Dispersion Barrier Performance in Folding Boxboard Substrates
Aqueous dispersion barrier performance depends on wet coat weight uniformity, film drying coalescence, and creasing matrix geometry that prevents score line cracking.
Air-Knife Bar Coating
Metering Mechanism
Controlled air pressure levels the thickness of a wet coating layer across the width of a moving paper web. An air-knife bar coating setup uses a high velocity jet of air to strip away excess fluid after a saturated roller or dip tank applies the initial volume. This method ensures a uniform finish that follows the topography of the substrate.
It is particularly effective for high coat weight applications where smoothness is required.
Fluid Dynamics
The volume of coating remaining on the board depends on the angle of the air jet and the distance from the nozzle to the surface. Adjusting the air-knife bar coating parameters allows operators to manage viscosity variations and solids content in real time. Because the air does not physically touch the web like a steel blade, it minimizes the risk of web breaks or streaks caused by debris.
Surface Quality
Finished boards exhibit a consistent appearance and receptive surface for subsequent printing or laminating steps. Since an air-knife bar coating follows the natural contour of the paper, it does not fill in low spots to create a perfectly flat plane. This characteristic makes it suitable for specialty grades such as thermal paper or carbonless sets where the functional layer must remain even.
Proper exhaust systems are necessary to capture the mist generated by the air blast. High speed operations often require specific enclosure designs to prevent the coating fluid from contaminating other parts of the machine.