Sublimation, Dyes, Polymers and Substrates
To ensure consistent results from the process, it is important to understand the technology. Firstly, the key terms associated with the process are
Sublimation is the change of a solid particle directly into a gaseous state, i.e., without the particle becoming liquid in this case using heat and pressure.
A dye is a substance used to color materials and fibers. To dye is to impregnate color into a material. Often, this color change is permanent. In comparison, pigment (particles of solid color) inks, such as those used in screen printing, are applied to the surface of a substrate.
A polymer is a chemical compound made of smaller and identical molecules (called monomers) linked together. Some polymers, such as cellulose, occur naturally, while others, such as nylon, are man-made. Because of their versatility, polymers are widely used in industry, including in the making of plastics, glass, and rubber.
Substrate is a term used to describe the base material onto which images are printed. Typical substrates include not only paper (coated and uncoated), but also fabrics, plastics, metal, films and foils.
Dye sublimation ink consists of a solid, heat-sensitive dye, which provides the color, dissolved in liquid. Under heat and pressure, the solid dye particles change into gas, bond with any receptive polymers, and change back into a solid. The high temperature used in sublimation opens the pores of the polymer and allows the gas to enter. When the substrate is removed from the heat source and is allowed to cool, the pores close, and the gas reverts to a solid, becoming a part of the polymer. As such, the dye particles can no longer be removed and will not wash out.
Digital dye-sublimation printing is achieved using inkjet printers, which deliver their ink through nozzles onto transfer paper. Sublimation inks are not ‘liquid’ they are solid particles in suspension. When enough heat is applied to the printed image on the transfer paper, the solid dye particles sublimate and the dye migrates from the paper to the substrate. The dye has very little color until heated, so the sublimated image will look very different from that which you see on the paper.
The dye particles are designed to bond only with polymers (such as polyester). The higher the polyester content in the material, the more dye will bond to it, and the brighter the final image will be. This is why it is not possible to sublimate 100% cotton fabrics as there are no fibers that are receptive to the dyes present. Similarly, other natural materials used in dye-sublimation, such as ceramic, glass and metal, are first coated with polymers before they can be used in sublimation.