A traveling web, such as of paper or cardboard, plastic or metal foil, is coated by a so-called curtain coater which applies the coating material (glue dispersion, ink, etc.) as a curtain dropping from a slot nozzle onto the web. In order for the curtain coater to form a uniform coating it is essential that the curtain dropping from the slot nozzle be stable, not move, and not form bubbles on the web. Thus the boundary air layer that forms on the web at high web-travel speeds of more than 400 m/min creates problems. The boundary air layer adhering to the web creates irregular disturbances in the curtain and makes bubbles that create irregularities in the coating thickness.
A curtain coater in EP 0,489,978 for creating photographic materials has upstream of the slot nozzle a shield-like element (“air shield”) which serves for stripping off the boundary air layer. The element is positioned near a deflecting roll for the web and extends in an arc over a predetermined angular portion of the deflecting roll. The element is constructed such that its upstream edge and downstream edge form zones in which the wind resistance is greater than in the zone between the two end regions. In the zone between the zones of greater wind resistance there is a chamber that is connected to a suction line to reduce its pressure. The spacing between the seal-like elements at the upstream and downstream edges and the deflecting roll is between 0.5 mm and 2 mm. The spacing between the downstream edge of the shield-like element and the curtain is between 5 mm and 30 mm.
USPTO Backgrounds
USPTO Backgrounds