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 Color Rheology
Flow Characteristics
Fluid resistance within aqueous mineral pigment dispersions governs the uniformity of surface application during high speed paper production. Coating color rheology defines the relationship between shear stress and shear rate for these complex mixtures. Shear thinning behavior allows for stable pumping and distribution at low shear rates while preventing excessive drag during metering at high shear rates.
Precise viscosity control prevents blade streaks and ensures consistent coat weight distribution across the substrate surface. Proper adjustment of solid content and binder chemistry dictates these physical properties.
Stability Impacts
Consistency of the pigment suspension prevents pigment settling and micro-flocculation during storage or circulation. Coating color rheology shifts when binder interactions or chemical additives introduce sudden viscosity spikes. Large fluctuations in shear resistance force mechanical adjustments at the coater head to maintain film thickness.
Excessive variation causes surface defects like orange peel or skipped patches on the finished sheet. Machine operators calibrate pump speeds and pressure settings based on these observed deviations in fluid behavior.
Measurement Procedures
Rotational viscometers determine low shear viscosity to predict pigment stability and drainage properties. Capillary or high shear devices replicate the intense forces present at the blade nip to model performance during the actual coating application. Results from these tests provide the data required to adjust chemical dispersion additives or alter pigment particle distribution to achieve optimal runnability.
Successful formulation prevents mechanical downtime by maintaining the desired fluid state under varying process conditions.