Performance-Solids Relationships for Engineered Carbonates, 2001 Coating Conference Proceedings

A. Legrix, C. Nutbeem--With the increasing use of narrow particle size distribution (p.s.d.) GCCs and PCCs in coating formulations, it has become important to address the runnability issue of these pigments. The principal aims of this study were to establish a comparison of runnability and paper performance between narrow and broad p.s.d. carbonates as a function of solids. A range of GCCs and PCCs were applied to an uncoated woodfree basepaper in an extensive lab and pilot coater programme. Narrow p.s.d. pigments were shown to run at lower coating solids than broad p.s.d. pigments, as expected from their ’poorer’ colour rheological properties. The brightness and opacity were controlled by the pore structure and the pigment intrinsic brightness, with little effect due to coating solids. The gloss was shown to decrease with decreasing solids. However, high gloss values could be obtained for narrow p.s.d. carbonates despite lower solids. All of the pigments gave good paper coverage at their maximum runnable solids. Gloss was mainly determined by the pigment mean particle size, with smaller size giving a more micro-smooth surface, hence better gloss. Overall, the best paper performance was achieved with narrower p.s.d. pigments, even though runnable solids were lower. Runnability may be further improved by optimising the blade geometry, which resulted in better paper performance for broad p.s.d. pigments. For narrow p.s.d. pigments, the gain in paper performance with higher runnable solids was minor as a result of a minor gloss/solids dependency.