EP0222060A2 - Device for the treatment of material by ultraviolet rays - Google Patents

Abstract

A device comprises a UV radiation source and a reflector. The reflector preferably consists of two parabolic or elliptical half- shells. One or more coatings for the reflection of UV radiation and, underneath, a coating for absorbing the longer-wavelength part of the spectrum of the UV radiation source are provided on the reflector surface. A diffusion barrier layer is arranged between these coatings. The reflection layer consists of alternately low-refracting dielectric layers of SiO2 and high-refracting layers of HfO2, the diffusion barrier layer consists of a dielectric layer of SiO2 having a physical thickness of at least 0.5 mu and the absorption layer consists of a black anodically oxidised layer, black chromium- or nickel-plating, anodisation or bronzing of a polished copper coating or nickel coating of the reflector body consisting of aluminium alloy. <IMAGE>

Description

The invention has a device for treating matter by UV rays, preferably for drying surfaces coated with UV rays or UV inks, for example for drying UV printing inks immediately after printing in a rotary printing press and for irradiating gases and liquids to the subject, which consists of a housing in which a UV radiation source and at least one reflector surface are arranged.

With multi-color rotary printing presses, it is necessary to dry the ink printed by one printing unit before another color is printed by another printing unit. It has therefore been proposed to arrange a drying device directly behind each printing unit, which usually consists of an intensive heat source.

The known drying devices are unsuitable for drying the so-called UV inks, which are increasingly being used, since they are not drying by evaporation of volatile constituents of the paint, such as water or solvent, but one

Polymerization process is under the influence of ultraviolet radiation. For drying UV inks, light sources are therefore predominantly proposed which emit the highest possible proportion of ultraviolet radiation. Commercial quartz lamps are used for this purpose, around which one or more reflectors are arranged, in order to direct as much of the 360 ° radiation from the quartz lamp onto the printed web of paper, plastic film or metal. Reflectors made of aluminum, anodized aluminum or stainless steel sheet are used.

The known UV lamps have the disadvantage, on the one hand, that not only the desired ultraviolet radiation, but also the entire radiation emitted by the radiation source, which extends over a large spectral range (approx. 200 to 1000 nm), onto the irradiated surface of the printed area Web is emitted directly or indirectly via the reflectors. Due to the high wall temperature of 650 to 800 ° C, caused by the high proportion of visible and infrared radiation from 400 nm, this leads to a very strong heating of the printed web and, depending on the type of material, to stretching and moisture-related distortions, softening Plastic film or scorching of the paper, so that measures must be taken to cool the printed web (maximum permissible web temperature 40 ° C).

Another disadvantage arises from the fact that, depending on the arrangement and nature of the reflectors, the theoretical portion of indirect radiation, which can be well over 50%, cannot be brought onto the printed web because of the limited reflectivity of the reflector material. The reflectivity in the range of 250 nanometers (nm) is 70% for anodized aluminum, 50% for non-anodized aluminum and only 40% for stainless steel.

On the other hand, the disadvantage is the very rapid aging of the reflectors. The reflective surfaces corrode extremely quickly due to the influence of radiation, heat and, under the simultaneous influence of vapors and gases rising from the printed web, of condensation water and due to the ozone formed when the quartz lamps are ignited, so that the reflection drops sharply after a relatively short period of operation. Investigations and measurements have shown that as a result of the escape of chlorinated hydrocarbons from the UV inks, which split up under the action of UV rays and heat and release chlorine into the atmosphere, hydrochloric acid, which forms the reflector material, forms together with the condensation water attacks. Vapors from the roller cleaner containing trichlorethylene can also produce similar effects.

Measurements have shown that for a perfect drying or polymerization of a UV ink print one with 80 m / min. required energy of ultraviolet radiation of 9 to 10 watt minutes / m ² drops below the minimum value after only 300 hours of operation. This requires that without replacing the reflectors, the device can only continue to be used as the web speed slows down, which is extremely disadvantageous economically.

