Davis explains how flash units can influence productivity and describes problems you'll see when they fail to keep their cool.
By Rick Davis
This problem is very evident when printing a bleed-resistant underbase. The bleed-resistant components within the ink film will begin to boil off, leaving small voids or craters in the overprinted ink films. This scenario typically occurs in dryers that have short infeeds because the flashed ink film does not have the time to cool prior to passing through the drying chamber. In many cases, larger shops have dryers with longer infeeds, allowing the temperature of the flashed ink films to drop. Garment-printing facilities that lack the luxury of long infeeds have a much greater need to ensure that the garments are flashed at as low a temperature as possible in order to minimize the potential for some of the problems described here.
Exposing garments and ink films to excessive heat also can trigger polyester dyes to sublimate in 50/50 fabrics. This effect may not be immediately evident at the end of the dryer, over time the polyester dyes can noticeably sublimate into the ink film and, consequently, bleed out. The sublimation and bleeding can occur anywhere from one day to six weeks, depending on the polyester dye content within the fabric and the degree to which the dyes sublimated during the curing process.
The role of the flash
The flash unit's job is only to set or gel the underbase ink film. The same holds true when you flash at the end of a printing sequence prior to adding a special effect. Although flash units are referred to as flash-curing units, curing the ink film really is the last thing you want them to do. A full cure would prevent ink layers from adhering to one another. All you want to do is to prepare one ink film to receive the ink that you'll deposit during the next print stroke.
Once you've determined the point at which the ink film is adequately set by the flash unit, you'll want to maintain that temperature carefully throughout the run. If necessary, you can combat the effect of platen temperature on the process by preheating your platens prior to production and then determining the minimum temperature needed from the flash unit to properly flash your underbases. The philosophy of more is better when it comes to setting flash temperatures in order to achieve faster production often causes many more problems than opportunities for you to increase efficiency.
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