Use the following tips to control the variables most commonly encountered in garment screen printing.
Flash or spot curing is used to set or dry to the touch one or more ink layers before printing the next. Flashing is necessary for creating an underbase layer, controlling dye migration, printing light inks on dark garments, printing multiple colors on nylon, solidifying multicolor prints, and printing special-effect inks.
Flashing is also a crutch for many printers, used to compensate for improperly prepared artwork, incorrect color/print order, poor registration, poor ink preparation, incorrect mesh counts, and poor screen tension. Ink problems such as screen buildup and smearing with butt-registered colors are often addressed with flashing as well. In these cases, flashing simply bandages the problem and can be an efficiency killer.
Flash time, distance, and temperature are the primary control points with a given flash unit. Together, these three variables dictate the heat exposure on the ink. Finding the most efficient balance can help a printer save countless hours, reduce scrap and improve production speed.
Flash time or dwell is the main adjustment for flash curing inks. Once the flash distance and heat level are setup, the flash time is the fine tuning to bring the ink just to gel stage. The term flash curing is misleading because the goal of flashing is not to cure the ink. Flash curing is only used to bring the ink to 160-275°F (71-135°C), depending on the ink.
While common practice, excessive flashing not only wastes production time, but it also can create other problems. Over flashing, or fully curing, an underbase layer can hinder adhesion of the subsequent colors. It will also overheat the platens, which can cause ink to start gelling in the screens. The high heat can make fabrics shrink, scorch, and cause the platen adhesive to melt. Additionally, over flashing synthetics can trigger dye migration into the ink film, and some inks may shift color if the flash heat is excessive.
Flashing plastisol ink is influenced by the same variables as fully curing the print and is not a one-time-fits-all situation. Variables include fabric type and weight, shirt color, ink color, ink thickness, ink modification, room temperature and relative humidity, and platen temperature. As these change, your flash dwell will need to be adjusted accordingly to maximize efficiency.
Flash distance is measured from the bottom of the panel to the surface of the garment. The closer the distance is set, the higher the cure efficiency and production rate. It is also important to level the panel over the platens and to ensure the platens are leveled one to another.
Flash temperature can be controlled, provided the flash unit has a heat controller/regulator. Those flash units without this option run at the same temperature all the time. Generally, temperature is not frequently adjusted unless the fabric type is sensitive to heat. The distance and dwell time are the chief means of regulating flash exposure.
Did you enjoy this article? Click here to subscribe to the magazine.