- April 01, 2007, David J. Bentley, Jr., Editor
The Use of Metallocene Polyethylene In Coextruded Lamination Films
by Richard W. Halle and Simone Vigano, ExxonMobil Chemical
APPLICATION: Metallocene polyethylenes provide significant value when properly employed in coextruded lamination films.
Adhesive lamination combines different substrates such as OPET, Al foil, and PE film, into multi-layer structures to achieve a range of end-use performance requirements. These end-use requirements typically include package integrity, barrier properties, and package appearance. In most cases, the sealant layer of the laminate is polyethylene-based. Coextrusions are increasingly finding more use to meet the target performance criteria most efficiently.
The films or substrates and the adhesives used to bond them together all contribute to overall laminate performance. Each component can have a different formulation. A key objective of this study was to determine the effects of the sealant film composition on heat sealing performance. Also examined were the impact of adhesive type, film re-treatment, and the impact of all the variables on film stiffness, film strength, and COF. Sixteen three-layer films were produced on a coextrusion blown film line under constant process conditions with the extruder temperature profile dependent on the resin type.
Heat sealing is the key attribute of PE sealant film used in laminated packaging structures. For coextruded PE sealant films, all the layers can impact the sealing performance of the laminated structure. The composition of the sealing layer is the main determinant in sealing performance. The best hot tack performance results from using mVLDPE. A plastomer sealing layer had the lowest SIT, but lower hot tack than mLLDPE. mLLDPE exhibits superior sealing performance compared with conventional grades of PE. The composition of the core/middle layer of a sealant film primarily influences the hot tack window. mLLDPE core layers provide the best hot tack performance. C4-LLDPE is defensive in hot tack strength. Even the laminating layer of the coextruded sealant film can influence its sealing performance. Laboratory hot tack and heat seal testing models the relative packaging line sealing performance well.
New And Old High Barrier Resins
by Jose M. Torradas, E. I. DuPont de Nemours & Co.
APPLICATION: After giving a comparison of barrier resins, the paper examines the effect of processing conditions, the resin chemistry, and the “final package” conditions on barrier properties.
The concept of high barrier resin usually relates to a resin with low OTR. High barrier packaging can also refer to barriers against other gasses, water vapor, chemicals, or UV light. The barrier properties of a specific resin relate to its chemistry. This includes molecular structure, polymer morphology, fractional free volume, and intermolecular adhesion. The properties of the permeant — size, shape, solubility, partial pressure, or concentration — are very important. The environmental conditions such as temperature and relative humidity at which barrier properties are measured may also affect those properties. Processing conditions and the presence of certain additives that can change the morphology (nucleants) or mechanical properties (modifiers) may alter barrier properties. Other additives to include oxygen scavengers may sometimes improve the barrier.
The leading “old” high barrier resins are still preferrable in packaging applications. Recent improvements in EVOH — thermal stability, orientation, and retort — will continue to benefit the growth of these resins. Despite the environmentalist pressure to replace it, PVDC continues to be a good and relatively cheap barrier option. Some “old” barrier resins such as MXD6 or Polyalkylketones seem to have found new life in niche applications. MXD6 with or without oxygen scavengers has received considerable attention in rigid packaging.
Polyamide based nanocomposites have attracted much attention, but the commercial success is limited due to high cost and limited performance improvement. Many polyester options exist beyond standard PET. The high cost of some resins and limited supply are still an issue. Biodegradable and bio-origin resins may receive a push due to recent oil price increases if cost and processability are acceptable. The lack of new resins has increased interest in blends and alloys.
To obtain the complete version of these papers, go to www.tappi.org, and select “the PLACE” under the Publications/Bookstore heading.