E T Polymers

Multi-layer PE Films:
A Critical Component in Flexible Packaging

P. P. Kharas
Chairman & Managing Director
Ecoplast Ltd., Mumbai.

The development of the �hot-tack� concept and equipment for its measurement in the laboratory brought a measure of relief to the film supplier.

Introduction

Multi-layer Polyethylene (PE) films produced by the �Blown Co-extrusion Process� was first introduced in India around 1978, for packaging of milk by the Maharashtra Government Milk Scheme and the National Dairy Development Board. Very few people realized at that time, that the advent of the multilayer PE film would revolutionize the growth of the Flexible Packaging Industry (FPI).

The Flexible Packaging Industry in the context of this article, predominantly refers to the Converting or Laminating industry, which uses PE films for lamination with one or more substrates such as: polyester film, bi-axial PP film, cast PP film, often in combinations with Aluminum foil depending upon the package requirements. The PE film forms the innermost layer � the heatseal layer � of the laminate and is in contact with the product packed.

In the early eighties, Imperial Chemical Industries was the main supplier of cast mono-layer PE films to the FPI. These film rolls apart from being small (about 250 mm) in diameter had several disadvantages, particularly with respect to their ability to maintain seal integrity on vertical form-fill seal lines.

The multilayer PE film gave the FPI several advantages:

You could tailor different properties on each side of the film; for example one side for adhesive lamination and the other side for machinability on the packaging line.
You could have a combination properties hitherto not possible monolayer films.
You could reduce the cost of high performance co-polymers by reducing the thickness to the optimum level required for the application, while the other layers were made up of lower priced commodity polymer, to provide bulk or desired thickness of the film.

As it happens with all pioneering efforts, the accumulated knowledge and experience was scarce, on designing a film structure for a specific application.

Each entity in the supply chain, shown below, gave their own version on the type and thickness of the film, that would work; while the end-user made little or no effort to define the performance requirements of the film, or laminate. In this scenario, the PE film supplier was invariably the target for package failures.

During this evolutionary phase, the raw material suppliers saw an opportunity to promote their PE grades with end-users, which led to the end-user specifying the grade to the Convertor who in turn, specified the raw material to the film supplier. The most important aspect of specifying the film or laminate performance for pack integrity, was still some distance away, in the thinking process.

Atleast one film supplier believed that this approach to developing film structures was not appropriate in providing value to the customer. They began to study each package failure, as it emerged and to determine its root cause. Over the early and mid-nineties, this Company had accumulated a pile of information, which was systematically arranged, to help development of film structures, for various packaging applications.

While this evolutionary process was on, a technical paper titled �Blown Film Bubble Forming and Quenching Effects on Film Properties�, by Butler and Patel of Dow Plastics, provided the evidence needed to convince end-users that specifying raw materials was not the solution.

....contd.

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