WO2022242960A1

WO2022242960A1 - Method and device for printing directly onto containers for filling products

Info

Publication number: WO2022242960A1
Application number: PCT/EP2022/059524
Authority: WO
Inventors: Robert Weikl; Georg Gertlowski; Zsolt ROZSNYAI
Original assignee: Krones Ag
Priority date: 2021-05-18
Filing date: 2022-04-08
Publication date: 2022-11-24
Also published as: DE102021112873A1

Abstract

The invention relates to a method and a device for printing directly onto containers for filling products, such as beverages. According to said method, a cationically curing ink is applied to the containers by means of at least one ink jet print head, particularly while conveying the containers in a direct printer. The applied ink is then cured by UV radiation. This makes it possible to produce more durable and fully cured ink jet prints with a low level of device and method-related outlay.

Description

Process and device for direct printing onto containers for filling products

The invention relates to a method and a device for direct printing on containers for filling products and a corresponding container.

Inkjet printing directly and digitally onto containers, such as beverage bottles, is a common technique in bottling plants. In principle, different materials can be printed with it, for example plastics (PET, PE, PP), glass but also metallic substrates. From the point of view of process technology, UV-curing inks have proven their worth because they can be fixed immediately after application using UV LEDs, which is also known as pinning or intermediate curing.

Inks (paints, varnishes) are usually used for this purpose, which harden/dry through free-radical polymerization when exposed to actinic radiation, since this enables rapid further processing of the substrate in the production process.

However, it is relatively difficult to achieve sufficient adhesion and mechanical resistance of free-radically polymerizing inks on containers. Plastic containers, such as those made of PET, PP or PE, often have different surface properties and contain relevant additives such as antioxidants, pigments or antistatic agents. Glass bottles are coated with a cold finish that impairs adhesion (e.g. polyethylene wax), cans with lacquer. To make matters worse, radical ink systems shrink during polymerisation. This also has a negative effect on adhesion to the substrate.

This is counteracted with complex pre-treatment processes. The tempered glass bottles are, for example, first flamed with the addition of a precursor in order to produce an SiOx layer. Then an adhesion promoter is applied. The bottles then have to be dried. Plastic bottles are usually flamed or given a plasma or corona treatment.

Such acrylate inks are usually applied first with white, then with CMYK and finally optionally with varnish. So that the inks do not run and do not seep into the layer below, they are fixed directly after application by pinning with a UV LED. Finally, the color layers are cured together using UV lamps doped with Hg, Fe or Ga. It has been found that a comparable through-curing with UV-LEDs can hardly be achieved, since their emission spectra (mostly in UV-A) do not allow good crosslinking of the surface, which is why it is usually too soft. To- The acrylate-based inks described above also have a limited selection of initiators for food applications. Furthermore, these often have to be used in high concentrations if curing is to take place with LEDs. If the UV curing and ink composition are not properly matched, residues of uncrosslinked initiator and acrylates can also remain in the print layer.

Due to the circumstances mentioned above, the expenditure on equipment for direct printing in bottling plants is very high overall, so that there is a need for improvement in this regard.

The task is solved with a method according to claim 1. Accordingly, this is used for direct printing on containers for filling products, in particular beverages or similar liquid products from the food sector. In the method, a cationically curing ink is applied to the containers by means of at least one ink jet print head, in particular during their transport in a direct printing machine. Furthermore, a hardening of the applied ink is triggered by means of UV radiation.

Surprisingly, it has now been found that cationically curing inks known for use in dot matrix printers and in flexographic printing, for example from DE 102011 106 039 A1, DE 195 00 968 and DE 43 07 766, can be used advantageously for direct printing on containers in bottling plants.

Cationic curing UV inks, whose curing is by definition triggered by UV radiation, i.e. by photoinitiation, have the advantage over UV inks curing by free radical polymerization that the decomposition products of the photoinitiator have a longer service life in cationic inks, which is why the curing reaction continues even after UV irradiation. This leads to an overall better hardening of the applied ink. In addition, cationic UV inks shrink less than radically polymerized UV inks. In comparison, this leads to improved adhesion of cationic UV inks.

