Impact of mineral extender morphology on performance of flexo inks - formulation and print characterisation

 
TiO2 is well known to be the primary pigment used to produce white paints and liquid inks and has superior performance to other minerals in this respect due to its high refractive index. This work concerns the optimisation of the use of TiO2 to deliver excellent quality in white water based flexo inks, by the inclusion of extender minerals. These inks often contain levels of TiO2 greater than 30% pigment volume concentration (PVC) in order to achieve the optical coverage required. In the dry ink layer, this means that TiO2 particles are close to each other and can become crowded, with each particle losing some scattering efficiency. This gives the opportunity for some mineral extenders of suitable size and shape to be used for better distribution of TiO2 particles. Additional benefits can be seen such as modification of the rheology and physical coverage of the ink, an improvement in the cost efficiency and the environmental credentials of the ink such as the carbon footprint. This paper reviews the effect of using GCC (ground calcium carbonate), PCC (precipitated calcium carbonate), kaolin and talc as extenders in water-based white flexo inks, focusing on the opacity and gloss performance. Advanced microscopic techniques are used to visualise the distribution of the TiO2 in the dried ink film and the impact of the extender on surface topography and show that 10-15% TiO2 extension using extenders is possible whilst minimising loss of gloss.