The flash dryer is a very important part of the screen printing process. A flash dryer is used in screen printing in one of two ways. In a production setting, a screen printing flash dryer is used to set or gel the ink in order to print another color beside or on top of it. A flash dryer can also be used to do a final cure of the ink but this is not optimal for production. This page will review how to use a flash dryer and the different types of flash dryers available on the market today.
Using a flash dryer for flashing.
Typically a flash dryer is placed 2-3 inches above the screen printing platen height. Depending on the wattage and type of the flash dryer the flash is positioned over the platen for anywhere from 3-15 seconds. Typically the ink needs to reach about 240-250 degrees Fahrenheit which is its gel point. The ink should not come up on your fingers if you touch it but still feel tacky. Screen printers should avoid flashing the ink for too long because if the ink has a chance to fully cure, the next layer of ink will not bond into the underbase which has already been fully cured, this is known as intercoat adhesion.
Using a flash drying unit to fully cure ink.
Both plastisol and green galaxy water based ink need to reach 320 degrees through the entire layer of ink to fully cure or set. While a flash dryer can accomplish this, it is not optimal for production or consistency. A flash dryer allows air to circulate under it which can change the curing parameters in a moment, it also sometimes is not large enough to cure the entire design which can cause the edges to wash out. To use a flash dryer to properly cure ink it is imperative to separate the shirt from the platen. Unlike flashing where the shirt stays stuck to the platen to maintain registration, the when fully curing a shirt with a flash it is important to remove the shirt from the platen surface. This allows the heat to penetrate the entire layer of ink and fully cure the ink. If using a temp gun to temp the surface of the ink it should reach 330-340 degrees F. Stretch testing and wash testing ink is always recommended. If you are using a flash to achieve final cure ensure that the air around the flash is stagnant so that air movement does not change the temperature and flash elements effectiveness.