The Inadequacy of Discharge Ink (in Screen and Inkjet Printing)
By Terry Combs

This article is referring to printing white ink on dark garments.
Note: The T-Jet™ line of printers do not and will not use discharge ink to print white on dark garments.

Discharge ink has been available to garment decorators for many years. As with other technologies that come and go in our industry, discharge printing is being tossed about yet again as a brand new concept. (My first article on discharge ink was written back in 1993. And the process was introduced many years earlier.) It's back again, and being touted as an all new idea.

The first time garment decorators see the discharge print result, they will react with surprise and excitement. No heavy underbase, and an ultra soft-hand print is the promise. "Great idea! Why hasn't anyone thought of this before?"

But, the excitement and anticipation wear off quickly when the details are exposed. Details such as the harsh chemicals involved, our employees' reactions to the risks and the odor, and the limited availability and expense of the actual garments required. Over the years, discharge inks have been repeatedly destined for the lonely shelf of passing fads in our shops.

Discharge Printing Process
The term "discharge" refers to a chemical reaction that destroys the ability of certain dyes to reflect a color. In simple terms, the discharge agent in the ink breaks down or bleaches the dye out of a specially prepared garment, leaving white, undyed fabric in the print area. When printed, discharge inks are almost transparent on the garment, activating only during the curing process.

Chemicals
Discharge ink is a water-based formulation (or a plastisol/water-based hybrid) that includes a discharge-activating agent to make it work. The activator used in most systems is zinc formaldehyde sulfoxylate (ZFS). That's right, discharge ink contains a formaldehyde compound!

During heating and curing of discharge inks, formaldehyde and sulphur dioxide develop as by-products of the discharge process. Therefore, it is extremely important that you properly exhaust your work area. As a safety precaution, you should have your shop's air quality tested to be certain that any formaldehyde levels are within permissible government limits.

To avoid liability, garment decorators who use discharge inks will commonly label shirts, recommending end users thoroughly wash the product before wearing. This home washing is meant to eliminate the residual formaldehyde and discharged dye on the fabric. The alert label on the shirt may be a deterrent to consumers, especially when buying children's garments.

Production Employee Reactions
While owners and managers decide to give discharge ink a try, it is often the production staff putting an unceremonious end to the plan. The MSDS sheet alone, explaining the formaldehyde component in the ink, is the first large red flag to employees. And then, the distinctive odor of rotten eggs will accelerate the flow of employee complaints. More often than not, coupled with the availability and limitations of specially prepared garments, this is enough to bring a great new idea to an inglorious end.

Garment Limitations
Not all textile dyes are dischargeable, and garments woven from blends of natural and synthetic fibers can further complicate the matter. In 50/50 garments, each type of fiber requires the use of a different family of dyestuffs. When attempting to use discharge ink on 50/50 shirts, the result will not offer the dynamic, bright effects that you can achieve on properly prepared 100% cotton garments.

If you choose to use your standard 100% cotton garments, the best result is a return to the original greige goods (before dying) color, which is not a true white. Pre-dyed traditional garments are usually a shade of grey, pink or yellow, rather than the white that most of us assume. Process ink colors (as used in current inkjet technology) applied onto this unbleached cotton stock will take on the color of the original pre-dyed fabric. And the end result will vary from batch to batch, often changing from size to size during a print run.

For best results, you must use discharge ready 100% cotton garments. These garments have the added step of being bleached white before being dyed to a dark color. Most if not all dark garments that you currently buy to decorate with screen printing or inkjet technology are NOT discharge ready. Using discharge inks on traditional 100% cotton garments will rarely give you an acceptable, salable finished product.

This additional step in the dying process adds substantially to the cost, making discharge printing more like sublimation transfer printing - a special garment required at a much higher cost than traditional garments. And, you are limited in your selection to the garments and colors specifically processed and sold as discharge ready. Printing on customer garments will rarely if ever be possible, since most consumer goods are not available with this pre-bleaching process before being dyed.

Conclusion
While discharge ink is an interesting concept that comes and goes, the drawbacks and limitations continue to make it simply a footnote upon the garment decorating industry, both as a direct screen printing process and as a component in the new inkjet technology.