CURING STATION AND METHOD FOR CURING PRINTING INK OF A DIRECT PRINT ON CONTAINERS

Abstract

A curing station for curing printing ink of a direct print on containers, comprising a conveyor for conveying the containers preferably in container holders, and further comprising at least one UV light unit for curing the printing ink, characterized in that the at least one UV light unit comprises a 2D arrangement of UV LEDs for generating a UV light field for curing the printing ink.

Claims

1. A curing station for curing printing ink of a direct print on containers, comprising: a conveyor for conveying the containers; and further comprising at least one UV light unit for curing the printing ink, wherein the at least one UV light unit comprises a 2D arrangement of UV LEDs for generating a UV light field for curing the printing ink.

2. The curing station according to claim 1, wherein the UV LEDs of the at least one UV light unit are configured to be controllable individually or in groups, so as to control the UV light field depending on conveyance positions of the containers relative to a curing and/or pinning section of the curing station.

3. The curing station according to claim 1, further comprising a control unit is configured to change the UV light field by controlling an output of at least one of the UV LEDs.

4. The curing station according to claim 3, wherein the control unit is configured to change the outputs of the UV LEDs on a basis of conveyance positions of the containers relative to a curing and/or pinning section of the curing station, so as to cause the UV light field to follow the conveyance of the containers.

5. The curing station according to claim 3, wherein the control unit is configured to change the output of the at least one of the UV LEDs based on a distance between a respective UV LED and a container to be cured, so as to homogenize the UV light field acting on the printing ink on the container.

6. The curing station according to claim 1, wherein the UV LEDs have assigned thereto at least one UV sensor for detecting and/or controlling a radiation intensity of one or of a plurality of the UV LEDs.

7. The curing station according to claim 1, wherein the conveyor is configured for conveying the containers with container holders, a respective one of the UV light units being arranged at each of the container holders such that it moves together therewith.

8. The curing station according to claim 1, wherein the at least one UV light unit is arranged stationarily at the curing station.

9. The curing station according to claim 8, wherein the conveyor is a carousel with a hollow shaft, and wherein the at least one UV light unit is arranged centrally on the hollow shaft.

10. A direct printing machine for printing a direct print on containers, comprising: at least one curing station according to claim 1; and at least one printing station for applying the printing ink of the direct print to containers, wherein the at least one printing station is configured as a separate unit which has a conveyor of its own and which is arranged upstream of the curing station, or wherein the at least one printing station is arranged at the conveyor of the curing station.

11. A method of curing printing ink of a direct print on containers, comprising: conveying the containers; and curing the printing ink by means of at least one UV light unit during such conveyance, wherein the at least one UV light unit generates a UV light field for curing the printing ink by a 2D arrangement of UV LEDs.

12. The method according to claim 11, wherein the UV light units move along with the conveyance of the containers, and wherein the UV light fields is generated depending on conveyance positions of the containers relative to a curing and/or pinning section of the curing station.

13. The method according to claim 11, wherein the at least one UV light unit is arranged stationarily, and wherein the UV light field is caused to follow a conveyance movement of the containers by controlling the UV LEDs depending on the conveyance movement.

14. The method according to claim 11, wherein the UV LEDs are controlled based on a distance between a respective UV LED of the UV LEDs and a container to be cured, so as to homogenize the UV light field acting on the printing ink on the container.

15. The method according to claim 11, wherein a UV sensor measures a radiation intensity of one or of a plurality of the UV LEDs, and wherein the radiation intensity is controlled based on the measured radiation.

