EDI: Dies that Coextrude up to 80 Exceedingly Thin Layers Raise Film and Coating Productivity, Lower Cost, and Boost Performance
A potentially revolutionary flat-die system produces films and coatings with an order-of-magnitude greater number of layers than conventional coextrusions, yielding microlayer structures that improve moisture and gas barrier, encapsulate gels and ‘un-melts,’ and enable manufacturers to make more economical use of high-cost materials, it was announced at NPE 2006 by Extrusion Dies Industries, LLC (EDI), which is exhibiting at Booth 4661. Microlayer technology will become widely used in barrier packaging, according to EDI.
The technology is based on a patented ‘layer multiplier’ system developed by The Dow Chemical Company and licensed from Dow by EDI. In a typical configuration, three or more extruders feed melt streams into an EDI-streamlined feedblock, which produces a uniform multi-layer ’sandwich’; this in turn is fed into a layer-multiplier device built by EDI using Dow’s patented design. In this device the layers are multiplied in stages: for example, three layers are multiplied into twelve, which are multiplied into forty-eight. The finished micro-layer structure is then distributed in an EDI coextrusion manifold to the target product width
‘We still do not know the practical upper limit,’ said EDI president and CEO Timothy C. Callahan, ‘but in my opinion it is possible to produce 50-micron film with 80 layers.’
EDI’s microlayer technology integrates the Dow layer multiplier into a complete custom-engineered system that includes the die, feedblock, and other tooling components for distributing the complex structure into a finished extrudate. The company will license the Dow technology to customers. ‘We are establishing relationships with licensees that enable film and coating processors to profit from the production economies and enhanced product performance made possible by the EDI / Dow multiplier system,’ Callahan said.
Microlayer Advantages Are Evident in Coextrusion Process and in End Use
As coextruded structures proliferate well beyond the standard limits of five, seven, or nine layers, here are some of the benefits cited by EDI:
• Enhanced barrier properties. The sheer increase in the number of barrier layers in the product yields an even more ‘torturous path’ for gas and moisture molecules.
• Economizing on costly materials. Because many key properties of a polymer do not decrease proportionately with layer thickness, microlayer technology makes it possible to economize on costly high-performance resins while still achieving target properties. In oriented PET film, for example, layers of more expensive high-intrinsic viscosity (IV) resins can be combined with layers of low-IV grades. The resulting film properties are superior to those of film produced from a physical blend of high-IV and low-IV PET grades.
• Fewer web breaks. The greater the number of layers, the less the likelihood of breakage caused by pinholes in film, particularly in biaxially oriented products subjected to post-extrusion stretching. This is because the large number of layer-to-layer interfaces increases the chances for gels and other defects to be encapsulated and rendered harmless.
• New combinations of properties. The same polymer exerts different effects on end product properties according to whether it is distributed into one or two layers or into many super-thin layers. Layer-multiplier technology makes it possible to produce film that is more flexible, for example, without reducing the overall amount of a rigid polymer used as one of the raw materials. One benefit is greater processing latitude in subsequent thermoforming processes.
‘EDI sees much of the barrier packaging sector adopting layer-multiplier technology in coming years,’ Callahan said. ‘Microlayer coextrusion also promises to speed the incorporation of nanocomposites in food packaging for enhanced barrier, thermal, and mechanical properties.’