EP3678790B1 - Irradiation tunnel for containers, and method for irradiating containers - Google Patents

Description

The invention relates to an irradiation tunnel according to the preamble of claim 1 and as known from DE 33 22 401 C1 and a method for irradiating containers in the irradiation tunnel.

In filling plants, containers are increasingly printed directly using UV-reactive inks. For the subsequent further processing of the containers, the finished but not yet sufficiently cured print images are preferably post-treated with broadband UV radiation in the UVC, UVB and UVA ranges and the inks are thus cured quickly and completely. Mercury vapor lamps, for example, can be used for this purpose.

The lamps are arranged one behind the other in an irradiation tunnel along a transport means in the transport direction in order to irradiate the containers from the side and to cure UV-curing printing inks (inks) present thereon. However, the irradiation levels required for curing cause considerable heating of the irradiation tunnel, which has hitherto been counteracted by suction of the air present in the irradiation tunnel and subsequent flows of cooler ambient air through the container inlet and outlet. However, such air cooling inside the irradiation tunnel has two fundamental disadvantages.

On the one hand, the heat exchange is so severely limited by the range of practicable volume flows on the affected surfaces that lamps can only be arranged on one side of the means of transport and cooling zones without lamps are required on the other side. However, since the containers must be irradiated on both sides, at least two zones, each with one-sided irradiation and associated cooling zones, must be set up one behind the other along the means of transport. This leads to an undesirably elongated design of the irradiation tunnel.

On the other hand, the air cooling is based on the intake of comparatively large amounts of room air through the container inlet and the container outlet. Since the air sucked in in this way can hardly be filtered, dust is introduced into the irradiation tunnel with the room air. This causes undesired contamination of the irradiation tunnel and possibly also of the container.

There is therefore a need for irradiation tunnels and methods for irradiating the containers and in particular for curing printing inks with UV radiation which are improved in comparison thereto.

The task is solved with an irradiation tunnel according to claim 1. Accordingly, the irradiation tunnel comprises a means of transport for containers, lamps arranged along the means of transport for UV irradiation of the containers, and a cooling device for cooling the interior of the irradiation tunnel. Furthermore, the cooling device comprises liquid-cooled heat sinks which extend into the irradiation areas of the lamps. According to the invention, the heat sinks are coated and/or anodized to absorb UV light.

The heat sinks are at least partially irradiated by opposite lamps.

The liquid-cooled heat sinks enable a more compact design of the irradiation tunnel, since both the heat sinks and the lamps can be arranged directly next to each other and on both sides of the means of transport. In addition, there is no need for supply air through the container inlet and/or the container outlet of the irradiation tunnel. Thus, contamination of the irradiation tunnel and the container with dust from the ambient air can be avoided.

Interior cooling of the irradiation tunnel means that the heat sinks are designed to dissipate energy that was introduced into the irradiation tunnel by the lamps as radiant energy and is absorbed by its inner walls, components and the air present inside.

In contrast, the interior cooling plays no or only a minor role for the cooling of the lamps themselves. The lamps are cooled using cooling systems known per se, for example using separate air or water cooling circuits for the individual lamps.

The heat sinks have no radiation function in the sense of reflecting and/or scattering the UV light and/or emitting thermal radiation after light absorption. Instead, the light energy absorbed by it and the thermal energy absorbed from the interior air via convection should be transferred as comprehensively as possible to the coolant flowing through the heat sink.

By definition, the irradiation areas are areas that are directly irradiated by the lamps, possibly also only intermittently through the transport gaps between the moving containers.

The lamps are preferably arranged on both sides of the means of transport, and the heat sinks are formed at least between the lamps, in particular around the lamps, viewed transversely to the direction of transport. Thus, the area of the lamps on the side of the means of transport can also be used for effective cooling of interior air and for the absorption of radiant energy. This enables a particularly compact irradiation tunnel.

