Infrared spectra of North American automobile original finishes. X: Analysis of perylene pigments—In situ identification of Perylene Red Y (C.I. Pigment Red 224) and mica-based red pearlescent pigments

Abstract

The perylenes are a family of high performance organic pigments that are used frequently in automotive paint and five perylenes were being marketed for this application when this study began in 1997. This work sought to determine which of the five were used in North American automobile (1974–2019) original finishes; how they can be differentiated and identified using infrared spectroscopy; and information about the types of finishes that they were used on. The perylene discussed in this paper, Perylene Red Y (C.I. Pigment Red 224), is probably the most readily-identified organic pigment in situ owing to its unusually high carbonyl stretching frequency (1774 cm−1). This absorption is the most intense spectral feature of Perylene Red Y and because it occurs at a higher frequency than the binder ester carbonyl stretch (1730 cm−1), its presence is usually quite conspicuous. Perylene Red Y was used predominantly in metallic finishes, but it was identified in less than 8% of the 143 red or maroon metallic basecoats surveyed. These particular basecoats were all produced in the 1980s and this perylene does not appear to have been used much after this period due to its incompatibility with waterborne finishes. Its identification in a basecoat can therefore be helpful for both hit-and-run investigations and for aiding in the determination of the significance of a comparative analysis. To facilitate this, a list of the metallic basecoats in which Perylene Red Y was identified and the vehicles they were used on is presented. Spectra are also presented illustrating the difficulties that may be encountered when attempting to determine the binder type for certain finishes containing heavy loads of this pigment. Perylene Red Y was often used with red mica, a pearlescent pigment that has distinct far-infrared absorptions, and the in situ identification of both Perylene Red Y and red mica are described.