Лако-красочные материалы — производство

Solid solution formation, where two or more components form one crystal lattice over a continuous range of compositions, is frequently observed in dye and pig­ment chemistry [49]. As a consequence, the X-ray diffraction (XRD) pattern of such a solid solution is the same or very similar to that of one of the components, the host. In analogy to liquid solutions, the “guest” molecules are dissolved into the crystal lattice of the “host.” In some cases this can also lead to a variation of

Figure 11.10 XRD and coloristics of a ternary and a binary solid solution (mixed crystal).

the coloristic and other properties as compared to a physical mixture of the indi­vidual pigments. A special case of solid solutions is a mixed crystal, where a spe­cific composition containing two components results in a unique diffraction pat­tern different from the XRD of either of the components. In this case, a loose analogy can be drawn to the formation of azeotropes in the liquid state. Both cases have been observed within DPP chemistry.

Solid solution formation between different DPPs can be achieved through a DPP synthesis using two (or more) nitriles [5, 42, 50] giving rise to a ternary solid

Binary solid solution

Binary mixed crystal Bluish Red

Figure 11.11 XRD and coloristics of a binary solid solution (mixed crystal) of AA and B’B’

solution, in which the components accommodate the crystal lattice of one of the symmetric DPPs or the crystal lattice of the asymmetric DPP. The formation of a solid solution is sometimes accompanied by a bathochromic or a hypsochromic shift of the solid state hue.

Alternatively, binary DPP-DPP solid solutions or mixed crystals can also be formed through an acidic or basic reprecipitation or through a milling process of two (or more) DPPs [51, 52]. Depending on the size and the interaction ofcompo — nents in the solid solutions or mixed crystal, coloristic shifts and changes of the pigmentary properties can also be observed.

Figure 11.10 illustrates both a ternary and a binary solid solution. The ternary solid solution of AA, AB, and BB accommodates the lattice of the asymmetric DPP AB. A binary combination of equimolar amounts of the symmetrical DPP AA (C. I. Pigment Red 255) and the symmetrical DPP BB (C. I. Pigment Red 254) form an entirely new binary mixed crystal in the lattice of the asymmetrical DPP

AB. The asymmetrical DPP and the two solid solutions all show a hypsochromic shift compared to the single components AA and BB.

Figure 11.11 illustrates how equimolar amounts of the symmetrical DPP AA (C. I. Pigment Red 255) and symmetrical DPP B’B’ (C. I. Pigment Orange 73) can be combined and form an entirely new binary mixed crystal in the lattice of the asymmetrical DPP AB’, again accommodating the coloristics of the asymmetric DPP. In this case, however, the asymmetric DPP and the solid solution show a bathochromic shift compared to the single components AA and B’B’ and the cor­responding physical mixture of AA and B’B’ [53].

Solid solutions between a DPP and some other pigments have been investigated as well. Due to the similar structure and rigidity, DPPs frequently form solid solu­tions with quinacridone pigments [54-58]. Often, the solid solution shows a shift in color compared to a physical mixture of the individual components.

Recently, combinations1 of DPP Pigments with yet other pigments like thiazine indigo, benzimidazolone triphenodioxazine, anthraquinones, azo pigments, ben — zimidazolones, and isoindolinones [59-61] have appeared in the literature. The value of these new combinations has yet to be established.

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