It is an object of the invention to the known UV lamps to improve so that the UV radiation ^g with simultaneous he reduction of the radiation of the entire longer wavelength portion increases the spectrum of the radiation source and thus increases the efficiency and life of the radiators and their reflectors becomes.

The solution to the problem is seen in a device consisting of a UV radiation source and at least one reflector, the at least one reflector surface having one or more coatings for reflecting the UV radiation from the UV radiation source and an underlying coating for absorbing the longer-wave Part of the spectrum of the UV radiation source is provided.

The reflector preferably consists of two parabolic or elliptical half-shells, since the necessary coatings are difficult to apply to strongly curved surfaces.

The half-shells are preferably arranged so as to be pivotable relative to one another in order to be able to focus the reflected radiation.

Aluminum or its alloys, copper, brass or steel has proven to be advantageous as the material for the parabolic half-shells.

The reflection layer applied to the absorption layer consists of a multitude of alternating layers of high and low burning material, which together form a so-called interference filter.

Anodizing, black chrome plating, anodizing, black nickel plating and bluing have proven to be advantageous as absorption layers. The parabolic or elliptical half-shells preferably consist of an aluminum alloy, which is offered under the trademark "Extrudal 50".

The absorption layer preferably consists of several, respectively polished coatings of copper and nickel, which are applied to the previously polished aluminum surface. The polished nickel layer is black chrome-plated.

The diffusion barrier layer made of a dielectric with a physical thickness of at least 0.5 μm is preferably arranged between the absorption layer and the reflection layer. The diffusion layer advantageously consists of Si0 ₂ , which on the one hand behaves optically advantageous, on the other hand in the fact that no additional coating source is required because of the other coating.

The parabolic half-shells are preferably provided with a cooling system for dissipating the absorbed heat.

The parabolic half-shells consisting of "Extrudal 50" preferably consist of a continuous casting hollow profile, the cavities of which are connected to a cooling system.

The UV emitter consisting of two parabolic half-shells and a quartz lamp arranged between them is preferably provided at its lower opening with a cover that is permeable to UV radiation.

The cover is preferably made of quartz glass. Furthermore, it is advantageous to arrange an impermeable cover on the lower opening of the UV lamp, which cover can quickly close the opening in order to be able to cover the radiation in the event of a sudden train stop.

It has also proven to be advantageous to ventilate the interior of the device, which is closed off by a quartz glass pane at the bottom, by introducing dry and filtered air or a protective gas in a closed or open circuit with a slight excess pressure, in order to ensure that dust is deposited and the precipitation of Prevent steam or gases on the reflectors.

To further explain the invention, reference is made to an exemplary embodiment of the invention illustrated in the accompanying drawings and diagrams.

• Figur 1 eine grafische Darstellung eines Vergleiches der Wirksamkeit bekannter UV-Strahler mit dem Gegenstand der Erfindung;
• Figur 2 eine schematische Darstellung bekannter UV-Strahler und des Gegenstandes der Erfindung mit einem Vergleich des UV-Strahlenwirkungsgrades;
• Figur 3 eine Figur 2 entsprechende Darstellung, bezogen auf den IR-Strahlenwirkungsgrad;
• Figur 4 eine Seitenansicht der Vorrichtung gemäß der Erfindung;
• Figur 5 einen Schnitt durch die Beschichtung der Oberfläche der parabolischen Halbschalenreflektoren;
• Figur 6 ein Diagramm, in dem das Reflexionsverhalten (in %) über der Wellenlänge λ aufgetragen ist;

Show it

• Figure 1 is a graphical representation of a comparison of the effectiveness of known UV lamps with the subject of the invention;
• Figure 2 is a schematic representation of known UV lamps and the subject of the invention with a comparison of the UV radiation efficiency;
• FIG. 3 shows a representation corresponding to FIG. 2, based on the IR radiation efficiency;
• Figure 4 is a side view of the device according to the invention;
• FIG. 5 shows a section through the coating of the surface of the parabolic half-shell reflectors;
• FIG. 6 shows a diagram in which the reflection behavior (in%) is plotted against the wavelength λ;

