Dye sublimation (or “dye diffusion”) printing is chosen for its high-quality photographic results. The printing process uses thermal transfer to transport varying amounts of coloured dye pigments from a carrier ribbon, or film, to the PVC printing surface to which the dyes bond chemically.
Inside a dye-sublimation printer is a roll of transparent film with a repeating series of yellow (Y), magenta (M), cyan (C), black (K), and clear (O) panels. The YMC panels contain thermally sensitive dyes corresponding to the three basic colours used in subtractive printing. By combining varying amounts of these dyes, any colour in the spectrum can be created, from white (no dye transferred on a white card) to black (full transfer of each of the three dyes).
The black and clear panels are also used in this thermal printing process, but they operate in a different way called “mass transfer” in which all of the material (in this case a plastic resin rather than a dye) is transferred once the carrier ribbon reaches the required transfer temperature. The black resin is used to apply dense black text and barcodes on top of the YMC colour image, and the clear panel is used to put a protective overcoat over the entire printed image.
The thermal printing process uses a printhead with many hundreds of individual heater elements (typically 300 per inch) which can each be separately controlled by software to transfer varying amounts of the YMC dyes and all or none of the black (K) panel and the clear (O) panel as the appropriate panel passes under it.
In the case of the YMC panels, the individual temperature of the elements causes varying amounts of dye to be vapourised and to permeate the glossy PVC card surface where it forms bonds with the plastic molecules. This is sublimation. Because the pigments go from solid to gas, and back to solid, there is little mess compared to inkjet printing which uses the liquid phase as part of the transfer process.
Because of the way the vapourised dyes permeate the surface of the card, a gentle gradation at the edges of each pixel is created, not the conspicuous border between colour and substrate produced by inkjets. Also, because the colour infuses and bonds with the card material, it is less vulnerable to fading and distortion over time.
Retransfer printing is a variation of dye sublimation that prints the colour image onto a clear substrate before laminating it onto a PVC surface. You can read more about the advantages of this process, here.
