Infrared spectra of North American automobile original finishes. XII: Analysis of perylene pigments—In situ identification of Perylene Bordeaux (C.I. Pigment Violet 29)

Abstract

The analyses of two perylene pigments used primarily in metallic automotive finishes, Perylene Red Y (C.I. Pigment Red 224) and Perylene Maroon (C.I. Pigment Red 179), were described in previous papers in this series. The in situ identification of Perylene Bordeaux (C.I. Pigment Violet 29), which is used in both metallic and nonmetallic automotive finishes, is discussed in this report. Perylene Bordeaux was identified primarily in paints having maroon hues. Because it is normally employed as a light to medium pigment load and is always combined with other pigments, its absorptions may not be as readily-recognized in paint spectra as those of the other two perylenes. Identification of its presence can be important for certain finishes, however, as it is often combined with Perylene Maroon, and this may result in a broad absorption centered near 1690 cm−1. Differentiation of certain acrylic urethanes from acrylic melamine enamels depends heavily on the presence of a broad 1690 cm−1 urethane absorption, but this distinction may be obscured when the two perylenes are present. In addition to Perylene Maroon, Perylene Bordeaux was found combined with several other pigments and examples of spectra illustrating the wide diversity of absorption patterns that result from these combinations are presented. In many cases, the individual pigments comprising these combinations can be identified, providing information about an automotive paint that can be useful for both comparative analyses and vehicle identifications.