55 Phthalocyanine blue pigments

Copper phthalocyanine is the dominant blue organic pigment by far, used extensively in printing ink, paint, plastics, and a range of other applications. A historical perspective of the development of phthalocyanine pigments, from their original serendipitous discovery, through the characterization of their molecular structures, to their development as pigments, is discussed in this chapter and in the separate chapter entitled Phthalocyanines: General Principles. Copper phthalocyanine exhibits polymorphism. The α- and β-forms are the most important crystal phases used as pigments, while the ε-form has only minor significance. Although structurally complex, the synthesis of copper phthalocyanine is relatively straightforward, involving readily available commodity starting materials to provide the products in high yield. After-treatments are required not only to convert the crude pigment into an appropriate pigmentary physical form, but also to provide stability towards crystal phase change and flocculation in application.