Furthermore, liquid-cooled heat sinks are preferably formed above the means of transport. The heat sinks can then be designed essentially in the form of a ceiling of the irradiation tunnel in order to absorb scattered radiation and to cool interior air rising upwards. These heat sinks are usually located outside of the irradiation areas.

The liquid-cooled heat sinks can, for example, have a total area of at least 0.5 m ² and in particular at least 1 m ² , the total cooling area being a cooling area that is in contact with the interior air.

The heat sinks preferably comprise hollow plates made from metal, in particular from an aluminum alloy. Such hollow plates allow an equally mechanically stable enclosing of the transport route for the containers as well as an effective heat transfer to the cooling liquid, which is in particular cooling water. The hollow plates have cooling channels that can be flexibly connected in parallel and/or in series between the flow and return in order to optimize the cooling capacity in individual areas of the irradiation tunnel. Aluminum alloys are particularly suitable for the production of hollow panels and can be easily anodized, for example.

Furthermore, the heat sinks have a light-absorbing coating and/or anodized with an average absorptance α of at least 0.5 in the spectral range from 200 to 450 nm.

The irradiation tunnel preferably also comprises at least one ventilation duct for blowing in supply air. With a controlled supply of supply air, convection can be forced in the irradiation tunnel to promote constant heat exchange from the indoor air and the heat sinks. Supply air of a suitable quality can be supplied in a targeted manner via the ventilation duct.

Preferably, the transport means is a conveyor belt for transporting the containers in an upright position, and the ventilation duct opens into the irradiation tunnel below the conveyor belt. This ensures sufficient air exchange in the area below the conveyor belt.

Preferably, the irradiation tunnel also comprises a blower supplying the ventilation duct and a suction device for exhaust air from the irradiation tunnel, the blower being designed at least to completely replace the extracted exhaust air. This makes it possible to avoid additional ambient air being sucked in through the container inlet and/or container outlet of the irradiation tunnel.

With essentially the same amount of supply air and exhaust air or with slightly less supply air than exhaust air, for example by at most 5% less, it is possible to prevent the ozone produced by the UV radiation from escaping from the irradiation tunnel.

On the other hand, the incoming air that is blown in could have a larger volume flow than the extracted air, so that excess incoming air flows out through the container inlet and/or container outlet. An entry of dust from the ambient air into the irradiation tunnel can thus be counteracted even more effectively.

Preferably, the lamps are separately cooled UV lamps for curing UV-curing inks on the containers. The lamps therefore have sufficient radiation power for curing the printing inks. The UV lamps do not significantly affect the interior of the irradiation tunnel due to their independent cooling with electrical power loss.

The stated object is also achieved with a direct printing machine for containers, which comprises printing units for printing UV-curing printing ink (ink) onto the containers and an irradiation tunnel arranged downstream of the printing units for UV-curing the printing ink, in accordance with at least one of the embodiments described above.

The stated object is also achieved with a method according to claim 10, in which containers are irradiated in the irradiation tunnel according to at least one of the embodiments described above, with UV-curing printing ink (ink) present on the containers being cured in the irradiation areas of the lamps and the liquid-cooled Heat sinks absorb direct UV radiation from the lamps with an average absorptivity α of at least 0.5 in the spectral range from 200 to 450 nm.

The containers are then preferably transported through the irradiation tunnel in a constant rotational position, and the lamps irradiate the containers on both sides and in particular over their entire circumference. UV-curable printing inks (inks) can thus be cured to an extent that is at least suitable for further processing and handling over a comparatively short transport distance.

The containers are then preferably transported at a clear distance from one another which is at least twice as large as the largest dimension of the containers in the direction of transport. As a result, radiation emitted obliquely by the lamps can fall to a sufficient extent on wall sections which are aligned in (or approximately in) the transport direction or in the opposite direction. Thus, a complete curing of UV-reactive printing colors (inks) or the like is possible.

