Proceedings Article | 26 June 2017
KEYWORDS: Quality measurement, Phase interferometry, Functional imaging, Doppler tomography, Profilometers, Image resolution, Coating, Optical coherence tomography, Ultrasonography, Optical coatings, Corrosion, Visualization, Interferometry, Scattering, Point spread functions, Multilayers
The multiple layer paint systems on modern cars serve two end purposes, they firstly protect against corrosion and
secondly give the desired visual appearance. To ensure consistent corrosion protection and appearance, suitable Quality
Assurance (QA) measures on the final product are required. Various (layer thickness and consistency, layer composition,
flake statistics, surface profile and layer dryness) parameters are of importance, each with specific techniques that can
measure one or some of them but no technique that can measure all or most of them. Optical Coherence Tomography
(OCT) is a 3D imaging technique with micrometre resolution. Since 2016, OCT measurements of layer thickness and
consistency, layer composition fingerprint and flake statistics have been reported. In this paper we demonstrate two more
novel applications of OCT to automotive paints. Firstly, we use OCT to quantify unwanted surface texture, which leads
to an “orange peel” visual defect. This was done by measuring the surface profiles of automotive paints, with an unoptimised
precision of 37 nm over lateral range of 7 mm, to quantify texture of less than 500 nm. Secondly, we
demonstrate that OCT can measure how dry a coating layer is by measuring how fast it is still shrinking quasiinstantaneously,
using Fourier phase sensitivity.