FIGS. 7 and 8 are diagrams in which the radiation intensity of the UV and IR radiation is compared with one another when the half-shells are pivoted differently. In the graphical representation of FIG. 1, the minimum value of the UV radiation required per m ^{2 of} an area to be dried is based on a specific 3 web width and a web speed of 80 m / min. specified with 9 to 9.5 W. As the two lower curves, which show the radiation of known UV lamps, show, the required minimum value is already fallen below after 400 operating hours because of the increasing reduction in the UV reflection of the reflectors due to the corrosion that has occurred. The upper curve represents the amount of radiation from a device according to the invention. This is still after 2,500 hours of operation well above the minimum value. The drop in the amount of radiation here is not due to corrosion of the reflectors, but to a decrease in the performance of the quartz lamp. In the schematic representation in FIG. 2, the known UV lamps A and B are compared with the device C according to the invention with regard to their efficiency, the total UV radiation of the device C being set at 100 percent.

The UV lamp A only achieves 37% of the radiation from C, the UV lamp B only 71%. The indirect radiation at A is only 10% due to the poor reflection of the reflector, while 27% is due to the direct radiation of the quartz lamp. Due to the poor efficiency, two UV lamps of type A must be used one behind the other in order to achieve the required performance. The output of UV lamp B is better at 71%, with 37.5% being indirect radiation and 33.5% being direct radiation. The UV lamp 3 gives hence on the operating time calculated the worst result, because of the high proportion of indirect radiation and the managerial set forth above stun ^g sabfall due to corrosion of the reflectors of the drop in the overall performance is particularly high.

In the device C according to the invention, the power ratio between direct and indirect radiation is almost the same, but does not lead to a significant drop in the power of the indirect radiation, since the reflectors are practically not subject to wear or corrosion. A major advantage of the device according to the invention is that, because of the considerably reduced visible and IR radiation, the radiation source can be arranged closer to the material web, which increases the incidence of UV radiation.

In FIG. 3, the comparison shown in FIG. 2 is based on the IR radiation, 100% of the IR radiation in the device C according to the invention likewise being assumed. Here the efficiency of the absorption layer according to the subject of the invention is clear. The proportion of indirect IR radiation at C is only 24%, while the proportion of indirect radiation at A is 68% and a total IR radiation of 122% compared to C.

In view of the fact that two emitters are required for an efficient drying performance at A, there is also a double IR portion of 245% and an indirect portion of approx. 135%.

It also becomes clear here when compared to the comparison of UV radiation that the known reflectors allow relatively more IR than UV radiation, that is to say a large proportion of the desired UV radiation (approx. 30 to 40%) is not reflected.

With the UV lamp 3, the ratio is even more unfavorable. Compared to C, the total IR radiation is approximately 171%. The indirect IR radiation here is over 100%. Here, too, it becomes clear that the indirect IR reflection is greater than the indirect UV reflection. The diagrams in FIGS. 7 and 8 show the effect of UV and IR radiation with different inclinations of the reflector shells relative to one another (7.5 ° and 20 ° C.). It is known that the curing of UV printing inks is less dependent on the irradiation time than on the penetration of the ink layer with the UV radiation. The comparison shows that by focusing the UV radiation with an inclination of the half-shells by 20 °, the radiation intensity can be increased significantly. Due to the significantly improved absorption of the IR radiation, it is still below the in focus Figure 2 to the UV dryer B shown at a reduced distance compared to known driers of the radiation source from the printing web by 20%. Focusing in known UV lamps would lead to such high temperatures on the printing web that it could catch fire.

