Organic Pigments

In principle, it is possible to distinguish organic pigments by their chemical constitution and the colour index (C.I.). They are roughly classified into the groups: azo pigments and non-azo (or polycyclic) pigments.

The production of organic pigments to some extent requires quite elaborate manufacturing processes. To explain the same would go far beyond the scope here owing to the complexity and the wide variety of pigments.

Azo pigments (as examples)

Monoazo pigments Disazo condensation pigments Naphthol / β-Naphthol
C.I. Pigment Yellow 74 C.I. Pigment Orange 34 C.I. Pigment Red 112
C.I. Pigment Yellow 83 C.I. Pigment Orange 5

Non-azo and/or polycyclic pigments

Phthalocyanine Quinacridone Diketopyrrolo-pyrolle (DPP) Dioxazine (Carbazole violet)
C.I. Pigment Blue 15:1 C.I. Pigment Red 122 C.I. Pigment Red 254 C.I. Pigment Violet 23
C.I. Pigment Blue 15:3 C.I. Pigment Violet 19
C.I. Pigment Green 7

Remarkably higher colour strengths and more brilliant colour shades can be obtained with organic pigments in contrast to inorganic pigments. Owing to the relatively small particle size on average, organic pigments require more dispersion energy and have lower covering power thus appearing more transparent.

The fastness properties are quite different among the various chemical classes and are often much worse than that of inorganic pigments. Therefore, all aspects have to be considered individually when it comes to the selection of the appropriate pigments. This applies to light and weather fastness as well as to solvent and migration fastness, efflorescence behaviour, fastness to recoating, heat stability, etc.