Trade press conference K 2004
on June 22 and 23, 2004, in Ludwigshafen
Efficient production of transparent thin films
New applications for S/B polymer: The second generation Styroflex
Report by Robert Huber,
Marketing Styroflex
Styroflex® is a styrene/butadiene and the only thermoplastic elastomer among BASF’s styrenic plastics (figure 1). Characterized by a combination of high resilience and toughness, optical clarity and processing stability as well as gas and water-vapour transmission, Styroflex is mainly used for transparent, stretchable packaging film. Following further improvements to the Styroflex production process, BASF’s researchers can now offer an even better product - Styroflex2G66, which launches Styroflex into its second generation.
The improvement work was pursued in several directions. A way was sought to produce extremely thin film, while retaining mechanical behaviour (e.g., resilience and puncture resistance) and optical properties. The presence of gel particles is a major cause of film tear, especially at very low gauges. BASF has optimized the manufacturing process in a way that makes Styroflex 2G 66 extraordinarily low in gel particles, enabling film thicknesses of just 10 microns to be achieved without problem.
Styroflex 2G 66 – greater stretch stretches costs
Styroflex offers the potential for significant cost reduction in the area of stretch packaging, a common method of wrapping food and protecting palletized goods.
Stretch packaging uses the property of certain polymer films to remain strong when stretched and at the same time exert a squeezing force as they try to return to their unstretched condition. This allows objects of different size and shape - palletized goods for example - to be secured. The Styroflex film clings closely to the packaged goods without tearing on sharp edges (figure 2). A new type of stretch packaging - stretch hood technology - involves a hood that is stretched over the object. Stretch hood technology is ideal for keeping loads clean and dry, and
represents a quick and cheap alternative to shrink wrap and stretch winding techniques.
Styroflex film is far superior to common polyethylene film thanks to its great elasticity and resilience. For instance, when stretched to 500% of its original length, a special polyethylene (PE) will at best recover to only 400%; Styrolux film on the other hand will recovery to 100% when the tension is released (figure 3). Styrolux's higher resilience means the size and weight of the wrapper can be halved.
Advantages of stretch hood technology
The use of low-elasticity tubular film usually limits the packer to one size of pallet. On the other hand, the stretchability of Styrolux allows him to use a single diameter of wrap to package objects of various size. That not only reduces downtime - by not having to change the film - it also saves on inventory costs since only one size of film has to be stored (figure 4).
Styroflex 2G 66 as high-performance additive for PE film
Apart from its use in stretch film, Styroflex can also be employed as a high-performance additive to increase the toughness properties of various other types of film. Makers of food-wrapping film in particular can profit from Styroflex 2G 66. PE in combination with the new Styroflex offers a cheap alternative to PVC film. The reason: when conventional PE film is coextruded with the elastomeric Styroflex 2G 66, it acquires the same high-level of resilience as PVC film - a property that, along with high oxygen transmission, is especially important for food-wrapping film (figure 5).
Styroflex 2G 66 can also be used to improve the mechanical properties of PE film, especially biaxial toughness. By finely distributing nano-sized particles of Styroflex in the polyethylene matrix, the puncture resistance of PE film can be increased by up to 60% with negligible loss in stiffness (figure 6). Such an effect gives film extruders numerous possibilities to optimize their systems.
Styroflex 2G 66 addition rates as low as 3 to 5% allow thinner films to be extruded while retaining the processing properties of PE-LD (low density) or PE-LLD (linear low density) film. Or the other way round: If PE films of a given thickness contain 4% of Styroflex 2G 66, their resistance to tearing is clearly increased (figure 7).