FLAT EXTRUSION DIE CHANNEL FEATURES THAT IMPROVE COEXTRUSION UNIFORMITY

摘要

Films used for flexible packaging applications are often fabricated from multiple coextruded layers. These multi-layer film structures may include barrier layers that generally require tight thickness uniformity tolerances to meet both functional and economic requirements. Common flat extrusion die systems used to produce barrier coextruded films include a single manifold die, whose primary purpose is to uniformly distribute the extrudate along the width of the die slot, in combination with an upstream coextrusion feedblock, which assembles the individual extrusion streams into a multi-layer "sandwich" that is delivered to the die. Given the demand for improved layer uniformity, extrusion die distribution manifold features have been developed which minimize the distortion of coextrusion interfaces. Tear-drop primary manifold shapes will be compared with elongated tear-drop primary manifold shapes of differing aspect ratios using three-dimensional computational fluid dynamics (CFD) software. Additionally, the effects of flow channel symmetry will be reviewed.