Thixotropic Rebuild Kinetics Governing High Speed Slot Die Coating Instabilities
Thixotropic rebuild delay shifts slot die bead rupture limits during high speed web acceleration.
Non Newtonian Slurry Fluid Dynamics
Meaning
Rheological behavior of complex multi-phase mixtures is characterized by a shear-dependent viscosity that deviates from linear proportionality. In electrode production, non Newtonian slurry fluid dynamics dictates the flow rate and pressure drop inside delivery pipes and coating heads. These formulations typically exhibit shear-thinning behavior, where the apparent viscosity decreases under high deformation rates.
Such responses ensure that the paste flows easily through the narrow slot die but resists running once it lands on the substrate.
Shear Response
Extreme shearing forces inside the slot-die lip region break down the temporary agglomerates formed by carbon black and binder chains. This rapid reduction in flow resistance allows for high-speed coating without demanding excessive pump pressures.
Flow Resistance
Measuring this behavior requires plotting viscosity across a wide range of shear rates, spanning from the slow movements of storage settling to the fast deformation of die extrusion. If the slurry possesses a high yield stress, it will require a specific start-up pressure before any flow begins in the pipes.
Processing Window
Inconsistent shear responses can lead to coating errors like edge bead formation or uneven wet film profiles. To prevent these failures, slurry temperature and mixing intensity must be tightly controlled to maintain stable rheological properties throughout the production run.