16. The curing station according to claim 1, wherein the conveyor conveys the containers in container holders.

17. The curing station according to claim 6, wherein the at least one UV sensor is connected to the control unit.

18. The method according to claim 13, wherein the UV LEDs are controlled by switching the UV LEDs on and off.

19. The method according to claim 11, wherein the containers are conveyed in container holders of the conveyor.

Description

[0045] Further features and advantages of the present invention will be explained in more detail hereinafter on the basis of the embodiments shown in the figures, in which:

[0046] FIG. 1A shows an embodiment of a printing station and of a curing station in a top view;

[0047] FIG. 1B-1C show detail views of the curing station according to FIG. 1A in a side view and in a top view;

[0048] FIG. 2A shows a further embodiment of a printing station and of a curing station in a top view;

[0049] FIG. 2B-2C show detail views of the curing station according to FIG. 2A in a side view and in a top view;

[0050] FIG. 2D-2E show, in a top view, the printing station and the curing station according to FIG. 2A with an additional treatment labyrinth during operation;

[0051] FIG. 3 shows a further embodiment of a curing station with a carousel as a conveyor in a top view;

[0052] FIG. 4 shows a further embodiment of a curing station with a linear conveying unit as a conveyor in a top view;

[0053] FIG. 5 shows a further embodiment of a curing station with a linear conveying unit as a conveyor in a top view; and

[0054] FIG. 6 shows an embodiment of a UV LED according to FIG. 1-5 with a UV sensor in a top view.

[0055] FIG. 1A-1C show an embodiment of a printing station 120 and of a curing station 100 in a top view. What can be seen are the containers 102, which are transferred by means of the infeed starwheel 104 to the conveyor 101, where they are received in the container holders 103. The conveyor 101 is here configured e.g. as a carousel, which rotates about a vertical axis in the direction T and thus moves the containers 102 past the printing station 120 for applying a direct print and past the UV light unit 110. Subsequently, the containers 102 are transferred to the discharge starwheel 105 and advanced so as to undergo further treatment steps.

[0056] The printing station 120 comprises a plurality of direct printing heads 121.sub.Y, 121.sub.M, 121.sub.C, 121.sub.K and 121.sub.W, each having one or a plurality of rows of nozzles operating according to the ink jet principle. In the printing station 120, the containers 102 have successively printed thereon a plurality of raster images in yellow, magenta, cyan, black and white, which overlap so as to form a color direct print identifying the content of the containers 102. The respective printing inks are curable with UV light and can therefore be dried very quickly. For circumferential printing or printing around the full circumference, the containers 102 are additionally rotated relative to the direct printing heads 121.sub.Y, 121.sub.M, 121.sub.C, 121.sub.K and 121.sub.W by means of the container holders 103. To this end, the container holders 103 each have a rotary table 103b, which is adapted to be rotated by a direct drive, and a centering bell 103a.

[0057] For curing the printing ink, the containers 102 are moved past the UV light unit 110, which is stationarily arranged at the curing station 100. The UV light unit 110 comprises a carrier plate 111 and a matrix arrangement of UV LEDs 112 for generating a UV light field 113. The UV light field 113 can thus be caused to follow the conveying direction T of the containers 102 by switching the UV LEDs on and off or dimming them in a suitable manner by the control unit. The printing inks are thus cured, so that they will no longer run into one another and will be scratch-resistant.

[0058] The structure of the UV light unit 110 is shown in more detail in FIG. 1B from the side and in FIG. 1C from above. In FIG. 1B it can be seen that the UV LEDs 112 are attached to the carrier plate 111 in a matrix arrangement. The 2D arrangement extends e.g. over the entire height of the containers 102 along the curing section A shown in FIG. 1A. In addition, all UV LEDs 112 work with a wavelength in the UV light spectrum, preferably in the UV-B or UV-C range.

[0059] The structure of the UV light unit 110 may comprise a mixed assembly of various types of UV LEDs with different UV light spectra in order to be able to process differently preset, UV-curing printing inks. The required UV light spectra can be activated according to demand and position, this means e.g. that a front print will be cured with 280 nm while a back print will be fixed with 310 nm.

[0060] It can also be seen that most UV LEDs 112a are switched off, since they are either not located opposite the container 102 or outside an irradiation zone for direct printing 102a, which does here not extend over the full height of the container 102 but only on the container belly. The UV LEDs 112b, however, are switched on with higher intensity and the UV LEDs 112c with lower intensity. As can be seen in more detail in FIG. 1C, this results in a UV light field 113 with higher intensity at the container areas spaced apart from the UV LEDs 112 at a greater distance and with lower intensity at the container areas spaced apart from the UV LEDs 112 at a smaller distance. This homogenizes the UV light field 113 acting on the direct print 102a and curing takes place in a particularly uniform manner.

