Analysis of contact pressure between a thermal print head and ink of a thermal transfer printer

摘要

The print head of a thermal transfer printer presses an ink ribbon on the printing paper. The ink of the ink ribbon is molten by micro heaters on the thermal print head and the molten ink is transferred to the printing paper. After a short cooling process the transferred ink is pressed again by the edge of the head near the micro heater for fixing. To melt the ink efficiently heat generated by the micro heaters must be sufficiently transferred to the ink ribbon. Thus the thermal print head has to be strongly pressed to the ink ribbon at the position of the micro heaters. Elastic analysis cannot point out the position where the contact pressure is the highest. Because the ink ribbon is made of a plastic material, it exhibits the viscoelastic behavior when pressed. The ink on the ribbon is also viscoelastic material. Therefore viscoelastic analysis is necessary to obtain the distribution of contact pressure between the thermal print head and the ink ribbon. A rheometer was used to measure rheological property of the ink. The three elements Maxwell model was used to calculate the contact pressure. We examined the effects of the shapes and the moving speed of the thermal print head on the distribution of contact pressure. The distributions of the contact pressure were calculated for several different moving speeds of the thermal print head. The calculation showed that the contact pressure became the highest behind the micro heaters. After printing, the thermal print head was inspected using an optical microscope and it revealed that the thermal head was most worn behind the micro heaters as the calculation predicted.