Standard Bench Viscometry Methods for Aqueous Paper Coating Emulsions
Bench viscometry of paper coating emulsions requires standardized temperature control, verified spindle geometry, and multi-shear profiling to ensure runnability.
Coating Solids Fraction
Mass Concentration
The quantitative ratio measures the dry pigment and binder weight relative to the total mass of a wet paper coating formulation. Standard mill operations utilize the coating solids fraction to determine the dry coat weight applied to the raw paperboard. It is determined by oven drying a wet sample at a specified temperature until the weight becomes constant.
The value does not account for volatile organic compounds that might evaporate alongside the water during the testing process.
Operational Control
Runnability on the coating line depends directly on maintaining the pigment concentration within narrow target limits. When the coating solids fraction rises above the target, the viscosity of the formulation increases dramatically, causing blade bleeding or coating streaks on the paper web. Operators must balance this risk against the economic advantage of high solids.
If the fraction is kept too low, more water must be removed in the drying section, which slows down the production speed of the entire mill.
Drying Dynamics
Evaporation of the carrier water initiates the consolidation process where the pigments and binders form a cohesive matrix. This consolidation happens more rapidly when the initial solids level is high, because the particles are already close together.