INK COMPOSITION FOR DOD PRINTERS WITH KRAFFT POINT NEAR THE DROP SELECTION TEMPERATURE

摘要

Drop selection by surface tension reduction is a drop-on-demand printing mechanism in which ink in a liquid state is retained in a printing nozzle at a pressure greater than atmospheric pressure, but insufficient to overcome the quiescent temperature surface tension of the ink and expel the ink from the nozzle. The surface tension of the ink decreases with increasing temperature, and the nozzle includes an electrically activated means of heating the ink to a temperature less than the boiling point of the ink. The surface tension reduces to a value insufficient to retain the ink in the nozzle, whereby a drop of the ink emerges from the nozzle. Inks with a large reduction in surface tension at the required operating temperature for drop selection can be prepared by adding a surfactant with a Krafft point which is substantially above the ambient or quiescent operating temperature of the print head, but below the maximum temperature reached by the heated ink. The surfactant is added in a concentration which is approximately equal to the CMC at the Krafft point. At the quiescent temperature, the surfactant is not completely in solution, and is therefore relatively ineffective. When the heater is activated, the temperature of the ink rises to above the Krafft point, and all of the surfactant becomes fully dissolved, thereby reaching maximum effectiveness in surface tension reduction.