Quinacridone conditioning

The DuPont company used the succinic acid ester process, in which diethyl succinate is first cyclised to diethyl succinylsuccinate (2.39) in a sodium/alcohol mixture. One mole of the product is next condensed with two moles of aniline under oxidising conditions, forming diethyl 2,5-dianilino-3,6-dihydroterephthalate (2.40). Ring closure at 250 °C gives dihydroquinacridone, from which quinacridone is obtained by oxidising away the two extra hydrogen atoms. 

The thermal requirements for pigments which are targeted for PETP melt extrusion are particularly severe. However, it is important to consider the individual conditions at the various stages of polymer coloration. Pigments, for instance, which are added during the so-called condensation process in a glycol dispersion prior to transesterification or condensation in the autoclave, are exposed to temperatures between 240 and 290°C for 5 to 6 hours [43]. These harsh conditions are only tolerated by very few polycyclic pigments, primarily by representatives of the quinacridone, copper phthalocyanine, naphthalenetetracarboxylic acid, and pery-lene tetracarboxylic acid series. 

Quinacridone pigments are manufactured by either the condensation of 2,5-diarylamino-terephthalic acid or the oxidation of dihydroquinacridones followed by subsequent conditioning to produce the product in a pigmentary form of colloidal dimensions. For example, in the first process, the use of 2,5-dianilinoterephthalic acid results in the formation of trans linear quinacridone, PV 19, by a simple ring closure condensation where water is evolved as a by-product. Substitution of the aniline used to produce the diarylaminoterephthalic acid will result in pigments such as PR 122 where ditoluidinoterephthalic acid is used at the condensation stage. 

A third route developed by Sandoz (22) shown in Scheme IV allov/s one to make unsymmetrically substituted quinacridones by stepwise condensation (Steps 1 and 2) of the two amines carried out under carefully controlled conditions (23). 

The K value observed in fibres coloured with quinacridone pagment is comparable to the value obtained during crystallization of polypropylene melt in quiescent conditions in the presence of very effective p nucleating agents. 

Similarly to fibres coloured with quinacridone at high take-up velodty above 1000 m/min, pigment does not participate in the nudeation process. In these conditions, under high molecular orientation numerous row nudei are formed. Row nudei quickly grow forming well oriented lamellar a crystals. In fibres the fibrillar structure is formed (Fig.5)... 

For fibres formed at higher velocities the crystallization conditions prefer the formation of the a form crystals. Similarly as for fibres coloured with quinacridone, the content of the P form rapidly decreases. 

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. 

Analytical studies of the PPA reaction processes by real-time infrared spectroscopy [19A] demonstrate that cycUzation to the corresponding quinacridones is very rapid at the typical reaction temperatures and although not confirmed directly, probably proceeds by a two-stage sequential mechanism. Analogous to the thermal process high dilution conditions favor monomolecular reactions and subsequently the quaUty of the ultimate products. The by-products of bimolecular reactions occasionally have been detected in some quinacridone pigments... 

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. 

Facile synthetic routes involve oxidation of quinacridone or 6,13-dihydroquina-cridone with sodium dichromate in strong acid [45] or oxidation of the latter with NaClOj catalyzed with V2O5 [46]. Conversely, QAQ can be reduced to quinacridone by means of finely divided metals under a variety of conditions. A good yield of quinacridone is obtained by reducing QAQ with zinc powder in 70% sulfuric acid or in a eutectic mixture of AlCf and NaCl [47]. 

Figure 21.23 shows the application of HPLC to the quantification of quinacridone mixtures such as C.l. PV54, C.I. PV19, and C.I. PR122. C.I. PR202 has also been chromatographed under similar HPLC conditions. 

Quinacridone Violet A versatile member of the quinacridone pigment family. It is used as a toning pigment used to neutralize yellow tones in whites. Various shades from yellowish red to bright violet, resistant to most environmental conditions, very lightfast and used where superb properties are required, but very... 

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