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  4. Multi-Angle Averaging Approach for Measuring the Coating Thickness on Thin Transparent Polymer Films
 
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2025
Journal Article
Title

Multi-Angle Averaging Approach for Measuring the Coating Thickness on Thin Transparent Polymer Films

Abstract
Polymer films with a thickness in the two-digit micrometer range are coated with nanometer-thin oxide layers in roll-to-roll coating systems. The coating improves the properties of the film, such as gas or water permeation. Maintaining a sufficiently large coating thickness is crucial to ensure its barrier function; thus, inline quality control of the thickness is indispensable. For this purpose, we have developed a sensing principle that addresses specific absorption bands of the coating via a reflection measurement in the infrared spectral range. However, for thin and weakly absorbing polymer substrates, light is reflected not only by the coating and the surface of the polymer. Partly it is also transmitted and reflected by the backside of the film, leading to interference effects that significantly affect the measurement signal. As industrial films vary in thickness by several percent and their exact values are unknown, determining the thickness of an oxide coating is hindered. In this paper, we demonstrate an approach for measuring coating thickness on such varying polymer films by averaging the interferences obtained at multiple angles of incidence. Calculations and measurements on industrial film samples indicate the effectiveness of our approach. It produces results with +/-2 nm precision and +/-5 nm accuracy for a thickness in the range of 5-100 nm. Furthermore, we discuss a possible implementation of this approach in an inline measurement system by fulfilling its requirements, for example, versatility and compactness.
Author(s)
Münch, Friederike  orcid-logo
Fraunhofer-Institut für Physikalische Messtechnik IPM  
Hauer, Benedikt  
Fraunhofer-Institut für Physikalische Messtechnik IPM  
Breunig, Ingo  
Fraunhofer-Institut für Physikalische Messtechnik IPM  
Carl, Daniel  
Fraunhofer-Institut für Physikalische Messtechnik IPM  
Journal
Applied spectroscopy  
Open Access
DOI
10.1177/00037028251334152
Additional full text version
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Language
English
Fraunhofer-Institut für Physikalische Messtechnik IPM  
Keyword(s)
  • Thin films

  • Polymer web

  • Infrared spectroscopy

  • Silicon oxide

  • Inline thickness measurement

  • Roll-to-roll coating systems

  • Production control

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