Mill Experience with Advanced Type of Free-Jet Coating Applicator, 1997 Coating Conference Proceedings

Three years ago the first installation of a new developed free jet coating applicator started up in a North American fine paper mill /I/. Since this first installation extended pilot trials and research work showed that the use of this type of applicator has almost no limitation. Meanwhile (Oct. 96) six other installations in on-line and off-line coating machines are in operation and prove the potential of the free jet applicator with regard to runnability and quality. Although free jet application is not a new technology, the demand for high quality at continuously increasing speed in combination with easy handling and better runnability than any other coating applicator were the reason for the revival of this type of coating equipment. It suits all kind of paper grades an covers machine speeds from 250 m/min up to 2000 m/min. Due to the different dewatering process, coating colours could be modified and require less additives like thickener /2/. The free jet applicator avoids any film splitting between paper and applicator roll and thus also colour splashing towards the blade. Coating colours can be optimized with regard to paper quality and coater runnability is not a problem any more. 2 WORKING PRINCIPLE A free jet of coating colour is generated by a hydrodynamically optimized nozzle which is located in the six-o’clock position underneath the coater backing roll like it is shown in figure 1. The approach flow of coating colour across the machine is provided by a distribution pipe and enters the nozzle chamber through a row of holes which cause a pressure drop high enough to ensure even distribution in cross direction /I/. The converging nozzle has a slice opening which can be adjusted between 0,6 and I,2 mm (23,6 to 47 mils). This gap determines the initial jet thickness and in combination with the applied flow rate the jet velocity.