In addition, the continued and ultimately complete crosslinking of cationic inks after irradiation is advantageous in terms of compliance for the food sector, since the reaction partners (ink components) can no longer migrate through the container wall into the filled food due to their complete crosslinking.

A cationic ink, coating and/or formulation is a system that cures via the cationic polymerization mechanism. For example, epoxides or oxetanes are crosslinked by ring opening. For this purpose, preferably photoini- tiatoren used, which form strong protonic acids after photolysis, such as diarylodonium salts. The respective fission products are relatively long-lived, which is why the reaction continues after exposure to UV light.

In contrast to the systems described at the outset, such cationic systems are based on free-radical chain polymerisation by crosslinking of acrylates, in which the initiators used (type I or II) lead to free-radical formation, which in turn triggers free-radical chain polymerisation.

The containers are in particular bottles. However, direct printing onto cans or similar containers is also conceivable. The filling products are, for example, liquid foods. However, pharmaceutical or cosmetic products or those from the hygiene sector are also conceivable.

The container surfaces to be printed are preferably subjected to a flame in preparation for the application of the ink, in particular without the simultaneous production of an SiOx layer (without the addition of a precursor), and then cooled. The ink is then applied in particular directly to the container surfaces that have been pretreated in this way, that is to say, for example, without the application of an additional adhesion promoter. As a result, the pretreatment of the containers, especially those made of glass, can be significantly simplified compared to the known direct printing processes. Optionally, however, the simultaneous production of a SiOx layer is possible and, depending on the application, may be technically advantageous.

The direct print preferably comprises a first partial print with application of a basic color, in particular white, and subsequent UV photo initiation of its curing and at least one subsequent second partial print with application of at least one color component of a color model, in particular CMYK, and subsequent UV photo initiation of its curing. This is done in each case with cationically curing ink of the appropriate color and enables the print to harden evenly through all the layers of color or ink applied.

Optionally, a primer (base coat) can be applied before the base color (white) to improve the print quality if necessary. It is also conceivable to apply a transparent primer (base coat) instead of the base color (white), as well as to supplement it to improve quality. The color components (CMYK) could also be printed directly onto the container surface. The base color is preferably intermediately hardened/fixed during the first partial print in a sequence of UV photo initiation for the subsequent application of the color components. Additionally or alternatively, in the second partial print, all the colors of the color model are first applied one after the other and then, as a result of joint UV photo initiation, at least intermediately cured/fixed and in particular final cured. Final curing is to be understood as meaning that this is photoinitiated by the last UV irradiation in each case, i.e. no further irradiation follows for the complete curing of the ink. The UV final curing is followed by an essentially radiation-free post-curing, for example during transport and/or storage of the printed containers.

Thus, the print quality of the print image can be controlled in a proven manner by intermediate curing/fixing of the cationically curing inks and, in addition, compared to known printing processes, improved through curing and resistance of the print can be achieved.

After UV-initiated final curing, the direct print is preferably cured without radiation for a predetermined period of time and during this time the direct print is protected against mechanical damage during transport and storage, for example by providing chafing edges on the containers. This allows the imprint to be fully hardened/hardened while at the same time protecting it from mechanical damage.

The curing of the cationic ink is preferably triggered exclusively with UV-A radiation, in particular an LED emission. Exclusive UV-A radiation is to be understood as meaning, for example, that at least 90% of the emitted power is emitted in the UV-A spectral range. This means that both intermediate curing/fixing and final curing are essentially triggered with UV-A light. This is advantageous with regard to the outlay on equipment. Corresponding LED light sources can be controlled comparatively easily, have a long service life and are comparatively inexpensive to purchase and operate.

The ink is preferably used to trigger intermediate curing with UV-A radiation of 0.1-0.5 J/cm ² , in particular 0.2-0.4 J/cm ² , and/or to trigger final curing with subjected to UV-A radiation of 0.5-1.5 J/cm ² , in particular 0.6-1.0 J/cm ² . Such irradiations can be generated comparatively easily with UV-A LEDs and render the use of more expensive mercury vapor lamps or the like unnecessary, particularly for final curing.

