Speaking at the recent Metallocenes Europe ‘97 conference, Wolfgang Lotz, general manager of Napiag Kunststoff- verarbeitung GmbH (Bahnhofstr. 3, A-8740 Zeltweg) shared his company's experience of using metallocene polyethylenes. Discussions with suppliers highlighted that metallocene-catalysed polymers could supplement the range of established polyethylene grades for flexible film applications. The key questions for Napiag to consider were: price, processing and what products these new materials could be used for.

In pricing terms metallocenes are currently at the top end of the materials most film extruders are likely to be using, with the exception of ionomers. Metallocene PE pricing is in the range of DEM 1.75-2.5/kg (based on end 1996 prices). Therefore it is going to be its technical performance rather than price alone which is the key consideration. The most likely route of development being its use in blends or coextrusion with conventional resins.

Metallocenes can be processed on extrusion lines designed for LLDPE without any problems, except for a slight fall in output. Blends of mPE with LDPE grades show an increase in melt temperature and melt pressure when processed on LDPE extrusion equipment but this leads to reduced bubble stability. Napiag also found that blends of mPEs with either MDPE or HDPE could also be processed on LDPE extrusion equipment.

So far Napiag has tried about 15 different types of mPEs from several different suppliers for certain flexible film applications. From the outcome of these trails it has concluded that despite some processing difficulties mPEs optimise the quality and performance of flexible film. For commodity products there will be an increase in performance, while for speciality products (already using high priced resins) an increase in performance and cost reduction may be achieved.

Napiag has selected six grades to use to improve and optimise some of its flexible packaging materials, in particular, frozen food film, liner film for drums, barrier film for deep drawing applications, foil/film laminates for hot fill applications and heavy duty packaging (f/f/s).

From its experiences, Napiag has found that metallocene polyethylene is more difficult to process and is more expensive than conventional resins, but these issues can be outweighed by the improved performance offered. However, Mr Lotz, pointed out that new products are coming on to the market all the time and processors should not be brow beaten into using them just because they are available. Every user has to decide with their product range and equipment whether the new materials will be of benefit to their company and their customers.

Conference proceedings for Metallocene Europe ‘97 are available from Schotland Business Research (16 Duncan Lane, Skillman, NJ 08558, USA) Fax: +1 609 466 8833.