Note: Descriptions are shown in the official language in which they were submitted.
206857~
28.5.91/He
91/043
TITLE OF THE INVENTION
Irradiation device having a high-power radiator
BACKGROUND OF THE INVENTION
S Field of the invention
The invention relates to an irradiation device
having a high-power radiator, especially for ultra-
violet light, having a discharge space, which is filled
with filling gas emitting radiation under dischar~e
conditions and the walls of which are formed by a first
and a second dielectric, which is provided, on its sur-
faces facing away from the discharge space, with first
metallic lattice-type or grid-type and second elec-
trodes, having an alternating current source, connected
to the first and second electrodes, to feed the
discharge.
In this case, the invention makes reference to
prior art as is disclosed, for example, in
EP-A 0,254,111.
Discussion of Backaround
The indu~trial application of photochemical
proce88e8 i8 to a great extent dependent upon the
availability of suitable W sources. The conventional
W radiators give low to medium W intensities at
certain discrete wavelengths, such as, for example,
low-pressure mercury lamps at 185 nm and especially at
254 nm. Really high W power levels are obtained only
from high-pressure lamps (Xe, Hg), which, however, then
distribute their radiation over a greater wavelength
range. The new excimer lasers have made some new
wavelengths available for photochemical fundamental
experiments, but at the present time, for reasons of
cost, are suitable for an industrial process really
only in exceptional cases.
A novel excimer radiator is described in the
initially mentioned EP Patent Application, or also in
the conference publication "Novel UV and VUV Excimer
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Radiators~ by U. Kogelschatz and B. Eliasson, dis-
tributed at the 10th lecture conference of the
~ssociation of German Chemists, Photochemistry
Technical Group, in WUrzburg (FRG) on 18-20 November
1387. This novel type of radiator is based on the
principle that it is also possible to generate excimer
radiation in silent electrical discharges, a type of
discharge which is employed in the production of ozone
on an industrial scale. In the filaments of current,
which exist only for a short time (~ 1 microsecond), of
this discharge, rare-gas atoms are excited by electron
collision, which atoms further react to form excited
complexes o~ molecules (excimers). These excimers have
a life of only a few 100 nanoseconds, and, upon
disintegration, give up their binding energy in the
form of W radiation.
Even as far as the power supply, the construc-
tion of such an excimer radiator corresponds to a large
extent to that of a conventional ozone generator, with
the essential difference that at least one of the elec-
trodes and/or dielectric layers bounding the discharge
space transmits the generated radiation. At least one
of these electrodes might shade off the qenerated
radiation only to a slight extent. A further require-
ment imposed upon the radiator i~ that, even at highpower densities, it too should radiate as little heat
as possible. This i6 particularly important in
applications in the graphics industry, where printing
inks frequently have to be hardened on a heat-sensitive
background.
SUMMARY OF THE INVENTION
Proceeding from the prior art, the object of
the invention is to provide an irradiation device
3~ having a radiator, especially for W or V W radiation,
the electrodes of which shade off the radiation as
little as possible and which radiator can optimally be
cooled.
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206857~
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In order to achieve this object, it is provided
according to the invention that the radiator is
immersed in a coolant bath, in such a manner that the
coolant flows around the first dielectric and at least
the first electrodes, and that at least one wall of the
coolant bath and the coolant itself transmit the
generated radiation.
An irradiation device constructed in this
manner satisfies all requirements encountered in
practice:
- The invention permits the construction of an
entirely cold radiator; this is especially impor-
tant in connection with the hardening of printing
inks on a heat-sensitive background.
1~ - The outer electrodes can be of simple construction
- it is sufficient to provide a few metal strips
or metal wires which extend in the longitudinal
direction of the radiator and which do not
neces~arily need to rest on the outer dielectric.
In this manner, the dielectric~ can readily be
exchanged.
- The coolant, pre~erably water, prevent~ external
dischar~es between the outer electrodes and outer
wall of the radiator. This prevents the formation
of ozone.
- As no further external discharges can develop,
metal deposition by sputtering is also prevented,
i.e. the W transmittance is not impaired, even
after a relatively long period of operation.
30 - In the event that the respective application per-
mits operation only with a coolant bath sealed off
on all sides and the W radiation can leave said
bath only through a window, the latter can readily
be cleaned or exchanged. This is significant for
the use of the radiator in the graphics industry,
where it is frequently the case that ink residues
have to be removed.
- The invention permits not only a strictly modular
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construction, but also the integration of a
plurality of radiators within the same bath.
A ~irst advantageous development of the subject
of the invention comprises providing the walls of the
coolant bath with a layer which reflects the W
radiation well, or, in the case of walls composed of
aluminum or an aluminum alloy, polishing said wall~. A
further variant comprise3 providing a part of the outer
~urface of the outer dielectric tube with a W-
reflecting layer. Yet a further variant provideQ theincorporation, in the coolant bath, of a separate
reflector which is designed so that a considerable part
of the W radiation generated by the radiator leaves
the bath without said radiation having to pass the
actual radiator once again.
In all these variants, the coolant bath can
also be utilized for the cooling of the electrical and
electronic components of the current source for feedin~
the radiator, e.g. in that the parts to b~ cooled are
mounted directly on the outer walls.
