(340e) Coating Color Pigments for Paper - How to Evaluate Them for Agricultural Residue Base Papers ?

Pigments used for paper coating for the manufacturing of quality paper form one of the most important constituents of coating color. There are various pigments used in Indian paper industry such as ground CaCO₃, precipitated CaCO₃, china clay and talc to improve the optical, surface and printing properties of coated paper so that it can be globally accepted. Unfortunately, the quality of these pigments varies from supplier to supplier, even for the same pigment. It is an established fact that particle size and its distribution is one of the most important properties of pigments playing dominant role in deciding some of the paper properties like gloss. Paper being the absorbing material, induces surface deformation in coating layer and as such it is difficult to know the exact behavior of coating pigments which varies with the change of particle size and its distribution. Unfortunately, both these parameters have not been evaluated in detail and quantitative information regarding particle size and their distributions are not available in paper literature. In the present work, the characteristic size of a different paper coating pigments were experimentally determined using the laser scattering techniques and analyzed using the five distribution equations (normal, log- normal, Rosin- Rammler, Gaudin- Schuhmann and Nikuyama- Tanasawa) which generally represent solid mixture depending upon the process of manufacture. Unlike, conventional method where the distribution equation is determined by trial- and –error procedure by which each of the distribution equation is tried separately with experimental data and the equation deviating least from the experimental data is selected, a direct systematic procedure is developed to determine the distribution equation. Analysis of different coating pigments were conducted in laboratory using laser scattering techniques distribution equations were determined using the procedure developed. Analysis revealed that the nature of particle size distribution of coating pigments does not follow normal probability distribution equation but it tends to follow the Log- normal probability distribution type.  The values found are well in correlation with the experimental values.