Micronizing Ceramic Pigments For Inkjet Printing: Part Ii. Effect On Phase Composition And Color

WOS: 000353176300050
Drop on demand ink-jet printing is turning to be the leading technique in the decoration of ceramic tiles. This technology makes use in most cases of pigmented inks which are manufactured by micronizing conventional ceramic pigments in the 0.2-0.6 mu m range (median diameter). Although significant improvements to optical properties are in theory put forth by reducing the pigment particle size, not all the expected advantages occur and still unanswered questions concern the color strength of micronized pigments. This is the second part of a study aimed at disclosing what happens during pigment micronizing; it is focused on phase composition and color in the submicrometric field. For this purpose, representative industrial pigments were selected: Cr-Sb-doped rutile (orange yellow), Co-Cr-Fe-Mn-Ni spinel (black), and V-doped zircon (turquoise blue). Such pigments were micronized in a pilot plant and characterized for particle size and morphology (SEM and HR-TEM), phase composition, crystallite size and unit cell parameters (XRD-Rietveld), optical properties (DRS) and color after application in glazes for porcelain stoneware tiles fast fired at 1200 degrees C (CIE L*a*b*). Results highlight a different behavior during micronization: crystal structural and optical features are substantially changed once pigment particles turn into submicronic size. A gradually lower particle dimension is accompanied by reduction of crystallite size and increasing frequency of lattice defects (inferred from variation of unit cell parameters and optical properties) up to amorphization that may attain 75 wt%. The formation of amorphous phase takes place below a critical crystallite size (30-40 nm) which discriminates two regimes with fast and slow comminution rates. These structural changes are associated to decreasing color strength and increasing brightness through the submicrometric field
Scientific and Technological Research Council of Turkey (TUBITAK) [111M773]; Ceramic Research Centre (SAM)
We would like to thank the Consiglio Nazionale delle Ricerche (CNR) and the Scientific and Technological Research Council of Turkey (TUBITAK) on behalf of the joint cooperation program under the contract number 111M773 and the title "Water based inks for ceramic tile decoration by inkjet printing", between the Department of Materials Science and Engineering of Anadolu University and the Institute of Science and Technology for Ceramics (CNR-ISTEC). Authors are also grateful to Ceramic Research Centre (SAM) for their financial and technical support.