Quantifying Matting Agent Displacement in Package Printing Overprint Coatings
Quantifying matting agent displacement requires z-axis Raman depth profiling and strict viscosity recovery control to stop gloss drift and scuff failure.
Buoyant Velocity
Hydrodynamic Measure
Terminal velocity measurements describe the rate at which a suspended particle rises through a fluid medium under the influence of gravity or centrifugal forces. The value of buoyant velocity is determined by the balance of density forces and viscous drag acting on the object. It dictates how quickly dispersed lightweight coatings or adhesive residues separate from pulp slurry during stock preparation.
Diagnostic Application
Hydrodynamic separation equipment utilises density differences to isolate and remove unwanted lightweight contaminants from reclaimed paper fibres. When pulp slurry enters a centrifugal cleaner, particles of lower density migrate toward the center of the vortex where they rise rapidly. This upward movement depends on the buoyant velocity of the individual contaminants, including hot-melt adhesives, wax coatings, paraffin residues and plastic film particles.
Engineers adjust fluid viscosity, temperature and rotational speed to optimise this separation process, ensuring that lightweight contaminants are rejected before the stock reaches the paper machine headbox.
Process Variable
Fluid dynamics calculations help determine the necessary dwell time in industrial flotation cells and settling tanks. Short residence times can lead to poor removal rates if the target particles do not have sufficient time to rise to the surface. Understanding the buoyant velocity of specific adhesive residues prevents these microstickies from carrying over into the paper machine where they can cause sheet breaks or print defects.