Acoustic ink printing: an application of ultrasonics for photographic quality printing at high speed

We have used Acoustic Ink Printing (AIP) to produce photographic quality prints at speeds that compare favorably against the state-of-the-art. In AIP an ultrasonic beam is focused on the free surface of the ink to eject discreet droplets of controlled diameter. Since the lateral dimensions of the acoustic beam determine the drop size, this "nozzleless" process enables generation of extremely small drops without sensitivity to small defects in nozzle geometry. We have used 1.5 pl drops and produced images at a quality level approaching standard silver halide processes. The printing is done at a spatial addressability of 600 spots per inch and the printed spot size can be varied by firing from 0 to 10 drops per pixel to achieve multiple gray levels at high resolution. The printheads were fabricated using conventional thin-film processes of the type used for liquid crystal display manufacturing. We have developed low-stress, high-efficiency thin-film ZnO transducers and 4-phase Fresnel lenses coated with Parylene matching layers for efficient generation and focusing of ultrasound in the 100-150 MHz frequency range. Printheads with 1024 ejectors were built at a nozzle density of 600 per inch to enable printing of a 1.7-inch-wide swath, operating at drop ejection rates up to 25 kHz. Printing has been done using aqueous based inks near room temperature on special coated papers, as well as using wax-based inks at 150 C for high quality printing on "plain" paper.