Air in the irradiation tunnel preferably sweeps along the heat sinks, in particular as a result of forced air convection, and in the process gives off thermal energy to a cooling liquid flowing through the heat sinks. The air convection can be forced, for example, by controlled supply air and/or the transport movement of the containers. The thermal energy absorbed by the heat sinks in this way is transported away effectively and controllably by the coolant.

The liquid-cooled heat sinks preferably absorb treatment radiation. The treatment radiation falls, for example, through the transport gaps between the containers in the transport direction, onto the heat sink. However, the cooling bodies also absorb directed and/or diffuse reflections, for example after reflection on the containers. The energy dissipated by light absorption is withdrawn directly from the irradiation tunnel and can therefore no longer contribute to heating the indoor air in the irradiation tunnel. This leads to a particularly efficient interior cooling of the irradiation tunnel.

Fig. 1

eine schematische Ansicht des Innenraums des Bestrahlungstunnels von oben durch die Schnittebene A-A der Fig.2; und

Fig. 2

eine schematische seitliche Ansicht durch die Schnittebene B-B der Fig.1.

A preferred embodiment of the irradiation tunnel is shown in the drawing. Show it:

1

a schematic view of the interior of the irradiation tunnel from above through the section plane AA Fig.2 ; and

2

a schematic lateral view through the sectional plane BB Fig.1 .

As the 1 reveals the irradiation tunnel 1 for containers 2 includes a housing 1a and a transport means 3, which is designed, for example, as a conveyor belt for upright containers 2. Lamps 4 for UV irradiation of UV-reactive printing inks (inks) 2a are arranged on the containers 2 on both sides of the means of transport 3 .

The lamps 4 can be arranged directly opposite one another, as well as overlapping in the transport direction 3a or without a lamp 4 directly opposite each other. The latter is in FIG 1 shown for an input-side and an output-side lamp 4. The middle lamps 4 are arranged directly opposite one another. Overlapping irradiation areas 4a with UV radiation are preferably formed in front of the lamps 4 .

First liquid-cooled heat sinks 5 extending at least into the irradiation regions 4a of the lamps 4 are designed as the cooling device for cooling the interior of the irradiation tunnel 1 . On the one hand, the first heat sinks 5 extend in the form of a side wall between the lamps 4. The first heat sinks 5 are preferably also formed above and below the lamps 4.

Preferably, there are also second liquid-cooled heat sinks 6 in the form of a lateral enclosure of the means of transport 3 . These heat sinks 6 can also be located at least partially in the irradiation areas 4a of the lamps 4.

There is preferably at least a third liquid-cooled heat sink 7 in the form of an intermediate ceiling or the like above the means of transport 3 or the containers 2 .

As the 2 can be seen in a view transverse to the transport direction 3a, the first heat sinks 5 preferably frame the lamps 4 completely. Recesses 5a for the lamps 4 are then formed in the first heat sinks 5 .

For this purpose, the first heat sink 5 can be composed of intersecting columns 5b and longitudinal bars 5c in segments around the recesses 5a, as is illustrated only on the right-hand side of FIG 1 is shown. In principle, a segment-like construction would also be conceivable for the second and third heat sinks 6 , 7 .

The heat sinks 5-7 are preferably double-walled, ie, for example, designed as hollow plates 8 with a front side 8a facing the containers 2, a rear side 8b facing away from the containers, and connecting webs 8c formed in between. Between these, a multiplicity of cooling channels 8d are provided, which can be connected in any manner in series or in parallel to a supply 9a and a return 9b for cooling liquid 9. Water provided under conventional line pressure is suitable as the cooling liquid 9 .

how 1 can also be seen, the lamps 4 are cooled separately, for example by means of closed air cooling circuits 10 (only indicated schematically on the right). These carry away the electrical power loss of the lamps 4 and possibly also ozone or the like occurring directly in front of the lamps 4 . The first heat sinks 5 are of little or no importance for the loss-related cooling of the lamps 4 .

