Rigid Packaging High-Performance Thermforming of Starch-Based Polymers By Uwe Heer Kiefel GmbH, Germany Anna Förster Plantic Technologies GmbH, Germany One field of application for bioplastics is thermoformed rigid packaging. Plantic ® is a high-amylose starch-based material, introduced onto the market by Australian Plantic Technologies Limited in 2003. Thermoformable Plantic film is available in many colours and in thicknesses currently up to 450 microns. Thermforming of Plantic: The optimum water-content of film material, which is approximately 12%, is negatively influenced during the thermoforming process by excessively high temperatures and by being heated for too long. As many of the conventional automatic roll-fed machines on the market often have no individual heater adjustment function, and are fitted with long-wave ceramic heaters, the results of the first tentative trials with Plantic were modest to say the least. The three-stage heating process to which the film material was subjected often resulted in pronounced dehydration (>0.5%) and increased brittleness of the thermoformed tray, particularly when automatic roll-fed machines fitted with a relatively slow-acting ceramic heater were used. Back in 2005, thermoforming machine supplier Kiefel from Freilassing, Germany, carried out trials with Plantic on a KMD 75 B machine, which helped the company reach the following conclusions: • Heating with a standard quartz heater is possible • It emerged that heating in a single stage was recommended if embrittlement of the material was to be avoided. The use of a heater with very high output and a very short wavelength (i.e. an induction heater) is recommended • High-speed forming leads to results that are more uniform • The heating station must be fitted with an individual adjustment mechanism for each heater, along with a tracking device designed to measure directly the surface temperature of the film material. These trials showed that a high-performance machine can be used to process Plantic at similar speeds and forming temperatures as those used for materials such as PET. Given the polymer properties of Plantic film material however, deep-drawing performance is somewhat limited, compared to PET, when a normal thermoforming unit is used. Development work and experience on the part of Plantic in recent years have shown that deep-drawing performance can be further improved by using a very high output, shortwavelength IR heater. These findings were implemented in a practical manner at the end of 2008, when Kiefel installed a KMD 78 B Speedformer machine at the German Plantic factory in Schorba, with a view to optimising the processing of Plantic film material on a high-performance thermoforming unit. The KMD 78 B Speedformer machine supplied was equipped with the following features: • 70 dry cycles per minute (instead of 55) • 750-Watt quartz radiator (instead of the 500-Watt unit fitted as standard) • One heating stage has been specially configured to operate with a very high output, short-wavelength IR radiator • Motor-actuated expansion units downstream of each station • Optimised intake system for fast filling of the tool with forming air 14 bioplastics MAGAZINE [02/11] Vol. 6
Rigid Packaging UV short medium long Radiation intensity (relative units) 250 200 150 100 Visible light Halogen 2600°C short-wave 2200°C Fast microwave 2200°C Carbon 1200°C microwave 900°C 50 0 0 1 2 3 4 5 Wavelenght µm • Measurement of film temperature during each cycle, including automatic temperature-tracking to ensure that processing always takes place within the optimum operating range The list of features also includes a modified heating station with special heating element, designed to make it easier for Plantic to ensure that high-quality output becomes standard, thanks to the company’s new Speedformer machine supplied by Kiefel. The Plantic Company itself is meanwhile pushing the development of its film material in an effort to improve its ductility and make it suitable for use in an even wider range of applications. The use of a very short, but highly effective, heat-up zone makes it clear that a medium-wavelength heater (quartz radiator) or a short-wavelength heater (IR radiator) produces better results than a long-wavelength ceramic heater (see graphic showing wavelengths). It would definitely be desirable for the packaging sector to be able to ensure its share of the overall market by offering biopolymers as an alternative to mass-market plastics such as polystyrene, polyester and polyolefin (and particularly the polypropylene used in thermoforming). Efficient processing on virtually standard, automatic roll-fed machines, coupled with the technical properties of the film material itself, contribute to the likelihood of such alternative materials obtaining their fair share of use in thermoforming applications. Depending on local, country-specific conditions, the use of biopolymers can also be interesting from an economic point of view. www.kiefel.de www.plantic.com.au C M Y CM MY CY CMY K magnetic_148,5x105.ai 175.00 lpi 15.00° 75.00° 0.00° 45.00° 14.03.2009 10:13:31 Prozess CyanProzess MagentaProzess GelbProzess Schwarz Magnetic www.plasticker.com for Plastics • International Trade in Raw Materials, Machinery & Products Free of Charge • Daily News from the Industrial Sector and the Plastics Markets • Current Market Prices for Plastics. • Buyer’s Guide for Plastics & Additives, Machinery & Equipment, Subcontractors and Services. • Job Market for Specialists and Executive Staff in the Plastics Industry Up-to-date • Fast • Professional bioplastics MAGAZINE [02/11] Vol. 6 15
