- December 01, 2004, David J. Bentley, Jr., Editor
Providing practical information to the converting and packaging industries
High Value Polypropylene Resins For Extrusion Coating
By M. Kirchberger and M. Stadlbauer, Borealis GmbH
Long chain branched polypropylene combines the elongational flow properties of long chain branched polymers such as LDPE with the stiffness and barrier properties of polypropylene. This combination provides unique opportunities for various applications. This paper discusses the processing behaviour of long chain branched polypropylenes and shows tools for the assessment of the extrusion coating behavior of a resin by using elongational and shear. It also compares the typical material properties of such polypropylene with other polymers used in extrusion coating. Two case studies show the potential of new applications achieved by using this polypropylene in extrusion coating for metal laminates and breathable film.
The basic correlations of rheologic measures and performance in extrusion coating are useful for quality control and product and recipe development. They save significant effort and cost for experiments. Long chain branched polypropylenes for extrusion coating exhibit these favorable properties and therefore show outstanding processing behavior in extrusion coating. With these new materials, extraordinarily high extrusion coating speed and low neck-in is possible. Thus, these resins enable new applications for polypropylene in this field and contribute to a significant improvement of process and converting efficiency as the case studies show.
New Sealant For High-Speed Packaging
By Julie Gibbons, Rob Cotton, and Nicole (Dowling) Pierce, The Dow Chemical Company
Vertical-form-fill-seal (VFFS) applications often involve complicated seal configurations due to gussets, sealing through multiple plies at package joints, sealing through package wrinkles or folds, or sealing through product contamination at the seal area. A new enhanced polyethylene (EPE) resin can extend the range of material options for converters and packagers. The resin fulfills the need to meet the continued demand by consumers for improved convenience and performance in VFFS packaging. This paper will compare and contrast the new EPE to other conventional and new-to-market resins relative to the performance requirements for VFFS applications.
EPEs offer a package designer improved performance with cost reduction by combining excellent optics, stiffness, and seal properties compared with traditional polymer choices. The new resins provide an improved combination of optics, sealability, tear strength, processability, machinability, and cost effectiveness compared with alternate materials or resin blends. The exceptional performance of EPEs can provide the following:
- Increased packaging speed on VFFS equipment with fewer leakers
- Downgauging (cost savings) without compromising properties
- Simplification of package structures with possible consolidation of multiple polymer inventories.
Generally, polymers produced with single-site catalyst or metallocene technology have narrow molecular weight distributions that provide improved physical properties. Consequently, the narrow molecular weight distributions decrease processability. EPEs overcome these processing obstacles by incorporating long-chain branching in the polymer backbone. This incorporation that decreases extruder amps and backpressure was previously possible only through blends and resulted in a decrease in abuse resistance properties. A new EPE resin provides a film with improved product differentiation due to improved optics, abuse resistance, and sealability over traditional LLDPEs in a single polymer.
In conclusion, the new EPE offers good caulkability for high-speed packaging applications and is a perfect choice of resin for performance improvement vs. LLDPE and a more cost effective alternative vs. POP. This newest sealant specifically provides a superior combination of optics, sealability, tear, processability, machinability, and cost effectiveness compared with alternate materials or resin blends. Based on attributes this fits into such targeted applications as freshly cut produce, pet food, snack foods, confectionary items, and dry powered goods.
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