Dynamic Strain Rate Modeling for Multi Ply Boxboard under Rapid Compression
Dynamic strain rate modeling predicts multi-ply boxboard Z-direction compression and interlayer shear collapse during high-speed converting and package drops.
Yield Stress Elevation
Rheological Adjustment
Increase in the minimum force required to initiate flow in a fluid or paste-like coating suspension determines the stability of the mixture on a paper web during application. A high yield stress elevation ensures that pigments and barrier polymers do not settle out during storage or run too deeply into the pores of the paperboard. It governs the transition of the coating from a solid-like state to a flowing liquid under the action of the applicator blade.
This rheological change is engineered through the use of synthetic thixotropic additives or natural starches.
Coating Performance
Blade and roll coating systems require precise control of flow resistance to maintain a uniform coat weight across the sheet. When the coating suspension exhibits high yield stress elevation, it behaves like a structured gel until the shear forces of the applicator exceed the yield point. This allows the coating to remain on the surface of the paperboard, creating a smoother and more uniform finish.
If the stress required to start flow is too low, the coating will penetrate the board, which reduces the brightness and opacity of the sheet.
Application Boundary
Excessive yield stress can lead to coating streaks or uneven distribution across the web. Formulators must balance the rheology to suit the specific speed of the run. This control ensures high-quality printability on the finished carton.