In a further favorable embodiment, the final curing of the ink is photo-initiated by an in particular supplementary UV-B and/or UV-C LED emission. This can speed up the final cure in certain printing applications.

In an alternative embodiment, the final curing of the ink is photoinitiated by emission from at least one Hg vapor lamp at an exposure of 0.1-0.4 J/cm ² . This, too, can bring about accelerated final curing in certain applications. The area surrounding the direct printing and/or a transport area/storage area of the containers is preferably air-conditioned. Here, for example, a relative humidity of 50% is not exceeded during the photo-initiated intermediate curing, photo-initiated final curing and/or in the case of post-curing of the ink without radiation. Air conditioning is advantageous, for example, in the area of the direct printing machine and, if necessary, when transporting containers, in order to limit the surface moisture of the container areas to be printed. This is for faster crosslinking of cationically curing inks.

The stated object is also achieved with a device according to claim 11. Accordingly, this is used for direct printing onto containers for filling products, in particular beverages, according to the method according to at least one of the embodiments described above. The device comprises a direct printing machine with an ink supply for providing cationically curing ink, with at least one inkjet print head connected to the ink supply for applying the ink to the containers, in particular during their transport in the direct printing machine, and with at least one UV light source for photo initiation of a hardening of the applied ink. The advantages described in relation to claim 1 are thus achieved.

Photo initiation relates to intermediate curing/fixing and final curing of the ink using UV radiation.

Preferably, the UV light source comprises at least one LED emitting in UV-A and is also designed to photoinitiate an intermediate curing/fixing with a UV-A radiation of 0.1-0.5 J/cm ² , the applied ink in particular 0.2-0.4 J/cm ² and/or for photo-initiation of a final curing with UV-A radiation of 0.5-1.5 J/cm ² , in particular 0.6-1.0 J/cm cm ² to apply.

Preferably, the device also comprises a flame tunnel for flame treatment of the containers to be labeled and a cooling tunnel for cooling the flame-treated containers. The flame tunnel and the cooling tunnel are then preferably arranged directly upstream of the direct printing machine. This means that there is no further pre-treatment of the containers in between, such as the application of an adhesion promoter.

The stated object is also achieved with a container for filling products, in particular beverages, according to claim 14. The container is produced with the method and/or the device according to at least one of the described embodiments. Accordingly, the container comprises a container body made of glass, plastic and/or a cellulose material and an inkjet print applied directly thereto, in particular without an intermediate layer, comprising a base color layer, in particular white, and a multicolored printed image layer, in particular made of CMYK, each consisting of cationically hardened tin te ndrop.

Preferably, the container includes at least one rubbing rim projecting outwardly beyond the inkjet printing. This allows the inkjet print to be protected from mechanical damage after final UV curing in a subsequent post-curing phase during transport and storage of the printed containers. In addition, the rubbing edge also offers appropriate mechanical protection during the subsequent order picking and when using the containers.

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

FIG. 1 shows a schematic representation of a device for printing containers with cationically curing ink;

FIG. 2 shows a schematic representation of a corresponding method; and

FIG. 3 shows a container printed with the method described.

As can be seen in Figure 1, the device 1 for direct printing on containers 2 for liquid filling products such as drinks, for example, comprises a direct printing machine 3 with an ink supply 4 for providing cationically curing inks 5 of different colors and with inkjet print heads 6 connected to the ink supply 4 for applying the Ink 5 on the containers 2. The direct printing machine 3 also includes a container carousel 7 or similar transport means known in principle for transporting the containers 2 during direct printing with the inkjet print heads 6.

The direct printing machine 3 comprises at least two UV light sources 8 to 10 for photo-initiating a curing of the ink 5 applied to the container 2.

In the example shown, a first UV light source 8 comprises at least one essentially UV-A emitting LED and is also designed to photoinitiate the previously applied ink 5 to fix it (intermediate curing) with a UV-A irradiation of 0.1 -0.5 J/cm ² . UV-A radiation of 0.2-0.4 J/cm ² is particularly preferred for this. The first UV light source 8 is used to harden a base color of the print to be produced, usually white, in order to fix the base color before applying color components of a color model, such as CMYK, and thereby prevent subsequently applied inks 5 from running and/or seeping in controlled and, if necessary, prevented.

