Polycyclic pigment

Apart from some nonclassified pigments such as Indanthrone Blue (P.131.60), the anthraquinone pigments, which are structurally or synthetically derived from the anthraquinone molecule, can be divided into the following four groups of polycyclic pigments. 

Such simplified considerations can only serve as approximations to a more complex problem even the shade of a polycyclic pigment basically depends on crystal characteristics, such as particle size, particle size distribution, and crystal modification. 

Fig. 50 Thermal decomposition of polycyclic pigments in the solid phase. Results of differential thermoanalysis performed on pigment powders in a nitrogen atmosphere.

These are the changes that are observed in a pigment powder as it is processed or heated in the application medium. Modifications in the sizes of the crystallites of a polycyclic pigment which is treated in its application medium under varying conditions [108] maybe derived from X-ray crystallographic data. Table 5 reflects a clear correlation between crystallinity and thermal stability increased crystallinity leads to improved heat fastness. 

Table 5 Changes in the crystallite size of some polycyclic pigments in coatings or plastics coloration as a result of heat exposure (calculated from the X-ray diffraction spectra).

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. 

It is only for reasons of simplified classification that the pigments which are described in this section, like azomethine metal complex pigments (Sec. 2.10.1.2), are listed in Chapter 2. Actually, rather than being azo pigments, these are azo methine and methine pigments, which in the classification system adopted in this book are formally located between azo pigments and polycyclic pigments. 

All polycyclic pigments, with the exception of triphenylmethyl derivatives, comprise anellated aromatic and/or heteroaromatic moieties. In commercial pigments, these may range from systems such as diketopyrrolo-pyrrol derivatives, which feature two five-membered heteroaromatic fused rings (DPP pigments) to such eight-membered ring systems as flavanthrone or pyranthrone. The phthalo-cyanine skeleton with its polycylic metal complex is somewhat unique in this respect. 

Most pigments derived from vat dyes are structurally based on anthraquinone derivatives such as indanthrone, flavanthrone, pyranthrone, or dibromoan-thanthrone. There are other polycyclic pigments which may be used directly in the form in which they are manufactured. This includes derivatives of naphthalene and perylene tetracarboxylic acid, dioxazine (Carbazole Violet), and tetrachloro-thioindigo. Quinacridone pigments, which were first introduced in 1958, and recently DPP pigments have been added to the series. 

In this section a number of polycyclic pigments are discussed which have been used for a long time as vat dyes for textile fibers. Heading the list are perylene, perinone, and thioindigo pigments, as well as pigments derived from anthraquinone. 

The term polycyclic pigments refers to pigments which are derived from the an-thraquinone skeleton, either by chemical structure or by synthesis. The complex fused-ring systems which are discussed in this context are all at least remotely related to the parent anthraquinone structure. 

This chapter classifies polycyclic pigments by chemical constitution. The resulting classes include aminoanthraquinones, hydroxyanthraquinones, heterocyclic and polycarbocyclic anthraquinone pigments. 

This polycyclic pigment, listed in the Colour Index under Constitution Number 507300, is synthesized by condensation of 5,6-diaminobenzimidazolone with a naphthalic anhydride in a high boiling solvent [3] ... 

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