We studied the thermal print head to achieve the multi-level tone in thermal transfer printing, which required appropriate heat control of heating elements on the head and variations in the amount of resin ink melted by the energized head edge, that is, varying dot diameter as needed. After a series of examination, we came to the conclusion that head form especially the part between the heating elements and head edge is deeply related to the property of the tone. This meant that optimization of the head form was the key to the solution. Thus we have attained multi-level-tone printing by varying dot diameter in 16 levels with the enhanced print head. We call this unique printing method Variable Dot Photo(VPhoto) print technology.
Hirotoshi Terao, Toshifumi Nakatani, Noboru Tsushima, Ikuo Hibino, "Study of a Thermal Print Head for Multi-level Tone Printing" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP16), 2000, pp 775 - 778, https://doi.org/10.2352/ISSN.2169-4451.2000.16.1.art00089_2