Instead, the heat sinks 5-7 serve to cool the interior of the irradiation tunnel 1 by means of, in particular, forced air convection 11 on the heat sinks 5-7. The air convection 11 is in the 2 indicated by flow arrows as an example.

In the 2 a ventilation duct 12 is also shown schematically, which supplies the irradiation tunnel 1 with the aid of a blower 13 with supply air 14 . In addition, there is a suction device 15 for exhaust air 16 from the irradiation tunnel 1.

The supply air 14 forces at least part of the air convection 11 in the irradiation tunnel 1, so that there is a constant exchange of air at the heat sinks 5-7. The heat sinks 5-7 thus constantly absorb thermal energy from the interior air flowing past them and transfer this to the coolant 9 . Thermal energy is thus continuously withdrawn from the interior of the irradiation tunnel 1 during operation.

The volume flow of the supply air 14 is at least as large as the volume flow of the exhaust air 16 in order to prevent ambient air from being sucked in through the container inlet 17 and/or container outlet 18 of the irradiation tunnel 1 .

The volume flow of the supply air 14 is preferably slightly smaller than the volume flow of the exhaust air 16, for example by at most 5%, so that a small amount of air flows through the container inlet 17 and the container outlet 18 into the irradiation tunnel 1. An entry of dust from the ambient air can thus be reliably avoided and at the same time an escape of ozone from the irradiation tunnel 1. Escaped ozone leads to unpleasant odors, even if the occupational limit concentration has not yet been reached.

As the 2 further clarified, the ventilation duct 12 preferably opens into the irradiation tunnel 1 below the transport means 3. Thus, there is also sufficient air exchange in the area below the transport means 3 to avoid heat build-up. The air convection 11 in the irradiation tunnel 1 can also be forced to a significant extent by means of the transport movement of the containers 2 . This is particularly advantageous since the first and second heat sinks 5, 6 extend into the irradiation areas 4a or into the immediate vicinity of the means of transport 3 and the container 2, so that the heat transfer there can be improved by the air convection 11 forced in this way.

In the 1 and 2 For the sake of completeness, visual protection locks 19 connected to the container inlet 17 and the container outlet 18 for shielding the UV radiation emitted by the lamps 4 are also shown. In the visual protection locks 19, the transport direction of the containers 2 preferably changes in such a way that the UV radiation cannot penetrate directly from the lamps 4 to the outside. For this purpose, beam traps 20 in the form of absorbing slats or the like can be arranged in the privacy locks 19 . The privacy locks 19 are used for occupational safety and in particular to avoid impermissible levels of UV radiation outside of the irradiation tunnel 1.

A combination of the interior cooling described with the privacy locks 19 is also particularly advantageous because the installation space required for the privacy locks 19 can be provided by the compact arrangement of the lamps 4 and the liquid-cooled heat sink 5-7.

The irradiation tunnel 1 is therefore also suitable for improved occupational safety with regard to the permissible immission of UV radiation.

As the 2 can also be seen, the containers 2 are preferably transported at a clear distance 21 from one another, which is at least twice as large as the largest dimension 22 of the container 2 in the transport direction 3a. This creates sufficiently large gaps between the containers 2 for obliquely incident UV radiation for irradiating the container 2 in side wall areas which are aligned approximately in the transport direction 3a or opposite thereto. Thus, a complete curing of UV-reactive printing inks (inks) 2a is possible even when the container 2 is in a fixed rotational position on the transport means 3 .

In production operation, the containers 2 are conveyed continuously through the irradiation tunnel 1, with the lamps 4 preferably emitting continuously, ie in the continuous wave method. In doing so, through the gaps between the containers 2 directly onto the first and second UV radiation incident on cooling bodies 5, 6 can already be largely absorbed there, depending on the degree of absorption α, in order to minimize the energy input into the irradiation tunnel 1. This also applies to radiation reflected on the containers 2 and/or on components in the irradiation tunnel 1 .

