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.
Yield Stress Measurement
Rheological Threshold Determination
A test identifies the minimum amount of force required to make a structured fluid begin to flow like a liquid. In the paper industry, yield stress measurement helps determine if a coating pigment will settle during storage or remain suspended. A fluid with a high yield stress resists the pull of gravity on its solid particles.
Structural Breakdown Analysis
The internal network of particles must be broken for the fluid to move. During yield stress measurement, a vane spindle or a rheometer gradually increases the load until a sudden change in movement occurs. This point represents the limit of the material’s internal strength.
Static Suspension Stability
Low values suggest that a coating might drip or sag after application to the paper surface. If the yield stress measurement is too high, the coating might not level out properly and could leave a rough texture. Balancing this property ensures a smooth finish and a stable shelf life for the chemical formulation.
Manufacturers use this data to select the appropriate type and amount of thickener for their specific pigment blend. Proper yield stress prevents the formation of a hard sediment layer in storage tanks that would be difficult to re-disperse. The measurement also correlates with the amount of energy required to restart the pumps after a weekend shutdown.