[0061] In addition, it can be seen in FIGS. 1B and 1C that the UV light field 113 is caused to follow the container conveyance in the direction T. To this end, the UV LEDs 112 of the UV light unit 110 are controlled, individually or in groups, depending on the respective conveyance position P.sub.1, P.sub.2, P.sub.3 of the containers 102 relative to the curing section A and the UV light unit 110, respectively. This means that the UV light field 113 virtually migrates along with the conveyance movement of the containers 102.

[0062] In addition, the containers 102 can be rotated in the container holders 103 by means of the rotary tables 103b while being conveyed in the direction T, so as to cure e.g. a rear direct print, which is here not shown.

[0063] Due to the fact that the UV light unit 110 comprises the matrix arrangement of UV LEDs 112, the UV light field 113 can be caused to follow the conveyance movement of the containers 102 during the curing process and will thus act on the printing ink of the direct print 102a over a longer period of time. Hence, the printing ink can be sufficiently cured with a lower radiation output of the UV LEDs 112, without ozone being generated and without the necessity of cooling a high heat output. In addition, the UV LEDs 112 can be switched very fast and the UV light field 113 can directly be adapted to various direct print sizes. A warm-up time can be dispensed with as well. Moreover, the UV LEDs work in UV-A and/or UV-B, so that eye protection will be less complicated. It follows that the curing station 100 and the direct printing machine 120, 100 are less complicated and more flexible in use.

[0064] FIG. 2A-2E show a further embodiment of a printing station 220 and a curing station 200. The embodiment essentially differs from the above insofar as, instead of the stationary UV light unit 110 according to FIG. 1A-1C, the UV light units 210 are arranged at the container holders 203 such that they move together therewith.

[0065] The printing station 220 comprising the direct printing heads 221.sub.Y, 221.sub.M, 221.sub.C, 221.sub.K and 221.sub.W corresponds, as regards structure and function, to the printing station 120 according to FIG. 1A-1C.

[0066] FIG. 2B-2C show a container holder 203 and the associated curing station 210a in a side view and in a top view, in which the container 202 is just being cured. This is done in the curing section A during conveyance after printing with the last direct printing head 221.sub.W has been carried out.

[0067] What can be seen is that the UV light unit 210 comprises a carrier 211 and a matrix arrangement of UV LEDs 212, which generates the UV light field 213 for curing the printing ink. The UV light unit 210 is arranged on the carousel 201 and is conveyed by the latter, together with the respective container holder 203, in the conveying direction T.

[0068] During printing with the direct printing heads 221.sub.Y, 221.sub.M, 221.sub.C, 221.sub.K and 221.sub.W, the UV light units 210a are deactivated by the control unit 206, so as to prevent a curing of printing ink in the printing nozzles, which may lead to malfunction.

[0069] However, the UV light units 210 are controlled by the control unit 206 in the pinning sections B.sub.1B.sub.4, i.e. depending on the conveyance position of the respective containers 202 between the direct printing heads 221.sub.Y, 221.sub.M, 221.sub.C, 221.sub.K and 221.sub.W, in such a way that the printing ink which has just been printed on is slightly cured (pinning) by the UV LEDs 212 so that it will not run into the subsequently applied printing ink.

[0070] In addition, the control unit 206 controls the outputs of the UV LEDs 212 on the basis of the conveyance position of the respective container holder 203, individually or in groups, such that, based on a distance of the respective UV LED 212 from the container 202, the UV LEDs will generate a homogeneously effective UV light field 213 in the curing section A. This is shown in more detail in FIGS. 2B and 2C. Since in this example, the direct print is only provided on the container belly, the upper UV LEDs 212 are deactivated, so that no unnecessary heat output will be generated. The two lateral UV LED groups 212b, however, are switched on with higher intensity and the UV LEDs 212c with lower intensity. As can be seen more precisely in FIG. 2C, this results in a UV light field 213 with a higher intensity at the container areas spaced apart from the UV LEDs 212 at a large distance and with a lower intensity at the container areas spaced apart from the UV LEDs 212 at a small distance. This homogenizes the UV light field 113 acting on the direct print 202a and curing takes place in a particularly uniform manner.

