A long-term aim of dyes research has been to combine the brightness and fastness properties of anthraquinone dyes with strength and economy of azo dyes. This aim is now being realized with heterocyclic azo dyes which fall into two main groups: those derived from heterocyclic coupling components and those derived from heterocyclic diazo components. All the heterocyclic coupling components which provide commercially important azo dyes contain only nitrogen as the hetero atom. They are indoles, pyrazolones, and especially pyridones, they provide yellow to orange dyes for various substrates. In contrast to the heterocyclic coupling component, all the heterocyclic diazo components that provide commercially important azo dyes contain sulphur either alone or in combination with nitrogen.
These dyes provide bright, strong shades that range from red through blue to green and therefore complement the yellow/orange colours of the nitrogen heterocyclic coupling components (Hunger, 2003). In continuation of our interest in synthesis of condensed arylazopyarzoles as new dyestuff (Elgemeie et al., 1987, 1989, 1991, 1994, 2003a, b, 2004; Helal, 2004).
Disperse dyes are used for printing synthetic fabrics in general by all techniques. Specially designed disperse dyes with specific molecular weight and sublimation properties are designed for use in transfer printing technique.
The sublimation transfer printing process involves the transfer of disperse dye from the paper to fabric and it is particularly popular for printing of 100 per cent polyester (EL-Kashoutie et al., 2000). It has been reported that the most suitable disperse dyes for transfer printing are those with molecular weights varying between 240 and 340mole/g. and it is important to work with those dyes which have similar sublimation temperature properties. The molecular weight cannot be taken as too rigid an indicator of the suitability of a dye, since a dye of high molecular weight with a less polar structure may sublime more rapidly than one with a lower molecular weight. (El-Molla et al., 1998;Vellins, 1973). Thus, it is clear that for adequate sublimation, it is generally accepted that a dye should have a molecular weight below 350mole/g. and should not contain an excessive number of non-ionic polar groups (NO2, CN, and SO2R, etc.). In particular, no ionized grouping should be present (Griffiths and Jones, 1977).
The authors M.A. El-Kashouti, M.M El-Molla, H.S. El-Sayad and K.A.E. Ahmed are associated with the Chemistry of Dyeing, Printing and Auxiliaries, Textile Division at National Research Centre, Cairo, Egypt and G.H. Elgemeie is from Chemistry Department at Faculty of Science, Helwan University, Cairo, Egypt