In the example, the second UV light source 9 also includes at least one LED that emits essentially in the UV-A range and is also designed to generate the aforementioned radiation values on the containers 2 . However, the second UV light source 9 is used to fix the color components of the color model together after they have been successively applied (intermediate hardening).

Alternatively, it would be possible to provide several second UV light sources 9 (shown in dashed lines) for fixing individual color components, ie for example to intermediately cure a specific or each individual color component in a suitable manner before applying the next one.

In the example, the third UV light source 10 also comprises an essentially UV-A emitting LED and is then, however, designed to photoinitiate a final curing of all previously applied inks 5 with a UV-A radiation of 0.5- 1.5 J/cm ² to be applied, in particular with 0.6-1.0 J/cm ² .

In general, it would be conceivable and possibly also advantageous to combine the second and third light sources 9, 10 and to control them for the simultaneous or successive generation of corresponding values of the radiation (see above).

An exclusive intermediate curing / fixing and final curing using UV-A radiation has the advantage that this can be produced with comparatively little equipment and in a particularly economical way with LEDs. Exclusive UV-A irradiation is to be understood here as meaning a proportion of the emission power or irradiance that is predominantly and in particular at least 90% UV-A.

Alternatively, it would be conceivable, especially for the joint final curing of the imprint, to supplement the intermediate curing/fixing by means of UV-A radiation with UV-B radiation and/or UV-C radiation for photo-initiation of the final curing. In principle, suitable LEDs are also available for this purpose.

Another alternative to photo initiation of the final cure is to irradiate the previously fixed print using a mercury vapor lamp or the like at an exposure of 0.1- 0.8 J/cm ² , in particular from 0.1 - 0.4 J/cm ² . Depending on the application, the third light source 10 could also be formed with conventional components such as are customary for free-radical polymerization (acrylate crosslinking).

The device 1 can further comprise an output sealing station 11 for sealing the photo-initiated imprint with varnish.

To pretreat the containers 2 for direct printing, the device 1 includes a flame tunnel 12 for flaming the containers 2 and a subsequent cooling tunnel 13 for cooling the containers 2 immediately before direct printing.

Preferably, no further pretreatment of the containers 2 is interposed, ie, for example, no station for applying an adhesion promoter to the previously flamed and cooled containers 2. This reduces the outlay in terms of apparatus and process technology for the pretreatment compared to known methods. This also means that when the container 2 is flamed, preferably no precursor is added in order to produce an SiOx layer on the container 2 . Such is not necessary in the case of the use of cationically curing inks 5 as described.

It goes without saying here that the pretreatment shown as an example is adapted for direct printing onto container 2 made of glass. The pre-treatment of the containers 2 depends primarily on the container material and, in the case of containers 2 made of plastic, includes, for example, a plasma treatment, corona treatment and/or flaming (without a precursor).

FIG. 1 also shows by way of example that the device 1 or at least the direct printing press 3 is air-conditioned with its inlet area 3a. This primarily serves to reduce / limit the humidity immediately before and during direct printing to a suitable level. For example, no moisture should be reflected by falling below the dew point on the incoming containers 2 from the cooling tunnel 13 . In addition, the cationic hardening of the inks 5 generally proceeds faster the lower the humidity acting on them.

The air conditioning can take place, for example, in a surrounding area 14 shown as an example in the form of a suitably separated room or at least within the housing 3b of the direct printing machine 3 and its inlet area 3a. As a result, the substrate moisture, ie the surface moisture of the container 2, and the ambient moisture from the cooling tunnel 13 can be reliably adjusted. A storage area 15 is also indicated schematically, in which the photo-initiated, finally cured imprints on the containers 2 can post-cure over a predetermined period of time under controlled conditions. This means that the final curing of the inks 5 is initiated by the UV irradiation, the complete curing in the sense of curing as a result of the underlying reactions continuing even after the end of the irradiation only after a substantially irradiation-free post-curing of the cationic inks 5 sets. For example, periods of several hours to days are conceivable for the post-curing. Post-hardening is also possible if the containers 2 are transported in a suitable, gentle manner.

