A Communication from the PLACE Div. of TAPPI

Published: May 31, 2006, By David J. Bentley, Jr., Contributing Editor

Providing practical information to the converting and packaging industries…

EXECUTIVE SUMMARY
Effects Of Machine Direction Orientation On The Moisture And Oxygen Barrier Properties of HMW-PE Films
by D. Ryan Breese, Lyondell Chemical Co. and Gregory Beaucage, University of Cincinnati

APPLICATION: Density and draw ration influence the barrier properties of machine direction oriented film.

Machine direction orientation is a process where a film is uniaxially stretched in the machine direction to enhance physical properties. Past work showed significant improvements through such processing in the moduli (both machine and transverse directions), yield and break strengths, and optical properties including haze and gloss of polyethylene films.

A significant decrease in both moisture and oxygen transmission rates occurs with the machine direction orientation of homopolymer HMW-PE films. Intermediate and lower density polymers do not show such a significant decrease and actually present a maximum at moderate draw ratios where the transmission rate is greater after orientation than that of the undrawn sample. This maximum probably results from the high degree alignment of the lamellar normals in the machine direction that opens inter- and intra- lamella stack voids for the transmission of both moisture and oxygen. At higher draw ratios, the lamella tilt to ±34.4&%176; of the machine direction making a crossing pattern that blocks the voids of the lamellae.

In addition, a linear relationship occurs between the moisture and oxygen transmission rates and the Herman’s orientation functions calculated from birefringence. This indicates a relationship between the barrier and the degree of orientation similar to that of the stress optical law. The good correlation with birefringence orientation data and weaker correlation with crystallographic techniques indicate that changes in both the amorphous and crystalline regions affect the barrier properties of the sample. Future work could use an additional technique that accounts for the orientation of both crystalline and amorphous phases such as IR dichroism to understand further the effect of each phase on barrier.

EXECUTIVE SUMMARY
Novel High Performance Collation Shrink Film
by Richard W. Halle, Donna S. Davis, Philipp Becker, and David R. Weisinger, ExxonMobil Chemical

APPLICATION: Metallocene LLDPE combined with a new high performance LDPE and a new HDPE in a coextruded blown film structure provides high performance in advertising display shrink film applications.

Collation shrink describes the type of secondary packaging used to bundle objects together by heat shrinking a film around the objects. Typical products that are shrink wrapped today include bottled water, beverage bottles and cans, juice boxes, health and beauty products, and a wide assortment of food product bottles, boxes, and cans.

The rapid evolution of the shrink film market focus from plain bundling to advertising display has added many new performance requirements that are best attained by using novel high performance coextrusions incorporating metallocene polyethylenes (mLLDPE) and new unique grades of LDPE and HDPE.

The new LDPE and HDPE can increase film stiffness as indicated by secant modulus. Adding the mLLDPE increases film strength. Both the machine direction and transverse direction secant modulus values can increase by 15–25%. Stiffness is particularly important in new high-speed packaging lines where film transfers quickly from the cutting area into the wrapping zone. The film must transfer flat to maintain package integrity and bull’s-eye shape. Film must also remain stable while wrapping around the contents.

Consumers highlight the importance of tensile strength for safely transporting products home. The tensile strength of these new shrink films is almost 20% higher than the incumbent commercial structures. Obviously, plastic film avoids problems experienced with “sweating” and water damage associated with paperboard alternatives.

In summary, this new shrink film technology will provide a good “billboard” for branding. It will help keep the bundle protected through retail. It will support faster packaging line speeds and bring new value. Through the combination of new materials and application research, technology provides the performance that the brand owner seeks.

EXECUTIVE SUMMARY
Choosing The Right Cure Mechanism For UV Curable Laminating Adhesives
by Debbie Smith, Sartomer Company

APPLICATION: A study of adhesives applied to a clear film and subsequently nipped to a second substrate with UV irradiation curing through the clear film studied lamp sources, photoinitiators, and various oligomers.

