Automotive Coatings Formulation: Chemistry, Physics und Practices

Azo pigments
Azo pigments are prepared by coupling reactions between aromatic diazonium compounds and 
various aromatic partner compounds. They include pigments which produce very brilliant and pure 
red colours. Unfortunately, the azo pigments have poor weatherability and some show a tendency to 
bleed. Since certain red colours are required, it is not possible to dispense with the entire pigment 
class. Accordingly, recourse is made to those members which offer the maximum resistance proper-
ties. These include the Naphthol AS pigments, which contain aromatic diazonium compounds and 
aromatic amides of hydroxynaphthoic acid by way of coupling component (see Figure 3.6.5)
Pigments of this kind cover the range from yellowish to bluish red.
Figure 3.6.5: Naphthol AS pigment (C.I. Pigment Red 170, e.g. “Novopermred” F 3 RK 70)
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Figure 3.6.6: Azo metal complex pigment (C.I. Pigment Green 10, e.g. “Bayfast” Yellow Y 5688)
Figure 3.6.9: Diketopyrrolopyrrole pigment (C.I. Pigment Red 254, e.g. “Irgazine” DPP Red BO)
Figure 3.6.8: Isoindolinone pigment (C.I. Pigment Yellow 110, e.g. Irgazine Yellow 2 RTL)
Figure 3.6.7: Benzimidazolone pigment (C.I. Pigment Orange 36, e.g. “Novopermorange” HL 70)
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Azo metal complex pigments
On account of their molecular structure, azo metal complex pigments are more resistant to sol-
vents and migration effects than other azo pigments. However, they are not as weatherable or 
resistant to chemicals. This class contains pigments which generate greenish yellow colours (see 
Figure 3.6.6 for an example).
Benzimidazolone
pigments
Coupling aromatic diazonium compounds with acetylacetamides of benzimidazole leads to yellow 
and orange pigments. These have high brilliance (colour saturation) and high tinting strength. 
Their fastness properties are very good and they offer acceptable weatherability (see Figure 3.6.7 
for example).