Enhanced identification of defective pre-coated paints on metal through simple temperature-perturbed infrared measurement in conjunction with two-trace two-dimensional correlation analysis

Abstract

A promising infrared (IR) spectroscopic method able to effectively identify defective pre-coated metal (PCM), a pre-painted metal panel, has been demonstrated. A temperature-perturbed IR measurement in conjunction with a two-trace two-dimensional (2T2D) correlation analysis was proposed as a strategy for enhancing defect identification. Our objectives were to induce dissimilar temperature-driven structural variations of base paints and added components, to recognize dissimilarities by 2T2D correlation analysis, and to use subsequent 2T2D correlation features to identify sample defects. For the exploratory examination, three defect cases were studied: 1) grey-silver PCMs with and without phosphate epoxy (2.0%), 2) normal and violet colorant-contaminated (0.2%) black PCMs, and 3) normal, violet (0.5%), and yellow colorant-contaminated (0.1%) white PCMs. The IR spectral features of the PCMs collected at 20 and 50 degrees C were different due to the temperature-dependent structural variations. Initial measurements at 50 degrees C allowed discrimination of normal and violet colorant-contaminated black PCMs. When using 2T2D slice spectra obtained from 2T2D correlation analysis using the spectra measured at the two temperatures, violet-as well as yellow colorant-contaminated white PCMs were identified, while these were unclear in the measurements at either 20 or 50 degrees C. The effective capture of dissimilar temperature-driven spectral variations of base paint and colorants (contaminants) by 2T2D correlation analysis was responsible for the improved defect identification.