Dynamic Contact Angle Relaxation Kinetics in High Speed Blade Coating Systems
Dynamic contact angle relaxation rates dictate air entrainment and streak defect thresholds in high speed blade coating systems operating above 1200 m/min.
Hydrodynamic Pressure Profile
Fluid Distribution
Spatial variation of pressure within a liquid film as it passes through a narrow gap between two rollers. Hydrodynamic pressure profile describes how the fluid forces are distributed across the nip in a coating or printing unit. These forces determine the thickness and uniformity of the resulting layer.
The profile is shaped by the geometry of the rollers and the speed of the operation.
Application Physics
Viscosity of the coating liquid generates a resistive force that peaks just before the narrowest point of the gap. This peak in the hydrodynamic pressure profile pushes the rollers apart and influences the final coat weight. High speed operations intensify these pressures and can lead to vibrations or ribbing defects in the liquid film.
Modern coating heads are designed to manage these pressure gradients to maintain a stable flow and consistent thickness. Operators adjust the pump speed and the blade angle to counteract these rising forces.
Structural Consequence
Compression of the paper web occurs as it encounters the rising pressure within the nip. The hydrodynamic pressure profile affects how deeply the liquid penetrates into the porous structure of the board. An uneven profile leads to variations in the coating thickness across the width of the machine.
Engineers use these profiles to calculate the necessary crown on the rollers to compensate for mechanical deflection under load. This ensures that the pressure remains constant across the entire contact area.