The post-curing without radiation is advantageous in terms of process technology, since the curing of all applied inks 5 is always complete when a minimum radiation for photoinitiation of the final curing is reached. This requirement can be complied with in a comparatively simple manner. In order to set the required hardness and resilience of the imprints produced with the cationic inks 5, only relatively little outlay is required for process control and monitoring. In this context, post-curing without radiation is to be understood as meaning that radiation is not necessary during this time. However, additional incidence of light also has no negative effect on the imprints produced.

Figure 2 shows an example and a schematic of the sequence of a preferred method 21 for direct printing onto the containers 2.

Accordingly, in a first step 22, the containers 2 are provided, for example in the form of glass bottles with a cold end coating or in the form of plastic bottles. Also conceivable are containers 2 made of a cellulose material (pulp), so-called pulp bottles.

In a subsequent second step 23, the containers 2 are flamed in the flame tunnel 12 without the addition of a precursor. The flaming cleans the containers 2 and oxidizes their surfaces. Optionally, the flaming can heat the container wall to at least 120° C. in order to additionally homogenize a cold finish of the container 2, in particular up to at least the melting temperature of the cold finish (of the coating) of 170° C., for example.

In a subsequent third step 24, the previously flame-treated containers 2 are cooled in the cooling tunnel 13 to a processing temperature suitable for direct printing. Here and during the subsequent transport of the containers 2 to the direct printing machine 3, the containers 2 are in a suitably air-conditioned environment. The cooling in the cooling tunnel 13 primarily avoids problems with ink wetting due to excessively high temperatures.

In a subsequent fourth step 25, the ink 5 of a primary color, usually white, is provided by the ink supply 4 and is applied by at least one inkjet print head 6 to the respective container 2.

The functions of the treatment positions circulating on the container carousel 7 (with individually rotatable turntables for the containers 2), the ink supply 4 and print heads 6 are known in principle and are therefore not explained at this point.

In a subsequent fifth step 26, the previously applied ink 5 of the base color is fixed (intermediate hardened) by UV-A irradiation in the manner described above.

In a subsequent sixth step 27, inks 5 from color components of a color model, for example the colors CMYK, are successively applied in a manner known in principle by the associated inkjet print heads 6 to produce a decoration/printed image.

In a subsequent seventh step 28, all previously applied inks 5 of the color model are fixed together (intermediate hardened) by UV-A radiation.

This can be followed by an optional eighth step 29, in which a varnish is applied to the previously fixed inks 5.

In a subsequent ninth step 30, the final curing of all previously applied inks 5 and optionally the varnish is photoinitiated together by UV irradiation.

In general, the process flow after the sixth step could be modified in many ways depending on the application. For example, it is conceivable to integrate the ninth step 30 into the seventh step 28, so that this can include a first sub-step 28a for intermediate curing of the inks 5 of the color model and a second sub-step 28b for photo-initiation of the final curing of all previously applied inks 5. The eighth step 29 could also be omitted or take place after the final curing. These variants depend on the requirements for direct printing on the respective type of container, for example depending on its material and/or surface finish.

Finally, the method 21 includes a final tenth step 31 for essentially radiation-free post-curing of the photo-initiated final curing. In the post-curing are no active measures required for complete hardening of the imprint. In principle, it is sufficient to protect the printed containers 2 from mechanical stress on the prints produced for a predetermined period of time.

Various variants are also conceivable with regard to the described irradiation parameters and combination of light sources 8-10. If, for example, the LED for intermediate curing / fixing / pinning does not provide a sufficiently high emission power for photo initiation of final curing, there is the option of integrating a separate UV LED for the purpose of photo initiating final curing.

