Nano-Sized Ceramic Inks for Drop-on-Demand Ink-Jet Printing in Quadrichromy

Nano-sized ceramic inks suitable for ink-jet printing have been developed for the four-colours CMYK (cyan, magenta, yellow, black) process. Nano-inks of different pigment composition (Co1-xO, Au0, TiO2:Sb,Cr, CoFe2O4) have been prepared with various solid loadings and their chemico-physical properties (particle size, viscosity, surface tension, zeta-potential) were tailored for the ink-jet application. The pigment particle size is in the 20-80 nm range. All these nano-suspensions are stable for long time (i.e., several months) due to either electrostatic (high zeta-potential values) or steric stabilization mechanisms. Both nanometric size and high stability avoid problems of nozzle clogging from particles agglomeration and settling. Nano-inks have a Newtonian behaviour with relatively low viscosities at room temperature. More concentrated inks fulfil the viscosity requirement of ink-jet applications (i.e., <35 mPa s) for printing temperatures in between 30 and 70°C. Surface tension constraints for ink-jet printing are fulfilled by nano-inks, being in the 35-45 mN/m range. The nano-sized inks investigated behave satisfactorily in preliminary printing tests on several unfired industrial ceramic tiles, developing saturated colours in a wide range of firing temperatures (1000-1200°C).