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 underbasing also makes true process printing on dark fabrics possible. For process printing, again, do not use a white discharge underbase. If the white pigment mixes with the transparent process inks, they will turn very pastel. Instead, work with a natural discharge underbase that will reveal the natural cotton background color. Major ink companies have triple-strength versions of their process-ink systems to compensate for the less than perfect background—these 3X inks overcome the off-white background color. The one kicker is that if the design contains any white color of its own, you’ll need to print a white highlight as part of the process design. Ink companies also provide a special white highlight ink that is designed to print with the process inks in this application.
Discharge printing is typically very cost effective from the standpoint of the initial product cost and per print cost. The increased production speeds compared to a strictly plastisol print on dark fabric makes these savings possible. Waste can be an issue should you activate too much ink for a particular job. However, you can minimize the amount of waste through proper shop procedures, ink estimating, and using expired ink on light fabrics (more on this later).
Safety issues in production
Screen printing involves chemicals. Some are safer than others. The chemicals involved in discharge printing must be used properly to be safe. The names of the activators even sound a little on the dangerous side: zinc-formaldehydesulfoxylate and thiourea dioxide. Both of these chemicals have their handling, environmental, and residual issues. Those who plan to use either system are advised to understand the chemicals and train their staffs to properly handle and use them in production.
ZFS has the rather unpleasant odor of formaldehyde and rotten eggs. It should be handled carefully in its crystalline form and blended into the ink by an employee who is properly trained in its use. Remember to blend the ZFS slowly until it is in solution to prevent the dust from becoming airborne. ZFS is relatively safe once in solution, but it still should be kept from contacting skin. Formaldehyde is a skin irritant.
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