A study of the mechanical properties of coated papers using elastica stiffness and low-load indentation

Mechanical properties of coated papers, and specifically of a coating layer, are important during printing and converting operations. Those properties can be associated with several paper defects, such as coating pick, cracking at the fold, and dusting at the slitter. We introduced two dynamic tests for quantifying coating dynamic mechanical properties: (1) a closed loop elastica test and (2) a low-load indenter test. To evaluate these tests, several coatings on lightweight coated paper were produced with varying compositions and made under variable laboratory processing parameters. Pigment type, starch level, binder glass transition temperature, binder particle size, binder level, and drying method were varied. The moduli of a coating layer were extracted from elastica stiffness using a two-layer model. The shape factor of kaolin coating pigments had a significant effect; large shape factor led to increasing in-plane moduli but decreased elastic moduli measured in compression. The level of starch addition proportionally imparted stiffness. Laboratory drying conditions and styrene-butadiene latex type had a small effect.