APEO-free black ceramic inkjet ink formulations based on Ni-substituted CoFeCrO4 spinel pigments

Abstract

Abstract This study reports the development of high-performance black digital ceramic inks based on a Ni 0.5 Co 0.5 FeCrO 4 spinel pigment. A series of Ni x Co 1- x FeCrO 4 ( x = 0–1) pigments was synthesized via solid-state reaction. Calcination temperature (900–1100 °C) and post-calcination milling duration were optimized to obtain phase-pure spinel with primary particle sizes predominantly below 400 nm, as confirmed by XRD, FTIR, and SEM analyses. Optical properties and color performance were evaluated using UV-Vis reflectance spectroscopy and CIE colorimetry. Among the investigated compositions, Ni 0.5 Co 0.5 FeCrO 4 pigments exhibited the deepest blackness ( L* = 29.5 after firing on glaze) and were selected for ink formulation. An APEO-free non-ionic polymeric dispersant (Dispex ® Ultra FA 4488, BASF) was employed as the sole dispersing agent. Within the investigated concentration range (1.0–3.0 wt%), the formulation containing 3.0 wt% dispersant showed the best overall performance, with a viscosity of 13.5 mPa s, a contact angle of 28.6° on ceramic glaze, and a zeta potential of -40.9 mV. After application onto glazed tiles and firing at 1200 °C, the selected ink formulation developed a deep, uniform black color. These results demonstrate that the combination of Ni 0.5 Co 0.5 FeCrO 4 pigment and Dispex ® Ultra FA 4488 enables the production of stable, environmentally compatible black ceramic inks candidates for industrial consideration.