Davis examines the variables to control when flash curing your garment prints and how artwork, mesh selection, and inks influence the flashing process.
By Rick Davis
Flashing an underbase on a dark garment in order to allow lighter colors to pop is a process garment screen printers have used for more than 25 years. At first, it was a process that printers only needed on rare occasions. But flash curing quickly became a day-to-day part of garment screen printing.
Even though flash curing is somewhat standardized in most garment-printing facilities, a learning curve awaits those who are new to the process and industry. This month, we'll look at the assorted considerations to keep in mind if you want to avoid headaches when flash curing plastisol inks.
One of the first considerations to address in underbase flashing is properly engineering the artwork for the process. Each graphic needs to be addressed on an individual basis in order to determine the best times and which colors to flash.
Keep in mind that flash curing only applies to about two-thirds of the colors you'll print on dark garments. Many novice printers work under the assumption that printing a multicolor graphic on a dark garment requires a solid underbase for every color. Many will get into trouble here. One of the first rules is to avoid wet-on-wet overlays when printing onto a solid, flashed underbase; otherwise, the result will be excessive mottling.
When printing onto a virgin fabric, you have the absorbency of the fabric that allows for the application of wet-on-wet colors. Once you flash an underbase, you then switch to printing on a dried sheet of non-absorbent plastic that doesn't allow for the wet-on-wet overlay process. For this reason, you want to minimize any wet-on-wet overlays. The exception to this rule is when you work with photographic separations and have a halftoned underbase. In that case, you have a percentage of open area (available fabric) that allows for wet-on-wet printing.
Another consideration when working with solid colors is to use underbase gapping. Many multicolor graphics involve colors that butt-register together. This is fine, except for the fact that most presses offer a minimal amount of registration variation. That means the butt-registered colors will typically begin to bleed together and mottle after a few prints. In this case, you'll want to produce your underbase by combining your respective colors and pull each one back a half point. This will produce a 1-pt gap in the underbase where the butt-registered colors meet. The result here is an absorbent gutter that gives the colors somewhere to go when they meet each other on the underbase. This technique allows you to maintain better resolution where the colors meet and avoid mottling.
Another simple trick for overprinting onto a flashed underbase is to allow for a slight overlay of the overprint onto the underbase. The easiest way to achieve this is to either spread the overprint (or choke the underbase) 1.5 to 2.0 points. The very slight overlay produced here will hide any registration variations your press may have and make the printing process that much simpler.
Proper mesh selection can make a big difference when underbases are involved in a garment-printing job. The mesh can make the difference between a garment with a soft, bright print and a bullet-proof graphic that has a hard and stiff feel. Even though the graphic determines the actual final sequence of colors and meshes, your objective should be to produce the brightest graphic possible while employing the finest mesh counts possible. The "more is better" philosophy leads to bullet-proof prints, use of more ink than necessary, longer flashing times, and potential curing issues. Table 1 presents some basic guidelines for mesh selection based on the ink type being used. However, remember that the right mesh also can vary according to the application, your equipment, and other factors.
Did you enjoy this article? Click here to subscribe to the magazine.