However, it has been found that in most cases a UV light source 8, for example an LED with a wavelength of 395 nm, is also sufficient for the photo-initiation of the final curing. Nevertheless, a combination of LEDs with different wavelengths / spectral ranges can be advantageous. For example, it has been shown that in certain cases a combination of UV-B and UV-C LEDs can be advantageous in order to achieve improved surface hardness immediately after the ink 5 has been applied. This facilitates the handling of the loading container 2 immediately after the direct printing. For example, a combination of wavelengths in the spectral range of 270-280 nm or 360-370 nm on the one hand and 390-400 nm on the other would be suitable. A combination with a UV-C LED is also conceivable, which emits in the range of 275 nm, for example.

Experimentally, it was found that although UV-A radiation of 0.2-0.4 J/cm ² leads to hardening of the ink 5, it is usually not yet abrasion-resistant immediately after the radiation. Post-curing for 24 hours then resulted in a fully dry and fully cured ink 5 with sufficient surface hardness. Due to higher values of the UV-A radiation, for example in the range of 0.6-1.0 J/cm ² , a sufficiently good crosslinking/surface hardness of the inks 5 could already be achieved immediately afterwards.

If a Hg vapor lamp emitting in the UV is used for the third light source 10, a lower level of irradiation is sufficient to achieve sufficient curing directly after the UV irradiation, for example an irradiation of 0.2-0.3 J/cm ² . However, the respective layer thickness of the inks 5 plays a role here, as does their composition.

Nevertheless, the photo initiation of the cationic intermediate curing and final curing using UV-A radiation offers an advantage over the photo initiation of radical UV inks, which then often have a surface that is too soft for further handling, in particular because of the UV-C component that is actually necessary for this. In addition, cationic curing requires a significantly smaller amount of photoinitiators and, due to the essentially radiation-free post-curing, enables essentially complete through-curing and reaction of the individual components, in contrast to free-radical polymerization, which often has an incomplete end result.

The final curing of the cationically curing inks 5, photoinitiated by means of UV radiation, can be adjusted relatively flexibly, depending on the further processing of the containers 2 and their design.

Ideally, the containers 2 are designed in such a way that the printed surfaces of individual containers 2 cannot touch one another during transport.

As FIG. 3 indicates schematically, the container 2 has, for example, a container body 2a made of glass with at least one rubbing edge 2b (scuffing edge) which protrudes outwards in a manner known in principle, opposite a surface 2c of the container body 2a printed as described.

Also shown schematically is an inkjet imprint 22 produced on the container 2 by means of the method 21 / described above with the device 1 described above. hardened ink drop.

Conceivable in combination with or instead of containers 2 with friction edges 2b (scouring edges) is transport in which the containers 2 do not touch one another.

If neither friction edges 2b nor non-contact transport methods are an option, the UV irradiation for photo-initiation of the final curing can be intensified so that even with conventional handling and/or design of the container 2 (which does not in itself offer any special mechanical protection) sufficient mechanical resistance of the inkjet print 22 is given until its complete hardening.

It is also conceivable to protect the printed containers 2 by finally spraying on a protective layer, for example made of polyethylene wax.

Compared to known direct printing processes for printing containers in bottling plants, the use of cationically curing inks 5 reduces the equipment and process costs. For example, there are no additional stations for adhesion promoters / primers, the assigned Drying tunnel and UV tunnel. This saves space and reduces the expenditure on resources such as consumables and energy costs.

Ink-carrying components of the direct printing machine 3, such as the print heads 6, can be shielded from stray UV radiation in a manner known in principle, based on known direct printing methods.

The method described offers, among other things, the following advantages over known methods based on free-radically polymerizing inks: significantly streamlined processes and thus lower acquisition and maintenance costs; less space required and lower operating costs; lower energy requirement, among other things, due to the omission of UV lamps that would otherwise be required; Primers are dispensable, and associated solvents, such as alcohol, can no longer evaporate; acceleration of the process flow; increased product safety (compliance) according to the requirements for food production; low residual odor of the cationically curing inks after their crosslinking; and overall better (complete) hardening of the inks, also largely independent of the radiation used, since only a minimum value of the radiation (a minimum dose) has to be observed.

