Concentration Profile Measurements in Polymeric Coatings During Drying by Means of Inverse-Micro-Raman-Spectroscopy

The Raman spectra in different layers of a solvent borne polymer coating during drying

Raman spectra at different depths of a polymeric solvent coating (polyvinylacetate-toluene) during the drying process, measured with the IMRS-technique (left): at the beginning of a drying process (t = 0s, initial film thickness: 150 μm) (right): after t = 60s of drying. The solvent ( =1010 cm-1) evaporates and the film shrinks to 50 μm.

There are many important industrial applications for solvent and waterborne coatings such as foils for LCD panels, varnishes, adhesives, paper coatings and even bio-medical applications such as transdermal patches. Coatings on these products and devices are often formed from dissolved coating components that are applied to the substrate material and then subsequently dried to create the desired end material.

The drying process of the coating often determines the performance and quality of the resulting product. In order to design and control such coating and drying processes, online moisture and solvent profile measurements during the coating formation become of significant interest.

The University Karlsruhe (TH) has applied a measuring technique called Inverse-Micro-Raman-Spectroscopy (IMRS) to a Confocal Raman Spectrometer (LabRAM INV - HORIBA Jobin Yvon) which was manufactured whereby the standard upright LabRAM microscope was replaced by an Inverted Microscope sampling system (in this case an Olympus IX50).

The preliminary work obtained in this collaboration showed many advantages in the use of Raman spectroscopy for the study of drying characteristics in coating materials.

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