Adding value to ceramic tiles by enhancing their aesthetical appearance is now pivotal. Ink-jet printing is a non-impact technology where ink droplets are projected onto a surface. In the drop-on-demand printers, ink is ejected by ceramic piezoelectrics that squeeze out the droplets. Many characteristics of ink-jet printing make it interesting for decoration of ceramic tiles. High resolution images can be achieved since this technology involves the smallest droplet volume compared to other decorating techniques. Besides, customized products can be obtained at lower cost by the quadrichromy process using four basic colours: cyan, magenta, yellow and black.

Although ink-jet printing has been applied to ceramic decoration since a few years at present it has not become a common technology yet. This is due to the severe requirements of both ceramic pigments and inks. The former must be highly refractory, withstanding the chemical corrosion during firing. The latter must have suitable physical and chemical properties (e.g. viscosity, surface tension) which govern both ink-jet printing and their interaction with substrates (i.e. wettability, penetration). In particular, viscosity and surface tension are critical for ink-jet printing: viscosity must be low enough to allow a fast ink flow through the nozzles of printhead, while surface tension must avoid both ink spreading over the nozzle and spilling by gravity .

Nowadays, ink-jet printing is carried out on ceramic tiles by using either organometallic dyes or micronized ceramic pigments. The former suffer for a limited colour palette and saturation as well as increasing environmental constraints; the latter cause nozzles clogging and are affected by settling and loss of colour strength. These problems can be overcome by using nano-sized ceramic inks, that are able to increase the image quality ensuring high reliability to the printing systems . This work is aimed at developing nano-inks suitable for the four basic colours (cyan, magenta, yellow and black) of ink-jet printing quadrichromy.

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