Particular refinements of the invention and the
further advantage~ attainable thereby are explained in
gre~ter detail hereinbelow with reference to the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention
and many of the attendant advantages thereof will be
readily obtained as the same becomes better understood
by reference to the following detailed description when
considered in connection with the accompanying drawing,
which shows embodiments of a high-power irradiation
device in a highly simplified form, and wherein:
Fig. 1 shows an irradiation device having a W
cylinder radiator which is immersed in a
coolant bath, and in which radiator the W
radiation can penetrate to the exterior through
a wlndow;
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Fiq. 2 shows a longitudinal section through the device
according to Fig. 1, along the line AA therein;
~ig. 3 shows a modification of the device according to
Fig. 1, having a separate reflector in the
5coolant bath.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, wherein like
reference numerals designate identical or corresponding
parts throughout the several views, in Figures 1 and 2
there is presented a diagrammatic representation of an
irradiation device which comprises a W high-power
radiator having an outer dielectric tube 1, e.g. of
quartz glass, an inner dielectric tube 2, which i8 dis-
posed concentrically thereto and the inner wall ofwhich 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 in a ga~-tight manner into the outer tube 1,
which was filled, in advance, with a ga~ or gas mixture
which, under the influence of silent electrical dis-
charges, emits W or V W radiation. The outer electrode
5 employed is a wide-mesh metal ~rid, or the latter
consists of individual metal wires or metal strip~
which extend in the longitudinal direction of the tube,
which grid e~tends over approximately the upper half-
circumference of the outer tube 1. In the case of a
strip-type electrode arrangement, the individual strips
are connected to one another at a plurality of axially
distributed points. ~oth the outer electrode 5 and also
the outer dielectric tube 1 transmit the generated W
radiation. The lower circumference of the tube 1 is
provided with a reflector 6. This can, for example, be
formed by a vapor-deposited aluminum layer. This
reflector is at the same electrical potential as the
outer electrode 5.
The radiator which has just been described is
immersed in a coolant bath 10, which is bounded by
2~6~37~
-- 6 --
metal walls 7, 8, 9, 17 and 18 and through which, via
coolant inlet 11 and coolant outlet 12 respectively,
coolant, preferably distilled water, flows. A
UV-transmitting window 13, e.g. of ~uartz glass, is
provided in the upper part.
Another possibility for directing the created
radiation in a preferred manner through the window 13
into the outer space comprises mirror-coating the
internal surface of the walls 7, 8 and 9; in the case
of aluminum walls, this can take place by polishing the
surfaces. For the mirror-coating of the vessel walls, a
preferred embodiment optionally provides for the
insertion of a separate reflector 14 into the floor
portion of the bath, which separate reflector exhibits
a multiplicity of perforations 15 and is at the same
electrical potential as the vessel walls. The perfora-
tions permit an adequate coolant flow from the inlet 11
to the outlet 12. The reflector 14 i8 formed 80 that it
reflects a major part of the W light emitted downwards
by the radiator, without the radiation having to pass
the dielectric tube or indeed the two dielectric tubes
1 and 2 once again. The cross-section of the reflector
14 can be considered a~ being composed of two parabolic
sections.
The electrodes 3 and 5 are passed to the two
terminals of an alternating current source 16. The
alternating current source 16 corresponds,
fundamentally, to those which are used for supplying
ozone generators. Typically, it delivers an adjustable
alternating voltage in the order of magnitude of
several 100 volts to 20,000 volts at frequencies within
the range of industrial alternating current, reaching
up to a few thousand kHz - depending upon the electrode
geometry, the pressure in the discharge space 4 and the
composition of the filling gas.
The filling gas is, for example, mercury, a
rare gas, rare gas/metal vapor mixture, rare
gas/halogen mixture, possibly with the use of an
2068~7~
-- 7
additional further rare gas, preferably Ar, He or Ne,
as buffer gas.
Depending upon the desired spectral composition
of the radiation, it is in this case possible to use a
substance/mixture of substances according to the
following table:
Fillina aas 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 - 2S5 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 to the above, a whole series of
further filling gases may be considered:
- A rare gas (Ar, He, Kr, Ne, Xe) or Hg with a gas
or vapor consisting of F2, I2, Br2, C12 or a com-
pound which in the discharge splits off one or
more F, I, Br or Cl atoms;
- a rare gas (Ar, He, Kr, Ne, Xe) or Hg with 2 or a
compound which in the discharge splits off one or
more O atoms;
- a rare gas (Ar, He, Kr, Ne, Xe) with Hg.
In the silent electrical discharge which is
formed, the electron energy distribution can be
optimally set by the thickness of the dielectrics 1 and
2 and their pressure and/or temperature properties in
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the discharge space 4.
Upon app].ication of an alternating voltage
between the electrodes 3 and 5, a multiplicity of dis-
charge channels (partial discharges) is formed in the
discharge space 4. These enter into interaction with
the atoms/molecules of the filling gas, which leads, in
the final analysis, to the W or V W radiation.
Obviously, numerous modifications and varia-
tions of the present invention are possible in light of
the above teachings. It is therefore to be understood
that within the scope of the appended claims, the in-
vention may be practiced otherwise than as specifically
described herein.
