Research project develops a film inspection system for multilayer films

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As part of the IRIS collaborative research project funded by the German Federal Ministry of Economics and Technology (BMWi), the Fraunhofer Institute for Laser Technology ILT has collaborated with the Institute of Plastics Processing (IKV) at RWTH Aachen University to develop a film inspection system for multilayer films.

The InnoNet project, which began in 2009, recently completed its final stage with the successful testing of the system on a flat film line under production conditions.

As the complexity of plastic packaging solutions requested by customers increases, this challenge is pushing manufacturers to place more and more emphasis on functionalising packaging films by offering complex layer structures. For example, adding a layer of ethylene vinyl alcohol (EVOH) copolymers creates a diffusion barrier against oxygen and water vapour which ensures that food products keep fresh longer.

Currently, the minimum thickness of individual functional layers lies between 2-100μm. In order to ensure they meet the minimum thickness requirements, plastics manufacturers apply more of the expensive functional material than is strictly necessary. As a result, EVOH and comparable plastics such as polyamide (PA) have come to represent a significant cost factor.

The challenge faced by manufacturers of multilayer films is to make the functional layers thick enough without using excessive amounts of material. This is where a film inspection system can make a real difference: The system's measuring beam is moved diagonally across the film from one side to the other and takes a series of readings that enable it to determine the thickness of each individual layer. The sensor is capable of measuring multiple layers simultaneously at production speed. A software program analyses the data and triggers an alert if the readings deviate from the target thicknesses. This enables the manufacturer to correct the ongoing process immediately after detecting an out-of-tolerance reading and to maintain quality by either reducing or increasing the quantity of material used in response to the inline measurements.

There is currently no other tool on the market capable of performing these inline measurements.
A further benefit of the film inspection system relates to the even distribution of the functional layer across the film's entire width. The nature of the production process means that the functional layer gets thinner towards the edge. As a result, manufacturers are forced to remove the edges of the film on both sides, representing a significant waste of material. Minimising this wastage is an important issue. The inline measurement system makes it possible to determine precisely where this critical drop-off in thickness begins, thereby keeping wastage to a minimum.

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