Dieter Finna (Click here for a German version)
Printing on tube laminates using UV inkjet poses several application-specific challenges. The tubes, which are bent and crushed during squeezing, require a flexible ink film. It must adhere well to the substrate, must not crack during handling and must meet all compliance requirements. In addition, the cost-intensive substrate requires a machine concept that includes the shortest possible web paths as well as the option of print finishing.
Seen in this light, it is not an easy task that the well-known laminate printers entrusted product development at Gallus Ferd. Rüesch AG with. The printing press manufacturer was able to adopt some of the solutions for the complex task from the results of another development project. On folding cartons, where the solids extend beyond the ink edges, there are comparable requirements for the flexibility of UV inkjet inks as for tube laminates. The challenge lies in preventing the UV inkjet film from cracking under mechanical stress. For a long time, the only way to avoid cracking of the brittle ink film was to avoid solids that extended beyond the folds by necessity in the packaging design.
Development of a flexible UV inkjet ink
For this reason, Gallus launched the »Flexible UV Inkjet Ink« project for folding carton printing along with a well-known brand manufacturer at the start of 2019. The complex development project took three years to complete, including all the development steps, suitability tests and six months of ink qualification. For product qualification, the brand manufacturer printed more than 900 km of board on a Gallus Labelfire 340 and produced around 8 million blanks. The requirement criteria in printing were for the ink film to be fully cured at a printing speed of 70 m/min and for a scratch-resistant, flexible ink film.
»During the tests, we found that the adhesion and flexibility of the new flexible UV inkjet ink showed good values. The digitally printed tube material could be processed in the same way as conventionally printed material«, Günther Forster, Prepress Manager, Business Unit Printing Product Manager Cosmetics at Permapack AG, describes the evaluation of the test results.
In the packer test, blanks printed over the entire surface had to be able to be processed at 1000 packs/minute without ink cracking. In addition, the UV inkjet printing ink had to pass the sensory test programme in the tobacco sector and fulfil all the requirements in the Regulatory Compliance & Toxical Assessment. This included the composition of the UV inkjet ink according to Swiss Ordinance requirements, the REACH conformity test for chemicals, the requirements of the RoHS Directive 2011/65EU and the EUPIA exclusion list for defined raw materials as well as proof of freedom from substances with carcinogenic, mutagenic or reprotoxic effects. The UV inkjet ink system developed in the project with the product name »UVF01« passed the tests and has been released for commercial production in the brand manufacturer’s folding box production since the beginning of this year. This provided the prerequisites for transferring the results of flexible UV inkjet inks from folding carton printing to the solution approach for tube laminates.
Modifications of the printing press system
Modifications to the Gallus Labelfire 340 were necessary to use the »UVF01« ink system. These related to the drying technology and web guide. The latter had to be designed for the shortest possible web paths for the cost-intensive substrate.
Gallus has broken new ground in radiation curing. In the Gallus Labelfire version for the new flexible UV ink system, LED-UV curing systems replace the mercury vapour lamps previously used. The advantage of LED-UV technology is that the energy penetrates the ink layers more effectively thanks to the high intensity of the UV-A beams, resulting in more uniform curing. Due to the high intensity of the UV-LEDs, the use of boosters to intensify drying can be dispensed with. This means that the temperature-sensitive tube laminate can be processed without heat effects. As an additional measure, inert gas is used for fast and complete curing of the ink film wherein cross-linking of the ink film in the inert chambers takes place in the absence of oxygen, which has been replaced by nitrogen in the sealed environment. The oxygen content in the inert chambers is continually monitored by sensors and kept below 500 ppm. The increase in curing performance achieved, as well as the reactivity of the photoinitiators result in complete curing of the ink film at a printing speed of 70 m/min. An added benefit is that a very good adhesion of the ink to the substrate is achieved without the use of primers.
