Coating Talc Does Not Have to Have Poor Rheology!, 2003 Spring Technical Conference Proceedings

Although lamellar pigments have proven beneficial for coverage and printability in light weight coated (LWC) rotogravure applications, pigments with high aspect ratios and narrow particle size distributions (PSD) can contribute to increased high-shear viscosity and shear-thickening rheology in slurries and coating colors. Such behavior is particularly detrimental to the screenability of pigment slurries, as well as the screenability and runnability of LWC rotogravure formulations, which utilize high proportions of high-aspect-ratio pigments and are extremely dependent upon high-shear viscosity.

This work describes how an experimental coating talc, produced using an innovative and highly confidential technology, provided significant improvements in slurry rheology and performance at higher solids and reduced chemical dosages in comparison to traditional coating talc. Pilot coater trial results indicate that the abundance of platey fines associated with the experimental coating talc allowed for improved LWC rotogravure coating color water retention and coater runnability. Although differences in coating structure related to the two products were apparent at 15 parts talc, experimental and traditional coating talc provided similar LWC rotogravure paper properties at 25, 30 and 40 parts talc.

The experimental coating talc also demonstrated ease of makedown and improved screenability compared to the traditional coating talc without compromising performance. The combination of improved slurry rheology and lower makedown capital and chemical costs should provide papermakers with more flexibility and control over their coating pigment applications.