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More layers deliver more value

Growth opportunities and progress in blown film extrusion

Market and consumer demands o­n blown films are increasing. More and more functions have to be integrated in the product. To a large degree, this can o­nly be achieved through more and more layers in the film. The upcoming K 2007, International Trade Fair Plastics and Rubber in Düsseldorf, will highlight current trends in this area. o­nce again, from 24 to 31 October this year, the fair will show that the trend towards multilayer signifies both growth and added value. The progress achieved in blown film extrusion since the last K has contributed to this, as this report sets out to illustrate.

This summer, the American packaging specialist General Films from Covington/Ohio, USA, plans to increase its production capabilities with a blown film line for 9-layer film. The US film producer hopes this investment will give it a competitive advantage o­n overseas markets, especially as the film types are grades with a particularly high barrier effect. The Ohio-based company has been producing custom barrier films for two decades. The new line, to be supplied by equipment manufacturer Battenfeld Gloucester Engineering, Gloucester, USA, will allow General Films to produce more complex film structures for a range of different customers. It can be used to process various PA, PE and EVOH materials. As well as film extrusion, the new line opens up opportunities such as the inline production of bags and the manufacture of tubular films.

Sights set o­n eleven layers
There can be no question that the demands placed o­n plastic films as used notably for food packaging have risen constantly in recent years and have now reached a level which can o­nly be met by employing a variety of different measures. Whereas in the past, three- and later five-layer films were enough to meet specific packaging criteria, today films with in some cases seven or even nine layers are needed. Lines which can blow eleven layers simultaneously have been o­n the horizon for some time now and are already said to be available as lab prototypes. These multiple layers are essential to guarantee the whole range of functions such as protection from sunlight and oxygen, guaranteed taste and aroma, effective barrier properties, sealability and printability. The wish list is endless. And each wish results in a new layer in the blown film.

As the number of film layers increases, so too do the organisational demands o­n the production line. It is important to maintain the flexibility of the overall concept. This is why almost all suppliers favour modular design. Another major aspect is control of the system, right through to automation of a complete line. Achim Greifenstein, head of research and development at Rheinische Kunststoffwerke (RKW) in Worms, a major manufacturer of polyethylene (PE) and polypropylene (PP) films, is familiar with the demands placed o­n the product from his day-to-day work. He knows how important reliable and fast-acting controls are for continuous reproducibility of film properties. And the more sophisticated these become, the more important it is to be able to set and maintain close control parameters.

The trade magazine “Plastverarbeiter” by Heidelberg-based Hüthig publishers, in researching a report o­n “Trends and market opportunities in film extrusion”, found that modern film blowing lines are operated by means of a single touchscreen. All components of a line, from granule feed to extruder to haul-off and winders, can be controlled from this o­ne monitor. To allow intervention from various levels, monitors are installed at several points in the line. Some suppliers integrate additional equipment such as the corona treatment station or the heat exchanger for film cooling into the general automation system in order to simplify operation.

Five layers instead of three
According to the Troisdorf-based Reifenhäuser group, the large raw material capacities in the Gulf and Asia Pacific regions as well as the desire for high film quality and high cost efficiency require new line concepts, in this case especially for the production of FFS heavy-duty sacks (FFS stands for Form, Fill, Seal) and stretch hoods. The company has tested new line components, various processes and raw materials of different formulations under real production conditions in its own technology centre. Through the use of the recently developed cooling system “Rei2cool” in combination with an optimised blown film die and low-temperature screws, performance increases of 20 to 35 percent have been achieved.

This is a major success, according to Peter Heimann, head of the blown film product area at Reifenhäuser. For Heimann, line performance improvements remain the No. 1 issue: “Greater output with the same or improved quality at the same or reduced prices”, is how he summarises customer demands. Bernd Schroeter, product manager blown film at Reifenhäuser, describes the path taken by the Troisdorf company in handling projects today: The product is the top priority. The answer to the question of which film is to be run for which application determines how the line is designed. The design also has to take into account the current state of materials development. According to Heimann, available raw materials are becoming more and more intelligent which, while opening up a wide range of different applications, also has to be taken into account in optimum machine design.

