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.
Aca Slit Viscometer
High Shear Characterisation
Laboratory instrument designed for high-shear rheological testing of paper coatings. The aca slit viscometer utilises a pressurised capillary channel to measure the viscosity of coatings under shear rates that exceed one million reciprocal seconds. This instrument mimics the conditions beneath the metering blade of a high-speed paper coater where other laboratory methods fail.
Pressurised Capillary Flow
Flow in this device is driven by high pneumatic pressure through a narrow rectangular slit rather than a round tube. This design minimizes the pressure drop across the entry and exit of the channel, which allows for accurate calculation of shear stress and shear rate. High-pressure sensors placed along the flow channel measure the pressure drop directly, providing data that are independent of end-effects.
Temperature-controlled chambers ensure that viscous heating does not compromise the measurements during the brief duration of the test. Solid-state sensors transmit raw millivolt signals to a microprocessor that converts them to pascal and reciprocal-second values.
High Speed Runnability
Blade bleeding and streaks on the coated paper board often relate directly to the high-shear viscosity of the coating color. Measurements from the aca slit viscometer help formulators adjust the dosage of rheology modifiers to prevent these defects. Dynamic runnability of the coating on a high-speed pilot line is predicted by these measurements.