The Fraunhofer Institute for Production Technology IPT in Aachen has developed an interferometric measurement method that can be used to reliably measure whether thin transparent layers of paint have been applied evenly: The possibilities offered by optical coherence tomography (OCT) for measuring such paint layers will be presented to the trade fair audience by the Fraunhofer IPT using a prototype at Control, the leading international trade fair for quality assurance from May 3 to 6, 2022 in Stuttgart.

OCT is a non-contact measurement method that was originally developed in ophthalmology. It can provide high-resolution two- and three-dimensional images of transparent and semi-transparent materials. With its high measuring frequency of over one hundred kilohertz, OCT also enables thin and transparent paint layers of one micrometer or more to be reliably measured in production using cross-sectional images.

In printing practice, for example, this offers a clear advantage: to date, there is no measuring device on the market that can reliably and directly check whether the coating layer on the printed sheet has a uniform thickness. The coating thickness of the individual printed sheet is only estimated by documenting the average coating consumption. However, this procedure is very imprecise and does not provide any information about the quality of the coating on each individual printed sheet. The same applies to other industrial applications, such as the application of automotive paint and paint layers for coating a wide variety of components.

Better orders with OCT

In the project "ifSidLa - Development of a method for interferometric layer thickness measurement of thin, printed coating films", the Fraunhofer IPT has created a measuring system based on interferometry that can be used to reliably measure thin, transparent coating layers. Thanks to its flexible design, the system can also be integrated into production, or more precisely: into an application machine. The system consists of a light source with a spectral bandwidth of around 300 nanometers. The light is fed in equal parts into a sample arm and a reference arm. In the reference arm, it is reflected back by a mirror. In the sample arm, the light is reflected by the sample. A beam splitter brings the two light components together - the superposition of the two light components is measured in a spectrometer. As the path of the light in the reference arm is always the same, the path in the sample arm varies due to the different samples and sample layers, individual layers of a sample can be examined and layer thicknesses of up to one micrometer can be measured.

The Fraunhofer IPT will be exhibiting the high-resolution OCT system from May 3 to 6, 2022 at Control in Stuttgart at the joint booth of the Fraunhofer-Gesellschaft in Hall 6, Booth 6301.