This guide explains how dye migration happens and outlines steps you can take to prevent it from harming your garment-decorating jobs.
Dye migration is an unwanted reaction between plastisol ink and the dye used in the garment fabric—polyester fabrics and blends, in particular.
Dye sublimation, migration, and bleeding
These three terms are often used interchangeably, but each actually describes a different step in a process that results in a printed ink film taking on the color of the garment. The dye in the fabric sublimates (converts from a solid to a gas without the intermediate step of becoming a liquid) under high temperatures, migrates into the ink layer, and the result is bleed a discoloration of the cured print.
Garment screen printers must deal with sublimation on a regular basis. Heat-set dyes are used in fabrics that contain polyester, and then these dyes are heated to their sublimation temperature, they convert to gas. If this sublimation process takes place in the presence of plastisol ink, the sublimated dye can migrate into the plastisol. The worst part is that the results of dye migration may take several days to show up after printing—perhaps after the garments have been packed and shipped to the customer.
Any fabric that contains polyester is vulnerable to dye migration and bleeding, including polyester/cotton blends (Figures 1A-1D). Some colors are more prone to dye sublimation than others. Red shades are notorious for being the worst, but all colors are capable of sublimating to some degree. The best rule of thumb is that every dark shade of fabric containing polyester should be treated with respect and tested.
The mechanics of dye migration
On polyester fabrics, the gaseous, sublimated dye becomes trapped underneath the plastisol ink, and it solidifies as it cools. But now, the bond between the dye and the polyester fabric is broken, which means the dye molecule is free to attach itself to something else. Plastisol is a wonderful solvent for dye and allows the color to migrate throughout the printed ink film. The discolored print represents the diffusion of the dye particles throughout the ink layer.
Polyester dyes sublimate at temperatures ranging from 360-420°F. Why is this a problem if you typically cure garments at 320°F? Well, when you set the dryer to 320°F, what you’re really doing is telling the dryer to maintain curing-tunnel temperature of 320°F. To compensate for heat loss and maintain the temperature you set, the dryer will reach temperatures beyond 320°F in certain locations.
Did you enjoy this article? Click here to subscribe to the magazine.