Coating a moving web surface uses a controlled feed pump capacity to set the amount of medium delivered to the applicator to determine the mean coating weight with little or no surplus residue

摘要

To apply a liquid or paste coating medium (14) to the surface (U) of a moving web, the mean coating weight of the layer (38) of the coating medium (14) applied to the web surface (U) is controlled by the capacity of the feed pump assembly (30), to set the amount of coating medium (14) pumped to the applicator (12) in a given time unit. The pump capacity is controlled according to the speed (V) of web surface (U) travel, directly proportional to the web movement speed. The pressure swings are dampened in the coating medium (14) at the applicator (12), as they develop. The web surface (U) is sprayed with a liquid, and preferably water, in front of the coating applicator (12). Water is also sprayed at the leading applicator limit (22), on the side of the applicator towards the incoming web surface (U). The lateral profile of the applied coating layer (38) is set by adjustment to the settings of the doctor (20) in zones across the web width. The residue of unused coating medium (14) is less than the coating layer (38) applied to the web surface (U), and is insignificantly small. An Independent claim is included for a web coating assembly with a feed pump system (30), and a unit (40) for dosing the volume of coating medium (14) fed to the applicator (12) by time units. The dosing unit (40) is connected to a control (42). Preferred Features: A damper (32) suppresses developing pressure swings in the coating medium (14) at the applicator (12). A water spray assembly (46,48) is in front of the applicator (12), in the direction (L) of web travel, to spray water at the web surface (U) and/or the applicator limit (22) at the leading edge of the applicator (12) in front of the doctor (20), towards the web surface (U). The water spray system (46,48) has a number of water jets. The applicator has a flexible doctor (20) and leading limit (22).