Quinacridone solid solutions

Two types of DPP-quinacridone solid solution pigments are available on the market. One is a yellowish, very transparent red for metallic and effect finishes with an unusual flop behavior. The durability in organic systems is good. The other type is a bluish shade transparent red for effect shades. 

Figure 21-22 X-ray powder diffraction pattern of quinacridone solid solution pigment.

Another phenomenon to be detected by X-ray crystallography is the formation of mixed crystals, as observed in the mixed coupling of azo pigments or the solid solutions of quinacridone pigments. A change in the angles of the reflected X-rays of a mixed crystal indicates a transition from one crystal phase to another. If, how-... 

DPP/quinacridone and DPP/DPP mixed pigments ( solid solutions ) are introduced or presently being offered to the market. 

DPP/Quinacridone Mixed Crystal Phase ( Solid Solutions ) Pigments... 

A third yellow derivative, quinacridonequinone (XV), made as shown in Scheme V or directly from the oxidation of quinacridone, is also not weatherfast by itself. However, chemists at Du Pont found that solid solutions of the quinone with quinacridone leads to pigments with improved fastness properties (30-32). 

Today a maroon containing about 60% quinacridone and 40% quinacridonequinone and a gold containing about 75% quinacridone-quinone are sold commercially. Solid solutions can also be prepared between variously substituted linear trans-quinacridones. and a scarlet containing a mixture of approximately 60% quinacridone and 40% 4,11-dichloroquinacridone (an orange) is also on the market. 

Solid solutions between a DPP and some other pigments have been investigated as well. Because of their similar structure and rigidity, DPPs frequently form solid solutions with quinacridone pigments l Often, the solid solution shows a shift in color compared to a physical mixture of the individual components. 

Figure18-11 Powder X-ray diffraction patterns of quinacridone and quinacri-donequinone solid solution, and physical mixture of the same ingredients.

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. 

Similarly, quinacridone forms solid solutions with 2,9-dimethyl or 2,9-dichloroquina-cridone at about a ratio of two moles of unsubstituted to one mole of the substituted compound, the X-ray diffraction patterns of which are virtually identical and are different from those of mixtures of the individual ingredients (Figure 18-13). One blue-shade red is an article of commerce (P.V. 42, CAS 71819-79-9. In fact, using quinacridone and three 2,9-disubstituted derivatives, a series of binary and ternary solid solutions are formed, as depicted in Figure 18-14. The large triangle is subdivided into four smaller triangles and the areas where binary and ternary solutions are possible are shown. It is obvious that solid formation is unpredictable and requires numerous experimental determinations to delineate areas of solid solution formation. 

Figure 18-14 Phase diagram of solid solutions formation between quinacridone, 2,9-dimethylquinacridone, 2,9-dichloroquinacridone, and 2,9-difluoro-...

An interesting quaternary orange solid solution consisting of quinacridone, 4,11-dichloroquinacridone, quinacridonequinone, and 6,13-dihydroquinacridone has been prepared, in which the last component has a positive effect on the photochemical stability of the system. 

There are many methods of solid solution preparation The essential step is to reduce the size of the component particles by the usual methods (milling, drowning strong add solutions of quinacridones, etc.) and then ripening the resultant smaller or amorphous pigment particles, if necessary in the presence of organic solvents, to afford the opportunity for incorporation of one substance into another. Since most solid solutions are thermodynamically stable combinations, they tend to form under reasonably favorable conditions. 

A specified mixture of aniline and one or more substituted anilines such as p-toluidine, p-chloro aniUne, and p-anisidine as examples is condensed with DMSS 7 to produce, after subsequent hydrolysis and oxidation of the resulting dihydrodiesters, a corresponding mixture of the diarylaminoterephthalic acids. An example using a para-substituted aniline is shown in Scheme 18.14. Cyclization of this mixture of terephthaUc acids in PPA followed by appropriate conditioning of the recovered crude product affords a ternary solid solution composed of quinacridone 2, 2-substituted quinacridone 27, and 2,9-disubstituted quinacridone 28. Several combinations are reported, providing a wide range of solid solutions and thus colors. 

QAQ is a yellow compound with deficient lightfastness, but by virtue of solid solution formation with quinacridone the resulting maroon pigment demonstrates outstanding photochemical stability. Evidently, the energy of the excited... 

Figure 18.12 Powder X-ray diffraction patterns ofthe solid solution of 4,11-dichloroquinacridone and quinacridone and the corresponding physical mixture of the individual components.

Similarly, at about a ratio of 2 M to 1, quinacridone forms solid solutions with 2,9-dichloro- or 2,9-dimethylquinacridone, the X-ray diffraction patterns of which are virtually identical but different from those of the physical mixtures of the individual components (Figure 18.13). 

An orange-colored quaternary solid solution [56], composed of QAQ, quinacridone, 4,11-dichloroquinacridone, and 6,13-dihydroquinacridone, is a system of interest as the latter component contributes a positive effect to its photochemical stability. 

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