The IR conveyor dryer has a home in applications beyond screen-printed garments.
One of the most critical steps in the screen-printing process is drying, or curing, of ink after it has been applied to the screen-printed product. This is accomplished by heating the ink to the temperature at which it cures, as a printed garment or other item passes through a dryer on a conveyor belt. Popular plastisol inks require cure temperatures of approximately 320-340°F, while other types of ink cure or bond at slightly different temperatures.
Choosing between gas and electric
Gas and electric dryers offer different advantages depending on budget, required capacity, available floor space, and the cost of gas and electricity.
Gas dryers have an open flame that heats air within a chamber and transfers the heated air to the area through which garments or other printed items are conveyed. The heat is then transferred to the ink by air convection, equivalent to heating food slowly in a gas oven.
An electric dryer, by contrast, uses infrared (IR) radiation that causes ink molecules to vibrate, generating heat that raises the temperature of the ink rapidly without heating the air around it, akin to heating food in a microwave.
The primary advantage of a gas dryer is its ability to maintain a constant temperature and avoid overheating of the ink. Some disadvantages are dwell times of two to three minutes to heat the ink, requiring long dryer lengths that increase capital cost and consume floor space. Additionally, thick insulation is needed to prevent the outer walls from reaching dangerous temperatures. As a result, gas dryers are generally recommended for large print shops, providing that natural gas or propane is available and less expensive than electric is locally.
Gas dryers are typically larger and more expensive than IR conveyor dryers for several reasons. Gas dryers handle significant volumes of high-temperature air, requiring costly air-handling systems with motors positioned away from the hot air stream. And finally, complex safety controls are required to protect operators from combustible, pressurized gas.
Gas dryers often feature more complicated designs than IR dryers, but they are capable of processing a wide range of printed inks, including discharge inks, water-based inks, plastisols, and specialty formulations. In addition, hot-air recirculation aids in thermal stability and enables hot-air dryers to cure a variety of ink types without risk of scorching.
Did you enjoy this article? Click here to subscribe to the magazine.