EFFECT OF PCC AS A PIGMENT IN MINERAL COATING FORMULATION

Abstract

The paper coating pigment plays an essential role towards the fulfillment of desired end paper qualities. The different pigment varieties are available for paper coating. Ground calcium carbonate (GCC) is the major one used frequently in coating formulation. Precipitated calcium carbonate (PCC) is gradually getting importance in paper coating as it can be prepared in different shapes and sizes. The present study was carried out to find out the influence of PCC pigments with different shapes and sizes on paper properties, and its limitations and advantages when blended with finer grade GCC. PCC pigments of calcite and aragonite crystalline polymorph having rhombohedral, orthorhombic and scalenohedral habits were selected for the study. It was observed that the viscosity and water holding capacity of coating color reduced with introduction of PCC in coating formulation. The PCC pigments show higher light scattering, opacity and smoothness of coated paper as compared to GCC pigment. The ink setting rate becomes slow with introduction of PCC in coating formulation. The clustered (rosette) shape of scalenohedral habit calcite PCC results in highest light scattering, opacity and surface strength amongst all PCCs. The aragonite PCC of orthorhombic habit and calcite PCC of rhombohedral habit show almost similar trend in coated paper properties with highest smoothness, paper gloss and print gloss. It has also been observed that the impact of base paper on final optical properties depends upon the light scattering through coated layer. The higher scattering through coated layer will lower the, effect of base paper, whether it is dark or bright. The effect • of base optics on coated paper was found less with narrow particle size distributed pigment and higher with broad particle size distributed pigment.