Neck-in and edge forming phenomenon in extrusion coating - Utilisation of representative non-dimensional numbers, 2017 European PLACE Conference

Extrusion of polymer films is used in a number of continuous web based technologies. Film Casting, embossing, lamination and extrusion coating are extrusion based processes for continuous production of thin sheet, film, laminates of polymer.  In extrusion of polymer films a melted polymer is formed through a thin slit (flat die), then stretched in air and finally cooled on a chill roller (Fig1) [11].  Polymer melt deformation between die exit and chill roller involves a plan extensional flow. In the air gap between die exit and chill roller, film web area, neck-in and film edge bead  (“dog bone”) are formed. Edge bead means a film area with a thickness typically 2-5 centimetres wide and three-five times as thick as at film web centre/middle [11]. Film thickness variations are undesired, creating issues in the downstream handle and winding equipment simultaneously with higher polymer consumption. In the same time it is established the polymer film stability is improved by having stable edge bead. In this paper, co-relation, between edge bead and neck-in as edge bead/neck-in formation approach are studied for a single polymer film. Three non-dimensional numbers are presented as representative for edge bead and neck-in characterisation.  

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