[0071] In addition, the curing section A spans a larger area of the conveying path subsequent to the printing station 220 and up to the discharge starwheel 205, so that the printing ink on the container 202 can be irradiated longer. In this way, a sufficient curing effect will be accomplished even with a lower radiation output of the UV LEDs 212.

[0072] It is imaginable that the UV light units 210 comprise UV LEDs 212 in the UV-A range for pinning as well as in the UV-B and/or UV-C range for curing.

[0073] Furthermore, the rotary tables 203b of the container holders 203 are configured to be rotatable by a direct drive. During the curing process, it is therefore possible to rotate the containers 202 so as to cure the printing ink of a direct print applied to the back of the container.

[0074] Since each container holder 203 has assigned thereto a UV light unit 210, the curing station 200 according to FIG. 2A-2C can be used in a particularly flexible manner.

[0075] In FIG. 2D-2E, the printing station 220 and the curing station 200 of FIG. 2A are shown in a top view with an additional treatment labyrinth 230 during operation. What can be seen is that the treatment labyrinth 230 with the shielding elements 231a, 231b and 232 is arranged on the conveyor 201 between the individual container holders 203. The shielding elements 231a, 231b define a housing for the container holders 203, and the shielding elements 232 do so likewise for the UV light units 210.

[0076] In this way, chambers are formed, which each contain a UV light unit 210 and a container holder 203, these chambers shielding the neighboring chambers from the stray light. In addition, the shielding elements 231a, 231b, 232 are configured such that for each chamber a first access opening 233 for the direct printing heads 221 and a second access opening for the respective associated UV light unit 210 is formed.

[0077] In FIG. 2D it can be seen that the containers 202 are just being cured subsequent to the last direct printing head 221.sub.W, the UV light units 210a between the last direct printing head 221.sub.W and the discharge starwheel 205 being here activated. Conversely, the other UV light units 210b are deactivated at this moment in time, since at some of the treatment positions containers 202 are just printed on by the direct printing heads 221 through the access openings 230. In this way, printing ink is prevented from being cured directly on the direct printing heads 221 and from thus impairing the function of the latter.

[0078] Furthermore, it can be seen in FIG. 2E that the conveyor 201 has been rotated a little further and that the containers 202 are just located at positions between the direct printing heads 221. In this area, stray light from the UV light units 210a is shielded off by the treatment labyrinth 230, preferably by the shielding elements 231a, 231b, such that it cannot arrive at the inactive direct printing heads 221. Consequently, this position of the conveyor 201 allows the UV light units 210a to be activated so as to pin, through the access openings 234, the printing ink between the individual direct printing heads 221. In this way, an even sharper print result is accomplished.

[0079] FIG. 3 shows a further embodiment of a curing station 300 with a carousel as a conveyor 301 in a top view. The embodiment differs from that in FIG. 1A-1C essentially insofar as the conveyor is configured as a carousel 301 with a hollow shaft 301a and the UV light unit 310 is arranged centrally in the hollow shaft 301a instead of peripherally on the outer circumference. In addition, the printing station is not arranged on the conveyor 301 of the curing station 300, but as a separate unit, which has its own conveyor and which is not shown here. The printing station is arranged upstream of the curing station, so that the containers 302 that have already been provided with the printing ink are transferred to the container holders 303 of the curing station 300 by means of the infeed starwheel 304.

