Influence of starch modification on the chemical composition and structureof coated layers

Colloidal interactions in clay coating colors have been modified with eithe r an anionic or a cationized starch cobinder. This paper reports on surface chemistry and structure of the coated papers as well as print gloss and in k demand. The thickness of the surface layer and the top layer of the coati ng was defined by the analyzing equipment and was about 0.01 mu m and a few mu m respectively. The internal structure of the coating layer was charact erized with air leak porosity and mercury porosimetry measurements. As expe cted, the coatings containing cationized starch gave a rougher surface and more porous layer structure. These coatings also had much higher amounts of starch in the surface layer, while the coatings containing anionic starch had a higher content of latex in the top layer. The ink requirement to reac h a certain print gloss was higher for the aggregated coatings i.e. those c ontaining cationized starch. A higher ink demand was initiated by a more po rous layer structure and a rougher surface.