Which is the ideal drying system to choose for a pad printing ink?
Although the printed ink used in pad printing is ready to handle in a short time, accelerating the drying process is recommended in certain applications
HOT AIR DRYING (DUE TO EVAPORATION)
For solvent-based inks, used in most cases in pad printing, the high temperature and poor ventilation which is generallyfound in ovens with radiant panels is not sufficient. In order to eliminate the solvent from the layer of ink quickly, anefficient oven must have a high volume of hot air with a direct flow to the material to be treated, with the possibility to regulate the temperature up to 200°C, evenly distributed throughout all areas of the baking chamber, in order to allow a correct drying process with low energy consumption.
I.R. INFRARED DRYING (DUE TO RETICULATION)
In order to obtain an article which is ready for other processing in a short time using two-component ink, which normally takes a few days to harden completely at room temperature, it is necessary to accelerate the reticulation between the ink and the catalyst. In this case, in addition to air, as solvent is also present in two-component ink, irradiation with I.R. infrared rays is ideal, above all on material such as glass, ceramics and metal. Infrared ray drying, with lamps with precise wavelengths, is the most effective and quickest system for transferring energy from a hot body to a cold one. By penetrating the layer of ink without overheating the article, the irradiated IR also allows quicker cooling.
U.V. ULTRAVIOLET DRYING (DUE TO POLYMERIZATION)
Drying using U.V. ultraviolet rays is based on the property of certain components to create internal reticulations and therefore harden if hit by this specific type of ray; the phenomenon is known as polymerization. UV inks contain groups of molecules (monomers + photoinitiators) which, if hit by the radiation emitted from UV lamps, trigger chain polymerisation. This drying system ensures that the ink film hardens in a fraction of a second. Unlike screen printing ink, UV ink for pad printing also contains a minimal percentage of solvent, necessary for transfer from the pad; a UV oven for pad printing must therefore take this aspect into consideration. Before exposure to UV irradiation, certain inks require a stage with infrared, IR, radiation, in order to improve the dilation of the layer of ink.
Modular combined oven leaflet (PDF)