Another way of improving the cost efficiency of blown film lines is to replace the conventional three-layer with five-layer films. Reifenhäuser has developed a special die for this with spiral mandrels designed to produce very thin layers. This offers great flexibility in the production of polyolefin films and in the processing of barrier materials such as EVOH, PA and CoPET. According to Bernd Schroeter, it is not always necessary from the point of view of the product to produce a five-layer film, but many customers are already looking towards future requirements and are ordering the five-layer variant. For the user, it opens up new opportunities and paves the way to reduce raw material costs and optimise the mechanical properties of the film.

Revised details
At the end of last year, Battenfeld Gloucester reported that it had enhanced details of its line technology for the production of silage films. Improvements were made not just to the injection system for polyisobutylene (PIB), the design of the conveying screw for PIB metering and the die, but also to the film haul-off and winding systems. The special haul-off system offered by the company now has non-stick turning bars, ceramic-coated steel nip rolls and a special roll coated with silicone rubber. All rolls in the haul-off system are water-cooled.

The US extruder and line manufacturer has tailored the new design of its blow-stretch systems to the production of silage films. These agricultural films, which have enjoyed significant growth in recent years, are usually of three-layer design. Increasingly, they are being made with a sticky inside or outside layer. Nevertheless, according to the supplier, they can be run without difficulty o­n lines with the recently revised design.

According to Battenfeld, advancing globalisation will result in increasing mergers and takeovers among converters. In addition, it will increase worldwide pressure o­n prices and result in further price falls. Companies’ strategies will differ. o­n the o­ne hand, there will be those who want to reduce their own engineering within a leaner organisation, and, o­n the other, there will be ambitious companies who want to intensify their already significant technological know-how. Equipment and line manufacturers who support their customers both as suppliers of turnkey production lines and as development partners in process and machine technology will continue to do well.

Conical design an advantage
“Maxicone” is the name of a nine-layer blown film die launched by Windmöller & Hölscher (W&H), Lengerich, at an in-house exhibition last year. According to the Westphalia-based company, the die is characterised by extreme layer ratios, perfect distribution of the individual layers, short residence times and high output. o­ne of the reasons for these positive features is the patented conical spiral mandrel and the resultant short melt paths. The conical design guarantees early encapsulation of the middle layer, which makes the die flexible enough to process viscous and temperature-sensitive materials.

Growth in multilayer
Jochen Hennes, technical manager at Kiefel Extrusion GmbH in Worms, sees major growth opportunities for his company and the industry in general in multilayer film extrusion. Kiefel, which used to describe itself as the market leader in HDPE technology, identified the new trend at an early stage and positioned itself as a full-line supplier. In autumn 2001, it launched a new series of production lines for monolayer and multilayer films of different plastics such as PE, PP, PA, EVOH, PET, PS and EVA under the trade name “Kirion”. The matching extruders are available with screws of 30 to 120 mm diameter depending o­n required output. Lines for the manufacture of barrier films with up to nine layers are o­ne speciality of the company, which was recently bought by the Bavarian Brückner group of Siegsdorf.

At an international press conference in April last year, Kiefel unveiled a so-called “MDO” module to upgrade its “Kirion” systems. The Machine Direction Orientation (MDO) technology allows targeted monoaxial stretching of films and film structures. According to Kiefel, this is an easy and effective way to endow both blown and cast films with special properties. A corresponding “MDO” line consisting of heating zone, stretch zone, temperature-control and cooling zone supports converters in their efforts to reduce film thicknesses and thus save raw materials and ultimately costs. In addition, the monoaxial orientation of the film increases the barrier effect against gas and water vapour. MDO is also said to improve the optical properties of the film with regard to gloss and transparency.

All this can be verified at K 2007 in Düsseldorf from 24 to 31 October this year, where further advances in blown film extrusion will be demonstrated and documented.

Text and photos by K 2007 Press Office
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