Thermal Dye Sublimation Printing / Thermal Transfer Printing
The print is formed with the use of an ink ribbon which is placed between the thermal print head and print-receiving material. The ink ribbon is made of a thin synthetic material and then applied to the external surface of a layer of solid ink (yellow, magenta, blue and black).
In the process of thermal dye sublimation printing, the thermal print head is heated and touches the inner surface of the ink ribbon. As a result, the solid ink on the ribbon heats up and evaporates. It is converted from a solid directly to a gaseous state without going through a liquid phase (that is why the process is called thermal dye sublimation). Due to the formation of a gaseous cloud of ink, the ink transfer occurs without direct contact of the print head and the ink ribbon with the surface of the print-receiving material. Therefore, the edges of the raster elements turn out to be blurred.
Characteristic features of the print:
- halftone color images render smooth transitions in tones;
- monochrome letters and figures have zigzag contours of inclined elements.
In the process of thermal transfer printing, the thermal print head presses the ink ribbon directly onto the surface of the print-receiving material, forming an impression without the ink turning into a gaseous state. As a result, halftone color images have a regular bitmap structure in the form of oval dots (traces of the print head).
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Fig. 1. Zimbabwe. Passport issued in 1998:
a — data page. Paper substrate; b — the same. Holder's portrait. Dye sublimation printing. Smooth transitions in tones, no raster elements; c — the same. Personalization data – text fragment. Thermal transfer printing. Steplike contours of inclined letter elements
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Fig. 2. Greece. Passport issued in 2014:
a — data page. Paper substrate; b — the same. Holder's portrait. Thermal transfer printing. Regular bitmap structure of the image; c — the same. Personalization data – text fragment. Thermal dye sublimation printing. Zigzag contours of inclined letter elements. The ink ribbon covers the impression with ink unevenly, when it comes in contact with the substrate