Coating & Laminating Extrusion coating dies


By Sam Iuliano, chief technologist at Nordson Extrusion Dies Industries.


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xtrusion coating is often the most economical way to combine the unique structural, barrier, or sealing properties of different materials.


Modern extrusion coating dies are designed to improve economy by minimising the consumption of coating materials and maximising production efficiency.


Extrusion dies are used to uniformly distribute molten polymers to the desired width. Die profiling features, such as flexible lips and multi-stage die temperature control zones, are used to fine-tune the coating uniformity.


To accommodate various substrate widths, internal deckle systems vary the width of the extrudate and can provide advanced capabilities.


These include edge profile control adjustments that allow the processor to reduce the mass of the edge trim waste, or edge encapsulation porting, which can enhance process stability.


Deckles, as shown in figure 2, allow for the extrudate width to be efficiently varied during production. By adjusting the internal deckle components at each end of the die, the overall coating width can be set.


Internal deckling seals the entire flow passage, so dead area is not created when reducing the width.


A combination of both internal and external deckles is recommended for leak-free operation. The extruded curtain of molten polymer falls through an air gap before it is nipped with the substrate.


In this air gap there is an imbalance of forces on the molten web that cause the edges to neck in. This will result in thicker edges that need to be trimmed.


To reduce waste, processors will profile the deckle components to reduce the size of the edges.


Edge profile control is provided by adjusting the relative positions of the internal deckle components. By driving the manifold quill inward, relative to the final lip flag and rod, flow within the die towards the edges is reduced.


To fine-tune this starving of the edges, such that the width of the on-target material is maximised, a secondary blade is positioned in board of the final lip flag and rod (to tune the flow near the edge).


Offset positions of the manifold quill and secondary blade often will dramatically reduce, as shown, both the bead size and overcoat requirement.


Deckles are normally positioned by iterative trials until the best result is reached. The optimised edge profile control setting then becomes the recipe for that processing


scenario (a particular resin type, coat weight, line speed, and air gap). The graphic in figure 6 shows how encapsulation streams can be introduced into the flow channel while still having a variable coating width. Flow is streamlined at all deckle positions and there is minimal overlap of the encapsulation stream with the useful coating edge. By introducing an extension stiffening material to each end of the die, unstable edges or ‘edge weave’ can be resolved. For example, when extrusion coating with biopolymers, which can have relatively low melt strength, the ends of the melt curtain can oscillate at higher line speeds. By introducing a highly branched and broad molecular weight LDPE to each edge, web stability is achieved – allowing for higher line speeds.


Extrusion coating dies are used to uniformly dispense coating material(s) across the width of the substrate.


Internal deckles allow for: rapid width adjustment, edge profile control for reduced trim waste, and can include edge encapsulation for edge stabilisation.


When all of these features are included as part a high-performance extrusion coating die system, product quality and production efficiency are maximised.


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Figure 2: Internal deckles provide for streamlined width adjustment without dead areas.


14 May 2022


Figure 6: Edge encapsulation porting with adjustable internal deckles.


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