Why does ghosting occur in screen printing?
Ghosting is a chemical reaction between ink and dye, in which the stacking of hot garments leads to the appearance of a faint transferred image on the shirt. The most aggravating aspect of this is that it can catch you by surprise since it’s not easy to recreate in a production environment. In fact, for this reaction to occur, a perfect storm of contributing factors must happen.
A recipe for disaster
1. The dye
Certain dyes must be present in a cotton or cotton-blend shirt for ghosting to occur. And though there are many suspect dyes, the most prevalent troublemaker is a reactive yellow dye. This dye adversely reacts to certain bleed-resistant ingredients contained in bleed-resistant lines of inks. In the past, polyester or cotton/polyester blend fabrics didn’t create this reaction, but now, this reaction has become more prevalent with these fabrics.
2. The ink
It must be ink that contains a non-peroxide, bleed-resistant agent. The majority of today’s most popular bleed-resistant plastisol inks are non-peroxide. The unpleasant odor attributed to peroxides forced the industry to move away from these products. When the new bleed-resistant technology came about, it was found that not only was the smell undetectable, but the bleed resistance was superior to the peroxide predecessors. Since then, the top-selling white inks and bleed-resistant bases have incorporated this technology. These “do-it-all” general-purpose products contain a non-peroxide component that attacks the dye in the fabric to keep it from migrating in the long term (after cure). That same component can lead to ghosting. It wasn’t until the trend of off-shore dye houses and the drive for less expensive dye procedures that this problem becomes so prevalent to demand attention.
3. Heat and pressure
This part of the recipe is usually caused by stacking hot garments at the end of the dryer or packing them immediately into boxes. The weight of several dozen shirts can create enormous pressure. Couple this with the residual warmth in the material, and you have created a situation that mimics a transfer press. The layers of fabric will isolate the heat in the stack for long periods, which prolongs the exposure of the bleed-resistant component to the dye.
4. Humidity
Humidity has proven to be the main trigger for the ghosting problem. The presence of water in the air (thus absorbed into the garment) will start the dye-degradation process. Even if all the other factors are in place, your chances of experiencing ghosting are drastically diminished if no humidity is present in the garment.
—PolyOne
