- May 31, 2006, David J. Bentley, Jr., Contributing Editor
Providing practical information to the converting and packaging industries…
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
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.
Novel High Performance Collation Shrink Film
by Richard W. Halle, Donna S. Davis, Philipp Becker, and David R. Weisinger, ExxonMobil Chemical
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.
Choosing The Right Cure Mechanism For UV Curable Laminating Adhesives
by Debbie Smith, Sartomer Company
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.
Cost Reduction Using Performance Products—A Case Study
by Lan Nguyen and Paul Tas, NOVA Chemicals Corp. Systems, Inc.
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.
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