Discharge inks are experiencing a renewed interest among garment screen printers. This article describes the types of ink systems available, proper use of these formulations, and the safety precautions you should employ when working with them.
By Mike Ukena
Discharge inks require an activator/catalyst to work. There are two different systems available, one of which is much more prevalent than the other. The predominant system relies on zinc-formaldehyde-sulfoxylate (ZFS) as its active ingredient. The newer, and less common, system relies on thiourea dioxide as its active ingredient. In both systems, the ink has a limited pot life once the activator is added. Most ink manufacturers cite a pot life of six to eight hours. My preference and recommendation is to work with activated quantities of what will last two to four hours in order to always keep the ink fresh.
Discharge requires a dryer that can extract, or steam off, all of the water in the time that it takes the fabric to pass through the chamber. True water-based discharge involves a lot more water to get rid of than the plastisol/water-based hybrid systems. For this reason, companies with smaller or less capable dryers are usually better off trying the hybrid systems first. Then, as their experience evel increases, and if they get a more powerful dryer, they can move to the pure water-base discharge products— if they really want to.
Water-based ZFSactivated discharge
Water-based ZFS-activated discharge is the most traditional and still the most versatile method of discharge printing. The availability of colors, the consistency of the prints, and the softness of the resulting finish are superior to other discharge systems. There is virtually no hand to the print, even on black fabric.
Printers can add pigment concentrates to the discharge base at any time, and the pigment-base combinations poses no pot-life constraints. The only time that the clock comes into play is when the discharge agent (ZFS) is added to the ink. Never take this step until you are ready to print.
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