Precise Measurement Technology for Complex Plastic Films Enables Resource Savings

Together with the Institute of Plastics Processing (IKV) of the RWTH Aachen University, the Fraunhofer Institute for Laser Technology ILT is presenting the prototype of a film monitoring system to measure individual layer thicknesses in multi-layered films at the International Trade Fair for Plastics and Rubber (Hall 14/ IKV Stand C16).

All over Europe, the average demand for plastic packaging is increasing by 5.5 percent annually. As the second largest producer worldwide, Germany has profited from this increased demand, ranging at 7.5 million tons of plastic packaging a year. In addition, consumers require more and more from plastic packaging, especially for foods. End users expect fresh products to have a longer shelf life and the packaging to have increasing functionality, such as a display of the degree of freshness. These increasing requirements upon packaging films are reflected technologically in a more and more complex layer composition and an increase of functional layers of plastic films.

As functional layers, expensive materials such as the plastic EVOH, for example, are commonly used. Thanks to its ability to act as a diffusion barrier for oxygen and water vapor, EVOH guarantees a longer shelf life of food. Due to the comparably high material price of the functional plastic, however, plastics processors have been making an effort to keep the share of the product's raw materials as low as possible while retaining functionality. The thicknesses of the functional layers produced here lie mostly between 1 µm and 20 µm. In order to guarantee a fully functional barrier effect, manufacturers must continuously monitor integrity and thickness of the functional layer. Until now such a film inspection system has not been available, one which can measure the layer composition of multi-layered films at production speeds of up to 450 m/min.

Cost Advantage through Precise Measurement Technology

"While the measurement of the total thickness during the production process is already state-of-the-art, but analyzing the layer construction still occurs in the testing laboratory and not directly at the plant itself. We want to close this technology gap," explains Janina Overbeck, leader of the working group Blown Film Extrusion at the IKV. "The contactless measurement of individual layer thicknesses during production is the most important step toward automated regulation of production plants for multi-layered plastic films."

Within the scope of the IRIS project, researchers from the Fraunhofer ILT together with the IKV are developing a system to measure plastic films. This measuring system is based on an interferometric sensor and uses infrared light to detect refractive index changes within a measurement sector. Such refractive index variations appear on the surface of the film as well as on the transitions between the individual film layers.

In addition to better process control, the interferometric sensor will enable a control concept for individual film thicknesses to be implemented. By saving raw materials, companies can attain significant cost reductions. For a machine of medium capacity, this can add up to around €100,000 per year. On the International Trade Fair for Plastics and Rubber (Düsseldorf, Oct. 27 - Nov. 3, 2010), the research partners will be presenting the prototypes of their film inspection system to trade experts at Stand C16 of the IKV in Hall 14.

Source: Fraunhofer Institute for Laser Technology (ILT)