EP0547366A1 - High power radiator - Google Patents

Abstract

By inserting an additional capacitance in the form of an additional moulding (12'') consisting of dielectric material into the interior of a UV excimer radiator, it is possible to force loss-free control of the axial and/or radial distribution of the power consumption and UV intensity. This measure is particularly advantageous for the irradiation of broad substrates, such as films, papers and the like coated with paints, varnishes or adhesives, when it is intended to irradiate all regions of the substrate with approximately the same dose. <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 dielectric, the outer surfaces of the outer dielectric being provided with first electrodes, with second electrodes Electrodes on the surface of the second dielectric facing away from the discharge space, and with an alternating current source connected to the first and second electrodes for supplying the discharge.

The invention relates to a state of the art, such as that which results from EP-A 254 111, US patent application 07/485544 dated February 27, 1990 or also EP patent application 90103082.5 dated February 17, 1990.

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 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 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 high-performance lamps mentioned are characterized by high efficiency, economical structure and enable the creation of large lamps, such as those used in UV polymerization and sterilization. Wide conveyor belts or cylinders often have to be irradiated by rod-shaped UV lamps. Typically, films, papers, cardboards, fabric frames, etc. coated with paints, varnishes or adhesives are irradiated by UV lamps approx. 1 meter long. Since the intensity of the lamps is normally evenly distributed over the length, the edge zones of the substrate naturally receive a lower radiation dose.

In order to obtain a dose that is sufficient for the process at the edge, the emitters would have to be made considerably longer than the substrate width. This is usually ruled out on systems with conveyor belts for design reasons. The other option is to increase the intensity of the lamps so that the dose is just sufficient on the edge. So you accept a considerable overexposure of the middle zones with a corresponding energy consumption.

Presentation of the invention

Starting from the prior art, the object of the invention is to create a high-power radiator, in particular for UV or VUV radiation, which is characterized in particular by high efficiency, is economical to manufacture, and in which the radiation can be emitted in a targeted manner. In particular, the proposed radiator is intended to enable flat substrates to be applied homogeneously.

To achieve this object, it is provided according to the invention in a high-power radiator of the type mentioned at the outset that means for influencing the radiation characteristic of the radiator are provided for locally changing the operating voltage of the discharge and / or the effective dielectric capacitance, and essentially coupling the second electrode to the discharge space takes place via a liquid with a dielectric constant that is at least 10 times higher than the dielectric constant of the dielectric, which liquid also serves to cool the radiator.

The invention makes it possible for the first time to create UV lamps whose intensity is distributed unevenly over the length and is slightly raised at the ends.

Embodiments of the invention and the advantages which can be achieved thereby are explained in more detail below with reference to the drawing.

Brief description of the drawings

Fig.1

einen UV-Zylinderstrahlers mit konzentrischer Anordnung des inneren Dielektrikumsrohres im Längsschnitt;

Fig.2

einen Schnitt durch den UV-Strahler nach Fig.1 längs deren Linie AA;

Fig.3

eine Ausführungsform des erfindungsgemässen Strahlers mit einem Entladungsraum, dessen Spaltweite im mittleren Bereich kleiner als im Randbereich ist;

Fig.4

eine Ausführungsform einer Bestrahlungseinrichtung analog Fig. 3, jedoch mit einem Entladungsraum, dessen Spaltweite im mittleren Bereich grösser als im Randbereich ist;

Fig.5

eine Ausführungsform mit einer Zusatzkapazität in Gestalt eines Dielektrikumsrohres im Inneren des inneren Dielektrikumsrohrs;

Fig.6

eine Ausführungsform mit einer Zusatzkapazität in Gestalt eines die zentrale Innenelektrode umgebenden Formkörpers;

Fig.7

eine Ausführungsform mit einer Zusatzkapazität in Gestalt eines Formkörpers, der sich an die Innenwand des inneren Dielektrikumsrohrs anschmiegt;

Fig.8

eine Ausführungsform mit einer Zusatzkapazität in Gestalt eines Formkörpers mit sichelförmigem Querschnitt, der sich in Umfangsrichtung nur über den halben Innenumfangs des inneren Dielektrikumsrohres erstreckt;

Fig.9

einen Schnitt durch den Strahler nach Fig.8 längs deren Linie BB;

Fig.10

eine Abwandlung Ausführungsform nach Fig.8 und 9 mit einer Zusatzkapazität in Gestalt eines Dielektrikum-Halbrohrs, das sich nur über den halben inneren Umfang des inneren Dielektrikumrohres erstreckt;

