A Communication from the PLACE div. of TAPPI

Published: January 31, 2005, By David J. Bentley, Jr., Editor

Providing practical information to the converting and packaging industries

Executive Summary
Performance Properties Of Electron Beam Curable Laminating Adhesives For Flexible Packaging Applications
by Stephen C. Lapin and Charles J. Wasserman, Northwest Coatings LLC

Application: Electron beam curable laminating adhesives give excellent film destruct bonds to a variety of flexible packaging substrates. The maximum strength at tear relates to the dynamic mechanical properties of the cured adhesives. Certain adhesive and substrate combinations produce excellent water and food product resistance.

Development of a new generation of lower voltage, lower cost, electron beam equipment generated strong interest in electron beam (EB) curable laminating adhesives starting approximately four years ago. The low voltage equipment allowed efficient energy deposition in coating or adhesive layers while minimizing adverse effects of the EB energy on substrates. The most obvious advantage for EB is the instant bonding characteristic. Commercial use in flexible food packaging has been slow due to the limited performance properties of the adhesives including limited water resistance. This paper discusses a new series of EB laminating adhesives that provide excellent bonding and food product resistance properties.

This study used a series of four EB curable adhesives whose composition varied to include a range of hydrophobic and dynamic mechanical properties. The adhesives were cured between the plates of a rheometer while monitoring viscosity. Viscosity increased rapidly upon cure. No significant difference in the reactivity of the adhesives occurred. Although curing was complete in approximately two seconds, the materials were cured for approximately eight seconds to ensure complete cure.

The study measured bond strengths under dry and wet conditions for the various substrate combinations. All substrates with all adhesive combinations gave film destruct bonds under dry conditions. The wet bond strengths increased for the series of adhesives with increasing hydrophobic composition. The maximum bond strength reached upon film destruct seemed to depend on the adhesive used. The relationship between the maximum bond strength and the Tg was different for the different film combinations.

Some adhesive/substrate combinations gave excellent bonding properties under dry and wet conditions and upon testing with different types of food products. With the processing advantages of EB laminating adhesives, this technology merits consideration in a variety of packaging applications.

Executive Summary
Can You Finally Get Foil Barrier Properties With a Metallized Film?
by Dante Ferrari, Celplast Metallized Products

Application: Using a new high oxygen barrier primer with metallized PET structures can provide oxygen barrier resistance very similar to foil.

The idea of replacing foil with metallized PET appeals to many converters. The cost with the ease of extrusion laminating and flexibility advantages of metallized PET over foil make it ideally suited for certain applications. Important remaining obstacles for metallized PET are its relatively poor oxygen and water vapor barrier properties relative to foil. Recently, a potential high oxygen barrier primer has become available. Application is with direct or offset gravure coating. This paper reports on the work pursued to combine this new primer with various metallized PET structures to determine the improvements in barrier that might be possible with this composite barrier system.

This work used resistive evaporation in a free span vacuum metallizer to apply thin layers of aluminum to the non-treated surface of one-side corona treated PET film. Some metallized and some unmetallized film were then coated with the oxygen barrier primer at a pilot coating facility using direct gravure application.

Based on barrier testing, the various primer/metal combinations tested in this work provide excellent oxygen barrier. It is approximately the same order of magnitude as foil. The primer actually inhibits the water vapor barrier capability of the metal layer. The nature of this primer makes it unsuitable for use with metallized PET in liquid packaging applications or for applications where these layers might be exposed to high levels of ambient humidity. One primed and metallized PET structure studied here would be ideally suited for dry, oxygen-sensitive packaging applications.

For information about the PLACE Division of TAPPI, access the TAPPI web page at tappi.org. To obtain the complete papers whose expanded summaries appear in this section, go to the TAPPI web site at tappi.org., then click on "the PLACE" in the section designated Journals.

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