In addition, the interior air flows constantly along the liquid-cooled heat sinks 5-7, in particular due to forced air convection 11, and in the process emits heat energy to them. In this case, for example, the flow temperature and volume flow of the cooling liquid 9 can be adapted in a known simple manner to the waste heat to be removed from the irradiation tunnel 1 .

The irradiation tunnel 1 is preferably part of a direct printing machine (not shown) with printing units known per se for printing the UV-curing printing ink (ink) 2a onto the containers 2. The UV-curing printing ink (ink) 2a can then immediately subsequently be placed in the irradiation tunnel 1 be fully cured with the help of lamps 4 for further processing/handling of the container 2.

Claims (13)

1. Irradiation tunnel (1) for containers (2), comprising: a transport means (3) for the containers (2); lamps (4) arranged along the transport means (3) for UV irradiation of the containers (2); and a cooling device for cooling the interior of the irradiation tunnel (1), the cooling device comprising liquid-cooled heat sinks (5, 6) which extend into the irradiation regions (4a) of the lamps (4), characterised in that the liquid-cooled heat sinks are coated and/or anodised so as to absorb UV light with an average absorptivity α of at least 0.5 in a spectral range of 200 to 450 nm.
2. Irradiation tunnel according to claim 1, wherein the lamps (4) are arranged on both sides of the transport means (3) and the heat sinks (5, 6), viewed transversely to the transport direction (3a), are formed at least between the lamps (4), in particular so as to frame the lamps (4).
3. Irradiation tunnel according to either claim 1 or claim 2, further comprising at least one liquid-cooled heat sink (7) formed above the transport means (3).
4. Irradiation tunnel according to any of the preceding claims, wherein the liquid-cooled heat sinks (5-7) comprise hollow plates (8) made of metal, in particular of an aluminium alloy.
5. Irradiation tunnel according to at least one of the preceding claims, further having at least one ventilation duct (12) for blowing in supply air (14).
6. Irradiation tunnel according to claim 5, wherein the transport means (3) is a conveyor belt for upright transport of the containers (2) and the ventilation duct (12) opens into the irradiation tunnel (1) below the conveyor belt.
7. Irradiation tunnel according to either claim 5 or claim 6, further having a fan (13) supplying the ventilation duct (12) and having an extraction means (15) for exhaust air (16) from the irradiation tunnel (1), wherein the fan (13) is designed at least to completely replace the extracted exhaust air (16).
8. Irradiation tunnel according to at least one of the preceding claims, wherein the lamps (4) are separately cooled UV lamps for curing UV-curing printing inks (2a) on the containers (2).
9. Direct printing machine for containers (2), comprising printing units for printing UV-curing printing inks (2a) onto the containers (2) and comprising an irradiation tunnel (1) according to at least one of the preceding claims arranged downstream of the printing units for UV-curing the printing inks (2a).
10. Method for irradiating containers (2) in the irradiation tunnel (1) according to at least one of the preceding claims, wherein UV-curing printing ink (2a) present on the containers (2) is cured in the irradiation regions (4a) of the lamps (4) and the liquid-cooled heat sinks (5, 6) absorb UV radiation directly incident from the lamps (4) with an average absorptivity α of at least 0.5 in a spectral range of 200 to 450 nm.
11. Method according to claim 10, wherein the containers (2) are transported through the irradiation tunnel (1) in a constant rotational position and the lamps (4) irradiate the containers (2) on both sides and in particular over the entire surface thereof.
12. Method according to either claim 11 or claim 10, wherein the containers (2) are transported at a clear distance (21) from one another which is at least twice the largest dimension (22) of the containers (2) in the transport direction (3a).
13. Method according to any of claims 10 to 12, wherein, due to in particular forced air convection (11), air in the irradiation tunnel (1) flows along the heat sinks (5-7) and thereby delivers thermal energy to a cooling liquid (9) flowing through the heat sinks (5-7).

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