Claims

Expectations

1. Method (21) for direct printing onto containers (2) for products to be filled, in particular beverages, wherein a cationically curing ink (5) is applied to the containers by means of at least one inkjet print head (6), in particular during their transport in a direct printing machine (3). applies and triggers a hardening of the applied ink by means of UV radiation.

2. The method according to claim 1, wherein container surfaces to be printed are flamed and then cooled to prepare the ink application, in particular without simultaneous production of an SiOx layer, and wherein the ink (5) is applied in particular directly to the container surfaces pretreated in this way.

3. The method according to claim 1 or 2, wherein the direct printing comprises a first partial print with application of a basic color, in particular white, and subsequent UV photo initiation of the curing and at least one subsequent second partial print with application of at least one color component of a color model and subsequent UV photo initiation which includes hardening.

4. The method according to claim 3, wherein the base color is intermediately cured in the first partial print as a result of UV photo initiation for the subsequent application of the color components and/or in the second partial print all colors of the color model are first applied one after the other and then at least intermediate hardened as a result of common UV photo initiation and in particular final hardening.

5. The method according to at least one of the preceding claims, wherein an inkjet imprint (22) produced by applying the cationically curing ink (5) to the containers (2) is post-cured over a predetermined period of time essentially without radiation as a result of its UV-initiated final curing and the imprint while protecting against mechanical damage during transport and storage, in particular by providing rubbing edges (2b) on the containers.

6. The method according to at least one of the preceding claims, wherein the curing is triggered exclusively with UV-A radiation, in particular an LED emission.

7. The method according to at least one of the preceding claims, wherein the ink (5) for triggering an intermediate curing with a UV-A radiation of 0.1-0.5 J / cm ² , in particular 0.2-0.4 J / cm ² , and / or to trigger the final curing with a UV-A radiation of 0.5-1.5 J / cm ² , in particular 0.6-1 J / cm ² , irradiated.

8. The method according to at least one of the preceding claims, wherein a final curing of the ink (5) is photo-initiated by an in particular supplementary UV-B and/or UV-C LED emission.

9. The method according to at least one of the preceding claims, wherein a final curing of the ink (5) is photo-initiated by emission from at least one mercury vapor lamp at an irradiation of 0.1-0.4 J/cm ² .

10. The method according to at least one of the preceding claims, wherein the area (14) surrounding the direct print and/or a transport area/storage area (15) of the container (2) is air-conditioned, and in particular a relative humidity of 50% in the case of photo-initiated intermediate curing photo-initiated final curing and/or in the case of essentially radiation-free post-curing of the ink (5) is not exceeded.

11. Device (1) for direct printing onto containers (2) for filling products, in particular drinks, according to the method according to at least one of the preceding claims, comprising a direct printing machine (3) with an ink supply (4) for providing cationically curing ink (5) , with at least one ink jet print head (6) connected to the ink supply (4) for applying the ink to the containers, in particular during their transport in the direct printing machine, and with at least one UV light source (8, 9, 10) for photo-initiating a hardening of the applied ink.

12. The device according to claim 11, wherein the UV light source (8, 9, 10) comprises at least one LED emitting in UV-A and is designed to the applied ink (5) for photo initiation of an intermediate curing with a UV-A Irradiation of 0.1-0.5 J/cm ² , in particular 0.2-0.4 J/cm ² , and/or to photoinitiate a final curing with a UV-A radiation of 0.5-1 , 5 J/cm ² , in particular 0.6-1 J/cm ² .

13. Device according to claim 11 or 12, further with the direct printing machine (3) in particular immediately upstream: a flame tunnel (12) for flame treatment of the container (2) and a cooling tunnel (13) for cooling the flame-treated container.

14. Container (2) for products to be filled, in particular beverages, comprising a container body (2a) made of glass, plastic and/or a cellulose material, and an inkjet imprint (22) applied directly thereto, in particular without an intermediate layer, comprising a base color layer and a multicolored printed image layer each consisting of cationically cured ink droplets.

15. The container according to claim 14, further comprising at least one rubbing edge (2b) protruding outwards beyond the ink jet imprint (22).