A Communication of the PLACE div. of TAPPI

Published: February 28, 2006, By David J. Bent David J. Bentley Jr., Contributing Editor

Providing practical information to the converting and packaging industries…

EXECUTIVE SUMMARY
Effects Of Converting Operations On The Barrier Levels Of Metallized Films
by Thomas Dunn and Eric Jordan, Printpack, Inc.

This paper presents actual production data generated in the same laboratory representing metallized base film and corresponding extrusion laminations made using those base films. Data represent a twelve month period from March 2004 to March 2005. Actual barrier values indicate that very low transmission rates are possible for metallized OPP and OPET (oriented polypropylene and polyester, respectively). Extrusion laminating influences overall barrier population means and distributions. Actual composition of the base sheets greatly determined the direction and magnitude of the effects. The highest oxygen and moisture barrier OPP film design out-performed metallized OPET. In all cases, extrusion laminating the metallized base film to (printed) OPP with polyethylene extrudate lowered moisture transmission rates. Use of a converter-applied OTR enhancement improved the OTR of a moderate oxygen-barrier OPP base sheet.

Our company metallizes many grades of OPP and OPET films primarily for internal use in extrusion laminations with reverse printed OPP. Confirmation testing confirms the effectiveness of process control efforts for both processes. The laboratory regularly measures the oxygen and water vapor transmission rates of product sampled from both processes. Information in the paper summarizes the test methods and conditions used to generate the results discussed. This paper attempts to analyze these data to understand better the barrier levels now possible with commercial metallized films, the effects of a commercial barrier process on those levels, and actual barrier levels delivered to form-fill-seal packaging operations.

Advanced technology with surface modification and hybrid OPP base films provides robust, reliable barrier performance through converting operations. While oxygen barrier is lost, initial values are sufficiently low to give finished laminations low OTR. As a result, current barrier performance from barrier metallized OPET and OPP films provides a substantial structural component in barrier packaging materials.

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EXECUTIVE SUMMARY
First Principles Cause of Melt Fracture in LLDPE
by Dave Smith and Mike Andrews, Battenfeld Gloucester Engineering

Since the introduction of LLDPE, industry has had to deal with problems caused by melt fracture in many processing situations with the worst problems typically occurring in the production of blown film. Over the years, many mechanisms have been proposed in an attempt to explain the cause and therefore possible cures for melt fracture. None of these mechanisms has been able to explain adequately the observed phenomena or provide sufficient insight to develop a cure for the problem. Based on experimental observations, a new mechanism based on volatile induced flow defects has been proposed. It explains many observations that could not previously be explained. This mechanism has allowed prediction of new methods for reducing melt fracture. Tests have proven these predictions correct. SEM photos of film samples provide additional evidence to support this proposed mechanism.

Ignoring all the previous information available, our work looked for a simple physical explanation to explain some strange process problems encountered when blowing LLDPE film. The paper does not discuss the long and complicated process that led us to our conclusions but only presents a few of many observations made.

The paper presents a new and as yet unproven theory and the data gathered in support of that theory. We recognize that it is difficult to have every detail of a new theory correct when only a small fraction of the required research has been completed. We fully expect others will modify and improve the theory as new data emerges. The new theory explains melt fracture in LLDPE resins using volatile induced flow defects (VIFD). The theory and its resulting techniques have worked as predicted. Additional work is necessary to prove or disprove the theory and expand on the knowledge base relating to it.

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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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