Ceepackaging

Profiles

Creating multilayer structures in plastics

A normal toothpaste tube, for instance, may consist of at least five layers, each with its own purpose. One layer acts as barrier material to keep aroma and fragrances in and oxygen out, another layer gives the tube its mechanical properties so that it doesn’t collapse, and yet another layer makes the tube suitable for printing. Layers of Yparex® adhesive can be used to bond the various layers.
Multi-layer structures offer a number of key benefits.  They provide a barrier to oxygen, flavour and water.  However, they also place a number of demands on the final solution, ranging from mechanical properties to esthetics, sealability, thermoformability, retortability and printability, to name but a few.  Adhesion has to be perfect and food contact approval is required.
Yparex, an extrudable adhesive tie-resin from DSM Engineering Plastics, has been available since 1993. In its original form this is polyethylene grafted with maleic anhydride. The Yparex range provides outstanding adhesion between all forms of polyethylene and barrier materials such as polyamide-6 (Akulon) and ethylene vinyl alcohol (EVOH). At the same time, Yparex also bonds to metals such as aluminum, steel and copper. Its bonding properties make it eminently suitable for the manufacture of multilayer structures. Yparex is commonly used in multi-layer barrier structures for food packaging with low oxygen permeation, but also multi-layer non-food packaging structures with good mechanical properties and puncture resistance. Other applications are multi-layer pipes for under floor heating and sanitary applications, multi-layer wall claddings, and high voltage cables.
In packaging applications, the bonding that Yparex provides between polyethylene and the other layers develops in the melt phase and depends on contact time and temperature. A major advantage of Yparex is that it can be processed easily. Multilayer packaging is often made by co-extrusion. Each of the various polymers, including Yparex, is melted in its own extruder and pumped to a die. In this way a multilayered film or sheet can be produced.  Alternatively, bottles or containers can be blow-molded. Yparex does not require these standard techniques to be adapted.

Developing PP based solutions
In the packaging industry we can identify a number of key trends.  Producers are looking for light-weight packaging solutions that are more flexible and easier to handle and make a contribution to the environment by creating less waste. There is an identified need for packaging with high-temperature resistance, for example for microwave food packaging, where the use of Polyethylene (PE) is less suitable.
Polypropylene (PP) offers significantly higher heat resistance, typically for temperatures > 130˚C.  This has led to an increased use of PP in multi-layer barrier structures, mainly because it provides retortability, microwave-ability and it can even be used in typical sterilization processes that often last 1 hour or more.
Thus customer demand has led to the development of a new Yparex grade, based on Polypropylene (PP).  This adhesive is able to withstand significantly higher temperatures, and doesn’t affect the transparency of the PP.

New tie-resin for sausage casings and shrink film
Sausage casings and shrink film are produced by a so-called double bubble process. This process is very demanding for the tie layer performance. DSM Engineering Plastics has developed a tie layer especially suitable for the double bubble process. Initial results in the market are excellent.
Developing new products and processes would have been virtually impossible without the lab-scale film production line that enables DSM Engineering Plastics to make and test multilayer films. Having a machine that is also used in the market allows DSM Engineering Plastics to quickly test how the material behaves under practical conditions.
Creating multilayer structures may appear to be pretty straightforward. However, bonding is a complex chemico-physical process. Besides composition of the tie-resin, other factors play an important role: a.o. the way the granular raw materials are processed, and the downstream processing of the material.

Outstanding Technical Support
In order to continue the development of new Yparex products, intensive collaboration between product and application developers and researchers is needed. Scientific specialists study adhesion in all its aspects, whereas Application Development Engineers are working with customers to help them to address their needs in an ever changing market. Where necessary, DSM process technologists of the Yparex® production plant in Genk (Belgium) are also involved, as are the analysts at DSM Resolve in Sittard-Geleen for mechanical and chemical testing of the material.
DSM is well-equipped to apply its technological and scientific knowledge and serve the customer in the best way possible. Working with locally based specialists, DSM Engineering Plastics is able to offer its world class technical support to customers anywhere in Europe.