A solution to the demands placed on plastics during rotational sintering will be detailed by BASF (Ludwigshafen / Germany; www.basf.com) at “K 2010” (www.k-online.de) in Düsseldorf / Germany in late October – see Plasteurope.com of 22.06.2010. “Irgastab” RM 68 is an additive system specifically developed for plastics that are processed by rotational sintering. The company says that it optimises the sintering process, improves the quality of the final product and helps to save energy by affecting the melting behaviour of the polymer during the shaping process.

Researchers at BASF have developed the additive Irgastab® RM 68 especially for plastics that are processed by means of rotational sintering. The patented combination of stabilizers optimizes the sintering process, improves the quality of the end product and helps to save energy. Rotational molding is suitable for shaping large hollow articles made of plastic, especially polyethylene (PE). These include recreational equipment such as toys and kayaks, but also all kinds of tanks and containers.

This allows the processing times to be shortened and the oven temperatures to be lowered, resulting in a wider processing window, which can be important when considering that rotational sintering often involves the use of different moulds at the same time in one machine. Andreas Thürmer, head of Technology and Product Management Additive Blends for Plastics at BASF Schweiz said: “If the residence time in the oven is the same, there is a risk that the polyethylene will not melt sufficiently in large moulds while, in contrast, it will already have degraded in the small moulds. In other words, the wider the processing window, the more robust the production process and thus the better the quality of the final product.”

Shorter processing times can also lead to lower degradation of other additives in the plastic, increasing the service life of the plastic part. Thürmer also pointed to other positive features of the additive system. For example, the inherent discoloration of the product during processing is reduced and the colour fastness on exposure to nitrogen oxide is increased. “The better stabilisation of the polymer chains against degradation improves the mechanical properties, especially the impact resistance of the plastic”, he added. The additive system also contains a light stabiliser that complies with the UV8 weathering standard, which stipulates an elongation at break of at least 50% of the original value after 8,000 hours of exposure to accelerated weathering. This corresponds to outdoor use in a subtropical climate for at least three years.

Only about one percent of all plastics in Europe is processed by means of rotational sintering. In 2008, “Irgastab” RM 68 was introduced onto the American market and this remains the main market for rotational sintering. The additive has been approved in polyethylene by the US Food and Drug Administration (FDA; www.fda.gov) for indirect contact with food products. In Europe, the method has become an alternative to blow-moulding in recent years. In conclusion, Thürmer said: “Rotational sintering can achieve decisive cost advantages in comparison to the technically very demanding blow moulding method, particularly for small production runs of large blow moulded parts. Thanks to the savings in terms of time and energy, but also due to the qualitative improvement of the final product, “Irgastab” RM 68 helps to optimise the process and thus contributes to its competitiveness in the market.”

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The chart-presentation given by Andreas Thürmer at BASF´s pre-K press conference can be obtained on the following webpage as a PDF document