Characterization of barrier layers by Spectroscopic Ellipsometry for packaging application

by Spectroscopic Ellipsometry

Materials such as the plastics and papers used in flexible packaging are permeable to different gases (O2, CO2, etc.), humidity and odours unless treated. Without the addition of barrier layers to the packaging, food or beverage contents spoil more quickly. Additionally layer transparency, to allow viewing of the contents and microwave compatibility are further performance parameters needed in an ideal, modern barrier layer.

This has lead to a new generation of materials and coatings, usually oxide based, being developed to meet the high-performance specifications required for today’s packaging. The oxide coated PET films are used as a barrier material for food packaging and deliver completely transparent coatings. For standard grade barrier coatings, a coating thickness of 40-60 nm is deposited on the PET film.

Spectroscopic ellipsometry is the ideal technique for very fast, reliable and non-destructive characterization of these barrier coatings. This application note details the ability of the UVISEL Spectroscopic Ellipsometer to ac-curately monitor in real-time both the thicknesses and quality of the transparent coatings that are applied us-ing high speed reel to reel machines running at up to 10m/s and handling web widths of 1-3 m. Based on the methodology provided by Prof. S. Logothetidis, Aristotle University of Thessaloniki Coordinator of FP5-GROWTH Project, G1RD-CT-2000-00334 "TransMach-Transparent Films Vacuum Coatings Machine with Integrated In-line Monitoring and Control'‘ during which, this ability of UVISEL Spectroscopic Ellipsometer was verified.

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