist dieses leicht zu reinigen oder auszuwechseln. Dies ist für die Verwendung des Strahlers in der grafischen Industrie bedeutsam, wo häufig Fabrrückstände entfernt werden müssen.
• Die Erfindung ermöglicht neben einem streng modularem Aufbau auch die Integration mehrerer Strahler im selben Bad.

An irradiation device constructed in this way fulfills all practical requirements:

• The invention enables the construction of an absolutely cold radiator, which is particularly important in connection with the curing of printing inks on a heat-sensitive surface.
• The outer electrodes can be of simple construction - a few metal strips or metal wires running in the longitudinal direction of the radiator are sufficient, which do not necessarily have to rest on the outer dielectric. In this way, the dielectrics can be easily replaced.
• The coolant, preferably water, prevents external discharges between the outer electrodes and the outer wall of the radiator. This prevents ozone formation.
• Because external discharges can no longer form, metal deposition by sputtering is also prevented, ie the UV permeability is not impaired even after a long period of operation.
• If the respective application only allows operation with a coolant bath sealed on all sides and the UV radiation can only leave it through a window, it is easy to clean or replace. This is important for the use of the heater in the graphic arts industry, where factory residues often have to be removed.
• In addition to a strictly modular structure, the invention also enables the integration of several radiators in the same bathroom.

For optimal cooling, the walls of the coolant bath must be provided with a layer that reflects UV radiation well, or, in the case of walls made of aluminum or an aluminum alloy, polished. The use of a grid-like or mesh-shaped metallic first electrode ensures a low level of shadowing of the radiation by the electrode.

Another variant consists in providing a part of the outer surface of the outer dielectric tube with a UV-reflecting layer. Yet another variant provides for a separate reflector to be installed in the coolant bath, which reflector is designed in such a way that a considerable part of the UV radiation generated by the radiator leaves the bath without it having to pass through the actual radiator again.

In all these variants, the coolant bath can also be used to cool the electrical and electronic components of the power source for feeding the radiator, e.g. in that the parts to be cooled are mounted directly on the outer walls.

Particular embodiments of the invention and the further advantages which can be achieved thereby are explained in more detail below with reference to the drawings.

Brief description of the drawings

Fig.1

eine Bestrahlungseinrichtung mit einem UV-Zylinderstrahler, der in ein Kühlmittelbad eingetaucht ist, und bei dem die UV-Strahlung durch ein Fenster nach aussen dringen kann;

Fig.2

Einen Längsschnitt durch die Einrichtung nach Fig.1 längs deren Linie AA;

Fig.3

eine Abwandlung der Einrichtung gemäss Fig.1 mit einem separaten Reflektor im Kühlmittelbad.

In the drawing, embodiments of the high-power radiation device are shown in a highly simplified form; shows

Fig. 1

an irradiation device with a UV cylinder emitter which is immersed in a coolant bath and in which the UV radiation can penetrate outward through a window;

Fig. 2

A longitudinal section through the device of Figure 1 along the line AA;

Fig. 3

a modification of the device according to Figure 1 with a separate reflector in the coolant bath.

Detailed description of the invention

The irradiation device shown schematically in FIGS. 1 and 2 comprises a UV high-power lamp with an outer dielectric tube 1, for example made of quartz glass, and an inner dielectric tube 2 arranged concentrically therewith, the inner wall of which is provided with an inner electrode 3. The annular space between the two tubes 1 and 2 forms the discharge space 4 of the radiator. The inner tube 2 is inserted gas-tight into the outer tube 1, which was previously filled with a gas or gas mixture that emits UV or VUV radiation under the influence of silent electrical discharges. A wide-meshed metal net is used as the outer electrode 5, or it consists of individual metal wires or metal strips running in the longitudinal direction of the tube, which extends over approximately the upper half circumference of the outer tube 1. In the case of a strip-shaped electrode arrangement, the individual strips are connected to one another at a plurality of axially distributed locations. Both the outer electrode 5 and the outer dielectric tube 1 are transparent to the UV radiation generated. The lower circumference of the tube 1 is provided with a reflector 6. This can be achieved, for example, with a vapor-deposited aluminum layer. This reflector is at the same electrical potential as the outer electrode 5.

