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Understanding Discharge Inks

(September 2007) posted on Wed Sep 19, 2007

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.

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By Mike Ukena

A direct correlation exists in all discharge systems between the amount of discharge agent used and the initial feel or hand of the fabric after printing. Too much discharge agent causes the finished print to have a harsher or heavier feel than a print done with the minimum amount of discharge agent. In addition, extensive testing has found no advantage to using a higher level of discharge agent than the minimum recommended amount for a given ink system. So, if a manufacturer’s instructions call for 6-9% discharge agent, the use of 6% will give the best results. Washing the garment for the first time after printing removes any harshness caused by the discharge agent and delivers the ultimate fabric softness.


Plastisol/water-basedhybrid discharge

Hybrid discharge inks have been around for more than 10 years. However, the major growth in their use has only occurred in the past two years. It is my opinion that the ease of using these inks is a major factor in fueling the present discharge craze. The most important advantage of plastisol/water-based-hybrid discharge inks is that they are much easier to use for those that have never used discharge or water-based ink systems.

Even though the ink is 50% water-based, the tendency to dry in the screen is much less than with 100% water-based products. In fact, the plastisol tends to have a retarding effect on the ink in the screen. Printers who use hybrid discharge inks are able to use a plastisolprinting procedure of having the screen unflooded between prints. A true waterbased procedure requires printers to keep the screen flooded between prints. And even when there is a break in the printing, where the screen starts to dry in, the effect usually can be reversed by the simple use of a double stroked squeegee in the discharge screen. Keeping the screen flooded between prints is still a better procedure. It helps to keep the screen ready for a proper print each time without the need for an extra cycle.


Water-based thioureadioxide-activated discharge

Thiourea-dioxide-activated discharge inks were developed to address the issue of formaldehyde exposure and residue associated with ZFS-activated discharge inks. They work in a similar fashion and with similar pot-life parameters. These products are still quite new to the textilescreen-printing market. I’ve heard from many printers who have tried them and reported having issues with color intensity in certain shades.


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