Continuous direct ink jet printing
This thesis describes the preparation and continuous printing of zirconia ink under different conditions, as well as the development of silver inks, for the same purpose. The dispersion of sub-micrometer zirconia powder in industrial methylated spirit using other additives such as dispersant and binder was investigated with different mixing methods and at varying powder and binder contents. The use of high shear mixing by triple roll milling followed by ultrasonic disruption as well as adequate sedimentation and filtration produced a homogeneous and stable ink of 2.5 vol. % ZrO2. The ink could be printed directly and continuously on a commercial jet printer without interruption of any kind and the phenomena occurring during printing were investigated. The optimum modulation frequency for printing was determined with the generation of pear-shaped and symmetrical droplets. Printing was made on substrates of surface free energies lower and higher than the surface tension of the Zr02 ink. Powder migration was observed within a relic of the printed dot on the second type of substrate. Layers were also overprinted on the second type of substrate by varying the following: print resolution, printing interval, print area, drying conditions and ink powder loading. These series of prints were accompanied by the appearance of ridges, spattering and non-vertical walls and the effects were investigated. The wettability and shrinkage of droplets of the ceramic ink was also studied in-situ by monitoring the evolution of contact angle, width of ink-substrate interface and droplet height with a video camera. The shape of the droplet experienced different dynamics on different types of substrate. Lastly, the sedimentation behaviour of ethanol-based silver inks dispersed with different types of dispersant was investigated with respect to the sediment volume and half-value time. Deflocculated ink was obtained at a low dispersant level and powder loading.