By Johnny Shell
With the growing popularity of ‘soft signage,’ where images are printed on textiles to create fabric graphics, many signmakers today are looking into dye sublimation, a highly specialized process with which many of them are not yet familiar.
Any ‘dye,’ by definition, impregnates a colour into a material. In many cases, this colour change is permanent. ‘Sublimation,’ meanwhile, refers to a change of matter from solid to gaseous state without it becoming a liquid at any point it the process.
So, during dye sublimation, solid dye particles are changed—using heat and pressure—into a gas. The gaseous particles are then bonded with a polymer, which consists of a linked series of repeated large, simple molecules. Finally, the dye becomes solid again.
The role of heat
The basic dye sublimation process uses special heat-sensitive dyes to print graphics and text onto a special transfer paper. This paper is then placed on a ‘sublimatable’ substrate—i.e. the aforementioned polymer, a polyester or a polymer-coated item—and they are both placed into a heat press together.
Once the press’ heating cycle is complete, the image on the paper has been transferred to the substrate. In fact, unlike some other types of printing, the graphic has actually become a part of the surface. If someone were to run his/her finger along the surface of the sublimated image, he/she would feel nothing apart from the usual surface of that object.
This is thanks to the high temperatures in the heat press. At these temperatures, the solid dye converts into a gas, without ever becoming a liquid, while the ‘pores’ of the polyester or polymer are opened, allowing the gas to enter. Then, when the temperature drops at the end of the heating cycle, the pores close and the gas reverts to a solid state, now part of the polymer.
Dye sublimation cannot be performed on natural materials, such as 100 per cent cotton fabrics. These natural fibres and non-coated materials have no pores to open and close.