This paper focuses on various studies that were designed to improve adhesion in radiation-curable (UV or EB) laminating adhesives. First, a typical laminating adhesive was cured on polyester terephthalate using various UV lamp sources and different types of photoinitiators to evaluate cure. Next, various oligomers were UV-cured on both polypropylene and polyester terephthalate to determine the best oligomer for each film. Various lamp sources and varying energy of cure were evaluated also.

First, various UV energy lamp sources were evaluated with photoinitiator options. Using this information, a simple formulated laminating adhesive was evaluated with the various lamps and photoinitiators. Next a variety of laminating adhesive oligomers were screened on both clear films using correct UV energy and photoinitiator selection. The results showed that users can successfully UV-cure laminating adhesives onto oriented polypropylene or polyester terephthalate using the correct photoinitiator with the correct lamp source.

One study in this paper evaluated laminating adhesive oligomers on various films by examining seven new oligomers designed to improve adhesion in various laminating adhesives. The testing used polypropylene and polyethylene terephthalate. In the study, the new oligomers underwent UV curing on both OPP and PET to determine the best oligomer for each film. Although some oligomers were specifically for rigid plastic applications such as polycarbonate and polymethyl methacrylate, their inclusion provided an evaluation of their adhesion to OPP and PET. The oligomers underwent evaluation for physical performance characteristics and various laminating adhesive qualities. To achieve cured film properties, the oligomers were each mixed with 5% 1-hydroxy-2-methyl-1-4(1-methylvinyl)phenyl propanone photoinitiator.

The oligomers underwent testing neat on the various films to determine what they contributed to the adhesive. Each oligomer was mixed with 0.5% bis (2,4,6-trimethylbenzoyl)-phenylphosphineoxide to evaluate it as a major component in an energy-curable laminating adhesive. A previous study had shown this material performed best on the PET film laminations. The procedure used for mixing the oligomer with the photoinitiator consisted of blending the two at 50°C for 30 minutes.

EXECUTIVE SUMMARY
Cost Reduction Using Performance Products—A Case Study
by Lan Nguyen and Paul Tas, NOVA Chemicals Corp. Systems, Inc.

APPLICATION: Using a case study on how to design alternative high performance polyethylene blends, this paper demonstrates that these high performance blends have improved product characteristics and increased throughput while simultaneously reducing overall cost.

Various trade journals have reported that polyethylene prices have risen steadily over the past few years due to the growth in the plastics industry, the effect of high demand and short supply, and the rising cost of crude oil and natural gas. Polyethylene manufacturers and converters alike are continuing their search for ways to reduce cost. In the converting industries, several strategies are possible for reducing cost. These include minimization of scrap although this is unavoidable during product start-ups, transitions, or shut downs. Another possibility is to increase plant capacity, but most converters have probably already exhausted their maximum capacity.

Another option is to use material that is not within specification. This is unwise because it may not meet FDA specifications or provide the proper physical performance. Use of a filler can be undesirable because it often significantly decreases physical performance, optical properties or both. Finally, one could use a high performance material replacement. While this may seem contradictory, it is not always necessarily so as the cases described in this study illustrate.

Material replacement can be a time-consuming process, and it may not provide significant economic benefits. By following a polyethylene material replacement flow chart, a user can identify and evaluate ways to obtain economic benefits. For example, a good reason to replace a lower cost polyethylene with a higher cost polyethylene can be improved performance that then provides the possibility to downgauge film and thereby reduce the overall cost. Readers will see that hexene LLDPE (hexene-LL) and butene LLDPE (butene-LL) can be fully or partially replaced by a single-site catalyzed octene LLDPE (octene-sLL).

The use of high performance products such as octene-sLL in place of general-purpose hexene-LL or butene-LL in films is often associated with higher cost. Using a cost vs. benefit analysis with strategic resin blend design, an overall improvement was possible. To realize this improvement, certain requirements are necessary.

By understanding the objectives of converters and benchmarking their existing products, resin producers can work with converters to strategically design and recommend blend compositions that will allow improved film performance while achieving significant financial benefits. Elaborate cost analysis software programs are available that can facilitate the identification of cost/performance benefits for the customers.

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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