Flexographic Aqueous Latex Barrier Coating Viscosity Measurement Fundamentals
Flexographic aqueous latex barrier coating viscosity requires multi-shear rotational measurement to ensure accurate anilox transfer and barrier film continuity.
Pseudoplasticity
Flow Property
Rheological behavior where a fluid’s viscosity decreases as the rate of shear force applied to it increases is a common trait of high-performance coatings and inks. In paperboard converting, pseudoplasticity is a critical feature of water-based adhesives and coatings that must flow easily under high pressure but set quickly once the pressure is released. This shear-thinning response allows for rapid application without spilling or dripping.
Mechanics of Flow
When the coating fluid is at rest, the long-chain molecules and pigment particles are tangled and offer high resistance to movement. When the application roller or blade applies a high shear rate, these molecules align in the direction of the flow, which significantly reduces the effective viscosity. This reduction in resistance is temporary, and the fluid returns to its thick state almost instantly when the shear force is removed.
This immediate recovery prevents the coating from running off the paperboard or penetrating too deeply into the porous fibre matrix before drying.
Converting Performance
High-speed folding carton lines rely on this shear-response behavior to apply adhesives cleanly to the glue flaps of boxes. The glue must thin down to exit the nozzle smoothly at high speed, but it must immediately thicken to prevent squeezing out and spoiling the package design when the board flaps are pressed together. This flow behavior ensures that printing and gluing operations can run at maximum speed with minimal defects.