A bad case of ghosting can ruin an otherwise profitable print run. Find out how to manage the variables that allow this problem to surface.
By Rick Davis
Ghosting is an issue that has plagued garment screen printers since the creation of bleed-resistant inks. The term refers to a phenomenon in which an image printed on a dark garment creates a faint lightening or bleaching effect on the surface of an adjacent dark garment. In the industry's early years, the ink manufacturers and garment producers would trade blame back and forth about who was actually responsible for the onset of ghosting. In the end, the screen printer was always left to resolve the situation.
Since those times, lots of research (mostly by ink manufacturers) has been conducted to identify the true reasons why ghosting occurs. The puzzle for many manufacturers and screen printers alike is determining why certain combinations of inks and fabrics promote ghosting while other combinations prevent the problem from arising.
As is the case with so many other aspects of the garment screen-printing process, controlling the variables is the key to keeping ghosting at bay. This month, I'll discuss precautions you can take to prevent ghosting and address the ways in which fabric composition and ink formulation contribute to the problem.
The two primary fabrics that garment screen printers deal with are 100% cotton and 50/50 cotton/poly. Most screen printers are aware that the synthetic side of 50/50-cotton/poly garments is the cause of undesirable color-transfer issues, namely dye migration and sublimation. But when they come across ghosting, they don't know what to make of it.
Dye migration occurs when the dyes in a 50/50 cotton/poly garment (or garments with even higher polyester content) get dissolved by the plasticizers in a printed plastisol ink film. The end result here is alteration of the ink film's shade to that of the fabric. Dye sublimation happens when the dyes in a 50/50 fabric are heated beyond 360°F. Above that temperature, the dyes in the fabric begin to sublimate (convert from a solid to a gaseous form without first becoming liquid). They then pass into the ink film and revert to a solid form, discoloring the ink with the same color shade as the garment, much like dye migration.
Ghosting, on the other hand, has nothing to do with the polyester dyes in a 50/50-cotton/poly garment, but rather cotton dyes that are used in some dark cotton garments. The effect takes place when printed garments are in close proximity to each other (typically while they're folded). What happens is that bleed-resistance agents in the ink may outgas and remove or discharge the dyes from a garment that makes contact with the printed surface of an adjacent garment. The end result is a faded, ghost-like image of the original print left on the garment. This scenario can also take place when T-shirts are hanging on a display rack and come into contact with each other. In this situation, the image on the front of one garment transfers onto the back of the adjacent garment.
The impact of garment selection
As the textile-manufacturing industry has gone off shore in the name of lower production costs, it has also pushed for lower manufacturing costs. For many foreign mills, this goal is achieved through the use of lower quality materials and processing techniques. One popular cost-cutting solution is to use cheaper dyestuffs, and the garments produced with these materials are the ones most susceptible to ghosting and other quality issues. Most large, brand-name garment manufacturers do not sacrifice on quality in this way, and the garments they produce are not likely to allow ghosting to take place. But if you are working with an off-brand garment, it is wise to test the fabric prior to production and determine whether there vvis a potential for ghosting to occur.
Using the right white ink
White bleed-resistant inks are typically the cause of ghosting on 100%-cotton garments. The simplest solution is to run a high-opacity white ink that is formulated for use on cotton, rather than a bleed-resistant ink. High-opacity whites do not contain the components that trigger the ghosting effect.
The main reason that ghosting occurs at all is because many screen printers who print on both 100% cotton and cotton/poly blends like to stick to a single type of white plastisol to minimize variables within their facility. Because they expect dye-migration problems on polyester-containing garments, the single ink they choose is usually of the bleed-resistant variety. Many printers feel that keeping both bleed-resistant and non-bleed-resistant inks on hand will increase the risk of the non-bleed-resistant formulation being used on cotton/poly blends. This is a weak excuse, however, because simple labeling and documentation procedures can be established to ensure that the right inks are used on the right garments.
Tips for one-white shops
If you are dead set on only using a single, bleed-resistant, white ink in your facility, regardless of the fabric type you are printing, you need to take some additional precautions to avoid problems with ghosting. Follow these tips to reduce the likelihood that you'll experience ghosting issues on dark cotton garments:
1. Minimize your ink deposit. Most printers have a more-is-better mentality and may print white underbases with a 110-thread/in. mesh, flash, and print a second hit. Not only is this much ink unnecessary for a 100%-cotton shirt, but the additional ink-film thickness also will amplify the potential for ghosting. It would be more effective to print only one layer of the white with a 110-thread/in. mesh. Better yet, I would recommend printing the underbase with a 230-thread/in. mesh, flash, and also use a 230-thread/in. mesh to print a highlight white. A setup like this minimizes the ink film to decrease the possibility of ghosting. It also allows you to flash faster and gives the garment a much softer hand.
2. Make sure you turn down your flash-curing unit when you work with finer mesh counts. You don't need as much heat to properly gel a thinner underbase.
3. Use retensionable screens. They allow you to print thinner ink films onto the surface of the fabric, as opposed to driving it into the fabric. Again, the less ink you apply to the garment, the less chance ghosting will occur.
4. Make sure to properly cure the entire ink film. An incomplete cure allows the bleed-resistant components in the ink to roam freely and fuels the ghosting effect.
5. Avoid cheaper fabrics. When possible, work with brand-name garments, which typically are constructed with higher-quality dyestuffs.
6. Avoid stacking printed garments until they cool.
The problem of ghosting doesn't have to haunt your printed garments. Just follow the recommendations provided here, and you'll be able to exorcise this demon from your shop.
Did you enjoy this article? Click here to subscribe to the magazine.