The machine layout of the modular Gallus Labelfire »Tube Edition« was designed to keep the web path in the machine as short as possible. Therefore only a single rewinder is used instead of the double rewinder. When selecting the flexographic printing units, the company opted for the Gallus ECS series. The main advantage of these printing units is that they have an ultra-short web path of just 1.1 metres from printing nip to printing nip, which significantly reduces waste during makeready and production. Given the high material costs of tube laminates, this is a major factor contributing to high profitability in the printing process. For example, the web path between unwinding and rewinding on the »Tube-Edition« is only around 25 m, compared to around 80 m on a comparable press for tube laminate printing. What’s more, the servo-driven Gallus ECS printing units allow for maximum substrate flexibility when using different thicknesses of laminates. The press layout of the Gallus Labelfire »Tube Edition« features the centrally arranged UV inkjet digital printing unit DEU, with an upstream and a downstream flexographic printing unit. The arrangement combines high print quality in digital printing with the cost benefits of flexographic printing, even for motifs with high ink coverage. The upstream printing unit is used to apply spot colours, cold foil or a primer (if required), while the downstream unit is used to apply the protective coating over the entire surface. At the user’s request, the digital production system can also be supplemented with an additional cold foil unit.
Qualifying comparison of digitally and conventionally printed tubes
Once the press concept and the ink series were available, the next step in the project was a practical comparison of digitally and conventionally printed tubes. This allowed an evaluation to be made as to whether, or to what extent differences between the designs were recognisable based on defined quality criteria. To this end, Permapack AG contributed its printing expertise in laminate printing to the project producing the conventionally printed tube samples. These were printed on a Gallus RCS 330 as a benchmark for digital printing and joint assessment with Gallus. The digital benchmark samples were printed on a Gallus Labelfire 340 running in industrial use and equipped with the »UVF01« inkjet series and modified dryer technology. The designs for the benchmark and the different tube laminates were selected according to typical market requirements.
The test results with the »UVF01« inkjet ink showed excellent results across all fastness requirements for the tube laminates PBL and ABL, which are predominantly used in the market, as well as on paper laminate. The evaluations exclusively show results in the »1-very good« range. »During the tests, we found that the adhesion and flexibility of the new flexible UV inkjet ink showed good values. The digitally printed tube material could be processed in the same way as conventionally printed material«, Günther Forster, Prepress Manager, Business Unit Printing Product Manager Cosmetics at Permapack AG, in describing the analysis of the test results. Only the digitally printed PP laminate, which is only used to a very limited extent on the market, showed a deviation in the aging test. With PP laminates, printing conditions and inkjet inks still need to be modified somewhat.
The family-owned company, founded in 1958 and headquartered in Rorschach, SG/CH, is divided into the divisions »Labels & Flexible Packaging« and »Construction, Industry, Retail«. Labels and packaging are printed in the in-house print division, with a growing share of laminate films for tube production. The target markets are the non-food, food and cosmetics sectors. Collaboration with Gallus in the print sector dates back to the company’s early days and continues to find expression in innovative products. To this end, Permapack’s printing experts make use of the technical possibilities offered by the company’s modern machinery and create highly unusual designs and products. The European Tube Manufacturers Association (etma) named Permapack’s paper tube »Tube of the year 2021« in the »Sustainability« category.
The Gallus Labelfire »Tube-Edition« together with the flexible »UVF01« inkjet ink presents itself as a pioneering alternative to purely conventional tube printing. Thanks to the high native resolution of 1200 x 1200 dpi, digital printing can score points in terms of print quality by outperforming the motifs usually printed in 54 screens in flexographic printing.
Besides print quality, the economic efficiency of a production system is the decisive criterion for its industrial use. Here the machine system meets a market situation in which run lengths in the tube market are declining. Since short to medium run lengths are a strength of digital printing, it can also demonstrate its strengths here. A break-even analysis of the costs of the print samples from the print comparison shows that the digitally conventionally printed runs up to a run length of approx. 5000 running metres are cheaper to produce than purely conventionally printed tubes. With a standard tube of 200 ml, this corresponds roughly to a quantity of 53,000 tubes and is considered an average run length in tube printing.
This project provided all of the evidence that qualifies the flexible UV inkjet ink for use in tube printing. This means that the Gallus Labelfire »Tube Edition« and the »UVF01« inkjet series are now ready for use in industrial laminate printing.