Dynamic Platen Impression Adjustments for High-Speed Multi-Ply Creasing Operations
Dynamic platen impression adjustment balances platen bow and speed-dependent viscoelastic strain to eliminate liner cracking in multi-ply cartonboard.
Shear Stress Rate
Fluid Dynamics
Rheological behavior in liquid coatings and adhesives depends on deformation velocity applied within narrow metering gaps. In continuous paperboard coating operations, shear stress rate quantifies the force per unit area applied to liquid formulations as blade or roll coaters meter them onto moving webs. High-speed applicators subject aqueous coatings and starch adhesives to extreme velocity gradients within fractions of a millimeter.
Understanding fluid deformation characteristics prevents film splitting defects and uneven coating distribution across paperboard surfaces.
Application Rheology
Non-Newtonian coating formulations exhibit shear-thinning or shear-thickening behavior under intense mechanical agitation in applicator heads. High shear stress rate conditions lower effective coating viscosity near blade tips, enabling smooth, thin film deposition onto moving paperboard webs. Converting coaters running at over one thousand meters per minute generate immense shear forces that can shear-degrade high molecular weight polymer binders.
Formulators balance pigment solids, rheology modifiers, and synthetic latexes to maintain stable flow behavior under variable machine speeds. Proper rheology control ensures uniform coat weight, optimal print smoothness, and consistent barrier properties across substrate rolls.
Viscosity Limit
Excessive fluid stress causes rheological breakdown and severe misting at high-speed printing nips or metering roll gaps. Inadequate shear stress rate leaves coating formulations too viscous, causing blade scratches, streak defects, and uneven absorption into raw paperboard fibers.