Quinacridone compositions

Novel quinacridone compositions via the PPA process have recently been published. The soUd solutions comprise of at least one unsymmetrical quinacridone and at least two symmetrical quinacridones [21A]. In common with the subject matter of Section 18.3.5, they have the unique distinction that unsymmetrical quinacridone 27 comprises a substantial part of the product composition. 

Later, it was shown that the phenomenon of solid solution formation is widespread in this family of pigments. The previously discussed scarlet pigment 4,11-dichloroquinacridone was greatly improved in weatherfastness by solid solution formation (P.R. 207, CAS 71819-77-7 ) with the parent compound. In this case the approximate composition is also two moles of quinacridone and one mole of the substituted counterpart, retaining largely the scarlet color of the latter and the photochemical stability of the former. The X-ray diffraction pattern of the solid solution is different from that of a mixture of the two ingredients (Figure 18-12) or those of the individual components. As in most cases, while the X-ray diffraction pattern of a mixture is simply additive and predictable, the solid solution shows a non-additive diffraction pattern and an unpredictable color effect. 

Common to quinacridone pigments, these compositions can be surface treated and/or particle size reduced or grown as required by specific applications. 

A series of binary and ternary solid solutions may be formed, as depicted in Figure 18.14 [38], from various combinations of quinacridone and the three designated 2,9-disubstituted derivatives. The large triangle is subdivided into four smaller triangles and the areas indicated where binary and ternary solutions are possible. It is obvious that the formation of solid solutions is unpredictable, requiring many experiments to determine their respective compositions. 

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