Selectively Multiplying a Single EVOH Core Layer into Several Microlayers Reduces Oxygen Transmission Rate by 60 to 80% while Increasing Manufacturing Productivity
CHIPPEWA FALLS, WI, U.S.A., June 14, 2010: Microlayer technology developed by Extrusion Dies Industries, LLC (EDI) for thick film and sheet promises to extend the shelf life of retort, hot fill, and flexible food packaging, while increasing formability in thermoforming, the company announced today. EDI will feature the technology at K 2010 in a display of its innovative “layer multiplier” system (Hall 2, Stand G06).
At its Technology Center in Chippewa Falls, EDI is carrying out the first scientifically rigorous study of the benefits and limitations of layer multiplication, according to Gary D. Oliver, vice president of technology. “One result thus far is the development of a technique for selective multiplication of the barrier-resin layer of a multilayer film or sheet structure,” Oliver said. “By transforming a single layer of a resin such as EVOH into several microlayers, it is possible to reduce oxygen transmission rate (OTR) by 60 to 80%. And while EVOH is a crystalline, relatively brittle material, replacing a single thick layer with multiple microlayers increases formability for thermoforming and flexibility for vacuum skin packaging.”
The resulting benefits for food packaging include:
● Prolonged shelf life. Besides reducing OTR, layer multiplication substantially reduces total oxygen ingress over an extended period.
● Enhanced quality and lower material consumption. In the case of deep-draw containers where corner-thinning has been a problem with less formable materials, for example, multiplication of the EVOH layer may eliminate the need to offset thinning by increasing sheet thickness.
An Advanced Layer Multiplier and Its Benefits for Food Packaging
The layer multiplier is a special tool that can be engineered to multiply some or all of the layers within a coextrusion “sandwich” provided by a feedblock. The resulting microlayer structure then passes into the manifold of an extrusion die, where it is transformed into film or sheet of target width and thickness profile. No matter how many microlayers there are in the structure, the overall thickness is no greater than that of a conventional coextrusion, and the structure contains the same amount of raw material.
In 2009, EDI introduced an advanced system that is easier to deploy, more compact, more accurate, and more versatile than any other layer multiplier, including one previously offered by EDI. It is available to purchasers without licensing or royalties.
In the research at its Technology Center, EDI used its new system to multiply the EVOH core layer in sheet used for thermoforming single-portion retort cups, such as those for packaging fruit cocktail and diced peaches. EDI extruded the sheet and used a commercial cup mold to solid-phase pressure form sheet with one, four, eight, and sixteen EVOH layers.
All sheet structures were 50 mils in thickness, with thick (41 to 43%) skin layers of polypropylene and tie layers between the skins and the EVOH core. Barrier resins included a standard general-purpose EVOH and a “retort” grade of EVOH.
Thirty days after retort, cups with a single layer of the “retort” grade of EVOH exhibited three to six times higher oxygen transmission rates (OTRs) than cups where a layer of similar material had been multiplied. In that same period, total oxygen ingress was also three to six times greater
“Layer multiplication is especially promising for sheet and thick film packaging such as rigid retort and hot-fill containers, stand-up retort pouches, and vacuum skin packaging for meats,” said Oliver. “Thickness matters—particularly in the case of barrier microlayers. Our researchers have found that barrier properties fall off as layer thickness goes below 1 micron. We recommend a target thickness per barrier layer of 4 microns.”
Choice of barrier materials also matters, according to Oliver. “While barrier properties improved markedly with use of a retort grade of EVOH, we found that performing exactly the same tests but with a general-purpose EVOH yielded portion cups with markedly higher OTR and oxygen ingress.”
Extrusion Dies Industries, LLC is a leading international supplier of flat dies for sheet, film, extrusion coating, fluid coating, and pelletizing. The company designs and manufactures dies, feedblocks, deckling systems, vacuum boxes, and related equipment. Its subsidiaries include EDI GmbH in Reichshof-Wehnrath, Germany, and EDI China in Shanghai. In the U.S.A., Germany, and China, EDI operates facilities dedicated to reworking its own dies and those built by other suppliers, and it has licensed a fourth rework facility in Japan. Headquartered in Chippewa Falls, Wisconsin, U.S.A., EDI is focused on supplying the global market. Visit www.extrusiondies.com and www.reworkdies.com. E-mail: email@example.com.