Fig.11

eine Abwandlung der Ausführungsform nach Fig.5 mit zentraler Elektrode und einer Zusatzkapazität in Form eines Dielektrikum-Halbrohres im Raum zwischen Innenelektrode und innerem Dielektrikumsrohr;

Fig.12

eine weitere Abwandlung der Ausführungsform nach Fig.5 mit zentraler Elektrode und einer Zusatzkapazität in Form eines Dielektrikumsformkörpers mit sichelförmigem Querschnitt im Raum zwischen Innenelektrode und innerem Dielektrikumsrohr;

Fig.13

eine weitere Abwandlung der Ausführungsform nach Fig.5 mit zentraler Elektrode und einer Zusatzkapazität in Form eines Dielektrikumformkörpers mit nierenförmigem Querschnitt im Raum zwischen Innenelektrode und innerem Dielektrikumsrohr.

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

Fig. 1

a UV cylinder lamp with a concentric arrangement of the inner dielectric tube in longitudinal section;

Fig. 2

a section through the UV lamp according to Figure 1 along the line AA;

Fig. 3

an embodiment of the radiator according to the invention with a discharge space, the gap width is smaller in the central region than in the edge region;

Fig. 4

an embodiment of an irradiation device analogous to Figure 3, but with a discharge space, the gap width is larger in the central area than in the edge area;

Fig. 5

an embodiment with an additional capacity in the form of a dielectric tube in the interior of the inner dielectric tube;

Fig. 6

an embodiment with an additional capacity in the form of a molded body surrounding the central inner electrode;

Fig. 7

an embodiment with an additional capacity in the form of a shaped body which nestles against the inner wall of the inner dielectric tube;

Fig. 8

an embodiment with an additional capacity in the form of a shaped body with a crescent-shaped cross-section which extends in the circumferential direction only over half the inner circumference of the inner dielectric tube;

Fig. 9

a section through the radiator according to Figure 8 along the line BB;

Fig. 10

a modification embodiment according to Figures 8 and 9 with an additional capacity in the form of a dielectric half-tube, which extends only over half the inner circumference of the inner dielectric tube;

Fig. 11

a modification of the embodiment of Figure 5 with a central electrode and an additional capacity in the form of a dielectric half-tube in the space between the inner electrode and the inner dielectric tube;

Fig. 12

5 a further modification of the embodiment according to FIG. 5 with a central electrode and an additional capacitance in the form of a shaped dielectric body with a crescent-shaped cross section in the space between the inner electrode and the inner dielectric tube;

Fig. 13

5 a further modification of the embodiment according to FIG. 5 with a central electrode and an additional capacitance in the form of a shaped dielectric body with a kidney-shaped cross section in the space between the inner electrode and the inner dielectric tube.

Ways of Carrying Out the Invention

The starting point for the invention to be described in the following is an eximer radiator according to FIGS. 1 and 2. An inner quartz tube 2 is 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 arranged coaxially. A helical inner electrode 3 bears against the inner surface of the inner quartz tube 2.

An outer electrode 4 in the form of a wire mesh extends over the entire outer circumference of the outer quartz tube 1.

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 quartz tubes 1 and 2 are closed or melted at both ends by a cover 5 and 6, respectively. The space between the two tubes 1 and 2, the discharge space 7, is filled with a gas / gas mixture which emits radiation under discharge conditions. The interior 8 of the inner quartz tube 2 is filled with a liquid with a high dielectric constant, preferably demineralized water (ε = 81). This liquid also serves to cool the radiator. The coolant is supplied or removed via the connections 9 and 10. As will be explained in more detail later with the designs with a central inner electrode, the cooling liquid serves for the electrical coupling of the inner electrode 3 to the inner quartz tube 2, so that it is not necessary for the helical electrode 3 to be in contact with the inner wall everywhere.

The two electrodes 3, 4 are connected to the two poles of an alternating current source 11. The alternating current source supplies an adjustable alternating voltage in the order of magnitude from 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.

Daneben kommen eine ganze Reihe weiterer Füllgase in Frage:

• 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.

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

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.

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

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.

wobei f die Frequenz der Speisespannung, C_D die Dielektrikumskapazität, U_B die mittlere Brennspannung der Gasentladung und β das Kapazitätsverhältnis Entladungsspalt-Kapazität/Dielektrikumskapazität (C_S/C_D) ist.In the case of a cylindrical radiator according to FIG. 1 or FIG. 2, the power consumption of a silent electrical discharge is described by the following formula:

${\text{P = 4 f C}}_{\text{D}}{\text{U}}_{\text{B}}{\text{(Û - (1 + β) U}}_{\text{B}}\text{) (1)}$

where f is the frequency of the supply voltage, C _{D is} the dielectric capacitance, U _{B is} the mean operating voltage of the gas discharge and β is the capacitance ratio of the discharge gap capacitance / dielectric capacitance (C _S / C _D ).

