Two-Lamp Curing UV Screen Ink
The total mJ values from two-lamp curing do not always provide the same curing result as a curing at the same levels with one lamp. UV curing takes place almost instantaneously. When a wet ink film is cured with a two-lamp system, the first lamp reacts most of the ink. The second lamp can provide additional cure, but its UV curing effects have to travel through a cured ink film to contribute to the total cure result.
Although using two lamps per head does help to cure an ink better, it is erroneous to combine dose (mJ) values of each lamp head to achieve the required mJ values needed to cure the ink. Most, if not all, of the curing should be achieved with one lamp. This also applies with top-curing the first layers of an ink and hitting the last printed layer with excessive UV output. This method of overall curing could result in a partial cure, resulting in lower adhesion, lower chemical and water resistance, higher odor, higher potential for blocking or higher potential for ink to re-wet itself or other inks.
Check out Nazdar's supply of UV Curable Screen Inks.