Communication from the PLACE div. of TAPPI

Published: February 28, 2005, By David J. Bentley, Jr., Editor

A Communication from the PLACE div. of TAPPI

EXECUTIVE SUMMARY
How To Apply An Oxygen Barrier Primer With A Roll Coater
by Ginger Cushing, Mica Corp., and Lee Ostness, Black Clawson Converting Machinery Inc.

Application: A water based primer that imparts oxygen barrier to films and metallized films gives excellent barrier and adhesion performance and may be suitable for out-of-line extrusion coating processes.

A new water based primer has excellent oxygen barrier properties and strong interlayer adhesion to multi-layer film structures. The coating has had use as a film coating, primer for extrusion coating, and adhesion promoter for ink. Converters of food packaging found that the coating improves oxygen barrier properties that inhibit spoilage and extend the shelf life of package contents.

Optimum barrier properties depend on a smooth continuous coating of the primer. The best techniques for applying a continuous film require smooth roll or differential offset gravure equipment. Most priming stations currently running commercially are direct gravure applicators without smoothing bars.

The formulation of the new coating enhances its characteristics to improve film formation performance. Trials with the new coating to compare direct gravure techniques on a production laboratory line demonstrated the improvement in processability and retention of barrier functionality.

The oxygen barrier primer is suitable for application on a direct gravure coater with the pickup roll running in the forward direction. Reformulation improved coating optics and continuity without the need for a smoothing bar. Although the smoothing roll slightly improved the coating clarity in the samples tested, it did not enhance barrier performance. More oxygen barrier data is necessary to demonstrate whether reverse gravure will also produce acceptable barrier properties. Tests on polyester film showed that the oxygen barrier performance and adhesion of the barrier primer were excellent. The primed surface adhered well to LDPE after three months aging implying that this primer may be suitable for out-of-line extrusion coating processes.

EXECUTIVE SUMMARY
High Performance Stretch Hood Packaging Films Using Metallocene Polyethylene
by Richard W. Halle, Stefan Ohlsson, and David R. Weisinger, ExxonMobil Chemical

Application: A combination of metallocene polyethylene with an EVA copolymer gives a coextruded film that outperforms conventional monlayer and coextruded films in several different stretch hood and shrink hood applications.

A stretch hood is a type of product protection system commonly used to unitize and secure palletized products during shipping and storage. Other types of protection systems are stretch film/stretch wrap, shrink hoods, and cardboard boxes. Technical advances in the design of stretch hood films have overcome the deficiencies of previous stretch hood films and have significantly upgraded their performance over other systems.

Stretch hood packaging systems have been available since the early 1990s. Issues that slowed early development efforts were that film structures were too expensive, lacked adequate performance with regard to load stability, or would fail at high stretch levels. If the film could undergo sufficient stretching for premium applications, the film would relax under high temperature warehouse conditions due to the low softening points of the high EVA materials typically used. This was an excellent opportunity to design a new film structure that incorporated the toughness and clarity of metallocene polyethylenes with new EVA copolymers to provide an economical stretch hood film to outperform films currently in use.

Stretch hood systems are a rapidly growing segment of the product protection market especially in the appliance packaging market segment to replace cardboard boxes. Although stretch hood packaging has many advantages over other pallet protection systems, the monolayer and coextruded polyethylene films historically used as stretch hood film have a number of technical and economic drawbacks. Metallocene polyethylene combined with an EVA copolymer produces a new high performance stretch hood film. This coextruded film outperforms conventional monolayer and coextruded films in several different stretch hood and shrink hood applications. The new film displays superb puncture and tear propagation resistance, has excellent clarity, and maintains its load retention characteristics even at elevated temperatures.

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