The device 1 shown in Figure 4 according to the invention consists of a housing 2 and a table 4, over which the printed web 5 at a web speed of 80 m / min. is pulled, is pivotally mounted. In the upper part of the housing 2, a quartz lamp 6 is arranged so that it can be replaced easily. Furthermore, two parabolic half-shell reflectors 7, 7 'are arranged in the housing 2. The hollow extruded profiles made of aluminum "extrudal 50" are provided with channels 8 for the flow of a coolant such as water or the like. The lower opening of the housing 2 is closed by a quartz glass plate 9. A blind 10 is arranged below the quartz glass plate 9, which can be quickly pulled in front of the quartz glass plate 9 by means not shown when the web is at a standstill and by means of a corresponding control. The surfaces of the parabolic half-shell reflectors 7, 7 'facing the interior of the housing are provided with an absorption layer 11, each made of a polished copper and nickel coating, which is black chrome-plated.

Tests have shown that the black chrome plating of the drawn extruded profiles of the aluminum alloy "Extrudal 50" can achieve the best results with regard to all parameters, although this does not necessarily achieve the best UV reflection. The absorption layer 11 must not only ensure good IR absorption, but also provide a good substrate for the quartz layers of the reflection layer 12 to be vapor-deposited.

The latter is the case with the black chrome plating of drawn aluminum surfaces. After the black chrome plating, the surfaces are matt and structureless and thus offer a very good adhesion surface, while, for example, a pure nickel plating offers an extraordinarily poor adhesion basis.

The reflection layer 12 consists of a total of 65 individual layers, of which the odd-numbered layers consist of hafnium dioxide and the even-numbered layers consist of silicon oxide. Each of these layers has a very specific thickness, which can be expressed as a multiple of λ / 4, where λ is the so-called "reference wavelength", which in the present case is 350 nm. The multiples of λ / 4 are only, for example, integers (e.g. 1.00); they are below 1.00 in numerous layers and only above 1.00 in the last (66th) layer, namely 1.36.

The resulting reflection curve (FIG. 6) clearly shows that the layer system has a reflection maximum limited by steep flanks in the range between 250 and 400 nm.

To produce the reflective layer, reflector half-shells made of black-chromed extruded aluminum alloy profiles "Extrudal 50" were placed on substrate holders in a vapor deposition system of the type 1100 Q (manufacturer: Leybold-Heraeus GmbH in Hanau, FRG) and the system was pressed within six minutes evacuated from 10 Pa. The substrates were then cleaned in a known manner by a glow discharge. The system was then evacuated to a pressure of 5 × 10 ^-3 Pa within a further 30 minutes and the substrates were heated to 260 ° C., whereupon oxygen was admitted as a scattering gas up to a pressure of 2 × 10 ^-2 Pa.

Subsequently, hafnium dioxide (Hf0 ₂ ), which was housed in an evaporation crucible, was degassed with an electron beam gun for two minutes until the pressure remained stable. Subsequently, the Hf0 ₂ was evaporated as the first layer and at the same time as an adhesion promoter with an evaporation rate of 1.3 nm / s. The regulation of the evaporation rate and the control of the orifices which can be swiveled in via the evaporators, by means of which the evaporation process for the respective layer was interrupted, was carried out using the known quartz crystal method. Following the Hf0 ₂ layer, a first Si0 ₂ layer was evaporated by means of a further electron beam gun with a vapor deposition rate of 1.0 nm / s, while the Hf0 _{2 was} kept at a sufficiently high temperature level by a lower energy supply. After the controlled closing of the diaphragm for the SiO ₂ evaporator, this was also kept at an elevated temperature level by means of low energy input and the electron beam gun for the Hf0 ₂ evaporation was again adjusted to the evaporation power. By alternating repetition of these coating processes, a total of 66 individual layers were deposited, each of which had a layer thickness which was a corresponding multiple of λ / 4, where λ is the so-called wavelength which was chosen to be 350 nm for the present purpose. The mentioned multiple of λ / 4 was varied between 0.66 and 1.00 for the second to sixty-fifth layers and was 0.46 for the first layer and 1.36 for the sixty-sixth layer consisting of SiO ₂ . The pressure in the vacuum chamber was kept constant throughout the process. After the last layer had evaporated, the evaporators were switched off and after they had cooled after five minutes the plant was flooded. Measurements of the reflection behavior led to the curve according to FIG. 6, which has excellent reflection behavior delimited by steep flanks in the wavelength range between 250 and 400 nm of interest here. The layer system adheres very well, is crack-free and has values over the entire area that lie between 87 and 97% (reflection). The infrared reflection was only about 5%.

