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

Area of Science:

• Materials Science
• Optical Engineering
• Surface Science

Background:

• Roll-to-roll coating systems apply nanometer-thin oxide layers to polymer films to enhance barrier properties like gas and water permeation.
• Maintaining precise coating thickness is critical for effective barrier function, necessitating inline quality control.
• Existing infrared reflection spectroscopy methods are challenged by interference effects from thin, weakly absorbing polymer substrates with variable thickness.

Purpose of the Study:

• To develop and validate a novel sensing principle for accurate inline measurement of nanometer-thin oxide coating thickness on polymer films.
• To address and overcome interference effects caused by variable polymer film thickness and backside reflections.
• To enable precise quality control for oxide-coated polymer films used in barrier applications.

Main Methods:

• Developed an infrared reflection measurement technique targeting specific oxide coating absorption bands.
• Implemented an approach averaging interference patterns obtained at multiple angles of incidence to mitigate substrate variations.
• Validated the method through calculations and measurements on industrial polymer film samples with oxide coatings.

Main Results:

• The developed approach effectively measures oxide coating thickness on polymer films with varying substrates.
• Achieved high precision ($$ nm) and accuracy ($$ nm) for coating thicknesses in the range of 5-100 nm.
• Demonstrated the potential for implementation in versatile and compact inline measurement systems.

Conclusions:

• Acoustic interferometry provides a robust solution for accurate inline thickness measurement of nanometer-scale oxide coatings on polymer films.
• The multi-angle incidence approach effectively compensates for substrate thickness variations and backside reflections.
• This technology is suitable for industrial inline quality control, ensuring the barrier performance of coated polymer films.