Extrusion International 4-2021

48 Extrusion International 4/2021 EXTRUSION COATING While conventional coextrusion yields two or more materials in horizontal layers, special encapsulating inserts developed by Nordson for its coextrusion feed- block make it possible to extrude additional material along either edge of this horizontal structure. Using this technique, SAM North America has found that encapsulating a PLA coextrusion with edges of LDPE makes it possible to offset deficiencies of PLA – in par- ticular its low melt strength – that have limited its melt curtain stability, draw-down ratio, line speed, and coat weight. “Using LDPE edge encapsulation on our pilot line, we have achieved line speeds in excess of 1200 fpm [366 mpm] with PLA, as against less than 600 fpm [183 mpm] with PLA alone,” said Ed Lincoln, V.P. Extrusion Sales of SAM North America. “We have seen coat weight re- duced from 16 gsm to less than 10 gsm.” The high melt strength of LDPE has helped make this polymer by far the most widely used in extrusion coat- ing. “For processors wishing to replace some portion of their LDPE usage with biopolymers, a main obstacle has been that their lower melt strength causes extreme neck-in and edge instability at desirable line speeds,” said Sam Iuliano, Chief Technologist for Nordson’s EDI ® extrusion die and feedblock business. “By intro- ducing a higher-melt strength material on each edge of the melt curtain, edge encapsulation minimizes the processing limitations posed by many biopolymers.” Neck-in is the tendency of the polymer web to become nar- rower as tension is applied when it exits the die. The result is Biopolymer Extrusion Coating with „Edge Encapsulation“ Increases Line Speed and Recuces Coat Technologies developed by SAMNorth America and Nordson Corporation have made it possible to increase throughput and reduce coat weight in the extrusion coating of biopolymers such as PLA by encapsulating the edges of the coating with LDPE Schematic above, with upper die and feedblock halves removed, shows encapsulation achieved with Nordson feedblock insert (circled); schematics below show a new EDI® EPC™die, with encapsulating polymer introduced in the die rather than in the feedblock