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In Mold Labelling for HP Indigo

In Mold Labelling for HP Indigo

The following are important primer application parameters: 

Corona on film 

Less is more! Since all the films are already provided with corona treated surface from the extruder, the main goal here is just "refreshing" the film surface. Time, humidity, storage conditions and contaminations have an effect on the film surface treatment level and decrease the dyne levels, therefore it is very critical to refresh the film with corona to allow for good printing. However, over-treating and over corona treatment on the film cause unwanted effects. This will not be visible during printing, but it will decrease dramatically the durability of the end product, and especially the humidity resistance. For all applications, but especially for the ones requiring humidity resistance of the end product, it is recommended to apply the lowest possible corona power. The best power level is “just enough” to allow good primer wetting of the substrate and good ink fixing. Not more. HP Indigo's trials have showed that the best corona watt density level for refresh is about 10-30 W*min/m2. Use your equipment specifications to calculate the watt power if your system is working on predefined power and not density. For example, if you are using BOPP film on HP Indigo WS6000 Series Digital Presses, use 100-200W power in the ILP for corona treatment. For best results it is recommended to run a short trial to find the best corona levels on your equipment and materials. 

● Coat weight Less is more! To achieve better drying, adhesion and durability, it is also recommended to use the lowest coat weight possible, “just enough” to allow for a good primer cover of the substrate, and good ink fixing. Also, most of the IML films are treated on both sides (print side and back side) to allow for better fixing during the molding. With high dyne levels on the back side, and a high primer coat weight, you may end up with a blocked roll after rewinding. The following are the coating parameters for HP Indigo recommended primers (listed in the table above): ◦ For offline standard flexo coating it is recommended to choose low volume anilox, such as 400-700 lpi (3.5-6.0 cm3/m2 volume). ◦ For inline on HP Indigo WS6000 Series Digital Presses, use standard coating settings (low or medium coat level). ◦ For inline on HP Indigo 20000 Digital Press, use low volume anilox (2.5 bcm). 

● Drying conditions and tension Dimensional stability of the label for IML is highly important since after die-cutting, and until molding, the label has no backing liner and has to perform by itself, staying flat without any deformations or curling. BOPP film is quite sensitive and unstable under increased heat and tensions, thus it is highly recommended to use the lowest possible values. Since we use water based primers, hot air is needed to dry the primer. Using higher airflow may allow you to use lower temperatures. Depending on the primer chemistry, film and process parameters, the drying temperatures may range between 50 °C and 90 °C. For best results, it is recommended to run a short trial to find the best drying temperature and tension, according to your equipment and materials. 

● Static To achieve a good IML production it is highly recommended to avoid static electricity, otherwise the labels will stick together and double-picking will be a major problem. Every process step must have ENWW Priming 11 either a passive or an active static discharge station at the end. For priming, it is very important in case of offline coating. High static may introduce pin holes in the primer layer, causing print quality issues. 

● Primer ageing There is a determined period of time during which you can still effectively print on primed film, before it becomes useless. It is irrelevant in case of inline coating, and very important for offline. Environment conditions (like humidity and temperature) and the primer chemistry will define how long a primed roll can wait before printing. To achieve better results, it is usually recommended to print as soon as possible (even on the same day), but some chemistries are more stable than others and remain reactive for days and even months.

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