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
ZFS discharge is safer on press. It won’t evaporate quickly, and very little ZFS can become airborne at this level. Proper procedure is most important during the curing stage. Dryers used for discharge curing should be properly vented. Unvented dryers should never be used for discharge curing.
Thiourea dioxide also should be handled carefully. It is a strong oxidizer and must be kept in a sealed container. All of the same precautions that are recommended for ZFS are also applicable to thiourea dioxide.
Both products are strong oxidizers and should be kept in sealed containers. When pouring the crystalline powder into the mixing container, efforts should be made to minimize dust. Neither product generates measurable volatile organic compounds, and no special reporting of use is required. Occasional direct contact exposure is not considered an immediate health threat.
Waste (leftover) discharge ink
Waste discharge ink, like all inks in a liquid state, is considered a hazardous waste. But even though it will no longer discharge after the pot life has expired, you can still use the ink to produce soft prints on light or white fabrics. An ink that would print a nice red on black fabric will give you the exact same color on white fabric. Many print runs have the same print on light and dark fabrics. In these cases, always print the darks first and then use the time-expired discharge inks on the lights. This workflow minimizes waste and improves cost control.
Garments printed with ZFS discharge have measurable levels of formaldehyde. Washing the garment removes all traces of the chemical. Garments that are allowed to sit for a time after printing in an unconfined state will outgas most of the formaldehyde within a few days. If at all possible, avoid folding and packing ZFS-discharged garments immediately after printing.
The best recommendation I can make is to let the end consumer know, through the use of a sticker or hang tag, that the garment should be washed before wearing. In my shop, we used a sticker that explained the wonders of the unique printing process and advised buyers to wash the fabric before wearing—all in one breath.
The European Union has a formaldehyde-exposure threshold of 75 ppm for apparel for small children and infants. A ZFS-discharged garment that has not been aired out for several days or washed after printing will not pass this test.
Discharge printing can be a valuable addition to your operation. It can improve productivity and print quality on dark fabrics, help increase the number of colors you can print, and produce extremely soft prints.
Discharge is not a panacea. It is not a turnkey use-it-and-forget-it product. Discharge printing comes with safety precautions, issues with finished goods, and considerations for shop health. None of these issues is that difficult to deal with, but none can be ignored. If you’re not prepared to properly handle the discharge products, don’t even try them. But if you’re ready to make the effort, you’ll be pleasantly surprised with the result. n
Mike Ukena is a 15-year screen-printing veteran who has owned a textile-printing company and worked in technical services for the Specialty Graphic Imaging Association Int’l as the director of education. A member of the Academy of Screen Printing Technology, Ukena is a frequent speaker on technical and management topics at industry events. He is currently a technical sales representative for Union Ink Co., Inc.
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