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A coextrusion die system from Nordson Corporation has enabled an extrusion processor specializing in PET-based semi-rigid packaging sheet to maintain layer uniformity well within tolerances while avoiding product defects arising from asymmetrical layer structures. |
Evertis de México S.A. de C.V., a manufacturer of thermoformable sheet for food packaging such as poultry, cheese, and processed meat, as well as non-food applications, recently installed a Nordson EDI coextrusion die system for producing a range of structures. These include standard multi-layer, medium-barrier, and high-barrier sheet with thicknesses from 180 to 1,016 µ (0.180 to 1.016 mm). The barrier sheet structures are often asymmetrical, in that the materials or layer thicknesses above the central layer differ from those below it. The precision flow control of the Nordson EDI system has made it possible to maintain tight layer tolerances in such structures while preventing “wave,” “zig-zag” and other defects caused by instabilities at the interface between layers.
“At Evertis we strive to improve our production methods and consistently supply high quality products,” said Aprigio Pinto, director of production at Evertis de México. “We work with avant-garde equipment suppliers whom we know we can count on for excellent customer service and assistance. This philosophy is crucial to Evertis de México, given our continuous growth in the markets we serve.”
“The immediate responses by the technical support team at Nordson means that Evertis de México is guaranteed high quality equipment and service at a competitive price in the market,” said Jacques Tillet, director of maintenance at Evertis de México. “At Evertis we produce semi-rigid barrier PET sheet for food and non-food applications, and it is essential that we maintain layer uniformity within tolerances at all times. The Nordson EDI die system allows us to control layer interfaces, and thereby avoid product defects such as waves. With this system in place we feel confident that our customers will receive high-quality products every time.”
Meeting the Challenges Posed by Asymmetrical Multi-Layer Structures
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Cut-away schematic of Nordson EDI die system supplied to Evertis de México shows Ultraflow™ V-S feedblock at left and Ultraflex™ die at right, with internal deckle (bronze-colored component) projecting from the die. The seven-layer film structure is asymmetrical, with different materials above and below the central layer. The cylindrical component in the feedblock is a selector spool for on-line changes to layer sequence. The six yellow teardrop-shaped components at points where layers converge are combining planes for fine-tuning of combination velocities. |
“Because critical layer interfaces are shifted into higher shear regions of the flow paths, coextrusion instabilities are more common with structures that are asymmetrical,” said Nordson EDI chief technologist Sam G. Iuliano. “Our die system yields streamlined melt streams and fine-tunes them at the point of confluence. In addition, the ease with which adjustments can be made enables the system to be quite versatile in both layer configuration and product width.”
Chief among the components of the Nordson EDI die system used by Evertis de México are the following:
Ultraflex™ die with Multiflow™ II-G manifold and internal deckle. Nordson has engineered the manifold, or flow channel, inside the die to reduce shear stress levels at the layer interfaces, resulting in improved layer uniformity. At the same time, the sections of the manifold at each end of the die are sized to accommodate adjustable internal deckles for making changes to product width.
Ultraflow™ V-S adjustable feedblock. A feedblock combines melt streams from separate extruders into a multi-layer “sandwich” that the extrusion die subsequently distributes to target product width. The Ultraflow V-S feedblock incorporates adjustable “combining planes” located where the melt streams join the central flow channel. These make it possible to balance the velocities of the combining streams. When operating in “free-float” mode, they automatically compensate for the changes in layer thickness ratios that accompany product structure changes. Adjustments can be made without taking the feedblock off-line, increasing up-time and end-product versatility. Another adjustment that can be carried out on-line is use of a selector spool that makes it possible to change layer sequences in the structure.
