Ultra-thin barrier layers on packaging can effectively protect food or medicines from contact with oxygen, moisture or harmful substances. The Film-Inspect sensor developed at Fraunhofer IPM measures the quality of such diffusion barriers in the coating process and enables process control for the first time.
Packaging today consists mainly of a material mix of different polymer layers. The composite materials have an excellent barrier effect, but are difficult to recycle. This is not the case with packaging made from monomaterials, whose pure plastics can be recycled excellently. In many cases, coatings can also be used to achieve a similarly good barrier function for monomaterials as for composite materials. For unmixed recycling, as required by the new European Packaging and Packaging Waste Regulation (PPWR), the proportion of foreign material due to the coating should be in the per mille range or lower. Plasma coating processes make this possible by depositing coatings - made of silicon or aluminum oxide, for example - as nanometer-thin layers on a polymer substrate. For reliable product protection, the quality of such superbarriers must be flawless, i.e. the required coating thickness and continuous coverage must be reliably ensured over the entire surface.
100 percent quality control nanometer-thin coatings
A team at Fraunhofer IPM has developed a measuring method to test the quality of coatings with a thickness of less than ten nanometers immediately after the coating process in the production line. The patent-pending method uses the material-specific infrared reflection of the coating. There is a linear relationship between the reflected infrared signal and the coating thickness, which enables statements to be made about the coating thickness. The Film-Inspect sensor uses this to measure coating thicknesses within just 0.2 seconds with an accuracy in the single-digit nanometer range. The optics are designed in such a way that measurements on complex three-dimensional surfaces are also possible. A measurement at one point on the surface is sufficient for reliable quality control. As the plasma expands spatially, it is ensured that the entire sample has been homogeneously coated, provided the surface in the measuring range has the desired coating thickness.
Process control realized in the plasma coating system
Several Film-Inspect sensors were installed in parallel at the project partner Plasma Electronic GmbH in a system for coating injection-molded polypropylene containers and integrated into the system control for process control. If the measured coating thickness does not meet the specifications, the coating process can be readjusted using parameters such as plasma power, process time, gas flow rates or chamber pressure. This means that Film-Inspect not only provides proof of quality, but also reduces waste and avoids overcoating.
In addition to superbarriers for packaging made of mono-material and packaging films, the scientists at Fraunhofer IPM have their sights set on other markets. "Ultra-thin barrier layers are also used in medical technology or in the aerospace industry, where they ensure sterility or reduce friction and corrosion," says project manager Dr. Benedikt Hauer. "Film-Inspect can also provide valuable information about the thickness and chemical composition of the coating here." (OM-2/26)
Further project information
The research work on the Film-Inspect-Sensor was funded as part of the RE-USE and DeWaste projects.
RE-USE project (Recyclable functional packaging for the food and pharmaceutical industries using ultra-thin barrier layers), funded as part of the Fraunhofer-Gesellschaft's Prepare program. The project was completed in 2025.
Project DeWaste (digitally monitored plasma coatings for safe and sustainable food packaging), funded by the Baden-Württemberg Ministry of Economic Affairs, Labor and Tourism (innovation competition "Climate-neutral production using Industry 4.0 solutions"). The project was completed in 2025.
Contact
Fraunhofer Institute for Physical Measurement Techniques IPM
Georges-Köhler-Allee 301
79110 Freiburg (Germany)
www.ipm.fraunhofer.de
About the Fraunhofer Institute for Physical Measurement Techniques (IPM)
The Fraunhofer Institute for Physical Measurement Techniques IPM develops customized measurement technologies and systems for industry. Many years of experience with optical technologies form the basis for high-tech solutions in production control, object and shape detection, gas and process technology as well as in the field of thermal energy converters.