Claims (21)

1. Device for the treatment of matter by UV rays, comprising a housing in which a UV radiation source and at least one reflector with a reflector surface are arranged, characterized in that the at least one reflector surface with one or more coatings (12 ) for reflection of the UV radiation from the UV radiation source and an underlying coating (11) for absorption of the longer-wave part of the spectrum of the UV radiation source (6) is provided. 2. Device according to claim 1, since the reflector consists of two parabolic or elliptical half-shells (7, 7 '). 3. Apparatus according to claim 2, characterized in that the parabolic or elliptical half-shells (7,7 ') are arranged pivotable to each other. 4. The device according to claim 2, characterized in that the parabolic or elliptical half-shells (7,7 ') consist of aluminum or its alloys, copper, brass or steel. 5. Device according to claims 3 and 4, characterized in that the parabolic or elliptical half-shells (7,7 ') consist of an aluminum alloy "Extrudal 50". 6. The device according to claim 1, characterized in that the reflection layer (12) consists of a plurality of individual layers which alternately consist of high and low refractive index dielectrics and, based on a reference wavelength λ of 350 nm, have layer thicknesses in the region of a quarter wavelength, such that that the reflection values in the wen length range between 250 and 400 nm are substantially greater than 80%. 7. The device according to claim 6, characterized in that the coating is applied to the reflection of the UV radiation of alternating low refractive index dielectric layers of Si0 ₂ and high refractive index dielectric layers of Hf0 ₂ by a vacuum coating method. 3. A device according to claim 7, characterized ekennzeich- ^g net, that the layer structure begins with the high refractive index dielectric layer and ends with the low refractive index dielectric layer. 9. The device according to claim 8, characterized in that the layers are applied at reflector temperatures between 100 and 300 ° C, preferably between 120 and 200 ° C. 10. The device according to claim 10, characterized in that the absorption layer (11) consists of a black anodization, black chrome plating, black nickel plating, anodizing or bluing. 11. The device according to claim 10, characterized in that the absorption layer of the parabolic or elliptical half-shells (7,7 '), which is applied to the polished surface of the half-shells, consists of a polished copper coating, a nickel coating and a black chrome-plated layer. 12. Device according to claims 6 and 10, characterized in that a diffusion barrier layer made of a dielectric with a physical thickness of at least 0.5 µm is arranged between the absorption layer (11) and the reflection layer (12). 13. The apparatus according to claim 12, characterized in that the diffusion barrier layer consists of Si0 ₂ . 14. The device according to claim 4, characterized in that the parabolic half-shells (7, 7 ') are provided with a cooling system for dissipating the absorbed heat. 15. The device according to claim 5, characterized in that the parabolic half-shells (7, 7 ') consist of a continuous casting hollow profile, the cavities of which are connected to a cooling system. 16. Device according to the preceding claims, characterized in that the lower opening facing the material web (5) is provided with a cover (9) which is transparent to UV radiation. 17. The apparatus according to claim 16, characterized in that the cover (9) consists of quartz glass. 18. Device according to the preceding claims, characterized in that the opening facing the material web is provided with a radiation fastener (10) which is impermeable to radiation. 19. The device according to claim 1, characterized ekennzeich- ^g net, da3 the interior of the closed with a quartz glass disc cover (10) device connected to a closed ventilation system is circulated through the dry and filtered air, or a dried and filtered inert gas. 20. The apparatus according to claim 1, characterized in that the interior of the device closed with a quartz glass pane cover is connected to an open ventilation system through which air dried and filtered under a slight excess pressure is supplied to the interior. 21. Use of the device according to one or more of the preceding claims for drying and curing UV printing inks on a web of paper, plastic or metal.

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