For a given voltage supply (frequency f and peak voltage Û fixed), the power consumption can be changed by changing the operating voltage U _B and / or by Dielectric capacitance C _D affect. If you only change these sizes locally, you can specifically influence the power consumption and thus the UV intensity along a tube and / or in the circumferential direction of the tube.

ist (Maximum der Leistungsparabel).In a melted-down discharge tube, for example according to FIG. 1, the pressure and the gas composition are the same everywhere. Since the operating voltage in the pressure range of interest is a monotonous, almost linear function of the gap width, the power can be controlled by varying the width of the discharge gap. A distinction must be made between two operating states of the discharge:
The power depends (with fixed f and Û) quadratically on U _B (see equation (1)). The maximum power is absorbed when

${\text{U}}_{\text{B}}\text{= Û / (2 (1 + β)) (2)}$

is (maximum of the performance parabola).

As long as U _{B is} smaller than this value, increasing the gap width leads to increased power consumption (Fig. 3). If U _{B is} greater than the value defined in (2), reducing the gap width leads to increased power consumption (Fig. 4).

The application of this knowledge to a radiator according to FIG. 1 leads to embodiments as shown in a simplified form in FIGS. 3 and 4. As stated above, two alternatives are possible, depending on how the operating voltage is relative to the maximum of the power parabola. In order to increase the intensity in the edge zones in a radiator according to FIG. 1 so that the dose is sufficient in this area, the gap width w _m in the middle section is smaller than the gap width w _r in the edge zone (FIG. 3), or vice versa versa (Fig.4).

The power consumed can also be increased by increasing the dielectric capacitance (see equation (1)). This can be achieved by reducing the wall thickness of the inner and / or outer quartz tube 2 or 1 in the edge zones, or by doping the quartz with substances such as TiO₂ or BaTiO₃.

The previously mentioned options for varying the power consumption in the longitudinal direction of the radiator are constructively very complex. It is much easier and more economical to insert an additional capacitance between the two electrodes 3 and 4, as is illustrated schematically in FIG.

In a departure from the radiators according to FIGS. 1 to 4, the radiator shown in FIG. 5 has a central electrode 3 ', over which a dielectric tube 12, which acts as an additional capacitance, is pushed. Its inside diameter is larger than the outside diameter of the central electrode 3 '. The length of this tube 12 is less than that of the outer and inner dielectric tubes 1 and 2. Because this additional capacitance (electrically) is connected in series to the capacities of the inner and outer dielectric tube, the effective dielectric capacitance C _D in the central part of the radiator is reduced . This automatically leads to a lower power consumption in the center of the radiator. The wall thickness and length of the tube 12 thus allow the axial intensity profile to be controlled and the dose to be largely homogenized on the substrate. The intensity profile can be controlled even more precisely if a molded body made of dielectric material is installed, which has a continuous transition, as shown in FIG. This molded body 12 'completely surrounds the central inner electrode 3' and tapers towards the edge. It consists of a dielectric, easily machinable material, e.g. made of PTFE (ε = 2.2), polyimide (ε = 3.5) or nylon (ε = 3.75).

A common feature of the embodiments according to FIGS. 5 and 6 is that the coupling of the central inner electrode 3 'to the inner quartz tube 2 (and thus to the discharge space 7) is not direct, but rather via the liquid filling the interior 8 of the inner quartz tube 2, preferably demineralized water. As a result of the high dielectric constant of water (ε = 81), the effective increase in the dielectric capacitance C _D is essentially only influenced by the molded body 12 ′ and hardly by the water.

Instead of a shaped body surrounding and supported by the central inner electrode 3 ', a tubular shaped body 12' 'can also be fastened to the inner wall of the inner quartz tube 2, which, as can be seen from FIG. 7, similarly to FIG. 6 against its two ends tapers towards it. Analogous to the embodiments according to FIGS. 1 to 4, a helical electrode 3 is used here, which rests in the middle section on the inner wall of the shaped body 12 ″ and in the edge zone on the quartz tube 2.

The axial power and intensity control described above can also be used, without going beyond the scope of the invention, for the radial control of the power consumed and thus of the UV intensity.