[0080] What can be seen is that the UV light unit 310 is configured with a columnlike, hollow cooling body 311, which defines a chimney and which is adapted to be forced-ventilated via the fan 314. The UV LEDs 312 are arranged on the outside of the cooling body 311 above the carousel plane such that they are directed radially outwards. In this way, the UV light field is radiated substantially radially outwards and the printing ink on the containers 302 is cured. In order to allow all container areas to be cured all around, the container holders 303 are configured to be rotatable, so that the containers 302 can be rotated about their longitudinal axes.

[0081] The outputs of the UV LEDs are controlled individually or in groups by a control unit, which is here not shown, based on conveyance positions of the containers 302 relative to the curing section A. Thus, the UV light field is caused to follow the conveyance of the containers in the direction T, without the necessity of rotating the UV light unit 310. As a result, the UV light unit 310 can be controlled without a rotary distributor and has therefore a particularly simple structural design.

[0082] FIG. 4 shows a further embodiment of a curing station 400 with a linear conveying unit 401 as a conveyor in a top view. What can be seen is that the containers 402, which have already been provided with printing ink by a printing station that is not shown, are conveyed by means of the linear conveying unit 401 along the UV light unit 410 and cured while moving therealong. The UV light unit 410 comprises also in this case a matrix arrangement of UV LEDs 412, which generate a UV light field for curing the printing ink.

[0083] It can also be seen that most of the UV LEDs 412a are switched off, since they are not located opposite the container 402. The UV LEDs 412b, however, are switched on with different intensities, based on a distance between the respective UV LED 412b and the container 402, so as to homogenize the UV light field acting on the printing ink on the container 402. In this way, curing takes place in a particularly uniform manner.

[0084] In addition, the UV light field is caused to follow the container conveyance by switching the UV LEDs 412. To this end, the UV LEDs 412 of the UV light unit 410 are controlled individually or in groups by means of a control unit, which is here not shown, depending on the respective conveyance position of the containers 402 relative to the curing section A and the UV light unit 410, respectively. This means that the UV light field virtually migrates along with the conveyance movement of the containers 402.

[0085] It follows that a curing station 400 with a 2D arrangement of UV LEDs 412 can also be used in the case of a linear conveying unit 401. The curing station 400 is thus comparatively uncomplicated and can be used in a flexible manner.

[0086] FIG. 5 shows a further embodiment of a curing station 500 with a linear conveying unit 501 as a conveyor in a top view. The embodiment differs from that in FIG. 4 only insofar as two UV light units 510a, 510b are here arranged in opposed relationship at the linear conveying unit 501. Each of the two UV light units 510a, 510b is provided with a carrier 511a, 511b and a matrix arrangement of UV LEDs 512a, 512b. Both UV light units 510a, 510b work like the UV light unit 410 that has been described above with respect to FIG. 4 and, accordingly, they are controlled by means of a control unit, which is here not shown, such that the UV light fields are caused to follow the conveyance of the containers 502.

[0087] Due to the fact that the UV light units 510a, 510b are formed at the linear conveying unit 501 on both sides thereof, both container sides can be cured simultaneously and without rotating the containers. The curing station 500 thus works in a particularly efficient manner. It is also imaginable that two opposed UV light units are arranged along the conveying path in the case of the curing stations 100, 200, 300 in FIG. 1A-3.

[0088] FIG. 6 shows an embodiment of a UV LED 112, 212, 312, 412, 512 of the type used for the curing stations 100, 200, 300, 400, 500 of FIG. 1-5. In addition, the UV sensor 15 can be seen, which measures the radiation intensity of the UV light and transmits a corresponding signal to the control units. Since the radiation output of UV LEDs varies in a production- and ageing-dependent manner, this can be detected by the UV sensor 15 and compensated for by means of an appropriate control, preferably current control, or change of the PWM.

[0089] It is also imaginable that the UV sensor 15′ is arranged at the conveyor 101, 201, 301, 401, 501 in opposed relationship with the UV LED 112, 212, 312, 412, 512, whereby the radiation intensity in the forward direction is particularly well detected.

[0090] It goes without saying that the features described in the above embodiments are not limited to these combinations, but can be provided individually or in any other combination.