(Quoted from Sign & Digital Magazine. Full article here.)
Printing with UV-cure inks is a great solution for many printing situations. However, there are some difficult substrates, such as plastics, metals and glass, where adhesion may be poor or non-existent. Many plastics have low-energy surfaces that actually repel inks; metals may have oils in them from the manufacturing process; and glass/ceramics are just too hard and non-porous for just about anything to stick.
In order for ink to bond properly, its surface tension must be lower than that of the surface it is supposed to bond to. Heating the substrate with heat lamps immediately before printing is sometimes effective, but this can damage some heat-sensitive plastics.
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