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A Communication from the PLACE Div. of TAPPI

Providing practical information to the converting and packaging industries…

Novel High Performance Collation Shrink Films For Bundling And Multipacks
by Philipp Becker, ExxonMobil Chemical Europe, Inc.

Collation shrink describes a type of secondary packaging to bundle objects together using shrink film. Objects being brought together include mineral water and soft drink bottles, milk cartons or bottles, and cans or boxes. Collation shrink has two main categories. Transportation film brings goods into a situation where the film will be removed and the goods stored on a shelf. Display or advertising collation shrink film wraps a package that a customer takes home after purchase.

The ideal display film requires a glossy surface for printing the message, a very clear protection film to feature the contents, a reliable bull’s eye for carrying, toughness and holding force to keep the contents together. To the film producer, that vision drives an emphasis on gloss, clarity, toughness, and puncture resistance. To the packer, it requires adequate stiffness and controlled shrink.

The new film in this paper is a coextrusion based on three polyethylene resins. They provide the necessary optics, toughness, and stiffness to excel in collation shrink. The technology is not a singular film structure but rather a design basis that requires optimization for packages of varying sizes and demands.

To date, new film formulations have had satisfactory use on packages from bottled water to canned soft drinks. They have performed reliably on state-of-the-art, high-speed packaging equipment. Applications are also possible for health and beauty products, other foodstuffs, and potentially even fully enclosed packages. This novel high performance collation shrink film technology combines high stiffness, tailored shrinking rates, excellent holding force, and improved mechanical and optical properties that offer significant downgauging potential.

The Influence Of Small Amounts Of LDPE On Surface Roughness And Resulting Haze Of LLDPE Blown Films
by P. Mariani, Polimeri Europa

Optical properties of films such as haze, transparency, or clarity and transmittance are key issues in applications such as packaging to allow the consumer to see through a film to check what is contained in it. Haze measurements can provide a method to measure the turbidity of a film and are the most common way to give an exact idea of the optical properties of a film. In the case of semicrystalline polyethylene films, haze is affected by light scattering and reflection or refraction because of bulk and surface roughness effects.

This work studied an evaluation of the presence of LDPE in the external layers of a three-layer blown film whose inner layer was made by an ethylene-octene LLDPE Z-N copolymer on haze. A small amount of LDPE greatly improved total and surface haze of the film. Attempts to correlate haze with overall melt elasticity in terms of recoverable shear strain were unsuccessful. The reason is that the mechanism by which surface roughness has been modified by the presence of LDPE is linked to a change in crystal morphology from spherulitic-like superstructure to row-nucleation due to the highest relaxation times of long chain branched molecules in LDPE.

Although these results have not been linked to any direct confirmation in terms of small angle x-ray scattering or atomic force microscope surface roughness determination, the strict correlation found between total and surface haze and Elmendorf tear resistance in machine direction is a convincing item strengthened by the fact that it is valid also for film obtained simply by blending LDPE and LLDPE in a monolayer manufacture.

Shape Up Your Cast Film Extrusion Process With A Contour Die
by Sam G. Iuliano, Extrusion Dies Industrires, LLC

Most extrusion tooling for cast film production lines has been traditionally designed for long runs with high output rates. The time required to change from Product A to Product B has historically been a lower priority design criterion because of relatively infrequent product changes. This traditional design is not well suited for many film markets today that are driving producers to shorter, more frequent, and highly specialized runs.

Rather than promote uniform die lip deflection by providing body bolts that are equidistant from the lip exit, one can achieve the same result by varying the die body thickness from center to ends. By using this concept, die designers can now return to the highly streamlined diminishing volume coat-hanger type of flow channel and offset the clam-shell effect via the external die shape. By making the steel die bodies thicker at the center where the body bolts are furthest from the lip exit, one can reinforce the lip in the location where it tends to deflect open the most in classic coat-hanger die designs. Modern manufacturing and design tools make this sculpted body approach both feasible and effective.

The increasing demand for tooling that can accommodate frequent product changes has driven die designers to develop new technologies. Flow channel designs have come full-circle in that the classic coat-hanger channel that is known to provide optimal flow path characteristics as a result of its diminishing volume design can now be incorporated into a novel sculpted exterior die body shape. This combination of a streamlined and accurate flow channel housed within a die shape that resists clam-shelling provides a user with the ability to change output rates and materials and return to saleable product tolerances quickly. This type of extrusion die is fit for use in today’s lean manufacturing environment.

These market forces have created a need for extrusion dies that can quickly achieve acceptable product tolerances after a product change. Some modern die designs have produced dies that maintain good thickness control and are mechanically stable for a broad range of rates and materials. They achieve this at the expense of flow streamlining. A novel die design has now been field proven to provide remarkably stable thickness control while simultaneously promoting rapid purging and low inventory time.

New Printing Adhesion Improvements Using Atmospheric Plasma Glow Discharge Technology
by Rory A. Wolf, Enercon Industries Corp.

The atmospheric plasma treatment (APT) process was developed for treating or functionalizing a wide range of materials. It has unique advantages over the presently used technologies of corona, flame, and priming treatments for flexible packaging applications. It allows creation of a uniform and homogenous high-density plasma at atmospheric pressure and at low temperature using a broad range of inert and reactive gases. The APT process treats or functionalizes material surfaces in a way that is similar to the vacuum plasma treatment process. APT production equipment testing has been successfully performed for the treatment of various materials including polypropylene, polyethylene, polyester, spunbonded polyolefin, polyamide, and polytetrafluoroethylene.

The APT process consists of exposing a polymer to a low-temperature, high density glow discharge, i.e. a plasma. The resulting plasma is a partially ionized gas consisting of large concentrations of excited atomic, molecular, ionic, and free-radical species. Excitation of the gas molecules is accomplished by subjecting the gas that is delivered within an open station design to an electric field typically at high frequency. Free electrons gain energy from the imposed high frequency electric field colliding with neutral gas molecules and transferring energy to dissociate the molecules to form numerous reactive species. It is the interaction of these excited species with solid surfaces placed in opposition to the plasma that results in the chemical and physical modification of the material surface.

Application of atmospheric plasma to finished films has been theorized and practiced to provide specific functionalities to the base film substrate adequate for improved adhesion relative to the corona treatment process. Since atmospheric plasma contains highly reactive species within a high density plasma at atmospheric pressure, it is proven to significantly increase surface area and to create polar groups on the surface of polymers so that strong covalent bonding between the substrate and its interface such as inks, coatings, and adhesives occurs.

The work described in this paper identified that untreated flexible packaging grade polyester film that was post-treated with the APT process exhibited high levels of peel adhesion relative to a corona post-treated polyester at a power density of 10W/m²/min. When post-treatment surface tension was equalized between APT and corona at 46 dynes/cm, the APT treatment process continued to promote strong ink anchorage relative to corona by approximately 50%. The analysis provides evidence that flexible packaging converters using aqueous inks on polyester-based structures may experience improvements in ink adhesion by employing APT-based surface treatment systems.

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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