The radiator just described is immersed in a coolant bath 10 delimited by metallic walls 7, 8, 9, 17, 18, through which coolant, preferably distilled water, flows through coolant inflow 11 or coolant outflow 12. In the upper part there is a UV-permeable window 13, e.g. made of quartz glass.

Another possibility of guiding the resulting radiation preferably through the window 13 into the outside space is to mirror the inside of the walls 7, 8 and 9, which can be done in aluminum walls by polishing the surfaces. A preferred embodiment optionally provides for mirroring the vessel walls to use a separate reflector 14 in the bottom section of the bath, which has a plurality of openings 15 and is at the same electrical potential as the vessel walls. The breakthroughs allow a sufficient coolant flow from the inlet 11 to the outlet 12. The reflector 14 is shaped in such a way that it reflects a large part of the UV light emitted downwards by the radiator without the radiation again passing through or even the two dielectric tubes 1 and 2 got to. The cross section of the reflector 14 can be thought of as being composed of two parabolic sections.

The electrodes 3 and 5 are led to the two poles of an AC power source 16. The AC power source 16 basically corresponds to those used for feeding ozone generators. Typically, it delivers an adjustable alternating 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 4 and composition of the filling gas.

The filling gas is, for example, mercury, noble gas, noble gas-metal vapor mixture, noble gas-halogen mixture, optionally under Use of 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, I₂, Br₂, Cl₂ oder eine Verbindung die in der Entladung ein oder mehrere Atome F, I, Br oder Cl ab spaltet;
• ein Edelgas (Ar, He, Kr, Ne, Xe) oder Hg mit O₂ oder einer Verbindung, die in der Entladung ein oder mehrere O-Atome abspaltet;
• ein Edelgas (Ar, He, Kr, Ne, Xe) mit Hg.

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

• An inert gas (Ar, He, Kr, Ne, Xe) or Hg with a gas or vapor from F₂, I₂, Br₂, Cl₂ or a compound which splits off one or more atoms F, I, Br or Cl in the discharge;
• a noble gas (Ar, He, Kr, Ne, Xe) or Hg with O₂ or a compound that releases one or more O 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 1 and 2 and their properties, pressure and / or temperature in the discharge space 4.

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

Claims (4)

1. An irradiation device with a high power emitter, in particular for ultraviolet light, which has a discharge chamber (4), filled with a filling gas emitting radiation under discharge conditions, the walls of which discharge chamber (4) are formed by a first dielectric (1), which first dielectric (1) is provided on its surface facing away from the discharge chamber with first metallic electrodes (5), and has second electrodes (3), and with an alternating current source (16) connected to the first and second electrodes (5;3) to supply the discharge, in which the high power emitter is immersed into a bath (10) of cooling medium, such that at least partially the first dielectric (1) and at least the first electrodes (5) have the cooling medium flowing around them, and that at least one wall (13) of the cooling medium bath (10) and the cooling medium itself are permeable by the generated radiation, characterised in that the walls of the discharge chamber (4) are additionally formed by a second dielectric (2), which is provided with the second electrodes (3) on its surface facing away from the discharge chamber, that the walls (7,8,9) of the cooling medium bath (10), with the exception of the wall (13) permeable to radiation, are provided with a layer reflecting UV radiation or in the case of walls (7,8,9) of aluminium or an aluminium alloy, the latter are polished and that the first metal electrode (5) is constructed in a grid- or network form.
2. An irradiation device according to Claim 1, characterised in that the first dielectric (1) is constructed as a tube and a part of its outer surface is provided with a UV-reflecting layer (6).
3. An irradiation device according to Claim 1, characterised in that a separate reflector (14) is incorporated into the cooling medium bath (10), which reflector is designed such that a considerable portion of the UV radiation generated by the emitter leaves the cooling medium bath (10) without it having to pass through the actual emitter once again.
4. An irradiation device according to one of Claims 1 to 3, characterised in that the cooling medium bath (10) is also able to be used to cool the electric and electronic components of the current source for supplying the emitter.

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