According to FIGS. 8 and 9, a shaped body 12a with a crescent-shaped cross section made of dielectric material extends only over the upper half of the inner circumference of the inner quartz tube 2 (FIG. 9). In longitudinal section, it corresponds to the shaped body 12 ″ of FIG. 7, ie on both Ends tapering in front of the edge area of the spotlight. An equivalent solution with a half tube 12b made of dielectric material without a leaking edge zone is shown in section in FIG. In both variants a helical inner electrode 3 is used.

Analogous to the embodiments according to FIGS. 5 and 6 with a central inner electrode 3 ', molded bodies made of dielectric material can also be introduced into the interior 8 of the inner quartz tube 2, which only partially surround this electrode. Thus, in the upper section of the interior 8 of FIG. 11, a half tube 12c made of dielectric material is arranged, in FIG. 12 a shaped body 12d with a crescent-shaped cross section and in FIG. 13 a shaped body 12e with a kidney-like cross section. All these additional capacitances 12a to 12e reduce the power consumption in the upper section of the discharge space 7, cause an increased power consumption in the lower section of the discharge space 7 and thus force a downward radiation.

As shown in Fig. 8 and 9, radial and axial power and intensity control can be easily combined in one radiator. This also applies to radiator arrangements, as shown in FIGS. 3 and 4. Depending on the internal voltage U _B, the inner quartz tube 2 can also be configured there so that the gap width is the same everywhere in the lower half in the axial direction, while in the upper half it is larger or smaller in the middle section than in the peripheral zone .

It is also evident from the exemplary embodiments that the measures according to the invention for power and intensity control can readily be applied retrospectively to existing radiators, so that in the case of radiators manufactured in series, loss-free control of the axial and / or radial ones is made by inserting an additional molded part in the inner cooling circuit Distribution of power consumption and UV intensity can force.

Claims (11)

High-power radiator, in particular for ultraviolet light, with a discharge space (7) filled with filling gas emitting radiation under discharge conditions, the walls of which are formed by an outer (1) and an inner dielectric (2), the outer surfaces of the outer dielectric having first electrodes (4 ) are provided with second electrodes (3; 3 ') on the surface of the second dielectric (2) facing away from the discharge space (7), and with an alternating current source (1) connected to the first (4) and second electrodes (3; 3') 11) for supplying the discharge, characterized in that means (12; 12a ...) are provided for influencing the radiation characteristic of the radiator for locally changing the operating voltage (U _B ) of the discharge and / or the effective dielectric capacitance (C _D ), and the coupling of the second electrode (3; 3 ') to the discharge space (7) takes place essentially via a liquid with a dielectric constant which is at least 10 times higher than the dielectric constant of the dielectric, which liquid also serves to cool the radiator. High-power radiator according to claim 1, characterized in that the liquid is water with a dielectric constant around ε = 80. High-power radiator according to Claim 1 or 2, characterized in that the gap width (w _m ) of the discharge space (7) in the central section of the radiator is different from the gap width (w _r ) in the edge zone of the radiator. High-power radiator according to Claim 1, 2 or 3, characterized in that the gap width of the discharge space (7) in the upper half of the radiator is different from the gap width in the lower half of the radiator. High-power radiator according to Claim 1 or 2, characterized in that an additional capacitance (12; 12a, ...) is provided between the second electrode (3; 3 ') and the second dielectric (2), which additional capacitance is formed as a molded body made of dielectric material is which shaped body extends essentially only over the central section and / or only over part of the circumference of the radiator. High-power radiator according to Claim 5 with a central electrode (3 ') as the second electrode, characterized in that the shaped body is a quartz tube (12) which is pushed over the central electrode (3') (Fig. 5). High-power radiator according to claim 5 with a central electrode (3 ') as the second electrode, characterized in that the molded body (12) is pushed onto the central electrode (3') and preferably tapers to the side edge of the radiator. High-power radiator according to Claim 5, characterized in that the additional capacitance is designed as a molded body (12 ''; 12a; 12b) which bears on the inner wall of the second dielectric (2) and that the first electrode (3) bears at least locally on the molded body . High-power radiator according to claim 8, characterized in that the molded body tapers towards the side edge of the radiator (Fig. 7). High-power radiator according to Claim 8 or 9, characterized in that the shaped body has a crescent-shaped cross section and extends only over part of the circumference of the second dielectric (2) (FIG. 9). High-power radiator according to Claim 5 with a central first electrode (3 '), characterized in that in the interior (8) of the second dielectric (2) between the central electrode and the second dielectric (2) and a molded body (12c, 12d) is distanced therefrom , 12e) is provided with a semi-tubular, sickle-shaped or kidney-shaped cross-section made of dielectric material.

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