Лако-красочные материалы — производство

The chemical class of colorants which is second in importance to azo dyes and pigments is characterised by the presence of a carbonyl (C=O) group, which may be regarded as the essential chromophoric unit. The vast majority of carbonyl dyes and pigments contain two or more carbonyl groups which, as illustrated in Figure 4.1, are linked to one another through a conjugated system, frequently an aromatic ring system.

Carbonyl colorants are found in a much wider diversity of structural arrangements than is the case with azo dyes and pigments. By far the most important group of carbonyl dyes and pigments are the an — thraquinones, to which a substantial part of this chapter is devoted. Other types which are of commercial importance in particular applica­tion classes include indigoids, benzodifuranones, coumarins, naphthalim — ides, quinacridones, perylenes, perinones and diketopyrrolopyrroles. Carbonyl dyes and pigments are capable of providing a wide range of colours, essentially covering the entire visible spectrum. However, a major reason for the importance of carbonyl colorants is that they are capable of giving long wavelength absorption bands with relatively short conjugated systems. This feature applies especially to anthraquinone and indigo derivatives, which are thus of particular importance in the blue shade area.

In terms of fastness properties, carbonyl dyes and pigments are often superior to their azo counterparts. They are thus commonly the colorants of choice when high technical performance is demanded by a particular

Figure 4.1 Structural arrangement in most carbonyl colorants application. In most textile dye application classes, carbonyl dyes (mostly anthraquinones) rank second in significance to azo dyes. A particular textile application class dominated by carbonyl dyes is the vat dye class, a group of dyes applied to cellulosic fibres such as cotton (see Chapter 7). In the vat dyeing of cotton, the ability of the carbonyl groups to undergo a reversible reduction to a water-soluble form is utilised. Azo dyes are inappropriate as vat dyes because of the instability of the azo group to the reduction process. A range of carbonyl pigments, including the quinac — ridones, perylenes, perinones and diketopyrrolopyrroles, impart extreme­ly high performance in their application. These products owe their high fastness to light, heat and solvents to the ability of the carbonyl group to participate in intra — and intermolecular hydrogen bonding.

The chemistry involved in the manufacture of carbonyl colorants is generally more elaborate and much less versatile than is the case with azo dyes. Often the synthetic sequence involves multiple stages and the use of specialist intermediates. Consequently, the number of commercial prod­ucts is more restricted and they tend to be rather more expensive. Indeed, certain carbonyl dyes, notably some anthraquinones, are becoming pro­gressively less important commercially, particularly for traditional textile applications, as a wider range of azo dyes absorbing at longer wavelengths have emerged and as the cost differential between azo dyes and carbonyl dyes increases. In the following sections of this chapter, the characteristic structural features of the most important types of carbonyl colorants are reviewed and an overview of some of the more important synthetic routes is presented.