Waterborne Barrier Dispersion Application Parameters on Folding Boxboard
Waterborne dispersion application on folding boxboard requires precise coat weight control, shear-matched viscosity, and staged drying to prevent pinholing.
Curtain Coater
Fluid Application
A fluid application method creates a continuous falling sheet of liquid that drops onto a moving substrate during high-speed manufacturing. The curtain coater enables the application of multiple functional layers simultaneously without the different fluids mixing before they hit the paper surface. Precise control of the pump speed and the web speed ensures that the liquid curtain remains stable across the entire width of the machine.
Operating Principle
Surface tension and gravitational force maintain the integrity of the falling film as it bridges the gap between the header die and the moving web. The curtain coater requires a specific minimum flow rate to prevent the sheet from breaking into individual droplets. Air curtains or vacuum boxes are often positioned near the impingement point to remove the boundary layer of air from the substrate.
This removal prevents air from becoming trapped beneath the coating and causing bubbles.
Coating Limitation
Substrates with high roughness or excessive porosity can disrupt the uniformity of the wet film during the initial contact. While the curtain coater is capable of extremely high speeds, it is sensitive to vibrations and air currents within the mill environment. Formulations must be carefully designed with specific rheological properties to ensure the curtain does not narrow or neck in at the edges.