Bringing a flash-curing unit onto your production floor gives you the ability to expand your garment-printing program to include dark garments, multicolor work, and designs that involve the use of specialty ink formulations. The primary goal of a flash unit is to properly gel a printed underbase prior to overprinting. Heat is heat, which makes the selection of a flash unit capable of performing this task fairly simple for many. Almost any heater is capable of producing temperatures sufficient to gel an underbase. However, one aspect that’s often overlooked is the residual effect that the flash unit can have on other parameters of the printing process. This month, we’ll look at different types of flash units and discuss their influence on the production of screen-printed garments.
Black-body flash units are the most widely used in the industry. These systems either work off of a thermostat, which controls the panel temperature by maintaining a constant temperature within x degrees, or a percentage timer, which maintains a ball-park temperature by turning the unit on for 50% of the time (say 5 seconds on and 5 seconds off). Of the two, the thermostat models are far more accurate at setting and maintaining a constant temperature.
The need for consistency in the flashing process is obvious. Any wide variations in flashing temperature can result in problems ranging from erratic after-flash tack to intercoat-adhesion issues between the underbase and overprinted colors. A good flash unit will maintain temperatures within ± 25°F.
Black-body flash units that employ hot air offer some versatility over standard black-body systems. As with large, gas-fired dryers, the addition of hot air to the flashing process can de-crease flash times because the ink film will absorb the heat more readily. Although the air can offer advantages, caution must be exercised to ensure that the ink film receives a uniform dispersion of heat and that the areas directly under the air knives do not receive an excessive amount of heat, which can result in a spotty underbase and potential intercoat-adhesion issues.
Most black-body and black-body units with air movement operate on either 110 or 220 v. Always know your building’s power limitations before you call the manufacturer or your supplier so that you can explain to them what you need and can handle.
Quartz flash units
Quartz flash units offered a slightly cooler alternative to the standard black-bodied units. Quartz units are designed to trigger from room temperature to 1400°F in seconds. They are also designed to cool down just as fast. This functionality offers the greatest advantage.
One consideration with this type of unit is that it targets intense, direct, infrared heat at the garment and ink. In the past, these units came with only an on/off setting. If you’re prone to taking a more is better attitude, you’ll need to exercise extreme caution when setting the unit’s operating parameters to prevent garments, platens, and ink films from exposure to excessive heat. Your goal is to gel underbases. A fully cured underbase creates problems with ink adhesion, print durability, and more.
Newer quartz units on the market today offer adjustable heat settings and built-in failsafe systems. These units are superior from the standpoint of efficiency and their ability to produce less overall heat. They can also flash faster when properly set for particular applications.
Another consideration to keep in mind is that quartz units require quite a bit more power as opposed to the black-body units. In addition, the replacement cost of a quartz bulb is expensive and requires great care when handling.
As you can see, each type of flash unit has its positives and negatives. Efficiency and cost are the primary concerns of most facilities, and they make the decision on which unit to purchase a toss up. One offers a greater operational efficiency at a higher operational cost, while the other offers consistency at a lower cost. It is up to you to weigh the benefits that each unit offers and determine which unit is right for your shop.
The actual surface temperature of the emitter panel is a number that few know or attempt to discover. Since the objective of a flash unit is to bring an ink film to the neighborhood of 125-250°F, I feel that it’s critical to determine this number in order to properly utilize the flash unit. Figuring out panel temperature is but one of your tasks. You also need to document the temperature variations that take place in all panels.
The high-performance fabrics that we have to deal with today represent but one really good reason to measure the heat coming from your flash unit. Most moisture-wicking or high-performance materials are now manufactured in 100% polyester with dyes of questionable qualities. These fabrics require extensive testing and control during the printing process in order to prevent the onset of migrate due to poor dyes or quality issues stemming from dye sublimation.
Printers have tried a number of different methods to determine the actual performance of their flash units. Many run heat tapes on the surface of the garment as it goes under the flash unit. The issue here is that heat tapes can’t react quickly enough to give an actual reading in relation to the garment or the ink film.
One popular way to read the surface of the flash unit is to use a non-contact pyrometer. These instruments are now widely used throughout the garment-screen-printing industry as a method of standardization for determining temperatures. Non-contact pyrometers allow the user to point a measuring gun at the heat source from a particular distance and determine the flash unit’s panel temperature. Although not exact, the non-contact pyrometer provides a good means of determining a ballpark temperature, as well as identifying any top-to-bottom or left-to-right variations in panel heat. It goes without saying that any side-to-side variation will wreak havoc on your flashing applications.
The next method to determine panel temperature is the on-contact pyrometer. On-contact models provide the most accurate readings, as they are in real contact with the flash units. Should any variations be identified, you should contact the manufacture of the unit to determine the best action to take to correct the inconsistencies.
Assessing panel temperature should become a routine measurement you take on a regular basis to ensure your flash unit is continuing to operate properly. Record your readings each time, and it will be easy to determine whether the unit is performing the way it should.
Rick Davis is the president of Synergy Screen Printing in Orlando, FL. A 27-year veteran of the textile-printing industry, Davis is a member of the Academy of Screen Printing Technology and has a background that spans production management, artwork engineering, application testing, and industry consulting. He is a frequent contributor to trade publications and a speaker at industry trade events.
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